Abstract
Objective
This study aimed to evaluate if the acetabulum's conservative reaming with preservation of the medial acetabular bone and anatomic placement of the acetabular implant in cementless total hip arthroplasty (THA) has any adverse effect on the radiological outcome, long term implant survival and patient satisfaction.
Methods
106 consecutive patients were identified from a single surgeon practice who underwent cementless THA from 2005 to 2010. Twenty-one were lost to follow up, and five patients died unrelated to THA. Eighty patients were available for the study. The mean follow-up was 8.6 years (range 5.7–11.6). The mean age was 61.9 years. Immediate pre- and postoperative radiographs were reviewed to calculate combined offset (Acetabular offset – AO, plus Femoral offset – FO). Implant failure, aseptic loosening, revision surgery, patient satisfaction and complications were assessed on long-term follow-up.
Results
Acetabular component survival was 100% with no aseptic failure. None of the patients had revision surgery for any cause. The mean difference in the acetabular offset and combined offset postoperatively was within 3 mm. One patient had a dislocation, and one had a prosthetic joint infection (PJI). 95% of the patients in this series would recommend the hip replacement procedure to others, with a mean satisfaction score of 8.7 (range; 1–10).
Conclusion
Conservative acetabular reaming with preservation of medial acetabulum bone with the anatomic placement of the acetabular implant in cementless THA is safe with no adverse effects on implant survival and patient satisfaction. It offers the advantage of preserving the patient's bone stock, which would potentially be of significant advantage to the patient and the surgeon in case of revision arthroplasty.
Keywords: Total hip arthroplasty (THA), Acetabular offset, Femoral offset
1. Introduction
Primary Total Hip Arthroplasty (THA) is one of the most common elective Orthopaedic procedures worldwide, with hip arthroplasty numbers rising yearly. The UK National joint registry (NJR) 20201 reported on over 3 million joint replacement procedures since the beginning of the registry in 2003. This includes 1,191,253 primary THA procedures representing almost 40% of all joint replacement procedures in NJR1 and cementless THA being the commonest fixation method in the last three years. Revision hip arthroplasty procedures are also becoming more routine with high living standards, improved quality of life, and an increasingly ageing population. There are 123,891 revision procedures recorded in the latest NJR report.1
Restoration of native global offset and soft tissue tension with the satisfactory placement of the implants is essential for stability, implant survival, good functional outcome and patient satisfaction in THA. In conventional acetabular preparation, reaming down to the true floor medialises the centre of rotation of the hip (CRH) and decreases the acetabular offset.2,3 It is also shown that to restore native global offset, and the femoral offset needs to be increased to compensate for reduced acetabular offset and maintain the normal stress on the hip abductors.4 This reduces forces on the femoral head, causes less wear, and increases implant survival.5,6 On the other hand, some surgeons prefer not to ream down to the true floor and preserve medial bone on the acetabular floor. This technique restores the normal acetabular offset while placing the acetabular implant more anatomical.6, 7, 8 Optimal implant positioning is essential for good functional outcomes in primary THA. Adequate reaming, implant positioning and restoring anatomy results in better functional outcome and longevity in implant survival.9 Maintaining good bone stock by minimally required reaming is essential while restoring the anatomy in primary THA. Furthermore, preserving acetabular bone stock is a significant advantage in revision arthroplasty.
This study aimed to examine CRH restoration measured on a plain radiograph (acetabular offset, femoral offset and combined offset) while preserving medial acetabular osteophyte. We evaluated acetabular implant survival as a primary outcome. The secondary outcome was patient satisfaction with the procedure and revision procedure for any cause. We also evaluated any associated complications in this group of patients. To our knowledge, this is the first study to assess acetabular implant survival and patent satisfaction in the context of acetabular reaming technique and acetabular bone preservation in primary THA.
2. Methodology
Patients who underwent cementless THA by a single surgeon in our centre between 2005 and 2010 were included in this study. A total of 106 consecutive patients were identified retrospectively and included in the study. Twenty-one patients were lost to follow-up, and five patients died due to unrelated causes. Eighty patients were available for follow up, of which 35 (44%) were male and 45 (56%) were female, with a mean age of 61.9 years (range 44–78). The mean follow-up was 8.6 years (range 5.7–11.6). Three patients in this study had bilateral THA, performed on separate occasions. A summary of demographics is given in Table 1.
Table 1.
