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Aseptic loosening of massive bone tumor implants is a major cause of prosthesis failure. Evidence suggests that an osteointegrated hydroxyapatite (HA)-coated collar would reduce the incidence of aseptic loosening around the cemented intramedullary stem in distal femoral bone tumor prostheses. Because these implants often are used in young patients with a tumor, such treatment might extend the longevity of tumor implants. Questions/purposes We asked whether (1) HA-coated collars were more likely to osteointegrate; (2) HA collars were associated with fewer progressive radiolucent lines around the stem-cement interface; and (3) HA-coated collars were associated with less bone loss at the bone-shoulder implant junction?Twenty-two patients were pair-matched to one of two groups--either (1) implants with a HA-coated ingrowth collar (HA Collar Group); or (2) implants without an ingrowth collar (Noncollar Group). Age, sex, and length of followup were similar in both groups. HA-coated collars were developed and used at our institution from 1992 to address the high failure rate attributable to aseptic loosening in patients with massive bone tumor implants. Before this, smooth titanium shafts were used routinely adjacent to bone at the transection site. The minimum followup was 2 years (mean, 7 years; range, 2-12 years). Radiographs obtained throughout the followup period were analyzed and osteointegration at the shaft of the implant quantified. Radiolucent line progression around the cemented stem was semi-quantitatively assessed and cortical bone loss at the bone-shoulder implant junction was measured during the followup period.Comparison of the most recent radiographs showed nine of 11 patients had osteointegrated HA collars, whereas only one patient in the Noncollar Group had osteointegration (p0.001). The radiolucent line score quantified around the cemented stem was lower in the HA Collar Group when compared with the Noncollar Group (p = 0.001). Results showed an increase in cortical bone loss at the bone-shoulder implant junction in the Noncollar Group when compared with the HA Collar Group (p0.001).Osteointegration at the implant collar resulted in fewer radiolucent lines adjacent to the intramedullary cemented stem and decreased cortical bone loss immediately adjacent to the transection site. These results suggest that the HA collar may help reduce the risk of aseptic loosening in patients with this type of implant, but longer followup and a larger prospective comparison series are necessary to prove this more definitively.

STUDY DESIGN Analysis of volumetric wear loss of retrieved growth guidance sliding devices LSZ-4D for treatment of early onset scoliosis and laboratory in vitro wear test for comparison of wear resistance of alloys Nitinol, Ti, and cobalt chromium (CoCr). OBJECTIVE To evaluate quantitatively the amount of wear debris from the sliding LSZ-4D device and to investigate the potential of using Nitinol for replacing Ti alloys in spinal instrumentation. To do that, wear resistance of Nitinol, Ti, and CoCr was compared. SUMMARY OF BACKGROUND DATA There are little data regarding the amount of wear debris associated with growth guidance sliding devices for patients with early onset scoliosis and the wear resistance of superelastic Nitinol compared with Ti and CoCr. METHODS Volumetric wear loss was measured on LSZ-4D devices made from titanium alloy Ti6Al4V and each consisted of 2 rectangular section (6 × 4 mm) rods and 40 ± 8 fixture elements (20 ± 4 hooks and 20 ± 4 clips) retrieved from 3 patients (implantation period, 3.5-5.8 yr). Images of wear scars were taken on Bruker interferometer microscope and incorporated into MATLAB software. Wear resistance of Nitinol, Ti, and CoCr was studied using reciprocation pin-on-disk wear test in bovine serum at 37°C ± 1°C. RESULTS The volume wear rate of LSZ-4D device was found to be 12.5 mm per year from which 5 mm³ per year is the wear debris of the rod and 7.5 mm per year is the contribution of fixtures. Wear resistance of Nitinol is 100 times higher than that of Ti and comparable with that of CoCr. CONCLUSION Application of wear-resistant coatings on Ti components in growth guidance sliding devices for the treatment of early onset scoliosis will be useful. High wear resistance of Nitinol combined with its superelastic and shape memory properties could make application of Nitinol rods for spinal instrumentation beneficial.

