Purpose: This in-vitro study was conducted to assess the effect of a computer-assisted method of performing shoulder hemiarthroplasty, in comparison to traditional techniques, on passive glenohumeral joint kinematics during abduction.

Methods: Seven pairs of fresh-frozen cadaveric shoulders were tested. One specimen from each pair was randomized to the computer-assisted technique, while the contralateral shoulder underwent a traditional hemiar-throplasty using standard surgical guides by an experienced shoulder surgeon. A simulated four-part proximal humerus fracture was created in each shoulder and was reconstructed using a modular shoulder hemiarthroplasty system (Anatomical Shoulder Hemiarthroplasty System, Centrepulse Orthopaedics Inc, Austin, TX). CT data and computerized simulations of anatomical characteristics were used in the computer-assisted technique. An electromagnetic tracking device (Flock of Birds, Ascension Technologies, Burlington, VT) in conjunction with custom-written software (LabVIEW, National Instruments, Austin, TX) enabled real-time intra-operative feedback.||Passive abduction of the glenohumeral joint was conducted and the resulting motion was quantified using the aforementioned tracking device. Coordinate systems, created on both the humerus and scapula from digitized anatomical landmarks, were used to transform the kinematic data into clinically relevant parameters. Statistical analyses were performed using one-way Analyses of Variance (ANOVAs) followed by post-hoc Student-Newman-Keuls multiple comparisons (p< 0.05).

Results: In the superior-inferior direction, a significant difference in joint kinematics (p=0.011) was found between the computer-assisted and the traditional technique, with the traditional technique resulting in a more inferiorly positioned humeral head at all angles of elevation. There was no difference in translation between the native shoulders and the computer-assisted hemiarthroplasty (p> 0.05). In the anterior-posterior direction there was no difference measured in the position of the humeral head between the two surgical techniques, which were both similar to the native shoulder (p> 0.05).

Conclusions: This is the first known study to examine the effects of a computer-assisted method for performing shoulder hemiarthroplasty. Our results show that the computer-assisted approach should allow improved restoration of glenohumeral joint kinematics relative to conventional techniques, potentially resulting in improved patient outcomes and implant durability.