As the global population ages, total hip replacement (THR) surgery has rapidly become one of the most frequent and transformative orthopedic interventions performed worldwide. With estimates suggesting over a million procedures annually, THR offers significant restoration of mobility and relief from debilitating pain caused by hip joint disease. Despite these benefits, THR is accompanied by notable risks, particularly in elderly patients whose comorbidities elevate the challenge of ensuring optimal postoperative outcomes. Among these risks, periprosthetic femoral fractures stand out as a critical complication, frequently necessitating revision surgeries that carry their own inherent hazards.
A femoral fracture occurring adjacent to the implant, especially within the first three months postoperatively, is one of the leading causes of early THR failure and necessitates complex reoperation. Such fractures compromise implant stability, prolong patient recovery, and increase healthcare costs. While patient factors such as age, bone quality, and comorbid conditions play undeniable roles in fracture susceptibility, implant design is a modifiable factor under the surgeon’s control. Identifying the optimal femoral stem configuration that mitigates the risk of early fractures remains a paramount goal in orthopedic research and clinical practice.
In a comprehensive retrospective investigation spearheaded by Assistant Professor Rui Hirasawa at Chiba University’s Graduate School of Medicine, researchers meticulously compared two dominant femoral stem designs used in THR: collared fully hydroxyapatite (HA)-coated stems versus flat-tapered wedge stems. This study analyzed an extensive dataset originating from 4,511 hip replacements performed by a single experienced surgeon over a fourteen-year period, spanning 2009 to 2023. Employing propensity score matching to control for confounding variables such as age, sex, body mass index, and osteoarthritis status, the investigators ensured rigorous comparability between 1,804 cases utilizing collared HA-coated stems and an equal number implanted with flat-tapered wedge stems.
The collared fully HA-coated femoral stem is distinguished by a circumferential collar that interfaces directly with the femoral calcar, providing immediate mechanical support and distributing load optimally. Moreover, the hydroxyapatite coating facilitates osseointegration by fostering direct bone apposition, thereby enhancing biological fixation and long-term stability. In contrast, flat-tapered wedge stems rely predominantly on geometric wedging within the intramedullary canal, lacking a collar and surface coating, which renders their fixation mostly dependent on the frictional fit between implant and host bone.
The study’s findings revealed a striking disparity in early postoperative femoral fracture rates favoring the collared HA-coated stem. Among matched cohorts, only two fractures were documented in the collared stem group compared to thirteen in patients receiving flat-tapered wedge stems. This significant reduction underscores the biomechanical and biological advantages conferred by the collar and HA coating, which collectively reduce micromotion and enhance early implant-bone stability during the vulnerable postoperative healing phase.
Intriguingly, despite their superior performance in preventing postoperative fractures, collared HA-coated stems exhibited a higher incidence of intraoperative femoral fractures. The procedural intricacies associated with implanting these stems—such as the necessity for precise seating of the collar and meticulous preparation of the femoral canal—may elevate the risk of bone injury during surgery. This paradox highlights the critical need for surgical expertise and tailored operative strategies to mitigate intraoperative complications while maximizing postoperative safety.
The implications of these findings extend beyond individual patient outcomes. Selecting collared fully HA-coated stems can potentially redefine standard practice by minimizing revision rates associated with early periprosthetic fractures, thereby improving long-term implant survival and reducing the overall burden on healthcare systems. As Professor Hirasawa emphasizes, informed implant choice grounded in evidence-based insights can translate directly into enhanced patient safety, expedited functional recovery, and durable joint performance.
From a biomechanical perspective, the collar acts as a load transmitter, decreasing peak stress concentrations at the proximal femur that could otherwise precipitate microfractures. Simultaneously, the bioactive HA coating promotes rapid bone ingrowth, facilitating a seamless biomechanical bond that counters loosening and subsidence. Conversely, the absence of these features in flat-tapered stems necessitates reliance on precise surgical technique to achieve a tight press-fit, a condition not always sustainable in compromised bone conditions commonly encountered in elderly patients.
The study’s rigorous methodology, leveraging one surgeon’s consistency in operative approach and standardized postoperative protocols, minimizes variability often inherent in multicenter studies. This design strengthens the validity of conclusions drawn regarding implant performance. Additionally, the advanced statistical adjustment for baseline characteristics addresses potential selection bias, reinforcing confidence in the observed associations between stem design and fracture risk.
While the protective effect of collared HA-coated stems against early postoperative fractures is compelling, the elevated risk of intraoperative complications necessitates further investigation. Refinements in implant design, surgical instruments, and operative techniques tailored to this stem type could reduce intraoperative fracture incidence. Moreover, preoperative assessment tools identifying patients at heightened intraoperative risk may guide individualized implant selection to optimize safety.
In the broader context of orthopedic innovation, this study exemplifies the synergy between material science, biomechanics, and clinical research. The use of HA coatings, a biomimetic surface treatment inspired by natural bone mineral, represents a paradigm shift from purely mechanical fixation toward biological integration, reshaping prosthesis longevity paradigms. Similarly, incorporating structural features like collars harnesses biomechanical principles to distribute forces in a manner harmonious with native femoral anatomy.
Future research directions may explore longitudinal outcomes extending beyond early postoperative periods to assess the durability of the protective effect conferred by collared HA-coated stems. Additionally, comparative analyses involving newer stem designs and different surgical approaches could further refine implant selection frameworks. Integration of advanced imaging modalities and computational modeling may elucidate the precise biomechanical interactions underpinning fracture mechanisms and implant performance.
In conclusion, the work led by Assistant Professor Rui Hirasawa and colleagues presents compelling evidence that collared fully hydroxyapatite-coated femoral stems significantly reduce the incidence of early postoperative femoral fractures in total hip arthroplasty when compared to flat-tapered wedge stems. Despite challenges related to intraoperative fracture risk, the biomechanical and biological advantages of these stems position them as a superior choice for enhancing patient outcomes. As total hip replacement surgeries continue to rise globally, such evidence-driven implant innovation stands to improve the lives of millions through safer, more effective joint reconstruction.
Subject of Research: People
Article Title: Collared fully hydroxyapatite-coated femoral components reduce early periprosthetic femoral fractures in total hip arthroplasty with the direct anterior approach
News Publication Date: October 1, 2025
Web References: https://doi.org/10.1302/0301-620X.107B10.BJJ-2024-1494.R1
Image Credits: Nakashima Health Force Co., Ltd.
Keywords: total hip replacement, periprosthetic femoral fracture, collared femoral stem, hydroxyapatite coating, femoral stem design, orthopedic implant, implant osseointegration, arthroplasty complications, implant biomechanics, surgical outcomes, bone integration, revision surgery
Tags: femoral stem configurationhealthcare costs of hip replacementsmitigating fracture risks in THRoptimizing outcomes in hip surgeryorthopedic interventions for elderlyorthopedic research advancementspatient recovery in hip replacementperiprosthetic femoral fracturespostoperative complications in hip surgeryrevision surgeries for hip implantssafer implant designstotal hip replacement surgery
