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Bone fractures at weight-bearing sites are challenging to treat due to the difficulty in maintaining articular congruency. An ideal biomaterial for fracture repair near articulating joints sets rapidly after implantation, stabilizes the fracture with minimal rigid implants, stimulates new bone formation, and remodels at a rate that maintains osseous integrity. Consequently, the design of biomaterials that mechanically stabilize fractures while remodeling to form new bone is an unmet challenge in bone tissue engineering. In this study, we investigated remodeling of resorbable bone cements in a stringent model of mechanically loaded tibial plateau defects in sheep. Nanocrystalline hydroxyapatite-poly(ester urethane) (nHA-PEUR) hybrid polymers were augmented with either ceramic granules (85% β-tricalcium phosphate/15% hydroxyapatite, CG) or a blend of CG and bioactive glass (BG) particles to form a settable bone cement. The initial compressive strength and fatigue properties of the cements were comparable to those of non-resorbable poly(methyl methacrylate) bone cement. In animals that tolerated the initial few weeks of early weight-bearing, CG/nHA-PEUR cements mechanically stabilized the tibial plateau defects and remodeled to form new bone at 16 weeks. In contrast, cements incorporating BG particles resorbed with fibrous tissue filling the defect. Furthermore, CG/nHA-PEUR cements remodeled significantly faster at the full weight-bearing tibial plateau site compared to the mechanically protected femoral condyle site in the same animal. These findings are the first to report a settable bone cement that remodels to form new bone while providing mechanical stability in a stringent large animal model of weight-bearing bone defects near an articulating joint.
Copyright © 2018 Elsevier Ltd. All rights reserved.
Bone grafts used to repair weight-bearing tibial plateau fractures often experience cyclic loading, and there is a need for bone graft substitutes that prevent failure of fixation and subsequent morbidity. However, the specific mechanical properties required for resorbable grafts to optimize structural compatibility with native bone have yet to be established. While quasi-static tests are utilized to assess weight-bearing ability, compressive strength alone is a poor indicator of in vivo performance. In the present study, we investigated the effects of interfacial bonding on material properties under conditions that re-capitulate the cyclic loading associated with weight-bearing fractures. Dynamic compressive fatigue properties of polyurethane (PUR) composites made with either unmodified (U-) or polycaprolactone surface-modified (PCL-) 45S5 bioactive glass (BG) particles were compared to a commercially available calcium sulfate and phosphate-based (CaS/P) bone cement at physiologically relevant stresses (5-30 MPa). Fatigue resistance of PCL-BG/polymer composite was superior to that of the U-BG/polymer composite and the CaS/P cement at higher stress levels for each of the fatigue failure criteria, related to modulus, creep, and maximum displacement, and was comparable to human trabecular bone. Steady state creep and damage accumulation occurred during the fatigue life of the PCL-BG/polymer and CaS/P cement, whereas creep of U-BG/polymer primarily occurred at a low number of loading cycles. From crack propagation testing, fracture toughness or resistance to crack growth was significantly higher for the PCL-BG composite than for the other materials. Finally, the fatigue and fracture toughness properties were intermediate between those of trabecular and cortical bone. These findings highlight the potential of PCL-BG/polyurethane composites as weight-bearing bone grafts.
Published by Elsevier Ltd.
We performed a retrospective cohort study of 84 patients to determine the incidence and predictors of acute kidney injury after antibiotic-impregnated cement spacer (ACS) placement for infected total knee arthroplasties. Acute kidney injury was defined as a more than 50% rise in serum creatinine from a preoperative baseline to a level greater than 1.4 mg/dL within 90 days postoperatively. Total incidence was 17% (n = 14; 95% confidence interval [CI], 10%-26%), and acute kidney injury was significantly associated with ACS tobramycin dose as both a dichotomous variable (>4.8 g; odds ratio, 5.87; 95% CI, 1.43-24.19; P = .01) and linear variable (odds ratio, 1.24 for every 1-g increase; 95% CI, 1.00-1.52; P = .049). Routine monitoring of serum creatinine and measurement of serum aminoglycoside levels in response to a threshold creatinine rise may be warranted after the placement of an aminoglycoside-containing ACS.
