5 THE HIP
Applied Anatomy
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 cm2 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 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.
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).
FIGURE 5-4 HIP BIOMECHANICS DURING SINGLE-LEG STANCE.
(From Gross J, Fetto J, Rosen E., eds.: Musculoskeletal Examination, 2nd ed. Malden, MA: Blackwell Publishing, 2002.)
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.
Common Painful Disorders of the Hip Region
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.
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.
Pain after Total Hip Arthroplasty
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.
