1.Anatomy of the ankle joint complex
The ankle joint complex consists of the bony structures of the ankle joint and its ligamentous structures. The bony structure of the ankle joint consists of the distal tibial articular surface vault, the internal and external ankle and the talus. It mainly consists of the joint between the saddle-shaped roof of the talus and the distal tibial articular surface and the joint between the lower tibia and fibula, in addition to the articular surfaces on both sides of the talus and the corresponding internal and external ankles.
The ligamentous structure of the ankle joint mainly consists of the inferior tibiofibular complex and the medial and lateral collateral ligament system. The inferior tibiofibular complex connects the distal tibiofibula and consists of three main parts: (1) the anterior inferior tibiofibular ligament, which connects the anterior tibial tuberosity to the external ankle; (2) the posterior inferior tibiofibular ligament, which connects the posterior tibial tuberosity to the external ankle; and (3) the interosseous ligament, which connects the fibula and tibia and continues upward to the interosseous membrane of the lower leg.
In terms of strength, the interosseous ligament is the strongest, followed by the posterior inferior tibiofibular ligament, and the anterior inferior tibiofibular ligament is the weakest. Therefore, injuries to the posterior aspect of the inferior tibiofibular union are usually characterized by avulsion fractures of the posterior tibial tuberosity, whereas injuries to the anterior aspect are usually tears of the anterior inferior tibiofibular ligament.
The lateral collateral ligament consists of the anterior talofibular ligament, the heel fibular ligament, and the posterior talofibular ligament. The anterior talofibular ligament begins at the anterior border of the lateral ankle and ends at the talar neck. The medial collateral ligament (also known as the deltoid ligament) consists of two parts, the superficial layer spanning both the ankle joint and the subtalar joint and the deep layer spanning only one joint of the ankle joint, but sometimes this is not absolute.
The superficial layer is divided into four bundles: the tibial navicular ligament (located most anteriorly, from the anterior border of the anterior mound of the medial ankle, entering the dorsal aspect of the navicular bone and possibly also partially ending at the talus), the superficial posterior tibial talofibular ligament (from the interdiscal sulcus, ending at the medial talar tuberosity and talar eminence), the tibial heel ligament (located deeper in the tibial spring ligament, from the medial surface of the anterior mound of the medial ankle, ending at the medial border of the talar eminence) and the tibial spring ligament (located most superficially, from the medial ankle The tibial spring ligament and the tibial navicular ligament are constant.
The deep layer of the triangular ligament consists of the posterior deep tibial talofibular ligament (originating from the intermural sulcus of the medial ankle and ending on the medial side below the articular surface of the talus) and the anterior deep tibial talofibular ligament (originating from the anterior malleolus and intermural sulcus of the medial ankle and ending far from the front of the medial articular surface of the talus), the former being the only one that exists at a constant level.
2. Biological role of the ankle joint complex
Under the action of the ankle joint complex, the joint surface of the talus and the entire ankle cavity remain in close contact in all positions of dorsiflexion or plantarflexion of the ankle joint, which is important for the uniform distribution of the ankle joint load.
The inferior tibiofibular complex forms the micro-motor connection of the lower tibiofibular segment, and the movement is mainly a combination of rotation and translation, which allows the ankle point to be stable while remaining somewhat flexible and adaptable.
At the same time, the inferior tibiofibular complex also has the role of transmitting and regulating the weight bearing of the fibula, about 1/6 of the weight is transmitted to the fibula through the inferior tibiofibular joint, and the load ratio of the tibiofibula can be dynamically fine-tuned. The triangular ligament is one of the most important anatomical structures in maintaining ankle stability, with the superficial layer limiting talar abduction and preventing talar tilt, and the deep layer being the main ligament preventing anterior rotation of the talus.
Michelson et al. performed in vitro tests and found that severing the deep layer of the deltoid ligament caused significant changes in the stability of the ankle joint in all directions. After further severing of the triangular ligament, there was a significant widening of the inferior tibiofibular joint, a 39% decrease in the contact area of the tibiofibular joint and a 42% increase in the peak pressure.
When the ankle is plantarflexed, the anterior talofibular ligament is the main structure that prevents the talus from shifting forward. This ligament is the weakest and is often easily injured in ankle inversion injuries. The talofibular ligament is oval, flat, and stronger than the anterior talofibular ligament, starting at the tip of the outer ankle and ending at the lateral aspect of the heel bone.
