Biomechanical properties of lumbar endplates and their correlation with MRI findings of lumbar degeneration.

How stiffness and strength of the human lumbar endplate vary with location, spinal level, and its correlation with MRI findings of lumbar degeneration, has not been reported in detail. 27 lumbar spines (16 male, 11 female, 31-49yrs) were harvested from cadavers without history of lumbar lesion or trauma. Disc and endplate degeneration was evaluated from MRI. Micro-CT was used to evaluate endplate microstructure. Indentation tests were performed to quantify stiffness and strength at 23 sites on each endplate from load-displacement graphs. Results showed that stiffness and strength increased from the centre of the endplate towards its periphery. There was no general age-related reduction in endplate stiffness or strength, although strength decreased slightly with age opposite the inner annulus. Disc degeneration was associated with a 39-46% decrease in stiffness, and a 21-30% decrease in strength, with effects being greatest near the endplate periphery. The presence of Modic changes had a similar effect. Strength and stiffness consistently increased at lower spinal levels, and were consistently greater in the inferior endplate (relative to the vertebra). Gender had little influence, although stiffness in the peripheral endplate was greater in males. BV/TV, SMI, Tb.Th and BMD were positively correlated with strength. We conclude that endplate properties reflect compressive stresses within adjacent intervertebral discs. Weaker and softer endplates may indicate reduced mechanical loading in decompressed discs that are stress-shielded by the neural arch. Preoperative MRI evaluation of endplate integrity could reduce the risk of implant subsidence following inter-body fusion.

Spontaneous resorption of lumbar disc herniation is less likely when modic changes are present.

STUDY DESIGN: A retrospective survey on 85 consecutive patients with primary single-level lumbar disc herniation (LDH). OBJECTIVE: To investigate associations between Modic changes (MCs) and the likelihood of resorption of herniated lumbar intervertebral discs. SUMMARY OF BACKGROUND DATA: Spontaneous resorption of LDH has been demonstrated, whereas the mechanisms are unclear. MCs are closely associated with disc degeneration, but research focusing on their association with spontaneous resorption of LDH has not been specifically investigated. METHODS: Eighty-five consecutive patients with LDH (52 males, 33 females, aged 20-66 yr) were included. Patients' diagnosis was based on clinical presentation, magnetic resonance imaging, and computed tomography. Patients were divided into surgical and conservative groups and further divided into MC and non-MC subgroups. Spontaneous resorption and clinical success in the conservative group were assessed by reduction in the herniated volume and Oswestry Disability Index. Disc tissues collected from the surgical group were examined histologically, and immunohistochemistry was used to identify endothelial cells and macrophages. RESULTS: In total, 35 of 85 patients showed MC, mostly type II. Herniated tissue in MC group contained relatively more hyaline cartilage endplate than that in non-MC group (on average, 50% vs. 8%, P < 0.05) but less nucleus pulposus (18% vs. 55%, P < 0.05). Conservative treatment reduced Oswestry Disability Index scores in non-MC group from 29.4 to 23.5 on average (P < 0.05), but reductions in MC group (30.1-29.0) were nonsignificant. Herniated volumes reduced after conservative treatment in non-MC group (0.44-0.21 cm3, P < 0.05) but not in MC group (0.52-0.45 cm3, P > 0.05). More neovascularization and macrophage infiltration was observed in herniated tissue from non-MC group than from MC group (P < 0.001). CONCLUSION: MCs in patients with LDH are associated with cartilaginous herniations that resorb poorly, so that patients respond less well to conservative treatments. Loss of cartilaginous endplate may explain the origins of MCs and their association with disc infection. LEVEL OF EVIDENCE: 3.

Basivertebral foramen could be connected with intravertebral cleft: a potential risk factor of cement leakage in percutaneous kyphoplasty.

BACKGROUND CONTEXT: Among different types of cement leakage in percutaneous kyphoplasty (PKP) for osteoporotic vertebral body compression fractures, leaks into the spinal canal are considered to be the most common complication. One potential structure causing this type of cement leakage is the potential connection between the basivertebral foramen and the intravertebral cleft, which is revealed clearly on magnetic resonance (MR) images, but is often ignored in the literature. PURPOSE: The purpose of this study is to assess the incidence rate of different types of cement leakage in PKP with or without intravertebral clefts and to determine whether the basivertebral foramen could be connected to the intravertebral cleft. STUDY DESIGN: This study is a retrospective assessment of the presence of an intravertebral cleft in osteoporotic vertebral bodies and the different types of cement leakage after PKP on radiographs, computed tomographic (CT) scans, and MR images. PATIENT SAMPLE: A total of 164 consecutive patients underwent PKP to treat 204 osteoporotic vertebral compression fractures. OUTCOME MEASURES: Outcome measures include the occurrence of different types of cement leakage in the groups with an intravertebral cleft and without intravertebral clefts. METHODS: A total of 204 vertebrae in 164 consecutive patients who underwent PKP to treat osteoporotic vertebral compression fractures were classified into two patterns based on preoperative radiographs, CT scans, and/or MR images of the treated levels: cleft pattern (with an intravertebral cleft in the vertebral body) and trabecular pattern (without intravertebral clefts). When an intravertebral cleft was identified, the investigators examined the basivertebral foramen and looked for a communication between the two structures on three-dimensional CT scans and MR images. On direct postoperative images, the patterns of cement leakage were classified as five types: type A, through a cortical defect into the paraspinal soft tissues; type B, through the basivertebral foramen; type C, via the needle channel; type D, through a cortical defect into the disc space; and type E, via the paravertebral vein. The association of the distribution of the cement leakage and the presence of an intravertebral cleft was analyzed retrospectively. Moreover, the association of type B leakage with the communication between the basivertebral foramen and the intravertebral cleft was also assessed. RESULTS: The average interobserver kappa values for determining the type of cement leakage and the presence of intravertebral cleft were 0.916 (range, 0.792-1) and 0.935, respectively. In 41 of 204 vertebrae (19.9%), an intravertebral cleft was confirmed on preoperative images. A communication between the intravertebral cleft and the basivertebral foramen was seen in 10 vertebrae (24.4%). Cement leakage was 36.2% in the group with a trabecular pattern and 41.5% in the group with a cleft pattern (p>.05). Leaks through the basivertebral foramen (type B; N=30, 14.7%) and through cortical defects into the disc space (type D; N=14, 6.9%) were more common than other types. Twenty of 163 vertebrae with the trabecular pattern (12.3%) and 10 of 41 vertebrae with the cleft pattern (24.4%) were identified as type B leaks, which reached statistical significance (p<.05). There was no statistical difference between the trabecular pattern and the cleft pattern on other types of leaks. CONCLUSIONS: Type B leaks are more common in vertebrae with an intravertebral cleft, which supports the presence of a connection between an intravertebral cleft and the basivertebral foramen. Thus, care must be taken when PKP is performed in these patients to avoid direct cement leakage into the spinal canal through the basivertebral foramen.