Abstract
Introduction
Hip resurfacing is a bone sparing approach to treating arthritis in younger or more active patients. Accurate positioning of the femoral component in the hip resurfacing procedure is essential for the success of the operation [1-2]. An alignment guide assisting the operator in accurately positioning the resurfacing implant may increases the success rate of the operation. This study focuses on the effectiveness of a CT based resurfacing alignment guide, shown in Figure 1.
Materials and Methods
Four full fresh frozen human cadaveric specimens were CT scanned to reconstruct bone models of the femoral head/neck geometries with no cartilage included in the segmentation. Femoral head resurfacing alignment guides were then created through computer aided design (CAD) modeling using landmarks from the reconstructed bone models for proper seating. A total of 12 resurfacing alignment guides (3 for each specimen) were prepared.
After the exposure of the hip joints, the first two out of three resurfacing alignment guides were used to asses the fit, stability, and visual assessment of valgus and version alignments. The third resurfacing alignment guide for each specimen was placed on the femoral head/neck region and the guide wire was drilled into the femur. A fluoroscopy image was taken to assess and measure the valgus and version alignment. The acceptance criteria for valgus alignment, as shown in Figure 2, is set to be ±2.5° from a line parallel to the medial calcar of the femoral neck, Similarly, the acceptance criteria for the version alignment was set to be ±2.5° from a line passing through the neutral axis of the femoral neck.
Results and Discussion
The resurfacing alignment guides were firmly secured on the femoral head; they were stable and their auxiliary guide wire placement features were allowed for visual assessments of the alignment. The planned and the measured valgus angles were in agreement and the version alignment neutral to femoral neck axis was within the acceptable range.
Current manual alignment guides require user experience for locating the entry point and trajectory for femoral head resurfacing. The CT based patient matched alignment guide offers a precise and reliable implant positioning, reducing the possibility of notching of the femoral neck and leaving any air pocket around the distal periphery of the implant which could lead to neck fracture or implant loosening, respectively.
This study demonstrates the effectiveness of a guide made based on the patient specific CT scan assisting the operator in the precise alignment of the femoral implant. The potential benefits of this technology are consistent and accurate alignment of the implant, reduced OR time and ease of use with reduced instrumentation.
