Purpose: The effect of patellar position on soft tissue balancing in total knee arthroplasty (TKA) is under debate. We developed the digital tensor system to measure the load (N) and the distance (mm) of extension and flexion gaps in medial and lateral compartment separately with setting of femoral component trial. The gap load and distance in extension and flexion position of posterior stabilized (PS) and cruciate retaining (CR) TKA in both patella everted and reset position were measured.

Materials and Methods: Thirty-four patients who underwent primary TKA for medial type osteoarthritis using medial parapatellar approach were included. The load was measured at the gap distance, which is equal to the sum of implants including polyethylene insert.

Results: In extension, there was no significant difference between the load in patella everted and reset position in both PS-TKA and CR.-TKA. In flexion, there was a significant decrease of the load, which is comparable to the increase of gap distance of approximately 2mm, by resetting the patella from eversion in PS-TKA.

There was, however, no significant difference in CR-TKA by resetting the patella.

There was no significant difference in the ratio of medial/lateral load in both PSTKA and CR.-TKA.

Conclusion & Significance: Soft tissue balancing of PS-TKA with medial parapatellar approach should be performed after resetting the patella.

Newer prosthetic total knee arthroplasty (TKA) designs as well as unicondylar TKAs spare the anterior cruciate ligament (ACL). Although success of these procedures requires near normal ACL function, little has been written about the arthritic ACL.

This study was designed to evaluate the relationship between cross sections of the intercondylar notch and the macroscopic condition of ACL degeneration. Thirty osteoarthritic patients who underwent TKA as a result of severe osteoarthritis were randomly selected. Occupation rate of the osteophytes to the notch width were measured at the anterior 1/3, middle 1/3, and posterior 1/3 notche images obtained from preoperative tunnel view. Macroscopic conditions of the ACL and PCL were classified into four types of Normal, Frayed, Partial rupture, and Absent.

The macroscopic ACL conditions were Normal: 9 cases, Frayed: 9 cases, Partial rupture: 9 cases, and Absent: 3 cases. The macroscopic PCL conditions were Normal: 24 cases, Frayed: 3 cases, Partial rupture: 3 cases, and Absent: 0 case.

Occupation rate of the osteophytes to the notch correlated to the preoperative femorotibial angle (p< 0.05). In terms of ACL, the occupation rate of the osteophytes to the notch were 22.9%, 28.8%, 46.0%, and 81.8% in Normal, Frayed, partial ruptured, and Absent, respectively. The patients with more than 40% occupation rate showed either partial rupture or absent of the ACL during the surgery.

We conclude that occupation rate of the osteophytes to the notch is a good predictor of evaluating the ACL degeneration in osteoarthritic knee.