Ankle fractures are commonly treated by orthopaedic surgeons worldwide. When operative intervention is necessary, the majority of patients have a good result. However, some patients have an unsatisfactory outcome; this is substantiated by the fact that the most common cause of ankle arthritis is a prior rotational ankle fracture1-3. Several investigators have attempted to identify variables predictive of outcome following operative treatment of ankle fractures. Many of these variables are innate to the patient or injury and as a result cannot be controlled or modified by the surgeon. However, the quality of surgical reduction is under the direct control of the orthopaedic surgeon. Fundamental teaching has supplied the notion that articular congruity is paramount for restoring mobility and optimizing function. However, this principle has not been carefully examined for ankle fractures. The purpose of this study was to scrutinize postoperative articular congruity in a strictly defined population of supination-external rotation (SER) ankle fractures treated with a uniform fixation strategy and determine its impact on outcome. We hypothesized that patients with immediate postoperative articular incongruity would have worse clinical results compared with patients with a congruent ankle joint.
Materials and Methods
Institutional review board approval was obtained for this study. A prospective database consisting of 176 Lauge-Hansen SER ankle fractures treated operatively from 2004 to 2010 by a single surgeon at a level-I trauma center was queried to identify patients for study inclusion. All patients were treated in a uniform fashion based on an established fixation strategy. This included internal fixation of all malleolus fractures, regardless of size, including the posterior malleolus. The internal fixation was performed through a posterolateral approach, as well as through a medial approach if necessary. The primary rationale for fixation of the posterior malleolus was not based on fragment size; rather, the purpose was to restore syndesmotic stability, as prior studies have demonstrated that anatomic fixation of the posterior malleolus effectively restores the function of the posterior inferior tibiofibular ligament, which is the most functionally robust component of the syndesmotic complex4,5. Patients wore a splint for two weeks and then transitioned to a walking boot to allow for early range of motion. Patients were kept non-weight-bearing for a total of six weeks. This was followed by progressive weight-bearing and strengthening under the guidance of a physical therapist.
Inclusion criteria consisted of an SER IV or SER IV-equivalent fracture pattern, clinical follow-up of more than one year, and availability of postoperative computed tomography (CT) scans of the operatively treated ankle. SER IV and SER IV-equivalent fractures included any of the following in an SER fracture-pattern configuration: fractures of the fibula, posterior malleolus, and medial malleolus; fractures of the fibula and posterior malleolus and injury to the deltoid ligament; fracture of the fibula, injury to the posterior inferior tibiofibular ligament, and fracture of the medial malleolus; and fracture of the fibula with injury to both the posterior inferior tibiofibular ligament and the deltoid ligament. Fractures were confirmed as having an SER IV or SER IV-equivalent pattern on the basis of radiographs, preoperative magnetic resonance imaging (MRI), and intraoperative findings. MRI was specifically utilized to confirm the presence or absence of injuries of the deltoid ligament and/or posterior inferior tibiofibular ligament as well as to provide insight into the morphology of the osseous injury. This information not only assisted in preoperative planning and creation of an anatomic fixation strategy, but it also allowed for confirmation of the exact injury pattern and thus a homogeneous study population with regard to the patient inclusion criteria. Patients were excluded from analysis if they were skeletally immature at the time of treatment, had clinical follow-up of less than twelve months, had injury patterns inconsistent with the SER IV injury pattern, or had incomplete documentation of the preoperative or postoperative course.
Patients were categorized as having a congruent or incongruent ankle joint by an orthopaedic surgery chief resident serving as an independent observer on the basis of a CT scan of the operatively treated ankle performed on postoperative day 1. CT imaging of postoperative ankle fractures is routinely performed at our institution to accurately assess fracture reduction, articular congruity, and the appropriateness of the implant placement and to ensure the absence of intra-articular loose bodies, as is similarly done for fractures of the pelvis and acetabulum. Images were reformatted in the axial, coronal, and sagittal planes. The ankle joint was considered incongruent if it met any one of three criteria: (1) an articular step-off of >2 mm (Fig. 1), (2) the presence of any loose bodies within the joint (Fig. 2), and (3) a gap in the joint surface of >2 mm despite an anatomic reduction of the cortex (Fig. 3). We postulated that this gap phenomenon was due to articular impaction and comminution, whereby small, unattached articular fragments are removed during joint irrigation and fracture site debridement.
The primary outcome measure for this study was the Foot and Ankle Outcome Score (FAOS), a validated, region-specific outcomes instrument that is intended to evaluate symptoms and functional limitation in individuals with generalized foot and ankle disorders6. The minimal clinically important difference for the FAOS is 10 points6,7. The secondary outcome assessed in this investigation was ankle motion measured at the time of the final clinical follow-up by the treating surgeon. The primary and secondary outcomes were assessed at a minimum of one year postoperatively.
