Insights on Repairing Ankle Syndesmosis Injuries With Screws

The easy part of evaluating an ankle following trauma is identifying bone injuries that are visible on X-rays or computed tomography (CT) studies. Soft tissue damage is mainly determined by physical examination and/or magnetic resonance imaging (MR 4000 I). X-rays may be helpful to identify soft tissue injury when there is profound subluxation of bones. When there is subtle injury, X-rays may have little benefit. The soft tissue structures of the ankle that are at risk of injury include the lateral ankle ligaments, deltoid ligament, and the syndesmosis. Ankle joint cartilage damage and tendon damage can also occur.

The ankle syndesmosis is comprised of the anterior inferior tibiofibular ligament (AITFL) and posterior inferior tibiofibular ligament (PITFL), the interosseous ligament (IL), and the transverse tibiofibular ligament (TTFL). The AITFL runs between the anterior aspect of the tibia and fibula and it functions to provide stability, resisting external rotation of the fibula during dorsiflexion of the ankle. The AITFL is usually the most susceptible part of the syndesmosis to injury and is the weakest aspect of the syndesmosis complex. The PITFL is a stronger ligament than the AITFL and connects the posterior aspect of the tibia and fibula. It functions to prevent posterior displacement of the fibula during plantarflexion of the ankle. The IL is a dense fibrous aspect of the interosseus membrane that runs the entire distance between the tibia and fibula. Its main function is to prevent widening or separation between the tibia and fibula. The last part of the syndesmosis complex is the TTFL, which is deep to the PITFL, adding more stability to the posterior aspect of the syndesmosis.

Physical Exam and Imaging Pointers

There are a number of physical examination tests to determine if there is a syndesmosis injury. First is the dorsiflexion/external rotation test. With the foot dorsiflexed to at least 90 degrees, the patient stabilizes the lower leg while externally rotating the foot. Pain in the region of the syndesmosis is a positive test. Perform the squeeze test by starting to squeeze the tibia and fibula together, starting in the proximal leg and advancing distally to the malleoli. A positive test is when there is pain in the region of the syndesmosis. Next, perform a dorsiflexion compression test by having the patient stand, and during weight-bearing, the examiner will squeeze the malleoli together while the patient is actively pushing forward to dorsiflex of the ankle. A positive test is when there is decreased pain or an increased ankle dorsiflexion. These tests may not be practical in the acute trauma setting where there are associated fractures, severe swelling, trauma blisters, etc. MRI can rule out a suspected syndesmosis injury in these instances.

X-rays will always be ordered and reviewed in an ankle injury. When assessing for a syndesmosis injury, scrutinize the position of the talus in the ankle joint. The first parameter is the tibiofibular clear space. One can measure the tibiofibular clear space on an AP or mortice view of the ankle 1 cm above the tibial plafond. This area is defined as the horizontal distance between the deepest
point of the fibular groove or posterior tibial tubercle and the medial edge of the distal fibula. Greater than 5mm is suggestive of a syndesmosis injury. Measure tibiofibular overlap on the AP view. Normally, there should be at least 10 mm of overlap; reduced overlap may indicate syndesmotic injury. With a weight-bearing X-ray (if feasible), the tibiofibular overlap should be more than 6 mm. 

Finally, medial clear space measures the space between the talus and the medial malleolus. A widened medial clear space may suggest instability in the syndesmosis and surrounding structures. Consider a contralateral X-ray comparison. One can also take stress X-rays, which are applicable only in high ankle sprains or chronic ankle instability scenarios.

A Closer Look at Syndesmosis Injuries

Neglected or missed syndesmosis injuries can lead to post-traumatic arthritis. We have all learned that a 1mm widening of the ankle mortise (doubling the amount of motion in asymptomatic individuals) decreases the tibiotalar joint contact area by 42%, causing instability, with resultant osteoarthritis.¹ That is why it is critical to have a low threshold for treatment, especially in the surgical arena.

Syndesmosis injuries are usually associated with rotational injuries. Approximately 50% of Weber B ankle fractures and all Weber C fractures have a syndesmosis injury. Even though we don’t immediately think about syndesmosis injuries in pilon fractures, Haller and colleagues have reported that 15% of pilon fractures (108/735) had a syndesmosis injury.² So, the take-home message is never to assume and always evaluate the syndesmosis in ankle trauma.

For this article, let us assume that we are managing ankle trauma with associated fractures. Syndesmosis injuries can include purely soft tissue ligamentous disruption and/or avulsion fractures. When the AITFL avulses bone off the tibia, this is called a Tillaux-Chaput fracture. If the avulsion occurs from the fibula, then it is called a Wagstaffe fracture. When the PITFL avulses bone from the tibia, this is a Volkmann fracture. The PITFL avulsion from the fibula is rare and undefined.

