When you study the location and role of the navicular bone, and the physical forces impacting the foot, particularly the loading of the distal interphalangeal joint as well as the biomechanical function and motion of the navicular bone, it is reasonable to hypothesize that excessive forces could cause trauma to the soft tissue in the palmar region of the equine foot. In turn, the ongoing trauma would cause an inflammatory process in the soft tissue structures of the distal limb, altering the equine foot's physical motion and functionality, especially its palmar loading. These forces of imbalance in the orthopaedic stance of the affected animal reduce the foot’s vascular perfusion (blood flow into the foot) in the short term, and longer-term, to the development of secondary features such as necrotic tissue in the hoof capsule, dysfunctional internal bars, digital cushions and supporting soft tissue structures of the equine foot, all of which will be followed by clinical changes in the animal’s attitude and locomotion.
The palmar section of the equine foot can be placed under extreme pressure during the swing phase of the stride. You should also understand that even in the stance phase, when the foot is in contact with the ground, the palmar section plays an integral part in the dissipation of energy. It should be easy to see why the animal presents with clinical symptoms in the palmar section of the foot when there is an imbalance in its upper body or in the foot itself.
Trying to understand clinical symptoms of palmar foot pain sent me on a quest for answers to the alterations in the physical motion and functionality of the palmar section of the equine foot and its relationship with the musculo-skeletal and neurological systems. This required carrying out a multitude of hoof resections and many years of clinical research on the complaint known as a navicular syndrome before they could comprehend the complexities of equine palmar foot pain and navicular syndrome.
My research revealed some consistencies of pathological and structural changes in a large percentage of these resections of horses that fulfilled the criteria of navicular syndrome or palmar foot pain, that being, pain in the palmar section of the foot and changes in the digital cushion shape, size, and location, structural changes in the internal bars, improper timing of break-over of the distal limb, and other dysfunctional soft tissue architecture affecting the distal Sesamoidean impar ligament, collateral Sesamoidean ligament and the deep digital flexor tendon, without conclusive evidence of the common diagnosis parameters of navicular disease.
On closer examination, my autopsies of these cases reveal that the deep digital flexor tendon presented with pathological changes due to the continuing stress; they were first inflammatory processes and secondly due to the diminishing vascular perfusion. The pathology changes are evident in the texture and color of the deep digital flexor tendon at its distal insertion to the distal phalanx, a yellowing of the body of the tendon as it passes over the flexion surface of the navicular bone, and signs of fibrous breakdown in the body of the deep digital flexor tendon itself.
Hoof dissection of horses with unresolved, long-term palmar foot pain revealed that the miss containment or the incorrect position of the distal Sesamoidean bone correlates with an imbalance of the distal interphalangeal joint caused by either hoof imbalance, or upper body misalignment, and compensation patterns. The dissections showed the distal Sesamoidean bone was situated more proximal on the palmar aspect of the middle phalanx than is structurally acceptable, thus changing both, its articulation within the distal interphalangeal joint, and its fulcrum effect on the deep digital flexor tendon, inducing bruising and texture changes to the centre of the tendon as it articulates over the misaligned central crest of the distal Sesamoidean bone, as well as vascular changes on the internal tendon sheath further up the affected limb. These structural changes to the distal Sesamoidean bone also altered the middle phalanx's articulation with the distal phalanx, and the effects of imbalanced loading were evident in the crest of the middle phalanx, and the articulation surface of the distal phalanx according to which side of the limb was dealing with the loading imbalance.
In our next blog we look at having a distal Sesamoidean bone that is situated more proximal on the palmar aspect of the middle phalanx.