Mechanical consequences to the annulus fibrosus following rapid internal pressurization and endplate fracture under restrained-expansion conditions

Intervertebral disc herniation is not a common injury in the adolescent population, but the correlation between trauma and herniation warrants concern. Previous research demonstrated the capacity for rapid internal pressurization to reduce the mechanical integrity of the intervertebral disc's annulus fibrosus, even in the absence of fracture. The purpose of this study was to modify previous internal pressurization procedures towards a more transferable injury model, then investigate the capacity for these procedures to damage the mechanical integrity of the annulus fibrosus. Porcine cervical motion segments with intact facet joints were confined between a vice and force plate under 300 N of static compression, then a single, manual, rapid internal pressurization was delivered. Posterolateral annulus samples were extracted and situated in a 180° peel test configuration, exposing the interlamellar matrix of samples to separations of 0.5 mm/s, until complete separation of the sample occurred. Multilayer tensile testing was performed on superficial and mid-span samples of annulus by applying uniaxial tension of 1 %/s to 50 % strain. Compared to unpressurized controls, rapid pressurization causing fracture resulted in reduced lamellar adhesion and increased toe-region stress and strain properties in the annulus. Morphological assessment reported similar fracture patterns between endplate fractures achieved in the present experiment and endplate fractures documented in human patients. Mechanical plus morphological results suggest that rapid internal pressurization resulting in endplate fracture may represent a potent mechanism for subsequent damage to the intervertebral disc.

Posterior ring apophysis separation combined with lumbar disc herniation in adults: a 10-year experience in the surgical management of 87 cases

OBJECT

The association of posterior ring apophysis separation (PRAS) with lumbar disc herniation (LDH) is uncommon and represents a true subgroup of disc herniation mainly seen in the adolescent population. The objective of this study was to describe a decade of experience in the care of adult patients with PRAS with LDH, giving particular attention to its diagnosis, surgical treatment, and outcome.

METHODS

This retrospective study focuses on a case series of adult patients with PRAS associated with LDH who underwent surgery for lumbar disc disease in the author's neurosurgical department between 1999 and 2008. Posterior ring apophysis separation was diagnosed in 87 (5.35%) of 1625 patients surgically treated for LDH; these patients made up the PRAS group. During a 6-month period in 2005, LDH without PRAS was diagnosed in 89 consecutive patients at the same facility; these patients constituted the control group. Presenting symptoms, physical examination findings, and preoperative imaging results were obtained from medical records. Immediate operative results were assessed, as were complications, long-term outcome, and the need for repeat surgery.

RESULTS

This study is the first to document the distinguishing features between adult patients with and those without PRAS. The difference in average age was statistically significant (p < 0.001) between the study group (36.22 years) and the control group (44.30 years), as was the incidence of male patients (86.20% vs 71.91%, p = 0.020), incidence of military patients (74.71% vs 57.30%, p = 0.015), average duration of symptoms (16.13 vs 8.4 months, p = 0.016), and incidence of reactive scoliosis (19.54% vs 4.49%, p = 0.002). The most common anatomical location of disc herniation in the PRAS group was L5-S1 (51.72%) versus L4-L5 (53.93%) in the control group (p = 0.017). In terms of previous injury, motor deficits, back and/or leg pain, lateral or central location of LDH, mean anteroposterior diameter of disc herniation, hard or soft discs, and surgical complications, there was no statistical difference between the 2 patient groups. Similarly, there was no difference in recurrence rates and clinical outcomes between the patients with or without PRAS.

CONCLUSIONS

Posterior ring apophysis separation with LDH is probably more common in adults than is generally recognized. It must be suspected when young male patients with persistent sciatic scoliosis and no history of injury show signs of calcified LDH. Computed tomography scanning with sagittal reconstructions is the procedure of choice for diagnosing. The L5-S1 intervertebral disc level is most commonly affected, especially the superior endplate of S-1. This condition needs more extensive surgical exposure and resection to relieve the nerve impingement. The occurrence of an apophyseal lesion was not associated with recurrent disc herniation or a fair outcome.

Magnetic resonance imaging of lumbar vertebral apophyseal ring fractures

Posterior lumbar vertebral apophyseal ring fractures are described in three adolescents presenting with severe low back pain, spinal tenderness and lower limb neurological deficit. Magnetic resonance imaging showed severe L4/5 posterior disc protrusion in all three patients. The actual fracture fragment was visualized with difficulty on MRI alone. The diagnosis of apophyseal ring fracture was made by either radiography or CT. Computed tomography delineated the size, shape and site of the fracture fragment. Surgical confirmation was obtained in all cases. Posterior lumbar vertebral apophyseal ring fractures may be difficult to visualize on MR imaging. Careful review of radiographs, supplemented by targeted CT, is necessary for the correct diagnosis and management of this entity.

Fracture of the vertebral limbus

An 18-year-old young man suffering from fracture of the limbus of L4 was admitted to the emergency ward after a car collision. Radiological evidence of the lesion was visible on plain film radiographs and CT scans. On surgery the posterior column was found to be intact. Treatment included a wide laminectomy, excision of the fragment, and osteosynthesis with Cotrel-Dubous-set instrumentation. The characteristics of these lesions are reviewed on the basis of the latest reports. The possibility of misreading these fractures is emphasized, especially in traumatic adult spine surgery.

Intervertebral disc herniations (limbus vertebrae) in pediatric patients: report of 15 cases

A revision of 15 cases of back pain and radiological features characteristic of anterior or posterior limbus vertebrae is presented. We comment on the radiological findings observed in the various imaging studies performed (conventional radiology, CT and MRI), which were attributed to the herniation of disc material into the vertebral body. In three patients who were followed up 12 years after the diagnosis, the initial roentgenograms of limbus vertebrae progressed in adult hood into radiological images characteristic of Schmorl's hernia as a sequela.