Degenerative Changes of the Posterior Complex

General characteristics

Degenerative changes are similar to those observed in peripheral joints and they include:

  • osteophyte formation,
  • hypertrophy of the articular processes,
  • fibrillation and fissuring of articular cartilage
  • osteosclerosis,
  • thinning of the articular cartilage with erosions and subchondral cyst formation,
  • vacuum joint phenomenon or joint effusion,
  • hypertrophy and/or calcifi cation of the joint capsule,
  • ligamentum flavum.

Osteophyte formation

Osteophyte formation is defi ned as excrescent new bone formation, lacking a medullary space, arsing from the margin of the joint. Osteophytes protruding ventrally from the anteromedial aspect of the facet joints may narrow the lateral recesses and intervertebral foramina causing central or lateral spinal canal stenosis (Wybier 2001).

Hypertrophy of the articular processes

Hypertrophy was defi ned as enlargement of an articular process with normal proportions of its medullary cavity and cortex (Carrera et al. 1980). Hypertrophy of the facet joints causes distortion of the articular surfaces which may be nerve root compression.

GradeCriteria
0Normal facet joint space (2–4 mm width)
1Narrowing of the facet joint space (<2 mm) and/or small osteophytes and/or mild hypertrophy of the articular processes
2Narrowing of the facet joint space and/or moderate osteophytes and/or moderate hypertrophy of the articular processes and/or mild subarticular bone erosions
3Narrowing of the facet joint space and/or large osteophytes and/or severe hypertrophy of the articular processes and/or severe subarticular bone erosions and/or subchondral cysts

Weishaupt et al. 1999

Fibrillation and fissuring of articular cartilage

Fibrillation and later fissuring and ulceration of articular cartilage will develop, progressing from the superfi cial to the deep cartilage layers (Weishaupt et al. 1999).

Vacuum joint phenomenon

Vacuum joint phenomenon in facet joint osteoarthritis. Axial CT shows the presence of gas within facet joints, which may be explained as a result of uneven apposition of the joint surfaces. Associated hypertrophy and juxta-articular calcifi cations and osteophytes are present.

Osteosclerosis

Facet joint subchondral bone changes. Axial CT image shows degenerative changes of both facet joints, which is more pronounced at the left side. Hypertrophy and osteosclerosis, joint space narrowing, osteophytes and subarticular bone erosions are present

Joint effusion

Whereas fluid accumulation in the facet joints is better seen on MR.

Hypertrophy and/or calcifi cation of the joint capsule.

Hypertrophy and calcifi cation of the joint capsule

Ligamentum Flavum Hypertrophy

Symmetrical thickening of the ligamenta fl ava is a frequently observed fi nding in facet joint arthropathy. It results from joint effusion, progressive ligamentous fibrosis, calcifi cation and/or ossifi cation (Wybier 2001).

Calcifi cations of the ligamenta fl ava have been observed in patients with: - diffuse idiopathic skeletal hyperostosis (DISH),
- ankylosing spondylitis, - renal failure, - hypercalcemia, - hyperparathyroidism, - hemochromatosis, - pseudogout.

The lower one-third of the thoracic spine (T9–T12) and lower lumbar (L3-S1) is the most common location, and the cervical spine is rarely affected.

Synovial cysts

Synovial cysts are periarticular cysts of the synovial membrane, with a membrane attached to the joint capsule. They contain clear or yellow mucinous fl uid or gas. The walls are of loose myxoid connective or fi brocollagenous tissue with a synovial lining. Synovial cysts of the facet joints are almost invariably associated with osteoarthritis of the facet joints. On MR imaging, intraspinal synovial cysts are depicted as sharply marginated epidural masses near the facet joint. In some cases, MR imaging may demonstrate the communication with the facet joint. The signal intensity of the cysts is equal to or slightly greater than that of cerebrospinal fl uid (CSF) on both T1- and T2-weighted images. Synovial cysts with high signal on T1- and T2-weighted images indicate the presence of subacute breakdown products of blood. All synovial cysts have a low signal intensity rim at the periphery that is accentuated on long TR/TE sequences. After administration of gadolinium these cysts show rim enhancement ( Tillich et al. 2001).

On CT is of a rounded mass of low attenuation adjacent to the facet joint. CT may show egg-shell calcifi cations of the wall of the cyst (Lunardi et al. 1999) and gas inside the cyst (Stoodley et al. 2000).

Ganglion cysts

In contrast, ganglion cysts have no connection to the joint and no synovial lining. They contain myxoid material. The consistency of fl uid within the cysts varies greatly because of hemorrhage and infl ammation (Stoodley et al. 2000).

Juxtafacet cysts

Juxtafacet cysts are not evenly distributed in the spine. An association of juxtafacet cysts with trauma (Paolini et al. 2002), rheumatoid arthritis, spondylolysis, chondrocalcinosis (Gadgil et al. 2002), and Baastrup’s disease (Chen et al. 2004) has also been reported.

Ligamentum flavum cysts

Ligamentum flavum cysts are rare (Terada et al. 2001). They are different from synovial and ganglion cysts in that they arise from, or are partially embedded in, the ligamentum fl avum rather than being closely related to the facet joint.

On imaging, an intraspinal, extradural mass adjacent to the ligamentum fl avum is found. On CT, the lesion has a low density attenuation. Unlike in synovial or ganglion cysts, rim calcifi cation has not been reported (Terada et al. 2001). On MRI, a welldefi ned, round to ovoid cystic mass lesion is observed. It has a high signal intensity on T2-weighted images with a low signal intensity rim. Thick peripheral enhancement after gadolinium injection is seen (Mahalatti et al. 1999).

Differential diagnosis of paravertebral cyst

The differential diagnosis of a well-defi ned, round, T2-hyperintense epidural lesion in the posterior or lateral spinal canal is broad, and includes juxtafacet cyst, ligamentum fl avum cyst, disc cyst, sequestered disc fragment, infectious (e.g. cysticercosis or hydatid) cyst, arachnoid cyst (rare in the lumbar spine), and neoplasm (cystic degeneration in a neurofi broma or schwannoma) (Mahallati et al. 1999; Apostolaki et al. 2000). It may be diffi cult to differentiate juxtafacet cysts from ligamentum fl avum hematoma in post-trauma cases (Hirakawa et al. 2000).

Neural Arch Intervertebral Neoarthrosis

Excessive lumbar lordosis is frequently associated with spine degeneration, especially in women after menopause. Approximation of adjacent vertebral neural arches may result in abnormal bony contacts in different areas and may even result in a neoarthrosis (Wybier 2001). Associated remodelling or bony sclerosis of the pedicles and laminae may occur in these patients.

Spinous Process Abnormalities (Baastrup’s Disease)

Baastrup’s disease, also known as kissing spine, has been described as a cause of low-back pain. It is characterized by close approximation and contact of adjacent spinous processes with resultant enlargement, flattening and reactive sclerosis of the apposing interspinous surfaces (Chen et al. 2004). Neoarthrosis between the spinous processes has been described.