The Effect of Patellar Position on the Flexion Gap in Total Knee Arthroplasty

ABSTRACT

PURPOSE: The aim of this study was to investigate the relationship between eversion or reduction of patella and the heights of the extension or flexion gaps. MATERIALS AND METHODS: Measurements of the heights of the extension and flexion gaps were obtained during 32 primary posterior-stabilized total knee arthroplasties in 25 osteoarthritic patients. A tensor device was introduced after femoral and tibial bony resections while putting the knees flat on the operating table to measure the extension gaps in the medial and lateral compartments, respectively. The knee was flexed 95 degrees, and the tensor was introduced to measure the flexion gaps in the same manner. A calibrated torque wrench permitted the application of the force of about 113.4N.cm both in extension and in flexion in right knee, and of about 152.4N.cm both in extension and in flexion in left knee. RESULTS: The average height of the extension gap with everted patella was 20.9+/-2.6mm medially and 23.6+/-2.5 mm laterally, respectively. The average height of the extension gap with reduced patella was 21.0+/-2.6mm medially and 23.7+/-2.4mm laterally, respectively. The average height of the flexion gap with everted patella was 20.7+/-2.5mm medially and 23.2+/-2.8mm laterally, respectively. The average height of the flexion gap with reduced patella was 22.1+/-2.3mm medially and 24.2+/-2.8mm laterally, respectively. After reducing the patella, the flexion gap height increased an average 1.4+/-1.1(range: 0~4)mm and 1.0+/-1.2(range: -1~3)mm in the medial and lateral compartments, respectively. CONCLUSION: The height of flexion gap would be increased by reducing the patella from everted position in posterior- stabilized total knee arthroplasty for the patient with good preoperative flexion. The flexion gap must be observed not with everted patella but with reduced patella to determine whether it appears symmetric and balanced.