Musculoskeletal Foundations: Tissue, Kinesiology and the Spine

Every orthopedic decision on the exam, from how soon a repaired tendon can be loaded to which way to glide a stiff joint and whether a patient with neck pain needs imaging, rests on a few foundations: how tissues heal, how joints move, and how to examine the spine without missing something dangerous. This chapter builds those foundations and then applies them to the cervical, thoracic, lumbar and sacroiliac regions, where clinical prediction rules, classification systems and safety screening are tested heavily.

Section 1Tissue healing and loading

The three overlapping phases

Soft tissue healing after injury or surgery proceeds through three overlapping phases. Their timelines vary with tissue type, blood supply, age, nutrition, smoking, diabetes and medications such as systemic corticosteroids, so the numbers below are typical ranges, not rules. What the exam tests is the biology of each phase and the type of loading that fits it.

The inflammatory phase begins immediately and lasts roughly the first 3 to 7 days. Vasoconstriction and clotting stop bleeding; then vasodilation and increased permeability bring plasma proteins and white cells to the area. Neutrophils arrive first, followed by macrophages, which clear debris and release growth factors that drive the next phase. The cardinal signs are redness, heat, swelling, pain and loss of function. Clinically, pain is felt before end range, at rest or with any stress. The goals are to protect the tissue, control edema and pain, and maintain motion in neighboring regions. Complete rest is not the goal; gentle, pain free movement within protected limits reduces stiffness and supports circulation.

The proliferative phase (also called repair or fibroplasia) overlaps inflammation and runs from about day 3 to about week 3 to 6. Fibroblasts lay down type III collagen, a thin, weak, randomly arranged collagen, along with new capillaries (angiogenesis) and granulation tissue. Wound contraction by myofibroblasts draws the edges together. The new tissue is fragile, and tensile strength is low. Controlled, low load stress now begins to orient the new fibers; too much load disrupts them and restarts inflammation.

The remodeling phase (maturation) begins at about week 3 and continues for months to more than a year. Type III collagen is gradually replaced by stronger type I collagen, fibers align along lines of stress, cross links form and the scar shrinks and strengthens. Even after a year, a ligament or tendon scar typically regains only a portion of its original tensile strength. Progressive loading, specific to the demands the patient will face, is the stimulus that drives this alignment.

Mechanical behavior: the stress strain curve

Connective tissues are viscoelastic: their response depends on how fast and how long they are loaded. On a stress strain (load deformation) curve for tendon or ligament, the first segment is the toe region, where crimped collagen fibers straighten with little force. The elastic (linear) region follows; deformation is proportional to load and fully recoverable when the load is removed. Beyond the yield point lies the plastic region, in which some fibers fail and deformation is permanent (a clinical sprain or strain). At the ultimate failure point the tissue ruptures. The slope of the elastic region is the stiffness (Young modulus).

Two viscoelastic properties are used in treatment. Creep is continued elongation under a constant load over time; it is why a low load, long duration stretch is more effective than a brief forceful one at producing lasting length change. Stress relaxation is the decline in internal force when tissue is held at a constant length; it is the principle behind serial casting and static progressive splinting. Tissues are also stiffer when loaded quickly, and warm tissue deforms more readily than cold tissue, which is why heat combined with prolonged stretch is effective.

How specific tissues respond

Bone healing

Fracture healing follows its own phases. In indirect (secondary) healing, typical of fractures treated with casts or flexible fixation, a hematoma and inflammation form in the first days, a soft callus of fibrocartilage bridges the gap over the next few weeks, a hard callus of woven bone replaces it (often visible on radiographs by 4 to 8 weeks), and remodeling into lamellar bone continues for months to years. Rigid fixation allows direct (primary) healing without callus. Fracture timelines and weight bearing status are covered in Chapter 4.

Wolff law states that bone adapts its density and architecture to the loads placed on it: bone is laid down where stress is applied and resorbed where it is absent. This explains osteoporosis with bed rest or spinal cord injury and the use of weight bearing and impact exercise to build bone. Davis law is the soft tissue counterpart: soft tissues remodel according to the demands placed on them, lengthening under sustained tension and shortening when kept slack. A patient whose knee is kept flexed in bed develops shortened hamstrings and posterior capsule; prolonged low load positioning can reverse it.

