Introduction
Talus bipartitus is a rare bony anomaly of the talus. It is defined as two non-fused talar fragments, with the posterior fragment located at the level of the posterior talar process. Strehle in his dissertation on talar anomalies described the first case in 1928 [
17]. Talus bipartitus needs to be distinguished from the more common os trigonum (or Shepherd fracture), which only includes the posterolateral tubercle of the posterior talar process [
10]. Also it should be distinguished from the Cedell fracture, for both its location and its aetiology. The Cedell fracture is an avulsion of the posteromedial tubercle of the posterior talar process and is thought to occur due to tensile forces from the posterior tibiotalar ligament [
2].
The prevalence of the talus bipartitus is unknown, and only a few case reports and small case series have been published. Little is known about its aetiology, clinical manifestations, treatment and outcome. Therefore, the purpose of this study was to provide an overview of the current literature. A systematic review of published case reports and small case series was performed. In addition, all patients that were treated over the last 15 years in our institution were reviewed. In this study, both the diagnostic process and the treatment of these patients will be described, including the long-term follow-up.
Materials and methods
Medline and Embase databases were searched for relevant publications, using the following terms (until 1 December 2015): (Talus OR Talar OR Astragalus) AND (bipart* OR partit* OR secondary OR fragment) OR frontal split. In addition, the CINAHL, Google Scholar and Web of Science databases were searched for scientific papers, book chapters and abstracts. Reference lists of relevant articles were reviewed. Titles were screened on relevance, and subsequently, full-text articles were assessed. The search was limited to articles describing humans.
Studies were only included if at least one case of a talus bipartitus was described, no language restriction was applied. Data on aetiology, clinical presentation, imaging and treatment were extracted. Due to the small amount of data, the presentation of data was descriptive. In addition to the literature review, three patients with a symptomatic talus bipartitus treated in our institution over the last 15 years were presented. Collection of data for this study was approved by the local research ethics committee (W12_237#12.17.0270).
Results
The literature search yielded 956 articles, of which 22 articles were selected for full-text screening. Of these, 11 articles were considered eligible. One article was added after screening literature lists on relevant papers. The included articles consisted of seven case reports [
1,
3,
6,
15,
16,
18,
22], one case description in a dissertation [
17] and four small case series [
5,
9,
12,
13]. These articles reported on 23 patients, of whom one patient had a bilateral talus bipartitus. Fourteen of them were males (61%). The median age at presentation was 15.5 years (IQR 14–24.3). In 21 of the symptomatic cases (96%), the patient experienced ankle pain, mainly on weight bearing. Thirteen had a restricted range of motion (54%). Two cases were coincidently detected following an ankle trauma. Most of the patients had no history of ankle trauma. In nine cases (38%), radiological imaging showed some signs of subtalar- and or talocrural joint degeneration. The size of the osseous fragment and extent of joint involvement varied widely. Surgical treatment had been performed in 19 cases (90%). In 13 cases (68%), excision of the fragment was performed by open surgery. Of these, due to ongoing symptoms, in four patients a secondary surgical procedure was performed, three patients underwent a subtalar fusion, and in one patient, a pantalar fusion was performed. In one case, the primary surgical intervention was a subtalar fusion, and in five cases, fixation of the bony fragment was performed. Due to the variety of presentations and limited descriptions on the specific treatment, a profound comparison of the outcomes was not possible. An overview of the published cases is presented in Table
1.
