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A Comparison of Screw Fixation and Suture-Button Fixation in a Syndesmosis Injury in an Ankle Fracture
The Journal of Foot & Ankle Surgery xxx (2016) 1–6
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Original Research
A Comparison of Screw Fixation and Suture-Button Fixation in a Syndesmosis Injury at an Ankle Fracture Jung-Han Kim, MD, PhD 1, Heui-Chul Gwak, MD, PhD 1, Chang-Rack Lee, MD 1, Hye-Jeung Choo, MD 2, Jeon-Gyo Kim, MD 3, Dae-Yoo Kim, MD 4 1
Professor, Department of Orthopedic Surgery, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea Professor, Department of Radiology, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea Fellow, Department of Orthopedic Surgery, District Hospital, Korea Army Training Center, Nonsan, Korea 4 Resident, Department of Orthopedic Surgery, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
The present study compared the quality of reduction and the clinical assessment between screw fixation and suture-button fixation with an ankle fracture accompanied by syndesmosis injury. We studied the clinical and radiologic findings 1 year postoperatively through retrospective examination of 24 patients who had undergone screw fixation from January 2011 to December 2012 and prospective examination of 20 patients who had undergone suture button fixation from January 2013 to May 2014. Regarding the tibiofibular clear space, tibiofibular overlap, and medial clear space, the screw fixation group had improvement from a preoperative mean of 6.97 (range 2.79 to 15.81) mm, 4.43 (range 0 to 7.87) mm, 7.90 (range 4.24 to 19.50) mm to a postoperative mean of 4.95 (range 2.72 to 9.08) mm, 6.29 (range 0 to 10.37) mm, and 4.32 (range 1.98 to 6.57) mm, respectively. The corresponding improvement for the suture-button fixation group was from a preoperative mean of 6.65 (range 3.94 to 13.73) mm, 5.39 (range 0 to 9.44) mm, 7.27 (range 4.04 to 16.00) mm to a postoperative mean of 5.15 (range 2.93 to 7.30) mm, 7.21 (range 2.15 to 10.30) mm, and 4.25 (range 2.97 to 5.71) mm. No statistically significant difference was found between the 2 techniques. Both suture-button and metal screw fixation are effective treatment methods for an ankle fracture accompanied by syndesmosis injury. However, a long-term and prospective analysis is needed. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: ankle fracture screw fixation syndesmosis injury TightropeÒ
Syndesmosis plays an important role in the function and stability of an ankle joint. It is widely known that 80% of syndesmosis injuries are accompanied by an ankle fracture (1). Chronic pain and edema can be caused by instability of an ankle joint unless the accompanying syndesmosis injury has been properly treated. Moreover, this condition can lead to traumatic arthritis. Thus, the presence of a syndesmosis injury will have a significant effect on the treatment and prognosis (2). A variety of operative methods for syndesmosis injury have been published. Moreover, many operative materials have been developed in relation to the stability of an ankle joint and the stiffness of a joint postoperatively (3–5). Currently, the screw fixation method is widely used. It has been reported that the screw fixation method is technically
Financial Disclosure: This work was supported by a 2009 research grant from Inje University. Conflict of Interest: None reported. Address correspondence to: Heui-Chul Gwak, MD, PhD, Department of Orthopedic Surgery, Busan Paik Hospital, 633-165 Gaegum-dong, Busanjin-gu, Busan 614-735, Korea. E-mail address: [email protected] (H.-C. Gwak).
easy and safe. Furthermore, it can help obtain excellent treatment results. Subsequently, suture-button fixation was developed, and the effect has been demonstrated in countries other than Korea. The present study prospectively and retrospectively compared the quality of the reduction and the clinical assessment between screw fixation and suture-button fixation among patients with an ankle fracture accompanied by a syndesmosis injury. Furthermore, the present study aimed to identify the effectiveness of suture-button fixation as an operative method for Korean patients with syndesmosis injury. Patients and Methods The present study examined 44 patients who were followed up for >1 year of the 50 patients who had undergone ankle fracture surgery accompanied by syndesmosis injury at Busan Paik Hospital from January 2011 to May 2014. We studied the clinical and radiologic findings 1 year postoperatively by retrospective follow-up examination of the data from 24 patients who had undergone screw fixation from January 2011 to December 2012 and by prospective follow-up examination of the data from 20 patients who had undergone the TightropeÒ (Arthrex, Naples, FL) suture-button fixation from January 2013 to May 2014. To determine whether a patient needed to undergo surgery for a syndesmosis injury after open reduction and internal fixation of an ankle fracture, we defined syndesmosis instability as follows (6): (1) movement of >3 mm when pulling the
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.05.002
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Fig. 1. Examples of syndesmotic injury with ankle fracture after surgery using a metal screw. (A) Preoperative radiographs. (B) Immediate postoperative radiographs. (C) Radiograph 12 weeks after surgery showing the hardware removed and an intact syndesmosis. distal end of the fibula with a towel clip to the lateral side during surgery; (2) a tibiofibular clear space enlarged to >6 mm on the ankle radiograph; (3) the tibiofibular overlap reduced to <6 mm; and (4) the medial clear space enlarged to >4 mm. The present study included patients treated with the screw fixation method from January 2011 to December 2012 and the suture-button fixation method from January 2013 to May 2014. We examined the simple radiographic results of 44 patients 1 year after surgery. Thus, we selected only those patients for whom an accurate radiologic assessment could be performed. Our findings confirmed the accuracy and sustainability of the radiologic findings after the reduction of syndesmosis in each patient. Additionally, we confirmed the clinical findings with a questionnaire. We measured the tibiofibular overlap and tibiofibular clear space from an anteroposterior radiograph before and after surgery. We also measured the medial clear space on the mortise view. For all the measurements, a mean value was obtained after 2 orthopedic surgeons (G.H.C. and K.J.G.) had repeated each measurement twice. The clinical outcomes were compared using the ankle-hindfoot score of the American Orthopaedic Foot and Ankle Society (AOFAS) and a visual analog scale (VAS) score.
