High tibial osteotomy (HTO) was developed to reduce eccentric medial load on varus knees. Changes in gait reported after HTO indicate improvement in biomechanical properties of osteoarthritic knees [1]. Among studies that describe gait after HTO, few reports have focused on varus thrust during gait. Varus thrust is sometimes observed in patients with medial compartment knee osteoarthritis (KOA) [2,3], which is one of the factors that influences development and progression of KOA [[2], [3], [4]] and risk of knee pain [5]. Therefore, persistence of varus thrust after HTO may affect mechanical pathology of OA knees.
Usually, varus thrust is visually detected. Koshino et al. [6] reported that of 136 knees after HTO, 112 knees with marked pain relief were free of varus thrust. Recently, quantification of varus thrust for knee OA using optical motion analysis has been attempted in several studies [[7], [8], [9], [10]]. In an investigation using knee angular velocity, HTO showed a significant decrease in varus thrust after HTO [10]. Using an electronic goniometer, varus thrust persisted in less than half of patients after HTO [7]; however, there is little information on factors associated with postoperative varus thrust.
While the use of gait analysis system is often limited because it requires large, expensive equipment and substantial examination space, inertial motor units (IMUs) are inexpensive, relatively easy to prepare, and can be employed in small space. There are several reports using IMUs to quantitatively detect varus thrust in patients with KOA [[11], [12], [13], [14]]. However, to the best of our knowledge, there is only one report that evaluated changes in varus thrust after HTO using accelerometry [15]. Among 35 knees treated with closed-wedge HTO, 25 knees (71%) showed a lateral thrust pattern preoperatively, and all knees changed this pattern after one year. Although the peak acceleration of the tibia decreased significantly after HTO, the relationship between walking speed and acceleration was not clear. A more detailed study of varus thrust using accelerometry to examine patients treated with HTO and normal, control subjects may provide useful information on pathological gait.
Usually, long-term follow up is required to evaluate clinical results and gait characteristics after surgery. To perform a long-term study, short-term results may be useful as reference data. We consider this a pilot study. Definitive conclusions must await a larger study. The main purpose of this study was to determine whether varus thrust during walking changes one year after HTO in patients with medial compartment KOA, and to ascertain whether it differs between OA patients and healthy, control subjects. To evaluate varus thrust quantitatively, we measured acceleration of the thigh relative to the lower leg in the coronal plane. Another purpose was to identify factors affecting thrust before and after HTO. We hypothesized that in patients with medial compartment KOA, varus thrust is higher than in normal subjects, but that it would decrease to near normal one year after HTO.
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