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Title page Title: Advances and disputes of posterior malleolus fracture: A review of literature Authors: Su FU, Zhenlyu ZOU, Gang MEI and Dan JIN* Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China * Correspondence Author: Dan Jin, MD PhD Department of Orthopaedics and Traumatology, Nanfang Hospital, Southern Medical University 1838, North Guangzhou Avenue, Guangzhou City, Guangdong Province, 510515, P.R.China Email: [email protected] Tel: +86-20-62787951 Fax: +86-20-61360066 Key words: posterior malleolus fracture; stability; CT; posterolateral approach; syndesmotic fixation ABSTRACT Objective to summarize the development of posterior malleolus fracture Data sources Data used in this review were mainly from Pubmed in English Study selection Articles were included in the review if they were related to the posterior malleolus or trimalleolar fracture. Results No consensus is found regarding what sizes of posterior malleolar fragments would lead to ankle instability thus affecting prognosis, and should be fixed. X-ray measurement is unreliable, while CT scan is widely recommended and it can recognize the occult posterior malleolar fractures associated with tibia shaft fractures, which is always undetected previously. Direct posterior malleolus fixation is suitable to stabilize syndesmotic injury. The basic and clinical researches support direct reduction and buttress plate fixation of posterior malleolar fracture through the posterolateral approach. Operative indications and timing of weight bearing are still in discussion. Conclusion Knowing whether ankle instability occurs and the proper methods to diagnose, evaluate and operate can help manage the fracture. Further biomechanical research is required on ankle stability and clinical study to compare various treatment methods. Malleolar ankle fractures are commonly encountered in orthopedic trauma practice, the overall United States average was 4.2 ankle fractures per 1000 Medicare enrollees.1 In 1822, Cooper was the first who described a fracture of the ankle involving the posterior malleolus. In 1932, Henderson defined the posterior malleolus as “the anatomic prominence formed by the posterior inferior margin of the articulating surface of the tibia” and was the first to use the term trimalleolar fracture. Posterior malleolus fractures (PMF) can be detected in various types of ankle fractures: trimalleolar fractures of which the incidence is about 14.2%;1 the isolated fractures of the posterolateral tibial lip (Volkmann's triangle) which are rare with an estimated incidence of 0.5%-1%;1-3 posterior malleolar fractures associated with a tibial shaft fracture of which the incidence is 1%-25% but still seems to be underestimated.2,3 Posterior malleolus fractures can lead to incongruity and cartilaginous damage and thus posttraumatic arthritis, and have a significantly worse functional outcome.4 However, how to evaluate the ankle stability has not been exactly known; the proper measurements to evaluate the posterior malleolar fractures are controversial; no universal consensus has been reached on the best method to reduce and stabilize the posterior tibial malleolus. This review give a brief introduction of biomechanical evaluation, diagnose, classification and surgical treatment of posterior malleolar fractures. Biomechanical Evaluation of Posterior Malleolar Fractures Roles of structures to ankle stability The significant role of the lateral supporting structures is demonstrated by many cadaver studies. It has been confirmed that if the fibula is stable in an anatomic position, no posterior talar subluxation would happen even with fragments consisting of approximately 30%-50% of the articular margin.5 The internal supporting structures may be unimportant, as the disruption of the deltoid ligament would not appear to alter contact area.6 Ankle stability depends substantially on the distribution of load, which is called the mechanism of ankle stabilization by redistribution of articular contact stress. When bearing load, the stresses were mainly distributed to the second and third central quadrants of the talotibial interface.7 When fragments exist, this load pattern is altered. However, there is no increase in contact stresses near the articular incongruity, but a shift in the location of the contact stresses to a more anterior and medial location following the fracture,8-10 which may be determined by the articular geometry.10 A review of the literature suggests the medial and lateral constraints of the ankle rather than the articular surfaces provide the majority of ankle stability.11 Impact of posterior malleolar fracture to ankle stability The main task is to determine which fragment size of the posterior malleolus would lead to instability. Two patterns are used for the osteotomy cuts of the distal end