By Rick Hammesfahr, MD, and Mark T. Serafino, MS, PT
Continuous passive motion following total hip arthroplasty can be instrumental in alleviating pain, edema, stiffness, deep vein thrombosis, and dislocation, as well as in containing costs.

For all of the individuals who have had traumatic orthopedic surgery, it is probably safe to argue that the effects of the surgery on the soft tissue are more detrimental to patient progress and recovery than the issue resolved by the procedure itself.

Total joint arthroplasty is a perfect example. Replacement of the osteoarthritic joint components significantly reduces the patient’s joint pain and improves the likelihood of voluntary movement, but the trauma to the soft tissue and resultant immobility can cause long-lasting impairment and disability if not addressed immediately and appropriately. Continuous passive motion (CPM) is one of the primary methods for decreasing the deleterious effects of immobilization and can deliver orthopedic, neurological, and even circulatory benefits to the patient. Immobilization, in turn, can create deleterious sequelae of physiological and functional impairments.



Effects of Immobilization

The effects of immobilization vs early motion, including those on the circulatory, respiratory, and musculoskeletal systems, have long been studied and debated, as evidence exists that rest and motion have varied as the treatment of choice following surgery or injury for many centuries.1,2Orthostatic hypotension, pneumonia, and soft tissue contractures are several of the many detrimental effects of immobilization. Others include edema, stiffness, and pain at the affected site, many of which correlate to the structure and function of connective tissues (CT).

To better understand the effects of immobilization and the need for early motion, it is important to first examine the composition of connective tissue, which is found in nearly every structure in the body and performs a myriad of physiological functions. Several of these functions include mechanical support, movement, fluid transport, and control of metabolic processes, with the structure of the particular connective tissue lending heavily to the role it plays within the body.3

The two main fibrous components of CT are collagen and elastin, components best represented by the aligned fibers of ligaments and tendons, which together give connective tissue its strength and extensibility. They have a strong capability of resisting tensile forces and torsion.3,4

Proteoglycans and glycoproteins, the other two main components of CT, are found in varying abundance depending on the primary role of the connective tissue. Proteoglycans and glycoproteins have mechanical roles such as hydrating the connective tissue matrix, stabilizing the collagen fibers, and resisting compressive forces, such as in articular cartilage.3

With such important roles in a majority of the soft tissue structures in the body, it is vital that CT avoid degradation, such as that which occurs in osteoarthritis and osteoporosis, wherein a progressive destruction of the articular cartilage or bony connective tissue matrix occurs, respectively.3

Additionally, trauma can cause CT dysfunction, as is the case with the soft tissue damage associated with orthopedic surgery. Lying primarily in a parallel fashion,3 the structure and function of these fibers are greatly impacted by the healing process. Immobilized, these components will heal in a haphazard fashion, lying down in a variety of directions, causing a phenomenon known as cross-linking.1 This cross-linking can lead to adhesion formation in the soft tissues, stiffness, and the subsequent loss of passive and active motion in the patient.

Finally, immobilization has clear, detrimental effects on CT and the surrounding tissues, including shortening, decreased tensile strength, edema formation, venous stasis, and atrophy. All of these may lead to injury and impairments, such as tissue failure under normal loading, muscular weakness, decreases in range of motion (ROM), and synovial joint dysfunction2,4,5; conditions that inevitably produce dysfunction and/or disability in the individual.

With all of the negative effects of immobilization, an argument can be made for early motion following trauma or surgery. Some methods include active motion, passive ROM by a skilled therapist, and passive ROM by means of an external device or CPM.


Rest vs Motion

As stated earlier, passive motion following injury or surgery has long been the topic of controversy and debate. Early practitioners such as Hugh Owen Thomas vehemently opposed the use of passive motion; however, at the beginning of the 20th century, Championniere and others started a trend toward manipulation and mobilization.1 Through alternating periods of acceptance and rebuke, passive motion has become a commonly practiced therapeutic modality following trauma.

CPM, as was developed by Robert Salter, MD, evolved over the course of several decades, and is based on deductions that the inventor formulated through clinical observation and practice. The first of these is that prolonged immobilization of synovial joints causes many problems, including persistent stiffness and pain, muscle atrophy, disuse osteoporosis, and eventually degenerative arthritis when the joints are actively mobilized at a later time.2 Second, beneficial effects of early active motion were seen clinically, such as decreased edema, decreased pain, and shorter rehabilitation time.2

Finally, observations of cardiac surgery wherein the heart muscle heals properly in the presence of constant motion, and in the costovertebral joints, where constant motion occurs throughout the life of the individual, yet where degenerative arthritis is rarely seen, led the inventor to pursue CPM development.2

Salter hypothesized that CPM would accelerate the healing of articular cartilage and periarticular structures, such as the joint capsule, ligaments, and tendons.2 He also believed that CPM would decrease the likelihood of joint contractures, therefore maintaining the ROM achieved during surgery.

The textbook definition of CPM might state, “CPM is a postoperative therapeutic modality that passively (without patient effort) moves a synovial joint through a prescribed ROM for an extended period of time.”

Early CPM machines were primitive-looking devices, often composed of noisy motors, gears, pulleys, ropes, and bars. Functionally, they were designed to take a particular joint (initially the knee), through a specific and limited ROM in a predictable pattern. Though more advanced than their predecessors in design and function, modern CPM machines adhere to the same basic principles, and have been developed for almost every joint imaginable, including the hip.


