We describe the survivorship of the Medial Rotation total knee replacement (TKR) at ten years in 228 cemented primary replacements implanted between October 1994 and October 2006, with their clinical and radiological outcome. This implant has a highly congruent medial compartment, with the femoral component represented by a portion of a sphere which articulates with a matched concave surface on the medial side of the tibial insert. There were 78 men (17 bilateral TKRs) and 111 women (22 bilateral TKRs) with a mean age of 67.9 years (28 to 90). All the patients were assessed clinically and radiologically using the American Knee Society scoring systems. The mean follow-up was for six years (1 to 13) with only two patients lost to follow-up and 34 dying during the period of study, one of whom had required revision for infection. There were 11 revisions performed in total, three for aseptic loosening, six for infection, one for a periprosthetic fracture and one for a painful but well-fixed replacement performed at another centre. With revision for any cause as the endpoint, the survival at ten years was 94.5% (95% CI 85.1 to 100), and with aseptic loosening as the endpoint 98.4% (95% CI 93 to 100). The mean American Knee Society score improved from 47.6 (0 to 88) to 72.2 (26 to 100) and for function from 45.1 (0 to 100) to 93.1 (45 to 100). Radiological review failed to detect migration in any of the surviving knees. The clinical and radiological results of the Medial Rotation TKR are satisfactory at ten years. The increased congruence of the medial compartment has not led to an increased rate of loosening and continued use can be supported

Aims

Between 15% and 20% of patients remain dissatisfied following total knee arthroplasty (TKA). The SAIPH knee system (MatOrtho, Surrey, United Kingdom) is a medial ball and socket TKA that has been designed to replicate native knee kinematics in order to maximize the range of movement, stability, and function. This system is being progressively introduced in a stepwise fashion, with this study reporting the mid-term clinical and radiological outcomes.

Introduction. Inability to reproduce 6-degrees of freedom (6DOF) kinematics, abnormal “paradoxical” anterior femoral translation and loss of normal medial pivot rotation are challenges associated with contemporary posterior cruciate retaining and posterior stabilized total knee arthroplasty (TKA). The removal of the anterior and/or both cruciate ligaments in CR/PS TKA, leading to significant kinematic alteration of the knee joint, has been suggested as one of the potential contributory factors in patients remaining dissatisfied after TKA. Bi-cruciate retaining (BCR) TKA designs allow preservation of both anterior and posterior cruciate ligaments with the potential to replicate normal knee joint kinematics. Physically demanding tasks such as sit-to-stand (STS), and deep lunging may be more sensitive tools for investigating preserved kinematic abnormalities following TKA. This study aims to compare in-vivo kinematics between the operated and the contralateral non-operated knee in patients with contemporary BCR TKA design. Methods. Twenty-nine patients (14 male; 15 female, 65.7±7.7 years) unilaterally implanted with a contemporary BCR TKA design featuring an asymmetric femoral component and independently designed medial and lateral bearings were evaluated. Mean follow-up time after BCR TKA was 12.7±5.1 months. All patients received a computer tomography (CT) scan from the pelvis to the ankles for the creation of 3D surface models of both knees (BCR TKA and non-operated). Patients performed single leg deep lunges and sit-to-stand under a validated dual fluoroscopic imaging system (DFIS) surveillance. Each patient's 2D dynamic fluoroscopic images, corresponding 3D surface bone models (for contralateral non-operated knee) and computer aided design (CAD) implant models (for the BCR TKA implanted knee) were imported into a virtual DFIS environment in MATLAB. An optimization procedure was utilized to perform matching between the 3D surface bone models and the 2D fluoroscopic image outlines. In-vivo 6DOF kinematics of the BCR TKA knees and contralateral non-operated side were quantified and analyzed. Results. When performing the high-flexion lunge, BCR TKA knees demonstrated less average femoral posterior translation (13±4mm) during terminal flexion when compared to the contralateral non-operated knees (16.6±3.7mm) (p=0.001). Similarly, during STS, less femoral rollback was observed (11.6±4.5mm vs 14.4±4.6mm, p<0.04) in BCR TKA knees. Overall, BCR TKA knees partially reproduced a normal “screw-home” motion, demonstrating reduced internal rotation during several intervals of the cycles for strenuous flexion activities. BCR TKA knees demonstrated less internal rotation during high-flexion lunge (4±5.6° vs 6.5±6.1°, p=0.05). Similarly, during STS, less internal rotation was observed (4.5±6° vs 6.9±6.3°, p=0.04, p=0.02, p=0.01, p=0.02) in BCR TKA knees. Conclusion. The BCR TKA design demonstrated asymmetries in flexion-extension and internal-external rotation, suggesting that in-vivo tibiofemoral kinematic parameters are not fully restored in BCR patients during functionally strenuous activities such as single leg deep lunges and sit-to-stand. Further studies are required to elucidate the importance of patient factors, surgical component orientation and implant designs in optimizing in vivo kinematics in patients with BCR TKA. For figures, tables, or references, please contact authors directly

Aims

Medial pivot (MP) total knee arthroplasties (TKAs) were designed to mimic native knee kinematics with their deep medial congruent fitting of the tibia to the femur almost like a ball-on-socket, and a flat lateral part. GMK Sphere is a novel MP implant. Our primary aim was to study the migration pattern of the tibial tray of this TKA.

