No detectable remodelling in adult human menisci: an analysis based on the C14 bomb pulse

Abstract

Objectives: Bone and other human tissues remodel through life, for example, as a response to increasing load, and this prevents permanent destruction of the tissue. Non-traumatic meniscal rupture is a common musculoskeletal disease, but it is unknown if it is caused by inability of the menisci to remodel. The aim of this study was to determine whether meniscal collagen is remodelling throughout life.

Methods: The life-long turnover of the human meniscal collagens was explored by the ¹⁴C bomb pulse method. ¹⁴C levels were determined in menisci from 18 patients with osteoarthritis and 7 patients with healthy knees.

Results: There was a negligible turnover of the meniscal collagen in adults. This low turnover was observed in menisci from patients with knee osteoarthritis and in healthy menisci.

Conclusion: This study provides evidence that essentially no remodelling occurs in the adult human meniscal collagen structure and explains the clinical degeneration that is often seen in menisci of middle-aged and elderly persons. It suggests that strengthening of the collagen structure of menisci, as response to physical activity, may occur during childhood, while it is not possible in the adult population.

Keywords: collagen; meniscus; metabolism.

Figure 1

¹⁴C content in menisci: ¹⁴C content in collagen purified from menisci in relation to birth year of donors. Solid black line shows the ¹⁴C level in per cent modern carbon (pMC) in the atmosphere based on Kueppers et al up to 2001 and Levin et al from 2002. The dotted line shows the 13-year moving average of the atmospheric ¹⁴C level, with each point representing the average atmospheric ¹⁴C level of the next 13 years. The horizontal dashed line represents the ¹⁴C level in the atmosphere at time of tissue sampling. (A) ¹⁴C levels in regional areas of menisci. (B) Median ¹⁴C content of four meniscal regions from the same donors of OA and healthy menisci. Vertically aligned symbols represent data from the same individual (except for the data points in 1946 (two donors), 1953 (three donors) and 1958 (two donors). OA, osteoarthritis.

Figure 2

Water, GAG and collagen content (shown as mean and SEM): (A) water content (%) (mean of inner and outer part) of medial (Med) and lateral (Lat) healthy and OA menisci; (B) GAG content in outer part of raw menisci; (C) GAG content in purified outer meniscal tissue; (D) GAG content in purified inner meniscal tissue; (E) collagen content in outer part of raw menisci; (F) collagen content (mean of inner and outer part) in purified meniscal tissue. *Significant differences between OA and healthy menisci (p<0.05); significant difference (p<0.05) between medial (Med) and lateral (Lat) menisci is indicated on the graphs. Error bars indicate SEM. GAG, glycosaminoglycan; OA, osteoarthritis.