We report a prospective study of 55 patients with acute primary patellar dislocation, all treated by operation and followed up for at least two years. Diagnosis was based on the history of a lateral displacement, with medial tenderness and a positive apprehension test; redislocations were excluded. Before operation, the difference in lateral shift on skyline views of the injured and control patellae was highly significant. At operation, rupture of the medial retinaculum of the patella was seen in all but one case. There were medial marginal fractures of the patella in 23 cases. Subjective results of the operation were excellent or good in 44 of the 55 at two years with a redislocation rate of only 9%. Most patients were able to return to the same level of sporting activity as before the injury.

(Ann Rheum Dis 1999;58:683-690)

In three patients a mechanically well-fixed Mathys Ceros 80 (Ha) hydroxyapatite-coated acetabular component was revised 2, 5 and 13 months after total hip replacement due to component malposition. In each case there was a thin cellular connective tissue membrane between hydroxyapatite and bone, the main cell type being fibroblast with only occasional giant cells. Immunohistological analysis revealed some MHC locus II antigen positive cells that were identified as monocytes. No interleukin-2 receptor positive cells were found. Under clinical cyclic loading conditions there does not seem to be chemical fixation or bony ingrowth into the hydroxyapatite coated prosthesis component. In human lymphocyte cultures, hydroxyapatite (Interpore 200, particle diameters 15-40 microns) did not cause an increase in lymphocyte DNA synthesis as assessed by the 3H-thymidine incorporation method on culture days 1, 3 and 5. As analysed with lymphocyte activation markers, the hydroxyapatite-dependent expression of MHC locus II antigen was modest and differed significantly (P less than 0.05) from that in culture medium only on day 3. Hydroxyapatite induced only a slight interleukin-2 receptor expression that did not differ from culture medium on days 1, 3 and 5. CD4 and CD8 positive lymphocytes as well as monocytes were not seen attached to hydroxyapatite particles during the culture days. Our findings suggest that hydroxyapatite is an immunologically inert implant material.

Transverse osteotomies of the midshaft of the tibia in 75 rabbits were stabilized with intramedullary nails which prevented rotational instability. In a further 36 animals intramedullary nailing was performed without preceding osteotomy. The animals were able to move freely immediately after the operation without any supporting case or splint. The structural changes in the bones were analysed radiographically 3 to 24 weeks after the operation. Fracture repair was accompanied by moderate periosteal callus formation and remodelling of the callus was seen from 9 weeks on. A sleeve of new endosteal bone surrounding the nail was found after 12 weeks. Porotic transformation of the diaphyseal cortical bone was seen in both osteotomized and non-osteotomized bones from 12 weeks onwards. It is concluded that intramedullary nailing provides favourable conditions for fracture repair and enables accurate radiographic assessment of the healing. Attention is focused on the causes and features of secondary porotic transformation of the cortical bone after intramedullary nailing.

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