1 Introduction

The most effective option for treatment of the distal tibiofibular syndesmosis has been a highly debated topic, with many systematic reviews with or without a meta-analysis reported frequently in the literature, especially within the past 10 years.^1–5 While many individual articles have reported similar outcomes between suture-button (SB) and syndesmotic screw (SS) fixation,^6,7 many recent systematic reviews conducted have reported better overall outcomes when using the SB technique for syndesmotic fixation.^2–5 The benefits described by these reviews have included fewer reoperation rates, earlier return to sport, and better patient reported outcome measures such as the American Orthopaedic Foot and Ankle Scores (AOFAS) and Foot and Ankle Disability Index (FADI) scores. Many of these reviews, however, include randomized controlled trials containing SS fixation without standardization or specification of how the SS was implanted, with varying use of tricortical screw (TS) and quadricortical screws(QS).^3,4,8–10 Utilizing either 3 or 4 cortices for syndesmotic fixation has also been studied as a potential variable to functional outcomes when utilizing a screw for syndesmotic fixation, which would necessitate appropriate separation of these 2 methods in meta-analyses to control for potential confounding variables. Additionally, some studies used 1 syndesmotic screw while others had 2.^8,11,12

As with all review articles, bias may arise in the study selection based on predetermined eligibility criteria. With such a large body of literature on the topic of which fixation method is the most appropriate for treatment of syndesmotic injuries, it is important to include only the most relevant articles that appropriately compare the different fixation methods. The purpose of this systematic review is to determine which type of fixation method for injuries of the distal tibiofibular syndesmosis—tricortical screw fixation, quadricortical screw fixation, or suture-button fixation—results in the best overall outcomes for patients by assessing multiple clinical, radiographic, and patient-reported outcome measures (PROMs). While limiting the review to randomized controlled trials would elevate the overall evidence, this review includes cohort studies to further elucidate the conclusions reached by existing evidence regarding the differing fixation methods, rather than reporting on outcomes. A secondary aim focuses on determining the current gaps in the literature regarding fixation methods rather than contributing to the already extensive pool of general comparative outcomes.

2 Methods

3 Results

The results of the search are reported in a Preferred Reporting Items for Systematic Reviews and Meta-analysis study flowchart (Fig. 1). The original search yielded 1840 articles (PubMed: 617; Scopus: 1223) with 1254 articles remaining after duplicates were removed. After title and abstract screening, 86 articles required full-text review to determine eligibility, which ultimately resulted in 40 articles being included in the final review (19 RCTs; 21 cohort studies).

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Fig. 1 PRISMA flowchart of study selection.

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The patient demographics along with risk of bias assessment for each study are outlined in Table 2.

Of the 21 cohort studies, 15 directly compared SB to SS fixation, 3 compared TS to QS fixation, 1 compared anatomic repair of the anterior inferior tibiofibular ligament to a SS, 1 compared no screw to SS, and 1 compared posterior malleolar fixation alone to SS fixation. Only the PROMs reported by Zhu et al. were determined to have a minimal risk of bias, 3 studies had a moderate risk of bias, 7 had serious risk of bias, and 10 had a critical risk of bias. For the RCTs, 12 compared SB to SS fixation, 1 study randomized patients to receive either no screw or a SS, 1 compared TS to QS fixation, 2 compared utilizing a bioabsorbable screw to a standard SS, 1 randomized patients to either routine screw removal or a standard SS, 1 randomized patients to either anatomic repair of the AITFL or a SS, and 1 compared the use of a hook plate or SS for syndesmotic fixation. Seven of the RCTS were determined to have a minimal risk of bias, 9 were determined to have “some concern” for risk of bias, and 2 were determined to have a high risk of bias.

Clinical outcomes are reported in Table 3. Fifteen studies reported on ankle range of motion (ROM) with 1 study favoring the SB over the SS for both ankle DF and PF, 1 study favoring the SB for DF alone, 1 study favoring PF alone when comparing anatomic AITFL fixation to SS fixation, and 1 study favoring PF alone when comparing hook plate fixation to SS fixation. Additionally, 1 study favored the use of a biologic screw over a SS for both DF and PF. All 5 studies that reported on time to weightbearing compared SB to SS fixation, 3 of which reported statistical significance favoring the SB. Six studies reported on differences in return-to-work rates. Four of these studies compared SB to SS, with 1 reporting significance. The study comparing AITFL repair to SS found significance in return-to-work rates while the hook plate versus the SS study did not. Three studies compared SB to SS regarding return-to-sport rate with 1 study reporting statistical significance. Of the 15 studies that compared reoperation rates in SB versus SS patients, 3 found a statistically significant difference in favor of the SB. Fourteen studies reported on joint malreduction with 1 study comparing SB to SS reporting statistical significance.

