Gel-type autologous chondrocyte (Chondron™) implantation for treatment of articular cartilage defects of the knee

As articular cartilage has only limited ability to regenerate, many treatment modalities have been developed during the past several decades to treat symptomatic articular cartilage injuries [1]. Among these treatment modalities, autologous chondrocyte implantation (ACI) has become a standard technique used to repair symptomatic, full-thickness, chondral injuries [2‐4].

The traditional ACI technique involves injection of cultured autologous cartilage cells into the prepared cartilage defect which is covered by a periosteal flap. The technique requires extensive surgical exposure in order for the sutures to be watertight as well as an additional incision for harvesting the periosteum. In addition, cell leakage, graft detachment, and graft hypertrophy are recognized as potential problems [5].

To solve the periosteum-associated problems, many biomaterials have also been used for a new generation of ACI techniques in which cells are combined with bioactive, resorbable biomaterials such as collagen membrance [6], hyaluronan polymer [7], and copolymers of polylactin and polyglactin [8]. Using this method, the necessity of a second incision to harvest tibial periosteum can be avoided and the surgery time can be shortened. ACI using a collagen matrix is currently used as a membrane on which chondrocytes are seeded and cultured for several days before the membrane is cut to the correct size and shape of the defect. Although this technique has advantages over conventional ACI due to its simplicity and the fact that it does not use periosteum, there are some potential disadvantages regarding cell loss and detachment of the membrane.

The technique using chondrocyte cell suspension cannot cover the total condyle so that it is watertight in an arthritic knee, and there is also a high risk of breakdown of the treated lesion and its subsequent progression to arthritis. In addition, the technique using collagen membrane has similar risks when treating a large lesion as those noted with the total condyle.

We have developed a new technique that reduces the surgical difficulties and facilitates the attachment and even distribution of chondrocytes in a defect. This method is based on the transplantation of in vitro cultured autologous chondrocytes mixed with fibrin glue into a cartilage defect.

For several years we have used gel-type autologous chondrocyte (Chondron™) implantation without using periosteum or membrane. Our current study involved evaluation of the clinical results of gel-type ACI (GACI) at many clinical centers and at various time points during the postoperative follow-up.

Data from 98 patients who underwent gel-type ACI (GACI) at ten Korean hospitals between January 2005 and November 2008, were included and were divided into two groups according to the length of the follow-up period, i.e. 13~24-month follow-up and greater than 25-month follow-up.

Institutional review board (Catholic University of Korea) approval was obtained for this study. Patient informed consent was not required by the institutional review board.

Among the 98 study patients, there were 54 males (55.1%), and 44 females (44.9%). Patient age ranged from 17 to 65 years (mean age = 43.72 years, SD = 9.10). The average defect size was 5.23 ± 2.70 cm² (range: 1.00 ~ 14.50 cm²), i.e. less than 4 cm² in 29 patients (29.6%), 4.0~7.9 cm² in 57 patients (58.2%), and greater than 8.0 cm² in 12 patients (12.2%). The average follow-up period was 24.35 ± 8.35 months (range: 13 ~ 52 months) with a 13~24-month follow-up in 58 patients (59.2%) and greater than a 25-month follow-up in 40 patients (40.8%) (Table 1).

The MTT assay showed that the viability of the cells in the gel remained above 90% of the initial viability for 72 hours (Fig. 3a). The cells were found to be well mixed with fibrin and evenly distributed within the gel (Fig. 3b). The viable status and distribution of chondrocytes in the gel were also confirmed based on the Calcein-AM/Ethidium homodimer-1 staining. The viability of the cells in the cell-gel mixture, according to the fluorescence staining, was found to exceed 90% after 72 hours of culturing the mixture, as shown in the MTT assay (Fig. 4). We found that the pores were evenly present within the fibrin gel. We was also noted that the chondrocytes were evenly distributed and maintained a round shape within the pores on the scanning electron microscopy (SEM) (Fig 5).

Clinician evaluations showed significant mean improvement in the tKSS-A and tKSS-B scores for the all of the data of the three, postoperative, follow-up periods (95% confidence interval, P-value < 0.05) (Fig. 6).

The tKSS-A score showed improvement from 43.52 ± 20.20 to 89.71 ± 13.69 (P < 0.05), while according to the tKSS-B scores, knees were shown to have improved from 50.66 ± 20.05 to 89.38 ± 15.76 (P < 0.05). The total improvement was from 94.18 ± 31.43 to 179.10 ± 24.69 (P < 0.05). Clinical evaluations showed significant mean improvement in the tKSS-A and tKSS-B scores for each postoperative follow-up period (95% confidence interval, P-value < 0.05) (Table 2).

