Isokinetic strength differences between patients with primary reverse and total shoulder prostheses ☆ Muscle strength quantified with a dynamometer Tjarco D.W. Alta a,e, ⁎, DirkJan (H.E.J.) Veeger b,c,1 , Joelly M. de Toledo d,2 , Thomas W.J. Janssen b,e,3 , W. Jaap Willems a,f,4 a Department of Orthopaedic Surgery and Traumatology, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands b MOVE Research Institute Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands c Faculty of Mechanical, Maritime and Materials Engineering, Section Biomechatronics and Biorobotics, Delft University of Technology, Delft, The Netherlands d Physical Education School, Exercise Research Laboratory, Federal University of Rio Grande do Sul, Porto Alegre, Brazil e Amsterdam Rehabilitation Research Center, Reade, Amsterdam, The Netherlands f Clinic “de Lairesse”, Amsterdam, The Netherlands abstract article info Article history: Received 29 January 2014 Accepted 18 August 2014 Keywords: Isokinetic strength Reverse shoulder arthroplasty Total shoulder arthroplasty Constant–Murley score Background: Range of motion after total shoulder arthroplasty is better than after reverse shoulder arthroplasty, however with similar clinical outcome. It is unclear if this difference can only be found in the different range of motion or also in the force generating capacity. Questions: (1) are isokinetically produced joint torques of reverse shoulder arthroplasty comparable to those of total shoulder arthroplasty? (2) Does this force-generating capacity correlate with functional outcome? Methods: Eighteen reverse shoulder arthroplasty patients (71 years (SD 9 years)) (21 shoulders, follow-up of 21 months (SD 10 months)) were recruited, 12 total shoulder arthroplasty patients (69 years (SD 9 years)) (14 shoulders, follow-up of 35 months (SD 11 months)). Pre- and post-operative Constant– Murley scores were obtained; two isokinetic protocols (ab-/adduction and ex-/internal rotations) at 60°/ s were performed. Findings: Twelve of 18 reverse shoulder arthroplasty patients generated enough speed to perform the test (13 shoulders). Mean ab-/adduction torques are 16.3 Nm (SD 5.6 Nm) and 20.4 Nm (SD 11.8 Nm). All total shoul- der arthroplasty patients generated enough speed (14 shoulders). Mean ab-/adduction torques are 32.1 Nm (SD 13.3 Nm) and 43.1 Nm (SD 21.5 Nm). Only 8 reverse shoulder arthroplasty patients (9 shoulders) could perform ex-/internal rotation tasks and all total shoulder arthroplasty patients. Mean ex-/internal rotation torques are 9.3 Nm (SD 4.7 Nm) and 9.2 Nm (SD 2.1 Nm) for reverse shoulder arthroplasty, and 17.9 Nm (SD 7.7 Nm) and 23.5 Nm (SD 10.6 Nm) for total shoulder arthroplasty. Significant correlations between sub-scores: activity, mo- bility and strength and external rotation torques for reverse shoulder arthroplasty. Moderate to strong correlation for sub-scores: strength in relation to abduction, adduction and internal rotation torques for total shoulder arthroplasty. Interpretation: Shoulders with a total shoulder arthroplasty are stronger. This can be explained by the absence of rotator cuff muscles and (probably) medialized center of rotation in reverse shoulder arthroplasty. The strong correlation between external rotation torques and post-operative Constant–Murley sub-scores demonstrates that external rotation is essential for good clinical functioning in reverse shoulder arthroplasty. © 2014 Elsevier Ltd. All rights reserved. Clinical Biomechanics 29 (2014) 965–970 ☆ Ethical Board Review statement: Approval was obtained. Study number WO 05.027. METC, Onze Lieve Vrouwe Gasthuis, P.O. Box 95500, 1090 HM Amsterdam, The Netherlands. ⁎ Corresponding author at: Amsterdam Rehabilitation Research Center, Reade, P.O. Box 58271, 1040 HG Amsterdam, The Netherlands. E-mail addresses: tdw.alta@gmail.com (T.D.W. Alta), h.e.j.veeger@vu.nl (D.(H.E.J.) Veeger), joellytoledo@hotmail.com (J.M. de Toledo), t.janssen@reade.nl (T.W.J. Janssen), w.j.willems@xs4all.nl (W.J. Willems). 1 Faculty of Human Movement Sciences, VU University, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands. 2 Physical Education School, Exercise Research Laboratory, Federal University of Rio Grande do Sul, Rua Felizardo 750, Jardim Botânico, Porto Alegre, RS, Brazil. 3 Amsterdam Rehabilitation Research Center, Reade, P.O. Box 58271, 1040 HG Amsterdam, The Netherlands. 4 Clinic “de Lairesse”, Valeriusplein 11, 1075 BG Amsterdam, The Netherlands. http://dx.doi.org/10.1016/j.clinbiomech.2014.08.018 0268-0033/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech