SEM analysis of the surfaces of the metals revealed large deep scratches of the CoCr implants which were aligned in the A-P sliding direction. Barium sulphate particles were seen embedded in the surface of the femoral component. Voids were seen in the surface of the cobalt chrome and particles of silicate polishing powder were seen in these voids. There was also evidence of scratches originating at these voids. By contrast oxidised zirconium, showed small amounts of superficial scratching with an intact surface and no evidence of third body particles.
Retrieved prostheses (in-situ for in excess of 25 years) were analysed for roughness and wear using a Mitutoya form tracer and an electron microscope.
In the retrieved prostheses the contact zones were found to be smoother (Ra 0.05mm), have fewer and smaller carbides, together with evidence of ‘self-healing’ when compared to the original surface (Ra 0.32mm). Blood and urine levels of Co &
Cr were significantly elevated. Co levels were exceptionally elevated in loose prostheses, but levels quickly fell following revision.
Bone marrow contains cells, known as mesenchymal stem cells (MSCs), which have the ability to differentiate into osteoblasts. To create a 3-dimensional structure necessary for the reconstruction of tissue, cells need to be grown on a scaffold, for which hydroxyapatite (HA) was used, as it is osteoconductive. In living bone, increased extravascular perfusion increases new bone formation. Thus, these physiological conditions were reproduced in our novel bioreactor by perfusing MSCs seeded on porous HA scaffolds at a rate of 6ml/hr.
Therefore, this culture method could potentially be used to convert MSCs, isolated from patients’ bone marrow, into tissue-engineered bone.
The hypothesis was tested on three groups of graft, with eight samples in each group. Firstly, freeze-dried ethylene oxide treated bone graft was tested (group 2). For a negative control, allograft was heated to 70°C to denature the osteogenic proteins (group 1). The final group tested the effect of additional osteogenic supplements (100nM dexamethasone, 0.05mM ascorbic acid and 10mM (-glycerol phosphate) on MSCs on allograft (group 3). Osteoblastic differentiation of MSCs was observed under scanning (SEM) and transmission (TEM) electron microscopy, and by measuring protein levels: alkaline phosphatase (ALP), osteopontin and type I pro-collagen over 14 days.
This study confirms that MSCs, derived from autologous bone marrow, could be used to increase the osteogenic potential of allograft, thereby increasing bony healing in patients.
Metal-on-metal hip bearings are being implanted into younger patients. The consequence of elevated levels of potentially carcinogenic metal ions is therefore a cause for concern. We have determined the levels of cobalt (Co), chromium (Cr), titanium (Ti) and vanadium (Va) in the urine and whole blood of patients who had had metal-on-metal and metal-on-polyethylene articulations We found significantly elevated levels of whole blood Ti, Va and urinary Cr in all arthroplasty groups. The whole blood and urine levels of Co were grossly elevated, by a factor of 50 and 300 times respectively in patients with loose metal-on-metal articulations when compared with the control group. Stable metal-on-metal articulations showed much lower levels. Elevated levels of whole blood or urinary Co may be useful in identifying metal-on-metal articulations which are loose.
Massive endoprostheses using a cemented intramedullary stem are widely used to allow early resumption of activity after surgery for tumours. The survival of the prosthesis varies with the anatomical site, the type of prosthesis and the mode of fixation. Revision surgery is required in many cases because of aseptic loosening. Insertion of a second cemented endoprosthesis may be difficult because of the poor quality of the remaining bone, and loosening recurs quickly. We describe a series of 14 patients with triplate fixation in difficult revision or joint-sparing tumour surgery with a minimum follow-up of four years. The triplate design incorporated well within a remodelled cortex to achieve osseomechanical integration with all patients regaining their original level of function within five months. Our preliminary results suggest that this technique may provide an easy, biomechanically friendly alternative to insertion of a further device with an intramedullary stem, which has a shorter lifespan in revision or joint-sparing tumour surgery. A short segment of bone remaining after resection of a tumour will not accept an intramedullary stem, but may be soundly fixed using this method.
