Musculoskeletal Disorders: Osteoarthritis, Osteoporosis, Gout & Back Pain

Musculoskeletal Disorders: Osteoarthritis, Osteoporosis, Gout & Back Pain

1. Osteoarthritis (OA): Pathophysiology, Presentation & Management

Osteoarthritis (OA) is the leading cause of joint dysfunction in adults, characterized by articular cartilage degradation, subchondral bone remodeling, osteophyte formation, and mild synovial inflammation. Unlike rheumatoid arthritis (RA), which is a systemic autoimmune polyarthritis, OA is a mechanical and degenerative process affecting load-bearing joints.

Clinical Presentation & Exam Findings

Patients present with localized joint pain worsening with activity and improving with rest. Advanced disease features pain at rest. Morning stiffness lasts less than 30 minutes ("gel phenomenon"). Exam reveals joint line tenderness, crepitus, restricted motion, and effusion without marked warmth. Hand manifestations include:

• Heberden's Nodes: Bony enlargements at distal interphalangeal (DIP) joints.
• Bouchard's Nodes: Bony overgrowths at proximal interphalangeal (PIP) joints.
• First CMC Joint Involvement: Squaring of the thumb base.

Diagnostics & Management Guidelines

Plain weight-bearing X-rays show asymmetrical joint space narrowing, subchondral sclerosis, cysts, and osteophytes. ESR/CRP are normal.

• Non-Pharmacological: Low-impact exercise, physical therapy, weight loss (1 lb weight loss removes 4 lbs knee pressure), assistive devices.
• Pharmacotherapy:
  • Topical NSAIDs: Topical diclofenac gel is first-line for knee/hand OA in older adults, offering pain relief equivalent to oral NSAIDs with minimal systemic absorption, avoiding GI, renal, and CV toxicity.
  • Acetaminophen: For mild pain; max daily dose is 2,000–3,000 mg/day in older adults (<2,000 mg/day in liver disease).
  • Oral NSAIDs: Effective but risky. Per Beers Criteria 2023, chronic oral NSAIDs should be avoided in older adults due to GI bleeding, acute kidney injury, hypertension, and heart failure risk. If needed, use celecoxib or an NSAID with a PPI for the shortest duration.
  • Injections: Intra-articular corticosteroids provide short-term relief (4–12 weeks) for acute flares.

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2. Osteoporosis & Bone Health Assessment

Osteoporosis is a systemic skeletal disease characterized by low bone mineral density (BMD) and microarchitectural deterioration, predisposing to fragility fractures.

Screening & Diagnostic Criteria

Screening via Dual-Energy X-ray Absorptiometry (DEXA) scanning is recommended for:

• All women aged >=65 years and men aged >=70 years.
• Postmenopausal women and men aged 50–69 with risk factors (smoking, alcohol, low BMI <20, steroid use >=3 months).
• Any adult sustaining a fragility fracture after age 50.

Diagnosis relies on WHO T-scores:

• Normal: T-score >= -1.0 SD.
• Osteopenia: T-score between -1.0 and -2.5 SD.
• Osteoporosis: T-score <= -2.5 SD at lumbar spine, femoral neck, or total hip, OR a low-trauma fragility fracture.

Pharmacological & Lifestyle Interventions

• Lifestyle: Weight-bearing exercise, fall prevention (STEADI tool), smoking cessation. Calcium total intake 1,200 mg/day; Vitamin D3 800–2,000 IU/day.
• First-Line Therapy (Bisphosphonates): Oral alendronate (70 mg weekly) or risedronate (35 mg weekly) inhibit osteoclast resorption.
  • Administration Protocol: Take immediately upon waking with 8 oz plain water, at least 30–60 minutes before food, drink, or medications. Remain upright for >=30 minutes to prevent esophageal ulceration.
  • Contraindications: Esophageal stricture, inability to sit upright, or severe renal impairment (eGFR <35 mL/min). Consider bisphosphonate holiday after 3–5 years to minimize atypical femur fracture and jaw osteonecrosis (ONJ) risks.
• Alternative Agents: Subcutaneous Denosumab (RANKL inhibitor) every 6 months is safe in renal impairment (eGFR <30 mL/min), but cannot be stopped abruptly due to rebound fracture risk.

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3. Gout & Crystal Arthropathies

Gout is an intensely painful inflammatory arthritis caused by monosodium urate (MSU) crystal deposition secondary to chronic hyperuricemia (serum uric acid >6.8 mg/dL).

Clinical Presentation & Diagnostics

Flares present with sudden monoarticular joint pain, swelling, warmth, and erythema, peaking within 12–24 hours. The first metatarsophalangeal (MTP) joint is involved in >50% of initial cases (podagra).

• Gold Standard: Arthrocentesis showing intracellular needle-shaped, negatively birefringent MSU crystals under polarized light. Serum uric acid may be falsely normal during acute flares; recheck in 2–4 weeks.

Flare Treatment vs. Chronic Urate-Lowering Therapy (ULT)

• Acute Flare: Colchicine (1.2 mg at onset, then 0.6 mg 1 hour later; total 1.8 mg within 36 hours), short-course NSAIDs, or oral prednisone (30–40 mg/day tapered over 7–10 days; preferred in older adults with renal/cardiac risk).
• Chronic ULT: Indicated for >=2 flares/year, tophi, or CKD stage 3–5. Allopurinol is first-line (start 100 mg daily; titrate to serum uric acid <6.0 mg/dL).
  • Safety Pearl: Screen for HLA-B*5801 allele in high-risk populations (Han Chinese, Thai, Korean descent, or African Americans with CKD) prior to allopurinol to prevent fatal Stevens-Johnson syndrome.
  • Prophylaxis: Co-prescribe low-dose colchicine (0.6 mg daily) or NSAID for 3–6 months during ULT initiation to prevent flare mobilization.

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4. Low Back Pain (LBP) & Vertebral Syndromes

Low back pain is a common primary care complaint requiring differentiation of benign mechanical causes from serious pathology.

Differential Diagnosis & Red Flag Screening

• Mechanical LBP (90%): Lumbar strain, degenerative disc disease, facet joint osteoarthritis.
• Radiculopathy: Nerve root compression (L4-S1) causing sharp pain radiating down the leg past the knee (sciatica).
• Spinal Stenosis: Narrowing of spinal canal causing neurogenic claudication (leg pain/weakness worse with extension/walking, relieved by sitting/forward flexion).
• Red Flags (Immediate Imaging/ER): Cauda Equina Syndrome (urinary retention, fecal incontinence, saddle anesthesia, bilateral motor loss), malignancy history, fever/chills (epidural abscess), major trauma.

Exam & Guideline Management

• Straight Leg Raise (SLR): Pain radiating below knee at 30–70 degrees elevation indicates nerve root irritation.
• Imaging Guidelines: Routine X-rays or MRI are not recommended within the first 4–6 weeks unless Red Flags are present.
• First-Line Care: Continued physical activity (avoid bed rest >2 days), heat application, short-term acetaminophen or NSAIDs. Skeletal muscle relaxants (cyclobenzaprine) carry high anticholinergic risk in elderly (Beers Criteria). Physical therapy for persistent pain (>2–4 weeks).

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Summary Matrix