Effects of positioning and notching of resurfaced femurs on femoral neck strength: a biomechanical test.

PURPOSE: To assess the effects of positioning and notching of resurfaced femurs on the mechanical strength of third-generation saw bone (TGSB) femurs using an in vitro analogue bone model. METHODS: 30 TGSB femurs were equally divided into 6 resurfaced femur groups (intact, anatomic, varus, valgus, anatomically notched, and valgus notched) for testing the load to failure, stiffness, and total energy. RESULTS: Compared to the intact femurs, the load to failure in all resurfaced femurs was significantly decreased by 29 to 57%. Among the resurfaced femurs, valgus and anatomic femurs had the highest load to failure, followed by valgus notched, varus, and anatomically notched femurs. Notching weakened the construct by a further 24 to 30%. CONCLUSION: To minimise the risk of femoral neck fracture, resurfaced femoral heads should be placed in an anatomic or valgus orientation, and the superior cortex of the femoral neck should remain intact.

Modulation of aggrecan and ADAMTS expression in ovine tendinopathy induced by altered strain.

OBJECTIVE: To evaluate histologic, immunohistochemical, and molecular changes in tendon induced by altered strain in a large-animal model. METHODS: A full-thickness partial-width laceration of the infraspinatus tendon was created in 5 sheep, while 5 sham-operated sheep were used as controls. Sheep were killed after 4 weeks, and 4 differentially stressed tendon regions (tensile or near bone attachment from overstressed or stress-deprived halves) were evaluated for histopathology, proteoglycan (PG) accumulation, and characterization of glycosaminoglycans and aggrecan catabolites. Gene expression of matrix components, enzymes, and inhibitors was analyzed by reverse transcriptase-polymerase chain reaction. RESULTS: Histopathologic changes were detected in both overstressed and stress-deprived tensile tendon, but only in stress-deprived tendon near bone. In overstressed and stress-deprived tensile tendon, levels of keratan sulfate, chondroitin 4-sulfate, and chondroitin 6-sulfate were increased. In overstressed tensile tendon, levels of ADAMTS-generated aggrecan catabolites were increased. There was increased matrix metalloproteinase 13 (MMP-13) and decreased fibromodulin and decorin expression in all regions. Increased MMP-1, MMP-9, MMP-14, and ADAMTS-1 expression, and decreased type II collagen expression were restricted to stress-deprived tendon. In stress-deprived bone-attachment regions, messenger RNA (mRNA) for aggrecan was decreased, and ADAMTS was increased. In overstressed tensile tendon, aggrecan mRNA was increased, and ADAMTS was decreased. CONCLUSION: The distinct molecular changes in adjacent tissue implicate altered strain rather than humoral factors in controlling abnormal tenocyte metabolism, and highlight the importance of regional sampling. Tendon abnormalities induced by increased strain are accompanied by increased aggrecan, decreased ADAMTS, and low PG expression, which may negatively impact the structural integrity of the tissue and predispose to rupture.

Periprosthetic bone remodelling of a collum femoris preserving cementless titanium femoral hip replacement.

Total hip arthroplasty represents a major surgical achievement for pain relief and restoration of lifestyle quality due to the joint disease of osteoarthritis. Total hip replacement has evolved over the past 30 years utilising a variety of biocompatible materials, geometric shapes and fixation techniques. The main objective of this study is to investigate the long-term effects of strain adaptive bone remodelling due to the influence of a novel titanium cementless femoral hip replacement. The period of on-growth has been taken into account and the simulation has been run to predict the remodelling behaviour for a 36-month period. The main conclusion from this analysis is that the implant does shield the calcar to a similar degree as other cementless femoral hip designs. It does, however, tend to cause bone to be laid down along its length. This may, in part, be due to the novel geometry of the implant interlocking with and loading the bone.

Computational bone remodelling simulations and comparisons with DEXA results.

