Keywords
fibula - syndesmosis - floating
Introduction
Isolated tibiotalar dislocations are very uncommon injuries. Due to the intrinsic
stability of the ankle joint and the mechanism of injury, these lesions are most often
combined with bone fractures.[1]
[2]
[3] The stability of the tibiofibular joint, both proximal and distal, are provided
by the strength of the capsule and its ligamentous complex. The simultaneous disruption
of both the proximal and distal syndesmosis is known as floating fibula.[3]
[4] There is only one case of this injury described in the literature, and we herein
present the first case associated with biceps avulsion (not only passive stabilizers
of the knee joint, but also active ones). We report a case of simultaneous proximal
and distal tibiofibular joint disruption resulting in a floating fibula, which was
stabilized with an implant of ankle syndesmosis repair system (INVISIKNOT, Smith &
Nephew, Watford, Hertfordshire, United Kingdom) and some metallic bone anchor (TWINFIX,
Smith & Nephew) implants.
Case Report
A 19-year-old woman injured her left leg in a traffic accident. Upon admission, the
clinical examination revealed considerable swelling, pain on palpation, and total
inability to move the ankle. She also suffered intense pain in her ipsilateral knee,
with bruises in both the external and internal sides of the knee. Similar injuries
appeared in both sides of the ipsilateral ankle as well ([Fig. 1A and B]). No neurovascular injuries were observed. The radiographs showed an isolated tibiotalar
dislocation with a significant diastasis of the syndesmosis associated to an ascending
talus without any malleolar fracture. Because of the injury mechanism, we suspected
an additional injury to the proximal tibiofibular joint, although there was no evidence
of it on the radiograph. ([Fig. 1C, D and E]).
Fig. 1 (A,B) Contusions on the external and internal sides of the knee. Similar injuries appeared
on both sides of the ipsilateral ankle as well. (C-E) Pure tibiotalar dislocation without fracture. (F,G) Postreduction radiograph showing persistence of the widening of the tibiotalar joint
(medial clear space). (H-K) Magnetic resonance imaging scan showing complete rupture of the ankle syndesmosis
and the deltoid ligament, and, proximally, an external non-displaced tibial plateau
fracture and an image suggestive of non-displaced fibular head fracture. (L) Repair of the distal syndesmosis with a TWINFIX implant. (M,N) Reduction of the distal and proximal syndesmosis withINVISIKNOT implants. (O) Repair of the collateral ligament and biceps tendon with a TWINFIX implant. (P) Repair of the deltoid ligament with another TWINFIX implant. (Q,R) Postoperative radiographs showing the reduction and maintenance through INVISIKNOT
and TWINFIX implants.
Immediate closed reduction of the dislocation was performed under local anesthesia
at the emergency room. The pulses of the distal ankle and dorsal pedis were intact
after the reduction maneuver, with no clinical evidence of compartment syndrome in
progress. A posterior splint was applied to temporarily immobilize the knee and ankle
joints. Postreduction radiographs showed that a slight widening of the tibiotalar
joint remained, especially in the medial clear space, but no changes were observed
in the tibiofibular overlap ([Fig. 1F and G]).
Due to the mechanism of injury and the extensive knee and ankle swelling, an emergency
magnetic resonance imaging (MRI) scan of the ankle and the knee was performed, which
showed complete rupture of the ankle syndesmosis, complete rupture of the deltoid
ligament, a non-displaced external tibial plateau fracture, and an image suggestive
of non-displaced fibular head fracture ([Fig. 1H], [I], [J] and [K]).
One day after the injury, we proposed the surgery to the patient, who agreed to undergo
it. We decided to repair the ligament injuries to reestablish/restore the stability
of the ankle and explore the concomitant injury to the proximal tibiofibular joint.
Before the performance of the surgery, we observed a severe valgus instability of
the knee that suggested a possible rupture of its collateral ligament or a complex
posterolateral instability of the joint that results in a proximal fibular dislocation,
which were all of the injuries the patient presented as a consequence of a high-energy
trauma: a pure tibiotalar dislocation with a proximal fibular luxation as a result
of a complex injury of the posterolateral complex of the knee.
Under general anesthesia, without tourniquet, we first reduced the fibula proximally
and distally, observing the absence of fractures, and repaired the distal syndesmosis
with a TWINFIX implant ([Fig. 1L]). After that, we maintained the reduction of the distal syndesmosis, and then, the
proximal syndesmosis, with INVISIKNOT implants ([Figs. 1M] and [N]). We also reinserted the lateral collateral ligament and the bicipital tendon posteriorly
to the fibular head, which was completely torn, with another TWINFIX implant ([Figs. 1O]). Finally, we reinserted the deltoid ligament with another TWINFIX implant ([Fig. 1P]). The patient then wore an immobilizing plaster cast for four weeks to enable the
healing of the ligaments, including the medial collateral ligament of the knee ([Fig. 1Q and R]).
After four weeks, we removed the plaster cast and sent the patient to rehabilitation.
After two months of rehabilitation, she was asymptomatic, and showed complete muscular
strength with a slight limitation in terms of dorsiflexion of the talus.
