Pathological conditions

Degenerative disease in peripheral joints

 

Although terminology for degenerative arthritis that is accepted worldwide has not yet been established, degenerative joint disease is the best general phrase to describe degenerative changes in any type of articulation (i.e., synovial, cartilaginous, or fibrous). The terms osteoarthritis and osteoarthrosis are reserved for degenerative disease of synovium-lined joints. Because in most of the affected articulations inflammatory changes are not pronounced, the suffix -osis appears more appropriate than -itis and therefore the term osteoarthrosis is used throughout this chapter.

Osteoarthrosis is defined as a non-inflammatory, localized degeneration of hyaline cartilage (Fig. 60). In comparison, rheumatoid arthritis is a disorder of the synovial membrane (i.e. synovitis) with secondary destruction of the articular cartilage (Fig. 60).

Etiology and pathogenesis of osteoarthrosis

The causes of this common articular disease are diverse. Both systemic factors (such as genetics, advancing age, nutritional and metabolic status, and physical activity) and local factors (such as trauma and preexisting

 

Figure 61. Subchondral lesion after joint instability. T1-weighted sagittal MR image of a femoral condyle in a 19 year-old woman, 9 months after complete tear of the anterior cruciate ligament (same patient as in Fig. 46). At open surgery the cartilaginous surface appeared normal, but at palpation the cartilage covering the defect was depressed.

articular disease or deformity) are important. Traditionally, degenerative alterations have been thought to begin in the articular cartilage with disruption of the cartilage matrix and degradation of the chondrocytes. However, an alternative theory emphasizes the initial role of subchondral bone abnormalities in the pathogenesis of osteoarthrosis. According to this theory, stress overload produces microfractures of the trabeculae in the subchondral region; rep air of these fractures subsequently leads to stiffness of the bone, exposing the overlying cartilage to increasing force and secondary degeneration.

Joint instability occurring after ligamentous tears plays an important role in the development of osteoarthrosis. In the knee joint after complete tear of the anterior cruciate ligament, the first signs of osteoarthrosis may appear in the subchondral bone of the femoral condyles as visualized by MRI (Fig. 61). These lesions consist of fibrovascular invasion of the bone marrow and osteonecrosis, and they may heal if the instability is reduced before further deterioration takes place.

In general, the progression of osteoarthrosis is slow, but joint instability in some joints (e.g. the tarsometatarsal) may lead to advanced osteoarthrosis in only a few months.

 

a

Figure 62. The natural course of osteoarthrosis of a knee joint. a) Weightbearing radiograph reveals medial joint space loss, subchondral sclerosis, marginal osteophytes (open arrows), and varus displacement as measured from the hip-knee-talus line (black lines). b) Weightbearing radiograph of the same patient four years later shows increasing varus deformation, lateral instability, femorotibial subluxation, and involvement of the lateral compartment (black arrow).

b

Imaging of osteoarthrosis: general aspects

Conventional radiography
The radiographic definition of osteoarthrosis is confined to the demonstration of a localized reduction of the joint space (Fig. 62).
One of the characteristic radiographic alterations of osteoarthrosis is the development of osteophytes at the margins of the joint (Fig. 62). Osteophytes, however, are not synonymous with osteoarthrosis and may be seen in other conditions without loss of cartilage. After cartilage loss, the subchondral bone reveals varying degrees of sclerosis (Fig. 62), and subchondral cyst formation is an important and prominent finding in osteoarthrosis (as well as in other articular disorders) (Fig. 60).

The routine radiographic examination must employ correct technique.Three conditions should be fulfilled (Fig. 63).
1. The direction of beam must be tangential to the subchondral bone

 

Figure 63. Radiographic examination in osteoarthrosis: technique. a) Normal joint. The beams from the tube (R) are tangential to the subchondral bone and the joint space (L) is correctly delineated on the film (F). b) Normal joint. The direction of beam is not tangential and joint space will appear reduced. e) Cartilaginous defect of apposing joint surfaces. The direction of the beam is correct, being tangential to the subchondral bone. The total extent of joint space loss will then be reflected on the film. d) Only the depth on the lower lesion of the cartilage will appear on the film. e) Apposing joint surfaces are resting on cartilage of normal height, and the joint space will appear normal. This situation commonly occurs at weightbearing examination of a knee joint in extension.

