Posterior malleolus fractures vary in morphology. A computed tomography scan is imperative to evaluate fragment size, comminution, articular impaction, and syndesmotic disruption. Despite an increasing body of literature regarding posterior malleolus fractures, many questions remain unanswered. Although, historically, fragment size guided surgical fixation, it is becoming evident that fragment size should not solely dictate treatment. Surgical treatment should focus on restoring ankle joint structural integrity, which includes restoring articular congruity, correcting posterior talar translation, addressing articular impaction, removing osteochondral debris, and establishing syndesmotic stability.
Key points
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Posterior malleolus fractures are varied in morphology.
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Posterior malleolar fractures may challenge syndesmotic stability by adversely affecting the functional integrity of posterior syndesmotic ligaments.
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A preoperative computed tomography scan is imperative for the evaluation of fragment size, comminution, articular impaction, and syndesmotic disruption.
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Fragment size (in terms of percentage of articular surface) should not dictate treatment.
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Treatment should restore ankle joint structural integrity by achieving articular congruity, correcting posterior talar translation, addressing articular impaction, removing osteochondral debris, and establishing syndesmotic stability.
Introduction
Ankle fractures are common, often require surgery, and represent about one-tenth of all fractures. Population based studies have shown that the incidence of ankle fractures has increased significantly since the 1960s, especially for elderly patients.
Overall, about two-thirds of ankle fractures are isolated malleolar fractures, one-fourth are bimalleolar, and the remaining 7% are trimalleolar fractures. These incidences are in accordance with a study by Koval and colleagues, although the investigators found that trimalleolar fractures represented about 14% of fractures. Isolated posterior malleolar fractures (PMFs) are rare, with an estimated incidence of about 0.5% to 1% of fractures.
An understanding of the posterior malleolus anatomy, the ligamentous attachments, and its contribution to ankle congruity and stability is critical in determining the appropriate treatment. Although management of lateral and medial malleolar fractures is well established, the treatment PMFs, which are heterogeneous in morphology, remains controversial. No consensus exists regarding their recommended management.
Anatomy
The ankle joint is a complex, 3-bone joint consisting of the tibial plafond, the distal fibula, and the talus. The ankle joint is saddle-shaped and derives its stability from a combination of bony and ligamentous structures. The significant role of the medial and lateral ligament complexes in ankle congruity and stabilization is well described.
In 1932, Henderson described the posterior malleolus as “the anatomic prominence formed by the posterior inferior margin of the articulating surface of the tibia.” With regard to PMFs, understanding of the distal tibiofibular joint is crucial in order to formulate appropriate treatment strategies. The distal tibia and fibula form the osseous part of the syndesmosis and are attached by the anterior inferior tibiofibular ligament (AITFL), the posterior inferior tibiofibular ligament (PITFL), the transverse ligament, and the interosseous ligament (IOL). Based on a cadaveric study, Ogilvie-Harris and colleagues showed that 42% of syndesmotic stability is provided by the PITFL, 35% by the AITFL, and 22% by the IOL. Because the PITFL extends from the posterior malleolus to the posterior tubercle of the fibula, PMFs challenge the structural integrity of the posterior syndesmotic ligaments, and may produce syndesmotic disruption ( Fig. 1 ).
Biomechanics
The complex geometry of the tibiotalar joint and its interrelations with static and dynamic stabilizers all influence load characteristics. The effects of PMF on ankle joint biomechanics, in terms of stability and contact stresses, have been the subjects of several studies.
Scheidt and colleagues created PMFs involving 25% of the articular surface. The investigators showed that this might lead to excessive internal rotation and posterior instability in a loaded ankle joint. Note that fracture fixation increased ankle stability, but not significantly.
In contrast, other investigators showed no such effect of PMFs on ankle joint stability.
Raasch and colleagues showed that a 200-N posteriorly directed force did not cause posterior translation of the talus with up to 40% osteotomy of posterolateral tibia, as long as the fibula and AITFL were intact. However, in tested cadavers, with transected AITFL and fibula, a significant posterior translation of the talus occurred after removal of 30% of the articular surface.
Harper and colleagues showed that no significant posterior translation of the talus occurred even with a PMF measuring 50% of the articular surface. However, if the fibula is not intact or there is disruption of the lateral ligamentous structures, significant posterior translation of the talus occurred.
