Chapter 9: Mechanisms and Characteristics of Musculoskeletal and Nerve Trauma

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Chapter 9: Mechanisms and Characteristics of

Musculoskeletal and Nerve Trauma


Mechanical Injury

• Trauma is defined as physical injury or wound, produced by internal or external force

• Mechanical injury results from force or mechanical energy that changes state of rest or uniform motion of matter


• Tissue Properties– Load

• An external force acting on the body causing internal reactions within the tissues

– Stiffness • Ability of a tissue to resist a load• Greater stiffness = greater magnitude load can resist

– Stress • Internal resistance to a load

– Strain• Internal change in tissue (i.e. length) resulting in deformation


Figure 9-1


– Body tissues are viscoelastic and contain both viscous and elastic properties

– Yield point • Point at which elasticity is almost exceeded is

the yield point• If deformation persists, following release of load

permanent or plastic changes result• When yield point is far exceeded mechanical

failure occurs resulting in damage


• Tissue Loading– Tension

• Force that pulls and stretches tissue

– Compression • Force that results in

tissue crush – two forces applied towards one another

– Shearing • Force that moves

across the parallel organization of tissue

Figure 9-2


– Bending • Two force pairs act at opposite

ends of a structure (4 points)• Three forces cause bending (3

points)• Already bowed structures

encounter axial loading

– Torsion• Loads caused by twisting in

opposite directions from opposite ends

• Shear stress encountered will be perpendicular and parallel to the loads

Figure 9-2


Traumatic vs. Overuse Injuries• Nature of physical activity dictates that over time

injury will occur

• Debate over acute vs. chronic injuries– When injury is acute – something has initiated the

injury process

– Injury becomes chronic when it doesn’t properly heal

• Could define relative to mechanism– Traumatic (i.e. a direct blow) vs. Overuse (i.e.

repetitive dynamic use over time)


Musculotendinous Unit Injuries

• High incidence in athletics• Anatomical Characteristics

– Composed of contractile cells that produce movement

– Possess following characteristics• Irritability• Contractility• Conductivity• Elasticity


– Three types of muscle• Cardiac• Smooth• Striated (skeletal)

Skeletal Muscle

Figure 9-3


• Muscle Strains– Stretch, tear or rip to muscle or adjacent tissue– Cause is often obscure

• Abnormal muscle contraction is the result of 1)failure in reciprocal coordination of agonist and antagonist, 2) electrolyte imbalance due to profuse sweating or 3) strength imbalance

– May range from minute separation of connective tissue to complete tendinous avulsion or muscle rupture


– Muscle Strain Grades• Grade I - some fibers have been stretched or actually torn

resulting in tenderness and pain on active ROM, movement painful but full range present

• Grade II - number of fibers have been torn and active contraction is painful, usually a depression or divot is palpable, some swelling and discoloration result

• Grade III- Complete rupture of muscle or musculotendinous junction, significant impairment, with initially a great deal of pain that diminishes due to nerve damage

– Pathologically, strain is very similar to contusion or sprain with capillary or blood vessel hemorrhage


– Time required for healing may be lengthy– Often involves large, force-producing

muscles– Treatment and recovery may take 6-8

weeks depending on severity– Return to play too soon could result in re-

injury


• Muscle Cramps– Painful involuntary skeletal muscle contraction– Occurs in well-developed individuals when muscle is in shortened

position – Experienced at night or at rest

• Muscle Guarding– Following injury, muscles within an effected area contract to splint

the area in an effort to minimize pain through limitation of motion– Involuntary muscle contraction in response to pain following injury

• Not spasm which would indicate increased tone due to upper motor neuron lesion in the brain


• Muscle Spasms

– A reflex reaction caused by trauma

– Two types• Clonic - alternating involuntary muscular contractions and

relaxations in quick succession

• Tonic - rigid contraction that lasts a period of time

– May lead to muscle or tendon injuries


• Muscle Soreness– Overexertion in strenuous exercise resulting in

muscular pain– Generally occurs following participation in

activity that individual is unaccustomed – Two types of soreness

1) Acute-onset muscle soreness - accompanies fatigue, and is transient muscle pain experienced immediately after exercise

2) Delayed-onset muscle soreness (DOMS) - pain that occurs 24-48 hours following activity that gradually subsides (pain free 3-4 days later)– Potentially caused by slight microtrauma to muscle or

connective tissue structures

– Prevent soreness through gradual build-up of intensity


• Tendon Injuries– Wavy parallel collagenous fibers organized in

bundles - upon loading • Can produce and maintain 8,700- 18,000 lbs/in2 • Collagen straightens during loading but will return to

shape after loading

– Breaking point occurs at 6-8% of increased length

– Tears generally occur in muscle and not tendon


– Repetitive stress on tendon will result in microtrauma and elongation, causing fibroblasts influx and increased collagen production

