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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.

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.

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.

We have performed endoprosthetic replacement after resection of tumours of the proximal tibia on 151 patients over a period of 20 years. During this period limb-salvage surgery was achieved in 88% of patients with tumours of the proximal tibia. Both the implant and the operative technique have been gradually modified in order to reduce complications. An initial rate of infection of 36% has been reduced to 12% by the use of a flap of the medial gastrocnemius, to which the divided patellar tendon is attached. Loosening and breakage of the implant have been further causes of failure. We found that the probability of further surgical procedures being required was 70% at ten years and the risk of amputation, 25%. The development of a new rotating hinge endoprosthesis may lower the incidence of mechanical problems. Limb salvage for tumours of the proximal tibia is fraught with complications, but the good functional outcome in successful cases justifies its continued use.

We have made a retrospective study of 1001 custom-made prostheses used as replacements after surgery for bone tumours. There were 493 distal femoral, 263 proximal femoral and 245 proximal tibial prostheses. Aseptic loosening was shown to be the principal mode of failure of the implants, and 71 patients had revision for aseptic loosening of a cemented intramedullary stem. The probability of a patient surviving aseptic loosening for 120 months was 93.8% for a proximal femoral replacement, 67.4% for a distal femoral prosthesis and 58% for a proximal tibial implant. In patients with distal femoral replacements the age of the patient at the time of operation and the percentage of bone resected were related to the risk of aseptic loosening. Young patients with distal femoral prostheses in whom a high percentage of the femur had been replaced had the poorest prognosis for survival without aseptic loosening. The percentage of bone removed had a significant effect in the proximal tibial replacement group, but the age of the patient did not. By contrast, neither the age nor the percentage of bone removed was a factor after proximal femoral replacement. The significance of these findings is discussed in relation to mechanical factors.

Aseptic loosening was identified as the predominant cause of implant related failure in a retrospective study of a consecutive series of 168 Stanmore custom made extendible endoprosthetic replacements used in skeletally immature patients. Most of the replacements were used in the treatment of bone tumor and the remainder for the revision of failed massive endoprosthetic replacements. Since the first Stanmore extendible endoprosthesis was inserted in 1976, 4 types of extension mechanisms have been used. Thirty eight of the 164 cases with followup data were revised, of which 19 were as a result of aseptic loosening. Survival analysis revealed that the overall probability of surviving an implant related failure was 0.512 (+/- 0.005) at 5 years, highlighting the high complication rate of these extendible replacements that required a revision procedure. Sixteen of the 19 aseptic loosening cases were distal femoral replacements. The probability of a patient with a distal femoral replacement surviving aseptic loosening was 0.773 (+/- 0.008) at 5 years. Other modes of implant related failure included jamming of the extending mechanism, infection, and maximum extension of the replacement before skeletal maturity had been reached.

The first 218 cases of limb salvage using cemented intramedullary Stanmore massive distal femoral arthroplasties with a single-axis hinged knee, followed for an average of 58 months with a maximum of 251 months, were reviewed. Loosening (5%), local recurrence (4%), intramedullary stem fracture (3%), and infection (2%) were the major complications requiring surgical intervention. Loosening and implant fracture were treated by the insertion of a second massive replacement in all but one case. All recurrences and all but one infected case required amputation. Survivorship analysis showed that the overall probability of one of these early prostheses surviving for 10 years was 65%, and for 20 years it was 53%. For cases of bone tumor, the probability of surviving for 10 years was 68% (not including recurrence), for primary knee replacement cases it was 32%, for other bony diseases plus trauma it was 86%, and for cases of revised massive prostheses it was 53%. It was concluded that this type of distal femoral arthroplasty provided good medium-term results, but showed some deficiencies in the long term, particularly in younger patients.

CADCAM (computer aided design/manufacture) production methods are often associated with mass production; working in the medical field at the Department of Biomedical Engineering, the requirement is for one-off, individualized implants. Using a knowledge-based system, implant designs are produced from X-ray data. Assembly from modular components has greatly reduced the production time of implants for bone tumour cases. CADCAM techniques are also used in the production of custom-made hip replacements using digitized data gathered from radiographs. Femoral canal shape is calculated and the optimal implant designed and manufactured from titanium alloy on the Department's CNC (computer numerically controlled) machines.