Summary of patient demographics.
| Total patients, n | 106 |
|---|---|
| Lost to follow up, n | 21 |
| RIP, n | 5 |
| Final number, n | 80 |
| Male: Female | 35:45 |
| Bilateral | 3 |
| Average age (years) | 61.9 (44–78) |
| Average F/u (years) | 8.6 (5.7–11.6) |
The indication for surgery was primary (hypertrophic) osteoarthritis with no cases of protrusio. Patients had a standard preoperative assessment and had an anterior-posterior (AP) radiograph of the pelvis. As part of the preoperative planning, the operating surgeon reviewed the radiograph to plan how much medialisation was required. The aim was to preserve medial acetabular bone as much as possible without compromising the coverage and stability of the acetabular shell. A cementless acetabular implant (Pinnacle®, DePuy Synthes, US) and a cementless femoral implant (Corail®, DePuy Synthes, US) were used, utilising an anterolateral approach. Patients followed a standard postoperative recovery protocol and were mobilised on the first postoperative day with the physiotherapist, weight bearing as tolerated with appropriate aids. Patients had routine postoperative AP pelvis and lateral hip radiographs before discharge. All patients had a standard follow up at six weeks for wound check and repeat radiographs. Radiographs were performed with the exact calibration in a standing position.
The combined offset was measured as the sum of the acetabular offset (AO), measured from the centre of the femoral head to the true floor of the acetabular, and the femoral offset (FO), measured as the distance between the anatomical axis of the femur and the centre of rotation of the femoral head (Fig. 2). Preoperative and immediate postoperative radiographs were reviewed to measure the combined offset and to assess whether preserving the medial osteophyte had led to any significant change in the combined offset and if there was any lateralisation of the centre of rotation of the hip (CRH) (Fig. 1, Fig. 2). Radiographs at six weeks and the final radiograph at the final appointment were also reviewed for any change in the position of the acetabular implant and any sign of loosening.
Fig. 2.
Postoperative AP pelvis radiograph showing the acetabular and femoral offset measurements after left THA.
Fig. 1.
Preoperative AP pelvis radiograph showing native acetabular and femoral offset measurements of the left hip.
The acetabular floor width or the medial osteophyte was measured from the true floor at the level of the teardrop to the nearest point of the acetabular implant (Fig. 3). This value was used to assess how much of the acetabular bone was preserved and to check the consistency in the inter-observer evaluation. The mean acetabular floor width (preserved medial osteophyte) was 2.4 mm, as demonstrated in Fig. 3.
Fig. 3.
Postoperative radiograph showing the distance between the true floor and the acetabular implant after right THA. Acetabular floor width demonstrated after the THA on the right side was 0.43 cm, and the native flood width of 0.67 cm on the left side.
Intraobserver and interobserver reliabilities of all the measurements were evaluated by three blinded observers, including two senior Orthopaedic trainees and the lead author. This demonstrated a high interobserver and intraobserver reliability for all measurements and an agreement within 2 mm.
Patients were asked five simple questions as part of their long-term follow-up, detailed in Table 2. The patient's overall satisfaction with the procedure was assessed with a score from 1 to 10. Patients were asked if they had any revision surgery after their THA and if they had any dislocations, manipulations under sedation, regional or general anaesthesia or any other complications.
Table 2.
5 questions asked on long-term follow-up.
| Q1. How happy are you with your surgery?1, 2, 3, 4, 5, 6, 7, 8, 9, 10 |
| Q2. Have you had any further surgeries on your Total Hip Replacement, including any revision? (Yes/No) |
| Q3. Did your Total Hip Replacement have had any dislocations since the operation? (Yes/No) |
| Q4. Are you on any painkillers since the Total Hip Replacement? (Yes/No) |
| Q5. Would you recommend this surgery to others? (Yes/No) |
2.1. Statistical analysis
Statistical analysis was performed using GraphPad Prism (version 6.00 for Windows, GraphPad Software, La Jolla, California, USA). To assess the difference between genders, unpaired t-test was used. Paired t-test was used to compare pre- and postoperative data. P < 0.05 was considered significant.
3. Results
There were no cases of aseptic loosening with 100% implant survival. None of the patients had revision surgery for any cause to the final follow-up.
