A series of 237 total hip replacements were analysed by means of a computer program. High body weight and postoperative fever, as well as several indications of a technically demanding operation, occurred significantly more often in the group of patients which developed paraarticular ossification postoperatively. The results point to a causal relation between tissue trauma and heterotopic bone formation. We wish to underline the importance of a gentle handling of tissues in the performance of a total hip replacement if the rate of ectopic bone is to be reduced to a minimum.
Patient data and radiograms from a series of 237 consecutive total hip replacements were evaluated by means of a computer programme in an attempt to study factors correlated with early loosening. We found that the loosening rate was significantly influenced by several factors. The CAD-prosthesis (Computer Assisted Design, Howmedica) was found to be superior to the Charnley-Müller-prosthesis. The viscosity of the cement seemed to be an important factor in that low viscosity was positively correlated to loosening whereas high viscosity showed a negative correlation. Several technical details in the performance of the operations as well as loosening correlated with the surgeon. Males who preoperatively had fairly unrestricted physical activity and high body weight were more prone to early loosening. No correlation was found with the diagnosis, previous hip surgery, age, osteoporosis or cortisone treatment preoperatively. We wish to underline the importance of a thorough technique and suggest that total hip replacement should be performed by specialized surgeons.
In a recent model for heterotopic bone formation (Michelsson et al. 1980). muscular oedema, swelling and necrosis is seen in the quadriceps muscle of rabbit hind limbs immobilized for at least 2 weeks when, from the second week, the immobilized limb is subjected to daily forcible mobilization lasting about 5 min. According to this model, heterotopic calcification develops gradually from the second week of forcible mobilization and is located in the vastus intermedius region. Between the fourth and fifth week of immobilization and forcible mobilization, heterotopic bone formation is seen in virtually all cases. The histological findings are similar to those in human ectopic bone formation. In the present investigation the labelled microsphere technique was used to study the regional blood flow effects in the early development of myositis ossificans with this model. The results are quite different from those reported by other investigators on immobilization alone and point to a causal relation between regional blood flow and forcible mobilization of the immobilized rabbit hind limb. Prostaglandins as mediators between the traumatic inflammation, a part of the circulatory effects observed and the induction of new bone is suggested.
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