2015 ISAKOS Biennial Congress ePoster #2123

Biomechanical Analysis of Translational- and Rotational-Loading on the 3D Motion of the Acromioclavicular Joint

Knut Beitzel, MD, MA, Cologne GERMANY
Elifho Obopilwe, ME, BSc, Farmington, CT UNITED STATES
John Apostoloakos, BA, Farmington, CT UNITED STATES
Mark P. Cote, PT, DPT, MSCTR, Farmington, CT UNITED STATES
Ryan P. Russell, MA, Farmington, CT UNITED STATES
Ryan Charette, MS, Farmington, CT UNITED STATES
Hardeep Singh, MD, Farmington, CT UNITED STATES
Robert A. Arciero, MD, Farmington, CT UNITED STATES
Andreas B. Imhoff, MD, Prof., Munich, Bavaria GERMANY
Augustus D. Mazzocca, MS, MD, Farmington, CT UNITED STATES

Department of Orthopaedic Surgery, UCONN Health Center, Farmington, CT, USA

FDA Status Not Applicable

Summary: Translational and rotational loading of the AC joint with cut AC ligaments while the CC ligaments were preserved resulted in significant distraction of the joint especially under rotational loading.

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Abstract:

Background

The clavicle is the anterior strut to the scapula, and the proper function of the acromioclavicular (AC) ligaments contributes to the physiologic joint motion. These structures not only control horizontal and vertical translation but also play an important role in controlling rotation. An anatomic repair should optimally reconstruct both the coracoclavicular (CC) ligaments and the AC ligaments to control the optimal physiologic function (translation and rotation). The purpose of this study was to evaluate the 3D motion of the distal clavicle under translational and rotational loading conditions with intact and cut AC ligaments while preserving the CC ligaments. The hypothesis was that such instability of the capsulo-ligamentous structures of the AC joint would result in significant distraction of the joint especially under rotational loading.

Methods

A total of 36 cadaveric shoulders were tested with a MTS 858 Bionix II Servohydraulic testing system. All specimens underwent bone density evaluation (Lunar DPX IQ; GE Healthcare). An optical measuring system using 2 digitizing cameras was used to evaluate the 3D movement of the specimen. Both cameras were set up to track the movement of these markers for 3D video motion analysis by using MaxTraq 3D (Innovision Systems Inc) software. The marker positions to determine the distraction of the AC joint (the change in distance between the clavicle and acromion) were the anterior, superior, and posterior AC ligament. Translational testing (70N) included anterior (AT), posterior (PT), and superior (ST) displacements. Rotational testing included evaluation of AC joint distraction under 20° anterior (AR) and 30° posterior rotation (PR) about the clavicle´s long axis (5° per second). The joint was tested first with intact and then cut AC ligaments while the CC ligaments were preserved.

Results

Anterior, posterior and superior translation resulted in significantly increased mean distraction (p<0.05) of all markers. (AT(native): 2.26±0.53mm; AT(cut): 6.31±1.26mm; PT(native): 4.87±1.33mm; PT(cut): 13.62±1.27mm; ST(native): 3.33±0.71mm; ST(cut): 4.67±0.51mm). Rotational analysis resulted in significant changes (p<0.05) of all markers. Anterior markers: AR(native):6.02±1.11mm, AR(cut):9.94±1.31mm, PR(native):9.18±1.75mm, PR(cut):13.14±1.46mm; the superior markers: AR(native):5.75±0.86mm; AR(cut):12.22±1.29mm; PR(native):8.15±1.52mm; PR(cut):14.73±1.25mm); and the posterior markers: AR(native):7.14±1.02mm; AR(cut):13.56±1.10mm; PR(native):10.76±1.13mm; PR(cut):15.50±1.64mm) respectively.

Conclusion

PT, AT and ST resulted in significant mean distraction of the joint. Rotational loads also significantly displaced all markers even though the CC ligaments were preserved. The most important finding was that the center of rotation (COR) moved anteriorly when the AC ligaments were cut (measured as significant more motion of the posterior markers compared to the anterior markers under rotational loads). This resulted in an increased distraction especially of the posterior joint. We therefore believe that failure of AC joint reconstructions may occur because of the persisting translational and rotational instability of the AC joint even if the CC ligaments are anatomically perfectly reconstructed. Thus it is critical, that anatomic reconstructions of the AC ligaments properly restore the posterior ligamentous structures of the AC joint and by this re-orientate the COR back into the centered axis of the joint.