Therapeutic Modalities, Equipment and Devices

Modalities, devices and equipment are where physics meets the patient: a setting that is too intense burns skin, a cane on the wrong side worsens a limp, and a prosthetic socket that is a few millimeters off produces a gait deviation the exam expects you to trace to its cause. Questions in this area are highly predictable because they test parameters, indications, contraindications and fitting rules. This chapter organizes those numbers and the reasoning behind them so you can choose the safest effective option for each patient.

Section 1Thermal agents and ultrasound

How heat moves

Heat transfers by four mechanisms. Conduction is transfer by direct contact between two materials at different temperatures (hot packs, paraffin, ice packs). Convection is transfer by a moving medium (whirlpool, fluidized therapy with heated cellulose particles). Radiation is transfer of electromagnetic energy without a medium (infrared lamps). Conversion changes another form of energy into heat within the tissue (ultrasound, diathermy). The amount of heating depends on the temperature difference, the duration of contact, the area treated and the thermal conductivity of the tissue. Fat is a poor conductor and insulates deeper tissue, so superficial agents heat only about 1 to 2 cm deep and mostly heat skin and subcutaneous tissue.

Superficial heat

Physiologic effects of heat include vasodilation and increased blood flow, increased metabolic rate (about 2 to 3 times for each 10 °C rise), increased nerve conduction velocity, reduced pain through the gate mechanism and reduced muscle guarding, and increased collagen extensibility when tissue is heated and then stretched. Heat is used for subacute and chronic pain, muscle guarding, joint stiffness and before stretching or mobilization.

Contraindications to heat: acute injury or inflammation, recent or potential hemorrhage, thrombophlebitis or DVT, malignancy in the area, impaired sensation or impaired mentation (cannot report burning), impaired circulation (tissue cannot dissipate heat), over the eyes, and over areas recently treated with topical counterirritants. Precautions: pregnancy (avoid raising core temperature, avoid heat over the abdomen and low back), cardiac insufficiency, edema, open wounds, metal in the area and poor thermal regulation in very young or very old patients.

Cryotherapy

Cold causes immediate vasoconstriction, slows metabolism and nerve conduction velocity, raises the pain threshold, reduces muscle spindle activity (temporarily reducing spasticity and spasm) and limits secondary hypoxic injury after acute trauma. Patients typically feel a predictable sequence: cold, burning or aching, then numbness; numbness usually arrives in about 5 to 10 minutes. Cold packs and ice packs are applied for about 10 to 20 minutes; ice massage for about 5 to 10 minutes over a small area; cold whirlpool water at about 0 to 27 °C (32 to 80 °F); vapocoolant spray is used with stretch for trigger points. A brief reflex vasodilation can follow prolonged intense cold (the hunting response), but its clinical importance is debated. Cold is used for acute injury, pain, edema control as part of rest, compression and elevation, postoperative pain, and temporary reduction of spasticity before functional training.

Contraindications to cold: cold hypersensitivity (cold urticaria), cryoglobulinemia, paroxysmal cold hemoglobinuria, Raynaud phenomenon, over regenerating peripheral nerves, over areas of compromised circulation or peripheral vascular disease. Precautions: over superficial nerves (the common fibular nerve at the fibular head and the ulnar nerve at the elbow can develop a cold induced palsy), hypertension (cold can raise blood pressure), impaired sensation or cognition, open wounds, and the very young or old.

Therapeutic ultrasound

Therapeutic ultrasound uses a piezoelectric crystal that vibrates at high frequency (the reverse piezoelectric effect) to produce acoustic waves that are absorbed in tissue and converted to heat. Absorption is highest in tissues with high collagen content (tendon, ligament, joint capsule, fascia) and lowest in fat, which makes ultrasound well suited to heating dense connective tissue. A coupling medium (gel or water) is required because air reflects nearly all ultrasound. Large reflections at bone and metal interfaces create "hot spots," including periosteal pain if intensity is too high.

