Background: Accurate measurement of acetabular cup position (CP), changes in leg length (LL), and offset (OS) are paramount in ensuring proper sizing and implantation of components during total hip arthroplasty (THA). LL/OS inaccuracies can cause low back pain, neurological deficits, and patient dissatisfaction, while inaccurate positioning of the acetabular cup can lead to instability, dislocation, and, ultimately, revision surgery. The objective of this study was to evaluate the accuracy of a mini-navigation tool in measuring CP and LL/OS differential during THA.
Materials and methods: Three board-certified orthopedic surgeons each performed four THA procedures via the posterior approach on six cadavers (12 hips) utilizing a novel mini-navigation tool. Imaging included pre- and post-operative radiographs and post-operative CT scans. Image analysis was performed by two radiologists not involved in the surgical procedures. System accuracy regarding measurement of cup position (anteversion and inclination) was determined by comparing the CT measurement of cup orientation with data gathered intraoperatively by probing the face of the implanted cup with the navigation tool and recording the coordinates.
Results: The mean absolute difference between CT and device measurements of cup position was 0.74º (SD: 0.47, range: 0.19-1.48) for anteversion and 0.97º (SD: 0.67, range: 0.27-2.57) for inclination. The mean difference between device and radiograph measurements of LL changes was 0.27 mm (SD: 3.61, range: -5.20-7.78) (absolute mean: 2.71±2.25 mm), while the mean difference in OS was 1.75 mm (SD: 3.00, range: -2.47-6.65) (absolute mean: 2.37±2.44 mm).
Conclusions: This novel mini-navigation tool measured CP, LL, and OS accurately when compared with implant position measured on imaging.