The bone spear has slightly lower attack bonuses than a steel spear aside from its strength bonus which is slightly higher. It also has a slower attack speed of six ticks, rather than the four-tick speed used by most spears.
Despite the stat bonuses, the bone spear is also the only one-handed spear, so it can be worn with a shield for higher defence bonuses, or a defender to advance the wearer's attack/defence bonuses.