Total shoulder arthroplasty: downward inclination of the glenoid component to balance supraspinatus deficiency.
OBJECTIVE
Supraspinatus deficiency associated with total shoulder arthroplasty (TSA) provokes eccentric loading and may induce loosening of the glenoid component. A downward inclination of the glenoid component has been proposed to balance supraspinatus deficiency.


METHODS
This hypothesis was assessed by a numeric musculoskeletal model of the glenohumeral joint during active abduction. Three cases were compared: TSA with normal muscular function, TSA with supraspinatus deficiency, and TSA with supraspinatus deficiency and downward inclination of the glenoid.


RESULTS
Supraspinatus deficiency increased humeral migration and eccentric loading. A downward inclination of the glenoid partly balanced the loss of stability, but this potential advantage was counterbalanced by an important stress increase within the glenoid cement. The additional subchondral bone reaming required to incline the glenoid component indeed reduced the bone support, increasing cement deformation and stress.


CONCLUSIONS
Glenoid inclination should not be obtained at the expense of subchondral bone support.
Terrier
Alexandre
A
Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédéral de Lausanne, Lausanne, Switzerland. alexandre.terrier@epfl.ch
Merlini
Francesco
F
Pioletti
Dominique P
DP
Farron
Alain
A
D019643:Arthroplasty, Replacement / Q000009:adverse effects* / Q000379:methods; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology / Q000517:prevention & control; D007595:Joint Prosthesis; D008953:Models, Anatomic; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular / Q000502:physiology*; D012680:Sensitivity and Specificity; D012785:Shoulder Joint / Q000503:physiopathology / Q000601:surgery*; D013314:Stress, Mechanical