Use of fully threaded cannulated screws decreases femoral neck shortening after fixation of femoral neck fractures

Background Femoral neck fractures (FNF) are becoming increasingly common as population ages. Nondisplaced fractures are commonly treated by cancellous, parallel placed, partially threaded cannulated screws (PTS). This allows controlled fracture impaction. However, sliding implants can lead to femoral neck shortening (FNS) that has been shown to be correlated with reduced quality of life and impaired gait pattern. Recently, in our institution we have changed the fixation of FNF to fully threaded screws (FTS) with or without an additional partially threaded screw in order to minimize this phenomenon. The aim of this study was to compare the FNS in patients treated with FTS as compared with our historical controls treated with PTS. Patients and methods Between 2014 and 2016, 38 patients with FNF were treated with FTS. Out of the 38, 24 were available for radiographic follow-up. 41 patients treated previously with PTS were available as a control group. Radiographic analysis was performed to assess the FNF in three vectors: Horizontal (X), Vertical (Y) and overall (Z) according to the neck-shaft angle. Results Time for admission to surgery was longer in the PTS group (p = 0.04). Patient demographics and major complication rates were similar in the two patient groups. Average FNS in the X axis was significantly smaller in the FTS group than in the PTS group (2.8 +/- 3.6 vs 7.6 +/- 4.2 mm, p < 0.01) as well as the Y axis (1.2 +/- 2.6 vs 4.9 +/- 4.2 mm, p < 0.01) and thus also decreased overall Z shortening (2.3 +/- 3.5 vs 6.23 +/- 4.5 mm, p < 0.01). There was a tendency towards a more valgus reduction in the PTS (137A degrees vs 134A degrees, p = 0.08). There was a significantly smaller number of FTS patients with moderate (5-10 mm) or severe (> 10 mm) FNS. Screw pull-out > 5 mm occurred in 17/41 patients in the PTS but none in the FTS group (p < 0.01). Conclusion This study proves that use of FTS improves the radiographic results following FNF fixation using cannulated screws.