Arthritis of the hip is a progressive, degenerative condition in which the normal, smooth surface of the ball-and-socket joint connecting the femur to the pelvis breaks down, causing pain and impeding function. Osteoarthritis of the hip is associated with age, obesity, prior trauma and structural abnormalities of the joint, such as hip dysplasia or a slipped epiphysis. The joint may also be damaged by osteonecrosis or inflammatory conditions such as rheumatoid arthritis. Early arthritis can be treated with pain medications, physical therapy, and injections. A cane in the contralateral hand (opposite of the affected hip) may help limit joint reactive forces and thus help relieve symptoms as well. Severe arthritis of the hip can be effectively treated with a total hip replacement.

Structure and Function

The articulating surfaces of the hip joint are the acetabulum (socket) of the pelvis and the head of the femur (Figure 1). These surfaces are covered with a layer of articular (hyaline) cartilage which serves as a shock absorber. Articular cartilage also helps to create smooth and frictionless movement throughout the entire range of motion of the hip.

In osteoarthritis, the articular cartilage breaks down, frequently without an identifiable cause. Structural abnormalities leading to disturbances of joint mechanics, such as developmental dysplasia or a slipped epiphysis, may accelerate wear and tear. Less commonly, osteoarthritis of the hip joint can occur following a fracture in which the joint is damaged directly or through dislocation, causing damage to the blood supply and osteonecrosis. In contrast, rheumatoid arthritis is caused by an autoimmune reaction against the synovium and articular cartilage. (Rheumatoid arthritis is discussed in the knee arthritis chapter a bit more extensively.) Arthritis of the hip is associated with obesity, which may be related to mechanical issues of loading, a circulating systemic factor, or other unknown confounder.

While mechanical abnormalities may initiate the process of osteoarthritis, inflammatory mediators have been implicated in disease progression. These include cytokines and proteolytic enzymes. As such, hip osteoarthritis is often accompanied by local synovitis. Synovitis is also a primary feature of rheumatoid arthritis.

Over time, hip osteoarthritis will progress from destruction of the cartilage surface to damage involving the bone as well. Once there is extensive cartilage loss, the articulating bones may take on a smooth appearance from repetitive friction, a process called eburnation. Thickening of the bone underneath the cartilage, subchondral sclerosis, also occurs. This subchondral sclerosis represents new bone formation in response to new (abnormal) mechanical loads. Similarly, osteophytes, or bone spurs, form at the periphery of joints due to irregular bone deposition (see Figure 2).

Patient Presentation

Patients with hip osteoarthritis present with stiffness, pain, and limited active and passive range of motion, and will often report a diffuse and dull aching pain. These symptoms most commonly occur in the groin area but can also involve the buttock, thigh or even the knee. The pain is often worse with activities that require weightbearing through the hip joint, such as walking or climbing stairs.

Pain at the lateral hip is less commonly from the hip joint itself and more commonly from a greater trochanteric bursitis. Pain that radiates into the buttocks might be from lumbar disk disease or spinal stenosis, rather than because of hip osteoarthritis.

A characteristic description of stiffness is an inability to reach and tie one’s shoes.

Physical exam may be significant for obesity, a limp, lost motion, and, if there is overt joint collapse, a shortening of the affected limb.

A characteristic limp seen with hip arthritis is a rocking stride pattern, similar to the “Trendelenburg Gait” that is classically associated with weakness of the gluteus medius and gluteus minimus muscles. With hip arthritis, the muscles are functionally “weak”: the patient (often without awareness) will be reluctant to use these muscles, as their action would load the joint and cause hip pain. Instead, they have a lurch, rocking over the affected hip, just as if there were weakness of these abductor muscles. This is termed an “antalgic gait,” namely, an alteration to the normal pattern of walking is response to (“ant”) pain (“algia”). In brief, when a person is standing on one leg, the body’s center of gravity tends to force rotation around the hip of the leg on the ground (pelvic tilt). To combat this tilt, the abductor muscles generate a powerful, countervailing force to keep the pelvis level. The net force on the hip is the sum of the body weight force and the abductor-muscle-generated force (adjusted for their “lever arm,” the distance from the center of the joint). If the patient, instead of trying to stand with a level pelvis, overshoots the straight point and lurches toward the affected side, they do not have to fire the abductor muscles; instead, the body simply takes advantage of the extra time to allow the unaffected foot to make it back to the ground. In this manner, the diseased hip is spared loads that it would normally experience (see Figure 3).

Objective Evidence

A weight-bearing anterior-posterior view of the pelvis, along with a lateral view of the hip, can confirm the diagnosis of hip osteoarthritis (as shown above in Figure 2).

Hip osteoarthritis is categorized based on the severity or stage of the disease. The stages are defined by the degree of joint space narrowing, sclerosis, and osteophyte formation.

When diagnosing hip osteoarthritis, it is useful to obtain radiographs of both hips as the disease often occurs on both sides. Of note, not all patients with significant radiographic findings will present with significant hip pain. Likewise, patients can have severe hip pain without much arthritis on imaging, though in that case the diagnosis is much less likely to be arthritis!