Total Hip Arthroplasty

Total hip arthroplasty (THA), like many other joint replacements, is a complex procedure involving many soft tissue structures in addition to the primary bony targets.

Access to the hip joint takes the surgeon through cutaneous, musculoskeletal, and capsular structures, which are primarily composed of the iliofemoral, ischiofemoral, and pubofemoral ligaments.6

Postsurgically, many issues arise in relation to rehabilitation, patient safety, and cost-control in the managed care setting. Choosing the proper treatment modalities and methods can help address all of these issues.

With surgical trauma to the soft tissues, secondary complications from the THA are more likely to occur. Natural byproducts of the surgery include pain, stiffness, edema, and possible deep vein thrombosis in the surgical area. If not addressed properly, these effects of trauma, inflammation, and immobilization can become inhibitors to rehabilitation and patient function.7

Pain, a normal response to trauma, can often limit an individual’s ability to function, especially when due to the combination of site pain as well as the pain of muscle guarding. Active exercises initiated immediately after surgery can be exceptionally painful, while slow, controlled passive motion actually helps to alleviate pain through the gate control mechanism of pain control.2

Stiffness, as a result of connective tissue cross-linking and adhesions, may occur readily in a postsurgical patient. If not addressed, functional limitations in ROM, particularly seen in gait, may occur in patients. It has been shown that early motion following surgery can assist connective tissue to heal in an acceptable manner, resulting in the typical parallel arrangement of collagen and elastin fibers.2,7,8

A product of inflammation and healing, edema is a concern for many physicians and patients. Particularly with immobilization, edema has a tendency to pool in the tissues secondary to the lack of muscle pumping and venous flow. CPM has been shown to significantly increase venous flow over active and passive ankle dorsiflexion, pneumatic compression, and manual calf compressions.9

Finally, deep vein thrombosis is a concern in many postsurgical patients, especially the elderly. Due to the vascular stasis that occurs secondary to bed rest and the immobility of the limb, deep vein thrombosis is a common occurrence following hip surgery with an incidence rate ranging from 34% to 75% following lower extremity surgery.9

In correlating the beneficial effects of CPM on venous flow, there is a positive beneficial effect on the ability of CPM to decrease the effects of limb immobility and venous stasis, the primary causes of a deep vein thrombosis. As the CPM creates alternating muscular tension and then relaxation, it can assist the venous pump and keep fluids moving.

A serious complication following THA, hip dislocation occurs with loosening of the prosthetic components, laxity of the supporting soft tissue structures, and/or excessive hip motion in the directions of flexion, adduction, and internal rotation on the part of the patient or caregiver.11 If unknowledgeable caregivers or inconsistent methods of manual passive ROM and/or active ROM are utilized post-THA, the patient might be at risk for dislocation. Conversely, early motion can be controlled consistently and accurately with the use of CPM. As most CPM devices support the limb in neutral alignment and limit the ROM through which the joints can travel, it is a modality, if applied correctly, that can help to prevent issues of hip dislocation following THA.


CPM vs Manual ROM

In the world of modern medicine and managed care, cost is inevitably an issue when deciding on treatment modalities postsurgically. With shorter length of stays following surgery, patients returning home sooner need to have the byproducts of surgery, as discussed earlier, addressed promptly and efficiently. Again, options for ROM include active ROM, passive ROM by a physical therapist, and CPM. In a study by Worland et al, it was found that in a group of patients who underwent total knee arthroplasty and received only CPM upon discharge from the hospital (as opposed to professional physical therapy), the cost was $10,582, as opposed to $23,994 for the physical therapy treatment group, with no statistically significant difference in ROM achieved.12


Hip CPM Machines

Although the variety of devices designed truly for the hip is limited, there are several devices that accommodate the need for early motion following THA.

One such device, although applied to the knee, can take the patient’s hip through a substantial ROM keeping the lower extremity in a neutral alignment with respect to the frontal and transverse planes, thus avoiding the possibility of excessive motion and hip dislocation. Additionally, the application of the device to the knee and lower leg helps to avoid discomfort and possible irritation at the incision site over the hip.

Finally, this device can take the hip through a safe ROM within the limits of the precautions for flexion, adduction, and internal rotation.

Early motion following surgery can be a valuable treatment modality. Issues of pain, edema, stiffness, deep vein thrombosis, hip dislocation, and cost containment, as well as the myriad of functional impairments for the patient, can be addressed through sound medical practice and the use of valuable treatment modalities.

Applied appropriately, CPM machines can work for the benefit of the patient in decreasing the deleterious effects of immobilization, while providing a safe, comfortable treatment to the patient.



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  10. Colan BJ. Keep it moving: continuous passive motion has proven to be effective in facilitating the rehab process. Advance. 1997;9(46):2-3.
  11. Way LW. Current Surgical Diagnosis and Treatment. 10th ed. Norwalk, Conn: Appleton and Lange; 1994:1050-1051.
  12. Worland RL, Arredondo J, Angles F, Lopez-Jimenez F, Jessup DE. Home continuous passive motion machine versus professional physical therapy following total knee replacement. J Arthroplasty. 1998;13:784-787.

Rick Hammesfahr, MD, is an orthopedic surgeon at the Center for Orthopaedics & Sports Medicine, Marietta, Ga. Mark T. Serafino, MS, PT, practices privately in home care in Scottsdale, Ariz.

Reprinted with permission of ORTHOPEDIC TECHNOLOGY REVIEW - Vol 3, No 2, March/April, 2002.

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