Summary Statement

The structure of bone inside a porous bone graft substitute can be quantified and compared by using a combination of novel measurements of surface area and connectivity. This allows for a numerical representation of the bone structure to be calculated.

INTRODUCTION

Autologous bone grafts are considered gold standard in the repair of bone defects. However they are limited in supply and are associated with donor site morbidity. This has led to the development of synthetic bone graft substitute (BGS) materials, many of which have been reported as being osteoinductive. The structure of the BGS is important and bone formation has been observed in scaffolds with a macroporous morphology. Smaller pores termed ‘strut porosity’ may also be important for osteoinduction. The aim of this study was to compare the osteoinductive ability of one silicate-substituted calcium phosphate (SiCaP) with differing strut porosities in an ectopic ovine model. Our hypothesis was that SiCaP with greater strut porosity would be more osteoinductive.

Background, Context and Motivation

“Increases in reconstructive orthopaedic surgery, resulting from advances in surgical practice and the ageing population, have lead to a demand for bone graft that far exceeds supply.”…Traditional bone grafting methods have been linked with a number of negative issues including increased morbidity due to secondary operation site and action as a vector for spread of disease. (Hing 2004). A solution to these insufficiencies would be the creation of a synthetic osteoinductive bone graft material. This would vastly improve bone graft surgery success rates and expedite post-op recovery times. The aim of this study was to classify then explore the dissolution rates of three experimental hydroxyapatite/silicate apatite synthetic bonegrafts in physiological solutions, (phosphate buffered saline, (PBS) +/− serum proteins, (PBS +FCS). The overall objective being to identify whether there is an explainable significant difference in ion exchange that could be behind the osteoinductive phenomena.

Introduction: Incorporation of Silicon into the HA structure enhances the bioactivity of Hydroxyapatite (HA). Silicon substituted calcium phosphate (SiCaP/SiHA) has been introduced as an osteoconductive material for bone formation. However, the osseoinductive capacity of this biomaterial has not been assessed. A previous study by Hing et al shows that bioactivity of stoichiometric hydroxyapatite bone substitute materials is enhanced by increasing the level of porosity within the implant struts [1].

The aim of this study was to test the hypothesis that SiCaP bone graft results in superior osseoinduction compared to stoichiometric HA and osseoinduction enhancement using high microporosity materials.

Methods: Implantation of 32 bone graft plugs (16 granular and 16 blocks) with 3 different strut porosities: 20% SiHA, 35% SiHA, 10% SiHA and 20% HA, all with matched 80% total porosity supplied by ApaTech Ltd into the paraspinalis muscle of 4 sheep for 12 weeks. HA and %SiHA locations were randomized at implant sites.

Following euthanasia at 12 weeks histomorphometry was carried out to calculate Percentage of bone, soft tissue and implant area and Percentage of the amount of bone in contact with the calcium phosphate surface (% Bone attachment). Further evaluation of Calcium, Phosphate and Silicon levels within the implants and surrounding bone was carried out by Scanning Electron Microscopy (SEM) and EDAX.

Results: Bone formation was observed within the pores of both granules and blocks of SiCaP and HA implants. Greater bone formation and attachment was detected in scaffolds with higher strut porosity (SiHA35) compared to implants of the same chemical composition but lower strut porosity (SiHA10, SiHA20. More bone formation and contact was observed in SiHA implants (SiHA20) compared to matched porosity HA implants where the amount of bone formed was minimal. Uniform distribution of Silicon (Si) was visible within the SiHA scaffold struts according to EDAX results. Greater quantities of Si existed in newly formed bone as compared to soft tissue adjacent to the SiHA implants. Silicon was not detected in either soft or hard tissues adjacent to HA implants.

Conclusion: Both microporous HA and SiCaP promote bone ingrowth, as ectopic bone formation was observed in all four groups of synthetic materials. Matched porosity SiCaP is more osseoinductive than HA. Increasing strut porosity results in promotion of osseoinductivity. High strut porosity (> 10%) block environment contributes to greater osseoinductive behaviour. In conclusion we report that presence of silicon and the strut porosity influence the osseoinductive capacity of calcium phosphate bone substitute biomaterials.

We undertook a prospective, single blinded, randomized, controlled trial of one hundred children treated with either an above or below elbow cast for treatment of closed, distal third forearm fractures requiring reduction. The re-manipulation rate in the below elbow group was 2% (95%CI: 0–11%) compared to 6% (95%CI: 2–15%) in the above elbow group, p=0.62. Above elbow casts do not appear to improve fracture immobilization nor reduce the requirement for re-manipulation in pediatric distal third forearm fractures.

