Wikipedia thinks so too...
"Thaw had a noticeable peculiarity of gait, his right leg showing evidence of "dorsiflexor paralysis" or foot drop, for which there have been several explanations. Some even speculated that he had a wooden leg below the knee, or that he had contracted polio as a child. Several sources state that it resulted from an accident at the age of 15 when he tripped over a curb and broke his foot rushing to catch a bus to school. However, in her autobiography, Hancock says that Thaw's grandfather had a withered leg and walked with a limp; Thaw apparently copied him and also walked with a limp all his life. A car accident in his early twenties exacerbated the problem."