Pain in the hip is the experience of pain in the muscles or joints in the hip/ pelvic region, a condition commonly arising from any of a number of factors. Sometimes it is closely associated with lower back pain.
Causes Causes of pain around the hip joint may be intra-articular, extra-articular, or referred pain from neighboring structures, such as sacroiliac joint, spine, symphysis pubis, or the inguinal canal.
Common etiologies include:
Trochanteric bursitis, caused by inflammation of the trochanteric bursa of the outer hip, often affecting both hips Arthritis of the hip, degeneration of the hip joint from osteonecrosis, trauma, sepsis, rheumatoid arthritis, or anatomic anomalies Meralgia paresthetica, a chronic neurological disorder of the lateral femoral cutaneous nerve, most common among those who are pregnant or have diabetes Hip avascular necrosis, cell death of bone tissue in the hip joint brought on by vascular occlusion or coagulation which is the result of old age, alcoholism, trauma, decompression sickness, or several other possible causes; the treatment is often total hip replacement Occult hip fracture, a fine crack somewhere in the hip socket, common in elderly women and those with osteoporosis, usually only in one hip Snapping hip, a condition caused by iliotibial band snap, iliopsoas tendon snap, and hip labral tear, usually only in one hip; may be accompanied by an audible "snap" when the hip joint is moved Paget's disease, enlarged or deformed bones of the hip, a genetic disorder; pain is usually in both hips simultaneously Malignancy, as cancer in the pelvis or proximal femur may cause pain; usually only one hip is affected Primary septic arthritis caused by an infection within the synovial fluid of the hip, a condition rare in adults except for those who are already immunocompromised as well as those who have artificial hips; only one side of the pelvis is affected, onset of pain is rapid Transient or acute synovitis or "irritable hip", a condition most common in children, more often in boys than girls, and clearing up on its own within 7–10 days; pain is only on one side Sciatica, a condition most often brought on by damage to the L4 or L5 nerve roots but sometimes caused by inflammation or tension in the piriformis muscle of the pelvis (which rests on the sciatic nerve), in which case the condition is called piriformis syndrome; pain usually only occurs in one side but may occur in the other side at other times or (rarely) both sides simultaneously Sacroiliac joint dysfunction, an uncommon neurological condition of the mostly-immobile sacroiliac joint of the hip brought on by previous trauma to the joint such as an automobile accident; pain will usually be in only one side Radiculopathy, a nerve disorder brought on by pressure or irritation of a nerve at its root (i.e., near the spine) often resulting from degeneration of a spinal disc, joint degeneration, or osteoarthritis, among other causes
Pain in the groin, called anterior hip pain, is most often the result of osteoarthritis, osteonecrosis, occult fracture, acute synovitis, and septic arthritis; pain on the sides of the hip, called lateral hip pain, is usually caused by bursitis; pain in the buttock, called posterior or gluteal hip pain, which is the least common type of hip pain, is most often caused by sacroiliac joint dysfunction as well as sciatica (whether from a hemorrhaged spinal disk or a tense piriformis muscle). Herpes zoster (shingles) may also cause posterior hip pain.
Clinical examination
Clinical tests are adapted to identify the source of pain as intra-articular or extra-articular. The flexion-abduction-external rotation (FABER), internal range of motion with overpressure (IROP), and scour tests show sensitivity values in identifying individuals with intra-articular pathology ranging from 0.62 to 0.91.
Medical imaging Projectional radiography ("X-ray") is the first imaging technique of choice in hip pain, not only in older people with suspected osteoarthritis but also in young people without any such suspicion. In this case plain radiography allows categorization as normal hip or dysplastic hip, or with impingement signs, pincer, cam, or a combination of both.Initially largely copied from: Attribution 4.0 International (CC BY 4.0) license
Need for clinical correlation Imaging of the hip needs to be complementary to the clinical history and physical examination because it is well known that imaging findings do not always correlate with the presence of pain and vice versa.
X-Ray Projectional radiography ("X-ray") is currently useful not only in older people in whom osteoarthritis of the hip is suspected but also in younger people without osteoarthritis, who are being evaluated for femoroacetabular impingement (FAI) or hip dysplasia.
Plain radiography allows us to categorize the hip as normal or dysplastic or with impingement signs (pincer, cam, or a combination of both). Besides these, pathologic processes like osteoarthritis, inflammatory diseases, infection, or tumors can also be identified (Figure 1).
Figure 1.
X-ray in pediatrics
X-ray of infants should be obtained with the pelvis in neutral position with the lower limbs held in neutral rotation and slight flexion.
Hip dysplasia
Despite the widespread of ultrasound, pelvis X-ray is still frequently used to diagnose and/or monitor hip dysplasia or for assessing other congenital conditions or bone tumors.
The most useful lines and angles that can be drawn in the pediatric pelvis assessing DDH are as follows:
Joint effusion
Legg-Calvé-Perthes disease (LCPD) Most cases of Legg-Calvé-Perthes disease (LCPD) develop between the ages of 4 and 10 years (Figure 3). Classification of its severity can be assessed by radiographs. Herring or lateral pillar classifications and the patient’s age strongly correlate with the outcome.
