Resorptive intramedullary implant between two bones or two bone fragments

What is this patent about?

’583 is related to the field of orthopedic implants, specifically intramedullary devices used for arthrodesis or osteosynthesis in small bones, such as those in the hand or foot. The invention addresses the challenge of providing stable fixation between two bone fragments using a resorbable material that eventually dissolves in the body. Traditional metal implants often require permanent placement or secondary removal, but resorbable polymers like PLA or PGA present unique mechanical challenges in maintaining primary stability and resisting shear forces during the healing process.

The underlying idea behind ’583 is the use of a hybrid anchoring geometry that combines two distinct mechanical fixation methods into a single-piece body to maximize stability in soft or healing bone. By utilizing a threaded cylindrical end on one side and a split flat bar with elastic legs on the other, the implant leverages both rotational threading and compressive expansion. This dual-action design ensures that one bone segment is rigidly engaged via a screw mechanism while the other is secured through the outward tension of deformable arms, providing a robust bridge that resists both pull-out and rotation.

The claims of ’583 focus on a one-piece elongated body featuring a threaded cylindrical anchor at the first end and a flat-cross-section anchor at the second end. The flat anchor is specifically characterized by a plurality of outwardly projecting teeth arranged in opposing pairs along its longitudinal axis to grip the internal bone structure. Furthermore, the independent claims specify a central transition zone or step that acts as a physical abutment, defining a perpendicular plane that prevents the threaded end from being over-inserted into the first bone fragment.

In practice, the implant is installed by first drilling and tapping a hole in the proximal bone to receive the threaded cylindrical section. The surgeon screws the implant in until the central abutment step sits flush against the bone face, ensuring precise depth control. The second bone fragment is then pressed onto the flat distal end. The opening in the flat section allows the two anchor arms to compress during insertion and then elastically expand, driving the teeth into the cancellous bone to create a secure, high-friction fit.

This design differentiates itself from prior art by optimizing the geometry for resorbable polymers, which lack the sheer stiffness of stainless steel or titanium. While previous implants used uniform shapes at both ends, the ’583 hybrid approach accounts for the morphology of the implantation site by allowing the two anchor zones to be angularly offset by up to 30 degrees. This bend, typically set at 10 degrees for foot arthrodesis, aligns the implant with the natural anatomical curvature of the joint while the central transition zone absorbs the shear and flexion forces that would otherwise cause a resorbable device to fail.