Patients have a wider stance following valgus high tibial osteotomy

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Purpose: Valgus high tibial osteotomy (HTO) has been shown to be an effective treatment for patients with medial compartment osteoarthritis (OA) in a varus knee. However, the precise mechanisms by which this operation has its clinical effect are unclear. Previous studies have suggested that a wider stance gait can reduce medial compartment loading via a reduction in the external knee adduction moment (KAM); a measure which has been implicated in the progression of medial compartment OA. This study aimed to measure to what extent a valgus HTO is associated with a postoperative increase in static stance width. Methods: 32 patients, recruited as part of the Biomechanics and Bioengineering Centre Versus Arthritis HTO study, underwent valgus (medial opening wedge) HTO and had preoperative and postoperative radiographs taken, showing both lower limbs whilst weightbearing. The horizontal distance was measured from a fixed point on the right talus to the corresponding point on the left. This was then divided by the talus width to give a standardised “stance width” for each radiograph. The difference between the preoperative stance width and postoperative stance width was compared for each patient and a paired sample t-test performed. Results: Preoperatively, the mean stance was 4.00 talar-widths but postoperatively this increased to a mean of 5.41. This mean increase of 1.42 talar-widths was statistically significant (p=0.001) and represents a mean proportional increase in stance width of 35.5% following high tibial osteotomy. Of the 32 patients, 23 showed increased stance width post-operatively and 9 decreased with a range of -4.64 to 6.00 talar-widths. Conclusions: These findings show that frontal plane surgical realignment at the proximal tibia via a medial opening wedge HTO is associated with an increased stance width on postoperative radiographs. Both a wider stance gait and HTO have been shown to affect the progression of medial compartment OA so these results may explain part of the mechanism behind the efficacy of HTO. However, the range of changes in stance width within this patient group suggests a significant degree of variability in how patients adapt at a whole-limb and whole-body level following surgical realignment at the proximal tibia.