Reasons for performing study: The equine fetlock joint has the largest number of traumatic and degenerative lesions of all joints of the appendicular skeleton.
Objective: To gain insight into the distribution of cartilage degeneration across the articularsurface in relation to age in order better to understand the dynamic nature and progression of osteoarthritis (OA).
Hypothesis: That there would be a specific age-related distribution pattern of cartilage degeneration in the equine metacarpophalangeal joint.
Methods: The proximal articular cartilage surfaces of the first phalanges (P1) of 73 slaughter horses (age range 0.4–23 years) with different stages of osteoarthritis were scored semiquantitatively on a 0 to 5 scale and also assessed quantitatively using the cartilage degeneration index (CDIP1), which ranges from 0 to 100%. Further more, CDI values were determined for special areas of interest; medial dorsal surface (CDImds), late ral dor sal surface (CDIlds), medial central fovea (CDImcf) and lateral central fovea (CDIlcf). Correlations were calculated for CDIP1 values and CDI values at the specific areas of interest with macroscopic scores and with age.
Results: There was a high correlation between the semiquantitative macroscopic score and the quantitative CDIP1 values (r = 0.92; P<0.001). A macroscopic score of 0 (i.e. no obvious cartilage degeneration) corresponded with a CDIP1 mean ± s.e. value of 2.5 ± 2.8% and a macroscopic score of 5 (i.e. severe cartilage degeneration in localised areas) with a mean ± s.e. value of 38.1 ± 7.9%. There was a moderate but highly significant correlation between the CDIP1 value and the age of the horses (r = 0.41; P<0.001). Highest CDI values were calculated for the medial dorsal surface (from 10.6 ± 2.8% at macroscopic Grade 0 to 63.1 ± 8.4% at Grade 5). At the lateral dorsal surface, these values were 5.9 ± 1.4% and 47.2 ± 10.4%, respectively. The CDImcf and CDIlcf were significantly lower (P<0.05) than the CDImds and CDIlds at all grades. The CDImcf ranged from 1.0 ± 2.9% at Grade 0 to 43.7 ± 9.1% at Grade 5; laterally, these values were 1.5 ± 2.6% and 15.2 ± 6.2%, respectively.
Conclusions: CDI grading increased from lateral to medial and from central to dorsal. This specific distribution pattern confirms the heterogeneous nature of the OA process and strongly supports an important role for biomechanical loading, superimposed on age-related changes, in the spread of the disorder over the joint.
Potential relevance: Knowledge of the development of OA across the articularsurface is essential forunderstanding the dynamic nature and progression of the disease and can form a basis for improvements in diagnostic and therapeutic approaches to degenerative joint disease.