Femoral periprosthetic bone loss following total hip replacement is often associated with stress shielding. Extensive bone resorption may lead to implant or bone failure and complicate revision surgery. In this study, an existing strain-adaptive bone remodelling theory was modified and combined with anatomic three-dimensional finite element models to predict alterations in periprosthetic apparent density. The theory incorporated an equivalent strain stimulus and joint and muscle forces from 45% of the gait cycle. Remodelling was simulated for three femoral components with different design philosophies: cobalt-chrome alloy, two-thirds proximally coated; titanium alloy, one-third proximally coated; and a composite of cobalt-chrome surrounded by polyaryletherketone, fully coated. Theoretical bone density changes correlated significantly with clinical densitometry measurements (DEXA) after 2 years across the Gruen zones (R2>0.67, p<0.02), with average differences of less than 5.4%. The results suggest that a large proportion of adaptive bone remodelling changes seen clinically with these implants may be explained by a consistent theory incorporating a purely mechanical stimulus. This theory could be applied to pre-clinical testing of new implants, investigation of design modifications, and patient-specific implant selection.

Plating of metacarpal fractures: unicortical or bicortical screws?

Mid-shaft transverse osteotomies were performed in 18 cadaveric metacarpals and randomly divided into two groups. Using dorsally applied plates for repair, one group was secured using 6mm unicortical screws, while bicortical screws were used in the second group. The metacarpals were tested to failure with a four-point bending protocol using a servo-hydraulic testing machine and a 1kN load cell. The mean load to failure was 596N (SD=142) for the unicortical and 541N (SD=171) for the bicortical group. The stiffness was 333N/mm (SD=116) for the unicortical and 458N/mm (SD=158) for the bicortical group. Both load to failure and stiffness were not statistically significant between the two groups. Failure occurred by fracture at the screw-bone interface in all specimens: no screw pull-out was observed. No biomechanical advantage was found when using bicortical screws in metacarpal fracture plating.

Cemented fixation with PMMA or Bis-GMA resin hydroxyapatite cement: effect of implant surface roughness.

Implant surface roughness is an important parameter governing the overall mechanical properties at the implant-cement interface. This study investigated the influence of surface roughness using polymethylmethcrylate (PMMA) and a Bisphenol-a-glycidylmethacyrlate resin-hydroxyapatite cement (CAP). Mechanical fixation at the implant-cement interface was evaluated in vitro using static shear and fatigue loading with cobalt chrome alloy (CoCr) dowels with different surface roughness preparations. Increasing surface roughness improved the mechanical properties at the implant-cement interface for both types of cement. CAP cement fixation was superior to PMMA under static and dynamic loading.

In vivo evaluation of resorbable bone graft substitutes in a rabbit tibial defect model.

Calcium sulfate as a bone graft substitute is rapidly resorbed in vivo releasing calcium ions but fails to provide long-term three-dimensional framework to support osteoconduction. The setting properties of calcium sulfate however allow it to be applied in a slurry form making it easier to handle and apply in different situations. This study examines the in vivo response of calcium sulfate alone and as a carrier for a coralline hydroxyapatite in an established bilateral corticocancellous defect model in rabbits. Defects were filled flush to the anterior cortex with a resorbable porous ceramic alone and in combination with calcium sulfate slurry, calcium sulfate slurry alone or calcium sulfate pellets and examined at time points up to 52 weeks. Specimens where assessed using Faxitron X-ray, light and electron microscopy. Calcium sulfate in either slurry or pellet form does indeed support new bone formation alone however, complete filling of the bone defect is not observed. Calcium sulfate in slurry form does however improve the surgical handling of particulate bone graft substitutes such as Pro Osteon 200 R, which remained as an osteoconductive scaffold for up to 52 weeks and may have played an important role in the ultimate closure of the cortical windows.

Spinal fusion using an autologous growth factor gel and a porous resorbable ceramic.