Copyright © 2012 Elsevier Inc. All rights reserved.
OBJECTIVE - We present a unique case of a recurrent osteoma within a cranioplasty performed with calcium phosphate bone cement.
CLINICAL PRESENTATION - The patient is a 7-year-old boy who had initially undergone a craniotomy for resection of a frontal cranial tumor followed by a cranioplasty with artificial bone matrix. On routine follow-up evaluation 2 years later, the patient had a mass expanding from the cranioplasty.
INTERVENTION - At the time of reoperation, the patient was found to have a histopathologically confirmed recurrent osteoma within the artificial bone matrix. The patient later underwent repair of the frontal cranial defect using a patient-specific implant.
CONCLUSION - We discuss this unusual case, treatment, and possible causes. We believe that a safety margin and curettage of the resection border as well as resection of the overlying periosteum might prevent recurrence.
Biostable polyurethanes (PURs) have been incorporated in biomedical devices since the 1960s. The mechanisms of degradation and compositions with improved in vivo biostability have been investigated extensively. In recent years, biodegradable PURs have been investigated for applications in regenerative medicine. In contrast to the biostable implants, these biomaterials are designed to undergo controlled degradation in vivo and promote ingrowth of new tissue. Tissue-engineered scaffolds have been fabricated from biodegradable PURs using a variety of techniques, including thermally induced phase separation, salt leaching, wet spinning, electrospinning, and carbon dioxide foaming. These materials have been reported to support the ingrowth of cells and tissue in vitro and in vivo, and undergo controlled degradation to noncytotoxic decomposition products. Due to their tunable biological, mechanical, and physicochemical properties, biodegradable PURs present compelling future opportunities as scaffolds for regeneration of tissue. This review article summarizes recent advances made in the synthesis of biodegradable PURs and the application of these materials as scaffolds for regenerative medicine.
OBJECTIVE - Most fractures treated with percutaneous vertebroplasty are subacute and less than 1 year old. We report our experience treating chronic vertebral fractures with vertebroplasty.
MATERIALS AND METHODS - Our database identified 41 patients with symptomatic fractures more than 1 year old. These patients were categorized into subgroups determined by fracture age: 12 months 1 day-24 months (n = 16) or more than 24 months 1 day (n = 25). Changes in pain and mobility for the study group were compared with those in 49 patients with fractures less than 1 year old.
RESULTS - Thirty-three (80%) of the 41 patients in the study group had improvement in pain-seven (17%) had complete and 26 (63%) had partial relief. Forty-five (92%) of the 49 control group patients had improvement in pain-24 (49%) had complete and 21 (43%) had partial relief. The number of patients achieving partial or complete relief of pain was not statistically different between groups (p > 0.05), although complete relief was significantly more frequent in the control group (p = 0.002). Twenty patients (49%) in the study group versus 34 patients (69%) in the control group had improved mobility after vertebroplasty (p = 0.047). Patients with fractures 12 months 1 day-24 months old had improvement in mobility similar to that in patients in the control group (p = 0.962). Fractures more than 24 months 1 day old were associated with significantly less improvement in mobility (p = 0.006).
CONCLUSION - Most patients with fractures more than 1 year old will experience clinical benefit from vertebroplasty. Complete relief of pain is more likely when less mature fractures are treated.
OBJECT - Traditionally, superior sulcus tumors of the lung that involve the chest wall and spinal column have been considered to be unresectable, and historically, patients harboring these tumors have been treated with local radiation therapy with, at best, modest results. The value of gross-total resection remains unclear in this patient population; however, with the recent advances in surgical technique and spinal instrumentation, procedures involving more radical removal of such tumors are now possible. At The University of Texas M. D. Anderson Cancer Center, the authors have developed a new technique for resecting superior sulcus tumors that invade the chest wall and spinal column. They present a technical description of this procedure and results in nine patients in whom stage IIIb superior sulcus tumors extensively invaded the vertebral column.