of the tibia. Macko et al recommended the pattern that the lateral point of the cut corresponds to one-fourth, one-third, and one-half of the distance from the posterior to the anterior margin.12 Using this pattern, fragments smaller than 25% would not lead to ankle instability. Raasch et al used the cross-sectional pattern of the ankle at the level of the maximum anteroposterior dimension and conclude that after removal of 30 percent of the articular surface, significant posterior translation of the talus occurred, which is consistent with another study.6,8 Posterior malleolus fractures lead to ankle instability and thus posttraumatic arthritis in clinical practice, which was confirmed in follow-up clinical studies of 6.9 and 13 years respectively.9,13 A cartilage biosynthetic transduction and injury characteristic is sensitive to changes in contact stress rates. It is not the peak pressure, but the changes of the center of stress leading to cartilage bearing significantly higher contact stresses, that plays a large role in posttraumatic arthritis development.11 Incongruity-associated changes in contact stress rates and incongruity-associated instability events may be important pathomechanical determinants of post-traumatic arthritis,14 but the exact pathomechanical cause of posttraumatic arthritis is unclear. Diagnose and classification of Posterior Malleolar Fractures Evaluation methods and classification Conventional plain radiography is still necessary in the primary diagnosis and the measurement, and the fracture of the dorsal tibial margin is best seen in the standard lateral view,15 but some unmarked fragments could not be demonstrated. An external-rotation lateral view (the average angle is 50 degrees) of the ankle may diagnose the fragments 16 effectively. The fragment size is conventionally measured on the lateral X-ray of the ankle joint: the length of the involved articular surface of the fragment divided by the length of the collective distal tibial articular surface (including the articular surface of the fragment).13 Using a curved ruler to measure the arc of the articular surface may be more accurate.17 However, the fracture lines appear to be highly variable and lack of regulation. The posterior malleolar fragment can range in size from a small extra-articular fragment to one comprising more than 40% of the articular surface of the tibia,18 thus making it hard to evaluate. CT scan provides a good visualization of the fracture. Preoperative using of CT is justified, because it can detect the greatly varied fracture lines that X-ray cannot distinguish.18 Plain films of the tibia may underestimate the size of the fragment and the amount of the joint surface affected,7 making patients delay the operation thus leading a serious clinical consequences, but mostly overrates the size of the fragment, which is unreliable in assessing the posterior fragment size. In addition, intraexaminer variability is high by using lateral radiograph,19 indicating a poor repeatability. CT-scan is emphasized on the diagnosing and measurement. Posterior malleolar fractures can be detected in: posteromedial fracture fragments in type A and posterolateral fracture fragments in type B and C of the Danis-Weber system; supination external rotation type Ⅲ-Ⅳ lesion(SEⅢ-Ⅳ) and pronationin external rotation type Ⅳ lesion (PEⅣ) in the Lauge Hansen classification system. Both of the two classifications do not evaluate the severity of fracture and they are not prognostic. Stability-based ankle fracture classification system can be practical.20,21 Haraguchi et al18 based on the orientation of the fracture line and classified the posterior malleolus fractures: the posterolateral-oblique type (67%), the medial-extension type (19%), and the small-shell type (14%). Tibia shaft fractures associated with posterior malleolar fractures Tibia shaft fractures, typically spiral low-energy fractures of distal third of the tibia, are often associated with occult posterior malleolar fractures with a high undetected rate. The posterior malleolar fractures may be overlooked while addressing more obvious and painful tibial shaft fractures and is not well-detected. Stuermer et al 22 suggested that added attention should be paid to the ankle with the following criteria such as the indirect trauma with a rotation component or pronationeversion trauma, spiral fracture of the tibia in the distal third, the tibial shaft fracture associated with fracture of the fibula in the proximal third or an intact fibula. These indications can be a clue to diagnose, but not enough to recognize the majority of theses combined injuries, therefore the radiographic examination becomes indispensable. The diagnose methods of tibia shaft fractures associated with posterior malleolar fractures have been in discussion. X-ray is mandatory but being suspected, especially in cases