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Deltoid ligament injury; Unstable ankle fracture; Bimalleolar equivalent ankle injury; Ankle fracture; Syndesmotic screw stabilization; Primary repair deltoid

Introduction

External rotation ankle fractures that disrupt the medial and lateral aspects of the ankle are challenging injuries for foot and ankle surgeons. In injury patterns in which the medial and lateral malleolus have obvious fractures, open reduction-internal fixation (ORIF) of both fractures is the standard of care. However, in the case of a lateral malleolus fracture with a deltoid ligament injury, known as a malleolar equivalent injury, there continues to be debate on whether or not to primarily repair the deltoid ligament or use a syndesmotic screw fixation to assist in stabilizing the ankle mortise [1-8]. When surgically repairing an ankle fracture one goal is to restore the stability of the ankle joint. The osseous injury that occurs during an ankle fracture can be accompanied by a ligamentous injury, specifically to the deltoid ligament complex.

Previous research is conflicting and has not come to a universal conclusion whether there is a need to repair the deltoid ligament with ankle fracture fixation to restore ankle stability [9-16]. Syndesmotic screw stabilizaiton offers the advantage of not having to make an additional incision since the lateral incision has already been made for the lateral malleolus ORIF. It does have the disadvantage of increasing the likelihood for additional surgeries for removal of the screw and the potential for malreduction of the syndesmosis [7]. Whereas deltoid ligament repair has the advantage of reducing and directly repairing the injured structure along the medial ankle for more of an anatomic reduction. The need for a second incision and increased operating room time are definitive disadvatages for the repair. Regardless of the technique, the ultimate goals for treatment of these unstable ankle injuries is to achieve anatomic reduction and restore ankle joint contact characteristics in order to decrease the risk for post-traumatic arthritis in the future. The purpose of this study was to evaluate the ankle joint contact characteristics within a cadaveric setting with a normal ankle, syndesmotic screw stabilization, and primary repair of the deltoid. Our hypothesis is that the deltoid ligament repair would more closely replicate normal ankle joint contact characteristics compared to the syndesmotic stabilization.

Methods and Materials

No IRB was required lfor this cadveric study. Five fresh frozen cadavers utilized for this study. The limbs were stored at -20虋C and subsequent preparation and testing was done after specimens had been thawed to room temperature. The specimens were examined for any indications of previous surgeries or pathology that could affect testing. None of the specimens were found to have any degenerative changes of the ankle joint or any anatomic pathology that could affect testing. The cadavers were thawed prior to the testing and the irrelevant soft tissue structures were carefully dissected along the posteiror, anterior, lateral, and medial ankle. Initial dissection preserved the ligamentous structures of the ankle joint complex. For each specimen testing, the room temperature and humidity was recorded. For each specimen, the ankle under 3 conditions: (1) Normal ankle, (2) Transected deltoid ligament off the medial malleolus with a syndesmotic screw stabilization, and (3) Transected deltoid with a direct repair of the deltoid ligament. The testing consisted of cutting Fujifilm Prescale Super Low Film (Fujifilm Medical Systems, Tokyo. Japan) to the approximate shape of the specimen’s superior articular surface of the talus. The film was then carefully sealed to ensure no liquid would contact the film per the manufacturer’s instructions. The initial testing was performed on the Normal Ankle. The super-low contact film was carefully placed from the anterior aspect and secured within the ankle joint. With each specimen secured in place in a custom-built specimen holder, an axial load of 100 psi was applied (Figure 1). Immediately after each individual speciem was tested, the film was carefully removed, labeled, and set aside in a clean and dark cabinet.

Figure 1: Axial Loading Normal Ankle.

Once the testing of the “Normal Ankle” was completed for each specimen, the deltoid ligament was carfully completely disected off of the medial malleolus (Figure 2). With the fibula left intact, (this would replicate rigid internal fixation with anatomic reduction hence the reason we elected not to fracture the fibula), next the syndesmotic screw stabilization was performed by placing a 2.5mm drill bit starting in the lateral aspect of the lateral malleolus approximately 2-3cm proximal to the ankle joint (Figure 3). The talus was properly reduced within the ankle mortise. The drill bit was angled approximately 30 degrees anteriorly, advanced into the tibia to exit along the center aspect of the tibia. A 3.5mm fully-threaded stainless steel non-compression syndesmotic screw was then placed enganging all 4 cortices (DePuy Synthes, Rayham, MA, USA). The super-low contact film was carefully placed from the anterior aspect and secured within the ankle joint. With each specimen secured in place, an axial load of 100 psi was once again applied. Immediatley after each individual speciem was tested, the film was carefully removed, labeled, and set aside in a clean and dark cabinet. Finally, the specimens were tested utilizing a primary repair of the deltoid ligament. The syndesmotic screw was removed. A 3.5mm suture anchor (Arthrex, Naples, FL, USA) was placed along the anterior colliculus of the medial malleolus. The talus was properly reduced within the ankle mortise. The suture was passed through the deltoid ligament complex, advanced proximally to the medial malleolus and secured with five suture knots (Figure 4). The super-low contact film was carefully placed from the anterior aspect and secured within the ankle joint. With each specimen secured in place, an axial load of 100 psi was once again applied. Immediately after each individual speciem was tested, the film was carefully removed, labeled, and set aside in a clean and dark cabinet. After testing of each specimen was complete, each of the Super Low films were scanned into a PC using an Epson Perfection V370 Scanner (Epson, Nagano, Japan). The films were analyzed for average pressure, maximum highest pressure, and pressed area using fuji film FPD-8010E Version 2.5.0.2 software for windows.

