Sept. 22, 2017
Total hip arthroplasty is a common surgery, with more than 330,000 procedures performed in the United States every year. However, there is significant controversy over the optimal muscle-sparing approach: mini-posterior approach (MPA) or direct anterior approach (DAA).
Incision for direct anterior approach
Illustration of the right hip demonstrates the location and size of the incision for the direct anterior approach. The approach continues between the sartorius and tensor fascia lata muscles, an internervous plane, avoiding the risk of denervation of the involved muscles.
Anteroposterior and lateral radiographs of the hip
Anteroposterior and lateral radiographs of the hip demonstrate the acetabular component, femoral head and femoral stem in appropriate positions after surgery using the direct anterior approach.
In a prospective, randomized study, researchers at Mayo Clinic in Rochester, Minnesota, found that Mayo Clinic patients who underwent DAA had objectively faster recovery than patients who had MPA hip arthroplasty.
The study used advanced, quantitative monitoring of activity to measure the recovery of 101 patients with end-stage unilateral hip osteoarthritis who were randomized to receive DAA or MPA surgery. Participants were evaluated preoperatively, and at two weeks, eight weeks and one year postoperatively.
"We found that functional milestones — such as discontinuing use of the walker, and walking half a mile — occurred about five days earlier with the anterior approach," says Michael J. Taunton, M.D., Orthopedic Surgery and assistant professor of orthopedics at Mayo Clinic's campus in Minnesota. "In experienced hands, DAA can provide faster functional recovery in the short term after surgery."
Mayo Clinic has orthopedic surgeons with expertise in both anterior and posterior hip replacement. Participants in the study were initially seen by one of four Mayo Clinic surgeons. After randomization to DAA or MPA, patients had surgery performed by a Mayo Clinic surgeon with expertise in the assigned procedure, regardless of whether the surgeon had consulted on the patient initially. Postoperative care was provided by patients' initial consulting surgeons.
"That cross-randomization was a unique aspect of our study," Dr. Taunton says. "We also were able to perform DAA for these patients with the necessary level of experience. That is key because there is a learning curve with the anterior approach. Serious complications can come from inappropriate execution."
Another unique aspect of the study was the use of a gait monitor developed at Mayo Clinic. The monitor — which patients wore at home preoperatively and at two weeks, eight weeks and one year postoperatively — has five sensors and is significantly more sensitive than commercial activity-monitoring devices.
"Consumer activity monitors don't typically measure your activity if you're moving slowly — for example, with a walker," Dr. Taunton says. "Our monitor can register the number of steps taken and percent of day active at activity levels ranging from very slow ambulation to running. It also measures entropy, a measure of the complexity of gait. At two weeks after surgery, we were able to see that our anterior patients not only walked more but also had better quality of gait."
Among other data, the study documented quicker recovery by DAA patients compared with MPA patients in:
- Discontinuing use of a walker (10 days after surgery versus 14.5 days)
- Discontinuing use of all gait aids (17.3 versus 23.6 days)
- Discontinuing use of narcotics (9.1 versus 14 days)
- Ascending stairs with gait aid (5.4 versus 10.3 days)
- Walking six blocks (20.5 versus 26 days)
There was no difference in monitored activity levels between the two groups preoperatively, and at two months and one year after surgery. The study also found no postoperative in-hospital complications in either group. Further studies comparing long-term outcomes are planned.
Meeting patients' expectations
Although recovery rates appear to equalize by eight weeks after hip replacement, the faster short-term recovery that's possible with DAA can be important for patients. "Their expectations have changed," Dr. Taunton says. "Patients who are losing the ability at age 72 to hike mountains or to bicycle want to regain those abilities. They want faster pain relief and as little interruption of life as possible."
DAA is often performed with fluoroscopy, to re-create as precisely as possible the patient's hip biomechanics. Precision is further increased at Mayo Clinic through the use of 3-D models of patient anatomy before surgery and of robotics during surgery that guide the implant's positioning. "The robot helps us understand down to the degree or millimeter the exact position for the implant or for the leg length and offset," Dr. Taunton says.
The faster recovery achieved after anterior hip surgery might even benefit patients with more-severe hip conditions. Dr. Taunton and colleagues are planning a randomized study comparing standard and anterior surgical approaches for femoral neck fractures.
"Those patients tend to be elderly and more debilitated," Dr. Taunton says. "But we might someday be able to provide better care for a 95-year-old who falls and breaks a hip. If we can fix the hip and get the patient up and moving more quickly, there may be less risk of pneumonia, narcotic-related delirium or any of the other conditions that can cause cascading deterioration for these patients."