Evaluation of hip arthroscopy using a hip-specific distractor for the treatment of femoroacetabular impingement

Tatiana Charles; Marc Jayankura

doi:10.1371/journal.pone.0246655

. 2021 Feb 11;16(2):e0246655. doi: 10.1371/journal.pone.0246655

Evaluation of hip arthroscopy using a hip-specific distractor for the treatment of femoroacetabular impingement

Tatiana Charles ^1,^#, Marc Jayankura ^1,^*,^#

Editor: Osama Farouk²

PMCID: PMC7877656 PMID: 33571305

Abstract

Background and study aims

Hip arthroscopy using an orthopaedic traction table has been associated with traction-related neurovascular complications. Since the use of a hip-specific distractor for performing hip arthroscopy hasn’t been associated with those specific complications we hypothesized that a hip-specific distractor might facilitate the learning curve of hip arthroscopy for beginner surgeons.

Material and methods

We reviewed retrospectively the first 56 hip arthroscopies performed to treat femoro-acetabular impingement using a hip-specific distractor. We tried to analyse the learning curve of this procedure using operative time, peri- and postoperative complications, hospital stay and patient satisfaction. We also evaluated pre- and postoperative sports activities and tried to identify some factors as poor postoperative prognostic factors.

Results

Only 1 major complication occurred. No traction-related complications have been encountered. The curves analysing intervention time and postoperative satisfaction rate showed improvement after 30 cases performed. In all cases, we were able to perform the whole planned gesture without difficulties accessing the hip joint.

Conclusion

The hip-specific distractor is a safe and reproducible method in performing hip arthroscopy without any traction-related complications or time limits.

Introduction

Femoroacetabular impingement (FAI), defined as an abnormal contact between head and neck junction and the acetabular margin, is now widely recognized as a cause of major chondrolabral lesions leading to early osteoarthritis of the hip [1, 2]. Hip arthroscopy has become a gold standard in order to treat FAI in early stages [2, 3]. Yet, hip arthroscopy remains a difficult procedure due to a challenging learning curve, difficulties of accessing the hip joint and the confined work space [3–5]. Access to the hip joint could only be made possible by adequate hip distraction [1, 6].

Complication rates of hip arthroscopy vary between 0 and 13% [7]. Most of these complications are neurological injuries seen with distraction or compression on a traction table [7–10]. Distraction- and compression-type complications are related to the length of the procedure, thus limiting certain cases of hip arthroscopy in a timely manner [8]. These complications tend to decrease with the increasing experience of the surgeon [4, 9]. Another possible problem encountered when using a traction table in hip arthroscopy is the accessibility of the joint, as up to 18% of hip joints are described as being difficult accessible and even 2% being inaccessible [4, 8].

Traction forces up to 500 N are required to allow sufficient hip distraction [11]. Using an orthopaedic traction table, traction is applied along the entire lower limb thus losing much of the traction applied by distracting the knee joint (for about 5mm) and the ankle joint (for about 5mm) [11]. A hip-specific distractor applies about 500N of traction force exclusively on the hip joint [11]. The Schanz screws used are specially designed for this hip-specific distractor and the force applied to the hip joint can be calculated based on the elasticity of those screws. When about 500N of traction force is obtained, the Schanz screws will start to bend as seen on the fluoroscopic controls [11]. Additionally, acetabular anteversion induces a tendency of the femoral head to translate anteriorly, thus reducing the anterior joint space. This can be addressed by internal rotation of the femoral head putting the sciatic nerve at risk when using a posterolateral portal [11]. But a hip-specific distractor presents with a controlled antero-posterior traction vector in neutral rotation [11]. For those reasons the hip-specific distractor hasn’t been associated with traction-related complications nor with difficulties accessing the hip joint, and could help beginner surgeons in performing hip arthroscopy [1, 11]. Therefore we hypothesized that the use of a hip-specific distractor might reduce complication rates such as neurovascular traction-related complications. The use of a hip-specific distractor might also decrease iatrogenic chondral and labral lesions when entering the joint because of better controlled joint opening, allowing surgeons to realize the entire planned procedure without time limits thus decreasing the learning curve in hip arthroscopy. The goal of this study was to evaluate the learning curve of hip arthroscopy using a hip-specific distractor and the complications related to this procedure.

Material and methods

We performed a retrospective analysis of all successive patients who underwent a hip arthroscopy using a hip-specific distractor in order to treat FAI from September 2007 to March 2015. Hip arthroscopy was performed by a single surgeon (MJ), thus allowing the evaluation of this surgeon’s learning curve. Hip arthroscopy with the use a hip-specific distractor is standard care at our institution.

All patients presented with a symptomatic FAI and a positive impingement test at the time of preoperative consultation. Preoperative work-up consisted of a standard X-ray of the pelvis and hip, arthro-CT and MRI or arthro-MRI of the hip. Classification of osteoarthritis was made using the Tönnis classification [12]. If the patients were sportsmen a total of 6 months of conservative therapy was applied and in all other cases a total of 1 year of conservative treatment was completed. All patients who presented with a clinically and radiologically proven FAI and failed conservative treatment were considered for an arthroscopic procedure.

Operative technique

The patient is positioned in lateral decubitus, opposite to the operated side (Fig 1), with a fluoroscopy placed at the level of the hip in order to control the placement of the hip-specific distractor and the arthroscopic portals. First, the hip-specific distractor (DR Medical AG, Solothurn, Switzerland) is placed. Two Schanz screws of 6mm diameter are positioned above the superior portion of the acetabulum (Fig 2) under fluoroscopic guidance. Two other screws are placed at the level of the lesser trochanter in the proximal femur. Screw placement technique is easy starting with blunt dissection and positioning of the tissue protecting sleeve to avoid any injury to surrounding soft tissues. Drilling is performed through the protecting sleeve followed by the insertion of the Schanz screw. The hip-specific distractor is then assembled allowing for an initial hip distraction followed by hip abduction (Figs 2 and 3). The Schanz screws (diameter of 6mm) were used to scale fluoroscopic images in order to be able to measure initial femoro-acetabular joint opening.

Fig 2 — Fluoroscopic control (left hip, front view) after positioning of the hip-specific distractor representing the amount of hip distraction obtained.

