The anterior quadrant contains the anterior joint recess, iliopsoas tendon, rectus femoris, sartorius, and tensor fascia lata (TFL). (Examination of groin hernias is covered in the hernia section.) The examination is performed with the patient supine and transverse (TS) and longitudinal (LS) images are obtained (Fig. 6.1). The anterior joint recess is evaluated with the probe aligned obliquely along the femoral neck to look for the presence of an effusion or large anterior labral injury in the normally hyperechoic labrum. The hyperechoic iliofemoral ligament can sometimes be seen overlying the anterior capsule (Fig. 6.2A).

The iliopsoas muscle is scanned in true longitudinal and transverse views (Figs. 6.2 and 6.3). It lies superficial to the capsule and lateral to the femoral neurovascular bundle. The hyperechoic iliopsoas tendon lies on the deep and medial aspect of the muscle and inserts distally on the lesser trochanter. The iliopsoas bursa lies between the anterior joint capsule and tendon, but is not seen unless bursitis or fluid are present. Superficial to iliopsoas is sartorius, which can be traced distally from the anterior superior iliac spine (ASIS). Tensor fascia lata is superficial and lateral and also originates from the ASIS and iliac crest (Fig. 6.3). The TFL courses laterally to blend into the anterior aspect of the fascia lata. Superficial and medial to iliopsoas is rectus femoris, which originates from the anterior inferior iliac spine (AIIS). Longitudinal views of these muscles and tendons should be performed when evaluating for tendinopathy and muscle tears.

For anatomical purposes these two quadrants are considered together. They incorporate the gluteal muscles and tendons. The hamstring origins and sciatic nerve will also be considered here.

For gluteal assessment, the patient is initially scanned in the lateral decubitus position with a high-frequency probe. Gluteus medius (deep) and gluteus minimus (superficial) can be traced cranially down to the greater trochanter in both long-axis and short-axis scans (Fig. 6.4). The TFL is adjacent to the anterior margins of these two muscles, and gluteus maximus overlies the posterior portion of gluteus medius. The echogenic tendons of gluteus minimus and medius insert into the anterior and lateral aspects of the greater trochanter, respectively. Long-axis and short-axis scans should be performed to detect tendinopathy and evidence of bursitis between the tendons and trochanter.

Evaluation of the hamstring origins is performed with the patient prone with the feet hanging over the end of the couch. Lower frequency probes may be required for larger patients. The ischial tuberosity is first identified, located medially at the junction of buttock and thigh (Fig. 6.5). The origin of the ischiocrural tendons (semimembranosus, long head of biceps femoris, and semitendinosus) attaches laterally (Fig. 6.6). They cannot always be appreciated separately at this level on
ultrasound, but individual tendons can be identified by tracing them caudally. They initially separate into the semimembranosus tendon (medial) and the conjoined tendon of semitendinosus and the long head of biceps femoris (superficial and lateral). The conjoined tendon then further divides into the muscle bellies of semitendinosus (medial) and biceps femoris (lateral). Evaluate them in longitudinal and transverse planes to assess for tendinopathy (Fig. 6.7). Lateral to the ischiocrural tendon origin, the sciatic nerve has the characteristic neural fascicular pattern (Fig. 6.6).

This quadrant contains the origins of the adductor muscles: longus, brevis, and magnus along with gracilis and the insertion of iliopsoas. The patient is scanned in the supine position with the thigh abducted and externally rotated and the knee flexed (Fig. 6.8). The insertion of iliopsoas can be best assessed in this position using LS views, as anisotropy is a common problem, with the leg in the adducted position.

Place the probe over the anterior aspect of the medial muscle compartment, medial to the neurovascular bundle to reveal the three adductor muscles separated by hyperechoic fascial planes (Fig. 6.9). Adductor longus is anterior, adductor brevis is intermediate, and adductor magnus lies posterior. Gracilis is found medial to adductor longus and superficial to adductor brevis. The muscles can be traced to their origin at the pubis to evaluate for tendinopathy and muscle tears using LS and TS views. Next, assess the
symphysis pubis joint space, found medial to the adductor insertion, for arthropathic changes (Fig. 6.10).

