Assessing the biomechanical properties of nitinol staples in normal, osteopenic and osteoporotic bone models: A finite element analysis.

OBJECTIVE: Bone staples are internal fixation devices that are frequently used in the foot, ankle, and hand to provide stabilization. Fixation stability is vital after fusion or fracture surgeries to ensure proper bone healing. Patients undergoing surgeries that require fixation to keep bones aligned and stable may present with diminishing bone mechanical properties, and this may compromise the ability of the fixation hardware to maintain a stable construct. The purpose of this study was to investigate the mechanical performance of shape memory and superelastic nitinol bone staples with different bridge geometries in normal, osteopenic, and osteoporotic bone models. Contact forces and maximum principal stress and strain in the bone were recorded. METHODS: Finite element simulations of a bone staple fixation procedure were performed to examine the initial and post-surgery contact force, as well as the maximum principal stress and strain of 15 mm bridge and 20 mm bridge staple-bone constructs. RESULTS: Shape memory nitinol staples exhibited higher contact forces compared to superelastic nitinol staples. Nitinol bone staples with 20 mm bridge lengths displayed higher contact forces and lower stresses in all bone types, as well as lower strains in osteoporotic bone models compared to nitinol staples with a 15 mm bridge length. CONCLUSION: Nitinol bone staple constructs with 20 mm bridge length staples provide higher contact forces and display lower stresses in the bone than 15 mm bridge staple-bone constructs, which may be beneficial in bone with diminishing mechanical properties. Both superelastic and shape memory effect nitinol staples provide adequate compression and stress relief. However, if osteopenia is present, shape memory effect nitinol staples with a 20 mm bridge length may provide more stress relief and compression, if the bone anatomy allows.

Soft-Tissue Tumors: A Pictorial- and Case-Based Guide to Diagnosis and Management.

General orthopaedic surgeons must learn how to appropriately evaluate patients with soft-tissue masses who present at their office. Although the incidence of benign soft-tissue sarcomas substantially outnumbers that of malignant soft-tissue sarcomas, the mismanagement of soft-tissue tumors markedly increases a patient's morbidity. The appropriate use of imaging modalities helps general orthopaedic surgeons accurately diagnose a soft-tissue mass, initiate appropriate management of a soft-tissue mass, and gain a better understanding of which patients with soft-tissue lesions should be referred to an orthopaedic oncologist.

Allograft cortical strut for reconstruction of space-occupying bone lesions.

Space-occupying bone lesions present orthopedic surgeons with clinical and operative challenges. Multiple reconstructive procedures have proven successful for small bone lesions but lack the structural support necessary for reconstruction of larger lesions. This study reports the clinical outcomes of patients undergoing excision and reconstruction of large bone lesions with allograft cortical struts without additional internal fixation. This retrospective outcomes study reviewed patients who underwent surgical curettage and cortical strut allograft reconstruction of any space-occupying bone lesion. Clinical, surgical, and imaging data were collected. The primary outcome measures were lesion healing, graft incorporation, long-term pain, return to activity, and presence of complications/recurrences. Seventeen patients met the inclusion criteria. At least partial lesion healing and allograft incorporation was identified in 15 of 17 lesions. Of the 15 patients who did not sustain a recurrence, only 1 did not return to full activities. Mean lesion volume was 107 cc. Average follow-up was 19.6 months. Two recurrences were identified, and no other major complications were identified.

Malakoplakia of Bone: A Case Report and Review of the Literature.

CASE: A sixty-one-year-old woman presented with right knee pain. Imaging demonstrated osteonecrosis, pathologic fracture, and a permeative lesion. A biopsy with irrigation and debridement was performed. Cultures grew Escherichia coli, and histology showed features of malakoplakia, a rare lesion of uncertain etiology usually found in the genitourinary tract. The patient was treated successfully with antibiotics. CONCLUSION: Malakoplakia, although rare, should be included in the differential diagnosis of permeative bone lesions, especially in an immunocompromised patient.

Maximizing phenotype constraint and extracellular matrix production in primary human chondrocytes using arginine-glycine-aspartate concentration gradient hydrogels.