Surgical Methods All patients underwent surgery in the supine position under general anesthesia or spinal anesthesia. Each fracture was treated by 1 surgeon. Arthroscopy was used to determine the presence of syndesmosis injury before fixation of the ankle fracture. Treatment consisted of the debridement of osteochondral lesions, removal of loose bodies, curettage, drilling, synovectomy, and abrasion of the subchondral bone. Ankle fixation was performed with the ankle in a neutral position. For fixation of the syndesmosis, 3 cortices from the fibular side were drilled to allow a 3.5-mm screw to pass to the inner cortical bone of the tibia in a lateral direction from a linear upward direction of the syndesmosis. The fixation was conducted in the proximal area 2 to 6 cm away from the tibia plafond. The fibula is located behind the tibia in the transverse plane. Thus, a screw should be inserted obliquely at 25 to 30 from the posterolateral side to the anteromedial side. Syndesmosis reduction should be maintained using reduction forceps while inserting the screw. This procedure can prevent a drilled hole from changing. When we used the plate for stability of the fibula, we inserted a screw in 1 of the empty metal holes, depending on the location of the metal plate (Fig. 1). When the syndesmosis injury was caused by high energy, 2 cortical screws were inserted.
J.-H. Kim et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–6
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Fig. 2. Examples of syndesmotic injuries with ankle fractures after surgery using the suture-button device. (A) Preoperative radiographs and (B) immediate postoperative radiographs. In the suture-button fixation group, reduction forceps were used to reduce and maintain the syndesmosis with the ankle in a neutral position. We then made a hole in the 4 cortical bones in a proximal area 2 to 6 cm away from the articular surface in the same manner, with insertion of the screw at a 30 angle in the coronal plane using a 3.5-mm drill bit. The suture-button device was also inserted using a screw hole on the metal plate after the metal plate had been fixed to the fibula. The inner side of tibia was fixed with a button by passing a thread from the inside to the outside with a needle. The thread was bound by hand on the outside of the tibia (Fig. 2). All the patients who had undergone either operative procedure were immobilized in a below-the-knee cast for 1 week in a non-weightbearing state. They then wore ankle walker boots to start ankle joint exercises. Those patients who had undergone screw fixation began partial weightbearing 6 to 8 weeks postoperatively. Those patients who had undergone suture-button fixation began partial weightbearing at 6 weeks postoperatively. All the patients also underwent clinical and radiologic assessments at 6 weeks, 6 months, and 1 year postoperatively.
postoperative mean of 5.15 (range 2.93 to 7.30) mm. The improvement in the screw fixation group was statistically significant (p ¼ .01), but the improvement in the suture-button fixation group was not (p ¼ .05). However, the suture-button fixation group fully recovered to a normal range of motion. The tibiofibular overlap was improved in the screw fixation group, from a preoperative mean of 4.43 (range 0 to 7.87) mm to a postoperative mean of 6.29 (range 0 to 10.37) mm. The suture-button fixation group also experienced improvement, from a
Statistical Analysis
Follow-up period (mo) Mean Range Sex Male Female Age (y) Mean Range Mechanism of injury Slip Fall Motorcycle TA Pedestrian TA In car TA Lauge-Hansen classification SER IV SER III SA I SA II PER IV PER III PA III PA II Number of implants 1 2 Broken screw
For statistical comparison of the clinical and radiologic findings between the 2 groups (screw fixation and suture-button fixation), we used SPSS, version 21.0 (SPSS, Chicago, IL), statistical software. Fisher’s exact test was used to analyze the gender differences between the 2 groups. The AOFAS score parameters followed a normal distribution. Therefore, we conducted statistical comparisons using the independent t test. The radiologic findings and VAS scores did not follow a normal distribution. Hence, we used the nonparametric Mann-Whitney U test. p Values of < .05 were considered statistically significant.
Results Of the 44 patients with an ankle fracture accompanied by a syndesmosis injury, 24 were treated by screw fixation (18 males and 6 females). Their mean age was 40.5 (range 16 to 78) years. Their median follow-up time was 14.6 (range 12 to 28) months. The suturebutton fixation group included 20 patients (14 males and 6 females). Their mean age was 51.3 (range 20 to 78) years. Their median followup period was 13.4 (range 12 to 23) months (Table 1). Categorical comparisons for the mechanism of injury and the Lauge-Hansen classification, by treatment group, showed a difference that is not statistically significant (p ¼ .833 and p ¼ .323). The screw fixation group had an improved tibiofibular clear space, from a preoperative mean of 6.97 (range 2.79 to 15.81) mm to a postoperative mean of 4.95 (range 2.72 to 9.08) mm. Similarly, the suture-button fixation group had an improved tibiofibular clear space, from a preoperative mean of 6.65 (range 3.94 to 13.73) mm to a
Table 1 Demographic data Variable
Screw Fixation (n ¼ 24)
Suture-Button Fixation (n ¼ 20)
14.6 12 to 28
13.4 12 to 23
18 (75) 6 (25)
14(70) 6 (30)
40.5 16 to 78
51.3 20 to 78
15 3 2 2 2
10 2 2 4 2
p Value .254
.438
.103
.833 (62.5) (12.5) (8.3) (8.3) (8.3)
(50) (10) (10) (20) (10) .323
10 (41.7) 1 (4.2) 1 (4.2) 1 (4.2) 8 (33.3) 2 (8.3) 0 1 (4.2)
8 (40) 3 (15) 0 0 4 (25) 2 (10) 3 (15) 0
20 (83.3) 4 (16.7) 5 (20.8)
18 (90) 2 (10) 0
.673
.032
Abbreviations: PA, pronation adduction; PER, pronation external rotation; SA, supination adduction; SER, supination external rotation; TA, traffic accident. Data presented as n (%), unless otherwise noted.
