Altogether, subtalar dislocations account for <2% of all dislocations of large joints1. Subtalar dislocation is defined as a simultaneous dislocation of the talonavicular and the talocalcaneal joint2. These dislocations occur most frequently in the third decade of life, with men experiencing them ten times more frequently than women3,4. The dislocations are subdivided into medial, lateral, anterior, and posterior types on the basis of the direction in which the distal part of the foot has shifted in relation to the talus2,5-7. Medial subtalar dislocations predominate in the literature, accounting for approximately 80% of reported dislocations1,4,5,8-12. Lateral dislocations (17%)4-6, posterior dislocations (2.5%), and anterior dislocations (1%) are much less common3,4,13. Although biomechanical studies have demonstrated a similar degree of ligament injury with both medial and lateral subtalar dislocations14,15, lateral dislocations appear to have a worse prognosis because they are associated more frequently with accompanying osseous and open soft-tissue injuries, usually as a result of the greater injury forces at work2,14,16-19. The frequency of an associated fracture has been reported to range between 50% and 100%, with such fractures being more common in lateral dislocations3,19-21.
Little has been reported to date regarding subtalar dislocation without an associated bone injury6, as the relatively small number of studies performed with larger numbers of patients usually have included patients with an associated osseous injury3,8,9,14,16,19,22-26.
The aim of the present study was to assess the functional and subjective results following subtalar dislocation without an associated bone injury.
The appropriate ethics committee approved this retrospective case series, and all included patients provided written informed consent.
A total of ninety-seven consecutive patients with a subtalar dislocation were treated at two major university trauma centers from January 1994 to March 2007. After reduction of the dislocation, a computerized tomographic scan was performed on all of the patients to rule out associated bone injuries such as avulsion fractures, osteochondral injuries, and peripheral fractures. After evaluation of all of the computed tomography scans, only twenty-three patients were found to exhibit a pure subtalar dislocation without any associated fracture. Only these patients were included in the present study. Of the remaining seventy-four subtalar dislocations with bone injuries, fifty-three were medial and twenty-one were lateral dislocations. It was possible to carry out clinical, functional, and radiographic examinations on all twenty-three patients with a subtalar dislocation without a bone injury at an average of 58.3 months (range, thirty-eight to 106 months) after the completion of treatment.
Details on all of the patients are provided in a table in the Appendix. Sixteen patients were male, and seven were female. The average age was 42.4 years (range, nineteen to eighty-five years) at the time of injury. The cause of the dislocation was a fall from a great height for eleven patients, a motor-vehicle accident for four patients, a sports injury for six patients, and a twisting injury of the foot for two patients.
There were sixteen medial, six lateral, and one posterior (Fig. 1) subtalar dislocations. Seven patients had an open irreducible dislocation; these included two lateral and five medial dislocations. The two open lateral dislocations were irreducible because of displacement of the tibialis posterior tendon or the flexor digitorum longus tendon to the lateral side of the neck of the talus. Therefore, an open reduction was necessary, and the reduction was stabilized with an external fixator. All five open medial dislocations were also irreducible by closed means. In these patients, the talar head was buttonholed through the extensor retinaculum or the extensor digitorum tendon itself was wrapped around the medial aspect of the talar neck. All five required an open reduction, and two of them needed a second incision to reduce the talar head. All five were treated by external fixation after open reduction.
Following a successful stable closed reduction, thirteen patients were managed with immobilization in a short leg cast or brace for a period of six weeks. After that, progressive weight-bearing and aggressive physiotherapy was begun. All patients were able to bear full weight on the leg at an average of 10.6 weeks (range, ten to 11.5 weeks) after the injury.
Two additional patients with a closed injury required open reduction of an irreducible dislocation. In these two patients, the exact reason for the irreducibility of the dislocation could not be ascertained from the charts. One additional patient with a closed injury underwent a successful closed reduction of the dislocation, and immobilization with an external fixator was selected because of massive soft-tissue swelling. Thus, in ten patients (nine after an open reduction), an external fixator was applied to protect the soft tissues from further swelling and to facilitate wound-healing. The fixator was removed at six weeks, and the patient began progressive weight-bearing. These patients were able to bear full weight on the legs by an average of 10.5 weeks (range, 10.0 to 11.9 weeks) after the injury.
