Posterior Inferior Tibiofibular Ligament Periosteal Sleeve Avulsion: New Classification for Posterior Malleolar Fracture of the Ankle

Abstract

Background

Not reducing the posterior malleolar fragment could have an impact on the alignment and stability of syndesmosis since the posterior inferior tibiofibular ligament (PITFL) originates at the posterior malleolar fragment. Given that these alignment and stability changes may contribute to discomfort and pain, further research may be required. We think that our new classification method will be able to help improve understanding of treatment methods for posterior malleolar fractures.

Methods

We retrospectively analyzed 206 patients who underwent surgeries for ankle fractures in our orthopedic clinic between April 2014 and December 2022 and were verified to have posterior malleolar fractures in plain radiography, computed tomography (CT), and magnetic resonance imaging (MRI). We performed a probing test to determine whether syndesmosis was stable.

Results

We were able to classify the 206 cases into the following 5 types: type 1 (31 cases, 15.0%), extraincisural fragment with an intact fibular notch; type 2 (98 cases, 47.5%), posterolateral fragment extending into the fibular notch; type 3 (37 cases, 17.9%), posteromedial 2-part fragment involving the medial malleolus; type 4 (19 cases, 9.2%), large posterolateral triangular fragment; and type 5 (21 cases, 10.1%), shell-like PITFL avulsion (< 2 mm) in a CT axial view or PITFL periosteal sleeve avulsion (PITPSA) in arthroscopic or MRI findings.

Conclusions

This new system that adds the PITPSA type for the classification of posterior malleolar fractures may be a useful approach to managing these injuries and may aid in treatment decision-making. It could be important to consider ligament surgery when treating PITPSA.

Ankle fractures are common lower extremity injuries and frequently require surgical treatment. Among those, fractures involving the posterior malleolus constitute up to 44% of all ankle fractures.¹,²,³⁾ These fractures often occur concurrently with other fractures, most commonly involving the lateral and/or medial malleolus. Isolated fractures of the posterior malleolus are uncommon and typically result from axial loading injuries with the foot in a plantar flexed position.³,⁴,⁵⁾

Regarding posterior malleolar fractures, consensus dictates that surgery is required for a step-off greater than 2 mm or a fracture involving more than 25% of the articular surface.⁶,⁷,⁸⁾ But in the case of a small-size posterior malleolar fracture and a step-off less than 2 mm, conservative treatment is often the preferred choice and the treatment of posterior malleolar fragment remains controversial.⁶,⁹,¹⁰⁾ Most patients show good clinical outcomes after both operative and conservative management. Still, clinical outcomes of ankle fractures that involve posterior malleolar fractures are sometimes not satisfactory. Despite routine rehabilitation and proper operative treatment of other parts such as the medial malleolus, lateral malleolus, and syndesmosis, unsatisfactory clinical outcomes continue to be a concern in posterior malleolar fractures.¹¹,¹²⁾ Even in the absence of postoperative complications, untreated small posterior malleolar fractures can result in poor clinical outcome.¹¹,¹³⁾ In addition, since the posterior inferior tibiofibular ligament (PITFL) originates at the posterior malleolar fragment, not reducing the posterior malleolar fracture fragment could affect the alignment and stability of syndesmosis.¹⁴,¹⁵,¹⁶⁾ Then, since these changes in alignment and stability can act as a pain source, a new study on them may be necessary. Previous studies have demonstrated the significance of restoring the function of the PITFL, which remains attached to a posterior malleolar fracture fragment.¹⁷⁾ There are various classification systems for posterior malleolar fractures and there are many studies on the relationship between posterior malleolar fracture and syndesmosis.¹⁸,¹⁹,²⁰,²¹⁾ However, a classification of posterior fractures that considers PITFL injuries is not yet established. With advancements in radiology and arthroscopic treatment of ankle fractures, very small posterior malleolar fracture fragments—often missed or deemed insignificant on x-rays and computed tomography (CT) scans—are sometimes detected through magnetic resonance imaging (MRI) and arthroscopy.⁵,²²,²³⁾ Previously unknown new findings related to posterior malleolar fractures were revealed, which were often in the form of sleeve avulsion. These lesions could be accurately identified by arthroscopy. We found some cases by arthroscopy and reexamined the x-ray, CT, and MRI images. In some cases, there was no specific finding on x-ray, and in some cases, it was visible on CT or MRI, but even when it was not visible, it could be confirmed by arthroscopy. When viewed by arthroscopy, the PITFL was not ruptured, and the posterior malleolus appeared in the form of a sleeve avulsion with a small fracture fragment. When the probe test was performed, unstable findings of more than 2 mm were shown in some cases. We named it PITFL periosteal sleeve avulsion (PITPSA), and thought that it may affect syndesmosis stability. Therefore, it would be necessary to apply a new concept, PITPSA, to the existing classification system and we would like to propose a new classification through our research. To restore syndesmosis function, treatment for these findings may need to be considered. There are several classifications of posterior malleolar fractures by pathoanatomy using CT. However, these classifications do not divide this type of periosteal sleeve avulsion injury.

