Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up. Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses. Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3–4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55–64 (hazard ratio 1.9; confidence interval 1.1-3.3, p=0.03). No association was found with gender, BMI or ASA. Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship

Objectives. Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty with isolated medial or lateral compartment osteoarthritis. However, polyethylene wear can significantly reduce the lifespan of UKA. Different bearing designs and materials for UKA have been developed to change the rate of polyethylene wear. Therefore, the objective of this study is to investigate the effect of insert conformity and material on the predicted wear in mobile-bearing UKA using a previously developed computational wear method. Methods. Two different designs were tested with the same femoral component under identical kinematic input: anatomy mimetic design (AMD) and conforming design inserts with different conformity levels. The insert materials were standard or crosslinked ultra-high-molecular-weight polyethylene (UHMWPE). We evaluated the contact pressure, contact area, wear rate, wear depth, and volumetric wear under gait cycle loading conditions. Results. Conforming design inserts had the lower contact pressure and larger contact area. However, they also had the higher wear rate and volumetric wear. The improved wear performance was found with AMD inserts. In addition, the computationally predicted volumetric wear of crosslinked UHMWPE inserts was less than half that of standard UHMWPE inserts. Conclusion. Our results showed that increasing conformity may not be the sole predictor of wear performance; highly crosslinked mobile-bearing polyethylene inserts can also provide improvement in wear performance. These results provide improvements in design and materials to reduce wear in mobile-bearing UKA. Cite this article: Bone Joint Res 2019;8:563–569

Background. Currently there are various knee prosthesis designs available each with its plus and minus points; there is no general consensus on whether mobile-bearing knees are functionally better than fixed-bearing ones. This study is designed to compare outcomes after total knee arthroplasty with both of the above prostheses. Materials & Methods. 50 patients (68 knees) who'd had a total knee arthroplasty between April 1999 and April 2008 at both Akhtar and Kian Hospitals for primary osteoarthritis were selected. In 30 cases a fixed-bearing knee (Scorpio(r), Stryker) and in the remaining 38 a mobile-bearing prosthesis (Rotaglide(r), Corin Group) was used. Patients' knees were scored before and after the operation according to the Knee Society Scoring System. The mobile-bearing group had an average age of 65 and 34 months' follow-up; in the fixed-bearing group the average age was 69 and the average follow-up 30 months. Results. The average knee score in the mobile-bearing group rose from 29 to 64 while in the fixed-bearing group the score changed from 31 to 68. The average functional score moved from 45 to 67 in the mobile-bearing group and from 34 to 57 in the fixed-bearing group. The average overall score, for the fixed-bearing group, moved from 65 to 125 and in the mobile-bearing group from 75 to 128. Conclusion. In both groups the average knee/functional knee scores increased after the operation and all patients were happy with the results, however statistically there was no meaningful relationship between pre-and post-operation scores. So regarding to our findings, there is no preference between these two types of prosthesis

Aims. Since redesign of the Oxford phase III mobile-bearing unicompartmental knee arthroplasty (UKA) femoral component to a twin-peg design, there has not been a direct comparison to total knee arthroplasty (TKA). Thus, we explored differences between the two cohorts. Patients and Methods . A total of 168 patients (201 knees) underwent medial UKA with the Oxford Partial Knee Twin-Peg. These patients were compared with a randomly selected group of 177 patients (189 knees) with primary Vanguard TKA. Patient demographics, Knee Society (KS) scores and range of movement (ROM) were compared between the two cohorts. Additionally, revision, re-operation and manipulation under anaesthesia rates were analysed. Results. The mean follow-up for UKA and TKA groups was 5.4 and 5.5 years, respectively. Six TKA (3.2%) versus three UKAs (1.5%) were revised which was not significant (p = 0.269). Manipulation was more frequent after TKA (16; 8.5%) versus none in the UKA group (p <  0.001). UKA patients had higher post-operative KS function scores versus TKA patients (78 versus 66, p < 0.001) with a trend toward greater improvement, but there was no difference in ROM and KS clinical improvement (p = 0.382 and 0.420, respectively). Conclusion. We found fewer manipulations, and higher functional outcomes for patients treated with medial mobile-bearing UKA compared with TKA. TKA had twice the revision rate as UKA although this did not reach statistical significance with the numbers available. . Cite this article: Bone Joint J 2016;98-B(10 Suppl B):28–33

