Diagnostic Radiology
Hypoplasia of the Lumbar Vertebral Body Simulating Spondylolisthesis 1 David F. Frank, M.D., and Jarrell E. Miller, M.D.
Fifty cases of spondylosis and spondylolisthesis were reviewed. In 9 of the 20 cases Interpreted as Grade I spondylolisthesis at L5-S1, the sagittal diameter of LS was shortened, creating a false Impression of vertebral slippage. Such cases are felt to represent spondylolysis with hypoplasia of the vertebral body rather than true spondylolisthesis. INDEX TERMS: Bones, growth and development (Lumbosacral spine, hypoplasia, 3(3).142; Spine, hypoplasia, 3(0).142) • Spine, dislocation (Lumbosacral spine, spondylolysis, spondylolisthesis, 3(3).423) Radiology 133:59-60, October 1979
isthmic spondylolisthesis at L5, 11 had posterior wedging of more than 20%. One patient had thinning of the isthmus without a complete defect, as well as 20 % wedging of the centrum. None of the patients with isthmic defects above L5 had 20 % posterior wedging of the affected vertebral body. One of the 7 patients with degenerative spondylolisthesis at L4-5 had >20 % posterior wedging of L5; none had >20% wedging of L4. Of the 50 patients in the control group, only 2 had >20% posterior wedging of L5; actual measurements were 22 and 21 %, respectively. Only 2 L4 bodies demonstrated a vertebral ratio greater than 10%; one was 12% and the other was 10.5%. In 9 of the 20 patients considered to have Grade I spondylolisthesis of L5, the anterior margin of the vertebral body had not slipped at all. In these patients, the anterior margin of L5 was higher than the posterior margin, giving it a wedge-shaped or trapezoid configuration. Six of these 9 patients had posterior wedging of greater than 20 % , associated with shortening of the sagittal diameter of the centrum; its posterior margin was situated farther forward than that of the body above and below, giving a false appearance of spondylolisthesis. We believe that these cases should not properly be classified as true spondylolisthesis, but rather as spondylolysis with a trapezoid vertebral body (Figs. 1 and 2).
spondylolisthesis, first used by Kilian in 1854 (3), indicates slippage of the vertebra, not necessarily accompanied by a defect in the neural arch. The arch defect is correctly designated spondylolysis. whether or not slippage has occurred. In reviewing cases interpreted as Grade I spondylolisthesis of L5, we noted a large number in which the anteroposterior diameter of the vertebral body was shortened, creating the impression of slippage, but no slippage had actually taken place. In our view, these cases are part of the spectrum of spondylolysis, rather than representing true spondylolisthesis.
THE TERM
I
>
MATERIAL AND METHODS
Fifty cases of spondylolysis and spondylolisthesis were reviewed. These were classified according to type and location. Patients with neural arch defects whose radiographs had been interpreted as showing spondylolisthesis were placed in this category, although it is our contention that some of these patients do not have true slippage of the vertebral body, as will be discussed further. A control group of 50 normal pre-employment lumbar spine radiographs was also studied (a few examinations displaying isthmus defects were not included). In the abnormal group, the anterior and posterior margins of the affected vertebra were measured. In patients with degenerative spondylolisthesis of L4 and in the controls, the anterior and posterior height of both L5 and L4 were measured. The posterior height was then subtracted from the anterior height and the difference divided by the anterior height. The resulting number gave the degree of posterior wedging of the vertebral body, expressed as a percentage. If the posterior height was equal to or greater than the anterior height, no wedging was present and it was graded as O.
