Abstract
Traditional medial soft tissue release for balancing of the varus knee in total knee arthroplasty can lead to an inconsistent reduction in medial tension. The purpose of this study is to establish whether sequential needle puncturing of the medial collateral ligament (MCL) can be a safe and predictable method for medial release.
Total knee prostheses were implanted in 14 cadaveric specimens by a single surgeon. Medial tension was measured in flexion and extension by a pressure sensor with implants in place, and calipers after removal of implants and gap distraction under constant tension. Measurements were performed after each of 5 sets of 5 punctures of the MCL with an 18-gauge needle and following 5 transverse perforations with an 11-blade. A consistent valgus force was applied after each set of MCL punctures with a pneumatic cylinder. Pearson's correlation was used to compare pressure sensor measurement with gap distance measurement under tension. The pressure as detected by the sensor after each set of 5 punctures was analyzed by a repeated measures two-way ANOVA and a Tukey multiple comparisons test to determine a significant decreases between puncture sets.
The pressure sensor device correlated more closely with systematic tissue release (r=0.59 for % change from baseline) than did measurements of gap increase under tension (r= −0.22). All knees had ≤5mm of medial opening with up to 25 needle punctures. Two knees had <5mm of medial opening in flexion after blade perforation. The mean pressure decreases in 90 degrees flexion, mid-flexion and extension were 11.2, 9.4 and 9.9 lbs respectively after 5 needle punctures and 8.1, 11.5 and 9.6 lbs between 5 and 15. Significant pressure decreases were seen after 5 and 10 needle punctures and again after blade perforation (p<0.05)
Needle puncture of the deep and superficial MCL leads to a significant and reliable decrease in medial tension over the first 15, with diminishing effect up to 25 punctures. This method may be employed when up to 20 lbs reduction in medial pressure is desired. Blade perforation after needle puncture should be approached with caution.
