Changes in sagittal and axial plane alignment in medial opening wedge high tibial osteotomy: a prospective observational study.

Purpose: Deformity correction during high tibial osteotomy is generally based on coronal plane alignment. The aim of this study was to measure changes in sagittal and axial plane alignment following medial opening wedge high tibial osteotomy [mHTO], using pre- and postoperative computed tomography [CT] scans, and correlate them with changes in coronal plane. The secondary objective was to correlate changes in functional outcomes with changes in alignment in each plane. The null hypothesis was that sagittal and axial plane alignment does not change significantly following mHTO.

Methods: This was a prospective, observational study including 30 patients of isolated medial compartment osteoarthritis of the knee joint, between 30 and 60 years of age. Preoperative and postoperative computed tomography scan of bilateral lower limbs from hip to ankle was performed. Varus angle, mechanical axis deviation [MAD] of the lower limb, medial proximal tibial angle [MPTA], tibial torsion and posterior proximal tibial angle [PPTA] were measured. Visual Analogue Scale [VAS 0-10 cm scale] was used for assessment of pain. Functional outcomes were evaluated using Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC], 12 Item Short Form Survey [SF 12] and Tegner Lysholm knee scoring scale.

Results: Mean age of patients was 44.59 ± 8.157 years. Mean preoperative varus deformity was 11.13 ± 1.5 degrees, which got corrected to a mean valgus alignment of 3.8 ± 0.93 degrees postoperatively. The mechanical axis deviation was 4.32 ± 1.76 mm lateral to the knee joint center postoperatively. Preoperatively, all knees had external tibial torsion [27.08 ± 2.18 degrees] which was corrected to a mean external tibial torsion of 19.80 ± 3.72 degree after the surgery [P < 0.001]. The overall decrease in sagittal alignment in the present study was 3.70 ± 3.14 degree, 3.97 ± 3.06 degree, 3.92 ± 2.33 degree, for medial, middle and lateral cuts, respectively. There was a significant correlation between change in varus/valgus angle and change in TT and PPTA. Significant positive correlation was seen between change in coronal alignment and functional outcome scores.

Conclusion: This study has shown that mHTO significantly changes torsional and sagittal alignment. This is the first study to establish relation between correction in coronal plane and associated changes in sagittal and torsional alignments.