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Osteoporosis is too little normal bone; osteomalacia is poorly mineralised bone
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| Feature | Osteoporosis | Osteomalacia |
|---|---|---|
| Problem | Reduced quantity of normal bone | Defective mineralisation |
| Cause | Ageing, oestrogen deficiency, steroids | Vitamin D deficiency, renal disease |
| Calcium | Normal | Low or normal |
| Phosphate | Normal | Low |
| Alkaline phosphatase | Normal | Raised |
| Parathyroid hormone | Normal | Raised (secondary) |
| Pain | Painless until fracture | Bone pain and proximal myopathy |
| Radiology | Reduced density | Looser zones (pseudofractures) |
Osteoporosis is defined by a bone mineral density T score of -2.5 or below; osteopenia is between -1 and -2.5. Fracture risk is assessed with tools such as FRAX, since density alone underestimates it.
Osteomalacia in children is rickets, with growth plate involvement giving bowing, widened metaphyses and rachitic rosary.
A useful third comparison is Paget disease, where turnover is grossly increased and disorganised, giving a markedly raised alkaline phosphatase with normal calcium and phosphate, and characteristic bone deformity and enlargement.