1. Osteotomy for osteoarthritis of the hip induces a fibrin layer over the exposed bone which forms the basis of a fibrocellular protective mantle that can differentiate towards cartilage.

2. The process is accompanied by bone remodelling, which reduces sclerosis, resolves osteolytic foci and, in company with bone formation in the fibrous mantle, restores the subchondral plate.

3. Many important aspects of the pathogenesis of osteoarthritis and of its partial repair by osteotomy remain to be elucidated.

1. Four cases of periosteal ganglion are described. Their relationship to other mucin-filled cysts of connective tissue, both in soft tissues and in bone, is discussed and the fact that they all result from mucoid degeneration of fibrous tissue is emphasised.

2. Treatment is by surgical excision, with removal of a margin of apparently normal periosteum as well as the lesion itself. The lesion may recur, even after apparently adequate excision, by mucoid degeneration taking place in the periosteum immediately adjacent to the operative site or in the connective tissues occupying the surgical defect.

1. The literature on pigmented villonodular synovitis has been reviewed and a series of eighty additional cases is reported.

2. The condition usually presents either as a nodule in a finger or knee, or as a diffuse lesion in a knee. The lesions, although benign, sometimes erode or invade the tissue of adjacent bones.

3. Distinction from malignant synovioma can be made on the basis of the macroscopic appearance of the lesion at operation (relationship to joints or tendon sheaths: villonodular appearance: pigmentation), and by histological examination.

4. Treatment of the nodular form by excision is satisfactory but extensive synovectomy for diffuse lesions of the knee gives poor results.

5. The etiology of pigmented villonodular synovitis is unknown, but it appears to be a self-limiting process, possibly inflammatory in nature.

1. A child with so-called ischio-pubic osteochondritis is reported from whom the affected ramus was resected. The features observed in the resected specimen were those of a normal closing epiphysis.

2. The literature is reviewed with emphasis on other children who had biopsies and on large scale radiographic surveys of normal children.

3. The conclusions are that the changes in the ischio-pubic synchondrosis cannot justifiably be called osteochondritis, and that they require further investigation, which can most profitably be done at necropsy.