Flexion-extension joint gap changes after lateral structure release for valgus deformity correction in total knee arthroplasty - A cadaveric study

At the time of total knee arthroplasty, the surgeon generally corrects exce ssive valgus knee alignment to anatomic valgus through release of lateral s upporting structures. This study used a cadaveric model to i) study the amo unt of correction achieved with each release step in 2 sequences of lateral release, ii) compare the amount of release in extension versus flexion, an d iii) measure any associated rotational changes of the tibia. Six fresh-fr ozen cadaveric knees were used to test the amount of change into varus afte r sectioning the iliotibial band (ITB), the popliteus tendon (Pop), the lat eral collateral ligament (LCL), and the tendon of the Lateral head of the g astrocnemius (LG). This sequence was then compared with a second sequence i n another 6 cadavers as follows: LCL, Pop, ITB, and LG. The amount of valgu s correction was tested in 90 degrees, 45 degrees flexion, and full extensi on. At each flexion angle, the corresponding releases were assessed with th e tibia oriented vertically under its own weight, under tibial distraction with equal support from the lateral and medial soft tissues, and under a ma ximal varus deforming stress. Results showed that complete lateral structur e release provides limited correction into a varus direction with a balance d distracted soft tissue gap or extension space (8.9 degrees with the LG re leased), and the lateral aspect of the flexion gap opens more than the exte nsion gap (8.9 degrees compared with 18.1 degrees in flexion). Early LCL re lease provided a more uniform release of the joint gap, and rotational chan ges were variable, tending toward external rotation of the tibia (6.0 degre es in full extension with release of the LCL). We suggest that when severe valgus deformities are present, the LCL should be considered first for rele ase and the Pop and ITB be used to grade the release.