An expandable prosthetic implant for engagement between vertebrae, comprising: - a first member having a first end , a second end , a plurality of extensions and a hollow interior portion extending from the first end to the second end, wherein the plurality of extensions extend from the first end to the second end , - a second member having a first end , a second end , a hollow interior portion extending from the first end to the second end , and a plurality of extensions extending from the second end to the first end , the plurality extensions of the first member configured to coaxially interdigitate with the second member and the plurality of extensions of the second member configured to coaxially interdigitate with the first member and wherein the first member is moveable relative to the second member along a longitudinal axis; - a ring positioned coaxial to the first member and the second member and axially fixed to the second member ; and - an actuator coupled to the second member and operationally coupled to the ring for locking the first member to the second member , - wherein at least one of the plurality of extension of the first member includes engagement features for coupling with the corresponding engagement element configured on an inner surface of the ring , - wherein the ring is configured to be rotated from a first position to a second position by rotation of the actuator, - wherein in the first position, the first member is freely moveable with respect to the second member and in a second position, the first member is locked in a position with respect to the second member , and - wherein the actuator is positioned within one of the plurality of extension of the second member . - a first member having a first end , a second end , a plurality of extensions and a hollow interior portion extending from the first end to the second end, wherein the plurality of extensions extend from the first end to the second end , - a second member having a first end , a second end , a hollow interior portion extending from the first end to the second end , and a plurality of extensions extending from the second end to the first end , the plurality extensions of the first member configured to coaxially interdigitate with the second member and the plurality of extensions of the second member configured to coaxially interdigitate with the first member and wherein the first member is moveable relative to the second member along a longitudinal axis; - a ring positioned coaxial to the first member and the second member and axially fixed to the second member ; and - an actuator coupled to the second member and operationally coupled to the ring for locking the first member to the second member , - wherein at least one of the plurality of extension of the first member includes engagement features for coupling with the corresponding engagement element configured on an inner surface of the ring , - wherein the ring is configured to be rotated from a first position to a second position by rotation of the actuator, - wherein in the first position, the first member is freely moveable with respect to the second member and in a second position, the first member is locked in a position with respect to the second member , and - wherein the actuator is positioned within one of the plurality of extension of the second member . <EOS>