Description

Varus deformity is the most common deformity (60-80%) in patients undergoing total knee arthroplasty (TKA). In varus knees, there could be shortening of medial structures; therefore, if mechanical alignment is the goal, perpendicular bone cuts could produce a trapezoidal gap between the femur and tibia, with a shorter medial side. This imbalance should be corrected through ligament balancing as it is seen as a prerequisite for good function and survival. Aunan et al. found ligament balancing to be necessary in 70 of 100 consecutive TKAs.

Several ligament balancing techniques exist and most focus on lengthening the soft tissue on the concave side of the knee. Bellemans' and Whiteside's techniques are examples of ligament balancing procedures. In varus knees Bellemans' technique is performed with multiple perforations (pie-crusting) of the medial collateral ligament (MCL), while Whiteside's technique is performed with sequential ligament and soft tissue release, where the MCL is evaluated first. However, no technique has proved clinically superior to others. In traditional methods, it is difficult to reliably predict ligament lengthening and it relies on the performing surgeons' feel and experience. Aunan et al. found wide variation in lengthening achieved using Whiteside's technique. Therefore, the investigators have developed a novel device, which aspires to further develop Bellemans' technique and produce repeatable soft tissue lengthening of the MCL.

In varus knees the most important structure in ligament balancing is the superficial and deep MCL (hereafter MCL). Bellemans' technique is a proven technique, which uses an end-cutting cannula to puncture the MCL by freehand, with the objective of severing some ligament fibers. When the force applied to the ligament is kept constant, each remaining fiber will be exposed to a higher force and lengthen. Bellemans' technique lacks an objective method of guiding the puncturing, and the execution and results therefore vary. The novel instrument invented by the investigators, has a specific grid that objectively guides perpendicular puncturing using an end-cutting cannula and evenly distributes punctures throughout the ligament, which will produce a predefined spread of punctures and severing of fibers. The investigators believe this grid is key to achieving repeatable lengthening of the MCL, and promising results have been shown in porcine and human cadaveric tissue.