• Repeated microtrauma may evolve into chronic muscle strain due to reabsorption of collagen fibers

• Results in weakening tendons• Collagen reabsorption occurs in early period of

sports conditioning and immobilization making tissue susceptibility to injury – requires gradual loading and conditioning


• Tendinitis– Gradual onset, with diffuse tenderness due to

repeated microtrauma and degenerative changes

– Obvious signs of swelling and pain– Key to treatment is rest– May require substitution of activity in order to

maintain fitness without stressing injured structure

– Without proper healing condition may begin to degenerate and be referred to as tendinosis

• Less inflammation, more visibly swollen with stiffness and restricted motion

• Treatment involves stretching and strengthening

Figure 9-5


• Tenosynovitis– Inflammation of synovial sheath– In acute case - rapid onset, crepitus, and

diffuse swelling– Chronic cases result in thickening of tendon

with pain and crepitus– Often occurs in long flexor tendon of the

digits and the biceps tendon– Due to nature of injury anti-inflammatory

agents may be helpful


• Myofascial Trigger Points– Discrete, hypersensitive nodule within tight band of muscle or

fascia

– Classified as latent or active

– Develop as the result of mechanical stress• Either acute trauma or microtrauma • May lead to development of stress on muscle fiber = formation of

trigger points

– Latent trigger point• Does not cause spontaneous pain• May restrict movement or cause muscle weakness• Become aware of presence when pressure is applied


– Active trigger point• Causes pain at rest• Applying pressure = pain = jump sign• Tender to palpation with referred pain• Tender point vs. trigger point• Found most commonly in muscles involved in

postural support


• Contusions– Result of sudden blow to body– Can be both deep and superficial– Hematoma results from blood and lymph flow into

surrounding tissue• Localization of extravasated blood into clot, encapsulated by

connective tissue• Speed of healing dependent on the extent of damage

– Chronically inflamed and contused tissue may result in generation of calcium deposits (myositis ossificans)

• Prevention through protection of contused area with padding



• Atrophy and Contracture– Atrophy is wasting away of muscle due to

immobilization, inactivity, or loss of nerve functioning

– Contracture is an abnormal shortening of muscle where there is a great deal of resistance to passive stretch

• Generally the result of a muscle injury which impacts the joint, resulting in accumulation of scar tissue


Synovial Joints Injuries• Each joint has both hyaline or articular cartilage

and a fibrous connective tissue capsule• Additional synovial joint characteristics

– Capsule and ligaments for support– Capsule is lined with synovial membrane– Hyaline cartilage– Joint cavity with synovial fluid– Blood and nerve supply with muscles crossing joint– Menisci (fibrocartilage)


Figure 9-8


• Ligament Sprains– Result of traumatic joint twist that causes stretching or

tearing of connective tissue

– Graded based on the severity of injury• Grade I - some pain, minimal loss of function, no abnormal

motion, and mild point tenderness• Grade II - pain, moderate loss of function, swelling, and

instability with tearing and separation of ligament fibers• Grade III - extremely painful, inevitable loss of function, severe

instability and swelling, and may also represent subluxation


• Can result in joint effusion and swelling, local temperature increase, pain and point tenderness, ecchymosis (change in skin color) and possibly an avulsion fracture

• Greatest difficulty with grade 1 & 2 sprains is restoring stability due to stretched tissue and inelastic scar tissue which forms

• To regain joint stability strengthening of muscles around the joint is critical


• Dislocations and Subluxations– Result in separation of bony articulating surfaces– Subluxation

• Partial dislocations causing incomplete separation of two bones• Bones come back together in alignment

– Dislocations• High level of incidence in fingers and shoulder • Occurs when at least one bone in a joint is forced out of

alignment and must be manually or surgically reduced• Gross deformity is typically apparent with bilateral comparison

revealing asymmetry


– Dislocation (cont.)• Stabilizing structures of the joint

are disrupted

• Joint often becomes susceptible to subsequent dislocations

• X-ray is the only absolute diagnostic technique (able to see bone fragments from possible avulsion fractures, disruption of growth plates or connective tissue)

• Dislocations (particularly first time) should always be considered and treated as a fracture until ruled out

• “Once a dislocation, always a dislocation”