Mobile-bearing total knee arthroplasty was developed to provide low contact stress and reasonably unrestricted joint motion. We studied the results of a cementless, posterior cruciate ligament (PCL)-retaining total knee arthroplasty (TKA), with a mobile-bearing insert in rotation and anterior-posterior (AP) translation (Innex. ®. Anterior-Posterior Glide, Zimmer). Kinematic analyses were performed on a series of 51 primary TKA. The patients’ mean age was 71±8 years at operation. Patients were studied at 23 months average follow-up with weight-bearing radiographs at full-extension, 30° flexion and maximum flexion (“lunge” position). Three dimensional position and orientation of the mobile-bearing relative to the femoral and the tibial component during flexion were determined using model-based shapematching techniques. The average weight-bearing range of implant motion was 110°±14°. In flexion, the mobile-bearing was internally rotated 3°±3° with respect to the femoral component (p< 0.0001) and the tibial tray was internally rotated 5°±7° with respect to the mobile-bearing (p< 0.0001). On average, the mobile-bearing did not translate relative to the tibial base plate from full extension to 45° flexion [0±2 mm (range −5 mm to 6 mm)]. However, the mobilebearing did translate anteriorly 1±2 mm (range −2 mm to 9 mm, p< 0.0001) between 45° flexion and maximal flexion. We conclude that the mobile-bearing insert showed a progressive increase in internal rotation during flexion. Most of this rotational mobility occurred between the mobile insert and the tibial base plate. With flexion, AP translation did occur between the femoral component and mobile-bearing, and between the mobile-bearing and tibial base plate, but mobile-bearing translation was unpredictable with this unconstrained design

We prospectively reviewed patients who had undergone a Revision Total Knee Replacement (TKR) to a mobile-bearing arthroplasty. We wanted to assess functional outcome and survival, and to determine whether the perceived advantages of a mobile-bearing arthroplasty could be expanded to the revision situation. We divided the patients into two groups. Group 1 consisted of 40 patients who were revised to a rotating platform, with or without stems and augments, and group 2 consisted of 41 patients revised to a varus-valgus constrained mobile-bearing device that still allowed rotation of the bearing. All were assessed with Knee Society Knee Scores, WOMAC, and New Jersey Knee Scores and standard radiographs by an independent examiner. Group 1 had an average age of 71 years at revision and a follow-up of 5–9 years. Seventy-six percent had excellent or good results with 89% survival at 9 years. Group 2 had an average age of 71 years at revision and a follow-up of 2–5 years. The patient satisfaction score was 8/10 and the normality score was 6.8/10. There was only one case of instability in both groups in a patient with a patellar fracture. A mobile-bearing TKR can be used in the revision situation with acceptable clinical results and patient outcome without compromising the stability or survivorship in the short-term. It has proved to be a “patellar-friendly” procedure with reduced re-operation for patellar complications; however longer-term studies are required to determine whether the rates of polyethylene wear are reduced by the use of a more congruent articulation

Aims. The aims of this retrospective study were to determine the incidence of extra-articular deformities (EADs), and determine their effect on postoperative alignment in knees undergoing mobile-bearing, medial unicompartmental knee arthroplasty (UKA). Patients and Methods. Limb mechanical alignment (hip-knee-ankle angle), coronal bowing of the femoral shaft and proximal tibia vara or medial proximal tibial angle (MPTA) were measured on standing, full-length hip-to-ankle radiographs of 162 patients who underwent 200 mobile-bearing, medial UKAs. Results. Incidence of EAD was 7.5% for coronal femoral bowing of >5°, 67% for proximal tibia vara of >3° (MPTA<87°) and 24.5% for proximal tibia vara of >6° (MPTA<84°). Mean postoperative HKA angle achieved in knees with femoral bowing ≤5° was significantly greater when compared to knees with femoral bowing >5° (p=0.04); in knees with proximal tibia vara ≤3° was significantly greater when compared to knees with proximal tibia vara >3° (p=0.0001) and when compared to knees with proximal tibia vara >6° (p=0.0001). Conclusion. Extra-articular deformities are frequently seen in patients undergoing mobile-bearing medial UKAs, especially in knees with varus deformity>10°. Presence of an EAD significantly affects postoperative mechanical limb alignment achieved when compared to limbs without EAD and may increase the risk of limbs being placed in varus>3° postoperatively. Clinical Relevance. Since the presence of an EAD, especially in knees with varus deformity>10°, may increase the risk of limbs being placed in varus>3° postoperatively and may affect long-term clinical and implant survival outcomes, UKR in such knees should be performed with caution

