Rolf Miehlke

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

This study analyzes the OrthoPilot navigation systems (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 systems 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.

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.

In Vitro Knee Wear, Kinematics, and Particle Morphology Among Different Bearing Geometries in a Mobile Bearing Knee System

Excellent clinical long term results were reported from individual clinical centers for both of the two fundamental design principles—fixed and mobile bearing knee designs. Several pre-clinical studies are dealing with a direct comparison between fixed and mobile bearing knee replacements, but to our knowledge there is no published data comparing the in vitro wear and kinematic behaviour of mobile bearing designs with floating, rotating and posterior stabilized gliding surfaces. The objective of our study was to evaluate the influence of the tibio-femoral bearing type on abrasive wear, tibio-femoral kinematics and particle release for a mobile bearing knee system with three different design alternatives. Wear simulator testing on 12 e.motion® TKA devices (Aesculap, Germany) was performed according to ISO 14243-1. The knee replacements were tested for 5 million cycles on a customized 4 station knee wear simulator (Endolab, Germany) in the bearing configurations floating platform (FP), ultra-concruent rotating platform (UC) and posterior stabilized (PS). The amount of wear in the polyethylene gliding surfaces was estimated to 4.4±0.9 mg/million cycles (FP design) to 2.3±0.1 mg/million cycles (UC) and 5.2±1.0 mg/million cycles (PS). The amplitudes of A/P displacement during 5 million cycles showed a mean value of 3.7±0.33 mm (FP design), 2.3±0.14 mm (UC) and 2.9±0.26 mm (PS). For the I/E rotation angle, the amplitudes of the recorded mean values were 6.3°±0.82° (FP design), 3.7±0.41° (UC) and 4.9°±0.48° (PS). The polyethylene particle release (mean size and morphology) is comparable for the mobile bearing articulations FP, UC, and PS. The present study demonstrates the influence of different mobile bearing types on abrasive wear, tibio-femoral kinematics, and particle release under elimination of bearing material influences.

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.

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.

Clinical Results of a Total Knee Prosthesis with Floating Platform at 5.5 Years

In this study, 117 patients who had received the e.motion FP prosthesis between 2001 and 2003 were followed up for 5.5 years to assess the clinical and radiological outcomes and survival of this mobile platform prosthesis. As this design is intended to improve the mobility of the replaced knee, particular emphasis was placed on the clinical and functional results. The hypothesis was that they would be comparable to the excellent results reported in the literature of state-of-the-art total knee arthroplasty. After 66months, the average Knee Society clinical and functional scores were 93.8 points (KSS-C) and 90.5 (KSS-F) points, respectively. The clinical and radiographical results were excellent, with a low rate of anterior knee pain of 2.3 %.