Computerized navigation system can improve THA cup positioning accuracy, study suggests

Freehand and computerized cup placement yielded similar mean abduction and anteversion angles, but navigation significantly reduced the percentage of outliers.

Total hip arthroplasty performed with the use of an imageless computer navigation system to aid cup positioning resulted in mean abduction and anteversion angles similar to freehand cup placement, according to a prospective study.

However, computerized navigation significantly reduced the number of outliers, the authors noted.

Sebastien Parratte, MD, and colleague Jean-Noel A. Argenson, MD, compared the accuracy of cup positioning between two age-, gender- and body mass index-matched groups, each containing 30 patients. In all cases, the surgeon implanted a cementless press-fit, hydroxyapatite-coated titanium acetabular component, a cementless fully hydroxyapatite-coated titanium femoral stem and the Hilock [Symbios] cementless press-fit cup.

All patients were randomly assigned to undergo total hip arthroplasty (THA) involving either freehand cup placement or cup placement performed using an adaptation of the Hiplogics Universal Protocol [Praxim Medivision], which is based on bone morphing, according to the study, published in the American edition of the Journal of Bone and Joint Surgery.

The surgeon used an anterolateral surgical approach in all cases, and the acetabular cup averaged 52 mm for both groups. Computer-aided cup positioning added an average of 12 minutes to surgery, but required no additional skin incision to accommodate the navigation system, according to the study.

The researchers found no significant differences between groups in mean cup abduction and anteversion angles, "but the computer-assisted-surgery system significantly reduced the percentage of outliers," the authors said in the study.

"The percentage of outliers was 57% (17 of 30) in the freehand placement group and 20% (six of 30) in the computer-assisted group. This difference in the percentage of outliers between the two groups was significant (P=.002)," the authors reported.

For patients in the freehand placement group, operative abduction angles averaged 32° ± 7.1°, radiographic abduction angles averaged 34° ± 7.62° and anatomical abduction angles averaged 38° ± 8°. Also for these patients, operative anteversion angles averaged 16.6° ± 10.4°, radiographic anteversion angles averaged 16.2° ± 9.6° and anatomical anteversion angles averaged 20.6° ± 10°, according to the study.

For patients in the computer-assisted placement group, operative abduction angles averaged 32° ± 4.8°, radiographic abduction angles averaged 34° ± 5.7° and anatomical abduction angles averaged 40° ± 5°. Operative anteversion angles averaged 14.8° ± 4.6°, radiographic anteversion angles averaged 14.4° ± 4.5° and anatomical anteversion angles averaged 18.6° ± 5°, according to the study.

No patients experienced neurovascular complications, and none had a dislocation during the first year of follow-up, they noted.

For more information:
Parratte S, Argenson JNA. Validation and usefulness of a computer-assisted cup-positioning system in total hip arthroplasty. J Bone Joint Surg Am. 2007;89-A:494-499.