We hypothesized that publishing a new classification system would have an impact on the diagnosis and treatment of these patients. Therefore, we would like to propose a new classification system based on this study.

METHODS

The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board and Human Research Ethics Committee of Soonchunhyang University Bucheon Hospital (IRB No. 2023-07-011, 17 July 2023). Written informed consent was obtained from the patients.

From April 2014 to December 2022, we retrospectively reviewed 206 patients who were confirmed as having posterior malleolar fractures in plain radiography, CT, and MRI and underwent operative treatment for ankle fracture in our orthopedic clinic. We excluded cases of comminuted ankle fractures, multiple traumas, and open fractures because in the case of high-energy trauma, as in the cases of our patients, the severity of multiple traumas cause comminuted fractures rather than avulsion fractures. The 206 rotational ankle fractures with posterior malleolar involvement were confirmed based on the above exclusion criteria. Each patient was classified by Lauge-Hansen classification according to the injury mechanism and imaging data. In these patients, posterior malleolar fractures were observed on plain radiography, CT, MRI, and arthroscopy. We classified the patients by Bartoníček classification and divided them into 5 types by adding a type (type 5, < 2 mm in CT axial view [Fig. 1] or PITPSA in MRI or arthroscopic findings [Fig. 2]) to the existing 4 types (excluding existing type 5, osteoporotic type).¹⁸⁾ In the manner described below, among 206 patients, we found 21 cases of PITPSA.

Fig. 1. An 18-year-old male patient showed a lateral malleolar fracture and a posterior malleolar fracture. The malleolar fracture did not show step-off and the size of fracture segment was measured as less than 2 mm.

Fig. 2. An 18-year-old male patient (same patient as in Fig. 1). (A, C) In magnetic resonance imaging, the continuity of posterior inferior tibiofibular ligament (PITFL) was maintained. (B, D) When viewed through an arthroscope, the continuity of PITFL appeared to be maintained, but periosteal sleeve avulsion occurred and syndesmosis turned out to be unstable in the probe test.

A professional musculoskeletal radiologist evaluated all CT and MRI scans to assess fracture characteristics and other accompanying ligament injuries including PITFL injury. We retrieved radiographic images using a picture archiving and communication system (PACS; DEJA-VIEW; Dongeun Information Technology). Radiographic measurements were performed using PACS software. After basic surgical preparation and imaging examination, depending on the patient's injuries, operative treatment was performed for medial malleolar fractures, lateral malleolar fractures, and posterior malleolar fractures, respectively. We preferred open reduction and internal fixation using a limited contact locking compression plate, tension band wiring, a cannulated screw for surgical option. After rigid fixation, we examined all patients' ankle joints by arthroscopy. Starting from an anteromedial portal to an anterolateral portal, we directly observed the congruency of the ankle joints, osteochondral lesions, ligament injuries such as in the anteroinferior tibiofibular ligament, posteroinferior tibiofibular ligament, and anterior talofibular ligament, deltoid ligament rupture, and PITPSA.

We conducted a probing test to check the stability of syndesmosis: in our protocol, if the result of the probe test was less than 2 mm, it was regarded as stable, 2 to 5 mm as equivocal, and more than 5 mm as an indication for surgical treatment for syndesmosis. For cases that required surgery, syndesmosis repair using an internal brace or tight rope (Fig. 3) was performed.

Fig. 3. Two patients diagnosed with trimalleolar fractures were confirmed to have posterior inferior tibiofibular ligament sleeve avulsion by arthroscopy, and the probe test showed unstable findings of more than 5 mm, so syndesmosis repair was performed using a tight rope (A) and an internal brace (B).

Postoperatively, a short leg splint was applied to patients; after a few weeks of outpatient follow-up, the splint was replaced with orthosis. During outpatient follow-up for several months, the patients successfully underwent rehabilitation by sequentially performing weight-bearing, one-leg standing, and heel-rise squatting and returned to their daily lives.

RESULTS

Among patients with rotational ankle fractures who visited our hospital, 206 cases were confirmed after excluding high-energy trauma. Each patient was classified by Lauge-Hansen classification according to the injury mechanism and imaging data (Table 1). We were able to classify the 206 cases into 1 of the following 5 types: 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, shell-like PITFL avulsion (< 2 mm) in a CT axial view or PITPSA based on arthroscopic or MRI findings (Fig. 4). The above information is summarized in Table 2.