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Table 2 Pre- and postoperative radiographic parameters stratified by treatment group Parameter
Screw Fixation
Tibiofibular clear space (mm) Preoperatively Postoperatively Tibiofibular overlap (mm) Preoperatively Postoperatively Medial clear space (mm) Preoperatively Postoperatively
Table 4 Clinical findings
Suture-Button Fixation
p Value
6.97 (2.79 to 15.81) 4.95 (2.72 to 9.08)
6.65 (3.94 to 13.73) 5.15 (2.93 to 7.30)
.795 .663
4.43 (0 to 7.87) 6.29 (0 to 10.37)
5.39 (0 to 9.44) 7.21 (2.15 to 10.30)
.472 .235
7.9 (4.24 to 19.50) 4.32 (1.98 to 6.57)
7.27 (4.04 to 16.00) 4.25 (2.97 to 5.71)
.891 .858
Data presented as mean (range).
preoperative mean of 5.39 (range 0 to 9.44) mm to a postoperative mean of 7.21 (range 2.15 to 10.30) mm. The medial clear space improved from a preoperative mean of 7.90 (range 4.24 to 19.50) mm to a postoperative mean of 4.32 (range 1.98 to 6.57) mm in the screw fixation group and from a preoperative mean of 7.27 (range 4.04 to 16.00) mm to a postoperative mean of 4.25 (range 2.97 to 5.71) mm in the suture-button fixation group (Tables 2 and 3). The intraclass correlation coefficient, which measures the degree of the consistency of the radiologic measurements between 2 observers, was 0.922. Thus, it was statistically significant (p < .001). From the clinical findings at the first year postoperatively, the screw fixation and suture-button fixation groups had an AOFAS score of 86.6 (range 75 to 96) and 88.1 (range 79 to 95), respectively. The corresponding VAS scores were 1.5 (range 0 to 3) and 1.4 (range 0 to 3). No statistically significant difference was found between the 2 techniques (p ¼ .663 and p ¼ .795; Table 4) However, both groups had excellent results. Bone union was achieved in all cases. At the 1-year radiographic follow-up visit, broken screws due to postoperative complications were found in 5 patients in the screw fixation group (Fig. 3). However, this damage did not affect the clinical findings. Discussion Syndesmosis consists of the anteroinferior tibiofibular ligament, posteroinferior tibiofibular ligament, interosseous ligament, and inferior transverse tibiofibular ligament (7). This is an important structure that preserves the gap between the distal tibia and fibula, thereby preventing the distal tibia and fibula from being separated by external forces, such as axial forces, torque and shear forces, and thus maintaining the normal function of the ankle joint (8). Of these components, the anteroinferior tibiofibular ligament provides approximately 35% of the stability of the posterolateral displacement of fibula, the interosseous ligament provides approximately 22% of the stability, and the posteroinferior tibiofibular ligament provides approximately 33% of the stability. Finally, the inferior transverse tibiofibular ligament provides approximately 9% of the stability (9).
Table 3 Pre- and postoperative radiographic parameters stratified by treatment group Parameter Screw fixation Tibiofibular clear space Tibiofibular overlap Medial clear space Suture-button fixation Tibiofibular clear space Tibiofibular overlap Medial clear space
Preoperatively
Postoperatively
p Value
6.97 (2.79 to 15.81) 4.43 (0 to 7.87) 7.9 (4.24 to 19.50)
4.95 (2.72 to 9.08) 6.29 (0 to 10.37) 4.32 (1.98 to 6.57)
.010 .003 .000
6.65 (3.94 to 13.73) 5.39 (0 to 9.44) 7.27 (4.04 to 16.00)
5.15 (2.93 to 7.30) 7.21 (2.15 to 10.30) 4.25 (2.97 to 5.71)
.050 .066 .001
Data presented as mean (range).
Measure
Screw Fixation
Suture-Button Fixation
p Value
AOFAS score VAS score
86.6 (75 to 96) 1.5 (0 to 3)
88.1 (79 to 95) 1.4 (0 to 3)
.663 .795
Abbreviations: AOFAS, American Orthopaedic Foot and Ankle Society; VAS, visual analog scale.
The etiopathogenic mechanism of a syndesmosis injury is external rotation. First, the anteroinferior tibiofibular ligament ruptures and an interosseous ligament ruptures. Finally, an interosseous membrane ruptures. A posteroinferior tibiofibular ligament acts as a hinge around which the fibula rotates. Thus, it is not easily torn apart, and it is rare that a posteroinferior tibiofibular ligament ruptures. From the Lauge-Hansen classification, this type of injury is often caused by pronation-external rotation, pronationabduction, and supination-external rotation. The Weber classification indicates that it is frequently accompanied by the C type. However, controversy exists regarding whether it is accompanied by the B type (10). A possibility exists of damage and instability associated with syndesmosis in ankle fractures. Thus, it is critical to diagnose and treat it accurately. The generally accepted treatment principle is operative treatment to maintain reduction if a syndesmosis injury is diagnosed. Each researcher uses different implants to achieve syndesmotic fixation. Operative treatments for syndesmotic injury include screw fixation, biologically absorbable screw fixation, and suture-button fixation. Of these treatments, screw fixation has been traditionally used in many settings. The most important advantage of screw fixation is that it can maintain reduction of distal syndesmosis under any weight condition. Its well-known disadvantage is synostosis and the ossification of the distal tibiofibular joint. Furthermore, screw fixation does not allow normal motion of the syndesmosis during healing because the screw can break or dissociation can occur. Also, occult fibular nonunion can present with syndesmotic diastasis after screw removal (11). In the present study, metal screws had broken in 5 of 24 patients (20.8%). To overcome these drawbacks, biologically absorbable screws have been proposed (3,12,13). van den Bekerom and Raven (14) have researched this problem. Additionally, many other studies have reported finding no difference between biologically absorbable screws and metal screws (15,16). However, some disadvantages have also been reported. For instance, a biologically absorbable screw has a lower degree of strength than a metal screw. Furthermore, a biologically absorbable screw might result in more frequent osteolytic and inflammatory reactions. Additionally, a biologically absorbable screw can be destroyed more easily (17). The suture-button device is a relatively new operative implant. It consists of a tibia-side rectangular button 6.5 mm in diameter, a fibula-side button 10 3.4 mm in size, and a double-ring shaped FiberWireÒ no. 5 suture (Arthrex). It has a tension of 888 214 N; thus, it provides a sufficient level of stability for fixing the distal tibiofibular joint. It does not require a second surgery to remove the implant using a double ring-shaped fixture. Additionally, it does not need an additional autograft or allograft. It also fixes less firmly than a metal screw, allowing for micromovement of the tarsal distal tibiofibular articulation and serving to replace a damaged ligament. Finally, it does not result in joint-related pain or loosening or breakage of a metal screw, which can otherwise occur when fixing with a metal screw. Therefore, weight loading can be achieved at an early stage. Thornes et al (4) conducted syndesmosis fixation with one 4.5-mm metal screw on 1 leg and a suture-button fixation on the other leg of 16 cadavers. They reported no significant differences in the malreduction rate between the 2 groups. However, the standard deviation
J.-H. Kim et al. / The Journal of Foot & Ankle Surgery xxx (2016) 1–6
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Fig. 3. Examples of broken metal screws. (A) Preoperative radiographs. (B) Immediate postoperative radiographs. (C) Radiograph 8 weeks after surgery showing a broken metal screw. (D) At 1 year after surgery, the radiograph shows the hardware had been removed, although the broken screw tip remained. However, the syndesmosis was intact.
