Magnetic resonance imaging morphology of lumbar paraspinal muscles following successful bilateral facet joint denervation

Purpose:
Low back pain (LBP) is the second most common presentation in general practice, with 60-80% of people experiencing it in some form in their lifetime1,2.

The aetiology of one type of LBP is from pathology of the facet joints (facetogenic LBP), whose synovial capsules are innervated by the medial branch of the dorsal rami of nerves exiting the spinal canal at the same level as the joint and one level above1.

If conservative management fails, these nerves can be targeted with analgesic injection or medial branch block. If the joint is the cause of the pain then it should respond, although the effect is temporary.

More long-lasting analgesia is offered through radio-frequency facet joint denervation (RFJD), or rhizolysis, a surgical procedure where the medial branch is irreversibly cut. The medial branch however, also supplies parts of the paraspinal musculature including multifidus (MM), an important stabiliser of the lumbar spine neutral zone2. Denervation atrophy may theoretically occur following this procedure, where skeletal muscle fibres are replaced with fat leading to reduced function and therefore increased instability. MM atrophy has previously been shown to be strongly related to low back pain4,5,6. It is theoretically possible that by treating facetogenic LBP with this method that pain may arise later due to a different cause.

There are currently no prospective human studies which assess the morphological changes of the paraspinal musculature on MRI after RFJD or the variables affecting the magnitude of this change and this was the purpose of our research.