Kim was 19 years old, athletic, physically fit, and had never suffered from a neck injury or an episode of prior neck pain; her past history was completely unremarkable.
While showering earlier that morning, she turned to reach for a bar of soap. She immediately experienced a sharp zap of left–sided neck pain. The pain was sharp and intense, 8/10 on a visual analogue scale, and persistent. To function at any level, she had to tilt her head to the right; any straightening of her neck caused immediate intense worsening of her pain.
Assuming she had somehow pinched a neck nerve, Kim’s mother made an appointment to see a local chiropractor.
Other than an inability to left laterally flex her neck because of severe pain, all examination and radiographic findings were unremarkable.
All mechanical joints require lubrication in order for them to glide and function efficiently, and to protect the joint from wear/tear and damage. This includes both inanimate joints (such as joints in automobiles and hinges on doors), and all of the joints in the human body.
Inanimate joints are lubricated with oil or grease. Human joints are lubricated with synovial fluid. The synovial fluid is held around the joint by dense ligamentous type of fibers called the joint capsule. The joint (articular) capsule is firmly attached to the adjacent bones to insure the synovial fluid does not seep away.
The oil or lubricant used in inanimate joints needs to be replaced (refreshed) or “topped off” as its supplies are depleted with use. We are all familiar with the occasional oil change that our automobiles require.
Human joint synovial fluid is replaced and enhanced as a consequence of proper joint motion. The joint synovial fluid is made from the blood that supplies the fibrous joint (articular) capsule. The inner wall of the joint (articular) capsule has a special group of cells called the synovial membrane. With motion, the synovial membrane produces the synovial fluid that lubricates the joint.
Although this is not the primary intent of this article, it is important to understand that when a joint does not move regularly through a complete range of motion, the quality of the synovial fluid is reduced, contributing to joint pathology, arthritis, and symptomology. This is one of the mechanisms by which chiropractic adjusting of joints (specific manipulation) helps people; the improved joint motion enhances synovial fluid production and as such enhances joint function, resulting in improved function and reduction of symptoms.
Importantly, parts of the synovial membrane actually project deeper into the joint cavity and lie between the articulation surfaces of the joints. This deeper inner component of the synovial membrane is classically called the meniscus. With certain quick or unexpected motions, the meniscus can become entrapped between the joint surfaces, an experience that is extremely painful.
Perhaps the most authoritative book written pertaining to the spine is Schmorl’s and Junghanns’ The Human Spine in Health and Disease. Georg Schmorl (1861-1932) was a German physician and pathologist. Herbert Junghanns (1902-1986) was the Chief of the Occupational Accident Hospital, Surgical Clinic, and Head of the Institute for Spinal Column Research, in Frankfurt, Germany. The fifth edition of their book was translated into English in 1971 (1). This book contains 500 figures of radiographs, histological sections, photographs, and drawings. The book has more than 500 pages and approximately 5,000 references in the bibliography.
In their book, Drs. Schmorl and Junghanns note:
“Like other body articulations, the apophyseal joints are endowed with articular capsules, reinforcing ligaments and menisci-like internal articular discs.” p. 251
“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.” pp. 221-222
If a joint is suddenly incarcerated within the range of its physiologic mobility, 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 (stretching, 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.” p. 376
Accompanying this quote and other pertinent discussions are 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.” p. 222
In September 1975, the Department of Physical Medicine and Rehabilitation of the California College of Medicine organized an international conference concerning Approaches to the Validation of Manipulation Therapy. The conference was held at the University of California, Irvine. Twenty-one global top experts on spinal manipulation participated in the conference. The proceedings from the conference were published in 1977 (2). Chapter 14 of the conference proceedings was authored by physician James Fisk from New Zealand, and is titled (3):
An Evaluation of Manipulation in the Treatment of the
Acute Low Back Pain Syndrome in General Practice
In this chapter, Dr. Fisk, in the section regarding possible lesions that cause low back pain, lists:
“Entrapment of a Meniscoid”
This chapter states:
“These meniscoids are richly innervated by pain producing nerve endings. There should be a rapid response to manipulation.”
