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Purpose: Component position is critical in knee arthroplasty. We propose using a navigated knee axis (NKA) that is kinematically determined using a navigation system as an alignment reference, instead of defining the transepicondylar axis (TEA) with bony landmarks. This paper investigates whether this NKA should be computed over small arc segments versus over a full range of motion. Methods: Twelve unembalmed cadaver knees were tested. A navigation system computed the NKA for segments and for the full arc of motion in multiple planes. Results: The NKA computed near extension was different from the plane perpendicular to the mechanical axis (P > 0.005), while the NKA computed in flexion matched the TEA. Conclusion: The NKA determined from the full arc of motion was more reproducible and more closely estimated important knee parameters.

Pain is routinely implicated as a factor when considering impaired movement in injured populations. Movement velocity is often considered during the rehabilitation process; unfortunately our understanding of pain's impact on shoulder movement velocity in rotator cuff tear patients is less understood. Therefore, the purpose of this study was to test the hypothesis that there would be an increase in peak and mean shoulder elevation velocities following the decrease of shoulder pain in rotator cuff tear patients, regardless of tear size. Fifteen subjects with full-thickness rotator cuff tears (RCT) performed humeral elevation and lowering in three planes before and after receiving a lidocaine injection to relieve pain. Pain was assessed using a visual analog scale. Humeral elevation velocity data were collected using an electromagnetic tracking system. A significant reduction in pain (pre-injection 3.53 ± 1.99; post-injection 1.23 ± 1.43) resulted in significant increases in maximum and mean humeral elevation velocities. Mean shoulder elevation and lowering velocities increased 15.10 ± 2.45% while maximum shoulder movement velocities increased 12.77 ± 3.93%. Furthermore, no significant relationships were noted between tear size and movement velocity. These significant increases in movement velocity provide evidence to further support the notion that human motion can be inhibited by injury-associated pain, and that by reducing that pain through clinical interventions, human movement can be impacted in a positive fashion.