CH 4 PART 2- Skeletal System Pathologies and Fractures

Fibrous Dysplasia (FD)

• Definition: A rare, non-hereditary, benign but potentially disabling skeletal disorder where normal bone is replaced by fibro-osseous tissue.

• Pathophysiology: Caused by a gene mutation resulting in abnormal bone remodeling, leading to deformity, pain, and increased fracture risk.

• Classifications:

  • Monostotic: Affects a single bone (most common form).

  • Polyostotic: Affects multiple bones.

  • McCune-Albright Syndrome (MAS): Polyostotic FD associated with endocrine abnormalities (hyperfunction of the thyroid, adrenal, or gonadal glands) and café-au-lait skin pigmentation.

• Clinical Manifestations:

  • Bone pain, swelling, and fractures commonly in long bones (femur, tibia), ribs, craniofacial bones, pelvis, and spine.

  • Craniofacial involvement may cause facial asymmetry, vision loss, or hearing loss.

  • Malignant transformation (osteosarcoma, chondrosarcoma) is a rare complication.

• Imaging Hallmarks:

  • Radiograph: "Ground-glass" appearance, bone expansion with maintained overall shape, cortical thinning, and endosteal scalloping.

  • Shepherd’s Crook Deformity: A specific $varus$ deformity of the proximal femur seen in polyostotic FD.

  • CT: Provides better definition of the ground-glass matrix and sinus involvement in craniofacial FD.

  • NM Bone Scintigraphy: Shows increased uptake due to high bone turnover; useful for detecting multifocal disease.

• Management: No cure exists; treatment is symptomatic. Bisphosphonates reduce bone pain and turnover. Surgery is used for deformity correction, fracture stabilization, or reconstruction.

Ischemic Necrosis of Bone (Avascular Necrosis)

• Definition: Also known as Osteonecrosis or AVN; characterized by loss of blood supply leading to bone cell death, collapse of bone structure, and secondary joint degeneration.

• Common Sites: Femoral head (most common), humeral head, knee, talus, and scaphoid.

• Etiology and Risk Factors:

  • Trauma: Fractures or dislocations disrupting blood supply.

  • Medications: Prolonged corticosteroid therapy, chemotherapy, and bisphosphonates.

  • Systemic Diseases: Sickle cell disease, lupus, Gaucher disease, vasculitis, renal transplant, and HIV.

  • Lifestyle/Other: Alcohol abuse, decompression sickness (caisson disease), pancreatitis, radiation, and pregnancy.

• Clinical Manifestations:

  • Early stage: Asymptomatic or mild pain.

  • Progression: Pain worsens with weight-bearing; restricted range of motion.

  • Complications: Collapse of subchondral bone leading to secondary osteoarthritis.

  • Juvenile form: Legg-Calvé-Perthes disease (idiopathic femoral head necrosis in boys aged $4-8$ years).

• Imaging:

  • Radiograph: Normal in early stages; later shows sclerosis, cystic changes, the "crescent sign," and collapse of the articular surface.

  • NM/Bone Scan: "Cold spots" in early ischemia; "hot rim" uptake in the reparative phase.

  • CT: Defines cortical collapse; may show a geographic sclerotic rim or cap-like extension (necrosis extent of $≈ 230$ degrees suggests poor prognosis).

  • MRI: The most sensitive modality; shows low-signal necrosis on T1-SE and high-signal bone marrow edema on STIR.

• Management: Early disease is treated with core decompression, bisphosphonates, and restricted weight-bearing. Advanced disease requires osteotomy, bone grafting, or joint replacement.

Benign Bone Tumors

• Osteochondroma:

  • Most common benign bone tumor; contains a cartilaginous cap covered by periosteum.

  • Arises near the metaphysis of long bones during childhood; growth usually stops after puberty.

  • Low malignant potential; risk increases with childhood total body irradiation.

  • Forms: Sessile, pedunculated (cauliflower-like).