In 1977, the National Institute of Neurological and Communicative Disorders and Stroke of the National Institutes of Health (USA), funded a grant for a Research Workshop on Neurobiologic Mechanisms in Manipulative Therapy. The workshop was held at Michigan State University, and had 38 worldwide participant experts. The Proceedings for the workshop were published the following year, in 1978 (4). The first chapter of the workshop proceedings is authored by Dr. Karel Lewit from Czechoslovakia, and is titled (5):
The Contribution of Clinical Observation to
Neurobiological Mechanisms in Manipulative Therapy
In this chapter, Dr. Lewit notes:
“The meniscoid has a soft base and a hard edge.”
“If the meniscoid is caught between the gliding surfaces of the joint facets the hard edge produces a cavity in the cartilage in which it is trapped.”
“The implications for the theory of manipulation are obvious: if we separate the joint facets the meniscoid can slip out.”
Dr. Lewit includes a similar discussion in his 1985 text titled Manipulative Therapy in Rehabilitation of the Locomotor System (6).
Also in 1985, 30 distinguished international multidisciplinary experts collaborated on a text titled Aspects of Manipulative Therapy (7). The comments in this text pertaining to the interarticular meniscus 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.” pp. 90-91
In 1986, physical therapist Gregory Grieve authored a text titled Modern Manual Therapy of the Vertebral Column (8). 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 1988, Rene Cailliet, MD, published the fourth edition of his book Low Back Pain Syndrome (9). At the time, Dr. Cailliet was the retired Chairman of the Department of Physical Medicine and Rehabilitation at the medical school at the University of Southern California. Dr. Cailliet states:
“A meniscus exists within facet joints that becomes entrapped.”
Dr. Cailliet also includes an explanation of the benefits of spinal manipulation to treat the meniscal entrapment.
In the second edition of his reference text, Common Vertebral Joint Problems, Gregory Grieve includes a section on the meniscoid block. While discussing Sudden Backache or Acute Lumbago, Greive’s text states (10):
“The small ‘meniscoid’ structures in the facet-joints are apparently susceptible to temporary impaction at times, with the chronic sequelae of the joint tissue damage probably adding to the natural process of senescence.” p. 201
“The patient with sudden backache due to presumed locking of a facet-joint is usually a young female but may be a young man, and there is often a degree of hypermobility. They often excel at athletics or ballet dancing, and during some activity which may be reaching up to open a window or adjust curtains, a lumbar synovial joint locks. No outside force is applied, the condition being consequent upon a body movement involving reaching or stretching. It is reasonable to suppose that the opposed joint faces of the hypermobile segment come apart more easily than usual, and the normally slight negative pressure within the joint cavity is further lowered by the greater distraction. A villus of synovial tissue is presumably ‘sucked in and nipped,’ and thus the meniscoid structure is impacted between joint surfaces. On resumption of normal posture the pain of impaction induces reactive muscle spasm, fixing the articulation rigidly to produce a locked joint.” p. 407
In her 1994 text Physical Therapy of the Cervical and Thoracic Spine, professor of physiotherapy from the University of South Australia, Ruth Grant writes (11):
“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.” p. 298
In his 2004 text titled The Illustrated Guide to Functional Anatomy of the Musculoskeletal System, Rene Cailliet, MD also comments on the anatomy of the interarticular meniscus, stating (12):
“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.” p. 95
Presumably it is this innervation that produces the pain associated with meniscoid entrapments.
Nikolai Bogduk, PhD, MD, is a most distinguished and respected physician, anatomist, and researcher. In the fourth edition of his textbook Clinical Anatomy of the Lumbar Spine and Sacrum (13), Dr. 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 the joint cavity.” p. 35
“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.” p. 195
The January 15, 2007 publication of the top ranked orthopaedic journal Spine contains an article titled (14):
High-Field Magnetic Resonance Imaging of Meniscoids in the Zygapophyseal Joints of the Human Cervical Spine
The authors note that meniscoids of the cervical facet joints contain nociceptors and may be a source of cervical facet joint pain; neck pain can be caused by pathological conditions of the meniscoids within the zygapophysial joints. They state:
“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.”