Usually, there is no role for MRI or CT scans. MRI can be used to look for other conditions if the diagnosis of arthritis is not certain. CT scanning may be helpful for pre-operative planning in some instances.

There are no laboratory tests for osteoarthritis, but testing may be performed to exclude other diagnoses. Laboratory findings that may be helpful for suspected rheumatoid arthritis include an elevated rheumatoid factor or antibodies against cyclic citrullinated peptides. Elevated values for c-reactive protein and erythrocyte sedimentation rate are common but not specific.

Epidemiology

Hip osteoarthritis is very common; Approximately 0.1% of the American population has symptomatic disease, though of varying severity. The hip is the most common location for osteoarthritis after the knee and hand, respectively.

Of note, the prevalence of hip osteoarthritis is higher in Western countries, perhaps due to higher rates of obesity. Osteoarthritis is likewise more prevalent among females.

The prevalence of osteoarthritis increases with age, as would be expected with a degenerative condition.

Differential Diagnosis

Hip arthritis is easily and reliably detected on radiographs. The question, however, is whether the radiographic finding is responsible for the symptoms.

A key element on the differential diagnosis list for hip-area pain is lumbar stenosis or degenerative disc disease. In general, lumbar disease does not produce groin pain and hip disease does not cause pain above the belt line; nonetheless, that rule is not reliable enough to be applied universally.

Hip pain in the setting of mild radiographic changes may be due to femoroacetabular impingement or labral tears (discussed in other chapters). Osteonecrosis without a history of trauma should prompt a search for its cause or for other joints that may be involved, though often no such cause will be found, and no other joints will be diseased. Pain coming from the sacro-iliac joint can be detected with the FABER test. This test is named according to the position of the hip, namely Flexion, ABduction and External Rotation. As shown in Figure 4, the patient’s hip is flexed, abducted and external rotated while the leg is pressed toward pelvis. The test is positive if pain is reported, but the location of the pain is important: anterior groin pain suggests hip arthritis; posterior groin pain on the contralateral side suggests sacro-iliac arthrosis. Therefore, this test should be performed bilaterally, as the FABER tests the left hip but the right sacro-iliac joint, and vice versa.

Figure 4: The FABER test. The patient’s hip is placed in flexed and abducted position, with the ankle resting on the contralateral leg, placing the hip in external rotation as well. The examiner uses the upper hand to stabilize the pelvis and then gently presses the affected leg toward pelvis with a force on the knee.

Red Flags

Knee pain suggesting knee arthritis without evidence on imaging may represent hip arthritis that is radiating to the knee joint.

Rheumatoid arthritis is a systemic disease, and thus discovering it in one joint should prompt a complete exam (with hopes of mitigating disease in other joints or non-musculoskeletal organ systems).

Treatment Options and Outcomes

Therapy to strengthen both hip and core (abdominal) muscles can be helpful for pain control and to increase function. Pain medications such non-steroidals (NSAIDs) and Tylenol can also relieve symptoms.

A cane in the contralateral hip can reduce reactive forces on the joint (see Figure 5).

Weight loss can reduce the forces on the hip joint, relieve symptoms and perhaps delay disease progression. Enduring weight loss is easy to recommend, but difficult to achieve.

Cortisone injections can be administered into the hip joint to reduce inflammation and pain. The joint is not reliably accessed by surface anatomic landmarks alone and thus fluoroscopy (see Figure 6) or ultrasonography can be used for guidance.

Operative Treatment

Operative treatment for hip arthritis is most often considered when patients have disabling symptoms that cannot be adequately addressed with non-operative management.

The most common procedure used to treat end-stage hip arthritis is a total hip arthroplasty (Figure 7). In a total hip arthroplasty, both the acetabulum and femoral head are replaced with prosthetic implants. This is a highly effective procedure but is associated with significant perioperative complications in about 1% of cases, and is, subject to mechanical wear and ultimate failure in the long term. Given how well patients do with this operation, older procedures such joint fusion (arthrodesis) are very rarely performed, even in younger patients who hope to be active.

Visco-supplementation injections, hip resurfacing surgery, arthroscopic debridement, and treatment for femoroacetabular impingement are controversial to varying degrees. These topics may be addressed in future editions of Orthopaedia if and when the controversies subside.

Risk Factors and Prevention

Risk factors for developing hip osteoarthritis include obesity, advanced age, genetic predisposition, developmental hip dysplasia, and hip trauma.

Miscellany

A patient with arthritis of the right hip would use a cane in the left hand, as described above. Perhaps counter to intuition, for the same reason, that person should prefer to carry a heavy load (i.e., a suitcase) in the right hand. If carried in the left, there would be even more tilting force (body weight and the load) that would have to be balanced by the abductors.

Key Terms

Hip osteoarthritis, degenerative joint disease, total hip replacement, hip arthroplasty

Skills

Recognize arthritis on imaging. Perform a reliable history and physical on patients with hip pain.