Prosthetic Hip dislocations remain one of the most common major complications after total hip arthroplasty procedures, which has led to much debate and refinement geared to the optimization of implant and bearing options, surgical approaches, and technique. The implementation of larger femoral heads has afforded patients a larger excursion distance and primary arc range motion before impingement, leading to lowered risk of hip dislocation. However, studies suggest that while the above remains true, the use of larger heads may contribute to increased volumetric wear, trunnion related corrosion, and an overall higher prevalence of loosening, pain, and patient dissatisfaction, which may require revision hip arthroplasty. More novel designs such as the dual mobility hip have been introduced into the United States to optimize stability and range of motion, while possibly lowering the frictional torque and modes of failure associated with larger fixed bearing articulations. Therefore, the aim of this study is to compare the effect of bearing design and anatomic angles on frictional torque using a clinically relevant model8. Two bearing designs at various anatomical angles were used; a fixed and a mobile acetabular component at anatomical angles of 0°,20°,35°,50°, and 65°. The fixed design consisted of a 28/56mm inner diameter/outer diameter acetabular hip insert that articulated against a 28mm CoCr femoral head (n=6). The mobile design consisted of a 28mm CoCr femoral head into a 28/56mm inner diameter/outer diameter polyethylene insert that articulates against a 48mm metal shell (n=6). The study was conducted dynamically following a physiologically relevant frictional model8. A statistical difference was found only between the anatomical angles comparison of 0vs65 degrees in the mobile bearing design. In the fixed bearing design, a statistical difference was found between the anatomical angles comparison of 20vs35 degrees, 20vs50 degrees, and 35vs65 degrees. No anatomical angle effect on frictional torque between each respective angle or bearing design was identified. Frictional torque was found to decrease as a function of anatomical angle for the fixed bearing design (R2=0.7347), while no difference on frictional torque as a function of anatomical angle was identified for the mobile bearing design. (R2=0.0095). These results indicate that frictional torque for a 28mm femoral head is not affected by either anatomical angle or bearing design. This data suggests that mobile design, while similar to the 28mm fixed bearing, may provide lower frictional torque when compared to larger fixed bearings >or= 32mm8. Previous work by some of the authors [8] show that frictional torque increases as a function of femoral head size. Therefore, this option may afford surgeons the ability to achieve optimal hip range of motion and stability, while avoiding the reported complications associated with using larger fixed bearing heads8. It is important to understand that frictional behavior in hip bearings may be highly sensitive to many factors such as bearing clearance, polyethylene thickness/stiffness, polyethylene thickness/design, and host related factors, which may outweigh the effect of bearing design or cup abduction angle. These factors were not considered in this study