 

2. The joint must be placed in such a position (e.g., flexion-extension) that the central beam is tangential to the most severely involved parts of the cartilaginous lesions
3. Stress views (e. g., weightbearing) are mandatory when examining some joints, most importantly the knee joint (Fig. 65).

Bone scan and MRI
Bone scans play an important role in the evaluation of osteoarthrosis in those cases in which the joint space appears normal on routine radiographs. Characteristically, a focal increased uptake at the site of the subchondral lesion and a slight, diffuse increased uptake as a result of

 

a	Figure 64. Medial osteoarthrosis of the knee joint. a) Weightbearing radiograph shows moderate joint space loss. b) Scintigraphy demonstrates a localized lesion of the medial tibial condyle and a slightly increased uptake generally within the knee joint. c) T1-weighted coronal MR image demonstrates a localized cartilaginous lesion and a large subchondral abnormality of the tibial condyle corresponding to increased uptake at scintigraphy, which were visible on the radiograph.
b
c

synovitis are seen (Fig. 64). The intensity of the uptake varies.

MRI has some limitations in the demonstration of early cartilaginous lesions but clearly allows visualization of some subchondral lesions not visible at arthroscopy (Figs. 61, 64, 66). There is some lack of correlation between the extent of joint degeneration as seen with routine radiography and the severity of symptoms, but this correlation is better for scintigraphy and MRI.

 

	Figure 65. Weightbearing examination of the knee joint, technique. The lower leg is placed with 5 to 10 degrees of inclination relative to the film plane. In this position the central beam will be tangential to the tibial condylar plane. In addition, the knee is examined in 10 to 15 degrees of flexion.
a	Figure 66. Osteoarthrosis of the hip joint. a) AP radiograph of the right hip shows slight reduction of the proximal joint space and subchondral sclerosis. b) Scintigraphy demonstrates localized increased uptake at the proximal joint space and slightly increased uptake generally in the joint due to secondary synovitis. c) T1-weighted coronal MR image of the hip shows a localized subchondral lesion (arrow) but only slight reduction of the cartilage height. These subchondral lesions often are not seen in T2-weighted images.
b
	Figure 67. Examination technique for osteoarthrosis of the hip joint. Oblique lateral radiograph, obtained in a standing position, shows total loss of the posterior joint space in the left hip (arrow). In the anteroposterior view the joint space appeared normal.

Radiology of osteoarthrosis in specific joints

Hip
Osteoarthrosis of the hip commonly is bilateral. The most common location of joint space loss is the superior aspect of the articulation (75 %) (Fig. 66). Less typically, joint space narrowing occurs medially. To visualize any associated anterior and posterior joint space loss, both AP and oblique views are required (Fig. 67). The commonly used Lauenstein projection has no place in the diagnosis of degeneration of the hip joint (Fig. 63 d).

Treatment is almost confined to total hip replacement (Fig. 10). The position of acetabular and fem oral components of the prostheses can be assessed on the postoperative radiographs (Fig. 10). Less than optimal position may result in mechanical loosening.

Knee
The knee joint is a common site of osteoarthrosis, with a female predominance (Figs. 62, 64). Either the medial (90%) or, rarely, the lateral joint space is affected. When diffuse joint space narrowing involves both the medial and lateral femorotibial compartments, rheumatoid arthritis should be considered. Osteoarthrosis of the patellofemoral compartment usually is combined with abnormalities of the femorotibial compartments but may be seen as an isolated finding.

 

Figure 68. The effect of a high tibial osteotomy in osteorthrosis of a knee joint. a) The varus deformity is corrected by cutting a wedge laterally in the proximal portion of the tibia. b) After surgery the femorotibial load is located at the lateral compartment, and (if subluxation is reduced) at the normal cartilage of the central portion of the medial compartment (white arrow). A joint space may appear (open arrow).

