Introduction: Based on the benefits of less postoperative pain and accelerated rehabilitation associated with minimally invasive implanted unicompartmental knee joint replacement new surgical approaches have been developed for total knee replacement. New side-cutting implantation instruments were proposed for the minimally invasive surgical technique. Different randomized studies have shown improved component position in association with the use of navigation systems for TKA as compared with standard implantation instruments. There is a lack of randomized studies showing whether the same level of accuracy provided by computer-assistance is possible when using a minimally invasive approach and the side-cutting jigs. We hypothesized an imageless navigation system leads to improved component positioning in the coronal and sagittal plane when compared with a non-navigated study group. Both cohorts were operated on with a mini-subvastus surgical approach using side-cutting instruments. We questioned whether clinical outcomes were affected by the application of the navigation system at 3 months followup.

Methods: 100 patients were randomized to undergo computer-assisted TKA or non-navigated TKA using a mini-subvastus surgical approach and side-cutting implant instrumentation. The radiographic parameters, clinical outcomes and knee scores were evaluated 3 months postoperative.

Results: The mechanical axis of the limb was within 3° varus/valgus in 76 % of the patients who had navigated procedures versus 66 % of patients who had conventional surgery. The tibial slope showed a rate of inaccuracy of 3° or less for 78 % of the patients in the navigated total knee arthroplasty group versus 66 % of the patients in the conventional group. Clinical outcomes and knee scores were similar in both groups.

Conclusion: The navigated study group showed a trend to a higher implantation accuracy but the differences were not significant. We think the reasons were the cutting direction from medial to lateral – longer cutting distance – and the insufficient cutting-jig fixation. We cannot recommend the use of the MIS Quad-Sparing™ instrumentation without a navigation system. With computer-assistance the implantation accuracy could duplicate the findings in the literature for non-navigated cohorts using a standard surgical approach. Using a navigation system for minimal invasive subvastus TKA did not influence the 3-month clinical outcome.

There is a renewed interest in unicompartmental knee arthroplasty. The present report describes the minimum ten-year results associated with a – unicompartmental knee arthroplasty design that is in current use.

Sixty-two consecutive unicompartmental knee arthroplasties that were performed with cemented modular Miller-Galante implants in 51 patients were studied prospectively both clinically and radiographically. All patients had isolated unicompartmental disease without patellofemoral symptoms. No patient was lost to follow-up. Thirteen patients (13 knees) died after less than 10 years of follow-up, leaving 38 patients (49 knees) with a minimum of 10 years of follow-up. The average duration of follow-up was 12 years.

The mean Hospital for Special Surgery knee score improved from 55 points preoperatively to 92 points at the time of the final follow-up. Thirty-nine knees (80%) had an excellent result, six (12%) had a good result, and four (8%) had a fair result. At the time of final follow-up, 39 knees (80%) had flexion to at least 120 degrees. Two patients (two knees) with well-fixed components underwent revision to total knee arthroplasty, at seven and 11 years, because of progression of patello-femoral arthritis. At the time of the final follow-up, no component was loose radiographically and there was no evidence of peri-prosthetic osteolysis. Radiographic evidence of progressive loss of joint space was observed in the opposite compartment of nine knees (18%) and in the patello-femoral space of seven knees (14%). Kaplan-Meier analysis revealed a survival rate of 98.0% +/−2.0% at ten years and of 95.7% +/− 4.3% at 13 years, with revision or radiographic loosening as the end point. The survival rate was 100% at 13 years with aseptic loosening as the end point.

After a minimum duration of follow-up of 10 years, this cemented modular uni-compartmental knee design was associated with excellent clinical and radiographic results. Although the 10 year survival rate was excellent, radiographic signs of progression of osteoarthritis in the other compartments continued at a slow rate. With appropriate indications and technique, this uni-compartmental knee design can yield excellent results into the beginning of the second decade of use.

Aim: Cycling is a common activity after TKA and it has been shown that up to 50 % of the TKA patients are riding a bike and 25 % think that cycling has an important place in their life. The specific contact mechanics of tibiofemoral joint is well known during walking, however, there is little data during cycling for TKA patients. The purpose of this study was to determine the tibiofemoral contact mechanics during cycling for TKA patients.

Methods: We recruited 10 patients implanted with a mobile bearing and 10 patients with a fixed bearing posterior stabilized prosthesis. An age-matched, asymptomatic control group consisted of 10 subjects. The patients were physically examined, and WOMAC index and knee society score were taken. Motion analysis was performed using a retroreflective marker based technique called “PCT”. Forces and moments during cycling were recorded with load cells at the crank shafts of the bike. Motion and load data were synchronized.

