Do oxidized zirconium heads decrease tribocorrosion in total hip arthroplasty? A study of retrieved components.

AIMS: The aim of this study was to evaluate fretting and corrosion in retrieved oxidized zirconium (OxZr; OXINIUM, Smith & Nephew, Memphis, Tennessee) femoral heads and compare the results with those from a matched cohort of cobalt-chromium (CoCr) femoral heads. PATIENTS AND METHODS: A total of 28 OxZr femoral heads were retrieved during revision total hip arthroplasty (THA) and matched to 28 retrieved CoCr heads according to patient demographics. The mean age at index was 56 years (46 to 83) in the OxZr group and 70 years (46 to 92) in the CoCr group. Fretting and corrosion scores of the female taper of the heads were measured according to the modified Goldberg scoring method. RESULTS: The OxZr-retrieved femoral heads showed significantly lower mean corrosion scores than the CoCr heads (1.3 (1 to 2.75) vs 2.1 (1 to 4); p < 0.01). Mean fretting scores were also significantly lower in the OxZr cohort when compared with the CoCr cohort (1.3 (1 to 2) vs 1.5 (1 to 2.25); p = 0.02). OxZr heads had more damage in the proximal region compared with the distal region of the head. Location had no impact on damage of CoCr heads. A trend towards increased corrosion in large heads was seen only in the CoCr heads, although this was not statistically significant. CONCLUSION: Retrieval analysis of OxZr femoral heads showed a decreased amount of fretting and corrosion compared with CoCr femoral heads. OxZr seems to be effective at reducing taper damage. Cite this article: Bone Joint J 2019;101-B:386-389.

Vascular endothelial growth factor pathway promotes osseointegration and CD31hiEMCNhi endothelium expansion in a mouse tibial implant model: an animal study.

AIMS: It is increasingly appreciated that coordinated regulation of angiogenesis and osteogenesis is needed for bone formation. How this regulation is achieved during peri-implant bone healing, such as osseointegration, is largely unclear. This study examined the relationship between angiogenesis and osteogenesis in a unique model of osseointegration of a mouse tibial implant by pharmacologically blocking the vascular endothelial growth factor (VEGF) pathway. MATERIALS AND METHODS: An implant was inserted into the right tibia of 16-week-old female C57BL/6 mice (n = 38). Mice received anti-VEGF receptor-1 (VEGFR-1) antibody (25 mg/kg) and VEGF receptor-2 (VEGFR-2) antibody (25 mg/kg; n = 19) or an isotype control antibody (n = 19). Flow cytometric (n = 4/group) and immunofluorescent (n = 3/group) analyses were performed at two weeks post-implantation to detect the distribution and density of CD31hiEMCNhi endothelium. RNA sequencing analysis was performed using sorted CD31hiEMCNhi endothelial cells (n = 2/group). Osteoblast lineage cells expressing osterix (OSX) and osteopontin (OPN) were also detected with immunofluorescence. Mechanical pull-out testing (n = 12/group) was used at four weeks post-implantation to determine the strength of the bone-implant interface. After pull-out testing, the tissue attached to the implant surface was harvested. Whole mount immunofluorescent staining of OSX and OPN was performed to determine the amount of osteoblast lineage cells. RESULTS: Flow cytometry revealed that anti-VEGFR treatment decreased CD31hiEMCNhi vascular endothelium in the peri-implant bone versus controls at two weeks post-implantation. This was confirmed by the decrease of CD31 and endomucin (EMCN) double-positive cells detected with immunofluorescence. In addition, treated mice had more OPN-positive cells in both peri-implant bone and tissue on the implant surface at two weeks and four weeks, respectively. More OSX-positive cells were present in peri-implant bone at two weeks. More importantly, anti-VEGFR treatment decreased the maximum load of pull-out testing compared with the control. CONCLUSION: VEGF pathway controls the coupling of angiogenesis and osteogenesis in orthopaedic implant osseointegration by affecting the formation of CD31hiEMCNhi endothelium. Cite this article: Bone Joint J 2019;101-B(7 Supple C):108-114.

Clinical and design factors influence the survivorship of custom flange acetabular components.

