top of page

Another Cause of Neck Pain: The Acute Locked Neck Synovial Fold Entrapment Syndrome

Kim was only nineteen years of age, yet she had already experienced three significant motor vehicle collisions, and in each she suffered injuries. Her injuries were always painful, but never debilitating; there were no fractures, dislocations, radiculopathies, myelopathies, or instabilities. After each collision she was medically evaluated, but there were no radiographs or other types of imaging. Her diagnosis for each was “soft tissue injury” or a “sprain-strain” type of injury. Her treatment was rest, soft collar, heat-pack and pain analgesics. After each injury, she seemed to slowly improve following this management advice.

About six months after her last injury, Kim was symptomatically much improved but not yet resolved; then she suffered something new and excruciating. While showering, she turned her head to the left to grab the shampoo which initiated a sharp, lightning-bolt sensation in the left side of her neck. After the initial shot of pain, her neck became very stiff and appeared to go into some sort of spasm. There was a lot of pain in her neck and her neck movements were greatly reduced.

That night Kim’s neck was still very painful and she could not move her neck. In bed she was unable to get comfortable which disturbed her sleep. The next day she was still unimproved, and she once again decided to go to her doctor.

Kim’s doctor observed a significant right antalgic lean of her cervical spine with significant spasms of her cervical muscles. However, deep tendon reflexes, upper extremity myotomal strength, and upper extremity superficial sensation with pinwheel and light touch were all normal. Once again, no imaging was performed. None-the-less, Kim’s doctor diagnosed her condition as a “pinched nerve” causing muscle spasms. He prescribed muscle relaxers, analgesics, and a white-colored soft cervical collar.

For the next six weeks, Kim dutifully took her medicines and wore her cervical collar. Yet, she did not appear to be improving. Her neck remained very painful, stiff, and bent at a funny angle. She was finding it nearly impossible to attend her college classes and complete the required assignments. Her sleep was also so poor that she was suffering from sleep deprivation fatigue. Now desperate, Kim decided to see a chiropractor.

Kim’s chiropractor’s was young, having graduated from school only the year before. His examination also found no problems with strength, sensation, or deep tendon reflexes in the upper or lower extremities. The chiropractor exposed radiographs, and the chief finding was a significant right antalgic lean, consistent with her postural presentation. Happily, the x-rays showed no fractures, degenerative disease, ligamentous instabilities, or any other type of acquired or developmental pathology.

The chiropractor recommended a treatment of an adjustment “to straighten out the antalgic lean.” Because Kim’s cervical spine was leaning to the right (a right antalgic lean), the adjustment was designed to contact the cervical spine on the left side at the C4 vertebra level (as C4 was the apex of the antalgic lean) while simultaneously contacting the head on the right side; a force was then delivered to the left side of the neck while bringing the head back from right to left; a left sided cervical spine adjustment. It made sense. It seemed logical. Somehow the spine had become stuck, and the adjustment on the left side would straighten it out.

Kim screamed, loudly, several times. The volume scared the young chiropractor and several of his other patients who were in the office. Kim cried a little because the adjustment hurt very much. It would have been worth it if it would had fixed her problem. But it did not. In fact she felt worse; there was more pain, more spasm, and her neck appeared to be more bent to the right. Her chiropractor did not know what to say or do.

The next day, Kim’s predicament was unchanged. A week later she was still unchanged, and now desperate. School and work were all but impossible. Both medical and chiropractic had failed to help her. She did not know where to next turn. Her next advice came unsolicited.

Fatigue and pain had taken its toll on Kim’s appearance; she looked awful for her mere nineteen years of age. A middle-aged woman at the cosmetics counter of a mall anchor store, while assisting Kim with products, inquired about her obvious neck condition (Kim was still wearing her cervical collar). Her recommendation was for Kim to see her chiropractor. In the conversation, Kim shared how her prior chiropractic experience did not help her and actually seemed to make her worse. The woman behind the cosmetic counter assured Kim that her chiropractor was different, smart, experienced, and the best. There was something about the cosmetic counter woman’s voice, mannerisms, and convictions. Desperate, Kim decided to consult the second chiropractor……….


The most recent comprehensive review of the Synovial Fold Entrapment Syndrome is written by Alexandra Webb and colleagues and will be published in the April 2011 issue of the journal Manual Therapy (Epub at this time, 2/15/11) (1).

In this article, Dr. Webb and colleagues note that intra-articular synovial folds are formed by folds of synovial membrane that project into the joint cavity. Cervical spine synovial folds extend 1–5 mm between the articular surfaces. Synovial folds are found in synovial articulations throughout the vertebral column. Synovial folds in the vertebral column were first documented in 1855.

Dr. Webb and colleagues note that the published literature uses a number of names to identify these synovial folds, including:

Anatomically, synovial folds contain an abundant vascular network and sensory nerve fibers (1).

The entrapment hypothesis is usually proposed to explain the clinical presentations of the synovial fold syndrome. “An abnormal joint movement may cause a synovial fold to move from its normal position at the articular margins to become imprisoned between the articular cartilage surfaces causing pain and articular hypomobility accompanied by reflex muscle spasm (1).”

“Synovial fold entrapment has been used to explain the pathophysiology of torticollis and the relief of pain and disability following spinal manipulation.” The traction forces generated during manipulation would cause release of a trapped fibro-adipose synovial fold from between the articular surfaces (1).

Additionally, contusions, rupture and displacement of the synovial folds have been reported at autopsy following fatal motor vehicle trauma; these injuries are not visible at post-mortem using conventional X-ray, CT or MRI (1).

