The pathogenesis of slippage and deformity in the pediatric lumbar spine: a radiographic and histologic study using a new rat in vivo model

Experimental Rat Model of Bony Defects in the Facet Joint Maintained with Bone Wax for the Study of Spinal Pain

Purpose

Studies using experimental rat models for low back pain due to facet-joint defects are scarce. This study used a novel experimental rat model to determine whether bony defects induced by facetectomy could be maintained by bone wax, thus mimicking spondylolysis, and to analyze the effect of the facetectomy on rat behavior.

Patients and Methods

Twelve 10-week-old male Wistar rats weighing 300–350 g were divided into group A (n = 6) that underwent unilateral facetectomy of the right L5-6 facet joint and group B (n = 6) that additionally applied water-soluble bone wax at the facetectomy site. The difference in the left and right stride length, detected by the footprint test, and change in the left and right facet joint area were compared before and 4 weeks after the experiment.

Results

Even though the difference between the left and right stride lengths of groups A and B was not statistically significant, in contrast to group A, group B showed a shorter stride length on the right side (p = 0.22 and 0.46, in group A and group B, respectively). The right facet joint area, where the facetectomy was performed, was significantly smaller in group B 4 weeks after surgery, but not in group A (p = 0.50 and < 0.01, in group A and group B, respectively).

Conclusion

Based on the results, we concluded that the bony defects, induced by facetectomy at the L5-6 facet joint, were maintained with bone wax. This study will provide an experimental model for bony defects in the facet joint.

Curve Characteristics and Response of Sciatic and Olisthesis Scoliosis Following L5/S1 Transforaminal Lumbar Interbody Fusion in Adolescent Lumbar Spondylolisthesis

BACKGROUND

Lumbosacral spondylolisthesis-induced scoliosis is a rare clinical entity. Sagittal reconstruction and the coronal curve evolution after surgery for spondylolisthesis have not been investigated in depth.

OBJECTIVE

To compare the curve characteristics between sciatic scoliosis and olisthetic scoliosis and to further investigate the effects of lumbosacral transforaminal lumbar interbody fusion (TLIF) on scoliosis evolution.

METHODS

Adolescents with sciatic scoliosis group (SS group) or olisthetic scoliosis group (OS group) who underwent L5/S1 TLIF from 2010 to 2017 and were followed up for at least 2 yr were retrospectively reviewed. Radiographic parameters and patient-reported outcomes were evaluated.

RESULTS

There were 20 patients in the SS group (M/F: 8/12; age: 15.6 ± 2.2 yr) and 16 in the OS group (M/F: 6/10; age: 16.8 ± 2.5 yr). Both groups had similar preoperative Cobb angles, but more patients with coronal imbalance were observed in the SS group. Moreover, the OS group showed significantly larger L5 tilt and rotation. After surgery, the slip reduction rate of the SS group and OS group were 76.1% ± 12.4% and 79.4% ± 9.6%, respectively. Scoliosis resolution was observed in all patients in the SS group but only in 9 patients (56.2%) in the OS group. Patients with failed scoliosis resolution in the OS group were older and had a larger Cobb angle and L5 rotation compared with those with successful scoliosis resolution.

CONCLUSION

Lumbosacral TLIF can achieve satisfactory slip reduction and scoliosis resolution. Sciatic scoliosis often presents with coronal imbalance but also a preferable curve prognosis. A large Cobb angle and L5 rotation may hinder the resolution of olisthetic scoliosis.

Bone Formation During Correction of Vertebral Rounding Deformity in a Rat Model of Pediatric Spondylolisthesis

STUDY DESIGN

A study using rat spondylolisthesis models.

OBJECTIVE

The aim of this study was to elucidate the mechanism for correction of vertebral rounding deformity.

SUMMARY OF BACKGROUND DATA

Vertebral rounding deformity is the strongest risk factor for high-grade slippage associated with spondylolisthesis in adolescents. We previously reported that inadequate endochondral ossification of the anterior upper corner of the vertebral growth plate in response to mechanical stress could be the pathological mechanism of vertebral rounding deformity.