Tissue temperature goals are described as mild (about 1 °C, increases metabolism and healing), moderate (about 2 to 3 °C, reduces pain and muscle spasm) and vigorous (about 3 to 4 °C, increases extensibility of collagen for stretching). Stretch during or immediately after vigorous heating, because the window of increased extensibility is short. Nonthermal effects (cavitation and acoustic streaming) alter cell membrane permeability and may support healing in the inflammatory and proliferative phases, though evidence for clinical benefit is mixed. Phonophoresis uses ultrasound to enhance transdermal delivery of a medication such as a corticosteroid; evidence for added benefit over ultrasound alone is limited.

Contraindications to ultrasound: malignancy in the area, pregnancy (over the abdomen, low back and pelvis), over the eyes, over reproductive organs, over a cardiac pacemaker or the heart, over the spinal cord after laminectomy, over areas of active bleeding or DVT, over infection, and thermal ultrasound in areas of impaired sensation or circulation. Precautions: open epiphyses in children, acute inflammation (use pulsed or avoid thermal), fractures, breast implants, and plastic or cemented joint components (methyl methacrylate and plastic heat rapidly). Metal implants are a precaution rather than an absolute contraindication because metal conducts heat away quickly, but the beam reflects strongly.

Diathermy and other electromagnetic agents

Shortwave diathermy (usually 27.12 MHz) heats by electromagnetic energy. Inductive applicators (drum or coil) induce eddy currents that heat conductive, well perfused muscle over a larger, deeper area than ultrasound; capacitive applicators (plates) preferentially heat low conductivity fat and skin. A towel absorbs perspiration, which would otherwise concentrate heat. Contraindications are broader than for ultrasound: any implanted metal or electronic device, metal jewelry, pregnancy, malignancy, eyes, open epiphyses, hemorrhage, ischemic tissue and impaired sensation. Low level laser (photobiomodulation) requires protective eyewear and is avoided over the eyes, malignancy and the pregnant abdomen.

Section 2Electrical stimulation

Currents and waveforms

Clinical electrical stimulation uses three broad current types. Direct current (DC) flows continuously in one direction for at least about 1 second; it produces chemical effects at the electrodes and is used for iontophoresis and for stimulating denervated muscle. Alternating current (AC) changes direction continuously; clinically it is delivered as medium frequency carrier waves such as interferential current and Russian current. Pulsed current (also called pulsatile current) delivers brief pulses separated by intervals of no current; pulses may be monophasic (one phase per pulse, as in high volt pulsed current), biphasic (two opposite phases, symmetric or asymmetric, balanced or unbalanced), or polyphasic (bursts of many phases). Most portable TENS and NMES units deliver biphasic pulsed current, which leaves no net charge under the electrodes when balanced, so skin irritation is minimal.

Electrode placement follows physics. Current density is highest under the smaller electrode, so a small active electrode over the motor point concentrates the effect and a large dispersive electrode spreads it comfortably. Electrodes placed closer together stimulate more superficially; electrodes placed farther apart drive current deeper. Impedance falls when skin is clean, warm and moist and rises with oil, hair and dry skin. Electrodes should not touch each other, and current should never cross the heart or chest in a patient with a cardiac device.

TENS for pain

Transcutaneous electrical nerve stimulation (TENS) reduces pain through two main mechanisms. Sensory level, high rate stimulation activates large diameter A beta afferents that inhibit nociceptive transmission in the dorsal horn (the gate control theory). Motor level, low rate stimulation triggers release of endogenous opioids (endorphins and enkephalins) with a slower onset and longer carryover. Electrodes go over or around the painful area, along the involved dermatome or over the peripheral nerve.

Patients habituate to constant stimulation, so modulating amplitude, rate or phase duration helps; opioids may blunt low rate TENS.

NMES for strengthening and function

Neuromuscular electrical stimulation (NMES) produces muscle contractions through the intact peripheral nerve. Its best supported use is quadriceps strengthening after total knee arthroplasty and ACL reconstruction, where reflex inhibition (arthrogenic muscle inhibition) limits voluntary activation. Commonly taught parameters: frequency about 35 to 50 pps (Russian current uses 50 bursts per second), phase duration about 200 to 400 µs for large muscles, ramp up about 2 seconds, on:off ratio about 1:3 to 1:5 initially (for example 10 seconds on and 50 seconds off), around 10 to 15 contractions per session, and intensity high enough to reach a meaningful percentage of maximal voluntary contraction (often at least 50% for strengthening). Electrically elicited contractions recruit motor units in a nonphysiologic order, with large, fast fatiguing units recruited earlier than in voluntary contraction (often described as a reversal of the Henneman size principle) and synchronous firing, so electrically driven contractions fatigue faster.