• Enchondroma:

  • Benign intramedullary cartilage tumor, most common in small bones of hands and feet.

  • Peak incidence: Ages $10-30$ years.

  • Imaging: Well-defined lytic lesion with chondroid calcification described as "rings and arcs."

• Giant Cell Tumor (GCT):

  • Locally aggressive, unpredictable osteolytic tumor affecting young adults (ages $20-45$).

  • Locations: Epiphysis of long bones, especially around the knee (distal femur, proximal tibia).

  • Management: Surgery (curettage/resection) is necessary to prevent bone destruction and recurrence; nonsurgical options include radiation or embolization.

• Osteoma:

  • Slow-growing tumor of mature compact or cancellous bone, usually in the craniofacial skeleton (paranasal sinuses, skull, mandible).

  • Often asymptomatic but larger ones can cause sinus obstruction.

• Osteoid Osteoma:

  • Benign bone-forming tumor in children/young adults (ages $10-35$).

  • Classic symptom: Night pain specifically relieved by aspirin or NSAIDs.

  • Imaging: Small radiolucent "nidus" on CT; "double density sign" on Bone Scan.

• Simple Bone Cyst (Unicameral Bone Cyst):

  • Fluid-filled cavity in children/adolescents; commonly in proximal humerus or femur.

  • Signs: "Fallen fragment sign" (fracture fragment within the cyst) and "Rising bubble sign."

• Aneurysmal Bone Cyst (ABC):

  • Vascular tumor with blood-filled cavities; affects ages < 20 in metaphysis or vertebrae.

  • Hallmark: "Fluid-fluid levels" and septations visible on MRI.

• Bone Island (Enostosis):

  • Sclerotic/dense lesion of compact bone within cancellous bone; shows "thorny radiations" on X-ray.

Malignant Bone Tumors

• Osteogenic Sarcoma (Osteosarcoma):

  • Most common primary malignant bone tumor; high-grade tumor that produces osteoid (immature bone).

  • Peak incidence: Ages $10-25$ years.

  • Common site: Metaphysis of distal femur, proximal tibia, or proximal humerus.

  • Clinical: Persistent localized pain (worse at night) and swelling; metastasis most common in lungs.

  • Imaging: Mixed lytic/sclerotic lesions, "sunburst" pattern, and Codman’s triangle (periosteal elevation).

• Chondrosarcoma (CS):

  • Produces cartilaginous matrix; typically affects adults aged > 40.

  • Axial tumors (pelvis, ribs) have worse prognosis than peripheral ones.

  • Treatment: Resistant to chemo/radiotherapy; requires wide surgical excision.

• Ewing Sarcoma:

  • Highly aggressive; affects children/adolescents (ages $10-20$).

  • Genetics: Chromosomal translocations involving the $EWSR1$ gene.

  • Imaging: "Moth-eaten" or permeative lytic lesion in the diaphysis; "onion-skin" periosteal reaction.

• Multiple Myeloma (MM):

  • Disseminated plasma cell disorder of bone marrow; remains incurable.

  • CRAB Criteria: Calcium elevation, Renal dysfunction, Anemia, Bone lesions.

  • Imaging: "Punched-out" lytic lesions on the skull, spine, and pelvis.

• Bone Metastases (METS):

  • Spread from primary tumors (most often breast, prostate, lung).

  • Colonize bone due to rich vascularity.

  • Imaging: NM Bone Scan is highly sensitive but less specific (false positives in arthritis).

Fractures and Bone Healing

• Stages of Healing:

  1. Hematoma Formation & Inflammation (hours to days): Ruptured vessels form hematoma; scaffold for stem cells.

  2. Soft Callus Formation ($2-3$ weeks): Fibroblasts/chondroblasts bridge the gap with fibrous tissue.

  3. Hard Callus Ossification ($3-6$ weeks): Endochondral ossification replaces cartilage with woven bone.

  4. Bone Remodeling (months to years): Woven bone becomes lamellar bone via Wolff's Law.

• Primary vs. Secondary Healing:

  • Primary: Rigid fixation, no visible callus, direct Haversian remodeling.

