http://www.bjj.boneandjoint.org.uk/content/95-B/12/1662.abstract

Screw fixation of medial malleolar fractures

A cadaveric biomechanical study challenging the current AO philosophy

1. L. Parker, BM, MRCS(Eng), FRCS(Tr & Orth), Specialist Registrar Trauma and Orthopaedic Surgery1 ; 
2. N. Garlick, FRCS(Orth), Consultant Orthopaedic Surgeon1; 
3. I. McCarthy, BSc, PhD, FIPEM, Principal Research Fellow2; 
4. S. Grechenig, Dr.med.Univ., Doctor3;
5. W. Grechenig, Prim.Prof.Dr., Professor4; and 
6. P. Smitham, PhD, MRCS(Eng), Clinical Lecturer, Specialist Registrar2

+Author Affiliations

1. 1The Royal Free Hospital, Pond Street, London NW3 2QG, UK.
2. 2Institute of Orthopaedics and Musculoskeletal Sciences, The Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
3. 3University Hospital Regensburg, Department of Traumatology, Franz-Josef-Strauss Allee, Regensburg, Germany.
4. 4AUVA Trauma Hospital, Graz, Gostingerstrasse 24, 8020, Graz, Austria.

1. Correspondence should be sent to L. Parker; e-mail: lee.parker06@gmail.com

Abstract

The AO Foundation advocates the use of partially threaded lag screws in the fixation of fractures of the medial malleolus. However, their threads often bypass the radiodense physeal scar of the distal tibia, possibly failing to obtain more secure purchase and better compression of the fracture.

We therefore hypothesised that the partially threaded screws commonly used to fix a medial malleolar fracture often provide suboptimal compression as a result of bypassing the physeal scar, and proposed that better compression of the fracture may be achieved with shorter partially threaded screws or fully threaded screws whose threads engage the physeal scar.

We analysed compression at the fracture site in human cadaver medial malleoli treated with either 30 mm or 45 mm long partially threaded screws or 45 mm fully threaded screws. The median compression at the fracture site achieved with 30 mm partially threaded screws (0.95 kg/cm2 (interquartile range (IQR) 0.8 to 1.2) and 45 mm fully threaded screws (1.0 kg/cm2 (IQR 0.7 to 2.8)) was significantly higher than that achieved with 45 mm partially threaded screws (0.6 kg/cm2 (IQR 0.2 to 0.9)) (p = 0.04 and p < 0.001, respectively). The fully threaded screws and the 30mm partially threaded screws were seen to engage the physeal scar under an image intensifier in each case.

The results support the use of 30 mm partially threaded or 45 mm fully threaded screws that engage the physeal scar rather than longer partially threaded screws that do not. A 45 mm fully threaded screw may in practice offer additional benefit over 30 mm partially threaded screws in increasing the thread count in the denser paraphyseal region.

Cite this article: Bone Joint J 2013;95-B:1662–6.

Footnotes

• The authors would like to thank Professor A. Weinberg, Department of Paediatric and Adolescent Surgery, Medical University of Graz, Austria, P. Ferlic and H. Dimai from Klinische Abteilung für Endokrinologie und Stoffwechsel, Graz, Austria for DEXA analysis, and S. Cro, Clinical Trials Unit, Medical Research Council, UK for statistical analysis.
  No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
  This article was primary edited by J. Scott and first-proof edited by G. Scott.
• Supplementary material. Two tables detailing the results of the studies of the compression at the fracture site for all four groups are available alongside the electronic version of this article on our website www.bjj.boneandjoint.org.uk

• Received July 20, 2012.
• Accepted May 24, 2013.

• ©2013 The British Editorial Society of Bone & Joint Surgery