Applied Anatomy
The low back, sacroiliac joint, and hip joints can all cause pain in a similar anatomic distribution, and each must be considered in the evaluation of a patient with complaints of pain in the region of the lower back, buttock, groin, or knee. Pain from the hip joint is poorly localized and may be felt in the groin, inner thigh, trochanteric area, buttock, anterior thigh, and/or knee.
The morphology of the sacroiliac (SI) joint varies considerably with age, among individuals, and even from side to side in the same individual. It represents the largest paraxial joint, with a surface area of more than 17 cm 2 in adults. The anteroinferior ventral part of the SI joint is synovial, whereas the posterosuperior part is a fibrous joint supported by powerful ligaments. The joint is surrounded by a thin capsule that may be absent posteriorly. Little movement occurs at the SI joint ( Figure 5-1 ; see also Figure 8-6 in Chapter 8 ). The SI joint is innervated by the L5 and S1 through S4 nerve roots.
HIP JOINT
The hip joint is a ball-and-socket, weight-bearing articulation that combines a wide range of motion (ROM) with considerable stability. The stability of the joint depends on the deep insertion of the femoral head into the acetabular socket, the strong capsule and ligaments, the powerful muscles surrounding the joints, and the circular fibrocartilaginous acetabular labrum. The latter forms a tight ring around the femoral head. The capsule is attached proximally to the edge of the acetabulum, acetabular labrum, and transverse ligament, which bridges the acetabular notch inferiorly. Distally, the capsule is attached to the intertrochanteric line anteriorly and to the femoral neck about 1.5 cm proximal to the intertrochanteric crest posteriorly. It follows, therefore, that a large part of the femoral neck is intracapsular.
The anterior capsule is reinforced by the powerful Y-shaped iliofemoral ligament, which prevents excessive hip extension and external rotation ( Figure 5-2 ). The weaker posterior capsule is reinforced by the thinner ischiofemoral ligament, which prevents excessive external rotation, and the pubofemoral ligament, which opposes excessive hip abduction ( see Figure 5-2 ). The ligamentum femoris teres —which is a channel for blood vessels to the femoral head, is located between the pit of the femoral head and the transverse ligament of the acetabulum. It provides little stability but nourishes a small area of the femoral head adjacent to the attachment of the ligament. Therefore, dislocation of the femoral head from the acetabulum is resisted primarily by the acetabular labrum and by the strong hip joint capsule, which incorporates the capsular Y ligament (see Figure 5-2 ). The fibers of the hip joint capsule are wound around the femoral neck so as to tighten with hip extension and internal rotation ( Figure 5-3 ). The position is uncomfortable for patients with hip arthritis because of tension on the capsular structures. The intracapsular space of the hip joint is smallest with the hip in extension and internal rotation, a position that produces maximum tension on the capsular Y ligament. Consequently, patients with inflammation of the hip joint often hold the extremity flexed and externally rotated as a position of relative comfort.
The iliotibial band is a thickened band in the fascia lata that connects the iliac crest to the Gerdy tubercle. It is attached to the entire length of the intermuscular septum between the vastus lateralis and the hamstring muscles over the greater trochanter. It is a mechanical tie between the iliac crest, sacrum, and ischial tuberosity proximally and between the lateral femoral and tibial condyles, particularly to the Gerdy tubercle on the anterolateral aspect of the proximal tibia, and the head of the fibula distally.
The synovial membrane lines the inner surface of the capsule and covers the acetabular labrum, ligamentum femoris teres, and parts of the femoral neck. There are three main bursae around the hip joint. The trochanteric bursa is the largest. It is a multiloculated bursa between the gluteus maximus and the greater trochanter. The ischiogluteal bursa lies between the gluteus maximus and ischial tuberosity. The gluteus maximus covers the ischial tuberosity in the neutral position, but with hip flexion, both the tuberosity and the bursa become uncovered. The iliopectineal bursa lies in the middle third of the inguinal region, between the iliofemoral and pubofemoral ligaments; in relation to the iliopsoas muscle and tendon, it lies just lateral to the femoral artery. The bursa communicates with the hip joint in about 15% of adults, and in patients with hip arthritis, it can manifest as a fluid-distended, cystic swelling in the groin.