Introduction. Total-knee-arthroplasty (TKA) is a well-established method to restore the joint function of the human knee. Different types of TKA designs are clinically available which can be divided in two main groups, the posterior-cruciate- ligament (PCL) sacrificing and retaining group. However, pre-operatively it is often difficult to plan for one or the other. Therefore, the research question was: Is it possible to develop a TKA bearing design which works for both the cruciate sacrificing and retaining technique? A medial-congruent (MC) bearing design was developed, characterized by a high medial sagittal conformity and lower lateral sagittal conformity, which can be used for both cruciate ligament states. This study compares the laxity and kinematics of this MC design to a contemporary PS design for the cruciate sacrificing technique and to a contemporary CR design for the cruciate retaining technique. Methods. Four specimen-specific computer models of the human knee, consisting of a femur, tibia and fibula bone as well as the contribution of the ligaments and capsule, were virtually implanted with three TKA designs in four constellations: 1) MC without PCL, 2) MC with PCL, 3) contemporary PS without PCL and 4) contemporary CR with PCL following the design specific surgical technique and tibia slopes. Laxity tests in internal-external rotation (moment ± 4 Nm) were performed with the implanted models for a weight bearing case (500N compression). In addition, a high demanding activity (lunge) was simulated. The resulting averaged laxities and kinematics were analysed and compared to each other. Results. When sacrificing the PCL, MC showed lower medial laxity throughout flexion and higher lateral laxity above 60° flexion compared to the PS design. When retaining the PCL, the MC resulted in lower medial laxity throughout flexion, lower lateral laxity in extension and similar lateral laxity in flexion compared to the CR design. When sacrificing the PCL in the lunge activity, the MC design had a more posterior position throughout flexion on both condyles until deep flexion when the engagement of the cam/spine occurred for the PS design and posterior motion of the medial condyle during mid-flexion as opposed to anterior motion for the PS design. When retaining the PCL in the lunge-activity, the MC design had a more posterior position throughout the activity, and similar medial and lateral condyle motion throughout flexion compared to the CR design. Conclusion. When sacrificing the PCL, MC behaved similar to a contemporary PS design with more medial stability, more lateral laxity in deep flexion, and a posterior position during a lunge activity that did not depend on a cam/spine mechanism. When retaining the PCL, MC behaved similar to a contemporary CR design with more medial stability, similar lateral laxity in deep flexion, and a posterior position during a lunge activity demonstrating that the increased medial conformity did not cause a kinematic conflict with the retained PCL. These findings illustrate the concept that the MC design can be used for both the PCL sacrificing and retaining technique

Total knee arthroplasty using navigation system is known to be more effective than conventional methods in achieving more accurate bone resection and neutral alignment. Mobile bearing is also known to reduce wear and automatically correct rotational mal-alignment of the tibia but the long-term follow-up results of more than 10 years are extremely rare. The purpose of this study is to investigate the results of clinical and radiologic long-term follow-up and complications of total knee arthroplasty using navigation and multi-directional mobile bearing. From 2003 to 2006, a total of 111 navigation TKAs using multi-directional mobile bearing design were carried out and reviewed retrospectively. TKAs were performed by two experienced surgeons at one institute. Of the 111 patients, 102 were women and 9 were men. The mean duration of follow-up was 11.4 ± 1.0 years (range, 10.1 to 14.08 years). Clinical outcomes were evaluated in terms of Knee Society Score, Hospital for Special Surgery score, Western Ontario and McMaster University (WOMAC) score, range of motion and complications. Long-term radiological outcomes and survival rates were evaluated at least 10 years. Average preoperative HSS score was 66.5 ± 9.8 and KSS pain and function score were 25.0 ± 11.8 and 44.5 ± 12.3, respectively. Scores improved to 94.1 ± 8.2, 46.6 ± 11.6 and 88.2 ± 14.6 at the last follow up, respectively. Mean preoperative WOMAC scores of 75.8 ± 16.5 improved to 13.8 ± 16.0 at last follow-up. Five knees required re-operation, two for liner breakage for liner wear, one for distal femoral fracture and one for infection. The estimated 10-year prosthesis survival rates for any reason and for prosthesis-related problems were 95.5% and 97.4%, respectively. TKAs using each techniques resulted in similar good clinical outcomes and post-operative leg alignments. Robotic and navigation TKA appeared to reduce the number of postoperative leg alignment outliers and revision rate compared to conventional TKA

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 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, How-medica 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). Thirty-three patients with a total of forty-two consecutive primary cemented TKA were included in a prospective, randomised study at Leiden University Medical Centre. There were no significant differences among the two groups with regard to age (66. 5 ± 12. 1 years). The pre-operative Knee Society Score did not differ significantly between the two groups. At the one-year follow-up the PS group showed a significantly lower function score (p=0. 04) compared to the mobile bearing group. 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. 003 ± 0. 192 mm and the mobile bearing knee tibial components subsided 0. 057 ± 0. 082 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 the 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 wide 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. Mobile bearing, Posterior Stabilised, RSA, Kinematics

INTRODUCTION

Wear and polyethylene damage have been implicated in up to 22% of revision surgeries after unicompartmental knee replacement. Two major design rationales to reduce this rate involve either geometry and/or material strategies. Geometric options involve highly congruent mobile bearings with large contact areas; or moderately conforming fixed bearings to prevent bearing dislocation and reduce back-side wear, while material changes involve use of highly crosslinked polyethylene. This study was designed to determine if a highly crosslinked fixed-bearing design would increase wear resistance.

