Page 30 - ISAKOS 2019 Newsletter Vol II

CURRENT CONCEPTS
Medial Stabilizing Gap Technique with Tibia First Cut in Total Knee Arthroplasty for Varus Knees
Umito Kuwashima, MD, PhD
Department of
Orthopaedic Surgery
Tokyo Women’s Medical University Tokyo, Japan
Ken Okazaki, MD, PhD
Department of
Orthopaedic Surgery
Tokyo Women’s Medical University Tokyo, Japan
Rationale for Medial Stability in Total Knee Arthroplasty
Ligament balancing is one of the key challenges for successful total knee arthroplasty (TKA). Preparing symmetrical rectangular gaps between the cut surfaces of the femur and tibia in both extension and flexion is recommended as the ideal goal. However, it can be difficult to balance the soft-tissue tension perfectly, especially in knees with severe coronal plane deformity. Okamoto et al. measured the length of the bone gap on the medial and lateral sides of varus knees and reported that lateral soft- tissue laxity increased with increasing preoperative varus deformity1. In contrast, the medial soft tissue did not contract with varus deformity. That study suggested that release of the medial collateral ligament (MCL) is needed in order to adjust its tension to be equal to that of the lateral soft tissue, which is stretched in knees with severe varus deformity. However, extensive medial release carries the risk of loss of medial tension in flexion because selective release in either extension or flexion is difficult. In addition, soft-tissue laxity is known to be greater on the lateral side than on the medial side in normal knees. Therefore, we hypothesized that an additional medial release should be avoided when enough of a gap is prepared for implantation and that residual lateral laxity can be allowed in varus knees rather than pursuing a symmetrical rectangular gap.
Gap balancing also means adjusting the soft-tissue tension to be equal in extension and flexion. Resection of the posterior cruciate ligament (PCL) during posterior-stabilized TKA often results in an enlarged flexion gap. Thus, the gap- balancing ligament-cutting technique, in which the thickness of the bone resection is determined on the basis of the gap length in extension and flexion, has been advocated in order to obtain equal gap lengths. A loose flexion gap can cause instability in flexion, affecting the kinematics of the knee in daily activities. Nakamura et al. reported that knees with loose medial flexion gaps showed nonphysiological anterior translation of the femoral component in deep knee flexion, whereas those with loose lateral flexion gaps did not2. Furthermore, several studies have shown that loose medial flexion gaps cause impaired knee function and decreased satisfaction after TKA3,4. Therefore, care should be taken to adjust the medial flexion gap to be equal to the medial extension gap by avoiding medial release and leaving lateral laxity in severely varus knees. We advocate a technique that can be used to balance the medial gap between extension and flexion without releasing the MCL to stabilize the medial side of the knee.
Surgical Technique
When using posterior-stabilized TKA systems in varus knees, we first resect bone with the same thickness as the implant from the proximal part of the tibia. It should be noted that, with this technique, the postoperative joint line will be maintained on the lateral (intact) side whereas it will be raised by 2 – 3 mm from the original joint line on the medial (arthritic) side. This is because the physiological (medially inclined) joint line will now be perpendicular to the tibial axis so that the medial and lateral sides of the joint line will be at the same level (Fig. 1). This situation necessitates adjustment of the medial flexion gap, which tends to increase after PCL resection for posterior-stabilized TKA. Femoral and tibial osteophytes on the medial side are completely removed, and the release of medial soft tissue is limited to minimal. After that, the gap balance between extension and flexion is evaluated with use of a force-controlled compartment- specific ligament tensioner with a distraction force of 60 N for each compartment or with use of spacer blocks of the same thickness as the tibial implant (Figs. 2-A, 2-B, and 2-C). The surgeon should note the difference between the medial extension gap and the medial flexion gap. Laxity of the lateral flexion gap can be ignored.
28 ISAKOS NEWSLETTER 2019: VOLUME II