[Unicameral cyst of the calcaneus: surgical indications, biomechanical calculations and results of follow-up studies].

Between April 1986 and August 1988, 7 patients (6 men, 1 woman) with unicameral calcaneal cysts were seen at the Trauma Hospital in Meidling. In one case both calcanei were affected. In all cases the findings were accidental, as a result of minor injuries. No familial preponderance was observed. The mean age of the patients was 26.6 years (19 to 33). In 3 patients, filling of the cyst was indicated due to risks from sport or occupational activities. Four cysts were therefore filled with fibrin-spongiosa (homologous bone chips). The mean follow-up interval was 19 months. No recurrent cyst formation was observed, and the patients had no complaints. Nor were there any complications. The importance of CT for preoperative diagnosis and postoperative verification of the result is indicated. On the basis of a strut framework model, it is proved mathematically that cyst formation is not of major importance for the "vertical load case"; on the other hand, bending moments occurring in "inclined load cases" (pronation, supination, extension, flexion), are substantially reduced if the cancellous bone in the cavity region is taken into account. As a logical consequence, surgery is indicated in individuals as risk due to occupational or sports activities; in cases which are not subject to stress peaks, however, therapy is unnecessary.