Functional electrical stimulation (FES) times stimulation to a task, such as dorsiflexion in swing after stroke or cycling after spinal cord injury. NMES can also reduce shoulder subluxation after stroke (posterior deltoid and supraspinatus).

Denervated muscle needs long pulses (over about 10 ms) or DC, with weak evidence of benefit; its strength duration curve shifts right, raising chronaxie (the duration needed at twice rheobase).

High volt pulsed current and wound healing

High volt pulsed current (HVPC) delivers very short twin peak monophasic pulses at high voltage, so it has polarity. It is an evidence supported adjunct for chronic wounds; the commonly taught pattern is the cathode over the wound early (antibacterial, attracts neutrophils and fibroblasts) and the anode later (epithelial migration), placed over saline moistened gauze.

Iontophoresis

Iontophoresis uses continuous direct current to drive charged medication ions through the skin. The principle is that like charges repel: a negatively charged drug is placed under the negative electrode (cathode) and a positively charged drug under the positive electrode (anode). The dose is current multiplied by time, expressed in milliampere minutes; a common dose is 40 mA·min (for example 4 mA for 10 minutes), with current usually limited to about 4 mA or less for comfort and safety. The cathode produces an alkaline reaction (sodium hydroxide) that causes more skin irritation than the acidic reaction at the anode, so the negative electrode is often made larger to lower current density, and skin is inspected after each treatment.

EMG biofeedback

Surface electromyographic biofeedback converts the electrical activity of muscle into a visual or auditory signal, so the patient can see and hear contraction or relaxation. It does not stimulate the muscle. For uptraining a weak muscle, the gain (sensitivity) is set high so that small signals register, with electrodes often placed farther apart to sample more motor units, and the threshold is raised as the patient improves. For downtraining or relaxation of an overactive muscle (for example upper trapezius guarding or a high tone pelvic floor), electrodes are placed close together over the target, and the patient tries to keep the signal below a threshold that is gradually lowered. Biofeedback is useful in pelvic floor training, after knee surgery to restore quadriceps activation, in stroke rehabilitation and for postural muscle relaxation.

Safety in electrical stimulation

Section 3Mechanical modalities

Spinal traction

Traction applies a distractive force to separate joint surfaces, reduce pressure on discs and nerve roots, stretch soft tissue and reduce muscle guarding. It may be mechanical, manual, positional or self applied, and static (sustained) or intermittent. Intermittent traction is often more comfortable; static traction is often chosen for disc protrusion, where sustained force allows gradual disc unloading. Evidence supports traction mainly for subgroups: cervical radiculopathy combined with exercise and manual therapy, and lumbar radicular pain with signs of nerve root compression, especially when symptoms peripheralize with extension or the crossed straight leg raise is positive.

Cervical traction is usually applied supine with a head halter or occipital wedge. The neck is flexed about 20 to 30 degrees to open the posterior elements and intervertebral foramina of the lower cervical spine; a more neutral position (0 to 5 degrees) targets the upper cervical region. An occipital harness avoids pressure on the temporomandibular joints. Lumbar traction uses a thoracic and pelvic harness on a split table, which eliminates the friction of the lower half of the body (roughly half of body weight), so less force is needed. Supine hook lying flexes the lumbar spine and opens the posterior elements and foramina; prone with neutral lumbar alignment may suit a patient whose symptoms improve with extension.

Sources differ; remember that cervical forces are small (start near 4 kg, never above about 13.5 kg) and that lumbar separation needs about half of body weight. Contraindications: spinal instability (including atlantoaxial instability in rheumatoid arthritis or Down syndrome), acute injury or inflammation, fracture, spinal malignancy or infection, spinal cord compression, osteoporosis (relative for mechanical force), vertebral artery compromise, pregnancy (lumbar), uncontrolled hypertension and conditions in which movement is undesired. Precautions: TMJ problems and dentures (cervical halter), claustrophobia, respiratory or cardiac problems that limit supine lying or harness pressure, and hiatal hernia or aortic aneurysm under the thoracic harness. If symptoms peripheralize during traction, reduce the force or stop.

