In-vitro analysis of the balancing capacity of the human knee in arthroplasty procedures

Objectives Depending on the implantation procedure and pathology of the patient far-reaching changes in the function of the soft-tissue envelope of the knee are necessary to rebalance the joint in knee arthroplasty procedures.

In this context, the question arises to what extent a natural joint balance can be restored?

The aim of this in-vitro study was therefore to investigate the functional structure of the soft-tissue envelope in context of knee arthroplasty procedures. In particular, the joint laxity of the knee in dependence of the soft-tissue condition were investigated in order to clarify to what extent the joint laxity is influenced by removal of the mesisci, the ACL, and parts of the soft-tissue envelope which are typically used forsoft-tissue balancing.

Methods 24 human cadaveric knee specimens were used for biomechanical analysis. Laxity of the knees were investigated by use of a robot based biomechanical test rig.

The specimens were divided equally into four groups to investigate the laxity of the knee in dependence of various soft-tissue conditions. The following structures were released or resected in four different resection sequences: menisci, ACL, PCL, LCL, dMCL, sMCL.

The knee joints were tested at 0°, 30°, 60° and 90° of flexion by subjecting the joint to seven loading cases: inferior, anterior and posterior force as well as varus, valgus, internal and external torque.

Differences between groups were analyzed by utilizing repeated-measures analysis of variance. Signifcant findings were further analyzed with Tukey’s post hoc test.

Results and Conclusion The laxity of the knee joint did not change significantly in any of the investigated directions due to the placement of the surgical approach (p > 0.16). The removal of the menisci had an influence on joint laxity. Compared to the physiological joint the laxity increased in internal rotation by up to 20.6 ±17.6° (p < 0.0001). The removal of the ACL significantly increased the laxity of the knee joint compared to the physiological joint: by up to 10.0±8.7 mm (p < 0.0001) in anterior direction and 30° flexion, by up to 1.2±3.0 mm in 90° flexion (p < 0.0001) and up to -3.6±4.4° (p =0.02) in inferior direction, up to 4.6±5.9° (p =0.008) in valgus rotation. The external rotation laxity values were increased after resection of the dMCL (p =0.002), while resection of the sMCL showed no significant effects.

In conclusion, the strong dependence of the knee laxity

on the flexion angle should be considered in order to preserve the natural joint function as much as possible. Balancing the joint tension only, involves the risk of balancing the joint in flexion too tightly, which might result in movement restrictions and a joint with unnatural function and kinematics.

The use of a prosthesis that maintains both cruciate ligaments is the only way to maintain the anterior-posterior stability of the joint in balance. Compensation of the cruciate ligament function solely through the prosthesis design and implant alignment is unlikely.

Stichwörter Soft-tissue balancing; knee; arthroplasty; laxity

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Artikel online veröffentlicht:
15. Oktober 2020