Abstract
Background
Automated broaching has recently been introduced for total hip arthroplasty (THA), with the goal of improving surgical efficiency and reducing surgeon workload. While studies have suggested that this technique may improve femoral sizing and alignment, little has been published regarding its safety, particularly with regard to calcar fractures. The purpose of our study was to evaluate the risk of calcar fracture during automated broaching, and to determine if this risk can be mitigated.
Methods
We queried our prospective institutional database and identified 1596 unilateral THAs performed by the senior author using automated impaction between 2019 and 2023. We identified the incidence of calcar fracture with automated impaction, and whether the fracture occurred during broaching or stem insertion. We additionally determined calcar fracture incidence within two consecutive subgroups of patients using different stem insertion techniques; subgroup (1): automated broaching with automated stem insertion for all patients; versus subgroup (2): automated broaching with automated stem insertion ONLY if a cushion of cancellous bone separated the broach from the calcar, otherwise the stem was placed manually. Continuous and categorical variables were analyzed with Student's t-test and Fisher's exact test, respectively.
Results
Seventeen calcar fractures occurred intraoperatively (1.1 %). Only two fractures occurred during automated broaching (0.1 %), while fifteen occurred during final stem impaction (0.9 %) (p = 0.007). Four calcar fractures (1.4 %) occurred in subgroup 1, compared to two in subgroup 2 (0.6 %) (p = 0.28).
Conclusions
Our study found a calcar fracture incidence of 1.1 % using automated impaction, consistent with historically reported rates of 0.4–3.7 %. We found that calcar fractures are more likely to occur during stem insertion than during femoral broaching. We recommend that if any part of the final broach is in direct contact with the calcar, the final stem should be impacted manually to minimize fracture risk.
Keywords: Automated impaction, Cementless femoral stem, Direct anterior approach, Hip arthroplasty, Periprosthetic fracture, Surgical automation
1. Introduction
Femoral broaching is an essential step during total hip arthroplasty (THA) to ensure optimal component sizing and alignment. Although broaching and stem impaction have been historically performed with durable results using a handheld mallet and impactor,1 this manual technique can occasionally lead to undesired outcomes. Suboptimal broaching technique can create off-axis and rotational forces leading to improper canal preparation and inappropriate final stem position, and in rare cases may cause intraoperative femur fractures.2,3 The use of a mallet also poses an occupational health risk. The average reconstructive surgeon will swing a mallet over four million times during their career, which is likely a large contributor to the 66 % of orthopaedic surgeons that will experience work-related injuries, with 31 % requiring surgery.4, 5, 6
A possible solution to these problems is the use of automated broaching and impaction systems, which can reproducibly deliver a precise, co-linear impaction force that is not dependent on surgeon experience or fatigue.7 Several studies have suggested that these automated systems offer some potential advantages. For example, the calibrated, unidirectional force vector delivered by automated impaction may reduce the variability inherent in the manual impaction technique,8 improve coronal alignment,9 and reduce operative time.9,10 However, little has been published regarding the safety of this device, particularly with regard to calcar fractures. A retrospective study of 2048 THAs performed by Strait et al. found that while powered broaching was as safe as manual broaching with regards to periprosthetic fracture and revisions overall, intraoperative calcar fractures were more frequent with automated broaching, although their findings fell just short of statistical significance (p = 0.06).11 Another retrospective review of 1453 THAs performed with automated impaction found an intraoperative calcar fracture risk of 1 %, however the authors did not report a clear mechanism for over 1/3 of these fractures.12 As intraoperative calcar fractures carry a 2.7-fold increase in risk of revision as well as an elevated 90-day mortality risk,13 more work is needed to better quantify the incidence and possible causes of calcar fractures when using automated impaction systems. Thus we designed the present study to answer the following research questions: 1) what is the incidence of calcar fracture during automated impaction for THA?; 2) when calcar fractures do occur, are they more common during broaching or with final stem impaction?; and 3) does the surgeon's technique with the device affect the fracture incidence?
