Characterisation of in-vivo mechanical action of knee braces regarding their anti-drawer effectReport as inadecuate

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* Corresponding author 1 Pôle des Technologies Médicales 2 CIS-ENSMSE - Centre Ingénierie et Santé 3 LGF-ENSMSE - UMR 5307 - Laboratoire Georges Friedel 4 LIBM Laboratoire de Physiologie de l-Exercice LPE - Laboratoire Interuniversitaire de Biologie de la Motricité 5 Service de chirurgie orthopédique, Centre Hospitalier et universitaire de Saint Etienne

Abstract : The knee is the largest joint in the body and supports high loads, up to several times the body weight. It is vulnerable to injury during sport or professional activities, potentially leading to chronic knee instability. This instability is a functional issue to the patient and is characterized by a -wobbly- feeling. Different internal structures take part in joint stabilization by passive ligaments, capsule or active neuro-muscular system and proprioception action. The most common injury involves the anterior cruciate ligament ACL complete or partial rupture: it is involved in 24% of all knee injuries and 59% of ligamentous injuries 1. In the United States,the annual incidence in the general population is approximately 1 in 3500 with 100,000 ACL reconstructions performed each year 2, 3. These conditions are a huge burden on individualsand healthcare systems. Diagnosis of knee instability involves a discussion with the patient and a clinical examination, usually the Lachman test. It consists in a manual anterior translation of the tibia aiming at putting the ACL in tension. By practice, the examiner is able to grade the laxity by severity 4. However, its sensitivity and specificity to detect complete ACL ruptures depends on the experience of the examiner, the patient’s body type and the delay between the accident and examination 5. In order to reduce this variability, arthrometers were developed.These devices apply an increasing force to induce a postero-anterior drawer and measure the corresponding translation. Displacement-load curves of the healthy and injured knees are compared; ACL rupture is ascertained when differential laxity is higher than a certain threshold. Well-known arthrometer devices are the KT-1000 developed by 6 and the GNRB® 7. The former is very popular and has been widely studied; its sensitivity to detect complete ACL ruptures is 77% and its specificity 90% threshold: differential laxity of 3 mm at 130 N. Thelatter was developed recently; two studies 5, 7 highlighted the superiority of this device compared to similar apparatus. A differential threshold of 3 mm at 134 N is used to determine complete rupture: its sensitivity is 70% and specificity 99%. This arthrometer device is also used to diagnose partial ruptures threshold of 1.5 mm at 134 N with a sensitivity of 80% and a specificity of 87%.Knee braces or orthoses are usually part of the standard therapy for knee instability and are commonly prescribed by physicians and medical practitioners. Their claimed mechanical effects are to support-align the joint and increase proprioceptive input 8. However, very few studies actually show significant actions, from biomechanical studies to therapeutic trials 9, 10. Mechanical- physiological effects have been emphasized, but the mechanisms of action have been poorly characterized 8, 9, 10, 11, 12, 13. What is more, subjective evaluations of patients highlight a large demand for these products; therefore, their efficiency is still widely discussed among medical experts. In particular, therelative importance of the two principal stabilizing mechanisms is not known:- joint stiffening by adding supporting structures, e.g. hinged bars secured to the joint by straps and fabric passive mechanism- neuromuscular control enhancement by proprioceptive effect active mechanismAs a consequence of these uncertainties, medical practitioners and manufacturers still lack a simple evaluation tool for knee orthoses. A French committee of experts highlighted this problem 14 and stated that orthoses must be evaluated by taking both the mechanisms of action and the desired therapeutic effects into account.Although the passive action of knee braces to prevent a drawer motion has already been characterized on surrogate limbs 15, 16, 17, only one attempt has been made to link these measures to corresponding expected in-vivo actions through numerical modelling 18, 19, highlighting a passive stiffening much lower than what is brought by intact ligaments. However, a real clinical study is still needed to validate the numerical results and investigate the influence of patient-specific factors such as morphology, injury severity, neuromuscular adaptation and instability feeling control.This study is aimed at objectively quantifying the joint stiffening action of various commercial braces in-vivo using a GNRB® arthrometer on a number of pathological patients.

Author: Baptiste Pierrat - R. Oullion - Jérome Molimard - Laurent Navarro - M. Combreas - Stéphane Avril - Rémi Philippot - P Calmels



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