Cancellous and cortical morselized allograft in revision total hip replacement: A biomechanical study of implant stability

Effect of synthetic bone replacement material of different size on shear stress resistance within impacted native and thermodisinfected cancellous bone: an in vitro femoral impaction bone grafting model

Antibiotic carrier particles of variable size might influence mechanic properties within impacted thermodisinfected and native cancellous bone different. Herafill®G containing calciumsulfate and calciumcarbonate provides high local concentrations of gentamicin being important for revision surgery in infected joint replacements. Native and thermodisinfected cancellous bone derived from 6 to 7 months old piglets was used for in vitro impaction bone grafting and supplemented each with Herafill®G granules of two different sizes. Micromovement of implants related to shear force was measured in 29 specimens distributed in 6 groups. Thermodisinfected cancellous bone revealed a significant higher shear force resistance than native bone with a mean difference of 423.8 mdeg/Nm (p < 0.001) ranging within 95% confidence interval from 181.5 to 666.0 mdeg/Nm. Adding small granules to thermodisinfected bone did not reduce shear force resistance significantly since adding large granules to native bone improved it by 344.0 mdeg/Nm (p < 0.003). Shear force resistance was found higher at the distal region of the implant compared to a proximal point of measurement throughout all specimens. Less impaction impulses were necessary for thermodisinfected bone. Thermodisinfected cancellous bone might achieve a higher degree of impaction compared with native bone resulting in increased resistance against shear force since impaction was found increased distally. Supplementation of thermodisinfected bone with small granules of Herafill®G might be considered for application of local antibiotics. Large granules appeared more beneficial for supplementation of native bone. Heterogeneity of bone graft and technical aspects of the impaction procedure have to be considered regarding the reproducibility of femoral impaction bone grafting.

Influence of antibiotic pellets on pore size and shear stress resistance of impacted native and thermodisinfected cancellous bone: An in vitro femoral impaction bone grafting model

Introduction

Morphology and mechanic properties of impacted cancellous bone are affected by carrier substances which provide high local concentrations of antibiotics.

Methods

Bone chips were taken from the femoral head of 6-7 months old piglets. One half was thermodisinfected and the other remained native. Ten specimens each were mixed with Herafill® antibiotic pellets and a control group of each 10 specimens respectively was examined. The cancellous bone was impacted according to Exeter technique and the implants were cemented. The distribution of the particles and the pores were defined with three dimensional computertomographic scan and shear force resistance was measured until failure.

Results

Shear force resistance was not measured significantly less for thermodisinfected (2.7 Nm) compared with native bone (3.5 Nm) and addition of antibiotic pellets reduced shear force resistance in both groups since this was significant for the native group. The average pore volume of the native bone specimens appeared significant smaller compared to the thermodisinfected group (p = 0.011) and the pore volume showed a negative correlation with shear force resistance (p = 0.044). Pore volume around the pellets was found significantly increased and it appeared smaller for native bone. The number of pellets located next to the implant showed a negative correlation with shear force resistance (p = 0.034) and the negative correlation increased for pellets below the tip of the shaft model (p = 0.024).

Conclusion

Adding antibiotic pellets to native and thermodisinfected impacted cancellous bone increased pore volume since the area around the pellets showed increased porosity which correlated with reduced shear force resistance. Computertomographic three dimensional measurement of porosity might predict shear force resistance of impacted cancellous bone and improve impaction of bone grafting intraoperatively.

Impaction Bone Grafting and Valgus Osteotomy: A Technical Trick for the Treatment of Femoral Neck Nonunions

Femoral neck nonunions in young adults is among the most challenging problems to treat. This is due to their inherent problems, such as neck resorption, increase in fracture gap, sclerosis of fracture margins, and avascular necrosis. Hip salvage in these cases, although challenging, is recommended in the Asian subcontinent where social and religious activities require squatting and sitting cross-legged. Muscle pedicle grafts and other vascularized bone grafting techniques are preferred treatment options, but they are technically demanding and require advanced microsurgical skills. Valgus osteotomy, although successful in certain cases, has a high failure rate in patients with poor bone stock. We present a simple technique of valgus subtrochanteric osteotomy, impaction bone grafting, and stabilization with a sliding hip screw. Here, we describe in detail about the surgical technique and present the clinical outcomes in 44 patients, with a mean follow-up of 3.4 years and a union rate of 95.5%.