Macko and colleagues showed with cadaver specimens that with increased size of the PMF to more than a third of the distal tibia, the surface area of contact decreased. Also, there were considerable changes in the load-distribution patterns, with increased confluence and concentration of loads as the size of the fragment increased. Similar findings were reported by Harttford and colleagues, who showed a decrease in tibiotalar contact area with increasing size of posterior malleolus fragments. Also, sectioning of the deltoid ligament did not alter the contact area.
In contrast, Vrahas and colleagues found that, even after removing 40% of the posterior malleolus, no increase in peak contact stress was detected. Similarly, Fitzpatrick and colleagues studied dynamic contact stress aberrations in a cadaveric 50% PMF model. With dynamic range of motion, there was no increase in peak contact stress but a shift in the location of the contact stresses to a more anterior and medial location following the fracture. Furthermore, even in the anatomically fixated model, the stress redistribution did not return to normal. The investigators concluded that, with no talar subluxation and no increase in contact stresses near the articular incongruity, it is more likely that posttraumatic arthrosis is caused by the remaining articular surface being exposed to an increased stress. This shift in the center of stress loads cartilage that normally is exposed to little load.
In summary, conflicting data exist regarding the biomechanical influence of PMFs on ankle joint stability and contact pressures, especially in terms of fragment size.
Introduction
Ankle fractures are common, often require surgery, and represent about one-tenth of all fractures. Population based studies have shown that the incidence of ankle fractures has increased significantly since the 1960s, especially for elderly patients.
Overall, about two-thirds of ankle fractures are isolated malleolar fractures, one-fourth are bimalleolar, and the remaining 7% are trimalleolar fractures. These incidences are in accordance with a study by Koval and colleagues, although the investigators found that trimalleolar fractures represented about 14% of fractures. Isolated posterior malleolar fractures (PMFs) are rare, with an estimated incidence of about 0.5% to 1% of fractures.
An understanding of the posterior malleolus anatomy, the ligamentous attachments, and its contribution to ankle congruity and stability is critical in determining the appropriate treatment. Although management of lateral and medial malleolar fractures is well established, the treatment PMFs, which are heterogeneous in morphology, remains controversial. No consensus exists regarding their recommended management.
Anatomy
The ankle joint is a complex, 3-bone joint consisting of the tibial plafond, the distal fibula, and the talus. The ankle joint is saddle-shaped and derives its stability from a combination of bony and ligamentous structures. The significant role of the medial and lateral ligament complexes in ankle congruity and stabilization is well described.
In 1932, Henderson described the posterior malleolus as “the anatomic prominence formed by the posterior inferior margin of the articulating surface of the tibia.” With regard to PMFs, understanding of the distal tibiofibular joint is crucial in order to formulate appropriate treatment strategies. The distal tibia and fibula form the osseous part of the syndesmosis and are attached by the anterior inferior tibiofibular ligament (AITFL), the posterior inferior tibiofibular ligament (PITFL), the transverse ligament, and the interosseous ligament (IOL). Based on a cadaveric study, Ogilvie-Harris and colleagues showed that 42% of syndesmotic stability is provided by the PITFL, 35% by the AITFL, and 22% by the IOL. Because the PITFL extends from the posterior malleolus to the posterior tubercle of the fibula, PMFs challenge the structural integrity of the posterior syndesmotic ligaments, and may produce syndesmotic disruption ( Fig. 1 ).
Biomechanics
The complex geometry of the tibiotalar joint and its interrelations with static and dynamic stabilizers all influence load characteristics. The effects of PMF on ankle joint biomechanics, in terms of stability and contact stresses, have been the subjects of several studies.
Scheidt and colleagues created PMFs involving 25% of the articular surface. The investigators showed that this might lead to excessive internal rotation and posterior instability in a loaded ankle joint. Note that fracture fixation increased ankle stability, but not significantly.
In contrast, other investigators showed no such effect of PMFs on ankle joint stability.
Raasch and colleagues showed that a 200-N posteriorly directed force did not cause posterior translation of the talus with up to 40% osteotomy of posterolateral tibia, as long as the fibula and AITFL were intact. However, in tested cadavers, with transected AITFL and fibula, a significant posterior translation of the talus occurred after removal of 30% of the articular surface.
Harper and colleagues showed that no significant posterior translation of the talus occurred even with a PMF measuring 50% of the articular surface. However, if the fibula is not intact or there is disruption of the lateral ligamentous structures, significant posterior translation of the talus occurred.
