The biceps femoris muscle extends from the superior spinous process of the sacrum to the region of the patella and the external surface of the thigh. Above, it is inserted into the sacrum and the posterior margin of the ischium, below into the supero-external surface of the tibia. It completely covers the coxo-femoral articulation, and its passage over the summit of the trochanter is lubricated by a serous bursa. The whole of its anterior margin is connected with the fascia lata by an aponeurotic expansion. From varying causes this aponeurotic layer may become fissured; during the backward and forward movements of the limb the summit of the trochanter may enter the fissure and become fixed there by the tension and resistance of neighbouring tissues. This accident has been described as “displacement or rupture of the biceps femoris muscle.”
According to Cruzel, fixation of the biceps femoris may occur, in very thin animals, without rupture of the musculo-aponeurotic layer, the process being then simply confined to stretching of the aponeurotic layer over the summit of the trochanter. Under such circumstances the musculo-aponeurotic layer presents a cup-like depression, into which the summit of the trochanter fits, and thus effectually prevents movement of the muscle.
Whether the accident is due to an actual fissure, or only to stretching of the aponeurosis, the symptoms are the same.
Causes. The principal predisposing causes are thin condition and malformation of the limbs (turning outward of the hind toes).
The accident may occasionally be caused by a slip backwards, or by extreme efforts in draught when ascending hills.
Symptoms. Immediately the accident occurs the limb becomes fixed in a position of maximal extension. The trochanter being caught, the femur can no longer be flexed, and the lower joints are also fixed in such a way that the limb can only be moved as a whole. The claws are dragged along the ground, and the affected limb, which can never be completely advanced, is brought forward with a mowing movement.
On local examination, the trochanter appears to be very prominent, and situated directly above a rigid cord which extends parallel with the anterior margin of the affected muscle.
If the accident consists merely in the formation of a depression in the muscle, in which the summit of the trochanter is fixed, and if there is no fissuring, the muscle and the femur are certainly immobilised, but the limb can be moved to a certain extent, the “mowing” movement is less marked, and there is no well-defined rigid cord along the anterior margin of the muscle.
Fig. 29.—Arrangement of the external ischio-tibialis muscle. 1, Anterior margin of the muscle; 2, fascia lata.