(P 511) SIGNIFICANCE OF TIP TO APEX DISTANCE IN PATHOLOGICAL 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 pathological and/or impending pathological fractures of the proximal femur in cancer patients is lacking. The aim of this study is to assess whether a high TAD correlates with failure rate in pathological and/or impending pathological proximal femur fractures.

Methods: A retrospective chart review was conducted on all patients who underwent intramedullary nailing (IM) of the proximal femur for pathological and/or impending pathological fractures from 2007-2023 (n=205). Patients who did not have postoperative radiographs were excluded (n=71). The 134 patients that remained following exclusion criteria consisted of 21 pathological fractures and 113 impending pathological fractures. Demographics, preoperative comorbidities, TAD, complications, device failure and reoperation rates were recorded.

Results: Failure was observed in 8/134 (6%) patients. Preoperative lesion presentation of the femurs that failed fixation included 1 complete fracture and 7 impending fractures. 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 IM rod at the level of the lag screw. Average TAD in devices that failed was 37±10 mm, whereas the average TAD in devices that did not fail was 30±10 mm, which was not statistically significant (p=0.068).

Conclusion: The results presented here suggest that TAD may not matter in appropriately selected patients, as 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 of TAD with cut out failure in non-pathological hip fractures, further investigation into TAD in pathological femur fractures with a larger patient population is warranted.