Arthritis of the Hip



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 may help limit joint reactive forces and thus helps relieve symptoms as well. Advanced degenerative joint disease of the hip can be treated effectively with a total hip replacement.

 

 

Structure and Function

The articulating surfaces of the hip joint are the acetabulum (socket) of the pelvic 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 through the range of motion of the hip.

 

Figure 1: X-ray of a normal hip joint (left), annotated at right showing the femur (red), pelvis (purple). (Modified from Wikipedia)
 

In osteoarthritis, the articular cartilage breaks down, often for idiopathic reasons. Anatomic disturbances leading to abnormalities of joint mechanics, for example, developmental dysplasia or a slipped epiphysis, may contribute. Less commonly, osteoarthritis of the hip joint can occur following a fracture in which the joint is damaged directly, or through dislocation leading to damage to the blood supply and osteonecrosis (covered in its own chapter). Rheumatoid arthritis is caused by an autoimmune reaction against the synovium that attacks the articular cartilage as well. (Rheumatoid arthritis is discussed in the knee arthritis chapter a bit more extensively, with links there to other reading.) Arthritis of the hip is associated with obesity, which may be related to mechanical issues of loading, but a circulating systemic factor (or other unknown confounder) may be responsible.

 

While mechanical abnormalities may initiate 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 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).

 

Figure 2: Osteoarthritis of the hip. As highlighted in the annotation (below), there is joint space narrowing (the blue box show the normal joint space, with an arrow highlighting the narrow one), subchondral sclerosis (black arrow), osteophyte formation (red circle and a subchondral cyst (green box). (Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 7389)
 

 

Patient Presentation

Patients with hip osteoarthritis present with stiffness, pain, and limited active and passive range of motion.

 

An individual suffering from hip osteoarthritis 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 as a result of hip osteoarthritis.

 

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

 

Physical exam might detect obesity, a limp, lost motion and, if there is overt joint collapse, a shortening of the affected limb.

 

One characteristic limping pattern is similar to the Trendelenburg gait, classically associated with weakness of the gluteus medius and gluteus minimus muscles. With hip arthritis, the patient (without awareness) will be reluctant to use these muscles, for their action causes hip pain. This patient thus has a lurch, rocking over the affected hip, 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, then, is the sum of the body weight force and the abductor-muscle-generated force (adjusted for their “lever arm,” namely the distance from the center of the joint). If the patient, instead of trying to stand with a level pelvis, rather overshoots the straight point and lurches toward the affected side, he or she does not have to fire the abductor muscles; instead, the body simply takes advantage of the extra moment to allow the unaffected foot to make it back to the ground. In this manner, the diseased hip is spared loads it would normally experience (see Figure 3).

 

Figure 3: The antalgic gait associated with hip arthritis. In the figure at left, a person standing on one leg must generate a powerful force with the abductor muscles (orange arrow) to balance the force of body weight (shown as a red arrow), in order to keep the pelvis level (yellow line) around the fulcrum of the hip joint (pink triangle). The hip thus experiences the sum of these forces, adjusted for their distance from the hip – well in excess of body weight! A person might “elect” (subconsciously, of course) to not fire the abductors and simply lurch toward the affected side, keep the pelvis level on average (that is, tilted to one side and then the other during the gait cycle) as shown in the right panel.
 

 

Objective Evidence

A weight-bearing anterior-posterior view of the pelvis, as well as 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 osteophytes 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 scanning. MRI can 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: about 0.1% of the American population has symptomatic disease, though of varying severity. The hip is the most common location for osteoarthritis behind the knee and hand.

 

Of note, the prevalence of hip osteoarthritis is higher in Western countries, perhaps due to higher rates of obesity.

 

 

Differential Diagnosis

Hip arthritis is easily and reliably detected on radiographs. The question is whether the radiographic finding is responsible for the symptoms. One key element on the differential diagnosis list for hip-area pain is lumbar stenosis/degenerative disc disease. In general, lumbar disease does not produce groin pain and hip disease does not cause pain above the belt line – but that rule is not reliable enough to be applied universally.

 

Hip joint pain in the setting of mild radiographic changes may be due to femoroacetabular impingement or labral tears (discussed in other chapters).
 
Osteonecrosis absent a history of trauma should prompt a search for its cause or to look for other joints that may be involved, though in many times, 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 on the contralateral side suggests sacro-iliac arthrosis. That is, to be clear, 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 any evidence on imaging of knee arthritis 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 staving off 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 the joint reactive forces (see Figure 5).

 

Figure 5: The role of a cane in hip arthritis. When standing on both legs (left), body weight generates a downward force, experienced by each hip 50%. When a person stands on one leg (which must occur during gait), the force of body weight tends to tilt the pelvis downward, to the side of the leg off the ground. This is balanced by the abductor muscles, such that the total force on the hip is many times body weight (center). If a cane is used (right), the pelvis is kept level by the cane, sparing the hip of all the abductor generated force.
 

Weight loss can reduce the forces on the hip, 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.

 

Figure 6: Fluoroscopic guidance for a hip injection (the contrast medium is highlighted). (Image modified from Image-Guided Injections of the Hip. J Nov Physiother Phys Rehabil 1(1): 039-048. DOI: 10.17352/2455-5487.000008)
 

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 (see 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, of course, subject to mechanical wear and ultimate failure in the long run. 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.

 

Figure 7: Radiograph and schematic of a total hip arthroplasty. As shown in the drawing to the right, the prosthetic device consists of a femoral stem (red), neck (gray) and head (orange), as well as a metal socket for the acetabulum (purple) in which a plastic line (blue) is placed. (Modified from https://en.wikipedia.org/wiki/Hip_replacement)
 

Visco-supplementation injections, hip resurfacing surgery, arthroscopic debridement, and treatment for femoroacetabular impingement per se are all controversial, to varying degrees. These topics may be addressed in future editions of Orthopaedia, once the editors can afford better legal representation.

 


Risk Factors and Prevention

Risk factors for developing hip osteoarthritis include obesity, advanced age, genetic predisposition, developmental hip dysplasia, and hip trauma. Females are more likely to develop hip arthritis than males.

 
 

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 (like a suitcase, say) 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.