Abstract
Purpose:
Imageless navigation has improved the accuracy of acetabular cup placement but relies on manual identification of pelvic anatomy. Thick soft tissues in obese patients could obscure these landmarks and result in large variances of cup placement. The purpose of this study was to investigate the relationship between BMI, soft tissue thickness, navigated cup and final post-operative cup position.
Methods:
Thirty patients with an average age of 66.5 years underwent primary navigated THA. Final intra-operative cup position was recorded. Soft tissue thickness and final post-operative cup alignment were measured on a multi-slice pelvis CT scan.
Results:
There were no significant relationships between the variables for inclination. Larger ranges were observed in the obese group. It reached significance for the difference between the desired and final post-operative cup position (p=0.007). There was a moderately significant relationship (r=0.41, p=0.0002) between soft tissue thickness and final cup anteversion and a strong and near significant correlation (r=0.6, p=0.07) for the difference between the desired and final post-operative cup position for anteversion. Similar to inclination larger ranges were observed in the obese group. However, significant differences were only observed for final post-operative cup position (p=0.002) and the difference between the desired and final post-operative cup position (p=0.0003).
Conclusion:
Despite the potential introduction of error with acquisition of landmarks, our data suggests that in obese patients the overlying soft-tissue thickness has no significant effect on the accuracy on acetabular cup inclination. In contrast anteversion is influenced by the overlying soft tissue thickness and obesity.