Fig 3 — This picture demonstrates the hip-specific distractor in place while distraction is applied.

After proper hip distraction, a first anterolateral portal is positioned under fluoroscopic guidance using cannulated needles. The arthroscope is inserted through this first portal, allowing for a rapid examination of the hip joint. A second portal is then placed, 2 fingers breadth anterior to the first anterolateral portal under fluoroscopic and arthroscopic guidance. If necessary, the third portal can be placed posterior to the greater trochanter. After insertion of all 2 to 3 portals, we perform a short partial anterior curved capsulotomy between the first and the second portal. First the central compartment is inspected. In cases of associated chondral lesions debridement or microperforations are performed. Chondral lesions were classified according to the Outerbridge classification [13]. Labral lesions are assessed and debridement was performed if required. Then, osteoplasty of the acetabular rim is performed in cases of Pincer-type lesions. Finally reinsertion of instable labral lesions is performed.

After addressing the central compartment, distraction is progressively removed allowing for a thorough inspection of the peripheral compartment, and osteoplasty of the femoral head-neck junction is performed in cases of CAM-type lesions. After completely removing of the hip-specific distractor, the femoral neck osteoplasty is completed and we control arthroscopically and fluoroscopically for any residual impingement. The removal of the hip-specific distractor allows us to perform dynamic testing of the hip under arthroscopic visualisation to control the absence of any residual impingement. If an impingement remains present, further regularisation of the femoral neck can be performed.

The portals entries were infiltrated with a diluted ropivacaïne 2% for postoperative pain control before wound closure.

During the postoperative period, patients were allowed a weight bearing up to 30kg for a period of 4 weeks associated with physiotherapy and indoor cycling to avoid capsular adhesions.

Data analysis

The study was performed in 2 steps. During the first phase we analysed for objective values as the surgical intervention time, hospital stay, peri- and postoperative complication rates and conversion rate to total hip arthroplasty (THA). Patients were also evaluated for global satisfaction and their possibilities to return to sports if they were sportsmen. Analysis of any association regarding patient’s satisfaction and THA conversion rate was performed with a Fisher’s exact test, with a p-value < 0.05 considered to be statistically significant.

The second phase of the study was to try to analyse the learning curve of this procedure. We divided all cases by sequential groups of 10 patients each (Group A, B, C, D and E); the last group of patients containing a total of 16 patients as a group of only 6 patients was assumed to be too small to be able to be compared to the other groups. Then we were able to make curves based upon the intervention time, complication numbers, hospital stay, patient’s satisfaction and conversion rate to THA. Differences in intervention time between the first 30 cases and the last 26 cases were also analysed. Data are given as mean ± SD. Homogeneity of variances was tested with a modified Levene test, and normality of the residuals was tested with the Shapiro-Wilks test. As these assumptions were rejected, the data were compared with the Mann-Whitney test. A global two-sided p-value <0.05 was considered statistically significant.

All statistical analyses were performed with the SAS University Edition (SAS Institute Inc., Cary, NC, USA) program. This study has been approved by the local committee of medical ethics at our institution (Comité d’éthique Erasme-ULB: P2017/483). Oral informed consent was obtained for all patients included in this study.

Results

General characteristics

Fifty-six hip arthroscopies were performed in 54 patients. There were 25 females and 31 males. Mean age of patients was 35 years old [17 – 59]. Six patients were lost of follow-up. Mean duration of follow-up was 53 months with a minimum of 12 months [12 – 101].

All patients benefitted preoperatively of a radiological work-up comprising conventional x-rays, MRI and arthro-CT showing signs of FAI in all symptomatic hips. In 26 hips isolated CAM-type lesions were identified whereas only 5 hips presented with isolated Pincer-type lesions. All other hips presented with signs of combined FAI. Thirty-three hips demonstrated no signs of osteoarthritis. Sixteen hips presented with a Tönnis grade 1 osteoarthritis, 6 hips with Tönnis grade 2 and 1 hip with a Tönnis grade 3 (S1 Table). Seven hips presented with at least 1 radiographic sign of acetabular retroversion. No patients presented with Developmental Dysplasia of the hip or sequelae of Legg-Calvé-Perthès disease.

Surgery related data

Mean femoro-acetabular widening was 12mm [6 to 20]. Four of the five hips presenting with less than 10mm of hip distraction presented no signs of hip osteoarthritis on preoperative x-rays. Of those patients, only one patient was female, all other patients presenting with less than 10mm of hip distraction were males. In all cases the hip was found to be sufficient distracted to be able to perform hip arthroscopy. We encountered no difficulties accessing the hip joint. Overall mean surgical time was 223 minutes [120–485]. In all cases the entire surgical procedure could be performed as planned without any time limits. Mean hospital stay was 2 days postoperatively.

After intra-operative evaluation of the hips, 26 isolated osteoplasties of the femoral head-neck junction were performed, 5 isolated osteoplasties of the acetabular rim and 25 combined procedures were performed (Table 1). Labral lesions were debrided in 47 hips and reinsertion could be performed in 6 hips. Interesting is that those labral reinsertion were only performed as from the 35^th case in the learning curve. Acetabular chondral lesions were treated with debridement in 22 hips and with microperforations in 9 hips.

Table 1. Operative gesture.

Treatment of FAI	n ^a
Isolated Pincer lesions: Osteoplasty of acetabular rim	5
Isolated Cam lesions: Osteoplasty of femoral head-neck junction	26
Combined FAI: Combined procedure	25
Treatment of associated labral lesions
Absence of lesions	3
Debridement	47
Reinsertion	6
Treatment of associated chondral lesions
No supplementary gesture	25
Debridement	22
Microperforations	9

Open in a new tab

Table 1 describes all operative gestures performed regarding the treatment of FAI and associated lesions as labral and chondral lesions.

^a n = numbers of hips.

Complication and total hip arthroplasty conversion rates

Total complication rate was 10,7% (Table 2). We encountered only 1 major complication represented by a hip subluxation. This patient benefitted of a THA 2 months following hip arthroscopy due to progressive hip dislocation and rapid osteoarthritis development (Fig 4). All other complications were minor complications and are summarized in Table 2.

