Musculoskeletal: Evaluation and Management

Evaluation of Back Pain

Back pain affects the majority of adults during their lifetime. Systematic evaluation distinguishes mechanical causes from serious underlying pathology.

Red Flag Assessment

Back Pain Red Flags Requiring Urgent Evaluation

Recent significant trauma (fall from height, motor vehicle accident)
Age greater than 50 years with new-onset back pain
History of cancer or current malignancy
Unexplained weight loss
Fever suggesting infection
Progressive neurologic deficits
Bowel or bladder dysfunction (suggests cauda equina)
IV drug use (increased infection risk)
Immunosuppression or chronic corticosteroid use
Severe osteoporosis or prolonged corticosteroid therapy

Categorization of Back Pain Etiology

Mechanical Back Pain (Most Common ~80%)

Mechanical etiologies account for the vast majority of back pain presentations. Muscle strain develops acutely, often after lifting or unusual activity, with localized muscular tenderness and no radiation. Degenerative disc disease and facet arthropathy produce chronic pain, often with positional components (worse with extension for facet disease). Lumbar strain typically responds to rest, NSAIDs, and physical therapy.

Non-Mechanical Back Pain (~10-20%)

Serious etiologies require imaging and urgent intervention. Malignancy in the vertebral column or epidural space presents with progressive pain, weight loss, and constitutional symptoms. Infection (epidural abscess, vertebral osteomyelitis) typically accompanies fever and systemic illness, particularly in immunocompromised hosts. Inflammatory conditions (ankylosing spondylitis, reactive arthritis) feature inflammatory markers and systemic symptoms. Referred pain from abdominal organs (ruptured AAA, renal pathology, pancreatitis) must not be overlooked.

Cauda Equina Syndrome: The Surgical Emergency

Cauda equina syndrome represents compression of multiple lumbosacral nerve roots in the spinal canal. This surgical emergency requires recognition and urgent decompression to prevent permanent neurologic injury.

Cauda Equina Syndrome: Classic Presentation

Saddle Anesthesia: Loss of sensation in buttocks, perineum, and inner thighs (S3-S5 dermatomes)
Bilateral Lower Extremity Weakness or Radiculopathy
Urinary Retention or urinary incontinence with overflow
Bowel Dysfunction: Loss of sphincter control
Severe Lower Back Pain with bilateral leg pain

Immediate Action: Stat MRI lumbar spine; emergency neurosurgical consultation; surgical decompression within hours of symptom onset

Diagnostic Approach to Back Pain

Back Pain Evaluation Strategy

No Red Flags: Conservative management with NSAIDs, physical therapy, activity modification; reassess in 4-6 weeks
Red Flags Present: Imaging workup indicated
X-ray: Initial imaging for fracture, alignment, degenerative changes
MRI: Gold standard for soft tissue, nerve compression, myelopathy; assess for cauda equina
Labs if infection/malignancy suspected: ESR, CRP, CBC, blood cultures
Red Flag Combinations:
Fever + IV drug use → MRI + blood cultures for vertebral osteomyelitis/abscess
Cancer history + weight loss → MRI for metastatic disease
Progressive neurologic deficit → Urgent MRI for myelopathy or cauda equina

Evaluation of Joint Pain

Joint pain represents inflammation, mechanical dysfunction, or systemic disease. Characterization as monoarticular, oligoarticular (2-4 joints), or polyarticular (≥5 joints) guides differential diagnosis.

Inflammatory vs Mechanical Joint Pain

Key distinguishing feature: Morning stiffness lasting ≥30 minutes suggests inflammatory arthritis.

