Musculoskeletal Flashcards
Basics of Bones and Joints

Arthritis
The hallmark of arthritis is cartilage destruction, which may be evident on radiographs as cartilage space narrowing.
In broad categories, arthritis can be divided into degenerative (osteoarthritis), inflammatory (rheumatoid arthritis, spondyloarthropathies, and juvenile idiopathic arthritis), crystal deposition (gout, calcium pyrophosphate dihydrate, and hydroxyapatite), hematologic (hemophilia), and metabolic changes.
Osteoarthitis overview
Also called osteoarthosis or degenerative joint disease, osteoarthritis (OA) is the result of articular cartilage breakdown from altered local mechanical factors in a susceptible individual. In addition to cartilage, OA is thought to involve the entire joint including bone, ligaments, menisci, joint capsule, synovium, and musculature.
OA is the most common cause of cartilage loss in the middle-aged and older population.
OA typically occurs in weight-bearing joints and the hands in a specific distribution.
When radiographic findings of OA are seen in younger patietns or in unusual locations, such as the shoulder, elbow, or ankle, then there is usually a predisposing prior trauma or other underlying arthritis.
The radiographic hallmarks of OA, regardless of location in the body, include:
Asymmetrical joint space narrowing.
Sclerosis of subchondral bone, stimulated by loss of hyaline cartilage and reactive remodeling.
Osteophytosis.
Subchondral cystic change, due to herniation of joint fluid into bone through a cartilage defect.
Lack of periarticular osteopenia.
Although joint space narrowing is present in all arthritides, osteoarthritis can be diagnosed with confidence when subchondral sclerosis, osteophytosis, and subchondral cystic changes are present and inflammatory erosions are absent.
When extensive subchondral cystic changes are present, calcium pyrophostae dihydrate crystal deposition disease (CPPD) should be considered as well.
Osteoarthritis in the hand
Similar to osteoarthritis of other joints, the radiographic hallmarks of OA in the hand include cartilage space narrowing, subchondral sclerosis, and osteophystosis. Erosions are absent.
In order of decreasing involvement, typical sites of OA is the hand include the distal interphalangeal joints (DIPs), the base of the thumb at the first carpometacarpal joint (CMC), and the proximal interphalangeal joints (PIPs).
The most common site of osteoarthritis in the hands is the second DIP.
Unlike rheumatoid arthritis, the metacarpophalangeal joints (MCPs) are less commonly affected.
Large osteophytes cause characteristic soft-tissue swelling surrounding the finger joints.
A Heberden node is a soft-tissue swelling around the DIP.
A Bouchard node is soft-tissue swelling around the PIP.
Osteoarthritis in the shoulder
The Grashey view (obtained posterioly in 40-degree obliqued external rotation) shows the glenohumeral joint in profile and best demonstrates cartilage space narrowing.
Osteoarthritis in the foot
The most common joint affected by OA in the foot is the metatarsophalgeal join (MTP) of the great toe, which may lead to hallux rigidus (a stiff big toe) from dorsal osteophytes.
Osteoarthritis also affects the talonavicular joint and is a cause of dorsal beaking.
Osteoarthritis in the knee
There are three joint compartments in the knee: the medial and lateral tibiofemoral compartments and the patellofemoral compartment. The typical pattern for OA of the knee is asymmetrical involvement of the medial tibiofemoral compartment. Severe osteoarthritis can involved all three compartments.
The following rule of thumb applies to OA in general, but especially in the knee: Osteophytes determine whether OA is present. The degree of joint space narrowing determines the severity of OA.
The degree of tibiofemoral cartilage space narrowing is best determined on standing weight-bearing veiws, often on standing films in flexion.
Bilateral involvement of the knees is typical.
Osteoarthritis in the hip
Similar to the knee, the involvement of hip oteoarthritis tends to be bilateral.
In addition to the typical features of OA including joint space narrowing, osteophytosis, subchondral cystic change, and sclerosis, hip OA also features characteristic migration of the femoral head in a superolateral direction. Less commonly, medial migration can be seen in hip OA.
In contrast, axial migration is seen more commonly in inflammatory arthritis.
Degenerative change in the spine
The vertebral body-disc articulations are cartilaginous joints. Vertebral body endplates are covered by hyaline cartilage that is anaolgous to articular cartilage in other joints. The intervertebral disk is composed of three components: The annulus fibrosus, nucleus pulposus, and the cartilaginous endplates.
Osteoarthritis only affects synovial joints. Therefore, in the spine, osteoarthritis can occur at the facet (zygapophyseal), atlantoaxial, uncovertebral joints ( in the cervical spine at C3-C7), costovertebral, and sacroiliac joints.
The spectrum of intervertebral disk degeneration is best described as degenerative disk disease (DDD), which is characterized by dessication of the intervertebral discs, endplate sclerosis, and osteophytosis.
