Development Of Spondylolisthesis Research Articles

Pelvic incidence effects pars interarticularis defect and spondylolisthesis

Aims: Pars interarticularis defect (PID) is a common problem in society and may be accompanied with low back pain and radiculopathy. Magnetic resonance imaging (MRI) can detect it with high sensitivity. If left untreated, it may progress to spondylolisthesis. In this study, we wanted to emphasize the importance of the pelvic incidence (PI) angle in terms of following the development of spondylolisthesis after PID by examining the relationship between PID and spondylolisthesis and PI.
 Methods: 118 patients who applied to Şanlıurfa Training and Research Hospital between 2021-2022 and underwent lumbar MRI were included in the study. The criteria for inclusion of patients in the study were the detection of a pars interarticularis defect on MRI, the ability to be evaluated by direct radiography or CT, and the ability to monitor the femoral head and sacrum in a way that PI could be measured. PI angle measurement was performed, confirmed by CT. The relationship between PID, spondylolisthesis and PI was examined.
 Results: Of the 118 patients participating in the study, 77 (65.3%) were women and 41 (34.7%) were men. Pars defect was most commonly seen at the L5 level (67.8%). The average pelvic incidence angle is 64.2±8.6. Half of the patients were calculated as Meyerding grade 0 and 95.8% were treated medically. The median pelvic incidence angle value of patients without spondylolisthesis was found to be 58.0, the median pelvic incidence angle value of patients with a Meyerding grading of one was found to be 68.0, and the median value of the pelvic incidence angle of patients with a Meyerding grading of one was found to be 78.0 (p

43. Comparison of radiographic adjacent segment pathology at five years following minimally invasive compared to open lumbar 1- to 2-level fusion surgery

<h3>BACKGROUND CONTEXT</h3> Adjacent segment pathology remains a major cause of morbidity among patients receiving posterior lumbar instrumented fusion. Its occurrence is proposed to be secondary to the increased motion and biomechanical stresses from fused to unfused segment. Additionally, progressive degenerative processes in the spine can also be influenced by surgery-related factors that alter the spine biomechanics as a result of muscle destruction and facet joint violation. Controversy in the rates of radiographic adjacent segment pathology (RASP) after lumbar fusion surgery has stemmed by and large from variable reporting in the literature with short long-term follow-up periods and no comparison between muscle splitting minimally invasive (MIS) approach and posterior midline open fusions. We report a single-center cohort analysis of patients undergoing lumbar fusion surgery and describe the rate of RASP between patients undergoing minimally invasive tubular approach (MIS) vs open posterior fusion technique. <h3>PURPOSE</h3> The objective of this study is to evaluate the rate of RASP between MIS and open lumbar fusion surgery within 5-year follow-up period. <h3>STUDY DESIGN/SETTING</h3> Observational study. <h3>PATIENT SAMPLE</h3> Adults with degenerative lumbar disease who underwent 1- to 2-level open and MIS fusion at our institution from January 2006 to December 2016. <h3>OUTCOME MEASURES</h3> Rate of radiographic adjacent segment pathology. <h3>METHODS</h3> The authors conducted a retrospective chart review of patients diagnosed with degenerative lumbar disease who had undergone 1- to 2-level fusion between January 2006 to December 2016. Cases with upright lumbar radiographs were included in this sub-analysis. The patients were divided into an MIS fusion group and an open surgery group based on the surgical technique performed. The two groups were compared for baseline demographic features, surgical variables and diagnosis at index surgery. Adjacent segment pathology was evaluated using radiographs taken at the 5-year follow-up period. RASP is defined by the presence of any one or combination of (1) disc degeneration (height loss), (2) development of spondylolisthesis and (3) coronal deformity/lateral listhesis. Analysis was confined to rates of development of RASP with no attempt of correlating with symptomatic adjacent segment pathology. Logistic regression analysis was performed to assess relationship of demographic factors with development of RASP <h3>RESULTS</h3> A total of 165 patients were included: MIS (n = 73) and (n = 92) open. There was no significant difference between two groups in age, sex, diagnosis at index surgery, level of fusion and baseline RASP. Fusion involved one level in 72.7 % of cases and 2 levels in 27.3%. The overall incidence of RASP was 41.2%, with incidence of 36.9% in MIS group and 44.6% in the open surgery group, showing no significant difference between the two groups (p = 0.5246). In those with RASP, the most common radiographic finding was disc degeneration (height loss) for both cohorts (100% vs 87.8%, p = 0.264) with the majority occurring cephalad to previous instrumentation. Logistic regression analysis did not show significant correlation between sex, age, index diagnosis, presence of baseline RASP and the prevalence of RASP at 5 years. <h3>CONCLUSIONS</h3> The prevalence of radiographic adjacent segment pathology did not statistically differ between MIS and open lumbar fusion surgery at minimum of 5-year follow-up. Baseline demographics or primary pathoanatomical diagnosis did not correlate to the presence of RASP 5 years following surgery in either group. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