METHODS - These patients underwent gross-total tumor resection via a combined approach that included posterolateral thoracotomy, apical lobectomy, chest wall resection, laminectomy, vertebrectomy, anterior spinal column reconstruction with methylmethacrylate, and placement of spinal instrumentation. There were six men and three women, with a mean age of 55 years (range 36-72 years). Histological examination revealed squamous cell carcinoma (three patients), adenocarcinoma (four patients), and large cell carcinoma (two patients). The mean postoperative follow-up period was 16 months. All patients are currently ambulatory or remained ambulatory until they died. Pain related to tumor invasion improved in four patients and remained unchanged in five. In three patients instrumentation failed and required revision. There was one case of cerebrospinal fluid leakage that was treated with lumbar drainage and one case of wound breakdown that required revision. Two patients experienced local tumor recurrence, and one patient developed a second primary lung tumor.
CONCLUSIONS - The authors conclude that in selected patients, combined radical resection of superior sulcus tumors of the lung that involve the chest wall and spinal column may represent an acceptable treatment modality that can offer a potential cure while preserving neurological function and providing pain control.
We examined the effects of vancomycin on the compressive strength and fatigue life of bone cement and the pharmacokinetics and antimicrobial activity against methicillin-resistant Staphylococcus aureus of vancomycin eluted from bone cement, both alone and in combination with tobramycin. Two cements, Palacos and Simplex, were tested. Three antibiotic preparations were tested: lyophilized vancomycin (vancomycin-L), vancomycin powder (vancomycin-P), and tobramycin powder (Lilly, Indianapolis, IN). Although antibiotics did not significantly affect compressive strength, the fatigue life of bone cement was significantly decreased with vancomycin. Thus, fatigue testing revealed effects on cement strength not apparent by compression testing. Vancomycin-P had a substantially less detrimental effect on fatigue strength than vancomycin-L. Vancomycin-P elutes less efficiently than tobramycin. Although relatively little vancomycin-P eluted from bone cement, it retained biologic activity.
OBJECT - Anterior approaches to the spine for the treatment of spinal tumors have gained acceptance; however, in most published reports, patients with primary, metastatic, or chest wall tumors involving cervical, thoracic, or lumbar regions of the spine are combined. The purpose of this study was to provide a clear perspective of results that can be expected in patients who undergo anterior vertebral body resection, reconstruction, and stabilization for spinal metastases that are limited to the thoracic region.
METHODS - Outcome is presented for 72 patients with metastatic spinal tumors who were treated by transthoracic vertebrectomy at The University of Texas M. D. Anderson Cancer Center. The predominant primary tumors included renal cancer in 19 patients, breast cancer in 10, melanoma or sarcoma in 10, and lung cancer in nine patients. The most common presenting symptoms were back pain, which occurred in 90% of patients, and lower-extremity weakness, which occurred in 64% of patients. All patients underwent transthoracic vertebrectomy, decompression, reconstruction with methylmethacrylate, and anterior fixation with locking plate and screw constructs. Supplemental posterior instrumentation was required in seven patients with disease involving the cervicothoracic or thoracolumbar junction, which was causing severe kyphosis. After surgery, pain improved in 60 of 65 patients. This improvement was found to be statistically significant (p < 0.001) based on visual analog scales and narcotic analgesic medication use. Thirty-five of the 46 patients who presented with neurological dysfunction improved significantly (p < 0.001) following the procedure. Thirty-three patients had weakness but could ambulate preoperatively. Seventeen of these 33 regained normal strength, 15 patients continued to have weakness, and one patient was neurologically worse postoperatively. Of the 13 preoperatively nonambulatory patients, 10 could walk after surgery and three were still unable to walk but showed improved motor function. Twenty-one patients had complications ranging from minor atelectasis to pulmonary embolism. The 30-day mortality rate was 3%. The 1-year survival rate for the entire study population was 62%.
CONCLUSIONS - These results suggest that transthoracic vertebrectomy and spinal stabilization can improve the quality of life considerably in cancer patients with spinal metastasis by restoring or preserving ambulation and by controlling intractable spinal pain with acceptable rates of morbidity and mortality.