Results: Resultant pedal forces showed no significant differences between study groups but the generated impulse was higher in the mobile bearing group. Patients with contra-lateral osteoarthritis showed higher forces and impulse at the operated leg. The motion analysis showed the following mean values ±SD for TKA patients/Normals: maximum flexion angle 132.5° ±16.0°/131.5° ±18.3°, minimum flexion angle 41.4° ±12.0°/40.3° ±15.7°, range of rotation in transversal plane 12.6° ±4.7°/9.9° ±3.6° and range of anterior-posterior translation 5.3 mm ±5.1 mm/2.7 mm ±0.4 mm. There were no significant differences between study groups.

Discussion: In this study, force and impulse of TKA patients with contemporary prostheses were comparable to healthy subjects indicating functional restoration of the joint. Contralateral osteoarthritis may cause higher forces at the operated leg and thus, relatively higher stresses at the artificial articulation.

As expected, the generated forces at the bike pedal were low (20–25% body-weight) calling for little muscle activity and low compressive joint forces. However, with a mean maximum flexion angle of 131.5°, the observed motion ranges were higher than expected. Prostheses not designed for high flexion activities could lose tibio-femoral contact during cycling with detrimental effects on wear. Still, the measured range of rotation in the transverse plane indicates that despite its posterior-stabilized design rotation is taking place with approximately the same amount as it occurs in normal subjects. This may have detrimental effects on the post at the tibial plateau and could explain the previously observed rotational damage patterns on retrieved posterior stabilized TKA specimens.

Data are suggesting that leisure activities should be considered to determine the appropriate TKA design. This study will provide useful data for future design and wear testing scenarios.

Aims: Because of the limitation of exposure inherent in minimally invasive surgical techniques for total knee replacement surgery, there is a significant risk of malalignment, malrotation, femoral notching and failure of soft tissue balance.

Methods: In this randomized study 50 patients with osteoarthritis of the knee, underwent TKR through a minimally invasive exposure using a navigation system; while a control group of 50 patients underwent the same surgery without navigation.

A subvastus approach was used with a less than 10 cm incision. Femoral component alignment is established with an intramedullary, and the tibial component, with an extramedullary alignment guide. The navigation system was used for fine adjustment and verification of cutting block position. The navigation system used for the study was the VectorVision® CT-Free Knee 1.5.1.

Results: The accuracy of prosthetic components positioning was significantly higher in the navigation group. The navigation system offered an objective analysis of medial and lateral ligament tension in full extension and 90 ° of flexion. In 8 cases navigation avoided femoral notching. No navigation related complications were registered. The additional surgery time for computer-assisted TKR was a mean 21 minutes. The nonnavigated implantation technique reached perfect component positioning in 62 % of the TKR.

Conclusion: Computer-assisted TKR results in predictable and accurate alignment, avoidance of femoral notching, avoidance of malrotation and appropriate balance of the soft tissue. Performing minimally invasive TKR without navigation has a higher risk of increased rate of unsatisfactory outcomes with shorter prosthetic survivorship when compared to the use of navigation.

Introduction: Optimal component position in all planes and well balanced soft tissues lead to a good clinical outcome and long-term survival after total knee arthroplasty. We investigated the implantation accuracy of navigated total knee arthroplasty at 3 months followup and the influence on the clinical outcome at 2 years followup.

Patients and Methods: Forty-four patients (44 procedures) were enrolled in our prospective study. One half of the surgeries were performed using a computed tomography based navigation system, and one half of the surgeries were performed without computed tomography navigation. Outcomes were based on the Insall knee score parameters, anterior knee pain, patient satisfaction, feeling of instability, and step test. The radiographic parameters were the mechanical axis, tibial slope, lateral distal femoral angle, and medial proximal tibial angle.

Results: The radiographic measurements showed no differences between both groups (patients within ± 3° inaccuracy range in computed tomography based/computed tomography free groups; mechanical axis 86%/81%, tibial slope 95%/91%, lateral distal femoral angle 95%/91%, medial proximal tibial angle 91%/95%). The cumulative error of alignment showed no difference between the study groups. Seventeen of 21 (81%) patients fulfilled four criteria in the CT based group, and 15 of 21 (71.4%) patients fulfilled four criteria in the comparison group. Nineteen of 21 (90.5%) patients in both groups achieved three criteria in an optimal manner. An increased (p < 0.001) Insall knee score was found for changes over time in both study groups; however, there were no differences between the CT based or CT free patient groups. The postoperative ROM in both groups showed no difference at the 3-month and 2-year followup examinations. Both groups had an increase (p ≤ 0.002) in ROM between the 3-month and 2-year followup examinations. The examination of ligament balancing in full extension showed a higher rate of a stable soft tissue situation in the CT free navigation group but the difference was not significant. In 30° of flexion we detected a better (p = 0.004) ligament situation medially and laterally in the CT free group. The anterior drawer test showed a better (p = 0.035) stability in the CT free navigation group.

Discussion: The computed tomography free system provided equal radiographic results, but we found improved ligament balancing in the computed tomography free group. The computed tomography based module has an optimal preoperative planning procedure, but is more expensive and time consuming.