Chapter 15 Understanding the Mechanics of Injury
Stress • Controlling the level of imposed stress is important in training various tissues and avoiding injury.
Stress Continuum (Fig 15.3, 343) • Distress (Causes malfunction) • Pathologic underload zone • Pathologic overload zone • Eustress (Causes positive adaptation) • Physiologic loading zone • Physiologic overload (training) zone
Distress Eustress Eustress Distress Phys Overload Path Overload Path Underload Phys Load
Relationship of magnitude and frequency to type of injury (Fig 15.5) • Acute loading • a single stress of sufficient magnitude to cause injury to a biological tissue. (Macrotrauma)
Repetitive loading • repeated application of a subacute stress that is usually of low magnitude (Microtrauma)
Injury Acute Definition (CDC) Injury is defined as physical damage to an individual that occurs over a short period of time as a result of acute exposure to one of the forms of physical energy in the environment, or to chemical agents, or the acute lack of oxygen. Excluded from this definition of injury are cumulative trauma disorders, musculoskeletal disorders of the back not caused by acute trauma, and effects of repeated exposure to chemical or physical agents. The three phases of injury control are defined as prevention, acute care, and rehabilitation.
Three Major Categories of Injury Intentional injuries result from interpersonal or self-inflicted violence, and include homicide, assaults, suicide and suicide attempts, child abuse and neglect (includes child sexual abuse), intimate partner violence, elder abuse, and sexual assault. Unintentional injuries include those that result from motor vehicle collisions, falls, fires, poisonings, drownings, recreational, and sports-related activities. Occupational injuries occur at the worksite and include unintentional trauma (for example, work-related motor-vehicle injuries, drownings, and electrocutions), and intentional injuries in the workplace.
Williams’ model of overuse injury (1993) Decrease Training Effort
Preventing overuse injury in young pitchers: controversy Split finger fastball vs Change up? Pain vs soreness? 75 pitch limit vs Complete Game? Science vs Tradition
Types of Fractures • Simple - no break in skin. • Compound - protrusion through the skin. • Comminuted - fragmentation of the bone. • Avulsions - bone chip pulled away • Spiral - twisting break. • Impacted - opposite ends compressed together. • Stress - repeated low magnitude loading
Avulsion fracture of the patella following B-PT-B repair of the ispsilateral ACL
Comminuted Fracture Low Energy High Energy
Types of Fractures What is the error?
Three Biological Phases to fracture healing • Inflammatory Phase • 3 to 7 days • immobilize the bone • activates cells for repair • step by step process that is critical to successful union
Three Biological Phases to fracture healing • Inflammatory Phase • Reparative Phase (bony union) • about one month • callus formation • provisional ==> bony
Three Biological Phases to fracture healing • Inflammatory Phase • Reparative Phase (bony union) • Remodelling Phase • restoration of original contour
Changes in ACL surgery • Anterior Cruciate Ligament • Prevents anterior translation of tibia relative to the femur • 3rd degree sprain of ACL • Ruptured ACL • Torn ACL • Early 1980s • B-PT-B surgery • Patella • Patellar tendon (ligament) • Tibia Tuberosity
Changes in ACL surgery • Now performed arthroscopically • May be self-donor, or cadaver • Bone plugs inserted into tibia and femur • Initial screw for stability, let nature do the rest • Wolff’s Law
The mechanical basis ofOsteoarthritis(Osteoarthrosis)
OA and Aging • Afflicts more persons than cardiovascular disease • 37 million Americans have OA • 5% at age 20 • 85% at age 65 Source: thehealthpages.com
And, of greater importance to many people, over 8,000,000 dogs. Source: www.pfizer.com
Why is OA a problem? • Pain • During motion • Night pain • Limping • energy cost • Shifts stress other joints • Limits ADLs of 35% over age 65 • Economic Cost • Medical • Time from work
Factors Associated with OA • Genetics • Aging • Gender • Body weight • Bone density • Previous trauma
Factors Associated with OA • Genetics ? • Aging • Gender • Body weight • Bone density • Previous trauma Mechanical Stress
OA is NOTan acute disease • Few cases develop from an isolated joint trauma (secondary OA)
OA is NOTan acute disease • Few cases develop from an isolated joint trauma (secondary OA) • Most diagnosed as idiopathic (no identifiable cause) • Eric Radin: OA reflects the cumulative effect of pathological load bearing • How the body deals with impulsive loading
Impulsive Load A load that reaches a relatively high magnitude in a short period of time. • Contact (impact) forces • collisions
Transmission & Attenuation of Impact Force (Impulsive Load)
Impulsive Load A load that reaches a relatively high magnitude in a short period of time. • Contact (impact) forces • collisions • Muscle force • bursts of high force