It is accepted that larger diameter heads are more difficult to dislocate due to the increased distance the head has to travel to come out of the cup. Currently larger femoral heads are being used for their resistance to dislocation however, there remains little reporting on the effect of design of cup on jump distance. Monoblock metal on metal cups, which were designed for hip resurfacing are typically less than a hemisphere internally in order to increase the range of motion (ROM) needed when the femoral neck is retained. This does however also reduce the jump distance. We investigated several designs of cup with a variety of head sizes in order to compare ROM using a computer range of motion tool and a two dimensional jump distance with the cup at 45 degrees inclination.

Jump distances were calculated for: Internally hemispheric cups in 28, 32 and 36mm bearing diameters; 28, 40 and 44mm polyethylene liners which were hemispheric but with an additional 2mm cylinder and a 0.7mm chamfer at the equator (Trident, Stryker, Mahwah, USA); 38, 48 and 54mm monoblock metal on metal resurfacing cups with a 3.5mm offset (BHR, Smith and Nephew, Memphis, USA); 40, 48, 58 dual mobility cups with an anatomic rim (Restoration ADM, Stryker, Mahwah, USA)

Range of motion modeling was carried out using custom-written software according to a previously published method2 with 5 degrees of pelvic tilt and a standard femoral component. For the present study, range of motion was assessed on a standard stem with a 132° neck angle. Inclination of the cup was set to 45° and anteversion to 20°. For each implant tested, the total ROM was computed in flexion/extension, ab/adduction, and int/external rotation.

Components tested for range of motion were: Trident 32, 36, 40 and 44mm Internal Diameter; Hemispheric 28 and 32mm Internal Diameter cups; MITCH TRH MoM Monoblock Resurfacing Cup (Stryker EMEA, Montreux, Switzerland) 46mm cup bearing diameter with a 2.75mm offset bore; Dual Mobility 40, 46 and 58mm cups. The metal on metal monoblock cups had a very high range of motion but a 48mm head has only a similar jump distance to a hemispheric 36mm design. The designs with the cylinder and chamfer have a markedly higher jump distance than their hemispheric equivalents but slightly reduced ROM. Interestingly, the dual mobility design has almost double the jump distance of an equivalently sized metal on metal resurfacing type cup and a higher jump distance than an equivalent head size in a conventional unipolar design. The dual mobility design has similar ROM to a 40mm head in the hemisphere with cylinder and chamfer design. ROM is slightly higher in the hemispheric and sub-hemispheric designs but this model does not take into account bony or soft tissue impingement. The role of design of ace-tabular component has a great effect on the range of motion and jump distance of bearings.

INTRODUCTION

The intact, healthy human knee joint is stable under anterior-posterior (AP) loading but allows for substantial internal-external (IE) laxity. In vivo clinical studies of the intact knee consistently demonstrate femoral rollback with flexion (Hill et al., 2000, Dennis et al., 2005). A tri-condylar, posterior stabilized (PS) total knee arthroplasty (TKA) with a rotating platform bearing (TKA-A) has been designed to address these characteristics of the intact knee. The third condyle is designed to guide the femoral component throughout the entire flexion arc (AP stability and femoral rollback with flexion), while the rotating platform bearing allows for IE rotation.

This study used a computer model to compare the AP and IE laxity of a new TKA-A to that of two clinically established TKAs (TKA-B: rotating PS TKA, TKA-C: fixed PS TKA) and to demonstrate improvements in AP stability, IE rotation, and femoral rollback.

