Pathophysiology of Bone and Joint Injuries

• The objective is to discuss the pathophysiology of common injuries and disorders of the bones and joints

Musculoskeletal Dysfunction

• Includes musculoskeletal injuries, disorders of the bone and disorders of joints

Soft Tissue Injuries

• Contusion: Blunt force trauma with intact overlying skin, hemorrhaging occurs below the surface
• Hematoma: Collection of blood due to larger local hemorrhage
• Laceration: Injury in which skin is torn

Joint Injuries

• Joint injuries include strain, sprain, and dislocation

Strain

• A stretching injury involving a tendon or muscle

Sprain

• A stretching injury involving a ligament

Dislocation

• Temporary displacement of bones in a joint where bone surfaces lose contact entirely

Subluxation

• Bone surfaces partially lose contact, a mild dislocation that is common for vertebrae

Fracture

• Any discontinuity/break of bone, as a result of applied force the exceeds strength of the bone
• Fractures most commonly affect the clavicle, tibia, and distal forearm in young people due to trauma, or hands and feet from workplace accidents
• Proximal femur, pelvis, and vertebrae fractures are common in the elderly due to osteoporosis

Ways of Classifying Fractures

• Clinically, a combination of classifications describe a fracture fully, including severity, intactness of the skin, geometry, degree of stability, completeness, position, cause and location

By Severity

• Categorized as simple fracture (single disruption with two fragments) or comminuted/complex fracture (several intermittent fragments)

By Intactness of Skin

• Classified as closed/noncommunicating where skin is not disrupted, or open/communicating/compound where skin is disrupted

By Geometry

• Classified as transverse (perpendicular to longitudinal axis), oblique (at an angle), linear or longitudinal (along the length), or spiral (in a spiral fashion)

By Degree of Stability

• Classified as stable if not movable, impacted if fragments driven to each other, or depressed if bone fragments driven inward, usually relating to the skull

Incomplete Fractures

• Bones still maintain some connection in greenstick fractures (splintering of inner bone) and bowing (bend in bone causing microfractures)

Position

• A displaced fracture means bone fragments are not anatomically aligned

Cause

• Traumatic injury is the most common cause
• Pathologic fractures are due to preexisting abnormality or disease that has weakened the bone
• Stress fractures are fractures caused by repeated low impact stress

Location

• Colle's fracture is a fracture of the distal radius and ulna, typical when falling toward hard ground and hand is outstretched
• Pott's fracture is a fracture of the distal fibula and tibia due to excessive force on the ankle, stepping down with force

Risk Factors and Manifestations of Fractures

• Manifestations include unnatural alignment, deformity, swelling, pain, loss of function and abnormal mobility
• Typically numb for the first ~30 min as a temporary/local shock, followed by severe pain compounded by muscle spasms

Pathophysiology of Fractures

• A fracture damages periosteum, blood vessels, cortical bone, marrow, and surrounding soft tissue
• The body repairs fractures in four phases:

Fracture Repair - Phase 1

• Phase 1: Hematoma formation
• Hemorrhage of bone/soft tissues leads to hematoma/clot formation
• Dead bone tissue/debris stimulates inflammatory response and WBC infiltration

Fracture Repair - Phase 2

• Phase 2: Fibrocartilaginous callus formation
• New blood vessels/angiogenesis infiltrate the fracture site
• Fibroblasts in periosteum/endosteum produce fibrocartilaginous soft callus, bridging the broken bones

Fracture Repair - Phase 3

• Phase 3: Bony callus formation
• Ossification by osteoblasts slowly replaces fibrocartilaginous callus with spongy bone, now called the bony callus/callus

Fracture Repair - Phase 4

• Phase 4: Remodeling
• Compact bone replaces spongy bone at periphery
• Excess materials removed from outside of bone shaft and from medullary cavity
• Fracture healing rates are faster in young vs. old, lower vs. upper limbs and spongy vs. compact bone

Treatment and Complications

• Treatment involves reduction or realigning and immobilization/minimizing movement, using splint, cast, traction, and fixation
• Complications include soft tissue injury due to fragments, hemorrhage, infection, venous thromboembolic disorders/DVT and possibly fat embolism/pulmonary infarction and possible deformity

Impaired Healing

• Malunion - healing of a bone in an incorrect anatomical position
• Delayed Union - union of bone ends does not occur for approx. 8-12 months, caused by low blood supply/infection
• Nonunion - failure of bone ends to grow together and gap fills with dense fibrous or cartilaginous tissue

Osteoporosis

• Most common bone disease but general cause is still unknown
• Risk factors include age, sex, genetics, nutrition, activity, and pathologies
• More common in women (1/3 women 50+, 1/5 men 50+)
• Osteoporosis is due to decreasing estrogen levels after menopause
• Men typically have higher bone density, and women usually perform less weight-bearing exercise
• Metabolic bone disease is characterized by reduced bone density and structural integrity
• Maximum bone density occurs around the age of 30
• Mild osteoporosis is referred to as osteopenia

Manifestations and Complications

• Osteoporosis is observed late in the course of disease and is a silent disease
• The most common signs are weight/height loss, deformity/kyphosis or hunchback, fractures, pain, and pulmonary fat embolism
• Spine abnormalities include fractures, kyphosis and scoliosis
• Complications include hip fractures

