Anatomy in Action Series: Understanding the Anatomy of Joints
Laurie Mueller
BA, DC, CFMP
Joints are Our Business
Doctors of chiropractic (DCs) are primary care professionals who specialize in neuromusculoskeletal issues and are trained to safely and effectively adjust the joints of the spine and extremities to provide optimum function. For chiropractic assistants, it is beneficial to understand the anatomy and physiology of different types of joints and how they function in the body.
What Is a Joint?
A joint is a juncture between bones that provides a mechanism of movement. It is also called an "articulation." The joint itself can encompass many tissues. The arrangement of bones, muscles, tendons, ligaments, and capsules with synovial fluid provides range of motion and enables the body to move. The three main types of joints in the body are:
• Fixed Joints have very little motion. They may also be called "sutures'" and are thin, fibrous bands of tissue that connect bone plates. An example of a fixed joint is the bones of the skull that accommodate a growing brain and then fuse and have minimal motion. Some DCs are trained to work on the cranial bones. Addressing the cranial sutures can offer very powerful results for patients with specific issues indicating cranial work, such as after a car accident or healing from other injuries to the head.
• Cartilaginous Joints contain tough cartilage to stabilize and cushion the area while still allowing some movement, much like a shock absorber. Examples include the intervertebral discs of the spine and the junction (symphysis pubis) between the bones of the pelvis at the front of the body. In the chiropractic office, working with patients who have different stages of disc herniation is common. DCs also adjust the pelvis, but typically the sacroiliac joints at the back of the body require attention, not the pubic symphysis.
• Synovial Joints are the most moveable. They have a joint capsule connecting the bones that is lined with a membrane that produces synovial fluid, a liquid that nourishes and lubricates the area and allows for smooth mobility. Examples are thejoints of the extremities and facet joints of the spine that are commonly adjusted in the chiropractic office. When a "popping" noise is heard during an adjustment or from popping your knuckles (formally called "cavitation"), the exchange of gases under pressure in the facet joint capsule actually makes that noise — not the result of bones cracking or rubbing together.
Synovial Joint Details
Synovial joints are utilized for a variety of movements and have their own categories. Some are limited to the motions of bending and straightening within a single plane, such as our fingers and toes. Other joints are more complex and function in multiple planes, offering a variety of bending and twisting motions, such as in our wrists, shoulders, and hips. Because different motions require different configurations for synovial joints, we find the following synovial joint classifications:
• Gliding: Found between the sternum and ribs, ribs and spine, and clavicle with scapula. Two bones meet at a flat or slightly curved surface to allow surfaces to shift positions. They are held together by ligaments.
• Hinge: Found at the elbows, knees, fingers, and toes, these joints have a protrusion on one bone that fits into an indentation in another bone, like a puzzle piece. These joints work in a single plane to allow bending and straightening.
• Pivot: Found in the elbow and the first two cervical vertebrae in the neck. These joints have a head on one bone that fits into a band of connective tissue on another, which allows the head to turn from side to side or for you to turn your hand from palm down to palm up while keeping the upper arm in place.
• Ball-and-socket: These are the most complex joints found in the hips and shoulders. These joints have the maximum mobility but are also more prone to injury. The joints are formed by the head of a long bone (humerus or femur) that fits into the socket, or cup portion, of another bone (scapula or pelvis). They allow motion in multiple planes and are surrounded extensively by other connective tissues, such as muscles, tendons, and ligaments.
The joints most adjusted in the chiropractic office are the facet joints of the spine. Facet joints are also called Z-joints, or zygapophysial joints. On the top of the vertebra, two facets face upward, articulating with the vertebra above, and two face downward that connect to the vertebrae below.
The direction that the joints are oriented and move varies with the shapes of the vertebral bones in the region of the spine involved. The shape dictates which motions are best carried out in the region. For example, in the upper cervicals, the bones have special shapes that are more conducive to rotational movements. Other cervical facets are oriented so that flexion extension, lateral flexion, and some rotation can all take place. In the thoracic region, the articulating surfaces are in the frontal plane to offer more lateral flexion. In the lumbar spine, the facet joints favor the sagittal plane to offer flexion and extension. At the last vertebrae (L5), the shape changes to articulate with the sacrum in a frontal plane to protect the spine from sliding forward on the sacrum.
Ask your DC to show you their model spine to visualize how the facet joints change with spinal regions. These changes dictate the angles that the doctor will use to adjust specific spinal regions on a patient.
Laurie Mueller, BA, DC, CFMP, served in private practice in San Diego, California. She was the postgraduate director at Palmer College from 2000 to 2010; served as the ACC postgraduate subcommittee chairfor six years; peer-reviewed for the Research Agenda Conference; and wrote the informal role determination study that aided in the development of FCLB's guidelines for chiropractic assistants (CCCAs). Dr. Mueller currently works as a private eLearning consultant with a focus on healthcare topics and functional medicine through her company, Impact Writing Solutions LLC, and subsidiaries CCCAonline.com and fxmedonline. com. She is a clinician, educator, and expert in online learning pedagogy.
