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General Orthopaedics

Improving Cup Positioning Using a Mechanical Navigation Instrument

The International Society for Technology in Arthroplasty (ISTA)



Abstract

Acetabular component malpositioning is the most common reason for instability and wear resulting in revision total hip arthroplasty (THA). The current study aimed to assess a novel mechanical navigation device which was designed to simply and efficiently indicate appropriate cup orientation during surgery. The accuracy was compared to a series of hip arthroplasties performed using CT-based computer-assisted cup placement.

The study group consisted of 70 THAs performed using the mechanical device. The control group consisted of 146 THAs performed using CT-based computer navigation. Postoperative cup positioning was measured using a validated 2D/3D-matching method. An outlier was defined outside a range of ± 10 degrees from the planned inclination or anteversion.

In the study group the mean accuracy for inclination was 1.3 ± 3.4 (-6.6 – 8.2) and 1.0 ± 4.1 (-8.8 – 9.5) for anteversion with no outliers for either parameter. In the control group the accuracy for anteversion (3.0 ± 5.8 [-11.8 - 19.6]; p=0.6%) and the percentage of outliers (6.8%; p=3.3%) differed significantly. The accuracy for inclination (3.5 ± 4.1 [-12.7 - 9.5]; p=21.4%) and the percentage of ouliers (4.8%; p=9.9%) did not differ significantly.

The use of this mechanical navigation device can result in similar accuracy of acetabular cup orientation compared with CT-based surgical navigation. All cups were placed within a zone of ± 10 degree range of inclination and anteversion. This mechanical navigation device allows accurate cup navigation with minimal additional time and equipment.


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