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Looser zones, also known as pseudofractures, are incomplete, transverse cortical radiolucent lines that represent stress fractures in areas of weakened, poorly mineralized bone.
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(a) Looser zones of osteomalacia in a case of tumour-induced osteomalacia in both pubic rami demonstrating broad bands of lucency, marginal sclerosis and absence of callus; (b) Looser zones of osteomalacia in a case of renal tubular acidosis located on medial shaft of left femur demonstrating two oblique lines; (c) atypical insufficiency fracture simulating Looser zone of osteomalacia due to osteoporosis demonstrating a broad band of lucency with marginal sclerosis in the neck of femur; (d) atypical insufficiency fractures due to osteoporosis simulating Looser zone of osteomalacia and AFFs demonstrating broad bands of lucency with marginal sclerosis on the medial shaft of the femur.
c, d: McKenna MJ, Kleerekoper M, Ellis BI, Rao DS, Parfitt AM, Frame B. Atypical insufficiency fractures confused with Looser zones of osteomalacia. Bone 1987; 8:71–8.
M.J. McKenna, E. Heffernan, C. Hurson, F.E. McKiernan, Clinician approach to diagnosis of stress fractures including bisphosphonate-associated fractures, QJM: An International Journal of Medicine, Volume 107, Issue 2, February 2014, Pages 99–105, https://doi.org/10.1093/qjmed/hct192
Pseudofracture appearance:
| Feature | Description |
|---|---|
| Orientation | Transverse (perpendicular to cortex) |
| Appearance | Narrow radiolucent bands with sclerotic margins |
| Location | Symmetrical, bilateral in typical stress-bearing locations |
• Common sites: Medial femoral neck, pubic and ischial rami, lateral scapula, ribs (posteriorly), ulna and tibia • Less common: Metatarsals | | Healing response | May show periosteal reaction if healing, but lack of healing if metabolic problem persists |
Mechanical stress of the main blood vessels overlying the uncalcified cortex of osteomalacic bones is regarded as the factor determining the location of the symmetrical pseudo fractures. The "pseudo-fractures" typically show as transverse zones of rarefaction, varying in width from 1 mm to 1 cm. They are multiple and generally symmetrical in distribution, and often occur in apparently normal bone. Their distribution is mainly ischio-pubis, ilio-pubis, femur, tibia, radius, fibula, or at the iliac bone. Other common sites are the lower ribs and the infraglenoid region of the scapula.
Ahmad F, Shah B, Nabi G, Sofi F. Looser's Zone. Oman Med J. 2010;25(2):141. doi:10.5001/omj.2010.38
Lateral radiographs of right & left tibiae and fibulae showing symmetrical Looser zones with evidence of healing on the right.
Tarazi M, P. Ellanti, McKenna MJ, Kilbane M, McCormick PA, Hurson C. Multiple Looser zones of osteomalacia in Byler disease with associated vitamin D deficiency, phosphaturia, and elevated FGF23. International Journal of Surgery Case Reports. 2015;19:150-153. doi:https://doi.org/10.1016/j.ijscr.2015.12.037
Bone Scintigraphy:
