Table 2.

Advantages and disadvantages of animal models

OA model	Advantage	Disadvantage
Primary
Naturally occurring	Mimics the spontaneous disease progression closely	Takes a longer time for animal skeletal maturity
Genetic engineering	Reproducible Allows study of the mechanism of disease	Not as suitable for therapeutic studies Single gene change does not recapitulate the complex signaling pathway
Secondary
Dynamic	Reproducible trauma Non-invasive	Requires expensive machinery
Synthetic	Quick onset of OA Reproducible Allows biomechanical characterization of cartilage (i.e., collagenase model) Less invasive than surgery Shows measurable changes in pain (i.e., MIA model)	Does not reflect primary OA
Surgical	Quick and consistent method of OA induction Mimic post-traumatic OA development as in human (ACL transection) Induce radiographic changes comparable to humans (medial meniscectomy) Can be used to evaluate biomaterials in OA (osteochondral defect)	Invasive to the animal Costly Relies on skill of surgeon Surgical protocols require thorough planning
Tertiary	May be used to treat therapeutics May allow faster OA induction than surgery alone Mimics post-traumatic OA	Cost intensive More invasive Surgical and exercise protocols require thorough planning Facilities/staff/housing of animals may not be available, especially in the case of large animal like horse
Miscellaneous (ex vivo)	May look closely into molecular and cellular pathways ex vivo Samples can be studied for months ex vivo allowing for several assays	Challenge to recapitulate OA mechanisms as seen in in vivo models