Orthopedic surgeons perform 300,000 hip replacements annually in the United States. This represents a 50 percent increase between 1990 and 2002.1 Patient satisfaction remains high, with 95 percent of patients reporting improvements in quality of life and pain reduction.
Despite these positive outcomes, only a quarter of patients clinically indicated for a total hip actually follow through with the operation.2 Many patients choose not to undergo total hip replacement surgery for fear of revision surgery resulting from component wear. Other barriers include prolonged rehabilitation, concerns of possible hip dislocation and the possibility of a postoperative leg length discrepancy.
A new minimally invasive procedure called the anterior total hip replacement (A-THR) addresses these concerns. The procedure utilizes an operating room table specially designed for this muscle-sparing approach (See image below). Anterior hip replacement is performed using highly durable bearing surfaces, which potentially last more than 30 years.
The Arthritic Process
Patients primarily require hip replacements for the treatment of osteoarthritis.
Osteoarthritis of the hip can have a variety of etiologies such as previous hip trauma, childhood or congenital conditions and inflammatory arthritis. The most common cause of osteoarthritis, however, is likely idiopathic.
The arthritic process causes degeneration of the articular cartilage on the femoral head and acetabulum (hip socket). The hip is the most classic example of a ball and socket joint and relies on a low friction articulation for range of motion. A number of large muscles power the hip during gait. The most important of these muscles are the abductor muscle group, which includes the gluteus minimus, gluteus medius, gluteus maximus and tensor fascia lata muscle. Together, these large muscles make up the buttock and lateral portion of the hip.
Smaller muscles located over the posterior hip capsule are responsible for posterior hip stability. These include the piriformis, obturator and gemelli muscles. Other muscles that assist in hip function are located over the anterior aspect of the hip and they include the rectus femoris, sartorius, and iliopsoas with their main function being the active flexion of the hip.
Patients who develop arthritis of the hip will typically complain of progressive stiffness of the hips. Vague complaints of occasional groin pain are very often associated with ambulation or after prolonged sitting.
As the articular cartilage degenerates and motion of the hip decreases, the muscles surrounding the hip begin to atrophy. Bone spurs (osteophytes) form within the hip joint, and patients develop a limp and increased pain. Often in progressive osteoarthritis, cartilage degeneration creates a significant amount of joint space loss, leading to a leg length discrepancy of up to 2 cm.
The diagnosis of hip osteoarthritis requires only a simple X-ray. An AP image of the pelvis and the hip will often reveal the presence and extent of the arthritic condition. MRI or CT rarely have a role in the diagnosis of hip arthritis. These should never be considered as first line studies for the diagnosis of the condition.
Total Hip Replacement
Patients with radiographic evidence of osteoarthritis, decreased hip motion and pain are candidates for total hip arthroplasty. In total hip replacement, the arthritic femoral head is removed along with the femoral neck. These are replaced with a prosthetic femoral neck and head. The acetabular cartilage remnant is removed along with the surrounding osteophytes. A metal cup-lined by either a plastic, ceramic or metal-bearing surface-is press-fit into position.
The positioning of the components during surgery as well as the surgical approach to the hip have been implicated in joint dislocation, leg length discrepancy and length of rehabilitation. Hip dislocation most commonly occurs posteriorly. It can be a consequence of component malposition, incompetent soft tissue restraints to dislocation, or failure of the patient to adhere to antidislocation precautions prescribed by their physician.
Leg length discrepancy of up to 2 cm can occur when intraoperatively the surgeon senses that the hip is unstable and prone to dislocate. In order to prevent dislocation, the surgeon must increase the length of the implanted prosthesis, thereby increasing the tension of the gluteal abductor muscles. This tension forces a "rubber band" effect, which maintains the hip in position.
The most common surgical approach to the hip in North America is the posterior method. In order to reach the hip joint posteriorly, the fascia lata and gluteus maximus must be split. Along with this, the obturator, gemelli, and piriformis muscles are divided off their insertion on the femur.
