Incidence of Compression-Induced Microinjuries in the Cartilage Endplate of the Spine.

Abstract

In vitro biomechanical study. This study investigated the incidence of microstructural endplate injuries caused by cyclic compression loading. The covarying effects of joint posture, loading duration, and peak compression variation were assessed. The endplate is physiologically and functionally important for the maintenance of spine health. Despite the ability to radiographically diagnose and classify macroscopic endplate injuries, the mechanical mechanisms of injury initiation and progression remain largely unknown. One hundred and fourteen porcine cervical spinal units were examined. All spinal units were exposed to preconditioning tests, followed by cyclic compression testing that differed by posture (flexed, neutral), loading duration (1000, 3000, 5000 cycles), and peak compression variation (10%, 20%, 40%). Microstructural injuries were examined via immunofluorescence staining for collagen I ( i.e. , subchondral bone) and collagen II ( i.e. , hyaline cartilage endplate). From the 678 acquired images, the incidence of node, avulsion, cartilage, and circumferential pore microinjuries were determined. The distribution of microinjuries between postures, spinal levels, and vertebrae were evaluated along with the associations of incidence and size of injuries with loading duration and variation. The incidence of avulsion injuries was significantly greater in caudal endplates (92%, P =0.006). No other injuries differed between vertebrae ( P ≥0.804) and no significant differences were observed between spinal units ( P ≥0.158). With respect to posture, 100% ( P <0.001) and 90% ( P <0.001) of avulsion and node injuries, respectively, occurred in flexed postures, whereas 82% ( P <0.001) of cartilage microinjuries occurred with neutral postures. Loading duration was significantly associated with microinjury incidence ( P <0.001) and lesion size ( P ≤0.003). Mechanical factors such as posture did not appreciably affect the incidence of endplate injury, but microinjury types were differently distributed between flexed and neutral postures. The duration of compression was shown to have an important role in the incidence of microinjury and lesion size.