Microfracture

This technique involves creating small holes in the bone beneath the cartilage defect to allow bone marrow cells to reach the damaged area. The surgeon uses specialised tools to penetrate the subchondral bone, creating channels for marrow elements containing stem cells to enter the defect site. These cells form a blood clot that eventually develops into fibrocartilage tissue. While not identical to native cartilage, this repair tissue can provide improved joint function and pain relief.

Autologous Chondrocyte Implantation (ACI)

ACI is a two-stage procedure that uses the patient’s own cartilage cells to repair defects. In the first procedure, the surgeon arthroscopically harvests a small sample of healthy cartilage from a non-weight-bearing area of the joint. These cartilage cells (chondrocytes) are then cultured and multiplied in a laboratory for several weeks. During a second surgery, the expanded chondrocytes are implanted into the defect site beneath a membrane that holds them in place while they generate new cartilage tissue.

Osteochondral Autograft Transfer (OAT/Mosaicplasty)

This technique involves transplanting small plugs of healthy cartilage and underlying bone from low-weight-bearing areas to the defect site. The surgeon harvests cylindrical plugs of cartilage and bone from donor sites within the same joint and precisely fits them into similarly sized holes created at the defect location. Multiple plugs may be placed in a mosaic pattern to resurface larger defects. This procedure provides immediate restoration with mature, native cartilage tissue.

Matrix-Induced Autologous Chondrocyte Implantation (MACI)

This technique incorporates the patient’s cultured chondrocytes onto a collagen membrane prior to implantation. After harvesting and expanding the patient’s cartilage cells, they are seeded onto a specialised collagen scaffold in the laboratory. The cell-laden scaffold is then cut to match the defect size and secured with fibrin glue. This technique simplifies the surgical procedure and provides a more even distribution of cells throughout the repair site.

Anaesthesia Administration

The procedure begins with appropriate anaesthesia to ensure patient comfort. General anaesthesia or regional anaesthesia (spinal or nerve block) is administered based on the technique and patient factors. Vital signs are continuously monitored throughout the procedure.

Surgical Approach

Access to the joint is gained through carefully planned incisions. Arthroscopic procedures like microfracture use small 5-10mm portals for a camera and instruments. ACI, MACI, and OAT/mosaicplasty may require larger incisions, particularly during implantation. The joint is thoroughly examined to confirm the defect’s location and dimensions.

Defect Preparation

The damaged cartilage area is cleaned and prepared according to the specific technique. Loose fragments are removed, and the borders are trimmed to create stable walls of healthy cartilage. For microfracture, the calcified layer is removed to expose subchondral bone. For ACI and MACI, precise measurements ensure proper cell placement. For OAT, recipient sites are prepared to match donor plugs.

Technique-Specific Implementation

• Microfracture: Specialised awls create small holes in the subchondral bone at 3-4mm intervals, allowing marrow cells to reach the defect site and form a reparative clot.
• ACI: Previously harvested and laboratory-expanded chondrocytes are injected beneath a membrane sutured over the defect.
• MACI: The cell-seeded collagen membrane is sized to match the defect and secured with fibrin glue for even cell distribution.
• OAT/Mosaicplasty: Cylindrical plugs of healthy cartilage and bone from non-weight-bearing areas are press-fitted into matching recipient holes, using multiple plugs for larger defects.

Additional Procedures

Concurrent issues affecting cartilage repair success are addressed. Ligament instability may require reconstruction, joint malalignment may need osteotomy, and meniscal tears are repaired to optimise the joint environment for the cartilage repair.

Closure and Dressing

The surgical site is closed in layers with appropriate sutures to restore anatomic structure. A sterile dressing is applied, and in some cases, a brace restricts motion during initial healing.