DISCUSSION
Posterior wedging and trapezoid configuration of L5 were considered to be secondary to slippage of the centrum by Newman and Stone (4), who found that they were associated with a dome-shaped configuration of the sacrum. Of the 19 patients with isthmic spondylolisthesis reviewed by Epstein et al. (2), all had a trapezoid L5; the difference in height between the anterior and posterior wall varied from 3 to 10 mm and was more pronounced in more advanced cases. However, a certain degree of posterior wedging of L5 is normal (1,4). Rosenberg (5) felt that decreased wedging of the fifth lumbar vertebral body is as-
RESULTS
Of the 9 patients with bilateral spondylolysis of L5 but without slippage. 5 had posterior wedging of greater than 20 %, compared to only one of the 5 with unilateral spondylolysis. Of the 20 patients considered to have
1 From the Department of Radiology (D.F.F_, Assistant Clinical Professor; J.E.M.• Clinical Professor), University of Texas, Southwestern Medical School, Dallas, Texas. Revised version received March 1. 1979 and accepted April 11. sjh
59
60
October 1979
DAVID F. FRANK AND JARRELL E. MILLER
1,2
Fig. 1. Spondylolysis at L5-S 1. The fifth lumbar vertebral body has a wedge-shaped appearance. Note that there is no actual slippage. Fig. 2. Spondylolysis at L5-S1. There is shorteningof the sagittal diameter of the fifth lumbar vertebral body, with posterior wedging but no slippage.
sociated with degenerative spondylolisthesis of L4. while increased posterior wedging is associated with isthmic spondylolisthesis. In his series of 200 patients with degenerative spondylolisthesis, the anterior margin of L5 averaged 2 mm greater than the posterior height. In 11 patients the posterior height was greater. In a control group of 100 normals. the average anterior height was 6 mm greater; and in 61 cases of isthmic spondylolisthesis at L5 the anterior height averaged 12 mm greater than the posterior height. The etiologic mechanism of the wedge-shaped L5 body is still not clear; however. it may be related to the same factors that produce spondylolysis. Wiltse (6) feels that isthmic spondylolysis is caused by two coexistent factors: (a) hereditary dysplasia. probably in the cartilage model of the arch of the affected vertebra. and (b) repeated stress and strain on the pars interarticularis secondary to erect posture. As a result of the dysplasia, the constant reparative metabolic process progresses more toward bone resorption than bone formation. It is possible that the same chronic stresses and strains (produced by erect posture) which act upon the pars interarticularis also serve to mold the configuration of the vertebral body. In the normal individual. repeated shear and compression forces model the L5 body into a slightly wedge-shaped structure. which acts as the keystone in the lumbosacral arch. In patients with congenital dysplasia of the pars interartlcularls, there may be a corresponding weakness in the vertebral body. Constant remolding of the vertebra throughout the course of childhood and adolescence would then produce a more
pronounced trapezoid configuration of the vertebral body. as well as the well-known isthmus defect of spondylolisthesis. As spondylolisthesis is defined as slippage of the vertebra, only those cases in which both the anterior and posterior margins of the vertebral body are displaced forward should properly be categorized as spondylolisthesis. Those cases in which the posterior margin of the centrum is displaced but the anterior margin exhibits normal alignment actually represent a hypoplastic wedge-shaped vertebral body associated with spondylolysis and should not be classified as spondylolisthesis. Such considerations may be of value in selection of patients for surgery or for disability benefits. 6011 Harry Hines Blvd., Suite 900 Dallas, Texas 75235
REFERENCES 1. Christenson PC: The radiologic study of the normal spine. Cervical. thoracic, lumbar, and sacral. Radiol Clin North Am 15: 133 -154, Aug 1977 2. Epstein BS, Epstein JA. Jones MD: Lumbar spondylolisthesis with isthmic defects. Radiol Clin North Am 15:261-273, Aug 1977 3. Kilian HF: De spondylolisthesi gravissimae pelvangustiae caussa nuper detecta commentatio anatomico-obstetricia. Bonnoe, 1854 4. Newman PH. Stone KH: The etiology of spondylolisthesis. J Bone Joint Surg [Brl 45:39-59, Feb 1963 5. Rosenberg NJ: Degenerative spondylolisthesis. Predisposing factors. J Bone Joint Surg [Am] 57:467-474, Jun 1975 6. Wiltse LL: The etiology of spondylolisthesis. J Bone Joint Surg [Am J 44:539-560, Apr 1962
Hypoplasia of the Lumbar Vertebral Body Simulating Spondylolisthesis 1 David F. Frank, M.D., and Jarrell E. Miller, M.D.