Incidence of and risk factors for spondylolisthesis, scoliosis, and vertebral fracture in rheumatoid arthritis.

Although lumbar lesions such as spondylolisthesis, scoliosis, and vertebral fracture are not specific to rheumatoid arthritis (RA), the prevalence is high in RA patients. However, no longitudinal study has evaluated lumbar lesions in RA. This study aimed to investigate the incidence of and risk factors for lumbar lesions in RA by a prospective longitudinal cohort study. The study cohort comprised 110 patients with RA from the 'analysis of factors for RA spinal disorders (AFFORD)' study who completed the secondary survey at a single orthopaedic outpatient RA clinic. Radiological examination included standing radiographs and magnetic resonance imaging (MRI) of the lumbar spine. New development of spondylolisthesis, scoliosis, and vertebral fracture were assessed between baseline and secondary survey. The incidences of spondylolisthesis, scoliosis, and vertebral fracture were 42%, 16%, and 12%, respectively, during a mean follow-up of 7years. The independent risk factor for de novo scoliosis was poor control of RA (adjusted odds ratio [aOR] 4.81, p = 0.011), while the independent risk factors for new vertebral fracture was use of glucocorticoid at secondary survey (aOR 14.87, p = 0.012). Patients with de novo scoliosis exhibited more severe low back pain and lower quality of life than those without. The incidence of scoliosis was related in patients with poor control of RA, while new vertebral fracture was more common in patients with use of glucocorticoid. Control of disease activity might be important in preventing radiological lumbar disorders in RA.

What is the difference in pedicle morphology of the fifth lumbar vertebra between isthmic and degenerative L5-S1 spondylolisthesis? An anatomic study of 328 patients via multi-slice spiral computed tomography.

The purpose of this study was to investigate and determine whether there are differences in L5 pedicles morphology between isthmic and degenerative L5-S1 spondylolisthesis. One hundred and nineteen patients with isthmic spondylolisthesis and 45 patients with degenerative spondylolisthesis at L5-S1 were enrolled in the IS group and DS group, respectively, and 164 lumbar disc herniation patients without spondylolysis or spondylolisthesis were classified into the normal (NL) group. A series of pedicle parameters of the fifth lumbar vertebra, including pedicle length (PL), pedicle width (PW), pedicle screw trajectory length (PSTL), pedicle height (PH), and the pedicle camber angle (PCA), were measured using multi-slice spiral computed tomography (MSCT). The slip distance of the L5 vertebra was measured on radiography, and the percentage of slip was also recorded. The pedicles of the fifth lumbar vertebra were shorter and wider, and the PCA was larger in the IS group compared to the DS group and NL group. On the contrary, the pedicles in the DS group were elongated and thinner, and the PCA was smaller. The pedicle parameters of PL were significantly positively correlated with the percentage of slip in the DS group, but PW and PCA were negatively correlated with the percentage of slip. There was no correlation between the percentage of slip and L5 pedicle parameters in the IS group. The L5 pedicles morphology in L5-S1 isthmic spondylolisthesis shows abduction, shortness, and width, while that in the degenerative spondylolisthesis shows adduction, lengthening, and thinning compared with the normal populations. The morphology changes may be the result of pedicle stress remodelling in the development of spondylolisthesis, which should be taken into consideration when placing at the insertion of pedicle screws.

EFFECTS OF SAGITTAL BALANCE DIFFERENCES ON SPONDYLOLISTHESIS.