Compression

External compression reduces edema by raising interstitial hydrostatic pressure, aids venous and lymphatic return and shapes residual limbs. Options include bandages (short stretch for lymphedema and venous insufficiency, long stretch elastic for acute injury support), garments (graduated compression stockings and sleeves, greatest pressure distally) and intermittent pneumatic compression (IPC). Commonly taught IPC pressures are about 30 to 60 mm Hg for the upper limb and 40 to 80 mm Hg for the lower limb, kept below diastolic blood pressure, with inflation and deflation cycles chosen for comfort (for example 3:1 on:off), for about 1 to 3 hours per day for edema; the limb is elevated during treatment. IPC is also used to prevent DVT in surgical patients who cannot take anticoagulants. Gradient compression garments are commonly grouped as about 15 to 20 mm Hg (mild), 20 to 30 mm Hg (moderate, common for venous disease), 30 to 40 mm Hg (firm, lymphedema and venous ulcers) and higher.

Before compressing a lower limb, check arterial status with the ankle brachial index: about 1.0 to 1.3 is normal, below about 0.9 indicates peripheral arterial disease, below about 0.8 calls for reduced or modified compression, and below about 0.5 contraindicates compression; values above 1.3 suggest noncompressible, calcified vessels (common in diabetes) and need further testing. Contraindications to compression: acute DVT (until anticoagulated and cleared), severe arterial insufficiency, acute pulmonary edema or decompensated heart failure, acute local infection, fracture or acute trauma, and, for IPC, a malignancy in the area as a relative contraindication.

Continuous passive motion

A CPM device moves a joint passively through a set arc. Evidence shows little long term benefit after uncomplicated TKA, and routine use is not recommended, though it may follow cartilage repair or joint release. When used, the arc is increased about 5 to 10 degrees per day, aligned to the anatomic axis, and knee extension must be preserved.

Hydrotherapy and aquatic therapy

Water has properties the therapist exploits. Buoyancy (Archimedes principle) is an upward force equal to the weight of displaced water; it assists movement toward the surface, resists movement away from it and unloads joints. Approximate weight bearing at different immersion levels: neck (C7) about 10% of body weight, xiphoid about 25 to 35%, and waist or ASIS about 50%. Hydrostatic pressure (Pascal law) increases with depth, assisting venous return and reducing edema; on immersion to the neck, central blood volume and cardiac preload rise and vital capacity falls slightly, so patients with heart failure or severe lung disease need caution. Viscosity and turbulence provide resistance that increases with speed and frontal area, so resistance is self graded. Specific heat and thermal conductivity make water efficient at transferring heat.

Whirlpools are no longer recommended for routine wound care (cross contamination, maceration, dependent edema); pulsed lavage with suction has largely replaced them. Contraindications to pool therapy: fever, infection or uncovered open wounds, unmanaged incontinence, uncontrolled seizures, unstable cardiac status, vital capacity below about 1 L and severe fear of water. Keep water cooler for multiple sclerosis.

Section 4Assistive devices, wheelchairs and transfers

Choosing an ambulatory device

Assistive devices widen the base of support, unload a painful or weak limb, and improve balance. In general, stability and weight unloading increase in this order: single point cane, quad cane (small then large base), hemi walker, forearm crutches, axillary crutches, standard walker, and parallel bars, while the speed and ease of use for community walking decrease. A standard (pickup) walker is the most stable but produces a slow, interrupted gait; a front wheeled walker allows a more continuous step pattern and is often preferred for patients with parkinsonism or limited upper limb strength; a four wheeled walker (rollator) with hand brakes and a seat suits patients who need endurance support but have adequate balance. Axillary crutches allow non weight bearing but require good upper body strength and balance; forearm crutches suit long term users such as those with paraplegia or spina bifida. A cane is held in the hand opposite the affected limb, which shifts the center of mass toward the cane and reduces the moment of the hip abductors on the affected side; a cane can unload the opposite limb by about 10 to 20%.

