1 Introduction

Deep vein thrombosis (DVT) and pulmonary embolism (PE) are significant complications following total hip (THR) and knee replacement (TKR). The American College of Chest Physician advocates the use of chemical prophylaxis.¹ However, a large number of orthopaedic surgeons resisted a standard regimen of chemical prophylaxis as suggested by cardio-pulmonology guidelines in favour of individualised judgements for the single patient.³

At our Institution, pneumatic foot compression devices (AV-Impulse system Orthofix Vascular Novamedix, Andover, UK) have been used for more than a decade as main tool of venous thromboembolism prevention in the postoperative in-hospital recovery period of patients undergoing elective THR and TKR. The AV-impulse foot compression system has shown a proven benefit in preventing thromboembolic events.^{6,10,11,13,15} Following a tendering process by the local District Health board, a new device, the Flowtron Universal compression system was introduced (Flowtron^®, ArjoHuntleigh, Luton, UK). This system, even if quite similar to the original AV-Impulse, lacks of published data for clinical validation.

The aim of this prospective study was to monitor safety and efficacy of the Flowtron foot pumps in the prevention of thromboembolic disorder in patients following THR and TKR.

2 Material and methods

All patients admitted at our institution from July 1011 to December 2012 with degenerative osteoarthritis of the hip or knee for THR or TKR management were considered for inclusion in the study. The criteria for exclusion were: diagnosed active malignancy; known bleeding diatheses; gastrointestinal ulceration or bleeding. The study was approved by the local Ethics Committee. All surgical procedures were carried out or directly supervised by experienced orthopaedic surgeons. Spinal anaesthesia was used in the large majority of patients. All patients used foot-pumps during hospital stay. The foot-pump slippers were fitted to both feet in the recovery room or in the ward as soon as possible after surgery, and the pneumatic machine was activated. The nurses were advised to fit and start the foot-pump system whenever the patient was not bearing weight. In some patients, the surgeon advised use of foot-pumps without simultaneous application of antithrombotic stockings.^11,16

Various chemicals were prescribed in combination with the foot-pumps. However, in some young and healthy patients the surgeon elected to use only foot pumps for prevention of venous thromboembolism. Low-molecular-weight heparin (LMWH, Clexane, 20–40 mg), Rivaroxaban (Xarelto), or Dabigatran (Pradaxa) were used in patients rated high-risk for DVT and PE (previous history of DVT/PE, positive family history of DVT/PE, high body-mass index and any other condition with expected difficulties to mobilise postoperatively). Aspirin was used in all other patients. Physical therapy, range of motion exercises, and mobilisation with partial or full weight-bearing were usually initiated on the first postoperative day.

The pneumatic compression cycle (30 seconds) of the Flowtron^® foot pumps differs from the AV-impulse system in that it inflates over a 3 s period compared to the 0.4 second inflation time followed by 3 second hold time of the AV-impulse system. Both devices inflate to a pressure of 130 mmHg. The foot pads are remarkably different, with a thinner, lighter design of the Flowtron system. Patients were free to terminate treatment with the foot-pump at any time. If foot-pump use was discontinued for more than 6 consecutive hours, the patient was excluded from the study, maintaining chemicals prophylaxis. At discharge, all patients were managed with graduated compression stockings and aspirin or other chemicals until full weight-bearing was permitted or at discretion of the surgeon.

Patients with clinical signs of DVT were investigated with ultrasound scans of lower extremity veins and those with clinical signs of PE underwent computed tomography pulmonary angiogram (CTPA). The patient commenced therapeutic LMWH with bridging warfarin therapy in case of DVT or PE imaging confirmation. Swelling and bruising of the thigh and oozing of the wound were assessed and scored using published criteria.^10,15

3 Results

A total of 464 consecutive patients were considered for allocation into the study. Eight patients were excluded and 32 patients discontinued the use of foot pumps during their hospital stay. The reason for termination was sleep disturbances and/or discomfort around the ankle. 424 patients were included in the study. Table 1 show the demographic detail of the 424 patients. Thirty patients were managed with Flowtron foot pumps only (7%). The remaining 394 patients were given additional chemical prophylaxis: 330 patients on Aspirin (78%), 34 patients on Clexane (8%), 4 patients on Dabigatran (1%), 26 patients on Rivaroxaban (6%). 137 patients did not use compression stocking while using the foot pumps.

The primary outcome measure of this study was the incidence of DVT and PE. Symptomatic DVT was detected in 7 patients (1.6%) (Table 2). All symptomatic DVTs occurred and were detected after discharge. One patient was diagnosed with DVT at day 6 postoperatively and the remaining six patients were diagnosed after day 10 postoperatively. Six of the 7 patients underwent TKR and received Aspirin as chemical prophylaxis. The patient who underwent THR, received prophylactic Clexane for four days as inpatient and then discharged home with oral aspirin. DVT was more frequent in the TKJR group compared to the THJR group but the difference is not statistically significant. All DVTs were detected in the operated extremity. Six DVTs involved distal deep veins and one was reported as muscular vein thrombosis (soleal vein). None of the DVT patient was clinically diagnosed with PE.

