In 13 unloaded living knees we confirmed the findings previously obtained in the unloaded cadaver knee during flexion and external rotation/internal rotation using MRI. In seven loaded living knees with the subjects squatting, the relative tibiofemoral movements were similar to those in the unloaded knee except that the medial femoral condyle tended to move about 4 mm forwards with flexion. Four of the seven loaded knees were studied during flexion in external and internal rotation. As predicted, flexion (squatting) with the tibia in external rotation suppressed the internal rotation of the tibia which had been observed during unloaded flexion. The aims of this study were to determine if the living knee could be imaged in a clinically practicable fashion in the same way as the cadaver knee 1 and whether tibiofemoral motion in the living unloaded knee was the same as that in the unloaded cadaver. We then examined the effect of load applied either externally as a tibial torque or by weightbearing and muscle action with and without tibial longitudinal rotation during flexion in the living knee. Subjects and MethodsTwo groups of volunteers were recruited in the Royal Hospital Haslar, Gosport (hospital A: six knees; five male, aged 21 to 32 years) and in St Mary's Hospital, London (hospital B: seven knees; seven male, aged 22 to 35 years). All the knees were normal and the volunteers Caucasian. Table I gives the details.Hospital A. Images during unloaded flexion were acquired using a Picker Outlook 0.23 Tesla Open Access MRI scanner (Picker International Inc, Cleveland, Ohio). A wooden template, which allowed accurate positioning of the knee in various degrees of flexion, was slotted into the scanner couch. The volunteer lay on the template in the lateral position with the knee to be scanned lowermost. The receiver coil was placed around the knee so that it overlaid the femoral condyles. The thigh was held by Velcro straps and a wooden peg was placed behind the popliteal fossa to prevent movement of the femur during flexion.The following images were obtained: four sagittal slices of 10 mm thickness with a 15 mm gap between cuts at -5°( quadriceps contracting), 10°, 20°, 40°, 50°, 90°, 90° (plus flexion against resistance), 90° (plus extension against resistance) and 110°, and 22 slices of 3 mm thickness centred on the intercondylar notch at 0° (quadriceps relaxed), 30°, 60° and 90°. This examination, with a practised radiographer, required about 40 minutes.A template was made by tracing images of the sagittal sections of the lateral and medial tibial condyles from the first scan. This was then overlaid on the monitor to ensure that the same point on the tibia was being scanned each time. Hospital B. MR images were obtained as previously described by Vedi et al. 2 With the volunteer seated, nonweight-bearing images at -5°, 10°, 45° and 90° were obtained with the foot supported by an examiner. At 90°, the knee was then rotated into tibial external rotation (ER) and internal rotation (IR) and an anteroposterior (AP) dra...