Mineralisation or ossification of the interosseous ligament of the centrodistal joint of the horse: is there an association with osteoarthritis?

Reasons for performing study:

There have been no detailed descriptions of the radiological appearance of the centrodistal joint interosseous ligament in horses with and without distal hock joint pain.

Objectives:

1) To describe the normal radiological appearance of the region of the centrodistal joint interosseous ligament; 2) to determine the frequency of occurrence of mineralisation or ossification of the interosseous ligament and to describe radiological abnormalities surrounding the interosseous space; 3) to describe concurrent radiological abnormalities in the tarsus. It was hypothesised that ossification of the interosseous ligament will be associated with radiological evidence of osteoarthritis of the centrodistal joint.

Study design:

Systematic radiological analysis using a predefined grading system, after a repeatability study, and descriptive statistics.

Methods:

Case records and radiographs of all horses which underwent radiographic examination of one or both tarsi over 7 years were reviewed.

Results:

There were 700 horses, including 470 examined bilaterally. The normal interosseous space was an oval-shaped radiolucent area surrounded by subchondral bone of uniform opacity and thickness. Changes in the region of the interosseous ligament of the centrodistal joint were evident in 190/1170 (16.2%) tarsi, including 50 horses examined bilaterally. In 33/190 (17.4%) tarsi there was complete loss of the ovalshaped radiolucent area, together with increased thickness of the adjacent subchondral bone, endosteal irregularity and increased opacity of the adjacent trabecular bone. In addition 157/190 tarsi had patchy increased opacity within the interosseous space and alterations of the adjacent subchondral and trabecular bone. There was radiological evidence of osteoarthritis of the centrodistal joint in 27/33 (81.8%) of tarsi with complete ossification of the centrodistal interosseous ligament, 17 of which (51.5%) had distal tarsal pain, and in 29/157 (18.5%) tarsi with other abnormalities of the centrodistal interosseous ligament.

Conclusions:

When evaluating the tarsus radiologically the region of the centrodistal joint interosseous ligament should be assessed.