Fifty cases of spondylosis and spondylolisthesis were reviewed. In 9 of the 20 cases Interpreted as Grade I spondylolisthesis at L5-S1, the sagittal diameter of LS was shortened, creating a false Impression of vertebral slippage. Such cases are felt to represent spondylolysis with hypoplasia of the vertebral body rather than true spondylolisthesis. INDEX TERMS: Bones, growth and development (Lumbosacral spine, hypoplasia, 3(3).142; Spine, hypoplasia, 3(0).142) • Spine, dislocation (Lumbosacral spine, spondylolysis, spondylolisthesis, 3(3).423) Radiology 133:59-60, October 1979
isthmic spondylolisthesis at L5, 11 had posterior wedging of more than 20%. One patient had thinning of the isthmus without a complete defect, as well as 20 % wedging of the centrum. None of the patients with isthmic defects above L5 had 20 % posterior wedging of the affected vertebral body. One of the 7 patients with degenerative spondylolisthesis at L4-5 had >20 % posterior wedging of L5; none had >20% wedging of L4. Of the 50 patients in the control group, only 2 had >20% posterior wedging of L5; actual measurements were 22 and 21 %, respectively. Only 2 L4 bodies demonstrated a vertebral ratio greater than 10%; one was 12% and the other was 10.5%. In 9 of the 20 patients considered to have Grade I spondylolisthesis of L5, the anterior margin of the vertebral body had not slipped at all. In these patients, the anterior margin of L5 was higher than the posterior margin, giving it a wedge-shaped or trapezoid configuration. Six of these 9 patients had posterior wedging of greater than 20 % , associated with shortening of the sagittal diameter of the centrum; its posterior margin was situated farther forward than that of the body above and below, giving a false appearance of spondylolisthesis. We believe that these cases should not properly be classified as true spondylolisthesis, but rather as spondylolysis with a trapezoid vertebral body (Figs. 1 and 2).
spondylolisthesis, first used by Kilian in 1854 (3), indicates slippage of the vertebra, not necessarily accompanied by a defect in the neural arch. The arch defect is correctly designated spondylolysis. whether or not slippage has occurred. In reviewing cases interpreted as Grade I spondylolisthesis of L5, we noted a large number in which the anteroposterior diameter of the vertebral body was shortened, creating the impression of slippage, but no slippage had actually taken place. In our view, these cases are part of the spectrum of spondylolysis, rather than representing true spondylolisthesis.
THE TERM
I
>
MATERIAL AND METHODS
Fifty cases of spondylolysis and spondylolisthesis were reviewed. These were classified according to type and location. Patients with neural arch defects whose radiographs had been interpreted as showing spondylolisthesis were placed in this category, although it is our contention that some of these patients do not have true slippage of the vertebral body, as will be discussed further. A control group of 50 normal pre-employment lumbar spine radiographs was also studied (a few examinations displaying isthmus defects were not included). In the abnormal group, the anterior and posterior margins of the affected vertebra were measured. In patients with degenerative spondylolisthesis of L4 and in the controls, the anterior and posterior height of both L5 and L4 were measured. The posterior height was then subtracted from the anterior height and the difference divided by the anterior height. The resulting number gave the degree of posterior wedging of the vertebral body, expressed as a percentage. If the posterior height was equal to or greater than the anterior height, no wedging was present and it was graded as O.
