The deficit of isometric muscle strength on the injured side compared with that of controls was explained by the voluntary-activation deficit and a true muscle weakness. On the other hand, the diminished muscle strength of the uninjured side was explained sufficiently by the voluntary-activation deficit alone. Considering the bilateral voluntary-activation deficit, functional muscle tests might not be valid when the uninjured extremity serves as reference.

No abstract

The loss of full muscle activation contributes to weakness of the quadriceps muscle in patients with deficiency of the anterior cruciate ligament (ACL). We examined whether a deficit of voluntary activation (VA) of the quadriceps muscle can be reversed by reconstruction of the ACL and assessed its influence on muscle strength and clinical parameters. We evaluated 12 male subjects with an isolated tear of the ACL and 12 matched control subjects before operation and two years after reconstruction of the ACL. Assessment included measurements of isometric knee-extension torque at maximal voluntary contraction (MVC force), knee stability tests, the International Knee Ligament Standard Evaluation Form and the Tegner activity score. A sensitive method of twitch interpolation was used to quantify the VA and to calculate true muscle force. Before operation we found a deficit of VA on both the injured (mean +/- SEM 74.9 +/- 3.5%) and the uninjured side (74.6 +/- 3.0%) in comparison with the control group (91 +/- 0.9%). Two years after reconstruction of the ACL the VA improved significantly on both sides but remained less than that of the controls. Correlation analysis revealed an improvement of the VA in patients who returned to a higher level of activity. The deficit of true muscle force, however, persisted regardless of the clinical outcome and ligament stability.

Central activation deficits have been recognised to be partially responsible for quadriceps muscle weakness after knee injuries effecting the injured as well as the uninjured leg. The purpose of this study was to assess the extent of bilateral activation deficits and its effect on functional muscle tests using the uninjured leg as reference. The study included 30 patients with isolated rupture of the anterior cruciate ligament (group 1), 42 patients with rupture of the anterior cruciate ligament and accompanying joint damage (group 2) and 34 healthy volunteers as reference. The maximum isometric knee extension torque and the maximal voluntary muscle activation (VA) were measured bilaterally using a sensitive twitch-interpolation method. The measured and the true functional deficit, adjusted to a physiological VA of the uninjured side, was calculated. Isolated rupture of the anterior cruciate ligament caused a minor VA-deficit and severe knee injuries more severe VA-deficits of the quadriceps muscles of the injured (VA group 1: 83.8 +/- 1.9 %; group 2: 76.9 +/- 1.8 %) and on the uninjured side (VA group 1: 85.9 +/- 1.8 %; group 2: 77.9 +/- 1.8 %) compared to the control group (VA 91 +/- 0.64 %). Due to contralateral VA-deficits the mean underestimation of the isometric muscle-force deficit was 22 % in group 1 and 48% in group 2. Unilateral knee injuries lead to significant VA-deficits of the quadriceps muscles on both the injured and uninjured legs related to the severity of injury. The validity of tests for the assessment of muscle function is questionable when using the uninjured side as reference.

We conclude that the use of hamstring grafts for ACL reconstruction can lead to different histological pattern of tendon-bone healing. Micromotion of the hamstring graft inside the drilled canal can be play a role in tendon-bone healing.