Biomechanical Comparison of Reconstruction Techniques for Disruption of the Acromioclavicular and Coracoclavicular Ligaments

Albert W. Pearsall IV, MD, J. Marcus Hollis, PhD, George V. Russell, Jr., MD, David A. Stokes, MD

Disclosures

J South Orthop Assoc. 2002;11(1) 

In This Article

Discussion

Severe injuries to the acromioclavicular joint impart tremendous force to disrupt both the acromioclavicular and coracoclavicular ligaments. Although closed treatment is advocated for the majority of these injuries, significant acromioclavicular joint subluxation or frank dislocation can lead to skin irritation, pain, arthritis, and shoulder weakness.[3] Operative treatment has been advocated in selected grade III and nearly all grade IV through VI injuries, and numerous surgical techniques have been described.[2,3,8,9,15,16,17,18,19] Of the more than 200 articles written on the surgical treatment of acromioclavicular joint injuries, more than 50% of them describe a modification of a previously described surgical technique.[20] However, only a limited number of articles have biomechanically analyzed currently used surgical constructs for reconstruction of the acromioclavicular joint.[11,13,15]

Many studies represent clinical outcome evaluations of various reconstruction procedures.[20,21] Bargren et al[15] assessed AC joint wiring in conjunction with coracoid loop fixation both clinically and biomechanically. Although only one cadaveric specimen was tested, the authors were able to show less coracoclavicular displacement using a Dacron loop around the coracoclavicular joint. Shortcomings in their study included imprecise measurements of displacement and the use of only one cadaveric specimen for biomechanical testing.[15]

Critical requirements to the successful reconstruction of the acromioclavicular joint are reduction of the joint and adequate construct strength to maintain joint reduction during healing.[7,8,10] Recently, published biomechanical studies have documented load to failure and stiffness of loop augmentation of the coracoclavicular ligaments similar to that of the native CC ligaments.[12,13] Motamedi et al[13] reported the failure load of the native AC joint ligament complex to be 724 N ± 230 N, with reconstructions of braided PDS placed through or around the clavicle showing no significant differences. Stiffness of the intact CC ligaments was 115 N ± 36 N. Reconstruction with braided PDS provided less stiffness than the native CC ligaments whether placed around the clavicle or through a clavicular drill hole (90 N versus 99 N).[13] In our study, the age of the specimens precluded biomechanical testing to failure. After preliminary tests showed clavicular fracture before failure of surgical construct, we elected to record coracoclavicular displacement at 50 N. Although load to failure of all groups could not be recorded, construct stiffness was determined for all groups.[12,13] The stiffness values calculated in the current study are in accordance with values reported by other authors.[12,13]

One limitation of the study was the inability to apply displacement loads greater than 50 N to any of the groups tested. Unfortunately, the cadaveric specimens tested were osteoporotic and several early specimens sustained clavicular fractures without failure of the construct. It was believed that a load of 50 N would enable data trends to be recorded without the risk of specimen fracture. A second shortcoming of our study is that all soft tissue restraints around the AC joint were removed before testing. This tissue provides a dynamic and static stabilizing effect in the clinical situation. The purpose of the current study was not to simulate these potential stabilizing forces in our biomechanical model. Finally, the current study evaluated only the initial strength of the tested reconstruction procedures and does not take into account the effects of ligamentous healing. Despite these limitations, we believe that the trends of displacement and stiffness noted for the intact and reconstruction groups were valid.

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