The American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot scale was used to evaluate the functional results of the subtalar joint complex and to assess the return of the patients to their work and activities27. A score of 90 to 100 points represented excellent function; 75 to 89 points, good function; 60 to 74 points, average function; and <60 points, poor function28.
The range of motion of the tibiotalar joint (extension and plantar flexion) was measured with a goniometer and compared with the contralateral side. The range of motion of the subtalar joint (inversion and eversion) was assessed with use of the method developed by Inman and Mann3,22, with the patient lying prone and the knee flexed to 135°. In this position, the axis of the subtalar joint is near the horizontal plane. A gravity goniometer was then attached to the heel to measure inversion and eversion. All measurements were performed by the same examiner (M.D.). A comparison with the unaffected, contralateral side was carried out as well.
At the time of the latest follow-up, radiographs of the injured foot and ankle in the anteroposterior and lateral projections were assessed uniformly by a radiologist who was not aware of the clinical results. The degree of arthritis of the subtalar, calcaneocuboid, talonavicular, and ankle joints was classified with use of the method described by Altman et al.22,29, in which 0 indicated normal, with no degenerative changes; 1, mild changes or changes involving up to one-third of the articular surface; 2, moderate changes or changes that affect between one-third to two-thirds of the articular surface; and 3, severe changes or changes affecting more than two-thirds of the articular surface.
Source of Funding
No external funding was used in support of this research.
For all twenty-three patients, regardless of the type of care they received, the AOFAS score averaged 82.3 points (range, 73 to 88 points). The thirteen patients treated without an external fixator attained an average AOFAS ankle-hindfoot scale score of 83.3 points (range, 75 to 88 points). The ten patients treated with an external fixator had an average AOFAS ankle-hindfoot scale score of 80.9 points (range, 73 to 88 points), which is also a good result. On the whole, twenty-one patients achieved a good result and two patients, a satisfactory result.
Radiographically, nine patients exhibited only minor degenerative changes (Altman grade 1) of the subtalar, calcaneocuboid, talonavicular, and tibiotalar joints; none of these changes could be associated with patient complaints or restrictions of movement.
The mean range of motion was 58.3° (range, 28° to 70°) for the tibiotalar joint on the injured side and 58.9° (range, 30° to 70°) for the unaffected tibiotalar joint. Range of motion (combined inversion-eversion) averaged 41.3° (range, 30° to 50°) for the injured subtalar joint compared with 42.6° (range, 35° to 53°) for the unaffected side. When both sides were compared, only three patients had moderate restrictions in the range of motion in the subtalar joint.
No patient had a redislocation, a sign of osteonecrosis of the talus, or an infection. No revision operation was performed. No patient displayed any change on visual assessment of his or her gait. Eighteen patients reported that they did not experience any pain in their daily and athletic activities.
The average AOFAS ankle-hindfoot scale score for the medial dislocations was 82.4 points (range, 73 to 88 points), and the average subtalar range of motion was 41.4° (range, 30° to 50°). For the lateral dislocations, the average AOFAS ankle-hindfoot scale score was 83 points (range, 74 to 88 points) and the average subtalar range of motion was 42.2° (range, 38° to 50°). With the numbers studied, no difference in AOFAS scores or subtalar range of motion was seen on the basis of the direction of dislocation.
All of the patients who were employed at the time of the injury were able to return to the same type of work by an average of 10.3 weeks (range, eight to fourteen weeks). Moreover, all of the patients who had participated in athletic activities before the injury were able to resume their usual sports activities at the same level of performance without any restrictions.
Subtalar dislocation without an associated fracture is an uncommon injury. While several studies with more than ten patients have been published over the last two decades3-5,8,16,17,22,25,26,30, we believe the present study is the largest series reported in the literature to date.
