Background

Medial opening wedge high tibial osteotomy (mHTO) is a well-established treatment for younger active individuals with medial compartment osteoarthritis. Coronal plane alignment is used as the basis for preoperative planning and postoperative assessment in mHTO. Sagittal and rotational plane alignments are usually given lesser importance.
Objectives
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. Functional outcomes of these patients have also been studied.
Study Design & Methods
This was a prospective, observational study including 30 patients of isolated medial compartment osteoarthritis of the knee joint, between 30 to 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 (TT) and posterior proximal tibial angle (PPTA) were measured. PPTA was measured in three sagittal cuts: medial sagittal cut, middle sagittal cut and lateral sagittal cut.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 42.59 +/- 8.157 years. Mean preoperative varus deformity was 11.13+/-1.5 degrees, which got corrected to a mean valgus alignment of 2.8±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 TT (27.08+/-2.18 degrees) which was corrected to a mean TT of 19.80+/-3.72 degree after the surgery (P<0.001). There was a significant decrease in mean posterior tibial slope.?There was a significant negative correlation between change in varus-valgus angle and change in TT. However, there was a positive correlation between change in varus-valgus angle and change in PPTA. There was a positive correlation between change in MAD and PPTA in all three sagittal cuts and a negative correlation with change in TT.?There was a significant negative correlation between change in varus-valgus angle and post-operative VAS (P:0.03) and significant positive correlation between change in varus-valgus angle and SF 12 and WOMAC (P:0.03 and P:0.01 respectively).

Conclusions

This study has shown that mHTO significantly changes the torsional deformity and sagittal alignment which may have a role in slowing down the progress of osteoarthritis of the knee. None of the previous studies have established any relation between correction in coronal axis and associated changes in sagittal and torsional alignments. The regression equation can help in better planning of this surgery by predicting the associated corrections beforehand.