Cartilage calcification of the ankle joint is associated with osteoarthritis in the general population

Abstract

Background: Cartilage calcification (CC) is associated with osteoarthritis (OA) in weight-bearing joints, such as the hip and the knee. However, little is known about the impact of CC and degeneration on other weight-bearing joints, especially as it relates to the occurrence of OA in the ankles. The goal of this study is to analyse the prevalence of ankle joint cartilage calcification (AJ CC) and to determine its correlation with factors such as histological OA grade, age and BMI in the general population.

Methods: CC of the distal tibia and talus in 160 ankle joints obtained from 80 donors (mean age 62.4 years, 34 females, 46 males) was qualitatively and quantitatively analysed using high-resolution digital contact radiography (DCR). Correlations with factors, such as the joint's histological OA grade (OARSI score), donor's age and BMI, were investigated.

Results: The prevalence of AJ CC was 51.3% (95% CI [0.40, 0.63]), independent of gender (p = 0.18) and/or the joint's side (p = 0.82). CC of the distal tibia was detected in 35.0% (28/80) (95% CI [0.25, 0.47]) and talar CC in 47.5% (38/80) (95% CI [0.36, 0.59]) of all cases. Significant correlations were noted between the mean amount of tibial and talar CC (r = 0.59, p = 0.002), as well as between the mean amount of CC observed in one ankle joint with that of the contralateral side (r = 0.52, p = 0.02). Furthermore, although the amount of AJ CC observed in the distal tibia and talus correlated with the histological OA-grade of the joint (r = 0.70, p < 0.001 and r = 0.72, p < 0.001, respectively), no such correlation was seen in the general population with relation to age (p = 0.32 and p = 0.49) or BMI (p = 0.51 and p = 0.87).

Conclusion: The prevalence of AJ CC in the general population is much higher than expected. The relationship between the amount of AJ CC and OA, independent of the donors' age and BMI, indicates that CC may play a causative role in the development of OA in ankles.

Keywords: Ankle joint; Calcium crystals; Cartilage; Cartilage calcification; Chondrocalcinosis; Osteoarthritis.

Fig. 1

Examplary samples of the ankle joint showing standardized, 4 mm cartilage-bone specimens (cut along the coronal plane) of the distal tibia and talus, as well as the corresponding digital contact radiographs. Calcification was detectable as radiopaque spots in the cartilage’s matrix

Fig. 2

Representative DCR-images (original size and 3× magnification as shown in red boxes) of the cartilage-bone specimens taken from the distal tibia and talus of three donors with different OA grades (i.e. OARSI = 0, OARSI < 3 and OARSI ≥3). The corresponding histological images of the distal tibial and talar cartilage are presented. Safranin-O staining was used to evaluate the histological OA grade of the hyaline cartilage. Calcification was histochemically confirmed using von Kossa staining

Fig. 3

a, b. Logarithmic scatter plots (with blue orthogonal regression lines) showing significant correlations between the mean amount of CC in (a) the right and left ankle joints and (b) between the talar and distal tibial cartilage. Data points have been adjusted to avoid over-plotting. c The mean amount of calcification in the distal tibial and talar cartilage is depicted as an Effect Plot (logarithmic)

Fig. 4

Logarithmic scatter plots (with blue orthogonal regression lines) showing correlations between the mean amount of CC and the histological degeneration grade (OARSI) of the distal tibial (a) of the talar cartilage (b) between the mean amount of CC and age for the distal tibia and (c) for the talus (d). Data points have been adjusted to avoid over-plotting