Having the femoral head situated in an offset position on the femoral shaft, through the femoral neck, minimizes bony impingement and maximizes normal hip ROM. It does, however, require strong muscular support to stabilize the trunk over the hip joints, especially in single-leg stance phase, when the body’s center of gravity is medial to the supporting leg. One can consider the hip joint as a fulcrum for a lever, with the body’s center of gravity acting approximately 1 cm anterior to the first sacral segment in the midline ( Figure 5-4 ). To counteract this load, the gluteus medius and minimus act in conjunction with the tensor fascia lata and gluteus maximus muscles, which function mainly through their insertion into the iliotibial band. Given the fact that the distance is twice as far to the center of gravity as it is to the gluteus insertion into the proximal femur, a force approximately equal to three times body weight is transmitted through the hip joint during single-leg stance, compared with one half of the body weight during normal bilateral stance ( Figure 5-5 ).
On anteroposterior radiographs of the hip, the normal femoral neck–shaft angle in an adult is 120° to 135°. In coxa vara the angle is less than 120°; in coxa valga, the angle is greater than 135°.
Hip Pain and History Taking
Patients who complain of hip pain often mean very different things, from pain in the lower back or buttock region to groin pain or thigh pain. Patients with true hip joint disease will classically complain of pain in the groin region, although this varies depending on the type of hip pathology. Pain typically radiates down toward the anterior aspect of the knee. Individuals who are experiencing pain on the lateral aspect of the hip, in the region of the greater trochanter, or pain in the lower back or in the buttock area may also complain of hip pain. To determine what the patient’s complaint of “hip pain” really means, it is essential to ask the patient to describe exactly where the pain is primarily located and where it radiates. Other than pain, the patient may complain of limited function, stiffness, limping, and audible or palpable clicking or snapping noises about the hip. As with any history, it is important to delineate the onset of these symptoms, their severity, whether they were preceded by injury or overuse, and whether there are any constitutional or systemic symptoms. Inflammatory arthritis generally affects multiple joints, and although the hip may be the presenting problem, it is important to inquire about similar symptoms in any other joints. It is essential to inquire about childhood hip problems, previous injuries, and the nature of any previous hip or spinal operations.
Symptoms in this region may originate from the hip or from the spine, SI joint, or soft tissues surrounding the hip, or it may be referred from a remote site. Occasionally a patient complains only of pain that is deep-seated about the knee joint, and the underlying hip pathology may be missed if the examination concentrates solely on the knee. As part of the physical examination, it is essential to evaluate other regions that may be the source of referred pain. Typically, the joint above and below an area that a patient is complaining about should be examined. For the hip joint this requires that the lower back and sacroiliac region, as well as the knee joint, be evaluated.
It is also useful to assess the magnitude of functional impairment and disability and the severity of the pain. This can be done using validated pain scales and functional measurement instruments, such as the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index. A clear understanding of the patient’s occupational, sports, recreational, and social activities and how the hip problem affects the patient’s quality of life is essential to the consideration of how a potential treatment might be planned so as to optimize patient function in light of the individual’s unique needs.
Based on the patient’s history, the clinician will generally have some idea what is generating the patient’s hip pain. A full hip examination should be performed along with examination of the knee and the back. A good history can guide the clinician toward the appropriate special tests on physical examination that will help accurately diagnose the patient’s problem. For example, if the patient tells you that the focus of their pain is in the lateral aspect of the hip, it will be important to palpate the greater trochanter for tenderness, looking for signs of trochanteric bursitis.
Common Painful Disorders of the Hip Region
OSTEOARTHRITIS AND INFLAMMATORY HIP ARTHRITIS
Hip arthritis typically causes pain in the groin or low buttock area, with possible radiation into the knee. The pain in osteoarthritis is generally worse with activity and is relieved by rest. In inflammatory arthritis, the patient may experience stiffness with inactivity and some improvement of this symptom with movement of the hip joint. Some patients experience very little pain but complain of stiffness, limping, and functional decline. The onset of pain and functional decline can be quite insidious, occurring over many years. Some patients consider these progressive symptoms to represent part of normal aging and do not seek help until quite late in the disease process. Functionally, the combination of stiffness and pain leads to complaints of a limp, difficulty getting up out of low chairs, difficulty descending and ascending stairs (requiring 36° and 67° of flexion respectively), inability to squat (120° of flexion, 20° of abduction, and 20° of hip external rotation required), and trouble with daily activities, such as putting on socks and shoes.