This study investigates the use of porous biphasic ceramics as graft extenders in impaction grafting of the femur during revision hip surgery. Impaction grafting of the femur was performed in four groups of sheep. Group one received pure allograft, group two 50% allograft and 50% BoneSave, group three 50% allograft and 50% BoneSave type 2 and group four 10% allograft and 90% BoneSave as the graft material. Function was assessed using an index of pre- and post-operative peak vertical ground reaction force ratios. Changes in bone mineral density were measured by dual energy X ray absorptiometry (DEXA) scanning. Loosening and subsidence were assessed radiographically and by histological examination of the explanted specimens. There was no statistically significant difference between the four groups after 18 months of unrestricted functional loading for all outcome measures.
When managing malignant bone tumours in the distal femur with limb salvage, resection and reconstruction with a distal femoral replacement (DFR) conventionally entails prosthetic replacement of the knee joint. In younger patients it is desirable to try to preserve the knee joint. We now use a new Joint-Sparing distal femoral prosthesis in those cases where it is possible to resect the tumour and preserve the femoral condyles. Purpose of study: To look at our early results with knee joint preserving DFR’s. Methods: Between June 2001 and March 2004 the prosthesis was implanted in 8 patients (5 males and 3 females) aged between 8 and 24 years at the time of surgery. The diagnosis was osteosarcoma in 6 cases and chondrosarcoma in 2 cases. All patients were followed regularly and knee range of movement was recorded as well as any complications that occurred. Patients were functionally evaluated using the MSTS Scoring System. Results: Six of the patients had a mean follow-up of 20 months (range 8–33) and in this group 4 had good knee flexion with a mean flexion of 122° (110–130), 1 patient had fair flexion of 60° and 1 patient had poor flexion of 20°. The mean fixed flexion deformity in the 3 patients who had such a deformity was 10° (5–15). There were no intraoperative complications but the patient with poor flexion required an arthrolysis and because of the poor result is under consideration for conversion to a conventional DFR. Two patients had follow-up periods of 3 months or less and are still in their early rehabilitation period. One patient in this group developed sepsis that resolved after an open washout. Conclusions: Our early results with this prosthesis, in the patients with adequate follow-up, have been good in the majority but the two cases of fair and poor knee flexion are disappointing. This particular problem may relate to design and technical factors, which will be discussed in detail.
When managing malignant long bone tumours in skeletally immature patients it is desirable, after resection, to reconstruct with a prosthesis that can be lengthened at appropriate intervals to keep pace with growth of the contralateral side. In an attempt to avoid multiple surgical procedures to achieve such lengthening we have recently developed a prosthesis that can be lengthened non-invasively.
Impacted morsellised allografts have been used successfully to address the problem of poor bone stock in revision surgery. However, there are concerns about the transmission of pathogens, the high cost and the shortage of supply of donor bone. Bone-graft extenders, such as tricalcium phosphate (TCP) and hydroxyapatite (HA), have been developed to minimise the use of donor bone. In a human cadaver model we have evaluated the surgical and mechanical feasibility of a TCP/HA bone-graft extender during impaction grafting revision surgery. A TCP/HA allograft mix increased the risk of producing a fissure in the femur during the impaction procedure, but provided a higher initial mechanical stability when compared with bone graft alone. The implications of the use of this type of graft extender in impaction grafting revision surgery are discussed.
Massive cemented endoprosthesis are used to enable early resumption of activity after tumour surgery. The longevity of the prosthesis varies with anatomical site, pros-thesis type, and mode of þxation. Revision surgery will be required in approximately 50% of cases of endopros-thetic replacements around the knee by 10 years because of aseptic loosening. Insertion of a second cemented endoprosthesis is a challenge because of the poor quality of the remaining bone and loosening recurs quickly. The use of extracortical plate þxation in joint sparing surgery where the remaining bone after tumour resection will not accept an intramedullary stem is also described. The þrst series of 14 patients with extracortical plate þxation in difþcult revision or joint-sparing tumour surgery with a mean follow-up of 5 years are described. The three-plate design incorporates well within a remodelled cortex to achieve osseomechanical integration with all patients regaining their premorbid level of function within 5 months. At 5 years the Enneking scores averaged 27.3. One revision was required in a femoral replacement because of loosening. It was possible to insert a new endo-prosthesis as the intramedullary bone had reconstituted. The preliminary results suggest that this technique may provide an easy, biomechanically friendly alternative to a device with an intramedullary stem, which has a shorter lifespan in revision tumour surgery.
