6.11 Osteonecrosis & Metabolic Bone Disease
Key Takeaways
- Hyperparathyroidism, Paget disease of bone, avascular necrosis and osteonecrosis, and osteogenesis imperfecta are the enumerated metabolic bone topics.
- Plain radiographs are normal in early osteonecrosis, so magnetic resonance imaging is required when clinical suspicion is high.
- Corticosteroid exposure and alcohol use account for the majority of non-traumatic osteonecrosis of the femoral head.
- Sickle cell disease, systemic lupus erythematosus, antiphospholipid syndrome and decompression illness are additional recognized causes of osteonecrosis.
- Osteogenesis imperfecta presents with recurrent fractures, blue sclerae, dentinogenesis imperfecta and early hearing loss.
1. Osteonecrosis (Avascular Necrosis)
Death of bone from interrupted blood supply. The femoral head is by far the most common site; others include the humeral head, femoral condyles, talus and scaphoid.
Causes
| Category | Examples |
|---|---|
| Corticosteroids | High cumulative dose; the leading non-traumatic cause |
| Alcohol | Chronic heavy use; the second leading cause |
| Trauma | Femoral neck fracture, hip dislocation — sites with a tenuous retrograde blood supply |
| Hemoglobinopathy | Sickle cell disease |
| Autoimmune | Systemic lupus erythematosus, antiphospholipid syndrome |
| Other | Decompression illness (caisson disease), radiation, Gaucher disease, pancreatitis, HIV, organ transplantation |
Corticosteroids and alcohol together account for the majority of atraumatic cases. In lupus, distinguishing steroid-induced osteonecrosis from a disease flare matters, because the reflexive answer — more steroids — makes osteonecrosis worse.
Presentation and diagnosis
Groin pain worsened by weight-bearing, with restricted internal rotation of the hip. Early on, the examination may be nearly normal.
The critical diagnostic point: plain radiographs are normal in early disease. Radiographic change — sclerosis, the subchondral lucency of the crescent sign, and eventual femoral head collapse — appears only after months. MRI is the test of choice and detects the lesion at a stage when joint-preserving intervention is still possible. A negative radiograph in a patient with risk factors and typical pain must not end the evaluation.
Staging progresses from a normal radiograph with MRI changes, through the crescent sign, to subchondral collapse and finally secondary osteoarthritis of the acetabulum. Pre-collapse disease may be managed with protected weight-bearing and core decompression; post-collapse disease generally requires arthroplasty. Bilateral involvement is common, so the contralateral hip should be imaged.
Medication-related osteonecrosis of the jaw
A distinct entity associated with high-dose intravenous bisphosphonate or denosumab therapy in oncology, and far less commonly with the doses used for osteoporosis. Risk factors include dental extraction, poor oral hygiene, and glucocorticoid use. Dental evaluation before initiating high-dose antiresorptive therapy is the preventive measure; the absolute risk at osteoporosis doses is very low and should not deter treatment of a patient at high fracture risk.
2. Hyperparathyroidism and Bone
Primary hyperparathyroidism is the leading cause of hypercalcemia in ambulatory patients and is usually detected incidentally. Its skeletal consequences are what place it in this blueprint subsection:
- Preferential loss of cortical bone, so the distal one-third radius is the site most likely to show a low T-score — and the site most often omitted from a standard densitometry protocol. It should be included whenever primary hyperparathyroidism is known or suspected.
- Osteitis fibrosa cystica — subperiosteal bone resorption along the radial aspect of the middle phalanges, brown tumors, a salt-and-pepper skull. Now rare, since most disease is detected early.
Surgical indications include age under 50, serum calcium more than 1 mg/dL above the upper limit of normal, a T-score of -2.5 or below at any site or a vertebral fracture, creatinine clearance below 60 mL/min, nephrolithiasis or nephrocalcinosis, and marked hypercalciuria. Parathyroidectomy improves bone density, which non-surgical management does not.
Secondary and tertiary hyperparathyroidism arise in chronic kidney disease and produce renal osteodystrophy, covered with chronic kidney disease-mineral and bone disorder.
3. Osteogenesis Imperfecta
A heritable collagen type I disorder, most often autosomal dominant.
Clinical features:
- Recurrent fractures with minimal trauma, beginning in childhood
- Blue or grey sclerae — thin sclera revealing underlying choroid
- Dentinogenesis imperfecta — discolored, translucent, fragile teeth
- Early-onset conductive or mixed hearing loss from otosclerosis and ossicular fragility
- Short stature, joint laxity, kyphoscoliosis, easy bruising
Milder adult presentations are readily mistaken for premature osteoporosis. Suspect osteogenesis imperfecta when low-trauma fractures occur at an unexpectedly young age, especially with blue sclerae, abnormal dentition or early hearing loss, or a family history of fractures. Bisphosphonates reduce fracture rate.
In a fracture-prone adult, remember the broader differential of secondary bone fragility: hyperparathyroidism, hyperthyroidism, multiple myeloma, hypercortisolism, celiac disease, mastocytosis, hypophosphatasia and chronic corticosteroid therapy all warrant consideration before attributing fragility to age alone.
4. Paget Disease of Bone
Covered in detail with disorders of calcium metabolism. In brief for this subsection: disordered bone remodeling producing an isolated elevated alkaline phosphatase with normal calcium and phosphate, focal bone pain, deformity such as bowing and increasing hat size, high-output cardiac states in extensive disease, cranial nerve compression including hearing loss, and a small but real risk of secondary osteosarcoma signaled by new pain or a rapidly rising alkaline phosphatase. A potent intravenous bisphosphonate is the treatment of choice.
A 39-year-old woman with systemic lupus erythematosus who has taken prednisone for six years presents with three months of right groin pain that worsens with weight-bearing. Internal rotation of the right hip is limited and painful. Plain radiographs of the pelvis are normal. Inflammatory markers are at her baseline. What is the most appropriate next step?
A 55-year-old woman with asymptomatic primary hyperparathyroidism undergoes bone densitometry that shows normal T-scores at the lumbar spine and total hip. Which additional measurement site is most likely to reveal osteoporosis and change management?