Figure 9-9


• Osteoarthritis– Wearing away of hyaline

cartilage as a result of normal use

– Changes in joint mechanics lead to joint degeneration

– Commonly affects weight bearing joints but can also impact shoulders and cervical spine

– Symptoms include pain (as the result of friction), stiffness, prominent morning pain, localized tenderness, creaking, grating

– Either generalized joint pain or localized to one side of the joint

Figure 9-10


– Bursitis• Bursa are fluid filled sacs that

develop in areas of friction• Sudden irritation can cause

acute bursitis, while overuse and constant external compression can cause chronic bursitis

• Signs and symptoms include swelling, pain, and some loss of function

• Repeated trauma can lead to calcification and degeneration of internal bursa linings

Figure 9-11


– Capsulitis and Synovitis• Capsulitis is the result of repeated joint trauma

• Synovitis can occur acutely but will also develop following mistreatment of joint injury

• Chronic synovitis can result in edema, thickening of the synovial lining, exudation can occur and a fibrous underlying develops

• Motion may become restricted and joint noises may develop


Bone Injuries

• Anatomical Characteristics– Dense connective

tissue matrix– Outer compact tissue– Inner porous

cancellous bone including Haversian canals

Figure 9-12


– Bone Functions• Body support• Organ protection• Movement (through joints and levers)• Calcium storage• Formation of blood cells (hematopoiesis)

– Types of Bone• Classified according to shape• Flat bones - skull, ribs, scapulae• Irregular bones - vertebrae and skull• Short bones- wrist and ankle• Long bones (humerus, ulna, tibia, radius, fibula, femur) - bones most

commonly injured


– Gross Structures• Diaphysis -shaft - hollow and cylindrical

- covered by compact bone

- medullary cavity contains yellow

marrow and lined by endosteum

• Epiphysis - composed of cancellous bone and

has hyaline cartilage covering

- provides areas for muscle attachment

• Periosteum - dense, white fibrous covering which penetrates bone via Sharpey’ fibers

- contains blood vessels and osteoblasts


– Bone Growth• Ossification occurs from synthesis of bones organic matrix (work

of osteoblasts and osteoclasts)• Involves growth of diaphysis and the epiphyseal growth plates

(towards one another)• As cartilage matures, immature osteoblasts replace to ultimately

form solid bone• Deforming forces, premature injury and growth plate dislocation

can alter growth patterns and/or result in deformity of bone• Bone diameter increases via the activity of osteoblasts adding to

the exterior while osteoclasts break down bone in medullary cavity• At full size, bone maintains state of balance between osteoblastic

and -clastic activity


• Changes in activity and hormonal levels can alter balance

• Bone loss begins to exceed external bone growth overtime

• As thickness decreases, bones are less resistant to forces --osteoporosis

• Bone’s functional adaptation to stresses follows Wolff’s Law --every change in form and function or in its function alone is followed by changes in architectural design


• Bone Fractures– Classified as either closed or open

• Closed fractures are those where there is little movement or displacement

• Open fractures involve displacement of the fractured ends and breaking through the surrounding tissue

– Serious condition if not managed properly– Signs & symptoms

• Deformity, pain, point tenderness, swelling, pain on active and passive movements

• Possible crepitus• X-ray will be necessary for definitive diagnosis


– Mechanism of Injury• Fracture may be direct (at point of force application) or indirect • Sudden violent and forceful muscle contraction

– Types of fractures• Greenstick• Comminuted• Linear• Transverse• Oblique• Spiral• Impacted• Depressed

Figure 9-13


– Less common types of fractures• Avulsion

– Separation of bone fragment from cortex via pull of ligament or tendon

• Blowout fracture• Serrated fracture• Depressed fracture• Contrecoup fracture


– Bone Strength & Shape• Strength of bone can be impacted by changes in shape

and direction– Long bones with gradual changes are less prone to injury

• Cylindrical and hollow nature of bones make them very strong - resistant to bending and twisting

– Bone Loading Characteristics• Bones can be stressed or loaded to failure by tension,

compression, bending, twisting and shearing


– Long Bone Load Characteristics (cont.)• Either occur singularly or in combination

• Amount of load also impacts the nature of the fracture

• More force results in a more complex fracture

• While force goes into fracturing the bone, some energy and force is also absorbed by adjacent soft tissues

• Bone has elastic properties allowing it to bend

• Typically brittle and a poor shock absorber– Brittleness increases under tension forces, more so than under compression


– Stress fractures• No specific cause but with a number of possible causes

– Overload due to muscle contraction, altered stress distribution due to muscle fatigue, changes in surface, rhythmic repetitive stress vibrations

