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Looser zones, also known as cortical infractions, Milkman lines or pseudofractures, are wide, transverse lucencies with sclerotic borders traversing partway through a bone, usually perpendicular to the involved cortex, and are associated most frequently with osteomalacia and rickets.
Given that these lesions are a type of insufficiency fracture, they are not themselves diagnostic of osteomalacia. Osteomalacia is the strongly favored diagnosis when these are bilaterally symmetric and in a classic location such as the axillary border of the scapula, rib, or posterior ulna. Other frequently involved sites include the superior and inferior pubic ramus, and medial side of the femoral neck. Complete fractures may occur through these weakened sites 4.
The term pseudofracture is a misnomer, as they are considered a type of insufficiency fracture. Typically, the fractures have sclerotic irregular margins and are often symmetrical.
Looser zones occur in the same locations as insufficiency fractures in weight-bearing bones:
medial femoral neck
medial proximal femoral shaft (cf. bisphosphonate-related fractures that occur on the lateral cortex of the proximal femoral shaft)
In non-weight-bearing bones, they often occur along nutrient foramina and represent true pseudofractures:
posterior proximal ulna
History and etymology
Looser zones are named after Emil Looser (1877-1936), a Swiss surgeon, working in Zurich 3.
Louis Arthur Milkman (1895-1951) was an American radiologist who described the findings in seminal papers in 1930 and 1934 2,3.