Table 2. Complications.

Type of complications	n
Major complications
Femoral fracture	0
Major bleeding	0
Complete dislocation	0
Hip subluxation	1
Minor complications
Painful oedema of the torso (spontaneous resolution)	2
Minor postoperative wound bleeding (spontaneous resolution)	1
Minor iatrogenic head injury	1
Minor labral injury	1

Open in a new tab

Table 2 summarizes all complications encountered in our series. Major complications were defined as complications which necessitated a prolonged hospital stay or reintervention. Minor complications were defined as complications without negative repercussions for the patient.

^a n = number of hips.

Fig 4 — This picture shows (A) the preoperative x-rays and (B) the postoperative x-ray 1 month after hip arthroscopy with progressive hip dislocation and rapid osteoarthritis.

The total conversion rate of THA was 17% (9 hips). Six patients benefitted of a THA during the first 2 years following hip arthroscopy for the treatment of FAI. One patient had a THA at 3 years, one at 4 years and a last patient at 6 years after arthroscopic treatment (S1 Table). Mean age of patient who had a conversion to THA was 39.4 years [24–53 y]. We found no association between the preoperative Tönnis classification and the conversion rate to THA (p-value 0.098)

Satisfaction and return to sports

Global satisfaction rate of the patients in this series elevated up to 78%. When focussing on the group of younger patients ≤ 35 years (31 hips with a mean age of 27 years [17–33 y]) satisfaction rate raised up to 89%. All patients who were satisfied assured us that they would undergo the same surgical procedure if they had to reconsider it. Even one patient who hadn’t been satisfied mentioned he would do it all over again if he had the choice. We found no association between satisfaction rate and the Tönnis classification (p-value 0.337).

Twenty-six patients were sportsmen. Of those patients, 75% were able to return to their sports after the postoperative rehabilitation. And almost half of those patients (43%) were able to perform their sports at the same level as they performed before the start of their symptoms related to FAI. We found no association between satisfaction rate and whether or not patients were sportsmen (p-value 0.097).

Learning curve

The curve based upon the intervention time (Fig 5) showed a good decrease in mean operating time over the cases performed. Mean intervention time for the first 30 cases was 250.8 ± 74.0 minutes compared to 191.1 ± 47.8 for the last 26 cases. This difference was statistically significant (p-value = 0.0002). The curve analysing patient’s satisfaction showed also an improved satisfaction of patients of the cases performed. Over time complication rate and hospital stay remained stable.

Discussion

In our series we noticed an overall decrease in operative time over time. A decrease of 22% of the total operative time has been noted between the first 30 cases and the last 26 cases of our series and this difference was found to be statistically significant (p < 0.05). This might be consistent with the cut-off described in the literature [4, 14].

Complication rate in our series remained quite stable over time. Although we had a change in nature of complications, as perioperative complications arose after the first 30 cases. This might reflect the increasing complexity of the interventions performed. Even if a decrease in complication rate has been expected over time, other authors also have described a change in complications instead [7, 9]. This might be in accordance with the belief that while a surgeon gains experience and thus comfort in performing a particular intervention, he starts to operate more complex cases over time [7, 11, 14]. This might also be noted in our learning curve as mean intervention time of group D (patients 31 to 40) increased slightly compared to group C. This could be explained as labral repair, a more difficult and time-consuming procedure was started from the 35^th case in the curve.

The overall complication rate (10.7%) in our series is similar as other complication rates described in the literature [1, 3, 7, 9]. We encountered only one major complication: a postoperative subluxation of the femoral head leading to an early conversion to THA. This complication has also turned up in another series and was thought to be related to an excessive resection of the anterior acetabular rim [7]. We believe this was also the case for this patient in our series who presented with postoperative subluxation of the hip, as an excessive acetabular resection induced a secondary hip instability with progressive dislocation and rapid hip osteoarthritis. We encountered only 1 minor postoperative complication probably related to the positioning of the patient on the operating table; a painful oedema of the torso which showed a spontaneous and early resolution in 2 patients.

Perioperative complications as labral and cartilage damage are thought to be underreported in the literature [1, 8, 10]. We encountered only 1 labral injury and 1 chondral injury in the late cases of our series. The labral injury might be due to a very stiff joint, as with sole distraction we were only able to achieve the minimal required distraction of the hip of 6mm to be able to start the procedure before capsulotomy. In the series of Park et al. those complications arose in the early and later phase of the learning curve [9]. As those lesions were supposed to be due to poor surgical technique and learning in the early phase, they were thought to be caused by stiff joints in the later phase [3]. Which might represent the gain in comfort of a surgeon in performing more difficult surgeries [7, 11, 14].

Most authors account the traction-related neurovascular complications as the most encountered complications following hip arthroscopy [7–10]. Traction-related complications can either be associated with the traction itself (distraction-type injury) or with the perineal post used as counter traction on orthopaedic traction tables (compression-type injury) [8]. Distraction-type injuries are described as transient neurapraxia, the sciatic and femoral nerves being the most vulnerable to prolonged and excessive traction [8]. Compression-type injuries are encountered in the area of the groin and can vary from pudendal nerve injuries to oedema, hematoma and pressure necrosis of the scrotum and labia majora [8]. Those complications can rise up to 10–15% [11] and are directly related to the technique, the length and the forces of the traction applied [5, 14, 15]. Souza et al found in their series that traction-related complications accounted for 58% of their total complication rate [7]. Another series presented a traction-related complication rate of 4% [4]. Lee et al described the presence of 3 traction-related complications in a series of 40 patients [5]. Traction-related complications are also described as being more frequently encountered during the first cases of a surgeon’s learning curve and tend to decrease with the experience of this surgeon [4, 9]. In our series we encountered no traction-related neurovascular complications. Other series, describing the use of a hip-specific distractor, showed also the absence of neurovascular complications [1, 16]. On a traction table distraction is applied at the level of the foot and to obtain a 10 mm distraction at the hip to be able to perform hip arthroscopy, the additional lengthening of the ankle and the knee might lead to an overall lengthening of that lower limb potentially at risk for the sciatic nerve [1]. With the use of an hip-specific distractor, the traction applied is focused on the hip only, avoiding the need of traction on the whole limb and the use of a perineal post, thus avoiding those traction-related complications both the distraction- and the compression-type injuries [8].