AIMS: Custom flange acetabular components (CFACs) are a patient-specific option for addressing large acetabular defects at revision total hip arthroplasty (THA), but patient and implant characteristics that affect survivorship remain unknown. This study aimed to identify patient and design factors related to survivorship. PATIENTS AND METHODS: A retrospective review of 91 patients who underwent revision THA using 96 CFACs was undertaken, comparing features between radiologically failed and successful cases. Patient characteristics (demographic, clinical, and radiological) and implant features (design characteristics and intraoperative features) were collected. There were 74 women and 22 men; their mean age was 62 years (31 to 85). The mean follow-up was 24.9 months (sd 27.6; 0 to 116). Two sets of statistical analyses were performed: 1) univariate analyses (Pearson's chi-squared and independent-samples Student's t-tests) for each feature; and 2) bivariable logistic regressions using features identified from a random forest analysis. RESULTS: Radiological failure and revision rates were 23% and 12.5%, respectively. Revisions were undertaken at a mean of 25.1 months (sd 26.4) postoperatively. Patients with radiological failure were younger at the time of the initial procedure, were less likely to have a diagnosis of primary osteoarthritis (OA), were more likely to have had ischial screws in previous surgery, had fewer ischial screw holes in their CFAC design, and had more proximal ischial fixation. Random forest analysis identified the age of the patient and the number of locking and non-locking screws used for inclusion in subsequent bivariable logistic regression, but only age (odds ratio 0.93 per year) was found to be significant. CONCLUSION: We identified both patient and design features predictive of CFAC survivorship. We found a higher rate of failure in younger patients, those whose primary diagnosis was not OA, and those with more proximal ischial fixation or fewer ischial fixation options. Cite this article: Bone Joint J 2019;101-B(6 Supple B):68-76.

Parathyroid hormone-related protein analog RS-66271 is an effective therapy for impaired bone healing in rabbits on corticosteroid therapy.

A new class of parathyroid hormone-related protein (PTHrP) analogs has been developed that causes a rapid gain in both trabecular and cortical bone in models of osteopenia. This study investigates the efficacy of the PTHrP analog, RS-66271 ([MAP(1-10)]22-31 hPTHrP(1-34)-NH(2)), as systemic therapy for impaired bone healing in corticosteroid-treated rabbits. A 1 mm defect was created bilaterally in the ulnae of 30 rabbits. Delayed healing was induced by daily injections of prednisone (0.15 mg/kg) beginning 2 months prior to surgery and continuing until killing. Rabbits in the experimental group received daily subcutaneous injections of PTHrP analog RS-66271 (0.01 mg/kg) starting 1 day after surgery. Control animals received subcutaneous normal saline. At the 6 week timepoint, nine of ten ulnae from PTHrP-treated rabbits achieved radiographic union, whereas only two of ten limbs achieved union in control rabbits (p < 0.01). In a separate part of the study, 20 animals (10 control, 10 RS-66271-treated) were killed when radiographic union was achieved bilaterally. In this portion of the study, all limbs in animals treated with PTHrP achieved union by 6 weeks. In the control animals that were allowed to heal for 10 weeks, only 20% of the limbs achieved radiographic union. In addition, ulnae in the PTHrP-analog-treated rabbits showed greater radiographic intensity (20%-40%), larger callus area (209% anteroposterior view, 417% lateral view) (mean area on AP radiographs: control, = 387 +/- 276 mm(2); PTHrP analog, 1195 +/- 408 mm(2)), and greater stiffness (64%) and torque (87%) when compared with controls. RS-66271 was shown to be an effective therapy for preventing impaired bone healing caused by prednisone in a rabbit model.

Immunolocalization and expression of bone morphogenetic proteins 2 and 4 in fracture healing.

