Changes of ankle inclinations after total knee arthroplasty

AIM: To evaluate the changes in ankle joint line inclination in patients who had total knee arthroplasty due to degenerative osteoarthritis. MATERIAL/METHOD: Sixty-two knees (with a mean age of 71,66±6,78 years, follow-up 52,34±27,42 months) which had undergone total knee arthroplasty between November 1996 and May 2014 were included in this retrospective study. The knee joint line orientations (KJLO) of the prosthesis and ankle joint line inclination (AJLI) relative to the floor were evaluated on postoperative standard standing long-leg X-rays. The AJLI relative to the floor was defined as the angle between the tangent to the subchondral plate of the talus and the horizontal grid line on radiographs. In order to determine the effects of KJLO and high varus on AJLI, patients were divided into two each groups that were pre-operative mechanical axes (MA) as <20° (n=35, group1) and >=20° (n=27, group2) and post-operative MA <3° (n=32, group a) and >=3° (n=30, group b). In addition, the changes in AJLI were compared between each group. The patients were regrouped as either <=3° (n=28, group i) or >3° (n=34, group ii), in terms of the postoperative KJLO. Inclination angles of the prosthesis were compared between each groups. Statistical analysis was performed with SPSS v18. RESULTS: Mean MA of pre-operative and post-operative were 16,35±6,56° and 3,92±3,35°, respectively. All ankle inclinations were lateralized. AJLI, were significantly decreased from pre-operative mean 7,37°±3,19° to post-operative mean 3,71°±2,22° (p<0,0001). The mean of change was 3,65°±3,03°. However, pre-operative AJLIs were significantly increased in high varus group (group1: 6,34°±2,54°, group2: 8,70°±3,48°, p=0,003); post-operative AJLIs did not differ significantly (group1: 3,55°±2,36°, group2: 3,92°±2,05°, p=0,516) with respect to the MA. The changes in preop-postop AJLI’s were significantly higher in high varus group again (p=0,009). When the KJLO groups were compared, pre-operative AJLIs were significantly different (group i: 6,25°±2,33°, group ii: 8,29°±3,53°, p=0,004) while post-operative AJLIs did not differ significantly (group i: 3,46°±2,38°, group ii: 3,92°±2,08°, p=0,489). CONCLUSION: Pre-operatively high varus knees also had high ankle varus, hence ankle deformity was corrected by the restoration of the optimal lower limb aligment. Obtaining parallel orientation of the components relative to the ground, restored the AJLI. Pre-operative planning and convenient implantation of the components lead to achieve optimum knee orientation which restored the ankle joint line orientation independent from mechanical axes. Not only the goal of optimum mechanical axes but also optimum knee joint line orientation’s importance was demonsrated.