2. Methods
2.1. Study design
We reviewed our institution's prospectively collected arthroplasty database to identify patients undergoing THA using automated impaction at an urban, high-volume specialty orthopaedic hospital. Approval for the study was obtained by the Institutional Review Board (IRB) prior to its undertaking. We included all consecutive patients undergoing elective primary direct anterior (DA) total hip arthroplasty by a fellowship-trained arthroplasty surgeon using automated impaction (KINCISE™ Surgical Automated System, Depuy Synthes, Warsaw IN, USA) between January 2019 and December 2023. We excluded all patients undergoing revision or conversion THA, primary THA using a posterolateral approach, or non-elective primary THA for femoral neck fractures. Application of our inclusion and exclusion criteria yielded a total of 1596 consecutive hips for final enrollment in the study population. We recorded perioperative patient demographic variables, which are reported in Table 1.
Table 1.
General characteristics of study population (N = 1596).
| Patient Characteristics | n | % | Mean (Range) |
|---|---|---|---|
| Age | 63.6 (13–96) | ||
| Sex | |||
| Male | 752 | 47.12 | |
| Female | 844 | 52.88 | |
| Laterality | |||
| Left | 732 | 45.86 | |
| Right | 864 | 54.14 | |
| Preoperative diagnosis | |||
| Osteoarthritis | 1489 | 93.30 | |
| Avascular Necrosis | 86 | 5.39 | |
| DDH | 7 | 0.44 | |
| Post-Traumatic Arthritis | 6 | 0.38 | |
| Synovial Chondromatosis | 3 | 0.19 | |
| Pseudoachondroplasia | 2 | 0.13 | |
| Rheumatoid Arthritis | 2 | 0.13 | |
| Perthes' Disease | 1 | 0.06 | |
DDH, developmental dysplasia of the hip.
In all cases, the acetabulum was prepared with a 1-mm (mm) press-fit for an uncemented acetabular component with a neutral polyethylene liner (PINNACLE®, Depuy Synthes, Warsaw IN), and the femur was prepared using an all-broach technique for an uncemented, fully hydroxyapatite-coated, triple-tapered stem with a collar (ACTIS®, Depuy Synthes, Warsaw IN). Importantly, while automated impaction was used in all cases during the study period, the senior author's technique did evolve. Early in the study period, automated impaction was performed for all steps of femoral preparation, including broaching as well as final stem impaction. However, later in the study period the author began selectively impacting the final stem by hand if there was felt to be an elevated risk of calcar fracture. By reviewing the operative notes and study database, we identified two subgroups of consecutive patients who underwent automated THA using one of two following variations. In subgroup (1): automated broaching was performed for all hips, with automated impaction of the final stem for all hips. In subgroup (2), automated broaching was performed for all hips, with automated impaction of the final stem ONLY if a cushion of cancellous bone separated the final broach from the calcar (Fig. 1); if any part of the final broach directly contacted the calcar, the final stem was impacted by hand (Fig. 2).
Fig. 1.
Intraoperative photo demonstrating the presence of a cancellous bone cushion between the implanted stem and medial femoral calcar.
Fig. 2.
Intraoperative photo demonstrating the absence of a cancellous bone cushion (indicated by arrow). The stem directly abuts the medial femoral calcar.
The primary outcome of the present study was the overall incidence of calcar fracture during automated impaction in the study population. For purposes of the study, we identified a calcar fracture as any vertical split of the calcar during automated impaction that required placement of a cerclage cable. Patients who had a small piece of the calcar peel off during calcar planning (five patients), as well as those who developed nondisplaced cracks around the femoral neck during manual backing out of a tightly-fitted broach by hand (three patients), were not counted as calcar fractures since their injuries did not occur during automated impaction. As a secondary outcome, we determined whether the calcar fracture occurred during broaching, or during final stem impaction. As an additional secondary outcome, we recorded the incidence of calcar fractures in the two subgroup variations of automated THA technique, as described above.
2.2. Data analysis
All data were entered, stored, and analyzed using Microsoft Excel (Microsoft Corporation, Redmond, WA, USA), GraphPad QuickCalcs (GraphPad Software, San Diego, CA, USA), and MedCalc (MedCalc Software LTD, Ostend, Belgium). Continuous variables were analyzed using Student's t-test, while categorical variables were analyzed using Fisher's exact test. In all cases, statistical significance was set at p = 0.05.