Debate exists regarding the benefits of using below elbow casts instead of above elbow casts for maintaining reduction in pediatric distal third forearm fractures. The literature indicates a loss of reduction rate of 14.6% of children treated in an above elbow cast and 2.5% in those treated with a below elbow cast.

We undertook a prospective, single blinded, randomized, controlled trial of one hundred children treated with either an above or below elbow cast for treatment of closed, distal third forearm fractures requiring reduction. Outcome measures included re-manipulation rate, fracture displacement during cast wear, and cast complications. One hundred patients were suitably enrolled; fifty-four received an above elbow cast, forty-six received a below elbow cast. The two groups were similar in terms of age and gender. The above elbow group contained a higher proportion of both bone fractures (41/54) than the below elbow group (27/46).

There were no significant differences between the two cast groups in initial, post-reduction or cast-off fracture angulation; nor any difference in the amount of fracture displacement during cast wear. The number of cast complications was similar between the two groups. The re-manipulation rate in the below elbow group was 2% (95%CI: 0–11%) compared to 6% (95%CI: 2–15%) in the above elbow group, p=0.62.

Above elbow casts do not appear to improve fracture immobilization nor reduce the requirement for re-manipulation in pediatric distal third forearm fractures.

Funding Hip Hip Hooray, Saskatoon

The use of porous ceramics as bone graft substitutes (BGS) has been under consideration for over 30 years [1]. In particular calcium phosphates such as hydroxyapatite (HA) have been promoted as a result of their osteoconductive properties, i.e. that they stimulate bone apposition within their macroporous structures.

It is well established that both pore size [1] and pore connectivity [2] are critical morphological elements for a successful BGS. Thus biologically ‘optimal’ structures, with relatively large levels of porosity (> 70%) are consequently low in mechanical strength, with typical UCS values of between 1–8 MPa depending on the precise level of porosity and the pore size distribution. The aim of this investigation was to study the biological response to a porous HA with a relatively low level of macro-porosity (64%), but which possessed a highly interconnected micro-pore structure within the HA struts.

Phase pure porous HA implants were manufactured using a novel technique [3] with a mean macro-pore size of 230 ìm and a mean pore interconnection size of 110 μm. Cylindrical specimens 4.5 mm in diameter were implanted in the distal femur of 6 month New Zealand White rabbits and retrieved for histological and histomorphometric analysis at 4 weeks. The mineral apposition rate (MAR) was determined through the administration of fluorochrome labels at 1, 2 and 3 weeks.

After 4 weeks new bone had penetrated deep within the macro-pore structure and at high magnification osteocyte-like cells were observed occupying micro-pores within the ceramic struts. Furthermore, there was a significant increase in the MAR of bone formed within and surrounding the PHA (5.21 ìm.day-1, 4.42 ìm.day-1) as compared to the normal turnover rate of control bone (2.07 ìm.day-1, 2.09 ìm.day-1) during weeks 1-2 and 2–3, respectively.

The micro-porous network within the scaffold struts clearly influenced the host response. This could be linked to an associated increase in roughness or surface area, or it may reflect the greater level of strut permeability underlining the importance of nutrient transfer and the promotion of angiogenesis in scaffolds for bone repair.

The operative technique and result of treatment of traumatic radio-ulnar synostosis in two patients are described. In both, the treatment was excision of the cross-union and interposition of a free non-vascularised fat transplant. The functional result was excellent, and there was no evidence of regrowth of the synostosis at two and three years respectively.

A survey was conducted to document the results of bracing and spinal fusion for scoliosis associated with osteogenesis imperfecta. Observations were made of 121 patients who underwent treatment by bracing or spinal fusion and who had been treated by 51 orthopaedic surgeons in 14 countries. The average curve before bracing measured 43 degrees. The braces were ineffective in stopping progression even in small curves. We were unable to determine whether braces slowed the rate of progression of curvature. The average age at fusion was 15 years 7 months, the average curve before operation measured 74 degrees, and the average correction was 36 per cent. The high incidence of complications was related to the size of the curve before spinal fusion, the use of Harrington instrumentation, and the presence of associated kyphosis. In the absence of pseudarthrosis or kyphosis, late bending of the fused spine did not seem to occur.