distribution of the screw fixation group was 0.64 mm more than that in the suture-button fixation group. Thus, the suture-button fixation group had more consistent performance. They also reported that suture-button fixation had almost the same level of performance as screw fixation. Seitz et al (18) conducted suture-button fixation on 12 patients with syndesmosis injuries accompanied by an ankle fracture. In the follow-up examination at 2 to 4 years, they found that bone union was observed in all cases without any malunion. They also did not observe any case related to instability of the syndesmosis. Therefore, they reported that suture-button fixation, which could allow for weightbearing at an early phase without removal, was a reliable method for recovering the strength of the syndesmosis. Coetzee and Ebeling (19) reported that the suture-button fixation group had a greater AOFAS ankle joint-hindfoot score (median and range of 94 points) than the screw fixation group (median and range of 88 points) after a 3-year follow-up period. Thus, the screw fixation group performed better clinically than the suture-button fixation group. However, they argued that this finding was not statistically significant (p ¼ .149). In our study, the radiologic findings 1 year after surgery in the screw fixation and suture-button fixation groups showed that the tibiofibular clear space was 4.95 (range 2.72 to 9.08) mm and 5.15 (range 2.93 to 7.30) mm, respectively. The tibiofibular
overlap was 6.29 (range 0 to 10.37) mm and 7.21 (range 2.15 to 10.30) mm for the screw fixation and suture-button fixation groups, respectively. The corresponding medial clear space was 4.32 (range 1.98 to 6.57) mm and 4.25 (range 2.97 to 5.71) mm. No statistically significant differences were found between the 2 groups. Clinically, the AOFAS ankle joint-hindfoot score was a median and range of 86.6 points in the screw fixation group and 88.1 points in the suturebutton fixation group 1 year postoperatively. Thus, the findings of our study are similar to those reported by Coetzee and Ebeling (19). The present study had several limitations. First, our study included a relatively small number of patients for a short follow-up period (1 year). Second, because the present study conducted a retrospective follow-up observation in the screw fixation group, it was difficult to accurately predict the clinical findings of a long-term follow-up examination on fixation of the syndesmosis accompanied by an ankle fracture in the screw fixation group. In addition, this was a nonrandomized study; hence, selection bias should be considered in the 2 group assignments. Many successful clinical results have been reported with suture-button fixation. We did not observe any complications in the suture-button fixation group. However, several investigators have reported some postoperative complications associated with the soft tissues with the use of the suture-button device.
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Thus far, no research has focused on periodic stability measurements after suture-button fixation and the durability at long-term follow-up. Thus, a long-term prospective analysis is desirable. In conclusion, despite these limitations, the present study has demonstrated that suture-button fixation would have at least equivalent radiologic and clinical findings compared with screw fixation. Furthermore, the former allows patients to walk at an early phase and is a relatively simple operative procedure. Finally, suture-button fixation does not usually require removal. Therefore, we believe that suturebutton fixation is a good operative treatment for syndesmosis injuries. References 1. Lin CF, Gross ML, Weinhold P. Ankle syndesmosis injuries: anatomy, biomechanics, mechanism of injury, and clinical guidelines for diagnosis and intervention. J Orthop Sports Phys Ther 36:372–384, 2006. 2. Clarke HJ, Michelson JD, Cox QG, Jinnah RH. Tibiotalar stability in bimalleolar ankle fractures: a dynamic in vitro contact area study. Foot Ankle Int 11:222–227, 1991. 3. Hovis WD, Kaiser BW, Watson JT, Bucholz RW. Treatment of syndesmotic disruptions of the ankle with bioabsorbable screw fixation. J Bone Joint Surg Am 84:26–31, 2002. 4. Thornes B, Walsh A, Hislop M, Murray P, O’Brien M. Suture-endobutton fixation of ankle tibio-fibular diastasis: a cadaver study. Foot Ankle Int 24:142–146, 2003. 5. Zalavras C, Thordarson D. Ankle syndesmotic injury. J Am Acad Orthop Surg 15:330–339, 2007. 6. Cotton FJ. The ankle and foot. In: Dislocations and Joint Fractures, WB Saunders, Philadelphia, PA, 1910, pp. 535–588. 7. Boden SD, Labropoulos PA, McCowin P, Lestini WF, Hurwitz SR. Mechanical considerations for the syndesmosis screw: a cadaver study. J Bone Joint Surg Am 71:1548–1555, 1989.
