Place des orthèses en pathologie ligamentaire du genou. Revue de la littérature

Characterisation of in-vivo mechanical action of knee braces regarding their anti-drawer effect

BACKGROUND

The knee joint is vulnerable to various injuries and degenerative conditions, potentially leading to functional instability. Usual treatments involve knee orthoses to support the joint. However, the level of mechanical action of these devices remains controversial despite high prescription and demand.

METHODS

The mechanical ability of three commercial hinged knee braces and one sleeve to prevent a static drawer was evaluated using a GNRB arthrometer. The testing of both pathological and healthy joints was performed on 16 patients with documented injuries involving the ACL, and an original method allowed decoupling the contribution of the brace.

RESULTS

The mean stiffness of the three hinged braces ranged between 2.0 and 7.1 N/mm. The most efficient brace was able to exert a restraining force on the joint equivalent to the one exerted by a healthy ACL, up to a 2.8 mm anterior displacement of the tibia. For higher anterior displacements, the restraining force of the brace dropped below the level of action of the intact ACL because of the particular non-linear behaviour of this structure. Finally, the most efficient brace was found to vary from subject to subject.

CONCLUSIONS

This study confirmed that fabric-based knee braces may effectively replace the passive mechanical role of the ACL within the low stiffness region of this structure. Although bracing may have other benefits (e.g., proprioception), this shows that they act as an effective passive restraint to low grade anterior laxities. Besides, a high patient-specificity of their effects highlighted the need of personalised objective testing for brace selection.

Evaluation of the mechanical efficiency of knee braces based on computational modeling

Knee orthotic devices are commonly prescribed by physicians and medical practitioners for preventive or therapeutic purposes on account of their claimed effect: joint stabilisation and proprioceptive input. However, the force transfer mechanisms of these devices and their level of action remain controversial. The objectives of this work are to characterise the mechanical performance of conventional knee braces regarding their anti-drawer effect using a finite element model of a braced lower limb. A design of experiment approach was used to quantify meaningful mechanical parameters related to the efficiency and discomfort tolerance of braces. Results show that the best tradeoff between efficiency and discomfort tolerance is obtained by adjusting the brace length or the strap tightening. Thanks to this computational analysis, novel brace designs can be evaluated for an optimal mechanical efficiency and a better compliance of the patient with the treatment.