Radiographic outcomes are reported in Table 4. Of the 5 studies that reported on anterior syndesmotic distance, 2 demonstrated results that were significant favoring the SB over the SS. One study demonstrated statistical significance between middle syndesmotic distance. For the studies that reported on syndesmotic area, 1 study demonstrated that both the SB and SS had a statistically significant difference in syndesmotic area when the operated ankle was compared to the healthy ankle. The study by Kocadal et al.⁴⁵ demonstrated a statistically significant difference between the upper syndesmotic area when comparing healthy and operated ankles in the SS group as well as a significant difference between the healthy and operated ankles for the lower syndesmotic area in the SB group. Two of the 8 studies that looked at the tibiofibular clear space between SB and SS demonstrated a statistically significant difference, while the other 6 did not. Only 1 of the 9 studies looking at tibiofibular overlap demonstrated a significant difference between the SB and SS groups. Only 2 studies looked at tibiofibular distance. The study that compared TS to QS found no significant difference; however, the study that compared SB to SS did find a significant difference. Klepacki et al.¹⁸ found a significant difference in medial clear space when comparing TS to QS fixation, while none of the SB vs SS studies found any difference. Three of the 4 studies that compared SB to SS regarding fibular rotation found a significant difference between the 2 groups that favored the SB.

Patient reported outcome measures are provided in Table 5. Of the 40 studies included, 33 studies reported PROMs across a wide variety of scoring systems. The most commonly used PROMs were the Olerud Molander Ankle Score (OMS) and the American Orthopaedic Foot and Ankle Score (AOFAS). With regard to the OMS score, 2 of the 12 studies that compared SB to SS found statistical significance in favor of the SB.^10,39 Fifteen SB vs SS studies used the AOFAS score with only 2 finding a significant difference in favor of the SB.^23,39 For studies that used the VAS pain system, 1 of 6 studies favored the SB.¹⁷ No studies comparing TS to QS showed any significant difference in any of the PROMs.

4 Discussion

This systematic review on syndesmotic fixation consolidates the extensive literature on the topic to determine the gaps that necessitate further study. Many studies found equivalent outcomes between the SB and SS, however, of those that demonstrated a significant difference, favored the SB. Only 1 study reported a statistically significant finding in favor of the SS regarding lower syndesmotic area.⁴⁵ However, this study was classified as having a serious risk of bias. This 1 radiographic parameter did not appear to correlate clinically, as none of the clinical outcomes or PROMs demonstrated a statistical significance in this study. Regarding TS vs QS, 1 study found a difference in MCS, but no other outcomes were significant when deciding to use a TS or QS.¹⁸ Additionally, this study was determined to be at critical risk of bias.

A strength of this review regards the quality assessment and number of studies examining outcomes comparing SB to SS, with the majority at serious or critical risk of bias. While oftentimes it is necessary to publish on preliminary results in the literature to justify future, higher quality studies, 11 of the 21 published cohort studies were determined to be at a critical risk of bias, 8 of which were direct comparisons of SB to SS. While the preliminary determination of confounding variables is somewhat subjective when using the ROBINS-I V2 tool (as outlined in the Methods section), it is essential across all studies for authors to try to control for confounding variables by providing demographic data and providing the appropriate information to determine if there was any significant difference in the demographics of the 2 populations being studied. Six of the 21 cohort studies had serious risk of bias. This left only 4 cohort studies that were moderate or minimal risk of bias. Of the RCTs included in this study, only 2 of the 19 studies were at a high risk of bias, with the remaining being either low (7) or having some concerns (10). Oftentimes, studies were classified as having “some concerns” due to the lack of blinding, which may inherently lead to a level of expectancy bias. Based on the extensive literature, future studies are no longer warranted when looking at general outcomes between a SB and SS in the general population.

On the other hand, only 4 studies that compared TS to QS fixation satisfied the eligibility criteria of this systematic review. Three of these were cohort studies (2 of which had critical risk of bias) and 1 was a RCT. Only 1 study demonstrated a significant difference between TS and QS fixation, and it was at a critical risk of bias. Thus, the literature is lacking regarding high quality studies reporting on outcomes between the use of TS or QS fixation. More high-quality studies examining TS and QS fixation are warranted. If a difference is demonstrated between the 2, this would then necessitate future RCTs comparing SB to SS using either TS or QS for the respective fixation method. Many RCTs in this review stated in the methods that a combination of both TS and QS were utilized in their studies while some specified that either a single TS or QS was used. These studies were then included in subsequent meta-analysis that have been reported in the literature.^2–4

An interesting finding in this review is that when the RCTs were split between SB vs. TS or SB vs. QS, based on the method of screw fixation outlined by the authors in their respective methods section, only 1 study included in this review found a significant difference between using a SB and a SS if it was specified that a TS was used. Altmeppen et al. performed a RCT with a 10-year follow-up comparing the SB to a SS, where they specified in their methods that a single TS was used for their SS group.¹⁹ Their study consisted of 21 patients in the SB group and 20 in the SS group. They found that patients in the SB group had a return to sport time that was superior to the SS group (14 weeks versus 19 weeks). Although the patients in the SB group had a return to sport time that was greater, this result did not have any correlation to any of the PROMs, including the FADI sport score. All other RCTs that compared SB to SS and specified using a TS for their SS group demonstrated no significant difference in any clinical, radiographic, or PROMs.^6,7,27,29 On the other hand, studies that examined SB versus SS that specified using a QS consistently found that SB was superior to the SS group in all but 1 study. Laflamme et al. reported a higher reoperation rate, improved reduction as measured on plain radiographs regarding the TFCS, and better OMS scores in the SB group.¹⁰ Raeder et al. found that their SB group had better postoperative ROM and better OMS and AOFAS scores.³⁹ Andersen et al. also found that the SB group had better maintenance of radiographic reduction compared to their SS group.⁹ Morales et al. was the only RCT that specified using a QS in their methods that found no significant difference between their SB or SS groups.³⁸ While it would be inappropriate to draw any conclusions considering the design of these studies focused on SS versus SB—they did not specifically look at using a TS or QS—these findings suggest that the use of a TS may be more beneficial than the use of a QS and future studies are warranted.