Gas in the intervertebral disc, also called vacuum phenomenon, is commonly seen and is pathognomonic for degenerative disease. It is important not to confuse vacuum phenomenon (gas in intervertebral disc) with Kummmel disease, which is gas in a vertebral body compression fracture representing osteonecrosis.
Complications of DDD include spinal stenosis, neural foraminal stenosis, and degenerative spondylolisthesis.
Diffuse idiopathic skeletal hyperostosis (DISH) is a distinct entity from degenerative disc disease, but appears similar due to exuberant osteophytosis. DISH is defined as flowing bridging anterior osteophytes spanning at least four vertebral levels, with normal disk spaces and sacroiliac joints. The etiology of DISH is unknown. It is usually asymptomatic but may be a cause of dysphagia when it affects the cervical spine. DISH occurs in elderly patients. DISH is associated with ossification of the posterior longitudinal ligament (OPLL), which may be a cause of spinal stenosis. OPLL may be difficult to identify on MRI and is best seen on CT.
Osteoarthritis in the sacroiliac joint
Only the inferior portion of the sacroiliac joint is a synovial (diarthrodial) joint. The superior portion is a syndesmotic joint.
The typical changes of OA are only seen in the inferior (synovial) portion of the SI joint.
Overview of erosive osteoarthritis
Erosive osteoarthritis combines the clinical findings of rheumatoid arthritis (e.g. swelling) with imaging findins and distribution that are more similar to osteoarthritis.
Erosive OA typically affects elderly females.
Erosive osteoarthritis of the hands
The distribution of erosive osteoarthritis is limited to the hands, where the distribution is the same as degenerative OA (DIPs, CMC of the thumb, and PIPs).
Erosive OA features a characteristic gull-wing appearance of the DIP joint due to central erosion and marginal osteophytes.
Overview of rheumatoid arthritis
Rheumatoid arthritis (RA) is an autoimmune disorder where the synovium is the target of a waxing and waning immune response. Rheumatoid factor (RF) is typically positive, although it is not specific. RF is an antibody directed against IgG, which activates the complement cascade. RA clinically presents with symmetrical joint pain, swelling, and morning stiffness.
RA first affects the small joints in the hands and wrists. Foot involvement may occur early, so foot radiographs are routinely obtained in suspected cases of RA. In more advanced cases, RA affects the cervical spine, knees, shoulders, and hips.
The radiographic hallmarks of RA include:
Marginal erosions, which first occur at the intracapsular margins in the “bare area”. The bare area is a region of exposed bone just within the joint capsule that is not covered by thick cartilage.
Soft-tissue swelling.
Diffuse, symmetric joint space narrowing
Periarticular osteopenia.
Joint subluxation.
Rheumatoid arthritis in the hand and wrist
The hands are commonly affected in patients with RA.
Typical joints involved are the MCPs, PIPs, and the carpal articulations. The DIPs are usually spared.
The earliest radiographic chnages of RA are soft-tissue swelling and periarticular osteopenia, reflecting synovitis and hyperemia.
Erosions occur early in disease, typically of the radial aspects of the second and third metacarpal heads, the radial and ulnar aspects of the bases of the proximal phalanges, and the ulnar styloid.
Joint subluxations are present in more advanced disease, which typically are not reducible and lead to several common deformities, including: Boutonniere deforemity (PIP flexion and DIP hyperextension). Swan neck deformity (PIP hyperextension and DIP flexion). Ulnar subluxation of the fingers at the MCP.
Late-stage rheumatoid arthritis may uncommonly cause ankylosis (fibro-osseous joint fusion occuring after complete cartilage loss) of the wrist. Juvenile idiopathic arthritis (discussed later), in contrast, has a higher propensity for carpal ankylosis.
Rheumatoid arthritis in the feet
The feet are commonly involved in RA. Typically, the metatarsophalangeal (MTP) joints in the forefoot and the talocalcaneonavicular joint in the midfoot are involved. Up to 20% of patients have the MTP joint as the first site of involvement.
Rheumatoid arthritis in the hip
RA causes concentric cartilage loss, leading to axial migration of the femoral head. In contrast, osteoarthritis more commonly causes superior acetabular cartilage space narrowing and superolateral femoral head migration.
In severe cases, RA may cause a protrusio deformity, which is defined as > 3 mm medial deviation of the femoral head beyond the ilioischial line in males and >6 mm in females.
Rheumatoid arthritis in the knee
All three joint spaces (medial and lateral tibiofemoral and patellofemoral) may be affected by RA in the knee. In contrast, OA tends to first affect the medial tibiofemoral articulation. If osteophytes and symmetrical cartilage space narrowing are present, then secondary osteoarthritis should be considered.
Unlike the smaller joints affected by rheumatoid arthritis, erosions are not a prominent manifestation of rheumatoid arthritis of the knee.
