10.2 Diagnosis: Bone and Joint Disorders

10.2 Diagnosis: Bone and Joint Disorders

Bone and joint disorders are a staple of NBCE Part II because they compress a large amount of clinical reasoning into short vignettes: age, joint distribution, duration of morning stiffness, fever, trauma mechanism, and a one-line imaging report. Your task is to recognize the pattern, name the most likely diagnosis, and know when chiropractic management is appropriate versus when the patient needs urgent orthopedic, rheumatologic, or emergency referral.

Osteoarthritis (OA)

Osteoarthritis is the most common arthritis — a degenerative process of articular cartilage with subchondral bone remodeling, not a primary autoimmune synovitis. Typical features include:

• Onset after age 40, insidious progression over months to years
• Mechanical pain that worsens with activity and improves with rest
• Brief morning stiffness, usually less than 30 minutes
• Predilection for weight-bearing joints (knees, hips), lumbar and cervical facet joints, and specific hand joints: distal interphalangeal (DIP) Heberden nodes, carpometacarpal (CMC) thumb base
• Bony enlargement, crepitus, limited range of motion, minimal warmth compared with inflammatory arthritis
• Imaging: joint-space narrowing, osteophytes, subchondral sclerosis, subchondral cysts

A high-yield hand distinction: OA affects DIPs and thumb CMC but spares MCPs. Symmetric MCP swelling points toward rheumatoid arthritis instead. Bouchard nodes at the PIP can occur in OA but isolated PIP/MCP inflammatory swelling is not the OA pattern.

Rheumatoid Arthritis (RA)

Rheumatoid arthritis is a chronic autoimmune symmetric inflammatory polyarthritis:

• Small joints first: MCPs, PIPs, wrists, MTPs; DIPs are classically spared
• Morning stiffness lasting more than 60 minutes, often with fatigue and systemic symptoms
• Soft-tissue swelling, warmth, and symmetry across both hands
• Laboratory: rheumatoid factor (RF) and especially anti-cyclic citrullinated peptide (anti-CCP) antibodies; elevated ESR and CRP
• Radiographs: periarticular osteopenia, marginal erosions, joint-space narrowing in a symmetric pattern
• Late deformities: ulnar deviation at MCPs, swan-neck and boutonniere deformities at fingers

Extra-articular manifestations — rheumatoid nodules, keratoconjunctivitis sicca, interstitial lung disease — may appear in stems as secondary clues. A hot, monoarticular knee with fever is septic arthritis until proven otherwise, not RA.

Ankylosing Spondylitis (AS)

Ankylosing spondylitis is a seronegative spondyloarthropathy centered on the sacroiliac joints and spine:

• Insidious low back or buttock pain persisting more than three months, often beginning before age 40
• Inflammatory pattern: stiffness worse in the morning, improves with exercise, not relieved by rest alone
• Reduced lumbar flexion (decreased Schobert test), reduced chest expansion
• Imaging: bilateral sacroiliitis (erosions, sclerosis, eventual fusion); advanced disease may show syndesmophytes and "bamboo spine"
• Strong association with HLA-B27 (not diagnostic alone)
• Enthesitis at Achilles insertion or plantar fascia; anterior uveitis (painful red eye, photophobia) is a classic extra-articular manifestation

Differentiate AS from mechanical low back pain: AS patients are often younger, report prolonged morning spinal stiffness, and improve with activity rather than bed rest. Flat back posture from reduced lumbar lordosis may appear in late disease.

Fracture

Fracture diagnosis rests on mechanism, focal bony tenderness, and imaging:

• Acute trauma with deformity, crepitus, rapid swelling, inability to bear weight (lower extremity), or loss of function
• Point tenderness directly over bone, not just surrounding soft tissue
• High-yield patterns: shortened and externally rotated leg after a fall in an older adult (femoral neck fracture); snuffbox tenderness after a fall on an outstretched hand (scaphoid fracture, repeat X-ray or MRI if initial film negative)
• Stress fracture: repetitive loading (runner's tibia, metatarsal in military recruits), localized bony pain worsened by activity, normal initial radiographs possible
• Pathologic fracture: minimal trauma in the setting of metastatic disease, osteoporosis, or underlying bone lesion

Red flags demanding emergency referral: open fracture, neurovascular compromise, high-energy mechanism with suspected spine injury, hip fracture, or any fracture with compartment syndrome signs (severe pain out of proportion, pain with passive stretch, tense compartment).

Osteomyelitis

Osteomyelitis is infection of bone, either hematogenous (children, IV drug users, bacteremia) or contiguous from a soft-tissue ulcer (classic in diabetic foot wounds):

• Fever, chills, and deep, localized bone pain; children may refuse to bear weight
• Markedly elevated ESR and CRP; WBC may be normal in subacute cases
• Focal bony tenderness out of proportion to superficial skin findings
• Plain radiographs may be normal for 10–14 days; MRI is the most sensitive early modality, showing marrow edema and periosteal reaction
• Staphylococcus aureus is the most common organism in adults

Distinguish osteomyelitis from cellulitis or abscess: infection confined to skin and subcutaneous tissue does not produce deep, focal tenderness directly over the metaphysis or cortex with systemic inflammatory markers as high as untreated osteomyelitis. Suspected osteomyelitis requires medical referral, blood cultures, and often biopsy or aspiration — not repeated manipulation over infected bone.

Avascular Necrosis (AVN)

Avascular necrosis (osteonecrosis) is ischemic death of bone, most famously the femoral head:

• Insidious groin, thigh, or buttock pain worsened by weight bearing and internal rotation of the hip
• Risk factors: prolonged corticosteroid use, heavy alcohol consumption, sickle cell disease, systemic lupus erythematosus, prior hip dislocation or fracture disrupting blood supply
• Range of motion loss, especially hip internal rotation and abduction, early in the course
• Plain films may be normal initially; MRI detects marrow changes before collapse
• Bilateral hip involvement is common when steroids are the etiology

Mimics include hip osteoarthritis (older patient, gradual loss of joint space), trochanteric bursitis (lateral hip pain), and referred lumbar radiculopathy. A Part II stem that mentions three months of prednisone for asthma and new groin pain should trigger AVN in the differential before labeling the complaint simple mechanical hip strain.

Comparative Table for Part II

Chiropractic Clinical Reasoning and Referral

Conservative musculoskeletal care is appropriate for uncomplicated OA and stable mechanical joint dysfunction when no red flags are present. Co-manage RA and AS with rheumatology; manual care may adjunctively address compensatory patterns but does not replace disease-modifying therapy. Never manipulate through an undiagnosed hot, swollen monoarthritis — aspirate to rule out septic arthritis first. Refer urgently for suspected fracture, osteomyelitis, AVN with collapse risk, or any neurovascular deficit.

Exam-Style Pearls

Classic pairings: symmetric MCP swelling with two-hour morning stiffness → RA; DIP bony nodes in a 65-year-old with knee crepitus → OA; 28-year-old man with buttock pain, morning spine stiffness relieved by swimming, bilateral sacroiliitis on X-ray → AS; diabetic foot ulcer, fever, and tenderness over the metatarsal shaft → osteomyelitis; groin pain after chronic prednisone, painful internal rotation, MRI ordered → AVN; elderly fall, shortened externally rotated leg → hip fracture. When imaging lags behind clinical suspicion in infection or AVN, trust MRI and inflammatory markers over a normal initial radiograph.