Importance of the Topic

Total knee arthroplasty (TKA) effectively reduces pain and improves function in most patients. It is also one of the most commonly performed orthopaedic procedures [7]; one projection suggests that in the United States alone, more than 1.3 million TKAs will be performed per year by 2020 [12]. However, knee stiffness complicates approximately 1.3% of TKAs, severely limiting patients’ function [11], reducing quality of life, and resulting in early revision [13].

Continuous Passive Motion (CPM) refers to the use of a motorized device that is applied to a patient’s lower extremity, and continuously moves the patient’s knee through a predefined arc of motion [8]. This device is typically used during the immediate postoperative period, and it has been theorized that early passive range-of-motion (ROM) can prevent the formation of adhesions that cause joint stiffness [15]. However, the cost of CPM devices can be high, and the efficacy of CPM is uncertain. This Cochrane systematic review and meta-analysis evaluated the efficacy of CPM in patients undergoing primary TKA [8]. Based on evidence from 24 randomized trials (pooled n = 1445), the authors concluded that there is very little advantage of using CPM after TKA.

Upon Closer Inspection

This review used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to rate confidence in the pooled outcomes. The highest rating given was “moderate” confidence for three outcomes: Active knee flexion at 6 weeks (10 studies); function at 6 months (six studies); and quality of life at 6 months (two studies). For each of these outcomes, no significant differences were detected between the CPM and control groups.

While CPM was shown to be advantageous in reducing the proportion of patients undergoing manipulation under anesthesia at 6 weeks followup (the only endpoint for which CPM was found to be effective), this finding received a GRADE confidence rating of “very low” due to imprecision of the pooled effect estimate, lack of blinding in trials reporting this outcome, and high level of heterogeneity among trials. Another possible explanation for this finding is changes in practice patterns over time. None of the trials published after the year 2000 favored CPM as an effective means to reduce the likelihood a patient will undergo manipulation under anesthesia, so it is possible that newer rehabilitation protocols or changing surgeon preferences pertaining to manipulation under anesthesia could have nullified the effects demonstrated in earlier trials [6, 14].

Take-Home Messages

The conclusions of this Cochrane review are consistent with previous systematic reviews [4], as well as recent recommendations of the American Physical Therapy Association to avoid use of CPM following TKA [1]. Two recently published randomized trials [3, 9] that were not included in this review have corroborated these conclusions as well, demonstrating no benefit for CPM over conventional physiotherapy. However, a poll taken at the American Association of Hip and Knee Surgeons annual meeting in 2009 demonstrated that the majority of orthopaedic surgeons (58%) used CPM following TKA [2], and no official recommendations pertaining to CPM have yet been made by any major American orthopaedic organization. Given its lack of efficacy as demonstrated in this Cochrane review, clinicians should consider discontinuing the routine use of CPM as an adjunct to standard physiotherapy following uncomplicated primary TKA and orthopaedic surgery clinical practice guidelines should consider incorporating this evidence into their recommendations.

Importantly, trials within this review predominantly included cases of uncomplicated primary TKA. Thus, the results of this review do not necessarily apply to other procedures of the knee, including revision TKAs, or to cases with unique considerations where clinical judgment is still important. For instance, some surgeons believe CPM is important after manipulation under anesthesia given the high risk for recurrence of joint adhesions and stiffness [5, 10]. Further research is required to determine whether there are specific indications where CPM may be beneficial following TKA.