For statistical analysis, patients were placed into two groups based on articular congruity, and a t test with Satterthwaite correction for unequal variances was used to compare associations between the two patient groups with regard to FAOS values. The Fisher exact test was used to compare associations between the two groups with regard to the proportion of the group with a normal ankle range of motion. P values of <0.05 were considered significant.
Source of Funding
There was no external funding source for this study.
The final sample of convenience consisted of 108 patients who met the inclusion criteria with an average duration of clinical follow-up of twenty-one months (standard deviation, twelve months; median, fourteen months; range, twelve to fifty-two months). The average age of the cohort was fifty-one years (standard deviation, eighteen years; median, fifty-three years; range, eighteen to eighty-six years), and seventy-three (68%) of the 108 patients were female. There were five open fractures. Seventy-two patients (67%) had a congruent ankle joint, and thirty-six (33%) had some element of articular incongruity based on the postoperative CT scan. Among the patients with an incongruent joint, nine had an articular step-off of >2 mm at the medial or posterior malleolus, and two of those also demonstrated intra-articular loose bodies that necessitated a second surgical procedure for removal. Twenty-nine patients with an incongruent joint had a gap in the joint surface of >2 mm with an otherwise anatomic reduction. Two patients in the incongruent group had both a gap and an articular step-off. The two groups (congruent and incongruent joints) were similar in terms of patient demographics, comorbidities, injury variables, and postoperative complications (Table I). There was a single nonunion of the fibula, treated successfully with revision open reduction and internal fixation.
When comparing FAOS results between groups, we found that those with an incongruent ankle joint had significantly worse outcomes in the domains of symptoms (66.8 versus 77.3, p = 0.012), pain (72.1 versus 84.6, p = 0.004), and activities of daily living (78.9 versus 87.4, p = 0.038). Additionally, the incongruent ankle group had, on average, a >10-point deficit (54.9 versus 65.8) in the FAOS sport domain compared with the congruent ankle group, although this difference was not significant (p = 0.095) (Table II). The percentage of patients with normal ankle motion was similar in the two groups.
In this study of 108 operatively treated SER IV ankle fractures treated with a comprehensive fixation protocol, one-third of the cohort had postoperative articular incongruity based on CT imaging. The incongruity was due to either articular step-off with or without loose bodies (seven of thirty-six), a gap in the articular surface (twenty-seven of thirty-six), or both (two of thirty-six). With the minimum clinically important difference in the FAOS considered to be 10 points, the patients with articular incongruity had significantly worse clinical outcomes from both a statistical and a clinical standpoint at a minimum of one year. Anatomic reconstruction of the joint surface is a tenet of periarticular fracture care well known to orthopaedic surgeons. This dogma has been supported by data pertaining to articular fractures of many varieties. Knirk and Jupiter were among the first to highlight the importance of restoration of the joint surface, especially for long-term outcomes, in their study of distal radial fracture treatment8. In that study, patients with >2 mm of residual displacement universally went on to develop wrist arthritis. Other studies have also supported the belief that >2 mm of articular displacement should not be accepted, and the value served as the threshold for a congruent joint in this investigation9-11. Despite this commonly held belief, numerous investigators seeking to identify predictors of clinical outcomes of the surgical treatment of ankle fractures have omitted articular congruity from consideration12-15. This is one of the few variables that the surgeon can control during the treatment of ankle fractures, and therefore the purpose of this article was to reexamine the impact of articular congruity, as a predictor of outcome, in a uniform population of operatively treated SER IV ankle fractures.
Studies specific to outcomes of ankle fracture treatment have generally supported the notion that an incongruent joint surface predicts a worse clinical outcome. This holds true for studies focusing on strictly SER IV fractures, fractures of the posterior malleolus16,17, and ankle fractures in the elderly. De Souza et al. examined the results of 150 operatively treated external rotation-abduction ankle fractures at an average of 3.5 years postoperatively and found that postoperative displacement of >2 mm correlated with worse clinical outcomes9. Malreduction correlated with worse outcomes in other heterogeneous ankle fracture series as well18-20. Studies including operative and nonoperative treatment of ankle fractures in the elderly have also delineated the prognostic importance of ankle joint malreduction in the ultimate clinical outcome21,22. Studies focusing on only the posterior malleolus have shown that reduction plays a major role in the clinical outcome. Jaskulka et al. highlighted the association of worse postoperative radiographic findings with inferior outcomes23, and Langenhuijsen et al. concluded that congruity of the posterior malleolus was predictive of outcome24. Lastly, Finnan et al. followed twenty-six of 156 patients with an SER IV ankle fracture and found that those with only fair radiographic reduction were more likely to experience negative effects on their quality of life25.
Not all of the literature concerning ankle fracture treatment has so strongly supported a link between fracture reduction and outcome. One study of conservatively treated fractures of the posterior malleolus showed that a gap at the fracture site had no impact on the ultimate clinical outcome after twenty years of follow-up26. In another investigation, the authors concluded that trimalleolar fractures with an anatomic reduction of the posterior malleolus were not associated with significantly better clinical outcome scores than those without an anatomic reduction of the posterior malleolus27.
