The incidence of an effusion in the knee in 155 consecutive elderly
patients who had been operated on for a proximal femoral fracture was
studied. The preoperative incidence had been 7.7 per cent in the
ipsilateral knee and 1.3 per cent in the contralateral knee.
Postoperatively, fifty patients (32.3 per cent) had an effusion on the
ipsilateral side. In seven of them, the effusion had been present before
the operation. All of the effusions subsided completely within three weeks
after the operation. Results of the laboratory analysis of a specimen of
the effused material from eight patients who were chosen at random showed
non-inflammatory fluid. Probably the effusions were traumatic in origin,
and it is likely that they were a response to stresses that had been
incurred during the operation or at the time of fracture.