Spinal implants such as interbody fusion devices are used to treat degenerative disc disease and other damages or defects in the spinal disc between adjacent vertebrae. The disc may be herniated or suffering from a variety of degenerative conditions, such that the anatomical function of the spinal disc is disrupted. Most prevalent surgical treatment for these conditions is to fuse the two vertebrae surrounding the affected disc. In most cases, the entire disc will be removed, except for a portion of the annulus, by way of a discectomy procedure. A spinal fusion device is then introduced into the intradiscal space and suitable bone graft or bone substitute material is placed substantially in and/or adjacent the device in order to promote fusion between two adjacent vertebrae.
Certain spinal devices for achieving fusion are also expandable so as to correct disc height between the adjacent vertebrae. Examples of expandable interbody fusion devices are described in U.S. Pat. No. 6,595,998 entitled “Tissue Distraction Device”, which issued on Jul. 22, 2003 (the '998 patent), U.S. Pat. No. 7,931,688 entitled “Expandable Interbody Fusion Device”, which issued on Apr. 26, 2011 (the '688 patent), U.S. Pat. No. 7,967,867 entitled “Expandable Interbody Fusion Device”, which issued on Jun. 28, 2011 (the '867 patent), U.S. Pat. No. 8,900,312, entitled “Expandable Interbody Fusion Device with Graft Chambers”, which issued on Dec. 2, 2014 (“the '312 patent”), and Non-Provisional patent application Ser. No. 14/474,555 entitled “Expandable Spinal Interbody Fusion Device”, which filed on Sep. 2, 2014 (“the '555 application”), all of which are owned by the assignee herein and the contents of which are hereby incorporated by reference in their respective entireties.
An issue that has arisen regarding such interbody fusion devices is, during a spinal fusion procedure, the difficulty in inducing changes in the angle between vertebral endplates to restore normal anatomic alignment, in particular for lordosis. While this can be achieved by altering angles of the endplates of the device, altering angle naturally increases initial implant profile. Accordingly, there is a need to develop an improved expandable interbody fusion device with a design such that the device remains in a minimum profile while being capable of inducing changes in the angle between vertebral endplates.