COMPARISON OF VALUES OF JOINT GAP DISTANCE AND ANGLE AFTER EACH STEP OF MEDIAL SOFT-TISSUE RELEASE BETWEEN OFFSET AND STANDARD TENSOR/BALANCERS IN TKA

Introduction The effect of each step of medial soft tissue release was assessed taking the expansion strength and patellar condition into account in five fresh frozen normal cadaver specimens. Methods In each cadaver specimen, only proximal tibia was cut. Then, ACL was cut, and deep MCL fiber was released. This condition was set as “the basic”. Joint gap distance and angle were measured at full extension, 30°, 60°, 90°, 120° flexion and in full flexion. The measurement was firstly done with the standard tensor/balancer with the patella everted, and the next with the offset tensor/balancer with the patella reduced. The torque of 10, 20 and 30 inch-pounds were applied through the specialized torque wrench. After the measurement in “the basic”, PCL, MCL superficial fibres, pes anserinus and semi-membranosus were released step by step. Measuring the joint gap distance and angle with the same scheme above were conducted after the each step. Results Joint gap distance: in the condition of PCL existence, the value of the gap distance was expressed longer with offset balancer than that of standard balancer when the same expansion strength was applied (Fig. 1). All releases did not change the joint gap distance significantly in extension. The effect of soft tissue release on joint gap is remarkable with increasing the degree of knee flexion. The average effect of the each step of the release with standard and offset balancers with 20 inch-pounds torque on the joint gap distance at 90° flexion were 4.8mm and 2.6mm, 2.6mm and 1.7mm, and 2.6mm and 2.0mm respectively (Fig. 2). Although the effect was larger with the standard balancer, no significant difference was found between tensor/balancers in full extension and at 90° flexion. Joint gap angle: in the condition of PCL existence, the value of the gap angle was expressed more varus with offset balancer than that of standard balancer (Fig. 1). All releases did not change the joint gap angle significantly in extension. The joint gap angle was getting more valgus after each step of soft tissue releases. The average effect of the each step of the release with standard and offset balancers with 20 inch-pounds torque on the joint gap angle at 90° flexion were 1.3° and 2.3°, 2.3° and 1.8° and 2.1° and 3.2°, respectively (Fig. 3). No significant difference was found between balancers in full extension and at 90° flexion. Discussion In extension, even though all medial soft tissues were released, the joint gap distance and angle were not changed. Therefore, no significant difference was found in full extension between two balancers. At 90° flexion in “basic”, the joint gap distance was expressed larger and the joint gap angle was expressed more varus with the offset balancer. When the effect of each step of medial soft tissue releases was compared, no significant difference was found between two balancers. With two different type of tensor/balancer, the condition of femoro-tibial joint was assessed with the standard balancer, and the condition of the whole knee joint was assessed with the offset balancer.