Abstract
Introduction
MERA Quest Knee System (Quest Knee) is a posterior cruciate ligament–retaining prosthesis considering the anatomical features and lifestyles of the Japanese. As for the anatomical features, we reduced the size of prosthesis and set a smaller interval of sizes because Japanese knees are smaller and flatter than those of Caucasians. As for the lifestyles, we evaluated in vivo patellar tracking during deep knee flexion and the condylar geometry in the axial plane of magnetic resonance imaging. It was found that the patella sank deeply into the intercondylar notch and that the articular surface of the lateral condyle began to curve steeply. We adopted this shape and engraved the lateral condyle deep to reduce the pressure of the patellofemoral joint and to get better range of motion (ROM). For the contact pressure rise in the femorotibial joint by engraving the lateral condyle, the insert was suited to the shape of the femoral component. Furthermore, we increased the thickness of the posterior flange of the femoral component and changed the posterior radius of curvature gradually, and this shape allowed the flexion of 155°. We have used Quest Knee for clinical applications from October 2009. We studied the short-term results of Quest Knee.
Methods
Between June 2010 and July 2013, the same senior surgeon performed 59 consecutive primary operations with Quest Knee. Forty patients (44 knees) were women, and 14 patients (15 knees) were men. The mean patient age was 72.5 years (range, 59–89 years). All were osteoarthritis knees. Coronal deformity was varus in 58 knees and valgus in one knee. All operations were performed with a measured resection technique, and all patellae were resurfaced. Clinical evaluations were assessed using the Japanese Orthopaedic Association knee rating score (JOA score), and clinical ROM and standing femorotibial angle (FTA) were measured. Additionally, three-dimensional motion analysis of the patellar component during squatting was performed by the image matching method with image correlations.
Results
The mean follow-up period was 17.4 months (range, 6–43 months). The JOA score at preoperative and follow-up were 57.5 ± 10.1 and 87.5 ± 5.6 points, respectively (P < 0.0001) (Fig. 1). The ROM at preoperative and follow-up were 127.4 ± 11.1 and 126.2 ± 9.0° (P = 0.47) (Fig. 2). The mean FTA at preoperative and follow-up were 184.2 and 172.3°. With regard to the three-dimensional motion analysis, the patella showed lateral shift during squatting (Fig. 3).
Discussion
As for the patellofemoral contact pressure at flexion in total knee arthroplasty, a biomechanical study has reported that the pressures of posterior cruciate ligament–retaining and posterior-stabilized knees were 3.2 and 2.8 times as much as the body weight. This report suggests that the reduction of the pressure of the patellofemoral joint during deep knee flexion results in better ROM. We suppose that Quest Knee reduced the pressure, led the patella to the lateral side, and achieved better ROM.
Conclusions
Short-term results of Quest Knee were good. More detailed studies are needed to get better function and long-term durability.