On average, males had higher preoperative and postoperative FO, and AO offset compared to females (p < 0.0001) (Table 3). Overall, pre and postoperative mean FO were 51 mm and 50 mm, respectively and mean AO measurements were 43 mm and 41 mm, respectively, in the whole series (Fig. 4). There was no statistically significant difference in overall mean pre- and postoperative combined offset, 94 mm and 91 mm, respectively (Table 4) (Fig. 4). The difference in the mean combined offset was -3mm, which suggests medialisation of the centre of rotation of the hip and reduction in the global offset by 3 mm. Postoperatively, the mean acetabular floor width (preserved medial osteophyte) was 2.4 mm (Fig. 3).
Table 3.
Acetabular Offset, Femoral Offset and combined offset in males and females.
| Mean values (mm) | Females (range) | Males (range) | P value |
|---|---|---|---|
| Preoperative FO | 48.0 (33–66) | 55.6 (39–66) | P < 0.0001 |
| Post-operative FO | 47.2 (34–58) | 53.0 (39–63) | P < 0.0001 |
| Pre-operative AO | 39.6 (30–49) | 46.9 (35–59) | P < 0.0001 |
| Post-operative AO | 38.4 (30–51) | 44.1 (34–56) | P < 0.0001 |
| Combined Preoperative Offset | 87.5 (70–105) | 102.5 (89–119) | P < 0.0001 |
| Combined Post-operative Offset | 85.6 (67–102) | 97.1 (82–114) | P < 0.0001 |
Fig. 4.
Graphs comparing pre and postoperative data (mean ± SD) and paired t-tests.
Table 4.
Overall pre and postoperative, mean Acetabular Offset, Femoral Offset and combined offset for the whole series.
| Preoperative | Postoperative | |
|---|---|---|
| Mean overall Femoral offset | 51 mm (33–66) | 50 mm (34–63) |
| Mean overall Acetabular offset | 43 mm (30–59) | 41 mm (30–56) |
| Mean overall combined offset | 94 (70–119) | 91 (67–114) |
P < 0.0001.
The patient's mean satisfaction score was 8.7 (range; 0–10). 95% of the patients in this series (76 patients) would recommend the THA procedure to others. None of the respondents had any revision surgery. However, One patient had dislocation treated with closed reduction, and one patient had a prosthetic joint infection (PJI). Patient with PJI is still waiting for revision surgery but is delayed due to the patient's circumstances (Table 5). Only 10 (12.5%) patients were still using painkillers, mainly due to pain in other joints.
Table 5.
Summary of the results from the questions on follow-up.
| Questions | Feedback |
|---|---|
| Q1. How happy are you with your surgery?1, 2, 3, 4, 5, 6, 7, 8, 9, 10 | Mean 8.7 (0–10) |
| Q2. Have you had any further surgeries on your Total Hip Replacement, including any revision? (Yes/No) | No = 80 (100%) Yes = 0 (0%) |
| Q3. Did your Total Hip Replacement have had any dislocations since the operation? (Yes/No) | No = 78 (97.5%) Yes = 2 (2.5%) |
| Q4. Are you on any painkillers since the Total Hip Replacement? (Yes/No) | No = 70 (87.5%) Yes = 10 (12.5%) |
| Q5. Would you recommend this surgery to others? (Yes/No) | Yes = 76 (95%) No = 4 (5%) |
Out of the four patients who did not advocate THA (Table: 5), one patient is awaiting revision surgery due to chronic infection with a discharging sinus. The other three patients did not give any clear reason for their dissatisfaction, and one of these patients had a hip replacement on the contralateral side seven months after the first surgery.
4. Discussion
The main finding of this study is that conservative, anatomical acetabular reaming in cementless THA with preservation of medial acetabular bone had excellent survivorship at medium to long-term follow-up. There were no cases of revisions for any cause in this series. This study also demonstrated that placing the acetabular implant in a more anatomical position still allows adequately medialising the CRH. In our study, the mean floor width (preserved medial osteophyte) was 2.4 mm postoperatively. This is comparable to a previous report by Merlee et al. 2, which showed the mean floor width of 2.6 mm. Kurtz et al.9 also showed that the conservative technique allows for maintaining the space between the cup and the true floor. The advantages of conservative acetabular reaming and maintaining AO are well known. This includes an increased range of motion of the hip with a decreased risk of bony and soft tissue impingement as shown by Kurtz WB10 and decreased risk of hip dislocation shown by Archbold HA7 and Kummer FJ et al. 11. However, more importantly, preservation of acetabular bone stock could be of a huge advantage at the time of revision surgery.
