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Comparison of tension band wire and cancellous bone screw fixation for medial malleolar fractures
Comparison of Tension Band Wire and Cancellous Bone Screw Fixation for Medial Malleolar Fractures A comparison study of the relative strength of tension-band fixation versus cancellous bone screw fixation of medial malleolar ankle fractures was performed on ten fresh-frozen lower limbs from five cadavers. The mean force recorded at clinical failure using cancellous screws was 60.98 N (range 33.49 to 117.86 N) compared with 129.30 N using tension-band fixation (range 85.20 to 194.64 N). Therefore, cancellous screws exhibited only 47. 16% the strength of tension-band wiring at clinical failure. (The Journal of Foot & Ankle Surgery 36(4):284-289, 1997) Key words: medial malleolus, ankle fracture, medial malleolar fracture, tension band fixation.
Brent A. Johnson, DPM 1 Lawrence M. Fallat, DPM, FACFAS2 AthOUgh ankle fractures are a common injury presenting in the Emergency Room, treatment criteria and options are controversial. The benefits of conservative versus surgical treatment have been debated in the literature, and it is now accepted that open reduction and internal fixation, using techniques developed and refined by AO International, provide superior clinical and functional results in displaced ankle fractures (lIS). Debate continues in the literature as to the optimal means of fixation of ankle fractures. Tension band figure-of-eight wire fixation and cancellous bone screws are routinely used to secure medial malleolar fractures, however, there is little criteria and few studies to indicate which type of fixation is superior. Ease of application, frequency of loosening of implants, and most importantly, protection of the fracture site by the most rigid osteosynthesis possible, are factors that need to be considered. Anatomy
The media malleolus is the most distal extension of the tibia and articulates laterally with the talus. This articular surface is slightly concave and is contiguous with the articular surface of the tibial plafond. The From the Department of Podiatric Surgery, Oakwood Hospital Downriver Center, Lincoln Park, MI 48146. 1 Submitted During First Year Surgical Residency, Oakwood Hospital Downriver Center. 2 Diplomate, American Board of Podiatric Surgery. Director, Podiatric Surgical Residency, Oakwood Hospital Downriver Center. Address Correspondence to: Director, Podiatric Surgical Residency, Oakwood Hospital Downriver Center, 20555 Ecorse Taylor, MI 48180. The Journal of Foot & Ankle Surgery 1067-2516/97/3604-0284$4.00/0 Copyright © 1997 by the American College of Foot and Ankle Surgeons
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medial malleolus consists of the anterior colliculus, posterior colliculus, and the intercollicular groove. The anterior colliculus usually descends approximately 0.5 em. lower than the posterior colliculus and is usually separated by an intercollicular groove of approximately 0.5 to 1.0 em. (16). The deltoid ligament attaches to the medial malleolus and consists of a deep and superficial component. The deep anterior talotibial portion originates on the intercollicular groove and posterior border of the anterior colliculus, and the deep posterior talotibial ligament originates on the intercollicular groove and the posterior colliculus. These two deep components insert on the medial surface of the talus (17). The superficial portion consists of the naviculotibial, calcanotibial, and superficial talotibial ligaments that attach to the navicular, tibia, and calcaneus. It should be noted that the superficial deltoid originates primarily from the anterior colliculus. The anterior colliculus can be involved in avulsion fractures with or without concurrent rupture of the deep deltoid ligament (18). Mechanism of Injury
Fractures of the medial malleolus can be either transverse or oblique as a result of an avulsion mechanism. These may result in combination with a Weber" type B or C fibular fracture, or of a vertical orientation, as seen with a Weber type A fibular fracture (19, 20). According to the Lauge-Hansen classification, Weber type B fractures are the result of a supination-external rotation or 3 Weber A fibular fractures occur below the level of the ankle joint, Weber B fractures occur at the level of the ankle, and Weber C fractures occur along the level of the ankle joint.
pronation-abduction mechanism, type C fractures are the result of pronation-external rotation force , and type A fractures are a result of supination-adduction forces (17, 21). Muller described a classification system for medial malleolar fractures. Type A fractures are avulsions of the tip of the medial malleolus, type B are avulsion fractures occurring at the level of the ankle joint, type C fractures are oblique fractures, and type D fractures are characterized by a vertical orientation. Both type A and B fractures are oriented horizontally. Avulsion fractures of the medial malleolus may present in several different variations. There may be an avulsion of the anterior colliculus, an anterior colliculus avulsion in combination with a rupture of the deep deltoid ligament, or an avulsion of the entire medial malleolus (18). Fixation Techniques
The technique of fixation recommended by AO/ASIF" for the open repair of Muller type D vertical medial malleolar fractures produced by Weber type A mechanisms involves the use of two small cancellous screws with the use of an additional buried Kirschner wire, as needed, to provide stability in comminuted fractures (20, 22, 23). For fractures resulting from an avulsion mechanism, AO/ASIF recommends the use of paired cancellous screws, a cancellous screw and a K-wire to provide rotational stability, or a tension band using interosseous wire with two K-wires (20, 22). AO/ASIF indicates that tension band fixation is most valuable for small fragments that preclude the use of a screw and for osteoporotic bone that would not allow adequate screw purchase. They state that considerable exposure is needed for implant removal with tension band fixation, and that they generally prefer, even with small avulsion fractures, to attempt fixation with one or two 4.0-mm. cancellous screws (20). Tension band fixation is a form of dynamic interfragmental compression that relies on eccentric loading of bone (20). Pauwels recognized the bracing characteristics of ligaments and muscles against normal stresses generated by weightbearing in the long bones of the lower extremity (24). It is these weightbearing forces, acting eccentrically through soft tissue across fracture planes, that provides dynamic compression when using tension-band techniques (20, 22). If a long bone is loaded concentrically, compression results at all points along the long axis of the bone (20). A bending deformation, caused either by eccentric loading parallel to the long axis of the bone, or the application of forces perpendicular to the long axis as seen in three- or 4 Arbeitgemeinschaft fur OsteosynthesisfragenJAssociation for the Study of Internal Fixation.
