Manufacturers and suppliers, described here as sponsors, who wish to have products approved and listed for use in Australian hospitals must follow a defined process.

They must obtain an Australian Registered Therapeutic Goods number (ARTG) for the product to be used.

For benefits to be paid for prostheses used under private health insurance arrangements a catalogue number is obtained after being approved through the Prosthesis Listing Advisory Committee (PLAC). Under PLAC each group of like prostheses is assessed by a Clinical Advisory group. (Hip Prosthesis Clinical Advisory Group, Knee Prosthesis Clinical Advisory Group).

Existing criteria are being enhanced as to the levels of evidence required for listing approval.

Essentially for joint replacements which are weight-bearing and in category three a two year clinical trial will almost always be necessary for any new prosthesis. Products must bw considered as non-inferior to comparator products.

The advent of the Australian National Joint Replacement Registry has been an outstanding success in identifying prosthesis with higher than average failure rates, but it is principally a measure of revision rates for specific prostheses.

In order to consider the causes of failure it is necessary to start at the point where prostheses are able to enter the Australian market through the Therapeutic Goods administration, Australian Registered Therapeutic Goods list (ARTG) and consider each of the steps of the joint replacement procedure from that point to well beyond the operation date.

This ARTG listing process as it now exists is described and an explanation of how this process may need to be reformed if the occasionally very inadequate prosthesis is to be eliminated from the Australian market. Other matters that may be predictors of variable outcomes include hospital case volume, surgeon experience, patient selection and pre-operative planning.

Intra-operative factors that lead to failure, including from infection, will include surgical approaches, operative technique, instrumentation, wound care and theatre discipline.

Post operatively patient factors, particularly falls and osteoporosis, will influence long-term outcomes as will prosthesis performance.

Further concern has been the advocacy by some by what might be considered, fashionable orthopaedics, but the literature to date has demonstrated little benefit from endeavours such as minimal invasive surgery and two-incision hip replacement. Gender specific prostheses and navigation have yet to make their mark as a universally accepted method of performing joint replacement surgery and there may be some negative issues with these matters.

The reproduction of ideal offset is an aim of hip replacement. Determining this measurement from traditional radiology techniques is inaccurate because femoral neck anteversion will foreshorten the femoral neck offset in a standard two dimensional x-ray making the measurement “apparent”. A novel method of determining offset is presented.

A computer software program has been developed for pre-operative planning of joint replacements, (Orthopaedic Work Station)

The program relies on using a CT scout film for magnification correction and to determine measurement parameters including leg length difference.

It was recognised that by collecting extra cross-sectional references that three-dimensional measurement of offset would be possible.

The CT scanner has software that allows determination of:

The location of the centre of the femoral head

For this study the line joining the two centroids is considered the longitudinal axis of the femur.

The CT scanner has software that also allows for the centroids to be moved along the longitudinal axis into the plane represented by a perpendicular line from the longitudinal axis to the centre of the femoral head.

It is a simple matter to measure the distance between the centroid and the centre of the femoral head to obtain a true offset.

A phantom femur was measured using the radiology method described and then measured directly. Exact correlation was established. A study of inter-observer measurement has shown statistically consistent agreement using six observers in twenty cadaver femurs.

The method is accurate and uses existing data collected as part of the pre-operative planning process. CT scanning prior to hip replacement, gives less radiation exposure and is more efficient with respect to radiology services than conventional radiology.

An intraoperative study may require ethics approval.

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 Dedicated software has been developed to allow computerised pre-operative planning for joint replacements where digital x-rays of known magnification are placed on a computer screen and templates are matched to produce an accurate plan. Improving efficiency, reducing error and improving patient outcomes are the goals.

Methods Two methods for determining magnification of x-rays have been considered. 1: a metal marker of known size is placed on the limb in the same plane as the joint and the software matches the template to the x-ray. Several problems arise including unrecognizable markers in the obese or when taking full pelvis x-ray. 2: a computer tomogram scout film provides a digital format, accurate magnification, a film of adequate quality and the capacity to plan on the normal hip in unilateral disease. The new software was developed using digital radiology to provide; certainty of patient identification, tools for measurement, tools for drawing and to allow linear and angular movement of components of the image. Risk management was undertaken. Data concerning component details completed the program.