Diagnosis and Treatment

• Commonly diagnosed after a fracture
• X-rays determine bone density, comparing to density of healthy adult of the same sex with standard deviation measurements
• Treatment options include regular weight-bearing activity, calcium, calcitonin, vitamin D supplements, and hormone treatments, though hormone treatment increases risk of breast cancer, heart disease, and stroke
• Bone cement injections/kyphoplasty can also be used as treatment

Osteomalacia

• Characterized by inadequate and delayed mineralization of osteoid, referred to as rickets in children
• Most commonly the result of deficiencies in calcium or vitamin D due to dietary intake, intestinal uptake, sunlight exposure, and renal disease

Manifestations and Treatment

• Leads to diffuse skeletal tenderness and pain, particularly in the hips and back
• Resistance to walk and compounded muscle weakness can lead to a waddling gait and skeletal deformities, along with fractures to the femur and radius
• Diagnosed with x-rays and blood tests to find stress fractures/poorly healed areas, and bone biopsies can confirm
• Treat with calcium and vitamin D, although malabsorption or renal disorders require treatments that target the problem

Paget's Disease

• Second most common bone disease
• Increased bone remodeling in disorganized bone creates chaotic bone formation and bone is easily bowed/fractured
• Genetic and environmental influences play a role, with 15-40% first degree relatives with the disease, and begins in mid-adulthood/more common later
• Initiates in localized spots throughout the body at random times and mostly affects the skull, vertebrae, sternum, pelvis, and femur

Symptoms, Diagnosis and Treatment

• Usually asymptomatic (70% discovered accidentally)
• May lead to brain compression causing headaches, vertigo and dementia
• Compression of cranial nerves cause sensory and motor changes like tinnitus
• Enlargement at joints causes arthritis, kyphosis and bone bowing, fractures
• It can cause aches, pain and stiffness and increases likelihood of osteosarcoma in 5-10% of patients
• Diagnosed through x-rays and blood tests looking for alkaline phosphatase, which is elevated due to osteoblast activity
• Treated with anti-inflammatories for pain
• Drugs to reduce bone resorption like calcitonin are given

Osteomyelitis

• Bacterial infection of bone and is severe
• Usually from Staphylococcus aureus, which adheres well to bone and hides in osteoblasts
• Endogenous osteomyelitis is due to spread from other infections by hematogenous spread and commonly seen in children
• Exogenous is from outside such as opened wounds, compound fractures, bites, surgery, and prosthetic joints
• Provokes an inflammatory response with rigid bone that has not a lot of space for swelling and exudation
• Blood vessels thrombose, exudate fills canaliculi and haversion canals, which may disrupt blood supply, and WBCs cannot enter small canaliculi
• This causes necrosis of infected bone/sequestrum formation
• New thick bone/involucrum is being produced around an area of necrotic bone

Manifestations and Treatment

• Begins with vague symptoms of fever, malaise, chills, and anorexia
• Pain during movement and local tenderness, and spreads to joints
• Weakens bone and causes delayed healing of fractures due to difficult penetration of immune cells and poor blood supply
• Infection may cause septicemia or blood poisoning
• Detected through x-rays, CT and MRI scans
• Biopsies obtain a sample cultured to identify causative agent
• Treated with antibiotics usually given prophylactically when undergoing bone surgery

Arthritis

• Affects 4.6 million Canadians with 7.5 million expected by 2036
• Damage/destruction occurs in the synovial membrane or articular cartilage of the joint
• Consists of 100+ disease states
• Localized/self-limiting or systemic autoimmune conditions

Osteoarthritis

• Most common form of arthritis is a leading cause of pain and disability in elderly
• Loss of articular cartilage in synovial joints
• Risk factors include age, race, sex, genetics, weight, bone mass, and previous trauma, especially for athletes
• Articular cartilage starts to erode, causing bones to grind together
• Joint space narrows and subchondral bone thickens and hardens, resulting in sclerosis and eburnation
• Fragments of cartilage and bone become dislodged and float around, joint mice may form
• Osteophytes or spurs form altering contours and enlarging joint, usually with non-specific inflammation of synovial membrane, causing synovitis

Manifestations and Treatment

• Clinical manifestations include swelling, joint effusion, pain, stiffness and limits to range of motion
• No cure exists with limited treatment plans
• Treatment includes minimize movement, anti-inflammatories, and replacement surgery

Rheumatoid Arthritis

• Systemic autoimmune disease causes chronic inflammation of connective tissue
• Affects women more than men 3:1
• Autoimmune disease with rheumatoid factor, thought to be genetic
• Synovial membrane is the first to get inflamed, then spreads
• 70-80% of patients produce rheumatoid factor or RF antibody that embeds in synovial membrane to activate immune system and inflammation/synovitis
• Immune complexes release enzymes degrading tissues in synovial joint
• Scar tissue/pannus forms in joints, immobilizing it

Manifestations and Treatment

• Clinical manifestations include symmetric, polyarticular pain and stiffness
• A loss of mobility can occur from pain and swelling and progressive joint destruction, subluxation causing deformities
• Treatment includes rest, therapeutic exercises, anti-inflammatories, and surgery