of low-energy distal tibial diaphyseal fractures,2 its undetected rate can be 44%-68%(a prognostic study included).23 The three separate radiographic views (the anteriorposterior, the mortise, and the lateral views) are recommended to help diagnose this fracture pattern.22 A "communication line" from plain radiograph, which connects the medial inferior apex of the spiral tibia fracture line and the posterior superior apex of the posterior malleolar fracture, may be a useful diagnostic clue.24 CT scan is recommended to be routinely performed in clinical practice while MRI may be a compensative method. Preoperative using of CT scan may prompt fracture stabilization25 and identify the type of posterior malleolar fractures.23 Surgical treatment of Posterior Malleolar Fractures Operative indications Operative indications for surgical treatment of posterior malleolar fractures are not currently well defined. Most orthopedic surgeons consider a posterior malleolar fracture fragment larger than 25% to 33% of the articular surface of the plafond or remaining displaced >2mm after fibular reduction an operative indication, with which the ankle is rendered unstable.7,18,26,27 In a recent meta-analysis, no consensus was found in the literature regarding which fragment sizes of posterior malleolar fractures should be fixed.11 Harper’s cadaver study has shown that if the fibula is stable in an anatomic position, no posterior talar subluxation would happen and posterior malleolar fractures need not to be fixed.5 The fragments smaller than 25% may need not to be fixed when reduced acceptably,13,28 While Langenhuijsen found that anatomic reduction should be achieved when the fragments larger than 10% of the tibial articular surface (the method did not always mean internal fixation, the mechanism of ligamentotaxis could work).9 Most avulsion fractures can be treated non-operatively with success. However, taking into account the biomechanics of the syndesmosis, some scholars recommend the fixation of all posterior malleolar fragments (only prospective study, Level II evidence).26 This may because of the significant role of syndesmotic reduction contributing to functional outcome29 and superior syndesmotic stability may be obtained by fixation of the posterior malleolus rather than by using a trans-syndesmotic screw fixation. Even minimal displacement may lead to post traumatic arthritis,12 suggesting that anatomic reduction of all the displaced posterior malleolus fractures can prevent posterior talar subluxation and restore articular congruency to minimize posttraumatic osteoarthritis and improves the prognosis of trimalleolar fractures.30 However, a retrospective research has shown that the syndesmotic fixation has no influence on functional outcome.20 Conservative treatment is needed for the isolated posterior malleolar fractures. The satisfactory long-term outcome were asserted31 and notably, for osteoarthritis, 95% patients had no signs (excellent) or osteophytes (good), suggesting a low risk of developing osteoarthritis. Surgical approaches Different approaches have been described for fixation of the posterior malleolus: the medial approach, posteromedial approach and posterolateral approach and so on. Many factors such as the type of posterior malleolus fracture, ankle stability, and the height of the fibular fracture line should be considered to choose the best approach.32 The most important factor to consider is the location of the fracture fragment because of the deep position difficult to reveal and easy rotation of posterior malleolus. The medial approach is suitable for the medial fragment. Approximately 20% of the posterior malleolar fracture lines (type II fractures according to the Haraguchi classification system) extend into the medial malleolus.18 The medial side can be exposed but the long medial incision requires extensive soft tissue stripping of the fracture fragments. Besides, the posterior location of tarsal tunnel makes tarsal tunnel easy to irritate and makes posterior to anterior screws difficult to be placed. The fixing of the medial side of fragment is not stable and displacement may occur during screwing. The posteromedial approach is suitable for the large posteromedial-biased fragment which allows fixation of the posterior and medial malleoli from the same incision.33,34 The skin incision follows the posteromedial border of the distal tibia and medial malleolus and continues in line with the tibialis posterior tendon toward the talonavicular joint. A retrospective study demonstrated the satisfactory short- and mid-term clinical results of this technique.34 However, this approach has limited visualization of the posterior malleolus fragment, an additional posterolateral approach may be required if the posterior malleolus is split in two parts. Interest has been growing in obtaining direct reduction