A new adjustable parallel drill guide for internal fixation of femoral neck fracture: a developmental and experimental study

Design and development

An orthopaedic surgeon and a design engineer developed the new adjustable drill guide design. After the concept and information were analysed, a three-dimensional model was created (Fig. 1).

The concept for development of this drill guide was based on the drill guide helping the surgeon insert the cannulated guide wire with an easily adjustable separation distance from the reference guide wire and produce good stability during insertion of the cannulated guide wire.

The drill guide consists of two parts: the reference part and the drilling part (Fig. 2). The reference part has a handle, reference tube for cannulated guide wire insertion and a square extension rod to support the drilling part that can slide along the extension rod (Fig. 3). There are scale numbers on the extension rod for length adjustment. The drilling part is slotted in the middle of the body to allow it to slide on the extension rod. The drilling part is able to move along the extension rod to maintain the drill guide tube parallel to the reference cannulated guide wire. A locking knob can tighten the drilling part to fix the position after adjustment of the distance. At the end of both guide rods, there are spikes to grip the bone to prevent drill slippage while drilling.

Simulated operation testing

This study was approved by the Ethics Committee and Institutional Review Board of the Faculty of Medicine at Prince of Songkla University, Songkhla, Thailand. This study was conducted in synthetic bones and not related to human subjects. So, an informed consent was unnecessary according to institutional regulations.

The experimental study evaluated the efficacy of the new drill guide compared to the conventional technique. The intraoperative setting was a simulated multiple screw fixation in femoral neck fracture with the patient in the supine position. The synthetic femoral bone made of foam cortical shell with cancellous inner material (Sawbones™, Pacific Research Laboratories, Inc., Vashon, Washington, USA) was placed on the operative table and fixed with a synthetic bone holder. The synthetic bone was covered with sponges to simulate the soft tissue compartment.

Eight orthopaedic surgeons were included in this study. They were given instructions and then practiced the technique to use this new drill guide. Each surgeon performed cannulated guide wire insertion for multiple screw fixation in six femurs using three guide wires for three-screw cannulated screw fixation in each femur. They performed the operation three times with the new drill guide and three times with the conventional technique. In the conventional technique group, guide wires were inserted using a standard parallel wire guide (Synthes 312.71 Parallel Wire Guide, Synthes, Paoli, Pennsylvania, USA) and protection sleeve. The operations were performed under C-arm fluoroscopy (Philips BV Libra, Philips Medical Systems North America Co., Bothell, Washington, USA) in the same operative theater environment.

The goal of each operation was to insert successfully three 2.0-mm cannulated guide wires to the target position. Three guide wires were inserted in the inverted triangle configuration. The first guide wire position was superior to the inner cortex of the inferior femoral neck (4 ± 1 mm) and parallel to the femoral neck in the anteroposterior view (Fig. 4-a). In the lateral fluoroscopic view, the first guide wire was in the middle of the femoral neck (±1 mm) and parallel to the femoral neck (Fig. 4-b). The second and third guide wire positions were in the middle of the femoral neck (±1 mm) and parallel to the femoral neck in the anteroposterior view. In the lateral view, the second guide wire was at 4 ± 1 mm posterior to the inner cortex of the anterior femoral neck and the third guide wire was at 4 ± 1 mm anterior to the inner cortex of the posterior femoral neck. The depths of all guide wire insertions were at the subchondral bone of the femoral head. The fluoroscopic time, total operative time, and surgeon satisfaction were recorded. The fluoroscopic time was recorded from the fluoroscopic machine and the level of satisfaction was evaluated by a visual analogue scale (VAS). The VAS consisted of a 10 cm line where 0 indicated no satisfaction at all and 10 represented total satisfaction.

Statistical methods

The statistical analysis was performed using R software version 3.1.0 (R Foundation). In order to compare fluoroscopic time and operative time, the differences between the groups used the Wilcoxon signed-rank test. The student t-test was used for comparison of satisfaction scores. Statistical significance was considered when P was less than 0.05.

A statistical power analysis was performed for sample size estimation based on data from a previous study [10]. To detect a 10 % difference in fluoroscopic time with a power set to 0.9 and a significance level set to 0.05, nine samples per group were required.