What Is a Syndesmosis Fracture and How Is It Treated?

A syndesmosis fracture refers to a fracture of the ankle that involves damage to the syndesmosis, the fibrous joint connecting the lower tibia and fibula just above the ankle. The term is sometimes used loosely for a “high ankle sprain” without a fracture, but in practice, syndesmotic injuries and ankle fractures frequently travel together, particularly in rotational injuries. What makes syndesmosis involvement significant is that it changes nearly everything about how an ankle fracture is managed: the diagnosis is harder to pin down, the surgery is more involved, and the recovery takes longer than a typical ankle break.

What the Syndesmosis Actually Does

The syndesmosis is held together by a set of ligaments: the anterior inferior tibiofibular ligament (often shortened to AITFL), the posterior inferior tibiofibular ligament (PITFL), the interosseous ligament, and the interosseous membrane that runs between the two bones higher up the leg. Together, these structures prevent the fibula from shifting sideways and keep the ankle mortise stable, which is the bony bracket that the talus bone sits in when you bear weight.¹ When the syndesmosis is disrupted, the mortise widens and the talus loses its snug fit. Even a couple of millimeters of widening alters how forces travel through the joint, which is why even moderate syndesmotic injuries can cause prolonged pain and eventual arthritis if not corrected.

Biomechanical testing has shown that the AITFL is the most critical structure resisting outward rotation of the foot. In cadaver studies, cutting just this one ligament reduced resistance to external rotation by about a quarter, while internal rotation remained relatively stable until most of the syndesmotic complex was destroyed.² This explains why external rotation injuries are the classic mechanism for this type of damage and why isolated AITFL tears are the most common starting point.

How These Injuries Happen

The two main forces that damage the syndesmosis are external rotation of the foot and forceful dorsiflexion (the foot being pushed upward), especially in combination.³ Both movements push the wider front portion of the talus into the mortise, forcing the tibia and fibula apart. This is why the injury is sometimes called a “high ankle sprain,” since the damage occurs above the ankle joint itself rather than at the lateral ligaments on the outside.

The exact position of the foot at the moment of injury matters. A cadaver study found that when the foot was everted (rolled outward) during external rotation, the AITFL failed in isolation, reproducing the classic high ankle sprain. When the foot was in a neutral position under the same rotational force, the deltoid ligament on the inner side of the ankle failed instead.⁴ Forced dorsiflexion on its own can also cause the injury, as can external rotation applied to an already dorsiflexed, loaded ankle.⁵ In sports, these mechanisms often happen simultaneously: a planted foot gets trapped while the body rotates, or another player lands on the back of the heel.

Why Diagnosis Is Tricky

Syndesmotic injuries are notoriously difficult to diagnose with clinical tests alone. A systematic review and meta-analysis found that no single bedside test is both highly sensitive and highly specific. The best test for ruling out syndesmosis injury was direct palpation of the syndesmotic ligaments, which caught about 92% of true injuries but also flagged many false positives. The squeeze test, where the examiner compresses the tibia and fibula together higher up the calf, was the most specific at around 85 to 88%, meaning it rarely gave a false alarm but missed a fair number of real injuries.⁶⁷

One practical clinical sign stands out: the inability to perform a single-leg hop on the injured side had the highest sensitivity of any presentation finding in one study, catching about 89% of syndesmosis injuries.⁸ Pain that seems disproportionate to the visible injury was also a useful clue, with reasonably high specificity. A clinician’s overall impression, combining all tests and the mechanism of injury, had a sensitivity around 73% and a negative predictive value near 89%, meaning that if an experienced examiner suspects the syndesmosis is fine, it usually is.⁹ But the reverse is less reliable, so imaging typically follows when there is any suspicion.

Imaging and the Limits of X-Rays

Standard X-rays are the first step but are poor at detecting syndesmotic injuries. A diagnostic meta-analysis found that plain radiographs had a pooled sensitivity of only about 53%, meaning they miss roughly half of true syndesmotic disruptions, although specificity was very high at around 98%.¹⁰ In practical terms, if an X-ray shows a widened syndesmosis, you can trust it. But a normal-looking X-ray does not rule the injury out. CT scans improve detection and are better at identifying malreduction after surgery.¹¹

