Review Question - QID 217509

In order to counteract the varus deformity, a blocking screw should be placed anterior-to-posterior medial to the nail in the proximal portion of the distal segment (B). To counteract the recurvatum deformity, a lateral-to-medial blocking screw should be placed anterior to the nail in the proximal portion of the distal segment (E).

Deformities during intramedullary nailing of supracondylar femur fractures are common secondary to the lack of tight cortical fit often achieved in mid-diaphyseal fractures. In the sagittal plane, recurvatum (extension) and posterior translation are related to the pull of the gastrocnemius muscle. A frontal plane valgus or varus deformity can occur due to the wide metaphyseal diameter of the distal fragment. Blocking screws, also known as Poller screws (derived from small metal devices placed in roads to block or guide traffic), function to decrease the width of the articular block. When the nail is placed it acts as a lever rotating and shifting the fragments into neutral position, with the blocking screw(s) preventing the nail from moving back into the wrong position. Determining location of blocking screw placement is critical. Deformities in coronal and sagittal planes should be considered separately. In varus or valgus deformity, the blocking screws should be inserted in the anteroposterior plane. Similarly, in procurvatum or recurvatum deformity, the blocking screws should be inserted in the mediolateral plane. A simple technique that is useful to determine the ideal location of the blocking screws is the "reverse rule of thumb" (Illustration A).

Muthusamy et al. provide a review describing the common deformities that occur in the femur and tibia with osteotomies at different locations while using an intramedullary nail in antegrade and retrograde technique. They describe a systematic approach to the appropriate use of blocking screws in these deformities and present their “reverse rule of thumb’’ rule as a quick reference to determine the ideal location(s) and number of blocking screws. They note that these principles are applicable to limb lengthening and deformity correction as well as fracture fixation using intramedullary nails.

Seyhan et al. provide a retrospective review on whether the use of blocking screws resolves varus or valgus and translation and recurvatum deformities in distal femur fractures. They report the main purpose of using blocking screws is to achieve reduction, but they are also useful for maintaining permanent reduction. They note that when inserting blocking screws, the screws must be placed 1 to 3 cm away from the fracture line to avoid propagation of the fracture. They conclude blocking screws provide an efficient solution for deformities encountered during intramedullary nailing of distal femur fractures.

Figure A demonstrates a right distal femur fracture with intraarticular extension. Figure B is an illustration of a varus deformity (right femur), and Figure C is an illustration of a recurvatum deformity.

Illustration A demonstrates the “reverse rule of thumb” technique. This technique involves three steps: (1) understand the direction of existing deformity that will be corrected with nailing; (2) envision trying to manually correct the deformity by holding the bone with both hands. The thumbs of both hands are placed on the convex side of the deformity near the apex, and the index fingers are placed away from the deformity on the concave side; (3) insert the blocking screws on the side of the nail OPPOSITE to where the thumbs and index fingers are placed on the bone.
While this technique suggests additional blocking screws far from the osteotomy site, these screws are rarely needed. The far ends of the nail are typically well secured in the bone. The metaphyseal bone near the fracture is least controlled by the nail and needs blocking screws.

Incorrect Answers:

Answers 2 - 5:
Point A: A blocking screw placed anterior-to-posterior lateral to the nail in the proximal portion of the distal segment would help correct a valgus deformity.
Point C: A blocking screw placed anterior-to-posterior lateral to the nail in the distal portion of the proximal segment would help correct a VALGUS deformity (again, just as it would if placed in the PROXIMAL portion of the DISTAL segment - Point A).
Point F: A blocking screw placed lateral-to-medial posterior to the nail in the proximal portion of the distal segment would help correct a procurvatum deformity.
Point H: A blocking screw placed lateral-to-medial posterior to the nail in the DISTAL portion of the PROXIMAL segment would similarly help correct a procurvatum deformity (just as it would if placed in the PROXIMAL portion of the DISTAL segment - Point F).

Note that a blocking screw placed in point D would also help correct a varus deformity, and a blocking screw placed in point G would also help correct a recurvatum deformity.