ACL Tears Bring Women Long-Term Bone Loss

Study found persistent deficits years after surgery

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By Alan Mozes
HealthDay Reporter

FRIDAY, March 24, 2006 (HealthDay News) -- Anterior cruciate ligament (ACL) tears are common and serious injuries, especially for sports-loving women.

Now, a new study finds that, two years after ACL surgery, young female athletes still show substantial bone loss around the knee, despite aggressive efforts at early, accelerated rehabilitation.

A team from the Mayo Clinic report that ACL injuries typically result in significant bone loss in the femur, tibia and patella (kneecap) areas, usually three to six months after corrective surgery.

Such loss, they found, was only partly reversed by two years of focused therapy.

"It is critically important that we pay attention to any bone loss that occurs in adolescents and those in their early 20s, when ACL injury is the most common," said study author Dr. Diane L. Dahm, an assistant professor of orthopedics at the Mayo Clinic in Rochester, Minn.

"This is the group that is supposed to be gaining bone density," she stressed. "So although this is a risk factor for men as well, it is perhaps even more critical for women because of their higher risk for osteoporosis and osteoporotic fractures later in life, when bone density drops."

Dahm's team presented the findings Friday at the American Academy of Orthopaedic Surgeons (AAOS) annual meeting, in Chicago.

According to the AAOS, recent figures indicate that about 9.5 million American men and women annually seek care from orthopedic surgeons for a range of knee problems. Dahm and her colleagues point out that athletes make up a majority of ACL injuries, since they are the group most likely to engage in activities that can negatively impact the knee.

The ACL connects the femur (thigh bone) to the tibia (shin bone). Injuries to the ligament occur when an individual rapidly changes direction, slows down after running, lands from a jump, is forcefully hit while playing sports, or accidentally struck.

Gender also plays a role, with women two to eight times more likely to suffer an ACL injury than men. Each year, an estimated 38,000 American women experience ACL tears, the AAOS say.

The reasons for this gender gap are not yet fully understood, but physicians believe women may be more vulnerable to injury as a result of sex differences in strength, hormones and muscle-firing patterns.

Pain, experts say, may not be noticeable immediately following an ACL injury, but subsequent swelling within the ensuing 12 hours will eventually be accompanied by pain when standing.

The study authors tracked 22 women between the ages of 16 and 40 who had experienced a complete ACL rupture.

All subsequently underwent ACL reconstructive surgery, after which they participated in a rigorous rehabilitation program involving routine visits with physical therapists and sports psychologists.

Just before surgery and then at six weeks, three months, six months, one year and two years post-surgery, the researchers measured the functional abilities and bone mineral density (BMD) of numerous body areas, including: the spine, femoral neck, distal femur, patella and proximal tibia.

Dahm and her team found that although no bone loss was found in the spinal region or at the unaffected limbs, bone loss in the injured area did occur -- most dramatically at the three-month point following surgery.

Bone loss was diminished by one year after surgery, but persisted, they add. By two years post-surgery, BMD around the injured knee was still significantly lower than it was around the non-injured knee.

In particular, women with a higher body mass index (BMI) suffered more bone loss than leaner women.

On the other hand, exercise, even walking, appeared to help minimize bone loss.

"We are going to do a larger study next to look at this particular aspect -- whether encouraging women to get into increased weight-bearing activities can prevent bone loss," said Dahm.

"We also need to look at calcium and vitamin D intake, to see whether simple dietary changes may be helpful," she added.

Dr. Robert Gotlin, director of Sports Rehabilitation at Beth Israel Medical Center in New York City, said that while the findings are interesting, they are based on a very small pool of patients, and require much more research before prematurely drawing conclusions.

"Is it purely the fact that women are much more prone to a loss of bone or that they're not bearing enough weight-bearing loads?," he asked. "I don't know. But I suspect that that the alarming message may not be so alarming. Over an even longer period of time -- beyond two years -- this bone loss may not be such a problem. It's not clear, and there are still a lot of questions to be asked."

More information

For more on ACL, visit the American Academy of Orthopaedic Surgeons.

SOURCES: Diane L. Dahm, M.D., assistant professor, orthopedics, Mayo Clinic, Rochester, Minnesota; Robert Gotlin, D.O., director, Sports Rehabilitation, Beth Israel Medical Center, New York City; Marc 24, 2006, presentation, American Academy of Orthopaedic Surgeons annual meeting, Chicago

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