Recently, it has become increasingly evident that fracture healing involves a complex interaction of many local and systemic regulatory factors. The roles of some of these growth factors have been described; however, little is understood about the presence of the bone morphogenetic proteins in fracture repair, despite the fact that they are the most potent osteoinductive proteins known. This study defines and characterizes the physiologic presence, localization, and chronology of the bone morphogenetic proteins in fracture healing with an established rat fracture healing model. With use of a recently developed monoclonal antibody against bone morphogenetic proteins 2 and 4 developed with standard avidin-biotin complex/immunoperoxidase protocols, frozen undecalcified fracture calluses were analyzed semiquantitatively for the percentage of various types of fracture cells staining positively. During the early stages of fracture healing, only a minimum number of primitive cells stained positively in the fracture callus. As the process of endochondral ossification proceeded, the presence of bone morphogenetic proteins 2 and 4 increased dramatically, especially in the primitive mesenchymal and chondrocytic cells. While the cartilaginous component of the callus matured with a concomitant decrease in the number of primitive cells, there was a concomitant decrease in both the intensity and the number of positively staining cells. As osteoblasts started to lay down woven bone on the chondroid matrix, these osteoblastic cells exhibited strong positive staining. The intensity of this staining decreased, however, as lamellar bone replaced the primitive woven bone. A similar observation was noted for the areas of the callus undergoing intramembranous ossification. Initially, within several days after the fracture, periosteal cells and osteoblasts exhibited intense staining for bone morphogenetic proteins 2 and 4. As the woven bone was replaced with mature lamellar bone, this staining decreased. These data, and the awareness of the strong osteoinductive capacities of bone morphogenetic protein, suggest that bone morphogenetic proteins 2 and 4 are important regulators of cell differentiation during fracture repair.

Future directions. Augmentation of osteoporotic vertebral bodies.

Because current medical and surgical treatments of vertebral body fractures are less than adequate, there is a need for interventions that decrease the likelihood of occurrence of these fractures and improve the treatment options once they have occurred. One such broad category of intervention involves the fortification or augmentation of the vertebral bodies. In addition to prophylactically stabilizing osteoporotic vertebral bodies at risk for fracture, augmentation of vertebral bodies that have already fractured may prove to be useful by reducing pain, improving function, and preventing further collapse and deformity. Vertebral body augmentation can also be used as an adjunct to fixation of internal hardware--for example, pedicle screws-in osteoporotic spines. A number of products are now available or are in clinical trials. The most promising products are injectable materials-polymethylmethacrylate or mineral bone cement. The early clinical results using polymethylmethacrylate in percutaneous vertebroplasty for fractured vertebral bodies and the results in vitro using an injectable mineral cement for vertebral body fortification are encouraging. Although the principle of vertebral body augmentation remains encouraging, data to support the widespread use of these techniques remain sparse, and the indications for their use should be more clearly defined.

An unexpected outcome during testing of commercially available demineralized bone graft materials: how safe are the nonallograft components?

STUDY DESIGN: Radiographic and histologic analyses of commercially available bone graft materials were performed. OBJECTIVE: To compare the osteoinductive efficacy of commercially available demineralized bone matrix material. SUMMARY OF BACKGROUND DATA: The relative in vivo bone formation and toxicology of the nonallograft components the make up various commercially available demineralized bone matrix products are not known. METHODS: An in vivo bone formation model was used in 30 athymic rats. Six different bone grafting materials were tested in subcutaneous and intermuscular locations. After 4 weeks, radiographic and histologic testing of bone formation was performed. RESULTS: Eight of nine rats implanted with Grafton demineralized bone matrix products died 1 to 4 days after implantation of the bone graft material. None of the remaining 10 animals implanted with the four other grafting materials died. The experiment was modified and completed with a lower dose of bone graft material. Pathologic analysis indicated that the cause of death was hemorrhagic necrosis of the kidneys, most likely caused by a toxic effect on the glomeruli and tubules. A possible causative factor may have been the glycerol in the graft material. CONCLUSIONS: Although the volume of Grafton product per kilogram of body weight used in this study was approximately eight times the maximum volume used in humans, the authors believe that this data must be reported because this product is used substantially in clinical settings. In addition, the osteoinductive performance and relative safety of the nonallograft components in all commercially available demineralized bone grafts are not known.

Fourier transform infrared spectral analysis of degenerative cartilage: an infrared fiber optic probe and imaging study.

A preliminary investigation into the diagnostic potential of an infrared fiber optic probe (IFOP) for evaluating degenerative human articular cartilage is described. Twelve arthritic human tibial plateaus obtained during arthroplasty were analyzed using the IFOP. Infrared spectra were obtained from IFOP contact with articular surface sites visually graded normal or degraded (Collins Scale grade 1 and grade 3, respectively). Comparisons of infrared spectral parameters (peak heights and areas) were made to elucidate spectral indicators of surface degeneration. IFOP spectral analysis revealed subtle but consistent changes between grades 1 and 3 sites. Infrared absorbance bands arising from type II collagen were observed to change with degradation. More degraded tissues exhibited increased amide II (1590-1480 cm(-1))/1338 cm(-1) area ratio (p=0.034) and decreased 1238/1227 cm(-1) peak ratio (p = 0.017); similar changes were seen with Fourier transform infrared imaging spectroscopy (FT-IRIS) analysis. Grades 1 and 3 cartilage showed consistent spectral differences in the amide II, III, and 1338 cm(-1) regions that are likely related to type II collagen degradation that accompanies cartilage degeneration. These results suggest that it may be possible to monitor subtle changes related to early cartilage degeneration, allowing for IFOP use during arthroscopy for in situ determination of cartilage integrity.