[Allogeneic bone transplantation in hip revision surgery : Indications and potential for reconstruction]

The increasing number of people having joint replacements will lead to increasing numbers of revision operations. The transplantation of allogeneic bones might reconstruct bone defects and improve long-term anchorage of the implant. A sufficient primary stability of the implanted construct is necessary to achieve osseous incorporation as well as tight contact between the implanted allogeneic and host bones. Transplantation of bone can contribute to downgrading acetabular defects and so avoid bigger reinforcement implants. An improvement of bone stock due to reconstruction of femoral bony defects might also reduce the size of the stem necessary since the indication might be limited in case of extensive bone defects. According to good longterm results of modular revision stems the Impaction-Bone-Grafting has not yet generally been established.

[Influence of thermodisinfection on impaction of cancellous bone : An in vitro model of femoral impaction bone grafting]

BACKGROUND

The reconstruction of bony defects during endoprosthesis revision surgery using "impaction bone grafting" leads to the possibility of a longstanding osseous integration to achieve good clinical results. Native allogeneic cancellous bone is often used for the procedure. This study examines the influence of thermodisinfection on the impaction behaviour of cancellous bone of different geometries and on the cement distribution.

METHODS

The cancellous bone was obtained from the femoral heads of 7‑month old pigs. One half of the head was thermodisinfected while the other remained native. Bone chips with sizes of 3-5, 5-8 and 8-10 mm were produced. The impaction was performed in a cylinder model with an internal diameter of 30 mm and with standardized impaction force using an impactor with a weight of 1450 g. The best particle combination was used for the subsequent computer tomography examination of the cement distribution and the contact surface to the bone in different parts of the shaft in seven investigations. For statistic measurements two-dimensional variance analysis including repetitions of measurement and Bonferroni correction, the LSD post-hoc-zest and the Mann Whitney U Test were used. The error probability was set at α = 5%. The SPSS® for Windows software was used for the statistical analysis.

RESULTS

The distribution of the cancellous and compacted bone also along the shaft revealed no significant difference between thermodisinfected and native cancellous bone at different levels (p > 0.05). Impacted native cancellous bone showed less inclusion of air, which resulted in a better distribution of density compared with thermodisinfected bone overall (p < 0.001). In the distal shaft area the cement volume was significantly larger in conjunction with the native bone. The overall area of cement penetration appeared to be significantly larger for native cancellous bone (p < 0.001).

CONCLUSIONS

The impaction of thermodisinfected and native cancellous bone showed greater deformation of the processed bone without any significant difference in the maximum density reached at different levels. Cement volume and cement penetration were pronounced proximally in native and processed cancellous bone. The cement distribution was significantly more distal for the native bone. Distally, the stabilization of the shaft appears to be increasingly dependent on the density of the impacted spongiosa, while proximally, the penetration of the cement into cancellous bone seems to correlate with porosity.

Efficient use of a limited resource femoral head allograft: A comparison of allograft preparation methods

PURPOSE

The purpose of the study was to compare the yield and compressed volume of femoral head allograft prepared by either hand morselization or a bone mill.

METHODS

Twenty human femoral head allografts were donated from a bone bank and morselized by two different methods. The heads were divided in half and split into two sample groups. One group underwent hand morselization with large bone nibblers, while the other was prepared using a bone mill. The volume of graft produced was measured. Ten-gram aliquots of each sample then underwent 30 impactions in a contained cavity, with the volume of graft compression measured.

RESULTS

Bone milling yielded approximately 31% more usable graft than hand morselization (81% to 50%; p = 0.0001). There was no difference between the compressed volume of graft prepared by either method ( p = 0.14).

CONCLUSION

This study demonstrates the efficacy of preparation of allograft with a bone mill and assists the clinician in determining the yield of graft by the weight of femoral head, thereby potentially minimizing excessive ordering and wastage.

