Green’s Dictionary of Slang

a bandy-legged person.

1611		Davies of Hereford Scourge of Folly 93: Against proud crooked-shankt Lucius.
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Crook Shanks. A Nick name for a Man with Bandy Legs. He buys his Boots in Crooked Lane, and his Stockings in Bandy-leg’d Walk; his legs grew in the Night, therefore could not see to grow Straight: jeering sayings of men with crooked legs.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1811		Lex. Balatronicum.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 59: Crookshanks — a knocked-kneed subject, or one whose shins are like cheese-cutters.