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Autologous Chondrocyte Implantation (ACI) Explained

Autologous chondrocyte implantation (ACI) is a surgical procedure used to repair cartilage defects by transplanting a patient's own cartilage cells back into the damaged joint area.

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Things worth knowing about "Autologous Chondrocyte Implantation"

Autologous chondrocyte implantation (ACI) is a surgical procedure used to repair cartilage defects by transplanting a patient's own cartilage cells back into the damaged joint area.

What is Autologous Chondrocyte Implantation?

Autologous chondrocyte implantation (ACI) is a biological, cell-based surgical technique used in reconstructive orthopaedics to treat localised cartilage defects. The procedure involves harvesting healthy cartilage cells (chondrocytes) from the patient, expanding them in a laboratory, and reimplanting them into the damaged area of the joint. The goal is to regenerate hyaline-like cartilage and preserve long-term joint function.

Indications

ACI is primarily indicated for patients with localised, full-thickness cartilage defects (ICRS Grade III–IV) in large joints, most commonly the knee. Typical indications include:

Traumatic cartilage damage from sports injuries or accidents
Osteochondritis dissecans (bone-cartilage defects)
Focal cartilage defects in young, physically active patients

ACI is generally not suitable for patients with widespread osteoarthritis, as the procedure is designed for defined defect sizes (approximately 2–10 cm²).

Procedure Overview

Step 1: Cartilage Biopsy

In the first minimally invasive procedure (arthroscopy), a small sample of healthy cartilage tissue is harvested from a low-load-bearing area of the joint. The sample contains viable chondrocytes that are then sent to a specialised laboratory.

Step 2: Cell Culture and Expansion

In the laboratory, the harvested chondrocytes are cultured under sterile conditions and expanded over approximately 4–6 weeks. Depending on the generation of the technique, cells may be prepared as a cell suspension, seeded onto carrier matrices (matrix-associated ACI, MACI), or incorporated into biocompatible gels.

Step 3: Implantation

In a second surgical procedure, the expanded cells are placed into the prepared cartilage defect. In classical ACI, the cells are secured beneath a periosteal flap or collagen membrane. In matrix-associated ACI (MACI), the cells are seeded onto a three-dimensional scaffold that is glued or sutured directly into the defect.

Generations of ACI

1st Generation: Cell suspension beneath an autologous periosteal flap
2nd Generation: Cell suspension beneath a collagen membrane
3rd Generation (MACI): Chondrocytes on a bioresorbable carrier matrix

Rehabilitation and Recovery

Recovery after ACI is a gradual process that requires patience and commitment to physiotherapy. Protecting the joint in the early post-operative period is essential to allow the implanted cells to integrate. A stepwise rehabilitation programme typically includes:

Weeks 1–6: Non-weight-bearing or partial weight-bearing with crutches, passive range-of-motion exercises (CPM device)
Weeks 6–12: Progressive full weight-bearing, targeted muscle strengthening
Months 3–6: Functional training and return to daily activities
From Month 12–18: Gradual return to sport

Benefits and Risks

Clinical studies show that ACI produces good to excellent long-term outcomes in terms of pain reduction and joint function, particularly in younger patients with isolated defects. Potential risks and complications include:

Tissue hypertrophy or delamination of the implant
Incomplete cell integration
Joint stiffness (arthrofibrosis)
Infection (rare)
Requirement for a second surgical intervention

References

Brittberg M. et al. - Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. New England Journal of Medicine, 1994; 331(14): 889–895.
Kon E. et al. - ACI and MACI - Current status and perspectives. Injury, 2013; 44 Suppl 1: S11–15.
Mithoefer K. et al. - The microfracture technique for the treatment of articular cartilage lesions in the knee. Journal of Bone and Joint Surgery, 2009; 91(2): 287–296.

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