Sagittal plane knee translation in healthy and ACL deficient subjects : a methodological study in vivo with clinical implications

Sammanfattning: This study on human subjects, comprises of four cross sectional and one prospective cohort study. The general purpose of this work was to develop a technique for measuring in vivo, sagittal anterior-posterior translatory motions in the knee joint using a computerized electrogoniometer (CA-4000, OS Inc., Hayward CA, USA). Healthy human subjects served as controls while patients with arthroscopically confirmed unilateral ACL deficiency served as the experimental group.The measurements were repeatable, accurate and valid. In all groups, as a consistent pattern, the tibia maintained an anterior position in relation to the femur during the load bearing phases and a posterior rosition in the non load bearing phases of step ascents and descents. Contraction of the gastro-soleus grour of muscles, before the lift off phase of ascent, resulted in an anterior positiOn of the tibia in relation to femur which was anterior to the posterior limit of static laxity testing. Step heights between 15 to 23 cm did not influence the amount of tibial translation.During step ascent the amount of femoral roll-forward per degree extension was significantly smaller in the ACL deficient knees than the contralateral noninjured or healthy control knees.ACL deficiency resulted in a larger than normal static space (125% to 257%) in the injured knees. It also resulted in an anterior shift of the tibia-femoral resting position of the injured knees.The amount of the static laxity space the ACL deficient knee utilised during stair climbing varied, depending upon the knee flexion angle. Nearer to extension it was 90% and near to mid flexion (50°--{50°) it was 42% of the maximal static laxity space. In the conservatively treated ACL deficient group, the contralateral healthy knees showed 28% increase in the static AP laxity at follow up when compared to the index measurement and the control knees.In the ACL reconstructed group, the increased static AP laxity and anterior shift of the tibia-femoral resting position in the reconstructed knees persisted at a minimum follow up of 21 months. Over the same period of time, the contralateral healthy knee also showed an anterior shift in the tibia-femoral resting position. The force at the anterior inflection point in static laxity testing, which was similar at index examination in both knees, diminished by 20% in the reconstructed knees at follow up.The ACL plays an important role in optimally positioning the tibia-femoral articulation and maintaining the position during quadriceps and gastro-soleus muscle contraction.