DISCUSSION
Posterior wedging and trapezoid configuration of L5 were considered to be secondary to slippage of the centrum by Newman and Stone (4), who found that they were associated with a dome-shaped configuration of the sacrum. Of the 19 patients with isthmic spondylolisthesis reviewed by Epstein et al. (2), all had a trapezoid L5; the difference in height between the anterior and posterior wall varied from 3 to 10 mm and was more pronounced in more advanced cases. However, a certain degree of posterior wedging of L5 is normal (1,4). Rosenberg (5) felt that decreased wedging of the fifth lumbar vertebral body is as-
RESULTS
Of the 9 patients with bilateral spondylolysis of L5 but without slippage. 5 had posterior wedging of greater than 20 %, compared to only one of the 5 with unilateral spondylolysis. Of the 20 patients considered to have
1 From the Department of Radiology (D.F.F_, Assistant Clinical Professor; J.E.M.• Clinical Professor), University of Texas, Southwestern Medical School, Dallas, Texas. Revised version received March 1. 1979 and accepted April 11. sjh
59
60
October 1979
DAVID F. FRANK AND JARRELL E. MILLER
1,2
Fig. 1. Spondylolysis at L5-S 1. The fifth lumbar vertebral body has a wedge-shaped appearance. Note that there is no actual slippage. Fig. 2. Spondylolysis at L5-S1. There is shorteningof the sagittal diameter of the fifth lumbar vertebral body, with posterior wedging but no slippage.
sociated with degenerative spondylolisthesis of L4. while increased posterior wedging is associated with isthmic spondylolisthesis. In his series of 200 patients with degenerative spondylolisthesis, the anterior margin of L5 averaged 2 mm greater than the posterior height. In 11 patients the posterior height was greater. In a control group of 100 normals. the average anterior height was 6 mm greater; and in 61 cases of isthmic spondylolisthesis at L5 the anterior height averaged 12 mm greater than the posterior height. The etiologic mechanism of the wedge-shaped L5 body is still not clear; however. it may be related to the same factors that produce spondylolysis. Wiltse (6) feels that isthmic spondylolysis is caused by two coexistent factors: (a) hereditary dysplasia. probably in the cartilage model of the arch of the affected vertebra. and (b) repeated stress and strain on the pars interarticularis secondary to erect posture. As a result of the dysplasia, the constant reparative metabolic process progresses more toward bone resorption than bone formation. It is possible that the same chronic stresses and strains (produced by erect posture) which act upon the pars interarticularis also serve to mold the configuration of the vertebral body. In the normal individual. repeated shear and compression forces model the L5 body into a slightly wedge-shaped structure. which acts as the keystone in the lumbosacral arch. In patients with congenital dysplasia of the pars interartlcularls, there may be a corresponding weakness in the vertebral body. Constant remolding of the vertebra throughout the course of childhood and adolescence would then produce a more
pronounced trapezoid configuration of the vertebral body. as well as the well-known isthmus defect of spondylolisthesis. As spondylolisthesis is defined as slippage of the vertebra, only those cases in which both the anterior and posterior margins of the vertebral body are displaced forward should properly be categorized as spondylolisthesis. Those cases in which the posterior margin of the centrum is displaced but the anterior margin exhibits normal alignment actually represent a hypoplastic wedge-shaped vertebral body associated with spondylolysis and should not be classified as spondylolisthesis. Such considerations may be of value in selection of patients for surgery or for disability benefits. 6011 Harry Hines Blvd., Suite 900 Dallas, Texas 75235
REFERENCES 1. Christenson PC: The radiologic study of the normal spine. Cervical. thoracic, lumbar, and sacral. Radiol Clin North Am 15: 133 -154, Aug 1977 2. Epstein BS, Epstein JA. Jones MD: Lumbar spondylolisthesis with isthmic defects. Radiol Clin North Am 15:261-273, Aug 1977 3. Kilian HF: De spondylolisthesi gravissimae pelvangustiae caussa nuper detecta commentatio anatomico-obstetricia. Bonnoe, 1854 4. Newman PH. Stone KH: The etiology of spondylolisthesis. J Bone Joint Surg [Brl 45:39-59, Feb 1963 5. Rosenberg NJ: Degenerative spondylolisthesis. Predisposing factors. J Bone Joint Surg [Am] 57:467-474, Jun 1975 6. Wiltse LL: The etiology of spondylolisthesis. J Bone Joint Surg [Am J 44:539-560, Apr 1962
