Facet joint capsule

The facet capsular ligaments encapsulate the bilateral spinal facet joints and are common sources of painful injury due to afferent innervation. These ligaments exhibit architectural complexity, which is suspected to contribute to the experimentally observed lack of co-localization between macroscopic strain and microstructural tissue damage. The heterogeneous and multiscale nature of this ligament, combined with challenges in experimentally measuring its microscale mechanics, hinders the ability to understand sensory mechanisms under normal or injurious loading ¹⁾.

The facet joint capsule is an area of connective tissue that covers the facet joint from top to bottom. The connective tissue creates a sort of bulky seam that holds the two bones forming the facet joint together.

Each vertebra has four facet joints – two on the top (called superior facets) and two on the bottom (called inferior facets), so there are four facet joint capsules for each spinal bone. The fibrous connective tissue of the capsule encases the whole joint, which contains synovial fluid. Synovial fluid is akin to WD-40 for the joint. It lubricates the facet joint and enables movement to occur.

Percutaneous radiofrequency denervation of the lumbar medial branch is often used in chronic low back pain of intervertebral lumbar facet joint etiology, which is sometimes difficult to perform and recurrence of pain often ensues.

Moussa and Khedr et al., theorized that shifting the target of RF coagulation to the facet joint capsule would provide an easier target and a longer-lived pain relieving response.

A prospective randomized controlled trial where 120 patients diagnosed with CLBP of a confirmed facet origin were randomly divided into three equal groups, the first was submitted to percutaneous radiofrequency coagulation of the facet joint capsule, the second underwent percuataneous denervation of the medial dorsal branch and the third did not receive radiofrequency lesioning. All the three groups received local injection of a mixture of local anesthetic and steroid. Cases were followed for up to 3 years.

87(72.5%) patients were females. By 3 months' post procedure, improvement in VAS was significantly better than pretreatment levels in all groups (p<0.05). The control group lost improvement by 1-year follow-up (p=0.017). At 2 years' follow-up, the joint capsule denervation group maintained significant improvement (p=0.033) whereas the medial branch denervation group lost its significant effect (p=0.479). By the end of follow-up period, only joint capsule denervation group kept significant improvement (p=0.026).

In CLBP of facet origin, shifting the target of percutaneous radiofrequency to the facet joint capsule provides an easier technique with an extended period of pain relief compared to the medial dorsal branch of the facet joint ²⁾.