ABSTRACTObjectives:This study aimed to compare the lumbar lordosis (LL) and spinopelvic parameters of patients with stage 1–2 spondylolisthesis to those of the normal population and demonstrate the importance of these parameters in sagittal balance.Methods:The lumbosacral parameters on the lateral radiographs of a total of 125 patients were retrospectively compared. Lumbosacral parameters including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), lumbar lordosis angle (LLA), L5 incidence (L5I), L5 slope (L5S), and sacral table angle (STA) were compared between groups.Results:Comparison of the parameters between groups revealed no sex-based differences (p > 0.05).Conclusions:Abnormal sagittal spinopelvic parameters are commonly examined for their effects on the development of spondylolisthesis and should be used in routine practice. We found that the low SS values in our study, unlike those of other similar studies, may be a compensatory mechanism developed to reduce pain and maintain sagittal balance. Level of Evidence II; retrospective study.

Effects of body mass index, mesenteric and abdominal subcutaneous adipose tissue on the spinopelvic parameters.

The purpose of this study was to investigate the effects of body mass index (BMI), thickness of the abdominal subcutaneous adipose tissue (ASAT), thickness of the mesenteric adipose tissue (MAT), weight and height on spinopelvic parameters. A total of 400 patients presented to the radiology department for whole abdominal computed tomography were included in the study. Patients' weight and height were measured to calculate BMI. Thickness of ASAT and MAT, lumbosacral angle (LSA), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI) were measured from the images obtained. We analyzed the effects of BMI, ASAT, and MAT on spinopelvic parameters. In addition, patients included in the study were screened for isthmic spondylolisthesis and transitional vertebrae. Statistical analysis was carried out using SPSS 15.0 package software. p < 0.05 Values were considered statistically significant. BMI and thickness of ASAT and MAT increased with aging both in male and female individuals. There was a positive correlation between PI and weight, thickness of ASAT and thickness of MAT, while a negative correlation was found between PI and height (p < 0.01). SS angle was positively correlated with weight (p < 0.01). A weak positive correlation was found between PT angle and thickness of MAT and height (p < 0.05). The rate of transitional vertebrae and isthmic spondylolisthesis was 2 and 4.6%, consecutively. PI and SS values were significantly higher in the subjects having spondylolisthesis than normal population (p < 0.01). It should be kept in mind that obesity might increase the risk for development of spondylolisthesis by causing increase in PI angle.

Disc Space Excessive Distraction is a Potent Risk Factor for Adjacent Segment Degeneration after Anterior Cervical Discectomy and Fusion

Introduction We reported that excessive disc space distraction caused by insertion of large cages during anterior cervical discectomy and fusion (ACDF) induces adjacent segment degeneration (ASD). Previous reports indicated that over distraction of disc space was an independent risk factor for ASD after posterior lumbar interbody fusion. We therefore hypothesize that the incidence of ASD after ACDF with larger size of cages should be higher than that ACDF with normal cages due to this loss of disc space distraction. Materials and Methods Radiographic ASD is defined as development of spondylolisthesis &gt;3 mm, decrease in disc height &gt;3 mm, or intervertebral angle at flexion lesser than −5 degrees. Symptomatic ASD is defined by a decrease of ≥ 4 points in Japanese Orthopedic Association score. A 130 patients with cervical spondylotic radiculopathy were treated with either ACDF with larger size of cages ( n = 45) or ACDF with normal cages ( n = 85) and followed up for a minimum of 2 years (mean, 39.2 months). Results Disc space distraction in the normal cage group was significantly smaller (0.4 mm) as compared with the larger size group (1.8 mm). The incidence of clinical ASD in the normal cage group (2%, 1/45) was also significantly less than that in the larger size group (15%, 13/85). Multivariate analysis showed that disc space distraction was the most significant risk factor. Conclusion Among various risk factors for ASD after ACDF, the excessive distraction of disc space proved to be a potent risk factor for ASD. Disclosure of Interest None declared

Disc space distraction is a potent risk factor for adjacent disc disease after PLIF

