What is OATS Knee Surgery?

OATS knee surgery, or Osteochondral Allograft or Autograft Transplantation Surgery, is a bone/cartilage transplant procedure used for treatment of varying degrees of articular cartilage lesion. This procedure works to preserve the existing joint by inserting donor material to help regenerate damaged tissue, rather than replacing the joint with an implant. In this article you will find information on the anatomy and physiology of the knee joint, pathophysiology of knee damage, treatment options and helpful information on OATS knee surgery.

Anatomy and Physiology of the knee

Understanding the anatomy and physiology of the knee joint may be helpful in comprehending health of the knee, injury sustained to the knee, and understanding treatment options for knee injury.

This article focuses on the injury to the osteochondral part of the knee and attempts to give an overview of other parts of the knee and focus on bone and cartilage injury.

The knee joint, similar other joints in the human body, is made up of bone, cartilage, muscles, tendons and ligaments, bursae and menisci.

Bones (referred to by the prefix osteo-) involved in the knee joint include the femur (thigh bone), patella (kneecap), and the tibia and fibula (shin bones).

The femur is a long bone that connects to the shin bones. At its distal end (the part that is considered part of the knee joint), it has two bony protrusions called condyles. These are covered in cartilage (referred to by the suffix -chondral).

Two menisci protect the two condyles on the end of the femur by providing cushion, shock absorption, and frictionless movement between the femur and the shin bones. As you can imagine, much weight and movement is sustained in the knee so these menisci are necessary in relieving some of the pressure of activities like walking, running, jumping, squatting, kneeling, pivoting, twisting and lifting.  Sometimes, too much weight, pressure or jerky movements are too much for the menisci to protect, so damage is caused to the cartilage and bone on the end of the femur. 


Chondral lesions, or cartilage damage can be caused by degenerative or traumatic injury. Degenerative refers to the wear and tear that happens over time, while traumatic refers to an acute event such as a twist, hard landing, pivot or fall.

Both types of injury can cause a lesion to develop in the cartilage on the end of the bone. The lesion may not appear right away, but rather can progress, over time. This may cause pain, stiffness, instability, or a ‘locked’ feeling in the knee.

Staging of injury

Medical professionals use a system of classification for injury to the osteochondral areas called staging in order to most effectively plan treatment. Staging is determined by level or degree of lesion or injury and advances from I-V.

Knee cartilage/bone damage can range from a small crack (fracture) to a piece chipping or breaking off.

Below is a list of the different grades or stages of injury:

Stage I:

  • Injury is limited only to the outermost layer of chondra (articular cartilage).

Stage II:

  • Injury or fracture has progressed to the next layer of chondra (subchondral layer).

Stage III:

  • Fracture has completely detached a piece in the osteochondral (cartilage and bone) area. This piece is detached but not displaced. In other words, it is broken but has not moved out of its original placement.

Stage IV:

  • Fracture can completely detach a piece in the osteochondral area. The broken piece has moved away from its original position.

Stage V:

  • A cyst (or sac-like pocket containing air, fluid or other tissues) develops in the subchondral area.

Treatment options:

  • Weight loss- as the knees already bear much of our bodies’ weight, people who are overweight can reduce the amount of stress on their knees significantly by achieving a healthy weight. If caught early enough, weight loss and change in activity may be enough to reverse or at least stop further damage.
  • Physical or occupational therapy
  • Wearing a brace or using assistive devices
  • Surgery
    • Microfracture knee surgery
    • OATS procedure

OATS Procedure

OATS is an acronym that stands for: Osteochondral Allograft Transplantation Surgery. No wonder they use an acronym! Let’s define those words:

  • Osteo- bone
  • Chondral- cartilage
  • Allograft- tissue that can be transplanted from a donor to a recipient
  • Transplantation: when a substance (tissue, fluid, organ, other material) is taken from a donor and placed into a recipient

OATS procedure is a surgical treatment that takes bone and cartilage from a donor and transplants it to the recipient’s affected knee allowing for healing and regrowth of the damaged cartilage and bone.

The OATS procedure is a type of “mosaicplasty,” which is the general surgical term referring to a procedure that addresses cartilage damage.

Who needs an OATS knee surgery?

