Cartilage Repair


  • the surfaces of the ends of the bones in the knee are covered in a layer of smooth white cartilage, called 'articular cartilage'

  • cartilage can be damaged by trauma or through wear and tear (arthritis)

  • cartilage damage can cause pain, swelling, clicking, giving way or locking in the knee

  • cartilage damage can be treated by keyhole surgery of the knee (arthroscopy)

  • mild cartilage damage can be treated by shaving it smooth

  • more severe damage can be treated by either 'microfracture' or 'cartilage transplantation'

  • microfracture involves drilling tiny holes in the base of a crater of missing cartilage, which encourages it to heal up on its own

  • cartilage transplantation involves taking a sample of a patient's own cartilage, growing it and multiplying it in a lab and then inserting in back into the knee 6 weeks later

  • microfracture may be more appropriate for small patches of cartilage damage

  • for bigger areas of damage cartilage transplantation is better

  • the results of cartilage repair are about 80% good-to-excellent at 5 years follow-up

Loose pieces of cartilage within the joint can be removed easily by arthroscopic (keyhole) surgery, which may alleviate mechanical symptoms such as locking or giving way.

Small patches of roughened or fibrillated cartilage can be smoothed off arthroscopically (by keyhole surgery) using miniature motorised shavers. This is referred to as 'abrasion chondroplasty'.

Severely damaged cartilage, for example where there are deep cracks and fissures, can be treated arthroscopically by radiofrequency ablation. This is where a special probe is inserted into the joint and used to 'melt' the top surface of the cartilage to smooth it off. A good analogy is to think of cartilage damage as flaky peeling paint on a rusty gate. If one just picks at the edges, more paint simply peels off. If one uses a blow torch then the edges of the pain are melted and become smooth and stuck down, preventing any further peeling.

Where there are areas of complete cartilage loss down to bone, a number of different surgical procedures have been developed to try and deal with the problem:-


This is where little holes are drilled in the area of missing cartilage. Small pegs of cartilage plus bone are then taken from non-weight bearing areas of the knee and plugged into the holes.
This procedure was popularised by Hangody in Hungary.

Diagram showing techniqe of mosaicplasty. Pegs of cartilage and bone are taken from 'non-weight-bearing' areas and inserted into the cartilage defect.

Intra-operative view of a mosaicplasty performed on a medial femoral condyle - note the multiple circular pegs.

However, there are issues with the procedure in that:-

  • It is an invasive open procedure
  • There is concern over the damaged caused to the 'donor site', where the cartilage/bone peg is actually taken from
  • Significant gaps are left in between the inserted pegs
  • The new cartilage surface can be uneven and irregular
  • There is significant scope for complications

For all of the above various reasons, mosaicplasty has recently fallen in popularity among many surgeons. Newer syntheic plugs offer an alternative to traditional mosaicplasty



Autologous Chondrocyte Implantation (aka Transplantation) is a procedure whereby an initial operation is performed to harvest some cartilage from a non-weight bearing area of the joint. This cartilage is then sent to a lab where it is grown in culture, to multiply the number of cells. Some weeks later (about 6 weeks) a second procedure is performed whereby the joint is opened up, the bare area of bone where the cartilage is missing is cleaned, a membrane of collagen (a natural material) is fastened over the defect and the cultured cells are injected under the membrane. This gives an appearance not too dissimilar to The London Dome!

Picture showing harvesting of cartilage cells from a 'non-weight-bearing' area of the knee (Stage 1 surgery).

Stage 2 surgery - the cells have been multiplied in the lab and are injected back into the knee under a covering (a membrane of collagen).

ACI was popularised by Lars Petersson in Finland, and in the UK most work with this procedure has been from two main centres; Stanmore and Oswestry. However, there are a number of significant concerns with the procedure of ACI:-

  • An initial operation has to be performed to harvest the cartilage cells. A second operation has to be performed to cover up the cartilage defect and insert the cells. Approximately 20% of patients will then go on to require a third operation to sort out potential complications such as overgrowth of the new cartilage.
  • The operation to insert the cartilage cells is an invasive open procedure.
  • Histology samples of the new tissue grown from ACI has shown it to be "hyaline-like", i.e. not normal hyaline articular cartilage, but more like part scar tissue.
  • It is a difficult and complex procedure, with time constraints and requiring significant special equipment at large expense.
  • The potential for complications is significant.


This is a procedure popularised by Steadman, from Vale, Colorado. Steadman is the knee surgeon who has operated on many international level professional athletes, including recently Michael Owen.
Microfracture involves making several small holes in the base of a cartilage defect, puncturing the surface layer of the underlying bone (the subchondral bone plate). This causes bleeding into the crater of cartilage loss. The blood clots and solidifies. The clot is rich in cells, including Stem Cells (cells within the body that have the potential to turn into any other type of cell). The clot therefore matures and develops into a patch of fibrocartilage.

Picture demonstrating the concept of microfracture.

Arthroscopic view of microfracture being performed.

Microfracture seems to be gaining significant popularity as the potential procedure of choice for the treatment of small to moderate patches of cartilage loss. The advantages are that:-

  • The procedure can be performed straight away, at the first sitting when a cartilage defect is first found intra-operatively.
  • Microfracture can be performed arthroscopically, without the need for open incisions.
  • The procedure uses simple basic equipment (ie, there is less to go wrong!)
  • Microfracture requires just 1 procedure (as opposed to ACI which requires 2 or even 3 operations).


When cartilage damage is severe, it may be necessary to replace part or even the whole joint with a mechanical prosthesis, eg unicompartmental knee replacement, patellofemoral joint replacement or total knee replacement.

Which procedure would I have?

The published results of ACI and Microfracture are, generally, better than those reported for mosaicplasty. The results for ACI and Microfracture are pretty much the same, with both having an approximately 80% success rate (when evaluated at a point 5-years post-operatively). A randomised trial from America directly comparing ACI vs Microfracture found no difference in the results between the two procedures. Microfracture is a single procedure, performed arthroscopically, with a low potential complication rate and is therefore my procedure of choice for the patients that I see with small to moderate areas of articular cartilage loss. However, when there are larger areas of cartilage damage, then microfracture is inappropriate, and ACI is the procedure of choice.

Microfracture - the procedure and the rehab

Microfracture can be performed as part of a simple day-case arthroscopy. The procedure only adds a few minutes onto the time of the arthroscopy, which is normally performed within 30 to 45 minutes.

Post-op rehab depends to some degree on the size of the region treated and the location within the joint. Normally, patients are kept partial weight bearing with crutches for the first 6 weeks, sometimes with a brace to keep the joint in a certain position (or prevent it from reaching specific positions, eg deep flexion). Intensive rehab is usually commenced at 6 weeks post-op, in order to regain the range of motion and strength in the joint and to retrain the reflexes (proprioception). Running and sport are often prohibited until at least 3 months post-op, and return to exercise and sport is normally advised to be under the supervision of an appropriately trained physiotherapist.

Article written by
Mr Ian McDermott
Consultant Knee Surgeon and Hip Surgeon, London & Northwood
Last updated 13/01/10

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