• Bone becomes susceptible early in training due to increased muscular forces and initial remodeling and resorption of bone

• Progression involves, focal microfractures, periosteal or endosteal response (stress fx) linear fractures and displaced fractures

• Early detection is difficult, bone scan is useful, x-ray is effective after several weeks


• Typical causes include– Coming back to competition too soon after injury– Changing events without proper conditioning– Starting initial training too quickly– Changing training habits (surfaces, shoes….etc)– Variety of postural and foot conditions

• Signs and symptoms – Focal tenderness and pain, (early stages) – Pain with activity, (later stages) with pain becoming constant and more

intense, particularly at night, (exhibit a positive percussion tap test)

• Common sites involve tibia, fibula, metatarsal shaft, calcaneus, femur, pars interarticularis, ribs, and humerus

• Management varies between individuals, injury site and extent of injury


– Epiphyseal Conditions • Three types can be sustained by adolescents (injury to

growth plate, articular epiphysis, and apophyseal injuries)– Occur most often in children ages 10-16 years old

• Classified by Salter-Harris into five types (see illustration on next slide)

– Apophyseal Injuries • Young physically active individuals are susceptible

– Apophyses are traction epiphyses in contrast to pressure epiphyses.

– Serve as sites of origin and insertion for muscles

– Common avulsion conditions include Sever’s disease and Osgood-Schlatter’s disease


Figure 9-15


– Osteochondrosis • Also known as osteochondritis dissecans and apophysitis (if

located at a tubercle/tuberosity)• Causes not well understood• Degenerative changes to epiphyses of bone during rapid

child growth• Possible cause includes 1)aseptic necrosis (disrupted

circulation to epiphysis, 2) fractures in cartilage causing fissures to subchondral bone, 3) trauma to a joint that results in cartilage fragmentation resulting in swelling, pain and locking

• With the apophysis, an avulsion fracture may be involved, including pain, swelling and disability


Nerve Trauma

• Abnormal nerve responses can be attributed to injury or athletic participation

• The most frequent injury is neuropraxia produced by direct trauma

• Lacerations of nerves as well as compression of nerves as a result of fractures and dislocations can impact nerve function


• Anatomical Characteristics– Provides sensitivity and communication from the CNS to

muscles, sense organs and various systems in the periphery

– Neuron cell body has a large nucleus with branched dendrites which respond to neurotransmitter substances

– Each nerve cell has an axon that conducts nerve impulse– Axons are encased in neurilemmal sheaths (Schwann

and satellite cells)– Various neurological cells in CNS help to form framework

for nervous tissue


• Nerve Injuries– Compression and tension are primary

mechanisms– May be acute or chronic– Physical trauma causes pain and can result in a

host of sensory responses (pinch, burn, tingle, muscle weakness, radiating pain)

– Long term problems can go from minor nerve problems to paralysis

– Neuropraxia• Interruption in conduction through nerve fiber• Brought about via compression or blunt trauma• Impact motor more than sensory function• Temporary loss of function

– Pain can be referred as well


Body Mechanics and Injury Susceptibility

• Body moves very effectively in upright position - able to overcome great forces even with inefficient lever system

• Body must overcome inertia, muscle viscosity and unfavorable angles of pull

• Mechanical reasons for injury - hereditary, congenital, or acquired defects may predispose athlete to injury

• Body build, structural make-up, habitual incorrect application of skill may also predispose individual to injury


• Microtrauma and Overuse Syndrome– Injuries as a result of abnormal and repetitive

stress and microtraumas fall into a class with certain identifiable syndromes

– Frequently result in limitation or curtailment of sports involvement

– Often seen in running, jumping, and throwing activities

– Some of these injuries while small can be debilitating

– Repetitive overuse and stress injuries include• Achilles tendinitis, shin splints, stress fx, Osgood-

Schlatter's disease, runner’s and jumper’s knee, patellar chondromalacia and apophyseal avulsion


• Postural Deviations– Often an underlying cause of injury

– May be the result of unilateral muscle or bony and soft tissue asymmetries

– Sports activities may cause asymmetries to develop

– Results in poor pathomechanics

– Imbalance is manifested by postural deviations as body tries to regain balance relative to CoG

• May be primary cause of injury


– Injury generally becomes chronic and athletic participation must stop

– Athletic trainer should attempt to correct postural conditions

– Postural conditions can make individual exceedingly more prone to injury

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Chapter 9: Mechanisms and Characteristics of Musculoskeletal and Nerve Trauma