Protected motion and progressive loading

Modern rehabilitation favors protected early motion over immobilization whenever the repair allows. Controlled motion reduces adhesions, maintains cartilage nutrition, limits atrophy and helps align new collagen. Protection means respecting the limits the surgeon or the tissue sets: range limits (for example, after a rotator cuff repair), load limits (weight bearing status), speed (slow before fast), and direction (avoiding the motion that stresses the repair). Within those limits, loading is progressed by one variable at a time, guided by the patient's response during and over the 24 hours after a session. Pain that is mild, settles quickly and does not increase the next morning is generally acceptable; pain that lingers, increasing swelling, or loss of motion means the load was too much.

Section 2Kinesiology essentials

Planes, axes and the language of motion

Motion is described from anatomical position: standing, facing forward, arms at the sides with palms forward. Each plane of motion has a perpendicular axis around which the motion occurs.

Open and closed kinetic chain

In an open kinetic chain (OKC) exercise the distal segment moves freely in space (a seated knee extension, a biceps curl). In a closed kinetic chain (CKC) exercise the distal segment is fixed against a surface and the proximal segments move over it (a squat, a push up, a step up). The distinction matters for joint loading and for which muscles work.

Open chain knee extension pulls the tibia anteriorly in the last 30 to 40 degrees, straining the ACL, so early ACL rehab favors closed chain work and limits open chain extension to a protected arc.

Arthrokinematics and the convex concave rule

Osteokinematics describes the movement of the bones (flexion, abduction). Arthrokinematics describes what the joint surfaces do: roll (new points on one surface meet new points on the other, like a tire rolling), glide or slide (one point on one surface contacts new points on the other, like a skidding tire), and spin (rotation around a fixed point, like the radial head in pronation). Most joints combine roll and glide.

The convex concave rule predicts the direction of glide. When a convex surface moves on a fixed concave surface, it rolls in the direction of the bone's movement but glides in the opposite direction. When a concave surface moves on a fixed convex surface, roll and glide occur in the same direction as the bone movement. Joint mobilization uses this rule: to restore a lost motion, the therapist glides the moving bone in the direction its surface should glide.

Close packed, loose packed and capsular patterns

In the close packed position the joint surfaces are maximally congruent and the capsule and ligaments are taut, so the joint is most stable and least able to be mobilized; it is also the position in which joints are typically injured by high loads and in which stability tests are often done. In the loose packed (resting) position the capsule is most lax, and joint play is greatest, so it is where mobilization usually begins. A capsular pattern is the characteristic proportional loss of motion when the whole capsule is involved (arthritis, adhesive capsulitis); a noncapsular pattern suggests a more local problem such as a ligament adhesion, internal derangement or extra-articular lesion.

Length tension, force velocity and insufficiency

The force a muscle can produce depends on its length. Active tension is greatest near resting length, where actin and myosin overlap optimally; at short lengths the filaments crowd and overlap, and at long lengths few cross bridges can form. Passive tension from connective tissue and the protein titin rises as the muscle is stretched beyond resting length. Total tension is the sum, which is why a muscle on stretch can still resist strongly even as its active force falls.

Active insufficiency occurs when a muscle that crosses two or more joints is shortened across all of them at once and cannot generate enough force to complete the motion: the hamstrings cannot fully flex the knee when the hip is already extended, and the finger flexors make a weak fist when the wrist is flexed. Passive insufficiency occurs when a two joint muscle is lengthened across both joints and its passive tension stops motion at the other end: tight hamstrings limit hip flexion when the knee is extended (the basis of the straight leg raise for hamstring length), and the rectus femoris limits knee flexion when the hip is extended (the Ely test). Tenodesis uses passive insufficiency deliberately: in a person with C6 tetraplegia, active wrist extension pulls the finger flexors taut and closes the hand for grasp, which is why finger flexors are not stretched over an extended wrist in these patients.

The force velocity relationship states that concentric force falls as shortening speed rises, isometric force is intermediate, and eccentric force exceeds isometric and rises with lengthening speed up to a plateau. Eccentric work therefore produces the highest forces at the lowest metabolic cost, and it is also the type most associated with delayed onset muscle soreness.

Muscle actions and roles

A concentric contraction shortens the muscle while it produces force; an eccentric contraction lengthens it under load (the quadriceps controlling descent into a squat or down stairs); an isometric contraction produces force without a change in length. Isokinetic exercise holds velocity constant with a machine that matches resistance to the force produced. A force couple is two or more muscles pulling in different directions to produce rotation: the upper trapezius, lower trapezius and serratus anterior upwardly rotate the scapula, and the deltoid and rotator cuff together elevate the arm while keeping the humeral head centered.

Levers and torque

Torque equals force multiplied by the perpendicular distance from the axis to the line of force (the moment arm). Muscle torque must overcome resistance torque, which is why the same weight feels heavier when held at arm's length and why a long lever arm is used to progress resistance (straight arm versus bent arm raises). The mechanical advantage is the ratio of the force arm to the resistance arm; a value above 1 favors force, below 1 favors speed and range of motion.

