The mobile-bearing variant of a single-radius design is assumed to provide more freedom of motion compared to the fixed-bearing variant because the insert does not restrict the natural movements of the femoral component. This would reduce the contact stresses and wear which in turn may have a positive effect on the fixation of the prosthesis to the bone and thereby decreases the risk for loosening. The aim of this prospective randomized study was to evaluate early migration of the tibial component and kinematics of a mobile-bearing and fixed-bearing total knee prosthesis of the same single-radius design.

According to a prospective randomized protocol 20 Triathlon single-radius posterior- stabilized knee prostheses were implanted (9 mobile-bearing and 11 fixed-bearing). Fluoroscopy and roentgen stereophotogrammetric analysis were performed 6 and 12 months post-operatively.

The 1 year post-operative roentgen stereophotogrammetric analysis results showed considerable early migrations in 3 mobile-bearing patients and 1 fixed-bearing patient. The range of knee flexion was the same for the mobile-bearing and fixed- bearing group. The mobile insert was following the femoral component during motion.

This study showed no apparent distinction in early migration and kinematics between mobile-bearing and fixed-bearing single-radius total knee prostheses. Des- pite the mobile insert was following the femoral component during motion, and therefore performed as intended, no kinematic advantages of the mobile-bearing total knee prosthesis were seen. It is concluded that a mobile insert in single-radius total knee prostheses is redundant and will not lead to additional benefits.

Purpose of study

To investigate the linear penetration rate of the polyethylene bearing in unicompartmental knee arthroplasty at twenty years.

The most widely accepted method to measure kneekinematics is using external movement registration with the aid of skin-mounted markers. However, a large error component appears due to skin movement relative to the underlying bone. The goal of this study is to use fluoroscopy to quantify skin movement artefacts in patients with a total knee prosthesis during a step-up task.

The most widely accepted method to measure knee kinematics is using external movement registration with the aid of skin-mounted markers. However, a large error component appears due to skin movement relative to the underlying bone. The goal of this study is to use fluoroscopy to quantify skin movement artefacts in patients with a total knee prosthesis during a step-up task.

Translational and rotational errors attributed to soft tissue movement were three times larger for the femur than for the tibia about allaxes. The mean of the absolute rotational differences for the femur were2.6, 3.3 and 1.7 degrees about the X, Y and Z axes respectively. Absolute peak differences for individual subjects were 9.1, 12.9 and 10.5 mm along the X, Y and Z axes respectively.

This is the first study examining the 3D relative motion between surface-mounted and bone-anchored markers without the use of cortical pins anchored to the tibia and/or the femur. The results revealed no regular pattern of soft tissue error between subjects indicating the unlikely success of numerical methods for modeling and removing soft tissue motion artifacts when using standard motion capture methods.

Various radiological classification systems exist for rheumatoid wrist progression but few have been evaluated for reliability and clinical application. In order to research these three sets of wrist radiographs of 35 rheumatoid patients, with an average duration of disease of 11 years, were classified according to four different classification systems (Larsen, Simmen, Wrightington and Modified Wrightington). The inter- and intraobserver reliability of each was calculated. The reliability of the Larsen and both Wrightington systems were good but the Simmen system had poor interobserver and intraobserver reproducibility. None of the classification systems satisfactorily assessed the distal radioulnar joint (DRUJ) and the Modified Wrightington system could not classify DRUJ disease in 6 of the 35 wrists.

Outcome measures must be valid, reliable and responsive to change criteria. The most common clinical outcome measures are Knee Society Scores, SF-36 quality of life scores, HAQ and DAS scores. However, performance based measures of functioning may not be dependent on patient report or observer judgment.

Examples of objective pre- and post-operative performance outcome measures are surface Electromyography (EMG) of muscles, kinematics and kinetics (gait analysis). For the evaluation of implant survival after joint arthroplasty, Roentgen Stereophotogrammetric Analysis (RSA) is the golden standard to assess micro-motion of the implants.

Surface EMG can be used to asses the stability of joints before and after intervention. Calibrating of raw EMG data is necessary to compare the data between subjects. It was shown that calibration of EMG data by means of isokinetic contractions on a dynamometer during flexion and extension was more reliable and repeatable than using a Maximum Voluntary Contraction in patients after total knee arthroplasty. After total knee arthroplasty RA patients have a lower net knee joint moment and a higher co-contraction than controls, indicating avoidance of net joint load and an active stabilization of the knee joint.

Fluoroscopy can be used to assess the kinematics of joints. In the pre-operative situation the use of CT models of the involved bones can be matched to the assessed fluoroscopic images. In the post-operative situation CAD models of the implants can be used for this purpose. In this way accurate 3D kinematics of joints can be assessed. During a step-up task of RA patients, the rotating platform of a mobile bearing knee showed no- or far less longitudinal rotation than the femur. Therefore, some of the theoretical advantages of this specific rotating platform knee prosthesis can be questioned. Fluoroscopy has also been used to assess soft tissue artifacts that occur in gait analysis i.e. displacements of skin-mounted markers relative to the underlying bone. The large soft tissue artefacts observed (displacements up to 17 mm and 12 degrees) question the usefulness of parameters found with external movement registration.

