Charlotte Brookes, Caroline Hing, William Roberts, Nelson Socorro, Andres Silberman.
Response/Recommendation: There is no conclusive evidence that continuous passive machine (CPM) reduces the risk of venous thromboembolism (VTE) following knee surgery. Three moderate quality studies demonstrate no difference in the risk of VTE in knee surgery with the use of continuous passive motion, with five low-quality studies showing a potential reduced risk of VTE.
Strength of Recommendation: Limited.
Rationale: VTE is a well-established complication of lower limb surgery. This is attributable to the nature of the lower limb surgery, which facilitates Virchow’s triad of venous stasis, endothelial damage, and hypercoagulability.
Since its invention in 1978, CPM has been used in total knee arthroplasty (TKA), septic arthritis, tendon repairs, and ligament reconstruction to improve range of motion and stimulate healing1. Studies have demonstrated that using CPM increases venous and lymphatic flow, thus reducing venous stasis and reducing risk for the development of VTE1,2.
Two moderate quality randomized-controlled trials (Goll et al.3, and Lynch et al.4), reported no statistically significant differences in the incidence of VTE following TKA with the use of CPM with concurrent aspirin (ASA) use, when compared to ASA alone.
Goll et al.3, evaluated the incidence of VTE and pulmonary embolism (PE) in 102 TKA patients via venography on day 12, and ventilation-perfusion (VQ) scanning on day 13. Their data demonstrated that 76% of venograms were positive for VTE in the control group, and 75% in the CPM group respectively. With regards to PE, 10 of the 50 patients in the control group and 8 of the 45 in the CPM group had positive VQ scans. Although no p-value was reported in this study, the authors have stated that there was no statistically significant difference in VTE outcomes between the groups.
Lynch et al.4, serially randomized 150 TKA patients treated with ASA, performing venography on day seven post-operatively. They reported positive venograms in 28 of the 75 patients in the control group, and 34 of the 75 in the CPM group, representing no statistically significant difference between the groups (although no p-value was reported).
A cohort study comprised of 103 patients by Ververeli et al.5, reported the incidence of PE as a secondary outcome in TKA patients on warfarin by the post-operative day seven. VQ scanning identified PE in two of the 52 control patients, and one of the 51 CPM patients. With regards to their reported VTE outcomes, this was low-quality evidence, and although suggestive of no statistical difference, the authors did not explicitly comment on this.
Contradicting the findings of the above studies, Fuchs et al.6, designed a randomized controlled trial (RCT) of 227 heparinized lower limb trauma patients allocated to control versus a method of ankle CPM. All patients were screened weekly with ultrasound and plethysmography. If suggestive of VTE, patients underwent venography for definitive diagnosis.
The data from Fuchs et al.6, demonstrated a statistically significant reduction in incidence of VTE in patients receiving CPM, recording 29% positive venograms in the control group, compared to 3.6% in the CPM group (p < 0.001). With regards to their data on knee surgery in particular (six patients total), one of three patients in the control group developed a deep venous thrombosis (DVT), with none reported in the CPM group. Although a high-quality study with a relatively large sample size of trauma patients, the small number of patients undergoing knee surgery limited the ability to make conclusions specific to VTE outcomes in this patient group.
In a cohort study of 40 TKA patients receiving ASA, Lynch et al.2, performed venography and VQ scanning on post-operative day five. In the control group, 50% had positive venograms and 30% had positive VQ scans. In the CPM group, 5% had positive venograms and none had a positive VQ scan. This represented a statistically significant difference in VTE incidence between groups in this low-quality study spanning 12-year, with p < 0.0007 for VTE and p < 0.0057 for PE respectively. This group had previously published7a very similar study with almost identical patient numbers, representing likely duplication of data.
Vince et al.8, analyzed 62 TKA patients using venography and VQ scans on post-operative days four and five, respectively. With regards to VTE, 75% of control patients had positive venograms compared to 45% of CPM patients. No PE were diagnosed in either group. However, it is not reported whether this difference is statistically significant, nor is it documented whether patients received any chemical VTE prophylaxis in this low-quality study.
A cohort study by Maloney et al.9, in 111 TKA patients receiving ASA reported four positive VQ scans in the control group (73 patients), compared to no positive scans in the CPM group (38 patients). Patients were only scanned if there was clinical suspicion of PE, representing high risk of selection bias. Moreover, the authors have not commented on whether their data was statistically significant.
In a low-quality cohort study by Wasilweski et al.10, 74 patients (91 TKAs) receiving ASA were screened for VTE on post-operative days three, six, eight, and twelve with phlebography and diagnosed using venography. PE was screened using clinical suspicion and diagnosed with VQ scanning. They reported five VTEs and one PE in the control group (44 TKA), compared to no VTE and one fatal PE in the CPM group (47 TKA). Although suggestive, it was not reported whether this difference was statistically significant. Moreover, there are discrepancies in their number of patients in the study, and confounding data as they included both knees in bilateral TKA patients. For these reasons, this is a low-quality study.
The vast majority of published articles on CPM identified in the literature search included VTE as a secondary outcome, and of these papers, only a small proportion11-14 actually report raw data (often grouped within ‘complications’). As a result, there is a high risk of bias of selectively reporting VTE, and most study designs preclude statistical analyses, thus rendering them low-quality evidence with respect to VTE outcomes.
In conclusion, the heterogeneity of the low to moderate quality evidence suggests there is no evidence that CPM reduces the incidence of VTE in knee surgery. Our recommendation is limited, as the current literature varies immensely in terms of chemical VTE prophylaxis used, methods for screening for VTE, as well as CPM prescription (hours per day and endpoints). Therefore, we recommend that additional research be undertaken to provide higher-quality evidence. Further, adequately powered RCT with larger sample sizes, standardized chemical VTE prophylaxis and CPM prescriptions, as well as VTE screening protocols pre- and post-operatively are necessary to answer the question.
We accept the risk of language bias in this systematic review, as studies not originally published in English were excluded.
References:
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