The posterior approach, by its very nature, is prone to destabilize the hip by removing the body's natural soft tissue constraints to a posterior dislocation. Consequently, patients must adhere to certain hip precautions for 6 weeks to 12 weeks post-operatively. During this period, the posterior structures of the hip scar down and stabilize the joint.
Some common hip precautions include refraining from bending past 90 degrees and avoiding crossing the legs. Patients must sleep on their back with a pillow between their legs, and they also require the use of a raised toilet seat.
Patients feel a certain level of anxiety when asked to adhere to these precautions. Their lifestyle is clearly limited, as most are unwilling to use public restrooms, ride in a car or achieve an overall independent lifestyle.
Anterior Total Hip Replacement
The anterior total hip replacement has been developed with the goal of accelerating rehabilitation time, decreasing the risk of dislocation and minimizing the possibility of a leg length discrepancy.
This procedure is the only approach to the hip that does not require splitting or dividing muscles and tendons from the femur in order to obtain access to the hip joint. The approach is undertaken via a natural interval among muscles (the tensor fascia lata muscle and the rectus femoris muscle) to enter the hip capsule.
Most patients with osteoarthritis of the hip are candidates for this approach. Less ideal patients for the anterior approach are those with significant deformities of their proximal femur due to previous trauma or dysplasia and previous acetabular fracture patients. The procedure is available for all age groups and also can be performed in obese patients.
Minimizing Patient Downtime
The anterior approach to the hip was first described in the late 1800's. It is routinely used for non-arthroplasty procedures around the hip. Only recently has it been innovated for total hip replacement.
The approach allows direct access to the acetabulum. Access to the femur for the purposes of instrumentation, however, is more difficult and less intuitive than the posterior or lateral approach to the hip. This has limited the availability of this procedure to many surgeons.
Recently, however, an operating room table has been developed which facilitates exposure of the femur through the same four-inch incision. The table allows independent manipulation of operative extremity permitting extension, external rotation, adduction and elevation of the proximal femur out of the wound.
Since the muscles that power the hip are not disturbed during surgery and the posterior capsule remains intact, the prosthetic hip attains near normal stability postoperatively. Patients are, therefore, not required to maintain the hip precautions required after posterior approaches to the hip.
More accurate and consistent component positioning is ensured, since the supine position and the radiolucent orthopaedic table facilitates the use of intraoperative fluoroscopy. This allows the surgeon to place the components in the appropriate position, which also serves to decrease dislocation rates.
The preservation of the posterior hip muscles and capsule as well as the stability that is attained by the artificial hip eliminates the need to increase the leg length in order to stabilize the hip. The live fluoroscopy also allows a very accurate matching of the operative hip to the contralateral hip achieving leg length equality.
Postoperatively, patients are encouraged immediate full weight bearing. Hip precautions are not required, and patients are encouraged to assume unrestricted activities of daily living. Many patients are able to abandon all assistive devices such as canes and walkers within one week for indoor ambulation. Most can ambulate unassisted outdoors within two weeks to three weeks. A limp may persist for up to 3 months until muscle strength in the previously atrophied muscles is regained via regular therapy.
Activities such as swimming and stationary bike are encouraged right away. High impact activities such as running, skiing or tennis, however, are restricted for three months postoperatively in order to allow bone ingrowth into the prosthesis.
The anterior total hip replacement offers patients an important treatment option to improve their quality of life. As more surgeons are trained on this procedure, it is likely to become a preferred surgical approach.
1. Kurtz S, Mowat F, Ong K, Chan N, Lau E, Halpern M. Prevalence of primary and revision total hip and knee arthroplasty in the United States from 1990 through 2002. J Bone Joint Surg Am. 2005;87(7):1487-1497.
2. Hawker GA, Wright JG, Coyte PC, Williams JI, Harvey B, Glazier R, Badley EM. Differences between men and women in the rate of use of hip and knee arthroplasty. N Engl J Med. 2000;342(14):1016-1022.
Roy I. Davidovitch, MD, is an attending orthopedic surgeon at the Hospital for Joint Diseases at New York University Langone Medical Center and orthopedic trauma service director at The New York Hip Center. Dr. Davidovitch is the only surgeon in New York City who performs the anterior hip replacement on the HANA table.