Two case reports of greater trochanter fracture at the site of femoral array placement after robotic-assisted hip replacement in the posterolateral approach

Introduction

Background

Total hip arthroplasty (THA) is a highly successful orthopedic procedure, yielding patient satisfaction rates of up to 95%. In Organization for Economic Co-operation and Development (OECD) countries, projections indicate an increase in THA incidence from 184 per 100,000 in 2015 to 275 per 100,000 by 2050 (1-5). Despite these advancements, 10% of primary THAs require revision within 10 years, emphasizing the need for ongoing improvements in technique and technology.

Rationale and knowledge gap

Robotic-assisted THA (RA-THA) promises greater implant accuracy and potentially better long-term survivorship, while emerging data is not that clear on short and mid-term results (6-8).

However, these systems involve temporary pin or screw placements that can lead to fractures, infections, and other local complications (9-11).

Only one published report to date has linked a tracker-pin site to a greater-trochanter fracture after navigation-assisted THA (not RA-THA), although pin-site fractures in other locations have been described (9,10), while Manufacturer and User Facility Device Experience (MAUDE) database review analysis of robotic arthroplasty recorded a single greater trochanter fracture and one femoral pin-site fracture among 68 patient-injury reports, suggesting the phenomenon is rare but documented (12).

More recently, population-level evidence has clarified that periprosthetic fractures may be more common after RA-THA (13).

Temporary tracker or array fixation is a plausible mechanism because navigation and robotic workflows often require self-drilling pins or screws inserted into the greater trochanter or proximal femur.

Despite manufacturer-defined “safe zones”, current guidance on optimal array placement remains empirical and rarely integrates patient-specific bone quality or the muscle-tendon footprints of the gluteus medius muscle and vastus lateralis muscle. The MAKO Total Hip Arthroplasty Surgical Technique Guide instructs the surgeon to seat the array on the lateral cortex of the proximal femur at the site displayed on the navigation screen (separate bone models are supplied for posterolateral vs. anterior-based approaches). A 2.5–3.0 mm pilot hole is drilled (a 4 mm bone pin is an accepted alternative), after which the dedicated self-tapping femoral cortical screw—its exact diameter is not published, but it measures roughly 6 mm in diameter—threaded in until snug, without over-tightening. The screw’s flange teeth must bite into cortex so the array cannot toggle; if any movement is felt while gently rocking the tracker, the screw is retightened. Once the camera can see the array in both the dislocated and reduced hip positions, the tracker is locked with the square driver (14).

The learning curve associated with RA-THA may further accentuate early complications (15). Addressing these knowledge gaps—and quantifying the true incremental fracture risk—requires both biomechanical research and detailed clinical reporting, such as the present cases.

Objective

We present two cases of greater trochanter fractures after RA-THA using currently recommended femoral array pin placement zones (14). This report is structured according to standard case report guidelines (CARE).

By the time these two fractures occurred, our MAKO series comprised eight cases. After we modified the pin-placement technique (see below), we carried out a further 28 consecutive RA-THAs that same year—bringing the total to 36 procedures—and none of the subsequent patients sustained a similar greater-trochanter fracture what would represent a cumulative incidence of 5.5%. We would like to mention that this number is center-specific and reflects a learning phase as well as a technique change. We present this article in accordance with the CARE reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-5/rc).

Case presentation

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Institutional review board approval was waived for this case presentation. The Committee of Ethics in Drug Research at the Institut de Recerca i Innovació en Ciències de la Vida i la Salut a la Catalunya Central in its meeting on 14.02.2024 (record of meeting 02/2024) notes the presentation of the clinical cases and considers it appropriate from an ethical and scientific perspective. Written informed consent was obtained from patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Patient information summary (Table 1)

Both patients were 74 years old at the time of surgery.

Patient 1: female, type 2 diabetes, hypothyroidism, body mass index (BMI) 29.1 kg/m².

