Passive Range of Motion

Passive ROM is motion of a joint that is performed without muscle contraction within the available ROM, using an external force to move the joint. In animals, passive ROM is performed by the therapist. Additional force applied at the end of the available ROM is defined as stretching. Passive ROM and stretching can be performed in conjunction with each other to help maintain and improve joint ROM.

The benefits of continuous passive ROM immediately after joint surgery were initially described by Salter and colleagues³ and include decreased pain and improved rate of recovery. The scar tissue deposited after an injury or surgery is laid down in a random fashion, and ROM helps this scar tissue to align along the lines of stress that the tissue normally undergoes. This results in a stronger scar and may help prevent future injury. However, it is critical that the therapist maintain a ROM that is comfortable to the patient and not injure tissues by exceeding their limits.

Tissues limiting passive ROM may be normal or pathologic and include the joint capsule, periarticular soft tissues, muscles, ligaments, tendons, skin, and scar tissue. For example, open wounds over joints that are allowed to heal secondarily by contraction and epithelialization may result in limitations to passive ROM. Surgical incisions may result in adhesions and fibrosis between skin, subcutaneous tissues, fascia, muscles, and bone, limiting the ability of tissues to glide over one another. Musculotendinous tissue may also be relatively shortened as a result of spasm or contracture. Any restriction of motion may result in resistance to joint movement and pain.

Passive ROM is used whenever a patient is unable to move joints on its own, or if active motion across a joint may be deleterious to the patient, such as with a tenuous articular fracture repair. Passive ROM is sometimes used to help relax an anxious patient. The most common indications for passive ROM exercises are immediately after surgery (before active weight bearing) to help prevent joint contracture and soft tissue adaptive shortening, maintain mobility between soft tissue layers, reduce pain, enhance blood and lymphatic flow, and improve synovial fluid production and diffusion.²

Another indication for passive ROM is the prevention of joint contracture during healing and recovery in paralyzed patients. Ideally, exercises should be performed two to six times per day to help maintain normal joint mobility. However, if the patient does not regain functional neuromuscular control (active motion), it is likely that joints will undergo some degree of contracture despite aggressive efforts. Although passive ROM may help slow muscle atrophy, it will not prevent muscle atrophy, increase strength, improve endurance, or be as effective in improving vascular and lymphatic flow as active ROM techniques.

Proper technique for performing passive ROM is important. The patient should be relaxed and comfortable. If active muscle contraction is not desired, it is especially important to be gentle and not create pain or discomfort. The bones proximal and distal to the joint should be supported to avoid excessive varus and valgus stresses on the joint. The therapist should gently hold the limb and avoid painful areas, such as incisions and wounds. The location of the therapist’s hands on the limb is also important; the closer the hands are to the joint, the less torque will be produced at the joint. This may decrease pain and the risk of patient injury. The motion should be smooth, slow, and steady with motion generally occurring by moving the distal limb with the proximal limb held steady. The patient should be continually monitored for any discomfort, and the technique altered if necessary to enhance comfort.

Active Assisted Range of Motion

Active assisted ROM occurs when the therapist guides joint motion and the patient’s muscle activity assists joint motion to some degree. In animal patients, the amount of muscle activity provided by the patient is difficult to control. In reality, because it is difficult to avoid muscle activation in patients that are not paralyzed, most ROM exercises in small animal patients involve a degree of active assisted ROM. In anxious patients or in those with upper motor neuron conditions, muscle contraction of antagonist muscle groups may oppose joint ROM exercises.

Active assisted ROM exercises are most useful for those patients that are weak or recovering from lower motor neuron conditions. In addition to assisted ROM with the patient in lateral recumbency, exercises may be performed with the patient supported by a sling, with the therapist assisting limb movement and joint ROM during ambulation. This may be performed while the patient is slowly walked over ground, on a ground treadmill, or on an underwater treadmill. Another form of active assisted ROM exercise is performed while swimming. Patients with limited ability to ambulate on the ground may benefit from controlled swimming, during which the therapist assists movement of the animal’s limbs and joints while in the water with the patient. The buoyancy of the water helps to support the weight of the limbs while the therapist concentrates on assisting the limb through a normal cycle of movement.

Active assisted ROM helps to combat the negative effects of immobilization on limbs, similar to those achieved with passive ROM. Some degree of active muscle contraction allows muscle strengthening and strengthening of bone at muscle origin and insertion sites. In addition, some neuromuscular reeducation, and proprioceptive and gait training may be achieved.

Active Range of Motion

Active ROM is the motion of a joint that may be achieved by active muscle contraction. In addition to increasing strength, coordination between muscle groups is necessary because the guidance of assisting the patient through ROM is no longer provided. The active ROM may be performed during a regular gait cycle, in which the excursion of joint motion is relatively limited, or under special conditions designed to expand motion and encourage more complete use of the full available ROM. Examples of these activities include swimming; walking in water, tall grass, snow, or sand; climbing stairs; crawling through a tunnel; and negotiating cavaletti rails.