The posterior talofibular ligament is stronger, starting at the medial aspect of the outer ankle and attaching posteriorly to the lateral tuberosity of the posterior talus, and travels in a subhorizontal position to prevent posterior talar rotational subluxation.
3. Site and mechanism of acute injury to the ankle joint complex
The mechanism and injury site of ankle complex injury are determined by the position of the foot and the direction of violence at the time of injury, usually accompanied by a fracture of the external ankle, while a fracture of the anterior or posterior malleolus of the internal ankle is rare, and simple injury is rare.
According to the AO and Lauge-Hansen fracture types of ankle fractures, the site of injury in the post-rotation-external rotation type (common in AO type B) is, depending on the magnitude of the violence, a rupture of the anterior inferior tibiofibular ligament – a spiral oblique fracture of the distal fibula – a rupture of the posterior inferior tibiofibular ligament or a posterior ankle fracture – a fracture of the internal ankle or a rupture of the triangular ligament
In the anterior-external rotation type (common in AO type C), the order of injury is a transverse fracture or rupture of the triangular ligament of the inner ankle – rupture of the anterior inferior tibiofibular ligament – short oblique fracture of the fibula above the ankle plane and tear of the interosseous ligament – tear of the posterior inferior tibiofibular ligament or posterior lateral tibial avulsion fracture; in the posterior-internal rotation type (common in AO type A), the order of injury is a transverse avulsion fracture of the fibula below the ankle plane or lateral The anterior-adductor type of injury is relatively uncommon.
In summary, injuries to the inferior tibiofibular complex and deltoid ligament are mainly caused by rotational violence, and when there is no medial ankle fracture, the AO subtype B fracture is preceded by an external ankle fracture, anterior and posterior inferior tibiofibular ligament injury and then deltoid ligament injury (not necessarily rupture); whereas the type C fracture is preceded by deltoid ligament rupture and then anterior and posterior inferior tibiofibular ligament, interosseous ligament rupture and external ankle fracture.
Given that the interosseous ligament is the strongest in the inferior tibiofibular complex, while type B fractures generally do not injure the interosseous ligament, so this type of fracture generally does not require treatment of the inferior tibiofibular joint, and depending on the situation, a rupture of the deltoid ligament can be treated, while type C fractures generally require treatment of both deltoid ligament and inferior tibiofibular joint injuries.
4. Diagnosis of acute injury of the ankle joint complex
In the past, the preoperative diagnosis of lower tibiofibular joint injury mainly relied on the frontal and lateral ankle joint and ankle cavity radiographs: ① the lower tibiofibular gap ≤6mm at the distal tibial joint surface near 1cm on anterior-posterior or ankle cavity radiographs; ② the tibiofibular overlap >6mm on anterior-posterior radiographs; ③ the tibiofibular overlap >1mm on ankle cavity radiographs, etc.
Nowadays, it is believed that the MPR cross-sectional images of multilayer spiral CT can clearly observe the width change of the lower tibiofibular joint gap, which can more accurately determine whether the lower tibiofibular joint is injured or not; MR examination can also be used to assess the lower tibiofibular joint injury, which has a high accuracy rate, but it is more difficult to be used in large-scale clinical application because it is more expensive.
Recently, the value of intraoperative arthroscopy for the diagnosis of inferior tibiofibular joint injury has been emphasized, and the damage to the anterior and posterior tibiofibular ligaments can be seen directly through arthroscopy and can be repaired, but the shortcoming is that the interosseous ligaments cannot be seen. The diagnostic methods of deltoid ligament injury include X-ray, ultrasound, MR, and arthroscopy.
If the medial gap of the ankle joint is >4mm, the possibility of deltoid ligament injury should be considered and further examination is needed to confirm. If the tilt of the talus is 5°~10° or even greater, it suggests deltoid ligament injury, but most patients cannot cooperate due to pain.
Ultrasound examination has the advantages of being inexpensive and rapid, but its results are highly dependent on the experience of the operator and are uncertain. MR examination can clearly show the deep and superficial ligament damage, which is important for assessing the prognosis and deciding the surgical plan.