Background: The objective of this study was to examine the degree of osteointegration into a hydroxyapatite-coated collar and relate this finding to aseptic loosening in patients with a distal femoral replacement used to treat primary bone cancer. Our hypothesis was that the implant collar would increase osteointegration and reduce the rate of aseptic implant loosening. Methods: Sixty-one patients treated with a primary cemented distal femoral prosthesis between 1992 and 2001 were included in this study. The mean duration of follow-up was 8.5 years (range, two to eighteen years). Extracortical bone growth into the grooved hydroxyapatite-coated collar was quantified radiographically. Histological sections through four hydroxyapatite-coated collars and four implants with no collar, retrieved following amputation due to local recurrence or at autopsy at a mean of 3.5 years (range, 1.4 to 6.1 years) after implantation, were evaluated as well. Results: Five (8%) of the implants were revised because of aseptic loosening, 3% of the implants fractured, and 3% were revised because of infection. Six limbs (10%) required amputation because of local tumor recurrence. On radiographs, osteointegration into the collar was seen to have occurred in 70% of the patients and did not correlate with sex, age, diagnosis, or length of time postoperatively. Histological analysis showed mature lamellar bone within the grooves of the hydroxyapatite-coated collar, and bone was observed in direct contact with the hydroxyapatite coating. Extracortical bone failed to make direct contact with the surface of the implants manufactured without a collar. Conclusions: The use of cemented distal femoral massive bone tumor prostheses with a hydroxyapatite-coated collar located at the shoulder of the implant was followed by a low (8%) rate of revision due to aseptic loosening. The use of hydroxyapatite grooved collars may lead to osteointegration of the implant shoulder (collar) and may reduce the rate of aseptic loosening. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

We report the first use of an endoprosthetic diaphyseal replacement after the excision of a midshaft radial tumor. We present a rare case of a solitary midshaft radial metastasis in a 72-year-old gentleman who was treated 8 years earlier for primary renal cell carcinoma by radical nephrectomy. Follow-up for this patient was 25 months after implant insertion and at the latest review was pain-free. Functional scores for the elbow (using the Mayo Elbow Performance Score) and the wrist (using the Mayo Wrist Score) were 80 and 60, respectively, both out of 100. Use of a midshaft radial endoprosthesis provides a good functional outcome and symptom relief after extensive tumor resection, with regard to functional outcome and symptom relief.

Despite the high level of survivorship of cemented and uncemented stemmed components, there is a need for a joint prosthesis that does not invade the femoral canal. This type of prosthesis would be useful in treating younger and more active patients, in whom the use of such a design would usefully prolong the time before a conventional total joint replacement design was necessary. We present the rationale for a femoral neck prosthesis and show its feasibility as an off-the-shelf system based on a morphologic analysis of the proximal femur. The new design concept consists of a barrel with longitudinal flutes that enters the neck of the femur, loads on the calcar, and contacts the lateral cortex below the greater trochanter. Areas of porous ingrowth are placed so that the load transfer between the implant and the bone resembles that of the two main trabecular patterns in the proximal femur. A new method, cluster analysis, was used for defining a set of 12 sizes that could fit a population of femurs with acceptable dimensional discrepancies. We conclude that this type of device could be implanted reproducibly so that it was a close fit against the target areas of bone in the proximal neck area and against the lateral cortex.