In order to assess the micromotion of implants after joint arthroplasty a measurement technique with a much higher accuracy than fluoroscopy is needed. RSA uses tantalum markers as landmarks bony structures and as landmarks on the implant. Recently a new RSA technique has been developed that does not rely on the attachment of artificial markers on the implant but uses CAD models of the implant instead. As an example of RSA as outcome measure, results showed that a calciumphosphate coating improves fixation of tibial components in RA patients, thus preventing mechanical loosening and subsequent long-term revision. In another clinical RSA study, it was found that mobile bearing knees are more predictable and forgiving with respect to micromotion compared to posterior stabilized tibial components in RA patients.

The results obtained by the above described performance outcome measures can be valued since the accuracy and precision of the used outcome measures are all published.

Introduction: In total knee arthroplasty (TKA) it remains a topic if cementless designs offer long-term stability equivalent to cemented procedures and if the components should be coated with calciumphosphate to enhance fixation. This study compares the three-dimensional migration patters of cemented and uncoated and periapatite (PA) coated tibial trays during a 2-year clinical follow-up study using roentgen stereophotogram-metric analysis (RSA) measurements as a predictor of long-term implant loosening (Ryds definition).

Methods: A double blind randomized prospective study was performed on 101 osteoarhtritic patients receiving 115 Duracon TKA. The tibial tray was either cemented (25), uncoated and uncemented (46) or PA-coated and uncemented (44). The groups were matched for sex, age, BMI and pre-op Insall score. Patients were evaluated at 1 week, 3, 6, 12 and 24 months post-operatively using standard radiographs and Insall scores. At each evaluation RSA measurements determined the translational (medial-lateral (ML), caudal-cranial (CC), anterior-posterior(AP)) and rotational (anterior tilt, external and valgus rotation) displacements of the tibial tray.

Results: Insall scores were not statistically different between the groups. Average component displacement was low for the cemented components in all directions. For the uncemented trays migration was highest in the CC direction (subsidence) and steep during the first 6 weeks. At two years the uncoated trays showed significantly more subsidence (−0.5 0.63 mm, range: −2.1 to 0.5 mm) than the cemented components (0.1 0.17 m, range: −0.2 to 0.4 mm, p< 0.05) and the PA-coated group (−0.1 0.60 mm, range: −2.8 to 0.3 mm, p< 0.05). Average subsidence of the cemented and PA-coated implants was nearly the same but variability was higher for the coated trays (p=0.01). Displacements in all other directions were not significantly different between the groups. Using Ryds definition, a total of 10 tibial trays from the cemented group (40%), 29 trays from the uncoated group (63%) and 11 trays from the PA-coated group (26%) were identified to be at risk for long-term loosening. In seven cases (all cemented) component tilt was critical.

Conclusion: At 2 years no clinical differences were found between cemented, uncoated and PA-coated tibial trays. However, RSA measurements showed significantly different migration patterns and predictions for long-term implant stability. Steep initial subsidence before stabilisation seems an inherent characteristics of uncemented fixation. In contrast, the cement layer below cemented trays can lead to AP tilt. Uncoated uncemented components migrate significantly indicating a high risk of late loosening. PA-coating reduces tray migration and the risk of long-term failure to levels equivalent to cemented fixation.

The advantages of high viscosity Simplex AF cement (PMMA) compared to low viscosity Simplex P are the low porosity, the high fatigue strength, the lower polymerization time, and the lower maximum polymerization temperature. A prospective, randomized, double-blind clinical study was conducted to assess the in vivo effects of viscosity of bone cement on the micromotion of a polished tapered stem and UHMWP-cup (Exeter, Stryker-Howmedica). Roentgen Stereophotogrammetric Analysis (RSA-CMS, Medis, The Netherlands) was used to measure micromotion.

Twenty patients were included in a Simplex AF group (70 ± 4.3 years), and twenty patients were included in a Simplex P group (71 ± 7.3 years). No significant differences in body mass index and clinical hip scores were observed between the two studied groups.

There was no significant difference of the subsidence of both high and low viscosity cemented Exeter stems. The subsidence was according to the literature and showed that the viscosity of the bone cement did not influence the cement-implant bond of this polished tapered stem design.

The total migration of the cups and the migration along the medial-lateral axis were significantly larger for the Simplex AF cemented cups compared to the Simplex P cemented cups (p=0.037). This can be explained by the higher cement mantle thickness in acetabular Gruen zone 2 (p=0.003) and 3 (p=0.004) of the Simplex AF cemented cups.

We conclude from this study that the viscosity of the bone cement has no effect on the subsidence of polished tapered stems and that a high cement mantle thickness around an UHMWP-cup has a negative effect on fixation.

A changed kinematic elbow axis can cause early loosening of elbow endoprostheses and can decrease the functional outcome. Therefore, these prostheses and their alignment tools are designed to reconstruct normal joint kinematics. We investigated whether it is possible to reconstruct the pre-operative kinematic axis of the elbow when an iBP^™ elbow endoprosthesis (Biomet) has been placed.

