Introduction and Aims: Computer-assisted surgery may significantly improve the accuracy of total knee arthroplasty. The reproducibility of acquiring points that facilitate the computer generation of joint morphology which is fundamental for guiding surgery remains unclear. The aim of this study was to assess inter- and intra-operator reproducibility using a computer guidance system.

Method: Three surgeons were involved in this study, who under instruction from a proprietary computer system acquired points on a sawbone model of the knee that correlated with specific anatomic landmarks. This process was performed five times each and repeated on another identical model. The points acquired allowed the computer to generate a knee joint model that predicted size, orientation and alignment of the knee joint. Inter- and intra-operator comparisons of the size of the prostheses, the amount of resection, the rotation of the prostheses, and the relationship of the epicondylar to the posterior femoral condylar axis were made.

Results: This study was commenced one day after an eight-hour hands-on workshop describing the use of the computer guidance system. The computer system accurately recorded the acquisition of points on a sawbone model. There was little difference in the time taken by each surgeon to acquire the points. Although, all iterations of point acquisition were performed sequentially, there was no clear reduction in the time taken for the process of acquisition. Despite the repetitive use of identical sawbone models, all three surgeons demonstrated significant variation within their own and between each others’ acquisitions. This resulted in variations of prosthetic sizes, amounts of bone resection and rotation of implants. The consistency at which certain indices differed suggested a specific bias between surgeons that may reflect technique or interpretation of anatomic landmarks, e.g. relationship between the epicondylar and posterior condylar axes.

Conclusion: An important reason for the variation may be the difference in interpretation of the location of anatomic landmarks. This may have a significant impact on the generation of computer model for guiding subsequent surgery. Clear definitions of landmarks and a robust education program is required if computer assisted surgery is to be accurate and meaningful.

Introduction The aim of this study was to assess the accuracy of CT-guided core needle biopsy of musculo-skeletal tumours.

Methods This is a retrospective study on a series of 127 patients with a musculoskeletal tumours. The biopsies were performed over a four year period from 1998 to 2001. The accuracy of the CT-guided core needle biopsy was determined by comparing the histology of the biopsy with the final histology of the specimen obtained at open biopsy or surgical resection of the tumour. The effective accuracy was determined by the accuracy of the biopsy to diagnose benign versus malignant.

Results CT-guided core needle biopsy in this series has an overall accuracy of 80%. The effective accuracy as determined by a malignant versus benign lesion was 89%. There were 86 malignant tumours with a biopsy accuracy of 81% and there were 41 benign tumours with a biopsy accuracy of 78%. The positive predictive value (PPV) of a malignant tumour is 100% and the PPV of benign tumour 94.9%. The most common site of biopsy was from the femur and thigh, together accounting for 39.4% of the tumours. The most common tumours in this series were liposarcoma (n=12), osteosarcoma (n=11) and giant cell tumour (n=11). There were no reported complications arising from the biopsy.

Conclusions CT-guided core needle biopsy is a safe and effective procedure that is important in the diagnosis and management of musculoskeletal tumours.

Introduction The double-tapered femoral stem is recognised for its excellent long-term results. The design allows greater cement engagement by capitalising on the phenomenon of cement creep. An additional third taper is thought to provide greater stability, fixation and improved femoral neck loading. This study compares prospectively the early clinical and radiological results between triple and double-tapered stems in cemented THA.

Methods Between March 1998 and October 2002, 391 patients (405 hips) underwent primary THA and received either a triple, 192 patients (200 hips) or double 189 patients (205 hips) tapered stem. The post-operative protocol was identical and patients were followed-up clinically and radiologically at approximately three, six and 12 months and yearly thereafter. Clinical outcomes were assessed with respect to mortality, complications, Harris Hip Score (HHS) and Merle d’Aubigne and Postel score (MDA). Radiological analysis was performed looking for evidence of radiolucent lines, aseptic loosening, subsidence, endosteolysis, heterotrophic ossification, cortical hypertrophy and cement fractures. Age, sex, weight, height, indications for surgery and the distribution of right and left hips were comparable between the two groups. The average follow-up in the triple and double tapered groups was 21 and 23 months respectively.

