Influence of Increased Intraarticular Pressure on the Angular Displacement of the Isolated Equine Distal Interphalangeal Joint

The equine distal interphalangeal joint (DIPJ) is commonly affected by palpable joint distension and degenerative joint disease, with microinstability considered a contributory factor. The aim of this kinematic study was to investigate DIPJ angles during axial compression loading (ACL) in a material testing machine with and without increased intraarticular pressure (IAP) due to joint distension. Our hypothesis was that increased IAP would lead to an increased speed of angular displacement of the DIPJ during ACL and that this would become more apparent with the hoof placed on an uneven surface. Bone markers were placed on the second and third phalanx of six left and right isolated forelimbs from adult Warmblood horses. Limbs were placed in a material testing machine, and synchronous measurements of the kinematics and the pressures within the DIPJ during loading were obtained. With the hoof in neutral position, as well as with 3° lateral and 3° medial elevation, the proximal articular surface of the second phalanx was preloaded with 100 Newton (N), and angles and IAPs were measured during loading to 6,000 N at 600 N/s, with and without joint distension. Joint distension in combination with lateral/medial hoof elevation increased flexion, lateromotion/mediomotion, and axial rotation. The finding that moderate joint distension increases the effect of a relatively mild mediolateral foot imbalance on speed of joint movement during loading has the potential for clinical relevance in the development of osteoarthritis.