Patient 2: male, arterial hypertension, prostate cancer in remission, BMI 20.7 kg/m².

See Table 1 for more details.

Case 1

A 74-year-old woman with 6 months of progressive hip osteoarthritis underwent RA-THA (MAKO protocol) via a posterolateral approach by experienced surgery team that performs more than 50 manual cases by surgeon annually. The femoral array screw was placed in a relatively proximal area, but inside suggests “safe zone”, aiming to avoid stem interference. Postoperative radiographs (Figure 1) showed no abnormalities, and she was discharged on postoperative day 2.

Figure 1 Postoperative radiograph demonstrating no visible fracture (Case 1).

One week later, she presented with acute hip pain and antalgic gait, denying any trauma. Radiographs (Figure 2) revealed a minimally displaced trochanteric fracture at the screw site. No postoperative protocol violation was documented by ward or outpatient staff. Given the minor displacement, conservative management was chosen. At final follow-up at 18 months after the surgery (Figure 3), she was ambulating pain-free but exhibited a limping gait due to gluteus medius insufficiency. Follow-up radiographs showed a persistent pseudoarthrosis of the greater trochanter as a probable cause of patients’ symptoms. By Clavien-Dindo criteria, this represents a grade I complication, as no pharmacologic, radiologic, or surgical intervention was necessary.

Figure 2 Radiograph illustrating minimally displaced trochanteric fracture (Case 1).

Figure 3 Follow-up radiograph (Case 1) showing fracture at last follow-up.

Case 2

A 74-year-old man, previously treated with a contralateral hip arthroplasty, underwent an RA-THA using the same MAKO protocol by the same team. The patient’s prostate cancer (Table 1) had been in biochemical remission for 5 years, with serial prostate-specific antigen (PSA) values consistently <0.4 ng/mL; therefore, no staging bone scan was repeated before THA. Intra-operative inspection revealed normal cancellous bone without suspicious lesions. As in Case 1, femoral array screws were placed in the same “safe zone”. Immediate postoperative imaging showed proper alignment (Figure 4), and he was discharged uneventfully on postoperative day 2.

Figure 4 Immediate postoperative radiograph (Case 2), no fracture evident.

Two weeks later, he returned with acute hip pain and inability to bear weight. Ward and outpatient records show full adherence to the postoperative protocol, with no documented breaches. Radiographs (Figure 5) revealed a displaced trochanteric fracture through the original pin site. Initial treatment involved open reduction and fixation with Kirschner wires (Figure 6); however, secondary displacement was noted (Figure 7), prompting revision surgery with transosseous sutures (Figure 8). Postoperatively, the patient developed a periprosthetic joint infection caused by methicillin-resistant Staphylococcus epidermidis requiring debridement, irrigation, and implant retention, then completed an 8-week course of linezolid 600 mg twice daily plus rifampicin 600 mg daily. At the latest follow-up (12 months after the last surgery), he reported no significant pain but continued to limp due to gluteus medius insufficiency, with no laboratory or clinical signs of infection (C-reactive protein and erythrocyte-sedimentation rate remained within normal limits). This sequence of events [fracture fixation, revision fixation, and DAIR (debridement, antibiotics, and implant retention) for infection] was each grade III-b of Clavien-Dindo criteria.

Figure 5 Radiograph revealing displaced trochanteric fracture (Case 2).

Figure 6 Intraoperative photograph of open reduction and internal fixation (Case 2) with evident fracture line through pin placement hole (white arrow).

Figure 7 Radiograph showing secondary displacement (Case 2) after failed open reduction and internal fixation.

Figure 8 Postoperative radiograph after revision surgery (Case 2) and fragment excision.

Discussion

Key findings

Both patients sustained fractures through the proximal femoral array pin site, highlighting a possible shortfall in the recommended “safe zone” for array placement (12,15).

Strengths and limitations

Strengths:

• Detailed documentation of clinical courses, imaging, and outcomes;
• Highlights a less-reported but significant complication of robotic THA.