METHODS

We created a model of spondylolisthesis using 4-week-old rats. They were divided into a tail suspension group that underwent tail suspension to decrease mechanical stress starting at 2 weeks postoperatively and a ground control group with no intervention. Radiographs and microcomputed tomography scans were obtained once weekly for 6 weeks postoperatively. The lumbar spines were then harvested for histological analysis. Immunohistochemical studies detected types I, II, and X collagen in the growth plate cartilage. Bone histomorphometrical analysis was also performed.

RESULTS

Radiological and histological evidence in the ground control group showed progress the rounding deformity with time as previously reported. Formation of normal cancellous bone was observed radiologically over time in the tail suspension group, indicating correction of rounding deformity. Histologically, the site showing radiological evidence of correction was derived from cartilage tissue. After starting tail suspension, the growth plate stained positive for type X collagen and the corrected site stained for types II and X collagen in a mosaic pattern. Chondrocytes expressing types I and II collagen and tartrate-resistant acid phosphatase-positive cells were also present at the corrected site. Histomorphometrically, more endochondral bone was detected at the corrected site than in the posterior aspect of the normal growth plate.

CONCLUSION

Correction of vertebral rounding deformity was associated with improvement of chondrocyte differentiation; furthermore, there is possible involvement of a third mechanism, namely transchondroid bone ossification.Level of Evidence: N/A.

Natural Correction and Adaptation of a Severely Deformed Sacral Dome in an Adolescent with Isthmic Spondylolisthesis: A Case Report

CASE

A spinal deformity with wedging of L5 and rounding of the surface of the sacral dome is very common in pediatric patients with spondylolisthesis at the L5 vertebral level, and it has been well documented that severe spondylolisthesis is a good indication for spinal arthrodesis. We report the natural correction and adaptation of a severely deformed sacral dome with slippage (40.8%) in a pediatric patient with nonoperative treatment.

CONCLUSION

Vertebral deformity in children can be reversible. Orthopaedic surgeons should be aware that pediatric patients with a severe deformity of the sacral dome and vertebral slippage can be managed nonoperatively.

Pediatric isthmic spondylolisthesis showing radiologic evidence of slippage after physis injury

The pathogenesis of slippage in pediatric spondylolisthesis is still unclear, although epiphyseal injury may account for many cases based on preclinical studies. However, no reports have described a pediatric case of isthmic spondylolisthesis showing radiologic evidence of epiphyseal injury. We report such evidence in a 13-year-old boy with low-back pain. Radiography revealed rounding of the S1 surface, a fracture line below the S1 endplate surface, and a bone marrow lesion in addition to slippage. Slippage and the rounding deformity were partially reversed (from 20 to 14% and from 42 to 27%, respectively) with conservative treatment and natural bone remodeling.

Biomechancial quantification of pathologic manipulable spinal lesions: an in vivo ovine model of spondylolysis and intervertebral disc degeneration

OBJECTIVE

The purposes of this study were to quantify the biomechanical and pathologic consequences of surgically induced spinal lesions and to determine their response to spinal manipulation (SMT) in an in vivo ovine model.

METHODS

Of 24 Merino sheep, 6 received L5 spondylolytic defects, 6 received L1 annular lesions, and 12 served as respective controls. Dorsoventral (DV) stiffness was assessed using oscillatory loads (2-12 Hz). Two SMT force-time profiles were administered in each of the groups using a randomized and repeated-measures design. Stiffness and the effect of SMT on the DV motions and multifidus needle electromyographic responses were assessed using a repeated-measures analysis of variance (α = .05). Postmortem histologic analysis and computed tomography validated the presence of lesions.

RESULTS

L5 DV stiffness was significantly increased (40.2%) in the spondylolysis (6.28 N/mm) compared with the L5 control group (4.48 N/mm) (P < 03). Spinal manipulations delivered to the spondylolysis group resulted in less DV vertebral displacement (P < .01) compared with controls. Dorsoventral stiffness of the disc degeneration group was 5.66 N/mm, 94.5% greater than in the L1 control group (2.91 N/mm) (P < .01). One hundred-millisecond SMTs resulted in significantly reduced DV displacements in the disc degeneration group compared with the L1 control group (P < .01). Animals in the disc degeneration group showed a consistent 25% to 30% reduction in needle electromyographic responses to all SMTs.

CONCLUSIONS

Quantifiable objective evidence of spinal lesions and their response to SMT were confirmed in this study. Neuromechanical alterations provide novel insights into quantifying manipulable spinal lesions and a means to biomechanically assess SMT outcomes.

