The Acumed SLIC screw system – a jointed screw and a targeting guide with accompanying instrumentation to place and insert the screw accurately – offers surgeons a new adjunct to the soft tissue (e.g. ligament) repair or reconstruction as it holds the bones reduced while soft tissue repair heals.
The SLIC screw is designed to maintain the anatomical reduction (spacing) of the scaphoid and lunate while allowing some rotation between the carpals. A radiolucent targeting guide is provided to aid in the initial reduction of the scaphoid and lunate and the placement of the screw in the central portion of these two carpals, affording the soft tissue repair the best opportunity for successful healing.
Scapholunate instability occurs when the ligament connecting these two carpals and secondary stabilizing ligaments are damaged – torn or stretched beyond their normal capacity.
The damage to the ligaments allows abnormal rotation and motion (kinematics) of the scaphoid and lunate, which can lead to wrist pain and eventually arthritic changes in the wrist. While the scaphoid and lunate bones themselves are not damaged, the rotation and gap between the two wrist bones increases, and this must be anatomically reduced in order to promote healing of the soft tissues and restore normal function.
The SLIC screw differs from other approaches, such as K-wires and conventional screws, in two significant ways. First, the SLIC screw has a joint that allows rotation between the scaphoid and lunate.
Second, the screw is designed to be removed in six to nine months, protecting the soft tissue repair and allowing more time for biological healing. By contrast, K-wires are typically removed 8 to 12 weeks post-operatively and many conventional screws are removed by four months post-operatively.
K-wires and conventional screws are removed early in order to allow more motion at the wrist and prevent stiffness. However, they stick out of the patient’s skin at the wrist during healing and among the problems K-wires can cause are infection, skin irritation, limited rotation of the wrist, and uncertainty of stability when the wires are removed.
“The new SLIC screw system provides mechanical support while the soft tissue repair heals and matures,” says orthopaedic surgeon William B. Geissler, M.D. “Prolonged stabilization of the involved carpal bones eliminates the potential complications of temporary Kirschner wire fixation.”
The joint of the SLIC screw resides in the interval between the scaphoid and lunate and allows for an approximate 15° to 22° toggle angle range of rotation. The screws come in three sizes – 22mm, 25mm, and 28mm – with the length variation in the scaphoid portion of the screw. The scaphoid portion of the screw varies in length in order to allow the surgeon to place the back end of the screw close to the scaphoid bone surface, easing removal of the screw in six to nine months or after biological healing of the soft tissue.
SL targeting guide
The SL targeting guide sits on the outside of the wrist and accomplishes several crucial functions: with the use of a joystick clip and temporary K-wires, it enables the surgeon to reduce the scaphoid and lunate bones back into position.
It allows the user to locate the screw trajectory accurately using fluoroscopy, locking the guide wire (for the screw) in one plane of motion while adjusting and locking it in the second plane. Further, the targeting guide aids in accurately placing the guide wire centrally through the bones from the lateral view. Once the guide wire is placed properly, the bones can then be drilled and the screw inserted.
The complete SLIC screw system including the screw, targeting guide and accompanying instrumentation is provided to customers as all-inclusive two-part sterile procedure packs.
The SLIC screw was designed for Acumed by orthopaedic surgeon William B. Geissler, M.D.; the SL targeting guide was designed by orthopaedic surgeon Michael G. McNamara, M.D.