Mobile Bearing Research Articles

Mid-term results of lateral unicondylar mobile bearing knee arthroplasty: a multicentre study of 363 cases.

The aim of this independent multicentre study was to assess the mid-term results of mobile bearing unicondylar knee arthroplasty (UKA) for isolated lateral osteoarthritis of the knee joint. We retrospectively evaluated 363 consecutive, lateral UKAs (346 patients) performed using the Oxford domed lateral prosthesis undertaken in three high-volume knee arthroplasty centres between 2006 and 2014. Mean age of the patients at surgery was 65 years (36 to 88) with a mean final follow-up of 37 months (12 to 93) RESULTS: A total of 36 (10.5%) patients underwent revision surgery, giving a survival rate of 90.1% at three years (95% confidence intervals (CI) 86.1 to 93.1; number at risk: 155) and 85.0% at five years (95% CI 77.9 to 89.9; number at risk: 43). Dislocation of the mobile bearing occurred in 18 patients (5.6%) at three years (95% CI 1.0 to 16.4; number at risk: 154) and in 20 patients (8.5%) at five years (95% CI 1.0 to 27.0; number at risk: 42). There were no significant differences in the dislocation rate between the participating centres or the surgeons. We were not able to identify an effect of each surgeon's learning curve on the dislocation rate of the mobile bearing. The clinical outcome in patients without revision surgery at final follow-up was good to excellent, with a mean Oxford knee score of 40.3 (95% CI 39.4 to 41.2), a mean Tegner activity score of 3.2 (95% CI 3.1 to 3.3) and a mean University of California, Los Angeles score of 5.7 (95% CI 5.5 to 5.9). Our data, which consists of a high number of patients treated with mobile bearing UKA in the lateral compartment, indicates a high revision rate of 15% at five years with dislocation of the mobile bearing being the main reason for implant failure. Despite the good functional and clinical results and the high patient satisfaction in our study group, we therefore discontinued using mobile-bearing lateral UKA in favour of a fixed-bearing component. Cite this article: Bone Joint J 2018;100-B:42-9.

Evaluation of 1031 primary titanium nitride coated mobile bearing total knee arthroplasties in an orthopedic clinic.

AIMTo evaluate the influence of the titanium nitride (TiN) coating on the results of a total knee arthroplasty (TKA).METHODSA total of 910 patients (338 men; 572 woman), with a mean age of 65 (range 36-94) undergoing 1031 primary TKAs were assessed. Clinical evaluation and patient-reported outcomes were gathered one year after surgery. The questionnaires included the Knee injury and Osteoarthritis Outcome Score (KOOS)-Dutch version, Visual Analogue Scale (VAS) pain scores in rest and during active knee movement, VAS-satisfaction scores, and EQ-5D-3L health scores. This was aimed to assess the overall knee function and patient satisfaction, and to enable us to make a gross comparison to other TKAs.RESULTSAt a mean follow-up of 46 mo (range 1-92) the overall implant survival was 97.7% and 95.1% for any operative reason related to the implant. Twenty-three knees (2.2%) required revision surgery. Arthrofibrosis was the most common indication for a re-operation. The clinical evaluation and patient-reported outcomes revealed good to excellent patient satisfaction and function of the arthroplasty. The median postoperative VAS-pain scores on a scale of 0-100, at one year after surgery were 1 in rest and 2 during movement.CONCLUSIONThe TiN coated, mobile bearing TKA results are excellent and similar to those of other widely used TKA designs. