Stephen J. Edmondston

The relationship between bone mineral density, vertebral body shape and spinal curvature in the elderly thoracolumbar spine: an in vitro study

Vertebral body geometry, defined by the anterior/posterior (A/P) and mid/posterior (M/P) vertebral body height ratios, was measured in 18 vertebral columns (T1-L5) from sagittal computed tomography scans. For each vertebra, the trabecular density (VTD) and bone mineral density (BMD) were measured using quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA), respectively. Lateral view radiographs were digitized to measure the thoracic curvature. The segmental correlations between vertebral shape and bone density were poor (r = 0.01-0.31). The mean thoracic BMD and VTD and the mean lumbar VTD were significantly correlated with the mean thoracic A/P ratio (r = 0.55-0.69). The thoracic curvature was significantly correlated with both the mean thoracic and the mean lumbar VTD and BMD (r = 0.55-0.73). In summary, the extent of vertebral wedging and thoracic curvature was moderately indicative of the mean BMD of the thoracic vertebrae, and lumbar spine densitometry is useful to assess the relative severity of osteopenia in individuals with thoracic vertebral deformities.

Accuracy of lateral dual energy X-ray absorptiometry for the determination of bone mineral content in the thoracic and lumbar spine : an in vitro study

Lateral scanning with dual energy X-ray absorptiometry (DXA) was undertaken on 153 thoracic and lumbar vertebral bodies from nine individuals (mean age 67; range 34-92 years) to establish their bone mineral content (BMC). All specimens were subsequently de-fatted and ashed to compare ash weight with BMC of the T1 to L5 segments. Linear regression analysis indicated a higher correlation between BMC and measured ash weights for each vertebral column (range: r = 0.97-0.99), with error for all vertebrae tested showing a standard error of 0.40 g, or 10.8%. For the L2-4 segments the accuracy error was 0.50 g or 7.9%. In both cases there was a mean trend towards underestimation of ash weight. Mean BMC values of the T1 to T5 segments were similar before a progressive increase caudally. These data affirm the utility of DXA for determining bone mineral content in the vertebral column across wide ranges of age, and segmental and bone density.

DOES FORMALIN-FIXATION ALTER THE EXTENT OF COLLAGEN AND ELASTIN CROSSLINKS IN HUMAN SPINAL INTERVERTEBRAL DISCS AND LIGAMENTUM FLAVA?

The effect of formalin-fixation on the extent of collagen and elastin crosslinks in the matrix of human spinal intervertebral discs and ligamentum flava tissues was evaluated. Fresh discs (n = 5) and ligamentum flava (n = 22) were harvested and separated into two samples. One sample was stored in 10% buffered formalin and the other control sample in a freezer at -20°C. Using HPLC the paired anular (n = 72), nuclear (n = 22) and liagmentum flavum (n = 58) samples were dried, hydrolyzed and assayed for collagen and elastin crosslinks over a 25-week period. There were no significant differences in the collagen, isodesmosine and desmosine content, and the extent of pyridinoline and deoxypyridinoline crosslinks, between fresh and formalin-fixed disc and ligament samples after 25 weeks of formalin fixation. Short-term formalin-fixation does not significantly influence the collagen and elastin crosslink content or the extent of insoluble collagen crosslinks in spinal disc and ligamentum flavum tissues.

Reliability of a modified grading scheme for MRI assessment of thoracic intervertebral discs

The study aimed to investigate the variability in interpreting magnetic resonance imaging (MRI) films for thoracic disc degeneration, using a 5-point MRI disc grading scale and a modified 3-point scale. Forty-six T2-weighted sagittal thoracic MRI films, comprising 18 males and 28 females, aged 7 to 73 years, (mean age =41±16.3 years), were randomly selected from 318 archived cases. Nuclear and anular degeneration, end-plate lesions and osteophytes were graded on the first 30 cases using a modified 3-point grading scale. The next 30 cases were evaluated using the 5-point grading scale. Repeat evaluations for both scales were conducted after a three- to six-month interval. The intra-rater kappa coefficient was higher using the 3-point scale (0.71 to 0.87, p < 0.001) compared to the 5-point scale (0.57 to 0.78, p < 0.001) for the end-plate–disc–end-plate components. The lowest intra-rater reliability was for osteophytes and the highest was for the nucleus. The intra-rater reliability was generally higher in the upper thoracic region compared to the mid and lower thoracic regions.

