A distractible intervertebral body fusion device for implantation into an intervertebral disc space in a patient's body, comprising:
- a top base plate having a top bearing surface configured to interface with an end plate of a superior vertebra of the intervertebral disc space;
- a bottom base plate having a bottom bearing surface configured to interface with an end plate of an inferior vertebra of the intervertebral disc space;
- a first arm hingedly connected to the top base plate and the bottom base plate;
- a second arm hingedly connected to the top base plate and the bottom base plate;
- an actuation member extending through the first arm and into the second arm, the actuation member configured such that actuation of the actuation member causes expansion of the first arm and second arm such that the top bearing surface and bottom bearing surface move away from each other into a distracted position, wherein the actuation member is threaded and is actuated by rotating the actuation member and the first arm includes a threaded portion through which the actuation member is inserted and the actuation member is attached to the second arm such that rotation of the actuation member in a first direction pulls the second arm towards the first arm without the actuation member moving translationally through the device and rotation of the actuation member in a second direction pushes the second arm away from the first arm without the actuation member moving translationally through the device;
- a third arm disposed adjacent the first arm and hingedly connected to the top base plate and the bottom base plate;
- a fourth arm disposed adjacent the second arm and hingedly connected to the top base plate and the bottom base plate;
- a second actuation member extending through the third arm and into the fourth arm, the second actuation member configured such that actuation of the actuation member in a first direction causes expansion of the third arm and the fourth arm, wherein the second actuation member is threaded and is actuated by rotating the second actuation member and the third arm includes a threaded portion through which the second actuation member is inserted and the actuation member is attached to the fourth arm such that rotation of the second actuation member in a first direction pulls the fourth arm towards the third arm without the second actuation member moving translationally through the device and rotation of the second actuation member in a second direction pushes the fourth arm away from the third arm without the second actuation member moving translationally through the device,
- wherein the actuation member includes a first threaded portion that extends through the first arm and a second threaded portion that extends into the second arm and the second actuation member includes a first threaded portion that extends through the third arm and a second threaded portion that extends into the fourth arm, and wherein the first threaded portion and the second threaded portion of each of the actuation members are reverse threaded relative to each other to cause the actuation members to remain translationally stationary when rotated in both the first direction and second direction;
- and
- means for stabilizing the top base plate and bottom base plate such that the device has zero, or fewer, degrees of freedom of movement in the distracted position, and wherein the device is designed to remain in the body and stably maintain the intervertebral disc space during vertebral fusion while in the distracted position.