Aims. Spontaneous osteonecrosis of the knee (SONK) mainly affects the medial femoral condyle, would be a good indication for UKA. The primary aim of this study was to assess the clinical, functional and radiographic outcomes at middle to long-term follow-up, of a consecutive series of fifty UKA used for the treatment of SONK. The secondary aim was to assess the volume of necrotic bone and determine if this influenced the outcome. Patients and Methods. We reviewed 50 knees who were treated for SONK. Patients included ten males and 38 females. The mean age was 73 years (range, 57 to 83 years). The mean height and body weight were, respectively 153 cm (141 ∼171 cm) and 57 kg (35 ∼75kg). All had been operated on using the Oxford mobile-bearing UKA (Zimmer-Biomet, Swindon, United Kingdom) with cement fixation. The mean follow-up period was 8.4 years (range, 4 to 15years). We measured the size (width, length and depth) and the volume to be estimated (width x length x depth) of the necrotic bone mass using MRI in T1-weighted images. The clinical results were evaluated using the Knee Society Scoring System (KSS) and Oxford Knee Score (OKS). The flexion angle of the knee was evaluated using lateral X-ray images in maximum flexion. Results. There were no implant failures, but there were 4 deaths (from causes unrelated to UKA) mean 6.6 years after surgery(5∼8), 3 cases were lost mean 3.3 years after surgery(2∼5). The mean size of the necrotic lesion were 17.2mm (14.7∼25.3) in width, 28.2mm (6.2∼38.3) in length and 11.3mm (3.2∼14.3) in depth. The mean volume of it was calculated to be approximate 5.4 cm. 3. (0.7∼11.1). The mean flexion of the knee, KSS Knee Score, Function Score and OKS increased from a preoperative 128.7 degrees (110 ∼ 140 degrees) to 137.5 degrees (110 ∼ 153 degrees), 52.3 (30 ∼ 64) to 91.3 (87 ∼ 100), 39.7 (15∼ 55) to 90.2 (65 ∼ 100) and 21.6 (12∼ 28) to 40.2 (34∼ 48), respectively at the latest follow-up. At last follow-up all patients had good or excellent OKS. Conclusions. There was a 100% survival rate of the Oxford Phase 3 UKA for SONK in the middle to long-term (up to 15 years after surgery) in this independent study. All patients had good/excellent results at last follow-up and there were no reoperations or major complications. This suggests that Oxford mobile-bearing UKA is a good and definitive treatment for medial femoral SONK, whatever the size of the lesion

Introduction: Many types of prosthesis are currently used for total knee arthroplasty. Controversy exists as to whether mobile-bearing or fixed-bearing implants make any difference in achieving earlier or better movement, resulting in earlier patient discharge. Aim: The purpose of our study was to compare the post-operative recovery and early results of 4 different mobile- and fixed-bearing knee implants. Method: Between 19/7/05 and 15/6/07 202 knees were implanted into 190 patients. Patients were randomly selected for 1 of 4 implants (2 mobile-bearing, 2 fixed-bearing). Outcomes were assessed using the American Knee Society Score (AKSS) and range-of-movement, both pre-operatively and at 1 year post-operatively. Range-of-movement was also recorded on discharge. Results: No significant difference was shown between the individual implant groups and the actual mean pre-operative and 1 year post-operative AKSS knee or functional scores or the change in knee score. A difference was noted however in the change in functional score between the 2 mobile-bearing knees (p=0.03). No significant difference was found between the 4 individual implants or the type of bearing used (mobile- or fixed-bearing) with regards to gender, age, length of stay or range-of-movement. Conclusion: The type of implant used does not affect the early or 12 month outcomes in relation to range-of-movement, length of stay or AKSS knee scores

