PASSIVE KNEE MUSCLE MOMENT ARMS MEASURED IN-VIVO WITH MRI

Objective. To determine moment arm lengths from seven knee muscles and the patellar tendon. The knee muscles were the biceps femoris, semite ndinosus, semimembranosus, gracilis, sartorius, and the lateral and me dial gastrocnemius muscles. Design. The moment arms were calculated ba sed on MRI measurements. Background. Moment arm lengths of different m uscles with respect to the joint centre of rotation (CR) or the centre of the contact point between joint surfaces are necessary basic data for biomechanical models predicting joint load. Methods. Ten male and seven female subjects participated. Using a 1.5 Tesla magnetic resonan ce imaging system, 3-dimensional coordinates of relevant points were r ecorded from a 3-D volume reconstruction of the right knee at knee fle xion angles of 0, 30 and 60 degrees. Muscular moment arms were calcula ted in both the sagittal and frontal planes. The recordings were all m ade during passive mode, which means that no muscular contraction was performed. Results. All muscles except the lateral gastrocnemius showe d statistically significant differences (P<0.05) of moment arm lengths between gender in the frontal plane. All muscles except biceps femori s and sartorius showed significant differences (P<0.05) of moment arm lengths between gender in the sagittal plane. Most muscles also showed a linear or quadratic trend of changing moment arms with varying knee angle. Conclusions. Our results indicate that for most biomechanical analyses involving knee muscles, gender- and angle-specific moment arm s should be used. Relevance Biomechanical data of muscle moment arms a nd their variation with joint angle and gender are essential in models predicting joint load. These models constitute basic data in endopros thesis design. Copyright (C) 1996 Elsevier Science Ltd.