Knee Joint Breakdowns - New Research Findings
New research has found that knee joint injuries are associated with internal collapse ("implosion") of the major knee joint (carpal) bones due to concussion and excessive loading in racing and equestrian horses. Whilst there is a link between heavy build and poor conformation, 3-4 year old horses in training are more prone to deterioration of the internal bone structure of their knees.
Studies by researchers in New Zealand and the United Kingdom confirm that knee joint breakdown is initiated by internal sheer stresses at the interface between the softer cartilage covering the bone and the denser underlying calcified bone, reinforced by bony columns within the bone architecture. Similar changes have been found in the joints of human runners.
Knee Joint Breakdown - How does it Happen?
Dr Radin, an orthopaedic researcher working in Michigan in the U.S.A., has found that, as the underlying layer of bone hardens and becomes more dense, a greater number of fatigue or stress 'cracks' develop in the soft overlying joint cartilage layer. Once full thickness cartilage damage occurs, there is separation at the underlying bone and cartilage junction. When loaded during exercise, the softer cartilage sheers from the underlying bone as it distorts, leading to the start of arthritis and joint breakdown. The joint swells, becomes puffy and if work is continued, degenerative changes to the joint cartilage begin a cycle of destruction and eventual arthritis.
Taking the Stress off the Knees
There is good reason to modify the conventional training process as horses reach 3-4 years of age to minimise the risk and incidence of knee joint arthritis. Adopt a similar early training program as for shin soreness, refer to page 2.
- Avoid over galloping a 3-4 year old horse once it becomes fit. Restrict all-out galloping to once every 10-14 days, but give short sprints over 300-400 meters to keep it fit and maintain maximum stamina and aerobic capacity.
- When turning a horse out for short spell, give it 10-14 days rest to freshen up, rather than a longer rest of 2-4 weeks, as in this time period, the unloaded joints are more likely to start to revert back to their lower pre-training bone density with softer, weaker cartilage.
- Ensure adequate intake of bone vitamins and minerals as for shin soreness.
Facts and Stats
- The loading forces imposed on the knee joints of a galloping thoroughbred have been measured to be in the order of 500psi, or 20,000 newtons per square centimetre
- The risk of repetitive toe-down impact, which results in higher load, increases as horses tire towards the end of a hard gallop or race as neuro-muscular co-ordination starts to fatigue
- A galloping horse's leading foreleg hits the ground 42 times per minute at the all-out gallop, causing repetitive compressive loading to the bones of the knee joint.
- The front limb provides a pivot for the high loading forces at the gallop, with the knee joint undergoing maximum internal compression as the limb reaches the vertical position during the stride.
- 80% of injuries occur in the front limbs of racing thoroughbreds, with 80% of these within the knee and structures of the lower limb