Purpose: Tumours of the calcaneus are exceedingly rare and the correct diagnosis is often missed. X-rays are the standard clinical examination tool and therefore we wanted to discover whether X-rays alone were a sufficient diagnostic tool for these tumours. Diard's classification was applied to define whether different types of lesions were characteristically distributed in the bone and in addition we analysed whether type and/or duration of symptoms were possible indicators of malignancy.
Methods: Ninety-two patients' files (59 men and 33 women) were retrospectively reviewed. Seventy-five patients with a mean age at surgery of 28 years (range five to 78) were surgically treated. Parameters analysed were sex, age at surgery, side, type and duration of symptoms, tentative diagnosis, biopsy prior to surgery, operative procedure, recurrence rate, revision and localisation of the lesion according to Diard. For each lesion the first documented radiological diagnosis and-in cases of malignancy-Enneking's classification was applied.
Results: Discrepancies between the radiological and definitive histological diagnosis occurred in 38 (41 %) of 92 cases. In eight (osteosarcoma n = 5, Ewing's sarcoma n = 2, metastases n = 1) of 17 malignant cases radiological examination initially gave no evidence of malignancy, resulting in an unplanned excision ("whoops procedure") in three cases of osteosarcoma. Applying Diard's system trabecular area 6 (radiolucent area) was highly affected in 64 (80 %) of 80 investigated plain X-rays, whereas areas 1 and 5 were affected in nine (11 %) and 16 (20 %) cases only.
Conclusions: In each case of an osteolytic lesion of the calcaneus a malignant tumour must be ruled out, and thus preoperative plain X-rays in two planes alone are not sufficient and should therefore be followed by magnetic resonance imaging. Applying the Diard system different types of lesions are not characteristically distributed in the bone. Increasing pain for more than ten days without previous trauma should always justify further examinations.