OBJECTIVETo assess the different causes of thoracic ossification of the ligamentum flavum (TOLF).

METHODSFrom July 1989 to November 2005, 142 cases were diagnosed the TOLF, in which 121 were operated. The lesions were classified into three types on the basis of the clinical result: (1) In such primary group (Group 1, 90 cases), without incorporation disease and Ca, P and AKP was all normal; (2) In systemic ossified TOLF group (Group 2, 30 cases), 6 cases ankylosing spondylitis, 3 cases DISH, 10 cases fluorosis, 11 cases OPLL; (3) In local spine disease group (Group 3, 22 cases), 5 cases fracture in spine, 4 cases spine TB, 13 cases posterior marginal intraosseous cartilaginous node. Such clinical feature was analysed, moreover surveyed the thoracic kyphosis angle, upper thoracic kyphosis angle, lower thoracic kyphosis angle and the vertebra body wedge change. The effect was assessed using Epstein Scale.

RESULTS(1) In Group 1, the mainly type was connected type (67/90, 74%). The ossified ligamentum flavum was mainly located at the lower thoracic and thoracic-lumber levels. The local type was less. In Group 2, the mainly type was connected type (21/30, 70%). The local type was none. The lesions figure was the most. In Group 3, the local type was the most (18/22, 82%). (2) In Group 1, the ossified ligamentum flavum was mainly located at the upper and lower thoracic levels (225/486, 47%). In Group 2, mainly located at the whole thoracic, some include cervix and lumber. In Group 3, mainly location was related with the location of primary disease. (3) In group 1, the curve was normal in 81% (73/90) of cases. In Group 2, the curve was abnormal in 87% (26/30) of cases. In Group 3, the curve was normal in the 82% (18/22) of cases.

CONCLUSIONSThe TOLF relates with systemic ossify disease, the change of load on the spine, aging and so on. It should be classified according to its causes.