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AAOS Now

Published 5/1/2011
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Terry Stanton

Hip dislocation: Is reduction timing key?

How much of a difference timing of reduction makes in the outcome of a hip dislocation remains a subject of debate. Although both the scientific and clinical evidence point to a beneficial effect with earlier surgery, some of the data are not so conclusive, especially with regard to outcomes over time.

During a symposium featuring a panel of trauma “Mythbusters” at the 2011 Annual Meeting in San Diego, J. Tracy Watson, MD, chief of the Orthopaedic Trauma Service at St. Louis University, tackled the proposition “Timing of reduction: does it matter?”

The basic science
Basic science evidence indicates that occlusive changes in the extraosseous large vessels do not consistently result in changes to the the intraosseous blood flow, due to collateral circulation, according to Dr. Watson. Early reduction may provide earlier blood flow to the femoral head by relieving tension across the femoral and circumflex vessels. Citing the results of a cadaver study, Dr. Watson noted that extraosseous large-vessel occlusive changes were observed with dislocation, “but again, the smaller vessels seemed to escape this due to the circumflex and collateral circulation.”

As the time to reduction lengthens, however, basic science studies begin to show a breakdown in blood flow and healing. Using single photon emission computed tomography, researchers found that patients who had undergone reduction within 9.1 hours of dislocation had low-flow scans, whereas patients who had reductions within 4.5 hours had normal scans. “So we start to see some breakdown in these small vessels over time,” Dr. Watson said.

An early (1977) rabbit model study found that early reduction enhanced early and complete recovery. But when the dislocation was reduced 12 hours or later after injury, “the recovery did not happen and some pathologic changes were observed,” Dr. Watson said. “So the basic science model is showing a watershed time of about 12 hours for reduction.”

A 1983 rabbit study, however, found that blood flow to the dislocated hip was never totally interrupted regardless of when the reduction occurred, but decrease in femoral head blood flow progressively grew more pronounced in association with time elapsed from reduction. Early reduction enhanced early and complete recovery of blood supply to the femoral head, but delaying reduction for 12 or more hours did not appear to affect the rate and extent of circulatory recovery of the femoral head.

Because the study found no significant difference in the blood flow to the femoral head, regardless of when reduction occurred, it concluded that pure traumatic dislocation of the hip—with no ancillary injury—can only rarely be the cause of osteonecrosis of the femoral head. “In other words,” Dr. Watson said, “even though the blood supply was diminished, they didn’t think it was the total cause of osteonecrosis of the femoral head.”

Reviewing the pathology of dislocation, Dr. Watson noted that few vessels along ruptured capsules and the ligamentum teres are irreversibly torn, and early reduction can reverse compression, traction, and spasm of most intact vessels. In prolonged dislocation, circulatory disturbance persists or worsens due to additional pathologic changes such as posttraumatic inflammatory changes.

Overall, basic science work seems to demonstrate a benefit to reducing the dislocation within a 6- to 8-hour window.

Clinical studies
Relevant clinical studies began in the early 1950s. The first of these found an approximately equal distribution of good-to-excellent and fair-to-poor results in hips reduced within 24 hours of the injury, while 95 percent of dislocations reduced more than 24 hours after injury had a fair-to-poor outcome. A more specific 1954 study recorded good/excellent results in 88 percent of hips reduced within 12 hours after dislocation and in 73 percent of those reduced at 12 to 24 hours. If reduction was delayed for more than 24 hours, however, 100 percent had poor results.

Subsequent studies examined procedure times more precisely and better stratified the data. A 1994 study at a German hospital examined results for hips that were reduced at less than 6 hours after dislocation; 54 percent had good-to-excellent results, and the incidence of osteonecrosis was 12 percent. Some patients underwent reduction shortly after entering the hospital, but no difference in the incidence of osteonecrosis was seen between 1-hour and 6-hour times of reduction.

Confounding factors
Overall, the clinical literature parallels the basic science indication of 12 hours as the “watershed” time after injury for reduction, with an appreciable suggestion that a shorter time might yield a better result. Dr. Watson stressed, however, that a number of confounding variables make precise conclusions more elusive than they may appear to be. He noted that many studies did not specify the direction of dislocation, and evidence that anterior dislocations in general fare better than posterior injuries has been found.

Method of reduction is also a factor, “probably due to the fact that open reduction might do a little more damage to the marginal vasculature than the basic science research indicates,” Dr. Watson said.

Associated fractures—femoral head and acetabular fractures—as well as fragments in the joint have an important, “really negative” effect on outcomes, Dr. Watson said. He noted that surgeons now can use arthroscopy to “wash out the joint atraumatically, remove these fragments and not have them grind on the hip,” and that results are poorer in patients with multiple severe injuries.

Because many studies did not differentiate between arthritis and osteonecrosis, “it is very difficult to identify whether the poor result was due to osteonecrosis or to severe posttraumatic arthrosis.”

Work status is another variable, because heavy labor occupations after injury pose an increased risk of poor outcomes.

Finally, a factor that looms over the entire issue is length of follow-up; results appear to worsen with length of follow-up, as seen in increased rates of arthritis over time.

Summing up, Dr. Watson said that basic science literature as well as much of the clinical evidence supports earlier reduction, yet the clinical evidence does not necessarily point to the timing of reduction as the sole prognosticator of how well the patient will do. The direction of dislocation and overall severity of all injuries—specifically, associated hip pathology—appear to have more effect on outcomes.

“If it is my hip,” he continued, “I want it reduced as soon as possible, but clearly 12 hours is the watershed limit. Six hours is even better.”

Thus, he declared “busted” the basic proposed myth that “timing doesn’t matter,” but for the issue in full, “in some respect it is plausible, because timing is only one piece of the puzzle. I would encourage surgeons to reduce the hip when it is safe and efficacious, but when the reduction is performed may not be the primary factor in how the patient does.”

Disclosure information: Dr. Watson—Accellolox, DePuy, Digimed, Smith & Nephew, Orthopaedic Knowledge Online, Foundation for Orthopaedic Trauma, Orthopaedic Trauma Association, National Trauma Institute, Twin Star Medical, Wright Medical.

Bottom line

  • Basic science supports 12 hours as the “watershed” time for reduction after hip dislocation.
  • In dislocation, only a minority of blood vessels are irreversibly torn.
  • Clinical studies also support the 12-hour watershed for reduction
  • Confounding variables in studies make conclusions elusive.
  • Time of reduction does not appear to be the sole prognosticator of outcomes.

Terry Stanton is senior science writer for AAOS Now; he can be reached at tstanton@aaos.org