Section 3Examination of the cervical and thoracic spine

Screening first

Neck pain is usually benign and mechanical, but the cervical spine sits next to the spinal cord, the vertebral and carotid arteries and the upper airway, so the exam weights screening heavily. Before any test that loads the neck, the therapist screens for fracture (after trauma), upper cervical ligamentous instability, cervical arterial dysfunction, cervical myelopathy, and nonmusculoskeletal sources such as cancer, infection and cardiac referral.

Upper cervical ligament integrity tests include the Sharp-Purser test (with the head slightly flexed, the examiner stabilizes C2 and glides the head posteriorly; a clunk or reduction of symptoms suggests atlantoaxial instability from transverse ligament laxity) and the alar ligament stress test (side bending or rotating the head while palpating the C2 spinous process, which should move immediately). Screening for cervical arterial dysfunction is now framed as a clinical reasoning process built on history and risk factors; positional tests such as sustained end range rotation have poor accuracy and should not be relied on alone.

Imaging after trauma: the Canadian C-spine rule

The Canadian C-spine rule decides whether an alert (Glasgow Coma Scale 15), stable adult trauma patient needs cervical radiographs. It is highly sensitive, so a patient who clears it has a very low probability of a clinically important injury.

Nerve root levels

Remember that cervical roots exit above the vertebra of the same number (the C6 root exits between C5 and C6), and C8 exits between C7 and T1. A C5 to C6 disc herniation therefore affects the C6 root. The C7 root is the most commonly involved in radiculopathy, followed by C6.

Cervical radiculopathy versus myelopathy

Cervical radiculopathy is compression or irritation of a nerve root, usually in the intervertebral foramen by a disc herniation in younger adults or by uncovertebral and facet osteophytes in older adults. It causes unilateral arm pain in a dermatomal pattern, paresthesia, and lower motor neuron signs in that root's distribution: myotomal weakness and a diminished reflex. Resting the hand on the head often eases symptoms (shoulder abduction sign).

The Wainner test item cluster diagnoses cervical radiculopathy with four tests: a positive Spurling test (extension, side bending and gentle compression toward the symptomatic side reproduces arm symptoms), a positive distraction test (lifting the head relieves symptoms), a positive upper limb tension test A (median nerve bias: scapular depression, shoulder abduction, forearm supination, wrist and finger extension, shoulder external rotation, elbow extension, then contralateral cervical side bending), and cervical rotation toward the involved side of less than 60 degrees. Three of four positive gives a moderate shift toward the diagnosis, and all four positive a large one (positive likelihood ratio about 30). The upper limb tension test A is the most sensitive single test, so a negative result helps rule radiculopathy out, while Spurling is the most specific and helps rule it in.

Cervical myelopathy is compression of the spinal cord itself, usually by degenerative spondylosis narrowing the central canal in people over 50. It causes upper motor neuron signs below the level: bilateral hand numbness and clumsiness (difficulty with buttons and handwriting), a broad based, unsteady gait, hyperreflexia, clonus, a positive Hoffmann sign (flicking the middle finger distal phalanx causes thumb and index flexion), a positive Babinski sign, an inverted supinator sign (tapping the brachioradialis tendon produces finger flexion instead of the expected response) and sometimes the Lhermitte sign (neck flexion sends an electric sensation down the spine). A five item cluster (gait deviation, positive Hoffmann, inverted supinator sign, positive Babinski, age over 45) helps: one or fewer positive makes myelopathy unlikely, three or more makes it very likely. Myelopathy is a contraindication to cervical manipulation and needs medical referral.

Neck pain classification and other conditions

Current neck pain practice guidelines classify patients by the dominant impairment: neck pain with mobility deficits (treated with thoracic and cervical mobilization or manipulation and exercise), neck pain with movement coordination impairments (commonly after whiplash; education, active exercise, deep neck flexor training), neck pain with headaches (cervicogenic headache; manual therapy and exercise) and neck pain with radiating pain (radiculopathy; mechanical intermittent traction combined with exercise, neural mobilization). A six item prediction rule for thoracic manipulation in neck pain (recent onset under 30 days, no symptoms below the shoulder, looking up not painful, low fear avoidance, reduced upper thoracic kyphosis, cervical extension under 30 degrees) was not well supported in later validation, but thoracic manipulation remains a reasonable option for mechanical neck pain.

