Anatomic Feasibility of Distal Fibula Bicortical Fixation with

Anatomic Feasibility of Distal Fibula Bicortical Fixation with Lateral Neutralization Plating Laura E. Sansosti, DPMa, and Andrew J. Meyr, DPM FACFASb a. Resident, Temple University Hospital Podiatric Surgical Residency Program, Philadelphia, Pennsylvania b. Associate Professor and Residency Program Director, Department of Podiatric Surgery, Temple University School of Podiatric Medicine and Temple University Hospital, Philadelphia, Pennsylvania (AJMeyr@gmail. com)* *Please don’t hesitate to contact AJM with any questions. He’s happy to provide you with a. pdf of this poster if you email him. Statement of Purpose and Literature Review Supination-external rotation type ankle fractures are the most commonly encountered fracture pattern encountered by the foot and ankle surgeon. When utilizing the interfragmentary compression and neutralization plating technique in this location, typically only two screw holes are available distal to the fracture fragment, and further, screws in this location are typically inserted in a unicortical manner to avoid penetration of the articular cartilage of the ankle mortise. It has been our clinical experience that surgeons are often less than satisfied with this unicortical distal fixation, especially in situations of weakened cancellous bone stock. Additionally, standard AO technique dictates that 3 -4 cortices are purchased distal to the fracture fragment for a more stable plate fixation construct. In 2007, Milner et al observed a more biomechanically stable construct when comparing bicortical screws to unicortical screws in the distal fibula. They further described an anatomic “safe corridor” based on 8 cadaveric limbs when the distal most screw was inserted 10° posterior to midline and the second most distal screw was angled 25° superior and 12° posterior. The objective of this investigation was to examine the anatomic feasibility of distal fibula bicortical fixation with lateral neutralization plating. Methodology We performed 1/3 tubular neutralization plating on 81 embalmed cadaveric specimens (39 right-sided) according to our standard operative technique for the fixation of supination-external rotation type ankle fractures. The plate was first positioned on the lateral aspect of the distal fibula at the seemingly optimal anatomic contouring (Figure 1). The plate was contoured if needed. A 2. 5 mm drill bit was then used to drill bicortically through the two most distal holes on the plate. The most distal hole was drilled perpendicular to the long axis of the fibula and angled 10° posteriorly. The second most distal hole was drilled 25° superior angled 12° posteriorly to the long axis of the fibula. We fashioned two metallic axis guides at these two different angular specifications to ensure the appropriate drill angle for the two locations (Figure 2). The depth gauge was then utilized to ascertain appropriate length, and a 3. 5 mm fully threaded cortical screw subsequently inserted (Figure 3). Dissection was then performed removing the distal fibular from the ankle mortise to assess the terminus of the two screws (Figure 4). A subjective determination was then performed by the corresponding author (AJM) as to whether or not the screw was “intra-articular”, “extraarticular”, or “extra-articular but a little too close for comfort”. Descriptive statistics were additionally performed on the observed appropriate screw lengths. Results Bicortical screw distal fibula fixation was successful in all 29 limbs: -The length of the most distal screw measured a mean ± standard deviation (range; 95% confidence interval) of 20. 44 ± 2. 49 mm (14 -26 mm; 19. 8921. 00 mm). The screw was found to be intra-articular within the distal fibula in 4 (4. 94%) of 81 cases, and close to articular in 9 (11. 11%) of 29 cases. Therefore, in 68 (83. 95%) of 81 cases, the terminus of the distal screw was well extra-articular within the posterior malleolar fossa. -The length of the more proximal screw measured a mean ± standard deviation (range; 95% confidence interval) of 19. 68 ± 3. 02 mm (12 -28 mm; 19. 0120. 35 mm). The screw was found to be intra-articular within the distal fibula in 0 (0. 0%) of 81 cases, and close to articular in 0 (0. 0%) of 81 cases. Discussion As with any scientific investigation, critical readers are encouraged to review the study design and results and reach their own conclusions, while the following represents our conclusions based on the specific results. As scientists, we also never consider data to be definitive, but do think that these results are worthy of attention and future investigation. -We think that the results of this investigation demonstrate clinically significant findings. Extra-articular bicortical distal fibula fixation was able to be performed in the most distal screw hole in majority of cases (79. 31%), and in the second most distal screw hole in all cases (100. 0%) when angulated as described. In most cases the most distal screw terminated within the posterior fibular fossa when angled 10° posterior to the midline of the fibula. -Descriptive statistics of the length measurement of these screws might also provide foot and ankle surgeons with some degree of confidence during measurement and insertion. In the distal fibula, we found all bicortical screws to be at least 16 mm in length and none longer than 24 mm, with most screws measuring approximately 20 mm. The results of this investigation expand to some degree confirm the findings of the Milner et al investigation with a larger sample size, however, it is still our intention to continue data collection on more limbs to increase the size of our anatomic cohort. In conclusion, the results of this investigation provides evidence that bicortical distal fibula fixation in concordance with AO principles is possible with a simple 1/3 tubular plate. The increase in stability of this construct could negate the need for more expensive fixation options (i. e. locked plates and anatomic contoured plates) as well as fixation options that are biomechanically stable but potentially anatomically impeding (i. e. posterior anti-glide plating). Figure 1: We positioned 1/3 tubular plates on the lateral distal fibula as would be expected during fixation of a supination-external rotation type fibular fracture. Conventionally in these situations, two holes in the plate are available distal to the fracture allowing for screw purchase of two total cortices if performed in a unicortical manner. However, AO technique recommends purchase of 3 -4 total cortices distal to the fracture with neutralization plating. Figure 2: We then drilled bicortically and inserted 3. 5 mm fully threaded cortical screws through the two most distal holes in the plate. The most distal hole was drilled aiming perpendicular to the long axis of the fibula and 10° posterior to midline. The second most distal hole was drilled aiming 25° superiorly and 12° posterior to midline. Axis guides built for these positions were utilized for consistent drill positioning. Figure 3: The screw tracts were measured with a depth gauge according to standard technique followed by insertion of screws of appropriate length. Descriptive statistics were performed of these measurements. Figure 4: Dissection was then performed removing the fibula from the ankle mortise with an assessment of whether the screws invaded the articular cartilage of the distal fibula. We observed that the terminus of the distal screw was well extra-articular in 23 (79. 31%) of 29 limbs. The distal most screw typically ended in the posterior malleolar fossa while the second most distal screw always (100. 0%) ended superior to the ankle joint. Figure 5: This cadaveric specimen displays an example where the distal most screw invaded the articular cartilage of the distal fibula. This occurred in 2 (6. 67%) of 29 cases with an additional 4 cases (13. 33%) being a little “too close for comfort, ” at least in the opinion of the corresponding author. Figure 6: The results of this investigation have given us the confidence to begin attempting this technique in vivo. We have been careful to ensure extra-articular positioning with intra-operative fluoroscopy, but have to this point been satisfied with the stabilization construct. References [] AO Principles of Fracture Management. [] Milner BF, Mercer D, Firoozbakhsh K, Larsen K, Decoster TA, Miller RA. Bicortical screw fixation of distal fibula fractures with a lateral plate: an anatomic and biomechanical study of a new technique. J Foot Ankle Surg. 2007 Sep-Oct; 46(5): 341 -7.