SAN DIEGO – It’s important to pay attention to both knees – the knee that was operated on as well as the knee that wasn’t operated on – after a unilateral, medial, opening-wedge high tibial osteotomy.
Joint load increases in the nonoperative knee following the procedure, which is used to correct varus malalignment, according to researchers at the University of Western Ontario, London.
The findings apply to a subset of opening wedge high tibial osteotomy (HTO) patients, those who present initially with significant bilateral varus, but in whom symptoms were severe enough to require surgery in only one knee.
In 38 such patients, 2 years after surgery "we noted a 0.25% [of body weight times height] increase in peak knee adduction moment in the non-operative limb," as well as a slight increase in vertical ground reaction force, said lead author and physiotherapist Angelo Boulougouris, a biomechanics doctoral candidate at the school. The external knee adduction moment measured during gait is an indicator of tibiofemoral joint osteoarthritis progression.
"The major point is to pay attention to what’s happening to the opposite knee, to make sure you are not ignoring it and focusing your entire treatment plan on just looking at the operative knee," he said.
An unloader brace, for instance, might be appropriate for the nonoperative knee, among other possible interventions, he said. An unloader brace is designed to lessen the stress on a knee with medial compartment knee osteoarthritis. This use of the unloader brace would be to prevent development of knee OA rather than to ease the discomfort associated with established disease
During HTO, a wedge of the cancellous bone allograft is placed in the proximal end of the tibia, correcting both varus deformity and weight distribution through the knee. "Our surgeons are particularly careful to not over-correct," Mr. Boulougouris said.
Of the 38 patients, 32 were men, the average age was about 50 and average body mass index (BMI) about 27 kg/m2. Varus malalignment in the operative limb was about 11 degrees and Kellgren-Lawrence grades ranged from 1 to 3. Varus malalignment was about 8 degrees in the nonoperative limb, with Kellgren-Lawrence grades ranging from 0 to 1.
Patients did well overall, reporting decreased pain and improved quality of life at 2 years. Varus malalignment was corrected in the operative limb, and unchanged in the nonoperative limb.
Knee adduction moment had also significantly decreased on the operative side (mean change, –1.99 % of body weight times height), but increased slightly on the nonoperative side. Gait changes also increased load on the nonoperative knee, including increased gait speed (mean change, 0.08 m/sec) and decreased trunk lean to the stance-phase limb (mean change, –1.43 degrees). The findings were statistically significant.
The reasons could include the operation itself, disease progression in the nonoperative knee, or the fact that patients had gained an average of about 4.5 pounds at the 2-year follow-up.
Mr. Boulougouris said that he doubts the weight gain had much to do with it. He and his colleagues hope to tease out the contributing factors in a regression analysis.
The study was funded by the Canadian Institute of Health Research. Mr. Boulougouris reported that he had no relevant financial conflicts of interest to disclose.