Results Clinically, in the triple-taper group, there was a mean improvement in HHS of 44 points and MDA of 5.8. Similar improvements were seen in the double-tapered group, with increases of 45 and 5.6 points in the HHS and MDA respectively. No significant difference was noted in terms of complications. In the triple-tapered group, evidence of radiolucency between the cement-stem interface was seen in only one patient in Zone 1, and this was associated with a small cement fracture in Zone 3. Cement-bone radiolucency occurred in one hip at Zone 1. In the double-tapered group, five hips showed cement-stem radiolucency, all in Zone 1. Radiolucency between the cement-bone interface was present in two hips, one in Zone 1 and the other in Zone 7. Average subsidence of the triple-tapered stems was 0.77 mm (range 0 to 2.5), which compared to 0.82 mm (range 0 to 2.5) in the double-tapered group. No stems were considered at risk of aseptic loosening. There was no significant difference in the extent of proximal femoral resorption and heterotopic ossification.

Conclusions In our study, the triple and double-tapered components performed equally well clinically and are comparable on radiological analysis. The triple-tapered stem is safe and is not associated with increased rates of loosening, subsidence or radiolucency, compared to the double-tapered stem. There is potential to translate the promising early results of the triple-tapered design into the future and expect similar long-term success.

Introduction Hyaline cartilage is a barrier to osteosarcoma invasion, however the mechanisms behind this resistance remain unclear. The aim of this study was to examine the temporo-spatial pattern of osteosarcoma growth and invasion of local tissue structures, including epiphyseal cartilage, and to investigate the molecular mechanisms behind the resistance of cartilage to malignant invasion.

Methods An in vivo mouse model of osteosarcoma was used, whereby osteosarcoma cells were orthotopically injected into the tibiae of nude mice. Animals were sacrificed at weekly timepoints. Control and tumour limbs were processed for histological examination of tumors at different stages of disease progression. Routine Haematoxylin & Eosin staining was used to examine morphology, and immunohistochemical staining using antibodies against proangiogenic vascular endothelial growth factor (VEGF) and anti-angiogenic pigment epithelium-derived factor (PEDF) was performed. PEDF from mouse liver was cloned into a mammalian expression vector in order to generate stably-transfected osteosarcoma cell lines.

Results Hyaline cartilage of the growth plate and articular surface was resistant to local invasion by osteosarcoma in all sections examined, despite increasing tumor size as well as extensive intra- and extra-osseous destruction. All tumours showed immunostaining for VEGF but not for PEDF. In the most advanced cases, only the lowermost layers of the hypertrophic zone of the growth plate were eroded. These layers displayed strong immunostaining for the potent angiogenic factor VEGF, and weak to absent immunostaining for PEDF. By contrast, the resting, proliferative and upper hypertrophic layers, which were resistant to osteosarcoma invasion in the cases studied, showed high expression levels of the potent anti-angiogenic factor PEDF.

Conclusions These results confirm that the balance of angiogenesis, influenced by pro and anti-angiogenic factors, determines tumour growth and invasion. Given the localization of PEDF specifically to the resistant cartilaginous layers and its exceptionally potent anti-angiogenic effects, there are exciting prospects for the use of PEDF in treatment for osteosarcoma as well as other cancers. To this end, we have established osteosarcoma cell lines that over-express PEDF and are currently characterizing these cells in vitro and assessing the propensity of PEDF to suppress tumour invasion in vivo. Growth plate cartilage is resistant to invasion by osteosarcoma. PEDF is likely to play an important role in this resistance. As such, it may have therapeutic applications in osteosarcoma as well as other malignancies.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.