Orthopedic surgery aims to repair damaged joint structures and restore mobility and function. Recovery initially focuses on managing pain and protecting the surgical site while encouraging joint movement. The body’s natural response to trauma and surgery, however, often initiates inflammation, leading to stiffness and reduced range of motion. To counteract post-operative immobility, medical rehabilitation uses specialized devices. These tools allow the joint to begin moving gently and safely before the patient can actively move it themselves.
Defining Continuous Passive Motion
The rehabilitation device facilitating this early movement is known as Continuous Passive Motion (CPM). A CPM machine is an external, motorized device that cradles a limb, such as the leg or arm, moving the joint through a controlled, repetitive arc. This motion is purely “passive,” occurring without any muscular effort from the patient.
The machine’s settings are adjustable, allowing the medical team to precisely control the range of motion and speed. For instance, a setting might dictate movement from 0 degrees of extension to 60 degrees of flexion, using a slow cycle time. This precise, repetitive action provides early mobilization while protecting the surgical repair.
The concept was developed in the 1970s, based on the understanding that prolonged immobilization harms joint health and tissue healing. The medical application is regulated to ensure the movement remains within safe, non-stressful limits. The machine provides a continuous, gentle stimulus to the joint environment, encouraging a favorable biological healing response.
How CPM Promotes Healing
The therapeutic benefits of CPM stem from physiological mechanisms addressing post-surgical recovery challenges. A primary function is enhancing the circulation of synovial fluid within the joint capsule. Articular cartilage lacks blood vessels and relies entirely on this fluid for nutrition.
The CPM machine’s gentle, rhythmic compression acts like a pump, driving synovial fluid across the cartilage surface. This improved fluid exchange ensures that chondrocytes, the cells within the cartilage, receive nutrients and clear metabolic waste. This process is important immediately post-operatively when the patient cannot bear weight or move the joint actively.
Constant, controlled movement also prevents the formation of dense, restrictive scar tissue, known as arthrofibrosis. Immobility after surgery allows fibrin and proteins to rapidly form adhesions that limit movement. By providing early, gentle mechanical stress, CPM disrupts the initial cross-linking of collagen fibers, minimizing internal restrictions and promoting pliable tissue repair.
CPM also creates a favorable cellular environment by exerting an anti-inflammatory effect. The movement helps clear inflammatory mediators and particles from the joint space, which contribute to pain and tissue degradation. By reducing localized edema and hemarthrosis (bleeding into the joint), continuous motion reduces post-operative pain.
Common Clinical Applications
CPM machines are adapted for use across various major joints, though they are most frequently associated with knee procedures. The knee is the most common site, especially following total knee arthroplasty (total knee replacement surgery), articular cartilage defect repair, or ligament reconstructions. The knee’s predictable bending motion makes it highly amenable to this mechanical support.
In the upper body, CPM devices are employed following shoulder procedures, such as rotator cuff repair or surgical releases for adhesive capsulitis (frozen shoulder). The controlled passive movement protects delicate tendon repairs while preventing joint stiffness during the immediate healing phase. Shoulder CPM devices facilitate movement in multiple planes, including elevation and rotation, mimicking the shoulder’s complex range of motion.
Elbow CPM machines treat stiffness, particularly after surgical release of contractures or complex fracture fixation. The elbow protocol often involves a “stretch-and-hold” technique. Here, the joint is held at its maximum tolerated flexion and extension for several minutes before resuming the continuous cycle. This method maximizes the range of motion achieved during the first few weeks after the operation.
The hip and ankle joints also benefit from CPM in specific surgical contexts. After hip arthroscopy, a specialized hip CPM may be prescribed to prevent stiffness and manage swelling. Ankle CPM is used after complex ankle fracture fixation to improve dorsiflexion and plantar flexion, minimizing the long-term risk of post-traumatic osteoarthritis.
Patient Use and Safety Considerations
Patient use of a CPM machine involves following a strict, individualized protocol prescribed by the surgeon and physical therapist. Usage duration varies, but a common regimen involves using the device for four to eight hours daily, often split into multiple sessions or used while sleeping. CPM therapy generally lasts between two and six weeks post-surgery.
The range of motion and speed settings are carefully calibrated and should only be adjusted under healthcare professional guidance. Patients are instructed to gradually increase the range of motion by a few degrees daily, pushing to a point of light stretch rather than significant pain. If the machine causes increased pain, warmth, or swelling, the patient must immediately stop the device and contact their medical provider.
While CPM is a non-invasive treatment, its use is not appropriate in certain medical situations. Contraindications include unstable joint fractures or fixation, which passive motion could compromise. The device should also be avoided if there is an active joint infection, such as septic tenosynovitis, or if the patient has uncontrolled bleeding or a severe open wound near the surgical site.