Enoxaparin, a low-molecular-weight heparin, has been used together with spinal or general anaesthesia in a prospective, randomised study of 188 consecutive elective hip replacements. Bilateral venography was performed on all patients on day 13 after operation. Group I (65 patients) received spinal anaesthesia and no immediate injection of enoxaparin. Group II (61 patients) received spinal anaesthesia and 20 mg of enoxaparin one hour after the onset of anaesthesia. Group III (62 patients) was operated on under general anaesthesia and received 40 mg of enoxaparin 12 hours prior to surgery. This group acted as the control group. In all three groups, 40 mg of enoxaparin was given 12 hours after the end of surgery and continued on a once-daily basis. Proximal DVT occurred in 6% of group I, 6.7% of group II and 6.5% of group III, not a significant difference. Distal DVT was present in 11% of group I, 5% of group II and 0% of group III; this was a highly significant difference (p = 0.007). Tolerance was good and the incidence of bleeding low in the three groups. Our results confirm the low rate of DVT in patients operated on under general anaesthesia with the standard procedure of 40 mg of enoxaparin on a once-daily basis started pre-operatively. The 40 mg-dose is also safe and effective in association with spinal anaesthesia if half the dose (20 mg) is injected an hour after the lumbar puncture.

Bilateral venography was performed between 12 and 15 days after total hip replacement in 745 consecutive patients, all of whom had heparin prophylaxis. Of these, 81 patients (10.8%) showed evidence of recent deep vein thrombosis: 23 (3%) distal, 44 (5.9%) isolated proximal, five (0.7%) both proximal and distal, and nine (1.2%) extensive thrombosis from calf to thigh. Compared with previous reports heparin appeared to have reduced the number of distal and contralateral thromboses, but was far less effective in reducing proximal femoral thrombosis. In a cadaver study, the femoral veins were inspected during simulated total hip replacement by either an anterior or a posterior approach. In every case the femoral vein became kinked or folded in the thigh position imposed during the preparation of the femur. Local damage appears to be an important factor in proximal thrombosis; care at operation could help to minimise trauma to the femoral veins and reduce the number of such cases.