Table 4.

The current hurdles in AC repair.

Treatment strategy	Hurdles
Palliative management	1. Short-term curative effect, long-term drug damage other organs
	2. Monosymptomatic resolution, often needs a combined drugs
	3. No effect on injury development and fails to regenerate new AC tissue
	4. Cannot solve the larger damage
Surgical intervention	1. Robbing Peter to pay Paul
	2. Short-term symptom relief and poor prognosis
	3. Complications
	4. Insufficient donors
	5. Incomplete chondrogenesis or rapid degradation and fibrosis of the repaired tissue
	6. The transplant tissue is difficult to preserve and integrate with the surrounding cartilage tissue
	7. Risk of disease transmission
	8. Long recovery time
	9. High costs
	10. Ineffective in repairing large cartilage defects
Gene regulation/ therapy	1. Requires the effective, safe and durable gene delivery vectors and supportive gene-activated matrices
	2. Short duration
	3. Low stability resulting difficult to store and transport
	4. Potential immunogenicity
Stem cell therapy	1. The stricter regulations on policy and ethics
	2. A long culture time and a complex culturing procedure
	3. Cell viability and differentiation capacity were greatly affected by age
	4. Poor cell adhesion and retention
	5. Phenotypic alteration
	6. Heterogeneity
	7. Allograft rejection
	8. High costs
	9. Potential tumorigenicity and immunogenicity
Materials scaffolds	1. Might intercept cell-cell signaling and exogenous stimulus signals
	2. The degradation rate does not match the regeneration rate
	3. Difficult to fully mimic the natural microenvironment resulting poor integration with surrounding cartilage tissue
	4. Complicated preparation process
	5. Solid material leads to inconvenient surgical implantation