This randomized clinical trial compares fixed- and mobile-bearing total knee prostheses in terms of the patients’ clinical outcome parameters (Knee Society Clinical Rating, WOMAC, SF-12), range of motion and performance during gait analysis for level-ground walking. Our results show no significant differences in the clinical outcomes and gait performance of the fixed- and mobile-bearing total knee arthroplasties. The purpose of this study was to compare the clinical outcomes and gait parameters of patients with a fixed-bearing or mobile-bearing total knee arthroplasty (TKA). Fifty-five patients were entered into a prospective, randomized clinical trial comparing fixed- versus mobile-bearing TKAs (Genesis II, Smith & Nephew, Memphis, TN). From this patient population, fifteen fixed-bearing and fifteen mobile-bearing TKA patients were matched based on age, sex and BMI to undergo gait analysis. Patients performed trials of level-ground walking at a self-selected velocity while three-dimensional kinetic and kinematic data were collected. The fixed-bearing and mobile-bearing TKA patient groups were comparable regarding Knee Society Clinical Rating (181 ± 22 versus 171 ± 28), WOMAC scores (7 ± 5 versus 9 ± 12), SF-12 and range of motion (121° ± 11° versus 125° ± 6°). Patients with fixed- and mobile-bearing TKAs performed similarly in the gait analysis in terms of their velocity, percent weight acceptance in the operated versus the non-operated limb, peak flexion in stance and swing phases, the support moments and extension moments at the ankle, knee and hip. Decreased peak extension in the mid-stance and swing phases was observed in the operative limb versus the non-operative limb for both fixed- and mobile-bearing TKAs (P=0.02 and 0.04). Decreased peak extension was also observed during mid-stance and swing phases in the mobile-bearing TKAs versus the fixed-bearing TKAs (P=0.064 and 0.052). Fixed-bearing and mobile-bearing TKAs perform similarly in terms of their clinical outcome measures and the kinetics and kinematics of level-ground walking. Funding for this project obtained from Smith & Nephew, Memphis, TN

The benefit of mobile-bearing mechanism in total knee arthroplasty (TKA) has been controversial. The aim of this paper is to analyse the rotation of polyethylene (PE) and its effect on the range of motion (ROM) in mobile-bearing, posterior stabilised TKA (LPS-Flex™, Zimmer Co. Ltd.). Thirty-four consecutive PS-Flex™ TKAs (28 patients) were analysed. Three tantalum markers were inserted in the PE and the tibia (one for medial side and two for lateral side; total six markers). The rotation of the PE and the tibia was analysed in fluoroscopically-controlled radiograph taken at one years in full extension, 90 degrees flexion and passive maximum flexion. The markers in the tibia were identifiable in 19 knees and the analysis was based on these knees. The tibia rotated internally relative to the femur by 7.1± 5.2 degrees (mean ± SD, range −1 to 20 degrees). The amount of tibial rotation has no correlation to ROM. The rotation of the PE relative to the femur was unpredictable showing three knees with external rotation and four knees without rotation (Average; 4.0 ± 4.5 degrees internal rotation). The rotation of the PE on the tibia was 4.2± 5.2 degrees and seven knees (37 %) showed no rotation and 12 knees (63 %) showed less than 5 degrees rotation. There was a positive correlation between the amount of PE rotation on the tibia and ROM, which approached to statistical significance (p = 0.0684). This study has demonstrated that the rotation of the PE on the tibial tray is generally small (< 5 degrees). Because not tibial internal rotation but PE movement on the tibia correlated to ROM, the essential benefit of the mobile-bearing mechanism could be to compensate the rotational mismatch between the components rather than to reproduce normal knee kinematics