four-point bending configurations, will result in com pression on the concave side of the bone and tension on the convex side (25, 26). The greater the distance of the point of application of the force from the central longitudinal axis of the column the more the column will bend and the greater will be the tensile and compressive stresses and strains. The magnitude of the stresses and strains is always greatest at the surface of the column and will decrease toward the center of the column (27). The place where the forces are zero is called the neutral axis (25-28). As the bending deformation continues, the cortex fractures on the convex, tensioned surface and the fracture propagates through the bone. As the fracture line moves toward the compression side of the bone, the neutral axis also continues to move. When the fracture is complete, only tensile forces act on the fracture site , which theoretically moves the neutral axis completely off the bone (Fig. 1) (29). A tension-band device, either in the form of dynamic compression plate, neutralization plate, or wire, is placed on the convex surface of the bone where tensile forces act on the normal, intact bone. This fixation prevents the fracture site from gapping and causes the neutral axis to fall on the interface between the fixation device and the bone, causing compressive forces to act along the entire fracture site . As stated previously, tension-band fixation relies on the presence of deforming eccentric forces across the fracture site . This method of fixation is best suited for avulsion fractures involving the olecranon of the ulna, the gre ater trochanter of the femur, patella, medial or lateral malleoli, or fifth metatarsal base fractures. The configuration of tension-band fixation for medial malleolar fractures was originally described by AO/ASIF as monofilament wire run through an interosseous hole in the tibia, proximal to the fracture site and looped in a figure-eight configuration around two proximally directed K-wires that are placed across the site. Absorbable suture has also been recommended for small fractures in the hand (22) and the ankle (30). The literature is divided as to the optimal method of fixation for medial malleolar fractures. Several authors recommend the primary use of cancellous screws with tension band fixation being reserved for use in small or osteoporotic fragments (5, 7, 8, 17, 31, 32) . Other authors recommend the exclusive use of tension-band wiring (6, 13, 18,29,33). Kanakis et al. reported on the use of tension band wiring in 104 closed medial malleolar fractures and 7 pseudarthroses with 92.3% excellent results in the fracture group and 6 excellent results in the pseudarthrosis group. Ostrum and Litsky had similar results in their series of 31 medial malleolar fractures (33). Georgiadis and White reported on a series of 22 patients with tension-band fixation and 21 satisfactory results (13). VOLUME 36, NUMBER 4, 1997
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1 a.
11 i I
b.
N.A.
1 c.
11
r1
N.A. FIGURE 1 A, Force applied concentrically to bone results in equal compression across fractu re site. B, Force appl ied eccent rically to bone results in tens ile forces acting on the convex surface and compressive forces acting on the concave surface. The neutral axis is the collection of points where neither compression nor tension arises. C, Tension-band fixation applied to the convex surface of the fracture site causes the neutral axis to fall on itself, result ing in compression occurring across the entire fracture.
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Because of the debate in the literature, the authors chose to make a comparative study to determine the relative and actual strength of fixation using two 4.0-mm. cancellous screws versus ten sion band wiring, as previously described. Materials and Methods
Ten fresh-frozen cadaver legs (paired specimens from five cadavers) were obtained. No specimen had any evidence of previous operative treatment of the ankle or of grossly abnormal motion. The average age of the specimens was 76 years with a range of 52 to 90 years. After thawing , the legs were dissected free of soft tissue from midshaft tibia to just proximal to the ankle with care taken to ensure that the ankle joint capsule and surrounding ligamentous attachments were preserved. All osteotomies and fixation were performed by the senior author. A transvers e osteotomy of the medial malleolus at the level of the ankle joint was performed on each specimen to simulate a Muller type B medial malleolar fracture. Fixation was then achieved using two 4.0-mm. partially threaded cancellous screws 40 mm. in length in the right ankles , and tension-band fixation using two 1.6-mm. K-wires extending 5 em. into bone, tension band wire, and a 4.0-mm. fully threaded 20-mm. cancellous screw in the left ankles. All fixation was done using Synthes" implants and instrumentation and utilizing the standard AO/ASIF technique. A 9164-inch Steinmann" pin was driven through the center of the talar body from medial to lateral. The specimens were mounted on a brace , and a bracket exactly 3.5 em. from the medial surface of the specimen was placed over the Steinmann pin . This bracket was attached to an Instron Model 8500 series servohydraulic system", and the specimens were loaded in an upward direction (Fig. 2). This resulted in an eversion force being applied to the foot, and a distraction across the medial malleolar osteotomy, recreating the forces that cause an avulsion fracture. A laser noncontacting extensometer'' measured the distance between reflective spots directly above and below the osteotomies for displacements data. Before this testing, the authors decided that a 2-mm. gap at the osteotomy site would constitute the clinical definition of fixation failure (Fig. 3). Distraction proceeded at a rate of 0.05-mm. per sec., and data was collected at a rate of two sets per sec. Each set consisted of activator position, Synthes (USA ), Paoli, PA. Zimmer, War saw, IN. 7 Instron, Canton, MA. s The extensometer uses a laser beam to reflect off two spots that act as reference points. As the simulated fracture distracted , the laser measured the increased distance between the points. 5 6
FIGURE 2 Specimen mounted before application of load. Note that it is mounted in an inverted position.
FIGURE 3 Specimen reveals displacement of fracture site after load application. The reflective strips used to measure displacement are clearly visible.
load application in newtons, and the laser-measured displacement.
