6.4 Mechanical Modalities: Traction, CPM, Compression Pumps
Key Takeaways
- Mechanical lumbar traction at roughly 50% of body weight is needed to separate vertebrae; about 25-30% of body weight is enough for muscle relaxation and soft-tissue stretch without significant joint separation.
- Cervical traction typically begins at 7-15 lb (about 7-10% of body weight) and progresses to 20-30 lb (up to 20-25% of body weight) at 20-30 degrees of neck flexion to open the posterior intervertebral foramen.
- Continuous Passive Motion (CPM) after Total Knee Arthroplasty (TKA) usually starts at about 0-30 degrees of knee flexion and progresses 5-10 degrees per session as tolerated, two or more hours daily, within the PT's plan of care.
- Sequential (multi-chamber) pneumatic compression generally outperforms single-chamber pumps for lymphedema because each cell inflates distally first and milks fluid proximally; pressures are usually 30-60 mmHg and never exceed diastolic blood pressure.
- Mechanical modalities share several contraindications: malignancy in the field, deep vein thrombosis, active infection, unstable fracture, uncontrolled hypertension or congestive heart failure (compression), and acute fracture or spinal instability (traction).
Mechanical Modalities
Spinal Traction
Spinal traction applies a distractive force along the spinal axis to separate vertebrae, open intervertebral foramen, unload discs, and reduce muscle guarding. Mechanical traction can be continuous, sustained, intermittent, or manual. Intermittent traction (alternating hold and rest periods) is generally better tolerated for joint and disc goals; sustained traction is used for short durations at higher loads.
Lumbar traction
| Goal | Force as % body weight | Notes |
|---|---|---|
| Muscle relaxation, soft-tissue stretch | 25-30% | Lower threshold; comfortable |
| Joint distraction (vertebral separation) | ~50% | Minimum needed to actually separate lumbar vertebrae |
| Disc problem with radiculopathy | 50%+ (often around 50%) | Higher loads, sustained or long-hold intermittent |
A split table or friction-reduction surface is required so the lower body slides freely with the pull; without it, much of the force is lost to friction. Treatment time is usually 10-20 minutes. Patient position is supine with hips and knees flexed (90/90 position) to favor the posterior structures, or prone for the anterior elements.
Cervical traction
| Goal | Typical force | Neck angle |
|---|---|---|
| Soft-tissue stretch, muscle relaxation | 7-10 lb (or ~7-10% body weight) | 0-15 degrees flexion |
| Posterior intervertebral foramen opening | 20-30 lb (or up to 20-25% body weight) | 20-30 degrees flexion |
Cervical traction is generally performed in supine with a halter or head harness rather than seated, both for comfort and to relax the cervical musculature. Greater flexion angles open the posterior foramina; a near-neutral pull stretches the anterior structures.
Indications and contraindications for traction
| Indications | Contraindications |
|---|---|
| Disc herniation with radiculopathy | Acute injury or strain |
| Spinal nerve root impingement | Spinal instability (e.g., rheumatoid cervical spine, Down syndrome instability) |
| Subacute joint hypomobility | Vertebrobasilar insufficiency (especially cervical) |
| Muscle guarding around the spine | Spinal cord compression with myelopathy |
| Subacute facet joint pathology | Acute fracture, malignancy, or infection in the spine |
| Discogenic pain | Uncontrolled hypertension, pregnancy (lumbar) |
Continuous Passive Motion (CPM)
A Continuous Passive Motion (CPM) machine moves a joint through a prescribed range without active muscle contraction. The most common use is after Total Knee Arthroplasty (TKA), but CPM is also used after some shoulder, elbow, hip, and ankle procedures. The goals are to maintain range of motion, reduce adhesions, and nourish articular cartilage early after surgery.
| Day | Range | Speed and time |
|---|---|---|
| Day 0-1 | 0-30 degrees to 0-45 degrees | 1 cycle/min, 2-4 hours/day in 1-2 hour blocks |
| Day 2-3 | Progress by 5-10 degrees per session as tolerated | Continue 2-4 hours/day |
| Discharge target | Often 90 degrees or more of knee flexion | Hospital protocols vary; follow the POC |
The PTA verifies machine settings against the POC, aligns the knee joint with the machine axis, checks for excessive pain, neurovascular compromise, or skin breakdown at pressure points, and adjusts range and speed within the documented parameters. Evidence is mixed on whether CPM changes long-term function, but it remains common in early post-operative care.
Contraindications: unstable fracture or fixation, uncontrolled bleeding, active joint infection, and inability to tolerate the device safely.
Pneumatic (Intermittent) Compression
Pneumatic compression pumps fit over the limb in a sleeve with one or more chambers that inflate to a set pressure. Common goals are reducing lymphedema, managing chronic venous insufficiency, preventing deep vein thrombosis (DVT) in selected post-surgical patients, and shaping a residual limb before prosthetic fitting.
| Pump type | How it works | Best for |
|---|---|---|
| Single chamber | One bladder inflates and deflates | Mild dependent edema |
| Sequential (multi-chamber) | Distal cells inflate first, then proximal, in a milking pattern | Lymphedema, more severe edema |
| Sequential with gradient | Each chamber inflates to a lower pressure moving proximally | Refractory lymphedema, chronic venous disease |
General parameters:
- Pressure: 30-60 mmHg for upper-extremity lymphedema; 40-80 mmHg for the lower extremity. Never exceed diastolic blood pressure to avoid arterial compromise.
- Inflation/deflation ratio: about 3:1 (e.g., 90 seconds on / 30 seconds off) is common; protocols vary.
- Duration: 30 minutes to several hours depending on the goal.
Contraindications: acute deep vein thrombosis, acute pulmonary edema, uncompensated congestive heart failure, acute infection or cellulitis in the limb, untreated malignancy in the limb, severe peripheral arterial disease, and unstable fracture in the area.
The PTA elevates the limb during treatment, takes baseline and post-treatment girth measurements, monitors distal pulses and skin color, and removes the device immediately for new pain, numbness, or color change.
Tilt Table and Standing Frames
Though not always grouped with mechanical agents, the tilt table is a mechanical device the PTA operates within the POC to address orthostatic hypotension, weight-bearing through long bones, and standing tolerance after prolonged bed rest or spinal cord injury. Progression is gradual, often in 10-15 degree increments, while the PTA monitors blood pressure, heart rate, and symptoms of lightheadedness, pallor, or nausea. If systolic pressure drops sharply or the patient reports dizziness, the PTA lowers the table and reassesses. An abdominal binder and lower-extremity compression help limit venous pooling during early sessions.
Putting Parameters Together
Mechanical modalities share a common workflow for the PTA: confirm the order and parameters against the POC, screen for the contraindications listed above, position and secure the patient, set conservative starting values, then monitor and progress within the documented range. The PTA never initiates a new mechanical modality for an unlisted problem, never exceeds the PT's parameter limits, and reports both adverse responses and a lack of expected progress so the PT can revise the plan.
A 165 lb patient with a sub-acute L5 disc herniation and radiculopathy is set up for mechanical lumbar traction in supine with hips and knees flexed. The PTA's goal, per the plan of care, is true vertebral separation. Which traction force is most appropriate?
A PTA is asked to set up a sequential pneumatic compression pump for a patient with chronic right upper-extremity lymphedema after axillary lymph node dissection. Which finding requires the PTA to STOP and contact the supervising PT before applying the pump?
On post-operative day 2 after a right Total Knee Arthroplasty (TKA), the supervising PT's plan of care directs the PTA to set up Continuous Passive Motion (CPM) with progression as tolerated. Which initial parameter set best matches typical protocols?