With repeated mechanical impingement between the articular surfaces, the synovial fold may differentiate into fibrous tissue to varying degrees. The fibrous apex of the synovial indents the articular hyaline cartilage, further entrapping the apex of the synovial fold. Manipulative therapy may traction and separate the articular surfaces apart, releasing the entrapped synovial fold. (Drawing below based on #1).

Historically, the entrapped synovial fold syndrome has been written about for decades. In the 1971 translation of their authoritative reference text The Human Spine in Health and Disease, Drs. Schmorl and Junghanns note (2):

“Like other body articulations, the apophyseal joints are endowed with articular capsules, reinforcing ligaments and menisci-like internal articular discs.”

“Like any other joint, the motor segment may become locked. This is usually associated with pain.” Chiropractors refer to such events as subluxations. These motor unit disturbances can cause torticollis and lumbago.

“Various processes may cause such ‘vertebral locking.’ It may happen during normal movement. The incarceration of an articular villus or of a meniscus in an apophyseal joint may produce locking.”

If a joint is suddenly incarcerated within the range of its physiologic mobility, as occurs with the meniscus incarceration of the knee joint, it is an “articular locking or a fixed articular block.”

“Such articular locking is also possible in the spinal articulations (apophyseal joints, intervertebral discs, skull articulations, lumbosacral articulations). They may be mobilized again by specific therapeutic methods (stretchings, repositioning, exercises, etc.). Despite many opinions to the contrary, this type of locking is today increasingly recognized by physicians. Many physicians are employing manipulations which during the past decades were the tools of lay therapists only (chiropractors, osteopaths). However, these methods have at times been recommended by physicians. They have also been known in folk medicine and in medical schools of antiquity.”

Schmorl and Junghanns’ text includes two photographs of anatomical sections through the facet joints showing these “menisci-like internal articular discs,” or meniscus. They also included three radiographs and one drawing showing abnormal gapping of an articulation as a consequence of meniscus entrapment in a facetal articulation. They note that such a meniscoid incarceration can cause acute torticollis, and they show a “follow-up roentgenogram after manual repositioning” resulting in “immediate relief of complaints and complete mobility.”

In 1985, 30 distinguished international multidisciplinary experts collaborated on a text titled Aspects of Manipulative Therapy (3). The comments in this text pertaining to the interarticular meniscus (synovial entrapment syndrome) include:

“Histologically, meniscoids are synovial tissue.”

“Their innervation is derived from that of the capsule.”

The current hypothetical model of the mechanism involved in acute joint locking is based on a phenomenon in which the “meniscoid embeds itself, thereby impeding mobility.”

“It is highly probable that the meniscoids do play an important role in acute joint locking, and this is confirmed by the observation that all the joints afflicted by this condition are equipped with such structures.”

In 1986, physical therapist Gregory Grieve authored a text titled Modern Manual Therapy of the Vertebral Column (4). This text boasts 61 international multidisciplinary contributors, contains 85 topic chapters, and is 898 pages in length. In the chapter titled “Acute Locking of the Cervical Spine” the text notes that a cause of acute cervical joint locking includes:

“Postulated mechanical derangements of the apophyseal joint include nipped or trapped synovial fringes, villi or meniscoids.”

In her 1994 text Physical Therapy of the Cervical and Thoracic Spine, professor of physiotherapy from the University of South Australia, Ruth Grant writes (5):

“Acute locking can occur at any intervertebral level, but is most frequent at C2-C3. Classically, locking follows an unguarded movement of the neck, with instant pain over the articular pillar and an antalgic posture of lateral flexion to the opposite side and slight flexion, which the patient is unable to correct. Locking is more frequent in children and young adults. In many, the joint pain settles within 24 hours without requiring treatment (because the joint was merely sprained or because it unlocked spontaneously), but other patients will require a localized manipulation to unlock the joint.”

In his 2004 text titled The Illustrated Guide to Functional Anatomy of the Musculoskeletal System (6), renowned physician and author Rene Cailliet, MD comments on the anatomy of the interarticular meniscus, stating:

“The uneven surfaces between the zygapophyseal processes are filled by an infolding of the joint capsule, which is filled with connective tissue and fat called meniscoids. These meniscoids are highly vascular and well innervated.”

In the fourth edition of his textbook Clinical Anatomy of the Lumbar Spine and Sacrum (7), physician, anatomist, and researcher Dr. Nikolai Bogduk writes:

“The largest of the meniscoid structures are the fibro-adipose meniscoids. These project from the inner surface of the superior and inferior capsules. They consist of a leaf-like fold of synovium which encloses fat, collagen and some blood vessels.”

“Fibro-adipose meniscoids are long and project up to 5 mm into he joint cavity.”

“A relatively common clinical syndrome is ‘acute locked back.’ In this condition, the patient, having bent forward, is unable to straighten because of severe focal pain on attempted extension.”

“Maintaining flexion is comfortable for the patient because that movement disengages the meniscoid. Treatment by manipulation becomes logical.”

The January 15, 2007 publication of the top ranked orthopaedic journal Spine contains an article titled (8):

High-Field Magnetic Resonance Imaging of Meniscoids

in the Zygapophyseal Joints of the Human Cervical Spine

Key Points From this article include:

1) Pain originating from the cervical spine is a frequent condition.

2) Neck pain can be caused by pathologic conditions of meniscoids within the zygapophysial joints.

3) “Cervical zygapophysial joints are well documented as a possible source of neck pain, and it has been hypothesized that pathologic conditions related to so called meniscoids within the zygapophysial joints may lead to pain.”

4) The meniscoids of the cervical facet joints contain nociceptors and may be a source of cervical facet joint pain.