Purpose. The aim of the present study was to look at survivorship and patient satisfaction of a fixed bearing unicompartmental knee arthroplasty with an all-polyethylene tibial component. Materials and Methods. We report the survivorship of 91 fixed bearing unicompartmental arthroplasties with all-polyethylene tibial components (Preservation DePuy UK), which were used for medial compartment osteoarthritis in 79 patients between 2004 and 2007. The satisfaction level of patients who had not undergone revision of the implant was also recorded. For comparison, we reviewed 49 mobile bearing unicompartmental arthroplasties (Oxford UKA Biomet UK Ltd), which had been used in 44 patients between 1998 and 2007. Results. Mean length of follow up of patients with the fixed bearing implant was 44.7 months (range 24 - 74 months) and for the mobile bearing replacement, the mean follow up was 67.6 months (24 - 119). In the fixed bearing design, at maximum follow up period of 74 months, 8 implants (8.8%) had been revised (or were listed for revision) to total knee replacement and in the mobile bearing design over the maximum follow up period of 119 months there had been only one revision (2.0%). Patients who had not undergone revision were asked if they were satisfied with their knee following the unicompartmental arthroplasty. In the fixed bearing design, 83.5% said that they were satisfied with the outcome of the operation compared to 93.9% of the patients receiving the mobile bearing design. Conclusion. We conclude that there is a higher incidence of revision of this fixed bearing design using an all-polyethylene tibial component compared to the mobile bearing design. We found that those patients who had not required revision had a lower rate of satisfaction with the fixed bearing compared to the mobile bearing design

Introduction. In an effort to provide a TKA bearing material that balances resistance to wear, mechanical failure and oxidation, manufacturers introduced antioxidant polyethylene. In many designs, this is accomplished through pre-blending the polymer with the antioxidant before consolidation and radiation crosslinking. This study reports the wear performance (in terms of thickness change) of a hindered phenol (PBHP) UHMWPE from analysis of an early series of knee retrievals and explores these questions: 1) What is early-time performance of this new bearing material? 2) Is there a difference in performance between fixed and mobile bearings in this design? 3) How does quantitative surface analysis help understand performance at the insert-tray modular interface?. Methods. A series of 100 consecutive Attune™ knee inserts (DePuy Synthes, Warsaw, IN) received at revision by an IRB approved retrieval laboratory between September 2014 and March 2019 were investigated. In vivo duration was 0–52 months. Both the fixed bearing design (n=74) and the rotating platform mobile bearing design (n=26) were included. Dimensional change was determined by measurement of each insert and compared to the as-manufactured dimensions, provided by the manufacturer. The insert-tray interfaces under the loaded bearing zones were analyzed with light interferometry using an optical surface profiler (NewView™ 7300, Zygo, Middlefield, CT). Statistical analyses to explore relationships between measured variables were conducted using SPSS. Results. Mean total through-thickness change of the inserts was 0.052 mm. Mean rate of thickness change for all inserts having in vivo duration > 12 months was 0.038 mm/year (fixed bearing 0.042, mobile bearing 0.029 mm/year). The rate of thickness change for all inserts showed a decreasing trend with duration that was not statistically significant, (rho -.244, p=.094); however, the mobile bearing cohort alone showed a significant decrease in thickness change rate with duration (rho= −.659; p=.014). Surface roughness (Sa) of the distal surface of the UHMWPE inserts under the bearing areas averaged 1.24 µm (range 0.12 – 8.53) and peak-to-valley height (PV) averaged 27.1 µm (range 4 – 95). Sa and PV both showed a decreasing trend with duration in vivo in the mobile bearing inserts, but that trend did not reach statistical significance (p= 0.05 criterion). Neither Sa nor PV showed correlation with measured thickness change. Discussion. This study indicates that the rate of thickness change of a relatively new antioxidant cross-linked bearing material is very similar to other reported wear rates of crosslinked knee inserts. Lower wear rate of mobile bearing inserts compared to fixed bearings also is consistent with earlier published studies. Direct comparison between quantitative thickness change and objective, quantitative surface metrology on the same series brings new information to the arena of measuring and reporting “wear” of UHMWPE and underscores the importance of the distinction between visual damage and actual thinning of the bearing. The systematic surface analysis of the modular interfaces showing that surface roughness (Sa) and total damage feature topography (PV) trend downward with in vivo duration of mobile bearings supports the hypothesis that relative motion at that interface may ‘polish out’ the surface topography over time. For any figures or tables, please contact authors directly

