Abstract
Introduction and Objective
Hip fractures represent one of the most challenging injuries in orthopaedic practice due to the associated morbidity, mortality and the financial burden they impose on the health care systems. By many still considered as the gold standard in the management of intertrochanteric fractures, the Dynamic Hip Screw utilizes controlled collapse during weight bearing to stabilize the fracture. Despite being a highly successful device, mechanical failure rate is not uncommon. The most accepted intraoperative indicator for lag screw failure is the tip apex distance (TAD), yet lateral femoral wall thickness (LWT) is another evolving parameter for detecting the potential for lateral wall fracture with subsequent medialization and implant failure. The aim of this study is to determine the mean and cut off levels for LWT that warrant lateral wall fracture and the implications of that on implant failure, revision rates and implant choice.
Materials and Methods
This prospective cohort study included 42 patients with a mean age of 70.43y with intertrochanteric hip fractures treated with DHS fixation by the same consultant surgeon from April 2019 to December 2019. The study sample was calculated based on a confidence level of 90% and margin of error of 5%. Fracture types included in the study are 31A1 and 31A2 based on the AO/OTA classification system. LWT was assessed in all patients preoperatively using Surgimap (Nemaris, NY, USA) software. Patients were divided into two groups according to the post-operative integrity of the lateral femoral wall, where group (A) sustained a lateral femoral wall fracture intraoperatively or within 12 months after the index procedure, while in group (B) the lateral femoral wall remained intact. All patients were regularly followed up radiologically and clinically per the Harris Hip Score (HHS) for a period of 12 months.
Results
At 12 months five patients (12%) suffered a postoperative lateral wall fracture, while in 37 patients (88%) the lateral femoral wall remained intact. The mean preoperative LWT of patients with a postoperative lateral wall fracture was 18.04 mm (SD ± 1.58) compared to 26.22mm (SD ± 5.93) in the group without a lateral wall fracture. All patients with post-operative lateral femoral wall fracture belong to 31A2 group, while 78.4% of the patients that did not develop post-operative lateral femoral wall fracture belong to 31A1 group. Eighty percent of patients in group (A) experienced shortening, collapse, shaft medialization and varus deformity. The mean Harris hip score of group (A) was 39.60 at 3 months and 65.67 at 6 months postoperatively, while that of group (B) was 80.75 and 90.65 at 3 and 6 months respectively, denoting a statistically significant difference (P<0.001). Treatment failure meriting a revision surgery was 40 % in group (A) and 8% in group (B) denoting a statistically significant difference (p<0.001). The cut-off point of LWT below which there is a high chance of post-operative lateral wall fracture when fixed with DHS is 19.6mm. This was shown on the receiver operating curve (ROC) by plotting the sensitivity against the 100 % specificity with a set 95% confidence interval 0.721 – 0.954. When lateral wall thickness was at 19.6 mm, the sensitivity was 100% and specificity was 81.8%. The area under the curve (AUC) was 0.838, which was statistically significant (P = 0.015).
Conclusions
Preoperative measurement of LWT in elderly patients with intertrochanteric hip fractures is decisive. The cut off point for postoperative lateral wall fracture according to our study is 19.6 mm; hence, intramedullary fixation has to be considered in this situation.
