| Objective: With new minimally-invasive approaches for locking platefixation of proximal humeral fractures, the need for the placement of obliqueinferomedial screws (calcar screw) has increasingly been discussed. The calcarcortex is defined as the inferomedial curvature region of the humeral head tothe surgical neck. Analysis of the histomorphometry and microstructuralarchitecture of the humeral head bone stock demonstrated that trabecularthickness and density are the greatest in the medial region. Inserting one ortwo screws running to the medial cortex tangentially will increase the stabilityof the fracture, and also prevent the varus removed. Comminuted proximalhumerus fracture fixation is always controversial. Some study suggest that theplacement of calcar screws in the locking plate fixation of proximal humeralfractures is associated with less secondary loss of reduction. Some reportsindicate that calcar screw can not maintain the reduction of fracturesindividually without the inferomedial contact. They were retrospective studybased on the clinical follow-up. There is little biomechanical study about therole of inferomedial cortex contact after locking plate fixation of proximalhumeral fractures. Our biomechanical test was performed in cadaveric humeri,amid to review the effect both inferomedial cortex contact and calcar screwafter locking plate of proximal humerus fractures.Methods: Six embalmed cadaveric specimens were harvested for thisstudy(Provided by the Hebei Medical University, Department of HumanAnatomy). All of them were the same race and region. Their weights rangesfrom55-70Kg, and their heights ranges from150-170cm, and old their ranges20-52Y，average38.2Y. Four males and two females. Disarticulate thehumerus from the shoulder and elbow joint, retain the brachium, and cleaned of the skin, muscles and soft tissue of the brachium, retaining only thehumerus. All specimens were received bone mineral density(BMD) test andX-ray examination, confirmed they did not had fractures, malformatins ofvariation, obvious osteoporosis, tumor, etc. Sequentially numbered to the12cadaveric humeri and using a table of random numbers to divide into3groupsrandomly. Inferomedial cortex contact with calcar screw (Group A);inferomedial cortex contact without calcar screw(Group B); non-inferomedialcortex contact but with calcar screw(Group C); four humeri each group. Ineach humerus did a osteotomy by using a an oscillating saw in order tosimulate proximal humerual fractures, then fixed each humerus. These threesubgroups were retested for axial, torsional, and shear stiffness. A11of thedatum were analysed by software—SPSS13.0,using one-way analyses ofvariance (ANOVA) test to analyze the difference, furthermore analyze thedifference between each two group by S-N-K, with a statistical significancethreshold of P＜0.05.Results: The differences of bone mineral density(BMD) between anysubgroups has no statistical significance (P>0.05). For axial stiffness test, themaximum load A>B>C：（321.368±9.881）N>（204.145±4.716）N>（160.593±6.402）N，the differences has statistical significance(P <0.01)；theaxial stiffness A>B>C：（502.327±15.299）N/mm>（303.138±9.606）N/mm>（221.693±12.935）N/mm, the differences has statistical significance (P<0.01), comparing between each two groups differences has statisticalsignificance(p<0.01), A>B>C. For torsional stiffness, the maximum torque A>B and C：（9.480±0.356）N m>（4.281±0.540）N m and（4.560±0.676）N m, the differences has statistical significance(P <0.01), but B and C werenot different(P>0.05); the torsional stiffness, A>B and C：（1.863±0.066）N m/°>（0.808±0.135）N m/°and （0.881±0.136）N m/°, the differenceshas statistical significance(P <0.01), but B and C were not different(P>0.05).For shear stiffness, the maximum load A>B>C：（512.075±10.888）N>（395.386±7.651）N>（342.405±9.427）N, the differences has statisticalsignificance (P <0.01), the shear stiffness A>B>C：（625.658±9.579）N/mm> （444.748±11.493）N/mm>（372.800±12.016）N/mm, the differences hasstatistical significance (P<0.01), comparing between each two groupsdifferences has statistical significance(P <0.01), A>B>C.Conclusion: This study assessed the relative mechanical effects ofinferomedial cortex contact and calcar screw on proximal humerus fracturefixation using locked plates in three differcens of fracture model. Achievingmechanical support of the inferomedial region of the proximal humerus seemsto be important for maintaining fracture reduction. Despite of axial, torsional,or shear stiffness, inferomedial cortex contact is more stabilized than absenceof inferomedial cortex contact. Obtaining mechanical support of theinferomedial region and add two calcar screws is the best fixation model.Achieving inferomedial cortex contact is really better than the insertion ofcalcar screw individually from the biomechanical test. |
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