TABLE 1 Force application at clinical failure
Results
Testing proceeded on all specimens with 4 mm. of displacement created, to record fixation failure characteristics. Peri-articular soft tissue failure (deltoid ligament and joint capsule) was noted to occur just after 2mm. displacement had been achieved during testing of the tension band fixated specimen from cadaver #1. Further displacement did not occur. All other specimens were successfully stressed to 4-mm. displacement with failure characterized by fixation pull-out rather than breakage of fixation. This was consistent for both tensionband wiring and cancellous screws. Comparison of load application at failure for all specimens is noted in Table 1. The mean force recorded at 2 mm. of distraction using cancellous-screw fixation was 60.98 N (range 33.49 to 117.86 N) compared with
Cadaver
Cancellous Screw Fixation (N)
Tension Band Fixation (N)
1
117.86 35.39 48.41 69.75 33.49
151.56 108.53 194.64 85.20 106.55
2 3 4 5
129.30 N using tension-band fixation (range 85.20 to 194.64 N). Therefore, cancellous screws exhibited only 47.16% the strength of tension-band wiring at clinical failure. Discussion
At our institution, we use 1.6-mm. K-wires, tensionband wire as provided in the AO sets, and a 4.0-mm. fully threaded cancellous anchor screw instead of the 3.5-mm. cortical screw (described by Cleak and Dawson) VOLUME 36, NUMBER 4, 1997
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150
100
Z
I I
Q)
o
0
u,
I
t
50
A
0
0
2
3
4
Fracture Displacement (mm) FIGURE 4 Test results of specimen number 5. The set of data points labeled "Au represents the tension-band fixated ankle. "8" represents the cancellous-screw fixated ankle. Results are representative of all specimens and, they indicate relationship of fracture displacement and force application for both tension-band fixation and cancellous-screw fixation.
that replaces the proximal interosseous tunnel (34). This anchor screw is technically easier to insert than the interosseous tunnel, which frequently requires greater periosteal dissection and retraction due to the broad, flat surface of the medial tibia and the need to drill from anterior to posterior. Often, difficulty arises in creating a suitable tunnel and inserting the wire through it. An anchor screw also decreases the chance of pull-through in osteoporotic bone, but it must be located within the concavity just proximal to the distal metaphyseal "flare" of the tibia in order to prevent possible soft tissue irritation. This configuration is the authors' preferred method of fixation for all medial malleolar fractures of an avulsion mechanism, as well as for medial malleolar osteotomies for exposure of medial talar dome transchondral fractures (35, 36). In our hands this technique provides rigid, reproducible fixation. An additional ad vantage of tension-band wiring is that, depending on the characteristics of the individual fracture, the wire loop can be tightened anteriorly, posteriorly, or both to fully reduce and apply compression. Some fractures of the medial malleolus are displaced more anteriorly or posteriorly; with tension band wiring, the surgeon has the ability to aid in reduction by selectively tightening the wire. Tension-band fixation is also very strong, and it is excellent when postoperative treatment includes the early use of continuous passive motion. Testing of each specimen but one continued until 4 mm . of displacement had occurred in order to measure the effects of increasing load and the resulting displacement, as well as to observe where and how fixation 288
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failure resulted. In four of the five pairs, the force needed to create continued displacement at the osteotomy site remained fairly constant in the ankles fixated with cancellous screws, but increasing force was needed to produce the continued displacement in the ankles fixated with tension-band wire. This indicates that tension-band fixation provides greater resistance against displacement at a fracture site as greater forces are applied, and it also provides superior pull-out strength as compared with cancellous screws. During the testing there was no sudden failure or "giving way," only a slow and steady opening of the osteotomy site. As the specimens were stressed past clinical failure, both types of fixation and medial malleolar fragments were noted to pull free from the intact tibia. The tension-band loops stretched, along with the medial malleolar fragment. In no instance was fracture of either bone or fixation observed (Fig. 4). In tension-band fixation of medial malleolar fractures, it is important that all soft tissue attachments be left in place; eccentric forces are transmitted across the fracture site through the deltoid ligament and joint capsule in the same manner that Pauwels noted forces to be transmitted through the tensor fascia latae across the femur (24). During the testing of the tension-band fixated specimen from cadaver #1, just after the osteotomy had reached 2 mm., the joint capsule and deltoid ligament failed, and further displacement did not occur. Therefore, in this instance, the failure of the soft tissue attachments occurred before further displacement could result. As previously noted, tension-band fixation has been recommended for use in osteoporotic bone. Four of the five cadavers used in this study were 77 years or older at the time of death, which may alter our results in terms of comparative strength of cancellous-screw fixation. Of interest, however, was cadaver #3, which was 52-yearsold at time of death. Although the youngest of the five cadavers, and noted to have extremely thick, strong cortical bone, fixation using cancellous screws was achieved only with great difficulty due to poor cancellous bone quality; when the tension-band fixated ankle was tested, the highest force (194.64 N) of the series was required to produce failure. Conclusion
Tension-band fixation provides both flexibility and ease of insertion. It is a technically undemanding method that can be used with small or osteoporotic fragments. The authors feel that tension-band fixation 's superior strength makes it the method of choice in all avulsion fractures of the medial malleolus.