Mesenchymal stem cells (MSCs) are pluripotential cells present in marrow, which have the ability to differentiate into osteoblasts, chrondrocytes and adipocytes. Potential skeletal tissue engineering uses include healing bone defects, spinal fusion and revision arthoplasty surgery. A means of storing viable mesenchymal stem cells is necessary in order for these cells to be readily available for clinical use. The aim of this study was to determine whether cryopreservation has any effect on the osteogenic potential of human bone marrow derived MSCs. Five normal iliac crest bone marrow aspirates were obtained following informed consent from patients. Each aspirate was divided into two equal samples. Ficoll-separation was used to isolate the MSCs. The fresh MSCs from one sample were cryopreserved, while the other was cultured as a control population. To assess the osteogenic potential of the MSCs after cryopreservation a sample of cells from each population was cultured with osteogenic supplements and the increase in alkaline phosphatase (ALP) and osteocalcin production was compared. Cryopreservation was not observed to effect the primary cultures of MSCs, which became confluent after a similar period in culture (12–14 days), forming colonies with recognized MSCs morphology. The expression of ALP and osteocalcin after stimulating the MSCs to differentiate with osteogenic supplements, was not significantly altered by the cryopreservation process (P>
0.05). In conclusion MSCs obtained from fresh human bone marrow aspirates can be cryopreserved without compromise to their proliferation rate or osteogenic potential, confirming that this is a useful means of storing viable cells for future clinical use.
Osteoblast progenitor cells can be isolated from human bone marrow and on an appropriate carrier following differentiation into osteoblasts a bone block could be formed. This supply of autologous, osteoinductive bone graft substitute would have significant implications for clinical use. The aim of the study was to assess whether osteoblast progenitor cells isolated from human bone marrow, seeded onto porous hydroxyapatite (HA) blocks adhere, proliferate and differentiate into osteoblasts under the influence of HA alone. After informed consent, bone marrow was aspirated from the iliac crest of 8 patients. The osteoblast progenitor cells were separated from the haematological cells and cultured in vitro. Evidence for the osteoblast progenitor nature of the cells was obtained by adding osteogenic supplements: dexamethasone, ascorbic acid and b-glycophosphate, and comparing alkaline phosphatase (ALP) and osteocalcin expression with that of unstimulated cells. Undifferentiated osteoblast progenitor cells were seeded at a density of 2x10 6 cells/porous HA cylindrical block (8 x 8 x10 mm). The cell adhesion to the HA was observed, and proliferation and ALP expression was measured over 15 days. In monolayer culture the isolated bone marrow cells were morphologically identified as mesenchymal stem cells. When osteogenic supplements were added the phenotype became consistent with the morphology of osteoblastic cells, and the ALP expression was significantly higher (P<
0.05) after 5 days in culture compared with cells that had not been stimulated to differentiate. On the HA osteoblast progenitor cells were adherent and became more osteoblastic, being separated from the HA surface by an osteoid matrix layer on electron microscopy. The ALP expression by these cells increased significantly (P<
0.05) over the 15 day culture period. Bone marrow contains mesenchymal stem cells with osteogenic potential that are known as osteoblast progenitor cells. In this study we have shown that osteoblast progenitor cells can be isolated from human bone marrow and will adhere to and proliferate on HA blocks in vitro, and differentiate into osteoblasts spontaneously under the influence of the HA scaffold. These constructs could be used as osteoinductive bone grafts.