Medium- to Long-term Results of Strut Allografts Treating Periprosthetic Bone Defects

Purpose

We evaluated the medium- to long-term outcomes of cortical strut allografts used to treat periprosthetic bone defects to better understand the correlation between radiological and clinical outcomes.

Materials and Methods

We retrospectively reviewed outcomes from 19 patients undergoing cortical strut allografts to treat periproshtetic bone defects from 2001 to 2015. The mean age at index operation was 59.4 years and the average follow-up period was 8.6 years. Surgeries were performed because of aseptic loosening (n=9), periprosthetic fractures (n=5), and infections (n=5). Each case was characterized and described in detail including the length of allograft and the union period; possible correlations between allograft length and detailed classification and union period was analyzed. Clinical evaluations included the Harris hip score and Kaplan-Meier survivorship.

Results

In revision total hip arthroplasty (THA), the average length of allografts used in patients experiencing fractures was significantly longer than those with aseptic loosening or infection. Of the 19 cases, incorporation was observed in 18 cases (94.7%). The average time to incorporation was 21.2 months and the time to incorporation was not significantly different among the two groups (fracture vs. aseptic loosening or infection). No positive correlation was identified between the length of allograft and incorporation period or in the time to cortical strut allograft incorporation among Paprosky or Vancouver subgroups.

Conclusion

Results of cortical strut allografts show excellent incorporation rates based on medium- to long-term follow-up. Cortical strut allografts may be considered useful for the treatment of femoral bone defects experienced during revision THA and following periprosthetic fracture.

Preparation of morselised bone for impaction grafting using a blender method

Impaction bone grafting is a method of restoring bone stock to patients suffering significant bone loss due to revision total hip surgery. The procedure requires morselised bone (MB) to be impacted into the site of bone loss in order to stabilise the prosthesis with the aim of the long term resorption and reintegration of the impacted bone graft. Currently, the method for producing MB requires the use of expensive surgical bone mills or manually-intensive rongeurs that can produce a limited variety of particle sizes and may have a low throughput. This study examines the potential to produce suitable MB using a domestic blender. The method produces a wide range of particle sizes without the need for an adjustment of the system. It was found through packing modelling that this particle distribution resulted in reduced initial graft porosity and thus a theoretical potential to increase the graft stiffness and ability of the graft to stabilise a prosthesis in comparison to a manually prepared roughly cut morselised bone samples. Mechanical testing confirmed the increased mechanical performance of the graft through both impaction testing and subsidence testing. The blended MB was found to exhibit greater graft stiffness under the same impaction conditions. The graft was also found to have subsided less in comparison to the rough cut, less well graded MB. Scanning electron imaging also confirmed the retention of the trabecular structure necessary for revascularisation and host bone ingrowth. In conclusion, the blender method offers a rapid and cheap way of obtaining morselised bone with favourable particle size distribution, particle morphology and mechanical properties with preservation of the bone trabecular structure.

The use of hardened bone cement as an impaction grafting extender for revision hip arthroplasty

Impaction bone grafting is a method of restoring bone stock to patients who have suffered significant bone loss due to revision total hip surgery. The procedure requires morsellised cancellous bone (MCB) to be impacted into the site of bone loss in order to stabilise the prosthesis with the aim of long term resorption and reintegration of the impacted bone graft. Due to financial cost and the potential to transmit disease, the use of supplementary material, known as an extender, is frequently used to increase the graft material volume. This study investigates the use of hardened Hydroset (Stryker Corp, MA, USA), an injectable bone cement (IBC), as an extender material and compares the performance of the IBC in different weight percent inclusions to a commercially available bone graft extender (GCP, BoneSave, Stryker Corp, MA, USA). The surgical impaction procedure was standardised and samples were evaluated in terms of graft stiffness and height. It was observed that 30wt% IBC extended samples had significantly improved graft stiffness (p = 0.02) and no significant different in height (p = 0.067) over a 100% MCB control sample. Cyclic loading, representative of gait, found that the IBC subsided similarly to the commercial bone substitute in wt% above 10%. Shear testing of the impacted grafts showed no significant differences between GCP and IBC with impaction forces determining the shear parameters of impacted grafts. The effects of the impaction and cyclical loading procedures on extender particle sizes was assessed via particle size analysis. It was found that the IBC extended samples demonstrated reduced friability, evident in the better retention of particle size as a result of both impaction and gait representative loading compared to that of the GCP samples. This indicates a potential reduction in issues arising from small particle migration to joint surfaces. Scanning electron microscopy of the MCB particles with both GCP and IBC as extenders showed retention of the porous trabecular structure post-testing which is essential for revascularisation and bone growth into the graft.