Acknowledgments
The authors thank Kurt Miller of Axel Products, Ypsilanti, MI for technical assistance in specimen testing, and Synthes (USA) for donating biomaterials used in this study. References 1. Ali, M. S., McLauren, C. A. N., Rouholamin, E., O'Connor, B. T. Ankle fractures in the elderly: non-operative or operative treatment. J. Orthop. Trauma 1:275-280, 1987. 2. Beauchamp, C. G., Clay, N. P., Thexton, P. W. Displaced ankle fractures in patients over 50 years of age. J. Bone Joint Surg. 65B:329-332, 1983. 3. Burwell, H. N., Charnley, A. D. The treatment of displaced fractures of the ankle by rigid internal fixation and early joint motion. J. Bone Joint Surg. 47B:634-660, 1965. 4. DeSouza, C. J., Gustilo, R. B., Meyer, T. J. Results of operative treatment of displaced external rotation-abduction fractures of the ankle. J. Bone Joint Surg. 67A:1066-1074, 1985. 5. Johnson, E. E., Daulin, L. B. Open ankle fractures: the indications for open reduction internal fixation. Clin. Orthop. 292:118-127, 1993. 6. Kanakis, T. E., Papadakis, E., Orfanos, A., Andreadakis, A., Xylouris, E. Figure of eight tension band in the treatment of fracture and pseudoarthroses of the medial malleolus. Injury 21:393-397, 1990. 7. Lund-Kristensen, J., Grieff, J., Riegels-Nielson, P. Malleolar fractures treated with rigid internal fixation and immediate mobilization. Injury 13:191-195, 1981. 8. Mast, J. W., Teipner, W. A. A reproducible approach to the internal fixation of adult ankle fracture: rationale, technique, and early results. Orthop. Clin. North Am. 11:661-679, 1980. 9. Pettrone, F. A., Gail, M., Pee, D., Fitzpatrick, T., Van Herpe, C. B. Quantitative criteria for prediction of the results after displaced fracture of the ankle. J. Bone Joint Surg. 65A:667-677, 1983. 10. Phillips, W. A., Schwartz, H. S., Keller, C. S. A prospective randomized study of the management of severe ankle fractures. J. Bone Joint Surg. 67A:67-78, 1985. 11. Roberts, R. S. Surgical treatment of displaced ankle fractures. Clin. Orthop. 172:164-170, 1983. 12. Tunturi, T., Kemppainen, K, Patiala, H., Svokas, M., Tomminen, 0., Rokkanen, P. Importance of anatomical reduction for subjective recovery after ankle fracture. Acta Orthop. Scand. 54:641-647, 1983. 13. Georgiadis, G. M., White, D. B. Modified tension band wiring of medial malleolar ankle fractures. Foot Ankle 16:64-68, 1995. 14. Michelson, J. D. Fractures about the ankle. J. Bone Joint Surg. 77A:142-152, 1995. 15. Schaffer, J. J., Manoli, A. The antiglide plate for distal fibular fractures. J. Bone Joint Surg. 69A:596-604, 1987. 16. Sarrafian, S. K. Osteology, ch. 2. In Anatomy ofthe Foot and Ankle, 2nd ed., pp. 45-47, J. B. Lippenecott Co., Philadelphia, 1993. 17. Hughes, J. The medial malleolus in ankle fractures. Orthop. Clin. North Am. 11:649-660, 1980.
18. Skie, M. c., Ebraheim, N. A., Woldenberg, L., Randall, K. Fracture of the anterior colliculus. J. Trauma 38:642-647, 1995. 19. Muller, M. E., Nazarian, S., Koch, P., Schatzker, J. Tibia/fibula, ch.d, In The Comprehensive Classification of Fractures of the Long Bones, pp. 190-191, Springer-Verlag, New York, 1980. 20. Muller, M. E., Allgower, M., Schneider, R., Willenegger, H. Screws and plates and their application, ch. 3. In Manual ofInternal Fixation, 3rd ed., pp. 226-228, Springer-Verlag, New York, 1991. 21. Lauge, N. Fractures of the ankle. Arch. Surg. 56:259-317, 1948. 22. Heim, D., Pfeiffer, K. M. General techniques for the internal fixation of small fractures, ch. 3, The ankle joint, ch. 16. In Internal Fixation of Small Fractures, 3rd ed., pp. 34-35, 295-296, SpringerVerlag, New York, 1988. 23. Toolan, B. c., Kovel, K. J., Kummer, F. J., Saunders, R., Zuckermann, J. D. Vertical shear fractures of the medial malleolus: a biomechanical study of five internal fixation techniques. Foot Ankle 15:483-489, 1994. 24. Pauwels, V. F. Uber die bedeutung der bauprinzipien des stutzund bewegungsapparates fur die beanspruchung der rohrenknochen (The functional significance of the apparatus for the support and movement ofthe long bones). Acta Anat. 12:207-227, 1951. 25. Alms, M. Fracture mechanics. J. Bone Joint Surg. 43B:162-166, 1961. 26. Cochran, G. V. B. Essential concepts for orthopedics, ch. 1, Biomechanics of orthopedic structures, ch. 3. In A Primer of Orthopedic Biomechanics, pp. 36-38, 161-164, Churchill-Livingstone, New York, 1982. 27. Evans, F. G. Stress and strain in the long bones of the lower extremity, AAOS Instructional Course Lectures, vol. 9, pp. 264271,1952. 28. Bechtol, C. O. Engineering principles applied to orthopedic surgery, AAOS Instructional Course Lectures, vol. 9, pp. 257-264, 1952. 29. Parkinson, D. E., Joseph, R., Edelman, R. Biomechanical principles of tension band wiring applied to fractures of the distal fibula and fifth metatarsal base. J. Foot Surg. 27:149-156, 1988. 30. Wissing, J. C., Van der Werken, C. Die zuggurtung sosteosynthese aus resorbierbarem material. Unfallchirurg 94:45-46, 1991. 31. Traffon, P. G., Bray, T. J., Simpson, L. A. Fractures and soft tissue injuries of the ankle. ch. 52. In Extremity Trauma, vol. 2, pp. 1925-1928, edited by J. Kennedy and F. W. Blaisdell, Thieme Medical Publications, New York, 1992. 32. Hamilton, W. A. External rotation injuries, ch. 10. In Traumatic Disorders of the Ankle pp. 147-151, edited by W. A. Hamilton, Springer-Verlag, New York, 1985. 33. Ostrum, R. F., Litsky, A. S. Tension band fixation of medial malleolus fractures. J. Orthop. Trauma 6:464-468, 1992. 34. Cleak, D. K., Dawson, M. H. O. Tension band wiring of avulsion fractures of the medial malleolus: a modified technique minimizing soft tissue injury. Injury 13:519-520, 1982. 35. Wallen, E. A., Fallat, L. M. Crescentric transmalleolar osteotomy for optimal exposure of the medial talar dome. J. Foot Surg. 28:389-394, 1989. 36. Ly, P. N., Fallat, L. M. Transchondral fractures of the talus: a review of 64 surgical cases. J. Foot Ankle Surg. 32:352-374, 1993.
