The articular cartilage covering the bony surfaces may become damaged or torn following a knee injury.
This type of injury is often associated with ligament tears or direct blows to the joint. Unfortunately the ‘hyaline’ cartilage covering the bone has poor healing potential and often leaves areas of bone exposed or a thin layer of scar tissue which doesn't work well.
If the area of cartilage injury is small or of only partial thickness, then symptoms may settle without any treatment or intervention. Small partial thickness flaps of cartilage may cause catching or crepitation symptoms in the knee and may be trimmed and smoothed using arthroscopic surgery.
If the area of cartilage damage is full thickness i.e. down to the bone this tends to cause more problems. Surgical techniques can be used to try and fill the gap in the cartilage with thicker, more durable tissue in an attempt to delay or prevent arthritis. Unfortunately the results of cartilage ‘regeneration & repair’ techniques are not yet producing a surface as good as the original hyaline cartilage.
The more common procedures for cartilage restoration include:
- microfracture
- autologous membrane induced chondrogenesis (AMIC)
- autologous chondrocyte implantation (ACI)
Microfracture is a surgical option used to treat smaller areas of damaged cartilage, not widespread arthritis. Microfracture is performed to stimulate new cartilage growth.
The microfracture procedure involves the surgeon making multiple small holes into the bone where the cartilage is absent and allowing an influx of blood, rich in growth factors, to coat the bone surface. This forms a blood clot that over time develops into new cartilage, also known as fibrous cartilage. This fibrous cartilage helps protect the damaged joint, however it is not as durable as the normal hyaline cartilage.
The microfracture procedure is usually performed arthroscopically as a day case procedure or with an overnight stay.
The real key to treatment is appropriate rehabilitation following the surgery. Rehabilitation must protect the area treated by microfracture as well as maintain the strength and motion of the knee joint. The rehabilitation regimen depends upon the location and size of the area being treated.
The general principles of the rehabilitation for microfracture are outlined below:
- protected weight-bearing – usually crutches are used for the first six weeks. The amount of weight put on the treated area must be limited allowing the new cells to grow and develop. Crutches are used for the first six weeks reduing the force passing across the knee. If the microfracture has been carried out on the kneecap (patella) or within the groove for the patella (trochlea) then a knee brace may also be worn to prevent the knee bending more than 30 degrees
- weight bearing is usually limited for six weeks, and then gradually increased over time. It may take six to nine months before returning to sporting activities, and even longer to return to competition. Professional athletes may be side-lined up to a year after microfracture surgery
- range-of-motion - is usually initiated early on after surgery. However, if the area of microfracture treatment is on the kneecap or within its groove, then motion will be limited for several weeks. The aim is to restore full range of movement with minimal force passing through the joint and this can be achieved using a cycling machine on the lowest resistance setting or sitting with your foot on a skateboard and slowly bending and straightening the knee. The reason for starting motion as early as possible is that the movement helps stimulate cartilage growth in the area of microfracture
Autologous matrix-induced chondrogenesis (AMIC) is a biological treatment option which can be used to treat cartilage damage. It combines microfracture surgery with the application of a complex membrane tissue made from collagen. The collagen membrane allows treatment of larger cartilage lesions that are not suitable for microfracture treatment alone.
The AMIC procedure is a minimally invasive, single step technique. Initially microfracture is performed to the area of damaged cartilage and unstable fragments of cartilage are removed. A protective Chondro-Gide membrane is then secured over the treated area, encouraging the migration of new cells into the injured area and protecting the developing cartilage tissue.
The rehabilitation following AMIC surgery is very similar to that of microfracture. For the first two days the knee is usually kept straight in a knee brace and then range of movement exercises are commenced. As with microfracture, weight needs to be kept off the knee for the first six weeks.
ACI is a biological treatment used to treat larger cartilage defects. It is not used to treat generalised arthritis or ‘wear-and-tear’ in the knee. Suitable patients would be generally young and healthy individuals, who have had an injury to the knee over the past few months or years, and have on-going pain, swelling and mechanical problems. Although cartilage damage is often associated with ligament and meniscal injuries, it is important that the knee is stable and that there are no major alignment problems, prior to cartilage repair.
ACI requires two surgical procedures. Initially healthy cartilage cells (chondrocytes) are harvested using arthroscopic surgery from a non-weight bearing part of the knee and sent away to be grown in a laboratory for approximately 6-8 weeks. A second, more invasive, procedure is then used to re-implant the ‘new’ cartilage cells into the damaged area.
Over time the new cartilage cells begin to produce protective cartilage in the damaged area. This new cartilage is not ‘normal’, however may be more protective in the longer term than the scar tissue formed following microfracture.
Rehabilitation is critical to a long-term recovery and your surgeon and physiotherapist will discuss this programme with you.