The mean difference in combined offset before and after surgery was -3mm. This means that the reconstructed offset postoperatively was marginally reduced by 3 mm compared to the patient's native global offset, but this was not statistically significant. We demonstrated that satisfactory restoration of the patient's anatomy could be achieved with conservative reaming of the acetabulum and without excessively increasing the femoral offset. Restoration of global offset has a significant bearing on functional restoration and patient satisfaction, as demonstrated by previous studies in the literature.12
Bonnin et al.4 assessed the AO in normal hips on a CT scan and compared it to the change in the CRH after conventional and anatomical cup implantation during THA. They analysed 100 CT scans of normal hips before and after simulating implantation of the acetabular component while performing the conventional preparation of acetabulum to the true floor versus conservative reaming of the acetabulum. In their study, they calculated the mean AO of 30.8 mm ± 3. The medial shift of the CRH was 1.6 mm ± 1.2 with the anatomical and 4.8 mm ± 1.9 with the conventional technique (p < 0.0001). They showed that the medialisation was greater than 5 mm in 44% of the cases when the conventional technique was used but occurred in no case when using the anatomical technique. They also showed a significant difference in medialisation between men and women, being 5.6 mm ± 1.6 and 3.5 mm ± 1.7 with the conventional technique and 2.0 mm ± 1.1 and 0.9 mm ± 0.9 with the anatomical technique, respectively. In our study, AO was also higher in males compared to females. Preoperative mean AO value in males was 46.9 mm (range 35–59 mm), compared to 39.6 mm (range 30–49 mm) in females. We also found a higher pre and postoperative FO in males (pre-op 55.6 mm vs 53.0 mm post-op) when compared to females (pre-op 48.0 mm vs 47.2 mm post-op) so as the combined offset (Table 3).
Merlee et al. 2 showed similar results in their study. They measured the AO on a plain AP radiograph and a CT scan in 131 patients. They showed that the AO could be reliably assessed on a standardised AP pelvis radiograph. They also evaluated the change in the global offset with the anatomic and conventional reaming techniques. Anatomic cup position showed medialisation of the CRH by 5.9 ± 3.4 mm where 64 hips (49%) did not require reaming to the true floor. With the conventional reaming technique, the medialisation of CRH was 6.8 ± 2.9 mm, with 34% of cases having medialisation of >8 mm.
In our study, the mean medial shift in the centre of rotation of the hip (CRH) was 3 mm. Compared to Bonnin et al.,4 where the mean medial shift of CRH was 1.6 mm ± 1.2 and Merlee C et al. 2, where the medial shift was 5.9 ± 3.4 mm in the anatomical technique (Table 7). Our study showed a relatively less medial shift of the CRH, which would have been more if the acetabular reaming was done conventionally down to the true floor of the acetabulum, as shown by Bonnin et al. 4 (>5 mm in 44% cases) and Merlee C et al.2 (6.8 ± 2.9 mm with 34% of cases). Our average medial shift of CRH is comparable to that of Bonnin et al. 4, who calculated their measurements on CT of the normal hips. The results of our study and the above 2 studies are comparable even though our measurements were based on plain radiographs. Our cohort's mean AO is high compared to Merlee C et al.2 and Bonnin et al. 2. This could be because most of the patients in our study had hypertrophic osteoarthritis of the hip, with significant medial osteophytes as opposed to normotrophic hip osteoarthritis (Table 7).
Table 7.
Comparison of acetabular offset (AO) and shift in the centre of rotation of the hip. NR (Not reported).
| Mean overall AO | Mean overall medial shift of CRH | Mean medial shift of CRH in males | Mean medial shift of CRH in females | |
|---|---|---|---|---|
| Bonnin et al.4 (Measurement on CT scan) | 30.8 mm | 1.6 ± 1.2 mm | 2 mm | 0.9 mm |
| Merlee C et al.2 (Measurement on CT scan) | 33.8 mm | 5.9 ± 3.4 mm | NR | NR |
| The current study (Measurement on plain radiograph) | 43 mm | 3 mm | 5.4 mm | 1.9 mm |
This study demonstrated 100% survival of the acetabular implant with the anatomical placement of the acetabular implant and preservation of the acetabular bone, with no aseptic loosening. There were no revisions for any cause in this series with a long follow up period. The only patient with dislocation is a 78 years old female who had surgery 7.3 years ago and has had 3 dislocations, the last being in 2016 but no other symptoms. This patient's radiographs showed that the acetabular implant abduction angle is 50°, with no signs of implant loosening and overall satisfactory alignment of implants. No further dislocations since 2016, and she is under close follow up. Out of the total 80 THA in this study, only 10 patients (Table 6) were still taking oral analgesics. Two patients reported lateral hip pain. Both female patients had 1 mm, and 2 mm lateralised CRH, respectively. Their lateral pain could be attributed to increased abductor muscle tension due to lateralising of the CRH and an increase in global offset. One patient, who had bilateral THA, has discharging sinus on one side and is awaiting revision surgery. Most of our patients are satisfied with their hip replacement, and 95% of our patients would recommend the procedure to others with high satisfaction scores. The only 2 articles on this topic by Bonnin et al. 4 and Merlee C et al. 2, who examined the anatomical acetabular reaming, only assessed the radiological outcomes. We believe that this is the first article to assess patient satisfaction in this group of patients.
