Poller screw

mechanics and usage of poller screw

1. POLLER SCREW Prepared by Siddharth Dubey

2. Learning objectives Understand the mechanical effects of poller screws Identify fracture patterns requiring poller screw augmentation Where to insert ?????? How to insert ??????

3. Introduction Poller screw Aka “blocking screw” Non interlocking screw placed outside the nail Improve reduction and enhance fixation in intramedullary nailing

4. Etymology Term Blocking screw was first introduced by Donald and Seligson in 1983 – as they “block” the nail from malreducing the fracture In 1994 - Krettek et al. introduced the term ‘‘Poller screws’’ Poller – German word meaning ‘‘bollard’’, a tubular structure used to guide traffic

5. Mechanical characteristics More rigid construct Effectively serving as a surrogate cortex in areas with insufficient nail-cortex contact

6. Narrows the medullary canal Centralising the guide wire in the medullary canal Indirect fracture reduction Maintenance of reduction by “Blocking effect”

7. Adjunct to interlocking screws Interlocking screws - length and rotation Blocking screws - stability against translation and angulation

8. Metaphyseal / Meta-diaphyseal fractures Higher tendency of settling in to mal alignment following intramedullary nailing Wide medullary canal - size discrepancy between diameters of nail and medullary canal – translation of nail along IL screw possible Poor nail to cortex contact – residual post fixation instability Higher muscular forces acting on the smaller fragment Krettek C, Schandelmaier P, Tscherne H (1995) Non-reamed interlocking nailing of closed tibial fractsoft tissue injury: Indications, technique and clinical results. Clin Orthop 315:34- 47 Freedman EL, Johnson EE (1995) Radiographic analysis of tibial fracture malalignment following intramedullary nailing. Clin Orthop 315:25-33

9. Saggital plane malreduction i.e. recurvatum or procurvatum - controlled by medio laterally placed interlocking screws Coronal plane deformities i.e. varus and valgus are more common

10. Oblique fracture patterns or severe comminution Guide wire tend to follow the “path of least resistance” Tends to migrate to the site with less bone

11. Revision nailing for mal-aligned fracture Previously malplaced nail Previous tract prevents placement of the new nail into the correct position as the nail may tend to slip again into the old nail path PS is placed to block the incorrect path

12. Where to insert ?????? Precise placement is necessary for optimal reduction False placement can exaggerate the deformity and may damage reamer tip or nail Requires good pre - operative planning

13. Stedtfeld et al Blocking screw in the short fragment close to the fracture on the concave side of the axial deformity Around 1 cm below the fracture line 5 to 6 mm away from the centre of the medullary canal i.e. close to the nail Establishes third point of three-point fixation in the shorter fragment

14. Why concave ????????? It is the site where the bone fails in compression hence causing more comminution and bone loss Guide wire has the tendency to displace toward more comminuted site

15. Most of the other authors also have the same opinion ie to place it on the cancave side of the expected deformity while avoiding the convex side Another description available in the literature is to place your blocking screws where you don’t want your nail to go Krettek C, Stephan 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. Ricci WM, O’Boyle M, Borrelli J, Bellabarba C, Sanders R. Fractures of proximal third of the tibial shaft treated with intramedullary nails and blocking screws. J Orthop Trauma 2001;15:264–70.

16. More recently a new technique has been described by Hannah et al More objective description regarding site and sequence of screw placement A. Hannah et al. / Injury, Int. J. Care Injured 45 (2014) 1011–1014

17. Draw a line down the long axis of the displaced, flared segment of bone Then draw a second line along the plane of the fracture ensuring to bisect the first line

18. As nearly all metaphyseal fractures having a degree of obliquity, this should create 4 angles; 2 acute and 2 obtuse

19. For correct reduction the screws need to be placed in the acute angles on the smaller metaphyseal fragment

20. When the nail comes into contact with the screw the course of the nail should be deflected so that the displaced segment becomes reduced in the desired direction

21. If a second screw is necessary should be placed in the other acute angle which will be nearer to the isthmus It will have less effect but will potentiate the effect of the first screw

22. Poller screw in Internal lengthening Nail The short metaphyseal bone fragment Deformities are usually predictable Can be pre operative, intraoperative or post operative during lengthening

23. Reverse rule of thumb By Muthusamy et al To Decide the ideal locations of the blocking screws Assess the deformity Envision trying to manually correct the deformity by holding the bone with both hands Thumbs of both hands are placed on the convex side of the deformity near the apex 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

24. How to place ????? Ideally blocking screw should be placed before placing the intramedullary guide wire Reaming should be done after the placement of blocking screw so that reamer reams through the centre of the medullary canal

25. Complications Ill placed screw may cause damage to the reamers and the nail There is also a risk of screw bending, breakage and difficulty in removal Difficulty in changing position of the screw

26. A. Shahulhameed et al - 3.9 mm steinman pin in place of screw during the process of nailing which was replaced by 5 mm interlocking screw once nailing with desired reduction was done If the Steinman pin is correctly placed it will spin while reaming as the reamer comes in contact with the Steinman pin Actual reduction of fragments can be seen in the fluoroscopy while the reamers pass across the Steinman pin

27. If the position of the Steinman pin is not satisfactory it is changed to a more accurate position Fluoroscopic images during the reaming process are performed to confirm the correct trajectory of the reamers

28. The canal is reamed to 1.5 mm above the size of the nail Nail is introduced Proximal and distal locking is performed The Steinman pin is then removed and a 5-mm interlocking screw is inserted in its place as a poller screw

29. Advantages It is easier to change the position of pin if found unsatisfactory during reaming Steinman pin has a smooth surface so damage to the reamers and nail is minimal The diameter of the Steinman pin is 3.9 mm which is ideal for a 5-mm locking screw Because the poller screw is inserted at the end of the procedure the risk of bending or breakage of the screws is also avoided

30. Case example

31. Take home messages Useful in preventing mal alignment in meta – diaphyseal fractures No clear consensus regarding accurate placement of blocking screw Proper pre operative planning and estimation of probable deforming forces Placement of poller screw where you don’t want your nail to go Most commonly the concave side but not universally true Depends on fracture pattern and comminution