Inflammatory: Symmetric polyarticular pattern; morning stiffness; systemic symptoms (fever, malaise); elevated inflammatory markers
Mechanical: Monoarticular or asymmetric; activity-related worsening; no systemic symptoms; normal inflammatory markers

Monoarticular Arthritis Differential

Condition	Typical Joint	Presentation	Key Finding
Gout	First MTP (hallux), ankle, knee	Acute severe pain; red, warm, swollen	Negatively birefringent monosodium urate crystals; male predominance; diuretic use
Pseudogout (CPPD)	Knee (most common)	Similar to gout but generally milder	Positively birefringent calcium pyrophosphate crystals; older patients
Septic Arthritis	Knee (most common); hip in young children	Acute monoarticular pain; fever; refusal to bear weight	Medical emergency; requires arthrocentesis and empiric antibiotics
Traumatic	Variable	Recent injury; mechanical symptoms	History of trauma; imaging findings

Polyarticular Arthritis Differential

Condition	Joint Pattern	Additional Features	Lab Findings
Rheumatoid Arthritis	Symmetric PIP, MCP, wrists	Morning stiffness >1 hour; hand deformities with chronicity	RF+ or anti-CCP+; elevated ESR/CRP
Systemic Lupus Erythematosus	Hands, wrists, knees	Malar rash, photosensitivity, oral ulcers, Raynaud	ANA+; low complement; thrombocytopenia
Viral Arthritis	Symmetric hands, wrists	Recent viral illness; self-limited	Viral serology; normal inflammatory markers initially
Reactive Arthritis	Lower extremities	Recent GI or GU infection; asymmetric	HLA-B27+; elevated inflammatory markers

Synovial Fluid Analysis

Arthrocentesis with synovial fluid analysis distinguishes inflammatory from non-inflammatory arthritis and identifies crystal arthropathy or infection.

Fluid Type	Appearance	WBC Count	PMN %	Interpretation
Normal	Clear	<200	<25%	Normal joint fluid
Non-inflammatory	Clear to slightly turbid	200-2000	<25%	OA, mechanical dysfunction
Inflammatory	Cloudy	2000-50000	>50%	RA, SLE, crystalline arthritis, viral
Septic	Purulent/turbid	>50000 (often >100000)	>75%	Medical emergency; culture essential

Crystal Analysis

Gout: Monosodium urate crystals; needle-shaped; negatively birefringent (appear yellow under parallel light)
Pseudogout (CPPD): Calcium pyrophosphate dihydrate crystals; rhomboid/rod-shaped; positively birefringent (appear blue under parallel light)

Septic Arthritis: Critical Management

Septic arthritis represents a medical emergency. Staphylococcus aureus causes approximately 50% of non-gonococcal septic arthritis. Neisseria gonorrhoeae predominates in sexually active young adults. Rapid diagnosis and treatment prevent permanent joint damage.

Septic Arthritis Management Protocol

Diagnosis: Immediate arthrocentesis with synovial fluid studies (cell count, differential, Gram stain, culture, crystals, glucose)
Empiric Antibiotics (start immediately, don't wait for culture):
Vancomycin 15-20 mg/kg IV q8-12h + Ceftriaxone 2g IV q12h
Adjust based on Gram stain and culture results (typically 2-4 weeks of IV antibiotics)
Source Control: Repeated arthrocentesis or arthroscopic drainage for large effusions or if clinical deterioration
Imaging: X-ray to exclude fracture; consider ultrasound for hip arthrocentesis

Approach to Polyarticular Arthritis

When evaluating polyarticular joint pain, consider the pattern (symmetric vs asymmetric), duration (acute vs insidious), and presence of systemic features.

Diagnostic Algorithm

Polyarticular Arthritis Workup

Clinical Assessment:
Timeline of onset (acute <6 weeks; insidious >6 weeks)
Joint distribution pattern
Morning stiffness duration
Systemic symptoms
Labs:
Inflammatory markers (ESR, CRP)
Rheumatologic panel (RF, anti-CCP, ANA, complement levels)
Infectious workup if indicated (viral serology, cultures)
Imaging:
X-rays of affected joints (assess for erosions suggesting RA)
Ultrasound for effusion documentation
Arthrocentesis: If diagnostic uncertainty or monoarticular component with fever

Special Populations

Young Woman with Polyarthritis: Consider SLE in differential. Screen with ANA, CBC (thrombocytopenia, leukopenia), and urinalysis (proteinuria/hematuria).

Older Adult with Acute Polyarthritis: Consider viral arthritis (parvovirus, hepatitis C), crystal arthropathy, and polymyalgia rheumatica (ESR >50, temporal headache).

IV Drug User with Monoarthritis: Rule out septic arthritis with empiric antibiotics while awaiting culture; screen for endocarditis.

Last update: April 12, 2026