1. Five cases of postero-lateral dislocation of the knee with capsular interposition are described.

2. The mechanism of the injury is considered in the light of the case histories and the findings at operation.

3. The constant clinical findings associated with this injury are described.

4. Open reduction is recommended: with early operation the prognosis for function and stability is good.

1. The distribution of the permanent paresis and paralysis in the muscles of 203 lower limbs affected by poliomyelitis is analysed and related to the destruction of motor nerve cells in the grey matter of the lumbo-sacral cord.

2. The tibialis anterior and tibialis posterior and the long muscles of the toes are more often paralysed than paretic; these muscles are innervated by short motor cell columns. Muscles such as the hip flexors and hip adductors that are more often paretic than paralysed are innervated by long cell columns.

3. Muscles innervated by the upper lumbar spinal segments are more frequently affected than those innervated by the sarcal segments. This agrees with the segmental incidence of motor cell destruction found in poliomyelitic spinal cords.

4. Each muscle or muscle group is associated in paralysis with other specific muscles. For instance, the long toe extensors with the peronei and the calf muscles (triceps surae) with the biceps femoris. Associated muscles are innervated by adjacent motor cell columns. The probability of recovery in a paralysed muscle can be determined by reference to the degree of involvement in its associated muscles.

5. The distribution of the paralysis in an individual lower limb is determined by the site and size of foci of motor cell destruction. The cell loss in certain common patterns of paralysis is described.

6. The practical application of these findings is discussed.

1. The results of a three-year study of recovery in 3,033 lower limb muscles and 1,905 upper limb muscles in 142 patients are presented.

2. The rate of recovery of partly paralysed muscles is the same in all muscles and muscle groups in the lower or upper limb. Clinical differences in the ability of individual muscles to recover depend upon the proportions of their number that remain permanently paralysed.

3. The rate of recovery is slowest in adults and most rapid in young children.

4. The amount of further recovery to be expected in a muscle can be predicted from a knowledge of its grade at any time after one month from the onset of the paralysis. Fourteen-fifteenths of the total amount of recovery takes place by the beginning of the twelfth month; with rare exceptions individual muscle recovery is complete after twenty-four months.

5. Ninety per cent of muscles that are still completely paralysed after six months remain permanently paralysed.

6. The prognosis of a completely paralysed muscle is related to the level of paralysis in muscles supplied by the same spinal segments.

7. Deterioration in power in a muscle is uncommon and, when it occurs, is associated with the presence of the strong opposing force of antagonist muscles or of gravity.

8. The application of these findings to the management of cases of paralytic acute anterior poliomyelitis is discussed.