Predictors of screw cutout in the surgical fixation of peritrochanteric hip fractures: A retrospective cohort study

INTRODUCTION

Peritrochanteric (PT) femur fractures can be associated with debilitating outcomes and reduced disability-adjusted life years.^[1,2] Thus, posing a substantial socioeconomic challenge,^[1-3] PT fractures encompass a group of fractures between the femur neck and subtrochanteric region and contribute to up to 50% of adult hip fractures. These fractures are often a result of low energy (e.g., falls) in elderly patients or high-energy trauma like road traffic accidents in younger populations.

Surgical treatment is the gold standard in managing this kind of injury to restore baseline pre-injury mobility and functionality, pain control, and avoid immobilization morbidity. Various surgical fixation methods exist based on the fracture pattern and stability, including dynamic hip screw (DHS) and cephalomedullary nail (CMN). CMN, such as Gamma nails, are usually used to fix unstable PT hip fractures (AO classification A2 and A3) due to the biomechanical advantages over plate fixation. However, stable PT fractures (AO classification A1) can be fixed with either implant.

Screw cutout or failure is one of the most serious complications associated with internal fixation of PT fractures, with a prevalence of around 1.9–3.2%.^[4-6] It is defined as varus collapse of the femoral neck-shaft angle (<130), which leads to screw extrusion or cutout from the femoral head.^[4] This complication often requires to be addressed surgically. Thus, identifying the predisposing risk factors helps prevent screw cutouts and reoperation following internal fixation of PT fractures.

Numerous variables have been described in the literature as predictors of screw cutout following fixation of such fractures.^[7,8] These include (1) a tip apex distance (TAD) ≥T5 mm,^[4,9] (2) unstable fracture patterns as per Orthopaedic Trauma Association (OTA)/AO classification (A2.2 or A2.3),^[10] (3) the presence of a posterolateral fragment (Jensen 3 or 4),^[11] (4) types of reduction pattern on anteroposterior (AP) (medial) and lateral (LAT) (intramedullary) radiographic images, and^[12] (5) unstable screw position (other than central-central or central-inferior).^[9,13]

The TAD is the total distance from the tip of the screw to the apex of the femoral head on both AP and LAT radiographs measured in millimeters after adjusting for magnification [Figure 1].^[6]

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Figure 1:

The measurement of tip apex distance (TAD) is illustrated in a line drawing, with the use of Dtrue to control for magnification. Dtrue is the known diameter of the lag screw, while Dap and Dlat represent the measured diameter of the screw on anteroposterior and lateral radiographs, respectively. Xap and Xlat are the distances from the screw tip to the center of the femoral head on the corresponding radiographs. This illustration is adapted from a study by Baumgaertner et al. (1995) on the predictive value of TAD in the failure of fixation of peri-trochanteric fractures of the hip.

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To the best of our knowledge, this is the first national study to investigate the value of these risk factors as predictors of screw cutout in both DHS and CMN implant fixation of PT fractures. Therefore, this study aimed to evaluate the impact of the TAD and other reported factors as predictors of the screw cutout after internal fixation of PT fractures.

MATERIALS AND METHODS

Eligibility criteria

All adult patients (≥18 years) with acute PT fracture who underwent DHS or CMN fixation between 2016 and 2018 with at least 3 months of follow-up were included in the study. Patients with inadequate post-operative radiographs and ipsilateral femur shaft fractures were excluded from the study. [Figure 2] shows the complete inclusion and exclusion process.

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Figure 2:

Eligibility criteria.

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RESULTS

A total of 117 cases of patients with PT hip fractures who underwent surgical fixation by either DHS or CMN were identified retrospectively. Sixty-eight (40 DHS cases and 28 CMN cases) patients met the inclusion criteria and were included in the final analysis [Table 1]. The mean age was 64 ± 20 years, with an average BMI of 25.5 and a minimum 3-month follow-up period. Patients were primarily males, 65% (44), and 35% (24) females.

Results were subclassified based on the TAD criterion into two main groups: Group A, where TAD is <25 mm, and Group B, where TAD equals or exceeds 25 mm. The mean age was 65 ± 20 years in Group A and 63 ± 20 years in Group B. The average BMI was 26 ± 4 in Group A and 25 ± 5 in Group B. Twenty-one patients (55.3%) and 23 (76.7%) were males in Groups A and B, respectively.

Regarding fracture stability, 51.4% (19) and 46.4% (14) cases were unstable in Groups A and B, respectively. Most cases were operated by trainees surgeon, with 65.8% (25) in Group A compared to 56.7% (17) in Group B. “Good” appropriate fracture reduction was achieved on postoperative AP and LAT radiographs across both groups. In Group A, the lag screw position was observed to be consistently centralized (central-central or central-inferior) in 86% of the cases. In Group B, central placement of the lag screw was found in approximately 72% of the cases, with 28% exhibiting screw malposition. The detailed analysis is shown in [Table 1].