We reported that excessive disc space distraction caused by insertion of large cages during posterior lumbar interbody fusion (PLIF) combined with pedicle screws (PS) induces adjacent segment disease (ASD). Spinous process plate (SPP) is known to allow cage subsidence when used in PLIF, since they cannot share vertical loads. We therefore hypothesize that the incidence of ASD after PLIF with SPP should be lower than that after PLIF with PS due to this loss of disc space distraction. Radiographic ASD is defined as development of spondylolisthesis > 3 mm, decrease in disc height > 3 mm, or intervertebral angle at flexion lesser than -5°. Symptomatic ASD is defined by a decrease of ≥ 4 points in Japanese Orthopedic Association score. One hundred and thirty patients with L4 spondylolisthesis were treated with either PLIF with SPP (n = 45) or PLIF with PS (n = 85) and followed up for a minimum of 2 years (mean, 39.0 months). L4-5 disc space distraction in the SPP group was significantly smaller (0.4 mm) as compared to the PS group (1.8 mm). The incidence of clinical ASD in the SPP group (2%, 1/45) was also significantly less than that in the PS group (15%, 13/85). Multivariate analysis showed that disc space distraction was the most significant risk factor. Among various risk factors for ASD after PLIF, the excessive distraction of disc space proved to be a potent risk factor for ASD.

High-grade child spondylolisthesis: A custom-made canulated screw to treat the so-called double instability

Describing and assessing of a new surgical procedure to achieve circumferential fusion and translumbosacral fixation using a custom-made canulated screw. Seven patients aged 13-18 years old underwent surgery with this technique (mean age: 15). All patients had high-grade spondylolisthesis (Meyerding stage III or IV). There were five girls and two boys. A posterior surgical approach alone was used in all cases. The posterior neural arch of L5 was removed and a sacral laminectomy, extending to S2, was performed. Sacral nerve roots S2 and S3 were carefully dissected and transposed. A K-wire was placed medially across the vertebrae from the posterior edge of S2 extending to the anterosuperior corner of L5. Fluroscopic perioperative fluroscopic control confirmed correct K-wire placement. The custom-made 10mm diameter canulated screw was then inserted along the K-wire as a guide. Screw fixation was obtained by placing a specific large diameter screw head to obtain compression by a lag screw effect. Once fixation was obtained, the sacral dome was excised and interbody fusion was performed (tricorticocancellous graft on each side of the screw). Additional bilateral posterolateral fusion was then performed. A half body custom fit thoracolumbar orthosis brace was prescribed 3 months postoperatively, followed by a Lombostat flexible lumbar support for an additional 3 months period. One neurological complication occurred. A dural tear occurred during dissection requiring simple repair. All of the patients were on their feet on the fifth postoperative day and began walking. The half bodybrace was worn for 4 months in four patients and 2 months in the three others. At final follow-up patients had no residual pain. The lumbar spine in children with high-grade spondylolisthesis adapts to the new mechanical conditions after surgery. Therefore the principal goal of treatment is to obtain stable osseous fusion. Our treatment philosophy is based on the concept of a dual instability. We believe that a general instability exists which causes the development of spondylolisthesis; this must be respected by not attempting to correct the displacement beyond what can be obtained on the operating table with complete muscle release. The other, locoregional instability, must be stabilized during circumferential fusion. The custom-made, 10mm screw has been shown to be effective in neutralizing the mechanical stress during circumferential fusion with a posterior approach alone, thus avoiding the risks of an anterior approach. Long-term results show that the preoperative posture is not the sole mechanical determinant in children and adolescents but that this posture is largely a reaction to pain. Level IV. Retrospective study.

Adjacent Segment Disease FollowingLumbar/Thoracolumbar Fusion With Pedicle Screw Instrumentation

Retrospective radiographic outcomes analysis. We had 3 hypotheses: 1) a longer fusion; 2) a more proximal instrumented vertebra, and 3) circumferential fusion versus posterior-only fusion would increase the likelihood of adjacent segment disease (ASD). The literature analyzing risk factors, prevalence, and presentation of patients with ASD is varied and without clear consensus. A total of 188 patients with minimum 5-year follow-up who had lumbar/thoracolumbar fusion with pedicle screw instrumentation for degenerative disorders were included. Radiographic ASD was defined by: 1) development of spondylolisthesis >4 mm, 2) segmental kyphosis >10 degrees , 3) complete collapse of disc space, or 4) more than 2 grades worsening of Weiner classification. Clinical ASD was defined as 1) symptomatic spinal stenosis, 2) intractable back pain, or 3) subsequent sagittal or coronal imbalance. Radiographic ASD occurred in 42.6% (80 of 188) of patients. Patients with radiographic ASD had worse Oswestry scores (20.3 vs. 12.5; P = 0.001) at ultimate follow-up than those without ASD. Clinical ASD developed in 30.3% (57 of 188) of patients. Clinical ASD manifested as spinal stenosis (n = 47), instability-type back pain (n = 5), and sagittal or coronal imbalance (n = 5). Age at surgery over 50 years and length of fusion were significant risk factors for the development of ASD in the lumbar spine. Fusion to L1-L3 proximally increased the risk of ASD when compared with L4 and L5. Circumferential fusion versus posterior fusion was not a significant factor in the development of ASD. Patients over the age of 50 were at higher risk of developing clinical ASD than those 50 years old or younger. Length of fusion was a significant risk factor in the development of ASD in the lumbar spine. Fusion up to L1-L3 increased the risk of ASD when compared with L4 and L5. Circumferential fusion, as opposed to posterolateral fusion, was not a statistically significant risk factor for the development of ASD.