Table 1
Overview of published cases
| 1928 | 14 | F | Left | Pain during walking | – | No | 8 | X-ray | TB, incongruent joints | – | – | – | – |
| 1975 | 13 | M | Right | Increasing pain lateral malleolus, radiating anteriorly | Restricted ROM TCJ and STJ | No | 0.4 | X-ray | TB | 2.5 × 2 × 2 cm, 100% STJ | Excision | – | – |
| 1985 | 15 | F | Left | Dull ankle pain over medial malleolus after exercise | Restricted. Dorsal flexion TCR, restr. ROM STJ, pain | – | 4 | X-ray, arthrography | TB, flattened talar dome | Both joints involved | – | – | – |
| 1987 | 18 | F | Left | Pain during activity | Restricted ROM AJ | No | 2 | X-ray | TB, sclerotic, congruent | 1/3 talar dome, both joints involved | – | – | – |
| 2003 | 15 | F | Left | Intermittent ankle pain during activity | Normal | No | 1 | X-ray, MRI | TB, incongruent fragments both joints, degenerative, aberrant aspect calcaneus | Posterior 1/3 of talar body | Subtalar arthrodesis | Decrease pain, recurrence after 2 y, conservatively treated | 2 |
| 2010 | 18 | M | Right | Increasing hindfoot pain | FROM TCJ, painful restricted ROM STJ | No | 4 | X-ray, CT | TB, degenerative changes | 4 × 2 × 1.5 cm, 50% post STJ | Excision + subtalar arthrodesis | Pain-free activity | 1 |
| | 16 | M | Right | Ankle pain and instability | Increased ROM STJ, instability | Sprain | 1.2 | X-ray, CT, MRI | TB, sclerotic irregular margins | 2.8 × 1.1 × 0.8 cm | Excision | Pain and instability improved | 0.5 |
| 2010 | 12 | M | Right | Intermittent dull ankle pain after heavy exercise | FROM, tenderness on palpation talus | No | 2 | CT, MRI | TB, cystic, sclerotic areas, BME | Posterior 1/3 | Fixation, 1 screw | Asymptomatic, participating in sports | 0.75 |
| 2010 | 14 | M | – | Ankle pain | 25% restricted ROM TCJ | No | – | CT | TB | 20–25% post STJ | Excision | Functional recovery after 4 mo | 2 |
| | 13 | F | – | Ankle pain | 25% restricted ROM TCJ | No | – | CT | TB | 20–25% post STJ | Excision | Limited recovery after 9 mo, no sports | 1.5 |
| | 15 | F | – | Ankle pain | – | No | – | CT | TB, flattened talar dome | 20–25% post STJ | Excision | Functional recovery after 4 mo | 5 |
| | 16 | M | – | Ankle pain during activities | 50% restricted ROM TCJ, 50% increased ROM STJ | No | – | CT | TB | 20–25% post STJ | Excision | Functional recovery after 6 mo | 3 |
| | 15 | M | – | Ankle pain during activities | 25% restricted ROM TCJ | No | – | CT | TB | 20–25% post STJ | Excision | Exercise-induced pain | 2 |
| 2012 | 31 | F | Right | Occasional ankle pain | Restricted ROM | Repetitive sprains | 1.2 | CT, MRI | TB, displaced fragment | 1/3 talar dome, both joints involved | Fixation, 2 screws | Pain-free ADL, FROM | 3 |
| | 25 | M | Right | Intermittent ankle pain during activity | Restricted ROM | No | 3 | CT, MRI | TB, irregular shape, degenerative arthritis | Posteromedial 1/3 talar body | Excision | Mild pain during exercise, unable to play soccer, no functional restriction | 2 |
| | 27 | F | – | Evaluation ankle sprain | – | Sprain | 0.2 | MRI | TB | Both joints involved | Conservative | Minimal symptoms | 3 |
| | 22 | F | Left | Increasing ankle pain | – | No | 2 | CT, MRI | TB, incongruent both joints, degenerative arthritis | – | Excision | No pain ADL, mild pain activity, no progression arthritis | 1 |
| 2012 | 30 | M | Right | Evaluation after sprain | Swelling | NR | 0 | X-ray, CT, MRI | TB | – | – | – | – |
| 2012 | 11 | M | Right | Ankle pain | Restricted ROM STJ, cavovarus deformity | No | 0.5 | CT, MRI | TB, congruent joints | 25% STJ | Fixation, 2 screws | FROM, pain-free, AOFAS 100 | 4.2 |
| | 15 | | Left | Ankle pain | – | No | – | X-ray, CT | TB, congruent joints | 15% STJ | Fixation, 2 screws | FROM, pain-free, non-union (broken screw), AOFAS 100 | 2.3 |
| | 19 | M | Left | Ankle pain | Subtalar complaints | No | Several years | X-ray, CT | TB, degenerative changes STJ | 25% STJ | Excision + subtalar arthrodesis | RTW, mild pain, AOFAS 75 | 4.2 |
