Step-wise medial collateral ligament needle puncturing in extension leads to a safe and predictable reduction in medial compartment pressure during TKA.

PURPOSE: Medial soft tissue release in a varus deformity knee during total knee arthroplasty is essential for accurate balancing of the reconstruction. This study attempts to quantify the effect of sequential needle puncturing of the medial collateral ligament (MCL) using a pressure sensor insert (Verasense by OrthoSensor) and gap measurement under tension.

METHODS: Cruciate-retaining arthroplasties were placed in 14 cadaveric knees. The MCL was elongated by step-wise perforation, in five sets of five perforations, with the use of an 18-gauge needle, followed by valgus stress. Following the fifth set of needle perforations, blade perforation was performed on the remaining tense fibers of the MCL. Following each step-wise perforation, corresponding medial compartment pressures and gap measurements under tension were recorded.

RESULTS: Sensor measurements correlated closely with step-wise tissue release (R = 0.73, p < 0.0001), and a significant decrease in pressure was found in early needle puncturing (mean 49 N after 5, 83 N after 15, p values < 0.05), although changes diminished at later stages of needle perforation (90 N after 20). Gap measurement demonstrated small gradual changes with early puncturing, but showed significant opening in the later stages of release. There was minimal variation in pressure or gap measurements in flexion versus extension. This finding suggests that MCL needle puncture will not lead to unequal gaps between flexion and extension. There were no cases of MCL over-release after 15 punctures, one case after 20 punctures, and three after blade perforation.

CONCLUSION: Needle puncturing of the MCL in extension for up to 15 punctures can be a safe and predictable way to achieve medial opening when balancing a varus knee during TKA as demonstrated in this cadaveric model. Blade perforation should be used with caution to avoid over-release. The needle puncture method can be used by surgeons to achieve reliable reductions in medial compartment pressures, to help achieve a balanced TKA, with minimal risk of over-release.