A scoping review and guide for in vitro healthy human knee joint laxity

Knee laxity is a well-studied concept with a vast repository of information in the literature. However, an often-overlooked challenge arises from the diverse methodological heterogeneity, making inter-study comparisons and overall knowledge of knee laxity confounded. Therefore, this review aimed to comprehensively summarise in vitro data on the intact knee laxity to discuss and highlight experimental trends to use the current methodological insights to establish a foundation for standardised testing guidelines.

A systematic search on PubMed, Embase, and Web of Science was conducted, spanning all publications up to 30 October 2024. Here, studies providing quantitative data on intact, primary or secondary, knee joint laxity (i.e., anterior-posterior, internal-external and varus-valgus) were synthesised together with their methodological procedures. Data were grouped based on loading intervals (i.e., 88-100 N, 130-134 N, 5 Nm and 10 Nm) and knee flexion angles (i.e., 0°, 15°, 30°, 45°, 60°, 90°, and 120°), based on the most available data.

A total of 161 studies comprising 1741 intact knee specimens were included. Anterior-posterior laxity was the most frequently reported, followed by internal-external and varus-valgus directions. Despite comparable experimental setups, substantial variability was observed in grouped data laxity values due to differences in coordinate system definition and kinematic constraints. In fact, specimen preparation, demographics and intactness were frequently incomplete or missing, limiting confidence in the validity of reported intact knee laxity measurements.

Due to limited field coherence and methodological transparency, guidelines are needed for laxity reporting in the future. Thus, the synthesised information from all the included articles was used to formulate foundational guidelines for standardised testing and reporting of knee laxity in the future. These guidelines cover specimen reporting, specimen knee intactness check, laxity reporting, experimental testing and measuring conditions to enable result comparisons and future meta-analysis.