Pittsburgh Zoo and PPG Aquarium Johnny, the 12-year-old mandrill, will undergo exploratory knee surgery today by orthopedist Dr. Freddie Fu. Click photo for larger image. Graphic: Double-bundle technique for ACL repair

Dr. Freddie Fu, chairman of the orthopedics department at the University of Pittsburgh School of Medicine, was expected this morning to scope the left knee of a patient that for three months has intermittently slapped at the joint and even tried to bite it.

As best as his keepers can tell, Johnny, a 12-year-old mandrill who resides at the Pittsburgh Zoo and PPG Aquarium, has a sore knee. Zoo chief veterinarian Dr. Cindy Stadler contacted Dr. Fu, who has performed arthroscopies on thousands of human patients, including elite athletes.

"It's more of an exploratory [look] than anything else," Dr. Stadler said. About five years ago, the young male mandrills began fighting for dominance, and it's possible that an injury back then led to debris or scarring in the joint that is causing Johnny some problems now.

"I would suspect that it is something having to do with some trauma," Dr. Stadler said. "He's fine most of the time, then every once in a while he'll either sit in a position or something will aggravate his left leg."

Dr. Fu wants to explore the mandrill's knee not only to alleviate the animal's discomfort, but also to build on a concept in human anterior cruciate ligament, or ACL, repair that he has pioneered.

Most surgeons fix a torn ACL by replacing the damaged tissue with a graft that is anchored in what he says is the wrong place on the bone.

But the ACL contains two, not one, bundles of tissue and each needs to be repositioned in the correct site for the knee to function properly.

If that's not done, the result can be like driving a car with unbalanced wheels, or hanging a door with only one hinge, he explained, noting that one study showed people who have conventional ACL repair were more likely five to 10 years later to have knee arthritis than those who didn't have the procedure.

Dr. Fu and his colleagues at UPMC's Center for Sports Medicine examined many cadavers of humans and animals, as well as fetal remains, to determine that the "double-bundle" ACL is the norm.

Yet they have had a difficult time convincing other surgeons that the typical ACL repair, where the ligament is regarded as a single bundle, is not the best approach.

A decade or more ago, "I would do 10 of these a day," Dr. Fu said. "It would take me about 20 minutes to do one. It was like a factory."

He doesn't do that many procedures anymore.

It takes him about 30 to 45 minutes to perform the double-bundle technique, which requires paying careful attention to the anatomical details of the patient's knee.

"I do less surgery now, but I have fun doing it," Dr. Fu said. "This takes a lot of time to do it. This is very interesting to me, but most surgeons will have nothing to do with this."

His fascination with knee anatomy has led him to reach out to experts at the Zoo and the Carnegie Museum of Natural History, and to others who have researched the evolutionary development of the joint.

Dr. Fu doesn't think Johnny the mandrill has a torn ACL, but he is eager to see what the animal's knee anatomy looks like.

"I think it's a meniscus tear," he said, referring to the tough cartilage that sits between the large leg bones of the knee joint.

"We're hopeful the ACL is intact, so we'll see how many bundles there are."