Introduction: In contrast to fixed-bearing total knee replacements (TKRs), mobile-bearing TKRs allow for unconstrained kinematics while providing a high congruency between the femoral component and polyethylene inlay. The concept of a mobile-bearing TKR is based on the mobility of the inlay. It has been suggested that inlay mobility may decrease due to the in-growth of fibrous tissue (. Lemaire 1998. ). Previous studies report a loss of inlay mobility between 0% and 50% at an average follow-up time between 1.5 and 6 years postop (. Bradley et al. 1987. , . Stiehl et al. 1997. , Hartfort et al. 2001). However these studies are retrospective and do not define a threshold for inlay mobility. Methods: In this prospective study, 61 mobile-bearing TKRs (SAL, Zimmer) in 60 patients were followed up 3, 12, 24 and 60 months post-op. The implant design allows for 6–9 mm (size dependent) inlay translation in the anteroposterior direction while the rotation is not constrained. A complete 60 month follow-up of 40 patients was available. At each follow-up the knees were X-rayed at 0, 30, 60 and maximal flexion. Using the 4 X-rays from each follow-up, digital image analysis was performed to compute inlay translation and rotation. An inlay was classified as mobile, if it translated more than 1 mm or rotated more than 5. Group means where compared using one-way ANOVA with a significance level of 5%. Results: No significant change in average inlay translation and rotation with time was found. The average inlay translation was 2.5 mm (s.d. 1.8 mm) at 3 months postop, 3.0 mm (s.d. 1.8 mm) at 1 year post-op, 3.1 mm (s.d. 1.9 mm) at 2 years post-op, and 3.1 mm (s.d. 2.0 mm) at 5 years post-op. The average inlay rotation was 6.6 (s.d. 3.4) at 3 months post-op, 6.7 (s.d. 4.0) at 1 year post-op, 7.9 (s.d. 3.9) at 2 years post-op, and 8.3 (s.d. 4.1) at 5 years post-op. At all follow-ups, the inlay was classified as mobile in at least 90% of the cases. The patterns of inlay motion were observed to be repeatable for the individual knee joints but varied substantially between subjects. Conclusion: In 40 mobile-bearing TKRs that were prospectively examined 3, 12, 24, and 60 months post-op, no significant change in average inlay motion or percentage of mobile inlays was found. The results do not support the hypothesis that inlay mobility is reduced due to in-growth of fibrous tissue. Mobile-bearing TKRs allow the kinematics to follow the knee specific soft tissue constraints

Background: Although many of the contemporary fixed- and mobile bearing total knee systems have been using extensively world wide, there is limited information available regarding the incidence of osteolysis of the well functioning total knee arthroplasties. We performed this study to evaluate the clinical and radiographic outcomes, the incidence of osteolysis, the revision rates and implant survivorship of the fixed- and mobile-bearing total knee arthroplasties at ten to seventeen years follow-up. Methods: We compared 488 patients (894 knees) who received a fixed-bearing total knee replacement and 445 patients (816 knees) who received a mobile-bearing total knee replacement. There were 187 men and 301 women (mean age, 58.6 years) in the fixed-bearing group and 167 men and 278 women (mean age, 55.7 years) in the mobile-bearing group. The mean follow-up was 12.6 years (range, ten to seventeen years) in the fixed-bearing group and 14.1 years (range, twelve to seventeen years) in the mobile-bearing group. Results: The mean postoperative Knee Society knee and functional scores were 92.9 points and 83.5 points, respectively in the fixed-bearing group. The mean postoperative Knee Society knee and functional scores were 90.7 points and 83.8 points, respectively. Incidence of osteolysis was 1.6% (fourteen of 894 knees) in the fixed-bearing group and it was 2.2% (eighteen of 816 knees) in the mobile-bearing group at the final review. Revision rate was 3.7% (thirty-three of 894 knees) in the fixed-bearing group and it was 2.7% (twenty-two of 816 knees) in the mobile-bearing group. Kaplan-Meier survivorship of the fixed-bearing group was 96.3% (95% confidence interval, 0.87–1.0) at 13 years follow-up and it was 97% (95% confidence interval, 0.90–1.0) of the mobile-bearing group at 14 years follow-up. Conclusions: The present study demonstrates that the clinical and radiographic outcomes, the incidence of osteolysis, the rate of revision and the implant survivorship were similar between the fixed-bearing and mobile-bearing total knee arthroplasties

