The prevention of deep vein thrombosis (DVT) and pulmonary embolism (PE) after orthopaedic surgery remains a controversial and challenging issue. Problems include the measurement and significance of end points, the prevalence of complications associated with interventions, the relevance of historical studies (which were associated with prolonged rehabilitation regimens), the numbers of subjects required to power studies adequately, and the bias introduced by industry funding of studies. What orthopaedic surgeons are looking for is a prophylactic modality that is effective, acceptable to patients, has minimal side effects, and is cost-effective. Prophylactic modalities can be split broadly into chemical (drugs) or mechanical. Chemical prophylaxis has dominated but is associated with bleeding and wound complications that have been underrepresented in the orthopaedic literature. In this study, Colwell et al. aimed to demonstrate that a new mobile foot pump device is at least as good as the currently accepted chemical prophylactic regimens after primary hip and knee arthroplasty, without the bleeding complications.
Three thousand and sixty patients undergoing primary hip or knee arthroplasty at ten high-volume U.S. centers used the portable foot pump device from the operating room for a minimum of ten days after surgery. All patients over the age of eighteen years were included unless they had a history of venous thromboembolism (VTE), coagulation derangement, or a solid tumor in the previous five years. Some of the patients also received aspirin at the treating surgeon’s discretion. Outcome measurements for VTE were symptomatic PE or DVT proven with duplex ultrasound or spiral computed tomography, which are the same criteria used by the American College of Chest Physicians and the American Academy of Orthopaedic Surgeons in their guidelines on VTE1,2. At three months, patients completed a follow-up questionnaire that aimed to identify any VTE events. The number of patients who declined to be involved was not recorded, and only one patient was lost to follow-up after one month after surgery.
There were twenty-eight symptomatic episodes of VTE (0.92%): twenty-three DVTs (three proximal) and five PEs. There were no fatalities from PE, although one patient died and had no autopsy to exclude VTE as a factor. The results were compared with selected historical studies using warfarin, enoxaparin, rivaroxaban, and dabigatran.
The authors present an interesting way of measuring the significance of their results that differs from what we normally expect in orthopaedic studies with the concept of a 1% “noninferiority” margin. Their argument is that this treatment has already been demonstrated to be safer than chemical prophylaxis with a significant reduction in major bleeding after primary joint replacement compared with enoxaparin in a previously published paper3. Hence, this device is still better, even if it only has a comparable rate of VTE. In fact, the results show that it does provide a noninferior risk of >1% compared with warfarin, enoxaparin, rivaroxaban, and dabigatran (except for total knee arthroplasty with rivaroxaban, which failed to reach the 1% noninferiority margin by 0.06%). However, this is perhaps the main issue for concern with the methodology in that the results of this study are compared with data from studies in the literature selected by the authors. This clearly is a major source of potential selection bias. Hence, although very encouraging, this study perhaps needs to be repeated directly against the chemical prophylactic controls, preferably in a randomized way.
The issue of extended prophylaxis is not explored in this paper but is directly relevant. We know that many VTE events occur after discharge from the hospital, and extended chemical prophylaxis has been supported for this reason2,4,5, so this device may be the first mechanical method that also addresses this issue. Furthermore, compliance with “nonmobile” devices is a problem, as they are removed every time a patient mobilizes6. This new device stays with the patient and hence should improve compliance also.
Certainly, this device seems at least equivalent to chemical prophylaxis, but without the bleeding complications, and potentially addresses the issues of compliance and prolonged prophylaxis associated with conventional foot pump devices. Further independent and properly controlled studies are required, but this device seems to fulfill the concept to primum non nocere, or “first do no harm.”