Syndesmosis sprains of the ankle The influence of

heterotopic ossification*


From the

Department of Surgery,

Division of

Orthopaedic Surgery,


University Medical

Center, Durham, North Carolina lent ankle function after recovery, unless there was a recurrent ankle sprain. In the absence of frank synostosis, the results were not affected by the formation of heterotopic ossification.

ABSTRACT A retrospective study of 50 syndesmosis sprains in 44 football players was performed. Five patients (6 ankles) were lost to followup, allowing review of 44 injuries. Average followup was 47 months. The patients were evaluated for recurrent injury, overall ankle function, and for persistent ankle symptoms, including stiffness, pain, limping, and swelling. Follow-up radiographs of the injured ankle were obtained in 22 patients. The average return time to full activity was 31 days. Pain with pushing-off was a major factor preventing return to activity. At final followup, 36% of the patients complained of persistent mild to moderate stiffness of the ankle. Twenty-three percent had mild to moderate pain, usually with activity. One patient had a mild limp with activity, and 18% of the ankles had persistent mild to moderate swelling. Ankle function was rated as good to excellent in 86%. All patients with fair results had recurrent ankle sprains. There were no poor results. Eleven of the 22 patients with follow-up radiographs developed heterotopic ossification within the interosseous membrane, but no patient developed a frank synostosis. The patients with heterotopic ossification required an average of 11 days more recovery time than those without ossification. There was no significant difference between the 2 groups’ ultimate ratings of ankle function or ankle symptoms, but the ankles with heterotopic ossification were associated with more recurrent lateral ankle sprains. We conclude that syndesmosis sprains require a longer recovery period than other types of ankle sprains. Most of these injuries showed good to excel-

Syndesmosis sprains of the ankle are uncommon injuries. There is little information about treatment regimens, longterm results, or even the mechanism of injury associated with syndesmosis sprains. Previous authors have shown that these sprains are characterized by delayed return to activity compared to other ankle sprains, and that heterotopic ossification of the interosseous membrane may occur during recovery.


Stability of the distal tibiofibular syndesmosis is maintained by four separate ligaments and the interosseous membrane. The ligaments include the anterior tibiofibular, the posterior tibiofibular, the transverse tibiofibular, and the interosseous (Figs. 1 and 2). The primary stabilizing ligaments are the anterior and posterior tibiofibular ligaments. The transverse tibiofibular ligament, which many authors do not categorize as separate from the posterior tibiofibular

= *

Presented at the 15th annual meeting of the AOSSM, Traverse City, Michigan, June 1989 t Address correspondence and repnnt requests to: Frank H Bassett III, MD, Duke Umversity Medical Center, P O Box 3004, Durham, NC 277100

Figure 1. Anterior (right) and posterior (left) views of the ankle syndesmosis demonstrating the anterior tibiofibular, posterior tibiofibular, and transverse tibiofibular ligaments. 146


time of injury by the team trainer, and subsequent examination was carried out within 24 hours by an orthopaedic surgeon. All patients had initial radiographs and none showed a fracture or diastasis of the ankle mortise. All patients were treated nonoperatively with a regimen of ice, whirlpool therapy, taping, and activity restriction. Prednisone, 20 mg taken orally once a day for 4 days, was prescribed in several cases. We currently use this prednisone dosing regimen to reduce acute inflammation caused by injury. Return to full activity was allowed when the ankle tenderness resolved and the patient had no functionally

limiting pain. Recovery times


obtained from medical records and

subsequent patient interviews. At final followup, the patients were interviewed to evaluate reinjury rate, overall ankle function, and persistent symptoms including stiffness, pain, limping, and swelling. Ankle function was graded on a 5-point subjective rating scale (Table 1). Radiographs of 22 injured ankles were obtained during followup. The average time from injury to final followup was 47 months (range, 14 to 84). Mann-Whitney nonparametric analysis was used to evaluate for statistical significance (P < 0.05). RESULTS

Figure 2. Cross

section of the

the interosseous


syndesmosis demonstrating

ligament, is located posterior to the talus and helps prevent posterior talar translation. The interosseous ligament is the weakest of the four syndesmosis ligaments. To provide better understanding about injuries to the syndesmosis ligaments we attempted to evaluate the results after recovery from syndesmosis sprains, and to determine if heterotopic ossification (HTO) formation influenced the results.

