INCIDENCE AND RISK-FACTORS IN THE APPEARANCE OF HETEROTOPIC OSSIFICATION IN SPINAL-CORD INJURY

Heterotopic ossification (HO) is a frequent complication in patients with a spinal cord injury (SCI), although the aetiology is unknown. A study was undertaken of 654 SCI patients with traumatic aetiology, admitted for the first time to the Hospital Nacional de Paraplejicos, Toledo, during 1988 and 1989. Of the total number of patients, 85 (13%) were diagnosed HO and 569 without HO. The diagnosis was mainly achieved by x-ray studies and clinical signs. From the 569 patients with traumatic aetiology without HO, 44 were selected at random, as were 44 of the 85 patients with HO. The mean time lapse between the occurrence of the accident and admission for patients with HO was 40.79 days (typical deviation (TD) = 45.2), and for patients without HO was 32.84 (TD = 38) days, resulting in a value of F = 0.796 through analysis of variance, which is not a statistically significant variation between the 2 groups. In both groups we have taken account of the following variables: age at time of lesion, lesion level, type of lesion (complete or incomplete), spasticity, urinary tract complications, deep vein thrombosis, important associated injuries occurring at the moment of lesion, time elapsed before admission and the existence of pressure sores. In those SCI patients with HO the number of ossifications and their localisations were also verified. By use of the chi square test (X2) over all 9 variables which were studied, we found that 3 variables (complete spinal lesion, presence of pressure sores and spasticity) were significantly related to HO formation. The risk factors appear to be cumulative: the presence of 2 risk factors in the same patient was found to result in HO appearing in 65 +/- 8% (P +/- SP), and when all the risk factors are present in the same patient, 85 +/- 7.9% had heterotopic ossification. Eighty two per cent of the patients who presented pressure sores had a time lapse to admission of more than 15 days, against 18% of those whose time lapse to admission was less than 15 days X2[1] = 17.8, p < 0.001. For those patients whose time to admission was less than 15 days, and whose progress we could follow from the start, from a total of 7 patients with sores, 6 developed HO while one did not, X2[1] = 4.2, p < 0.05.