THE NATURAL HISTORY OF SPONDYLOLYSIS AND SPONDYLOLISTHESIS: 45–YEAR FOLLOW–UP*

Bruce E. Fredrickson, MD1;
Daniel Baker, MD,
deceased; Albert M. Murtland, MD2;
Colleen A. Sweeney, MA1;
William J. Beutler, MD1
1SUNY Upstate Medical University, Syracuse, New York,
2Guthrie Clinic, Sayre, Pennsylvania, USA

INTRODUCTION:
In 1955 a prospective study was initiated to better understand the natural history of spondylolysis and spondylolisthesis. The study population included 500 first grade children. A total of 30 children (20 male, 10 female) were eventually identified to have spondylotic abnormalities of the lumbosacral spine. This sub–population was followed over the subsequent 45 years with serial x–ray, MRI, and clinical follow–up questionnaires. The purpose of this report is to delineate the natural history of spondylolysis and spondylolisthesis as the study population passes through adulthood.

METHODS:
The 30 study subjects were contacted in 1988 and 1999. AP, lateral, oblique, standing, and prone radiographic studies were done. MRI was included in 1999. Subjects completed a back pain questionnaire in 1988 and the SF–36 in 1999. Measurement of percent slip, percent lumbar index, slip angle, disc height at the level of slip and above, and sacral inclination was completed on each follow–up study. MRI studies were scored for disc degeneration, pars defects, spondylolisthesis, disc herniation, and foraminal compression.

RESULTS:
Twenty–two children (4.4% of the original 500) were found to have unilateral or bilateral pars interarticularis defects of the lumbar spine at the age of six years. Eight subjects developed a defect later. Twenty–five had bilateral pars defects at L5; the remaining five subjects had unilateral defects (one at L1, one at L2, one at L4, and two at L5). All subjects were available for follow–up in early adulthood. In 1988 data could be collected on 24 of the original 30 subjects. In 1999, fifteen subjects completed follow–up, four subjects were reported to have died, three refused further participation, and eight are still being sought. Subjects with unilateral pars defects never slipped over the course of the study. Of those 25 subjects with bilateral defects, 16 initially had no slip. The remaining nine had both pars defects and spondylolisthesis on the initial radiographs in 1955. Of the 16 with no slip initially, 10 went on to develop spondylolisthesis, 5 never slipped, and one was lost to follow–up in the later years of the study. Of the 10 that developed spondylolisthesis after initially not having a slip, eight developed the slip as a teenager, and the remaining two between age 20 and 40. Progression of slip was documented to be slow. The average percent slip of the nine subjects with slip on initial evaluation was 12%. These subjects progressed slowly over the 4 decades of the study to an average slip of 19%. Similar slow progression was noted in those 10 study subjects who developed spondylolisthesis over the course of the study, with an average 18% slip at 40 years follow–up. The largest percent slip on completion of the study was 39%. Only five subjects developed a slip of 25% or more. Slip progression was greatest early in life. The nine subjects with spondylolisthesis on initial evaluation had an average slip of 12% (first decade). Slip progression for all subjects in the second decade was 7.5%. In the third and fourth decades the slip progressed 2% and 5%, respectively. In the fifth decade slip progression was only an average of 1%. Disc height of the involved segment (as a ratio of the disc above to the involved level) decreased over the 40 years. Of those with development of slip, the disc height ratio went from 1.1 (both discs of the same height), to 1.6 (greater loss of height of the L5–S1 disc). Of those subjects that never slipped, the ratio only went from 1.3 to 1.2. MRI data was obtained on 15 subjects in 1999 (9 with spondylolisthesis and 6 without slip). Disc degeneration was graded from 0 to 3. Marked disc degeneration at the level of the slip was seen in only 3 subjects (two with listhesis and one without). Moderate disc degeneration was seen primarily at the level above the level of the slip. Minimal or no disc degeneration was seen at the higher levels. No disc herniation in any subject was noted, but minimal bulging was seen in six subjects, Foraminal stenosis was severe in only one subject. Three study subjects had surgery as adults. Two had surgery, without fusion, for acute disc rupture at the L4–5 level (one subject with listhesis, and one without). The third had a fusion without decompression in 1987. Pain assessment was completed via questionnaire each decade. In 1988 no subject reported anything more than moderate, infrequent pain (n=24). In 1999 the SF–36 pain sub–score was an average of 66 for all subjects (mild pain). Only 4 subjects scored pain worse than moderate in 1999 (two with listhesis, and two without). Of the five subjects with 25% or greater slip, two reported no or minimal pain, two had severe pain episodes, and one did not complete the SF–36 questionnaire.

DISCUSSION:
The incidence of spondylolysis is 4.4% at age six, and 6% in adulthood. No unilateral pars defects went on to spondylolisthesis. The degree of initial listhesis is dependent on the specific physiology of the individual at the time of the development of bilateral pars defects. The progression of the slip is associated with further disc degeneration. Progression of slip appeared to be slow, with the greatest progression in the first and second decades of life. At the onset of the sixth decade, of the 19 subjects with spondylolisthesis, only five had progressed to a grade II. Pain did not appear to be associated with slip progression and no subject reported disability.

*This study was supported by a grant from the North American Spine Society.