MATERIALS AND METHODS We performed a retrospective study of 50 consecutive syndesmosis sprains in 44 collegiate football players occurring over an 8-year period. Six patients had bilateral syndesmosis sprains. Five patients (6 ankles) were lost to followup, allowing review of 44 ankle injuries. The diagnosis of syndesmosis sprain was based on the physical finding at the time of injury of tenderness over the syndesmosis ligaments, primarily the anterior tibiofibular ligament, with or without tenderness extending up the interosseous membrane. Examination was performed at the

The average return to full activity following the syndesmosis sprain was 31 days. Pain while pushing-off on the injured side was a common complaint preventing return. All patients stated that they had persistent ankle pain and stiffness lasting several months that did not prevent full participation. At final followup, there were no patients who had severe symptoms. There was mild stiffness present in 10 ankles (23%) and moderate stiffness in 6 (14%). Ten ankles (23%) had pain, usually with activity, that was rated as mild in 9 (20%) and moderate in 1 (2%). One patient noted a mild limp with activity, and 8 (18%) had persistent swelling that was mild in 7 (16%) and moderate in 1 (2%). The average rating for all symptoms at final followup was greater than 4 (i.e., mild symptoms to no symptoms). There were 19 (43%) ankles that were reinjured after recovering from the original syndesmosis sprain. Twelve of the injured ankles had several subsequent recurrent lateral ankle sprains, 3 had one subsequent lateral ankle sprain, 1 had a bimalleolar fracture, and 3 had a second syndesmosis sprain. Ankle function was rated excellent in 18 (41% ) and good in 20 (45%). There were no poor results. The average ankle function rating was 4.2. There were 6 ankles (14%) rated as TABLE 1

Rating scales for ankle symptoms and function


fair, all of these patients complained of recurrent ankle sprains. In fact, patients with recurrent sprains had the worst ankle function at followup; an average of 3.6 for all recurrent sprains (15 ankles), 3.6 for recurrent inversion sprains (12 ankles), and 3.7 for recurrent syndesmosis sprains (3 ankles). Eleven of the 22 ankles with follow-up radiographs develwithin the interosseous membrane. No patient in this series developed a frank synostosis. The 11 patients with HTO did require an average of 11 days more recovery time than the 11 patients without ossification (43 days; range, 14 to 98 versus 32 days; range, 14 to 56). Although the average recovery time was almost 2 weeks longer in the groups with HTO, this difference did not achieve statistical significance, most likely because of the small sample sizes and wide range of values. Average recovery time for the 22 patients who had follow-up radiographs was 37.5 days. Average recovery time for the 22 patients that did not have follow-up radiographs was 25 days (range, 10 to 84), resulting in an average recovery time of 31 days for the entire series of 44 patients. Ankle function and ankle symptoms ratings at final followup in the 22 patients with follow-up radiographs were very similar for the group with HTO and those without HTO (Table 2). Reinjury was more common in the HTO group, with 5 patients sustaining recurrent lateral ankle sprains, 1 with a single subsequent lateral sprain, and 1 with recurrent syndesmosis sprains. In the group without HTO there were 2 patients with recurrent lateral ankle sprains, 1 with a single subsequent lateral sprain, and 1 with a recurrent syndesmosis sprain. In the patients without follow-up radiographs there were 5 with recurrent lateral sprains, 1 with a subsequent lateral sprain and 1 with recurrent syndesmosis

oped HTO

sprains. There was a wide variation in the amount of heterotopic bone formation and the recovery times tended to be longer in ankles with larger amounts of heterotopic ossification. Radiographs shown in Figure 3, obtained 3 months after an external rotation injury, demonstrated HTO within the interosseous membrane and also within the posterior tibiofibular ligament. This patient had anterior tibiofibular and anterior talofibular ligamentous tenderness; was treated with ice, taping, whirlpool therapy, and a 4-day course of prednisone; and required 56 days to return to full activity. At final followup, this ankle was asymptomatic, had not been reinjured, and was rated as 5 (excellent). TABLE 2

Comparison of final results in ankles with and without heterotopic ossification

An ankle with less HTO is shown in Figure 4 in a radiograph obtained 11/z years after an eversion injury. This patient originally had tenderness over the anterior tibiofibular ligament, with mild anterior talofibular ligament tenderness. He was treated with ice, whirlpool therapy, taping, and a 4-day course of oral prednisone, and returned to full activity 17 days after injury. At final followup, the patient rated his ankle pain and stiffness at 4.5 (no symptoms to mild symptoms) and did not have a limp or swelling. He rated his ankle function as 3 (fair) because of recurrent lateral ankle sprains.