Introduction. In total knee arthroplasty, the alignment of leg depends on the alignment of the component. In unicompartmental knee arthroplasty, it is determined by the thickness of the implant relative to the bone excised mostly. After initial scepticism, UKA is increasingly accepted as a reliable procedure for unicompartmental knee osteoarthritis with the improvements in implant design, surgical technique and appropriate patient selection. Recently, computer assisted UKA is helpful in accuracy and less invasive procedure. But, fixed bearing or mobile bearing in UKA is still controversy. We compared the early clinical and radiological results of robot-assisted unicompartmental knee arthroplasty using a fixed bearing design versus a mobile type bearing design. Materials and Methods. A data set of 50 cases of isolated compartmental degenerative disease that underwent robot-assisted UKA using a fixed bearing design were compared to a data set of 50 cases using a mobile bearing type design. The operations were performed by one-senior author with the same robot system. The clinical evaluations included the Knee Society Score (knee score, functional score) and postoperative complications. The radiological evaluations was assessed by 3-foot standing radiographs using the technique of Kennedy and White to determine the mechanical axis and femoro-tibial angle for knee alignment. Operative factors were evaluated including length of skin incision, operation time, blood loss, hospital stay and intraoperative complications. Results. There were no statistically significant differences in operation time, skin incision size, blood loss and hospital stay. (p > 0.05) There were no significant differences in Knee Society Scores at last follow up. An average preoperative femorotibial alignment was varus alignment of −1° in both groups. Postoperative patients with fixed-bearing implants had an average +2.1° valgus and the patients with mobile bearing implants had +5.4° valgus in femorotibial alignment, which was different.(p<0.05) There was one case of medial tibia plateau fracture in fixed bearing group in 3 months postoperatively. And there were one case of liner dislocation with unstable knee in 6 weeks postoperatively and one case of femoral component loosening in 1 year postoperatively in mobile bearing group. There was no intraoperative complication. The average preoperative knee score was 45.8, which improved to 89.5 in fixed bearing group and 46.5, which improved to 91.2 in mobile bearing group at last followup. The average preoperative function score was 62.4 which improved to 86.5 in fixed bearing group and 60.7 which improved to 88.2 in mobile bearing group at last followup. Conclusion. In ourearly experience, two types of bearing of robot-assisted UKA groups showed no statistical differences in clinical assessment but there was statistical difference in postoperative radiological corrected alignment. But in aspect of early complications, we think that mobile bearing seems to be requiring more attention in surgery

Aim: This study aims to establish whether or not mobile bearing TKR delivers the often stated benefits improved function and range of motion when compared to its fixed bearing equivalent. Methods and Results: A total of 357 patients undergoing TKR were randomly allocated to receive either a Mobile Bearing (181 knees) or a Fixed Bearing (176 knees) PSTKR. Further subrandomisation into patella resurfacing or retention was performed for both designs. All knees were scored using standard tools (Oxford, AKSS and SF12) preoperatively and at intervals postoperatively by independent observers. The range of motion increased from an average of 96 deg. (pre-op) to an average of 109 deg. at 1 year post-op for both the fixed and mobile bearing design. The management of the patella had no effect in either group. The knee society and knee function scores increased equally for both the fixed bearing and mobile bearing knees with no differences noted. Conclusion: There were no measurable differences in range of motion and clinical outcome scores at 1 year post-op for a mobile bearing design over its fixed bearing equivalent. It is likely that any potential advantages of a mobile bearing design will manifest in longevity rather than function