Up to 18% of hips are described as difficult accessible [8]. Konan and al. found 2% of hips inaccessible in their series [4]. In this series, representing a single surgeon learning curve, there were also 3 hips in which the surgical gesture couldn’t be finished due to lack of time on the traction table [4]. Another author presented difficulties in starting the hip arthroscopy as 1.9% of the hips were found to be insufficient distracted to be able to start with the intra-articular compartment [3]. In those cases hip arthroscopy might be started through the peripheral instead of the central compartment [10]. In our series, all hips were found to be sufficient distracted to be able to perform hip arthroscopy, as planned starting with the intra-articular compartment. Also, in our experience, hip distraction was always increased after capsulotomy thus allowing for more working space. We could also perform the entire operative gesture in all cases as the use of a hip-specific distractor decreased the limit described when using the traction table [11]. This similarity has also been described using a hip-specific distractor in other series [1, 16].

Other potential positive aspects of a hip-specific hip distractor can be represented by the direct and immediate control that a surgeon has over the traction forces applied by the device [11]. External distraction can also easily be removed for dynamic testing of eventual residual impingement [11] which might be more difficult in our opinion on a traction table. Potential drawbacks for the use of a hip-specific distractor are the slightly increased operative time, as it takes approximately 18 minutes to position a hip-specific distractor [1]. In our personal experience, the time of positioning of the device can be decreased with the experience of the surgeon and good assistance. It is also more invasive than standard hip arthroscopy on a traction table [1, 8, 11]. Another question that can be raised is the potential conflict of the presence of the device while performing arthroscopic gestures. We never encountered any difficulties in performing the planned gestures while the hip-specific distractor was positioned. In our experience we also never had to abort an intervention nor change the planned intervention for lack of time. We personally believe this hip-specific distractor to be a very useful tool and therefore we continue to use this device when performing standard hip arthroscopy at our institution.

Although we were not able to decrease the learning curve of a surgeon using a hip-specific distractor, it might be helpful in the early phase as beginner surgeons wouldn’t have to worry about distraction time and traction-related complications [11]. Another way to decrease early complications has been shown to be supervision [3]. Dietrich et al evaluated the learning curve of 2 different surgeons; the second surgeon being supervised by the first surgeon after his learning curve had been completed [3]. They showed a significant decrease in complication rates in the early cases performed by the second surgeon [3]. Therefore, the use of a hip-specific distractor might be useful for those beginner surgeons who could not possibly benefit of a guided supervision and help.

THA conversion rate in our series elevated up to 17%, which seems to be higher than those described in other series. Philippon et al. described a THA conversion rate of 9% after hip arthroscopy to treat FAI [17]. Byrd et al. described also a specific series of hip arthroscopy for Cam-lesions and showed a conversion rate to THA of 0.5% [15]. We believe that the THA conversion rate found in our series was related to a broader patient selection as some patients were 50 years and older of age. When analysing the curve we noticed that in the first 30 cases operated 7 out of 9 THA were performed, whereas only 2 patients were converted to THA in the last 26 cases performed. This could reflect the learning of the surgeon but it could also be biased as follow-up of the first cases performed was much longer than last cases.

The satisfaction rate of 78% in our series is comparable to results found in the literature. A small series described a treatment failure rate of 20% [5]. Byrd et al. showed also a general postoperative improvement of 83% [15]. Another series using an invasive distractor showed an overall satisfaction rate of 79% [16].

In our series we were also able to notice a change in indication as the surgeon operated younger patients with less signs of osteoarthritis. This might also account for the increased satisfaction rate and decreased THA conversion rate in the later phase of our study.

We were not able to correlate a poor postoperative evolution with the presence of osteoarthritis. This might be due to the small number of patients in our series. Although, presence of osteoarthritis has been found to be a poor postoperative prognostic factor [16–19].

The strength of this study probably lies in the fact that all cases were performed by the same surgeon for the same operative indication at the same institution.

One of the major limitations of this study relies in its retrospective nature as we had a few losses of follow-up (10%) and lacked patient’s satisfactions and evolutions. A second limitation of our study is represented by its relatively small size as only a total number of 56 cases were operated. This made the analysis of early evolution in a surgeon’s experience possible but we were not able to evaluate his further progression as the curves didn’t reach a real plateau yet.

Conclusion

Hip arthroscopy for FAI using a hip-specific distractor is a safe and reproducible intervention with complications rate comparable to those found in the literature.

One of the major advantages of a hip-specific distractor is the absence of neurovascular traction-related complications with this technique. As those complications occur especially during the first part of a surgeon’s learning curve [4, 9], a hip-specific distractor might be helpful at the beginning of a surgeon’s experience as there is no time pressure and the procedure can be entirely performed as initially planned.

Supporting information

S1 Table

(DOCX)

Click here for additional data file.^{(17.1KB, docx)}

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0246655.r001

Decision Letter 0

Osama Farouk

17 Aug 2020

PONE-D-20-12351

Advantages of hip arthroscopy using an external hip distractor for the treatment of femoroacetabular impingement.

PLOS ONE

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PLOS ONE

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Comments to the Author

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Reviewer #1: Partly

Reviewer #2: Partly

**********

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Reviewer #1: I Don't Know

Reviewer #2: N/A

**********

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Reviewer #1: No

Reviewer #2: Yes

**********

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Reviewer #1: Study Hypothesis: the use of Hip distractor for Hip arthroscopy was not associated with traction or compression complications, it would facilitate the learning curve. The aim of the study was to evaluate the learning curve of hip arthroscopy using a hip-specific distractor and the complications related to this procedure

The authors provided a good introduction stressing the fact that the use of external hip distractor during hip arthroscopy has not been associated with any of the traction or compression type complications, that otherwise could be associated with the use of traction table, hence They hypothesized that the use of a distractor would relieve the surgeon from the burden of Time stress during traction And will allow him completing the whole planned procedure without fear of traction or compression type complications.

They conducted a retrospective analysis with inclusion of all cases treated from September 2007 to March 2015 In a single center by a single surgeon. The operative technique is adequately described. They mention clear inclusion criteria.

