When inserting a lag-screw across an arthrodesis, stress is concentrated under the screw head risking asymmetrical force distribution and fracture of the cortical bone bridge. The IO FiX (Extremity Medical, NJ USA) is a new intraosseous device comprising an X-Post on one side of and parallel to the arthrodesis and a lag-screw inserted through the head of the X-Post which reinforces the cortical bone bridge. The X-Post behaves as an internal washer improving force distribution across the arthrodesis. Being intraosseous, near to the neutral axis of bend also means the device is fatigue-resistant and soft tissue irritation is reduced.

The IO FiX has not been independently verified and therefore we analysed its performance in a human cadaveric ankle model. Our null hypothesis was there is no difference in force generation and contact area in an ankle arthrodesis when the IO FiX is compared with partially-threaded lag-screws.

We used ten randomized cadaver ankles with a mean age of seventy-one years (44–84 years) prepared with flat arthrodesis cuts. A Tek-scan (Boston, USA) pressure transducer was used to measure force and contact area produced when the IO FiX was compared with a standard lag-screw and washer.

The median average force in the IO FiX group was 3.95 kg and 2.35 kg in the lag-screw group (p=<0.01 Wilcoxon signed-rank). The IO FiX was able to create a more uniform contact area within the arthrodesis with a median average of 3.41 cm² compared with 2.42 cm² in the lag-screw group (p=<0.03 Wilcoxon signed rank).

Our results suggest the IO FiX improves force generation and contact area across the arthrodesis. With the theoretical advantages of reduced soft tissue irritation and a lower risk of fatigue failure, the IO FiX offers a significant advantage compared with traditional fixation techniques.

Introduction

Venous thromboembolism (VTE) represents a major cause of morbidity, mortality and financial burden to the NHS. Acquired risk factors are well documented, including immobilisation, lower limb plaster cast and surgery. NICE guidance on VTE prophylaxis within orthopaedics currently excludes operative ankle fracture fixation (ankle ORIF).

The management of unstable ankle fractures is challenging due the difficulty in differentiating between stable and unstable fracture patterns. The aim of our study was to examine our practice and to determine if the operative management of unstable ankle fractures resulted in significantly improved radiographic parameters.

Between June 2008 and December 2008, we identified all skeletally mature patients who were diagnosed with an ankle fracture after having radiographs in the radiology department at our institution. We analysed the case notes and radiographs of these patients retrospectively. The fractures were classified according to the Weber and Lauge-Hansen classification. Radiographs were evaluated for shortening of the fibula, widening of the joint space, or malrotation of the fibula. Three measurements were used to ascertain whether the correct fibular length has been restored – the circle sign, the talocrural angle, and the tibiofibular (or Shenton) line.

Of 1064 patients who had radiographs, 123 patients sustained a fracture of the ankle. There were 61 females and 62 males, with a median age of 47 years. There were 20 Weber A, 80 Weber B and 12 Weber C ankle fractures. Eleven fractures could not be classified according to the Weber classification. According to the Lauge-Hansen classification there were 44 Supination-External rotation (SER) stage II fractures, 35 Supination-External rotation (SER) stage IV fractures, and 7 Pronation-External rotation (PER) stage III fractures. In the unstable SER stage IV fractures, 30 of the 35 patients had operative treatment and there was no statistically significant difference in the average Talocrural angles in the operative (78.9°) and nonoperative groups (83.4°). None of the patients with an SER stage IV fracture managed nonoperatively had an adequate circle sign compared to 14 of the 30 patients in the operative group who had an adequate circle sign. In the PER stage III fractures 4 of the 7 patients had operative treatment. The average Talocrural angle in the operative group was 79.1° versus 75.3° in the nonoperative group, with all patients in the operative group having an adequate circle sign compared to none in the nonoperative group. The patient numbers in the PER stage III group however were too small to show a statistically significant difference. In 4 patients with unstable fracture patterns, the use of a third tubular plate to bridge a fibula fracture without an inter-fragmentary lag screw led to inadequate restoration of fibular length in all cases.

It is important to recognise unstable ankle fracture patterns and, in patients treated operatively, to restore fibular length and rotation. Operative management of unstable SER stage IV and PER stage III ankle fractures can restore normal radiographic parameters. We highlight certain technical pitfalls in restoring fibular length such as the inappropriate use of the semi-tubular plate as a bridging plate.