As the patient improves ROM of a joint, it is helpful to continue to perform passive ROM and stretching to achieve as complete ROM as possible, and then perform active ROM through this increased motion to emphasize more complete use of the limb. Greater strength is required for patients to perform active ROM, and some of the special conditions require more muscle strength than normal ambulation during walking or trotting. Therefore for those exercises, a transition between active assisted and active ROM may be necessary. Active ROM exercises may be a prelude to other strengthening activities. Owners may also be involved with active ROM exercises in helping with a home care program for their pet.

Precautions and Contraindications to Range of Motion

All forms of ROM exercises are contraindicated when motion may result in further injury or instability. Such examples include unstable fractures near joints and unstable ligament or tendon injuries. Communication between the surgeon and therapist is critical to be certain that appropriate ROM exercises are performed and that the limits of the range are not exceeded, which may result in damage to the tissues. In most cases, early passive ROM is felt to be beneficial if the therapist stays within a ROM that is reasonable for the patient and condition being treated. In addition, the therapist should perform the exercises at a reasonable speed that is not painful for the patient.

Range of Motion Studies

In some canine conditions, active ROM is a prerequisite to a successful outcome. For example, it is critical that puppies with distal femoral physeal fractures have early passive and active ROM exercises to avoid fracture disease and tiedown of the quadriceps muscle group.⁴ Similarly, dogs with condylar fractures of the distal humerus must begin active ROM to prevent permanent joint stiffness.

In one study of dogs following surgery for cranial cruciate ligament rupture, patients not receiving early passive and active ROM exercises had reduced stifle extension (Figure 25-1).⁵ This loss of motion appeared to be permanent in some dogs if extension was not achieved within 2 weeks. In contrast, those dogs receiving appropriate rehabilitation had return of near-normal stifle extension. There also appears to be an association of stifle extension with weight bearing, with improved weight bearing in dogs with near-normal stifle extension (Figure 25-2). However, the cause and effect of this relationship are unknown.

The association of stifle ROM with function following surgery for cranial cruciate ligament disease in clinical patients has been further evaluated.⁶ In 412 dogs treated with tibial plateau leveling osteotomy (TPLO) for treatment of cranial cruciate ligament rupture, dogs were determined to have no loss of extension or flexion (n = 322), less than 10 degrees loss of extension or flexion (n = 78), or 10 degrees or more loss of extension or flexion (n = 12). Loss of extension or flexion greater than 10 degrees was associated with significantly greater lameness in comparison with no loss, or loss of extension or flexion less than 10 degrees. In addition, osteoarthritis of the stifle joint was significantly correlated with loss of extension, and loss of extension greater than 10 degrees was less tolerable and less amenable to physical rehabilitation than flexion loss. The authors concluded that loss of extension or flexion should be assessed in dogs with persistent lameness after TPLO so that early intervention can occur.

An explanation for the restricted ROM in clinical cases may include physical restrictions, such as joint capsule fibrosis, soft tissue approximation, or bony impingement that may occur with osteophytes as a result of joint disease. Another possible explanation is an increase in intraarticular pressure with joint motion, resulting in stretch of the joint capsule and creation of pain. One study evaluated the intraarticular pressure and volume relationships in the knee joint of dogs.⁷ In general, infusion of fluid into the joint did not result in intraarticular pressure changes between 125-110 degrees of stifle motion. However, increasing flexion from 110 to 50 degrees resulted in an increase in pressure, which was greater with increased intraarticular volume. Increasing the intraarticular volume also resulted in decreased total ROM of the joint.

The functional and structural consequences of remobilization of the shoulder joint after 12 weeks of immobilization were studied in 10 beagle dogs.⁸ It was found that after 12 weeks of immobilization, the passive ROM was markedly impaired, intraarticular pressure increased during movement, and the filling volume of the joint cavity was reduced. On histologic examination, the capsule showed hyperplasia of the synovial lining and vascular proliferation in the wall, but there was no increase of collagen in the capsular wall. Both the functional and structural changes were unaltered after 4 weeks of remobilization, but after 8 weeks they began to reverse, and they returned to normal after 12 weeks, indicating that functional and structural changes after immobilization of an uninjured shoulder joint are potentially reversible. The timing and degree of improvement may not be similar in patients with pathologic injury to the shoulder.

Another study of dogs evaluated the effects of joint mobilization treatment on carpal joints of dogs.⁹ The right carpal joints of 12 dogs were immobilized for 6 weeks, which resulted in joint hypomobility. The treated group received mobilization therapy daily for 4 weeks following the immobilization period. In control and treated groups, passive ROM, peak angles of extension and flexion of the carpal joint, and the amount of time required in the gait cycle to reach these peak points were evaluated cinematographically during gait before immobilization and once weekly for 4 weeks after immobilization. The treated group had improved passive ROM and motion during gait.