Introduction. Total-knee-arthroplasty (TKA) is used to restore knee function and is a well-established treatment of osteoarthritis. Along with the widely used fixed bearing TKA design, some surgeons opt to use mobile bearing designs. The mobile-bearing TKA is believed to allow for more freedom in placement of the tibial plate, greater range of motion in internal-external (IE) rotation and greater constraint through the articular surface. This current study evaluates 1) the kinematics of a high constraint three condyle mobile bearing TKA, 2) the insert rotation relative to the tibia, and 3) compares them with the intact knee joint kinematics during laxity tests and activities-of-daily-living (lunge, level walking, stairs down). We hypothesize that 1) in contrast to the intact state the anterior-posterior (AP) stability of the implanted joint increases when increasing compression level while 2) maintaining the IE mobility, and that 3) the high constraint does not prevent differential femorotibial rollback during lunge. Methods. Six fresh-frozen human cadaveric knee joints with a mean donor age of 64.5 (±2.4) years and BMI of 23.3 (±7.3) were tested on a robot (KR140, KUKA) in two different states: 1) intact, 2) after implantation of a three condyle mobile bearing TKA. The tibia plateau and the insert of each tested specimen were equipped with a sensor to measure the insert rotation during testing. Laxity tests were done at extension and under flexion (15°, 30°, 45°, 60° 90°, 120°) by applying subsequent forces in AP and medial-lateral (ML) of ±100N and moments in IE and varus-valgus (VV) rotation (6Nm/4Nm, 12 Nm/-). Testing was performed under low (44N) and weight bearing compression (500N). Loading during the lunge, level walking and stairs descent activity was based on in-vivo data. Resulting data was averaged and compared with the kinematics of the intact knee. Results. Increasing the joint compression resulted in a 90% reduced AP laxity (increased stability) for the implanted case while the intact knee laxity stayed similar. In high compression the implanted IE mobility was reduced by 45% for low and mid flexion angles and by 20% for high flexion angles, while the intact knee IE mobility was reduced by 30% at low and mid flexion and 20% at high flexion. The trend of the rollback behaviour was similar for the implanted and intact joints and showed higher lateral than medial rollback (Figure 3 A). The average insert-rotation was highest during level walking (+ 5° to −2.5°) and lowest during lunge (−3.5° to 2.5° over flexion). Conclusion. The established hypotheses were supported by the above listed results. Increasing the joint compression in the mobile bearing design stabilized the knee in the AP direction and maintained the IE mobility similar to the intact knee. This can be directly related to the design of the TKA articular surface, which has a high impact on constraint as soon as the joint is loaded. However, the high constraint of the TKA did not prevent differential rollback