New systematic approaches are necessary to determine and optimize the chemical and mechanical scaffold properties for hyaline cartilage generation using the limited cell numbers obtained from primary human sources. Peptide functionalized hydrogels possessing continuous variations in physico-chemical properties are an efficient three-dimensional platform for studying several properties simultaneously. Herein, we describe a polyethylene glycol dimethacrylate (PEGDM) hydrogel system possessing a gradient of arginine-glycine-aspartic acid peptide (RGD) concentrations from 0mM to 10mM. The system is used to correlate primary human osteoarthritic chondrocyte proliferation, phenotype maintenance and extracellular matrix (ECM) production to the gradient hydrogel properties. Cell number and chondrogenic phenotype (CD14:CD90 ratios) were found to decline in regions with higher RGD concentrations, while regions with lower RGD concentrations maintained cell number and phenotype. Over three weeks of culture, hydrogel regions containing lower RGD concentrations experience an increase in ECM content compared to regions with higher RGD concentrations. Variations in actin amounts and vinculin organization were observed within the RGD concentration gradients that contribute to the differences in chondrogenic phenotype maintenance and ECM expression.

Primary human chondrocyte extracellular matrix formation and phenotype maintenance using RGD-derivatized PEGDM hydrogels possessing a continuous Young's modulus gradient.

Efficient ex vivo methods for expanding primary human chondrocytes while maintaining the phenotype is critical to advancing the sourcing of autologous cells for tissue engineering applications. While there has been significant research reported in the literature, systematic approaches are necessary to determine and optimize the chemical and mechanical scaffold properties for hyaline cartilage generation using limited cell numbers. Functionalized hydrogels possessing continuous variations in physico-chemical properties are, therefore, an efficient three-dimensional platform for studying several properties simultaneously. Herein we describe a polyethylene glycol dimethacrylate (PEGDM) hydrogel system with a modulus gradient (~27,000-3800 Pa) containing a uniform concentration of arginine-glycine-aspartic acid (RGD) peptide to enhance cell adhesion in order to correlate primary human osteoarthritic chondrocyte proliferation, phenotype maintenance, and extracellular matrix (ECM) production with hydrogel properties. Cell number and chondrogenic phenotype (CD14:CD90 ratios) were found to decline in regions with a higher storage modulus (>13,100 Pa), while regions with a lower storage modulus maintained their cell number and phenotype. Over 3 weeks culture hydrogel regions possessing a lower Young's modulus experienced an increase in ECM content (~200%) compared with regions with a higher storage modulus. Variations in the amount and organization of the cytoskeletal markers actin and vinculin were observed within the modulus gradient, which are indicative of differences in chondrogenic phenotype maintenance and ECM expression. Thus scaffold mechanical properties have a significant impact in modulating human osteoarthritic chondrocyte behavior and tissue formation.

ECM production of primary human and bovine chondrocytes in hybrid PEG hydrogels containing type I collagen and hyaluronic acid.

The development of advanced materials that facilitate hyaline cartilage formation and regeneration in aging populations is imperative. Critical to the success of this endeavor is the optimization of ECM production from clinically relevant cells. However, much of the current literature focuses on the investigation of primary bovine chondrocytes from young calves, which differ significantly than osteoarthritic cells from human sources. This study examines the levels of extracellular matrix (ECM) production using various levels of type I collagen and hyaluronic acid in poly(ethylene glycol) dimethacrylate (PEGDM) hydrogels in total knee arthroplasties, compared with the results from bovine chondrocytes. The addition of type 1 collagen in both the presence and absence of low levels of hyaluronic acid increased ECM production and/or retention in scaffolds containing either bovine or human chondrocytes. These findings are supported consistently with colorimetric quantification, whole mount extracellular matrix staining for both cell types, and histological staining for glycoaminoglycans and collagen of human chondrocyte containing samples. While exhibiting similar trends, the relative ECM productions levels for the primary human chondrocytes are significantly less than the bovine chondrocytes which reinforces the need for additional optimization.

Potential for thermal damage to articular cartilage by PMMA reconstruction of a bone cavity following tumor excision: A finite element study.