Five cases (7.35%) of screw cutouts were observed in this cohort study; four of which [Cases 1–4 in Table 2] were fixed with DHS and one [Case 5 in Table 2] by CMN. A sub-analysis assessed the relationship between these predicting factors (TAD, age, BMI, fracture classification, lag screw position pattern of fracture reduction on AP and LAT views, implant type, and performing surgeon level) and their impact on screw cutout. It was shown that age, BMI, fracture classification, and the level of performing surgeon were statistically insignificant (P = 0.617, P = 0.535, P = 0.707 and P = 0.445, respectively) in predicting screw cutout.

Furthermore, the proportion of failed cases in CMN use was 3.6%, and the proportion in DHS device use was 10%. A two-sample proportion test found no statistically significant difference in the proportion of failed cases between CMN use and DHS device use (P = 0.157), indicating that both treatment modalities have similar failure rates [Table 2].

In contrast, the measurement of TAD (in 80%, the TAD was more than 25 mm), lag screw malposition, and the fracture malreduction in AP (40%) and LAT views (20%) radiographs were statistically significant factors (P = 0.02, P = 0.03, P = 0.02 for AP and P = 0.024 LAT, respectively). A sub-analysis of screw cutout cases is summarized in [Table 2].

DISCUSSION

There has been considerable debate regarding the optimal implant that ensures anatomical reduction and the best clinical outcome. DHS and CMN (Gamma nails) are the most representative extramedullary and intramedullary fixation devices.

The most important finding of the present study is that the TAD of equal or more than 25 mm, pattern of the lag screw position, and fracture reduction on AP and LAT views were statistically significant contributing factors for screw cutout. However, the age, BMI, fracture classification, and level of performing surgeons were statistically insignificant in predicting screw cutout.

In line with other studies, our present study shed light on multiple factors that affect the TAD, resulting in fixation failure. Various factors have been associated with implant failure in PT hip fractures, including patient age, bone quality, fracture pattern, fracture reduction stability, implant angle, and lag screw position within the femoral head.^[16] However, there is currently no consensus on each factor’s interrelationships or relative importance. Accurate screw placement has been widely recognized as crucial, but methods for evaluating screw position have proven to be cumbersome and of limited predictive value in clinical settings. In this cohort, most of the screw cutout cases (80%) were fixed with DHS. In contrast to our findings, a meta-analysis conducted by Matre et al.^[8] found no significant difference in fixation failure (cutting-out or non-union) between Gamma nails and proximal femoral nails anti-rotation (PFNA) or DHS. However, a significantly lower risk of fixation failure was found in the PFNA group compared to DHS. Moreover, implant cutout and other complications were significantly associated with higher TAD, poor reduction, or reduction in varus and that these factors were independent of the implant type.^[8] Thus, achieving surgical perfection is paramount to selecting the implant to address this issue. In addition, using a CMN may lead to a reduced incidence of medialization >5 mm due to its resistance to excessive sliding along the axis of the lag screw.

Among the aforementioned factors, a retrospective analysis conducted by Fujii et al.^[17] confirmed that only a TAD of >20 mm was associated with screw cutout after internal fixation of intertrochanteric fractures with PFNA systems.

Due to the retrospective nature of the study, it is important to acknowledge several limitations, such as the presence of selection bias and the absence of randomized comparative groups. However, a sub-analysis based on the TAD within the same cohort was conducted to mitigate these limitations. In addition, one of the setbacks of this study was lacking power analysis and the small sample size due to the limited number of cases meeting the inclusion criteria. Future prospective studies, ideally multicentric, are needed to adjust for these drawbacks.

CONCLUSION

This study demonstrated that a TAD of ≥25 mm, lag screws malposition, and inappropriately reduced fracture in post-operative radiographs are statistically significant risk factors for screw cutout in DHS and CMN fixation of PT fractures. However, this finding should be applied in context, given.

AUTHOR CONTRIBUTIONS

All authors contributed to the study’s conception and design. Material preparation, literature review, data collection, and quality assessment were performed by MA, LAS, and AMA. Statistical analysis was performed by AMA and LAS. The first draft of the manuscript was written by MA, MH, and GK, and all authors commented on previous versions of the manuscript. All authors have critically reviewed and approved the final draft and are responsible for the manuscript’s content and similarity index.

ETHICAL APPROVAL

The Institutional Medical Research Centre at Hamad medical corporation approved this retrospective study on the March 23, 2020, with the reference number MRC–01–19–267 and can provide access to protocol on direct request.

USE OF ARTIFICIAL INTELLIGENCE (AI)-ASSISTED TECHNOLOGY FOR MANUSCRIPT PREPARATION

The authors confirm that there was no use of Artificial Intelligence (AI)-Assisted Technology for assisting in the writing or editing of the manuscript and no images were manipulated using the AI.