Discussion of specific areas for improvement

Major points:

1. although the primary objective of the study was clearly defined, The descriptive and statistical analysis of the learning curve was inadequate.

the construction of such learning curve, how and why it was grouped into those unequal 5 groups is not clear in the text and was only mentioned in the figure 4 caption

2. Another major point is the lack of description of any statistical method or test used to evaluate changes in the learning curve

Other points to be considered

1. In the methodology, there is no mention of exclusion criteria. Were there any?

2. In the section of outcome measurement, no functional scores were collected perioperatively to objectively measure the outcome and only patient satisfaction (subjective) and total hip conversion rate were collected.( questionable value with short follow up which in some cases as short as one year)

3. The authors describe That all cases head preoperative imaging studies (X-rays, CT and MRI) however there is no reporting of the radiological parameters commonly used to measure The cam and pincer deformities whether pre- or postoperatively to control the adequacy of the performed surgery. This is important to support the claim of completeness of the surgical gesture in all the cases.

4. In the statistics section of the methodology, there is only mention of the used statistics software.

There is no mention of any statistical method or statistical test performed . Also whether the mentioned differences in the learning curve for intervention time and patient satisfaction were statistically significant or not.

5. also In the methodology, why selection was limited to the 56 hips although the authors described that until currently the learning curve is still ever changing. Was there power calculation for this sample size determined?

6. Line 111: labral reinsertion is performed after osteoplasty not vice versa.

7. The number of labral reinsertions in relation to the number of pincer/ mixed impingement treated is relatively low, here one would like to know where these more advanced time consuming reinsertions are located in the learning curve.

8. line 191: patients younger than 35, how many are they? A more detailed age description for example with the median value should be included.

9. line 192, 193 reconsider this sentence.

10. Concerning the 17% total hip arthroplasty conversion (9 hips) which was explained by the older age, here again the age of those patients should be mentioned (range and mean)

Secondly The cartilage condition intra operatively (grade and extent of cartilage damage) was not described this might be directly related.

Where in the learning curve are those cases located? persistence of symptoms, dissatisfaction and eventually total hip replacement could also occur in the beginning of learning curve, the adequacy of resections as mentioned before should be proven by radiological measurements?

Reviewer #2: Please review attached Doc in which I wrote all my requested changes

Thank you

Title - Advantages of hip arthroscopy using an external hip distractor for the treatment of femoro-acetabular impingement.

Comment 1 – looks irrelevant to the hypothesis and goal

“The goal of this study was to evaluate the learning curve of hip arthroscopy using a hip-specific distractor and the complications related to this procedure.” line 70

Removal/replacement of the word advantage with evaluation will reflect the idea better.

The word “advantage” draws the attention towards more benefits than the conventional traction table, however this is not the case here. Its only an evaluation of this traction technique.

Comment 2 – I prefer sticking to one name for the distractor used; either “external hip distractor” used in title or “hip-specific distractor” used in the introduction

Abstract

Comment 1 – word “per” should be replaced with peri

Comment 2 – poorly written. Needs to be re-written in a more attractive and informative way. Keeping in mind that this is the most read part of the paper. If not attractive, the reader will refrain from reading the paper.

Introduction

Generally, well-written covering the gap available in working with conventional traction table, and goal behind the study.

Comment 1 - Line 55: Distraction- of compression-type complications are related to the length of the……. Replace “of” with “and”

Comment 2 – I prefer sticking to one name for the distractor used; either “external hip distractor” used in title or “hip-specific distractor” used in the introduction

Materials and Methods

Generally, the materials and methods section lack the most important part the readers will be waiting for which is a precise and complete description of this specific distractor. Nothing was mentioned about the distractor apart form an intraoperative photo (Figure 3).

This is a major defect in this section that should be properly addressed under a specific subtitle together with proper illustrative photos or diagrams explaining its application and biomechanics.

Points of strength

• Type of study = retrospective September 2007 to March 2015

• Single disease = FAI

• Single Surgeon

Comment 1 – no reference was there for the preoperative conservative treatment protocol. On which basis this, 6m for athletes and 1-year conservative treatment protocols were set?

Comment 2 – Special mechanical analysis and attention should be paid and mentioned for the biomechanics of this distractor

? Material

? Line of forces pull, and Maximum force withstand

? Method of distraction in this instrument? Is it manual?

? Others, to be provided by manufacturer

Comment 3 – Lines 113,114 “Then, the peripheral compartment is assessed, and osteoplasty 113 of the femoral head-neck 114 junction is performed in cases of CAM-type lesions.”

I understood that you start working on the PC while traction is still applied… what is the advantage for this?

Comment 4 - Nothing was mentioned about the exclusion criteria or contraindication of using this distractor. Do you still use it in all patients? Even in osteopenic or osteoporotic bone?

Comment 5 – Supra- acetabular area is the pathway of the superior gluteal bundle supplying the gluteus medius, minimus and tensor facia lata muscles…. Did you have any injury for these important structures? I can see none in the results section…. Please describe your insertion technique to avoid these structures.

Results

Poor numbers for proper evaluation

• 56 hips were performed in 54 patients in 8 years

• 23 hips with OA

• 6 patients lost at follow up

Comment 1 – Line 154: Mean femoro-acetabular widening was 12mm [6 to 20].

The method of measurement was not described and verified in the M and M section. Please mention?

Comment 2 – Line 155: In all cases the hip was found to be sufficient distracted to be able to perform hip arthroscopy

Please verify and relate the distraction distances in different tonnis grades and different Genders?

Theses are the two main factors that affect the distraction power, these needs special results analysis and correlation.

Comment 3 - Complication and total hip arthroplasty conversion rates

This section is a critical section as its will be of main concern to the readers to understand the complications expected from this distractor.

1. I do not understand the major complication of the “hip subluxation”

Did it happen immediately postoperative or later? What was the expected reason? and why rapid conversion to THA? Were other treatment methods consumed?

I can see in the discussion section a brief analysis of this complication, however, no exact reason was detected or explained.

If available, please provide the postoperative radiology for this case, to share this abnormal complication with the readers.

