POLLER OR BLOCKING SCREW

Dr.Avik SarkarKB Bhabha Municipal General Hospital

TerminologyThe concept of Poller screw was first popularized by Krettek et al in 1999. They called the screws “poller screws” because the screws guided the nail like the “poller” (retractable bollard) traffic control devices guide traffic in Europe.

Uses• They are used as blocking screws

in stabilising tibial and femoral fractures treated with

small diameter intramedullary nails [1]

• The medial and lateral blocking screws can increase the primary stability of distal and proximal metaphyseal fractures after nailing [2]

• Manage malunited fractures during revision [3]

1. Krettek C, Stepha C, Schandelmaier P, Richter M, Pape HC, Miclau T. The use of Poller screws as blocking screws in stabilising tibial fractures treated with small diameter intramedullary nails. J Bone Joint Surg Br. 1999;81:963–8.

2. Krettek C, Miclau T, Schandekmaier P, Stephan C, Mohlmann U, Tscherne H. The mechanical effect of blocking screws (‘Poller screws’) in stabilising tibia fractures with short proximal or distal fragments after the insertion of small diameter intramedullary nails. J Orthop Trauma. 1999;13:550–3.

3. L Dodd, M Jackson, and R Varma. Poller Blocking Screws and Intramedullary Nailing in Tibial Malunion. Ann R Coll Surg Engl. 2007 Nov; 89(8): 816–818.

• The nails are typically smaller than the intramedullary canal at proximal tibia in metaphyseal fractures at this level causing the segment to drift, because the nail may not have dominant purchase on the proximal segment. By using Blocking screws the effective canal of the proximal metaphyseal fragment can be narrowed to an appropriate corridor for the nail to pass.

• By placing a blocking screw from medial to lateral and having the nail pass anteriorly to this screw forces the nail anteriorly in the canal and can also prevent a sagittal plane deformity.

One rule of thumb is to apply the screws on the concave side of a

deformity [4]

4. Stedtfeld HW, Mittlmeier T, Landgraf P, Ewart A. The logic and clinical applications of blocking screws. J Bone Joint Surg Am 2004;86:17-25.

Medio-lateral placement of screws

Antero-posterior placement of screws

Alternatives of Poller Screws

Schanz Screw

K-Wire

Steinman Pin

Preparation

• Screw placement must be as close to the fracture as possible.

• Monocortical insertion is used in the proximal fragment and Bicortical Insertion in the distal fragment.

• A T-handle can be used for easier manipulation.

Forces Acting

Technique for accurate Poller Screw placement [5]

• Draw a line down the long axis of the displaced, flared segment of bone.• Draw a second line along the plane of the fracture, ensuring to bisect the first line.• Identify your acute angles 

5. A novel technique for accurate Poller (blocking) screw placement. Andrew Hannah , Tariq Aboelmagd, Grace Yip, Peter Hull. Injury, Int. J. Care Injured 45 (2014) 1011–1014

• Place your screw in the acute angle of the metaphyseal or flared segment.• Insert your guide wire under fluoroscopy guidance, ensuring the tip passes the correct side to ensure reduction.• Insert your nail, which should be deflected on engaging the screw providing reduction and compression at the fracture site

• If reduction could be improved further by the addition of a further screw, this should be placed in the acute angle nearer to the isthmus.

The use of transmedullary blocking screws in combination with an intramedullary nail is an important additional option that can be used to improve reduction and fixation of long-bone fractures at the metaphyseal-diaphyseal junction, where there is a strong tendency for axial displacement.

The blocking screw around the nail relieves axial strain in the fixation construct, while the interlocking screws through the nail control length and rotation.

The transmedullary support screw provides a point of support on the side of the nail for the short fragment in an intramedullary three-point construct. Hence these screws are also called transmedullary support screws.