Arthroscopy has recently received attention. Ankle arthroscopy can observe the deep triangular ligament injury, and using auxiliary instruments such as probing hooks, the ligament tightness and degree of injury can be probed, and the presence of articular cartilage injury can be observed, which is important for deciding whether the triangular ligament injury needs to be repaired by incision.
5. Indications for surgery for acute injury of the ankle joint complex
The indications for surgery to fix the lower tibiofibular joint are: (1) unrepaired triangular ligament injury of the inner ankle, with the fracture line of the fibula more than 3 cm above the horizontal gap of the ankle joint; (2) proximal fibula fracture without fixation combined with injury of the lower tibiofibular joint; (3) old lower tibiofibular separation; (4) unstable repositioning of the lower tibiofibular joint. The Cotton test and the stress external rotation test are often used to determine the stability of the lower tibiofibular joint intraoperatively.
Cotton test refers to fixing the distal tibia after fixing the internal and external ankle fracture, and gently pulling the fibula outward with a pointed hook and observing, if the movement is more than 3~4mm, it indicates a significant lower tibiofibular instability and needs to be fixed.
It is also possible to perform ankle stress external rotation test after fixation of the internal and external ankle fractures. If the tibiofibular gap is wider than before by >3mm on fluoroscopic lower ankle cavity X-ray, it is considered unstable and requires fixation of the lower tibiofibular union.
Some scholars believe that the anatomical characteristics of the deltoid ligament, especially the deep layer, make it difficult to repair, and in the past, simply fixing the fracture without repairing the deltoid ligament could also achieve better clinical results, advocating that repair of the deltoid ligament is not needed unless there is a deltoid ligament embedded in the medial space of the ankle joint leading to difficulty in repositioning before considering incision and exploration.
And there are many scholars who believe that if the deltoid ligament is injured and does not affect the stability of the ankle joint, conservative treatment can be considered, while when the deltoid ligament is completely ruptured especially in the deep layer, recent in vitro biomechanical tests have confirmed that it will significantly affect the stability of the ankle joint, such as fixation by plaster or brace and expecting its own healing, it is often difficult to achieve the ideal result, for one, the tension is not enough and it is easy to The second is often a scar repair with poor mechanical strength and elasticity of the ligament; therefore, it is believed that surgical repair of deltoid ligament rupture should be performed, especially in young patients, athletes and patients with high functional requirements.
The authors believe that the most important basis for deciding whether to repair or not is the stability of the ankle joint. If a patient with a combined simple external or posterior external ankle AO fracture type B without significant inferior tibiofibular joint injury has medial ecchymosis and pressure pain, and the medial gap of the ankle joint is still widened by 3 to 4 mm or more after fracture fixation and stress external rotation test, medial instability is considered and incisional repair is required.
If the ankle joint is combined with an AO type C fracture of the lateral or posterior ankle, the triangular ligament has been broken first and is usually accompanied by the rupture of the interosseous ligament in the inferior tibiofibular complex. If the medial space of the ankle joint is still widened by 3~4mm or more after the fracture is fixed and the stress external rotation test is performed, the triangular ligament and the inferior tibiofibular complex should be considered for surgical treatment.
6. Treatment of acute injury to the ankle joint complex
If there is no instability of the ankle joint, the acute injury of the complex can be treated conservatively with 6~8 weeks of cast or brace immobilization followed by gradual weight bearing. If the conditions listed above as indications for surgery are present, surgical treatment is required to restore stability to the ankle joint.
The inferior tibiofibular joint fixation is usually made with l to 2 cortical screws of 3.5 to 4.5 mm in diameter (in general, 2 screws or 1 thicker screw provides more stability) immediately above the inferior tibiofibular joint, parallel to the tibial talar joint surface and inclined 25o to 30o from posterior to anterior, fixing the 3 cortical layers (bilateral fibula and lateral tibial cortex) with the tip of the screw in the tibial medullary cavity. The purpose is to accommodate the normal micro-movement of the inferior tibiofibular joint when the ankle joint is moving, so that screw fracture is not easy to occur; the screw can also penetrate 4 layers of cortex, one can provide better stability, and the second is that if screw fracture occurs, the broken nail can be easily removed from the medial tibial window.
