The role of postoperative piriformis fossa and greater trochanter tubercle distance to predict cutout failure after cephalomedullary nail fixation

Abstract

Background: This study investigated the association between postoperative piriformis fossa and greater trochanter tubercle distance (distance from the deepest point of piriformis fossa to the most lateral greater trochanter tubercle [PG]) and cutout failure after cephalomedullary nail (CMN) osteosynthesis for intertrochanter fracture (ITF). A rotating femur model was designed to analyze PG variation during femur rotation. Methods: From 2005 to 2010, 311 patients diagnosed of ITF (Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association [AO/OTA] 31-A2 and A3) underwent CMN fixation at our institute were reviewed. Of these, 281 (90.3%) patients achieved union without complication, 21 (6.8%) had cutout failure, six (1.9%) had femoral head osteonecrosis, and three (1%) had nonunion during postoperative 2-year follow-up. The side difference of postoperative PG compared to contralateral uninjured hip (dPG) was analyzed between patients who had cutout failure and those who did not. In the rotating femur model, the PG was measured for every 2.5° increments of internal and external rotation from 0° to 50°. Results: The dPG was significantly higher in the failure group (10.2±4.2 vs 6.6±3.5mm, p <0.001). The odds ratio for lag screw cutout was 6.35 (95% CI, 1.10-11.6, p =0.003) for every 1mm dPG increment. dPG exhibited high diagnostic performance in predicting cutout failure according to receiver operating characteristic curve analysis. The area under the curve was 0.774 (95% CI, 0.711-0.837). dPG yielded the greatest sensitivity (78.4%) and specificity (78.4%) to predict lag screw cutout when cutoff value being 8.65mm. In rotating femur model, PG change from baseline demonstrated significant (p <0.001) positive and negative correlation with increased external and internal rotation, respectively. Conclusion: Increased dPG is a risk factor of cutout failure for ITF osteosynthesis with CMN. In conjunction with tip-apex distance, fracture displacement, and reduction quality; dPG can help surgeons interpret postoperative radiograph and predict failure. However, it should be noticed that a proper and standard patient positioning is critical for accurate dPG measurement.