Table 1. The Number and Proportion of Fracture Patterns Based on the Lauge-Hansen Classification.

Fracture pattern type	Number of cases (%)
SER III	37 (18.0)
SER IV	117 (56.8)
PER III	8 (3.9)
PER IV	44 (21.3)

SER: supination external rotation, PER: pronation external rotation.

Fig. 4. A new classification for posterior malleolar fractures of the ankle. Lateral ankle radiographs, 3-dimensional reconstructed computed tomography (CT), axial views of CT, and arthroscopic views of the posterior malleolar fracture. (A) Type 1: extraincisural fragment with an intact fibular notch. (B) Type 2: posterolateral fragment extending into the fibular notch. (C) Type 3: posteromedial 2-part fragment involving the medial malleolus. (D) Type 4: large posterolateral triangular fragment. (E) Type 5: posterior inferior tibiofibular ligament periosteal sleeve avulsion fracture.

Table 2. The Number and Proportion of Each Type.

Type	Number of cases (%)
Type 1	31 (15.0)
Type 2	98 (47.5)
Type 3	37 (17.9)
Type 4	19 (9.2)
Type 5	21 (10.1)

All PITPSA lesions could be accurately identified by arthroscopy, and a total of 21 cases were found. PITPSA was suspected when a fracture fragment smaller than 2 mm was seen in the PITFL footprint on the CT axial view, and 6 cases were confirmed with an arthroscopy. In MRI, PITFL continuity was maintained and a fracture line was seen in the PITFL footprint area, which was suspected, and arthroscopy confirmed 11 cases. In 6 cases, PITPSA was suspected due to imaging findings on both CT and MRI and confirmed by arthroscopy. Among the cases identified as PITPSA by arthroscopy, there were 3 cases visible only on CT and 5 cases visible only on MRI. Unusually, there were 6 cases showing sleeve avulsion on arthroscopy, although there were no suspicious findings on CT or MRI.

DISCUSSION

In our study, PITPSA was found in a total of 21 cases (10.1%). This has not been found in other studies to the best of our knowledge. Since PITPSA is often found in arthroscopy, it seems that these lesions can be identified more accurately if surgery is performed arthroscopically. In support of this fact, many literatures related to the necessity of an arthroscope in evaluating syndesmosis has been published.²²,²⁴,²⁵⁾

Among shoulder joint diseases, there is a lesion called anterior labrum posterior sleeve avulsion (ALPSA). This lesion involves an avulsion fracture of the glenoid bone, but the current surgical approach focuses on ligament repair.²⁶⁾ Like ALPSA, PITPSA should be recognized as a ligament problem in surgery rather than a fracture. As to posterior malleolar fractures, consensus dictates that surgery is required for a step-off greater than 2 mm or a fracture involving more than 25% of the articular surface.⁶,⁷,⁸⁾ In light of these criteria, PITPSA is not indicated for surgery. However, considering the stability of syndesmosis, surgical treatment may affect the patient's clinical outcome even in the case of PITPSA.

A reliable classification system assists orthopedic surgeons in identifying and characterizing a condition, predicting potential outcomes, and guiding the selection of appropriate treatment methods. A thorough understanding of morphology is essential for achieving optimal therapeutic outcomes. Although it is not yet possible to accurately evaluate the significance of this new classification in a clinical setting, it may allow for a more proactive approach to surgery compared to the indications based on the previous classification. And it seems that good results can be expected for not only accurate intraarticular reduction but also reduction and stability of syndesmosis through active management.²⁵⁾

There are some limitations in this study. First, there were some cases lost to follow-up and there were patients who had not reached the 1-year mark after surgery, all of which were due to the insufficient number of cases. Additionally, it is not yet known how much clinical impact these lesions will have. Therefore, in this study, whether symptoms change after management of PITPSA lesions has not yet been recognized, and we intended to show such a pathoanatomy, proposing a modified classification system. The lack of information on how the lesion affected clinical outcomes is another limitation of this study. Follow-up studies will be needed to determine how much these lesions affect stability and, if so, whether adding stability through surgery will help improve clinical symptoms. It seems that a prospective study with a sufficient number of cases is needed to determine whether additional management of PITPSA lesions is significantly helpful.

This new classification of posterior malleolar fractures that adds the PITPSA type may be a useful approach to managing these injuries and aid in treatment decision-making. It could be important to consider ligament surgery when treating PITPSA .