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.

Fracture of the coccyx can occur, usually from a fall on the more exposed coccyx of the female. It has been described during obstetric procedures. During childbirth, the coccyx is forced backward up to 2 cm or greater. This is allowed by a healthy sacrococcygeal joint. Sometimes forceful movement of the coccyx is recommended during difficult deliveries when a stiff sacrococcygeal segment impedes delivery. Injury to the coccyx may occur, leading to fibrosis and stiffness. Manipulation or fracture of this stiffened segment may be required in future deliveries.

Chronic strains and osteoarthritis may also result from repetitive trauma. Joint motion is usually restricted, and activities that move the coccyx are painful. Complete bony ankylosis may even result, with the coccyx fusing in a deformed position. Fractures of the tip of the sacrum or coccyx also occur but usually do not produce long-term symptoms unless a painful pseudarthrosis or traumatic arthritis ensues. “Tailbone” (sacrum or coccyx) fractures are actually quite uncommon. The roentgenogram is often misinterpreted because of the normal sacrococcygeal and intercoccygeal spaces.

The sacrum and coccyx are commonly the site of pain referral from visceral structures or lumbar disc degeneration. However, in most cases the exact etiology of coccygodynia is unknown.

CLINICAL FEATURES

Pain on sitting is the most common complaint. This pain is aggravated by slumping, sitting on a hard seat, or activity. Many symptoms begin with an injury and may be aggravated by constipation or rectal disease. The symptoms are more common in women. Local pain and tenderness at the sacrococcygeal joint and adjacent soft tissues are common physical findings. A rectal examination should always be performed and often reveals pain on sacrococcygeal motion. This pain often radiates into the buttocks.

Depending on the history, the roentgenogram may occasionally reveal recent injury or degenerative arthritis. Fractures, when they occur, usually involve the lower part of the sacrum or first sacrococcygeal segment (Fig. 9-5). Osteoarthritis may be noted at the sacrococcygeal joint. The alignment or configuration of the sacrum or coccygeal segments visualized roentgenographically seems to have little importance in coccygodynia.

Fig. 9-5 Fracture of the lower portion of the sacrum (arrow) just above the sacrococcygeal joint.

TREATMENT

All forms of painful coccyx are treated with warm sitz baths and a soft doughnut-shaped pillow. Constipation should be avoided. Analgesics and antiinflammatory drugs are prescribed as necessary. Local injections of a steroid/lidocaine mixture are often beneficial for chronic inflammation or osteoarthritis. Because it is difficult to pinpoint the exact source of coccygeal pain in many patients, surgery is rarely indicated. The occasional patient with painful osteoarthritis or a rigid deviated coccyx who does not respond to conservative measures may benefit from coccygectomy, but even this procedure is rarely performed. Acute injuries are all treated conservatively for at least 6 months, even when significant anterior angulation of the coccyx is present.

Back and Pelvic Pain in Pregnancy

More than half of all women develop low back pain during pregnancy. It usually begins around the fifth month, and the exact cause is unknown. It is more common in multiparous patients and those with a previous history of back pain. Postpartum pain may also develop in some patients.

Several theories have been advanced to explain the pain, but much of the information regarding the problem is anecdotal. Most of them relate to changes (hormonal, vascular, and mechanical) that may occur during pregnancy. One theory suggests that lumbar spine pain develops because of the forward shift of the center of gravity with development of an increase in the lumbar lordosis. Combined with the increased pelvic tilt, this could explain the midline lumbar discomfort that occurs in many pregnant women. The development of pain does not seem to follow the distribution of weight gain during pregnancy, however, and whether lordosis increases or decreases during pregnancy is unclear. Although lumbar disc herniation is rare, disc “protrusion” may also play some role. The intervertebral joints could also be more relaxed than normal, leading to lumbar strain.

Another explanation involves the production of relaxin and the relaxation of the SI joints and the symphysis pubis. The symphysis pubis widens from a normal of 0.5 mm to a maximum of 12.0 mm after delivery. The SI joint is normally stable as a result of its broad interlocking surfaces, and most studies show that very little motion occurs at the joint. Excess pelvic relaxation and symphysiolysis may rarely lead to “instability” at the SI joint or symphysis pubis and result in inflammation, although physical tests to assess SI motion are generally unreliable.

Direct pressure by the gravid uterus may also play some role in the onset of pain, especially in late pregnancy.

A vascular cause for back pain has also been theorized. It is known that the relaxed gravid uterus can compress the aorta and vena cava. It is also known that venous return is increased at night when the dependent edema of the lower extremities returns to the vascular space at rest with the legs elevated. This could lead to some compromise of the circulation to the lumbar neural elements and produce the back and leg pain with cramping seen at night during some pregnancies.

