(P 279) SIGNIFICANCE OF TIP-APEX DISTANCE IN ACTUAL AND IMPENDING PATHOLOGICAL FRACTURES OF THE PROXIMAL FEMUR

Objective: The tip-apex distance (TAD) is a metric that accounts for the position and depth of a screw in the femoral head and has been shown to be associated with risk of screw cut-out. Traditionally, TAD > 25 mm is correlated with high failure rates. Application of this metric to actual and/or impending pathological fractures of the proximal femur in cancer patients is lacking. Therefore, the aim of this study is to assess whether a high TAD correlates with failure rate in actual and/or impending pathological proximal femur fractures.

Methods: A retrospective chart review was conducted on all patients who underwent intramedullary nailing of the proximal femur for pathological/impending pathological fractures from 2007-2023 (n=306). Patients who did not have post-operative radiographs were excluded (n=71). 235 patients remained, of which 37 of those patients had completed and 197 impending fractures prior to surgery. Demographics, preoperative comorbidities, TAD, complications, device failure and reoperation rates were recorded, and statistical analysis was completed.

Results: The mean age was 62.7 years old. Mean follow up was 12 months from surgery (range 1 – 100 months). Failure was observed in 3.4% (8/235) of patients. The mode of device failure included 4 progressions of the fracture at the original fracture site, 1 nonunion, 2 failed distal locking screws and 1 due to bending of the proximal aspect of the intramedullary rod at the level of the lag screw. There was no significant difference in TAD between those that failed and those that did not (30.1 vs. 28.7 mm, p=0.7). Only 4 proximal femur hardware failures occurred, and all were due to disease progression. There were 0 screw cut outs. There was no significant difference in TAD between those that failed proximally and those that did not (26.9 vs. 28.8 mm, p=0.7). Median time to hardware failure was 7.5 months (0.5 to 15.5 months). There was no significant difference in TAD between patients with completed and impending pathological fractures (27.5 vs. 29.5, p=0.4).

Conclusion: The results presented here suggest that the rate of screw cut out is low in patients with impending pathologic fractures; indeed, all the hardware failures happened at the site of the lesion or distally at the interlocking screws. Furthermore, TAD was not significantly different between devices that failed and those that did not. Given the robust correlation TAD has with cut out failure in non-pathologic hip fractures, these findings warrant further investigation into the application of TAD in pathological femur fractures with a larger patient population.