A new study 1 sought to create an etiology-based system of classification by identifying and characterizing typical endplate irregularities and found that tidemark avulsions were a predominant pathology in the cadaveric spine sample images. This represents a previously unidentified observation and, along with the histologic classification system developed in the study, should assist practitioners in organizing their patients into categories that will help to diagnose, research, and treat their spine symptoms.
Researchers used magnetic resonance imaging (MRI) to analyze and categorize 15 donated human cadaveric spines from 11 males and four females between the ages of 49 to 67 years old. Each of the spine samples showed evidence of moderate to severe disc degeneration. Motion segments were excluded if they appeared with imaging to have experienced pre-mortem surgery, deformity, or fracture. No medical history about the donors was obtained.
Spinal segments were extracted using a band saw, and their various features were stained with different colors for observation. Each of the sections were imaged with polarized lights under a microscope, and two raters developed a classification system to identify and record various focal tissue-scale endplate irregularities and their anatomical location.
Researchers noticed a novel histological phenomenon wherein there appeared to be a separation of the annulus from the vertebra at the tidemark (the insertion point of outer annular fibers into the calcified layer of cartilage). They immune-stained the “tidemark avulsions” to search for the 9.5 neuronal marker protein gene using a polymer detection system. Each of the slides was then analyzed to identify the presence or absence of nerves in the bone nearest the endplate irregularity.
Each spine was studied via MRI to identify the presence of absence of tidemark avulsions, and their location was noted. Two orthopedic specialist clinicians were used to assess the findings. These researchers—neither of whom was previously used as a rater— were blinded to the histologic findings.
The endplate irregularities were grouped into three categories based upon their features and location. They were then subcategorized to further classify their pathologies.
The categories and subcategories identified were:
- Avulsions: There was a separation of the tissue at the place where the disc joined the vertebra. Two types of avulsions were observed—tidemark (separation occurring at the tidemark location, where outer annulus fibers join the layer of calcified cartilage, and CEP-bone avulsion—occurring where the bone meets the cartilage endplate (CEP).
- Nodes: Traumatic nodes occurred when there was a herniation of the nuclear materials reaching through the endplate. When abnormal fibrocartilage ingrowth or bony erosions were found, the were classified as Erosive.
- Rim degeneration: This classification was reserved for samples that showed loss of organization in the annular fiber, bone marrow alterations, or degradation of the bone-marrow interface.
Endplate Irregularity Observations
The most common irregularities noted were rim degeneration (50 %) and avulsions (35%). Nodes were less common (15%) and found mostly in the thoracic spine, where the avulsions and rim degenerations were found in the lumbar spine samples. Eighty-seven percent of the noted avulsions were found in the anterior discs.
Though linear regression showed little association between endplate irregularities and age, the largest number of tidemark avulsions (90%) were found in the oldest spine samples. Interestingly, the annular fibers in the tidemark avulsions appeared to change their direction after crossing the tidemark. Of the 35 discs that showed tidemark avulsions, 14 of them contained multiple avulsions. Marrow changes and increased innervation was noted along vertebral bones beside endplate irregularities. An increase of nerve density was observed even in bones adjacent to very small tidemark avulsions.
The ability to identify tidemark avulsions on MRI may help practitioners identify and treat disc-vertebra injuries in a targeted way. High density images in the study showed that fluid can collect around avulsion irregularities, potentially creating gas in the extra-cellular spaces surrounding thee separation. High-intensity regions in MRI may indicate disc delamination or potentially painful lesions. It is possible that tidemark avulsions may create anterior widening and create a scenario wherein the disc may detach from the vertebra. Overall, the findings of this study should contribute to a beneficial system of classification, allowing clinicians to more effectively diagnose and treat their lower back pain patients.
KEYWORDS: endplate irregularities, tidemark avulsions, endplate pathologies, histologic classification system, separation of the annulus from the vertebra at the tidemark, CEP-bone avulsion, traumatic nodes, rim degeneration