Physical findings may include a combined Trendelenburg and antalgic gait, actual or functional shortening of the limb due to collapse of the hip joint, and soft-tissue contractures around the hip joint. Early hip joint arthritis is associated with pain on hip extension and internal rotation, as the capsule tightens, and early loss of internal rotation in flexion and extension. Fixed flexion deformity and limited abduction and adduction are common with more advanced disease.
TROCHANTERIC BURSITIS
This condition is extremely common. The greater trochanteric bursa may become inflamed due to direct trauma or overuse with strenuous physical activity, such as running or jumping. A tight iliotibial tract, with a positive Ober test, may be present. The inflamed bursa becomes painful with activities that compress it between the greater trochanter and the overlying iliotibial band. Patients may be unable to lie on the affected side, and they usually experience pain with weight bearing, especially in a single-leg stance, as the iliotibial band tightens to maintain the body’s upright posture. Tenderness over the greater trochanter with direct palpation and pain with resisted hip abduction are typical physical findings. A fluid-distended bursa associated with a palpable fluctuant swelling may be palpated on rare occasions in a thin patient.
SNAPPING HIP (COXA SALTANS)
Young patients may present with complaints of snapping or clicking about the hip. Some may believe that the hip is dislocating, which is highly unlikely without significant trauma or underlying hip joint arthroplasty. Snapping or clicking about the hip can be caused by intraarticular pathology or by causes external to the hip joint. Intraarticular causes include loose bodies (synovial chondromatosis, fracture fragments, broken-off osteophytes), labrum tears, and, rarely, a true subluxing hip joint, especially after total hip replacement surgery. Intraarticular clicking caused by loose bodies may be intermittent and can sometimes be demonstrated during active and passive ROM testing. If a labrum tear is suspected, internal rotation of the flexed hip in adduction with axial compression may cause pain. Extraarticular causes are far more common; they include sliding of the iliotibial band or fibers of the gluteus maximus muscle over the greater trochanter and, less commonly, snapping of the iliopsoas tendon over the femoral head. Generalized ligamentous laxity is a common finding in these individuals. The patient can often demonstrate the clicking voluntarily by active movement of the hip, and the underlying snapping or clicking can often be felt laterally over the greater trochanter, as the iliotibial band snaps back and forth. Palpable, and sometimes audible, medial clicking from the iliopsoas tendon is best demonstrated during active hip flexion and external rotation, followed by active hip extension.
PERIARTICULAR FRACTURE
A displaced hip fracture through the subcapital or intertrochanteric region is a dramatic event that results in sudden severe pain and inability to bear weight or to move the affected hip. Most acetabular or pelvic fractures are the result of high-energy trauma with an equally dramatic presentation that allows ready diagnosis of the problem.
A fall in an elderly patient can lead to complaints of hip pain that may be due simply to soft-tissue injury, stable lateral compression pelvic fracture, undisplaced subcapital hip fracture, or a fracture of the acetabular dome region. These fractures, especially acetabular dome fractures, are easily missed, even on plain radiographs. Careful physical examination and a high index of suspicion should lead to appropriate investigations, such as a CT scan, that can help to confirm the diagnosis. Usually the history involves a low-energy traumatic event, but in the case of a fragility fracture through osteoporotic bone, there may be no history of trauma whatsoever. The patient may have difficulty bearing weight on the affected extremity, but in some cases, patients have been known to walk on a fractured hip for many weeks before the diagnosis is made.
