Abstract
Introduction: When the spine is subjected to compressive loading in-vivo and ex-vivo, there appears to be a predisposition for the cranial endplates to fracture before the caudal. We hypothesise that this fracture pattern arises from an underlying structural asymmetry. Endplate damage is common in elderly people, and closely related to disc degeneration and pain.
Methods: 47 human thoracolumbar motion segments aged 62–90 yrs were compressed to failure while positioned in moderate flexion. Damage was assessed from radiographs and at dissection. Two 2mm-thick slices were obtained from each vertebral body in the sagittal plane. Microradiographs were analysed to yield the following: thickness and image greyscale density (IGD) of the cranial and caudal cortex at 10 locations (94 vertebrae), and IGD of the cancellous bone in three regions adjacent to each endplate (34 vertebrae).
Results: Endplate damage occurred cranially in 39/47 vertebrae, and caudally in 4/47. Mean thickness of cranial and caudal endplates was 0.77mm (SD 0.27) and 0.90mm (SD 0.29) respectively (p=0.01). Thinnest regions were located centrally on cranial endplates. Endplate thickness increased at lower spinal levels for caudal (p< 0.01) but not cranial endplates. IGD was similar in cranial and caudal endplates, but IGD of trabecular bone adjacent to the endplate was 3–8% lower cranially than caudally (P< 0.01).
Discussion: In elderly spines, cranial endplates fracture more readily because they are thinner and supported by less dense trabecular bone. Endplate thickness may be minimised by the need to allow nutritional access to adjacent discs, and the vulnerability of cranial endplates may be associated with asymmetries in blood supply, or proximity to the pedicles.
Correspondence should be addressed to: Mr John O’ Dowd, SBPR, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
