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 ).