The use of a novel bone allograft wash process to generate a biocompatible, mechanically stable and osteoinductive biological scaffold for use in bone tissue engineering

Fresh-frozen biological allograft remains the most effective substitute for the 'gold standard' autograft, sharing many of its osteogenic properties but, conversely, lacking viable osteogenic cells. Tissue engineering offers the opportunity to improve the osseointegration of this material through the addition of mesenchymal stem cells (MSCs). However, the presence of dead, immunogenic and potentially harmful bone marrow could hinder cell adhesion and differentiation, graft augmentation and incorporation, and wash procedures are therefore being utilized to remove the marrow, thereby improving the material's safety. To this end, we assessed the efficiency of a novel wash technique to produce a biocompatible, biological scaffold void of cellular material that was mechanically stable and had osteoinductive potential. The outcomes of our investigations demonstrated the efficient removal of marrow components (~99.6%), resulting in a biocompatible material with conserved biomechanical stability. Additionally, the scaffold was able to induce osteogenic differentiation of MSCs, with increases in osteogenic gene expression observed following extended culture. This study demonstrates the efficiency of the novel wash process and the potential of the resultant biological material to serve as a scaffold in bone allograft tissue engineering.

The locking attachment plate for proximal fixation of periprosthetic femur fractures--a biomechanical comparison of two techniques

PURPOSE

Mechanical properties of a locking attachment plate construct (LAP-LCP), allowing bicortical screw placement laterally to the prosthesis stem, are compared to a cerclage-LCP construct.

METHODS

Eight right synthetic femora with implanted uncemented hip endoprosthesis were cut distally and fixed with LCP, monocortical locking screws and either LAP (n = 4) or cerclage (n = 4). Cyclic testing was performed with monotonically increasing sinusoidal load until failure. Relative movements at the plate-femur interface were registered by motion tracking. Statistical differences were detected by unpaired t-test and general linear model repeated measures.

RESULTS

Stiffness of the LAP-LCP was significantly higher at the beginning (875.4 N/mm ± 29.8) and after 5000 cycles (1213.0 N/mm ± 101.1) compared to the cerclage-LCP (644.96 N/mm ± 50.1 and 851.9 N/mm ± 81.9), with p = 0.013. Relative movements for AP-bending (B) and axial translation (T) of the LAP-LCP at the beginning (0.07° ± 0.02, 0.20 mm ± 0.08), after 500 cycles (0.16° ± 0.10, 0.26 mm ± 0.07) and after 5000 cycles (0.26° ± 0.11, 0.31 mm ± 0.07) differed significantly from the cerclage-LCP (beg.: 0.26° ± 0.04, 0.28 mm ± 0.05; 500 cyc: 0.47° ± 0.03, 0.53 mm ± 0.07; 5000 cyc.: 0.63° ± 0.18, 0.79 mm ± 0.13), with B: p = 0.02, T: p = 0.04. Relative movements for medial bending were not significantly different between the two constructs. Cycles to failure (criterion 1 mm axial translation) differed significantly between LAP-LCP (19,519 ± 1,758) and cerclage-LCP (11,265 ± 2,472), with p = 0.035.

CONCLUSIONS

Biomechanically, the LAP-LCP construct improves proximal fixation of periprosthetic fractures compared to the cerclage-LCP construct.