Hematological seeding during bacteremia is the most common cause of septic arthritis, most often due to Staphylococcus aureus.³ Risk factors include IV drug abuse, endocarditis, indwelling catheters, advanced age, immunosuppression, and preexisting joint injuries.⁵ Other causes include adjacent surgery or direct extension of infection from the abdomen via iliopsoas. Rapid diagnosis is vital as delay worsens the prognosis.³ Bacterial arthritis results in irreversible loss of joint function in 25% to 50% of patients and 5% to 15% fatality rates.⁶ The appearances of the effusion in terms of complexity and echogenicity do not predict infectious or inflammatory nature.⁷ Ultrasound cannot prove sepsis and if suspected, analysis of aspirated fluid is usually required. However, large joint effusions with extra-articular extension in painful prosthetic hips are strongly associated with infection.⁸

Inflammatory arthritides, both seropositive and seronegative, cause hip effusions. Immunosuppressive treatment increases the risk of avascular necrosis and infection, which themselves cause effusions. Increased synovial power Doppler flow suggests an inflammatory rather than noninflammatory cause, but does not differentiate between types of inflammation, for example, infective or noninfective.⁹ Marginal erosions may rarely be seen at the bone-cartilage interface at the femoral head and neck in inflammatory arthropathy.

Benign tumors of bone and soft tissue, including synovial osteochondromatosis, pigmented villonodular synovitis, osteoid osteoma, and giant cell tumors of bone can be associated with hip effusions.¹⁰ Effusions in association with malignant tumors of bone may indicate joint involvement or be a consequence of underlying pathological fracture, but MRI and plain radiographs provide the optimum method of assessment.

Effusions can occur in osteoarthritis. Synovitis and debris in the joint and underlying osteonecrosis may occur.¹⁰ Osteophytes at the femoral head/neck junction can also be demonstrated, but are better shown on plain radiographs, computed tomography (CT), and MRI.¹

For clinically suspected fracture not confirmed by radiographs, MRI is the investigation of choice. Ultrasound is not very sensitive or specific in these cases, but may occasionally show a femoral neck fracture. In addition to the resulting hip effusion/hemarthrosis, the fracture may be seen as a step or breach of the hyperechoic cortex.¹ An osteochondral injury could also result in effusion, but would not itself be visible on ultrasound.

Postsurgical complications such as infection, aseptic loosening, or wear debris can all result in effusion. Ultrasound appearances of hip replacement will be discussed later in the chapter.

An effusion appears as a hypoechoic layer between the hyperechoic bone cortex of the femoral neck and the
overlying psoas muscle, extending along the anterior recess on the femoral neck (Fig. 6.11). The optimal probe position is an oblique longitudinal scan along the femoral neck. Hip joint effusions as small as 1 to 2 mL may be identified,¹¹ although small effusions may “disappear” into the posterior recess and become undetectable on ultrasound.

Effusion can be difficult to distinguish from the synovial thickening. Under normal circumstances, synovium is not visible on ultrasound, and the fibrous layer is a thin hyperechoic band (Fig. 6.11). Aging, degenerative disease, synovitis, and surgery can result in thickening of the synovial layer or joint capsule, and this may be mistaken for an effusion (Fig. 6.12).

It is important to be aware that other pathologies may mimic effusions on USS.

In the early postoperative period, a hypoechoic track extending from the skin incision to the hip represents
the path of surgical access. Collections may routinely be identified along this path or around the prosthetic joint or the femur. The surface of the prosthesis is highly echogenic, more so than normal bone cortex, and may generate reverberation artifact (Fig. 6.12). A study of 47 postoperative hips at the second and fifth postoperative day concluded that a bone-to-capsule thickness of up to 6 mm, deep soft tissue fluid collections up to 21 mm, and superficial collections up to 28 mm were all considered to be normal.¹⁶ Communication with the joint is an important distinction that is usually demonstrable by ultrasound, though it may be more readily demonstrated by arthrography.¹⁹

Subsequently, thickening of the joint capsule may be seen due to fibrosis and previous hemorrhage¹⁰ (Fig. 6.12). Effusions and extra-articular collections are not normal after the first few weeks (Fig. 6.13D).