TYPES OF JOINTS

Skeletal joints, the sites of articulation between one bone or cartilage and another, are generally of three types: fibrous joints (skull-type sutures), cartilaginous and fibrocartilaginous joints (discovertebral joints), and synovial joints (most limb joints).

Fibrous joints, or skull-type articulations, are called synarthroses: one bone is joined to another by an unossified fibrous membrane or residual plate of cartilage. Fibrous joints, such as skull sutures, allow little or no movement. Bones united by ligamentous attachments, such as the proximal and distal tibiofibular joints and the superior sacroiliac joints, are called syndesmoses.

Cartilaginous joints are amphiarthroses and are of two types: fibrocartilaginous and cartilaginous. Bony surfaces coated with hyaline cartilage and united by fibrocartilaginous disks are symphyses (fibrocartilaginous joints). Examples include discovertebral, manubriosternal, xiphisternal, and costosternal joints and symphysis pubis. United epiphyseal hyaline cartilage is an example of a cartilaginous amphiarthroidal joint. Amphiarthroses allow a limited range of movement but provide considerable stability.

Synovial joints or diarthroses are freely movable joints. The bony surfaces are coated with hyaline cartilage and united by a fibrous articular capsule. The synovial membrane lines the inner surface of the capsule but does not cover the articular cartilage (Figure 1-1). The capsule is strengthened by collateral ligaments. Synovial joints comprise most of the joints of the extremities and are the most accessible joints to direct inspection and palpation. Synovial joints share important structural components: subchondral bone, hyaline cartilage, a joint cavity, synovial lining, articular capsule, and supporting ligaments.

FIGURE 1-1 A, Structure of the synovial joint. B, An example of a synovial joint in sagittal section.

Synovial joints serve a variety of functions and differ in configuration, permitting specific movements while restricting others. Synovial joints can be subdivided into seven major types:

STRUCTURE OF SYNOVIAL JOINTS AND SUPPORTING TISSUES

The articular cartilage is an avascular, aneural, resilient, low-friction, load-bearing tissue covering the articulating bony surfaces. It is capable of absorbing impact by virtue of its compressibility, elasticity, low hydraulic permeability, and self-lubrication (squeeze-film hydrodynamic lubrication). It derives its nourishment through diffusion from the synovial fluid that bathes its surface.

The synovial membrane provides an unobtrusive, flexible, low-friction, well-lubricated lining for diarthrodial joints, tendon sheaths, and bursae. Histologically the synovium consists of two layers: an intimal or synovial lining cell layer—made up of one to three layers of cells or synoviocytes—and a subintimal or subsynovial layer of loose, vascular, fibro-fatty connective tissue. Synovium has important phagocytic functions and produces synovial fluid. Table 1-1 shows different types of synovial effusions.

Joint capsules, ligaments, and tendons are dense fibrous tissues with a major role in musculoskeletal function. Collectively they allow and guide joint motion while resisting high tensile loads without deformation. Laxity or adaptive shortening of these structures affects joint motion and may lead to injury (see Figure 1-1).

Joint capsules attach around articular surfaces to form a continuous envelope for the joint. Capsular cells are predominantly fibroblasts with a dense fibrous matrix surrounding them. The capsule is lined with synovium that provides lubrication for the joint. Ligaments attach bone to bone and function to stabilize adjacent bones by restricting abnormal movements. Ligaments may be intracapsular, capsular, or extracapsular, and they share similar cell and matrix characteristics with the joint capsule and tendon tissues.

The anterior cruciate ligament (ACL) is an intracapsular ligament that connects anterior aspect of intercondylar eminence of tibia with medial surface of lateral femoral condyle.

The medial (tibial) collateral ligament (MCL) is a capsular ligament connecting the medial epicondyle of the femur with the medial surface of the medial tibial condyle; it is continuous with the capsule and is essentially a thickening of the capsule.

The lateral (tibial) collateral ligament (LCL) is an extracapsular ligament, not part of the fibrous capsule of the knee; it connects the lateral epicondyle of the femur with the fibular head.

Tendons vary in size and shape, but all attach muscles to bone to transmit the force of muscle contraction to bone. Maintaining tendon tension plays a role in homeostasis of the tendon. Overuse and repetitive trauma results in degenerative changes that outweigh the regenerative process and weaken the tendon.

CATEGORIES OF MUSCULOSKELETAL PROBLEMS

Musculoskeletal problems and rheumatic diseases can be practically classified into five major categories, defined by the tissues predominantly affected: periarticular, articular, bone, nerve, and extraarticular.