Augmenting healing through a single application of an exogenous growth factor or bone morphogenetic protein is not a new concept. The use of autologous growth factors through platelet isolation and concentration provides multiple endogenous growth factors to the healing site. A posterolateral fusion model in aged sheep (5- to 6-year-old ewes) was used to examine the effects of the addition of growth factors through autologous platelet isolation on the biomechanic and histologic properties of the fusion using a resorbable coral bone graft substitute. At 6 months the combination of autologous growth factors to the Pro Osteon 500R plus aspirated bone marrow resulted in the greatest bending stiffness but not ultimate load. Autologous growth factors can be isolated from platelets and concentrated to provide multiple growth factors to the fusion site to aid in spinal fusion.

A resorbable porous ceramic composite bone graft substitute in a rabbit metaphyseal defect model.

The success of converted corals as a bone graft substitute relies on a complex sequence of events of vascular ingrowth, differentiation of osteoprogenitor cells, bone remodeling and graft resorption occurring together with host bone ingrowth into and onto the porous coralline microstructure or voids left behind during resorption. This study examined the resorption rates and bone infiltration into a family of resorbable porous ceramic placed bilaterally in critical sized defects in the tibial metaphyseal-diaphyseal of rabbits. The ceramics are made resorbable by partially converting the calcium carbonate of corals to form a hydroxyapatite (HA) layer on all surfaces. Attempts have been made to control the resorption rate of the implant by varying the HA thickness. New bone was observed at the periosteal and endosteal cortices, which flowed into the centre of the defect supporting the osteoconductive nature of partially converted corals. The combination of an HA layer and calcium carbonate core provides a composite bone graft substitute for new tissue integration. The HA-calcium carbonate composite demonstrated an initial resorption of the inner calcium carbonate phase but the overall implant resorption and bone ingrowth behaviour did not differ with HA thickness.

In vitro assessment of proximal polyethylene contact surface areas and stresses in mobile bearing knees.

Wear of the polyethylene (PE) insert in total knee arthroplasty remains a significant problem. The generation of biologically active wear particles may ultimately affect implant longevity through osteolysis or premature/catastrophic PE failure. The rate and pattern of wear is influenced by many factors, including component geometry and individual loading conditions, which determine the contact surface area and kinematics of the reconstructed knee. Contact areas and stresses at the proximal femoral-PE insert interface and distal PE-tibial interface contact surface areas were measured in nine mobile bearing total knee designs at 0, 30, 60, 90 and 110 degrees of flexion at 3600 N (5 x body weight) using a standardized test method. Proximal and, to a lesser degree, distal interface contact area footprints decreased significantly with increasing flexion angle based on the conformity of the designs, resulting in a corresponding increase in the mean and peak stresses.

The influence of design parameters on cortical strain distribution of a cementless titanium femoral stem.

The strain distribution imposed on a femur following a total joint replacement is an important factor, in proximal bone loss due to stress shielding, and long term clinical success. This study investigated how five different design parameters of a cementless titanium femoral prosthesis influenced cortical strains. Test loads were applied and strains were measured with and without an abductor force simulation, using six human cadaveric femora. The cementless design used demonstrated significant calcar loading proximally and a similar strain distribution to the intact femur distally. Implant gross geometry was the major factor in determining the cortical strain distributions under abductor simulation in both axial and torsional loading.

Co-operative learning processes of students: a longitudinal multilevel perspective.

BACKGROUND: This article describes the outcomes of a longitudinal, multilevel observational study in which the relationship between the processes of co-operation and giving explanations was compared between classes trained in communication skills and classes that were untrained. AIMS: This study examined the effects of training in basic communication skills on the processes of co-operation and giving explanation in co-operative groups. In particular, the study investigated: (a) How the processes of co-operation and giving explanations develop over time; (b) How the underlying processes of co-operation and giving explanations are related; (c) Which factors at the student and class level facilitate or hinder these processes. SAMPLE: The study involved 192, Year 6 primary school children (mean age = 134.3 months) who worked in four-person, mixed ability, gender-balanced groups on a social studies unit of work for 12 weeks. RESULTS: The students in the trained classes were more co-operative and gave more explanations to each other than their peers in the untrained classes. Giving solicited explanations could be traced back to co-operation and this process was enhanced by ability. In other words, the higher the individual ability levels of the students, the more co-operation was transformed into giving solicited explanations. Furthermore, over and above the effects of student ability, the higher the class' ability level, the more explanations the students gave. CONCLUSION: The results of this study are useful in explaining why high-ability students benefit more from co-operative learning than low-ability students and why solicited explanations are more effective than unsolicited explanations. By opening the black box of co-operative learning, our analysis enables us to attribute the effects of co-operative learning to peer interactions with more able peers and this is promoted by class ability level. These factors have been mentioned in the literature as a possible explanation of 'contextual effects' but not investigated empirically.