Spondylolysis and spondylolisthesis: a narrative review of etiology, diagnosis, and conservative management

OBJECTIVE

To review current literature regarding the etiology, diagnosis, and conservative treatment of spondylolysis and spondylolytic spondylolisthesis.

METHODS

The PubMed database was searched for articles on spondylolysis and/or spondylolisthesis and their incidence, diagnosis, imaging, treatment, and prognosis. The bibliographies of articles determined to be relevant were also reviewed.

RESULTS

A PubMed search of spondylolysis or spondylolis-thesis yielded over 800 citations. Sixty-eight articles were selected based on an opinion of perceived relevance to the subjects of spondylolysis and spondylolisthesis.

CONCLUSIONS

Spondylolysis affects approximately 6% of the population. The lesion likely represents a stress fracture and the typical age of onset is early childhood and adolescence. Most individuals are asymptomatic. Adolescents with low back pain may have an impending or new pars defect. A high index of suspicion for a new pars defect should prompt utilization of physiologic imaging to determine the likelihood of pars union in young patients. Restrictive bracing may lead to healing of the fracture and cessation of pain. Spondylolisthesis is a common complication of spondylolysis. Spondylolisthesis progression is typically small and most likely in young individuals. Significant progression in adults is rare. The finding of spondylolysis and spondylolisthesis in an adult patient is usually incidental and not likely to be a direct source of pain unless there is concurrent instability.

Conservative treatment of lumbar spondylolysis in childhood and adolescence

It has been noted that bony union of a pars defect can be achieved in children if they wear a trunk brace. Our aim was to evaluate how the stage of the defect on CT and the presence or absence of high signal change in the adjacent pedicle on T2-weighted MRI were related to bony healing. We treated 23 children conservatively for at least three months. There were 19 boys and four girls with a mean age of 13.5 years (7 to 17). They were asked to refrain from sporting activity and to wear a Damen soft thoracolumbosacral type brace. There were 41 pars defects in 23 patients. These were classified as an early, progressive or terminal stage on CT. The early-stage lesions had a hairline crack in the pars interarticularis, which became a gap in the progressive stage. A terminal-stage defect was equivalent to a pseudarthrosis. On the T2-weighted MR scan the presence or absence of high signal change in the adjacent pedicle was assessed and on this basis the defects were divided into high signal change-positive or -negative. Healing of the defect was assessed by CT.

In all, 13 (87%) of the 15 early defects healed. Of 19 progressive defects, only six (32%) healed. None of the seven terminal defects healed. Of the 26 high signal change-positive defects 20 (77%) healed after conservative treatment whereas none of the high signal change-negative defects did so. We concluded that an early-stage defect on CT and high signal change in the adjacent pedicle on a T2-weighted MR scan are useful predictors of bony healing of a pars defect in children after conservative treatment.

Pediatric iatrogenic spinal deformity

This article reviews current published literature regarding pediatric iatrogenic spinal deformity, with particular emphasis on the cervical spine. The results of published series reporting the incidence, etiology, age, risk factors, surgical techniques, and treatment options are summarized. Iatrogenic deformity resulting from radiation therapy and a variety of surgical procedures are addressed.

Three dimensional finite element analysis of the pediatric lumbar spine. Part II: biomechanical change as the initiating factor for pediatric isthmic spondylolisthesis at the growth plate

A non-linear 3-dimensional finite element pediatric lumbar spine model with vertebral growth plate and apophyseal bony ring was developed. Lumbar spondylolysis was simulated in the model. The Von Mises stresses in the structures surrounding the vertebral growth plate, including apophyseal bony ring and osseous endplate were calculated in various loading modes. Instantaneous axis of rotation (IAR) path from flexion to extension was also analyzed. The results were compared with those of the intact model and the literature. The IAR path was at the posterior disc-endplate space of the lower vertebra in the intact spine, and moved cranially towards the upper-posterior disc space in the lytic spine. This was in agreement with in vivo radiological data by Sakamaki et al. [19]. During various loading modes, stresses in the spondylolytic pediatric model were higher than that of the intact model; ranging from 1.1 to 6.0 times, with the highest value in extension at the growth plate. In conclusion, FE models indicate that stress concentrations in the lytic model increase at the growth plate which may lead to physis stress fracture leading to spondylolisthesis.