1. The semilunar cartilages are part of the rotator mechanism of the knee joint.

2. Movement of the weight-bearing knee comprises synchronous lateral rotation of the tibia with extension and medial rotation of the tibia with flexion.

3. When this synchrony is disturbed, injuries to the semilunar cartilages result.

4. Damage to the anterior two-thirds of the medial cartilage blocks lateral rotation of the tibia, with consequent physical signs that are pathognomonic of the retracted and the bowstring cartilage, which are the most common types of injury.

5. Each type of cartilage injury produces its own pattern of erosion of articular cartilage and its own sequence of symptoms as so-called arthritis develops.

6. The sequence of symptoms may be halted and often reversed by removal of the torn cartilage. Operation is warranted in most cases however long the history and whatever the age of the patient.

7. The development of medial retropatellar arthritis is explained. The symptoms are often relieved by removal of the medial semilunar cartilage and adequate post-operative rehabilitation.

1. Coracoid transplantation for recurring dislocation of the shoulder is described.

2. In my experience of over thirty cases only once has true dislocation recurred after this operation. Recurrence was due to avulsion of the bone block.

3. Failure to repair the original detachment of the glenoid labrum is a frequent cause of recurrence of dislocation of the shoulder. An explanation is offered for this failure; namely that the injured labrum adheres to the deep surface of the subscapularis muscle instead of reattaching itself to bone. This reinforces Watson-Jones's advice that the original dislocation should be treated by complete immobilisation in full medial rotation for three weeks.