8. Snedden MH, Shea JP. Diastasis with low distal fibula fractures: an anatomic rationale. Clin Orthop Relat Res 382:197–205, 2001. 9. Ogilvie-Harris DJ, Reed SC, Hedman TP. Disruption of the ankle syndesmosis: biomechanical study of the ligamentous restraints. Arthroscopy 10:561–568, 1994. 10. Kennedy JG, Soffe KE, Dalla Vedova P, Stephens MM, O’Brien T, Walsh MG, McManus F. Evaluation of the syndesmotic screw in low Weber C ankle fractures. J Orthop Trauma 14:359–366, 2000. 11. Ebraheim NA, Mekhail AO, Gargasz SS. Ankle fractures involving the fibula proximal to the distal tibiofibular syndesmosis. Foot Ankle Int 18:513–521, 1997. 12. Thordarson DB, Hedman TP, Gross D, Magre G. Biomechanical evaluation of polylactide absorbable screws used for syndesmosis injury repair. Foot Ankle Int 18:622–627, 1997. 13. Thordarson DB, Samuelson M, Shepherd LE, Merkle PF, Lee J. Bioabsorbable versus stainless steel screw fixation of the syndesmosis in pronation-lateral rotation ankle fractures: a prospective randomized trial. Foot Ankle Int 22:335–338, 2001. 14. van den Bekerom MP, Raven EE. Review of operative techniques for stabilising the distal tibiofibular syndesmosis. Foot Ankle Int 28:1302–1308, 2007. 15. Cox S, Mukherjee DP, Ogden AL, Mayuex RH, Sadasivan KK, Albright JA, Pietrzak WS. Distal tibiofibular syndesmosis fixation: a cadaveric, simulated fracture stabilization study comparing bioabsorbable and metallic single screw fixation. J Foot Ankle Surg 44:144–151, 2005. 16. Kaukonen JP, Lamberg T, Korkala O, Pajarinen J. Fixation of syndesmotic ruptures in 38 patients with a malleolar fracture: a randomized study comparing a metallic and a bioabsorbable screw. J Orthop Trauma 19:392–395, 2005. 17. Blasier RD, Bucholz R, Cole W, Johnson LL, M€ akel€ a EA. Bioresorbable implants: applications in orthopaedic surgery. Instr Course Lect 6:531–546, 1997. 18. Seitz WH Jr, Bachner EJ, Abram LJ, Postak P, Polando G, Brooks DB, Greenwald AS. Repair of the tibiofibular syndesmosis with a flexible implant. J Orthop Trauma 5:78–82, 1991. 19. Coetzee JC, Ebeling P. Treatment of syndesmoses disruptions: a prospective, randomized study comparing conventional screw fixation vs TightRopeÒ fiber wire fixationdmedium term results. SA Orthop J 8:32–37, 2009.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Original Research
A Comparison of Screw Fixation and Suture-Button Fixation in a Syndesmosis Injury at an Ankle Fracture Jung-Han Kim, MD, PhD 1, Heui-Chul Gwak, MD, PhD 1, Chang-Rack Lee, MD 1, Hye-Jeung Choo, MD 2, Jeon-Gyo Kim, MD 3, Dae-Yoo Kim, MD 4 1
Professor, Department of Orthopedic Surgery, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea Professor, Department of Radiology, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea Fellow, Department of Orthopedic Surgery, District Hospital, Korea Army Training Center, Nonsan, Korea 4 Resident, Department of Orthopedic Surgery, Busan Paik Hospital, College of Medicine, Inje University, Busan, Korea 2 3
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 4
The present study compared the quality of reduction and the clinical assessment between screw fixation and suture-button fixation with an ankle fracture accompanied by syndesmosis injury. We studied the clinical and radiologic findings 1 year postoperatively through retrospective examination of 24 patients who had undergone screw fixation from January 2011 to December 2012 and prospective examination of 20 patients who had undergone suture button fixation from January 2013 to May 2014. Regarding the tibiofibular clear space, tibiofibular overlap, and medial clear space, the screw fixation group had improvement from a preoperative mean of 6.97 (range 2.79 to 15.81) mm, 4.43 (range 0 to 7.87) mm, 7.90 (range 4.24 to 19.50) mm to a postoperative mean of 4.95 (range 2.72 to 9.08) mm, 6.29 (range 0 to 10.37) mm, and 4.32 (range 1.98 to 6.57) mm, respectively. The corresponding improvement for the suture-button fixation group was from a preoperative mean of 6.65 (range 3.94 to 13.73) mm, 5.39 (range 0 to 9.44) mm, 7.27 (range 4.04 to 16.00) mm to a postoperative mean of 5.15 (range 2.93 to 7.30) mm, 7.21 (range 2.15 to 10.30) mm, and 4.25 (range 2.97 to 5.71) mm. No statistically significant difference was found between the 2 techniques. Both suture-button and metal screw fixation are effective treatment methods for an ankle fracture accompanied by syndesmosis injury. However, a long-term and prospective analysis is needed. Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: ankle fracture screw fixation syndesmosis injury TightropeÒ
Syndesmosis plays an important role in the function and stability of an ankle joint. It is widely known that 80% of syndesmosis injuries are accompanied by an ankle fracture (1). Chronic pain and edema can be caused by instability of an ankle joint unless the accompanying syndesmosis injury has been properly treated. Moreover, this condition can lead to traumatic arthritis. Thus, the presence of a syndesmosis injury will have a significant effect on the treatment and prognosis (2). A variety of operative methods for syndesmosis injury have been published. Moreover, many operative materials have been developed in relation to the stability of an ankle joint and the stiffness of a joint postoperatively (3–5). Currently, the screw fixation method is widely used. It has been reported that the screw fixation method is technically
Financial Disclosure: This work was supported by a 2009 research grant from Inje University. Conflict of Interest: None reported. Address correspondence to: Heui-Chul Gwak, MD, PhD, Department of Orthopedic Surgery, Busan Paik Hospital, 633-165 Gaegum-dong, Busanjin-gu, Busan 614-735, Korea. E-mail address: [email protected] (H.-C. Gwak).
easy and safe. Furthermore, it can help obtain excellent treatment results. Subsequently, suture-button fixation was developed, and the effect has been demonstrated in countries other than Korea. The present study prospectively and retrospectively compared the quality of the reduction and the clinical assessment between screw fixation and suture-button fixation among patients with an ankle fracture accompanied by a syndesmosis injury. Furthermore, the present study aimed to identify the effectiveness of suture-button fixation as an operative method for Korean patients with syndesmosis injury. Patients and Methods The present study examined 44 patients who were followed up for >1 year of the 50 patients who had undergone ankle fracture surgery accompanied by syndesmosis injury at Busan Paik Hospital from January 2011 to May 2014. We studied the clinical and radiologic findings 1 year postoperatively by retrospective follow-up examination of the data from 24 patients who had undergone screw fixation from January 2011 to December 2012 and by prospective follow-up examination of the data from 20 patients who had undergone the TightropeÒ (Arthrex, Naples, FL) suture-button fixation from January 2013 to May 2014. To determine whether a patient needed to undergo surgery for a syndesmosis injury after open reduction and internal fixation of an ankle fracture, we defined syndesmosis instability as follows (6): (1) movement of >3 mm when pulling the
1067-2516/$ - see front matter Ó 2016 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2016.05.002
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Fig. 1. Examples of syndesmotic injury with ankle fracture after surgery using a metal screw. (A) Preoperative radiographs. (B) Immediate postoperative radiographs. (C) Radiograph 12 weeks after surgery showing the hardware removed and an intact syndesmosis. distal end of the fibula with a towel clip to the lateral side during surgery; (2) a tibiofibular clear space enlarged to >6 mm on the ankle radiograph; (3) the tibiofibular overlap reduced to <6 mm; and (4) the medial clear space enlarged to >4 mm. The present study included patients treated with the screw fixation method from January 2011 to December 2012 and the suture-button fixation method from January 2013 to May 2014. We examined the simple radiographic results of 44 patients 1 year after surgery. Thus, we selected only those patients for whom an accurate radiologic assessment could be performed. Our findings confirmed the accuracy and sustainability of the radiologic findings after the reduction of syndesmosis in each patient. Additionally, we confirmed the clinical findings with a questionnaire. We measured the tibiofibular overlap and tibiofibular clear space from an anteroposterior radiograph before and after surgery. We also measured the medial clear space on the mortise view. For all the measurements, a mean value was obtained after 2 orthopedic surgeons (G.H.C. and K.J.G.) had repeated each measurement twice. The clinical outcomes were compared using the ankle-hindfoot score of the American Orthopaedic Foot and Ankle Society (AOFAS) and a visual analog scale (VAS) score.