3. Results
Of the 1596 THAs included in the study population, a total of 17 hips suffered a calcar fracture (17/1,596, 1.1 %) during automated impaction. All fractures were treated with cerclage cabling and allowed immediate weight bearing. Only two calcar fractures occurred during automated broaching (2/1596; 0.1 %), while fifteen calcar fractures occurred during impaction of the final stem (15/1596; 0.9 %) (RR = 7.5; 95 % CI: 1.7–32.7; p = 0.007).
There were four calcar fractures (4/285, 1.4 %) within subgroup 1 (automated broaching for all patients, and automated final stem impaction for all patients). Conversely, there were two calcar fractures (2/363, 0.6 %) in subgroup 2 (automated broaching for all patients, and automated final stem impaction only if a cushion of cancellous bone separated the final broach from the calcar) (RR = 0.39; 95 % CI: 0.07–2.13, p = 0.29). The number needed to treat (NNT) to potentially prevent one calcar fracture using the technique variation in subgroup 2 was 117 patients. A summary of the results is displayed in Table 2.
Table 2.
Calcar fracture risk by surgical step and technique variation subgroup.
| n | Fractures | % | RR | 95 % CI | P-value | NNT | |
|---|---|---|---|---|---|---|---|
| Overall | 1596 | 17 | 1.1 | ||||
| During broaching | 2 | 0.1 | Ref. | ||||
| During final stem impaction | 15 | 0.9 | 7.5 | 1.7 to 32.7 | 0.007 | ||
| Technique Variation Subgroups | |||||||
| Subgroup 1 | 285 | 4 | 1.4 | Ref. | |||
| Subgroup 2 | 363 | 2 | 0.6 | 0.39 | 0.07 to 2.13 | 0.28 | 117 |
RR, relative risk; CI, confidence interval; NNT, number needed to treat.
4. Discussion
Automated impaction in THA has been suggested to potentially improve surgical outcomes while optimizing the operative workflow and eliminating the physical burden associated with the use of a mallet.8, 9, 10, 11 However, there is still a paucity of data regarding the safety of this new technique. Our retrospective review of 1596 unilateral THAs demonstrates that the overall calcar fracture risk with automated impaction is 1.1 %. Importantly, we find that while rare, the risk of calcar fracture was markedly higher during automated impaction of the final stem, with 15 out of 17 fractures (88.2 %) occurring during this step while only two of 17 fractures (11.8 %) occurred during automated broaching. Finally, by adjusting the surgeon's technique (to only using automated impaction for the final stem if a cushion of cancellous bone separates the final broach from the calcar) (Fig. 1), we reduced the incidence of fractures by more than half (from 1.4 % to 0.6 %, RR = 0.39), however this risk reduction was not statistically significant with the numbers available.
There are several limitations to this study. First, as with all retrospective studies, there is an inherent risk of selection bias. We attempted to mitigate this risk by including a prospectively collected, consecutive series of THAs with well-defined inclusion and exclusion criteria. Another limitation is the single-surgeon, single-center study design. As calcar fracture risk is highly dependent on both surgical technique and patient-specific characteristics,14, 15, 16, 17 our results may not be generalizable to other surgeons with varying techniques and patient populations. Additionally, we did not collect data on patients’ Dorr classification, and therefore cannot report on the relationship between femoral Dorr type and risk of calcar fracture with automated impaction. Lastly, it is possible that our study is underpowered. Since calcar fracture is a relatively rare event during THA, our study population of 1596 patients may not have sufficient power to fully identify the risk factors leading to calcar fracture during automated broaching and stem insertion, particularly within our subgroup analysis where the numbers are smaller.