New Concepts on the Pathogenesis and Classification of Spondylolisthesis

A review of the literature in the English language pertaining to the pathogenesis and classification of spondylolisthesis. To review the morphology and biomechanics of the lumbosacral junction as it relates to spondylolisthesis. To present contemporary theories of the development and progression of spondylolisthesis and an etiology-based classification system. The proper treatment of spondylolisthesis is dependent on recognizing the type of slip and its natural history. Although a number of clinical and radiographic features have been identified as risk factors, their role as primary causative factors or secondary adaptive changes is not clear. In particular, confusion persists over the classification of slips with "isthmic defects." The early identification of spondylolisthesis that will progress to a high grade without intervention remains elusive. A review of English language literature regarding the pathogenesis and classification of spondylolisthesis. RESULTS.: Current literature suggests that spinopelvic parameters, in addition to the morphology and biomechanics of the lumbosacral junction, play a causative role in the development of spondylolisthesis. Progression of developmental slips may be due to growth deficiencies of the anterosuperior sacrum, analogous to Blount's disease at the knee. The Marchetti-Bartolozzi classification system emphasizes the distinction between developmental dysplastic slips and acquired laminar stress fractures, both of which may have isthmic defects. These two types of spondylolisthesis have significantly different natural histories, suggesting the need for different treatment strategies. The Marchetti-Bartolozzi system also allows for the classification of postsurgical, pathologic, and degenerative forms of spondylolisthesis. The morphology of the lumbosacral junction resists high shear and compressive forces. The loss of the posterior restraint through an incompetent bony hook may result in the forward displacement of one vertebra on the subjacent vertebra. The spinopelvic parameters, such as pelvic incidence, may be greater determinants of development and progression than previously appreciated. The Marchetti-Bartolozzi classification system is applicable to all forms of lumbar spondylolisthesis,and seems to be clinically relevant in terms of treatment decisions. Their system emphasizes the distinction between developmental spondylolisthesis with lysis and acquired spondylitic spondylolisthesis, which have been included together in previous classification systems and caused confusion over natural history and treatment. Developmental slips have a greater propensity toward progression, which may be secondary to growth deficiencies of the upper sacrum. Further study is required to confirm these observations.

Union of defects in the pars interarticularis of the lumbar spine in children and adolescents. The radiological outcome after conservative treatment.

Lumbar spondylolysis can heal with conservative treatment, but few attempts have been made to identify factors which may affect union of the defects in the pars. We have evaluated, retrospectively, the effects of prognostic variables on bony union of pars defects in 134 young patients less than 18 years of age with 239 defects of the pars who had been treated conservatively. All patients were evaluated by CT scans when first seen and more than six months later at follow-up. The results showed that the spinal level and the stage of the defects were the predominant factors. The site of the defects in the pars, the presence or development of spondylolisthesis, the condition of the contralateral pars, the degree of lumbar lordosis and the degree of lumbar inclination all significantly affected union.

Pelvic lordosis and alignment in spondylolisthesis.