Physical examination may reveal bruising and tenderness over the greater trochanter, suggesting local trauma. With undisplaced or minimally displaced subcapital hip fractures, the findings may be quite subtle: limb shortening; external rotation deformity; pain on internal rotation, which tightens the capsule; global reduction in ROM due to pain; and, often, difficulty initiating a straight leg lift (inability to lift the heel of the extended lower extremity off the examining table because of the forces generated across the hip joint during this activity). Striking the heel of the extended leg with the examiner’s fist is usually quite painful in the presence of a subcapital or acetabular dome fracture, but this maneuver typically does not cause pain with soft-tissue bruising, because the involved soft tissues are not moved or stretched. To look for possible subcapital femoral neck fractures, the proximal femur should be imaged in the anteroposterior plane with the hip in internal rotation to better visualize the entire length of the femoral neck (considering that the femoral neck is anteverted relative to the femoral shaft). A lateral radiograph of the proximal femur should also be obtained and assessed for fracture angulation. Stable compression pelvic fractures can be diagnosed by tenderness to palpation anteriorly along the pubic ramus and posteriorly along the sacrum and SI region. Compressing the pelvis by pushing the two iliac crests together usually increases pelvic pain.
Plain radiographs of the pelvis, including inlet and outlet views, are required to confirm the examiner’s suspicion of a lateral compression pelvic fracture. If plain radiographs do not show evidence of proximal femoral or pelvic fracture, and suspicion for a significant bony injury remains, a CT scan of the acetabular dome and proximal femur should be obtained, because plain films usually do not reveal the presence of an acetabular dome fracture.
SACROILIAC JOINT PAIN
Inflammation of the SI joint (sacroiliitis) can be the source of buttock and upper thigh pain. This is seen classically as ankylosing spondylitis and the other seronegative spondyloarthropathies. The combination of maximal pain below L5 plus pain in the region of the posterior superior iliac spine (PSIS) and tenderness in the sacral sulcus region has a positive predictive value of 60%. The classic feature of sacroiliitis on history is that the back pain is improved with activity and exacerbated by rest. This pain will usually waken a patient from sleep at night. SI imaging, plain films, or MRI can be used for definitive evaluation of the SI joint. On physical examination it will be important to stress the SI joint with a flexion abduction external rotation (FABER) test.
OSTEITIS PUBIS
Pain in the region of the anterior pelvis due to inflammation and erosive lesions of the symphysis pubis, or osteitis pubis, is an uncommon disorder of diverse causes that include spondyloarthropathies, trauma, infection, distance running, and multiple deliveries. The condition is characterized by insidious-onset midline anterior pain that may radiate to either groin. The pain is exacerbated by passive abduction and resisted adduction of the hip, and tenderness is found on palpation over the anterior border of the symphysis pubis and adjacent pubic rami; exacerbation with pelvic internal and external stress is also seen.
CONSIDERATIONS IN PATIENTS AFTER TOTAL HIP REPLACEMENT
Safety Considerations
Special care should be taken when evaluating the hip joint of a patient who has previously undergone total hip replacement. In the early postoperative period, the clinician should ask patients whether their surgeon has informed them of any specific restrictions. For example, hip revision surgery may involve compromise to the hip abductor muscles, and active hip abduction may be contraindicated in the early postoperative period. Similarly, patients may be instructed to avoid weight bearing during the initial 6 weeks after complex revision hip reconstructive surgery and occasionally after uncemented or complicated primary hip replacement surgery. Hip precautions in the early postoperative period are meant to minimize the risk of hip dislocation, although with the newer surgical techniques, these restrictions are being relaxed. The restrictions involve limiting hip flexion beyond 90°, internal rotation of the hip in flexion, external rotation of the hip in extension, and hip adduction beyond the midline. When testing ROM, the risk of anterior dislocation of the hip is greatest with the hip in extension, adduction, and external rotation. The risk of posterior dislocation is greatest when the hip is flexed, internally rotated, and adducted.
Leg Lengths
In the early postoperative period after total hip replacement surgery, the clinician should be careful with respect to the evaluation of leg lengths. Hip arthritis is commonly associated with joint collapse, fixed flexion deformity, and adductor tendon contraction that leads to significant functional shortening of the involved lower extremity. The limb may initially appear functionally long to the patient after surgery, given the correction of the deformity that is achieved intraoperatively. Residual soft-tissue contractures about the ipsilateral or contralateral hip, or pelvic tilt secondary to degenerative scoliosis, may also give the patient the perception of having a relatively short or long lower limb after surgery. Even if a small, true leg-length discrepancy is discovered after careful examination, it may be best to wait for at least 6 months after hip replacement surgery before recommending corrective shoe raises or inserts. This time frame allows for some contractures to resolve, and many patients will no longer require leg-length adjustment.