MRI offers the best sensitivity at around 93%, which makes it the strongest tool for confirming or excluding a syndesmotic injury when clinical suspicion is high.¹² For subtle or borderline cases, weight-bearing CT is an emerging option. When you scan the ankle under the patient’s body weight, an unstable syndesmosis widens in a way that static imaging can miss. Three-dimensional volume measurements taken up to 5 centimeters above the ankle joint line have shown sensitivity above 95% and specificity above 83% for detecting instability.¹³ Adding an external rotation stress during the weight-bearing scan further increases the gap between injured and uninjured sides, which may help catch the most subtle cases.¹⁴

Stable Versus Unstable and What That Means for Treatment

The single most important question after diagnosis is whether the syndesmosis is stable or unstable. This distinction drives the entire treatment plan. Syndesmotic injuries are generally graded from I to III: grade I involves a stretch or partial tear of the AITFL without frank instability, grade II is a more extensive tear that may or may not leave the joint unstable, and grade III is a complete disruption of the syndesmotic complex with clear instability.

Stable injuries, including grade I and stable grade II injuries, are typically managed without surgery. European consensus guidelines recommend three weeks of non-weight-bearing in a below-knee cast, followed by progressive rehabilitation with proprioceptive exercises.¹⁵ Athletes treated conservatively for stable injuries tend to return to sport faster than those who need surgery.¹⁶

Unstable grade II and all grade III injuries require surgical fixation. Leaving an unstable syndesmosis unfixed allows the mortise to remain widened under load, altering how forces distribute across the ankle joint. Cadaver research has shown that even moderate syndesmotic instability produces measurable changes in joint contact mechanics, which likely explains why these injuries are prone to long-term dysfunction and post-traumatic arthritis.¹⁷

Surgical Fixation Options

When surgery is needed, the main debate is between rigid screw fixation and flexible “dynamic” fixation, typically using a suture-button device like TightRope. Both work well, and the choice often comes down to surgeon preference, cost, and patient-specific factors.

Syndesmosis screws have been used for decades. They are placed through the fibula and into the tibia to hold the joint in its reduced position while the ligaments heal. A common question is whether the screw should pass through three cortices (the two fibular cortices and the near tibial cortex) or four (through both tibial cortices as well). Biomechanical testing has found no meaningful difference in stability between the two approaches.¹⁸ A randomized trial did show that patients with three-cortex screws had less pain and better function at three months, though the difference evened out by one year.¹⁹

Whether to remove syndesmosis screws after healing is another persistent question. Many screws loosen or break on their own, and a randomized trial found no significant difference in function, pain, range of motion, or X-ray measurements at one year between patients who had their screws removed and those who did not. About three-quarters of patients in the retention group had a loose or broken screw by the one-year mark.²⁰ A broader literature review reached a similar conclusion: leaving screws in place does not appear to harm outcomes, and routine removal is not justified unless the screw is causing specific symptoms like restricted dorsiflexion.²¹

Suture-button devices offer the theoretical advantage of allowing some natural motion at the syndesmosis, which screws do not. A randomized study using CT follow-up found that screw fixation had slightly more cases of malreduction than TightRope, though the difference was not statistically significant, and functional scores and arthritis rates were comparable between groups after at least two years.²² A prospective pilot study using gait analysis found that the dynamic fixation group generated higher ankle moments during walking, suggesting slightly better biomechanical recovery, though both groups still showed impaired push-off compared to their uninjured side.²³ The dynamic fixation group in a separate retrospective study had no hardware complications, while the screw group had cases of reduction loss and screw breakage.²⁴

The Cost Question

Suture-button implants cost more upfront than screws, which complicates the comparison. One cost-effectiveness analysis found that whether the suture button was worth the extra cost depended almost entirely on how often symptomatic screws needed to be removed. If fewer than about 14% of screw patients required removal surgery, screws were more cost-effective. If the removal rate exceeded roughly 18%, the suture button won out.²⁵ A separate analysis using a 20% screw removal rate found that a single suture button was the dominant strategy in terms of cost per quality-adjusted life-year, beating out two screws, one screw, and two suture buttons.²⁶ The real-world removal rate at your institution ends up being the swing factor.

