Is a continuous passive motion (CPM) machine and a Cryo unit (active cold unit with mechanical pump) medically necessary for post-operative rehabilitation after a total knee arthroplasty (TKA)?

Medical Necessity Determination for CPM and Active Cryotherapy After Total Knee Arthroplasty

Neither continuous passive motion (CPM) machines nor active cold compression units (cryotherapy devices with mechanical pumps) are medically necessary for post-operative rehabilitation after total knee arthroplasty, as both interventions have been demonstrated to provide no clinically meaningful improvement in patient outcomes.

Continuous Passive Motion (CPM) - Not Recommended

Guideline Evidence Against CPM

The American Academy of Orthopaedic Surgeons provides strong evidence that CPM after knee arthroplasty does not improve outcomes (strength of recommendation: Limited, based on strong evidence). 1

The AAOS guideline explicitly states that CPM should not be used because it fails to improve pain, function, range of motion, or quality of life. 1

Supporting Research Findings

• A comprehensive Cochrane systematic review of 24 randomized controlled trials (1,445 participants) found that CPM provides no clinically important benefits: 2

  • Active knee flexion improved by only 2 degrees (95% CI 0-5°), which is not clinically meaningful 2
  • Pain reduction was minimal at 0.4 points on a 10-point scale (95% CI -0.8 to 0.1) 2
  • Function decreased by 1.6 points on a 100-point scale (95% CI -6.1 to 2.0) 2
  • Quality of life improved by only 1 point on a 100-point scale (95% CI -3 to 4) 2

• CPM increases adverse effects including higher analgesic requirements and significantly increased blood loss (1,558 ml vs 956 ml without CPM, p=0.005) 3

Clinical Context

While some older meta-analyses showed statistically significant improvements in short-term active knee flexion and reduced hospital stay 4, 5, these benefits are not clinically meaningful and do not justify the expense, inconvenience, and increased adverse effects of CPM. 2, 3

Active Cryotherapy Devices (Cryo Units) - Not Recommended

Guideline Evidence Against Active Cryotherapy

The American Academy of Orthopaedic Surgeons provides moderate evidence that cryotherapy devices after knee arthroplasty do not improve outcomes (strength of recommendation: Moderate). 1

This recommendation specifically addresses active cold compression units with mechanical pumps and portable refrigerators, which is exactly what the Kinex ThermoComp system represents. 1

Insurance Coverage Determination

The member's certificate of coverage explicitly excludes experimental, investigational, or unproven services, and Aetna's policy specifically lists active cold units with mechanical pumps (including the types mentioned in this request) as experimental and investigational because they have not been proven to offer clinically significant benefits over passive cold compression therapy. [@Question Context@]

Recommended Alternative Interventions

Evidence-Based Rehabilitation Strategies

Instead of CPM and active cryotherapy devices, the following interventions have strong evidence for improving outcomes after TKA:

• Early mobilization starting on the day of surgery reduces hospital length of stay and improves pain and function (strength of recommendation: Strong) 1

• Supervised exercise program during the first 2 months after TKA improves physical function (strength of recommendation: Moderate for function; Limited for pain) 1

• Simple cryotherapy (ice packs) in the first postoperative week for pain control is appropriate and cost-effective 6, 7

Common Pitfalls to Avoid

• Do not confuse statistical significance with clinical significance: Some studies show statistically significant improvements with CPM, but the magnitude of benefit (2 degrees of flexion) is not clinically meaningful 2

• Do not assume newer technology is better: Active cryotherapy devices with mechanical pumps have not demonstrated superiority over simple ice application despite higher cost 1

• Do not delay early mobilization: Waiting to start rehabilitation while relying on passive modalities like CPM can lead to worse outcomes 1, 6

Authorization Recommendation

Both the CPM machine (Kinex CONNECT) and the active cryotherapy unit (Kinex ThermoComp) should be denied as they do not meet medical necessity criteria. 1, 2 The member should be directed toward evidence-based rehabilitation including early mobilization, supervised physical therapy, and simple ice application for pain control. 1, 6