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Validation and Usefulness of a Computer-Assisted Cup-Positioning System in Total Hip Arthroplasty

A Prospective, Randomized, Controlled Study

¹ Service de Chirurgie Orthopédique, Hôpital Sainte-Marguerite, 270 Boulevard Sainte-Marguerite, 13009 Marseille, France. E-mail address for J.-N.A. Argenson: jean-noel.argenson{at}ap-hm.fr

Investigation performed at the Department of Orthopedic Surgery, Aix-Marseille University, Hôpital Sainte-Marguerite, Marseille, France

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

Methods: A randomized, controlled, matched prospective study of two groups of thirty patients each was performed. In the first group, cup positioning was assisted by an imageless computer-assisted surgical system based on bone morphing. In the control group, the cup was placed freehand. All of the patients were operated on by the same surgeon through an anterolateral approach. Cup anteversion and abduction angles were measured on three-dimensional computed tomography reconstructions postoperatively for each patient by an independent observer using special cup-evaluation software.

Results: There were sixteen men and fourteen women in each group, and the mean body-mass index was approximately 25 in each group. The computer-assisted procedure took a mean of twelve minutes longer than the freehand procedure. Fifty-seven percent (seventeen) of the thirty cups placed freehand and 20% (six) of the thirty in the computer-assisted group were outside of the defined safe zone (outliers). This difference was significant (p = 0.002). There were no differences between the computer-assisted group and the freehand-placement group with regard to the mean abduction and anteversion angles, but there was a significant heterogeneity of variances, with the lowest variations in the computer-assisted group.

Conclusions: Use of an imageless navigation system can improve cup positioning in total hip arthroplasty by reducing the percentage of outliers.

Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

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