Targeting a New Safe Zone: A Step in the Development of Patient-Specific Component Positioning for Total Hip Arthroplasty

Alexander S McLawhorn, Peter K Sculco, K Durham Weeks, Denis Nam, David J Mayman
American Journal of Orthopedics 2015, 44 (6): 270-6
Surgeons often target the Lewinnek zone, with its mean (SD) inclination of 40° (10°) and mean (SD) anteversion of 15° (10°), for acetabular orientation during total hip arthroplasty (THA). However, matching native anteversion (20°-25°) may achieve optimal stability. We conducted a study in a large single-surgeon patient cohort to determine the incidence of early postoperative dislocation with increased acetabular anteversion and the accuracy of imageless navigation in achieving target acetabular position. Soft-tissue repair through a posterolateral approach was performed in 553 THAs that met the inclusion criteria. Mean (SD) target acetabular orientation was 40° (10°) of inclination and 25° (10°) of anteversion. Software was used to measure acetabular positioning on postoperative radiographs. Incidence of dislocation within 6 months after surgery was determined. Mean (SD) inclination was 42.2° (4.9°), and mean (SD) anteversion was 23.9° (6.5°). Approximately 82% of cups were placed in the target zone. Variation in anteversion accounted for 67.3% of outliers. Only body mass index was associated with inclination outside the target range (P = .017), and only female sex was associated with anteversion outside the target range (P = .030). Six THAs (1.1%) experienced early dislocation, and 3 (0.54%) of these were revised for multiple dislocations. There was no relationship between dislocation and component placement in either the Lewinnek zone (P = .224) or the target zone (P = .287).

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