Loss of the Posteromedial Support: A Risk Factor for Implant Failure After Fixation of AO 31-A2 Intertrochanteric Fractures
Intertrochanteric fractures (ITFs) are a significant clinical challenge, particularly in the elderly population. With the global aging trend, the incidence of hip fractures, including ITFs, is projected to rise dramatically, reaching up to 6.3 million cases annually by 2050. ITFs account for approximately half of all hip fractures, and their management typically involves internal fixation followed by early mobilization. Despite advancements in surgical techniques and implant designs, the rate of fixation failure remains a concern, especially in unstable fractures. Fixation failure can lead to severe complications, including pain, disability, and even mortality, particularly in elderly patients. Therefore, identifying and mitigating risk factors for fixation failure is crucial to improving patient outcomes.
One of the key factors associated with fixation failure in ITFs is the loss of posteromedial support. The posteromedial cortex, including the lesser trochanter (LT), plays a critical role in stabilizing the fracture and distributing the load from the femoral neck to the shaft. When this support is compromised, the risk of implant failure increases significantly. This study aimed to investigate the relationship between the loss of posteromedial support and implant failure in patients with AO 31-A2 intertrochanteric fractures, a specific subtype of ITFs characterized by a fracture line extending from the greater trochanter to the lesser trochanter.
Materials and Methods
This study was a retrospective analysis of 394 patients who underwent operative treatment for AO 31-A2 ITFs at a single institution between January 2003 and December 2017. The inclusion criteria were: (1) AO 31-A2 ITFs; (2) fresh closed fractures treated with closed reduction and internal fixation; (3) American Society of Anesthesiologists (ASA) score of 3 or less; (4) regular radiological follow-up until bone union or failure; and (5) a minimum of one year of follow-up unless failure occurred. Exclusion criteria included open fractures, multiple injuries to the same leg, pathological fractures, subtrochanteric fractures, ASA scores greater than 3, pre-existing walking disabilities, fractures classified as AO 31-A1 or A3, bilateral ITFs, and incomplete follow-up data.
Patients were divided into two groups based on the presence or absence of posteromedial support post-operatively. Group A (n = 153) included patients with intact posteromedial support, while Group B (n = 241) included those without posteromedial support. The loss of posteromedial support was defined as a bone-to-bone defect in the inner side of the fracture site, as observed on post-operative radiographs. The primary outcome measure was radiological failure, which included varus deformity, cut-out or movement of the lag screw, breakage of the implant, periprosthetic fracture, and malunion, delayed union, or nonunion.
The study also compared patients based on their final outcomes, dividing them into Group C (failed cases, n = 66) and Group D (normal outcomes, n = 328). Various factors, including age, sex, ASA score, affected limb side, fixation method (intramedullary or extramedullary), time from injury to operation, blood loss, operative time, and length of stay, were analyzed to identify significant differences between the groups. A logistic regression analysis was performed to determine whether the loss of posteromedial support was an independent risk factor for fixation failure.
Results
The study population had an average age of 76.36 years, with a range of 27 to 95 years. The cohort included 131 men and 263 women, with 209 left-sided and 185 right-sided fractures. All fractures were caused by low-energy trauma, and the majority of patients (n = 362) were treated with intramedullary fixation, while the remaining patients (n = 32) underwent extramedullary fixation. The mean follow-up period was 28.4 months.
The failure rate in Group B (24.07%) was significantly higher than in Group A (5.23%) (P < 0.001). The most common types of failure in Group B were varus deformity (48.28%) and cut-out (17.24%). In the comparison between Group C (failed cases) and Group D (normal outcomes), significant differences were observed in the fixation method (P = 0.005), operative time (P = 0.001), blood loss (P = 0.002), and length of stay (P = 0.033). However, there were no significant differences in age, sex, affected side, ASA score, or time from injury to operation between the two groups.
The logistic regression analysis revealed that the loss of posteromedial support was an independent risk factor for implant failure, with an odds ratio (OR) of 5.986 (95% CI: 2.667–13.432, P < 0.001). This finding suggests that patients without posteromedial support were nearly six times more likely to experience fixation failure compared to those with intact posteromedial support.
Discussion
The femoral calcar, a compact bone connecting the posteromedial cortex of the femoral neck and shaft, plays a crucial role in stabilizing ITFs. When the calcar and lesser trochanter are fractured and not adequately reduced post-operatively, the loss of posteromedial support can lead to increased stress on the implant, resulting in fixation failure. This study highlights the importance of assessing the integrity of the posteromedial cortex pre-operatively and considering reconstruction of the posteromedial wall in cases where it is compromised.
Varus deformity was the most common type of failure observed in this study, particularly in patients without posteromedial support. The femoral calcar acts as a buttress against the transmitted load from the femoral neck. When the calcar is fractured, the load is redistributed, leading to varus collapse of the fracture site. This finding is consistent with previous biomechanical studies, which have shown that the highest stress in the femur is concentrated in the medial femoral calcar. The absence of posteromedial support increases the risk of varus deformity, as the fracture site is unable to withstand the compressive forces.
Cut-out of the lag screw was the second most common complication, often occurring in conjunction with varus deformity. The loss of posteromedial support increases the load on the lag screw, leading to micro-fractures in the cancellous bone around the screw tip. Over time, this can result in screw displacement or cut-out. Previous studies have emphasized the importance of bone-to-bone contact in reducing the tensile stresses on the implant and preventing cut-out. The findings of this study suggest that special attention should be paid to avoiding cut-out in patients with osteoporosis or compromised posteromedial support.
Implant breakage, including breakage of the plate, screw, or nail, was another type of failure observed in this study. The loss of posteromedial support increases the load on the implant, particularly at the inferomedial junction of the nail and screw in intramedullary fixation. When the load exceeds the fatigue threshold of the implant, breakage can occur. Extramedullary fixation devices, which rely on the bone to transmit the load, are particularly vulnerable in the absence of posteromedial support. This study supports the use of intramedullary fixation for unstable ITFs, as it provides better stability in cases where the posteromedial cortex is compromised.
Periprosthetic fractures were observed in two cases, both of which occurred in Group B and were treated with the Proximal Femoral Nail Antirotation (PFNA) system. The design of the PFNA, with its medial-lateral angle and uniform diameter, can lead to nonuniform contact between the nail and the bone, resulting in stress concentration at specific points. The loss of posteromedial support exacerbates this issue, increasing the risk of periprosthetic fracture. This finding underscores the importance of careful implant selection and placement in patients with compromised posteromedial support.
Conclusion
The loss of posteromedial support is a significant risk factor for implant failure in patients with AO 31-A2 intertrochanteric fractures. Patients without posteromedial support are nearly six times more likely to experience fixation failure compared to those with intact posteromedial support. The most common types of failure in these patients include varus deformity, cut-out, implant breakage, and periprosthetic fractures. These findings highlight the importance of assessing the integrity of the posteromedial cortex pre-operatively and considering reconstruction of the posteromedial wall in cases where it is compromised.
Further research is needed to determine the optimal surgical techniques for reconstructing the posteromedial wall and whether fixation of the lesser trochanter fragment can improve outcomes in patients with AO 31-A2 ITFs. Standardized procedures for addressing the loss of posteromedial support should be developed to reduce the risk of fixation failure and improve patient outcomes.
doi.org/10.1097/CM9.0000000000000587
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