Achieving accurate glenoid component placement during total shoulder arthroplasty is one of the most challenging aspects of the procedure. In most cases, there is substantial arthritis-related bone deformity with limited exposure of the glenoid surface intra-operatively, making it difficult to visualize. April D. Armstrong, M.D., chief, shoulder and elbow surgery, Bone and Joint Institute, says, “When the glenoid component isn’t accurately placed, it tends to loosen and eventually requires a revision procedure.” Using traditional placement techniques in one investigation, errors in version and inclination of the central drill line, on average, were approximately 9 degrees and version error correlated with the degree of arthritic glenoid version.¹
To improve glenoid positioning accuracy, Dr. Armstrong teamed with bioengineer Gregory Lewis, Ph.D., assistant professor, orthopaedics and rehabilitation, Penn State College of Medicine, to successfully develop and test a novel, patient-specific pin array guide device. The findings were described in a podium presentation at the March 2015 meeting of the American Academy of Orthopaedic Surgeons (AAOS) and recently published in the Journal of Shoulder and Elbow Surgery.¹ Dr. Lewis explains, “We aimed to develop a re-useable device that is customizable for each patient and cost-effective. It stands apart from available devices, which can be costly, have production-related wait times or don’t fully adjust to the individual’s glenoid surface.” The prototype guide is an acrylic disk with a central hole to guide drilling and glenoid placement. The central hole is surrounded by an array of six screws (or “pins”) that can each be adjusted in length to conform to a patient’s unique anatomy. (Figure)
In their recent study using 3-D printed polymer models of patient scapulas, Armstrong, et al., found that the guide led to more accurate glenoid component placement, with significantly smaller version and inclination errors (approximately 3 degrees ±2 degrees, P≤0.02), compared to errors with traditional, unassisted placement using the finger centerline method to estimate drill position (9 degrees ±6 or 7 degrees). Dr. Armstrong adds, “During pre-operative planning, patient CT scans are used to create a digital 3-D scapula surface reconstruction. Based on this virtual model, we can determine the central drill line and needed length of each guide pin to find a ‘best fit’ for each patient’s unique anatomy.” (Figure)
Dr. Lewis notes, “More research and development is needed to make this device broadly available. It has not yet been used clinically.” Dr. Armstrong adds, “The procedures and polymer models for our proof-of-concept study also could be used for the purpose of training medical students and residents in glenoid positioning for arthroplasty.”
April D. Armstrong, BSc(PT), M.Sc., M.D., FRCSC
Professor, Orthopaedics and Rehabilitation
Chief, Shoulder and Elbow Orthopaedic Surgery
FELLOWSHIPS: Orthopaedic surgery, shoulder and elbow, Washington University Barnes-Jewish Hospital, St. Louis, Mo.; Orthopaedic surgery, hand and upper extremity, London Health Sciences Centre, London, Ontario
RESIDENCY: Orthopaedic surgery, hand and upper extremity, London Health Sciences Centre, London, Ontario
MEDICAL SCHOOL: University of Western Ontario Schulich School of Medicine and Dentistry, London, Ontario
Gregory S. Lewis, Ph.D.
Assistant Professor, Orthopaedics and Rehabilitation
POSTDOCTORAL FELLOWSHIP: Orthopaedic surgery, Penn State College of Medicine, Hershey, Pa.
DOCTORAL STUDY: Mechanical engineering, The Pennsylvania State University, University Park, Pa.
- Lewis GS, Stevens NM, Armstrong A. 2015. Testing of a novel pin array guide for accurate three-dimensional glenoid component positioning. J Shoulder Elbow Surg. 24:1939-47.