A thighbone shaft has a pole and a bolt. The pole defines an inclined threaded hole therein. Tooth portions are respectively formed at opposite sides of the pole. A head is arranged on a front portion of the pole. A sleeve is provided on the head. A threaded portion is formed on the bolt and is retained in the inclined threaded hole for engaging the bolt and the pole. The thighbone shaft is assembled easily, reduces planting area and replacement cost, decreases stress force, and promotes planting fixedness.