Part I: Pseudo-fractures and foundational approach to myositis ossificans
A. Pseudo-fractures
Definition and basic concept
Pseudo-fractures, also called Looser zones or Milkman lines, are incomplete, transverse or slightly oblique radiolucent lines occurring in abnormal bone. They resemble fractures radiographically, but usually develop because of defective mineralisation, reduced bone strength, repetitive mechanical stress, or impaired healing. The term is descriptive rather than etiological; therefore, the underlying metabolic, renal, nutritional, drug-related, or skeletal disorder must always be identified.
They are most characteristically seen in osteomalacia, in which inadequate mineralisation of newly formed osteoid produces soft bone. Repetitive loading causes microdamage and incomplete cortical failure. Instead of progressing to a complete fracture, the defect becomes lined by unmineralised osteoid and fibrous tissue. This accounts for the persistent radiolucent appearance and poor healing until the underlying mineralisation defect is corrected.
Causes
- Osteomalacia: vitamin D deficiency, malabsorption, chronic liver disease, anticonvulsant therapy, renal tubular phosphate wasting, and hereditary hypophosphataemic disorders.
- Chronic kidney disease: renal osteodystrophy, particularly when secondary hyperparathyroidism, phosphate retention, and defective vitamin D metabolism coexist.
- Hypophosphataemic states: tumour-induced osteomalacia, X-linked hypophosphataemia, and other phosphate-wasting disorders.
- Hyperparathyroidism and other high-turnover metabolic bone diseases.
- Long-term drug therapy: anticonvulsants and, in selected settings, prolonged…