The OATS knee surgery is geared toward people who have a chronic knee injury but who do not need (or want) a knee replacement.

What do I need to know before I have my OATS procedure?


As with any surgical procedure you’ll want to make sure that you go through the following checklist in order to prepare:

  • Ask your doctor any questions or concerns you have about the procedure and recovery.
  • Get plenty of good rest.
  • Eat healthily and drink lots of water.
  • Follow your doctor’s instructions about eating/not eating and taking/not taking medications the night before or day of your surgery.
  • Prepare your home. (For example, think about what you use on a daily basis that you normally need to bend down to reach and move it to waist height. Or, consider making a bed for yourself on the same level as the bathroom and kitchen so you do not need to go up or down stairs.)
  • Pick up any devices you might need. (Example: crutches, braces, ice packs, bandages)
  • Arrange for help with food, children or pets.


Upon arrival at the hospital, you will be asked a variety of health history questions. You may be given some medications and asked to sign a consent form. A nurse may start an IV to give you fluids and other medications during the surgery.

You will then be taken to an operating room and put to sleep, as OATS knee surgery is done under general anesthesia.

OATS knee surgery is done using a technique called arthroscopy. Simply, arthroscopy means a small scope is inserted through the skin into the knee joint for the physician to view the joint on the inside. Usually, a few puncture holes are made in the skin around the knee so that the scope and other tools can be inserted as well in order for the surgeon to actually complete the procedure on the joint.

It is through these puncture wounds that the donor cartilage is inserted and placed into the recipient’s knee joint.

Afterward, the wounds are stitched together and bandaged. You will receive instructions from your surgeon about caring for the wound.

Then, you will be taken to a recovery room and assisted in waking up from the anesthesia. Your doctor, surgeon and likely physical therapist will help decide when you can go home and give you more instructions for your recovery.



For the surgery, you may be given or prescribed some medications. Some of these medications will be administered at the same time or during the surgical procedure and others you will be directed by your physician to take after the surgery. Medications may include the following:

  • Pain medication
  • Anti-inflammatory- to reduce swelling
  • Thrombolytic- to prevent blood clots
  • Antibiotic – to prevent infection

To ensure a healthy and long-lasting outcome, physical therapy is essential.

You will likely be referred to a physical therapist who will coach and guide you in your recovery. Therapy may be recommended for many months following this type of surgery, and your doctors may even encourage you to keep doing certain exercises or stretches for years in order to maintain the health and function of your knee joint.

Because this is not a total knee replacement, you may be susceptible to a similar type of injury again in the future. For this reason, it is important to listen to your doctors and follow their rehabilitation recommendations.

Length of recovery

The length of recovery for an OATS procedure will depend on your unique anatomy (age, physical abilities, the severity of damage, how quickly the graft/transplant begins to integrate and produce a healthy joint).

A typical recovery can be estimated between six to 12 weeks.

You will likely need to follow recommendations for non-weight bearing and/or limited weight bearing throughout the course of your recovery. Therefore the use of crutches will be indicated. Your doctor may also have you use other assistive devices such as a continuous passive motion machine or brace.

During your recovery, you will be under the advice and guidance of a physical therapist as well as your orthopedic doctor, surgeon and/or family doctor. They will do many follow-up checks as well as give you instructions for how to slowly begin using your knee after surgery.


Possible complications of an OATS knee surgery may include the following:

  • Skin nerve damage (numbing)
  • Bleeding
  • Blood clot
  • Infection
  • Transplant rejection
  • Transplant cartilage does not fully integrate with recipient’s cartilage
  • Need for another surgery

Expected outcome:

Overall the procedure can be very successful for the right candidate. OATS knee surgery can provide pain relief, increased mobility, strength and stability for those who have suffered from injury for years.

One study, completed in 2016 reported that 72% of patients showed overall success after an OATS surgery.

Factors contributing to a higher success rate are:

  • Lower age
  • Less severe injury or damage
  • No prior knee surgeries

Talk to your doctor about your knee pain to see if an OATS knee surgery is right for you.

Kelly Frey Martin
Kelly Frey Martin

Kelly is a labor and delivery nurse from Goshen, Indiana. She is now using her talents in Colombia, South America where she and her husband work with youth to develop life and leadership skills.