By Dr. Alison Gault

Pelvic instability at the sacroiliac joint is a condition that occurs only to a small percentage of women during pregnancy and tends to worsen as the pregnancy progresses. The sacroiliac joints or SIJs are the joints between the sacrum or triangular bone at the base the spine and the two Innominate bones.  These joints are located at the dimples on your low back. Sacroiliac joint instability is a type of pelvic instability and occurs when the ligaments that support the Sacroiliac joints are loose and not performing their normal function.  This results in sharp pain in the joints and surrounding muscle tightness.  This is a condition that can become quite severe and is in the group of conditions called pelvic girdle pain in pregnancy or PGPP.

Primary symptoms of sacroiliac joint instability

Pain is located primarily at either or both of the dimples on your low back at the sacroiliac joint. This pain is generally achy but may grab sharply with certain movements. You may feel as if your pelvis is going to fall apart or give way.   Your pelvic joints may clunk or crack occasionally when moving. The location of the primary pain is the same as with sacroiliac joint dysfunction however the intensity of pain and effect on function is much greater with instability.

The symptoms most commonly begin around the 18th week of pregnancy.  The severity of the symptoms tends to increase as the pregnancy progresses.  Only very rarely, is a woman severely affected throughout the entire pregnancy.

Secondary symptoms of sacroiliac joint instability

  • You may be experiencing some aching in your gluteal or hip muscles lateral to the dimples and deep within the buttock.
  • You may feel the pain radiating down the inner or front of the thigh and at the pubic symphysis or groin area.  This can just be an ache or quite sharp.
  • The symptoms are similar to sacroiliac joint dysfunction but are more severe and debilitating.   The other joint effected by pelvic instability is the pubic symphysis with a condition called diastasis symphysis pubis.  With this condition, most of the pain in located in the anterior pelvis at the pubic symphysis joint.

Aggravating factors

  • You may find most types of physical activity challenging and may only be able to do something for a very short period before the pain starts.
  •  Common activities that tend to trouble women with pregnancy related sacroiliac joint instability are:
  • Walking going from sitting to standing standing still  lifting house work turning over in bed getting out of bed  standing on one foot such as getting dressed
  • You may briefly feel better lying but can be woken up each time you turn over with the pain.  Some women find they can get a couple of pain free hours of sleep initially but after that lying down itself is also very painful.

What causes sacroiliac joint instability?

Sacroiliac instability occurs when the ligaments that support the joint are looser or more lax than they should be.  The pelvic muscles compensate for the lack of ligamentous support within the joint by contracting and tightening.  These muscles achieve an increase in the stability of the joint but eventually, they begin to become hypertonic (excess tightness) and fatigue.  This muscular contraction and fatigue itself is painful but also results in an increase in the inflammation within the SIJ as the stability decreases.  Over the long term, this muscle contraction can then lead to muscular weakness and further aggravation of the condition.

Very rarely and in the most extreme cases, the muscles don’t function properly from early in the pregnancy and the woman experiences a high level of disability and pain.

The nature of the bony pelvis ring, is that all joints are connected and cannot function independently of each other. Therefore, dysfunction occurring at one joint effects all joints.   This is why pubic symphysis instability and pain often occurs in conjunction with the SIJ symptoms.  For the purposes of simplification, when most of the pain is at the groin, we are calling that pubic symphysis instability or diastasis symphysis pubis.

Softening and stretching of ligaments is a normal and necessary part of pregnancy to enable the pelvis to widen enough to birth the baby.  This occurs because of the actions of the hormones relaxin, oestrogen and progesterone.  Interestingly, studies have shown no correspondence between levels of relaxin in the blood stream and an increased incidence of instability.  Therefore, a high relaxin level is not a predictor for instability.  This study showed an increased incidence of instability in women with prior history of low back problems indicating that relaxin effects different pelvis’s in different ways.

 For more information on treatment and prevention of sacroiliac joint instability in pregnancy please follow the link.