Musclskeltal disorder
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I now have enough from the library and my own knowledge to give you a thorough exam-focused overview. Let me compile this now.
Musculoskeletal Disorders (MSDs) - Overview & Classification
Source: Miller's Review of Orthopaedics 9th Ed; Firestein & Kelley's Textbook of Rheumatology
What Are Musculoskeletal Disorders?
Musculoskeletal disorders (MSDs) are conditions affecting the bones, joints, muscles, tendons, ligaments, cartilage, bursae, and spinal discs. They are among the leading causes of disability worldwide.
Classification (Exam-Ready Framework)
1. Degenerative / Wear-and-Tear
| Condition | Key Features |
|---|---|
| Osteoarthritis (OA) | Cartilage loss, osteophytes, subchondral sclerosis; affects weight-bearing joints (hip, knee), DIP/PIP in hands |
| Degenerative Disc Disease | Loss of nucleus pulposus hydration; back/neck pain |
| Spondylosis | Vertebral osteophytes + disc degeneration |
Hand OA joint order: DIP > Thumb CMC > PIP > MCP - Miller's Review of Orthopaedics
2. Inflammatory / Autoimmune
| Condition | Key Features |
|---|---|
| Rheumatoid Arthritis (RA) | Synovial inflammation, symmetric small joints, MCP + PIP (spares DIP); RF/anti-CCP positive |
| Systemic Lupus Erythematosus (SLE) | Multi-system; arthritis, rash, renal disease |
| Psoriatic Arthritis | Asymmetric, DIP involvement, nail changes, "sausage digits" |
| Ankylosing Spondylitis | Axial skeleton; bamboo spine; HLA-B27 |
| Reactive Arthritis | Post-infection (GI/GU); triad: urethritis, arthritis, conjunctivitis |
| Juvenile Idiopathic Arthritis (JIA) | Arthritis < 16 yrs for > 6 weeks; multiple subtypes |
RA hallmarks: ulnar drift at MCP, swan-neck/boutonnière deformities, rheumatoid nodules, Vaughan-Jackson syndrome (extensor tendon rupture), Mannerfelt syndrome (FPL rupture over volar STT osteophyte) - Miller's Review of Orthopaedics
3. Crystal-Induced Arthropathies
| Condition | Crystal | Birefringence | Joint |
|---|---|---|---|
| Gout | Monosodium urate (MSU) | Negative (needle-shaped) | 1st MTP, ankle, knee |
| Pseudogout (CPPD) | Calcium pyrophosphate dihydrate | Positive (rhomboid) | Knee, wrist |
| Hydroxyapatite disease | Calcium hydroxyapatite | - | Shoulder (Milwaukee shoulder) |
Joint aspiration in gout = negatively birefringent MSU crystals - Miller's Review of Orthopaedics
4. Metabolic Bone Diseases
| Condition | Defect | Key Findings |
|---|---|---|
| Osteoporosis | Decreased bone mass; T-score ≤ -2.5 | Fragility fractures (hip, vertebrae, wrist) |
| Osteomalacia/Rickets | Defective mineralization (Vit D deficiency) | Bowing of legs, "looser zones" |
| Paget's Disease | Chaotic bone remodeling | Elevated ALP, hat size increase, "picture frame" vertebrae |
| Hyperparathyroidism | Excess PTH → bone resorption | "Brown tumors," osteitis fibrosa cystica |
5. Infectious Musculoskeletal Disorders
- Septic arthritis - most commonly Staphylococcus aureus (adults); Neisseria gonorrhoeae (sexually active young adults)
- Osteomyelitis - hematogenous (children: metaphysis) or direct inoculation
- Septic bursitis - common in olecranon and prepatellar bursae
- Bacteria need >10⁵ CFUs in a normal host to cause infection (only ~100 CFUs if a foreign body is present) - Miller's Review of Orthopaedics
6. Soft Tissue Disorders
| Condition | Description |
|---|---|
| Tendinitis/Tendinopathy | Overuse; rotator cuff, Achilles, patella |
| Bursitis | Inflammation of bursa; olecranon, subacromial, prepatellar, trochanteric |
| Fasciitis | Plantar fasciitis (most common cause of heel pain) |
| Myofascial Pain Syndrome | Trigger points; regional pain |
| Dupuytren's Disease | Palmar fibromatosis → finger contracture; associated with diabetes, alcohol, epilepsy medications, tobacco |
7. Musculoskeletal Tumors
| Category | Examples |
|---|---|
| Benign bone | Osteochondroma, enchondroma, giant cell tumor, osteoid osteoma |
| Malignant bone | Osteosarcoma (age <20, distal femur), Ewing sarcoma (diaphysis, "onion skin"), Chondrosarcoma (40-60 yrs) |
| Soft tissue | Lipoma (benign), liposarcoma, synovial sarcoma |
8. Congenital & Developmental
- Developmental dysplasia of the hip (DDH)
- Clubfoot (CTEV)
- Scoliosis (idiopathic most common in adolescent girls)
- Osgood-Schlatter disease (tibial tubercle apophysitis in adolescents)
9. Avascular Necrosis (AVN) / Osteonecrosis
- Kienböck's disease - AVN of the lunate; young men; dorsal wrist pain; associated with ulnar negative variance - Miller's Review of Orthopaedics
- Legg-Calvé-Perthes disease - AVN of femoral head in children (4-8 yrs)
- Frieberg's infraction - AVN of 2nd metatarsal head
- Risk factors for AVN generally: steroids, alcohol, SLE, sickle cell disease, trauma, caisson disease
Quick Memory Framework (ACID-MS)
| Letter | Category |
|---|---|
| A | Autoimmune/Inflammatory (RA, SLE, AS) |
| C | Crystal-induced (Gout, CPPD) |
| I | Infectious (septic arthritis, osteomyelitis) |
| D | Degenerative (OA, disc disease) |
| M | Metabolic (osteoporosis, Paget's) |
| S | Soft tissue / Structural (tendinitis, bursitis, tumors) |
Key Exam Distinguishers
| Feature | OA | RA | Gout |
|---|---|---|---|
| Onset | Gradual | Gradual | Acute |
| Joints | DIP, large weight-bearing | MCP, PIP (symmetric) | 1st MTP ("podagra") |
| Morning stiffness | <30 min | >1 hour | None typically |
| Fluid | Non-inflammatory | Inflammatory | Crystals (MSU) |
| X-ray | Osteophytes, joint space narrowing | Periarticular erosions, periarticular osteopenia | Punched-out erosions with sclerotic margins |
This overview covers the major MSD categories tested in exams. Let me know if you want a deep dive into any specific category, such as RA management, fracture classification, tumor staging, or metabolic bone disease workup.
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