ORIGINAL ARTICLES Neer Award 2006: Biomechanical assessment of inferior tuberosity placement during hemiarthroplasty for four-part proximal humeral fractures G. Russell Huffman, MD, MPH, a John M. Itamura, MD, b,c Michelle H. McGarry, MS, b Long Duong, BA, b Jeremy Gililland, BS, b James E. Tibone, MD, b,c and Thay Q. Lee, PhD, b Long Beach and Los Angeles, CA; and Philadelphia, PA Tuberosity malpositioning commonly occurs and is associated with a decline in clinical function after prosthetic shoulder reconstruction for proximal humeral fractures. This study assesses the biomechanical effects of inferior tuberosity position on glenohumeral joint forces and humeral head position at multiple positions. Eight fresh-frozen cadaveric shoulders were tested. Hemiarthroplasty was performed with preservation of anatomic tuberosity height and with 10 mm and 20 mm of inferior tuberosity displacement. The rotator cuff, deltoid, pectoralis major, and latissimus dorsi muscles were statically loaded. Contact forces and humeral head position were recorded within a functional range of motion. Glenohumeral joint forces shifted significantly superiorly ( P <.05) at 30  of abduction after both 10 mm and 20 mm of tuberosity displacement. At 60  of glenohumeral abduction, glenohumeral joint forces remained significantly altered after tuberosity displacement of 10 mm and 20 mm compared with the intact height ( P < .005). This study demonstrates that, during hemiarthroplasty performed for proximal humeral fractures, malpositioning the tuberosities inferiorly results in significant superior glenohumeral joint force displacement. These findings suggest that the mechanical advantage of the shoulder abductor muscles is compromised with inferior tuberosity malpositioning and may help to explain inferior functional results seen in these patients. (J Shoulder Elbow Surg 2008;17:189-196.) Shoulder hemiarthroplasty remains a common treat- ment for displaced 4-part fractures of the proximal humerus. Reported success with this treatment, how- ever, has varied. Typically, pain relief is reliably achieved, yet functional outcomes depending on mus- cle strength and range of motion are less consistently achieved. 2,14,17,18 Intrinsic, or patient-related, factors influencing outcome include age, bone quality, frac- ture comminution, and comorbidities. 18 Technical fac- tors associated with outcome include restoration of humeral head height, proper retroversion of the hu- meral component, stable tuberosity fixation, and union of the tuberosities to the humeral shaft. 3,11,14,18 Tuberosity malpositioning has also been shown to affect functional outcomes adversely after hemi- arthroplasty for 3- and 4-part proximal humeral fractures. 3,14,15,18 Frankle et al 7 examined the biome- chanical consequences of tuberosity malreduction in the horizontal plane (ie, malpositioning of the tuberosi- ties medially on the humeral shaft) and showed that tuberosity malpositioning leads to both abnormal gle- nohumeral kinematics and increased torque require- ments for shoulder rotation. A more common technical concern, however, is placement of the tuberosities in an inferior position at the time of reconstruction. Diffi- culty arises in the surgical treatment of 4-part proximal humeral fractures associated with comminution at the surgical neck. As restoration of humeral height is neces- sary for component stability, obtaining stable fixation of the greater and lesser tuberosities to the humeral shaft From a Penn Sports Medicine Center, University of Pennsylvania, Philadelphia, b Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System and University of California, Irvine, Long Beach, and c Department of Orthopaedic Surgery, University of Southern California, Los Angeles. This study received the Charles Neer Award at the annual American Shoulder and Elbow Surgeons Meeting, Chicago, Illinois, Sep- tember 2006. Reprint requests: Thay Q. Lee, PhD, Orthopaedic Biomechanics Lab- oratory, VA Long Beach Healthcare System (09/151), 5901 E 7th St, Long Beach, CA 90822 (E-mail: tqlee@med.va.gov). Copyright ª 2008 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2008/$34.00 doi:10.1016/j.jse.2007.06.017 189