Pelvic morphology and lumbopelvic lordosis were measured on standing radiographs of 75 patients with greater than 10% L5-S1 spondylolytic spondylolisthesis. The findings were compared with those of 75 volunteers to determine significant differences between the two groups. Etiology of isthmic (lytic) spondylolisthesis remains uncertain. Causation appears to be multifactorial. The relationship between pelvic morphology and spondylolisthesis deserves additional study. Both groups had a standing lateral radiograph of the thoracolumbar spine and pelvis taken that included both hips. Three radiographic angles for pelvic morphology (pelvisacral, pelvic incidence, and pelvic lordosis) were measured by two observers. Each offered similar reliability. Measurement of the pelvic lordosis angle by the pelvic radius technique required fewer steps. It also allowed calculation of the combined angles comprising both the pelvic morphology component for lordosis (the constant pelvic lordosis angle) and the lordosis in the lumbar spine (the variable lumbar lordosis from T12-S1) that should complement the fixed pelvic lordosis (the complementary lumbopelvic lordosis). Mean values and statistical correlations were then computed for each group and compared. The mean slippage for patients was 30% (range, 11-85%), with 34 patients (45%) having Grade I slips, 32 (43%) having Grade II slips, and nine (12%) having Grade III and IV slips. The mean measurements between patients and volunteers were significantly different (P < 0.01) for lumbar lordosis, pelvic lordosis, and lumbopelvic lordosis. Subgroups of patients with increasingly larger slips (Grade I-III) had significantly smaller mean angles for pelvic lordosis. The pelvic and lumbopelvic parameters studied were different in patients compared with controls. The contribution of the pelvis to lordosis was significantly smaller in the subgroups of patients with increasingly larger grades of spondylolisthesis. Pelvic morphology may play a role in the development of spondylolisthesis. Measurement of the combined lumbar and pelvic (lumbopelvic) lordosis on standing radiographs is important.

Endoscopically Assisted Open Removal of Laterally Herniated Lumbar Discs

Background Adequate treatment of laterally herniated lumbar discs presents a surgical challenge. All fragments compressing the nerve root should be removed without destruction of the overlying facet joint. To accomplish this goal many techniques have been proposed, each with specific limitations. Methods In a small group of patients we have used a small malleable endoscope to assist in the removal of laterally herniated discs. Via a small laminotomy, the nucleus was removed in a standard manner and then the lateral disc material removed under direct endoscopic visualization. Results There were no operative complications and the nerve root was visualized and decompressed in all patients. There has been no recurrence of pain or development of spondylolisthesis. Conclusion This technique negates removal of portions of the facet joint and provides adequate nerve root decompression.

Incidence of spondylolisthesis in ambulatory cerebral palsy patients.

We prospectively studied 50 consecutive ambulatory cerebral palsy (CP) patients to determine the incidence of isthmic spondylolisthesis. In addition, we examined the relationship of hip flexion contractures to development of spondylolisthesis and low back pain. Three patients who had undergone previous spine operation were eliminated from the study group. Of the remaining 47 patients, one patient (2%) demonstrated an asymptomatic grade I spondylolisthesis. Another patient (2%) demonstrated spondylolysis without spondylolisthesis. Only six patients reported occasional low back pain. Pain did not correlate with increasing age, increasing hip flexion contracture, or decreasing sacrofemoral angle. The incidence of spondylolisthesis in this group of ambulatory CP patients with hip flexion contractures is similar to that in the general population. Hip flexion contractures did not predispose the group to spondylolisthesis or low back pain. Periodic screening of asymptomatic ambulatory CP patients for spondylolisthesis is not recommended.

Development of spondylolisthesis after growth arrest

Based on the observation of three clinical cases of late onset (after growth arrest) spondylolisthesis, the different pathogenetic factors for lumbar instability in adulthood are discussed. A causal classification based on functional and morphological criteria clearly separates the "genuine" traumatic spondylolisthesis from other forms causing instability (with spondylolysis) within a lumbar motion segment. The possibility of developing spondylolisthesis even after growth arrest is hereby proven. Consequences for appraisal procedures are discussed, and an example for possible surgical management is given.

The Incidence and Aetiology of Avian Spondylolisthesis (‘Kinky Back’)

Summary A radiographic study of the patterns of architecture of the thoracic vertebral columns of groups of fowls of various ages and strains exposed to differing experimental treatments is described. Subclinical spondylolisthesis was found to be common in the several broiler strains of fowls examined but was not seen in birds of a slower growing laying strain. Spondylolisthesis was not a congenital problem but one which developed during the first few weeks of life. The development of spondylolisthesis appeared to be related to the early and rapid development of lordosis in the thoracic 5 to 7 region of the vertebral column. The incidence of spondylolisthesis appeared to depend upon the age, genotype and rate of early growth of the birds.