Differences in anatomy and kinematics in Asian and Caucasian TKA patients: influence on implant positioning and subsequent loading conditions in mobile bearing knees.

The objective of our study was to determine the mechanical stress conditions under tibiofemoral loading with an overlay of knee kinematics in deep flexion on two different mobile bearing designs in comparison to in vivo failure modes. This study investigates the seldom but severe complication of fatigue failure of polyethylene components at mobile bearing total knee arthroplasty designs. Assuming a combination of a floor-based lifestyle and tibial malrotation as a possible reason for a higher failure rate in Asian countries we developed a simplified finite element model considering a tibiofemoral roll-back angle of 22° and the range of rotational motion of a clinically established floating platform design (e.motion FP) at a knee flexion angle of 120° in order to compare our results to failure modes found in retrieved implants. Compared to the failure mode observed in the clinical retrievals the locations of the occurring stress maxima as well as the tensile stress distribution show analogies. From our observations, we conclude that the newly introduced finite element model with an overlay of deep knee flexion (lateral roll-back) and considerable internally rotated tibia implant positioning is an appropriate analysis for knee design optimizations and a suitable method to predict clinical failure modes.

Early results of a new rotating hinge knee implant.

BACKGROUND: Indication for rotating hinge (RH) total knee arthroplasty (TKA) includes primary and revision cases, with contradictory results. The aim of this study was to report prospective early results of a new modular rotating hinge TKA (EnduRo). For this implant several new design features and a new bearing material (carbon-fiber reinforced poly-ether-ether-ketone) have been developed. Furthermore, we tried to establish a new classification of failure modes for revision TKA. METHODS: 152 EnduRo rotating-hinge prostheses were implanted in two centers. In 90 patients a primary implantation has been performed and 62 patients were revision cases. Knee Society Score (KSS), Western Ontario and McMaster Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS), and Range of motion (ROM) were assessed before surgery, 3 months postoperatively, 12 months postoperatively, and annually thereafter. We defined 3 types of complications: Type 1, infection; type 2, periprosthetic complications; type 3, implant failures. RESULTS: KSS, WOMAC, OKS, and ROM revealed significant improvements between the preoperative and the follow-up investigations. There were 14 complications (9.2%) leading to revision surgery, predominantly type 2. CONCLUSION: Our study shows excellent clinical results of the EnduRo TKA. Furthermore, no premature material failure or unusual biological response to the new bearing material could be detected.

Biotribology of a mobile bearing posterior stabilised knee design--effect of motion restraint on wear, tibio-femoral kinematics and particles.

The objective of our study was to evaluate the impact of a biphaseal anterior-posterior (AP) and internal-external (IE) motion restraint system on the wear behaviour, tibio-femoral kinematics and particle release of a mobile bearing posterior stabilised knee design in comparison to the widely used linear restraint. in vitro wear simulation was performed using a posterior stabilised total knee replacement with a mobile rotating platform gliding surface design to compare the standard ISO 14243-1:2002 (E) protocol with a linear AP and IE motion restraint and the new ISO 14243-1:2009 (E) protocol with a biphaseal AP and IE motion restraint. For the mobile gliding surfaces, an increase in wear rate by more than a magnitude was measured applying the biphaseal protocol (8.5±1.6 mg/million cycles) in a direct comparison to the linear protocol (0.33±0.07 mg/million cycles), with statistically significant difference. The amplitudes of AP displacement were 3.22±0.47 mm for the biphaseal test, compared to 1.97±0.22 mm in the linear test and the amplitudes of the IE rotation angle had mean values of 7.32°±0.91° under the biphaseal setup, compared to 1.97°±0.14° under linear motion restraint test conditions. From our observations, we conclude that the changes in AP translation and IE rotation motion restraints from ISO linear to ISO biphaseal test conditions highly impact the knee joint kinematics and wear behaviour of a mobile bearing posterior stabilised knee design.

Full versus surface tibial baseplate cementation in total knee arthroplasty.

The use of a keel in the tibial component during modern primary total knee arthroplasty (TKA) has become common, and its cementation may affect the future performance of the prosthesis. Although proponents of cementing the entire tibial component argue that this technique provides better initial fixation and may prevent aseptic loosening, reasons exist to apply cement only to the tibial baseplate. In this study, 232 patients who underwent TKA using full or surface cementation of the tibial baseplate were evaluated at an average 5.6-year follow-up to assess survivorship and clinical results. The cumulative survival rate at 8 years was 97.1%. With revision of either component for any reason considered the endpoint, no significant difference was noted between full and surface cemented groups. Knee Society Score, range of motion, and femoro-tibial mechanical angle significantly increased postoperatively. Multivariate analysis revealed that good preoperative range of motion and Knee Society Scores were related to good postoperative range of motion and Knee Society Scores. Follow-up length was a negative predictor of postoperative Knee Society Score. The use of full or surface cementation of the baseplate was unrelated to the postoperative clinical outcomes. Clinical outcomes did not differ according to the tibial component cementation technique. The results of this study suggest that cementing the keel of the tibial component during primary TKA has no advantage for patients. Longer-term follow-up and proper patient randomization are required to confirm these findings.

Single-radius, multidirectional total knee replacement.

