Aims: To detect discriminant features in the cyclic kinematic patterns generated during selected upper limb activities of daily living by a normative and a distal radial fracture group, so as to reduce the multidimensionality of the kinematic analysis.

Methods: Cyclic activities of daily living were performed using a protocol that allowed comparison between the resulting kinematic patterns or waveforms. Twop groups were measured:

Group A: 11 subjects with normal hand function (average age: 31.5ys, SD: 8.7ys).

Group B: 5 subjects having undergone treatment for distal radial fracture was tested using the same methods (average age: 34.2ys, SD: 16.8ys).

Task presented here, (one of 5) performed by turning a key 90 degrees clockwise. Principal component analysis (PCA) was applied to the waveforms of group A, using the procedure illustrated by Deluzio et al.,1997 for use with walking gait patterns. A 90% trace criterion was used to calculate the number of principal components (PCs) to retain.

Results: Looking at elbow pronation/supination (PS). Two PCs were retained. The first component consisted of a simple pronation pattern. The opposite signs of Y1 differentiated left-hand users (utmost right), who required pronation to rotate the key, from right-hand ones, who required supination, with the exception of subject 3 group B. The second component consisted of pronation (cycle first half) followed by supination (second half). Subject 3 stood out because of limited elbow supination, which resulted from the combination of pronation (Y1) and supination (Y2) components.

Conclusions: Upper limb analysis can employ the statistic tools of gait analysis provided a cyclic and repeatable protocol is used. PCA was applied to elbow PS to identify statistically different movements of the distal radial fracture group and underline their main characteristics. This is particularly important in the presence of a large data group, when the identification and evaluation processes need to be both rapid and accurate. Limited PS was identified as a discriminant feature, supporting the follow-up studies for this injury that measured a reduction of PS by about 80% compared to that of the unaffected side. The cycle stages concerned can be identified on the basis of the contribution given by each component.

Radiolucencies are generally thought to be a manifestation of loosening. They are commonly seen under the tibial component of the Oxford Unicompartmental knee replacement. However, they are not associated with long term failure [1]. The aim of this study was to investigate any relationship between radiolucencies and component migration.

Eight medial Oxford Unicompartmental knee prostheses were examined post-operatively, at 12 months and at 24 months using Roentgen Stereophotogrammetric Analysis (RSA). The serial radiographs were calibrated and three dimensional CAD models were matched to the extracted component shapes. Implanted bone marker balls were then selected on all radiographs. The components were superimposed. Migration calculation was achieved by comparing relative positions of components to bone marker balls in the serial radiographs. Fluoroscopically screened X-rays were taken to determine whether there were any radiolu-cencies under the tibial component.

By 12 months, the femoral component had migrated significantly anteriorly (0.35 mm) and proximally (0.61 mm). The tibial component had migrated significantly distally (0.42 mm) and anteriorly (0.47 mm). Although on average there appeared to be a small further migration between 12 and 24 months, this was not statistically significant in any direction.

Six of the eight patients had radiolucencies at 24 months. None of the radiolucencies were was complete. The maximum radiolucency was 1 mm thick and the average was 0.57 mm. There was no correlation between radiolucency and migration.

The proximal femoral migration and distal tibial migration can be explained by the load across the knee. We cannot yet explain the anterior tibial migration. Radiolucencies almost always occur and are not related to migration.This confirms they are not associated with loosening.

Polyethylene wear can be an important cause of knee replacement failure.

Six TKRs in young, active patients with excellent Oxford Knee Scores and Knee Society Scores, mean 76 months post knee replacement and 5 control patients, 2 weeks post TKR, were selected. Each patient had weight bearing stereo radiographs of at 0, 15, 30, 45 and 60 degrees of flexion while standing in a calibration grid. These x-rays were analysed using our Radio Stereometric Analysis (RSA) system. The three-dimensional shape of the TKR (manufacturer’s computer aided design model) was matched to the TKR silhouette on the calibrated stereo radiographs for each angle of flexion. The relative positions of the femoral and tibial components in space were then determined and the linear and volumetric penetration was calculated using Matlab software.

The accuracy of the system was found to be 0.3mm (CAD model tolerance 0.25mm). The mean linear wear in the control patients was 0.02mm (range −0.19 to +0.23mm). Average linear penetration in the study group was found to be 0.6 mm at 6 years, giving an overall linear wear rate of 0.1mm/year. Average penetration volume at 76 months was 399mm3. The average volumetric wear rate was 63mm3/year.

It is possible to measure volumetric wear in vivo using RSA. Volumetric wear rate was found to be 63mm3 per year. Studies on retrieved normally functioning hip replacements have shown volumetric wear rates of 35mm3 per year. However, clinical outcomes of knee replacements are comparable to those of hip replacements, suggesting that the knee has a more effective mechanism for dealing with polyethylene wear particles.

Introduction: Polyethylene wear can be an important cause of knee replacement failure.

Method: Six TKRs in young, active patients with excellent Oxford Knee Scores and Knee Society Scores, mean 76 months post knee replacement and 5 control patients, 2 weeks post TKR, were selected. Each patient had weight bearing stereo radiographs of at 0, 15, 30, 45 and 60 degrees of flexion while standing in a calibration grid. These x-rays were analysed using our Radio Stereometric Analysis (RSA) system. The three-dimensional shape of the TKR (manufacturer’s computer aided design model) was matched to the TKR silhouette on the calibrated stereo radiographs for each angle of flexion. The relative positions of the femoral and tibial components in space were then determined and the linear and volumetric penetration was calculated using Matlab software.

Results: The accuracy of the system was found to be 0.3mm (CAD model tolerance 0.25mm). The mean linear wear in the control patients was 0.02mm (range −0.19 to +0.23mm). Average linear penetration in the study group was found to be 0.6 mm at 6 years, giving an overall linear wear rate of 0.1mm/year. Average penetration volume at 76 months was 399mm³. The average volumetric wear rate was 63mm³/year.

Conclusion: It is possible to measure volumetric wear in vivo using RSA. Volumetric wear rate was found to be 63mm³ per year. Studies on retrieved normally functioning hip replacements have shown volumetric wear rates of 35mm³ per year. However, clinical outcomes of knee replacements are comparable to those of hip replacements, suggesting that the knee has a more effective mechanism for dealing with polyethylene wear particles.

*Oxford Hip and Knee Group: P McLardy-Smith, C Dodd, D Murray & R Gundle