Most previous studies were not differentiated between pure subtalar dislocations and dislocations with associated bone or osteochondral injuries that can occur frequently as a result of shear forces. Among all of the subtalar dislocations seen over a thirteen-year period at two major trauma centers, 76% of the patients had an associated bone injury identified by computed tomography. In the literature, associated bone injuries have been reported for 50% to 100% of such dislocations3,5,16,25,26,30,31. Bohay and Manoli found a high rate of occult fractures in their follow-up examinations using computed tomography30, and they and Bibbo et al.31 recommended that computed tomographic imaging be used to identify associated injuries following a subtalar dislocation.
In the present study, there was a predominance of medial dislocations (70%) compared with lateral (26%) and posterior dislocations (4%), as has been reported in other series3,4,25,26. Many authors have reported that lateral dislocations are associated with poorer final results because, in general, they result from higher-energy injuries2,5,14,16,17,19. Although it is difficult to compare our results with other investigations, as they did not specifically study injuries without bone lesions, we did not observe any functional differences between medial and lateral subtalar dislocations3,6,16,22. It is important to remember, however, that the AOFAS ankle-hindfoot scale score used in our study is not a validated outcome score. Another weakness of this study is the small number of patients examined. Thus, our findings are not absolute and should not be generalized. Although we cannot provide a comparison with historical controls, the absence of associated talar and peritalar injuries could be a possible explanation for the almost identical results found for both medial and lateral subtalar dislocations in this study. This is in contrast to the commonly held opinion in the literature that the decisive factors in the long-term prognosis are primarily the type of dislocation, the degree of damage to the soft tissues, and the duration of immobilization3,6,14,32. The results of the study by Perugia et al.5 also support this viewpoint. As in our study, all patients in their series had a good functional result and good subtalar range of motion regardless of the direction of the dislocation. It should be noted, however, that not all of the patients in that study had a computed tomography scan.
The initial treatment for a subtalar dislocation hinges on an immediate closed reduction in order to prevent additional damage to the soft tissues and minimize neurovascular complications22,25,26. Closed reduction is usually successful in most dislocations22,26,33. In our study as well, closed reduction succeeded in 65% of the patients. When closed reduction fails, however, we believe that open reduction should be carried out in the operating room in order to avoid additional damage to soft tissues resulting from overaggressive manipulation.
Reported complications following subtalar dislocations include posttraumatic arthritis, osteonecrosis of the talus, and ankylosis of the subtalar joint9. We did not observe the two latter complications, and only nine patients exhibited mild, asymptomatic degenerative changes in the area of the subtalar, talonavicular, and/or the tibiotalar joint. These good results possibly can be attributed to the absence of osseous or osteochondral injuries.
With respect to the occurrence of arthritis, the follow-up period in the present study was only 58.3 months. With an average follow-up of 61.6 months, Bibbo et al. found severe degenerative changes in 89% of their patients26. As a result of marked posttraumatic arthritis, four of their patients underwent an arthrodesis in less than twenty-four months. Ruiz Valdivieso et al. described severe degenerative changes among 57.9% of their patients after an average of 7.9 years8. DeLee and Curtis3 reported similar results with an average follow-up of thirty-five months. Only longer follow-up will allow us to compare our results with these other series.
On the basis of the results of our study, we recommend the following treatment regimen: (1) A dislocation in which a closed reduction is possible and that has only minor swelling of the soft tissues should be managed with immobilization for six weeks in a short leg cast or brace. (2) For an open dislocation, a dislocation with considerable swelling of the soft tissues, or a dislocation that requires an open reduction, an external fixator can be applied for six weeks. (3) Regardless of the method of immobilization, after a six-week period, aggressive rehabilitation and full weight-bearing are recommended.
In conclusion, the functional and subjective results of subtalar dislocation without an associated bone injury and regardless of direction are good if reduction is performed quickly and the limb is immobilized for six weeks. Early posttraumatic arthritis generally does not occur when there is no associated bone injury.