VALIDITY OF THE RETROSPECTIVE APPLICATION OF OXFORD HIP AND KNEE SCORES

The Oxford Hip Score (OHS) and Oxford Knee Score (OKS) are validated, reliable and reproducible outcome measures, however their use retrospectively has not been examined. The aim of this prospective cohort study was to examine the accuracy and reliability of patients ability to recall their OHS and OKS in a retrospective manner. A total of 137 patients undergoing primary hip (40) or primary knee (97) arthroplasty with a mean age of 70.8 years (range, 47–88) and a mean time to follow up of 27.2 months (range, 6–46) were included in the study. The mean retrospective OHS and OKS decreased compared to the pre-operative score (OHS = 1.6 ± SD, p = 0.36, OKS = 4.7 ± SD, p < 0.001). There was only a weak positive relationship between the actual pre-operative scores and the retrospective scores (OHS: r2 = 0.30, OKS: r2 = 0.19). Bland–Altman analysis demonstrated 95% limits of agreement between scores of -19.9 to 23.1 for the OHS and -15.3 to 24.8 for the OKS. This study shows that patients are poor at retrospectively recalling their pre-operative OHS and OKS and therefore these scores should not be used in a retrospective manner.

COLLAGEN AND ELASTIN CROSSLINKS IN HUMAN INTERVERTEBRAL DISCS AND LIGAMENTUM FLAVUM: AGE, GENDER AND SPINAL LEVEL INFLUENCES

The collagen and elastin content and extent of collagen crosslinks were determined in human formalin-fixed and unfixed intervertebral discs and ligamentum flava. Tissue samples from cadaveric spinal discs (n = 77) and ligamentum flava (n = 364) were obtained from 24 formalin-fixed and 2 fresh spines. The mean age of all cases was 57±26 years. Spinal ligament and disc samples were harvested and analyzed for collagen, and crosslinks of pyridinoline, deoxypyridinoline, and elastin crosslinks isodesmosine and desmosine. Collagen and elastin crosslinks were extracted from hydrolyzed samples by cellulose partition chromatography, and analyzed by reverse-phase HPLC. Elastin crosslinks were only detected in 4 lumbar discs (mean 0.04±0.01 nmol/mg dry wt) but yielded results for all ligamentum flavum samples (mean 20.2±6.4 nmol/mg dry wt). For ligamentum flavum, the collagen and collagen crosslinks increased significantly with age (p < 0.05), whereas elastin content decreased significantly with age but only for the lumbar region (p < 0.05). Collagen and elastin content were significantly higher in females (p < 0.01) and collagen, pyridinoline and isodesmosine were significantly higher in the lumbar region (p < 0.01). Elastin detected in lumbar discs was significantly less than that found in ligamentum flavum. The collagen and elastin content and extent of collagen crosslinks in ligamentum matrix varied significantly depending on the age, gender and spinal region.

Patterns of thoracic disc degeneration using MRI: Age, gender and spinal level influences

The present retrospective study reviewed and examined the prevalence of thoracic disc degeneration, end-plate lesions and osteophytes in the thoracic spine using T2-weighted sagittal magnetic resonance images (MRI). The sample comprised 216 thoracic spine cases (101 males and 115 females), aged from 1 to 85 years (mean age = 42±19.7 years). Nuclear and anular degeneration, end-plate lesions and osteophytes were graded using a 3-point scale. The prevalence of degeneration was highest in the nucleus (86%) and lowest in the end-plates (63%). Males had a higher prevalence of degeneration in the nucleus, anulus and end-plates, and a lower prevalence of osteophytes compared to females. Increasing cranio-caudal trends in the prevalence of degeneration in the nucleus, anulus and end-plates were observed, and these trends were statistically significant (p<0.01). Vertebral body osteophytes were most prevalent in the mid thoracic region. Osteophytes and degenerative changes in the nucleus and anulus increased significantly with age (p<0.05). These regional and age-related degenerative trends may influence the interpretation of thoracic spine pathology from MRI investigations.