PLAIN FILM EVALUATION OF DEGENERATIVE DISK DISEASE AT THE LUMBOSACRALJUNCTION

Objective. Diagnosing degenerative disk disease (DDD) at the lumbosacr al junction (LSJ) on plain films is often difficult, compared with oth er disk levels. The purpose of this study was to determine whether cri teria for diagnosis of DDD at the LSJ can be established for plain fil ms. Design and patients. We retrospectively reviewed 100 lumbar MRI sc ans of patients who also had lumbar plain films. Using MRI as the refe rence standard, the LSJ was classified as normal (n=35) or exhibiting mild (n=45) or severe (n=20) DDD by two radiologists using accepted cr iteria. Measurements were performed on the plain films by two other ra diologists and the average measurements were tabulated according to th e three categories of DDD defined by MRI. Plain film measurements incl uded the anterior and posterior disk heights (ADH, PDH), Farfan's rati o, determined by adding ADH to PDH and dividing that number by the mea sured anteroposterior (AP) length of the inferior end plate of L5 [(AD H+PDH)/AP length of L5], and lumbosacral angle (LSA). Subsequently, fi ve additional radiologists interpreted the radiographs by visual inspe ction only, for DDD at the LSJ, both before and, several weeks later, after being provided with the quantitative data for normal versus DDD. Results and conclusion. There was a statistically significant differe nce between normal disk and increasing severity of DDD on radiographs using the parameters of PDH and Farfan's ratio. There was no statistic ally significant difference regarding ADH or LSA. Diagnostic accuracy by visual inspection was not significantly altered using the quantitat ive data for interpretation of DDD (68% correct before, 69.5% correct after). Analysis sis of results indicates that PDH is the most reliabl e and easily used criterion for detection of DDD at the LSJ. A PDH les s than or equal to 5.4 mm on plain lateral film indicates DDD; PDH gre ater than or equal to 7.7 mm indicates the absence of DDD on plain fil m.