Rheumatoid arthritis in the spine
The cervical spine is involved in up to 70% of patients. Involvement is increased with more severe and long-standing disease. The thoracic and lumbar spine are almost never involved.
The general pattern of rheumatoid arthritis in the cervical spine includes subluxation at multiple levels, osteopenia, and erosions of the odontoid, facet joints, vertebral endplates, and spinous processes. Unlike osteoarthritis, there is no bone production.
A characteristic finding of rheumatoid arthritis is atlantoaxial (C1-C2) subluxation. Atlantoaxial subluxation may occur in multiple directions, including anterior (most common), posterior, vertical (atlantoaxial impaction), rotatory, and lateral.
Anterior atlantoaxial subluxation is caused by inflammation of adjacent bursa and resultant laxity of the transverse ligament. Anterior atlantoaxial subluxation may not be apparent if flexion radiographs are not obtained. Anterior atlantoaxial subluxation is present if the atlanto-dental interval (ADI) is >2.5 mm (>5 mm in children). The atlanto-dental interval is the distance between the anterior aspect of the dens and the posterior aspect of the anterior ring of C1, as measured at the inferior aspect of the C1-C2 articulation.
Vertical atlantoaxial subluxation (also called atlantoaxial impaction) results from C1-C2 facet erosion and collapse, leading to protrusion of the odontoid through the foremen magnum. This may compress the midbrain. Direct visualization of the odontoid is usually not possible on a lateral radiograph, but impaction may cause the anterior arch of C1 (normally in line with the odontoid) to sink to the level of the body of C2.
In the setting of RA, posterior atlantoaxial subluxation is usually due to odontoid erosion. It may also be caused by odontoid fracture.
Rheumatoid arthritis in the shoulder
Rheumatoid arthritis causes chronic rotator cuff tears leading to the classic high riding humerus.
Erosions tend to occur in the lateral aspect of the humeral heads. At the acromioclavicular (AC) joints, erosion may lead to “penciling” of the distal clavicle.
Rheumatoid arthritis in the elbow
Rheumatoid arthritis involves the elbow in approximately one third of patients.
Overview of seronegative spondyloarthropathies
The seronegative spondyloarthropathies are a group of four inflammatory arthropathies, which by definition have negative rheumatoid factor. Patients are usually HLA-B27 positive.
The four seronegative spondyloarthopathies are ankylosing spondylitis, psoriatic arthritis, reactive arthritis (previously called Reiters arthropathy), and inflammatory bowel disease (IBD) associated arthropathy.
Sacroilitis is a hallmark of the spondyloarthopathies
Similar to involvement in OA, only the inferior aspect of the sacroiliac (SI) joint is affected in seronegative spondyloarthropathies because only the inferior portion is a synovial (diarthrodial) joint. Erosions first involve the iliac aspect of the SI joint.
Symmetric sacroilitis is caused by IBD and ankylosing spondylitis (mnemonic: both start with vowels).
Asymmetric sacroilitis is caused by psoriatic arthritis and reactive arthopathy (mnemonic: both start with consonants)
An important cause of unilateral sacroilitis is septic arthritis, especially in an immunocompromised patient or with intravenous drug abuse. Septic arthritis usually presents with erosive changes in a patient with fever and SI joint pain.
Inflammatory bowel disease
Sacroilitis associated with inflammatory bowel disease can be seen in patients with ulcerative colitis, Crohn disease, Whipple disease, and status post gastric bypass.
IBD-associated sacroilitis is typically symmetrical.
Ankylosing spondylitis
Ankylosing spondylitis (AS) is predominantly seen in young men with HLA-B27 and presents with back pain and stiffness. AS can be associated with pulmonary fibrosis (upper lobe predominant), aortitis, and cardiac conduction defects.
The earliest radiographic signs of AS are symmetric erosions, widening, and sclerosis of the sacroiliac joints.
Subsequently, the spine invariably becomes involved, with radiographic findings following a specific sequence, which ascends from the lumbar to the cervical spine.
Romanus lesions are erosions of the anterior spine or inferior edges of the vertebral body endplates caused by enthesitis (inflammation at a ligament or tendon insertion site) at attachment of the annulus fibrosus to the vertebral body.
Shiny corners represent sclerosis of prior Romanus lesions at the corners of the vertebral bodies.
Squaring of the vertebral body disc margins develops due to erosions and bone loss.
Delicate syndesmophytes represents bony bridging connecting adjacent vertebral margins, which create the classic bamboo spine (spinal ankylosis) in late-stage disease.
In advanced disease, the fully ankylosed spine is at a very high risk of fracture with even minor trauma. CT is necessary for evaluation of even minimal trauma in a patient with advanced AS and pain after trauma.
An Andersson lesion is a pseudoarthosis occurring in a completely ankylosed spine.



