DISCUSSION Previous studies on syndesmosis sprains have emphasized the prolonged recovery time and interosseous heterotopic ossification associated with these injuries. Guise’ presented 16 cases of pronation-external rotation sprains in professional football players that resulted in injury to the syndesmosis ligaments. He found a longer recovery time relative to the supination-internal rotation injury. He also noted that some pronation-external rotation injuries could be diagnosed retrospectively by the finding of calcification of the interosseous membrane. Hopkinson et a1.3presented eight cases of syndesmosis sprains in West Point cadets. Their diagnosis was dependent on a positive squeeze test (pain with compression of the fibula to the tibia at the mid-leg level). They found ossification of the syndesmosis in all eight cases. Also, patients with syndesmosis sprains were restricted from activities almost twice as long as patients with other third-degree ankle sprains. Our results concur with the finding of prolonged return to full activity (an average of 31 days in this study). We also found that heterotopic ossification often occurred after syndesmosis sprains (50% of the 22 ankles with radiographs). Unlike Hopkinson et al., we did not see the formation of heterotopic ossification in all cases. In this study, the diagnosis of syndesmosis sprain was based on syndesmosis tenderness. As a result, many of the injuries may have been less severe than injuries where there is a positive squeeze test. Along with the squeeze test, stress radiographs of the injured ankle can be helpful in assessing the severity of syndesmosis

injury.’,’ patients who had injuries ligaments in addition to the syndesmosis ligament injury. Some of these injuries may have been primarily lateral ankle sprains with lesser injury to the syndesmosis ligaments, which may also help explain why only 50% formed HTO. The follow-up findings were very good in the absence of recurrent ankle sprains. The only fair functional results occurred in patients who had reinjured their ankles. Two of these patients had recurrent syndesmosis sprains within the year prior to final followup. These two patients may not have fully recovered from their reinjury. The other four patients who rated their ankles as fair complained of recurIn




also included

to the medial and lateral ankle

rent lateral ankle



Figure 3. Mortise (right) and lateral (lateral) views of the right ankle showing extensive heterotopic ossification of the interosseous membrane and the posterior tibiofibular ligament. In the absence of recurrent injury, only good and excellent functional ratings were present, despite the long recovery period. These results suggest that rehabilitation should be directed toward prevention of recurrent syndesmosis or lateral ankle ligamentous injuries through proprioceptive, flexibility, and strengthening exercises. In this series, the recovery time for the patients with HTO was over one-third longer than for those patients without HTO (43 versus 32 days). The longer recovery time is most likely an indication of the severity of the injury. Formation of HTO may, therefore, be indicative of a more severe injury. With more severe sprains, there would be more extensive disruption of the syndesmosis extending proximally into the interosseous membrane, and a greater probability of HTO formation. Although the presence of HTO is a delayed finding, and therefore not of prognostic significance, technetium scanning, as suggested by Marymont et al.,4 may be of short-term prognostic value in regard to recovery time. The presence of HTO does not appear to influence ankle function after recovery from the initial injury. The ankle function and ankle symptom ratings were almost the same for those with and without HTO (Table 2). There were, however, more recurrent inversion ankle sprains in the group with HTO. We suspect that this may have been caused by greater proprioception loss in the more severe syndesmosis sprains, resulting in a higher incidence of lateral ligamentous injuries of the ankle. Exercises to enhance proprioception during rehabilitation should be helpful in reducing the number of recurrent injuries.

