Allografts are used to compensate for bone defects resulting from revision surgery, tumor surgery and reconstructive bone surgery. While it is well known that the reduction of fat content of allografts increases mechanical properties, the content of liquids were not assessed with known grain size distribution so far. The aim of the study was to compare the mechanical properties of dried allografts (DA) to allografts mixed with a saline solution (ASS) to allografts mixed with blood (AB) having a similar grain size distribution.

Fresh-frozen morsellized bone chips were cleaned chemically, sieved and reassembled in specific portions with known grain size distribution. A uniaxial compression was used to assess the yield limit of the three groups before and after compaction with a fall hammer apparatus.

No statistically significant difference could be found between all three groups for the yield limit (p=0.339) before compaction. After compaction no statistically significant difference could be found between DA and ASS (p=0.339) and between ASS and AB (p=0.554). AB showed a statistically significant higher yield limit than DA (p=0.022). At the yield limit 3 outliers were removed in DA, 1 in ASS and 1 in AB before compaction and 2 in DA and 1 in AB after compaction.

Excluding the effect of the grain size distribution on the mechanical properties it was shown that allografts have a lower yield limit, when lipids are present. The liquid content of allografts seems to play an inferior role as no statistically significant difference could be found between DA and ASS. It is suggested in accordance with other studies to chemical clean allografts before implantation to reduce the contamination risk and the fat content. An optimum liquid level still remains to be defined. The considerations here described are relevant for filling up bigger bone defects, while in smaller defects the differences between different preparation methods may be less prominent.

Femoral impaction bone grafting (IBG) may be used to restore bone stock in revision total hip arthroplasty (THA) and allow use of a shorter, than otherwise, length prosthesis. This is most beneficial in young patients who are more likely to require further revision surgery. This study aimed to assess the results of femoral IBG for staged revision THA for infection. A prospective cohort of 29 patients who underwent staged revision THA for infection with femoral IBG and a cemented polished double-tapered (CPDT) stem at the final reconstruction was investigated.

The minimum follow-up was two years (2 – 10 years, median 6 years). Stem subsidence was measured with radiostereometric analysis. Clinical outcomes were assessed with the Harris Hip, Harris Pain, and and Société Internationale de Chirurgie Orthopédique et de Traumatologie Activity (SICOT) Scores. The original infection was eradicated in 28 patients. One patient required a repeat staged revision due to re-infection with the same organism. At two-year follow-up, the median subsidence at the stem-bone interface was −1.70 mm (−0.31 to −4.98mm). The median Harris Hip Score improved from 51 pre-operatively to 80 at two years (p=0.000), the Harris Pain Score from 20 to 44 (p=0.000) and the SICOT Score from 2.5 to 3 (p=0.003).

As successful eradication of infection was achieved in the majority of patients and the stem migration was similar to that of a primary CPDT stem, this study supports the use of femoral IBG during the final reconstruction of the femur after staged revision THA for infection.

AIM

Avascular necrosis (AVN) of the femoral head is a potentially debilitating disease of the hip in young adults. Impaction bone grafting (IBG) of morcellised fresh frozen allograft is used in a number of orthopaedic conditions. This study has examined the potential of skeletal stem cells (SSC) to augment the mechanical properties of impacted bone graft and we translate these findings into clinical practice.

Disease transmission, availability and economic costs of allograft have resulted in significant efforts into finding an allograft alternative for use in impaction bone grafting (IBG). Biotechnology offers the combination of skeletal stem cells (SSC) with biodegradable polymers as a potential solution. Recently polymers have been identified with both structural strength and SSC compatibility that offer the potential for clinical translation.

The aim of this study was to assess whether increasing the porosity of one such polymer via super critical CO2 dissolution (SCD) enhanced the mechanical and cellular compatibility characteristics for use as an osteogenic alternative to allograft in IBG.

High molecular weight PLA scaffolds were produced via traditional (solid block) and SCD (porous) techniques, and the differences characterised using scanning electron microscopy (SEM). The polymers were milled, impacted, and mechanical comparison between traditional vs SCD created scaffolds and allograft controls was made using a custom shear testing rig, as well as a novel agitation test to assess cohesion. Cellular compatibility tests for cell number, viability and osteogenic differentiation using WST-1 assays, fluorostaining and ALP assays were determined following 14 day culture with SSCs.

SEM showed increased porosity of the SCD produced PLA scaffolds, with pores between 50-100 micrometres. Shear testing showed the SCD polymer exceeded the shear strength of allograft controls (P<0.001). Agitation testing showed greater cohesion between the particles of the SCD polymer (P<0.05). Cellular studies showed increased cell number, viability and osteogenic differentiation on the SCD polymer compared to traditional polymer (P<0.05) and allograft (P<0.001).

The use of supercritical C02 to generate PLA scaffolds significantly improves the cellular compatibility and cohesion compared to traditional non-porous PLA, without substantial loss of mechanical shear strength. The improved characteristics are critical for clinical translation as a potential osteogenic composite for use in impaction bone grafting.

Impaction bone grafting with milled human allograft is the gold standard for replacing lost bone stock during revision hip surgery. Problems surrounding the use of allograft include cost, availability, disease transmission and stem subsidence (usually due to shear failure of the surrounding allograft).

The aim of this study was to investigate various polymers for use as substitute allograft. The ideal graft would be a composite with similar mechanical characteristics as allograft, and with the ability to form de novo bone.

High and low molecular weight (MW) forms of three different polymers (polylactic acid (PLA), poly (lactic co-glycolic) acid (PLGA) and polycaprolactone (PCL)) were milled, impacted into discs, and then tested in a custom built shear testing rig, and compared to allograft.

A second stage of the experiment involved the addition of skeletal stem cells (SSC) to each of the milled polymers, impaction, 8 days incubation, and then tests for cell viability and number, via fluorostaining and biochemical (WST-1) assays.

The shear strengths of both high/ low MW PLA, and high/low MW PLGA were significantly higher than those of milled allograft (P<0.001, P<0.001, P<0.005 and P<0.005) but high and low MW PCL was poor to impact, and had significantly lower shear strengths (P<0.005, P<0.001). Fluorostaining showed good cell survival on high MW PLA, high MW PCL and high MW PLGA. These findings were confirmed with WST-1 assays.

High MW PLA as well as high MW PLGA performed well both in mechanical testing and cell compatibility studies. These two polymers are good contenders to produce a living composite for use as substitute human allograft in impaction bone grafting, and are currently being optimised for this use via the investigation of different production techniques and in-vivo studies.