[Margins and torsion of the human fibula]

The borders and ridges of the fibula show a difficult aspect caused by the bone-forming musculature. These structures are an occasion for misunderstanding and mistaken denominations, which even had a noticeable effect on the PNA. Two thirds of all human fibulae exhibit a clearly prominent 'crista musculi tibialia posterioris', giving tendinuous attachment to the tibialis posterior muscle. In diagnosis of borders this crista may lead to errors, because it branches off from the interosseous border underneath the upper fourth of the fibula and reaches the medial crest in the middle of the bone. Most of the borders of the fibula show a twisted course corresponding to the direction of the shaping musculature and effecting a fictitious torsion of the shaft. The proper torsion of the fibula, however, is substantiated by the difference between the absolute torsion (= twist of the two ends of the bone) and the accompanying torsion (= twist enforced by the torsion of the tibia).