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I'm an athlete with a big problem. I have a deep hole in my right knee joint. I've opted to have a procedure called chondrocyte implantation. I'm trying to find out what happens after surgery. All I know is that I'll be in physical therapy for at least two months. Can you give me any more details than that?

Much has been written about the use of autologous chondrocyte implantation (ACI) to treat deep or large defects in the knee joint cartilage. Your question about what happens afterwards is a good one. We found a well-written article on this very topic. A group of orthopedic surgeons from the Department of Orthopedic Surgery at the University Hospital Freiburg in Germany are the authors. They reviewed all previous studies published on the topic of postoperative rehabilitation following autologous chondrocyte implantation (ACI). They summarized their findings in this article. The goal of the procedure is to create biologic remodeling of the cartilage. The basic technique involves harvesting healthy cartilage cells from a non-weight bearing surface of the patient's knee joint. Those cells are transplanted and used to fill in the defect (hole) in the damaged cartilage lining the joint surface. But as you have discovered, that's only part of the total picture. The athlete still has to regain knee motion and strength. Recovering normal nerve and motor control over all movements is essential. Athletes must be able to make quick changes in direction, move from one position to another, jump, and pivot over and over. Without normal neuromuscular control, reinjury is a real concern. Rehab must be guided according to what's happening with the transplanted tissue. Studies show that these transplanted chondrocytes (cartilage cells) start to stick right away. Care must be taken not to disturb them. Load and shear forces must be avoided. At first, the area remains more liquid than solid (like jello just starting to set up). But movement is important because the old saying, motion is lotion is still true. Movement and the pumping action of the knee as it bends and straightens is what help deliver blood to the area. Blood with its oxygen and nutrients feeds the chondrocytes. So how do we keep the knee moving without walking on it? That's where rehab specialists (physical therapists) come in. The therapist moves the leg for the patient starting on day one after surgery. This is called passive range of motion (PROM) exercise. Some surgeons are trying continuous passive motion (CPM) machines with patients. The leg is placed in this motor-driven device and moved continuously bending and straightening the leg for the patient. Studies using CPM following knee replacement surgery have not shown an overall benefit. There is limited evidence to support the use of CPM after autologous chondrocyte implantation. More studies are clearly needed. Whether passive motion is delivered by hand or by a machine, the goals are the same: prevent scar tissue from building up, restore joint motion, and keep the quadriceps muscle tuned up. The physical therapist addresses other areas as well. The knee joint (including the patella or kneecap) is manually (a hands-on treatment technique) mobilized or moved. The therapist does this without moving the joint by gently applying traction and tiny oscillations (movements) to the bones that make up the joint. Mobilization techniques are also applied to the soft tissues around the joint to keep them soft, moveable and free of adhesions. Other treatment modalities (tools) used by the therapist during the early post-operative phase include cold therapy (called cryotherapy) and manual lymph drainage. These two therapies may help decrease swelling, pain, and decrease the temperature around the healing cartilage. Cryotherapy is important because studies show that too much heat in a joint can cause breakdown of the chondrocytes (cartilage cells). When the repair tissue starts to solidify (moves from a jello to spongy consistency), then there is enough strength to withstand some partial weight-bearing activities. How much weight and how soon the patient can put weight on the knee are still unknown areas. Some therapists have experimented with partial weight-bearing (minimal loading of the knee) as early as two weeks after implantation. Around eight weeks after surgery, the transplant has filled in the defect and new, healthy cartilage cells are present. As the tissue continues to build and remodel over the next weeks (the patient is now three to six months out from the surgery), the therapist steps up the rehab program. Patients are instructed how to increase weight-bearing and improve walking pattern. Pool-therapy is especially helpful in starting gait training. Full weight-bearing on land is usually allowed eight to 12 weeks after the implantation procedure. Around six months post-op, the transplanted tissue changes from spongy to the consistency of soft plastic. Now the therapist can progress the rehab program to focus on strengthening, endurance, and functional training. Studies consistently show that quadriceps strength is a major factor in the success of this procedure. In fact, regaining full quadriceps strength is considered the most important goal of rehab following autologous chondrocyte implantation (ACI). Additional areas of focus in rehab include restoring proprioception (joint sense of position) and sensorimotor control. Full return-to-sports can still take a while. The final healing phase of the chondrocytes is called maturation. If there are no complications (e.g., wound infection, overgrowth of the graft, graft failure), the entire process from start to finish can take two to three years. The biggest deterrent to recovery is putting weight on the joint too early and/or another traumatic injury disturbing the delicate transplanted tissue. We hope this information gives you a general idea what to expect. Each athlete is different so rehab may flow at a slightly slower or faster pace. Some of this depends on how strong and coordinated your muscles were before surgery. Patient compliance (following the surgeon's and physical therapist's recommendations carefully) can also make a difference.


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