The present study substantiates and adds to the prevailing notion that a noncongruent ankle joint places the patient at risk for an inferior clinical outcome. This study had many strengths. First, this cohort represents a homogeneous collection of operatively treated ankle fractures. All were SER IV fractures and all were treated by a single surgeon utilizing a consistent, anatomically based fixation strategy and a consistent postoperative rehabilitation protocol.
Second, all cases in this study were subjected to the most rigorous evaluation of postoperative reduction reported in the literature, to our knowledge. All aspects of the ankle were examined, including the lateral, posterior, and medial malleoli, rather than the evaluation being limited to a specific portion. Furthermore, CT was used to detect malreduction. All of the prior studies mentioned above that examined the impact of reduction on outcome utilized radiographs to determine if a malreduction of the articular surface was present. Several studies have shown that radiography is rather poor at detecting fracture displacement about the ankle, and there is a lack of consensus on how these radiographs should be evaluated28,29. This is particularly true of fractures of the posterior malleolus: radiographs can drastically underestimate the amount of articular impaction and comminution of such fractures30-32. CT provides a superior, multidimensional evaluation of the joint surface and allows for an accurate determination of postoperative articular congruity, which in two of our patients necessitated a second surgical procedure for loose-body removal. The use of CT scanning also enabled the analysis of fractures with a gap in the articular surface despite an anatomic reduction at the cortical surface (Fig. 3). This was most commonly observed in the posterior malleolus, a finding that would be essentially impossible to detect with radiographs alone, as the literature suggests30-32. We surmise that this articular gap is the result of articular impaction and comminution. Once these fractures have been exposed, debrided, and fixed anatomically with use of the outer cortex as a guide, a gap in the articular surface can remain. This could be explained by the fact that the small fragments of impacted/comminuted subchondral bone have been removed through the process of fracture site manipulation, irrigation, and debridement. We believe that this gap not only generates articular incongruity, but also serves as a surrogate marker of articular impaction and damage, which correlates with inferior clinical outcomes.
One-third of the SER IV ankle fractures in our patient cohort had articular incongruity. The high rate of incongruity is likely attributable to the efforts taken to examine this variable in detail with CT. However, this study has shown that this matters, as those patients with an incongruent joint had inferior outcomes early (at a minimum of one year postoperatively) compared with those with a congruent joint. Given that radiography grossly underestimates the rate of articular incongruity, this can be an underappreciated cause of short-term pain and disability in patients treated for an ankle fracture.
There are limitations to this study. Follow-up data were collected at a minimum of one year (average, twenty-one months) postoperatively. While this gives meaningful insight into the short-term outcomes of these patients, no firm conclusions on their long-term results can be drawn. Longer-term follow-up is needed to determine if the articular incongruity observed in this study serves as a risk factor for ongoing sequelae—namely, the development of ankle arthritis. In addition, a single outcome measure, the FAOS, was used as the primary outcomes instrument. While the FAOS is a validated, patient-based outcome-assessment tool, it was not conceived specifically for patients with an ankle fracture6. Instead, it has been applied to foot and ankle conditions in general. However, the same can be said for different outcome measures utilized in other published studies involving ankle fractures. Another limitation of this study concerns the assessment of ankle motion, which was determined by the treating physician at the time of the final clinical follow-up, perhaps resulting in observer bias. However, the surgeon was not aware of the exact CT findings for each patient when assessing motion during the postoperative period, which helped to minimize this form of bias. Another limitation of this study is that no formal sample-size calculation or power analysis was performed. Fortunately, a significant difference was shown for the primary outcome (FAOS). However, since no difference in ankle motion was shown between groups, and no power calculation was performed to determine if a conclusion of no difference can be accurately made, the results regarding ankle motion should be interpreted cautiously. Lastly, postoperative CT imaging, while providing superior assessment of the quality of the postoperative articular reduction and congruity, is not widely used. While cost concerns limit its general applicability, the use of radiographs and fluoroscopy greatly underestimates the presence of articular congruity. The intent of this investigation was to define the problem of articular incongruity following operative treatment of SER IV ankle fractures, not recommend an intraoperative or postoperative imaging algorithm to best identify and limit incongruity. Future investigation is necessary to identify the best solution(s) for this problem.
In conclusion, in this group of operatively treated SER IV ankle fractures, the presence of postoperative articular incongruity of >2 mm correlated with inferior clinical outcomes at an average of twenty-one months postoperatively. This study helps to emphasize the importance of anatomic articular reduction as one of the major variables affecting early clinical outcomes in these patients and as one of the few variables that surgeons can directly influence in treating this fracture. Orthopaedic surgeons should scrutinize ankle fracture reductions carefully and strive for perfection in fracture reduction to allow the best possible patient outcome.
NOTE: The authors thank Monica Daigl, MS, for her assistance with statistical analysis on this project.
Investigation performed at New York Presbyterian Hospital and Hospital for Special Surgery, New York, NY
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Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.