[Developmental spondylolysis].

Spondylolysis is generally regarded as a stress-fracture acquired early in life by predisposed persons. However, the early stages of spondylolysis are seldom recorded in clinical practice. This can be explained by the fact that the delayed roentgenological detection of early stress lesions of bone in general, is aggravated by technical difficulties encountered at the level of the low lumbar spine. Consequently, healing of spondylolysis is extremely scarce in the experience of most clinicians who essentially observe old and usually inactive pars separations. Therefore, two radiological patterns of developing spondylolysis are stressed: 1: an isolated stress sclerosis of both pedicle and pars, reflecting the overload of the corresponding posterior elements and 2: partial cracks of the isthmus starting at its antero-inferior cortex, near the pedicle. Such developing defects were observed in 20 patients: in 5 cases of primary spondylolysis, as an isolated finding, and in 15 other cases during formation of a pars defect at the opposite side of a primary unilateral spondylolysis. Bilateralization of primary unilateral defects is indeed a common sequence of events. In addition, healing of bilateral defects of L4 or L5 was observed in 7 adolescent patients: 5 boys and 2 girls aged 8 to 16 (mean 12.5). The corresponding defects were invariably of recent origin. Therefore, in case of low back pain in adolescent patients engaged in athletic activities, it should be remembered that routine roentgenograms showing an apparently normal pars do not completely rule out a developing defect. In such cases, a repeated X-ray study with close scrutiny of the pars could then reveal an early spondylolysis which is still apt to heal.