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Brent A. Johnson, DPM 1 Lawrence M. Fallat, DPM, FACFAS2 AthOUgh ankle fractures are a common injury presenting in the Emergency Room, treatment criteria and options are controversial. The benefits of conservative versus surgical treatment have been debated in the literature, and it is now accepted that open reduction and internal fixation, using techniques developed and refined by AO International, provide superior clinical and functional results in displaced ankle fractures (lIS). Debate continues in the literature as to the optimal means of fixation of ankle fractures. Tension band figure-of-eight wire fixation and cancellous bone screws are routinely used to secure medial malleolar fractures, however, there is little criteria and few studies to indicate which type of fixation is superior. Ease of application, frequency of loosening of implants, and most importantly, protection of the fracture site by the most rigid osteosynthesis possible, are factors that need to be considered. Anatomy
The media malleolus is the most distal extension of the tibia and articulates laterally with the talus. This articular surface is slightly concave and is contiguous with the articular surface of the tibial plafond. The From the Department of Podiatric Surgery, Oakwood Hospital Downriver Center, Lincoln Park, MI 48146. 1 Submitted During First Year Surgical Residency, Oakwood Hospital Downriver Center. 2 Diplomate, American Board of Podiatric Surgery. Director, Podiatric Surgical Residency, Oakwood Hospital Downriver Center. Address Correspondence to: Director, Podiatric Surgical Residency, Oakwood Hospital Downriver Center, 20555 Ecorse Taylor, MI 48180. The Journal of Foot & Ankle Surgery 1067-2516/97/3604-0284$4.00/0 Copyright © 1997 by the American College of Foot and Ankle Surgeons
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medial malleolus consists of the anterior colliculus, posterior colliculus, and the intercollicular groove. The anterior colliculus usually descends approximately 0.5 em. lower than the posterior colliculus and is usually separated by an intercollicular groove of approximately 0.5 to 1.0 em. (16). The deltoid ligament attaches to the medial malleolus and consists of a deep and superficial component. The deep anterior talotibial portion originates on the intercollicular groove and posterior border of the anterior colliculus, and the deep posterior talotibial ligament originates on the intercollicular groove and the posterior colliculus. These two deep components insert on the medial surface of the talus (17). The superficial portion consists of the naviculotibial, calcanotibial, and superficial talotibial ligaments that attach to the navicular, tibia, and calcaneus. It should be noted that the superficial deltoid originates primarily from the anterior colliculus. The anterior colliculus can be involved in avulsion fractures with or without concurrent rupture of the deep deltoid ligament (18). Mechanism of Injury
Fractures of the medial malleolus can be either transverse or oblique as a result of an avulsion mechanism. These may result in combination with a Weber" type B or C fibular fracture, or of a vertical orientation, as seen with a Weber type A fibular fracture (19, 20). According to the Lauge-Hansen classification, Weber type B fractures are the result of a supination-external rotation or 3 Weber A fibular fractures occur below the level of the ankle joint, Weber B fractures occur at the level of the ankle, and Weber C fractures occur along the level of the ankle joint.
pronation-abduction mechanism, type C fractures are the result of pronation-external rotation force , and type A fractures are a result of supination-adduction forces (17, 21). Muller described a classification system for medial malleolar fractures. Type A fractures are avulsions of the tip of the medial malleolus, type B are avulsion fractures occurring at the level of the ankle joint, type C fractures are oblique fractures, and type D fractures are characterized by a vertical orientation. Both type A and B fractures are oriented horizontally. Avulsion fractures of the medial malleolus may present in several different variations. There may be an avulsion of the anterior colliculus, an anterior colliculus avulsion in combination with a rupture of the deep deltoid ligament, or an avulsion of the entire medial malleolus (18). Fixation Techniques
The technique of fixation recommended by AO/ASIF" for the open repair of Muller type D vertical medial malleolar fractures produced by Weber type A mechanisms involves the use of two small cancellous screws with the use of an additional buried Kirschner wire, as needed, to provide stability in comminuted fractures (20, 22, 23). For fractures resulting from an avulsion mechanism, AO/ASIF recommends the use of paired cancellous screws, a cancellous screw and a K-wire to provide rotational stability, or a tension band using interosseous wire with two K-wires (20, 22). AO/ASIF indicates that tension band fixation is most valuable for small fragments that preclude the use of a screw and for osteoporotic bone that would not allow adequate screw purchase. They state that considerable exposure is needed for implant removal with tension band fixation, and that they generally prefer, even with small avulsion fractures, to attempt fixation with one or two 4.0-mm. cancellous screws (20). Tension band fixation is a form of dynamic interfragmental compression that relies on eccentric loading of bone (20). Pauwels recognized the bracing characteristics of ligaments and muscles against normal stresses generated by weightbearing in the long bones of the lower extremity (24). It is these weightbearing forces, acting eccentrically through soft tissue across fracture planes, that provides dynamic compression when using tension-band techniques (20, 22). If a long bone is loaded concentrically, compression results at all points along the long axis of the bone (20). A bending deformation, caused either by eccentric loading parallel to the long axis of the bone, or the application of forces perpendicular to the long axis as seen in three- or 4 Arbeitgemeinschaft fur OsteosynthesisfragenJAssociation for the Study of Internal Fixation.
four-point bending configurations, will result in com pression on the concave side of the bone and tension on the convex side (25, 26). The greater the distance of the point of application of the force from the central longitudinal axis of the column the more the column will bend and the greater will be the tensile and compressive stresses and strains. The magnitude of the stresses and strains is always greatest at the surface of the column and will decrease toward the center of the column (27). The place where the forces are zero is called the neutral axis (25-28). As the bending deformation continues, the cortex fractures on the convex, tensioned surface and the fracture propagates through the bone. As the fracture line moves toward the compression side of the bone, the neutral axis also continues to move. When the fracture is complete, only tensile forces act on the fracture site , which theoretically moves the neutral axis completely off the bone (Fig. 1) (29). A tension-band device, either in the form of dynamic compression plate, neutralization plate, or wire, is placed on the convex surface of the bone where tensile forces act on the normal, intact bone. This fixation prevents the fracture site from gapping and causes the neutral axis to fall on the interface between the fixation device and the bone, causing compressive forces to act along the entire fracture site . As stated previously, tension-band fixation relies on the presence of deforming eccentric forces across the fracture site . This method of fixation is best suited for avulsion fractures involving the olecranon of the ulna, the gre ater trochanter of the femur, patella, medial or lateral malleoli, or fifth metatarsal base fractures. The configuration of tension-band fixation for medial malleolar fractures was originally described by AO/ASIF as monofilament wire run through an interosseous hole in the tibia, proximal to the fracture site and looped in a figure-eight configuration around two proximally directed K-wires that are placed across the site. Absorbable suture has also been recommended for small fractures in the hand (22) and the ankle (30). The literature is divided as to the optimal method of fixation for medial malleolar fractures. Several authors recommend the primary use of cancellous screws with tension band fixation being reserved for use in small or osteoporotic fragments (5, 7, 8, 17, 31, 32) . Other authors recommend the exclusive use of tension-band wiring (6, 13, 18,29,33). Kanakis et al. reported on the use of tension band wiring in 104 closed medial malleolar fractures and 7 pseudarthroses with 92.3% excellent results in the fracture group and 6 excellent results in the pseudarthrosis group. Ostrum and Litsky had similar results in their series of 31 medial malleolar fractures (33). Georgiadis and White reported on a series of 22 patients with tension-band fixation and 21 satisfactory results (13). VOLUME 36, NUMBER 4, 1997
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1 a.
11 i I
b.
N.A.
1 c.
11
r1
N.A. FIGURE 1 A, Force applied concentrically to bone results in equal compression across fractu re site. B, Force appl ied eccent rically to bone results in tens ile forces acting on the convex surface and compressive forces acting on the concave surface. The neutral axis is the collection of points where neither compression nor tension arises. C, Tension-band fixation applied to the convex surface of the fracture site causes the neutral axis to fall on itself, result ing in compression occurring across the entire fracture.
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Because of the debate in the literature, the authors chose to make a comparative study to determine the relative and actual strength of fixation using two 4.0-mm. cancellous screws versus ten sion band wiring, as previously described. Materials and Methods
Ten fresh-frozen cadaver legs (paired specimens from five cadavers) were obtained. No specimen had any evidence of previous operative treatment of the ankle or of grossly abnormal motion. The average age of the specimens was 76 years with a range of 52 to 90 years. After thawing , the legs were dissected free of soft tissue from midshaft tibia to just proximal to the ankle with care taken to ensure that the ankle joint capsule and surrounding ligamentous attachments were preserved. All osteotomies and fixation were performed by the senior author. A transvers e osteotomy of the medial malleolus at the level of the ankle joint was performed on each specimen to simulate a Muller type B medial malleolar fracture. Fixation was then achieved using two 4.0-mm. partially threaded cancellous screws 40 mm. in length in the right ankles , and tension-band fixation using two 1.6-mm. K-wires extending 5 em. into bone, tension band wire, and a 4.0-mm. fully threaded 20-mm. cancellous screw in the left ankles. All fixation was done using Synthes" implants and instrumentation and utilizing the standard AO/ASIF technique. A 9164-inch Steinmann" pin was driven through the center of the talar body from medial to lateral. The specimens were mounted on a brace , and a bracket exactly 3.5 em. from the medial surface of the specimen was placed over the Steinmann pin . This bracket was attached to an Instron Model 8500 series servohydraulic system", and the specimens were loaded in an upward direction (Fig. 2). This resulted in an eversion force being applied to the foot, and a distraction across the medial malleolar osteotomy, recreating the forces that cause an avulsion fracture. A laser noncontacting extensometer'' measured the distance between reflective spots directly above and below the osteotomies for displacements data. Before this testing, the authors decided that a 2-mm. gap at the osteotomy site would constitute the clinical definition of fixation failure (Fig. 3). Distraction proceeded at a rate of 0.05-mm. per sec., and data was collected at a rate of two sets per sec. Each set consisted of activator position, Synthes (USA ), Paoli, PA. Zimmer, War saw, IN. 7 Instron, Canton, MA. s The extensometer uses a laser beam to reflect off two spots that act as reference points. As the simulated fracture distracted , the laser measured the increased distance between the points. 5 6
FIGURE 2 Specimen mounted before application of load. Note that it is mounted in an inverted position.
FIGURE 3 Specimen reveals displacement of fracture site after load application. The reflective strips used to measure displacement are clearly visible.
load application in newtons, and the laser-measured displacement.
TABLE 1 Force application at clinical failure
Results
Testing proceeded on all specimens with 4 mm. of displacement created, to record fixation failure characteristics. Peri-articular soft tissue failure (deltoid ligament and joint capsule) was noted to occur just after 2mm. displacement had been achieved during testing of the tension band fixated specimen from cadaver #1. Further displacement did not occur. All other specimens were successfully stressed to 4-mm. displacement with failure characterized by fixation pull-out rather than breakage of fixation. This was consistent for both tensionband wiring and cancellous screws. Comparison of load application at failure for all specimens is noted in Table 1. The mean force recorded at 2 mm. of distraction using cancellous-screw fixation was 60.98 N (range 33.49 to 117.86 N) compared with
Cadaver
Cancellous Screw Fixation (N)
Tension Band Fixation (N)
1
117.86 35.39 48.41 69.75 33.49
151.56 108.53 194.64 85.20 106.55
2 3 4 5
129.30 N using tension-band fixation (range 85.20 to 194.64 N). Therefore, cancellous screws exhibited only 47.16% the strength of tension-band wiring at clinical failure. Discussion
At our institution, we use 1.6-mm. K-wires, tensionband wire as provided in the AO sets, and a 4.0-mm. fully threaded cancellous anchor screw instead of the 3.5-mm. cortical screw (described by Cleak and Dawson) VOLUME 36, NUMBER 4, 1997
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150
100
Z
I I
Q)
o
0
u,
I
t
50
A
0
0
2
3
4
Fracture Displacement (mm) FIGURE 4 Test results of specimen number 5. The set of data points labeled "Au represents the tension-band fixated ankle. "8" represents the cancellous-screw fixated ankle. Results are representative of all specimens and, they indicate relationship of fracture displacement and force application for both tension-band fixation and cancellous-screw fixation.
that replaces the proximal interosseous tunnel (34). This anchor screw is technically easier to insert than the interosseous tunnel, which frequently requires greater periosteal dissection and retraction due to the broad, flat surface of the medial tibia and the need to drill from anterior to posterior. Often, difficulty arises in creating a suitable tunnel and inserting the wire through it. An anchor screw also decreases the chance of pull-through in osteoporotic bone, but it must be located within the concavity just proximal to the distal metaphyseal "flare" of the tibia in order to prevent possible soft tissue irritation. This configuration is the authors' preferred method of fixation for all medial malleolar fractures of an avulsion mechanism, as well as for medial malleolar osteotomies for exposure of medial talar dome transchondral fractures (35, 36). In our hands this technique provides rigid, reproducible fixation. An additional ad vantage of tension-band wiring is that, depending on the characteristics of the individual fracture, the wire loop can be tightened anteriorly, posteriorly, or both to fully reduce and apply compression. Some fractures of the medial malleolus are displaced more anteriorly or posteriorly; with tension band wiring, the surgeon has the ability to aid in reduction by selectively tightening the wire. Tension-band fixation is also very strong, and it is excellent when postoperative treatment includes the early use of continuous passive motion. Testing of each specimen but one continued until 4 mm . of displacement had occurred in order to measure the effects of increasing load and the resulting displacement, as well as to observe where and how fixation 288
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failure resulted. In four of the five pairs, the force needed to create continued displacement at the osteotomy site remained fairly constant in the ankles fixated with cancellous screws, but increasing force was needed to produce the continued displacement in the ankles fixated with tension-band wire. This indicates that tension-band fixation provides greater resistance against displacement at a fracture site as greater forces are applied, and it also provides superior pull-out strength as compared with cancellous screws. During the testing there was no sudden failure or "giving way," only a slow and steady opening of the osteotomy site. As the specimens were stressed past clinical failure, both types of fixation and medial malleolar fragments were noted to pull free from the intact tibia. The tension-band loops stretched, along with the medial malleolar fragment. In no instance was fracture of either bone or fixation observed (Fig. 4). In tension-band fixation of medial malleolar fractures, it is important that all soft tissue attachments be left in place; eccentric forces are transmitted across the fracture site through the deltoid ligament and joint capsule in the same manner that Pauwels noted forces to be transmitted through the tensor fascia latae across the femur (24). During the testing of the tension-band fixated specimen from cadaver #1, just after the osteotomy had reached 2 mm., the joint capsule and deltoid ligament failed, and further displacement did not occur. Therefore, in this instance, the failure of the soft tissue attachments occurred before further displacement could result. As previously noted, tension-band fixation has been recommended for use in osteoporotic bone. Four of the five cadavers used in this study were 77 years or older at the time of death, which may alter our results in terms of comparative strength of cancellous-screw fixation. Of interest, however, was cadaver #3, which was 52-yearsold at time of death. Although the youngest of the five cadavers, and noted to have extremely thick, strong cortical bone, fixation using cancellous screws was achieved only with great difficulty due to poor cancellous bone quality; when the tension-band fixated ankle was tested, the highest force (194.64 N) of the series was required to produce failure. Conclusion
Tension-band fixation provides both flexibility and ease of insertion. It is a technically undemanding method that can be used with small or osteoporotic fragments. The authors feel that tension-band fixation 's superior strength makes it the method of choice in all avulsion fractures of the medial malleolus.