Gait patterns

• Two point (with a cane or with bilateral crutches): the device and the opposite limb move together, then the other limb. With a cane in the right hand for a weak left limb, the cane and left foot advance together.
• Three point (non weight bearing or partial weight bearing): both crutches (or the walker) and the involved limb advance together, then the uninvolved limb steps through. A modified three point pattern allows partial weight bearing on the involved limb.
• Four point (slow, stable, bilateral involvement): right crutch, left foot, left crutch, right foot, so three points are always in contact.
• Two point with bilateral crutches: right crutch with left foot, then left crutch with right foot; faster than four point and closer to normal reciprocal gait.
• Swing to and swing through: both crutches advance, then both legs swing to (or past) the crutches; used in paraplegia with KAFOs. Swing through is the fastest crutch gait.

Weight bearing status determines the pattern: non weight bearing (no contact), toe touch or touchdown (contact for balance only), partial (a stated percentage or amount, trained with a scale), weight bearing as tolerated, and full. Patients who are non weight bearing on a lower limb and have poor balance or limited upper limb strength usually need a walker rather than crutches.

Stairs, curbs and guarding

The rule for stairs is "up with the good, down with the bad." Ascending, the uninvolved limb leads, followed by the involved limb and the device; descending, the device and the involved limb lead, followed by the uninvolved limb. With a handrail, the patient holds the rail with one hand and both crutches (or the cane) in the other. The guarding therapist stands behind and slightly to the involved side during level gait, behind and below the patient when ascending stairs, and in front of and below the patient when descending, always using a gait belt. If a patient begins to fall, the therapist guides the patient toward the therapist's body or lowers them to the floor rather than trying to hold them upright.

Wheelchair measurement and seating

Measurements are taken with the patient seated on a firm surface in the posture they will use. A seat that is too wide makes propulsion difficult and encourages leaning and scoliosis; too narrow causes pressure on the greater trochanters. A seat that is too deep presses into the popliteal fossa and pulls the pelvis into a posterior tilt (sacral sitting); too shallow increases pressure under the ischial tuberosities. A seat that is too high makes the chair hard to propel and to fit under tables; too low raises the knees and loads the ischial tuberosities. A standard adult chair is about 46 cm (18 in) wide, 41 cm (16 in) deep and 50 cm (19.5 to 20 in) high from the floor; a hemi height chair is lower (about 43 to 45 cm, 17 to 17.5 in) so a patient with hemiplegia can propel with the uninvolved foot and hand.

Ultralight rigid frames with adjustable axles suit active users; moving the rear axle forward eases propulsion and wheelies but reduces backward stability, so anti tip bars help. Elevating leg rests manage edema but are contraindicated with knee flexion contractures. Tilt in space rotates the whole seat backward, redistributing pressure without shear or triggering extensor spasm; recline opens the hip angle, which helps catheterization and orthostatic hypotension but creates shear. Power mobility suits patients who cannot propel functionally, such as C4 tetraplegia with sip and puff or head array controls. At risk patients need a pressure redistribution cushion and weight shifts at least every 15 to 30 minutes, held about 1 to 2 minutes.

Wheelchair skills and accessibility

To go up a curb, the user pops the casters up, then pushes the rear wheels up; going down, rear wheels go first (or a controlled wheelie for skilled users). Commonly tested accessibility values: ramp slope no steeper than 1:12, ramp width at least 36 in (91 cm), level landings 60 in (152 cm) long at each end and after every 30 in (76 cm) of rise, handrails when rise exceeds 6 in (15 cm), doorway clear width at least 32 in (81 cm), and a 60 in (152 cm) turning circle.

Transfers and bed mobility

Before a transfer, lock the brakes, remove the armrest and footrest on the transfer side, angle the chair about 30 to 45 degrees to the target, and apply a gait belt. A stand pivot transfer moves toward the stronger side; a sliding board transfer suits patients with good sitting balance who cannot stand; a depression transfer needs strong shoulder depressors and triceps; and a mechanical lift is used for patients who cannot assist. The therapist keeps a wide base, neutral spine and the load close, and pivots with the feet. Assistance levels: independent, modified independent, supervision, contact guard, minimal assist (patient does 75% or more), moderate (50 to 74%), maximal (25 to 49%) and dependent (less than 25%).