Benign, giant cell tumors are often treated by intralesional excision and reconstruction with polymethylmethacrylate (PMMA) bone cement. The exothermic reaction of the in-situ polymerizing PMMA is believed to beneficially kill remaining tumor cells. However, at issue is the extent of this necrotic effect into the surrounding normal bone and the adjacent articular cartilage. Finite element analysis (ABAQUS 6.4-1) was used to determine the extent of possible thermal necrosis around prismatically shaped, PMMA implants (8-24cc in volume), placed into a peripheral, sagittally symmetric, metaphyseal defect in the proximal tibia. Temperature/exposure time conditions indicating necrotic potential during the exotherm of the polymerizing bone cement were found in regions of the cancellous bone within 3mm of the superior surface of the PMMA implant. If less than 3mm of cancellous bone existed between the PMMA implant and the subchondral bone layer, regions of the subchondral bone were also exposed to thermally necrotic conditions. However, as long as there were at least 2mm of uniform subchondral bone above the PMMA implant, the necrotic regions did not extend into the overlying articular cartilage. This was the case even when the PMMA was in direct contact with the subchondral bone. If the subchondral bone is not of sufficient thickness, or is not continuous, then care should be taken to protect the articular cartilage from thermal damage as a result of the reconstruction of the tumor cavity with PMMA bone cement.

Bacterial Pyomyositis.

Bacterial pyomyositis has been defined as a subacute, deep bacterial infection of the soft tissues. The entity was originally described only in tropical climates, but it is increasing in incidence in temperate climates, such as in the United States. This is mainly attributed to the presence of immunocompromising states such as HIV/AIDS or liver disease. The etiology of pyomyositis remains a mystery, but its characteristics are well-described. If untreated, the disease process progresses through three distinct stages. The first stage is defined by vague complaints, muscle pain, and a low-grade fever. The second stage presents as worsening pain, swelling, fever, and actual abscess formation in the muscle. If the patient remains untreated, pyomyositis progresses to the third stage, which includes septicemia and possible septic shock. Large muscles around the pelvis are most commonly affected, and Staphylococcus aureus is the bacteria seen in most documented cases. To make a timely diagnosis and prevent serious sequelae, physical examination, laboratory results, imaging studies, and a high clinical suspicion must all be combined. Magnetic resonance imaging is the diagnostic study of choice, but it may be inconclusive early in the disease process. Definitive diagnosis must be made with aspiration or surgical drainage. Once diagnosed, treatment consists of appropriate intravenous antibiotics and possible surgical intervention. A full recovery is expected if appropriate treatment is initiated early in the process.

Enchondroma and chondrosarcoma of bone: clinical, radiologic, and histologic differentiation.

Intraosseous cartilage tumors are commonly encountered by orthopaedic surgeons during evaluation of a patient for undetermined pain; however, the possibility of missing a malignancy during examination is cause for concern. Surgery for enchondromas is not generally necessary but when clinical and radiographic features suggest a potential chondrosarcoma, prompt referral is necessary. Chondrosarcoma almost always occurs in adults. Patients usually present with pain and have characteristic findings on staging studies. Lucencies developing within the calcification, periosteal reactions, and a soft-tissue mass all are characteristic features of chondrosarcoma. Biopsies are not typically indicated because of the histologic similarity of benign and malignant cartilage lesions.

Osteochondritis dissecans involving the trochlea: report of two patients (three elbows) and review of the literature.

Osteochondritis dissecans (OCD) is an idiopathic lesion of subchondral bone resulting in separation of the articular cartilage and subchondral bone. Osteochondritis of the elbow primarily involves the capitellum. Only two cases involving the trochlea have been reported, one in the English literature and one in the German literature. Osteochondritis dissecans has been confused with other joint surface abnormalities, and therefore the orthopaedic literature must be read with scrutiny. Some of these other conditions include osteochondral fractures, osteonecrosis, accessory centers of ossification, and hereditary epiphyseal dysplasia. The authors describe two patients (one bilateral) with OCD involving the trochlea of the humerus. The first is a 12-year-old boy in whom an open biopsy was performed to rule out neoplastic lesions. The second is a 14-year-old boy with bilateral OCD that was recognized secondary to the similarity to the first patient. This patient was successfully treated conservatively. The first patient illustrates how recognition of OCD in the trochlea may prevent unnecessary biopsy. Osteochondritis dissecans should be part of the differential of lesions involving the trochlea.