Introduction. Special high-flexion prosthetic designs show a small increase in postoperative flexion compared to standard designs and some papers show increased anterior knee pain with these prosthesis. However, no randomised controlled trails have been published which investigate difference in postoperative complaints of anterior knee pain. To assess difference in passive and active postoperative flexion and anterior knee pain we performed a randomized clinical trial including the two extremes of knee arthroplasty designs, being a high flex posterior stabilized rotating platform prosthesis versus a traditional cruciate retaining fixed bearing prosthesis. We hypothesised that the HF-PS design would allow more flexion, due to increased femoral rollback with less anterior knee pain than the CR design. We specifically assessed the following hypotheses:. Patients have increased flexion after HF-PS TKA compared to CR TKA, both passive and active. Patients show an increased femoral rollback in the HF-PS TKA as compared to the CR TKA. Patients receiving a HF-PS TKA design report reduced anterior knee pain relative to those receiving the CR TKA. Methods. In total 47 patients were randomly allocated to a standard cruciate retaining fixed bearing design (CR) in 23 patients and to a high-flexion posterior stabilized mobile bearing design (HF-PS) in 24 patients. Preoperative and one year postoperative we investigated active and passive maximal flexion. Furthermore, we used the VAS pain score at rest and during exercise and the Feller score to investigate anterior knee pain. A lateral roentgen photograph was used to measure femoral rollback during maximal flexion. Results. The HF-PS did show a significantly higher passive postoperative flexion; 120.8° (SD 10.3°) vs. 112.0° (SD 9.5°) for the CR group (p=0.004). The active postoperative flexion, VAS-pain score and Feller score did not show significant differences between both groups. Sub analysis with the HF-PS group showed a higher VAS-pain for the patients achieving ≥130° of flexion; 30.5 (SD 32.2) vs. 12.2 (SD 12.5) (p=0.16). The rollback was significantly lower in the CR group compared to the HF-PS group; 4.4 (SD 3.0) vs. 8.4 (SD 2.1). Conclusion. The present study showed a significant higher passive flexion in the Posterior Stabilised-High Flexion mobile bearing compared to a Cruciate Retaining fixed bearing prosthesis. However, this difference disappeared when comparing active flexion. The difference in passive flexion was probably related to a significantly lower rollback causing impingement in the CR prosthesis. No difference in anterior knee pain was found between both groups. However, a suggestion is raised that achieving high-flexion might lead to more patellofemoral complaints/anterior knee pain

There is ongoing debate on the benefits of fixed versus mobile bearing Unicompartmental Knee Replacement (UKR). We report the results from a randomised controlled trial comparing fixed and mobile bearing of the same UKR prosthesis. Forty patients were randomized to receive identical femoral components and either a fixed or mobile bearing tibial component. At 6.5 years follow-up 37% of the mobile bearing design had been revised and 14% for the fixed bearing design. The main reasons for revision were pain and loosening. These results were compared with data from The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) that show a cumulative percent revision of 24.2% for the mobile bearing Preservation UKR at 6.5 years. All locally explanted mobile bearings were examined microscopically, and 83% demonstrated significant backside wear. Constraint on the undersurface of the bearing coupled with a congruent upper surface may have contributed to the excessive revision rate. This is the first randomised controlled trial examining mobile and fixed variations of the same UKR prosthesis and shows this design of UKR with the mobile bearing has an unacceptably high revision rate and patients with this knee design should be closely monitored

High flexion designs are intended to provide a greater range of knee flexion and possibly improve flexion in stiff knees. This study assessed the effects of two implant designs. A posterior stabilised high flexion mobile bearing (MB) design vs a cruciate retaining standard fixed bearing (FB) design. The aim of this study was to assess whether implant design has an effect on the functional outcome one year after total knee arthroplasty (TKA). Methods. Ninety patients with knee osteoarthritis on the waiting list for unilateral TKA were recruited and randomly allocated to either the MB or FB group. Patients were assessed between one and four weeks before, and one year after TKA. Primary outcome was knee flexion during high flexion activities of daily living such as stair ascending and descending and squatting as measured using gait analysis. Knee flexion in long sitting using a manual goniometer and the WOMAC were also recorded. Two sample t-tests were used to investigate statistical differences between the two groups pre- and postoperatively. Results. Average age was 69 years. Thirty-three received the MB design and 39 the FB design. Age, gender balance and pre-operative flexion (112 and 113 degrees in the FB and MB groups respectively) were the same in both groups. There were no statistically significant differences in post-operative knee flexion during functional activities. Knee flexion in sitting and the stiffness and function components of the WOMAC were also similar between the two groups (p>0.05). However, post-operatively the WOMAC pain component was slightly higher in the MB group (4.2 vs 2.4 points, p<0.05). Conclusion. In our patient group with a mean pre-operative flexion of 112.7 degrees, the high flexion mobile bearing design did not improve knee flexion during high flexion functional activities of daily living

