We agree with Dr. Zaveri that on the basis of just the one study by Haentjens (1), weight-adjusted low-molecular-weight heparin does not seem to significantly reduce the incidence of thromboembolic events compared with fixed-dose low-molecular-weight heparin. Only the latter was used in the nine studies that we reviewed. The question about the timing of administration and duration of thromboembolic prophylaxis has yet to be answered satisfactorily. In the studies that we reviewed, therapy with most agents was started on hospital admission. Noble and colleagues' review (2) focuses only on patients undergoing joint replacement. Thus, it is questionable whether these data are applicable to patients with hip fracture. Patients with cancer are at substantial risk for the development of thromboembolic disease after orthopedic surgery, and it is unclear at this time what the appropriate thromboembolic prophylaxis should be. Lin and colleagues (3) observed no significant differences in the development of deep venous thrombosis between patients receiving warfarin and intermittent compression, those receiving heparin and intermittent compression, those receiving intermittent compression alone. However, this study was underpowered to detect a difference (for example, only 1 of 17 [5.9%] patients receiving warfarin developed deep venous thrombosis compared with 17 of 115 [14.8%] who received no anticoagulant).

Recent reports suggest that low-molecular-weight heparins used concurrently with spinal or epidural anesthesia may cause bleeding or hematomas in the spinal column (4). Many of the trials of low-molecular-weight heparin that we reviewed did not report the type of anaesthesia. No cases of epidural bleeding were reported in those trials, and the trials were not powered to detect this uncommon complication in the subgroup receiving spinal or epidural anesthesia. Until more data are forthcoming, we believe that the current U.S. Food and Drug Administration recommendations—that patients receiving epidural or spinal anesthesia and receiving concurrent low-molecular-weight heparin be monitored frequently for signs and symptoms of neurologic impairment—are appropriate (4). At any rate, it should be noted that this recent Food and Drug Administration report only involves patients receiving low-molecular-weight heparin; it should not deter prophylaxis with low-dose heparin where indicated.