Macko and colleagues showed with cadaver specimens that with increased size of the PMF to more than a third of the distal tibia, the surface area of contact decreased. Also, there were considerable changes in the load-distribution patterns, with increased confluence and concentration of loads as the size of the fragment increased. Similar findings were reported by Harttford and colleagues, who showed a decrease in tibiotalar contact area with increasing size of posterior malleolus fragments. Also, sectioning of the deltoid ligament did not alter the contact area.
In contrast, Vrahas and colleagues found that, even after removing 40% of the posterior malleolus, no increase in peak contact stress was detected. Similarly, Fitzpatrick and colleagues studied dynamic contact stress aberrations in a cadaveric 50% PMF model. With dynamic range of motion, there was no increase in peak contact stress but a shift in the location of the contact stresses to a more anterior and medial location following the fracture. Furthermore, even in the anatomically fixated model, the stress redistribution did not return to normal. The investigators concluded that, with no talar subluxation and no increase in contact stresses near the articular incongruity, it is more likely that posttraumatic arthrosis is caused by the remaining articular surface being exposed to an increased stress. This shift in the center of stress loads cartilage that normally is exposed to little load.
In summary, conflicting data exist regarding the biomechanical influence of PMFs on ankle joint stability and contact pressures, especially in terms of fragment size.
Radiographic assessment and fracture classification
Conventional radiography is indicated for initial diagnosis and treatment of ankle fractures, with identification of posterior malleolar injury best evaluated on the lateral view. Although the size of the posterior malleolar fragment can be estimated as a percentage of the tibial articular surface on the lateral view, several investigators have shown that radiograph-based measurement is poorly reliable and accurate.
The authors recommend, in accordance with other studies, that computed tomography (CT) scan should be performed for all PMFs to evaluate fragment size, comminution, articular impaction, and syndesmotic disruption. Several investigators have shown that preoperative CT changed the surgeon’s treatment and operative plan.
Previous investigators classified PMFs based on the fragment size. However, this has been subjected to significant scrutiny. There is much debate on the correlation between fragment size and treatment indication. Haraguchi and colleagues studied 57 cases of PMF. Based on preoperative CT scans, the investigators classified the fracture into 3 types: type I, the posterolateral-oblique type (67% of cases); type II, the medial-extension type (19% of cases); and type III, the small-shell fragment (14% of cases) ( Fig. 2 ). The investigators acknowledged that great variation in fracture patterns exists, and that preoperative use of CT scans may be justified. Mangnus and colleagues performed CT-based PMF mapping in a series of 45 patients. They showed that there is a continuous spectrum of Haraguchi type III to I fractures and identified Haraguchi type II as a separate pattern. The investigators concluded that the morphology of the fracture might be more important than fragment size alone for clinical decision making.
Bartoníček and colleagues suggested an alternative classification system. Based on CT scans, these investigators recognized 5 fracture patterns: type 1; extraincisural fragment with an intact fibular notch; type 2, posterolateral fragment extending into the fibular notch; type 3, posteromedial 2-part fragment involving the medial malleolus; type 4, large posterolateral triangular fragment; and type 5, nonclassified, irregular, osteoporotic fragments.
Also, it is important to address the term posterior pilon variant. This fracture is characterized by an additional posteromedial fragment as well as comminution and marginal impaction.
Management of posterior malleolar fractures
Principles of Treatment
Isolated, nondisplaced PMFs should be treated conservatively. Several investigators have shown that, with nonsurgical treatment of these fractures, satisfactory outcomes can be achieved.
The indications for reduction and fixation of displaced PMFs remain controversial. In the past, the size of the posterior malleolar fragment was the main consideration for whether it should be addressed surgically. It was recommended that, if fragment size is greater than 25% to 33% of the articular surface, then it should be reduced and fixated. However, this conception was based in part on biomechanical evidence of altered joint biomechanics and tibiotalar instability, rather than on the goal of restoring ankle joint stability and preventing posterior translation.
The authors suggest that surgical criteria for the reduction and fixation of the PMF should be based on the concept of restoring ankle joint structural integrity. The preoperative radiographs and CT scans should be thoroughly analyzed to formulate a good understanding of the specific fracture characteristics. Surgeons should assess the amount of articular incongruity caused by the posterior malleolar fragment, evidence of loose bodies and articular impaction, and whether the syndesmosis instability is caused by the fracture pattern (as shown, for example, in Fig. 1 ).
