The scaffold is composed of purified type I collagen isolated from bovine Achilles tendon without any noncollagenous materials and lipids. The collagen fibers are enriched with glycosaminoglycans, including chondroitin sulfate and hyaluronic acid. The fibers are then cross-linked to improve stability and ease implantation and handling. Sterilization is performed with gamma radiation [21]. The implant has no carcinogenicity, pyrogenicity, or cytotoxicity [27]. Biopsies, in second-look arthroscopies, have proved extensive resorption of the scaffold in 12–18 months and ingrowth of newly formed tissue, replacing the scaffold. The implant promoted migration of fibrochondrocytes into the scaffold, establishing a new functional tissue matrix [6, 7, 24, 28, 29].

In a study with a large number of patients, with either acute or chronic meniscal injury, CMI was found to improve the clinical results in the chronic injury group providing a greater recovery of function whereas it was not that useful for patients with acute injury [26]. In a recent study by Zaffagnini et al. [30], long-term clinical, radiological, and magnetic resonance imaging (MRI) results of CMI were compared with partial medial meniscectomy. Significant improvements in pain, activity level and radiological outcomes were recorded in the CMI group at a minimum 10 years follow-up when compared with the partial meniscectomy group. One of the most remarkable findings of the study was that the improvements in the International Knee Documentation Committee (IKDC), Tegner, Short Form-36, and visual analogue scale scores (VAS) were significant; however, there were no difference in Lysholm and Yulish scores. Bulgheroni et al. [11] reported clinical, radiological, and MRI results of CMI application at 5 years. In this study, there was a significant increase in both Lysholm and Tegner scores and no further degeneration of the chondral surfaces was seen after CMI application. The new tissue was reported to have no negative effects. In another series of 22 patients, followed-up for a minimum of 10 years, Monllau et al. [31] reported significant improvement in functional and pain scores at 1 year and the functional status of the patients was the same in the last controls. There were no reported complications and the failure rate was 8%.

CMI is found to be useful for treating partial meniscus defects in numerous studies. After implantation, the scaffold is invaded by cells and undergoes resorption. Subsequent formation of a regenerated tissue is seen in majority of cases. The new tissue matures over time but the size is usually smaller than the normal meniscus and the shape is irregular. Key factor for achieving a satisfactory result is selecting the suitable patient.

Implantation of CMI does not preclude accompanying surgical procedures in most cases and combined surgical procedures are rather common. Anterior cruciate ligament (ACL) reconstruction for ACL deficient knees improves meniscus healing and thus combined reconstruction of both structures is recommended. Reconstruction may be performed in one stage or if concurrent procedures are preferred, CMI implantation should be performed in the first stage, as it is more difficult to implant CMI after ACL reconstruction, due to increased tightness of the knee. Varus or valgus malalignment deformities should be corrected either with or prior to CMI implantation (Fig. 27.2). Chondral lesions detected within the knee should also be managed with the appropriate treatment modality such as microfracture, mosaicplasty, or osteochondral transplantation. Main concern about management of chondral lesions is about timing as an altered, rough chondral lesion is considered as detrimental for the newly implanted CMI [11, 32, 33].

Though, experience with lateral CMI is lower when compared to medial CMI, and clinical results are similar to those obtained with the medial implant. Whether medial or lateral, swelling and residual compartmental pain are the most commonly reported complications after CMI implantation [27].