Standardised balancing goals are not able to reconstruct individual laxity-functional knee phenotypes in more than 50 % of knees

Purpose

Laxity Phenotype (LP) analysis has revealed a wide range of variability among knees, showing three phenotypes in extension and three in flexion. Based on this variability recently a Laxity-Functional Knee Phenotype (L-FKP) matrix was created. This study aimed (1) to assess how well-standardised balancing goals reproduce individual LPs, and (2) to develop a treatment algorithm to convert critical L-FKP groups into optimal ones.

Methods

Eighty-six knees were simulated using a validated alignment simulator to create and analyse the L-FKP matrix. Knees were classified as optimal (LP matched “all gaps equal” or lateral flexion laxity <6 mm), intermediate, and critical (presence of medial laxity in extension and/or flexion). A three-step treatment algorithm was developed for optimizing L-FKP; first, by adjusting bony anatomy within defined boundaries, second by targeting soft tissue releases if correction remained >1 mm, and third, by using additional constraint if option 1 and 2 were not sufficient.

Results

Only 37 % of knees showed optimal L-FKP patterns after restoring the patient-specific B-FKP. Another third of the knees was classified as suboptimal, which could be transferred to optimal L-FKP matrix groups with minor bone adaptions, finally reaching 70 % of optimal L-FKP patterns. Still, 30 % remained within the critical L-FKP matrix groups. The algorithm enabled the structured conversion of these cases into optimal groups.

Conclusions

Standardized balancing goals reconstruct optimal L-FKP groups in less than 40 % of knees, even if a personalized B-FKP workflow is applied. By minor bony modifications this amount can be increased to 70 %. A structured algorithm to restore optimal L-FKP is presented.