The presence of scoliosis does not seem to have any adverse effects on the outcome of pregnancy, although some studies suggest that there may be a slight progression of the curve during pregnancy. Unless the curve is severe, it does not appear to contribute to back pain.

Episacral Lipomas

Two types of pain in the fatty tissue of the low back have been described. The most common is the tender fatty nodule in the SI area, sometimes called the episacroiliac lipoma or “back mouse.” Although it has been speculated that some fatty tissue may herniate through the normal deep fascia and become edematous and the source of pain, the significance of these nodules is highly disputed. Clinically, the patient may complain of pain in the tender nodules, which are palpable and often bilateral. The “mass” is usually palpable as a mobile soft tumor that slips beneath the examining finger. The treatment ranges from ignoring the lesion as insignificant to multiple puncturing and injection of the nodule with local anesthetic, followed by massage. Surgical removal does not seem justified because of the uncertainty regarding the significance of these lipomas.

A less common area of pain is the normal presacral fat pad. The patient is most often female, and the pain may be related to the menstrual cycle. There may even be complaints of a sense of “swelling” in the area, although none is usually present on examination. Most likely, pain in this normal fat pad is referred from elsewhere, but the cause remains obscure.

Fractures of the Pelvis

The pelvic ring is essentially a rigid circle with very little motion at the interpubic or sacroiliac areas. Fractures involving the ring are generally classified as stable or unstable (see Chapter 16). Stable fractures are those in which the ring is completely broken only at one point (for example, superior and inferior pubic ramus fractures on the same side). With unstable fractures, the ring is broken in two or more areas (for example, both pubic rami on the same side plus an SI dislocation). Stable fractures commonly result from low energy minor falls, especially in elderly, osteoporotic females. These fractures may be treated symptomatically with a short period (1 to 2 days) of rest followed by ambulation and weight bearing as tolerated, usually with a walker.

Unstable fractures (Fig. 9-6) are often serious and potentially life threatening. They may be accompanied by genitourinary or other visceral injuries. Posterior fractures in particular may damage the adjacent venous and arterial system and produce massive retroperitoneal bleeding. The initial care is therefore directed at general stabilization of the patient. The fracture usually requires prolonged immobilization and occasionally surgical repair.

Fig. 9-6 An unstable fracture of the pelvis. In addition to the fractures of the pubic bones, a sacroiliac separation is present on the ipsilateral side. Whenever displacement is present in a fracture at the pubic ramus, injury to another point in the pelvic ring is likely.

Fractures of the acetabulum occasionally involve the main weight-bearing surface of the hip joint (Fig. 9-7). Reduction, either surgically or by traction on the femur, may be needed to restore a smooth surface and prevent the development of traumatic arthritis.

Fig. 9-7 Fracture of the acetabulum (arrow). Reduction of the weight-bearing portion was able to be obtained by skeletal traction.

PELVIC INSUFFICIENCY FRACTURES

This injury is a type of stress fracture that almost exclusively occurs in older females. Stress fractures can be of two types: fatigue and insufficiency. Fatigue fractures develop when unusually high stress is applied to a normal bone. Insufficiency fractures occur in weak bone undergoing normal stress. Osteoporosis is the usual predisposing cause, but inactivity, long-term steroid use, and other types of metabolic bone disease may also play a role. The usual sites of fracture are the pubic bones, ilium, and sacrum (Fig. 9-8). Because there is usually no history of trauma, the injury is often overlooked or misinterpreted as metastatic disease. Multiple areas may even be involved. (Compression fractures of the vertebrae and femoral neck fractures may act in a similar fashion but are generally easier to recognize.)

Fig. 9-8 Insufficiency fracture of the pubic bone (arrow). The patient had recently been able to increase her walking activity following successful joint replacement. Normal weight-bearing activities had previously been limited due to arthritis, which led to the transient bony weakness.

ROENTGENOGRAPHIC FINDINGS

When the fracture involves the sacrum, it is usually vertical and may be bilateral. The findings of early resorption or late sclerosis may be easily missed because of superimposed bowel gas as well as the subtle appearance of the fracture. Iliac involvement is usually above the acetabulum.

Bone scanning is extremely sensitive for this injury as well as other similar conditions. Fractures may be detected as early as 3 days after the onset. (Scans may also remain slightly positive for 1 to 2 years.) Computed tomographic evaluation will usually allow differentiation from metastatic disease. MRI is also valuable in defining the lesion and differentiating it from tumor or sacroiliac joint disease.

TREATMENT

Only symptomatic care is needed. A walker is helpful. Pain may last several weeks.