SummaryThe aspect of calcified tissues involved in fracture healing was studied by means of backscattered electron imaging. Bilateral transverse midshaft osteotomies were performed in the tibiae of 16 dogs. The osteotomies were reduced by means of a type II external skeletal fixator, and the clinical and radiographic course was assessed weekly until the moment of euthanasia, one, two, four and eight weeks after the operations. The osteotomized areas were removed and their structure examined in the scanning electron microscope, using backscattered electron images, to determine the general aspect of the extracellular matrix of the calcified tissues present. Four different tissues were observed: lamellar bone, woven bone, calcified cartilage and chondroid tissue. The backscattered electron contrast and fibre arrangement of the matrix, as well as the size and shape of the cellular lacunae, allow identification of the tissue. Chondroid tissue, which seems to have a leading role in the early phases of fracture healing, shows a characteristic pattern of a highly calcified and fibrous matrix with a large number of irregular and confluent cell lacunae.The morphological characteristics of the calcified tissues involved in fracture healing were studied by means of backscattered electron imaging. Lamellar bone, woven bone, calcified cartilage and chondroid tissue were the four calcified tissues observed during the healing process of canine midshaft tibial experimental fractures.

Retrospective review of 30 patients with nonunion of the humeral shaft treated from 1984-1999 revealed nine patients with an initial fracture pattern which to our knowledge was not described previously. Humeral fractures originated at the junction of the proximal and middle thirds of the diaphysis as an hemitransverse medial fracture that extended with a great lateral butterfly third fragment with its distal portion long and sharp. The patients were women approximately 60 years old. Eight fractures progressed to nonunion after initial conservative treatment. All fractures followed the same pattern: the proximal humeral fragment healed with the proximal portion of the third fragment, but an atrophic nonunion between the proximal humeral fragment, the distal humeral fragment, and the distal portion of the third fragment developed. The treatment required a technique adapted to this type of nonunion consisting of retrograde flexible intramedullary nailing, cerclage wires, and bone grafts.Humeral shaft fractures result in nonunion in at least 10% of the cases, regardless of the treatment used. 3 However, there are predisposing factors related to the initial treatment, the patient's associated health status, and the fracture type. 2,[4][5][6]8 The relevance of the current study was to draw attention to the existence of a special fracture pattern of the humeral shaft that to our knowledge has not been identified previously and that is not included in the classifications most commonly used. This fracture pattern has a poor prognosis and is difficult to treat. All the patients presented with similar epidemiologic conditions and the initial fracture resulted from a low energy accident. The operative technique adapted to the special characteristics of the fracture and poor quality of the bone is presented. Between 1984 and 1999, 30 patients with nonunion of the humeral shaft were treated at our institution. The results of these patients were presented previously. 1 While reviewing this series, nine patients (30% of all nonunions) with a special fracture pattern were seen. All but one progressed to nonunion after initial conservative management. They shared the same development and had common epidemiologic characteristics. MATERIAL AND METHODSThe mean age of the nine patients was 66 years (range, 54-71 years), and all were women. The initial fracture resulted from a fall from a standing height (eight patients) or from bumping into somebody (one patient). The right arm was involved in seven patients and the left arm in two patients. The initial treatment was nonoperative for eight patients: a cast brace in five patients, a hanging cast in two patients, and a sling in the last patient. In one patient the initial treatment was operative consisting of retrograde flexible intramedullary nailing inserted through the epicondylar portal.

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