Discussion
Floating fibula is described as a simultaneous disruption of both the proximal and
distal tibiofibular syndesmosis.[4] The first case was described by Pelc et al.,[2] and no other cases have been described in the literature. Pure tibiotalar dislocation
associated with a proximal tibiofibular injury is an uncommon entity, because the
ligaments are usually stronger than bone structures.[3]
[5]
[6] Such ligament structures, both proximal and distal, are considered static stabilizers
of the joints, enabling an external rotation of ∼ 5° to 6° of the fibula with respect
to the tibia during walking, and a widening of the distal tibiofibular joint of ∼
1, 5 mm during dorsiflexion of the foot to prevent ankle instability.[7]
[8] We herein present a case of divergent dislocation without bone fracture, so it is
important to distinguish it from the cases of dislocations de to transsyndesmotic
ankle fracture, which are also called “log-splitter” injuries, a rare condition produced
by vertical loads or by combined rotational force.[6]
Lamraski and Clegg[1] presented a patient with a divergent dislocation of the ankle without an associated
lesion in the proximal tibiofibular joint, and they treated the lesion in the syndesmosis
with a transsyndesmotic screw; similarly, Alami et al.[3] presented another case of lesion in the distal tibiofibular joint without proximal
injury, and they treated the disruption of the syndesmosis by means of two transsyndesmotic
screws. In their case, the patient presented a luxation different from that of the
case herein presented, because the fibula had rotated externally, posteriorly displacing
the tallus attached to the fibula. In our case, the fibula did not rotate externally,
so the tallus was not displaced posteriorly, but anteriorly.
Edwards and DeLee[9] planned a classification of divergent ankle dislocations, but not considering a
possible association with damage to the proximal tibiofibular joint: type I consists
of an isolated lateral subluxation of the distal fibula without lateral deformity;
type II is isolated lateral subluxation of the distal fibula with deformity; type
III is rotational posterior subluxation of the distal fibula; and type IV, superior
dislocation of the talus, grazing the fibula and the distal tibia. We propose a subclassification
of this type taking into account a possible affectation of the proximal tibiofibular
joint, which would be subdivided into type IVa if there is no involvement of the tibiofibular
joint, and type IVb, which is the case herein presented, which affects the proximal
tibiofibular joint.
Tears to the interosseous membrane lead to the potential risk of developing acute
compartment syndrome because of the injury to the tibialis posterior artery or to
some of its branches. As we observed, there was no clinical evidence of compartment
syndrome in progress in our case, but cases of compartment syndrome after syndesmotic
or ankle injuries have been described in the literature, such as those by Imade et
al.[10] and Mathews and Mutty.[11]
As aforementioned, to date, only Pelc et al.[2] have described this association of lesions both at the proximal and distal levels
acquiring a combined pathophysiology that can lead to instability of the ankle and
knee if it is not properly diagnosed and treated. In addition to the distal and proximal
tibiofibular syndesmosis, we need to mention the importance of the external collateral
ligament and the femoral biceps tendon as stabilizers in varus of the knee joint,
but, at the same time, stabilizers of the proximal tibiofibular joint.[12] The external collateral ligament is the most important stabilizer of the posterolateral
complex of the knee, along with the popliteus complex, limiting the varus and external
rotation of the tibia in relation to the femur. Likewise, the bicipital tendon plays
an important role in limiting the anterior translation of the fibular head. Pelc et
al.[2] presented a patient with a divergent ankle dislocation associated with a superior
dislocation of the proximal fibula caused by complete rupture of the external lateral
ligament and the anterior articular capsule, as we described in our case, with an
avulsion of the iliotibial band of the Gerdy tubercle as well. We add to our case
complete avulsion of the bicipital tendon, which plays an important role in the stability
of the proximal fibula, limiting the anterior translation. To date, a case of divergent
ankle dislocation associated with a proximal dislocation of the fibula as a result
of complete lesion to the external lateral ligament and the femoral biceps tendon
has not been described.
Ogden[13] described the types of proximal tibiofibular dislocation: type I occurs due to ligament
laxity and, for the most part, without a history of trauma; type II is anterolateral
dislocation, which occurs in up to 85% of the cases, and it what our patient presented;
type III corresponds to posteromedial dislocation, it is associated with peroneal
nerve injury, and is the result of direct trauma; and type IV corresponds to upper
dislocation, which is uncommon and associated with high-energy ankle injuries. The
case herein reported could be classified as an Odgen type-IV dislocation.
Just as Pelc et al.,[2] we performed a repair of the distal and proximal tibiofibular syndesmosis using
suture anchor and suture-button implants. One of the main advantages of this technical
repair is that it enables the temporary control of the reduction of both joints simultaneously.
Another advantage is the easy control of the defects of rotational reduction because
it is an elastic system, while the rigid insertion of the screw requires perfect reduction
and positioning of the implant, which is of paramount importance in cases of floating
fibula with complete rupture of the syndesmosis. Another reason to use this system
is that it usually does not require removal of the implant and has a lower failure
rate compared with fixation with screws fixation. In case of rupture, its removal
is easy, and it usually does not cause periosteal reaction or heterotopic ossification,
which have been observed in cases of syndesmosis repair with transsyndesmotic screws.
Moreover, patients with syndesmotic injuries treated with this technique experience
a faster functional recovery and return to work, as well as shorter periods of rehabilitation,
than patients treated with screws.[14]
[15]
[16]
[17]
Conclusion
Floating fibula is a rare entity, and, to date, only one case has been described in
the literature. It involves disruption of the proximal and distal tibiofibular joint,
which can manifest as a high-energy trauma and may lead to great knee and ankle instability
if not properly treated. Therefore, in cases of high-energy trauma to the ankle, careful
examination of the ipsilateral knee is necessary.