Films obtained during weightbearing or varus and valgus stress are necessary in early stages of osteoarthrosis of the knee joint. Ideally, the weightbearing radiographs should be obtained with a patient standing only on the involved leg in 15 to 20 degrees of knee flexion (Fig. 65). Additional exposures using other degrees of knee flexion may be necessary to demonstrate the loss of joint space, especially in the lateral compartment. With the knee in extension, early joint space loss may not be seen (Fig. 63). The weightbearing technique also allows more accurate delineation of subluxation, varus or valgus angulation, and lateral instability (Fig. 62).

The treatment of osteoarthrosis of the knee joint includes joint replacement of one, two, or three compartments and, less commonly, high tibial osteotomy. With osteotomy, the femorotibial alignment in the frontal view is restored (or overcorrected) and when successful, subluxation and lateral instability will disappear (Fig. 68). Regeneration of cartilaginous erosions may occur.

Ankle and loot
In the absence of previous significant trauma, osteoarthrosis of the ankle is infrequent, but when it occurs, symptoms may be disabling. If joint

 

Figure 69. Osteoarthrosis of the first carpometacarpal joint with obliteration of the joint space (white arrow) and osteophytes (black arrow).

space loss is inapparent on the routine AP and lateral views, films obtained during valgus and varus stress should be used as a supplement. Scintigraphy and MRl also may play an important role in the assessment of the ankle joint. Significant degenerative changes may develop at the first tarsometatarsal joint.

Upper extremity
Shoulder pain is common and usually results from degenerative disease of the cervical spine, rotator cuff disease, or calcified tendinitis (Fig. 35). Osteoarthrosis affects the glenohumeral joint, but severe involvement is rare in the absence of a history of physical injury.

Osteoarthrosis of the elbow joint is uncommon. It usually follows accidental or occupational trauma (particularly in miners and drillers). lnvolvement of the first carpometacarpal joint is not uncommon and can lead to prominent clinical abnormalities. It is best demonstrated in stress views of the thumb (Fig. 69). Such involvement commonly is bilateral and combined with degeneration in the scaphoid-trapezoid joint.

Osteoarthrosis of the distal interphalangeal and proximal interphalangeal joints of the hand is extremely common, particularly in the middle-aged postmenopausal women. Clinically detectable bony enlargements about the distal interphalangeal joints are designated Heberden's nodes. Symptoms are not prominent and cause little disability.

 

a	Figure 70. Stress fracture of the medial tibial condyle. 50-year-old man, who appeared with spontaneous pain medially in the knee. Weightbearing radiograph was normal. a) Scintigraphy demonstrates intensive uptake in the medial tibial condyle, suggesting a stress fracture. b) T1-weighted coronal MR image confirms the presence of a stress fracture.
b

Differential diagnoses

Osteoarthrosis is associated with a localized loss of joint space. The appearance of diffuse joint space loss usually indicates another disease process, such as rheumatoid arthritis or septic arthritis. Seronegative spondyloarthropathies (e.g., ankylosing spondylitis, psoriatic arthritis, and reactive arthritis) are most common in younger patients. A characteristic appearance of hip involvement in ankylosing spondylitis is bony proliferation at the lateral junction of the head and neck of the femur.

If there is clinical suspicion of osteoarthrosis in the hip, knee or ankle joints but the conventional radiographs are normal, the following differential diagnoses should be considered:

 

a

Figure 71. Bilateral idiopathic osteonecrosis of the femoral head in a 25-year-old man. a and b) T1-weighted coronal MR images of the right and left hips, respectively. On the right, there is lower signal intensity within the osteonecrotic portions of the femoral head, with segmental collapse of the proximal joint surface and a moderate joint effusion. On the left, there is relatively high signal intensity within the region of osteonecrosis, representing fat degeneration.

b

(1) osteoarthrosis (i.e., insufficient examination technique) (Fig. 63), (2) stress fracture (Figs. 70, 109), or (3) osteonecrosis (early).

Bone scans and MRI play an important diagnostic role in this situation. About the knee, spontaneous osteonecrosis is most common in the medial femoral condyle and stress fractures are most frequent in the medial tibial condyle (Fig. 70). With stress fractures of the femoral neck, bone scan and MRI will demonstrate the lesion, most commonly located in the medial aspect of the neck.

 

Niels Egund, Kjell Jonsson, Holger Pettersson and Donald Resnick