A locking assembly is provided for securing a rod in a rod receiving channel of a polyaxial bone anchoring device for use in spinal or trauma surgery, said locking assembly cmprising a first locking element (9) having a first end (91) and a second end (92), a longitudinal axis of rotation (C) and an outer surface portion with an external thread (93), a coaxial bore passing through said first locking element, an internal thread (94) provided at a portion of said bore, and an engagement portion (95, 96) for a driver to rotate the first locking element, a second locking element (10) having a first end (101) oriented towards the first end (91) of the first locking element, and an opposite second end (102), an outer surface portion with an external thread (103a) cooperating with the internal thread (93) of the first locking element and a portion (105) that prevents the second locking element from rotating when inserted into the rod receiving channel (12) of the bone anchoring device, wherein when the first locking element (9) is rotated to move in a first axial direction the second locking element (10) is configured to move relative to the first locking element (9) in an opposite axial direction.本案提供一種鎖定總成,可把桿件保固於脊椎或創傷手術所用多軸式骨骼固定裝置的桿件容納槽溝內,該鎖定總成包括第一鎖定元件(9),有第一端(91)和第二端(92),縱向轉動軸線(C)和具有陽螺紋(93)之外表面部,貫穿該第一鎖定元件之共軸腔孔,設於該腔孔一部份之陰螺紋(94),以及轉動第一鎖定元件的起子用之結合部(95,96);第二鎖定元件(10)有第一端(101),定向朝第一鎖定元件之第一端(91),和對立的第二端(102),外表面部有陽螺紋(103a),與第一鎖定元件之陰螺紋(93)嚙合,並有一部位(105),在插入骨骼固定裝置之桿件容納槽溝(12)內時,可防止第二鎖定元件轉動,其中當第一鎖定元件(9)轉動,按第一軸向運動時,第二鎖定元件(10)構成按相反軸向,相對於第一鎖定元件(9)運動。9‧‧‧第一鎖定元件10‧‧‧第二鎖定元件91‧‧‧第一鎖定元件頂端92‧‧‧第一鎖定元件底端93‧‧‧陽螺紋94‧‧‧陰螺紋95‧‧‧共軸圓筒形凹部96‧‧‧結合結構101‧‧‧第二鎖定元件頂端102‧‧‧第二鎖定元件底端103‧‧‧第一部位103a‧‧‧第一部位之陽螺紋104‧‧‧第二部位104a,104b‧‧‧第二部位之鞍部106‧‧‧預定斷裂點108‧‧‧小結合部C‧‧‧縱向轉動軸線
