Abstract
Introduction
Hip resurfacing arthroplasty (HRA) is currently regaining positive attention as a treatment of osteoarthritis in young, active individuals[1]. The procedure is complex and has low tolerance for implant malpositioning [2]. ‘Precision tools', such as imageless navigation and patient specific instruments, have been developed to assist with implant positioning but have not been shown to be fully reliable [3]. The aim of this study is to present and validate the first step of novel quality control tool to verify implant position intra-operatively. We propose that, before reaming of the femoral head, a handheld structured light 3D scanner can be used to assess the orientation and insertion point of femoral guide wire.
Methods
Guide wires were placed into the heads of 29 solid foam synthetic femora. A specially designed marker (two orthogonal parallelepipeds attached to a shaft) was inserted into the guide wire holes. Each bone (head, neck and marker) was 3D scanned twice (fig 1). The insertion point and guide wire neck angle were calculated from the marker's parameters. Reference data was acquired with an optical tracking system. The measurements calculated with the 3D scans were compared to the reference ones to evaluate the precision. The comparison of the test retest measurements done with the new method are used to evaluate intra-rater variability.
Results
The difference between the entry point measured with the 3D scanner and the reference data was 1.68 mm (SD 2.23 mm). The difference of the measured guide wire axis and the reference axis is 2.44 degrees (SD 2.29). The intra-rater difference was 0.02 mm (SD 0.55mm, ICC 0.9995) for the entry point and 0.20 degrees (SD 0.20, ICC 0.9975) for the guide wire insertion axis.
Conclusions
The results of this study indicate that a structured light based 3D scanning technology is accurate in assessing orientation and insertion point of the femoral guide wire during HRA. A small precision bias was identified and further work will need to investigate the cause. Also, inter-rater variability needs to be assessed. This simple verification tool can be used by any hip surgeon and will be most beneficial to those in low-volume centres or in training. It has a potential to be used during teaching and to decrease the learning curve through a self-feedback mechanism. Further studies could use the tool to asses final implant position and focus on other joint replacement procedures requiring high degree of accuracy.