Aims

The Oswestry-Bristol Classification (OBC) is an MRI-specific assessment tool to grade trochlear dysplasia. The aim of this study is to validate clinically the OBC by demonstrating its use in selecting treatments that are safe and effective.

Aims

The extensive variation in axial rotation of tibial components can lead to coronal plane malalignment. We analyzed the change in coronal alignment induced by tray malrotation.

Aims

The removal of the cruciate ligaments in total knee arthroplasty (TKA) has been suggested as a potential contributing factor to patient dissatisfaction, due to alteration of the in vivo biomechanics of the knee. Bicruciate retaining (BCR) TKA allows the preservation of the cruciate ligaments, thus offering the potential to reproduce healthy kinematics. The aim of this study was to compare in vivo kinematics between the operated and contralateral knee in patients who have undergone TKA with a contemporary BCR design.

Aims

The morphometry of the distal femur was largely studied to improve bone-implant fit in total knee arthroplasty (TKA), but little is known about the asymmetry of the posterior condyles. This study aimed to investigate the dimensions of the posterior condyles and the influence of externally rotating the femoral component on potential prosthetic overhang or under-coverage.

Objectives

Throughout the 20th Century, it has been postulated that the knee moves on the basis of a four-bar link mechanism composed of the cruciate ligaments, the femur and the tibia. As a consequence, the femur has been thought to roll back with flexion, and total knee arthroplasty (TKA) prostheses have been designed on this basis. Recent work, however, has proposed that at a position of between 0° and 120° the medial femoral condyle does not move anteroposteriorly whereas the lateral femoral condyle tends, but is not obliged, to roll back – a combination of movements which equates to tibial internal/ femoral external rotation with flexion. The aim of this paper was to assess if the articular geometry of the GMK Sphere TKA could recreate the natural knee movements in situ/in vivo.

We used three-dimensional movement analysis by computer modelling of knee flexion from 0° to 50° in 14 knees in 12 patients with recurrent patellar dislocation and in 15 knees in ten normal control subjects to compare the in vivo three-dimensional movement of the patella. Flexion, tilt and spin of the patella were described in terms of rotation angles from 0°. The location of the patella and the tibial tubercle were evaluated using parameters expressed as percentage patellar shift and percentage tubercle shift. Patellar inclination to the femur was also measured and patellofemoral contact was qualitatively and quantitatively analysed.

The patients had greater values of spin from 20° to 50°, while there were no statistically significant differences in flexion and tilt. The patients also had greater percentage patellar shift from 0° to 50°, percentage tubercle shift at 0° and 10° and patellar inclination from 0° to 50° with a smaller oval-shaped contact area from 20° to 50° moving downwards on the lateral facet.

Patellar movement analysis using a three-dimensional computer model is useful to clearly demonstrate differences between patients with recurrent dislocation of the patella and normal control subjects.

The rotational alignment of the tibia is an unresolved issue in knee replacement. A poor functional outcome may be due to malrotation of the tibial component. Our aim was to find a reliable method for positioning the tibial component in knee replacement.

CT scans of 19 knees were reconstructed in three dimensions and orientated vertically. An axial plane was identified 20 mm below the tibial spines. The centre of each tibial condyle was calculated from ten points taken round the condylar cortex. The tibial tubercle centre was also generated as the centre of the circle which best fitted eight points on the outside of the tubercle in an axial plane at the level of its most prominent point.

The derived points were identified by three observers with errors of 0.6 mm to 1 mm. The medial and lateral tibial centres were constant features (radius 24 mm (sd 3), and 22 mm (sd 3), respectively). An anatomical axis was created perpendicular to the line joining these two points. The tubercle centre was found to be 20 mm (sd 7) lateral to the centre of the medial tibial condyle. Compared with this axis, an axis perpendicular to the posterior condylar axis was internally rotated by 6° (sd 3). An axis based on the tibial tubercle and the tibial spines was also internally rotated by 5° (sd 10).

Alignment of the knee when based on this anatomical axis was more reliable than either the posterior surfaces or any axis involving the tubercle which was the least reliable landmark in the region.