Limitations:

• Small sample size (two cases);
• Study design (case report);
• No biomechanical testing to confirm the exact cause of the fractures, or of suggested change in practice, it is based on single-center clinical experience.

Comparison with similar research and literature review

The largest database analysis to date supports our finding: an analysis of 1.2 million primary THAs in the U.S. Nationwide Readmissions Database identified 18,417 robot-assisted cases (1.5%). These recorded a 30-day periprosthetic-fracture rate of 0.42%, compared with 0.26% for conventional THA, giving an adjusted odds ratio of 1.63 [95% confidence interval (CI): 1.35–1.98]—a 63% relative increase in risk (13). These population-level data lend quantitative support to our clinical observation that femoral-array pin sites may act as stress risers in RA-THA.

Previous reports have identified pin site fractures in navigated or robotic THA, but greater trochanteric fractures specifically remain less reported. The Food and Drug Administration (FDA)-MAUDE database lists a single greater-trochanter fracture but provides no denominator to indicate how many robotic procedures were performed, while Perets et al. recorded three trochanteric fractures among 168 robot-assisted cases (1.9%). Both sources therefore offer limited detail on the nature and context of the complication (9-12). These cases underscore the need to reconsider screw placement site during THA through posterolateral approach when using robotic systems.

Explanations of findings

In 2024, the narrative review of “Management of isolated greater trochanter fractures associated with total hip arthroplasty” (16) proposes a practical three-type classification (tip-avulsion, mid-substance, and basal) with evidence-based treatment algorithms. Our fractures correspond to their type 2 (mid-substance, fracture line located between gluteus medius muscle and vastus lateralis muscle insertion points) pattern, which the review identifies as the group most prone to displacement, non-union, and symptomatic limp—precisely the course observed in our second patient. Fraval et al. note that surgical fixation of type 2 injuries is controversial, with hardware irritation and non-union rates approaching 25–40%, a caution reflected in the re-operation required in Case 2.

Temporary pins or screws in the proximal femur can create a stress riser, particularly in patients with potential bone weakness or comorbidities (e.g., diabetes, advanced age). Minor stress or subtle motion may be sufficient to propagate a fracture or to displace fracture that went unnoticed during surgery, even without a clear traumatic incident (9).

Implications and actions needed

Beyond refining guidelines for array placement, surgeons should weigh bone quality and incorporate alternative referencing points [e.g., more distal or lateral zones, so the possible fracture line would produce fracture with relatively better prognosis—type 3 (16)]. Figure 9 demonstrates a suggested safe zone that avoids high-stress areas on the greater trochanter, using footprints of vastus lateralis muscle and gluteus medius muscle. After we adopted this revised technique, the complication rate fell noticeably. Although the cohort is small and patient impact precludes a rigorous hypothesis test, we consider the observed reduction important enough to report. Ongoing biomechanical research is critical to establish reliable zones that reduce the risk of periprosthetic fractures.

Figure 9 Suggested “safe zone” for femoral array screw placement, avoiding the greater trochanteric region at risk (see the text). Proximal zona was at superior right corner of the image and distal at inferior left corner. GM, gluteus medius; VL, vastus lateralis.

Conclusions

These two cases highlight trochanteric fractures originating at the femoral array screw site in RA-THA. Although the literature suggests a low incidence of such complications, emerging evidence advocate for more cautious approach due to possible elevated rate of periprosthetic fracture in peri-operative period of RA-THA, these events may be preventable with improved placement protocols. We recommend further biomechanical studies and adaptation of surgical guidelines to account for individual variations in trochanteric morphology.

