This invention relates to a cannulated orthopedic screw having particular application in the distal proximal fixation of lateral malleolus fractures. The ankle joint is made up of three bones coming together. The tibia, which is the main bone of the lower leg, makes up the medial, or inside, anklebone. The fibula is a smaller bone that parallels the tibia in the lower leg and makes up the lateral, or outside, anklebone. The enlarged distal ends of both the tibia and fibula are known as the malleoli (singular “malleolus”). Together, they form an arch that sits on top of the talus, one of the bones in the foot. These three bones (tibia, fibula, and talus) make up the bony elements of the ankle joint. A fibrous membrane called the joint capsule, lined with a smoother layer called the synovium, encases the joint architecture. The joint capsule contains the synovial fluid produced by the synovium. The synovial fluid allows for smooth movement of the joint surfaces. The ankle joint is stabilized by several ligaments, which hold these bones in place.
Ankle fractures occur when one or both of the malleoli are broken. These fractures are very common. Ankle fractures can happen after falls, car accidents or severe twisting of the ankle. One, two or all three malleoli can be broken. Fixation procedures for a lateral malleolus fracture have evolved over many years. Initial preferred treatment was a closed reduction of the fracture and immobilizing the malleolus with a cast or splint. Later practices have included the use of rush rods, screws and simple plates that join the fracture but without axial compression. More recent treatments have included the use of stronger and wider plates with screws or locking plates that still join the fracture but without axial compression.
Patients are instructed in non-weight bearing or minimal weight-bearing activities based on the fracture pattern, bone density, weight of the patient, mental condition and level of fixation obtained at surgery. Accurate and complete fixation in young patients is essential for good long-term results but even with accurate fixation, some patients develop non-union or articular cartilage damage and require some type of replacement later due to the cartilage damage or infection.
Older patients with osteopenia or age-related physical problems require a different approach. Most fixations of the lateral malleolus, if displaced, require open stripping of tissue from the distal fibula and plate fixation with multiple cortical and cancellous screws. A distal-to-proximal fixation of the lateral malleolus offers another way to reduce and stabilize the lateral malleolus. Such a procedure alleviates the need for open fixation, i.e., an incision and tissue retraction along the length of the ankle through which plates are mounted to the side of the bones with laterally-inserted screws. Lateral fixation with plates and screws is particularly problematic in older patients with Alzheimer's, osteoporosis, and other medical conditions. A distal-to-proximal fixation of the lateral malleolus permits a quicker fixation with a retrograde screw from the distal tip of the lateral malleolus up the medullary canal of the proximal fibula. Applicant's U.S. Pat. No. 9,655,661 discloses one advancement in lateral malleolus fixation utilizing a screw that includes screw threads along the entire length of the shaft of the screw.
The present application discloses a further improvement in with a screw that has enhanced features that permit a more accurate and robust fixation that is more resistant to displacement during healing.