THE NERVES OF THE LOWER LIMB 499 



phalanges is parallel to the ground. In hallux rigidus the base 

 of the metatarsal sinks downwards so that its long axis is brought 

 into line with the axis of the phalanges. At the same time the 

 head of the bone becomes rotated upwards and the dorsal portion 

 of its articular cartilage ceases to be articular. This exposed 

 area undergoes fibrous change, and attempts at dorsi-flexion 

 cause severe pain. Reflex spasm of the muscles occurs and the 

 toe is kept rigid. 



THE NERVES OF THE LOWER LIMB. 



The Nerves of the Lower Limb are derived from the 

 lumbar and sacral plexuses (L. 2 S. 3). Plexus injuries are 

 very rare, and with the exception of the common peroneal nerve, 

 the nerves of the lower limb are seldom damaged by violence. 



The Femoral Nerve (L. 2, 3, and 4) is sometimes injured 

 in gun-shot or stab wounds, or it may be involved by a psoas 

 abscess, but the lesion is rarely complete. The quadriceps 

 femoris is paralysed, and the leg, therefore, cannot be extended, 

 but it can be brought forwards in walking " by using the 

 adductors, after the leg has been everted " (Sherren). 



The sensory disturbance is most marked over the distal two- 

 thirds of the leg and the adjoining part of the foot, on their 

 medial aspects, i.e. over the distribution of the saphenous nerve. 



The Sciatic Nerve (L. 4, 5, S. i, 2, and 3) consists of two 

 portions, the tibial (L. 4, 5, S. i, 2, and 3) and the peroneal 

 (L. 4, 5, S. i, 2), which, although enclosed in a common sheath 

 in the proximal part of the thigh and in the buttock, are 

 separable up to their origins from the plexus. The sciatic nerve 

 may be injured by penetrating wounds, dislocations of the hip- 

 joint, or fractures of the pelvis. The lesion is usually incomplete, 

 and in 90 per cent of cases (Makins) it is referable to the peroneal 

 part of the nerve. 



When the injury is complete, all the muscles of the leg and 

 foot are paralysed, and if the nerve is divided in the gluteal 

 region, the hamstrings are also involved. Flexion of the leg, 

 however, may be carried out by the gracilis (obturator n.) and 

 the sartorius (femoral n.). 



Sensory disturbances are limited to the foot and the lateral 

 aspect of the leg. 



32 a 



