We assume you are referring to autologous chondrocyte implantation (ACI), the fairly new cell-therapy for cartilage defects of the knee. The first study published on the topic was in the early 1990s. So it’s been around for about 20 years but it is still being studied and improved upon.
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. The goal of the procedure is to create biologic remodeling of the cartilage.
Rehab must be guided according to what’s happening with the wound (incision sites) and 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).
Of course, pool therapy is usually held off until the skin wounds have healed. In the meantime, 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.
Passive range of motion (PROM) exercise can be started on day one after surgery. Some surgeons are trying continuous passive motion (CPM) machines with patients. 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.
As a physical therapist, you will be addressing other areas as well. The knee joint (including the patella or kneecap) can be mobilized or moved. Mobilization techniques can also be applied to the soft tissues around the joint to keep them soft, moveable and free of adhesions.
Other treatment modalities (tools) used by other therapists 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 incisions heal, patients can indeed begin aquatic (water-based) therapy. Aquatic therapy is considered beneficial throughout the postoperative period. As you know, working in the water reduces the effects of gravity and therefore unloads the joint. The weight-bearing force placed on the joint is only 25 percent of the body weight when the water is up to the armpits. Moving through water at waist level reduces the load to 50 per cent of the person’s body weight.
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. Both land-based and aquatic therapies can be used during this phase as well.
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. Once again, this is where water-based therapy can be so helpful.