Mirels Classification for Risk of Pathological Fracture

The Mirels system classifies the risk of pathologic fracture based on scoring four variables on a scale of 1-3: location of lesion, radiographic appearance, size, and pain. An overall score is calculated, and a recommendation for or against prophylactic fixation is made.

	1	2	3
Location	Upper extremity	Lower extremity	Intertrochanteric
Radiographic appearance	Blastic	Mixed	Lytic
Sizea	< 1/3	1/3 - 2/3	>2/3
Pain	Mild	Moderate	Functionalb
a  Size is determined as a fraction of the cortical thickness. b  Functional pain is defined as severe pain or pain aggravated by limb function.

Score	Fracture Risk	Recommendation
≥9	33%-100%	Prophylactic fixation is recommended
=8	15%	Clinical judgment should be used
≤7	<4%	Observation and radiation therapy can be used

As an example, the lytic, intertrochanteric lesion shown above takes up >2/3 of the cortical thickness, getting an overall score of 9 in the absence of any clinical information about the degree of pain.

References

Mirels H. Metastatic disease in long bones. A proposed scoring system for diagnosing impending pathologic fractures. Clin Orthop Relat Res. 1989 Dec;(249):256-64.