Figure 2: Transected Deltoid Ligament.

Figure 3: 2.5mm Drill bit demonstrating syndesmotic stabilization screw location approximately 3.0cm proximal and parallel to the ankle joint.

Figure 4: Deltoid ligament repair with suture anchor.

Results

The films were analyzed for average pressure, maximum highest pressure, area of high pressure and measured area using fuji film FPD-8010E Version 2.5.0.2 software for windows (Table 1) (Figure 5). The average pressure for the Normal Ankle was 0.60 Mpa (range 0.36 to 0.94 Mpa), syndesmotic screw stabilization 0.70Mpa (range 0.48 to 0.96), and the deltoid ligament repair was 0.54 Mpa (range 0.37 to 0.83). Statistical analysis demonstrated no significant differences between groups (one-way ANOVA, p = 0.495; Tukey HSD post-hoc comparisons, all p >0.90). between the two fixation groups compared to the Normal Ankle group. (Figure 6) The Highest Maximum Pressure average for the Normal Ankle was 2.15 Mpa (range 0.91 to 3.06), 2.11 Mpa (range 1.08 to 3.06) for the syndesmotic screw fixation, and 1.38 Mpa (range 0.68 to 2.18) for the deltoid primary repair. No statistically significant differences were identified (one-way ANOVA, p = 0.318; Tukey HSD post-hoc comparisons, all p > 0.55) between the two type of repair. (Figure 7) The average Area of High Pressure for the Normal Ankle was 188.6 mm² (range 2-435), 194.8 mm² (range 10-581) for the Syndesmotic Screw Stabilization, and 139.0mm² (range 1-498) for Primary Deltoid Repair. Statistical analysis revealed no significant differences among the groups (one-way ANOVA, p = 0.958; Tukey HSD post-hoc comparisons, all p > 0.98). (Figure8) The average measured area for contact pressure on the normal ankle was 265.2mm (range 61-513), 307.2mm (range 47-802) for the Syndesmotic Screw Stabilization, and 239.6mm (range 34– 685) for the Primary Deltoid Repair. Statistical analysis revealed no significant differences between conditions (one-way ANOVA, p = 0.922; Tukey HSD post-hoc comparisons, all p >0.87). (Figure 9)

Table 1: Results of the contact pressure computer analysis comapring the Normal Ankle, Syndesmotic Screw, and Deltoid Repair

Figure 5: Contact Pressure Film. A: Normal Ankle, B: Syndesmostic Screw Stabilization, C: Deltoid Primary Repair.

Figure 6: Boxplots illustrating the distribution of average pressure values (MPa) for the Normal Ankle (n = 5), Syndesmotic Screw Stabilization (n = 5), and Primary Deltoid Repair (n = 5) groups. The boxes represent the interquartile range with the median indicated; whiskers denote the full observed range. Although the Normal Ankle and Syndesmotic Screw Stabilization groups exhibited higher median pressures compared with the Primary Deltoid Repair group, substantial overlap was present among all groups.

Figure 7: Boxplots showing the distribution of highest maximum pressure (MPa) for the Normal Ankle (n = 5), Syndesmotic Screw Stabilization (n = 5), and Deltoid Primary Repair (n = 5) groups. The boxes represent the interquartile range, with the median indicated; whiskers denote the full observed range. Although the Normal Ankle and Syndesmotic Screw Stabilization groups demonstrated higher median pressures than the Deltoid Primary Repair group, substantial overlap was present among all groups.

Figure 8: Boxplots showing the distribution of highest maximum pressure (MPa) for the Normal Ankle (n = 5), Syndesmotic Screw Stabilization (n = 5), and Deltoid Primary Repair (n = 5) groups. The boxes represent the interquartile range, with the median indicated; whiskers denote the full observed range. Although the Normal Ankle and Syndesmotic Screw Stabilization groups demonstrated higher median pressures than the Deltoid Primary Repair group, substantial overlap was present among all groups.

Figure 9: Boxplots illustrating the measured contact area (mm²) for the Normal Ankle (n = 5), Syndesmotic Screw Stabilization (n = 5), and Deltoid Primary Repair (n = 5) groups. The boxes represent the interquartile range with the median indicated; whiskers denote the full observed range. Although the Normal Ankle group demonstrated slightly larger median contact areas compared with the Deltoid Primary Repair group, there was substantial overlap among all three groups. Statistical analysis revealed no significant differences between conditions (one-way ANOVA, p = 0.922; Tukey HSD post-hoc comparisons, all p > 0.87).