and fixation of the posterior malleolus using a posterolateral approach, which allows good visualization and stable fixation of the posterior malleolus, and many studies demonstrated the satisfactory clinical outcomes using this approach.35-38 The longitudinal skin incision is made in the interval between the posterior border of the fibula and the lateral border of the Achilles tendon, which allows for simultaneous reduction and fixation of the lateral malleolus through the same skin incision, and fracture is revealed between the peroneus brevi and flexor hallucis longus muscles. This approach provides the good visualization and reduction.36 Alternative surgical techniques The majority of posterior malleolus fractures are avulsion fractures, therefore most fractures reducing spontaneously after the fibular fracture is reduced. The method of fixation of the posterior malleolus was traditionally from the anterior aspect by using indirect reduction and an anteroposterior screw, relying on the attachment of the ligament to reduce posterior malleolus, which is supported by a recent study which confirmed that almost all the posterior malleolar fractures were attached to an intact posterior inferior tibiofibular ligament,29 but this type of reduction cannot always ensure adequate articular reduction. Debate arises regarding the best treatment. Questionnaires have shown that trauma-trained surgeons were significantly more likely to choose antiglide plate fixation compared to screw-only fixation and new techniques such as direct exposure and plating of the posterior malleolus are chosen more frequently than traditional method.27 A biomechanical and clinical study has shown that screw-only fixation(two screws) are enough to supply the stability for some small fragments involve only 1/4 of the posterior articular facet; but for the fractures involve more than 1/4 facet, the plate fixation supplies more stable fixation and is superior to simply screws.35 Bioabsorbable screws fixation is also suitable.36 The buttress plate maintains reduction, prevents superior migration of fragment,37 and can be placed in the intermuscular plane through the posterolateral approach thus causing less irritation. The excessively large or crushed fragment can be fixed by screw in combination with the support plate, and external fixation or traction can be used. Chronic displacement of the posterior malleolus fragment can be gradually reduced with Taylor spatial frame,40 which can minimize the soft tissue dissection. Relationship between posterior malleolus fracture and syndesmotic injuries With a small or large posterior malleolus fracture, the syndesmosis can be reduced accurately using a clamp, although it can be obliquely malreduced or slightly compressed.41 Then the syndesmotic injury can be fixed by standard trans-syndesmotic fixation, which has a high rate of syndesmotic malreduction (about 52%),42 or open posterior malleolus fixation when the posteroinferior tibiofibular ligament is intact. Now the advantages of posterior malleolus fixation have been justified.31,43,44 Gardner et al45 discovered that fixation of the posterior malleolus was biomechanically superior to syndesmotic screw fixation in a cadaver study, while Miller et al compared the functional outcomes (FAOS scores, which is similar among groups) of three groups with open posterior malleolus fixation, locked syndesmotic screws and combined fixation, and suggested that syndesmotic fixation through the posterior malleolus at least equivalent to syndesmotic screw.26 This may because the short duration outcomes of Miller’s follow-up (mean, 15 months) did not fully demonstrate the advantages. Postoperative management and prognosis Protected weight bearing may be started immediately. Harager K’s study acquired satisfactory outcomes of patients who took weight-bearing from 3 weeks, to full weight-bearing after 6 weeks,43 and he recommended immediate weight-bearing after surgery, even in the elderly, but the trail is not randomized and prospective. The early weight bearing could facilitate recovery and recommended utilizing it, but some scholars found minimal benefit from early weight bearing in the first few weeks after surgery.44,46 Walking cast, crutches and functional brace are needed to help weight bearing; the functional brace may provide superior results over plaster.44 Posterior malleolus fracture may indicate unstable ankle resulting from high energy, and it seems to result in worse outcomes.30,47 A study compared the outcomes of unstable fractures with or without posterior malleolar fragment and found significant differences at the first year, definitely in pain status and function, but mostly attenuated at the second year, no significant difference in the complication rates and radiographic outcomes.47 DISCUSSION Biomechanical evaluation of posterior malleolar fractures