Previous meta-analysis have reported better outcomes for use of the SB compared to the SS.^4,9,34 Shimozono et al. performed a meta-analysis that included 5 RCTs. Their results demonstrated that the use of the SB was superior to the SS due to superior functional outcomes and lower rates of broken implants and joint malreduction.⁴ As explained in their review, joint malreduction or loss of reduction is negatively associated with clinical outcomes. It has long been understood that malreduction of the ankle syndesmosis leads to decreased contact area and an increase in peak pressures across the ankle joint.^47–49 While many studies in this review did not necessarily demonstrate a correlation between radiographic and clinical outcomes, many of these studies were limited to 1–2 years follow-up. It can be assumed reasonably based on previous literature that these studies would show worse outcomes in the patients with malreduced joints if the follow-up period were to be extended to 10 or more years post-operative.

While the topic of SB versus SS has been well studied regarding outcomes in general populations, there is justification to compare outcomes of the 2 fixation techniques based on certain patient populations or injury types. Multiple studies examined the use of SB versus SS in specific types of ankle fractures, some of which were included in this review.^7,20,27,36 Another important consideration when deciding which type of fixation method to use would be patient comorbidities or BMI. While most studies used patient age, comorbidities, BMI, and associated injuries as exclusion criteria, this review found no studies comparing outcomes between SB and SS or TS vs QS in specific patient populations such as diabetic patients, osteoporotic patients, elderly patients, or patients over a certain BMI that met our inclusion criteria. The use of trans-syndesmotic screw fixation has been described to be of benefit in diabetic patients or patients with osteoporotic bone, however, the authors could not find any long-term studies comparing outcomes between the SB or SS in these patient populations.⁵⁰ One study performed by Black et al. compared radiographic outcomes of the SB and SS across various BMIs in 79 patients.⁵¹ The results of this study were not included in our final analysis as the average follow-up was less than 1 year (5.5 months). Their results demonstrated that both the SB and SS demonstrated similar results across all BMIs, supporting the use of both the SB and SS in overweight and obese patients.⁵¹ Future studies should investigate these specific areas to determine if certain patient demographic factors or comorbidities should play a role in deciding which method of syndesmotic fixation will provide the best outcomes in certain patient populations.

There are certain limitations and potential bias of this study that should be considered. The first reason is that this review was limited to only the PubMed and Scopus databases. Another limitation is that this review included both RCTs and cohort studies, leading to a heterogeneity of results. While this makes our study a lower level of evidence, this was necessary to achieve our goal of determining current gaps in the literature. Additionally, the use of the RoB-2 and ROBINS-I V2 adds transparency to which studies are of higher quality evidence and which are not. There is also the inherent nature of publication bias that may limit many studies that did not demonstrate a difference between certain fixation techniques from being published.

5 Conclusion

The use of SS or SB fixation for syndesmotic disruption has been extensively studied in the general population, and the majority demonstrates no difference between them. However, of those that demonstrated a significant difference, all but 1 study found that SB is superior for faster return to sports, better radiographic outcomes, and better PROMs. Direct comparison of a TS and a QS has also, in general, shown equivalent outcomes. However, this particular subtopic has received very limited attention in the literature. Based on the limited literature, a TS may result in superior outcomes compared to the QS. Thus, these methods of screw fixation should be separated when comparing the SB to the SS for syndesmotic fixation. Future studies should focus on the gaps that remain when determining which method of syndesmotic fixation is superior, including RCTs comparing the SB vs. the SS in specific patient populations, and directly comparing QS and TS to SB.

Guardian/patient's consent

Consent for minors was not needed for this study.

Ethical statement

University of Missouri Institutional Review Board approval was not needed to conduct this systematic review.

Credit author statement

Conceptualization: B.A.P., C.U., J.L.C., and K.M.S.; Formal analysis: B.A.P., C.U., J.L.C., and K.M.S.; Investigation: B.A.P., C.U., J.L.C., and K.M.S.; Surgical expertise: J.L.C. and K.M.S. Resources: J.L.C. and K.M.S.; Supervision: J.L.C. and K.M.C.; Writing – original draft: B.A.P., C.U., J.L.C., and K.M.S.; Writing – review & editing: B.A.P., C.U., J.L.C., and K.M.S.

Funding statement

No funding from an external source was needed to conduct this study.