The main reason for using cortical bone screws is to maintain the normal position of the inferior tibiofibular joint rather than to put pressure on it, thus narrowing the inferior tibiofibular joint and limiting the dorsiflexion of the ankle joint. The lower tibiofibular joint should be fixed with the ankle in dorsal extension because the talar body articular surface is slightly wider anteriorly and narrower posteriorly, thus avoiding the narrowing of the ankle cavity that could lead to dorsiflexion.
It has also been suggested in the literature that the position of the ankle joint during inferior tibiofibular fixation does not affect function. In addition to screws, tibiofibular hooks can be considered for joint fixation of the lower tibiofibula. The tibiofibular hook is hooked posteriorly to the fibula and the ring is fixed anteriorly to the tibia and secured with cancellous screws through the ring. The advantage is that it allows for normal micromovement of the inferior tibiofibular joint and is less prone to fracture.
The disadvantage is that the stability of the lower tibiofibular joint is not maintained as well as that of the screws. Alternatively, one to two 4.0 mm or 4.5 mm resorbable screws can be used to fix the inferior tibiofibular, which has the advantage of avoiding secondary surgical removal of the internal fixation. This is particularly useful in proximal fibular fractures combined with inferior tibiofibular union and deltoid ligament injuries.
Recently, the clinical use of high-strength sutures for fixation of the inferior tibiofibular joint has become more widespread, and the advantages reported in the literature include earlier return to daily activities, but the reliability of fixation is still controversial.
Most of the literature suggests that the inferior tibiofibular joint screws should be routinely removed after surgery to avoid restricting the ankle joint activities or causing screw fracture, but the time should not be too early to prevent the inferior tibiofibular joint from separating again because it has not yet healed, and it is more appropriate to remove the screws after 8-12 weeks after surgery.
The screws should be removed after 8-12 weeks postoperatively. Before removal, the weight-bearing of the ankle joint should be restricted to avoid screw fracture. It has been suggested that postoperative weight-bearing is permissible with screw fixation of the 3-layer cortex and that the screws can be retained until they are removed for internal and external ankle fixation, with no significant adverse consequences. For repair of the deltoid ligament, an additional medial incision is made, with a 4-5 cm longitudinal incision centered 2 cm anteriorly below the tip of the medial ankle.
The skin is incised subcutaneously, taking care not to injure the saphenous vein and the accompanying saphenous nerve at the anterior border of the medial ankle. If the injury to the deltoid ligament is severe, a complete tear of the internal ankle capsule is visible, and the bony structures of the internal ankle and its injured superficial and deep deltoid ligaments are clearly visible.
If the injury is mild, the superficial tendon sheath of the posterior tibial tendon should be incised transversely, and the deeper layer of the tendon sheath, the superficial layer of the deltoid ligament, should be seen by pulling away the superficial layer.
After revealing the ligament, the rupture site is divided into three categories: one is from the inner ankle stop; the other is from the middle; and the third is from the talar stop. The first type of injury was repaired by screwing in two absorbable or metal anchors at the medial ankle stop. Those broken from the middle are repaired directly with 1-0 absorbable sutures.
Ruptures from the talar stop are repaired by screwing two absorbable or metal anchors through the stop. In general, ligament exploration and prepositioning of anchor nails and sutures are best performed before fixation of the external ankle fracture, so that it is not yet repositioned and the internal ankle gap is wider and easier to operate, while the tensioning and knotting of sutures should be performed after fixation of the external ankle fracture.
When tying the suture, attention should be paid to keep the original ligament length slightly shortened to maintain a suitable medial gap in the ankle joint through direct visualization, and not to tie it too tightly to avoid too much ligament shortening and affecting the later functional recovery.
After the deep deltoid ligament repair, a stress external rotation test was performed under fluoroscopy. If the test was negative, the repair effect was satisfactory; if the test was still positive, the suture was checked to see if it was too loose and needed to be re-treated.
Postoperatively, a short leg brace in 90° ankle dorsiflexion position was applied to immobilize the affected ankle for 4 weeks, during which the patient was instructed to actively extend and flex the toes 100 times a day and actively extend and flex the ankle joint, but not more than 10°, 10 times a day.
After 4 weeks, the active ankle angle was increased to 30° per day, still 10 times per day. For those who did not have inferior tibiofibular fixation, if the X-ray showed scab formation, partial weight-bearing on crutches was allowed at 6 weeks after surgery, and full weight-bearing at 8 weeks after surgery.