is to find a proper assessment of ankle stability, which is the foundation of therapy. Ankle stability largely depends on the medial and lateral structures, especially the fibular acting as the primary factor of ankle stability and the correct distribution of load, which is consistent with the excessive internal rotation caused by posterior malleolar fractures without the supporting effect of fibula.48 Therefore, we should restore this lateral constraints and the articular congruity. Plain radiographic measurement is effective but does not accurately reflect the real status of ankle, making plenty of malreduced syndesmoses (about 69%) undetected.42 It is difficult to found occult posterior malleolar fragment by x-ray examination, and the various types of fracture lines make a generally accepted position hard to be made to best demonstrate all the fracture lines. Unlike the inconsistent and unreliable plain radiograph, CT scan does not have images overlapping, two-dimensional imaging and could be a useful tool to detect the occult fragments when associated with tibial shaft fractures, which is justified by many studies.24,28,49 Traditional operative indications are being challenged now. Because the fragment size cannot represent the ankle stability, factors such as stability other than fragment size most impact surgical indications. In some cases, satisfactory outcomes of fracture fragment larger than 25% are achieved without an internal fixation,13,17 which means that even large posterior fragments do not have to be fixed. A stability-test performed using intraoperative fluoroscopic images may help decide whether to operate on the fragment smaller than 25 % of the articular surface.50 Questionnaires have shown that fragment size still affected treatment decisions and significant variation existed regarding the operative indications of posterior malleolar ankle fracture. 27 The posterolateral approach is more frequently used. Fragments can obtain direct exposure, reduction and fixation using a, which is safe, effective, stable but invasive. The hardware with the posterolateral approach is deep in the ankle, with good soft tissue coverage (under the muscle tissue rather than the skin), thus making wound dehiscence will not lead to disastrous complications. This approach is safer, though more invasive than other approaches, leading to good results with few local complications.51 The complications such as a slightly higher rate of noninfected healing complications,52 wound infection (4.4%) and reoperation (12.5%)53 should be noticed. The managing sequence is posterior malleolus, fibula, and then medial malleolus described by Helmy N et al and Irwin T A et al.54,55 Compared with the conventional lateral approach, several characters should be noticed: more invasive; difficult 36 to fix the medial malleolus; complications. Therefore, the posterolateral approach is suitable for displaced fractures that involve more than 30% of the distal articular tibial surface and that continue to be displaced more than 2 mm after closed reduction of the ankle. The treatment of syndesmotic injury still remains a matter of debate. Posterior malleolar reconstruction is more accurate and more stable than syndesmotic screw fixation, but even with attention to detail, reduction sometimes remains imprecise.56 When posterior malleolus avulsion fractures involved, reduction and fixation of the fragment can eliminate the need for syndesmosis transfixation to fix the syndesmosis. Patients who use a syndesmotic screw may undergo additional fixation of the posterior fragment, so it seemed that 16-36% of syndesmotic screws may be unnecessary(a retrospective cohort study included).29,57 The syndesmotic screw may be an injury to the posterior tibial blood vessels and nerve, while the potential stress riser formation, and precludes early weight bearing are also the disadvantages. Excellent outcomes needs the stable fixation.58,59 Early weight bearing can be adopted after the first postoperative week, if the posterior fragment was fixed through a posterolateral or posteromedial approach, because the posterior ankle joint surface remained unloaded when bearing load in an experimental study.7 The plaster cast should be made to maintain the ankle in neutral position and protect the posterior malleolus from axial load. CONCLUSION Experimental and clinical studies have shown the advances such as the role of CT scan in detecting occult fracture, the advantage of plate fixation using a posterolateral approach and so on, but debates such as ankle stability and operative indications still need further research. Acknowledgements This work was supported by Projects in the Guangzhou Science & Technology Program(2012Y2-00023). References 1. Koval KJ, Lurie J, Zhou W, Sparks MB, Cantu RV, Sporer SM, Weinstein J. 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