Cervicogenic headache is unilateral, starts in the neck, is provoked by neck postures and shows reduced C1 to C2 rotation on the flexion rotation test.

Whiplash associated disorders follow acceleration and deceleration injury and are graded by the Quebec Task Force system.

Thoracic outlet syndrome is compression of the brachial plexus (neurogenic, by far the most common), subclavian vein or subclavian artery at the interscalene triangle, the costoclavicular space or beneath the pectoralis minor. Neurogenic symptoms most often follow the lower trunk (C8, T1: medial forearm and ulnar hand). The Adson test (head extended and rotated toward the tested side with a deep breath while the radial pulse is monitored) targets the scalenes, the costoclavicular (military brace) test the space between clavicle and first rib, the Wright hyperabduction test the pectoralis minor, and the Roos elevated arm stress test (arms at 90 degrees abduction and external rotation, opening and closing the hands for 3 minutes) reproduces symptoms. Pulse changes occur in many healthy people, so reproduction of symptoms is more meaningful than pulse loss.

In the thoracic spine, think first of visceral referral: cardiac (left chest, arm, jaw, interscapular), gallbladder (right scapula), kidney (flank), aortic dissection (tearing interscapular pain). Minimal trauma in an older adult suggests an osteoporotic compression fracture; a young adult with morning stiffness over 30 minutes that improves with exercise and reduced chest expansion suggests ankylosing spondylitis.

Section 4Examination and management of the lumbar spine and sacroiliac region

Red flags in low back pain

Most low back pain is nonspecific and has a favorable course, and imaging is not recommended in the absence of red flags. The examination therefore begins by excluding the small number of serious causes.

Screen psychosocial risk as well (for example with the STarT Back tool, which stratifies risk of persistent disability), and track outcomes with the Oswestry Disability Index.

Lumbar radiculopathy and neural tension tests

Lumbar roots exit below the pedicle of the vertebra of the same number (the L4 root exits between L4 and L5). Because the common posterolateral disc herniation hits the root that is traversing the disc on its way down, an L4 to L5 posterolateral herniation compresses the L5 root and an L5 to S1 herniation compresses S1. A less common far lateral herniation at L4 to L5 catches the exiting L4 root.

The straight leg raise is positive when it reproduces radicular leg pain between about 30 and 70 degrees; it is sensitive for disc related radiculopathy, so a negative test helps rule it out. The crossed straight leg raise (raising the uninvolved leg reproduces pain in the involved leg) is specific and helps rule it in. The slump test adds trunk and neck flexion; release of neck flexion that eases symptoms confirms neural tension. The prone knee bend (femoral nerve tension) tests the L2 to L4 roots.

Treatment based classification

The treatment based classification (TBC) system sorts patients with low back pain into subgroups that respond to different treatments. The classic version, still widely tested, has four categories.

A shortened two item version of the manipulation rule (symptoms under 16 days and no symptoms below the knee) is also used. The prone instability test is done with the patient prone, trunk on the table and feet on the floor; posterior to anterior pressure provokes pain, and the test is positive when the pain disappears as the patient lifts the legs and contracts the back extensors. The updated TBC reframes care by goal: symptom modulation for highly irritable patients, movement control for those with moderate irritability and motor control deficits, and functional optimization for low irritability patients ready for full loading.

Centralization is the movement of referred symptoms from distal to proximal toward the spine during repeated movements or sustained positions. It is a strong good prognostic sign. Peripheralization, symptoms spreading distally, means that direction should be avoided for now. Pain in the back may increase as leg symptoms centralize; that is still a good response.

Stenosis and spondylolisthesis

Lumbar spinal stenosis narrows the central canal or lateral recesses, usually through disc degeneration, facet hypertrophy and ligamentum flavum thickening in older adults. It produces neurogenic claudication: buttock and leg pain, numbness or heaviness with standing and walking that eases with sitting or flexion (flexion widens the canal and foramina). Patients lean forward on a shopping cart. Helpful findings include age over about 48, bilateral symptoms, leg pain worse than back pain, pain while walking or standing and relief with sitting. A two stage treadmill test separates stenosis from other causes: symptoms begin sooner when walking level than walking on an incline (the incline flexes the trunk).

Management emphasizes flexion based exercise, manual therapy to the spine and hips, cycling or body weight supported treadmill walking, and conditioning; surgery is considered for progressive deficits or failed conservative care.