Pain after Total Hip Arthroplasty
Although a comprehensive review of the evaluation of the painful total hip replacement is beyond the scope of this chapter, the following possible causes are considered.
MECHANICAL FAILURE
Hip dislocation and periprosthetic femur or acetabular fracture typically result in severe functional impairment, usually with complete inability to walk, severe pain, and often characteristic deformity. The emergency management of these conditions is similar to that for a traumatic hip joint dislocation or femur fracture and includes a thorough neurovascular examination.
INSTABILITY OF THE ARTICULATION
Complete dislocation can be associated with spontaneous reduction. The patient may recall sudden groin pain, sometimes associated with a “clunking” sound or sensation. Anterior subluxation commonly occurs when the ipsilateral leg is planted on the ground, and the upper body rotates to the opposite side, resulting in relative extension and external rotation, often also with adduction, of the ipsilateral hip. Typically, the anteriorly dislocated hip lies in an abducted and externally rotated position. Posterior subluxation is more common and can occur while the patient is lying in bed on the opposite side with the ipsilateral hip flexed, adducted, and externally rotated. Typically, the posteriorly dislocated hip lies in an adducted and internally rotated position. A “push-pull” test can be safely performed to assess the soft-tissue tension around an artificial hip joint. This involves stabilizing the pelvis and placing the hip in extension, neutral rotation, and abduction. The examiner attempts to distract the hip joint by applying a traction force to the limb and then pushing it back into place. Very little movement should be detectable through the hip joint.
IMPLANT LOOSENING AND INFECTION
Loosening of the implant–bone interface may be associated with pain. Important causes of loosening include traumatic mechanisms, osteolysis due to implant wear, and infection. The examiner should inquire about recent falls or other injuries and the relationship of these events to the onset of pain. Information regarding how long the hip replacement has been in situ can provide clues regarding the possibility of implant wear. Finally, potential sources of infection and its systemic manifestations should be sought. Low-grade infections may go undetected for many months before implant loosening or systemic manifestations are noted. Typically, pain due to infection is always present and is not relieved with rest, whereas mechanical loosening may result in intermittent pain, usually with activity. Pain in the groin region is more commonly associated with acetabular implant problems, including loosening or impingement, and thigh pain is more commonly seen with loosening of the femoral component. When the patient is arising from a low chair, a considerable force is placed on the femoral component, which may rotate slightly when loose and cause pain.
BURSITIS
Trochanteric bursitis is common after total hip replacement surgery, especially with lateral approaches that involve dissection of the soft tissues from the greater trochanter during surgery. Symptoms include pain with single-leg stance and with active hip abduction and discomfort when lying on the ipsilateral side. The trochanter is tender to palpation.
TENDINITIS AND CONTRACTURES OF TENDONS AND MUSCLES
Before hip replacement surgery, contractures may have formed in the soft tissues around the hip as a consequence of arthritis-related joint stiffness. These muscles and tendons may become painful as a consequence of increased ROM and tension on the structures after successful joint replacement surgery that allows greater ROM. The hip abductors and flexors are most commonly affected. The patient may complain of a deep anteromedial or medial pain that is worse with active hip flexion or active adduction. Tenderness should be evaluated over specific tendons, although the iliopsoas tendon usually cannot be palpated because of its deep insertion. Pain with active contraction of the affected tendon–muscle unit and pain with passive stretch are consistent with the diagnosis of tendinitis.
REFERRED AND UNRELATED PAIN
Patients with degenerative hip arthritis commonly also have lumbosacral spine arthritis. Persistent buttock and thigh pain may be referred from the lower spine or the SI joint. These patients may not manifest any signs of nerve root irritation. Other unrelated sources of pain may include groin hernias, peripheral vascular disease, meralgia paraesthetica, and metabolic disease such as Paget disease.
