Mid-flexion laxity in the asymptomatic native knee is predominantly present on the lateral side

Abstract

Purpose During total knee arthroplasty (TKA), an orthopaedic surgeon is focused on soft-tissue balance in extension (0°) and in lexion (90°). Patients with instability problems of the knee often report a feeling of instability during daily life activities, at around 30° knee lexion. There are no reference values available for knee laxity of healthy subjects in mid-lexion (30°) and lexion (90°) for comparison with the TKA population. Therefore, the aim was to quantify varus and valgus knee laxity in extension, mid-lexion and lexion in the asymptomatic native knee. Methods In 40 healthy volunteers matched for age, gender and BMI with the TKA-population, varus and valgus knee laxity in extension (0°), mid-lexion (30°) and lexion (90°) was measured on low-dose radiographs. For each subject, one randomly selected knee was stressed in extension, mid-lexion and lexion (with 15 Nm) using a stress device. Results Varus laxity in mid-lexion was higher than in extension and lexion (p < 0.01). Valgus laxity tended to be highest in mid-lexion laxity; however, no diferences in knee laxity between lexion angles were seen (n.s.). Varus knee laxity in extension was higher in females than in males (p < 0.05). Conclusions Mid-lexion laxity in the native knee is more prominent on the lateral side of the knee, while the medial side is more stable and constrained. Varus knee laxity in extension was shown to be higher in females than in males. Level of evidence Prognostic Level II.

The language of knee alignment

“…40 In both flexion and extension, medial (valgus) laxities are less than lateral (varus), with the medial side being more isometric and constrained. 40,41 The lateral (varus) laxities increase in higher degrees of knee flexion. 42 In the context of TKA, PCL resection produces a greater increase in the flexion gap relative to the extension gap, and also increases lateral laxities more than medial.…”

How reproducible are clinical measurements in robotic knee surgery?

“…The result obtained in terms of HKAa showed higher repeatability for the measurements at the flexion angles typically taken as reference during the calibration (0° and 90°) [ 21 ], hence justifying this choice as they are able to provide reliable and robust info on which base the surgical cuts. Flexion angles like 30° and 60°, on the other hand, suffer the effects of the so called mid-flexion instability [ 21 ] and therefore are characterized by higher variability if compared to full-extension and 90° configurations, but it is noticeable that also in these sub-optimal cases the comparison did not return remarkable differences.…”

Medial stability and lateral flexibility of the collateral ligaments during mid-range flexion in medial-pivot total knee arthroplasty patients demonstrates favorable postoperative outcomes

“…Watanabe et al reported that patient‐reported pain and instability were adversely affected by greater laxity [18], while Kamenaga et al found greater lateral laxity at extension significantly correlated with better patient satisfaction [37]. In healthy knees, it is generally recognized that the lateral knee shows greater laxity than the medial knee due to the medial‐pivot motion [38]. Our study revealed that the longer the LCL length and the higher the elongation rate during mid flexion, the better the Knee Score of the MP patients.…”