The aim of this study was to investigate how the rotational axis of the wrist moves as the hand goes from full ulna to full radial deviation.

Fifty normal wrists in 25 subjects were assessed with a Polhemus Fastrak (TM) magnetic tracking system. The subjects, aged 19 to 57, placed their palms on a flat wooded stool. Sensors were attached over their 3rd metcarpal and distal radius. The sensors then recorded movement from ulna to radial deviation. The translational and rotational measurement accuracies were 1 mm and 1 degree respectively.

The mean range of movement was 45 degrees (SD 7). In ulna deviation the axis was in the region of the lunate. As the hand moved towards radial deviation, the axis moved distally. At the end of the movement the mean distal displacement was 21 mm (SD 15). In 32 wrists the distal displacement was accompanied by a mean displacement towards the ulna of 12 mm (SD 8). In 18 wrists the distal displacement was accompanied by a mean displacement towards the radius of 8 mm (SD 5).

The rotational axis position indicates how the wrist is moving during radial deviation. In early movement, when the axis is proximal, there is a high degree of sideways translation. In later movement, when the axis is distal, there is more rotational movement. In some cases the axis moved distally and toward the radius, whereas in other cases it moved distally and toward the ulna. This spectrum of movement may support the theory of 2 types of carpal movement proposed by Craigen and Stanley (J. Hand Surg, 20B, 165–170, 1995).

Introduction: The anterior drawer test for anterior cruciate ligament (ACL) deficiency, requires a subjective assessment of joint movement, as the tibia is pulled forward. The aim of this study was to objectively quantify this movement using a magnetic tracking device.

Materials and Methods: Ten patients aged 24 to 44 years were assessed as having unilateral ACL deficiency with conventional clinical tests. These patients were then re-assessed using a magnetic tracking device (Polhemus Fastrak). Patients had magnetic sensors attached around their femurs and tibias using elasticated Velcro straps. The Anterior Drawer test was then performed with the patient lying within range of the system’s magnetic source. The test was performed three times on the normal and injured knees of each patient, using a spring balance to apply a standard 20 lb (=89 N) force. During the tests, sensor position and orientation data was collected with an accuracy better than 1 mm and 1 degree, respectively. The data was sampled at 10Hz and stored on a computer for post-test analysis. This analysis deduced the tibial displacement resulting from each anterior drawer.

Results: During the anterior drawer test the supine patient’s knee is in 90 degrees flexion, with the foot planted on the examination couch. As the tibia is pulled anteriorly, it rotates upwards from the foot and the femur experiences a corresponding rotation from the hip. These complex coupled movements are best quantified in terms of absolute displacement of the tibia from the femur. In the normal knees, the mean displacement of the tibia from the femur was 4.2 mm (SD=1.6). In comparison the ACL deficient knees had a mean displacement of 6.3 mm (SD=2.9). This is 50 % more. A paired t test of this data showed a highly significant difference, with P = 0.005.

Conclusion: This study has quantified the movement produced during the Anterior Draw test for ACL deficiency. The tracker’s lightweight sensors caused minimal disturbance to the established clinical test. The system therefore provides objective measurement data to augment the clinicians subjective assessment.

Purpose: Femoral roll causes the sagittal plane axis of the knee to move posteriorly and anteriorly with flexion and extension. The aim of this study was to measure this movement with a surface marker imaging system and assess the effect of Anterior Cruciate Ligament (ACL) deficiency on the Sagittal Axis Pathway (SAP) of the knee.

Method: Twelve normal and fourteen unilateral ACL deficient subjects were video recorded as they flexed and extended their knees in the sagittal plane. Video stills were captured at 150 intervals from 90o flexion to full extension. An imaging system was then used to extract the co-ordinates of leg markers from each still. These co-ordinates were then processed to derive the SAP for each knee throughout its range of movement.

Results: Pooling all the normal results together (24 bilateral + 14 unilateral = 38 knees), it was found that a 90° knee extension caused the sagittal axis to displace anteriorly with a mean value of 20.0mm (SD=7.8). In comparison the 14 ACL deficient knees were found to have a mean anterior displacement of 9.2 mm (SD=8.0). A bilateral comparison of the 12 pairs of normal knees showed no significant difference between left and right sides (paired-t, p=0.99). However, a bilateral comparison of the 14 unilateral ACL deficient patients showed a significant difference between normal and injured sides (paired-t, p=0.00025). In this group, the normal knees axis at full extension had a mean location 28.9mm (SD=8.8) posterior to the front of the tibial plateau. In comparison the injured knees axis has a mean location 37.8 mm (SD=8.5) posterior to the front of the tibial plateau. Again, this was highly significant (paired-t, p=0.0001).

Conclusion: These results indicate that normal knees have a mean forward roll of 20 mm for a 90° knee extension. In comparison ACL deficient knees have a reduced roll of 9.2 mm which occurs at the rear of the joint. This reduction in roll is consistent with the abnormal ligament biomechanics.