Physical Examination
Patient evaluation is not a linear process but involves a constant reevaluation of clinical evidence gained from the history and physical assessment. It is impossible to record the specific order of evaluation that an experienced clinician might pursue, because it depends entirely on the unique presentation of the particular patient. By convention, the physical examination is presented as inspection, palpation, movement, and special tests. However, an experienced clinician moves fluidly back and forth through these evaluation modalities, gathering essential information and perhaps also asking additional questions as new evidence emerges. The clinician should have some knowledge as to the sensitivity and specificity of the clinical evaluation maneuvers being performed, so that the most useful tests are considered first. Another basic principle is to minimize patient change in position as much as possible, especially in a patient with significant discomfort or difficulty during movement. Therefore, while the patient is standing, all relevant examinations requiring this posture might be undertaken before the patient is asked to lie on the examining table. Then, all tests that require the supine position are done before the patient is asked to move to the lateral decubitus position and, finally, to the prone position.
INSPECTION
The evaluation requires that the patient be undressed down to shorts or underwear, including removal of shoes and socks. One should consider having a family member or a health care professional of the same gender present during the examination, especially if the patient seems ill at ease.
Inspection always begins with an evaluation of the patient as a whole, or a general inspection. Are there clues as to the presence of a chronic systemic condition, such as rheumatoid arthritis? Is the patient generally fit in appearance, or is he or she above ideal body weight for height? Localized inspection involves an assessment of the following:
- 1.
Skin and superficial tissues: Skin incisions or scars should be explained, and any relationship to the current symptoms should be explored. Skin discoloration, ulceration, and distal hair loss may be associated with vascular insufficiency. Characteristic psoriatic skin and nail lesions are helpful clues.
- 2.
Deep tissue: Evaluation should include the subcutaneous tissues and muscles. Asymmetric swelling over one greater trochanter may be associated with underlying trochanteric bursitis. An abdominal pannus (apron) may cause meralgia paraesthetica, a condition in which the lateral femoral cutaneous nerve becomes compressed as it runs beneath the lateral end of the inguinal ligament, resulting in pain and numbness in the proximal lateral thigh. A cystic swelling in the middle third of the inguinal region may represent a fluid-distended, communicating iliopectineal bursa. Disuse atrophy of the proximal quadriceps muscle is common in hip arthritis. This can be assessed by tape measurement comparing the two sides. Asymmetry of the gluteus maximus or other muscles can be caused by peripheral nerve injury or nerve root impingement that causes muscle wasting.
- 3.
Bony landmarks: The hip joint itself lies hidden from direct inspection, although assessment of surrounding bony landmarks can provide clues to the underlying hip pathology. These include the lumbosacral spinous processes, iliac crest, anterior superior iliac spine, greater trochanter, ischial tuberosity, posterior superior iliac spines, overlying “dimples of Venus,” and symphysis pubis.
It is often easiest to divide the inspection portion of the exam into that which can be done with the patient standing and then that which should be done with the patient supine. With the patient standing, the examiner should inspect the patient’s gait (see Gait Analysis). The examiner should then examine the standing patient from the front, from each side, and from the back. In this position it is easier to detect the presence of spinal curvature and pelvic tilts. These are assessed by examining the relationship between the adjacent spinous processes and the left and right iliac crests. A leg-length deformity may be apparent while the patient is standing with the feet together. If the patient needs to flex one knee to keep the pelvis level, the side with the flexed knee might be long. Conversely, if the pelvis is tilted to one side and the knees are fully extended, the side on which the pelvis is lower may be short. Gross varus or valgus deformity of the knee can also be evaluated (see Chapter 6 ). When the patient moves to a supine position, a more detailed inspection of skin, superficial, and deep tissues can be performed.
GAIT ANALYSIS
Normal gait involves a complex integration of muscle and joint activity that results in forward propulsion of the body with minimum displacement in the vertical and horizontal planes. Each leg alternates between a stance phase and a swing phase ( Figure 5-6 ). During normal gait, the stance phase accounts for approximately 60% of the gait cycle. With faster walking speed, stance time is reduced and swing time is increased. The stance phase includes heel strike, foot flat, midstance, heel lift, and toe lift. Swing phase begins after toe lift and involves an initial period of acceleration, followed by midswing and a period of deceleration before heel contact and the stance phase begin again.