To combat the high incidence of aseptic loosening for young patients and for patients with failed implants after resection for bone tumors, intramedullary cementless fixation of massive tumor implants was investigated. These implants consist of a hydroxyapatite coated titanium stem. To date, 47 of these prostheses have been inserted for the treatment of primary bone tumors. Radiographs indicate that the stems are osseointegrated. Radiolucent lines have not been seen between the implant and the bone. Bone remodeling changes have been observed. In several cases in which the implant was not seated properly on the transaction site, bone grew to the shoulder of the implant. Bone remodeling was particularly evident in stems that were coated over their entire surface. In these cases, the implant induced local bone resorption so that the bone around the midstream region became thinner, with resorption of cortical bone on the periosteal surface and maintenance of bone on the endosteal surface adjacent to the stem. This effect was attributed to stress shielding, and a three-dimensional finite element model using loading data obtained from a telemetry study indicated that, where the stem was bonded to the bone over the entire surface, stresses in the outer cortex became reduced. In the finite element model, reducing the region of hydroxyapatite coating to approximately 1/3 of the stem length reduced the extent of the low-stress area in the outer cortex. Subsequently, prostheses have been coated with hydroxyapatite over only approximately 1/3 of their stem. This method of fixing the massive endoprosthesis to the bone is thought to be successful in the short-term and offers an alternative to cemented fixation.

This article begins to address the validation requirements of wear testing on total knee replacements in a knee simulator. The knee simulator has four stations. The axial force is variable but reaches a maximum of 2.3 kN. Physiologic anteroposterior shear force and rotational torques are supplied to the knee. The forces and displacements are timed to coincide with those of a typical gait cycle. Kinematics of the simulator are dependent on the type of knee being tested. Tests of designs with well known clinical histories were done to 10 million cycles. The relative amounts and types of wear shown by the designs were similar to that found in their clinical histories. Wear tracks on more conforming designs were larger, and the penetration into the plastic appeared to be less. This did not necessarily mean that wear, as measured by loss of material, was reduced on conforming designs. Delamination of the plastic was achieved only after aging the tibial components. Wear particles isolated from the lubricating fluid were similar in size and shape to those isolated from in vivo specimens. However, the relative amounts of wear particle shapes were different depending on the design. At the start of the tests, all of the flexibly mounted tibial components showed more motion than after 5 million cycles, indicating that the surface of the plastic became more conforming. This study showed that knee wear similar to wear observed in vivo can be reproduced in the laboratory. The parameters and methods elucidated in this introductory study should form the basis for use in preclinical wear tests of total knee replacements.

Although rarely required, extendable reconstruction devices for replacing the entire femur offer children with malignant bone tumors the opportunity of a nearly normal development by overcoming an expected leg length discrepancy. Femoral integrity can be restored, allowing most patients to walk without the use of aids. There are no data available to provide evidence regarding long term results and morbidity in such patients. Six patients (range 2-12 years of age), three with osteogenic osteosarcoma and three with Ewing's sarcoma, were treated between 1988 and 1996 with custom made Stanmore extendable prosthetic total femoral replacements. One patient died 12 months after surgery because of complications relating to pulmonary metastasis. The remaining five patients were observed between 2.7 and 8.9 years (average, 5 years). No tumor recurrence has been recorded and no amputation has been performed. All surviving patients underwent an average of 9.4 operative procedures (range, 4-16 procedures) including 6.4 extension procedures (range, 3-10 procedures), and one prosthetic revision (range, 0-3 procedures). Five revisions in two patients were necessary because of infection, loosening of the prosthesis, mismatch between femoral head and acetabulum, or full extension of the extending mechanism. The functional results were measured in accordance with the Musculoskeletal Tumor Society rating score, with an average result of 77.3%. Total femoral replacement in a growing individual achieves good functional results yet has various risks for an uncertain outcome. Careful selection of the patient and realistic appraisal of the long term prospects are essential for successful treatment.