Continuous passive ROM has been assessed in several studies to evaluate its use in the management of cartilage defects. Salter and colleagues¹⁰ demonstrated that young rabbits with a full-thickness defect in the articular cartilage managed with continuous passive motion had healing of 52% of the defects with hyaline-type cartilage. Similar results were obtained in adult rabbits, in which 44% of the defects were repaired with hyaline cartilage. Passive motion may also help to reduce cartilage destruction following infection of a joint.^11,12 The optimal daily dose of passive ROM and the total duration of treatment are unknown. However, one study of rabbits found that at least 8 hours of passive motion per day was necessary to achieve the level of healing obtained by Salter.¹³ The effect of active motion on cartilage healing is unknown in animals because of the difficulty in achieving consistent limb use after cartilage injury.

Continuous passive motion has also been recommended to prevent contracture of periarticular tissues and to restore joint function. Immobilization results in shortening of fibrous tissues and loss of motion, depending on the position of immobilization. There is a loss of collagen mass after immobilization, and there is collagen cross-linking of periarticular connective tissues, which may lead to increased stiffness. Passive motion may reduce these changes and prevent joint stiffness. In one study, 16 hours or more of continuous motion prevented increased joint stiffness following articular cartilage damage.¹⁴ Longer durations of passive motion may be necessary to help maintain normal quantities and turnover of collagen and glycosaminoglycans (GAGs), as well as to help maintain the normal alignment of collagen fibers and prevent shortening and cross-linking.

It has been suggested that continuous passive ROM may be somewhat antiinflammatory in patients with inflammatory joint disease. In one study, the effects of continuous passive ROM on early inflammatory events were evaluated in meniscal fibrocartilage of rabbits with antigen-induced arthritis.¹⁵ Rabbit knees injected with bovine serum albumin and Freund’s complete adjuvant were treated with 24 or 48 hours of continuous passive ROM or were immobilized. Within 24 hours, immobilized knees had marked degradation of GAGs in meniscal fibrocartilage. Inflammatory mediators, including matrix metalloproteinase 1, cyclooxygenase 2, and interleukin (IL) 1b, increased within 24 hours and continued to increase. Knees undergoing continuous passive ROM had reduced GAG degradation and inflammatory mediators during treatment, and increased synthesis of the antiinflammatory cytokine IL-10. These results suggest that continuous passive ROM suppresses the deleterious effects of inflammatory arthritis more than immobilization and provide information regarding the involved molecular events.

The duration of daily passive motion treatment has varying effects. For example, relatively short daily passive motion may reduce stiffness immediately after treatment, but there may be greater long-term stiffness.¹⁴ In fact, shorter durations of passive motion may be detrimental.^14,16 One study indicated more stiffness with 10 to 30 minutes of passive motion per day than if the joints were immobilized,¹⁴ whereas another indicated increased stiffness with less than 8 hours of daily passive motion.¹⁶ Although somewhat surprising, these results suggest that there may be increased trauma associated with breakdown of soft adhesions that form when motion is not occurring, and that very frequent motion is necessary to keep the tissues mobile.

Both continuous motion and as little as 4 hours of daily passive motion help to preserve muscle mass in rabbits.14,17 In fact, 5% to 15% greater limb muscle mass may occur in rabbits with passive motion as compared with those that are immobilized.

The effects of passive motion on bone loss are less clear. It is well documented that immobilization results in a decrease in bone mineral content; however, 16 or 24 hours of passive motion resulted in the loss of greater bone mineral than immobilization.¹⁴ It was suggested by these authors that the increased joint stiffness that resulted from less than 16 hours of motion may have increased the bending stresses and load on the bones, whereas greater duration of passive motion maintained normal joint stiffness and prevented the additional loading on the bones.

In people, the use of active and passive knee motion in the immediate postoperative period and a treatment plan for early postoperative limitations in knee motion has proven highly effective in restoring motion after anterior cruciate ligament reconstruction.¹⁸ In one study of 207 knees, 91% regained full ROM. The remaining patients did not regain motion as rapidly and were placed in an early postoperative phased treatment program of serial extension casts, early gentle manipulation under anesthesia, or arthroscopic treatment of intraarticular adhesions and scar tissue. Most of these patients regained full ROM. Those patients who failed to follow the rehabilitation program had permanent and significant limitation of motion. The incidence of postoperative motion problems was related to the extent of the surgical procedure. Patients who had more extensive surgery, such as a concurrent meniscus repair or a medial collateral ligament repair, had a higher incidence of restricted motion.