Are shoulders with a reverse shoulder prosthesis strong enough? A pilot study.
BACKGROUND
It has been suggested that limited active ROM of reverse shoulder prostheses relates to lack of strength. However, the postoperative strength has not been quantified.


OBJECTIVE
We therefore measured joint torques in patients with reverse shoulder prostheses and correlated torques with functional scores.


METHODS
We recruited 33 patients (age, 72 ± 8 years) with a reverse prosthesis (37 shoulders, 21 primary and 16 revisions). We obtained Constant-Murley, DASH, and Simple Shoulder Test ([D]SST) scores, and performed two isokinetic protocols (abduction/adduction and external/internal rotation) at 60° per second. Minimum followup was 4 months (average, 23 months; range, 4-63 months).


RESULTS
Twenty-three patients (24 shoulders; 13 primaries, 11 revisions) were able to perform at least one of the defined tasks. Mean abduction and adduction torques were 15 Nm ± 7 Nm and 16 Nm ± 10 Nm (19%-78% of normal shoulders). External and internal rotation tasks could be performed by only 13 patients (14 shoulders; nine primary, five revisions) generating 9 Nm ± 4 Nm and 8 Nm ± 3 Nm, respectively (13%-71% of normal shoulders). We found moderate correlations between Constant-Murley, DASH and (D)SST (D = Dutch translation) scores and abduction and external rotation.


CONCLUSIONS
Patients with a reverse prosthesis had reduced strength when compared with normal values reported in the literature (only 65% of patients could perform the protocol). This effect was greatest for external rotation and might explain clinical outcomes with which a moderately strong relationship was observed. Our observations suggest limited strength is a major factor in reduced ROM.
Department of Orthopaedic Surgery and Traumatology, Onze Lieve Vrouwe Gasthuis, Amsterdam, The Netherlands. tdw.alta@yahoo.com
Tjarco D W
TD
Alta
H E J
HE
Veeger
Thomas W J
TW
Janssen
W Jaap
WJ
Willems
D000368:Aged; D019643:Arthroplasty, Replacement / Q000009:adverse effects / Q000379:methods*; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D053581:Muscle Strength Dynamometer; D010865:Pilot Projects; D011183:Postoperative Complications; D011475:Prosthesis Failure; D016059:Range of Motion, Articular / Q000502:physiology; D020127:Recovery of Function; D012782:Shoulder / Q000503:physiopathology* / Q000601:surgery; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery; D019415:Torque