Acknowledgments
The authors thank Kurt Miller of Axel Products, Ypsilanti, MI for technical assistance in specimen testing, and Synthes (USA) for donating biomaterials used in this study. References 1. Ali, M. S., McLauren, C. A. N., Rouholamin, E., O'Connor, B. T. Ankle fractures in the elderly: non-operative or operative treatment. J. Orthop. Trauma 1:275-280, 1987. 2. Beauchamp, C. G., Clay, N. P., Thexton, P. W. Displaced ankle fractures in patients over 50 years of age. J. Bone Joint Surg. 65B:329-332, 1983. 3. Burwell, H. N., Charnley, A. D. The treatment of displaced fractures of the ankle by rigid internal fixation and early joint motion. J. Bone Joint Surg. 47B:634-660, 1965. 4. DeSouza, C. J., Gustilo, R. B., Meyer, T. J. Results of operative treatment of displaced external rotation-abduction fractures of the ankle. J. Bone Joint Surg. 67A:1066-1074, 1985. 5. Johnson, E. E., Daulin, L. B. Open ankle fractures: the indications for open reduction internal fixation. Clin. Orthop. 292:118-127, 1993. 6. Kanakis, T. E., Papadakis, E., Orfanos, A., Andreadakis, A., Xylouris, E. Figure of eight tension band in the treatment of fracture and pseudoarthroses of the medial malleolus. Injury 21:393-397, 1990. 7. Lund-Kristensen, J., Grieff, J., Riegels-Nielson, P. Malleolar fractures treated with rigid internal fixation and immediate mobilization. Injury 13:191-195, 1981. 8. Mast, J. W., Teipner, W. A. A reproducible approach to the internal fixation of adult ankle fracture: rationale, technique, and early results. Orthop. Clin. North Am. 11:661-679, 1980. 9. Pettrone, F. A., Gail, M., Pee, D., Fitzpatrick, T., Van Herpe, C. B. Quantitative criteria for prediction of the results after displaced fracture of the ankle. J. Bone Joint Surg. 65A:667-677, 1983. 10. Phillips, W. A., Schwartz, H. S., Keller, C. S. A prospective randomized study of the management of severe ankle fractures. J. Bone Joint Surg. 67A:67-78, 1985. 11. Roberts, R. S. Surgical treatment of displaced ankle fractures. Clin. Orthop. 172:164-170, 1983. 12. Tunturi, T., Kemppainen, K, Patiala, H., Svokas, M., Tomminen, 0., Rokkanen, P. Importance of anatomical reduction for subjective recovery after ankle fracture. Acta Orthop. Scand. 54:641-647, 1983. 13. Georgiadis, G. M., White, D. B. Modified tension band wiring of medial malleolar ankle fractures. Foot Ankle 16:64-68, 1995. 14. Michelson, J. D. Fractures about the ankle. J. Bone Joint Surg. 77A:142-152, 1995. 15. Schaffer, J. J., Manoli, A. The antiglide plate for distal fibular fractures. J. Bone Joint Surg. 69A:596-604, 1987. 16. Sarrafian, S. K. Osteology, ch. 2. In Anatomy ofthe Foot and Ankle, 2nd ed., pp. 45-47, J. B. Lippenecott Co., Philadelphia, 1993. 17. Hughes, J. The medial malleolus in ankle fractures. Orthop. Clin. North Am. 11:649-660, 1980.
18. Skie, M. c., Ebraheim, N. A., Woldenberg, L., Randall, K. Fracture of the anterior colliculus. J. Trauma 38:642-647, 1995. 19. Muller, M. E., Nazarian, S., Koch, P., Schatzker, J. Tibia/fibula, ch.d, In The Comprehensive Classification of Fractures of the Long Bones, pp. 190-191, Springer-Verlag, New York, 1980. 20. Muller, M. E., Allgower, M., Schneider, R., Willenegger, H. Screws and plates and their application, ch. 3. In Manual ofInternal Fixation, 3rd ed., pp. 226-228, Springer-Verlag, New York, 1991. 21. Lauge, N. Fractures of the ankle. Arch. Surg. 56:259-317, 1948. 22. Heim, D., Pfeiffer, K. M. General techniques for the internal fixation of small fractures, ch. 3, The ankle joint, ch. 16. In Internal Fixation of Small Fractures, 3rd ed., pp. 34-35, 295-296, SpringerVerlag, New York, 1988. 23. Toolan, B. c., Kovel, K. J., Kummer, F. J., Saunders, R., Zuckermann, J. D. Vertical shear fractures of the medial malleolus: a biomechanical study of five internal fixation techniques. Foot Ankle 15:483-489, 1994. 24. Pauwels, V. F. Uber die bedeutung der bauprinzipien des stutzund bewegungsapparates fur die beanspruchung der rohrenknochen (The functional significance of the apparatus for the support and movement ofthe long bones). Acta Anat. 12:207-227, 1951. 25. Alms, M. Fracture mechanics. J. Bone Joint Surg. 43B:162-166, 1961. 26. Cochran, G. V. B. Essential concepts for orthopedics, ch. 1, Biomechanics of orthopedic structures, ch. 3. In A Primer of Orthopedic Biomechanics, pp. 36-38, 161-164, Churchill-Livingstone, New York, 1982. 27. Evans, F. G. Stress and strain in the long bones of the lower extremity, AAOS Instructional Course Lectures, vol. 9, pp. 264271,1952. 28. Bechtol, C. O. Engineering principles applied to orthopedic surgery, AAOS Instructional Course Lectures, vol. 9, pp. 257-264, 1952. 29. Parkinson, D. E., Joseph, R., Edelman, R. Biomechanical principles of tension band wiring applied to fractures of the distal fibula and fifth metatarsal base. J. Foot Surg. 27:149-156, 1988. 30. Wissing, J. C., Van der Werken, C. Die zuggurtung sosteosynthese aus resorbierbarem material. Unfallchirurg 94:45-46, 1991. 31. Traffon, P. G., Bray, T. J., Simpson, L. A. Fractures and soft tissue injuries of the ankle. ch. 52. In Extremity Trauma, vol. 2, pp. 1925-1928, edited by J. Kennedy and F. W. Blaisdell, Thieme Medical Publications, New York, 1992. 32. Hamilton, W. A. External rotation injuries, ch. 10. In Traumatic Disorders of the Ankle pp. 147-151, edited by W. A. Hamilton, Springer-Verlag, New York, 1985. 33. Ostrum, R. F., Litsky, A. S. Tension band fixation of medial malleolus fractures. J. Orthop. Trauma 6:464-468, 1992. 34. Cleak, D. K., Dawson, M. H. O. Tension band wiring of avulsion fractures of the medial malleolus: a modified technique minimizing soft tissue injury. Injury 13:519-520, 1982. 35. Wallen, E. A., Fallat, L. M. Crescentric transmalleolar osteotomy for optimal exposure of the medial talar dome. J. Foot Surg. 28:389-394, 1989. 36. Ly, P. N., Fallat, L. M. Transchondral fractures of the talus: a review of 64 surgical cases. J. Foot Ankle Surg. 32:352-374, 1993.
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