Two-stage exchange hip arthroplasty for deep infection.

Although the risk of infection after total hip arthroplasty has decreased over the last three decades with the use of prophylactic antibiotics, laminar airflow operating rooms and whole-body exhaust suites, deep infection after total hip arthroplasty remains a serious complication. Significant morbidity to the patient and the cost to the health care system remain. During this period of time, diagnostic techniques also have improved including the use of polymerase chain reaction amplification. Treatment options now include: suppressive antibiotics, irrigation and debridement with retention of components, one-stage reimplantation, two-stage reimplantation, and salvage procedures. Based on the medical literature, the successful eradication of a total joint replacement infection with a two-stage reimplantation protocol is over 90% while the success rate with a one-stage protocol is approximately 80%. These success rates may decline however as the prevalence of antibiotic resistant organisms increases. Current controversies regarding two-stage reimplantation protocols include: duration of intravenous antibiotic therapy, timing of the reimplantation, the use of allograft bone in the reconstruction, the choice of fixation (cement versus cementless), and the use of antibiotic-loaded cement spacers.

Osteoinductive growth factors in preclinical fracture and long bone defects models.

Fracture healing is a specialized form of the reparative process that the musculoskeletal system undergoes to restore skeletal integrity. This biologic process is a consequence of a complex cascade of biologic events that result in the restoration of bone tissue, allowing for the resumption of musculoskeletal function. Several growth-promoting substances have been identified at the site of skeletal injury and appear to play a physiologic role in fracture healing. This article reviews the effects of these osteoinductive growth factors on bone healing as elucidated by both preclinical in vivo fracture and diaphyseal defect healing models.

Bone growth factors.

Osteoblastic culture models, experimental, and clinical models have revealed that bone growth factors influence cellular activity. Growth factors including bone morphogenetic proteins, transforming growth factor beta, platelet-derived growth factor, insulin-like growth factors I and II, and acidic and basic fibroblast growth factors, are powerful tools for fracture healing and bone grafting. Understanding the role that bone growth factors play in bone repair is necessary to apply these factors in a clinical setting.

A biomechanical evaluation of the long stem intramedullary hip screw.

Despite the advantages associated with short-stem intramedullary hip screw devices for the treatment of intertrochanteric fractures, recent reports have shown an increased incidence of femoral shaft fractures after their insertion. These findings led to the hypothesis that an intramedullary hip screw with a longer stem may more effectively redistribute loads to the distal end of the femoral shaft, where they may be more readily absorbed by the increased bony cross-sectional area. To characterize the load patterns of a long-stem device in the femur, 10 fresh-frozen adult femurs were instrumented with unidirectional strain gauges. A total of eight strain gauges were placed in the direction of principal femoral strains on the medial and lateral surfaces of each femur. Each femur was held in a steel vice at 15 degrees of adduction in the coronal plane and vertical in the sagittal plane. The femurs were then subjected to successively increasing vertically applied compressive loads from 0 N to 1,400 N at 200-N increments using a servohydraulic testing machine. Strain values were recorded at each load after a 5-min equilibration period. Each femur was tested under five conditions: (a) intact, (b) after insertion of the long-stem intramedullary hip screw device, (c) with an experimentally created two-part fracture, (d) with a stable four-part fracture, and (e) with an unstable four-part fracture with the posteromedial fragment removed. Half the femurs were randomly assigned to have two distal interlocking screws placed before fracture. The remaining half were loaded without distal interlocking screws.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatigue testing of cerclage stainless steel wire fixation.

