Osteomalacia & Rickets
Summary
Osteomalacia (adults) and Rickets (children) are disorders of defective bone mineralisation. They share the same pathophysiology: a lack of Calciferol (Vitamin D) leads to insufficient Calcium and Phosphate absorption, resulting in the failure to mineralise osteoid.
- Rickets: Occurs before growth plate closure. Skeletal deformities (bowing/cupping).
- Osteomalacia: Occurs after growth plate closure. "Soft bones" causing pain, myopathy, and fractures. [1,2]
Clinical Pearls
Proximal Myopathy: A classic but often missed sign. Patients present with "difficulty climbing stairs" or "can't brush hair". This is due to hypophosphataemia affecting muscle ATP. It resolves rapidly with Vitamin D.
Looser's Zones: The radiological hallmark of Osteomalacia. These are pseudofractures (radiolucent lines) perpendicular to the cortex, typically found on the medial femoral neck, pubic rami, or scapula. They represent unmineralised osteoid at sites of stress.
Alfacalcidol in Renal Failure: Standard "Cholecalciferol" (D3) is inactive. It requires hydroxylation in the liver (25-OH) and then the kidney (1-alpha). In CKD, the kidney step fails. You MUST give Alfacalcidol (1-alpha-hydroxylated Vit D) to bypass the kidney. Supplements like Adcal-D3 will not work.
Demographics
- Prevalence: Re-emerging in Western nations.
- Risk Groups:
- Dark Skin: Melanin absorbs UV, preventing Vitamin D synthesis (Asian/Afro-Caribbean populations in high latitudes).
- Covered Skin: Cultural or religious clothing.
- Housebound: Elderly/Institutionalised.
- Diet: Vegans (unless supplemented).
Aetiology
- Vitamin D Deficiency: (Nutritional/Sunlight) - >90% of cases.
- Malabsorption: Coeliac, Gastrectomy, Pancreatic insufficiency.
- Renal Disease: CKD (Renal Osteodystrophy).
- Hereditary: X-Linked Hypophosphataemia (Vitamin D Resistant Rickets).
The Vitamin D Axis
- Synthesis: UV-B light converts 7-dehydrocholesterol in skin to Cholecalciferol (or dietary intake).
- Activation: Liver (25-hydroxylase) -> Kidney (1-alpha-hydroxylase) -> 1,25-dihydroxyvitamin D (Calcitriol).
- Action: Calcitriol increases Calcium and Phosphate absorption from the gut.
- Mineralisation: Calcium + Phosphate = Hydroxyapatite (Cement) which hardens the collagen matrix (Osteoid).
In Deficiency
- Low Ca/PO4 -> No Cement.
- Secondary Hyperparathyroidism: Parathyroids sense low calcium -> Secrete PTH -> Bones are stripped of calcium to maintain serum levels ("Robbing Peter to pay Paul").
- Outcome: Soft, unmineralised bones.
Rickets (Children)
Osteomalacia (Adults)
- Chest: Palpate ribs (tenderness).
- Legs: Measuring inter-condylar or inter-malleolar distance.
- Gait: Trendelenburg / Waddle.
Biochemistry ("Bone Profile")
| Marker | Finding | Mechanism |
|---|---|---|
| Calcium | Low / Normal | Maintained by PTH stripping bone. |
| Phosphate | Low | PTH dumps phosphate in urine ("Phosphaturia"). |
| ALP | High | Osteoblasts working overtime to fix bone. |
| PTH | High | Secondary Hyperparathyroidism. |
| Vit D | Low | less than 25 nmol/L. |
Radiology
- Rickets:
- Widening of growth plates.
- Cupping (Metaphysis cups inwards).
- Fraying (Indistinct margins).
- Osteomalacia:
- Looser's Zones.
- Codfish Vertebrae (biconcave).
Management Algorithm
SUSPECTED OSTEOMALACIA / RICKETS
(Bone Pain, Myopathy, High ALP)
↓
CHECK VITAMIN D + BONE PROFILE
↓
CONFIRMED DEFICIENCY (less than 30nmol/L)
↓
IS RENAL FUNCTION NORMAL?
┌─────────┴─────────┐
YES NO (eGFR less than 30)
↓ ↓
CHOLECALCIFEROL ALFACALCIDOI
(Standard Vit D3) (Active Vit D)
↓ ↓
LOADING REGIMEN NEPHROLOGY
(High Dose) (Complex)
↓
MAINTENANCE
(800 IU daily lifelong)
Regimens (NICE CKS)
- Loading: To rapidly replenish stores.
- Adults: 300,000 IU over 6-10 weeks (e.g., 50,000 IU weekly x 6).
- Maintenance: 800 - 2000 IU daily.
- Calcium: Supplement if dietary intake low (less than 700mg/day).
Monitoring
- Recheck Calcium in 1 month (Ensure no hypercalcaemia, though rare).
- Recheck Vitamin D at 6 months.
- Deformity: Permanent bowing (may need osteotomy).
- Pelvic Outlet Narrows: Risks for future childbirth.
- Seizures: Acute hypocalcaemia.
- Adults: Pain resolves in weeks. Myopathy in months. Looser's zones heal.
- Children: Early treatment corrects deformity (bone remodels). Late treatment leaves permanent deformity.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Vitamin D | NOS / ROS (UK) | Thresholds for treatment (less than 25 Deficient, 25-50 Insufficient). |
| Global Consensus | Horm Res Paediatr | Prevention of nutritional rickets. |
Landmark Evidence
1. ROS Guidelines
- Established the modern loading protocols, moving away from low-dose daily replacement which fails to correct severe deficiency.
What is Osteomalacia?
Bone is like reinforced concrete. It has a steel frame (protein) and concrete cement (calcium). Osteomalacia means you have the frame, but the concrete never sets. The bones remain soft and bendy.
Why do I have it?
You are low in Vitamin D. Vitamin D is the "key" that unlocks the door to let calcium from your food into your body. Without it, the calcium just passes straight through you.
But I drink milk?
You can drink all the milk in the world, but if you don't have the Vitamin D key, you can't use the calcium.
How do we fix it?
High dose Vitamin D capsules. The bone will harden up ("mineralise") over the next few months. The aches and pains will go away.
Primary Sources
- National Osteoporosis Society (Royal Osteoporosis Society). Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management. 2013 (Updated 2018).
- Munns CF, et al. Global Consensus Recommendations on Prevention and Management of Nutritional Rickets. Horm Res Paediatr. 2016.
- Holick MF. Vitamin D deficiency. N Engl J Med. 2007.
Common Exam Questions
- Biochemistry: "Hypocalcaemia + Low Phosphate + High ALP?"
- Answer: Osteomalacia (Vit D Deficiency).
- Radiology: "Pseudofractures on femoral neck?"
- Answer: Looser's Zones.
- Pharmacology: "Drug for Renal Osteodystrophy?"
- Answer: Alfacalcidol (bypasses kidney).
- Paediatrics: "Craniotabes?"
- Answer: Rickets.
Viva Points
- Osteoporosis vs Osteomalacia:
- Osteoporosis: Normal bone composition (Ratio of Mineral:Protein is normal), but less of it. Brittle. Normal bloods.
- Osteomalacia: Abnormal composition (Low Mineral:Protein ratio). Soft. Abnormal bloods.
- Oncogenic Osteomalacia: A rare paraneoplastic syndrome where a tumour secretes FGF23, causing massive phosphate wasting.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.