It is generally stated that the process of cartilage calcification and ossification is the same in the physeal (primary growth center) and epiphyseal (secondary growth center) growth plates. Reexamination of osteophyte growth led to the proposal that these growth plates differ. This proposition was tested by examining rabbit and human material from both sites before and after maceration; both tissue preparations were processed for light microscopy, and the macerated tissues were also studied by scanning electron microscopy (SEM). The physis showed the well-recognized, longitudinal calcified tubal structures in which capillaries make direct contact with and resorb the nonmineralized, transverse septal cartilage. In the epiphysis, the transverse septal cartilage was also mineralized, producing a continuous calcified sheet, perforated only by a limited number of channels and susceptible only to osteoclastic removal. This variation in mineral distribution modifies the way in which the primary spongiosa is formed during growth.

s / International Journal of Surgery 10 (2012) S53–S109 S55 ABSTRACTS 0128: TRUNNION DESIGN AND FEMORAL HEAD DIAMETER INCREASE CORROSION AT THE TAPER INTERFACE IN RETRIEVED LARGEDIAMETER METAL-ON-METAL TOTAL HIP ARTHROPLASTY Adam Hexter , Anna Panagiotidou , Gordon Blunn , John Skinner , Alister Hart . 1 London Implant Retrieval Centre, Imperial College London, London, UK; Royal National Orthopaedic Hospital, London, UK Aim: To characterise corrosion at the taper interface in large diameter metal-on-metal total hip arthroplasty and the effect of femoral head diameter. Method: Corrosion was qualitatively assessed using a peer-reviewed grading system for 111 components from three different manufacturers (ASR, BHR, Durom). Unexpectedly a ridged appearance was commonly observed on the female taper surfaces, which corresponded exactly with the ridges of the trunnion surface. A new grading system was created to measure this imprinting phenomenon. Results: 92% of the components experienced corrosion, with at least moderate corrosion seen in 61%. The manufacturer did not influence corrosion both for head components (p1⁄40.52) and trunnions (p1⁄40.20). A strong positive correlation (r1⁄40.776, p1⁄40.01) was observed between the imprinting scores and corrosion scores. Larger head diameters showed higher corrosion (r1⁄40.241, p1⁄40.02). Conclusions: Corrosion affects all manufacturers and is associated with the presence of ridges on the female taper surface. It appears that the rough surface of the trunnion causes extensive mechanical damage at the female taper surface and creates a hostile corrosive environment. Femoral head diameter correlates with corrosion, which is clinically significant considering the increasing use of larger head sizes. Future work must now clarify the optimum trunnion design and femoral head diameter. 0129: WEAR AND CORROSION AT THE TAPER INTERFACE IN RETRIEVED ASR XL METAL-ON-METAL TOTAL HIP ARTHROPLASTY Adam Hexter , Anna Panagiotidou , Gordon Blunn , Johann Henckel , John Skinner , Alister Hart . 1 London Implant Retrieval Centre, London, UK; Royal National Orthopaedic Hospital, London, UK Aim: To quantify wear at the ASR XL taper interface and determine the relationship between taper corrosion and blood metal ions. Method: Corrosion was qualitatively assessed using a peer-reviewed grading system for 52 ASR XL femoral head components. Blood metal ion levels in hips showing at least moderate corrosion was compared with those without moderate corrosion. Profilometry was performed in hips (n1⁄412) that failed due to debris-induced synovitis in the presence of low bearing surface wear (

From a literature survey, it was evident that a wide variety of kinematic conditions occur at the femoral-tibial bearing surfaces, including various degrees of rolling and sliding. A test machine was constructed to reproduce these conditions, applied to spherical-ended metal 'femoral' components acting on a flat polyethylene 'tibial' plateau. The load was cyclic at 2.2 kN for 10 million cycles with distilled water lubricant. For cyclic load only, a shiny depression was formed. With oscillating and sliding superimposed, there was severe surface and subsurface cracking resulting in high wear. When rolling motion was applied, a shiny wear track was formed with minimal cracking and wear. Such surface phenomena were observed in retrieved knee specimens, probably reflecting the kinematics associated with the knee. Low-conformity components inserted with high ligamentous laxity are susceptible to anteroposterior sliding and hence high wear. More-conforming components are less susceptible to wear because they limit sliding as well as reduce contact stresses.