The maintenance of cooperative and helping behaviours in cooperative groups.

BACKGROUND: This study was a full-year investigation of whether children, who had previously been trained to cooperate and help each other, were able to use these behaviours in reconstituted groups without additional training one year later. AIMS: (i) To examine whether children who have previously been trained to cooperate demonstrate more cooperative and helping behaviours in their groups than children who had no been trained and (ii) to determine the effect of prior training on children's learning. SAMPLE: The study involved 144 Grade 2 children (mean age = 94.5 months; third year of schooling), from nine schools in a similar socio-demographic area of Brisbane, Australia. Sixty-four children, who had been trained in cooperative group behaviours in the previous year, were assigned to the Trained groups and 80 children, who had not received any training, were assigned to the Untrained groups. METHOD: The children worked in four-person, mixed-ability (high-, medium-, and low-ability), gender-balanced groups (2 males, 2 females) for one six-week social studies unit of work each term for three school terms. Videotaping occurred in the 5-6 week of each work unit. Videotapes were coded for behaviour and verbal interactions. Learning outcomes data were also collected. RESULTS: The children in the trained groups exhibited more cooperative behaviour and they provided more explanations, both in response to explicit and implicit requests for help across the three periods of time. The children in the trained groups used higher level cognitive strategies such as providing specific concrete facts and reasons in their interactions and they also obtained higher scores on the learning outcomes questionnaire than their untrained peers. CONCLUSION: Young children who have been trained to cooperate and help each other are able to demonstrate these behaviours in reconstituted groups without additional training a year later.

Use of technology by people with physical disabilities in Australia.

PURPOSE: This study aimed to quantify the extent to which computers and assistive devices were being used by people with physical disabilities and the levels of computer training being undertaken by this group. METHOD: With the help of Queensland disability associations a written survey was distributed to people over 15 years in age with physical disabilities living in the greater Brisbane metropolitan area. Responses were received from 82 people (comprising spinal cord injuries (n = 71), cerebral palsy (n = 8), muscular dystrophy (n = 3)). RESULTS: Indicate that 60% of respondents were computer users, while only 15 respondents used assistive devices. Computer ability was correlated to age and time of disability onset. Respondents with quadriplegia had higher levels of computer ability than those with paraplegia. The study indicates that while many people with disabilities have used computers and assistive devices, many have not. CONCLUSIONS: The low rate of assistive device use by people with high-level quadriplegia is of concern. This study suggests that increased levels of training in the use of computers and assistive devices needs to be provided to people with physical disabilities.

Relationship between use of technology and employment rates for people with physical disabilities in Australia: implications for education and training programmes.

This study examined the impact of computer and assistive device use on the employment status and vocational modes of people with physical disabilities in Australia. A survey was distributed to people over 15 years in age with physical disabilities living in the Brisbane area. Responses were received from 82 people, including those with spinal cord injuries, cerebral palsy and muscular dystrophy. Of respondents 46 were employed, 22 were unemployed, and 12 were either students or undertaking voluntary work. Three-quarters of respondents used a computer in their occupations, while 15 used assistive devices. Using logistic regression analysis it was found that gender, education, level of computer skill and computer training were significant predictors of employment outcomes. Neither the age of respondent nor use of assistive software were significant predictors. From information obtained in this study guidelines for a training programme designed to maximize the employability of people with physical disabilities were developed.

Nerve sheath ganglion of the superficial radial nerve.

Nerve sheath ganglia are infrequent and most commonly involve the peroneal nerve. We describe the previously unreported involvement of the superficial branch of the radial nerve.