Human knee surgeons took their expertise, their curiosity and their scopes to the Pittsburgh Zoo & PPG Aquarium yesterday to figure out what ailed Johnny, a 12-year-old mandrill.

	Post-Gazette Dr. Freddie Fu shows the flexibilty of the mandrill's knee compared to a human one. Dr. Fu, an orthopedic surgeon and chairman of the orthopedic department at the University of Pittsburgh School of Medicine, operated on Johnny the mandrill yesterday morning at the Pittsburgh Zoo. Click photo for larger image.

After a 90-minute procedure that might be a first for mandrills, Dr. Freddie Fu, chairman of the orthopedics department at the University of Pittsburgh School of Medicine, determined that the anterior cruciate ligament, or ACL, in Johnny's left knee was the culprit.

"This mandrill monkey has a partial ACL tear," he said, adding that Johnny will "have to live with this or he'll have to adjust his lifestyle" because a repair is not practical. The surgeon did clear away inflamed tissue in the joint, which could provide some pain relief.

According to a zoo spokeswoman, the mandrill appeared to be doing well after the arthroscopy. Two small holes, one on each side of his knee for insertion of the scopes, will heal uncovered.

The ACL injury surprised Dr. Fu, who thought debris in the joint or damage to the meniscus, or cartilage pad, would turn out to be the cause of Johnny's sore knee. He praised keeper Suellen Stanley's attentiveness for spotting that the mandrill had been grabbing and poking at his knee intermittently for a few months.

Because of her observations, zoo veterinarians contacted Dr. Fu, who developed an interest in knee evolution while refining ACL repair in humans.

He and his colleagues at UPMC's Center for Sports Medicine have learned the human ACL is actually a merger of two bundles of tissue, and each attaches to the leg bones in specific places.

But in conventional repair, the ACL is regarded as a single bundle and replacement grafts are often anchored in locations that are not anatomically accurate, potentially leading to a knee joint that doesn't work as well as it should.

While it's a good procedure, "there is big room for improvement," Dr. Fu said.

He and his team are gathering information from humans and animals to demonstrate that the "double-bundle" approach to ACL repair better reflects normal anatomy and is better for patients.

From yesterday's procedure, Dr. Fu learned that the mandrill has three bundles in its ACL, and the one that is most important to knee rotation was torn in Johnny. A comparable injury occurs in humans, but it is rare, the surgeon said.

He's performed about 400 double-bundle arthroscopies and seen partial tears, meaning one rather than both of the two bundles has been damaged, in 20 cases, 10 of each kind.

Examination of rhesus monkey cadavers indicates that they, too, have a triple-bundle ACL, just as goats do, while rabbits have just one. Dr. Fu's research team will examine the ACLs of lemur, woolly monkey and howler monkey specimens.

"I'd like to scope an elephant, an ostrich, a kangaroo," Dr. Fu added.

His fascination with knees led him to contact experts at the Carnegie Museum of Natural History, where he's checked fossils for a bony ridge on femurs, or thigh bones, that indicate a double-bundle ACL.

"The fact that evolution has maintained this structure for millions of years means it's functionally important to the way that knees move and bend," said Christopher Beard, the museum's head of vertebrate paleontology.

As a person squats or straightens, the femur rotates with respect to the tibia, or shin bone, so "your knee joint is not quite as simple as a door hinge," he explained. Dr. Beard noted the work with Dr. Fu grew in part out of a collaborative program with the medical school called the Natural History of Medicine.

Dr. Fu plans to meet next week with renowned paleoanthropologist C. Owen Lovejoy, of Kent State University, who has long studied the knee. The orthopedic surgeon will probably learn more about "old knees," the fossil expert about "living knees," and they'll "meet in the middle," Dr. Lovejoy said.

"Human knees are very different from any other primate knee," he said. "We have lots of specialization that allows us to walk upright effectively, without injuring ourselves too much."

Dr. Lovejoy's research indicates that the ACL is made of many fibers of different lengths, so if pulled upon they wouldn't all pop apart at the same time.

"If I had a torn ACL, I'd want [Dr. Fu] to reconstruct it," Dr. Lovejoy said, chuckling. "He clearly recognizes the subtleties of the structure."