Acknowledgments

During the writing of this article, ChatGPT model 4 was used to improve readability and check for grammatical errors. Postprocessed text was reevaluated by the corresponding author to confirm it validity. We acknowledge the support of Angela Zumel in protocol development and ethical board evaluation.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-5/rc

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-5/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-5/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Institutional review board approval was waived. The Committee of Ethics in Drug Research at the Institut de Recerca i Innovació en Ciències de la Vida i la Salut a la Catalunya Central in its meeting on 14.02.2024 (record of meeting 02/2024) notes the presentation of the clinical case and considers it appropriate from an ethical and scientific perspective. Written informed consent was obtained from patients for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007;89:780-5. [Crossref] [PubMed]
2. Kurtz SM, Ong KL, Lau E, et al. Impact of the economic downturn on total joint replacement demand in the United States: updated projections to 2021. J Bone Joint Surg Am 2014;96:624-30. [Crossref] [PubMed]
3. Liebs TR, Herzberg W, Rüther W, et al. Quality-Adjusted Life Years Gained by Hip and Knee Replacement Surgery and Its Aftercare. Arch Phys Med Rehabil 2016;97:691-700. [Crossref] [PubMed]
4. Arden NK, Kiran A, Judge A, et al. What is a good patient reported outcome after total hip replacement? Osteoarthritis Cartilage 2011;19:155-62. [Crossref] [PubMed]
5. Pabinger C, Lothaller H, Portner N, et al. Projections of hip arthroplasty in OECD countries up to 2050. Hip Int 2018;28:498-506. [Crossref] [PubMed]
6. Kamara E, Robinson J, Bas MA, et al. Adoption of Robotic vs Fluoroscopic Guidance in Total Hip Arthroplasty: Is Acetabular Positioning Improved in the Learning Curve? J Arthroplasty 2017;32:125-30. [Crossref] [PubMed]
7. Katz JN, Wright EA, Wright J, et al. Twelve-year risk of revision after primary total hip replacement in the U.S. Medicare population. J Bone Joint Surg Am 2012;94:1825-32. [Crossref] [PubMed]
8. Kort N, Stirling P, Pilot P, et al. Clinical and surgical outcomes of robot-assisted versus conventional total hip arthroplasty: a systematic overview of meta-analyses. EFORT Open Rev 2021;6:1157-65. [Crossref] [PubMed]
9. Brozovich A, Lionberger DR. Periprosthetic Fracture of Greater Trochanter in Total Hip Replacement Stemming from Pin Site Placement in Navigation-Assisted Surgery. Case Rep Orthop 2019;2019:1945895. [Crossref] [PubMed]
10. Kamara E, Berliner ZP, Hepinstall MS, et al. Pin Site Complications Associated With Computer-Assisted Navigation in Hip and Knee Arthroplasty. J Arthroplasty 2017;32:2842-6. [Crossref] [PubMed]
11. Perets I, Walsh JP, Close MR, et al. Robot-assisted total hip arthroplasty: Clinical outcomes and complication rate. Int J Med Robot 2018;14:e1912. [Crossref] [PubMed]
12. Pagani NR, Menendez ME, Moverman MA, et al. Adverse Events Associated With Robotic-Assisted Joint Arthroplasty: An Analysis of the US Food and Drug Administration MAUDE Database. J Arthroplasty 2022;37:1526-33. [Crossref] [PubMed]
13. Singh A, Kotzur T, Peng L, et al. Robot-Assisted Total Hip Arthroplasty is Associated With an Increased Risk of Periprosthetic Fracture. J Arthroplasty 2024;39:S353-8. [Crossref] [PubMed]
14. Mako. 2023. Available online: https://www.stryker.com/es/es/portfolios/orthopaedics/joint-replacement/mako-robotic-arm-assisted-surgery.html
15. Redmond JM, Gupta A, Hammarstedt JE, et al. The learning curve associated with robotic-assisted total hip arthroplasty. J Arthroplasty 2015;30:50-4. [Crossref] [PubMed]
16. Fraval A, Hegeman EM, Krueger CA. Management of Isolated Greater Trochanter Fractures Associated With Total Hip Arthroplasty. J Am Acad Orthop Surg 2024;32:196-204. [Crossref] [PubMed]