Long spine board, a medical device used for the immobilization and transportation of patients with suspected spinal injuries (aka backboard)
Lisa takes gymnastics (and gets yelled at by the Russian coach for being too old), Bart gets tricked into taking an etiquette class by a black man dressed as a gangsta rapper (who happens to be the husband of the prim and proper etiquette teacher), and Homer participates in a basketball class for men over the age of 35, but suffers a torn ACL after a dunk attempt ends with the backboard crashing down on his leg.
This was due to a hand injury sustained by the Swiss player, Marc Rosset, when he punched the backboard in frustration at having not taken match points.