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File:Humerus spiral fracture.png

An x-ray image of a spiral fracture to the left humerus of a 27-year-old male. The injury was sustained during a fall.

A spiral fracture (a.k.a. torsion fracture) is a bone fracture occurring when torque is applied along the axis of a bone.[1] While torsional forces are being applied along the parallel axis of a bone, planes perpendicular to this axis are not affected. Tension is exerted upon one part of the bone, while compressive forces are exerted upon the other. When these forces have exceeded the limit tolerable by the bone, fracture occurs.[1]


Although the primary cause of spiral fractures are the application of torsional forces along the axis of a bone, said forces may be the result of one or more occurrences. Studies have shown that torsional forces may be applied along the axis of a bone (i.e. the humerus) when antagonistic muscle action occurs (e.g. when muscles oppose each other) during activities involving exerting a high force on another object.[2]

Breaking Torque and Angle for Human Limbs[1]
Bone Torque (Nm) Angle (Degrees)
Humerus 60 5.9°
Radius 20 15.4°
Ulna 20 15.2°
Femur 140 1.5°
Tibia 100 3.4°
Fibula 12 35.7°


  1. 1.0 1.1 1.2 "Spiral Fracture". Harvard University. Retrieved 25 November 2010.
  2. Liang Chao, Shang; Miller, Teng (July 1971). "A Mechanism of Spiral Fracture in the Humerus". Journal of Trauma-Injury Infection & Critical Care 11 (7): 602-605. Retrieved 25 November 2010.

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