Section 5Orthotics and prosthetics

Preprosthetic care and the residual limb

Prosthetic success starts with the residual limb. Goals are wound healing, edema control, shaping into a cylinder (transfemoral) or tapered form (transtibial), desensitization, contracture prevention, strengthening and single limb mobility. Shaping uses elastic bandages wrapped in a figure of eight pattern with greater pressure distally and no circular turns that could act as a tourniquet, rewrapped every 4 to 6 hours, or a shrinker sock, or a rigid removable dressing for transtibial amputation. Contracture prevention is critical: transfemoral limbs tend toward hip flexion, abduction and external rotation, and transtibial limbs toward knee flexion. Patients lie prone for periods each day, avoid pillows under the residual limb or between the thighs, avoid prolonged sitting with the knee flexed, and use a board to keep the knee extended in the wheelchair after transtibial amputation. Phantom sensation is common and normal; phantom pain may respond to mirror therapy, desensitization and medication.

Energy cost rises with level: commonly quoted increases are about 10 to 20% for unilateral transtibial and about 60 to 70% for transfemoral amputation (sources vary), so the most distal level that heals is preferred, and vascular patients need cardiac monitoring.

Prosthetic components

Medicare functional levels (K levels) guide prescription: K0 no ability to ambulate or transfer safely with a prosthesis; K1 household ambulator at fixed cadence on level surfaces; K2 limited community ambulator who can manage curbs, stairs and uneven surfaces; K3 community ambulator with variable cadence; K4 exceeds basic ambulation with high impact or stress (children, active adults, athletes).

In a transtibial socket, pressure tolerant areas are the patellar tendon, medial tibial flare, pretibial muscles, popliteal fossa (moderate) and the shaft of the fibula; pressure sensitive areas are the fibular head (common fibular nerve), the tibial crest and tubercle, the distal tibia and fibula, and the hamstring tendons. Skin is inspected after every wearing session; redness that persists longer than about 20 to 30 minutes after removal means excessive pressure. Sock ply is adjusted as the limb volume changes during the day: a limb that shrinks needs more ply.

Prosthetic gait deviations

The exam typically gives a deviation and asks for the most likely cause, which may be in the prosthesis or in the patient. The approach is to ask what the deviation achieves (often clearing a limb that is functionally too long, or stabilizing a knee that might buckle) and then which alignment or impairment explains it.

Upper limb prostheses

Body powered upper limb prostheses use a figure of eight harness and cable; scapular protraction and humeral flexion operate the terminal device (and flex an unlocked transhumeral elbow). A voluntary opening device is closed at rest with grip set by bands; a voluntary closing device lets the user grade grip. Body powered devices are durable, light and give harness feedback; myoelectric devices use surface electrodes and motors for stronger grip and better cosmesis but are heavier and costlier. Early fitting improves acceptance.

Lower limb orthoses

Shoe modifications include a metatarsal pad placed just proximal to the metatarsal heads to unload them in metatarsalgia, a metatarsal bar or rocker bottom sole to reduce forefoot motion and pressure (hallux rigidus, diabetic forefoot ulcer risk), a heel lift for leg length difference or Achilles tendinopathy, medial wedges for pronation and lateral wedges for supination, and an extra depth shoe with custom insoles for the insensate diabetic foot.

Spinal and upper limb orthoses

Cervical orthoses range from a soft collar (a reminder) through rigid collars and cervicothoracic orthoses to the halo vest, the most restrictive (never lift the patient by the halo). A hyperextension TLSO limits flexion after stable thoracolumbar compression fractures. A custom TLSO treats idiopathic scoliosis of about 25 to 45 degrees in skeletally immature patients; curves above about 45 to 50 degrees usually go to surgical consultation. Upper limb orthoses include a resting hand orthosis (rheumatoid arthritis, stroke), a wrist cock up for radial nerve palsy and carpal tunnel syndrome, a thumb spica for de Quervain tenosynovitis and CMC arthritis, and a tenodesis orthosis for C6 to C7 tetraplegia.

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