Radiographic assessment of the equine carpal joint under incremental loads and during flexion

Abstract

Non-physiologic loading of the carpal bones is believed to result in osteochondral fractures, ligament rupture and axial instability in the equine forelimb; however, the mechanism of carpal damage due to non-physiologic loading of the carpus is largely unknown. To investigate carpal stability (alignment and direction of carpal bones’ movement) under load and during flexion, some previously described carpal parameters were measured on radiographs obtained from 24 equine cadaver limbs (aged 10.71±4.15 years). The limbs were transected at the antebrachial midshaft, axially loaded in a commercial press and serially radiographed under a range of incremental loads (extension) and 2 flexion positions. The extensions were measured by a 10° decrease in the dorsal fetlock angle (DFA) from 160° to 110° (DFA160 to DFA110) using the jacking system of the press; and flexions at palmar carpal angle of 45° and 90° (PCA45 and PCA90). As loading increased from DFA160 to DFA110 there was a progressive significant increase in Third Carpal bone Palmar Facet Angle (C3PalFCA: 86.46±2.54° to 88.60±2.51°) but a decrease in Dorsal Carpal Angle (DCA: 173.03±3.47° to 159.65±4.09°); Medial Carpal Angle (MCA: 186.31±1.90° to 184.61±2.26°); and Groove width of the Cr-Ci intercarpal ligament (GW.Cr-Ci ICL: 9.35±1.20° to 8.83±1.13°) while no significant differences were observed for Distal Radial Slope Carpal Angle (DRSCA) and Intermediate carpal bone Proximal Tuberosity-Radial Angle (CiPxTRA). A generalised medio-distal directional displacement in the carpal bones’ movement were observed. In conclusion, increased load on the forelimb (carpus) produced carpal hyperextension with measurable radiographic changes in the position and alignment of the carpal bones. The non-stretching (strain) or shortening of the Cr-Ci ICL during loading, indicated by the decrease in GW.Cr-Ci ICL, suggests a relaxed intercarpal ligament within a confined space which appears to absorb compressional load transferred from carpal bones and redistribution of concussion forces within the carpal joint during loading thereby providing a useful mechanism to minimise carpal damage.

Morphometric analysis of the intercarpal ligaments of the equine proximal carpal bones during simulated flexion and extension of cadaver limbs

“…(e) At full flexion, the Cr‐Ci ICL was completely stretched while the gliding motion of Cr against Ci was at maximum (green arrow) as indicated by the sliding height difference of Cr and Ci (Cr‐Ci SHD). Cr‐Ci SHD was a parameter developed to measure the height difference between Cr and Ci during locomotion (Olusa, 2018; Olusa et al., 2019) and was observable on both radiographs and gross dissection. The thick white arrow shows the extent of transverse movement of the distodorsal wedge of Ci which was in ‘close‐packed position’ with C3 and C4 during weight bearing.…”

“…The length of Cr‐Ci ICL could not be measured directly because it was inaccessible to a caliper. It was however measured indirectly as previously described (Olusa, 2018; Olusa, Murray, & Davies, 2019), by using radiography to assess the groove width/diameter of the Cr‐Ci intercarpal ligament (GD.Cr‐Ci ICL). Intercarpal ligaments between Ci and Cu (Ci‐Cu ICL): This was measured using a similar procedure/protocol used to measure the thickness (depth) and widths of Cr‐Ci ICL.…”

“…The length of Cr-Ci ICL could not be measured directly because it was inaccessible to a caliper. It was however measured indirectly as previously described (Olusa, 2018;Olusa, Murray, & Davies, 2019), by using radiography to assess the groove width/ diameter of the Cr-Ci intercarpal ligament (GD.Cr-Ci ICL).…”

“…mid distance from the dorsal to the palmar end) of the Cr-Ci groove on the Ci and the palmar width was measured at its palmar region (dashed white arrows) . Cr-Ci SHD was a parameter developed to measure the height difference between Cr and Ci during locomotion (Olusa, 2018;Olusa et al, 2019) and was observable on both radiographs and gross dissection. The thick white arrow shows the extent of transverse movement of the distodorsal wedge of Ci which was in 'close-packed position' with C3 and C4 during weight bearing.…”

“…This is because a 2-row carpal joint without this central gliding joint would be less effective, unable to withstand the strain of compressional loading and prevent force redistribution within the carpus for two reasons. The mechanism of carpal damage would not be unrelated to uneven carpal loading and carpal hyperextension during repetitive high-speed exercise (Bramlage et al, 1988;Burn, Portus, & Brockington, 2006;Olusa et al, 2019;Palmer et al, 1994). During loading, axial compression of the dorsal articular surface of the carpus would occur as the proximal row of carpal bones slides into position across relatively congruent articular surfaces of the Cr and C3 (Bramlage et al, 1988;Olusa et al, 2019).…”