Another possible explanation for the increased incidence of recurrent sprains is decreased fibular mobility and altered ankle biomechanics. Disrupted distal fibular migration and fibular axial motion can alter normal ankle function.’ With HTO, one would expect less elasticity in the interosseous membrane, and therefore reduced fibular motion relative to the tibia. The resultant alteration in ankle function may predispose the ankle to inversion sprains. Alternatively, the higher incidence of inversion sprains in the HTO group could suggest that the recurrent sprains were responsible for HTO formation. Rarely were radiographs obtained between the initial injury and subsequent inversion sprains, so it is not possible to determine definitively which injury resulted in HTO. Other authors’-’,9 have shown that interosseous membrane ossification can occur following inversion ankle sprains. However, it seems more logical that the HTO formation in our series was the result of the initial injury, with documented syndesmotic injury on physical examination, than the result of more common injuries to the lateral ankle ligaments. In any case, the presence of HTO, while associated with a higher incidence of inversion sprains, was not associated with any significant functional or symptomatic difference compared to injured ankles without HTO. It should be emphasized that no synostosis formed in the ankles with HTO in this study. Other studieS6,8, ’ have demonstrated that synostosis formation can be disabling, occasionally requiring synostosis resection.

150 3. Hopkinson WJ, St Pierre P, Ryan JB, et al. Syndesmosis sprains of the ankle. Foot Ankle 10: 325-330, 1991 4. Marymont JV, Lynch MA, Henning CE: Acute ligamentous diastasis of the ankle without fracture: Evaluation by radionuclide imaging. Am J Sports Med 14: 407-409, 1986 5. McConkey JP: Ankle sprains, consequences and mimics. Med Sci Sports

23: 39-55, 1987 6. McMaster JH, Scranton PE: Tibiofibular synostosis: A cause of ankle disability. Clin Orthop 111. 172-174, 1975 7. Outland T: Sprains and separations of the inferior tibiofibular joint without important fracture. Am J Surg 59: 320-329, 1943 8. Scranton PE, McMaster JH, Kelly E: Dynamic fibular function. A new concept. Clin Orthop 118: 76-81, 1976 9. Whiteside LA, Reynolds FC, Ellsasser JC: Tibiofibular synostosis and recurrent ankle sprains in high performance athletes Am J Sports Med 6:



Mortise view of the right ankle. This ankle had less HTO than the ankle shown in Figure 3, but a lower ankle function rating at final followup because of recurrent lateral ankle sprains.

Figure 4.


Syndesmosis sprains are followed by a relatively long recovery period. However, the ultimate expected ankle function should be good to excellent, unless there are recurrent ankle sprains. The positive results after recovery from the syndesmosis sprains do not appear to be affected by the presence of heterotopic ossification. REFERENCES . GS, DeLee JC Ankle diastasis without fracture. Foot Ankle 4 305-312,1984

1. Edwards

2. Guise ER Rotational ligamentous Sports Med 4: 1-6, 1976


to the ankle in football. Am J

Charles E. Henning, MD Wichita, Kansas: This paper retrospectively reviews the results of syndesmosis sprains in 44 football players with 14 to 84 months’ followup (average, 4 years). The diagnosis was established by physical examination, including examination of the syndesmosis and deltoid ligaments, and by reviewing the probable mechanism of injury. One case had tenderness specifically over the deltoid ligament; nine more were tender over both the medial and lateral collateral ligaments. Although most patients had plain radiographs, no abduction stress tests were performed. The lack of stress tests makes it impossible to further classify these syndesmotic sprains and to make the long-term followup more meaningful. At long-term followup, 39% had mild to moderate stiffness, 25% mild to moderate pain, one limped, and 18% had persistent mild to moderate swelling. One observation in reviewing this paper was that the patients who were the slowest to return to full activity had the best long-term results. One-half of the 22 patients who had followup radiographs showed heterotopic ossification. This group tended to have slightly lower functional ratings, but the correlation with this wide variation and the amount of heterotopic bone was poor. Thirty-nine percent of all patients suffered recurrent sprains, with the majority being lateral ankle sprains. This emphasizes the point that multiple or even sequential mechanisms are probably common and careful physical examination and a high index of suspicion are essential when evaluating a suspected syndesmotic sprain. Finally, there was no mention of traumatic arthritis in the follow-up radiographs. I suspect that the evidence would be subtle at 4 years, and these athletes were only in their midtwenties. Perhaps bone scanning will be helpful to us in understanding arthritis as a possible cause of symptoms in approximately one-third of these patients.

Syndesmosis sprains of the ankle. The influence of heterotopic ossification.

A retrospective study of 50 syndesmosis sprains in 44 football players was performed. Five patients (6 ankles) were lost to follow-up, allowing review...
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