When there is a suspected syndesmosis injury, how does one evaluate for that intraoperatively? The following assessment studies include the Cotton test (hook test). Do this under fluoroscopy, using a hook to pull the fibula away from the tibia and check for instability or separation of the two bones. Next, do an external rotation stress test under fluoroscopy looking for an increase in medial clear space and/or visual signs of separation of the tibial and fibula. Conduct a dorsiflexion stress test under fluoroscopy to determine if there is any displacement of the talus and/or widening between the tibia and fibula.

When there is a confirmed syndesmosis injury and surgery is indicated, there are 3 basic approaches for repair. The most common intervention is placing a fixation device holding the fibula and tibia together. If there is an avulsion fracture that is large enough for open reduction and internal fixation (ORIF), then using a screw or other fixation device to fixate the fracture can indirectly repair the ligament as it is not torn. Finally, one can do a direct ligamentous soft tissue repair with sutures, though this is less frequently performed.

The Advantages of Screw Fixation

As with most reconstructive foot and ankle surgeries, whether elective or trauma-related, there is usually controversy as to the best method for repair and/or fixation. The main goal of syndesmosis repair is to restore stability, alignment, and function of the ankle joint to ensure proper biomechanics, prevent degenerative changes, and allow a return to normal activities without chronic pain or instability.

Some of the controversies related to tibiofibular transfixation include endobutton versus traditional screw fixation. Furthermore, in the screw fixation group, there is controversy as to the number of screws and cortices fixated. Proponents of endobutton fixation state there is less rigidity in the construct, which allows the syndesmosis to have some normal give and take. Proponents will also say the endobutton avoids a second surgery to remove the hardware.

My personal preference is screw fixation. Postoperatively, I like to see the entire implant on X-ray to determine if there is a problem. So, for example, let’s say the patient is having persistent pain after ORIF of an ankle fracture and syndesmosis repair. X-rays facilitate a more straightforward interpretation with screw fixation looking for periosteal reaction around the screw head, radiolucency around the threads, the screw backing out, or frank fracture of the screw. With endobutton repair, all you can see are the metallic buttons and that may not help you with identifying the integrity of the fixation. Secondly, with the endobutton technique, there are times when you may have difficulty getting the button to lie flat on the medial tibia, and you need to make an incision on the medial aspect of the lower leg to flip the button. This could lead to accidental injury to the saphenous nerve or vein.

Next, I would like to review some of the literature related to the topic. For screw fixation, Li and colleagues state that screw placement level above the ankle (< 1cm, 2–3 cm, or > 3cm) does not affect the clinical outcomes in ankle fractures with syndesmotic injury.³ So that takes the guesswork out.

What about the number of cortices? Kaftandziev and colleagues performed a comparative study of 3- or 4-cortex screw transfixation for syndesmosis injury. They found no statistically significant differences between the 2 groups in clinical outcome or resultant screw breakage. Furthermore, researchers found the group with broken screws had the best clinical outcome and no widening of the syndesmosis after screw removal. They recommend performing routine screw removal.4 In my mind, if screw removal is necessary, it is simple and has very low morbidity.

Most of the literature, I have noted, including meta-analyses, will state that the endobutton technique is superior due to the fact that the reoperation rate is higher with the screw fixation group due to hardware failure and subsequent removal. Personally, and based on my experience, I recommend leaving the broken screw intact unless it is backing out and the screw head is an irritant. From a functional standpoint, I feel it is still a toss-up between the 2 groups.

In Conclusion

Surgeons need to promptly identify and treat syndesmosis injuries in ankle trauma. Anatomic fibular alignment in the tibial incisura is critical. We need to be mindful of overtightening, although this concept is debatable, according to Tornetta and colleagues,5 and avoid fibular rotation during repair when using reduction forceps. Careful analysis of technique and fixation options by each surgeon can go a long way in optimizing outcomes in these cases.

Dr. Fishco is a Fellow of the American College of Foot and Ankle Surgeons and a faculty member for the Podiatry Institute. He practices in Anthem, AZ.

Lead photo courtesy of Spencer Monaco, DPM

References
1. Ramsey, PL, Hamilton W. Changes in tibiotalar area of contact caused by lateral talar shift. JBJS. 1976;58-A(3):356-357.
2. Haller JM, Githens M, Rothberg D, Higgins T, Barei D, Nork S. Syndesmosis and Syndesmotic Equivalent Injuries in Tibial Plafond Fractures. J Orthop Trauma. 2019;33(3):e74-e78.
3. Li JK, Yu Y, Wu YH, Wang J, Zeng XT, Zhao JG. Does the level of syndesmotic screw reinsertion affect clinical outcome after ankle fractures with syndesmotic instability? Orthop Surg. 2023;15(1):247-255.
4. Kaftandziev I, Spasov M, Trpeski S, Zafirova-Ivanovska B, Bakota B. Fate of the syndesmotic screw--Search for a prudent solution. Injury. 2015;46 Suppl 6:S125-S129.
5. Tornetta P 3rd, Spoo JE, Reynolds FA, Lee C. Overtightening of the ankle syndesmosis: is it really possible? J Bone Joint Surg Am. 2001;83(4):489-492.