period of 5–7 weeks to increase the number to approximately 2–5 million (13). Once the cell-culturing process is complete, only a very small window of time exists for the implantation process to be performed, as freezing affects the cells’ viability. In the second operation, the clinician makes a small incision into the knee to visualise the damaged area, which is cleaned thoroughly. A collagen membrane is then sutured on to the defect and the chondrocytes injected beneath (Fig. 3). Over several months, these cells create a matrix to re- establish the articular surface to the level of the surrounding cartilage. However, technical difficulties and problems with cell leakage and delamination and graft overgrowth (hypertrophy) have been reported (14,18–21). The implantation of cultured chondrocytes in suspension has led to concerns about the uneven distribution of chondrocytes within the defect and the potential for cell leakage (21). In order to avoid such problems, and to simplify the implantation process, biodegradable scaffolds seeded with chondrocytes have been developed. The second-generation technique

now allows for chondrocytes to be cultured within a collagen matrix. This matrix is then glued directly on to the defect, allowing for a much smaller incision and reduced surgical time. The technique has become known as “matrix-guided autologous chondrocyte implantation” (MACI) (Figs. 4,5) (15,16). A further advantage of this method of cell delivery is that the scaffold may act as a barrier to invasion of the graft by fibroblasts, which may otherwise induce fibrous repair (22).

By far the best results have been

achieved in localised and confirmed defects surrounded by otherwise healthy surface cartilage (Figs. 5,6). The success is reduced in so-called bipolar lesions where defects are present on opposing surfaces, and those located in the patellofemoral joint (14,15). Many people are still under the

misapprehension that ACI or MACI may facilitate the reconstruction of joints affected by osteoarthritis. Unfortunately, however, this is not feasible with the currently available technologies, primarily due to the fact that in osteoarthritis the whole joint is affected by changes in biomechanics and biochemistry, creating an environment unsuitable for cartilage implantation (7).

8

POSTOPERATIVE REHABILITATION The first week after surgery is usually spent with the leg in an elevated position, with regular ice applications and some isometric muscle exercises. Physical therapy usually commences once wound healing is complete. Motion is important to prevent formation of adhesions (tissues that grow together during the healing process) and stiffness following surgery. The continuous passive motion (CPM) machine will help to restore movement to the knee without requiring muscle activity (23,24). In addition to CPM, manual manipulation and massage around the scar and particularly mobilisation of the kneecap are also recommended to help prevent the formation of adhesions. The rehabilitation process after cartilage cell transplantation is critical to the healing process and the success of the procedure. Although the recovery period can be extensive and needs commitment, most patients can perform necessary low-impact activities such as walking and driving relatively early in the programme. Defects on the weight- bearing surface (tibiofemoral joint) need to be offloaded, and patients usually stay on crutches for up to 3 months. Physiotherapy is particularly important during the initial postoperative period and should focus on maintaining muscle function and joint flexibility. Hydrotherapy, including underwater jogging, has proved to be very popular at this stage. Return to work depends on the demands placed on the knee. Patients may resume desk jobs at around 6–8 weeks, while physically demanding activities should be refrained from for at least 12 weeks. Recovery depends on the size, severity and location of the cartilage injury, the patient’s age and physical condition, and any additional surgery performed at the time of the implantation (eg. ACL reconstruction, high tibial osteotomy). Depending on the size and location

of the cartilage injury, low-impact activity such as swimming and cycling may be resumed as early as 3 months following treatment. Higher-impact sports such as jogging, running and aerobics, however, should be refrained from for at least 9–12 months. Most surgeons verify cartilage integrity by obtaining an MRI scan during the rehabilitation period. In some cases, a second-look arthroscopy may be necessary, especially if the patient complains of mechanical symptoms such as locking or clicking. Return to a full level

Figure 4: Chondrocytes are loaded onto a collagen scaffold (membrane) and delivered in a sterile medium for implantation

Figure 5: Minimally invasive opening of the knee joint and implantation of MACI type membrane

Figure 6: Pre- and postoperative MRI scan demonstrating a large full-thickness chondral defect treated with MACI. At 9 months the lesion is almost completely filled with newly grown surface cartilage

of sporting activities, especially those involving twisting and turning (e.g. football, rugby, tennis, squash), may compromise the durability of the repair and generally should not be considered until 12–18 months after surgery. It is important, however, to realise that

sporting activities do enhance the outcome of the procedure, as Kreuz et al. have pointed out (25). They saw significantly better results at 36 months after surgery in patients performing sport at least one to three times per week compared with those with rare sports involvement of no more than three times a month. The authors concluded that “Physical training improves long-term results after autologous chondrocyte implantation of the knee and should be carried out for at least 2 years after surgery” (25).

sportEX medicine 2009;40(Apr):6-9