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Ligamentomuscular and muscular stretch reflexes are known to contribute to knee joint stability. After anterior cruciate ligament (ACL) injury, a more intense and adjusted muscular response is required to maintain joint stability, but this neuromuscular control of the knee has not been clearly proved. The aim of the study is to record electromyography (EMG) signal and muscular fibre length variations in quadriceps and hamstrings of the knee with and without ACL, and to analyze and integrate the ligament strain and the muscular reaction to forced anterior tibial translation (ATT). In 17 knees from 12 cats, EMG electrodes and ultrasonomicrometry crystals were inserted into four main periarticular muscles, with strain gauges on periarticular ligament insertions. Their output signal was compared before and after ACL surgical section in series of ATT (at 90 degrees and 30 degrees knee flexion), and also during knee flexion and extension. Linear regression analysis was performed between the EMG signal and muscular fibre length variations, and between the EMG signal and the strain on ligament insertions, in the search of this reflex neuromuscular response. In the ACL deficient knees, the studied muscles showed a poor adjustment to motion of EMG firing, inversely to controls. The muscle stretch reflexes showed poorer correlation with post-peak EMG activity than the ligaments. ATT control depended mainly on hamstrings activity in control knees, whereas in unstable knees, quadriceps activity was associated with more tibial translation. Acute ACL-deficient knees showed poor neuromuscular control with weak ligamentomuscular reflexes and no muscular stretch reflexes, suggesting the ineffectiveness of acute muscular reaction to provide early mechanical knee stabilization after injury.

Background Operative and nonoperative treatment of anterior cruciate ligament (ACL) injuries is often associated with a lack of proprioception and persistent muscle weakness of unknown origin.Methods This long-term study in the cat experimentally compares both neural and muscular activity in the articular nerves of the knee (PAN and MAN), quadriceps and hamstrings, in the chronic unstable knee, and in the reconstructed knee. We also investigated changes in neuromuscular response due to the mechanical competence of the graft, comparing stable and unstable reconstructed knees.Results We found increased periarticular muscle activity during anterior tibial translation in chronically unstable knees. Both reconstructed and non-reconstructed knees lost fast reactive activity in the articular nerves. When stability was recovered after reconstruction, the knees showed a more adjusted-although incomplete-muscular reaction.Interpretation ACL-injured knees in the cat, with or without reconstruction, show definite abnormalities in neuromuscular reaction in the long term. Regaining stability with a competent graft in the reconstructed knee is crucial for reduction of this anomalous reaction.

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Gold chloride technique can be combined with Adobe Photoshop® software to yield a quantitative assessment of the different areas in heterogeneous structures as are ligament. A semi-automatized method based on the sum of two- and three-dimensional morphological criteria upon colorimetric criteria allows the identification and measurement of the area occupied by a structure of interest. It also allows the quantification of color intensity to differentiate structures with similar staining avidity, like vessels and nerves. This computer-assisted, semiquantitative procedure for computerized morphometry is relatively simple to perform. The accuracy, efficiency, and reproducibility of this method based on a commercially available imaging program were considered adequate when tested on the anterior cruciate ligament of the cat. Image normalization by trained observers using a commercially available software package designed for photography, applied to a sample randomly chosen, has provided the means of making reproducible measurements of heterogeneous structures.