PURPOSE: The present study was designed to evaluate the mid-term (5- to 8-year) survival rate of a new total knee replacement (TKR) with a single-radius femoral component and a multidirectional, highly congruent tibial component, in comparison with an historical group (TKR with multi-radius design and fixed bearing). METHODS: Four hundred and thirty patients were included, of which 369 patients (86 %) completed the 5-year follow-up with Knee Society Score evaluation and radiograph examination (study group = 387, control group = 83). RESULTS: There was a significant improvement for all analysed items between pre-operative status and late follow-up. Mean knee score was 93 ± 9 points in the study group and 88 ± 16 points in the control group (p < 0.001). Mean flexion angle was not different (118 ± 11 vs. 114 ± 13 degrees). Mean functional score was 87 ± 16 points in the study group and 71 ± 24 points in the control group (p < 0.001). Survival rate at 5-year follow-up was 98.8 % (vs. 98.0 %) for mechanical revisions only, and 96.4 % (vs. 98.1 %) for all revisions. CONCLUSIONS: The new TKR allowed obtaining significantly better results than the fixed-bearing TKR. These results are in line with the best series published in the current literature, but there was no evidence of any superiority of this TKR against already published standards.

First ray resection arthroplasty versus arthrodesis in the treatment of the rheumatoid foot.

BACKGROUND: Different options exist for the operative treatment of forefoot problems and deformities in rheumatoid arthritis (RA). The current study compared first ray and resection arthroplasty with respect to patient satisfaction, clinical and functional outcome. MATERIALS AND METHODS: In a retrospective study 53 RA patients were investigated with a minimum followup of 2 years after corrective forefoot surgery. Two patient groups were distinguished: One group had been treated with arthrodesis of the first metatarsophalangeal (MTP) joint whereas the other group had been treated with a first ray resection arthroplasty. Both groups underwent resection arthroplasty at the lesser metatarsal heads. Our arthrodesis patients were significantly younger than patients with resection arthroplasty. Five patients had been treated bilaterally so that the results of 58 feet were analyzed. RESULTS: Patient satisfaction was lower in the arthrodesis group as compared to the resection arthroplasty patients. However, the arthrodesis patients revealed better functional results and showed a push-off from the hallux. No significant radiographic difference was seen in the mean hallux valgus angles. Younger patients revealed a higher disease activity and a worse general health status than older patients. Pedobarographic results demonstrated significant differences in selected foot regions, predominantly in the hallux. Peak pressures were significantly higher in the lateral midfoot and the hallux after arthrodesis as compared to the resection arthroplasty group. CONCLUSION: Patients with arthrodesis revealed better foot function during the dynamic roll-over process even though the resection arthroplasty patients were subjectively more satisfied.

Learning curve in navigated total knee replacement. A multi-centre study comparing experienced and beginner centres.

This study analyzes the OrthoPilot navigation system's (Aesculap, Tuttlingen, FRG) learning curve in beginner vs. experienced centres. We conducted a prospective, controlled, multi-centre study in 13 European orthopedic centres. Overall, 368 total knee replacements (TKR) were included in this study, with 150 TKR performed in experienced centres (control group) and 218 TKR in beginner centres (study group). The study parameters were implantation accuracy, clinical outcome, operation time and complications. No difference was found between both groups, except for operating time which was significantly longer in the study group. However, this increase in operating time disappeared after 30 implantations in all beginner centres. So, we conclude that the system's learning curve levels off at this point. Given the high accuracy of implantation when using the OrthoPilot navigation system, we believe this learning curve to be acceptably low.

Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case-control study of 235 cases compared with 235 conventionally implanted prostheses.

The aim of the study was to assess the consistency of the non-image-based navigation system OrthoPilot, Aesculap, Tuttlingen, Germany, in total knee arthroplasty (TKA) implantation in 5 European centers. Two hundred thirty-five TKAs implanted with this navigation system were matched (according to severity of the preoperative coronal deformation and body mass index) to a historical control group of 235 TKAs implanted with a conventional technique. Consistency of implantation was studied on a 3-month postoperative radiological control with coronal long-leg and sagittal standard x-rays. The use of the OrthoPilot navigation system allowed a statistically significant improvement in the consistent placement of both tibial and femoral components. In accordance with current literature, survival of the navigated implanted prostheses is expected to be longer.

Advanced navigation planning including soft tissue management.

The OrthoPilot TKA Version 4.2 (B. Braun-Aesculap, Tuttlingen, Germany) offers software support for orthopedic surgeons. The system provides nearly normal manual workflow, creates perfect cuts, allows for sophisticated management of soft tissue, and respects individual anatomies. The OrthoPilot TKA Version 4.2 displays information to guide surgical decisions. However, surgeons decide if the information will be used during the resection. The most important advancements in the Version 4.2 software are the calculation of perfect rotation of the femoral component and optimal gap balancing.

Experience using the latest OrthoPilot TKA software: a comparative study.

The OrthoPilot (Aesculap, Tuttlingen, Germany) Knee Navigation System represents a computed tomography (CT)-free system. In older software versions, a rigid-body at the iliac crest was necessary to calculate the centre of the hip. The latest software versions, 3.0 and 4.0, use a new mathematical algorithm to reconstruct the mechanical axis. Using the OrthoPilot system, an intraoperative cinematic study can be done that results in calculation of the mechanical axis and navigation of resection cuts. According to flexion- and extension-gap balancing, the anterior/posterior (a.p.) position and rotation of the femoral component also are navigated. Thirty navigated SEARCH (Aesculap, Tuttlingen, Germany) total knee arthroplasties (TKA) using the software version 3.0 of an uninterrupted series were evaluated, versus 30 navigated knees using older software and a manual group. Results concerning alignment were determined to be superior to the older navigation and manual groups. The number of cases with a good mechanical axis, 0; low; or 2 of deviation from optimum, was reached in 17 of the manual, 19 of the older-version, and 27 of the newer-version navigation cases. More features were solved in a convincing manner. The numbers of ouliers were diminished. Navigation in TKA using the OrthoPilot has become more safe and effective.