The restoration of pain-free stable function in gleno-humeral arthritic cases in various situations such as rotator cuff deficiency, old trauma and failed total shoulder arthroplasty is a challenging clinical dilemma. The Bayley-Walker shoulder has been designed specifically for very difficult cases where surface replacement devices do not provide sufficient stability. This device is a fixed-fulcrum reversed anatomy prosthesis consisting of a titanium glenoid component with a CoCrMo alloy head that articulates with an UHMWPE liner encased in a titanium alloy humeral component that has a long tapered grooved stem. The centre of rotation of the Bayley-Walker shoulder is placed medially and distally with respect to the normal shoulder in order to improve the efficiency of the abductor muscles. An important problem in devices of this type is obtaining secure and long-lasting fixation of the glenoid component. The glenoid component relies on fixation through the cortical bone by using threads, which protrude through the anterior surface of the scapula at the vault of the glenoid. It is HA coated for subsequent osseointegration. The purpose of this study was to investigate fixation of the glenoid component. A 3D finite element model of the glenoid component implanted in a scapula was analysed using Abaqus. The implant was placed in position in the scapula, with the final 2–3 screw threads cutting through the cortical bone on the anterior side at the vault of the glenoid due to the anatomy in this region. The analysis was performed for two load cases at 60° and 90° abduction. A histological study of a retrieval case, obtained 121 days after implantation, was also conducted. The FEA results showed that most of the forces were transmitted from the component to the cortical bone of the scapula, the remaining load being transmitted through cancellous bone. In particular the area where the threads of the glenoid component penetrated the scapula showed high strain energy densities. Histology from the retrieved case showed evidence of bone remodelling whereby new bone growth resulting in cortical remodelling had occurred around the threads. Both the FEA and histological study show that fixing the component at multiple locations in cortical bone may overcome the problems of glenoid loosening associated with constrained devices. The Bayley-Walker device has been used on a custom basis since 1994; 81 Bayley–Walker shoulders for non-tumour conditions and 43 Bayley-Walker glenoid components have been used in association with a bone tumour implant, with good early results. Radiographically, radiolucencies have not been observed and overall the comparisons with the original Kessel design are positive.
The aim of this study is to evaluate the early results of gleno-humeral reconstruction after tumour excision with a new design of endoprosthesis. The prosthesis is a fixed fulcrum gleno-humeral replacement consisting of a hydroxyapatite (HA) coated glenoid component with a polyethylene liner and a cemented stem with HA coated collar. Between 1997 and 2000 we inserted the prosthesis into 15 patients with primary bone tumours of the proximal humerus. There were nine males and six females with a mean age of 38 years (range: 8–71 years). Twelve stems were cemented and three uncemented. Two skeletally immature patients had an extendible stem inserted, one subsequently having a successful lengthening procedure. The mean follow-up was 28 months (range: 12–41 years). Functional outcome was assessed using the Musculoskeletal Tumour Society (MTS) scoring system. There were two early dislocations and one superficial wound infection. Three patients died of their disease and one underwent forequarter amputation for local recurrence. The remaining eleven had satisfactory functional outcomes with a mean MTS score of 81%. Radiologically there has been no evidence of early loosening. Microscopic analysis of the components in the amputated arm showed excellent osseointegration around the HA coated components.
The three-dimensional architecture of bovine articular cartilage collagen and its relationship to split lines has been studied with scanning electron microscopy. In the middle and superficial zones, collagen was organised in a layered or leaf-like manner. The orientation was vertical in the intermediate zone, curving to become horizontal and parallel to the articular surface in the superficial zone. Each leaf consisted of a fine network of collagen fibrils. Adjacent leaves merged or were closely linked by bridging fibrils and were arranged according to the split-line pattern. The surface layer (lamina splendens) was morphologically distinct. Although ordered, the overall collagen structure was different in each plane (anisotropic) a property described in previous morphological and biophysical studies. As all components of the articular cartilage matrix interact closely, the three-dimensional organisation of collagen is important when considering cartilage function and the processes of cartilage growth, injury and repair.