Surgical Methods All patients underwent surgery in the supine position under general anesthesia or spinal anesthesia. Each fracture was treated by 1 surgeon. Arthroscopy was used to determine the presence of syndesmosis injury before fixation of the ankle fracture. Treatment consisted of the debridement of osteochondral lesions, removal of loose bodies, curettage, drilling, synovectomy, and abrasion of the subchondral bone. Ankle fixation was performed with the ankle in a neutral position. For fixation of the syndesmosis, 3 cortices from the fibular side were drilled to allow a 3.5-mm screw to pass to the inner cortical bone of the tibia in a lateral direction from a linear upward direction of the syndesmosis. The fixation was conducted in the proximal area 2 to 6 cm away from the tibia plafond. The fibula is located behind the tibia in the transverse plane. Thus, a screw should be inserted obliquely at 25 to 30 from the posterolateral side to the anteromedial side. Syndesmosis reduction should be maintained using reduction forceps while inserting the screw. This procedure can prevent a drilled hole from changing. When we used the plate for stability of the fibula, we inserted a screw in 1 of the empty metal holes, depending on the location of the metal plate (Fig. 1). When the syndesmosis injury was caused by high energy, 2 cortical screws were inserted.
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Fig. 2. Examples of syndesmotic injuries with ankle fractures after surgery using the suture-button device. (A) Preoperative radiographs and (B) immediate postoperative radiographs. In the suture-button fixation group, reduction forceps were used to reduce and maintain the syndesmosis with the ankle in a neutral position. We then made a hole in the 4 cortical bones in a proximal area 2 to 6 cm away from the articular surface in the same manner, with insertion of the screw at a 30 angle in the coronal plane using a 3.5-mm drill bit. The suture-button device was also inserted using a screw hole on the metal plate after the metal plate had been fixed to the fibula. The inner side of tibia was fixed with a button by passing a thread from the inside to the outside with a needle. The thread was bound by hand on the outside of the tibia (Fig. 2). All the patients who had undergone either operative procedure were immobilized in a below-the-knee cast for 1 week in a non-weightbearing state. They then wore ankle walker boots to start ankle joint exercises. Those patients who had undergone screw fixation began partial weightbearing 6 to 8 weeks postoperatively. Those patients who had undergone suture-button fixation began partial weightbearing at 6 weeks postoperatively. All the patients also underwent clinical and radiologic assessments at 6 weeks, 6 months, and 1 year postoperatively.
postoperative mean of 5.15 (range 2.93 to 7.30) mm. The improvement in the screw fixation group was statistically significant (p ¼ .01), but the improvement in the suture-button fixation group was not (p ¼ .05). However, the suture-button fixation group fully recovered to a normal range of motion. The tibiofibular overlap was improved in the screw fixation group, from a preoperative mean of 4.43 (range 0 to 7.87) mm to a postoperative mean of 6.29 (range 0 to 10.37) mm. The suture-button fixation group also experienced improvement, from a
Statistical Analysis
Follow-up period (mo) Mean Range Sex Male Female Age (y) Mean Range Mechanism of injury Slip Fall Motorcycle TA Pedestrian TA In car TA Lauge-Hansen classification SER IV SER III SA I SA II PER IV PER III PA III PA II Number of implants 1 2 Broken screw
For statistical comparison of the clinical and radiologic findings between the 2 groups (screw fixation and suture-button fixation), we used SPSS, version 21.0 (SPSS, Chicago, IL), statistical software. Fisher’s exact test was used to analyze the gender differences between the 2 groups. The AOFAS score parameters followed a normal distribution. Therefore, we conducted statistical comparisons using the independent t test. The radiologic findings and VAS scores did not follow a normal distribution. Hence, we used the nonparametric Mann-Whitney U test. p Values of < .05 were considered statistically significant.
Results Of the 44 patients with an ankle fracture accompanied by a syndesmosis injury, 24 were treated by screw fixation (18 males and 6 females). Their mean age was 40.5 (range 16 to 78) years. Their median follow-up time was 14.6 (range 12 to 28) months. The suturebutton fixation group included 20 patients (14 males and 6 females). Their mean age was 51.3 (range 20 to 78) years. Their median followup period was 13.4 (range 12 to 23) months (Table 1). Categorical comparisons for the mechanism of injury and the Lauge-Hansen classification, by treatment group, showed a difference that is not statistically significant (p ¼ .833 and p ¼ .323). The screw fixation group had an improved tibiofibular clear space, from a preoperative mean of 6.97 (range 2.79 to 15.81) mm to a postoperative mean of 4.95 (range 2.72 to 9.08) mm. Similarly, the suture-button fixation group had an improved tibiofibular clear space, from a preoperative mean of 6.65 (range 3.94 to 13.73) mm to a
Table 1 Demographic data Variable
Screw Fixation (n ¼ 24)
Suture-Button Fixation (n ¼ 20)
14.6 12 to 28
13.4 12 to 23
18 (75) 6 (25)
14(70) 6 (30)
40.5 16 to 78
51.3 20 to 78
15 3 2 2 2
10 2 2 4 2
p Value .254
.438
.103
.833 (62.5) (12.5) (8.3) (8.3) (8.3)
(50) (10) (10) (20) (10) .323
10 (41.7) 1 (4.2) 1 (4.2) 1 (4.2) 8 (33.3) 2 (8.3) 0 1 (4.2)
8 (40) 3 (15) 0 0 4 (25) 2 (10) 3 (15) 0
20 (83.3) 4 (16.7) 5 (20.8)
18 (90) 2 (10) 0
.673
.032
Abbreviations: PA, pronation adduction; PER, pronation external rotation; SA, supination adduction; SER, supination external rotation; TA, traffic accident. Data presented as n (%), unless otherwise noted.