2. There is no need to repeat the complications twice in paragraph and table format.

3. There is no need to mention the zero complications in the table format

Discussion

General unaddressed issue: as mention traction results into distraction and compression type problems. I can understand that this distractor avoids the compression problems, however, you mentioned that it avoids both despite using it without time limits!!!

Line 256- In our series we 256 encountered no traction-related neurovascular complications.

Line 63 could help beginner surgeons in performing 63 hip arthroscopy without concerning about the surgical time and thus traction-related 64 complications [1, 11].

I agree that traction here is focused on the hip as mentioned in the discussion but is this enough to avoid all the NV complication for distraction for anytime limit. I think time limit is still a very important factor and should never be underestimated. Please verify and discuss further….

The discussion is lacking the biomechanical values of the distractor. For example, the lines of pull it provides. We know that you need a lateral and distal line of pulls for the best hip asses and this is provided by putting the perineal post slightly laterally (not in midline) and adducting the hip to provide lateralization force with leg traction.

Can you explain and discuss similar pulling forces by the distractor and advantage/ disadvantage of it?

The discussion is focused on the surgeon learning curve, which I can see is not related to the device used. Please revise your discussion and focus it on the device used, which is the main issue here, explaining and discussing all aspects of its use.

**********

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Reviewer #1: Yes: Mohammad A. Masoud MD

Reviewer #2: No

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PLoS One. 2021 Feb 11;16(2):e0246655. doi: 10.1371/journal.pone.0246655.r002

Author response to Decision Letter 0

14 Oct 2020

Dear Editor and Members and Reviewers of the Editorial Board,

Dear Editor in chief and reviewers, we thank you for the attention you’ve given our manuscript so far and we hope the changes we made to it will be to your liking. We’ve carefully read all your comments and we do hope that following answers and changes will help to clarify your decision.

Journal Requirements: When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

a. Response: We controlled and ensured that our manuscript meets PLOS ONE’s style requirements, including those for file naming.

a. Response: Our manuscript has been carefully proofread as asked for potential typographical errors.

a. Response: The corresponding author (MJ) has validated his ORCID iD in the Editorial Management as requested

a. Response: Caption for supporting file has been added.

Discussion of specific areas for improvement

Major points:

1. although the primary objective of the study was clearly defined, The descriptive and statistical analysis of the learning curve was inadequate. the construction of such learning curve, how and why it was grouped into those unequal 5 groups is not clear in the text and was only mentioned in the figure 4 caption

Response: We adjusted the descriptive of the analysis of the learning curve as requested in the section material and methods.

We adjusted also the part in material & methods describing the creation of the learning curves, but we didn’t perform any tests to evaluate changes as Hoppe et al stated in their systematic review that “Conceptually, a learning curve should be identified as a graph in which a consecutive number of cases are presented on the horizontal axis and some measure of proficiency or learning is presented on the vertical axis” (sic) http://dx.doi.org/10.1016/j.arthro.2013.11.012; Also testing between groups of 10 patients each might not clinically nor statically have a lot of meaning in our opinion.

2. Another major point is the lack of description of any statistical method or test used to evaluate changes in the learning curve

Response: Also testing between groups of 10 patients each might not clinically nor statically have a lot of meaning in our opinion. (see response to previous point)

Other points to be considered

1. In the methodology, there is no mention of exclusion criteria. Were there any?

Response: No, there were no exclusion criteria, except for a patient’s possible refusal to participate to this study. A learning curve is the analysis of all successive patients who underwent a specific surgery for a specific indication, if there were other exclusion criteria, it might not reflect a proper learning curve. For example, if we had to exclude patients of older age, we might have had to exclude some of the first patients which would not reflect the actual learning of a surgeon in this specific setting.

Response: Most learning curves limit themselves in analysing operative time and perioperative and postoperative complications. We actually also evaluated patient’s satisfaction rates and conversion/revision rates, which are parameters rarely evaluated when evaluating learning curves. The strong point of this study is that it actually evaluates the learning of hip arthroscopy for one specific indication, as some authors suggest that every gesture in hip arthroscopy might present with its personal learning curve. Indications are not mixed in this study.

Response: In the section results (subtitle general characteristics) preoperative radiological evaluation of all patients has been described in general. The claim of completeness is not in accordance of the whole CAM or the Whole pincer that has been corrected; I don’t think that anyone can claim that as easy. We claim that we could do all we planned to do, without concerning about time and traction-related complications. We were able to correct deformities, treat labral lesion and chondral lesion and control the absence of residual impingement with dynamic testing under fluoroscopic and arthroscopic visualisation.

4. In the statistics section of the methodology, there is only mention of the used statistics software.

Response: We adjusted the description of the statistics used in this manuscript.

Response: No there was no power calculated for this study. When starting the study, we had only those first 56 patients who presented with at least 1 year of follow-up. We could not include others as follow-up was less than 12 months.

6. Line 111: labral reinsertion is performed after osteoplasty not vice versa.

Response: Line 111: you are correct. We changed this; sorry for this mistake in the manuscript, we must have overlooked it

Response: Where are those more time-consuming labral lesions situated in the learning curve? A very interesting question indeed. This has been added in the result section as those labral repairs were performed as from the 35th case and not earlier, thus slightly increasing mean intervention in the learning curve. I also took the liberty to add a note in the discussion regarding this.

8. line 191: patients younger than 35, how many are they? A more detailed age description for example with the median value should be included.

Response: Line 191: has been addressed in the revised manuscript.

9. line 192, 193 reconsider this sentence.

Response: Line 192: has been rewritten.

10. Concerning the 17% total hip arthroplasty conversion (9 hips) which was explained by the older age, here again the age of those patients should be mentioned (range and mean)

Secondly The cartilage condition intra operatively (grade and extent of cartilage damage) was not described this might be directly related.

Response: This has been addressed in the revised manuscript.

Reviewer #2: Please review attached Doc in which I wrote all my requested changes

Thank you

Title - Advantages of hip arthroscopy using an external hip distractor for the treatment of femoro-acetabular impingement.

Comment 1 – looks irrelevant to the hypothesis and goal

“The goal of this study was to evaluate the learning curve of hip arthroscopy using a hip-specific distractor and the complications related to this procedure.” line 70

Removal/replacement of the word advantage with evaluation will reflect the idea better.