The purpose of this study was to compare the clinical and radiological results of the PFC flex mobile bearing design with those of the LPS flex fixed bearing design in high-flex total knee arthroplasty. Between January 2005 and November 2006, forty-six patients who received PFC flex mobile bearing prosthesis in one knee and LPS flex fixed bearing prosthesis in the contralateral knee followed up for a minimum 2 years were evaluated. Clinical results were assessed using the ROM, HSS score, the Knee rating systems of the knee society, WOMAC score and SF-36. Radiological results were evaluated tibio-femoral angle and loosening or osteolysis of components. We subdivided preoperative less 90 degree and more 90 degree in each group. Mean ROM range of last follow up was increased to 131.1 degree in LPS group and 130.1 degree in PFC group. But there was no significant difference between the two groups. HSS score, knee pain and function score, WOMAC score, SF-36 score didn’t differ significantly between two groups. But descending stairs, rising from sitting, bending to the floor more improved significantly in LPS group. T-F angle was changed from preoperative 8.2 degree varus to a postoperative 4.8 degree valgus. No knee had aseptic loosening or osteolysis. Postoperative ROM was increase significantly in both groups. We found no significant differences between the two groups with regard to clinical and radiological parameters excepts descending stairs, rising from sitting, bending to the floor in WOMAC score. There was no aseptic loosening or osteolysis but needed long term observation about these concerns

Introduction The historical degradation of polyethylene produced a direct relationship between contact stress and wear in knee prostheses(. 1. ). However, with the recent introduction of stabilised polyethylene and designs with reduced contact stress, the significance of this relationship has not been re-assessed. The purpose of this study was to analyse the contact mechanics of three currently available knee designs (two rotating platform and one fixed bearing) prior to and after long term simulator wear testing. Materials and Methods Implants (six of each design) were loaded with 2600N at flexion angles of 0°, 30° and 60°. Contact areas were measured using Fuji Pre-scale pressure sensitive film, which was scanned and digitised using Image Pro Plus software. Results The average contact stresses of the worn knee components are shown in Figure 1. Previously reported wear results for the three designs are shown in Figure 2 (. 1. ,. 2. ). Stresses reduced slightly following wear testing. Conclusion The three designs tested produced stresses below the elastic limit of the polymer at all flexion angles. The two rotating platform designs had significantly reduced stress compared to the fixed bearing design. Both rotating platform designs tested de-couple the rotation and produce reduced cross-shear compared to the fixed bearing design. It is postulated that both low stress and reduced cross-shear are important in reducing the wear of knee prostheses

This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implantation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured. Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1,500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration(500 ± 287m;e;), and the fixed bearing configuration (500 ± 286m;e;). In response to 10° internal rotation, this strain increased to 782 ± 371m;e; and 1000± 389m;e; for the mobile and fixed tibial component, respectively. In 10° external rotation, minimal principal strain decreased to 421 ± 233m;e; for the mobile bearing, but increased to 632 ± 293m;e; for the fixed bearing. These differences between mobile and fixed bearing scenarios were highly statistically significant. For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia than the fixed bearing tibial component. The difference in strain levels may be of importance for bone remodeling and osseointegration

Aim: This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Methods: Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implementation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured. Results: Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1′500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration (500 ± 287 με), and the fixed bearing configuration (500 ± 286 μ ε). In response to 10° internal rotation, this strain increased to 782 ± 371 μ ε and 1000 ± 389 μ ε for the mobile and fixed tibial component, respectively. In response to 10° external rotation, minimal principal strain decreased to 421 ± 233 μ ε for the mobile bearing, but increased to 632 ± 293 μ ε for the fixed bearing. These differences between mobile and fixed bearing scenarios were statistically highly significant. Conclusion: For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia as the fixed bearing tibial component. The difference in strain levels may be of importance to understand bone remodeling and osseointegration