Adamantite Spear doesn't require any level to wield (bug, inauthentic)
They can be wielded at any level, which may be a glitch, as the non-poisoned version requires 30 Attack and 25 Ranged to wield.
Not sure if there's a replay for this, but probably somewhere. All spears should be audited.
In OpenRSC, you can wield the regular non-poisoned Adamantite spear with all lvl 1 combat stats.