There were 5 PEs detected in this study (1.2%) (Table 2). Two patients underwent THR and 3 underwent TKR. Four patients were diagnosed after discharge and one as inpatient. There was no fatality from the symptomatic PEs. Three patients received prophylactic Clexane postoperatively and were given Rivaroxaban at discharge, while two of them were given only Aspirin. Therapeutic anti-coagulation was started after occurrence of PE. All patients recovered uneventfully within one month after occurrence of the embolism.

The secondary outcome measures were those related to adverse side-effects of venous thromboembolism prophylaxis. Measurements for secondary outcomes are depicted in Table 3. One patient who underwent TKR presented major wound bleeding causing a large haematoma that required operative evacuation and washout. The mean difference of swelling of thigh pre-versus postoperatively was only 22.8 mm (±3.5 mm).

4 Discussion

The primary aim of this prospective study including 424 consecutive patients was to establish the efficacy of Flowtron^® Universal foot pumps in preventing symptomatic DVT and PE following elective THJR and TKJR. Chemical prophylaxis, in particular with Low-molecular-weight heparin (LMWH) and oral anti-coagulant of the last generation like Rivaroxaban, has been shown to reduce the occurrence of deep vein thrombosis significantly.⁵ However untoward side effects including haemorrhagic complications and heparin induced thrombocytopenia (HIT) syndrome are frequent.^{2,3,8,12,14,17} The controversy between the Orthopaedic surgeons and Cardiopulmonary physicians is still ongoing.^1,5 Therefore, we adopted an individualised strategy with mechanical prophylaxis as main tool against DVT and PE.³ A-V Impulse foot pumps are effective and safe in THR.^11,13,15 After TKR, the effectiveness of foot-pumps is less certain, with some studies reporting a benefit, whereas other did not.^4,17,18

To our knowledge, this is the first prospective trial performed to establish efficacy and safety of the Flowtron^® foot pump system, a widely used device, but apparently not sufficiently validated in clinical settings. Symptomatic DVT was detected in 7 patients (1.6%). Five non-fatal pulmonary embolisms occurred (1.2%). This outcome is similar to findings reported in AV-Impulse foot pump pneumatic compression clinical trials.^13,15 The DVT incidence is lower in the present study than in a previous clinical trial carried out in the same institution using AV-Impulse foot pumps (20/800, 2.5%).¹¹ However, patient managed with the original AV-Impulse foot pumps had less non-fatal PE events (4/800, 0.5%).

The reduction of side effects with pneumatic compression with foot pumps has been regarded as a major advantage.^10,15 In this study only one patient presented a major wound bleeding episode (0.2%). The incidence of postoperative surgical site bleeding is higher in the present study (65/424, 15.3%) compared to a previous investigation (48/800, 6%).¹¹ However, no chemical prophylaxis was used in that study. The mean difference of swelling of thigh pre-versus postoperatively was only 22.8 mm. This confirms findings of other studies.^10,15

Compliance and tolerance has been reported to be problematic with the use of pneumatic compression systems.⁴ In a previous study, we reported a termination rate of 13.8% (16 of 116 patients).¹⁰ The main reason for discontinuation was sleep disturbance at night due to the noise produced by the device. Warwick et al reported a discontinuation rate of 3%.¹⁵ In the present study, the discontinuation rate was 7%.

The present study has some limitations. Firstly, the use of foot-pumps was not randomised. Secondly, additional chemical prophylaxis was used in the majority of patients. Undoubtedly, this factor influenced the outcomes of the study. Aspirin was the most commonly used prophylactic chemical in the study. Efficacy of aspirin for prevention of DVT after THR and TKR is unclear.^12,18 A large multicentre, randomised study showed that aspirin does not significantly affect the rate of DVT and PE after joint replacement procedures.¹² A randomized clinical trial showed that the prevalence of DVT after TKR was 27% in the group treated with pneumatic plantar compression and aspirin, compared with 59% in the patients managed with aspirin alone.¹⁷ Therefore, we assume that the low rate of DVT and limited side effects observed in the present study were mainly related to the use of the foot-pumps. In the present study, duplex ultrasonography screening of DVT was not performed in all patients. Only patients with symptoms suggesting postoperative DVT were investigated with serial duplex ultrasonography. This explains the low rates of DVT observed in our patients. We assume that a routine duplex ultrasonography would have detected a number of non-symptomatic venous thrombi, otherwise not identified with clinical examination.⁹ The incidence of asymptomatic DVT has been estimated to be more than 20% in patient undergoing THR and TKR.¹ Due to lack of justification, the AAOS guideline recommends against postoperative routine ultrasonography screening of DVT.⁷

In conclusion, this prospective study shows that management of patients with Flowtron^® foot-pumps in combination with an individualised chemical prophylaxis appears adequate in preventing DVT and PE after THR and TKR. The Flowtron^® foot pumps appear not inferior when compared to the original AV-Impulse system.

Conflicts of interest

All authors have none to declare.