Results The phase one trial demonstrated that the tool achieved the goals set. A digital image could be matched to implant component data. The tools allowed; measurement of relevant anatomy, consideration of leg length difference, and angular deformity, identification of landmarks such as center of rotation of the socket and offset, and comparison between the normal and pathological sides. Components could be chosen and errors detected, such as incompatible components or wrong side, and an order generated for forwarding to the supplier. Choice of stem was always within one size of pre-operative templating. Choice of socket was within two sizes.

Conclusions The explanation for discrepancy may be the intra-operative desire to judge size according to “feel” at surgery. A surgeon may wish to demonstrate accuracy by “forcing” intra-operative decision towards verifying pre-operative planning. What is surprisingly is that surgeons do not have uniform views as to the “ideal” socket position or stem position.

In relation to the conduct of this study, one or more the authors have received, or are likely to receive direct material benefits.

Introduction The decision to offer a patient a knee replacement is usually based on a patient’s perception of their reduction of quality of life. The choice between unicompartmental (UCKJR) and total knee joint replacement (TKJR) is usually guided by surgeon preference. This preference has been extensively debated in the literature.

Methods The author has a series of 130 UCKJR and 370 TKJR performed over similar time spans. Oxford knee scores have been collected comparing outcomes. Radiological signs of loosening or subsidence have been recorded.

Results Short term function is superior in terms of range of motion and capacity for activities of daily living in those with UCKJR compared to TKJR. Three UCKJR and 12 TKJR have been revised. Of the three revisions of UCKJR two have been revised for pain of uncertain cause and one was loose. Three UCKJR are unsatisfactory and will come to revision. Two are showing signs of subsidence and one is painful, presumed loose without radiological signs of looseness.

Conclusions Comparing revision rates from one surgeon’s series suggests a slightly higher rate of revision with UCKJR but since prosthesis selection is made on different criteria when making the original decision to proceed, comparisons are difficult. A 95% survival figure can be given to patients about the result of this procedure. The functional outcome, earlier recovery, and shorter hospitalisation can be given as other factors to favor the procedure. The literature supports the satisfactory results of conversion of UCKJR to TKJR. A confounding argument is the frequent reporting of 98% to 100% survival of TKJR at 15 years.

Various assumptions must be made during total hip replacement when placing the acetabular component within the reamed acetabulum with regards to its orientation. Various methods have been described for different acetabular components, some relying on knowledge of the existing anatomy and some relying on the use of jigs to align the component. Many of these assumptions are based on opinion rather than science and the current study was designed to define the position of the acetabulum in relation to a fixed position of the pelvis.

A neutral position of the pelvis must be defined and this is represented by having a line from the anterior superior iliac spine to the pubis fixed in the coronal plane and taking measurements of the perpendicular axis of the pelvis taken from this.

A variety of measurements were made using measurement techniques and the conclusion was reached that the average angle for operative inclination is 43 degrees ± 5 degrees and the average angle for operative anteversion is 29 degrees ± 8 degrees. These figures should give a preliminary guide to the correct placement of the acetabular socket in total hip replacement although other factors may need to be taken into account.

At this time the majority of acetabular replacements in total hip replacement rely on bone ingrowth or bone ongrowth. Long term success has been well established but is this success the result of good luck or good management? Numerous systems exist with the simplest perhaps being that of the placement of a hemispherical cup in a hemispherically reamed acetabulum. Beyond this, a wide variety of added complexity exists with the presumption that these increased complexities provide improved stability and hence more secure primary and secondary fixation.

The computer model that has been established demonstrates the geometry of fixation of hemispherical cups as compared to rim fit cups and looks at the requirements of acetabular distortion before secure fixation can be achieved. The model attempts to explain why on some occasions an apparently ideally reamed acetabulum is not secure without some form of augmentation of fixation.

The model provides a basis for considering the various options of acetabular fixation.