Abstract
Introduction
Deformity of knee joint causes deviation of mechanical axis in the coronal plane, and the mechanical axis deviation also could adversely affect biomechanics of the ankle joint as well as the knee joint. Particularly, most of the patients undergoing total knee arthroplasty (TKA) have significant preoperative varus malalignment which would be corrected after TKA, the patients also may have significant changes of ankle joint characteristics after the surgery. This study aimed 1) to examine the prevalence of coexisting ankle osteoarthritis (OA) in the patients undergoing TKA due to varus knee OA and to determine whether the patients with coexisting ankle OA have more varus malalignment, and 2) to evaluate the changes of radiographic parameters for ankle joint before and 4 years after TKA.
Methods
We evaluated 153 knees in 86 patients with varus knee OA who underwent primary TKA. With use of standing whole-limb anteroposterior radiographs and ankle radiographs before and 4 years after TKRA, we assessed prevalence of coexisting ankle OA in the patients before TKA and analyzed the changes of four radiographic parameters before and after TKA including 1) the mechanical tibiofemoral angle (negative value = varus), 2) the ankle joint orientation relative to the ground (positive value = sloping down laterally), 3) ankle joint space, and 4) medial clear space.
Results
Of the 153 knees, 59 (39%) had radiographic ankle OA. The knees with ankle OA had significantly more varus mechanical tibiofemoral angle preoperatively than those without ankle OA (− 11.9° vs. − 9.3° on average, respectively; P = 0.003). Compared to the preoperative condition, the ankle joint orientation relative to the ground significantly changed after TKA (from 9.0° to 4.8° on average, P<0.001) while ankle joint space and medial clear space did not.
Conclusions
Our study revealed that coexisting ankle OA would be common in patients with varus knee OA, particularly in patients with more varus malalignment. TKA also significantly changes the ankle joint orientation relative to the ground which shows more parallel to the ground. However, its effect on ankle joint space and medial clear space seems to be minimal upto 4 years after TKA. Our findings warrant consideration in preoperative evaluations of ankle OA in varus knee OA patients undergoing TKA, and further studies should evaluate prospectively the clinical implications of radiographic change of the ankle joint after TKA.