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Table 2 Pre- and postoperative radiographic parameters stratified by treatment group Parameter
Screw Fixation
Tibiofibular clear space (mm) Preoperatively Postoperatively Tibiofibular overlap (mm) Preoperatively Postoperatively Medial clear space (mm) Preoperatively Postoperatively
Table 4 Clinical findings
Suture-Button Fixation
p Value
6.97 (2.79 to 15.81) 4.95 (2.72 to 9.08)
6.65 (3.94 to 13.73) 5.15 (2.93 to 7.30)
.795 .663
4.43 (0 to 7.87) 6.29 (0 to 10.37)
5.39 (0 to 9.44) 7.21 (2.15 to 10.30)
.472 .235
7.9 (4.24 to 19.50) 4.32 (1.98 to 6.57)
7.27 (4.04 to 16.00) 4.25 (2.97 to 5.71)
.891 .858
Data presented as mean (range).
preoperative mean of 5.39 (range 0 to 9.44) mm to a postoperative mean of 7.21 (range 2.15 to 10.30) mm. The medial clear space improved from a preoperative mean of 7.90 (range 4.24 to 19.50) mm to a postoperative mean of 4.32 (range 1.98 to 6.57) mm in the screw fixation group and from a preoperative mean of 7.27 (range 4.04 to 16.00) mm to a postoperative mean of 4.25 (range 2.97 to 5.71) mm in the suture-button fixation group (Tables 2 and 3). The intraclass correlation coefficient, which measures the degree of the consistency of the radiologic measurements between 2 observers, was 0.922. Thus, it was statistically significant (p < .001). From the clinical findings at the first year postoperatively, the screw fixation and suture-button fixation groups had an AOFAS score of 86.6 (range 75 to 96) and 88.1 (range 79 to 95), respectively. The corresponding VAS scores were 1.5 (range 0 to 3) and 1.4 (range 0 to 3). No statistically significant difference was found between the 2 techniques (p ¼ .663 and p ¼ .795; Table 4) However, both groups had excellent results. Bone union was achieved in all cases. At the 1-year radiographic follow-up visit, broken screws due to postoperative complications were found in 5 patients in the screw fixation group (Fig. 3). However, this damage did not affect the clinical findings. Discussion Syndesmosis consists of the anteroinferior tibiofibular ligament, posteroinferior tibiofibular ligament, interosseous ligament, and inferior transverse tibiofibular ligament (7). This is an important structure that preserves the gap between the distal tibia and fibula, thereby preventing the distal tibia and fibula from being separated by external forces, such as axial forces, torque and shear forces, and thus maintaining the normal function of the ankle joint (8). Of these components, the anteroinferior tibiofibular ligament provides approximately 35% of the stability of the posterolateral displacement of fibula, the interosseous ligament provides approximately 22% of the stability, and the posteroinferior tibiofibular ligament provides approximately 33% of the stability. Finally, the inferior transverse tibiofibular ligament provides approximately 9% of the stability (9).
Table 3 Pre- and postoperative radiographic parameters stratified by treatment group Parameter Screw fixation Tibiofibular clear space Tibiofibular overlap Medial clear space Suture-button fixation Tibiofibular clear space Tibiofibular overlap Medial clear space
Preoperatively
Postoperatively
p Value
6.97 (2.79 to 15.81) 4.43 (0 to 7.87) 7.9 (4.24 to 19.50)
4.95 (2.72 to 9.08) 6.29 (0 to 10.37) 4.32 (1.98 to 6.57)
.010 .003 .000
6.65 (3.94 to 13.73) 5.39 (0 to 9.44) 7.27 (4.04 to 16.00)
5.15 (2.93 to 7.30) 7.21 (2.15 to 10.30) 4.25 (2.97 to 5.71)
.050 .066 .001
Data presented as mean (range).
Measure
Screw Fixation
Suture-Button Fixation
p Value
AOFAS score VAS score
86.6 (75 to 96) 1.5 (0 to 3)
88.1 (79 to 95) 1.4 (0 to 3)
.663 .795
Abbreviations: AOFAS, American Orthopaedic Foot and Ankle Society; VAS, visual analog scale.
