FRACTURES - Femoral Neck
These fractures can be classified as occult, impacted, displaced, or nondisplaced. Occult fractures may occur in the elderly after little or no apparent trauma. The patient complains of persistent groin pain on weight bearing. A crack, initially undetectable on x-ray, can continue to propagate across the femoral neck with the cyclic stresses of walking. Weight bearing must be avoided, or eventually, complete displacement can occur. Bone scans or magnetic resonance imaging reveals the fracture before x-rays.
Patients with impacted and nondisplaced femoral neck fractures also present with groin pain and no deformity on physical examination. The Garden classification system describes the extent of impaction and displacement of hip fractures. X-rays of impacted fractures (Garden I) show the femoral head slightly tilted inward (valgus deformity) with an incomplete fracture line, leaving the medial cortex intact. Nondisplaced fractures extending across both cortices of the femoral neck (Garden II) are more unstable. Patients with displaced femoral neck fractures (Garden III and IV) present with groin pain and a shortened, externally rotated leg that is too painful to move (see Fig. FR1).
Fig. FR1. Subcapital femoral neck fracture.
The Garden classification reflects the degree of disruption of the blood supply to the femoral head and has crucial implications for treatment and prognosis. Because the femoral head is intra-articular, its sole blood supply comes from vessels traversing three structures: the bone of the femoral neck, the surrounding hip capsule, and the ligamentum teres (see FIG. FR2). A displaced fracture completely disrupts the blood vessels of the femoral neck and can tear those of the hip capsule. The vessels in the ligamentum teres do not function in 2/3 of adults. Thus, a displaced fracture often completely devascularizes the femoral head. Although a devascularized femoral head can heal if securely stabilized, poor healing is common. Nonunion occurs in 15% to 20% of patients, and osteonecrosis of the femoral head occurs in another 15% to 30%.
Fig. FR2. Blood supply to femoral head.
Occult, impacted, and nondisplaced femoral neck fractures are usually treated by internal fixation with multiple pins (see FR3). This stabilization permits immediate full weight-bearing ambulation and prevents later displacement. Since the blood supply to the femoral head is not significantly disrupted, these fractures usually heal well. Nonambulatory, demented patients who have limited pain perception can be treated with bed rest followed by transfer from bed to chair.
Fig. FR3. Internal fixation of subcapital fracture with pins.
Displaced fractures have two main treatment options--operative stabilization and prosthetic replacement. Each has advantages and disadvantages. Open reduction and internal fixation is usually reserved for vigorous patients < 70 yr of age who are able to comply with a postoperative regimen of limited weight bearing using crutches. The procedure preserves the femoral head, and with successful healing, the hip is nearly normal. However, if osteonecrosis or nonunion occurs, the result is a painful, nonfunctional joint that requires total hip replacement. For this reason, less active elderly patients with displaced fractures often undergo primary prosthetic replacement of the femoral head (hemiarthroplasty). This permits immediate, full weight bearing and a faster return to independent functioning with a minimum chance of needing a second procedure.
The simplest prosthesis (the Moore prosthesis) consists of a smooth metal sphere attached to a stem that is wedged into the medullary canal of the femur (see FIG. FR4). Drawbacks include a tendency to wear away the acetabular articular surface and pain from a loose fit of the stem in the femoral medullary canal. A loose fit can be remedied by a prosthesis designed to be stabilized inside the femur with either acrylic cement or a special coating of hydroxyapatite or porous metal that facilitates direct bone fixation. A bipolar prosthesis with an internal metal-polyethylene bearing can reduce acetabular wear. Patients who develop acetabular arthritis may require total hip replacement. Primary total hip replacement in acute femoral neck fractures is reserved for patients with severe preexisting arthritis because this more extensive operation has a higher morbidity than either hemiarthroplasty or internal fixation with pins.
Fig. FR4. Treatment of displaced femoral neck fractures.
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