| | 55 | M | Right | Severe ankle pain | Painful and restricted ankle and subtalar motion | No | – | X-ray, CT | TB, oblique separation line, degenerative changes both joints | 25% STJ | Excision + pantalar fusion, hindfoot nail | Generalized hind and mid-foot pain requiring analgesia, limited ADL. AOFAS 53 | 5.6 |
| | 26 | M | Right | Severe hindfoot pain | Stiffness, painful STJ | No | – | X-ray, CT | TB, degenerative changes STJ | 20% STJ | Excision + subtalar arthrodesis | Clinical and radiographical fusion | 0.3 |
| 2013 | 14 | M | Left | Pain after sprain | No ROM STJ, pain plantar flexion | Sprain | | X-ray, CT | TB, horizontal talar fracture | Both joints involved | Fixation, 1 screw | No pain | 1 |
Over the last 15 years, three patients with a symptomatic talus bipartitus were identified in our institution and one had a bilateral talus bipartitus.
Discussion
Most important finding of this study was the wide variety in presentation of patients with symptomatic talus bipartitus. The presented manuscript provides an overview of the available literature on talus bipartitus. Patients with a symptomatic talus bipartitus predominantly develop non-specific ankle pain on activity. A limited range of motion was noticed in half of the patients. This condition can remain asymptomatic for at least a couple of years, and two cases were detected coincidently after the follow-up of an ankle sprain. There was a wide variety in shape and size of the posterior fragment. In 38% of the patients, signs of degenerative changes were present, and the extent of these changes depended on the congruency of the fragments in both the ankle and subtalar joints. In the reviewed literature, patients had a median age of 14 years, with a single patient aged 55 years as an outlier. The youngest patient was 11 years old. This is in accordance with the age at which the development of a second talar ossification centre was completed [
10].
In the literature, talus bipartitus is also known as ‘talus bipartita’, ‘talus partitus’ or ‘frontal split of the talus’ [
1,
15]. It is a rare congenital anomaly, in contrast to the more common and well-known os trigonum. The symptomatic os trigonum often can successfully be treated by Arthroscopic resection [
14]. The os trigonum is located at the posterolateral tubercle of the posterior process, whereas a true talus bipartitus involves both the posterolateral and posteromedial tubercles. In addition, in contrast to an os trigonum, the talus bipartitus can also extent into the ankle joint. This extension of the fragment makes it a different entity, in terms of clinical presentation, treatment and prognosis.
The prevalence of talus bipartitus is unknown. Pfitzner investigated 841 feet and reported on the prevalence of anomalies. He did not mention a single case of talus bipartitus [
11]. Also Tsaruta et al., in their radiological study on 3460 ankles, did not find a case of talus bipartitus [
19]. Together with the three cases presented in this study, we identified 26 patients with a talus bipartitus. Of them, only two had a bilateral talus bipartitus. In addition, Rammelt et al. reported also on imaging of a case in a book chapter [
7,
12]. This concerned a 13-year-old boy with ankle pain for more than a year. In this case, excision of the dorsal fragment was performed. Because of the persistence of complaints, a subtalar fusion was performed as a secondary procedure. However, this case was never published separately.
The majority of the cases have been published over the last decade. This was possibly due to advancements in additional diagnostics. CT and MRI are more sensitive to detect a talus bipartitus in comparison with conventional radiographs. Especially in case of the oblique running cleft, it might be missed on plain radiographs. Probably talus bipartitus is underreported in the literature, as it might be mistaken for a non-union of a talar fracture. A thorough history taking should, however, distinguish already between a talus bipartitus and a talar fracture.