The threshold force required for femoral impaction grafting in revision hip surgery

BACKGROUND AND PURPOSE

Femoral impaction grafting requires vigorous impaction to obtain adequate stability without risk of fracture, but the force of impaction has not been determined. We determined this threshold force in a preliminary study using animal femurs.

METHODS

Adult sow femurs were used because of their morphological similarity to human femurs in revision hip arthroplasty. 35 sow femurs were impacted with morselized bone chips and an increasing force was applied until the femur fractured. This allowed a threshold force to be established. 5 other femurs were impacted to this force and an Exeter stem was cemented into the neomedullary canal. A 28-mm Exeter head was attached and loaded by direct contact with a hydraulic testing machine. Axial cyclic loading was performed and the position sensor of the hydraulic testing machine measured the prosthetic head subsidence.

RESULTS

29 tests were completed successfully. The threshold force was found to be 4 kN. There was no statistically significant correlation between the load at fracture and the cortex-to-canal ratio or the bone mineral density. Following impaction with a maximum force of 4 kN, the average axial subsidence was 0.28 mm.

INTERPRETATION

We achieved a stable construct without fracture. Further studies using human cadaveric femurs should be done to determine the threshold force required for femoral impaction grafting in revision hip surgery.

BMP-2/PLGA delayed-release microspheres composite graft, selection of bone particulate diameters, and prevention of aseptic inflammation for bone tissue engineering

Autogenous bone grafts are widely used in the repair of bone defects. Growth factors such as bone morphogenetic protein 2 (BMP-2) can induce bone regeneration and enhance bone growth. The combination of an autogenous bone graft and BMP-2 may provide a better osteogenic effect than either treatment alone, but BMP-2 is easily inactivated in body fluid. The objective of this study was to develop a technique that can better preserve the in vivo activity of BMP-2 incorporated in bone grafts. In this study, we first prepared BMP-2/poly(lactic-co-glycolic acid) (PLGA) delayed-release microspheres, and then combined collagen, the delayed-release microspheres, and rat autologous bone particulates to form four groups of composite grafts with different combinations: collagen in group A; collagen combined with bone particulates in group B; collagen combined with BMP-2/PLGA delayed-release microspheres in group C; and collagen combined with both bone particulates and BMP-2/PLGA delayed-release microspheres in group D. The four groups of composite grafts were implanted into the gluteus maximus pockets in rats. The ectopic osteogenesis and ALP level in group D (experimental group) were compared with those in groups A, B, and C (control groups) to study whether it had higher osteogenic capability. Results showed that the composite graft design increased the utility of BMP-2 and reduced the required dose of BMP-2 and volume of autologous bone. The selection of bone particulate diameter had an impact on the osteogenetic potential of bone grafts. Collagen prevented the occurrence of aseptic inflammation and improved the osteoinductivity of BMP-2. These results showed that this composite graft design is effective and feasible for use in bone repair.

Cement penetration and primary stability of the femoral component after impaction allografting

This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting.

Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured.

Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum.

The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.

A laboratory simulation for morselized bone graft fusion: apparent modulus under operatively based femoral impaction kinetics

The purpose of this study was to determine the apparent modulus changes accompanying a novel procedure for simulating in situ fusion of morselized cancellous bone femoral impaction grafts. An experienced surgeon's habitual intra-operative impaction grafting protocol was first quantified in human cadaver femurs, using a customized impulse force hammer. A corresponding standardized impaction procedure was then defined, and was used to prepare impaction grafts in axisymmetric metallic fixturing designed to replicate the nominal geometry of femoral canal confinement. Impaction graft fusion was simulated by mixing morselized cancellous bone with an amine-based epoxy adhesive before the impaction, then allowing the mixture to fuse after the impaction (J. Biomech. 34 (2001) 811). Force/deflection behavior of the unfused and fused impaction grafts was measured for both the (tapered) proximal and (untapered) distal portions of the grafts. Apparent modulus was then calculated from force/deflection stiffness. The impaction graft fusion simulation increased apparent modulus by an order of magnitude over the unfused state, for mixture parameters appropriate to have the fused graft apparent modulus be comparable to the compressive modulus of intact femoral cancellous bone.