The posteromedial or posterolateral surgical approaches readily enable surgeons to address these components of the injury. Once lateral malleolus fracture is reduced, the posterior malleolar fragment is often reduced with ligamentotaxis of the PITFL. If this is not the case, and articular congruity is not achieved, this is an indication for reduction and fixation of the posterior fragment. Furthermore, if posterior talar translation persists, as judged by lateral fluoroscopy, then the posterior malleolar fragment should be addressed. In cases in which small osteochondral fragments may interfere with anatomic reduction or become loose bodies, or articular impaction is recognized, then it is advisable to approach the fracture site and address this before attempting reduction and fixation of lateral malleolus fracture. In addition, assessing ankle joint syndesmotic and rotatory instability is of paramount importance, and is a major component of surgical indication. The effect of posterior malleolar fragment and PITFL on ankle joint syndesmotic and rotatory stability was emphasized and described earlier. The fixation of posterior malleolar fragments to achieve stability, thereby restoring ankle joint structural integrity, has been supported by several studies. In a cadaveric study by Gardner and colleagues, the investigators showed that, compared with intact specimens, syndesmotic stiffness was restored to 70% after fixation of the posterior malleolus and to 40% after syndesmotic screw fixation. This finding is supported by several investigators comparing syndesmotic stabilization with trans-syndesmotic screw to posterior malleolar fixation/PITFL repair. The investigators concluded that direct posterior malleolar fixation or PITFL repair is at least equivalent to syndesmotic screw fixation.
Surgical Approach and Technique
Several surgical approaches are available for the treatment of PMFs. The type of the PMF, and the existence of medial and/or lateral malleolus fractures, are all considered in terms of approach and patient positioning. Direct visualization of the posterior malleolar fragment can be achieved with posterior approaches to the ankle joint.
The posteromedial approach is appropriate for a posteromedial fragment, and allows concomitant treatment of the medial malleolus. This approach is based on a skin incision that follows the posteromedial border of the distal tibia and medial malleolus and continues in line with the tibialis posterior tendon. Exposure of the tibia is made with deeper incision between the posterior tibialis tendon and flexor digitorum longus, or between both tendons and the neurovascular bundle. A retrospective study by Bois and colleagues showed good short-term and midterm clinical results with the posteromedial approach and fracture buttress plate fixation of large posterior malleolar fragments ( Fig. 3 ). The posterolateral approach has gained much popularity, and allows good visualization of the posterolateral malleolar fragment. Furthermore, concomitant treatment of the fibula fracture is easily performed. Usually the patient is placed in a prone position, and the skin incision is made midway between the lateral border of Achilles tendon and the posterior border of the fibula, or directly over the posteromedial border of the fibula. During superficial dissection, the sural nerve must be identified and protected where it courses through the surgical field. The deep dissection develops the plane between the flexor hallucis longus (FHL) and peroneals. Once the FHL muscle belly is elevated from the fibula and lateral tibia, and retracted medially, the posterolateral fragment is visualized. While exposing and manipulating the fragment, great care should be taken to preserve the PITFL. Reduction is facilitated with dorsiflexion of the ankle. A ball spike or bone tamp aids in achieving reduction, and a temporary fixation with Kirschner wire can be performed, with reduction checked with fluoroscopy. Once the fragment is properly reduced, a slightly undercontoured plate can be used in an antiglide technique. The fibula fracture can be addressed with mobilization of the peroneal tendons and posterior plating. Which fracture should be addressed first is a matter of debate. Although first fixating the fibula restores length and facilitates the posterior malleolar reduction, the fibular plate can hinder adequate visualization of the posterior malleolar reduction with fluoroscopy ( Fig. 4 ). For these reasons, the authors’ preferred technique is to address the fibula first. Once the length and fibular fracture reduction is achieved, provisional fixation of the fibula is done with Kirschner wire or a reduction clamp. Attention is then given to the reduction and fixation of the posterior malleolus, without the interference of a fibular plate in fluoroscopy ( Fig. 5 ). Only then is definitive fixation of the fibula performed. If fixation of the medial malleolus is required, it can be done with the patient in the prone position, or, if more complex medial malleolar fractures are present, the patient can be repositioned to the supine position. Alternatively, indirect reduction by ligamentotaxis of the PITFL can be attempted. However, this type of reduction cannot always ensure adequate articular reduction or treatment of impacted plafond or small osteochondral debris. The most common method of PMF fixation with this technique is with anterior-to-posterior (AP) screws. O’Connor and colleagues compared patients who underwent posterior plating with patients who were treated with AP screw fixation and showed that patients treated with plating had superior clinical outcomes at follow-up compared with those treated with AP screws.
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