Table 6.
Details of analgesic use of ten patients. Paracetamol, Codeine Phosphate or a combination are classed as simple analgesia.
| Patient No | Age | Follow-up (years) | Side | Shift in CRHa (mm) | Comments |
|---|---|---|---|---|---|
| 1 | 49 | 10.1 | R | 3 | Discharging sinus, awaiting revision. On simple analgesia |
| 50 | 8.7 | L | −6 | On simple analgesia | |
| 2 | 51 | 9.9 | L | −1 | On simple analgesia |
| 3 | 65 | 9.8 | R | 7 | Lateral pain gradually improving |
| 4 | 78 | 8.8 | L | 9 | On simple analgesia |
| 5 | 65 | 8.5 | L | 1 | New onset lateral pain |
| 6 | 74 | 8.3 | R | −2 | On simple analgesia |
| 7 | 51 | 7.1 | L | 4 | Gabapentin, codeine, acupuncture |
| 8 | 49 | 6.9 | R | 3 | On simple analgesia |
| 9 | 48 | 8.3 | R | 1 | On simple analgesia |
| 10 | 61 | 8.8 | R | −0.7 | Sensitive scar |
Shift in CRH denotes medicalisation of the CRH, but where there is a minus sign, it denotes lateralisation of CRH.
We acknowledge that this study has a few limitations. This is a retrospective review of a small case series from a single surgeon practice. All measurements were on a plain radiograph with standard calibration as CT is not a routine preoperative investigation at our centre. This potentially can lead to miscalculation when looking at small margins. However, routine postoperative CT scan in THA patients is not a common investigation in any institution. Merlee et al. 2 found no difference in the measurement of AO on corresponding AP pelvis radiographs (33.9 ± 7.3 mm) and CT scans (33.7 ± 4.9 mm, P = 829). In their study, AO measurements on AP pelvis radiographs and CT showed a good correlation (R = 0.74, P < 0.001), demonstrating that native AO of patients with primary end-stage hip OA can be accurately and reliably determined on conventional AP pelvis radiographs. This series does not have a comparative group as a control. We used a novel, simple questionnaire to assess patient satisfaction and did not evaluate function with validated hip scores. This is because we wanted to design a questionnaire to assess the patient's satisfaction with the procedure, but at the same time find if the patient had any complications or revision surgery (Table 2).
To our knowledge, this is the first study to report the radiological outcome of patients with anatomic acetabular reaming, implant survival, and patient satisfaction on a medium to long term follow up. The study demonstrated that conservative acetabular reaming in THA is safe with no adverse effect on implant survival and patient outcome. Our findings support a critical review of the preoperative radiograph in all cases to carefully evaluate and plan the depth of the acetabular reaming. Given our results, we recommend that the surgeons consider conservative reaming of the acetabulum when performing a cementless THA where possible while ensuring that good primary fixation of the cup is achieved with a satisfactory orientation of the implants. While hip offset is traditionally discussed as FO, it is also vitally important to assess and restore the acetabular offset to restore the hip's centre of rotation and restore normal anatomy and function.
Contributions
S Hussain; Data collection, data analysis, writing manuscript. S Malik: Data collection, data analysis, writing manuscript. B Budair: Data collection. D Prakash: Data analysis, manuscript review.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Declaration of competing interest
The Authors declare that there is no conflict of interest.
Acknowledgment
None.
Contributor Information
Shakir Hussain, Email: shakirhussain@nhs.net.
Shahbaz S. Malik, Email: shahbazmalik@nhs.net.
Basil Budair, Email: b.budair@nhs.net.
Divya Prakash, Email: d.prakash@nhs.net.
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