Table 3.
Summary of major findings regarding facet joint biomechanics and associated key references
| Tissue Components |
| Facet cartilage is not uniform in thickness [41]. |
| The capsular ligament exhibits anisotropic viscoelastic properties [9,10]. |
| Capsular strains are not uniform and vary with the joint loading scenario [8,107–109,111]. |
| Failure strains of the human cervical capsular ligament are large: |
| 94 ± 85% in shear [109] |
| 104 ± 81% to 148 ± 28% in tension [8,9] |
| Structural damage occurs in the capsule at strains of 51 ± 12% of those required for its failure [120]. |
| Facet Joint Loading |
| The facets carry between 3–25% of the spinal load in axial compression [2,4,5,96,322–324]. |
| The joints of Luschka increase the amount of primary motion while the uncinate processes reduce it [312]. |
| The forces/pressures in the facet joint are non-uniform and vary spatially in different spinal regions and with the loading scenario [11,106,131,132,137– 139,141,162–165,271,331]. |
| Lumbar stresses in the facet capsule are predicted to double when the rate of rotation increases by two orders of magnitude during 5 deg of flexion [334]. |
| Facetectomy decreases the stiffness and increases the mobility of the spinal motion segment in all modes of loading [98–104,313,327,328]. |
| Segmental mobility increases after capsulotomy [105,106,195,206,209]. |
| Disc arthroplasty modifies facet loading at index and adjacent spinal levels [132,134,200,263,269,270,273]. |
| Geometric parameters of a disc implant influence facet joint contact during loading [269,314,330]. |
| Mechanotransduction Processes Identified in Conjunction with Facet Joint Loading |
| Physiologic capsular stretch of the cervical spine is associated with neuroinflammatory processes in the dorsal root ganglion and the spinal cord and afferent modulation in animal models of pain [116,124,155]. |
| Injection of an anesthetic into the facet joint relieves pain symptoms [154]. |
| Facet Joint Injury and Spine Biomechanics |
| Facet joint injury increases spinal mobility and weakens its mechanical properties [193,195,201,207]. |
| Spinal fusion increases segmental rotation at adjacent levels, which can lead to increased loading of the facet joints [211–216]. |
| Subcatastrophic stretching of the facet capsule induces pathophysiological responses in the dorsal root ganglion and the spinal cord in animal models [111,113–119,123,124]. |
| Non-physiologic loading of the cervical spine leads to facet capsule damage that induces laxity [120,194]. |
| Facet Joint Degeneration |
| Intervertebral disc and facet joint degeneration have many independent, common, and/or associated processes [245, 254]. |
| Spinal asymmetry might be associated with a greater risk of spinal degeneration [192,283,285–292]. |
| Osteophytes decrease lumbar segmental motion [294]. |
| Local hypertrophy and extensive fibrocartilage metaplasia of the facet joint tissues result from greater mechanical loading in degenerated lumbar spines [295]. |
| Leakage of cytokines from the degenerated joint into the intraspinal space can initiate pain cascades [298]. |