Manual Therapy April 2011; Vol. 16; No. 2; pp. 118-124 Alexandra L. Webb, Patricia Collins, Hamid Rassoulian, Barry S. Mitchell FROM ABSTRACT The synovial folds of the cervical spine are regarded as a potential source of neckpain and headache, especially following whiplash injury.Damage to the synovial folds following motor vehicle trauma has been welldocumented in post-mortem studies.However, methods of identifying injury to the synovial folds in the survivors ofmotor vehicle trauma have proven elusive to date. Recently, it has beenmade possible to image the synovial folds in vivo using magnetic resonanceimaging. This now makes it feasible to investigate the potential involvement ofsynovial folds in the generation of neck pain and headache and its relief using spinal manipulation. This paper reviews critically the morphology of the synovial folds of the cervicalspine that underpins the hypotheses proposed to explain their functional and clinicalsignificance and a new system of naming and classifying the synovial folds ispresented. These findings have implications for understanding the anatomical basis of neckpain and headache and the rationale for the use of spinal manipulation in theirmanagement. KEY POINTS FROM THIS ARTICLE: 1) Intra-articular synovial folds are formed by folds of synovial membrane(synovium) that project into the joint cavity and are found in synovial articulationsthroughout the vertebral column. 2) The earliest description of synovial folds in the vertebral column occurred in1855. 3) The published literature uses a number of names to identify these synovialfolds, including: * Synovial fold is the most accurate name to apply to these structures. * Meniscus / Menisci * Meniscoid * Intra-articular inclusions * Intra-articular discs 4) Cervical synovial folds extend 1 – 5 mm between the articular surfaces. 5) Synovial folds have been identified in all synovial articulations of the cervicalspine. 6) Synovial folds are most commonly found in adult lateral atlanto-axial andcervical zygapophysial joints. 7) Synovial folds contain an abundant vascular network. 8) With repeated mechanical impingement between the articular surfaces, thesynovial fold may differentiate into fibrous tissue to varying degrees. Collagen-producing,activated fibroblasts have been observed within synovial folds.Consequently, the process of fibrous change may involve inflammation and repair. 9) The presence of nerve fibers and endings has been demonstrated in synovialfolds. These nerve fibers have been identified both alongside and independent ofblood vessels in the cervical synovial folds. The function of these nerves may benociceptive, proprioceptive and/or vasomotor. There are a number of studiessupporting the nociceptive function in particular for these joint structures. 10) The synovial folds are believed to adapt themselves intimately to the contourof the joint space in all positions of the joint and act as passive space-fillers thatfill peripheral non-congruent parts of the joint in its neutral position but displacewhen the joint moves. 11) The synovial folds may protect and/or lubricate the articular surfaces,enhance joint congruity and stability, assist weight-bearing or dissipate stress. 12) The synovial folds may have a mechanosensory role. The synovial fold tissuesare fibro-fatty in composition, and innervated adipose tissue is thought to beimportant in giving proprioceptive feedback for sensorimotor control which would beespecially important in the upper cervical spine which has direct neurophysiologicalconnections via cervical proprioceptors to the vestibular and visual systems. 13) Disturbances in balance and vision have been reported to accompany uppercervical pain and dysfunction and are areas of increasing interest particularly inrelation to whiplash. 14) The entrapment hypotheses, is usually proposed to explain the clinicalpresentations of the synovial fold syndrome. 15) Intra-articular adhesions and synovial fold impingement following whiplashmay cause deformation and/or inflammation within the synovial folds, irritating thesensory nerves. Consequently, spinal manipulation and mobilization may effectivelytreat the associated spinal pain and disability. [Important] 16) An abnormal joint movement may cause a synovial fold to move from itsnormal position at the articular margins to become imprisoned between thearticular cartilage surfaces causing pain and articular hypomobility accompanied byreflex muscle spasm. 17) Synovial fold entrapment has been used to explain the pathophysiology oftorticollis and the relief of pain and disability following spinal manipulation. Thetraction forces generated during manipulation would cause rupture of a trappedfibro-adipose synovial fold from the fibrous capsule causing intra-articularhaemarthrosis and loose body formation. 18) In habitually immobilised or under-used joints, the synovial folds may act asa nidus for fibrous tissue proliferation resulting in the formation of adhesions thatreduce joint motion. [Reduced motion resulting in fibrosis] 19) The majority of evidence regarding the possible role of synovial folds in thegeneration of neck pain relates to their potential to become injured during whiplashassociated with motor vehicle trauma. 20) Contusions, rupture and displacement of the synovial folds have beenreported at autopsy following fatal motor vehicle trauma in addition to jointhaemarthrosis caused by synovial fold disruption. Such injuries are not visible atpost-mortem using conventional X-ray, CT or MRI. 21) Discolouration of the dorsal synovial folds has been observed months afterthe initial injury in post-mortem studies of motor vehicle trauma survivors who diedlater from other causes. Therefore injury to the synovial folds following whiplashmay be a potential source of both acute and chronic neck pain. COMMENTS FROM DAN MURPHY: My orthopedic training (from the late, great Richard Stonebrink, DC) advises thatthe best adjustment approach for the synovial fold entrapment syndrome is toadjust on the low side of the rainbow, i.e. to make the antalgic lean worse. Thisapproach is most likely to gap the contralateral facet joint, freeing the entrappedsynovial fold. The result is immediate improvement of antalgic lean and improvement in the range of motion. Dr. Stonebrink referred to the synovial foldentrapment syndrome as a meniscoid block.