Quantifying Baseline Fixed Charge Density in Healthy Human Cartilage Endplate: A Two-point Electrical Conductivity Method

Overview

Journal Spine (Phila Pa 1976)

Specialty Orthopedics

Date 2017 Jul 13

PMID 28699925

Citations 11

Authors

Yongren Wu

Sarah E Cisewski

Yi Sun

Brooke J Damon

Barton L Sachs

Vincent D Pellegrini Jr

Elizabeth H Slate

Hai Yao

Affiliations

Soon will be listed here.

Abstract

Study Design: Regional measurements of fixed charge densities (FCDs) of healthy human cartilage endplate (CEP) using a two-point electrical conductivity approach.

Objective: The aim of this study was to determine the FCDs at four different regions (central, lateral, anterior, and posterior) of human CEP, and correlate the FCDs with tissue biochemical composition.

Summary Of Background Data: The CEP, a thin layer of hyaline cartilage on the cranial and caudal surfaces of the intervertebral disc, plays an irreplaceable role in maintaining the unique physiological mechano-electrochemical environment inside the disc. FCD, arising from the carboxyl and sulfate groups of the glycosaminoglycans (GAG) in the extracellular matrix of the disc, is a key regulator of the disc ionic and osmotic environment through physicochemical and electrokinetic effects. Although FCDs in the annulus fibrosus (AF) and nucleus pulposus (NP) have been reported, quantitative baseline FCD in healthy human CEP has not been reported.

Methods: CEP specimens were regionally isolated from human lumbar spines. FCD and ion diffusivity were concurrently investigated using a two-point electrical conductivity method. Biochemical assays were used to quantify regional GAG and water content.

Results: FCD in healthy human CEP was region-dependent, with FCD lowest in the lateral region (P = 0.044). Cross-region FCD was 30% to 60% smaller than FCD in NP, but similar to the AF and articular cartilage (AC). CEP FCD (average: 0.12 ± 0.03 mEq/g wet tissue) was correlated with GAG content (average: 31.24 ± 5.06 μg/mg wet tissue) (P = 0.005). In addition, the cross-region ion diffusivity in healthy CEP (2.97 ± 1.00 × 10 cm/s) was much smaller than the AF and NP.

Conclusion: Healthy human CEP acts as a biomechanical interface, distributing loads between the bony vertebral body and soft disc tissues and as a gateway impeding rapid solute diffusion through the disc.

Level Of Evidence: N/A.

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