e. Sciatic nerve palsy - The sciatic nerve may be paralysed in fractures of the pelvis when the pelvis is displaced upwards. It also may be damaged in posterior dislocations of the hip especially when there is an associated fracure of the posterior rim of the acetabulum.
A complete sciatic nerve palsy will lead to paralysis of both dorsiflexion and plantarflexion of the foot.

There will also be numbness over both the dorsum and plantar slkurface of the foot.

 

f. Medial popliteal nerve - The medial popliteal nerve may be injured following fractures, dislocations and wounds of the knee and leg. Isolated injuries will lead to weakness of plantarflexion and numbness over the sole of the foot.

g. Common peroneal nerve - This nerve is much more commonly paralysed than is the medial popliteal nerve. Injuries round the knee, fractures of the upper fibula and pressure over the nerve as it winds round the neck of the fibula may all cause paralysis. There will be a foot drop with numbness over the dorsum of the foot.

h. L.5 root lesion - The 5th lumbar nerve root may be paralysed by a prolapsed intervertebral disc between L4 and L5. This is usually due to degeneration of the disc, and is often associated with an injury. Clinically the patient complains of back pain and a shooting pain radiating down the leg to the dorsum of the foot. There is marked diminution of straight leg raising, and dorsiflexion of the foot when the leg is lifted to its limit will stretch the nerve and cause severe pain, Lasegues' sign. There is weakness of dorsiflexion of the foot, and numbness over the dorsum of the foot. There is usually severe spasm of the back muscles and limitation of movement and often a tilt of the spine to one side or the other.

i. S.1 root lesion - This is due to prolapse of the disc between L5 and S1. The cause and effects are very similar to an L5 root lesion. Clinically the patient complains of back pain and a shooting pain radiating down the leg to the plantar surface of the foot. There is marked diminution of straight leg raising, and dorsiflexion of the foot when the leg is lifted to its limit will stretch the nerve and cause severe pain, Lasegues' sign. There is weakness of plantarflexion of the foot, and numbness over the sole of the foot. There is usually severe spasm of the back muscles and limitation of movement, and often a tilt of the spine to one side or the other.

j. Central prolapse of intervertbral disc - Prolapse of a disc in the lower lumbar region is usually to one side or the other due to the strong posterior longditudinal ligament of the vertebrae which prevents central protrusion. Occasionally this ligament may be degenerate, and a disc in the lower lumbar region will prolapse backwards and cause pressure on the cauda equina. The symptoms and signs are very different from a lateral prolapse of a disc. Although there will be back pain, the main finding is numbness in the perineum and perianal region, with paralysis of the bladder. Unlike lateral prolapse of an intervertbral disc which should be initally treated conservatively, a central prolapse is a surgical emergency and the disc requires operation within 6 hours, and within 3 hours if possible.