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DURHAM, N.C. – In the first such review of its kind, Duke University Medical Center researchers have analyzed their experiences in treating eight football players with a rare but potentially devastating hip injury suffered by American football players, and they have offered their recommendations for diagnosis and treatment of the injury.

The researchers said that prompt diagnosis and proper treatment of hip subluxation – which in many cases is dismissed simply as a hip "sprain" or "strain" – is important because it appears that up to 25 percent of such injuries may lead to bone death within the hip joint.

Subluxation is a partial dislocation of the joint. In a complete dislocation, the "ball" at the top of the femur which rotates within the hip joint pops completely out of the joint. In subluxation, the ball moves in and out of the joint without tearing the capsule surrounding the joint. Hip subluxation is the injury that forced Oakland Raiders running back Bo Jackson to retire from football.

"Hip subluxation is an unusual, although potentially devastating injury that is an inherent risk of participating in American football," said Claude T. Moorman, M.D., orthopedic surgeon and director of the sports medicine program at Duke. The results of Moorman's analysis were published this month (July 2003) in the Journal of Bone and Joint Surgery.

"There is very little medical information out there to guide physicians in how to best take care of these patients," he continued. "This analysis is intended to raise awareness of this injury, so that we can determine the best way to care for these patients."

Although most players who are properly treated can eventually return to the field, the injury can lead to a condition known as avascular necrosis (AVN). AVN is caused when the ball of the hip joint no longer receives an adequate supply of blood. The resulting death of the bone causes the joint to collapse, necessitating either an artificial hip joint or a vascularized bone transplant.

While the number of players involved in the study is small, Moorman said the study represents the first step toward identifying the injury and helping physicians take better care of patients. As the injury becomes better appreciated, Moorman expects that more players in football, and even other sports like hockey and basketball, will be diagnosed.

For their analysis, Moorman's team --which included orthopedic surgeons at the Hospital for Special Surgery in New York -- followed eight football players who sustained traumatic hip subluxation over a seven-year period. Three of the players played in the National Football League, one played at the collegiate level and the remaining four were high school players. They included four running backs, two linebackers, one wide receiver and one lineman.

Two out of the eight players, or 25 percent, went on to develop AVN.

The researchers examined the medical records, radiographic images, as well as videotapes of the injuries to better understand how the injury occurred and which treatments appeared to be most effective.

"In six out of eight of the players, the injury occurred after a fall on a bent knee with the hip joint popping out backwards," Moorman said. "In all cases, the players suffered extreme pain and were unable to return to the game."

The challenge for physicians is to diagnose the subluxation, according to Moorman. Standard x-ray exams do not reveal the tell-tale joint fracture characteristic of subluxation; only an obliquely angled x-ray can detect it. However, Moorman's team found that magnetic resonance imaging (MRI) can be helpful both at the time of injury as well as later to detect any early signs of AVN.

"The joint is encased in a capsule, and when there is subluxation, the resulting blood and fluid buildup within this confined space appears to put pressure on the blood vessels, potentially cutting off or limiting the supply of blood," Moorman said. "In a complete dislocation, these fluids are dispersed, so in this way, a partial dislocation can possibly lead to a worse outcome than complete dislocation if not diagnosed and treated."

Extreme buildup of fluids can be detected early by MRI, allowing physicians to remove the fluids through a needle to reduce the immediate pain and lessen the chances of AVN. Moorman recommends that another MRI be performed six weeks later to detect any early signs of AVN.

As far as treatment, the results of Moorman analysis indicate that patients should stay on crutches for at least six weeks, without putting any weight on the hip. If the follow-up MRI reveals no early manifestations of AVN, the player can slowly resume normal activities, he said.

"Six of the eight players studied showed no signs of AVN, and they all eventually returned to their previous level of competition," Moorman. "Another player never returned to the sport, and the other played for three years against the advice of physicians. Both have since required complete hip joint replacement."

Moorman and colleagues in Duke's Orthopedic Research Laboratory are beginning studies in animal models to better understand why subluxation causes AVN while total dislocations do not.

The study was supported by Duke University Medical Center and the Hospital for Special Surgery.