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ORTHOPAEDIC MEDICINE CARTILEAGE REGENERATION
inconspicuous or overshadowed by adjacent fat tissues and hence may not be easily identifiable. If symptoms do point towards the pathology, then the clinical suspicion should be high, and a diagnostic arthroscopy (keyhole procedure) should be considered.
to improve with conservative measures and if the mechanism of injury would be in keeping with a potential internal knee derangement.
A large proportion of patients suffer
acute stabbing pain immediately after the injury, while swelling often occurs several hours later. If knee swelling develops almost instantaneously, damage to internal ligaments such as the anterior cruciate ligament (ACL) is likely and needs to be ruled out. Weight-bearing may be painful and difficult during the first few days. Thereafter, patients may suffer from locking or giving-way of the knee, particularly when twisting, turning or descending stairs. If the surface cartilage is fissured during the initial injury, it may take several days or even weeks before a cartilage flap develops and breaks off. Under these circumstances, a loose body forms in the joint, which may subsequently impinge and cause locking of the knee. Once the damage has occurred, almost all patients describe a localised, toothache-like discomfort, particularly after any type of physical activity. Rest usually helps to ameliorate symptoms.
DIAGNOSIS
Most clinicians examine the knee and may raise the suspicion of cartilage damage but are unable to confirm this unless further investigations are undertaken. Magnetic resonance imaging (MRI) has been the investigation of choice as it allows visualisation of all soft-tissue structures, including ligaments, menisci and surface cartilage, with high accuracy (10). Standard radiographs fail to demonstrate cartilage, which is radiolucent, and merely show the bony structure of the knee joint. MRI should, however not be considered the panacea in the diagnostic process, as many cartilage defects are small and somewhat
Figure 1: Large full thickness surface cartilage defect in the weight bearing zone of the knee
REPAIR OF DAMAGED CARTILAGE Traditional cartilage repair techniques are all based on stimulating the bone marrow below the joint surface. This can be facilitated by abrading the surface using a burr (abrasion arthroplasty) or through producing little indentations with a metal awl or spike (microfracture). In both cases the clinician injures the subchondral surface, creating a temporary blood supply and subsequent development of fibrous cartilage (11,12). The technique is not new and was first described by Kenneth Hambden Pridie from Bristol in 1959, but it has re-emerged through
the ability to perform the procedure arthroscopically (3). Unfortunately fibrous cartilage is mechanically inferior to hyaline cartilage and hence more likely to wear. A breakthrough in the creation of
hyaline cartilage came in the 1970s, when Bentley and Greer observed that transplanted chondrocytes (cartilage cells) enhanced the healing of cartilage defects in rabbits (4). Two Swedish orthopaedic surgeons took up the idea and were able to report on their first series of chondrocyte implantation performed on humans in 1994 (Figs. 2 and 3) (13). They called their technique “autologous chondrocyte implantation” (ACI). The basic principles of this operation have not changed since its inception and are based on obtaining a small sample of the patient’s own (autologous) cartilage, which is cultured in the laboratory and later re- implanted into the surface defect (14–19). Thereafter, the implanted chondrocytes set in motion a complex process of matrix regeneration, which eventually leads to the development of tissue closely resembling hyaline cartilage (8).
Figure 2: First stage procedure: arthroscopic assessment of
exact size and location of surface cartilage defect combined with cartilage biopsy. Cartilage may be harvested from non weight bearing areas in the joint periphery or from loose
cartilage flaps within the lesion. (Image provided courtesy of Genzyme Therapeutics, Oxford, UK)
Figure 3: Autologous chondrocyte implantation
technique (ACI): A
membrane is sutured onto the defect and sealed using fibrin
glue. Cartilage cells are then injected into the space beneath it.
THE PROCEDURE Unless a preoperative MRI has confirmed the patient’s suitability for chondrocyte implantation, the final decision must rest with the clinician, who will have a much better appreciation of the damage when looking inside the joint. The surgery is performed in two stages. During the first operation, a keyhole procedure, the surgeon obtains a cartilage biopsy, mostly taken from loose cartilage flaps in the periphery of the defect or from non-weightbearing aspects of the joint (Fig. 2). The biopsy is immediately sent to a laboratory in Denmark or Germany, where the cells are cultured over a
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