Because wire fixation continues to be used extensively in the practice of orthopaedic surgery, despite a high incidence of wire breakage, understanding the mechanism of this failure is of important clinical interest. The aim of this study was to investigate the failure of cerclage stainless steel wire using an in vitro cyclic loading device. A stainless steel testing fixture consisting of two half cylinders with a combined diameter of 2.5 cm was mounted in a servo hydraulic testing machine. Specimens of number 18 gauge (0.97 mm diameter) and number 16 gauge (1.22 mm diameter) 316L stainless steel wire were mounted around the two half cylinders in a cerclage manner using three different fastening methods: a uniform symmetrical twist, a knot twist, and a square knot. Single-load-to-failure and cyclic load tests were performed under controlled tensile displacement. The cerclage wire system fastened with a twist resulted in failure at loads significantly lower than systems fastened with the knot twist and the square knot. Cyclic loading of the wire fastened with twists also showed decreased fatigue properties when compared to those fastened with the knot twist and the square knot. In all tests, the 16-gauge wire was found to be clearly superior to the 18-gauge wire. For both wires, fatigue strengths at 100,000 cycles were only 30-37% of the static ultimate strength. These results show that wire diameter and fastening system are two important factors affecting the mechanical properties of the resulting fixation.

Cancellous bone screw thread design and holding power.

This study was designed to isolate and evaluate the parameters of host density, outer diameter (OD), root diameter (RD), and pitch in cancellous bone screw design and their effect on holding power. Special emphasis was placed on screw pitch, which has been evaluated infrequently in the literature. Three groups of stainless steel V thread screws (group I, OD 4.5 mm, RD 3.0 mm; group II, OD 6.4 mm, RD 3.5 mm; group III, OD 6.4 mm, RD 4.2 mm) were machined with progressive increases in pitch from 12 to 32 threads per inch (TPI). Two densities of synthetic cancellous bone material (Pedilen, Ottobock, Minneapolis, MN, U.S.A.), 0.15 g/ml and 0.22 g/ml, were then prepared and molded into sheets 1.9 cm thick and the screw threads completely engaged. Push-out tests were performed using a servohydraulic testing machine (MTS, Minneapolis, MN, U.S.A.). Fifteen trials of each screw were tested in each material. The effect on holding power of the different parameters of the custom screws in order of importance was (a) host material density, (b) OD (c) pitch, and (d) RD. The groups with a 6.4-mm OD had a much greater holding power than did the group with a 4.5-mm OD (p < 0.001). A decrease in screw pitch (increased threads per inch) did itself have a significant improved effect on fixation for all groups in both pedilen densities (p < 0.001). In the two 6.4-mm screw groups studied, the difference in the two root diameters (4.2 mm vs. 3.5 mm) showed the smaller root diameter to give a greater holding power in the less dense 0.15 g/ml pedilen (p < 0.001). In the more dense 0.22 g/ml pedilen there was no difference (p = 0.26) between the root diameters. To optimize holding power, cancellous screws may be designed with a decreased pitch (increased TPI) over those commercially available today. Cannulated screws must have a larger cancellous thread root diameter to leave room for the central cannulation; this may decrease their holding power in less dense cancellous bone but not in denser bone.

A rare case of a bisphosphonate-induced peri-prosthetic femoral fracture.

An 81-year-old woman presented with a fracture in the left femur. She had well-fixed bilateral hip replacements and had received long-term bisphosphonate treatment. Prolonged bisphosphonate use has been recently linked with atypical subtrochanteric and diaphyseal femoral fractures. While the current definition of an atypical fracture of the femur excludes peri-prosthetic fractures, this case suggests that they do occur and should be considered in patients with severe osteopenia. Union of the fracture followed cessation of bisphosphonates and treatment with teriparatide. Thus, this case calls into question whether prophylactic intramedullary nailing is sufficient alone to treat early or completed atypical femoral fractures.

A review of the treatment of pelvic discontinuity.

Pelvic discontinuity is a complex entity with a high surgical complication rate and no standardized treatment to date. Revision hip arthroplasty in cases of massive bone loss remains a difficult and unsolved problem. The goal of the surgeon is to preserve limb function by restoring bone stock and the biomechanics of the hip. In cases of severe acetabular bone loss, biologic fixation is often inadequate, requiring extensive bone grafting and reconstructive cages. Reconstructive cages are the most commonly used devices and are designed to bridge bone defects, protect the bone graft, and reestablish the rotation center of the hip. A major limitation of current cages is that they do not allow for biologic fixation. We review the options for treating patients with massive bone loss and pelvic discontinuity and discuss therapeutic options and the clinical and radiological criteria for success.