At each point in your evaluation—as you gather essential historical, physical, and selected laboratory information—ask what tissues are primarily affected. Thinking of musculoskeletal problems in this way provides a useful framework for organizing clinical information. Recognizing the pattern of predominant tissue involvement then directs your attention toward well-defined members of each category, helping to organize your differential diagnosis (Table 1-2).

TABLE 1-2 MUSCULOSKELETAL PROBLEMS AND RHEUMATIC DISEASES, AFFECTED TISSUES, AND PATTERNS OF INVOLVEMENT

CHARACTERISTICS OF MUSCULOSKELETAL PAIN

Pain in nearly any location can be well delineated using the mnemonic OPQRST, where O = onset, P = precipitating (and ameliorating) factors, Q = quality, R = radiation, S = severity, and T = timing. This information, combined with the pattern of joint involvement, is helpful in narrowing the preliminary differential diagnosis. The number of joints involved (monoarticular, oligoarticular, or polyarticular); the presence of symmetry or asymmetry; peripheral versus axial joint involvement; small and/or large joint involvement; and a fixed, migratory, or additive pattern of evolution of arthritis are all important features of clinical pattern recognition. Careful questioning about any past joint complaints may supply missing data relating to the location of prior articular problems and the time course and pattern of evolution of previous musculoskeletal symptoms and signs.

ESSENTIAL CONCEPTS

A central axial spine, paired peripheral joints, and symmetric musculature provide the basis for essential side-to-side comparison during the musculoskeletal examination. Recognizing asymmetry is important and may provide an initial clue in diagnosing an abnormality.

Both active and passive ranges of motion are important in assessing joint function. Active range of motion is patient-initiated movement of the joint that tests integrated function and requires intact innervation, muscle and tendon function, and joint mobility. Passive range of motion is examiner-initiated movement of a joint and tests only joint mobility. The combined use of passive as well as active range of motion minimizes the need for patient instruction and maximizes the speed and efficiency of the exam (Figure 1-2). Whenever joint movement is anticipated to be painful, it is best to first observe active range of motion (patient-initiated movement) to appreciate the degree of pain and dysfunction before gently attempting passive range of motion (examiner-initiated manipulation).

FIGURE 1-2 ACTIVE AND PASSIVE RANGE OF MOTION.

EXAMINATION COMPONENTS

There are four essential steps in the examination of joints: inspection, palpation, active and passive range of motion, and the assessment of supporting structures and special testing. Inspect the joint for asymmetry, erythema, swelling, and deformity. Palpate for tenderness; warmth; synovial thickening; effusion (in inflammatory synovitis); bony, osteophytic swelling (in primary and secondary osteoarthritis); and crepitus. Take the joint through a combination of active (patient-initiated) and passive (examiner-initiated) range-of-motion tests appropriate to the specific joint. Finally, assess supporting structures—such as ligaments, tendons, and muscles—and perform special testing using regional evaluations specific to particular joints. Examples of special testing include manual muscle testing, impingement testing (shoulder), and testing for Tinel sign (entrapment neuropathies).

Recording Exam Findings

A brief record of abnormalities can be made by organizing your examination into the following categories: upper extremities (fingers, wrists, elbows, and shoulders); lower extremities (hips, knees, ankles, and feet); spine (cervical, thoracic, lumbosacral, and sacroiliac joints); and gait (noting uneven rhythm, limp, and asymmetry). Abnormalities such as tenderness, swelling, altered range of motion, and deformity can then be easily reviewed and compared by subsequent examiners.

For example, a patient with significant generalized, primary osteoarthritis might have a joint examination record as follows:

UE: multiple Heberden nodes; mild tenderness and cool swelling; R second and fourth and L fifth PIPs; subluxation and “squaring” of first CMCs; nontender acromioclavicular osteophytes.

LE: R hip: flexion 90°, ER 40°, IR 10° with groin pain at end IR; L hip: flexion 120°, ER 60°, IR 40° and painless; bilateral hallux valgus.

C SPINE: mild ↓ flexion; 40° R and L rotation; ↓↓ extension with mild pain posteriorly.

LS SPINE: full flexion; ↓ lateral bend; ↓↓ extension with pain at lumbosacral junction without radiation.

GAIT: antalgic gait with R groin discomfort.

Use of cartoon diagrams to record findings can also be quite helpful (Figure 1-3).

FIGURE 1-3 DIAGRAM FOR RECORDING MUSCULOSKELETAL EXAM FINDINGS.