The sacrum is a large, triangular bone at the end of the spine that sits in between the two hip bones. It consists of three fused vertebrae in dogs, and is the last part of the spine before becoming the tail. The ilium is the uppermost part of the pelvis, and the “wings” of the ilium are what are commonly referred to as the hip bones. The joint in between the sacrum and the ilium is called the sacroiliac joint, and is the connection of the spine to the pelvis. The bones of the joint are held together with strong ligaments. Compared to joints such as the hip or knee, the sacroiliac joint is rigid and has very little range of motion. A sacroiliac luxation, or dislocation, is when the joint is torn loose and shifts out of place. (show normal rads and label anatomy)
Sacroiliac luxation can occur in any dog, regardless of age, breed, or gender.
Dogs with a luxation of the sacroiliac joint are usually non-weight-bearing on the affected limb. Animals with severe displacement of the ilium may show signs of extreme pain when moving. If both sides of the pelvis are affected, the animal may be unable to walk at all. It is also important to note that a sacroiliac luxation can result in neurological deficits. This is because the sciatic and femoral nerves lie close to the joint. Both nerves are important in normal function of the hind limbs, and damage to the SI joint can cause concurrent nerve damage. If there is injury to the nerve, the animal may have no or decreased sensation in the toes of the affected limb.
When the patient is sedated, the veterinarian can manipulate the joint and gauge movement of the ilium if the joint has been disrupted. Radiographs are important in assessing the degree of damage to the pelvis and identifying any fractures that may be present. The veterinarian will also evaluate nerve function in the area, as well as making sure that no organ damage was sustained in the accident.
A sacroiliac luxation is the result of a blow to the hind end that results in dislocation of the sacroiliac joint. Such trauma can disrupt the joint on one side, or may affect both the right and left. The most common type of injury that causes a sacroiliac luxation is being struck by a vehicle, or sustaining a fall. In some cases just the sacroiliac joint is affected. However, it is not uncommon to see luxation of the joint in combination with one or more fractures to the pelvis and/or sacrum.
In some cases, conservative treatment is acceptable if the sacroiliac joint is minimally displaced and the patient is in minimal discomfort. Conservative therapy includes a period of strict rest and NSAIDs to control pain and inflammation. Physical therapy should also be performed to prevent joint and muscle contracture and atrophy. Surgery is usually recommended for all patients, because those that undergo conservative treatment are painful for much longer that those that undergo surgery. There are two techniques that are used to surgically repair the joint. Traditional surgery involves making a sizeable incision along the side of the pelvis and exposing the joint. Screws are used to secure the joint in place. The minimally invasive method involves putting the joint back into place from the outside, making a small incision along the side of the pelvis and placing screws to secure the joint using fluoroscopy or digital radiography.
Sacroiliac luxation is usually the result of acute trauma to the hind end; therefore there are no real preventative measures.
The majority of dogs that are treated with conservative management regain normal function. However, lameness can last up to 12 weeks, and if the joint doesn’t heal in correct alignment, it can result in narrowing of the pelvis. In these cases, surgery is required to widen the pelvic outlet, or constipation or difficulty birthing can occur. Patients that undergo surgical repair of the joint usually heal well, but it may take about 2 months for full recovery. However, patients that have sciatic nerve injury frequently regain normal or near normal function. In some instances, the nerve does not heal, and the patient won’t have use of the limb.