For microfracture: performed arthroscopically. Small holes are drilled into the bone beneath the cartilage defect, releasing stem cells that form a repair tissue (fibrocartilage). For MACI: a two-stage procedure. First, a small sample of cartilage is taken arthroscopically and sent to a laboratory where the cells are grown on a scaffold for several weeks. In the second operation, the scaffold with cells is implanted into the defect through a small incision or arthroscopically.
Cartilage repair is considered for patients with localised, full-thickness cartilage defects in the knee causing pain and swelling, typically in younger, active patients. It is not suitable for widespread arthritis.
Physiotherapy, weight management, activity modification, anti-inflammatory medication, and intra-articular injections (corticosteroid, hyaluronic acid, or PRP). Osteotomy may be considered if alignment contributes to the problem.
MRI scan to assess the defect. For MACI, the first stage (cartilage biopsy) is a minor arthroscopic procedure. The second stage is planned four to six weeks later.
The aim is to reduce pain, improve function, and potentially delay or prevent the need for joint replacement. Microfracture produces fibrocartilage (less durable than normal cartilage). MACI produces hyaline-like cartilage with potentially better long-term durability.
Prolonged recoveryExpected
Cartilage repair requires extended rehabilitation with restricted weight-bearing.
Knee swellingExpected
Common during the healing phase.
StiffnessCommon
Temporary loss of movement requiring physiotherapy.
Graft failureUncommon
The repair tissue may not fully develop or may break down over time.
InfectionRare
Joint infection.
Blood clotsUncommon
DVT with prolonged restricted weight-bearing.
Continued symptomsUncommon
Pain may not be fully relieved, particularly if there are associated problems like misalignment.
General or spinal anaesthesia.
Non-weight-bearing or partial weight-bearing for six to eight weeks. Continuous passive motion (CPM) machines may be used. Physiotherapy is essential and continues for six to twelve months. Return to impact sport at nine to twelve months. Full maturation of the repair tissue takes twelve to eighteen months.
Regular reviews at two weeks, six weeks, three months, six months, and one year. MRI may be used to assess repair tissue maturation.
What is the difference between microfracture and MACI?
Microfracture is simpler but produces fibrocartilage, which is less durable. MACI uses your own laboratory-grown cartilage cells and may produce more durable hyaline-like cartilage. MACI is typically recommended for larger defects.
Will this prevent arthritis?
Cartilage repair aims to restore the joint surface and may delay the onset of arthritis, but it cannot guarantee prevention, particularly if the cartilage was significantly damaged.
Why is recovery so long?
The repair tissue takes many months to mature and strengthen. Premature loading can damage the new cartilage.