PITTSBURGH -- A first-of-its-kind primate procedure was performed at the Pittsburgh Zoo and PPG Aquarium Wednesday.

Dr. Freddie Fu, chairman of orthopedic surgery at the University Of Pittsburgh School Of Medicine, performed an arthroscopic knee procedure on an 11-year-old mandrill monkey.

Keepers at the zoo suspected the mandrill, who is named Johnny, was having some pain in his knee.

Zoo veterinarians teamed up with the nationally known orthopedic surgeon to find out what was troubling Johnny.

Fu found that Johnny’s anterior cruciate ligament, ACL, was partially torn.

Human ACLs have two bundles of tissue, but Fu discovered that this mandrill has three.

In order to treat his patients effectively, Fu and his staff have been looking at how the knee functions in different species.

The standard method of treating an ACL injury is to repair one bundle of tissue even though there are two.

Fu, however, contends that knee surgery must replace both bundles to be truly successful.

In the United States, about 200,000 people a year tear the ACL.

This procedure was an exploratory surgery to find out what was wrong with the mandrill’s knee.

Fu said the mandrill’s knee damage can not be repaired. He did clear away some inflamed tissue, which he said may give the mandrill some relief from his pain.

After the procedure, Fu said doctors must treat all ACL injuries on an individual basis.

He also said that taking part in procedures like this helps him continue learning, which he said is vital to being the best surgeon he can be.