Reconstruction of the AC Joint
ABSTRACT & COMMENTARY
Synopsis: Reconstruction of the acromioclavicular (AC) joint for acromioclavicular joint separations can reproduce strength and stiffness similar to the intact coracoclavicular ligaments, but only some repairs do so.
Source: Harris RI, et al. Structural properties of the intact and the reconstructed coracoclavicular ligament complex. Am J Sports Med 2000;28:103-108.
Shoulder separations commonly occur during athletics and frequently can be treated without surgery. When surgery is necessary, several techniques exist to reconstruct the acromioclavicular (AC) joint.1 The method that is biomechanically strongest is unclear. Harris and colleagues in a cadaver model performed a biomechanical experiment to test the strength and stiffness of an intact coracoclavicular ligament complex (conoid, trapezoid ligaments). They measured average ligamentous stiffness (103 N/m) and elongation to failure (7.7 mm) in 19 cadaver specimens. They then tested several reconstruction methods with the same testing conditions for load to failure. The coracoclavicular slings (polyester tape) and suture anchors provided similar strength but significantly greater deformation than intact ligaments.2 The Bosworth screw provided similar strength and stiffness to the intact ligaments, but only if inserted with bicortical fixation.3 The coracoacromial ligament transfers (Weaver-Dunn procedure) were the weakest and least stiff.4 Harris et al suggest supplementation of the Weaver-Dunn procedure with another technique. They also state that coracoclavicular slings are strong but elastic. Coracoid screw placement strength depends upon accurate placement. Harris et al conclude that these biomechanical factors should guide the surgeon both in choice of fixation and in progression of rehabilitation.
COMMENT BY STEPHEN B. GUNTHER, MD
Most AC separations do not require surgical reconstruction. However, the ideal fixation for the few cases that do require surgery has been controversial, and most of these surgical procedures have a significant failure rate. This laboratory experiment answers important questions about both the intact and the reconstructed coracoclavicular ligament complex. The intact coracoclavicular ligament failed at midsubstance or by avulsion at approximately 500N. The conoid ligament appears to be the primary restraint to superior translation, with the trapezoid playing a relatively secondary role. This is the first study to describe the ultimate structural properties of the intact coracoclavicular ligament complex.
None of the reconstructions reproduced the native biomechanical characteristics of the intact coracoclavicular ligament complex, but some were relatively comparable. These results provide important quantitative data about the immediate mechanical behavior of a few types of reconstruction for AC joint separations. This information is important because the reconstructive procedures have a significant complication rate, which includes screw loosening, pin migration, recurrent deformity, clavicle fracture, and others. The surgeon must carefully screen patients to avoid unnecessary surgery, and must also attend to detail in order to reproduce biomechanical strength and stiffness for surgical repairs.
References
1. Rockwood CA, et al. Injuries to the acromioclavicular joint. In: Rockwood CA, et al, eds. Fractures in Adults. vol. 2, 4th ed. Philadelphia, Pa: Lippincott-Raven; 1996: 1341-1413.
2. Neviaser RJ. Injuries to the clavicle and acromioclavicular joint. Ortho Clin N Am 1987;18:433-438.
3. Bosworth BM. Acromioclavicular separation: New method of repair. S Gynecol Obstet 1941;73:866-871.
4. Weaver JK, Dunn HK. Treatment of acromioclavicular joint injuries, especially complete acromioclavicular separation. J Bone Joint Surg Am 1972;54:1187-1194.
Which of the following AC joint reconstruction techniques were weakest and least stiff?
a. Coraco-acromial ligament transfer (Weaver-Dunn)
b. Bosworth screw with bicortical fixation
c. Coracoclavicular sling (polyester tape)
d. Suture anchors
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