The calibrated Flock of Birds® electromagnetic tracking device registered controlled passive elbow flexion of ten embalmed upper extremities. The pre-operative kinematic elbow axes were established using helical axes.

Results were expressed in the humeral coordinate system defined by the glenohumeral joint rotation centre and the lateral and medial epicondyle of the humerus. The glenohumeral joint rotation centre was determined using a regression method. The senior author implanted the iBP^™ elbow endoprosthesis using standard instrumentation for humeral component alignment. The post-operative kinematic axes were then calculated. A Student’s t-test was performed to compare the pre- and post-operative axes.

No significant differences were found in the direction of the kinematic elbow axes before and after surgery, indicating no alteration in the valgus/varus angle or change in longitudinal rotation of the ulna with respect to the humerus. However, the axis was located significantly more distal (mean difference 7.0 mm, p = 0.004) after surgery. The ventral-dorsal location of the kinematic axis was not significantly different (p = 0.748) after surgery, but there was some variation in individual axes. The iBP^™ Elbow System enables the reconstruction of the direction of the pre-operative kinematic elbow axis. While the exact position of the pre-operative axis could not be reproduced in vitro, the kinematic axis of the elbow is expected to be less distal in vivo as a result of the extensive destruction of the rheumatoid elbow. Individually adjustable alignment tools might enable more precise reconstruction.

The aim of this study was on the one hand to compare the fixation of a posterior stabilised prosthesis (PS) and a PCL retaining mobile bearing design (Interax, Howmedica Osteonics, Rutherfort, USA) and on the other hand to measure the mobility of the mobile bearing. All measurements were carried out by means of Roentgen Stereophotogrammetric Analysis (RSA-CMS, Medis, Netherlands).

A prospective,randomised,double-blind study (N=28) was conducted to assess the micromotion of the components. At the one-year follow-up evaluation, the micromotion of the PS-components and the mobile bearing components were not significantly different. The PS-tibial components subsided −0.063 ± 0.177 mm and the mobile bearing knee tibial components subsided 0.067 ± 0.084 mm. The PS tibial component showed a higher variability in the migration results indicating a number of PS with rather large micromotion.

For three patients, the in vivo motion of the mobile bearing with respect to the metal backing was assessed at 30, 60 and 90 degrees of passive flexion. Two of mobile bearings moved posteriorly (2.4 and 2.9 mm) at respectively 60 and 90 degrees of flexion and showed a medial-lateral translation of 0.03 and 3.5 mm. One mobile bearing moved only 0.4 mm posteriorly at 90 degrees of flexion but showed a lateral-medial translation of 3.1 mm.

The broad range of kinematic patterns of mobile bearings during flexion that is observed in fluoroscopic studies is also observed in this study. A possible positive effect of mobile bearing movement may be found in the smaller variability of the micromotion of the mobile-bearing knees compared to the PS knees. The assumption was that shear forces in tibial bones implanted with a mobile bearing prosthesis would be better dissipated from the prosthesis-bone interface resulting in less micromotion. The kinematics of an additional number of mobile bearing knees -already included in the micro-motion study- will have to be assessed in order to determine the relation between mobility and micromotion.

The common factor in all (mechanical) prosthetic failure mechanisms is the induction of osteolysis around the endoprosthesis with subsequent prosthetic migration and finally loosening of the prosthesis. Both initial prosthesis-bone fixation and long-term prosthesis survival depend on the quality of the peri-prosthetic bone mass. The effects of treatment of RA patients with prednison are inhibition of osteoblastic activity and inhibition of calcium resorption from the intestines. The bone mass loss during the first six months of prednison treatment is substantial and will seldom be regained. Bisphosphonates are known to decrease osteoclastic activity and may therefore stop osteolysis at the bone-prosthesis interface.

The aim of the study was to evaluate a possible association of bisphosphonates with reduced migration of total knee prostheses (Interax, Howmedica Osteonics, Rutherfort, USA) in a high-risk group. Roentgen Stereophotogrammetric Analysis (RSA-CMS, Medis, The Netherlands) was used to measure the micromotion.

Retrospectively a group of nine RA patients treated with prednison (non-bisphosphonates group) and a group of fourteen RA patients (bisphosphonates group) treated with prednison in combination with bisphosphonates (Etidronate) were included from a prospective randomized study of 82 patients (Nelissen et al., 1998).

At the two-year follow-up evaluation, functional scores and knee scores did not differ significantly among the two groups. At the two-year follow-up evaluation, the non-bisphosphonates group subsided −0.47 ± 0.8 mm, and the bisphosphonates components subsided 0.07 ± 2.9 mm. In the analysis of variance with repeated measurements, with correction for follow-up time, sedimentation rate, and prosthesis fixation type, the bisphosphonates group migrated 1.20 mm less in the total migration (95% c.i.: 1.07–1.30 mm) compared to the non-bisphosphonates group.

In this study, bisphosphonates medication in addition to corticosteroid medication was associated with reduced migration of knee prostheses compared to corticosteroid medication alone.