Introduction

Chondral and osteochondral defects may affect any major joint, but they more often affect the large weight-bearing joints such as the knee and ankle joints. They may be of traumatic or hereditary origin (osteochondrosis dissecans). The original hyaline cartilage may as yet not be restored, so a permanent loss of the original cartilaginous surface is inevitable and responsible for premature arthritis and eventually destruction of the affected joint. However, a stable fibrous cartilage may develop from mesenchymal stem cells invading the defects from the underlying blood vessels, which will yield the patient pain free and slow down the process of joint destruction. Several methods in cartilage reconstruction are available such as ACT/ACI (autologous chondrocyte transplantation/implantation),¹ matrix-induced autologous chondrocyte transplantation/implantation (MACT/MACI)^2,3,4,5,6 and microfracturing. The membrane-associated chondrogenesis is well documented in vitro. A variety of collagen scaffolds is commercially available and may be applied. Fixation is possible either with fibrin glue (allogenic or partially autologous) or sutures.

An advantage of the autologous matrix-induced chondrogenesis (AMIC) procedure is that it is a one-step process for the patient, allowing the blood clot yielded after microfracturing to stay at the desired location and the chondrocytes to develop on a collagen scaffold in situ. Any collagen matrix will suffice.

Surgical Principles and Objective

Step 2: Miniarthrotomy

Debridement of lesion: degenerated and detached cartilage is completely removed, microfracturing with a sharp awl or pick, and, if necessary, a mallet to perforate the subchondral bone every 5 mm; a template is made that matches the size of the defect, not overlaying the defect (Figs. 4C-1, 4C-2, and 4C-3).

FIGURE 4C-1 Identify the lesion and perform a miniarthrotomy after arthroscopy.

FIGURE 4C-2 Thorough curettage of the lesion is mandatory before microfracturing may be performed. An aluminium template is helpful for defining the lesion’s extent. At this time, a bone graft may be implanted in osteochondral lesions.

FIGURE 4C-3 After curettage of the lesion, the microfracturing may be performed every 5 mm.

Step 5: Fixation of Matrix with PAF

The matrix is glued directly onto the prepared defect and is adjusted digitally. Finally the knee joint is held in an extended position for 5 minutes (Fig. 4C-4, A-H).

FIGURE 4C-4 The repair with AMIC, seen in a sequence. A, B, and C, Cartilage defect, preparation by microfracturing with sharp awl or pick, and removal of debris. D, Preparing a template that matches the defect size. E and F, Glue is directly applied, and matrix is glued directly onto prepared defect. G and H, Matrix in place.

Afterward, flex the knee 10 times to test the stability and correct position.

Postoperative Treatment

Thrombosis prophylaxis should be used from the start of the operation. Medication, ice application, lymph drainage, and muscle stimulation or electrotherapy can be part of the postoperative treatment.

Dangers, Errors, and Complications

The patients must be compliant and aware of a lengthy postoperative therapy. The absence of work may be considerable.

Undersizing the matrix is mandatory, especially when the fixation with fibrin glue is chosen. An oversized membrane is likely to dislocate!

The patient should be aware that an arthrotomy is performed, and that the risks of an intraarticular infection are higher than with simple arthroscopy.