The current study aimed to analyze in vivo kinematics during deep knee bending motion by subjects with fully congruent designed mobile-bearing total knee arthroplasty (TKA) allowing axial rotation and anterior/posterior (AP) gliding. Twelve subjects were implanted with Dual Bearing-Knee (DBK, slot type: Finsbury, UK) prostheses. These implants include a mobile-bearing insert that is fully congruent with the femoral component throughout flex-ion and allows axial rotation and a 4–6 mm limited AP translation. Sequential fluoroscopic images were taken in the sagittal plane during loaded knee bending motion. In vivo kinematics of knee prostheses were computed accurately using a 2D/3D registration technique, which uses computer-assisted design models to reproduce the spatial position of metallic femoral and tibial components from calibrated single-view fluoroscopic images. The average femoral component demonstrated 13.4° external axial rotation for 0° to 120° flexion. On average, the medial condyle moved anteriorly 6.2 mm for 0° to 100° flexion, then posteriorly 4.0 mm for 100° to 120° flexion. On average, the lateral condyle moved anteriorly 1.0 mm for0° to 40° flexion, then posteriorly 8.7 mm for 40° to 120° flexion. The average subject experienced a lateral pivot pattern from −5° to 60° flexion, a central pivot pattern from 60° to 100° flexion, and a rollback pattern which bilateral condyles moved backward from 100° to 120° of knee flexion. Subjects with DBK mobile-bearing TKA in some-degree reproduced femoral external rotation during increasing knee flexion and bicondylar posterior rollback during terminal flexion, due to surrounding soft tissue structures. The geometry of replaced articular surfaces and mobility of the mobile-bearing insert produced lateral-to-central pivoting motions during the flexion cycle, a phenomenon not typically observed in normal knees. Using the current technique, we characterized the unique kinematics of fully congruent designed DBK mobile-bearing knee prostheses

Aims: The purpose of this study was to determine the intra-subject repeatability of the motion pattern of the PE inlay in a mobile-bearing total knee replacement (TKR) with respect to the post-op time. Methods: 75 mobile-bearing TKRs in 73 patients were included in this prospective study. Sagittal radiographs at 0°, 30°, 60° and maximum flexion were taken 3, 12, and 24 months post-op. On each X-ray, the AP position and the rotation of the PE inlay with respect to the tibial baseplate were determined based on a 2D algorithm. The accuracy of the method was ± 0.2 mm for the AP position and ± 1.7° for the angle of rotation. To classify the repeatability, the mean AP and rotation motion with respect to the flexion angle for each patient was computed and the overall standard deviation (STD) of all measurements with respect to the mean curves was calculated. The repeatability was defined as ‘excellent’ if the STD in the AP direction was less than 0.5 mm and the STD in rotation was less than 2.5°. It was defined as ‘good’ if the STD in the AP direction was less than 1 mm and the STD in rotation was less than 5°. Results: 19 of 75 knees (25%) showed an excellent repeatability and 33 of 75 knees (44%) displayed a good repeatability of the PE motion. Motion patterns were more repeatable between the 12 and 24 month results than between the 3 and 12 month results. Conclusions: The majority of the mobile-bearing knees exhibited a repeatable, patient specific motion pattern of the PE inlay. The fact that the repeatability was higher between 12 and 24 months may be attributed to a more stable state after rehabilitation. Mobile-bearing knees support patient specific motion in contrary to constrained fixed bearing knees

Mobile-bearing total knee replacement (TKR) designs are advocated for their theoretical ability to self-align and accommodate small errors in rotational (axial) alignment. However, for many mobile-bearing TKR, the relationships between axial alignment, knee axial rotation and bearing motion during knee flexion are undefined. This study evaluates whether mobile-bearing TKR with axial alignment outside surgical norms have different rotations and motions compared to well-aligned TKR. This prospective study included 67 patients implanted with cruciate-retaining mobile-bearing TKR with a rotating platform polyethylene bearing (Scorpio PCS, Stryker). Axial alignment of femoral components relative to the transepicondylar axis and tibial components relative to the medial tibial tuberosity was measured from postoperative CT scans. TKR were categorized as “normal” or “outliers” according to defined tolerances for surgical axial alignment relative to anatomic landmarks (+3° for femur, +10° for tibia) and combined axial mismatch (+5° between femoral and tibial components). Knee kinematics and axial rotation were measured from fluoroscopic images acquired immediately after TKR during 0° to 120° of passive knee flexion. Total knee axial rotation (relative motion between the femoral component and tibial baseplate), femoral component axial rotation on the bearing articular surface, and bearing axial rotation on the tibial baseplate were determined using published shape-matching techniques. External rotation during knee flexion averaged 8.4°+6.1°, with two phases of axial rotation motion distinguished in all groups. External rotation from 0°–80° occurred primarily due to bearing axial rotation on the tibial baseplate. Beyond 80°, there was combined bearing rotation and external rotation of the femoral component on the polyethylene articular surface, with the latter dominating the motion pattern. Axial rotation varied with the component axial alignment. Among TKR with normal axial alignment, external rotation steadily increased with knee flexion. Among anatomic landmark outliers, there was a transition to internal rotation from 20°–50° and limited (< 1°) axial rotation beyond 80°. Among combined axial mismatch outliers, the magnitude of axial rotation was significantly less than normal TKR throughout the flexion range (p< 0.001) due to opposite rotations between the femoral component and polyethylene bearing. Achieving appropriate axial alignment using defined bony landmarks remains a challenge. In this study, approximately 30% of TKR did not have suitable axial alignment, with notable combined axial mismatch in tibial-femoral alignment. Axial rotation misalignment affected the kinematics and knee rotation motions over the passive flexion range and appears to result in opposite rotations of the femur-bearing and bearing-base-plate articulations

