A numerical study of the contact geometry and pressure distribution along the glenoid track.

The glenoid track geometry and the contact forces acting on the glenohumeral joint at static positions of 30°, 60°, 90° and 120° of abduction with 90° of external rotation were evaluated using a finite element model of the shoulder that, differently from most usual approximations, accounts the humeral head translations and the deformable-to-deformable non-spherical joint contact. The model was based on data acquired from clinical exams of a single subject, including the proximal humerus, scapula, their respective cartilages concerning the glenohumeral joint, and the rotator cuff and deltoid muscles. The forces acting on the glenohumeral joint were estimated using a simulation framework consisting of an optimization procedure allied with finite element analysis that seeks the minimum muscle forces that stabilize the joint. The joint reaction force magnitude increases up to 680.25 N at 90° of abduction and decreases at further positions. From 60° onward the articular contact remains at the anterior region of the glenoid cartilage and follows an inferior to superior path at the posterior region of the humeral head cartilage. The maximum contact pressure of 3.104 MPa occurs at 90° abduction. Although translating inferiorly throughout the movement, the projection of the humeral head center at the glenoid plane remains at the central region of the glenoid surface. The model results qualitatively matched the trends observed in the literature and supports the consideration of the translational degrees of freedom to evaluate the joint contact mechanics.

Glenoid track evaluation by a validated finite-element shoulder numerical model.

BACKGROUND: The limits of the glenoid track have been defined through methods that do not take properly into account the physiological articular forces involved in the articular contact, which may interfere with its size. Finite elements numerical models can simulate joint forces more realistically. OBJECTIVE: To evaluate the glenoid track in a finite element numerical model of the shoulder. METHODS: We developed a finite element numerical model of the shoulder, based on imaging exams of a volunteer, including the proximal humerus, scapula, their respective articular cartilages, and the rotator cuff muscles. An algorithm to balance the weight of the arm calculated muscle, wrapping, and articular reaction forces. The model has freedom of translation in three axes. The articular contact characteristics and glenoid track's dimensions according to the literature references were evaluated in 60°, 90° and 120° of abduction, all at the 90° external rotation. RESULTS: The model's anatomy and physiology were validated. The value of the glenoid track (according to Yamamoto's parameters) was 86% of glenoid length at 90° abduction before loading of forces, and 79% afterwards. The glenoid track at 60°, 90° and 120° of abduction (Omori's parameters) corresponded, respectively, to 71%, 88% and 104% of glenoid length before loading of forces, and 76%, 84% and 103% afterward. CONCLUSION: The numerical model is suitable for the shoulder articular contact evaluation. The articular contact analysis ratifies the glenoid track concept and contributes to its evolution. This value is influenced by glenohumeral joint forces, which should be considered for the analysis. LEVEL OF EVIDENCE: Basic Science Study; Computer Modelling.

Prognostic factors for clinical outcomes after rotator cuff repair.

OBJECTIVE: To identify prognostic factors of postoperative functional outcomes. METHODS: Retrospective case series evaluating patients undergoing rotator cuff repair, analyzed by the UCLA score (pre and 12-month postoperative) and Magnetic Resonance Imaging (preoperative). Patients' intrinsic variables related to the injury and intervention were evaluated. Multivariate linear regression analysis was performed to determine variables impact on postoperative functional assessment. RESULTS: 131 patients were included. The mean UCLA score increased from 13.17 ± 3.77 to 28.73 ± 6.09 (p<0,001). We obtained 65.7% of good and excellent results. Age (r= 0.232, p= 0.004) and reparability of posterosuperior injuries (r= 0.151, p= 0.043) correlated with the functional assessment at 12 months. After multivariate linear regression analysis, only age was associated (p = 0.008). CONCLUSIONS: The surgical treatment of rotator cuff tears lead to good and excellent results in 65.6% of patients. Age was an independent predictor factor with better clinical outcomes by UCLA score in older patients. Level of Evidence IV, Case Series.

Fatores prognósticos para o resultado clínico após o reparo do manguito rotador / Prognostic factors for clinical outcomes after rotator cuff repair

Objetivo: Identificar fatores prognósticos do resultado funcional pós-operatório. Métodos: Série de casos retrospectiva avaliando pacientes submetidos ao reparo do manguito rotador, analisados através da escala funcional da UCLA (no pré-operatório e aos 12meses pós-operatório) e por Ressonância Magnética (pré-operatório). Foram avaliadas variáveis intrínsecas ao paciente relacionadas à lesão e à intervenção. Foi realizada regressão linear multi variada para definir o impacto das variáveis na avaliação funcional pós-operatória. Resultados: Foram incluídos 131 pacientes. Pela escalada UCLA, evoluíram de 13,17 ± 3,77 para 28,73 ± 6,09 (p<0,001). Foram obtidos 65,7% de bons e excelentes resultados. A idade(r=0,232, p=0,004) e a reparabilidade das lesões posterosuperiores(r=0,151, p=0,043) correlacionaram-se com a avaliação funcional de 12 meses. Após regressão linear multivariada, apenas a idade esteve associada (p=0,008). Conclusão: O tratamento cirúrgico das roturas do manguito rotador levou a resultados bons e excelente sem 65,6% dos pacientes. A idade foi um preditor independente, com melhores resultados clínicos pela escala da UCLA nos pacientes mais idosos. Nível de Evidência IV, Série de Casos.

Objective: To identify prognostic factors of postoperative functional outcomes. Methods: Retrospective case series evaluating patients undergoing rotator cuff repair, analyzed by the UCLA score (pre and 12-month postoperative) and Magnetic Resonance Imaging (preoperative). Patients’ intrinsic variables related to the injury and intervention were evaluated. Multivariate linear regression analysis was performed to determine variables impact on postoperative functional assessment. Results: 131 patients were included. The mean UCLA score increased from 13.17 ± 3.77 to 28.73 ± 6.09 (p<0,001). We obtained 65.7% of good and excellent results. Age (r= 0.232,p= 0.004) and reparability of posterosuperior injuries (r=0.151, p= 0.043) correlated with the functional assessmentat 12 months. After multivariate linear regression analysis, onlyage was associated (p = 0.008). Conclusions: The surgical treatment of rotator cuff tears lead to good and excellent results in 65.6% of patients. Age was an independent predictor factor with better clinical outcomes by UCLA score in older patients. Level of Evidence IV, Case Series.