Spondylolysis is a defect (often a stress fracture) of the pars interarticularis, most often at L5, common in adolescent athletes who repeatedly extend and rotate (gymnastics, diving, football linemen, cricket bowlers). An oblique radiograph shows a "collar on the Scotty dog." Spondylolisthesis is the forward slip of one vertebra on the one below. Isthmic spondylolisthesis follows bilateral pars defects, usually L5 on S1 in younger people; degenerative spondylolisthesis occurs with intact pars from facet arthritis, usually L4 on L5 in older women. The Meyerding grade describes slip as a percentage of the vertebral body width below: grade I up to 25 percent, II 26 to 50, III 51 to 75, IV 76 to 100, and V (spondyloptosis) beyond 100 percent. A palpable step off may be felt. Treatment avoids end range extension early, emphasizes trunk stabilization and hamstring flexibility, and may include bracing and activity modification for an acute pars fracture in an adolescent.

The sacroiliac joint

Sacroiliac pain is felt over the posterior superior iliac spine and buttock, typically below L5, and can refer to the thigh. Single SI tests are unreliable, so the exam expects the Laslett provocation cluster:

• Distraction: supine, posterolateral pressure on both anterior superior iliac spines gaps the front of the joints.
• Thigh thrust: supine with the hip flexed to 90 degrees, a posterior force along the femur shears the SI joint.
• Compression: side lying, downward force on the iliac crest.
• Sacral thrust: prone, posterior to anterior force on the sacrum.
• Gaenslen test: one hip flexed to the chest while the other leg drops off the table into extension, tested on both sides.

Two of the first four positive, or three or more of all tests, supports SI joint pain; all negative makes it unlikely. The cluster works best once a discogenic source has been excluded (no centralization).

Section 5Manual therapy and therapeutic exercise for the spine

Joint mobilization grades

Joint mobilization is a passive, skilled movement of a joint at a speed the patient can stop. The two grading systems the exam uses describe where in the available range the movement occurs and how large it is.

Oscillations run at about one to three per second for 30 to 60 seconds and are repeated. Begin in the resting position for irritable joints, glide according to the convex concave rule or distract perpendicular to the treatment plane, and stabilize the proximal segment.

Effects are both mechanical (stretching capsule, restoring glide) and neurophysiological (spinal and descending pain inhibition, reduced guarding), which is why a thoracic thrust can ease neck pain.

Thrust manipulation: indications, contraindications and precautions

Thrust manipulation (Maitland grade V) is a high velocity, low amplitude movement, often accompanied by an audible cavitation (which is not required for benefit). It has good evidence for acute low back pain in patients who fit the prediction rule, for mechanical neck pain (particularly thoracic thrust) and for cervicogenic headache. The decision to thrust is a risk benefit judgment; rare but serious adverse events, especially with cervical thrust, make screening essential.

Motor control training

People with recurrent low back pain often show delayed activation of the transversus abdominis and atrophy or poor activation of the lumbar multifidus, and people with neck pain show poor endurance of the deep neck flexors (longus colli and longus capitis) with overactivity of the sternocleidomastoid and anterior scalenes. Motor control training first teaches isolated activation of the deep muscles, then integrates it into posture and function.

• Abdominal drawing in maneuver: gently draw the lower abdomen in without moving the spine or holding the breath; a pressure biofeedback unit under the abdomen in prone (starting near 70 mmHg) should drop a few mmHg with a correct contraction.
• Multifidus: palpated contraction in prone or side lying, progressed to quadruped arm and leg lifts (bird dog).
• Craniocervical flexion test and training: supine with a pressure unit under the neck inflated to 20 mmHg, the patient nods to raise the pressure in steps of 2 mmHg up to 30 mmHg, holding each for 10 seconds without superficial muscle substitution.
• Progression: supine bridges, side planks, curl ups (the classic "big three" emphasize trunk endurance with low spinal load), then standing, lifting, and sport or work specific tasks with a neutral spine.

General exercise works about as well as specific motor control training for many with chronic low back pain; progressive, functional active exercise is the key.

McKenzie principles

Mechanical Diagnosis and Therapy, developed by Robin McKenzie, uses repeated movements and sustained positions to classify spinal pain into three mechanical syndromes.

The typical extension progression for a posterior derangement is prone lying, prone on elbows, prone press ups, then standing extension. A lateral shift (the trunk displaced away from the painful side in most cases) is corrected before extension. When extension peripheralizes symptoms, it stops; flexion or lateral movements are explored instead.

Return to function

Current guidelines recommend staying active, reassuring education (including pain neuroscience education for persistent pain), exercise, and manual therapy combined with exercise; passive modalities and rest are not primary care. For fear of movement, graded activity (quota based increases regardless of pain) and graded exposure (gradual confrontation of feared movements) reduce disability, and work conditioning or hardening prepares the return to work.

Words worth knowing