The word “advantage” draws the attention towards more benefits than the conventional traction table, however this is not the case here. Its only an evaluation of this traction technique.

Response: Title has been changed according as requested.

Comment 2 – I prefer sticking to one name for the distractor used; either “external hip distractor” used in title or “hip-specific distractor” used in the introduction

Response: As requested, we also paid attention and from now on, the only term referring to the device used is “hip-specific distractor”.

Abstract

Comment 1 – word “per” should be replaced with peri

Response: This has been changed.

Response: I tried to make the abstract more attractive and hope you will prefer that way.

Introduction

Generally, well-written covering the gap available in working with conventional traction table, and goal behind the study.

Comment 1 - Line 55: Distraction- of compression-type complications are related to the length of the……. Replace “of” with “and”

Response: Has been changed.

Comment 2 – I prefer sticking to one name for the distractor used; either “external hip distractor” used in title or “hip-specific distractor” used in the introduction

Response: We changed every “external hip distractor” with the term “hip-specific distractor”, so we stuck to only 1 term referring to the device as requested.

Materials and Methods

This is a major defect in this section that should be properly addressed under a specific subtitle together with proper illustrative photos or diagrams explaining its application and biomechanics.

Response: Regarding your comment of major defect in our section of material and methods…. I adjusted the introduction of the article, explaining a bit more about the line of work and how the hip-specific distractor works in a biomechanical way, so our hypothesis seems more concrete and better understandable for those who does not apply regularly this device. On the other hand, the main goal of this manuscript was not to describe the biomechanics of the hip-specific distractor but to describe a series (with learning curve) using the device. The biomechanics with diagrams as requested have already been described in other works published by other authors. (Sadri H. Techniques in hip arthroscopy and joint preservation surgery; Elsevier Saunders, 2011: pp 113-120)

Points of strength

• Type of study = retrospective September 2007 to March 2015

• Single disease = FAI

• Single Surgeon

Comment 1 – no reference was there for the preoperative conservative treatment protocol. On which basis this, 6m for athletes and 1-year conservative treatment protocols were set?

Response: No, the duration of conservative treatment before planning hip arthroscopy is still debated in the literature and not very clear. We know that some patients respond to conservative treatment hence surgery is not always warranted. But athletes tend to wait less before surgery because they need to restart their sports activities and cannot wait 1 year for conservative treatment to be completed followed by at least 6 months of rehabilitation after arthroscopic surgery.

Comment 2 – Special mechanical analysis and attention should be paid and mentioned for the biomechanics of this distractor

? Material

? Line of forces pull, and Maximum force withstand

? Method of distraction in this instrument? Is it manual?

? Others, to be provided by manufacturer

Response: See response to the same point raised above (I adjusted the introduction of the article, explaining a bit more about the line of work and how the hip-specific distractor works in a biomechanical way, so our hypothesis seems more concrete and better understandable for those who does not apply regularly this device. On the other hand the main goal of this manuscript was not to describe the biomechanics of the hip-specific distractor but to describe a series (with learning curve) using the device. The biomechanics with diagrams as requested have already been described in other works published by other authors.)

Comment 3 – Lines 113,114 “Then, the peripheral compartment is assessed, and osteoplasty 113 of the femoral head-neck 114 junction is performed in cases of CAM-type lesions.”

Response: you are correct. We changed this; sorry for this mistake in the manuscript, we must have overlooked it.

I understood that you start working on the PC while traction is still applied… what is the advantage for this?

Response: Distraction is progressively diminished when we start to work on the PC compartment. This has been adjusted.

Comment 4 - Nothing was mentioned about the exclusion criteria or contraindication of using this distractor. Do you still use it in all patients? Even in osteopenic or osteoporotic bone?

Response: To answer your question, we still indeed use it in every case of hip arthroscopy we perform. We feel that the joint opening offered by the hip-specific distractor allows us to treat much better all lesions encountered in the joint. Nowadays, we can associate labral reinsertion with cartilage repair techniques with great ease, which we feel might be much more difficult without the hip-specific distractor. Since hip arthroscopy is mainly indicated in a young sportive population, osteoporotic bone is rarely a major concern.

Response: Avoiding soft tissue damage: Placement of the schanz screws after blunt dissection and positioning of the protecting sleeve in the correct position. Drilling is performed through the protecting sleeve followed by screw insertion. This has been adjusted and added in the material and method, subsection ‘surgical technique’.

Results

Poor numbers for proper evaluation

• 56 hips were performed in 54 patients in 8 years

• 23 hips with OA

• 6 patients lost at follow up

Comment 1 – Line 154: Mean femoro-acetabular widening was 12mm [6 to 20].

The method of measurement was not described and verified in the M and M section. Please mention?

Response: The Schanz screws (diameter of 6mm) were used to scale fluoroscopic images in order to be able to measure femoro-acetabular joint opening. This has also been added in the material and methods to clarify our measurement methods.

Comment 2 – Line 155: In all cases the hip was found to be sufficient distracted to be able to perform hip arthroscopy

Please verify and relate the distraction distances in different tonnis grades and different Genders?

Theses are the two main factors that affect the distraction power, these needs special results analysis and correlation.

Response: we reviewed those cases as asked and added this to the manuscript. But it is very disappointed as 4 of the 5 hips presented no signs of osteoarthritis and 4 of the hips were males.

Comment 3 - Complication and total hip arthroplasty conversion rates

This section is a critical section as its will be of main concern to the readers to understand the complications expected from this distractor.

1. I do not understand the major complication of the “hip subluxation”

Did it happen immediately postoperative or later? What was the expected reason? and why rapid conversion to THA? Were other treatment methods consumed?

I can see in the discussion section a brief analysis of this complication, however, no exact reason was detected or explained.

If available, please provide the postoperative radiology for this case, to share this abnormal complication with the readers.

Response: this complication has been further clarified in the manuscript as asked. We did modify this section so complications were not repeated both in text and table as asked. And we removed the “zero” complications of the table as asked, although this was to highlight the absence of traction-related complications.

