Facet Joint Capsulitis

The spine is a complex and delicate structure with many moving parts. A variety of things can go wrong in any one of the pieces, as well as at any level of the column, whether in the cervical, thoracic, lumbar, or sacral areas. Examples of oft-experienced conditions affecting spinal structures include disc herniation, muscle strain, ligament sprain, and spinal arthritis. And the list goes on.

One less commonly experienced problem that also belongs on this list is facet joint capsulitis. In this condition, the connective tissue capsule that surrounds the facet joint, which is located at the back of the column, becomes inflamed. Let's unpack this a bit.

First, the term facet joint. 

A doctor holds a model of the spine and points to a structure.
Mary Kate Denny/The Image Bank/Getty Images

What Is a Facet Joint?

A facet joint is an interconnection between two square-shaped projections of bone that are located on the back of the spinal column. At every level (with the exception being the very first vertebra) at the back of the spinal column, two pairs of facets, which are the bony projections, emanate on the right and left sides.

There's a pair of facets at the top part of each vertebra and a pair at the bottom. A facet joint is made when a projection from a bone below fits with one (on the same side) from the bone immediately above it. Generally, there are four facet joints per spinal level, two on the right, and two on the left.

The purpose of facet joints is to both guide and to limit excessive movements, thereby keeping the spine stable and helping to prevent injury.

Facet joints are also known as zygapophyseal joints.

As with many joints in the body, facet joints are surrounded by a connective tissue capsule. The capsule plays an important role in the joint's movement functions.

Capsulitis is a term that refers to inflammation of any anatomical capsule, facet or otherwise. Perhaps the most well-known form of capsulitis is adhesive capsulitis or frozen shoulder.

Facet Capsule and the Synovium

In the facet joint, the capsule is known as a "pain generator," which means it is one of several structures making up the facet joint that may be responsible for back pain and/or dysfunction.

As mentioned above, the facet capsule is made of fibrous connective tissue that surrounds the whole joint. Inside the capsule and joint is a lining that secretes synovial fluid. The synovial lining and fluid are collectively called the synovium.

The job of synovial fluid is to lubricate the surfaces of the joints so that movement can occur smoothly and painlessly. You might think of synovial fluid as the joint's WD-40. 

Just as the facet joint capsule can become inflamed, so can the synovium.

The Role of the Capsule in Facet Joint Arthritis

According to a 2014 article published in the journal Nature Reviews Rheumatology, the capsule is one of several structures whose "failure" can cause facet arthritis. This is true even though facet joint arthritis is mainly understood as a bone and cartilage condition.  

How does your doctor or physical therapist know when your facet joint capsule is inflamed? One way is by evaluating the "capsular pattern." An inflamed facet joint tends to stretch the fibers of the capsule, which causes pain as well as movement limitation. Specifically, the motions of side bending, rotation and extension become overstretched in this situation.

Other areas affected by facet arthritis include ligaments, synovium, muscles, and disc. The authors say that the disc tends to degenerate along with the facet joint, which means these two adjacent structures are each implicated in degenerative disc disease.

A March 2018 article published by StatPearls Publishing reported that facet joints were involved in up to 42 percent of neck pain and up to 44 percent in back pain.

Inflammatory Capsulitis

Capsulitis is often found at the sacroiliac joints of people who have an inflammatory arthritic disease such as spondylitis. In these cases, capsulitis is considered to be an active inflammatory lesion. For people with spondylitis, an MRI using one of several specialized techniques is generally necessary to find evidence of capsulitis as well as other active inflammatory lesions. 

Other types of active inflammation include osteitis, enthesitis, and synovitis. All, including capsulitis, are early signs of sacroiliitis or spondylitis. The difference between them lies in the location of the inflammation. For example, synovitis is inflammation of the synovial lining inside a joint, osteitis is inflammation of the bone, and so forth.

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