Cat's Eye Screws for Nailing Distal Tibial Fractures

Austin F. Smith, MD; Carl Kure, DO; David Seligson, MD


Curr Orthop Pract. 2021;32(6):611-613. 

In This Article

Abstract and Introduction


A blocking screw technique in intramedullary nailing of the tibia and femur has many applications and is useful in assisting fracture reduction and nail centralization, as well as stabilization of the implant. Blocking screws have been described as early as 1983 by Donald and Seligson[1] in a review of 50 consecutive cases of tibial fractures that were treated with Küntscher nailing.[2] Later Krettek et al.[3,4] coined the term "Poller screw," named for a resemblance to devices that are placed in the road to block or guide traffic, in two manuscripts discussing the use of these screws in intramedullary nail treatment of tibial and femoral fractures. An even earlier account of a blocking-type screw can be seen in the second edition of Campbell's Operative Orthopaedics[5] where a "snub screw" is used to help guide an intramedullary implant. Over the years, other methods of blocking screw technique have been described, including the use of alternative blocking devices such as Kirschner wires or the use of Steinmann pins for provisional blocking prior to placing a blocking screw.[6,7] Regardless, the basic principles remain that blocking screws assist with reducing a fracture and centralizing a nail and, of particular interest here, stabilizing a nail in the medullary canal.

Fractures of the tibia that are not in sufficient proximity to the isthmus do not allow circumferential cortical contact, leading to a less stable implant where the medullary canal is wide. This problem also exists when smaller diameter nails are used. Further, metaphyseal fracture with significant comminution or hypotrophic nonunion or osteomyelitis are especially associated with instability due to decreased bone stock. This problem of nail stability in a long bone fracture away from the isthmus was solved by Küntscher[2] by either reaming to make the medullary canal bigger or by enlarging the nail to increase the cortical contact such as the case of a stacked V-nail (Orthopedia GmbH, Kiel, Germany). An additional method of stabilization has been described by Stedtfeld et al.[8] with the use of two transmedullary support screws that are placed on either side of a nail to stabilize the nail. Here, the authors describe a similar method of stabilization with a screw placed on either side of a nail in an area without sufficient cortical contact and a relatively unstable nail. The so-called "cat's eye" screws have the appearance of eyes after placement. A blocking technique may still be used to advance the nail into the desired position, and typically one of the "cat eye" screws is used in a blocking capacity distally. After the nail is placed, a second screw is placed adjacent to the nail at the level of the first screw on the opposite side to provide added stability in the metaphyseal bone. Patient informed consent was not required for this retrospective study that presented deidentified patient data.