Aetiology and pathology of beat knee.

The object of this study was to determine the mechanism of the production of beat knee and its relation to pathological findings. A clinical study was made among 598 coal-face workers at one large colliery: 579 were examined of whom 233 showed evidence of past or present beat knee. A considerable preponderance of non-inflammatory lesions, most commonly in the prepatellar bursa, was demonstrated. It was concluded that the single common factor in the causation of non-inflammatory or acute recurrent bursitis was the trauma of kneeling. Experimental investigation of the pressures exerted showed great variations in the pressure on the knee as a whole and on different parts of its weight-bearing surfaces. The view that these localized and extreme variations in pressure may lead to rupture of a vessel found confirmation in the aspiration of blood from the bursae of 29 out of 30 patients. Histological sections from chronically enlarged bursae showed intense fibrosis in the wall of the bursa and sometimes deposition of haemosiderin. In the management of a new case of acute simple bursitis immediate aspiration of the blood and the instillation of hyalase proved successful in all 12 cases. Aspiration was also successful in certain cases of acute recurrent simple bursitis. Surgical removal of chronically enlarged fibrotic bursae allowed eight out of 12 patients to return to the coal-face. It is suggested that in order to reduce the incidence of beat knee the use of a knee pad that will not only protect the skin of the front of the knee from trauma by coal particles but will also cushion the knee from the effects of extreme variations in pressure may be desirable.