According to the follow-up period, improvement of the score of the 'greater than 25 months' group was statistically greater than that of the other group (Table 3). Improvements in tKSS-A and B scores were not found to be related to age, gender, defect size, defect location, the number of vials of chondrocyte used for implantation or the time interval between cartilage harvesting and ACI.

The surgical procedure of conventional ACI can be summarized as consisting of debridement of the cartilage defect, harvesting of periosteum, suturing the periosteum, and chondrocyte implantation [10]. Among these procedures, periosteum suturing is a difficult and time-consuming procedure for the surgeon, and periosteal harvesting and periosteum suturing procedures have some risk of patient morbidity. Conventional ACI is not preferred because of the periosteal grafting component which requires an additional operation to harvest the periosteum. In addition, for water-tight suturing of the periosteal graft to the surrounding cartilage, a large surgical incision is required, thus presenting the potential problem of subsequent leakage of injected cells from the defect as well as graft detachment [11].

To overcome these potential problems, some researchers have proposed using collagen membrane rather than periosteum [5, 11, 12]. If the surgeon's preference is to not use periosteum, methods using collagen membrane can eliminate the need for a second incision for periosteal harvest as well as reducing the long surgical time and extensive suturing. However, with this approach there are also some potential problems such as the loss of critical chondrocytes caused by the cutting and repeated manipulation of the seeded membrane. There is also the possibility of detachment of the collagen membrane from the cartilage defect. Therefore, it is becoming increasingly evident that it is necessary to develop a new method.

In the gel-type ACI (GACI), the fibrin can already maintain the shape of the articulation approximately five minutes after injection, thus allowing the cells to remain at the injected sites. And even if there is a defect along the chondral margin, fibrin helps to maintain the shape of the graft according to the articulation [13]. The 5-mm-deep holes serve an important function by increasing the adhesive force of the graft to the defect during knee motion. In the surgical procedures, in order to prevent both the formation of fibrocartilaginous tissue [14] and detachment of the injected cell and fibrin mixture, bleeding control is very important. Fortunately, fibrin sealants are biological adhesives that mimic the final step of the coagulation cascade and therefore help with the bone bleeding control [15]. Also, any commercially available fibrin product can be used because of the similar range of the amounts of fibrinogen and thrombin. Following surgery, we check the stability of the graft by flexion and extension knee-motion exercise. If the graft adequately remains in the defect site, we finish the surgery.

The number of cells introduced in initial explants is important as the seeded chondrocyte number is linearly related to biosynthetic activity [16]. In that respect, GACI can have an advantage over other treatments such as ACI-C and MACI. Collagen membrane occupies quite a substantial amount of space in a cartilage defect, although the cell-gel mixture occupies the space in the GACI. Although the optimal number of required cells has not been determined, high cell densities seem to be desirable [17] and one vial of Chondron™ could cover a total condyle defect. The 96 patients (98.0%) we treated achieved measurable postoperative improvement and only two patients (2.0%) showed deterioration of their 'no change'. One patient required repeat surgery, and all of the patients who underwent surgery showed substantial improvement during the follow-up period. The authors regard these as encouraging results compared with those of other reports regarding marrow stimulation or ACI [18]. In fact, our repeat surgery rate is far less than that associated with other forms of knee surgery [19, 20].

However, it is difficult to conclude that this technique is superior to other techniques, such as ACI-C or MACI, as this study is not a comparative study. Many successful results have also been reported using other techniques [6, 21, 22]. In this study, the authors used a telephone-based scoring system. If the patient does not feel any discomfort, he/she would not need to come to the hospital as job and time limitations frequently prevent patients from checking in with their doctors. Therefore, the necessity and benefits of telephone or internet consultation are increasing. There is also a continuing necessity to develop a new, remote scoring system which can handle the other knee condition evaluations.

Swedish researchers have reported improvements for longer than two years following ACI [23]; similarly, in our study, improvements were more apparent after 24 months. However, the preoperative score of greater than 25-month follow-up group was lower than that of 13~24-month follow-up group. Therefore, it is difficult to insist the same result as Swedish report.

An even more positive aspect of this study is that clinical improvement was apparent even during the short-term, post-op follow-up period of less than two years following surgery.

With respect to the surgical success based on the size of the articular cartilage defects, there was no statistical difference in the results. There was one case of 1 cm² of cartilage defect and the others were over 2 cm². A small cartilage defect can cause severe discomfort and pain if a patient's activity level is high. The pressure generated during weight-bearing is so high that it stimulates a weak articular cartilage area even though the defect size may be very small. Therefore, covering a cartilage defect with healthy cartilage is very important, and GACI offers a successful treatment option for both small and large cartilage defects.

GACI used to repair of articular cartilage defects of the knee appears to be a safe and effective method for restoring patient knee function.