Tibiofemoral Rotational Mismatch Post Gemini MK-Ⅱ Mobile Bearing Total Knee Arthroplasty

Objective: To evaluate the tibiofemoral rotational mismatch post primary total knee arthroplasty(TKA) with Gemini MK-II mobile knee prosthesis and its relative factors. Methods: From February 2012 to December 2013, 74 cases(79 knees) who underwent Gemini MK-II knee replacement for varus knee osteoarthritis were recruited. There were 15 males and 59 females, mean age 66.87 ± 6.68 years old. All surgeries were performed with 3 °fixed external rotation for femoral component rotation, and self seeking method applied to determine tibial prosthesis rotation alignment. Weight bearing knee X-ray and CT scan were measured, the rotational mismatch angle(RMA) was compared pre and post TKA surgery. The independent risk factors for rotational mismath were invested by logistic regression analysis. Results: 74 cases(79 knees) were followed up for 6 to 29 months, with an average 20.2 months. RMA changed from-0.202° ± 4.652° preoperative to-0.684°± 6.604 °postoperative without significant statistics difference(P = 0.543). There were 2 knees with RMA> 10 ° preoperative, and the number significant increased to 8 knees post TKA(P = 0.050). After TKA, 89.87%(71/79) had a safe RMA range(0° ± 10°). 4 knees post TKA had femoral prosthesis malrotation>5°, and 17 knees suffered tibial malrotation >8°. The RMA mismath ratio in the 17 knees with TRA lager than 8° was 41.2%(7/17), while the ratio significantly declined to 1.6% in the 62 knees with TRA less than 8°(Χ2=22.946,P=0.000). Conclusion: In primary TKA for varus knee osteoarthritis with Gemini MK-II prosthesis, there was a tendency of rotational mismatch with fixed 3° femoral external rotation and self seeking method for tibial rotational alignment. The TRA and RMA per surgery and TRA post TKA were correlated to the tibiofemoral RMA postoperative. TRA lager than 8° should be avoided to prevent tibiofemoral mismath.