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 joint’s 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 Student’s 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 glenoid’s concavity. Right – deltoid split employed to create rotator-cuff tears