• Mao Lin He, Zeng Ming Xiao, Ming Lei, Ting Song Li, Hao Wu, and Jun Liao.
• Division of Spinal Surgery, 1st Affiliated Hospital of Guangxi Medical University, 22 Shuangyong Road, Nanning, Guangxi, China, 530021.
• Cochrane Db Syst Rev. 2014 Jul 29; 2014 (7): CD008207CD008207.

BackgroundTotal knee arthroplasty (TKA) is a common form of orthopaedic surgery. Venous thromboembolism (VTE), which consists of deep venous thrombosis (DVT) and pulmonary embolism (PE), is a major and potentially fatal complication after TKA. The incidence of DVT after TKA is 40% to 80% and the incidence of PE is approximately 2%. It is generally agreed that thromboprophylaxis should be used in patients who undergo TKA. Both pharmacological and mechanical methods are used in the prevention of DVT. Pharmacological methods alter the blood coagulation profile and may increase the risk of bleeding complications. When pharmacological methods cannot be used the mechanical methods become crucial for VTE prophylaxis. Continuous passive motion (CPM) is provided through an external motorised device which enables a joint to move passively throughout a preset arc of motion. Despite the theoretical effectiveness and widespread use of CPM, there are still differing views on the effectiveness of CPM as prophylaxis against thrombosis after TKA. This is an update of the review first published in 2012.ObjectivesThe aim of this review was to determine the effectiveness of continuous passive motion (CPM) therapy for preventing venous thromboembolism (VTE) in patients after total knee arthroplasty (TKA).Search MethodsFor this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched February 2014), CENTRAL (2014, Issue 1), Ovid MEDLINE (to week 1 February 2014) and EMBASE (to Week 07 2014).Selection CriteriaRandomised controlled trials (RCTs) comparing the use of CPM with control in preventing DVT or PE after TKA. People aged 18 years and older who had undergone TKA were included in this review. We excluded studies of patients who presented with DVT at baseline. The experimental and control groups received similar postoperative care and therapy other than the CPM.Data Collection And AnalysisTwo review authors independently assessed the citations retrieved by the search strategies for reports of relevant RCTs. They independently selected trials that satisfied the inclusion criteria, extracted data and undertook quality assessment. Effects were estimated as risk ratios (RRs), mean differences or standardised mean differences with 95% confidence intervals (CIs). Meta-analyses were performed using a fixed-effect model for continuous variables. Where heterogeneity existed (determined by the I(2) statistic) a random-effects model was used.Main ResultsEleven RCTs involving 808 participants met the inclusion criteria. The methodological quality of the included studies was variable and most of the predefined outcomes were reported by only one or two studies, therefore the quality of the evidence was low. Five studies with a total of 405 patients reported the incidence of DVT. In the CPM group (205 patients) 36 developed DVT (18%) compared to 29 (15%) in the control group (200 patients). The results of the meta-analysis showed no evidence that CPM had any effect on preventing VTE after TKA (RR 1.22, 95% CI 0.84 to 1.79). One trial (150 participants) did not find PE in any of the patients during hospitalisation or in the subsequent three months. PE was not reported in the other included studies. None of the trials reported deaths among the included participants.Authors' ConclusionsThere is not enough evidence from the available RCTs to conclude that CPM reduces VTE after TKA. We cannot assess the effect of CPM on mortality because no such events occurred amongst the participants of these trials. The quality of the evidence was low. The results are supported by only a small number of studies, most of which are of low to moderate quality.

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