Aim:

To determine if patients with coronal plane deformity in the lumbar spine have a higher grade of lumbar spine subtype compared to controls.

Introduction

Herniated disc tissue removed at surgery is mostly nucleus pulposus, with varying proportions of annulus fibrosus, cartilage endplate, and bone. Herniated nucleus swells and loses proteoglycans, and herniated annulus is invaded by blood vessels and inflammatory cells. However, little is known about the significance of endplate cartilage and bone within a herniation.

Introduction

Disc degeneration is often scored using macroscopic and microscopic scoring systems. Although reproducible, these scores may not accurately reflect declining function in a degenerated disc. Accordingly, we compared macroscopic and microscopic degeneration scores with measurements of disc function.

Introduction

Physical disruption of the extracellular matrix influences the mechanical and chemical environment of intervertebral disc cells. We hypothesise that this can explain degenerative changes such as focal proteoglycan loss, impaired cell-matrix binding, cell clustering, and increased activity of matrix-degrading enzymes.

Introduction

Decreasing endplate porosity has been proposed as a risk factor for intervertebral disc degeneration, because it interferes with disc metabolite transport. However, endplate porosity has recently been shown to increase with age and disc degeneration. We hypothesise that this increase reflects adaptive remodelling in response to altered loading from adjacent discs.

Introduction

Dual energy X-ray absorptiometry (DEXA) is the gold standard for assessing bone mineral density (BMD) and fracture risk in vivo. However, it has limitations in the spine because vertebrae show marked regional variations in BMD that are difficult to detect clinically. This study investigated whether micro-CT can provide improved estimates of BMD that better predict vertebral strength.

The belief that an intervertebral disc must degenerate before it can herniate has clinical and medicolegal significance, but lacks scientific validity. We hypothesised that tissue changes in herniated discs differ from those in discs that degenerate without herniation. Tissues were obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration as assessed by the Pfirrmann grade. Thin sections were graded histologically, and certain features were quantified using immunofluorescence combined with confocal microscopy and image analysis. Herniated and degenerated tissues were compared separately for each tissue type: nucleus, inner annulus and outer annulus.

Herniated tissues showed significantly greater proteoglycan loss (outer annulus), neovascularisation (annulus), innervation (annulus), cellularity/inflammation (annulus) and expression of matrix-degrading enzymes (inner annulus) than degenerated discs. No significant differences were seen in the nucleus tissue from herniated and degenerated discs. Degenerative changes start in the nucleus, so it seems unlikely that advanced degeneration caused herniation in 21 of these 32 discs. On the contrary, specific changes in the annulus can be interpreted as the consequences of herniation, when disruption allows local swelling, proteoglycan loss, and the ingrowth of blood vessels, nerves and inflammatory cells.

In conclusion, it should not be assumed that degenerative changes always precede disc herniation.

Cite this article: Bone Joint J 2013;95-B:1127–33.

Osteoporotic vertebral deformities are conventionally attributed to fracture, although deformity is often insidious, and bone is known to “creep” under constant load. We hypothesise that deformity can arise from creep that is accelerated by minor injury.

Thirty-nine thoracolumbar “motion segments” were tested from cadavers aged 42-92 yrs. Vertebral body BMD was measured using DXA. A 1.0 kN compressive force was applied for 30 mins, while the height of each vertebral body was measured using a MacReflex optical tracking system. After 30 mins recovery, one vertebral body from each specimen was subjected to controlled micro-damage (<5mm height loss) by compressive overload, and the creep test was repeated. Load-sharing between the vertebral body and neural arch was evaluated from stress measurements made by pulling a pressure transducer through the intervertebral disc.

Creep was inversely proportional to BMD below a threshold BMD of 0.5 g/cm² (R²=0.30, P<0.01) and did not recover substantially after unloading. Creep was greater in the anterior cortex compared to the posterior (p=0.01) so that anterior wedge deformity occurred. Vertebral micro-damage usually affected a single endplate, causing creep of that vertebra to increase in proportion to the severity of damage. Anterior wedging of vertebral bodies during creep increased by 0.10^o (STD 0.20^o) for intact vertebrae, and by 0.68^o (STD 1.34^o) for damaged vertebrae.

Creep is substantial in elderly vertebrae with low BMD, and is accelerated by micro-damage. Preferential loss of trabeculae from the anterior vertebral body could explain greater anterior creep and vertebral wedging.

To investigate whether restoration of mechanical function and spinal load-sharing following vertebroplasty depends upon cement distribution.

Fifteen pairs of cadaver motion segments (51-91 yr) were loaded to induce fracture. One from each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Various mechanical parameters were measured before and after vertebroplasty. Micro-CT was used to determine volumetric cement fill, and plane radiographs (sagittal, frontal, and axial) to determine areal fill, for the whole vertebral body and for several specific regions. Correlations between volumetric fill and areal fill for the whole vertebral body, and between regional volumetric fill and changes in mechanical parameters following vertebroplasty, were assessed using linear regression.

For Cortoss, areal and volumetric fills were significantly correlated (R=0.58-0.84) but cement distribution had no significant effect on any mechanical parameters following vertebroplasty. For PMMA, areal fills showed no correlation with volumetric fill, suggesting a non-uniform distribution of cement that influenced mechanical outcome. Increased filling of the vertebral body adjacent to the disc was associated with increased intradiscal pressure (R=0.56, p<0.05) in flexed posture, and reduced neural arch load bearing (F_N) in extended posture (R=0.76, p<0.01). Increased filling of the anterior vertebral body was associated with increased bending stiffness (R=0.55, p<0.05).

Cortoss tends to spread evenly within the vertebral body, and its distribution has little influence on the mechanical outcome of vertebroplasty. PMMA spreads less evenly, and its mechanical benefits are increased when cement is concentrated in the anterior vertebral body and adjacent to the intervertebral disc.

Introduction

Osteoporotic fracture reduces vertebral stiffness, and alters spinal load-sharing. Vertebroplasty partially reverses these changes at the fractured level, but is suspected to increase deformations and stress at adjacent levels. We examined this possibility.

Introduction

Vertebral osteoporotic fracture increases both elastic and time-dependent (‘creep’) deformations of the fractured vertebral body during subsequent loading. This is especially marked in central and anterior regions of the vertebral body, and could explain the development of kyphotic deformity in life. We hypothesise that vertebroplasty can reduce these creep deformations.

Background

Fissures in the anulus fibrosus are common in disc degeneration, and are associated with discogenic pain. We hypothesise that anulus fissures are conducive to the ingrowth of blood vessels and nerves.