Impact of a Unilateral High Tibial Osteotomy With a Large Correction on Functional Lateral Acetabular Coverage of the Hip Joint.

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Changes in limb length and coronal pelvic tilt, which occur along with changes in limb alignment, may affect the functional lateral acetabular coverage of the hip joint under weightbearing conditions. To analyze the functional lateral acetabular coverage after unilateral closed-wedge and open-wedge high tibial osteotomies with a large wedge correction of ≥10 mm. Cohort study; Level of evidence, 3. A retrospective analysis was conducted for 107 unilateral closed-wedge high tibial osteotomies (CWHTOs) and 100 unilateral open-wedge high tibial osteotomies (OWHTOs) with a wedge correction of ≥10 mm and without correction loss during a 2-year follow-up. Limb length and coronal pelvic tilt were measured. Functional lateral acetabular coverage was evaluated using the lateral center-edge angle (LCEA), acetabular index, sharp angle, and femoral head extrusion index (FHEI) with reference to the ground horizontal line. Appropriate ranges of the LCEA (22° to 40°), acetabular index (-8° to 14°), sharp angle (34° to 43°), and FHEI (11% to 27%) were investigated. Limb length significantly decreased after CWHTO (-7.2 mm) and increased after OWHTO (11.5 mm). The pelvis of the operative limb tilted downward after CWHTO (-1.0°) and upward after OWHTO (2.1°). The mean parameters for functional lateral acetabular coverage significantly changed toward more coverage after CWHTO and less coverage after OWHTO (change in LCEA, acetabular index, sharp angle, and FHEI = 1.2°, -1.1°, -1.0°, and -0.7%, respectively, in CWHTO and -1.3°, 1.8°, 1.6°, and 2.7%, respectively, in OWHTO). When evaluating the appropriateness of each parameter for coverage, cases of conversions from undercoverage to appropriate coverage (1.9% to 4.7%) and appropriate to overcoverage (0.9% to 5.6%) after CWHTO and from overcoverage to appropriate coverage (0% to 8%) and appropriate to undercoverage (2% to 7%) after OWHTO were observed. The functional lateral acetabular coverage increased after CWHTO and decreased after OWHTO. Surgeons may want to consider the acetabular coverage of the ipsilateral hip joint when performing a unilateral high tibial osteotomy with a large correction.