In Group A, which has a better prognosis, there are no loss of height in the lateral third of the femoral head and little density changes; in Group B, there is lucency and lateral height loss of less than 50%; and in Group C, the most severe form, there is more than 50% loss of lateral height. Group B/C is considered when the loss of lateral pillar height is at 50%. People who are over the age of 8 years at the time of onset and have a hip in the lateral pillar B group or B/C border group have a better outcome with surgical treatment than they do with conservative treatment. Group B hips in children who are less than 8 years at the time of onset have a very favorable outcome unrelated to the treatment, whereas Group C hips in children of all ages usually have poor outcome unrelated to the treatment.
Slipped capital femoral epiphyses (SCFE) Slipped capital femoral epiphyses (SCFE) usually affect 11- to 14-year-old adolescents (Figure 4). Radiographs may show widening and irregularity of the physis and posterior inferior displacement of the capital femoral epiphysis. On the AP view Klein’s line, tangent to the lateral aspect of the femoral neck, does not intersect the femoral head indicating that it is displaced. SCFE may compromise the blood supply to the femoral head and cause avascular necrosis, mainly when there is instability between the fragments.
X-ray in adults
Hip dysplasia
Measurements of hip dysplasia in adults are quite different from those in children.
Osteoarthritis In adults, one of the main indications for radiographs is the detection of osteoarthritic changes (Figure 1(e)). Nevertheless, radiographs usually detect advanced osteoarthritis that can be graded according to the Tönnis classifications. The grading system ranges from 0 to 3, where 0 shows no sign of osteoarthritis. Intermediate grade 1 shows mild sclerosis of the head and acetabulum, slight joint space narrowing, and marginal osteophyte lipping. Grade 2 presents with small cysts in the femoral head or acetabulum, moderate joint space narrowing, and moderate loss of sphericity of the femoral head. Grade 3 is the severest form of osteoarthritis, which manifests as severe narrowing of the joint space, large subchondral cyst with productive bone changes that may lead to deformity of the bone components of the joint, while secondary osteoarthritis due to calcium pyrophosphate deposition can be diagnosed when calcification of hyaline cartilage and fibrocartilage is detected.
There are other pathological conditions that can affect the hip joint and radiographs help to make the appropriate diagnosis. Acute bacterial septic arthritis can be diagnosed by radiographs when a fast regional osteoporosis and destructive monoarticular process develops (Figure 1(f)). In case of tuberculous or brucella arthritis it is manifested as a slow progressive process, and diagnosis may be delayed.
Synovial chondromatosis can be confidently diagnosed by X-ray when calcified cartilaginous chondromas are seen. However, other synovial proliferative processes, such as pigmented villonodular synovitis, require MRI for accurate diagnosis, although noncalcified synovitis can be suspected in radiographs by indirect signs, such as soft tissue swelling and/or erosions in the femoral head, femoral neck, or acetabulum (Figure 7).
Figure 7:
Radiological signs of transient osteoporosis of the hip include localized osteoporosis of the femoral head and neck (Figure 8). Nevertheless, final diagnosis has to be made with MRI to differentiate it from avascular necrosis and from insufficiency or stress fractures of the femoral head or neck. In case of AVN, radiographs can only demonstrate delayed or advanced signs. Staging according to Ficat classification ranges between normal appearance (stage I), slight increased density in the femoral head (stage II), subchondral collapse of the femoral head with or without “crescent” sign (stage III), and advanced collapse with secondary osteoarthritis (stage IV). In the case of stress or insufficiency fractures X-ray sensitivity has been proven to be much lower than MRI, which is currently the gold standard.
Figure 8:
Magnetic resonance imaging Many pathological conditions of the hip are detected early by MRI due to its high soft tissue resolution and sensitivity. Its accuracy in studying acute hip pain in children has proved to be superior to ultrasound and plan film radiography. However, MRI accessibility and the need of sedation relegate its use to selected cases in which diagnosis is not clear with less demanding techniques. These include differentiating transient synovitis from a septic arthritis or osteomyelitis, diagnosis of inflammatory joint disease or bone tumors, and early detection and follow-up of Perthes disease.
MRI findings correlate with prognosis in LCPD. These include extent and distribution of epiphyseal necrosis, subchondral ossified nucleus fracture, involvement of the lateral pillar, and disturbance of physeal growth, including presence of transphyseal neovascularity or bridging.
Recent studies have been focused on the role of diffusion weighted MRI because it does not need contrast medium administration. ADC ratio of the femoral metaphysis was positively correlated with the Herring classification. ADC ratio superior to 1.63 indicates bad prognosis with 89% sensitivity and 58% specificity.
In adults, MRI is currently playing a definite role in the assessment of osteoarthritis. Although traditionally belonging to the arena of radiographs, the role of MRI has been stressed after the term femoral acetabular impingement was coined in 2003. Growing interest has been focused in accurate diagnosis of the acetabular and femoral morphological abnormalities that may lead to early osteoarthritis.
MR imaging is considered paramount to these objectives, mainly when surgery is considered, due to the ability of MRI to portray the whole section of the femoral neck surface, as well as to image the labrum and articular cartilage.