Purpose. The mobile-bearing total knee arthroplasty was designed to increase the contact area with the polyethylene bearing, through the functional range of motion, and subsequently decrease the wear rate previously seen in fixed-bearing implants. In the literature there is no clear clinical advantage between the different designs in the short to mid-term follow-up. The purpose of this study was to compare the results between a cruciate retaining mobile-bearing design (SAL II, Sulzer) and two cruciate retaining fixed-bearing designs (AMK, Depuy, and the Genesis II, Smith and Nephew). Method. Ninety patients were randomised to receive either the mobile-bearing or one of the two fixed-bearing designs between 2000 and 2002. Patients were evaluated preoperatively and postoperatively using the WOMAC and the SF-12, both of which are validated scores. One patient was withdrawn due to dementia before three months and eleven patients died. Two patients were revised due to infection (both had received the SAL II). One patient was revised for aseptic loosening and one patient was revised for pain (both had received the Genesis II). Of the 74 patients (77 knees) that remain, they were last seen on average 6.4 years (2–10) after their surgery. Their average age at the surgery was 69.2 years (52–81). Results. There was no statistically significant difference between the change scores (postoperative score minus preoperative score) for each of the outcome measures between the mobile-bearing and the two fixed-bearing designs. Conclusion. In conclusion, after mid-term follow-up there is no clinical difference between a cruciate retaining mobile-bearing design and two cruciate retaining fixed-bearing designs

Introduction. Accurate soft tissue balancing in knee arthroplasty is essential in order to attain good postoperative clinical results. In mobile-bearing UKA (Oxford Partial Knee unicompartmental knee arthroplasty, Biomet), since determination of the thickness of the spacer block depends on the individual surgeon, it will vary and it will be difficult to attain appropriate knee balancing. The first objective of the present study was to investigate flexion and extension medial unicompartmental knee gap kinematics in conjunction with various joint distraction forces. The second objective of the study was to investigate the accuracy of gap measurement using a spacer block and a tensor device. Methods. A total of 40 knees in 31 subjects (5 men and 26 women) with a mean age of 71.5 years underwent Oxford UKA for knee osteoarthritis and idiopathic osteonecrosis of the medial compartment. According to instructions of Phase 3 Oxford UKA, spacer block technique was used to make the extension gap equal to the flexion gap. Adequate thickness of the spacer block was determined so that the surgeon could easily insert and remove it with no stress. Following osteotomy, the tensor devise was used to measure the medial compartmental gap between the femoral trial prosthesis and the tibial osteotomy surface (joint component gap) (Fig. 1 and 2). The medial gap was measured at 20° of knee flexion (extension gap) and 90° of knee flexion (flexion gap) with 25N, 50N, 75N, 100N, 125N, 150N of joint distraction force. Corresponding size of bearing was determined for the prosthesis. The interplay gap was calculated by subtracting the thickness of the tibial prosthesis and the thickness of the selected size of bearing from the measured extension and flexion gaps. Results. The selected bearing size was 3 mm: 3 knees, 4 mm: 20 knees, 5 mm: 15 knees and 6 mm: 2 knees. The mean flexion gap in the medial compartment was 25N: 8.4 ± 1.6 mm, 50N: 9.4 ± 1.6 mm, 75N: 10.4 ± 1.5 mm, 100N: 11.0 ± 1.4 mm, 125N: 11.6 ± 1.5 mm, 150N: 11.9 ± 1.4 mm. The mean extension gap was 25N: 7.8 ± 1.6 mm, 50N: 8.8 ± 1.6 mm, 75N: 9.7 ± 1.6 mm, 100N: 10.4 ± 1.5 mm, 125N: 11.1 ± 1.5 mm, 150N: 11.4 ± 1.5 mm. The mean flexion interplay gap was 25N: 0.5 ± 1.2 mm, 50N: 1.5 ± 1.2 mm, 75N: 2.4 ± 1.1 mm, 100N: 3.1 ± 1.0 mm, 125N: 3.6 ± 1.1 mm, 150N: 4.0 ± 1.1 mm. The mean extension interplay gap was 25N: −0.2 ± 1.2 mm, 50N: 0.8 ± 1.1 mm, 75N: 1.7 ± 1.2 mm, 100N: 2.5 ± 1.2 mm, 125N: 3.1 ± 1.2 mm, 150N: 3.5 ± 1.2 mm. When flexion and extension of the interplay gap were compared, the extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force (p < 0.05). Conclusion. The mean extension interplay gap was shown to be significantly smaller compared with the flexion interplay gap at every joint distraction force even though the extension gap was adjusted to the flexion gap using the spacer block. This suggests that in the actual UKA operative technique using a spacer block there is a potential that the extension gap will be smaller than the flexion gap. Surgeons should be aware of this fact and adjust the flexion and extension gaps with caution when performing mobile-bearing UKA

Introduction: We compared the early results of mobile-bearing knee prosthesis with fixed-bearing knee prosthesis in 20 patients who had one-stage, sequential, bilateral replacements. Patients and Methods: In each patient, a Low Contact Stress (LCS, Depuy) rotating-platform prosthesis was inserted in one side, and an Anatomic Modular Knee (AMK, Depuy) posterior-stabilised prosthesis was inserted in the other side. The same surgical routines were adopted for both sides in each patient. The LCS and AMK knees were comparable in Knee Society knee scores, knee flexion and flexion contracture before surgery. Results: There were significant improvements in the Knee Society knee and functional scores after surgery (p < 0.001) for both LCS and AMK knees. Although the LCS knees had better Knee Society knee score, better knee flexion, and less residual flexion contracture at final follow-up, all these were not statistically significant when compared with the AMK knees. Discussion and Conclusion: The results of mobile-bearing knee replacements were as good as those that followed fixed-bearing knee replacements

Introduction: Common failure modes of revision total knee arthroplasty (TKA) include aseptic component loosening and damage to constraining mechanisms which are often required in revision TKA. Mobile-bearing (MB) revision TKA components have been developed in hopes of lessening these failure mechanisms. Our objective was to evaluate the early clinical outcomes for the use of MB in revision TKA with a minimum 2-year follow-up and to evaluate bearing complications. Methods: Retrospective clinical and radiographic evaluation of 84 MB revision TKAs with minimum 2-year follow-up was performed. Revision TKAs were performed using PFC Sigma and LCS revision rotating platform implants (Depuy, Warsaw, IN). Indications for revision include aseptic loosening (31 knees), instability (30 knees), failed unicompartmental knee replacement (8 knees), infection reimplantation (7 knees), arthrofibrosis (3 knees), chronic hemarthrosis (3 knees), failed patellofemoral replacements (1 knees), and nonunion of a supracondylar femur fracture (1 knee). Results: At a mean follow-up of 3.7 years, the average Knee Society clinical and function scores had increased from 50.3 points preoperatively to 89.1 points and from 49.3 points to 80.1 points, respectively. Average motion improved from 99.8° preoperatively to 116.5° postoperatively. Radiographic review demonstrated excellent fixation with no evidence of component loosening upon latest follow-up. No cases of bearing instability were observed. Conclusion: This evaluation of 84 MB revision TKAs has demonstrated favorable early results at a mean follow-up of 3.7 years with no occurrence of bearing instability. Longer follow-up is required to evaluate for potential advantages of reducing polyethylene wear, lessening fixation stresses, and protection of constraining mechanisms