Inferior Subluxation of Humeral of Head after Surgery for Fracture of Proximal Humerus

PURPOSE: To study the development of inferior shoulder subluxation after surgery for proximal humerus fractures. To analyze the mechanism development of such subluxation and the association between different types of proximal humerus fractures, quality of reduction achieved the method of operation performed. MATERIALS AND METHODS: A retrospective analysis of 45 proximal humerus fractures that were treated by surgery between March 1997 and July 2002 was done. All patients had a minimum of 12 months of postoperative follow up. Preoperative radiographs were classified by the Neer's classification. Different operative treatment methods, post reduction alignment and the degree of postoperative subluxation if present, were analysed. In order to evaluate effect of loss of negative intraarticular pressure, we compared this series with 15 cases of recurrent shoulder dislocation treated by open Bankart operation. RESULTS: 13 patients out of 45 (29%) developed immediate postoperative inferior shoulder subluxation. 3-part fractures of the proximal humerus showed a higher incidence of the same than the 2-part types. The better reduced fractures had lesser rates of subluxation. Open reduction (39%, 11 patients) results in an increased incidence of inferior subluxation than closed methods of reduction (13%, 2 patients). CONCLUSION: Inferior subluxation of the humeral head after surgery for the proximal humerus fracture can occur and persist till postoperative period of 2 months. Deltoid muscle tone affected by shortening of humeral neck plays an important role. Early active exercise for restoration deltoid tone may be effective in prevention of inferior subluxation.

Biomechanical Analysis of Hybrid External Fixation for the Distal Tibial Fractures: A FEM Study

PURPOSE: To analyze the biomechanical effects of different frame configurations of the hybrid external fixators for distal tibial fractures on the frame stiffness and stress distribution with a finite element method (FEM). MATERIALS AND METHODS: Five configurations were simulated: Group I: two wires with convergence angle of 60degrees, Group II: 3rd wire on a bisector axis of the group I. Group III: two wires with 30degrees. Group IV: 3rd wire on a bisector axis. Group V: two wires with 30degree and a half pin on the distal articular fragment. Each group was simulated under compression, torsion, anterior-posterior and lateral-medial bending load. Stiffness, stress and deformation values were calculated. RESULTS: The overall stiffness was increased by 15~30% with the addition of a third wire, and by 150~400% with a anteromedial half pin on the articular fragment. The half pin decreased the stress level of the frame by about 43% and the deformation of the 5/8 ring by about 30%. CONCLUSION: The addition of a half pin on the articular fragment is not only a method of increasing the stiffness but also a way of decreasing the stress concentration and the deformation of the frame.