The sacroiliac (SI) joint is a critical joint, where the pelvis meets the spine, transferring the action of the hindlimbs to the back aiding forward motion. The SI joint is designed to aid stability and shock absorption. However, in some cases horses can experience pain or dysfunction in these joints.
SI dysfunction is common in horses however, they are generally difficult to diagnose due to subtle signs often mistaken for other physical or behavioural concerns. SI dysfunction can be caused by a fall or accident in which the joint becomes damaged in some way. Other horses may develop SI problems due to wear and tear of the joint. Under stress the SI joint can be injured in a multitude of ways including ligament damage, stress fractures, and joint inflammation and pain.
Anatomy of the Sacroiliac
The sacroiliac is a region of the horse where the back (sacrum) meets the pelvis (ilium), hence sacro-iliac. Two sacroiliac joints connect these bony structures and they sit on either side of the spine. The joint surfaces are almost flat and rely on three major sets of ligaments for support (interosseous sacroiliac ligaments, ventral sacroiliac ligaments, dorsal sacroiliac
ligaments). The muscles surrounding the SI joint also play a vital role in its function.
Injuries to the SI joints tend to fall into two main categories:
Primary Sacroiliac Damage
Acute SI damage is usually due to a serious traumatic injury. Pain may be caused by a fracture or sprain or injury to the ligament. Noticeable lameness may be present and localised sensitivity of the soft tissues. These injuries will often require immediate veterinary treatment to support the healing process and reduce pain.
Chronic Sacroiliac Disease
SI disease can include a range of conditions that are possibly affecting the SI joint. This may mean that either the joint itself, or the ligaments surrounding the joint, or both are affected.
SI pain may also be developed secondary to lameness in the hindlimb.
Clinical Signs
SI problems are challenging to spot, and as the joint is well covered by muscles and fat it is difficult to see or feel. Some clinical signs of an issue with the SI region may include:
Poor performance
Resistant behaviour
Asymmetrical hindlimb muscle
Reduced hindlimb propulsion and engagement
Bucking
Poor quality canter
Disunited canter/bunny hops
Toe dragging
Pelvic asymmetry
Prominent tuber sacrale
Poor lateral work
Surrounding muscle dysfunction
Change in hindlimb placement (close/wide)
Worsening of clinical signs when ridden
The 'Hunter's Bump'
What is commonly known as the 'Hunter's Bump' is a hump that develops on the croup of the horse, when the tuber sacrales are more prominent than usual. In some cases they can be caused by displacement, dislocation, or ligament injury to the SI joint. It can affect one or both sides depending on the type of injury. In some cases, an injury that has gone untreated will result in a chronic Hunters Bump. However, in some cases the Hunters Bump is not a sign of SI dysfunction and it may have occurred naturally due to conformation or pelvic asymmetry which causes the tuber sacrale to protrude upwards even if there is nothing physiologically wrong with them. Muscular atrophy or dysfunction to the gluteals may also result in a hunters bump appearance. Lastly, a postural shift due to potential compensations may also cause the ileum to shift upwards resulting in a hunters bump appearance. If you are ever concerned about a conformation change in your horse it is always best practice to have them seen by a vet so that dysfunction and pain can be ruled out first.
Diagnosis
Clinical veterinary examination
Veterinary imaging (ultrasound, nuclear scintigraphy)
Diagnostic anaesthesia
Exclusion of other causes of lameness
Treatment
Treatment will vary and it depends greatly on the injury or type of dysfunction.
Medication can be used and anti-inflammatories can be deposited to the muscles surrounding the joints. This is usually done under standing sedation and local anaesthesia using a large needle with an ultrasound machine to ensure correct placement.
Rest will be required when a primary SI injury has occurred, and in some cases healing can be slow, especially if a ligament has been damaged.
Within treatment, there should also be focus on restoring the muscular support which can include building muscles such as the Multifidus and Gluteals.
Comments