2. There is no need to repeat the complications twice in paragraph and table format.

Response: This has been addressed in the revised manuscript.

3. There is no need to mention the zero complications in the table format

Response: This has been addressed in the revised manuscript.

Discussion

Line 256- In our series we 256 encountered no traction-related neurovascular complications.

Line 63 could help beginner surgeons in performing 63 hip arthroscopy without concerning about the surgical time and thus traction-related 64 complications [1, 11].

Response: Regarding you concern about time limit and potential NV complications. Up to now, all series describing the use of a hip-specific distractor have never been associated with traction-related complications regardless of the intervention time as seen in series using an orthopaedic traction table. I admit, not a lot of surgeons do use a hip-specific distractor as some might think it less attractive due to its more invasiveness than an orthopaedic traction table, so there are not a lot of studies describing the use of hip-specific distractor, which is one of the reasons why this one might be very interesting. But its use has never been associated with traction-related complications regardless of the intervention time. I don’t think that this needs further description in the discussion section. Nevertheless, I do agree that time is a very important factor. A hip arthroscopy should not take a whole day to be performed, for the patient’s sake.

Can you explain and discuss similar pulling forces by the distractor and advantage/ disadvantage of it?

Response: This is a retrospective case series describing the use of the distractor. It is not a biomechanical study evaluating the feasibility of the hip-specific distractor. Others authors have already described this. (Also see previous response regarding similar comment.) But I don’t think that a text-book description of the biomechanics of the hip-specific distractor has its place in the discussion of this study.

Response: Personally, I don’t understand why we should revise the entire discussion, since this study is describing “a learning curve”, it might be normal that it is compared to other published learning curves in order to see if there might be potential advantages in using this device. Throughout the entire first part (1 page) of the discussion we discuss complications associated or not with the device, which is very important since avoidance of traction-related complication is one of the major reasons why a hip-specific distractor is so interesting. Lines 281 to 293 are dedicated to the pros and cons of the device. Repeating the description of the surgical technique has no necessity in the discussion in our opinion.

Thank you for considering our manuscript,

Thank you for your revision and comments, they were very helpful.

Sincerely,

The authors,

Marc Jayankura & Tatiana Charles

Attachment

Submitted filename: Rebuttal letter.docx

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PLoS One. doi: 10.1371/journal.pone.0246655.r003

Decision Letter 1

Osama Farouk

30 Nov 2020

PONE-D-20-12351R1

Evaluation of hip arthroscopy using a hip-specific distractor for the treatment of femoroacetabular impingement.

PLOS ONE

Dear Dr. Jayankura,

Please submit your revised manuscript by Jan 14 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

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We look forward to receiving your revised manuscript.

Kind regards,

Osama Farouk

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

**********

6. Review Comments to the Author

Reviewer #1: 1- Response to point 1: the statement by Hoppe et al in their systematic review that “Conceptually, a learning curve should be identified as a graph in which a consecutive number of cases are presented on the horizontal axis and some measure of proficiency or learning is presented on the vertical axis” (sic)

http://dx.doi.org/10.1016/j.arthro.2013.11.012; does not contradict a statistical significance testing. In the same article, a cut off of 30 cases could be identified, this could have been used in this study to make 2 bigger groups for testing instead of testing between groups of 10 patients each with little meaning.

The authors in the current study describe already a 22% improvement in intervention time between the first 30 cases and the following cases. Is this difference statistically significant?

2- Again Concerning the 17% total hip arthroplasty conversion (9 hips) the authors in their revision gave more information about the age of this group, however, they did not mention how these cases plotted on the learning curve and again the cartilage condition intra operatively (grade and extent of cartilage damage) still needs to be described.

Some of the important causes of total hip conversion could be either a high Tönnis grade of arthritis preoperative, extensive cartilage damage or inadequate FAI-correction or even over-correction which is common in the beginning of learning curve.

where in the learning curve are those cases located was still not mentioned in the revised manuscript. Unfortunately, the authors could not provide a perioperative radiological evidence of adequate deformity correction. For example, a perioperative alpha angle correction and some of the acetabular measures as the CE angle should be provided.

3- Minor spelling errors:

• Line 30 correct to performed

• Line 53 Complications: remove S

• Line 96 proven FAI and failed conservative treatment where considered for an arthroscopic procedure: correct to were?

• Line 116 hip-specific external hip distractor: remove 2nd hip

• Lines 128, 129: Labral lesions are assessed and debridement if required. The sentence is not complete, correct to : Labral lesions are assessed and debridement was performed if required.

• Line 154 to analyse de learning curve: correct to the ?

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Reviewer #1: Yes: Mohammad Dr. Masoud

PLoS One. 2021 Feb 11;16(2):e0246655. doi: 10.1371/journal.pone.0246655.r004

Author response to Decision Letter 1

4 Dec 2020

Subject Letter:

Response to reviewers

Dear Editor and Members and Reviewers of the Editorial Board,

Response to Reviewer #1:

1- Response to point 1: the statement by Hoppe et al in their systematic review that “Conceptually, a learning curve should be identified as a graph in which a consecutive number of cases are presented on the horizontal axis and some measure of proficiency or learning is presented on the vertical axis” (sic) http://dx.doi.org/10.1016/j.arthro.2013.11.012; does not contradict a statistical significance testing. In the same article, a cut off of 30 cases could be identified; this could have been used in this study to make 2 bigger groups for testing instead of testing between groups of 10 patients each with little meaning.

The authors in the current study describe already a 22% improvement in intervention time between the first 30 cases and the following cases. Is this difference statistically significant?

Response: As requested we calculated whether or not this difference of intervention time between the first 30 cases and the last 26 cases was statistically significant. It was statistically significant with a p-value of 0.0002. Statistical tests applied and results were added in the material & methods section as well as in the result section.

Response: In the result section describing THA conversion rates we also refer to table S1 with complementary results representing all cases performed (from the first case to the last). The table shows exactly where those cases of THA conversions are situated in the learning curve as well as the exact operative gestures performed during hip arthroscopy. We added a column resuming acetabular chondropathy graded during the intervention. We also added a few comments on the subject in the hope it clarifies this further for the readers in the discussion section.

3- Minor spelling errors

• Line 30 correct to performed