Rockwood Adults CH64

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CHAPTER 64 • Ankle Fractures

Posterior Malleolar Fractures

However, in 1977 Yablon et al. 423 observed that fixation of the medial malleolus alone often resulted in incomplete fibular and talar reduction and the later development of posttraumatic arthritis. They memorably stated that the “displacement of the talus faithfully follows that of the lateral malleolus” and demon- strated, in both a cadaveric model and in surgical patients, that open reduction of the lateral malleolus more predictably restored tibiotalar congruence and resulted in a satisfactory clinical outcome. At the same time, Svend-Hansen et al. also reported that 16 of a cohort of 29 (55%) patients with bimalleolar ankle frac- tures, treated by fixation of the medial side only, experienced unsatisfactory results after a mean of almost 5 years, 367 also emphasizing the difficulty of obtaining and maintaining ankle joint reduction. Pankovich 295 in his clear description of the sub- types of medial-sided injury demonstrated why anterior collic- ular fractures might remain unstable despite fixation: Although the competence of the superficial deltoid is reestablished by fracture fixation, the deep deltoid, which is attached to the pos- terior colliculus and has ruptured at the time of displacement, remains incompetent. Tornetta 384 undertook a study of ankle stability confirming this variation. He performed a stress radio- graph intraoperatively following medial malleolar fixation, but before lateral malleolar fixation. He demonstrated that a quar- ter of fractures remained unstable. Thus fixation of the medial malleolus only in a bimalleolar ankle fracture can reestablish stability in only three-quarters of cases. Fixation of Medial and Lateral Malleoli Several studies have compared surgical fixation with conserva- tive treatment. Yde and Kristensen 427 retrospectively reviewed the results of their patients in 1980 and reported good results in 20% of their conservatively treated fractures compared to 92% of those operatively treated. Pettrone et al. 301 described a similar retrospective cohort and reported that conservative treatment and fixation of the medial malleolus alone gave sim- ilar results, but better results were obtained after combined fixation of both the medial and lateral malleoli. A small num- ber of prospective RCTs have also been reported. Bauer et al. 26 randomized 111 patients with displaced AO type A or B frac- tures to operative or nonoperative management; short-term results showed a significant benefit to those treated with sur- gical fixation but at final follow-up, 7 years post injury, there was no significant difference between groups. Makwana et al. reported better functional outcomes and range of movement in their patients randomized to operative treatment but equal levels of satisfaction and pain. 230 Phillips et al. reported the results of a randomized trial in 1985, and although follow-up was only 51%, reported significantly better results in (predom- inantly SER 4) fractures treated with internal fixation than with conservative management. 302 Hughes et al. 164 also found better results in AO type B and C fractures when treated surgically, a result replicated by Colton 67 in PER 3 and 4 fractures. Surpris- ingly, then, there remains considerable geographical variation in practice. Koval et al. reported that the proportion of patients in the United States who received ankle fracture surgery varied geographically from 14% to 72%. 196

Fractures of the posterior malleolus were first described by Sir Percival Pott’s grandson Earle in 1828, 98 but the injury received relatively little attention until the remarkable surge of enthu- siasm for fixing these fractures that has emerged in the last decade. Around one-third of ankle fractures involve the pos- terior malleolus, 76 and the outcome for these is worse than for ankle fractures without posterior malleolar involvement. 242,256,280 This is likely to be due to articular cartilage damage at the time of injury, or result from talar instability, posterior subluxation, and ankle incongruity. 86 However, there remains considerable controversy regarding almost every other aspect of the posterior malleolus: its biomechanical contribution to ankle stability, its optimal treatment and whether this is determined by mortise stability or fragment size, 124 the preferred method by which fractures should be fixed, and whether surgery might lead to better clinical results. Surveys have revealed a wide range of surgical practice and preference. 124 Early papers on posterior malleolar fractures reported a ten- dency of the talus to sublux with larger fragment sizes, vari- ously reported as 25%, 33%, or 50% of the anterior to posterior tibial plafond length as seen on plain radiographs. These sizes have become enshrined in orthopedic orthodoxy as suggested indications for surgery in themselves, although it should be remembered that these sizes are of only indirect importance in that they correlate with an increased tendency for talar sub- luxation, 124,242 particularly with inadequate stabilization of the medial and lateral sides of the ankle. Biomechanical studies have sought to determine the role of the posterior malleolus. Perhaps surprisingly, these have shown that it contributes very little to joint contact, load bearing or ankle stability. 296 The reduction in joint contact area after fracture is surprisingly modest: a fracture involving 25% of the joint as seen on the lateral radiograph results in no significant decrease in contact area, a 33% fracture reduces it by only 15% and a 50% fracture by around 30%. 145,226 It follows that a posterior malle- olar fracture should not greatly alter the forces across the pla- fond, and this is confirmed by biomechanical studies 112,402 : In an unconstrained and loaded cadaveric model with a 50% fracture, contact stresses were not increased but were seen to be redis- tributed toward more anterior and lateral locations, 112 and thus away from the fracture line and the supposedly vulnerable carti- lage at the fracture edge. Most interestingly, posterior malleolar resections of up to 50% of the plafond surface are stable in the presence of intact (or fixed) medial or lateral structures. 112,140,312 The relationships between stability, contact area, contact stress, surface shear and clinical osteoarthritis are not linear, and this represents an uncertain scientific base from which to embark on an understanding of the clinical benefits of surgery. Defining posterior malleolar fractures on plain radiographs is difficult because both the orientation and configuration of these fractures is highly variable, and is rarely in the plane of the lateral radiograph. 130,247 Haraguchi 138 has described a CT-based classi- fication system which groups these diverse patterns into three types: type 1 fractures consist of a single posterolateral fragment (66% cases), the fracture line passing obliquely from the incisura fibularis to a point behind the medial malleolus. Type 2 fractures