  • Secondary: Non-rigid fixation (casts/nails), involves callus formation.

• Fracture Classifications:

  • Complete: Discontinuity between fragments.

  • Incomplete: Partial discontinuity (e.g., Greenstick in children).

  • Comminuted: Shattered into multiple fragments.

  • Segmental: Shaft segment isolated by two fracture lines.

  • Open (Compound): Bone protrudes through skin.

  • Avulsion: Fragment pulled off by tendon/ligament tension.

  • Compression: Compaction of bone trabeculae (e.g., in the spine).

  • Depressed: Seen in the skull or tibial plateau.

  • Spiral/Torsion: Corkscrew appearance from twisting forces.

  • Pathologic: Occurs in bone weakened by disease (e.g., osteoporosis, METS) with minimal force.

  • Stress: Overuse injury (metatarsals, tibia) showing bone marrow edema on MRI.

Specific Common Fractures and Dislocations

• Colles Fracture: Transverse fracture of distal radius with dorsal displacement; "dinner fork" deformity; common in older adults with osteoporosis from falls.

• Scaphoid Fracture: Most common carpal fracture; caused by FOOSH (Fall On Outstretched Hand).

• Boxer’s Fracture: Fracture of the $5^{th}$ metacarpal neck (below the knuckle).

• Monteggia vs. Galeazzi Fractures:

  • Monteggia: Fracture of the proximal ulna + dislocation of the radial head. (Mnemonic: "A" is proximal).

  • Galeazzi: Fracture of the distal third of the radius + dislocation/subluxation of the distal radioulnar joint (DRUJ). (Mnemonic: "Z" is distal).

• Jones Fracture: Transverse fracture at the base of the $5^{th}$ metatarsal; prone to poor healing due to low blood supply.

• Shoulder Dislocation: Humeral head displaced from glenoid fossa; $95\%$ are anterior.

• Hip Dislocation: Traumatic emergency; $90\%$ are posterior (e.g., dashboard injury). Reduction required within $6$ hours to prevent AVN of the femoral head.

• Battered Child Syndrome (BCS):

  • Non-accidental pediatric injuries; hallmark is multiple fractures in different stages of healing and subdural hematomas.

Spinal Injuries and Conditions

• Three-Column Model of Stability:

  • Anterior Column: Anterior longitudinal ligament + anterior vertebral body.

  • Middle Column: Posterior vertebral body + posterior longitudinal ligament.

  • Posterior Column: Posterior elements (facets, spinous process) + Posterior Ligamentous Complex (PLC).

  • Unstable: Injury to $2$ or more columns.

• Specific Spinal Fractures:

  • Jefferson’s Fracture: Burst fracture of $C1$ (atlas) from axial loading (e.g., diving accidents). Unstable if lateral mass displacement is > 7\,mm.

  • Hangman’s Fracture: Bilateral fracture of the pars interarticularis of $C2$ (axis); traumatic spondylolisthesis from hyperextension.

  • Clay Shoveler’s Fracture: Avulsion fracture of spinous processes at $C6$, $C7$, or $T1$.

  • Seat Belt (Chance) Fracture: Flexion-distraction injury shattering the vertebral body and posterior elements; unstable.

• Intervertebral Disk Herniation:

  • Nucleus pulposus protrudes through the annulus fibrosus, compressing nerve roots.

  • Most common at $L4-L5$ or $L5-S1$.

• Scoliosis: Abnormal lateral curvature > 10^{\circ}. Measured via the Cobb angle on X-ray.

• Spondylolysis and Spondylolisthesis:

  • Spondylolysis: Stress fracture of the pars interarticularis (usually $L5$); shows "Scottie dog" sign on oblique X-rays.

  • Spondylolisthesis: Anterior slippage of one vertebra over another; often progresses from spondylolysis.