Porcine-Derived Collagen-Augmented Chondrogenesis Technique for Treating Knee Cartilage Defects
Authors: Kim Man Soo , Koh In Jun , In Yong 
Published: July 2021

Background:
Articular cartilage is virtually incapable of self-healing in the event of a defect. Microfracture is the most frequently used bone marrow stimulation technique
1
, but there is the limitation of unpredictable quality of the cartilage repair following bone marrow stimulation
2
. To resolve the shortcomings of the microfracture technique, various reinforcing technologies have been developed, including the porcine-derived collagen-augmented chondrogenesis technique (C-ACT)
3
. The collagen gel utilized in that procedure is a product called CartiFill (Sewon Cellontech), made from highly purified pig-derived type-I collagen. It has been modified into an atelocollagen, by removing telopeptides, to virtually eliminate the risk of rejection. The collagen matrix provides not only a 3-dimensional structure for cartilage differentiation, but also mechanical support
3,4
.

Description:
Porcine-derived C-ACT is initiated by creating a mixture of atelocollagen, thrombin, and fibrinogen. First, thrombin is mixed with atelocollagen and placed in one arm of an assembled Y-shaped syringe, and fibrinogen is placed in the other arm. The articular cartilage defect site is confirmed in a routine arthroscopic procedure. The articular margin is debrided, and the calcified lesion is cleanly removed. Then, microfractures are created. After creating a more extended incision at the anteromedial portal, the microfracture site is prepared by removing moisture. The prepared atelocollagen mixture is applied to the defect site as a single layer, although a second layer can be formed 1 to 2 minutes later. After 5 minutes, the stability is verified by range of motion of the knee.
Indications for this procedure include (1) cartilage defects in the knee, including knee osteoarthritis and knee traumatic arthritis; (2) knee osteoarthritis with a Kellgren-Lawrence grade of 3 or less; (3) hip-knee-ankle malalignment of <5° or a deformity that is able to be surgically corrected; and (4) knee stability, or instability that is able to be surgically corrected.
Contraindications for this procedure include (1) patient or family history of autoimmune disease, (2) history of anaphylactic reaction, (3) history of hypersensitivity to an implant, (4) history of allergy to porcine or bovine protein, and (5) inflammatory arthritis such as rheumatoid and gouty arthritis.
C-ACT is a procedure for cartilage repair, and the effects of this procedure can be limited in cases with a deep subchondral bone defect; however, there is no limit to the size of the cartilage defect in terms of patient selection for C-ACT.

Alternatives:
There are several alternatives to C-ACT, ranging from the simple microfracture technique to autologous chondrocyte implantation
5
, matrix-induced autologous chondrocyte implantation
6
, autologous matrix-induced chondrogenesis
7
, osteochondral autograft transplantation
8
, and stem cell therapy. There are various ways to recover from an articular cartilage defect, but C-ACT does not require a 2-stage technique, as is necessary with both autologous chondrocyte implantation procedures. Therefore, C-ACT has the advantages of ease of operation and being a single-stage procedure
3,9
.

Rationale:
C-ACT can be classified as an upgraded version of microfracture, which is the most common treatment method for articular cartilage defects. With the microfracture technique, repaired cartilage is limited to fibrous cartilage and does not include hyaline cartilage
3,4
. However, a recent study reported that C-ACT exhibited a superior quality of repaired cartilage compared with microfracture
3,4
.

Expected Outcomes:
Previous studies have reported favorable results with the use of C-ACT
3,4
. Kim et al.
4
compared atelocollagen augmentation with microfracture alone in patients undergoing medial opening wedge high tibial osteotomy for the treatment of medial compartment osteoarthritis. Although there was no clinical difference between the 2 groups, the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score and the International Cartilage Repair Society II score were superior in the atelocollagen augmentation group. In addition, the microfracture group formed fibrous-like cartilage compared with the hyaline-like cartilage created in the atelocollagen augmentation group. A recent multicenter randomized study compared the use of C-ACT and microfracture and found that C-ACT exhibited significantly better results in several MOCART subscores and quantitative T2 mapping, indicating a histologically superior form of repaired cartilage compared with microfracture
3
. According to recent research, microfracture is superior to autologous chondrocyte implantation in terms of cost-effectiveness
10
. Similar results appear to be applicable to C-ACT. C-ACT requires an additional $1,300 for material costs; however, C-ACT showed better cartilage regeneration on magnetic resonance imagining and histology
3,4
, and higher rate of patients meeting the 20%-improvement rate in visual analogue scale pain scores at 24 months postoperatively compared with microfracture
3
. Long-term studies will be needed to assess whether histological superiority of C-ACT is reflected in meaningful improvements to clinical outcomes.

Important Tips:

Debride all of the damaged cartilage to subchondral bone and remove the calcified layer without interfering with tissue repairTake special care when creating the atelocollagen mixture to ensure that it is accurately manufacturedDry the defect site with use of suction or gauze to aid in atelocollagen adhesion when applying atelocollagen.