Jig rotation and its effect on guide-wire angle in dynamic hip screw fixation

Dynamic hip screw (DHS) fixation is a common surgical procedure for intertrochanteric hip fractures. Accurate guide-wire placement is critical for optimal screw position and long-term implant stability. While the impact of jig malposition on guide-wire angle is intuitively understood by orthopedic surgeons, the precise quantification of this error and its potential clinical implications remain underexplored in the literature. This study aimed to quantify the change in guide-wire insertion angle resulting from varying degrees of jig rotation during DHS fixation and to discuss the potential biomechanical and clinical consequences of such inaccuracies. A novel method for measuring the guide-wire insertion angle was developed using a transparent mathematical protractor. A curved guide-wire jig (135°) from the Stryker Omega3 DHS system was rotated about a fixed, well-seated, distal point, in increments of five degrees (0° to 15°), and guide-wires were inserted into separate sawbones (n=4 per rotation increment). The resultant angle between the guide-wire and the lateral femoral cortex (wire-cortex angle) was then measured by a blinded assessor. Due to the experimental setup and limited sample size, formal statistical analysis was not performed; descriptive statistics are presented. At 0° and 5° proximal jig rotation, the mean wire-cortex angle was 135°. At 10° jig rotation, this angle increased to a mean of 139° (4° valgus), and at 15° jig rotation, the angle reached a mean of 140° (5° valgus). These findings demonstrate a quantifiable change in guide-wire angle directly proportional to jig rotation. Even small degrees of jig rotation can lead to measurable alterations in guide-wire insertion angle. While the observed angular changes are modest, their potential amplification by the moment-arm of the implant construct may contribute to suboptimal screw placement, potentially influencing the neck-shaft angle and increasing the risk of mechanical complications such as superior cut-out. This study highlights the importance of meticulous jig seating and suggests a need for further research into jig design improvements and the clinical impact of such technical inaccuracies. The limitations of this in vitro study, including the small sample size and use of sawbones, necessitate cautious interpretation of the findings and emphasize the need for future clinical validation.