Total knee replacements and high tibial osteotomies are commonly performed orthopaedic operations with low complication rates. Both of these procedures involve surgery in close proximity to the popliteal artery with the use of power tools and sharp instruments. The behaviour of the popliteal artery during knee flexion, in particular the change in distance between itself and the posterior tibial cortex, is poorly understood. Many previous studies have been on stiff embalmed knees or with the patient lying supine, so as to subject the popliteal artery to an anterior pull from gravity.

We used duplex ultrasonography on 100 healthy knees to determine the distance of the popliteal artery from the posterior tibial surface at 0 and 90 degrees of flexion. One observer was used throughout. At 1–1.5cm below the joint line, we found the artery was closer to the posterior tibial surface in 24% of knees when the knee was flexion. This was also the case for 15% of knees at 1.5–2cm below the joint line. These two levels were chosen as they represent the usual positions for the tibial cuts performed in total knee replacement and tibial osteotomy. We provide an anatomical account to help explain our findings using cadaveric dissections, arteriography and static MRI studies. The first of our explanations for this posterior movement of the artery is the increase in the antero-posterior thickness of the popliteus muscle during knee flexion. We also observed a posterior pull on the popliteal artery from the sural vessels.

6% of the knees had a high branching anterior tibial branch. We highlight this anatomical variant as an example of an extremely vulnerable vessel. We review the existing literature regarding the popliteal artery dynamics, and conclude that 90 degrees of knee flexion is the safer position for tibial procedures, but repeat the warning that the surgeon must still take great care.

1. A study of the late results of 343 soundly united tibial shaft fractures was carried out. Limitation of ankle and/or foot movement occurred in twenty-one patients (6 per cent) and was found to be the most important cause of disability. Knee stiffness (2·3 per cent of cases) and shortening of up to three-quarters of an inch (5·5 per cent of cases) caused little functional impairment.

2. Stiffness of the foot and ankle was correlated with the severity of injury, occurring in 1 per cent of minor, 5 per cent of moderate and 22 per cent of major injuries.

3. One-third of the patients with limitation of foot and ankle movement had clinical evidence of ischaemic contracture.

4. It is argued that, in the absence of direct injury to the joint, persistent joint stiffness is caused by replacement fibrosis of soft tissues. This may result either from direct tissue injury or from associated vascular damage.

1 . A series of 343 tibial shaft fractures proceeding to sound union in adults, and 192 fractures in children, was studied. Groups of fractures differing from each other only in the one particular variable under consideration were compared.

2. The severity of the injury (as assessed by the degree of displacement, of comminution and of compound wounding) was found to be an important determinant of speed of fracture union and of incidence of delayed and non-union. A simple classification of severity of injury is described.

3. Distraction delayed healing. Traction which avoided distraction had no effect on the rate of union of fractures of moderate severity compared with cases of similar severity of injury treated by immobilisation only. Major fractures subjected to traction did take longer to unite on the average, but there was no increase in the incidence of delayed or non-union.