Hyaline cartilage is a very specialised tissue; it´s main constituents are proteoglycans that attract and retain water and highly organized type II collagen fibers oriented in an arcade like structures. Due to this composition and confirmation, it can transmit mechanical forces and act as a shock absorber1. In addition, hyaline cartilage has a zonal orientation with the lamina splendens being the uppermost layer. The lamina splendens provides the smooth layer for the smooth movement of articular joints, it is very rich in lubricin and collagen fibers run parallel to the surface of articulation2. So, articular cartilage can function due to its composition and their confirmation. This leads to the question whether repairing a cartilage defect is good enough3.
Most of the currently used treatment procedures for cartilage defects do not provide a repair tissue that is similar to the native articular cartilage, or they come with other disadvantages.
For instance for microfracture it is well known that the repair tissue is more fibrocartilage-like that is rich in type I collagen instead of hyaline cartilage-like4. Although it provides satisfying outcomes on the short-term, the fibrocartilage cannot take over the function of hyaline cartilage and is more prone to degeneration on the long-term. Therefore, microfracture is only suitable for small defects and in larger defects the initial satisfactory outcomes can decline after a few years5. For larger (osteo)chondral defects autologous chondrocyte implantation or osteochondral allografts (if available) or other new upcoming treatments might provide a suitable treatment6-9. However, also these treatments do not provide 100% success. In addition, the question whether repair is good enough or not is also hampered by the lack of correlation between structural repair (MRI and / or histology) and patient reported outcome measures10. So even for a set of patients the tissue is repaired with a tissue that is similar to healthy cartilage, but there are still knee problems. On the other hand cartilage damage can be a surprise finding on imaging or during arthroscopy and be asymptomatic11.
1. Sophia Fox AJ, Bedi A, Rodeo SA. The basic science of articular cartilage: Structure, composition, and function. Sports Health. 2009;1(6):461–8.
2. Kumar P, Oka M, Toguchida J, Kobayashi M, Uchida E, Nakamura T, Tanaka K: Role of uppermost superficial surface layer of articular cartilage in the lubrication mechanism of joints. J Anat. 2001;199: 241-250.
3. Hunziker EB. The elusive path to cartilage regeneration. Adv Mater. 2009;21:3419–3424.
4. Steadman JR, Briggs KK, Rodrigo JJ, et al. Outcomes of microfracture for traumatic chondral defects of the knee: average 11-year follow-up. Arthroscopy 2003;19:477-84.
5. Mithoefer K, McAdams T, Williams RJ, et al. Clinical efficacy of the microfracture technique for articular cartilage repair in the knee: an evidence-based systematic analysis. Am J Sports Med. 2009;37:2053–2063.
6. Saris DBF, Vanlauwe J, Victor J, Almqvist KF, Verdonk R, Bellemans J. Treatment of Symptomatic Cartilage Defects of the Knee Characterized Chondrocyte Implantation Results in Better Clinical Outcome at 36 Months in a Randomized Trial Compared to Microfracture. Am J Sport Med. 2009;37:10–9.
7. Brittberg M, Recker D, Ilgenfritz J, Saris DBF. Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture: Five-Year Follow-up of a Prospective Randomized Trial. Am J Sports Med. 2018;46(6):1343–51.
8. Vonk LA, Roël G, Hernigou J, Kaps C, Hernigou P. Role of Matrix-Associated Autologous Chondrocyte Implantation with Spheroids in the Treatment of Large Chondral Defects in the Knee : A Systematic Review. Int J Mol Sci. 2021;22:7149.
9. Chahla J, Sweet MC, Okoroha KR, et al. Osteochondral Allograft Transplantation in the Patellofemoral Joint: A Systematic Review. Am J Sports Med. 2019;47(12):3009-3018.
10. De Windt TS, Welsch GH, Brittberg M, Vonk LA, Marlovits S, Trattnig S, et al. Is magnetic resonance imaging reliable in predicting clinical outcome after articular cartilage repair of the knee?: A systematic review and meta-analysis. Am J Sports Med. 2013;41:1695–702.
11. Horga LM, Hirschmann AC, Henckel J, et al. Prevalence of abnormal findings in 230 knees of asymptomatic adults using 3.0 T MRI. Skeletal Radiol. 2020;49(9):1099-1107.