Mechanical properties of 7-10mm bone grafts and small slurry grafts in impaction bone grafting

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.

Assessing the Local Mechanical Environment in Medial Opening Wedge High Tibial Osteotomy Using Finite Element Analysis

High-tibial osteotomy (HTO) is a surgical technique aimed at shifting load away from one tibiofemoral compartment, in order the reduce pain and progression of osteoarthritis (OA). Various implants have been designed to stabilize the osteotomy and previous studies have been focused on determining primary stability (a global measure) that these designs provide. It has been shown that the local mechanical environment, characterized by bone strains and segment micromotion, is important in understanding healing and these data are not currently available. Finite element (FE) modeling was utilized to assess the local mechanical environment provided by three different fixation plate designs: short plate with spacer, long plate with spacer and long plate without spacer. Image-based FE models of the knee were constructed from healthy individuals (N = 5) with normal knee alignment. An HTO gap was virtually added without changing the knee alignment and HTO implants were inserted. Subsequently, the local mechanical environment, defined by bone compressive strain and wedge micromotion, was assessed. Furthermore, implant stresses were calculated. Values were computed under vertical compression in zero-degree knee extension with loads set at 1 and 2 times the subject-specific body weight (1 BW, 2 BW). All studied HTO implant designs provide an environment for successful healing at 1 BW and 2 BW loading. Implant von Mises stresses (99th percentile) were below 60 MPa in all experiments, below the material yield strength and significantly lower in long spacer plates. Volume fraction of high compressive strain ( > 3000 microstrain) was below 5% in all experiments and no significant difference between implants was detected. Maximum vertical micromotion between bone segments was below 200 μm in all experiments and significantly larger in the implant without a tooth. Differences between plate designs generally became apparent only at 2 BW loading. Results suggest that with compressive loading of 2 BW, long spacer plates experience the lowest implant stresses, and spacer plates (long or short) result in smaller wedge micromotion, potentially beneficial for healing. Values are sensitive to subject bone geometry, highlighting the need for subject-specific modeling. This study demonstrates the benefits of using image-based FE modeling and bone theory to fine-tune HTO implant design.

Impaction bone grafting for the reconstruction of large bone defects in revision knee arthroplasty

OBJECTIVE

Regeneration of autologous bone stock and formation of a stable implant bed by impaction of morselized bone allograft.

INDICATIONS

Bone loss after septic and aseptic loosening or tumour resection.

CONTRAINDICATIONS

Persistent infection, one-stage septic revision, poor therapeutic compliance, extensive uncontained metaphyseal defects with cortical thinning of the diaphysis.

SURGICAL TECHNIQUE

Whilst the surgeon removes the loose prosthesis, the assistant prepares the graft. The medullary canal is sealed with a cement restrictor. Graft particles of different sizes are densely impacted around a trial stem. The highest level of stability is achieved by using large particles interspersed with small filler particles. Low-viscosity cement facilitates cement penetration and ensures strong interdigitation with the impacted graft mass after implantation of the prosthesis. Uncontained metaphyseal defects are treated with prosthetic augments.

POSTOPERATIVE MANAGEMENT

Gait training, physiotherapy with isometric quadriceps exercises, partial weight-bearing for 6 weeks, resistance training begins 8 weeks postoperatively.

RESULTS

Between 2010 and 2012, 28 patients with large bone defects [Anderson Orthopaedic Research Institute (AORI) grade: 21 × F3, 3 × F2, 13 × T3, 8 × T2] underwent total knee revision with impaction bone grafting. The mean follow-up was 27.7 months (range 21-47 months). On average, patients had undergone 2.5 previous revisions. Implant survival was 82.0 % (95 % CI = 62.5 %-92.1 %) for any reason of revision as the endpoint and 93.1 % (95 % CI = 74.5-98.4 %) for aseptic revision as the endpoint. The mean postoperative Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score was 35.4 (range 3.3-101.6, SD ± 26.2). The mean KSS was 70.6 (range 20-100, SD ± 26.8).

Use of cementless acetabular component with a hook and iliac flanges in revision arthroplasty for massive acetabular defect

BACKGROUND

Revision hip arthroplasty of massive acetabular defect, severe combined defect, or pelvic discontinuity is challenging. The purpose of this study was to determine the midterm outcome and survivorship of a new revision technique using cementless acetabular cup supplemented with a hook and three iliac flanges in massive acetabular defects.

MATERIALS

From January 2000 to June 2004, we revised 17 severe acetabular defects, 14 combined defects and three pelvic discontinuities according to the American Academy of Orthopaedic Surgeons (AAOS) classifications, in which bone stock at the dome was not available to provide support for the cup. These revisions were performed using a cementless porous-coated hemispherical cup with a hook and flanges.

RESULTS

One patient (one hip) underwent resection arthroplasty due to infection 1 year after the revision. The remaining 16 hips were evaluated at a mean of 6.8 (range 5-9) years postoperatively. Thirteen acetabular components (81%) showed no migration and were stable with bone ingrowth. Three hips showed progressive medial and upward migration during the 18-24 months after the index revision, after which migration was not progressive. The Merle d'Aubigné hip score was 14.5 (range 12-18) points at the latest follow-up evaluation. Survival rate was 94.4% when revision for any reason was considered as the end point [95% confidence interval (CI) 83.9-100%] and 82.0% (95% CI 62.8-100%) when loosening of the cup was considered as the end point.

CONCLUSION

Results of this type of revision were superior to previously reported results of acetabular revisions with the use of various techniques and devices.