Indications for Surgery

The following are possible indications for prosthetic replacement of the proximal femur.
• Acute, displaced intracapsular (subcapital, transcervical) fractures of the proximal femur in an elderly patient with poor bone stock and an anticipated low-demand level of activity after surgery
• Failed internal fixation of intracapsular fractures associated with osteonecrosis of the head of the femur
• Severe degeneration of the head of the femur (but an intact acetabulum) associated with long-standing hip disease or deformity resulting in disabling pain and loss of function that cannot be managed with nonoperative procedures.

Patients with preexisting degenerative hip disease who sustain a femoral fracture are candidates for primary THA rather than hemiarthroplasty. Acute, severely comminuted intertrochanteric fractures are infrequently managed by primary hemiarthroplasty.

Procedures
Background. Historically, acute displaced fractures of the proximal femur in the elderly were treated with unipolar (fixed head), uncemented metal-stemmed endoprostheses with marginal results. With the introduction of cement fixation during the 1960s, these results improved. The primary complication associated with the single-component unipolar implants, regardless of design or fixation, was progressive erosion of the acetabular cartilage and subsequent pain.

To decrease the problem of acetabular wear, the bipolar hemiarthroplasty was developed. The bipolar design is composed of multiple components: a metal ball-and-stem femoral prosthesis (may be modular) that moves within a free-riding polyethylene shell, which in turn inserts into a metal cup that moves within the acetabulum. The purpose of the multiple-surface, load-bearing design is to displace forces incurred by the acetabulum through the interposed components rather than directly to the acetabulum to lessen erosion of the acetabular cartilage. Both current-day modular unipolar and bipolar prostheses are in use today. Considerable differences of opinion exist among surgeons regarding the advantages and disadvantages of one design versus the other.

Operative procedure. As with THA, a posterolateral approach is most commonly used. After removing the head of the femur, the metal-stemmed prosthesis is inserted into the shaft of the proximal femur. The femoral stem is usually cemented in place, although bioingrowth fixation has also been used. Procedures for closure are consistent with THA.

Postoperative Management

There are no studies in the literature that have examined the effects of comprehensive postoperative exercise programs exclusively for patients who have undergone current-day hemiarthroplasty. This is because, for the most part, considerations and precautions for positioning and ADL, as well as the components and progression of the exercise and ambulation program, are similar to those for postoperative management of THA. These guidelines are detailed in the previous section of this chapter. As with postoperative management after THA, selection and progression of exercises and functional activities after hemiarthroplasty also tend to be based on the opinions of surgeons and therapists as to the potential of specific exercises to remediate impairments and improve functional performance. Consequently, the effectiveness of exercise after hemiarthroplasty also remains unclear. Only limited information on the impact of specific exercises and gait-related activities on the hip joint per se after hemiarthroplasty is available in the literature. Some findings from several single-subject studies of two patients with femoral endoprostheses have already been discussed in the previous section of this chapter on THA.

PRECAUTION: Given the significant concerns for long-term erosion of acetabular cartilage after hemiarthroplasty, it may be even more critical to avoid exercises that impose the greatest compressive or shearing forces across the hip joint and therefore pose the greatest potential for eroding the cartilaginous surface of the acetabulum. Exercises should be performed initially at a submaximal level and then progressed gradually. Unassisted heel slides and maximum effort gluteal setting exercises may need to be avoidedduring the acute phase of postoperative rehabilitation. During the postacute period of rehabilitation exercises, such as maximum-effort manually resisted hip abduction may actually generate greater forces across the hip than protected weight-bearing activities.

OutcomesPresent-day modular unipolar and bipolar hemiarthroplasty procedures appear to yield similar results in pain relief, functional outcomes, and type and rate of complications.
Although acetabular wear was identified as the primary concern after the unipolar replacement used during the 1960s and 1970s, the mechanical effectiveness of the bipolar prosthesis in preventing acetabular erosion has yet to be firmly established. In a study of community-dwelling patients age 65 years or older (mean age 80 years) who had undergone hemiarthroplasty with either a bipolar implant or a modular unipolar implant, there were no significant differences between the two groups at 1 year and 4 to 5 years of follow-up with regard to functioning in daily activities or rates of dislocation, infection, or mortality. Another study has suggested that joint ROM may decrease over time after bipolar hemiarthroplasty possibly due to the design of the implants. This decreased range was not associated with diminished functional abilities.

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