Excision and fixation can both be considered while treating talus bipartitus surgically. The surgical preference depends on the size of the fragment and its involvement in surface area of both the talocrural and or subtalar joint. Two authors previously proposed a treatment algorithm. According to Rammelt et al. [
12], observation was indicated for asymptomatic patients, for symptomatic patients fixation was preferred in case of congruent fragments, and resection for incongruent fragments. Joint fusion was indicated when signs of progressive osteoarthritis were present. Rose et al. proposed excision of the fragment when less than 20% of the subtalar articular surface was involved and fixation if the fragment exceeded 20% [
13]. However, they did not mention how this should be measured. In our opinion, fixation is recommended when the fragment involves the joint surface of both the ankle and subtalar joint. Excision in those circumstances will lead to a decreased joint surface area which might lead to progressive osteoarthritis. In case the talus bipartitus only involves the subtalar joint, the decision to excise or fix is more challenging. Fixation is theoretically preferred over excision; however, the outcome depends on the size of the fragment, surgical skills and preexisting osteoarthritic changes. In our cases, more than 50% of the posterior subtalar joint was involved, as measured in the sagittal plane. The first presented patient was treated with excision, whereas in the second one the fragment was stabilized. Both patients had good short- and long-term outcomes. Therefore, optimal treatment has to be tailored to the patient and depends on severity of complaints, activities of the patient, size of the fragment, joint involvements and the presence of degenerative changes at presentation.
Two cases were presented in which both fixation and excision were performed using an arthroscopic technique. To our knowledge, this is the first surgical description on the arthroscopic-assisted treatment of talus bipartitus. Arthroscopic treatment is preferable over open surgery because of the advantage of shortened hospital stay, rapid rehabilitation and smaller scars. Posterior ankle arthroscopy has been proven to be a safe and effective treatment option for several hindfoot problems [
14]. Although we described only two cases, it seems that the two-portal hindfoot approach is also appropriate and safe for the treatment of symptomatic talus bipartitus. In this study, the first long-term outcomes are reported.
The talus ossifies from two ossification centres [
8,
10]. Based on a literature study and a histological study about the chondrification of tarsal primordia in human embryos and foetuses, Cihak concluded that the talus is formed out of the
tibiale and
intermedium. The
tibiale forms the corpus tali and the
intermedium will develop into the posterior process [
4]. In case of independent ossification or failure of fusion, this part is responsible for the os trigonum, or possibly also for a talus bipartitus.
A direct traumatic injury is not likely to cause a bipartition of the talus. Eichenbaum hypothesized partition of the talus as a result of traumatic injury during osseous immaturity [
5]. However, talar fractures only occur in high-energy trauma, especially in children even higher forces are needed to cause a talar fracture. Therefore, absence of significant trauma rules out a fracture by definition. A possible alternative theory could be that the fusion of the secondary ossification centre with the talar body is prevented by a single or repetitive trauma during adolescence [
10]. In addition to the ontogenetic and traumatic causes, also endocrine factors have to be excluded, since an association between hypothyroid epiphyseal dysgenesis and bipartition of hand and foot bones was described [
9].
In the third case, the talus was severely deformed as a result of a congenital clubfoot. This patient had bilateral clubfeet, with a talus bipartitus at the right ankle which became symptomatic later on in life. It is unknown whether there is a direct relation between the talus bipartitus and clubfeet.
This study has several limitations. Due to the rarity of talus bipartitus, only case reports and small cases series were included. The level of evidence is therefore low; however, this review provides the most comprehensive overview of the available evidence. Only two patients that underwent arthroscopic-assisted treatment for symptomatic talus bipartitus were included. Therefore, it was not possible to compare the results of the arthroscopic approach with results of open surgery.