Purposes: Minimal incision surgery (MIS) total knee arthroplasty (TKA) is widely promoted as a possible improvement over conventional TKA, and accurate implantations have recently been reported using navigation systems. However, soft tissue balance during MIS-TKA remains challenging. Therefore, in this report, joint gap (component gap) and ligament balance (varus angle) were assessed during MIS-TKA using a tensor, which enables soft tissue balance assessment with a reduced patellofemoral joint and femoral component in place.
Methods: Results were compared to those of conventional TKA. Posterior stabilized TKA were performed in 50 knees (25 knees: MIS-TKA using quadriceps-sparing approach; 25 knees: conventional TKA using medial parapatellar approach) with varus osteoarthritis. Component gap and varus angle were measured using the tensor with a reduced patellofemoral joint at 0, 10, 45, 90, and 135°.
Results: Whereas the component gap in MIS-TKA was significantly larger through the entire arc of flexion compared with conventional TKA, the pattern of joint looseness showed no difference between the two procedures. The varus angle in MIS-TKA was significantly larger than that in conventional TKA at 0, 90, and 135° of knee flexion.
Conclusions: MIS-TKA may lead to ligament imbalance due to the difficulties induced by a limited working space. Understanding this pattern allows surgeons to be able to adjust the soft tissue balance more accurately and thereby expect a better post-operative outcome even in MIS-TKA.