Checking Stability During Surgery

Deciding whether to fix the syndesmosis is not always obvious even with the ankle open on the operating table. Surgeons use intraoperative stress tests to check for instability. The Cotton or Hook test, where a bone hook pulls the fibula laterally under fluoroscopy, is considered more reliable than the external rotation stress test for detecting instability in ankle fractures.²⁷ A torque test, applying a measured rotational force, has shown high diagnostic accuracy: at a threshold of 3.5 millimeters of widening, it was 90% sensitive and 100% specific for injuries involving two or more torn ligaments.²⁸

One important limitation is that all of these manual tests struggle to detect isolated AITFL injuries, the mildest form of syndesmotic disruption. Direct visualization and arthroscopy outperform the Hook test and external rotation test in this scenario.²⁹ When only one ligament is torn, the joint may feel stable under standard stress maneuvers but still behave differently under physiologic loading. This is one reason why borderline cases are so challenging.

Rehabilitation and Early Weight Bearing

Traditionally, patients with surgically fixed syndesmotic injuries were kept non-weight-bearing for six weeks or longer. Recent evidence challenges this timeline. A study comparing early weight bearing (starting at two weeks after surgery) to late weight bearing (starting at six weeks) found that the early group had significantly better functional scores, less pain, and greater range of motion at six weeks post-surgery. They also returned to work and sports earlier. By six months and one year, the two groups had converged, with no significant differences in any outcome measure and no increase in complications in the early group.³⁰ The takeaway is that early weight bearing does not appear to compromise the repair, and it gets people back to their lives faster, though the long-term result is the same either way.

Return to Sport

For athletes, the central question is how long until they can compete again. A meta-analysis of elite athletes found an overall return-to-sport rate of about 96%, with an average time to return of roughly 58 days. Athletes treated without surgery returned at around 29 days on average, while those who had surgical fixation (mostly with suture-button devices) returned at about 50 days.³¹ A separate meta-analysis reported an even higher return rate of 99%, with non-operative athletes back in about four weeks and surgical athletes in about seven weeks.³²

In professional football players with unstable injuries requiring surgery, the timeline stretched further: sport-specific rehabilitation began at about 37 days, return to team training at around 72 days, and the first official match at roughly 103 days.³³ Getting back to playing and getting back to pre-injury performance are not always the same thing: in a study of competitive athletes who had surgery, all returned to athletic activity, but only about 64% reported returning to their pre-injury level of function.³⁴ Despite this, satisfaction rates were high, with nearly all patients describing their outcome as normal or nearly normal.

Complications Worth Knowing About

Heterotopic ossification, where bone forms in the soft tissue around the syndesmosis, is surprisingly common after surgical fixation. One study found that it developed in about 61% of patients who had syndesmosis screw fixation for ankle fractures. The ossification was strongly associated with screws that had loosened or broken: it appeared in 92% of patients with broken screws, 75% with loose screws, and 44% with intact screws.³⁵ A separate analysis found frank tibiofibular synostosis (complete bony bridging) in about 19% of patients, and use of syndesmosis screws was identified as a risk factor.³⁶ Whether this bone formation matters functionally is debated: some studies find restricted motion, while others report no significant effect on patient-reported outcomes. It is common enough that patients should know about it, and it occasionally requires further treatment if it limits ankle motion.

Platelet-Rich Plasma as an Adjunct

A small but growing body of evidence suggests that platelet-rich plasma (PRP) injections may speed recovery from syndesmotic injuries, at least in athletes. A randomized controlled trial in elite athletes found that those who received PRP returned to play in about 41 days compared to about 60 days in the control group, and they had less residual pain when they got back.³⁷ A separate study in rugby players with syndesmotic injury found that a single PRP injection led to faster return to play and better agility and vertical jump performance afterward.³⁸ These are small trials in high-level athletes with access to intensive rehabilitation, so how well the results translate to a recreational runner or weekend hiker remains an open question. The concept is promising but far from standard of care.

Why Accurate Reduction Matters More Than the Implant

Across the surgical literature, one theme emerges more consistently than any debate about screw size, screw number, or implant type: getting the reduction right matters most. Malreduction, where the fibula is not seated properly in its groove on the tibia, is the strongest predictor of poor outcomes. Computer-assisted navigation has been tested in cadavers as a way to improve reduction accuracy, and early results show that it can reliably restore the normal anatomy of the joint.³⁹ Weight-bearing CT is also being studied as a postoperative tool to confirm that the syndesmosis has been properly reduced, since standard X-rays can miss subtle malpositioning.⁴⁰ Whether these technologies become routine will depend on cost and availability, but the direction of the field is clearly toward more precise assessment of reduction quality rather than more elaborate hardware.