Calcar fracture is the most common periprosthetic femoral fracture during primary THA, accounting for at least 60 % of fractures found in two large retrospective joint registry studies in the USA and UK.17,18 There is an abundance of literature documenting the specific risk factors associated with calcar fracture. These factors include age (<60 or >80),17,19 female sex,12,14,17, 18, 19, 20, 21, 22, 23 hip dysplasia,16 proximal femur morphology (varus neck, narrow proximal femoral canal, and Dorr type C),16 ASA score ≥ 317, history of prior ipsilateral hip surgery,19 left-sided surgery,17 cementless implants,17, 18, 19,21,22 smaller stem size,14,20 use of the anterolateral or Hardinge approach,16,19,21 surgeon inexperience,16 and surgeries performed for indications other than osteoarthritis.17,19 Although these fractures can be managed intraoperatively with cerclage wiring, revision to a diaphyseal-engaging stem, or both,24 they are not benign. Miettinen et al. performed a retrospective review of 3207 cementless arthroplasties and found a nearly 3-fold increase in revisions in patients who sustained a calcar fracture.16 As the majority of these calcar fractures occur during broaching or stem insertion,18,23 it is imperative to assess the impact of the increasingly popular automated systems on calcar fracture risk. Thalody et al. demonstrated that automated impaction led to an increase in stem size and no change in fracture risk, though it should be noted no fractures were recorded in either the automated or manual broaching/impaction groups.9 Bhimani et al. similarly showed an increase in average stem size with the use of automated broaching and impaction, with only one fracture noted in the automated group, which was not a statistically significant difference (p = 0.46).10 A recently published study by Osondu et al. looking at 1453 THAs performed using automating impaction found a 1.2 % intraoperative fracture risk, 15 of which were calcar fractures. Of these 15 calcar fractures, they reported that 4 occurred during broaching, 1 during calcar planing, 1 during stem preparation, 4 during component placement, and 5 were reported to have occurred with “no mechanism”.12 The largest study to date by Strait et al. reviewed 2048 THAs, 800 performed with manual impaction and 1248 using an automated system. The authors found that while automated broaching and impaction was as safe as the manual technique overall, there was an increase in calcar fracture in the automated group (12 automated vs two manual, p = 0.06), although this finding was not statistically significant with the numbers available.11
The present study adds to this previous work, reporting an overall calcar fracture risk of 1.1 % when using automated impaction, comparable to previous studies demonstrating an intraoperative calcar fracture risk of 0.4–3.7 % during primary THA.16,17 Importantly, we found that the majority of calcar fractures occurred not during broaching, but rather during impaction of the final stem (RR = 7.5). This emphasizes the need for care when using automated impaction for final stem insertion.
In the experience of the senior author, the risk of calcar fracture during final stem insertion can be mitigated by gently impacting the stem manually if any part of the final broach is in direct contact with the medial calcar (Fig. 2). However, if there is a circumferential cushion of cancellous bone protecting the broach from the calcar, we recommend proceeding with automated impaction of the final stem. In our study, we found a reduction in the incidence of calcar fractures from 1.4 to 0.6 % (RR = 0.39) if this technique was observed, however it should be noted that this result did not reach statistical significance with the numbers available (p = 0.28). Given the relatively recent introduction of automated broaching and impaction and the rare nature of calcar fractures, more data is needed to further investigate the optimal fracture risk mitigation strategy.
Ethical statement
Authorship Declaration: All authors listed meet the authorship criteria according to the latest guidelines of the International Committee of Medical Journal Editors, and all authors are in agreement with the manuscript.
Funding statement
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Guardian/patient's consent
This is not applicable to the current research project.
CRediT authorship contribution statement
Dan Gordon: performed, Writing – original draft, Writing – review & editing, Visualization. Justin M. Cardenas: performed, Conceptualization, Writing – review & editing. David Fawley: performed, Conceptualization, Writing – review & editing. Kurt J. Kitziger: performed, Conceptualization, Writing – review & editing. Brian P. Gladnick: performed, Conceptualization, Investigation, Formal analysis, Writing – original draft, Writing – review & editing, Project administration, Supervision.
Acknowledgements
None.
Contributor Information
Dan Gordon, Email: dan.gordon@bswhealth.org.
Justin M. Cardenas, Email: juscardenas@gmail.com.
David Fawley, Email: dfawley1@its.jnj.com.
Kurt J. Kitziger, Email: kkitziger@carrellclinic.com.
Brian P. Gladnick, Email: bgladnick@carrellclinic.com.
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