Discussion

Both the deltoid ligament and syndesmosis play a crucial role in ankle stabilization and preserving the ankle joint contact characteristics. Foot and ankle surgeons need to diligently evaluate for instability intraoperatively in order to prevent malalignment and reduce the risk for post traumatic arthritis in the future. There continues to be debate about ideal treatment for medial deltoid inuries in bimalleolar equivalent ankle fractures [1-9,12,14,15,17-27]. While some surgeons opt for a direct repair of the deltoid ligament, others prefer medial stabilization through syndesmotic repair. Both with the goal of anatomic reduction and restoration of ankle joint contact characteristics to decrease the risk for post-traumatic arthritis. Jones and Nunley retrospective study of 27 patients comparing bimalleolar equivalent ankle fractures treated with lateral malleolus open reduction and internal fixation with trans syndesmotic fixation versus lateral malleolus ORIF with deltoid ligament repair⁴. Fifteen patients were treated with trans syndesmotic fixation and 12 were treated with deltoid ligament repair. Their study found no statistically significant differences between the 2 groups. However, all patients in the syndesmotic fixation group underwent a subsequent procedure for removal of the syndesmotic fixation. The authors concluded that deltoid ligament repair at the time of lateral malleolus fixation demonstrates outcomes comparable with lateral malleolus fixation with syndesmotic fixation for bimalleolar equivalent ankle fractures. Whitlock et al retrospectively compared functional outcomes of distal fibula fractures treated with ORIF and either deltoid repair, syndesmotic repair or combined fixation repair [26]. Their study included 108 subjects. The syndesmotic repair group consisted of 66 patients who had fixation with either suture button or screw placement. Sixteen patients were in the deltoid ligament repair group and 26 patients underwent combined fixation repair. Mean AAOS-FAM scores were collected and analyzed. No significant difference was found among the three groups in regards to patient reported outcomes. The syndesmotic repair group was found to have a higher rate of reoperation both for symptomatic and asymptomatic hardware removal as expected. Wang et al performed a systematic review looking at the role and outcome of deltoid ligament repair of ankle fractures with syndesmotic instability [25]. The study consisted of 9 articles, two of which looked at malreduction rates and found that deltoid ligament repair offered significantly lower malreduction rates when compared to non-repair groups. One study by Wu et al compared malreduction rates between those who had deltoid ligament repair and those who underwent reduction by trans syndesmotic screw fixation. The malreduction rate was found to be 9% for the deltoid ligament repair group versus 45% in the syndresmotic repair group. Sogard et al found similar results in their systematic review and meta-analysis. Five level-3 studies were reviewed and found to have higher rates of malreduction and hardware removal within the syndesmotic fixation group compared to the deltoid repair group [7]. They also found that there was no significant difference in wound complications, reoperations and functional outcomes using AOFAS and VAS scores when comparing the two groups. Yu et al retrospectively looked at 106 patients with ankle fractures associated with deltoid ligament ruptures²⁷. Comparable to previous biomechanical study, they found that the location of the deltoid rupture varies. Almost 53% were found to have deltoids avulsed from the talarinsertions, while 28% and 19% were found to be from the medial malleolus and midsubstance respectively. Their technique for deltoid repair was based off their intraoperative findings and location of rupture. With an average follow up of 27 months, they found that the medical clear space was <1 mm and patients had no evidence of post traumatic arthritis on final radiographs. Limitations to the present study include small sample size, cadaveric nature and use of only screw syndesmotic fixation. The specimens where only tested during the midstance of gait as well with a single axial compression. We elected not to fracture the fibula or create a posterior-type of injury. This study does not take into account varying locations and techniques for repairs of deltoid ligament injuries. As mentioned previously, Yu et al found that almost 53% of deltoid ruptures were noted to be avulsions from the talus. In our study, the deltoid ligament was transected off the medial malleolus and was primarily repaired using a suture anchor in the medial malleolus. More research is needed to determine the effect rupture location and repair techniques have on adequate ankle stabilization. While the authors used direct visualization for syndesmotic screw placement, no radiographs were used to verify placement. There are inherent variations between cadaveric specimens. Although attempts are made to simulate conditions close to real life, cadaveric testing cannot replicate patient anatomy and exact mechanisms of injury.

The purpose of this study was to evaluate the ankle joint contact characteristics within a cadaveric setting with a normal ankle, deltoid rupture, syndesmotic screw stabilization, and primary repair of the deltoid. Our hypothesis was that the deltoid ligament repair would more closely replicate normal ankle joint contact characteristics compared to syndesmotic stabilization. The results of our cadaveric study disproved our hypothesis as we found that there was no significant difference between the deltoid ligament repair group and the syndesmotic screw fixation group. Research has shown that both deltoid ligament repair and syndesmotic repair can stabilize the ankle mortise with successful long terms outcomes and high patient satisfaction. It’s important to understand however that lack of anatomic reduction through inadequate fixation or malreduction caused by trans syndesmotic fixation, can have negative long-term outcomes and increase the risk for post traumatic arthritis in patients with bimalleolar equivalent ankle fractures.

Acknowledgements

Thank you to The Podiatry Foundation for their research grant funding this research project.

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