Femoral Neck Shortening and Varus Collapse After Navigated Fixation of Intracapsular Femoral Neck Fractures

Objective: Assessing femoral neck shortening (FNS) and varus collapse after internal fixation of femoral neck fractures using computerized navigation (CN). Design: Retrospective cohort study. Settings: Academic Level I trauma center. Patients and Methods: Forty-one patients who had healed femoral neck fractures treated with CN between the years 2003 and 2008. Average age was 65 years (range, 14-91 years). Thirty-six patients had nondisplaced fractures and five had displaced fractures. Intervention: Screws were placed using CN in an inverted triangle formation Follow-up films were digitized into a PACS system, calibrated, and analyzed using CAD software. Outcome Measures: The following parameters were recorded: abductor lever arm shortening (termed x), corresponding vertical femur shortening (termed y), and the resultant femoral neck shortening vector (z). Fifteen patients were available for clinical outcome measures by the means of SF-12 survey Results: Significant FNS of the x component (greater than 5 mm) occurred in 30 of 42 (71%) patients with severe shortening (greater than 10 mm) in 25% of the patients. Significant y shortening occurred in 43% of the patients and severe shortening in 17%. Overall (z) femoral neck shortening occurred in 56% of the patients with severe shortening in 22% of patients. Varus collapse (greater than 5 degrees) did not occur in any patient. Screw pullout (greater than 5 mm) occurred in 17 (41%) patients. Seven patients required late (greater than 6 months) arthroplasty postoperatively. FNS did not significantly correlate with fracture type, quality of reduction, age, or neck shaft angle. SF-12 results were negatively correlated with overall FNS. Conclusions: Our results show a high degree of FNS associated with the use of CN for fixation of femoral neck fractures, similar to recently published series using nonnavigated implants. However, no varus collapse occurred in our series. Our preliminary clinical data show a trend toward an adverse effect of FNS on quality-of-life measures.