Stabilization of distal femur fractures with periarticular locking plates can cause inconsistent and asymmetric formation of periosteal callus. A larger bridge span only minimally improves callus formation. The more flexible titanium plates enhanced callus formation compared with stainless steel plates.

Biological activity can be added to synthetic scaffolds by incorporating functional peptide sequences that provide enzyme-mediated degradation sites, facilitate cellular adhesion or stimulate signaling pathways. Poly(ethylene glycol) diacrylate is a popular synthetic base for tissue engineering scaffolds because it creates a hydrophilic environment that can be chemically manipulated to add this biological functionality. Furthermore, the acrylate groups allow for encapsulation of cells using photopolymerization under physiological conditions. One complication with the addition of these peptides is that aromatic amino acids absorb light at 285nm and compete with the ultraviolet (UV)-sensitive photoinitiators such as Irgacure TM 2959 (I2959), the most commonly used initiator for cytocompatible photoencapsulation of cells into synthetic scaffolds. In this study we defi ne non-toxic conditions for photoencapsulation of human mesenchymal stem cells (hMSC) in PEGDA scaffolds using a visible light photoinitiator system composed of eosin Y, triethanolamine and 1-vinyl-2-pyrrolidinone. This visible light photoinitiator produced hydrogel scaffolds with an increased viability of encapsulated hMSCs and a more tightly crosslinked network in one-third the time of UV polymerization with I2959.

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Background Several mechanical studies suggest locking plate constructs may inhibit callus necessary for healing of distal femur fractures. However, the rate of nonunion and factors associated with nonunion are not well established. Questions/purposes We (1) determined the healing rate of distal femur fractures treated with locking plates, (2) assessed the effect of patient injury and treatment variables on fracture healing, and (3) compared callus formation in fractures that healed with those that did not heal. Patients and MethodsWe retrospectively reviewed 82 patients treated with 86 distal femur fractures using lateral locking plates. We reviewed all charts and radiographs to determine patient and treatment variables and then determined the effects of these variables on healing. We quantitatively measured callus at 6, 12, and 24 weeks.The minimum time for telephone interviews and SF-36v2 TM scores was 1 year (mean, 4.2 years; range, 1-7.2 years). Results Fourteen fractures (20%) failed to unite. Demographics and comorbidities were similar in patients who achieved healing compared with those who had nonunions. There were more empty holes in the plate adjacent to fractures that healed; comminuted fractures failed to heal more frequently than less comminuted fractures. Less callus formed in fractures with nonunions and in patients treated with stainless steel plates compared with titanium plates. Complications occurred in 28 of 70 fractures (40%), 19 of which had additional surgery. Conclusions We found a high rate of nonunion in distal femur fractures treated with locking plates. Nonunion presented late without hardware failure and with limited callus formation suggesting callus inhibition rather than hardware failure is the primary problem. Mechanical factors may play a role in the high rate of nonunion. Level of Evidence Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

The glycosaminoglycan of decorin, dermatan sulfate (DS), has been suggested to contribute to the mechanical properties of soft connective tissues such as ligaments and tendons. This study investigated the mechanical function of DS in human medial collateral ligaments (MCL) using nondestructive shear and tensile material tests performed before and after targeted removal of DS with chondroitinase B (ChB). The quasi-static elastic material properties of human MCL were unchanged after DS removal. At peak deformation, tensile and shear stresses in ChB treated tissue were within 0.5% (p > 0.70) and 2.0% (p > 0.30) of pre-treatment values, respectively. From preto post-ChB treatment under tensile loading, the tensile tangent modulus went from 242 AE 64 to 233 AE 57 MPa (p ¼ 0.44), and tissue strain at peak deformation went from 4.3 AE 0.3% to 4.4 AE 0.3% (p ¼ 0.54). Tissue hysteresis was unaffected by DS removal for both tensile and shear loading. Biochemical analysis confirmed that 90% of DS was removed by ChB treatment when compared to control samples, and transmission electron microscopy (TEM) imaging further verified the degradation of DS by showing an 88% reduction (p < .001) of sulfated glycosaminoglycans in ChB treated tissue. These results demonstrate that DS in mature knee MCL tissue does not resist tensile or shear deformation under quasi-static loading conditions, challenging the theory that decorin proteoglycans contribute to the elastic material behavior of ligament. ß