Anatomy

The bony pelvis is formed by the innominate bones, the sacrum, and the coccyx. Each hip (innominate) bone is composed of three elements: the ischium, the ilium, and the pubis. These three components meet at the acetabulum and are united by the triradiate cartilage until the age of 16 years, when fusion takes place. The sacrum is composed of five vertebrae, and the coccyx usually consists of four. The coccyx and sacrum are situated more posteriorly in women than in men and thus are more exposed to trauma. Very little motion occurs at the sacroiliac (SI) and interpubic joints because of strong ligamentous structures at these areas. Some motion occurs at the sacrococcygeal joint, but little is present between coccygeal segments.

Roentgenographic Anatomy

The pelvis can be well visualized by a routine anteroposterior roentgenogram (Fig. 9-1). In addition, the sacrum and coccyx may be studied by lateral views and anteroposterior views angled 15 degrees cephalad and caudad.

Fig. 9-1 Pelvic roentgenogram. S, Sacroiliac joint; A, anterior superior iliac spine; P, pubic symphysis; I, ischium; W, wing of the ilium.

Osteitis Pubis

Osteitis pubis is a painful inflammation of the pubic symphysis that is usually self-limited. The cause is unknown, but the condition frequently develops after urologic procedures or infections, after childbirth, or following repetitive stresses associated with certain athletic activities.

CLINICAL FEATURES

The onset is gradual, with symptoms developing a few days after the traumatic event. Pain and tenderness over the symphysis pubis are usually present. Coughing may aggravate the pain, which radiates along the adductor and rectus abdominis muscles. Stretching these muscles may reproduce the pain. Symptoms may be unilateral or bilateral. Radiation to the groin, scrotum, or perineal area is common. Examination reveals local tenderness over the symphysis pubis and adjacent soft tissue. Passive abduction of the hips and active adduction of the hips against resistance are painful.

Roentgenograms of the pelvis taken early in the disease course may be normal. Later, variable amounts of spotty demineralization, widening of the symphysis pubis, and sclerosis may be noted (Fig. 9-2). Bone scanning is often positive. Magnetic resonance imaging (MRI) is also valuable. Reossification occurs over several months.

Fig. 9-2 Osteitis pubis.

TREATMENT

Treatment consists of nonsteroidal anti-inflammatory drugs (NSAIDs), rest, and stretching exercises. This may be supplemented by deep heat or ice. A local steroid/lidocaine injection may also be helpful. The disease has a tendency toward spontaneous recovery in most cases, but this may take several weeks. The activity level of the patient is allowed to increase as tolerated.

Disorders of the Sacroiliac Joint

The SI joints consist of large, broad, irregular articular surfaces made of depressions and ridges. This interlocking nature, along with extensive capsular and ligamentous support, contributes to its considerable inherent stability. Very little movement occurs in these joints.

There is considerable controversy surrounding conditions that may affect the SI joints. Although these joints may occasionally be involved with infection or inflammatory diseases, such as the spondyloarthropathies, they are rarely the source of other pathology. Although some textbooks continue to discuss various disorders, “dysfunctions,” and injuries (“going out”), most have never been proven. Pain from the lumbar spine is often referred to this area, which can be a further source of confusion. Finally, except for the presence of local tenderness, there are no good, reliable clinical tests or maneuvers that can be used as a part of the physical examination to localize pain to this joint. Provocative testing using joint injection has been used with inconclusive results, and except in late cases, roentgenographic evaluation is usually of limited value as well.

OSTEITIS CONDENSANS ILII

This is a lesion of unknown etiology in which bilateral sclerosis of a fairly large area of ilium adjacent to the SI joint occurs (Fig. 9-3). It is most common in multiparous women. Its importance lies in distinguishing it from ankylosing spondylitis (Marie–Strümpell disease). Ankylosing spondylitis is usually associated with an increase in the sedimentation rate and roentgenographic involvement on both sides of the SI joint. Ankylosing spondylitis also occurs primarily in men and is associated with pain. However, there is disagreement as to whether osteitis condensans ilii is ever a painful condition, and it is usually considered to be an incidental radiographic finding. It may be associated with similar lesions in the pubic bones near the symphysis pubis like those seen in osteitis pubis.

Fig. 9-3 Osteitis condensans ilii. The iliac portions of the sacroiliac joints are sclerotic and white. The joints themselves are not involved.

DEGENERATIVE JOINT DISEASE

Symptomatic involvement of these joints by osteoarthritis is unusual. Even when findings are present roentgenographically, symptoms may be minimal or absent completely (Fig. 9-4). Treatment is symptomatic in these rare cases; surgery is almost never recommended, partly because of the difficulty in the diagnosis. Therapeutic steroid injections may be tried but usually require the inconvenience of fluoroscopic guidance.

Fig. 9-4 Pelvic roentgenogram showing bilateral osteoarthritic joint changes that were asymptomatic in this patient.

Disorders of the Sacrococcygeal Region

The coccyx consists of three to five segments and usually angulates forward to a variable degree. The sacrococcygeal junction is a symphysis. In the normal, erect sitting position, with weight on the thighs, the coccyx does not have pressure against it. With flattening of the lumbar lordosis and sitting in the slumping position, however, the coccyx can reach the seat, and pain may develop over its tip (coccygodynia). Coccygodynia is not really a disease but simply a symptom. Disorders of the coccyx are uncommon.

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