The etiopathogenic mechanism of a syndesmosis injury is external rotation. First, the anteroinferior tibiofibular ligament ruptures and an interosseous ligament ruptures. Finally, an interosseous membrane ruptures. A posteroinferior tibiofibular ligament acts as a hinge around which the fibula rotates. Thus, it is not easily torn apart, and it is rare that a posteroinferior tibiofibular ligament ruptures. From the Lauge-Hansen classification, this type of injury is often caused by pronation-external rotation, pronationabduction, and supination-external rotation. The Weber classification indicates that it is frequently accompanied by the C type. However, controversy exists regarding whether it is accompanied by the B type (10). A possibility exists of damage and instability associated with syndesmosis in ankle fractures. Thus, it is critical to diagnose and treat it accurately. The generally accepted treatment principle is operative treatment to maintain reduction if a syndesmosis injury is diagnosed. Each researcher uses different implants to achieve syndesmotic fixation. Operative treatments for syndesmotic injury include screw fixation, biologically absorbable screw fixation, and suture-button fixation. Of these treatments, screw fixation has been traditionally used in many settings. The most important advantage of screw fixation is that it can maintain reduction of distal syndesmosis under any weight condition. Its well-known disadvantage is synostosis and the ossification of the distal tibiofibular joint. Furthermore, screw fixation does not allow normal motion of the syndesmosis during healing because the screw can break or dissociation can occur. Also, occult fibular nonunion can present with syndesmotic diastasis after screw removal (11). In the present study, metal screws had broken in 5 of 24 patients (20.8%). To overcome these drawbacks, biologically absorbable screws have been proposed (3,12,13). van den Bekerom and Raven (14) have researched this problem. Additionally, many other studies have reported finding no difference between biologically absorbable screws and metal screws (15,16). However, some disadvantages have also been reported. For instance, a biologically absorbable screw has a lower degree of strength than a metal screw. Furthermore, a biologically absorbable screw might result in more frequent osteolytic and inflammatory reactions. Additionally, a biologically absorbable screw can be destroyed more easily (17). The suture-button device is a relatively new operative implant. It consists of a tibia-side rectangular button 6.5 mm in diameter, a fibula-side button 10 3.4 mm in size, and a double-ring shaped FiberWireÒ no. 5 suture (Arthrex). It has a tension of 888 214 N; thus, it provides a sufficient level of stability for fixing the distal tibiofibular joint. It does not require a second surgery to remove the implant using a double ring-shaped fixture. Additionally, it does not need an additional autograft or allograft. It also fixes less firmly than a metal screw, allowing for micromovement of the tarsal distal tibiofibular articulation and serving to replace a damaged ligament. Finally, it does not result in joint-related pain or loosening or breakage of a metal screw, which can otherwise occur when fixing with a metal screw. Therefore, weight loading can be achieved at an early stage. Thornes et al (4) conducted syndesmosis fixation with one 4.5-mm metal screw on 1 leg and a suture-button fixation on the other leg of 16 cadavers. They reported no significant differences in the malreduction rate between the 2 groups. However, the standard deviation
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Fig. 3. Examples of broken metal screws. (A) Preoperative radiographs. (B) Immediate postoperative radiographs. (C) Radiograph 8 weeks after surgery showing a broken metal screw. (D) At 1 year after surgery, the radiograph shows the hardware had been removed, although the broken screw tip remained. However, the syndesmosis was intact.
distribution of the screw fixation group was 0.64 mm more than that in the suture-button fixation group. Thus, the suture-button fixation group had more consistent performance. They also reported that suture-button fixation had almost the same level of performance as screw fixation. Seitz et al (18) conducted suture-button fixation on 12 patients with syndesmosis injuries accompanied by an ankle fracture. In the follow-up examination at 2 to 4 years, they found that bone union was observed in all cases without any malunion. They also did not observe any case related to instability of the syndesmosis. Therefore, they reported that suture-button fixation, which could allow for weightbearing at an early phase without removal, was a reliable method for recovering the strength of the syndesmosis. Coetzee and Ebeling (19) reported that the suture-button fixation group had a greater AOFAS ankle joint-hindfoot score (median and range of 94 points) than the screw fixation group (median and range of 88 points) after a 3-year follow-up period. Thus, the screw fixation group performed better clinically than the suture-button fixation group. However, they argued that this finding was not statistically significant (p ¼ .149). In our study, the radiologic findings 1 year after surgery in the screw fixation and suture-button fixation groups showed that the tibiofibular clear space was 4.95 (range 2.72 to 9.08) mm and 5.15 (range 2.93 to 7.30) mm, respectively. The tibiofibular
overlap was 6.29 (range 0 to 10.37) mm and 7.21 (range 2.15 to 10.30) mm for the screw fixation and suture-button fixation groups, respectively. The corresponding medial clear space was 4.32 (range 1.98 to 6.57) mm and 4.25 (range 2.97 to 5.71) mm. No statistically significant differences were found between the 2 groups. Clinically, the AOFAS ankle joint-hindfoot score was a median and range of 86.6 points in the screw fixation group and 88.1 points in the suturebutton fixation group 1 year postoperatively. Thus, the findings of our study are similar to those reported by Coetzee and Ebeling (19). The present study had several limitations. First, our study included a relatively small number of patients for a short follow-up period (1 year). Second, because the present study conducted a retrospective follow-up observation in the screw fixation group, it was difficult to accurately predict the clinical findings of a long-term follow-up examination on fixation of the syndesmosis accompanied by an ankle fracture in the screw fixation group. In addition, this was a nonrandomized study; hence, selection bias should be considered in the 2 group assignments. Many successful clinical results have been reported with suture-button fixation. We did not observe any complications in the suture-button fixation group. However, several investigators have reported some postoperative complications associated with the soft tissues with the use of the suture-button device.
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Thus far, no research has focused on periodic stability measurements after suture-button fixation and the durability at long-term follow-up. Thus, a long-term prospective analysis is desirable. In conclusion, despite these limitations, the present study has demonstrated that suture-button fixation would have at least equivalent radiologic and clinical findings compared with screw fixation. Furthermore, the former allows patients to walk at an early phase and is a relatively simple operative procedure. Finally, suture-button fixation does not usually require removal. Therefore, we believe that suturebutton fixation is a good operative treatment for syndesmosis injuries. References 1. Lin CF, Gross ML, Weinhold P. Ankle syndesmosis injuries: anatomy, biomechanics, mechanism of injury, and clinical guidelines for diagnosis and intervention. J Orthop Sports Phys Ther 36:372–384, 2006. 2. Clarke HJ, Michelson JD, Cox QG, Jinnah RH. Tibiotalar stability in bimalleolar ankle fractures: a dynamic in vitro contact area study. Foot Ankle Int 11:222–227, 1991. 3. Hovis WD, Kaiser BW, Watson JT, Bucholz RW. Treatment of syndesmotic disruptions of the ankle with bioabsorbable screw fixation. J Bone Joint Surg Am 84:26–31, 2002. 4. Thornes B, Walsh A, Hislop M, Murray P, O’Brien M. Suture-endobutton fixation of ankle tibio-fibular diastasis: a cadaver study. Foot Ankle Int 24:142–146, 2003. 5. Zalavras C, Thordarson D. Ankle syndesmotic injury. J Am Acad Orthop Surg 15:330–339, 2007. 6. Cotton FJ. The ankle and foot. In: Dislocations and Joint Fractures, WB Saunders, Philadelphia, PA, 1910, pp. 535–588. 7. Boden SD, Labropoulos PA, McCowin P, Lestini WF, Hurwitz SR. Mechanical considerations for the syndesmosis screw: a cadaver study. J Bone Joint Surg Am 71:1548–1555, 1989.
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