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  • Alterations in Glenohumeral Force Distribution Following Rotator Cuff Injury and Repair

    Elan Golan*, Ryan Krochak, Maya-Deza Culbertson, Garret Garafolo-Gonzales, Jack ChouekaBiomechanics Laboratory, Division of Orthopedic Surgery, Maimonides Medical Center, Brooklyn, NY

    Department of Orthopaedic Surgery Maimonides Medical CenterBrooklyn, NY, USAegolan@maimonidesmed.org.org Copyright 2016 Maimonides Medical Center Department of Orthopedic Research

    CONCLUSION:While a rotator cuff tear creates glenohumeraldisassociation and an unbalanced shoulder, re-approximation of a larger sized rotator cuff lesion can similarly result in potentially detrimental imbalances secondary to overtensioning of the glenohumeral joints soft-tissue stabilizers.

    INTRODUCTION The rotator cuff represents one of the key dynamic stabilizers of the glenohumeral

    joint, functioning to maintain appropriate glenohumeral contact via a force couple mechanism.1

    Injury to the rotator cuff which compromises this protective function, often resulting in an unbalanced shoulder that experiences increases in glenohumeral force loads, potentially predisposing to degeneration and arthritis

    Studies have demonstrated high-tension repairs to result, and repair of larger lesions to result in less favorable clinical outcomes

    Recent biomechanical data has demonstrated the presence of a rotator cuff tear to correlate with increased incidence of glenohumeral degeneration.2

    The ability of rotator cuff repair to restore glenohumeral force loads to a baseline uninjured level remains largely unknown

    HYPOTHESISReapproximation of larger rotator cuff lesions will result in increased force-loading about the glenohumeral joint, even following anatomic re-approximation of a lesion.

    MATERIALS AND METHODSTransduction mapping was performed on the glenohumeral joint of ten fresh-frozen cadaveric shoulder specimens via insertion of a calibrated pressure-mapping sensor. Sensors were inserted through the rotator interval via a standard deltoid splitting

    approach to ensure soft-tissue stabilizers were not violated Following a baseline force measurements, analysis of force intensity and total

    glenohumeral contact area was performed in each specimen for 6 simulated injury and treatment conditions:

    A) A 1 cm supraspinatus lesion; B) 2-suture repair of the 1 cm lesion; C) removal of the 2-suture repair; D) a 2 cm supraspinatus lesion; E) 4-suture repair of the 2 cm lesion and; F) removal of the 3-suture repair.

    Repairs were performed via bone with data including glenohumeral force, contact-area, and force per unit area (pressure) recorded over 60s intervals.

    Values for each lesion, repair, and post-repair condition were expressed as a proportion of baseline measurements. Means and standard deviations were derived and compared via Students t-tests.

    Specimen Testing Images: Left A medial to lateral tear recreated using a pre-measured stencil as originally described by Beherens et al.3Right - re-approximation of a larger 2cm tear employing 4 mattress

    sutures passed laterally through bone tunnels.

    DISCUSSION Rotator cuff injury leads to alterations in glenohumeral forces,

    with significant increases in glenohumeral contact-pressures following repair of larger supraspinatus lesions.

    These findings offer a possible explanation for the high rate of degenerative changes demonstrated following rotator cuff repair.

    Further study is warranted to determine how current treatment methods might be improved to result in glenohumeral contact pressures resembling those experienced prior to injury.

    References:1. Burkhart SS, Esch JC, Jolson RS. The rotator crescent and rotator cable:

    an anatomic description of the shoulder's "suspension bridge". Arthroscopy. 1993;9(6):611-616.

    2. Hsu HC, Luo ZP, Stone JJ, Huang TH, An KN. Correlation between rotator cuff tear and glenohumeral degeneration. Acta Orthop Scand. 2003;74(1):89-94.

    3. Behrens SB, Bruce B, Zonno AJ, Paller D, Green A. Initial fixation strength of transosseous-equivalent suture bridge rotator cuff repair is comparable with transosseous repair. Am J Sports Med. 2012;40(1):133-140.

    Figure: Force-tracings of glenohumeral distribution forces for 2cm tear conditions. Following baseline (A) measurements, a decrease in total loading is seen with creation of a 2cm tear (B), with subsequent repair (C)yielding large increases. Finally, removal of repair (D) resulted in loading below baseline levels.

    Testing Images: Left Mounted specimen with sensor implanted via rotator interval. Middle Arthroscopic confirmation of sensor placement within the glenoids concavity. Right deltoid split employed to create rotator-cuff tears

    Alterations in Glenohumeral Force Distribution Following Rotator Cuff Injury and RepairElan Golan*, Ryan Krochak, Maya-Deza Culbertson, Garret Garafolo-Gonzales, Jack ChouekaBiomechanics Laboratory, Division of Orthopedic Surgery, Maimonides Medical Center, Brooklyn, NY

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