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The Infamous ’SI’ Joint

10 Nov 2018

By Sue Van Evra, BSc.PT, MSc, BHScPT, Dipl. Canine Rehab

 The SI joints (or Sacroiliac Joints) are very important joints, but unfortunately are often overlooked as a source of your dog’s hind end pain and dysfunction.  These joints are part of the pelvis and play an important part in connecting the spine and the hind limbs. 


At the tail end of the vertebral column is a small bone called the sacrum. The sacrum lies between the lumbar spine and the tail. On either side of the the sacrum are two bones (one on each side) called the ilium. The joints between the sacrum and the ilium on each side are the sacroiliac joints.  On each side, the ilium is fused together with two other bones – the ischium and pubis. These fused bones along with the sacrum make up the pelvis. 

This is a view from the ‘top’ of the pelvis (as if you are standing behind a dog and looking down from above) – this picuture shows the end of the spine, the sacrum, the ilium, ischum and pubis fused together on each side, as well as the first few segments of the tail (in humans this is where the tailbone sits) :

Sacroiliac Joint

You can see when you look at the canine skeleton from the side the pelvis connects the spine to the hind limbs. The hip joints are ‘ball and socket’ joints – the top of the femur (thigh bone) makes the ball and the socket of the hip is actually part of the pelvis: 


Pelvis  Pelvis2


The sacroiliac joints themselves are partly synovial joints (meaning there is joint lubricating and nourishing fluid within the joint) and partly fibrocartilaginous (meaning there are areas of the joint that are made up of strong thick cartilage). The sacroiliac joints are held together and supported by extremely strong thick ligaments – some of the strongest ligaments in the entire body!)

There are a many muscles that affect the movement of the sacroiliac joints. The muscles that have the most influence are: 

(1) the Iliopsoas (hip flexor) – this muscle attaches to the femur as well as the underside of the pelvis and spine,



 (2) the Piriformis - this muscle crosses the dorsal (‘back’) side of the sacroiliac joint,



and (3) Hamstrings – these muscles attach to each side of the back of the pelvis.



When a dog is weight bearing through a hind limb there is weight on the hock (ankle), stifle (knee), hip AND sacroiliac joints. 

The bones on each side of the pelvis are fused together on each side, but are not fused from right to left. This means that each side of the pelvis moves independently. When a dog is walking or running and swinging its legs, the two sides of the pelvis ‘swivel’ on the sacrum. Each of the ilium bones rotates a small amount and the movement happens at the sacroiliac joints. 

All of this is important because when a dog is moving, the sacroiliac joints help to distribute force between the hind limbs and the spine.


Sacroiliac Joint Dysfunction:

Sacroiliac Dysfunction is a term that we use to describe pain in or around the region of a sacroiliac joint (SIJ). Sometimes SIJ dysfunction can be the primary problem for a dog, and sometimes other injuries (cruciate ligament sprain or tear, back strain, Achilles tendon injury, etc.) can result in SIJ dysfunction. 

Causes of SIJ Dysfunction:

  1. If a dog has no other injuries, the most probable cause of SIJ dysfunction occurs when the dog is running and makes a sharp turn/change in direction – as mentioned above, the ilium bones ‘swivel’ around the sacrum when the dog is running, and sometimes a quick turn will cause the ilium to swivel and to stay in a rotated position – this can lead to pain and inflammation in the joint when the dog continues to walk and weight bear through the SI joint. This sounds like something that would look very obvious, but it only takes a few degrees of rotation ‘off’ of the normal position to cause a problem and often there are only subtle signs of dysfunction (see ‘Signs of Dysfunction’ below). 
  2. If a dog has an injury such as a hind limb cruciate sprain or tear in the stifle/knee and they are limping and not weight bearing equally through the hind limbs – this changes the way that the muscles work around the hip and pelvis. Some muscles overwork and others don’t work enough. This ‘imbalance’ in the hind limb and pelvis musculature can cause one side of the pelvis to rotate into an abnormal position. This can also happen when a dog has back pain – from a strain, or arthritis or surgery – remember that the iliopsoas muscle attaches to the spine, pelvis and femur. If there is pain in the spine, the iliopsoas muscle can react and tighten causing one side of the pelvis to rotate into an abnormal position.
  3. Trauma can also be a cause of SIJ dysfunction – a fall onto one side of the pelvis or an accident.


Signs of SIJ Dysfunction:

SIJ dysfunction can be more obvious (i.e. non weight bearing on the dysfunctional side) or can be (and is usually!) more subtle:

  • Not sitting ‘squarely’ – i.e. sitting with one leg out to the side
  • Decreased weight bearing on one hind limb – this can be subtle (i.e. always shifting the bodyweight to the other hind limb when standing)
  • Always choosing to lie on the same side
  • Always wanting to turn one direction, but not the other
  • Swinging hips more to one side when walking

Management of SIJ Dysfunction:

SIJ dysfunction is often overlooked and missed (especially when it is subtle!) but is very treatable! The assessment involves having a canine rehab therapist look at and feel both sides of the pelvis to determine if there is an asymmetry of the pelvis, and if so which side of the pelvis is the ‘abnormal’ side and which direction it is rotated abnormally. The canine rehab therapist would then do a thorough check of the spine and both hind limbs to screen for any other injuries, and to check each muscle, ligament and tendon attaching to the pelvis.

Once it is determined that there is an SIJ dysfunction, the treatment would include: (1) manual therapy – i.e. gentle movements of the pelvis to restore the normal position (which always feels like a big relief to the dog!), (2) modalities such as Laser or PEMF (pulsed electromagnetic field) to help reduce any inflammation or discomfort, (3) therapeutic exercises (including a home program) to re-educate the muscles surrounding the pelvis so that they can maintain the normal position, and (4) education for the dog owner re ways to minimize the risk of dysfunction.

**If you suspect that your dog may have SIJ dysfunction, it is best to get an assessment sooner rather than later – if left untreated, the dog can develop secondary problems from moving asymmetrically/compensating such as shoulder tendonitis or back strain***

Please call the Canine Fitness Centre 204-0823 for more info!



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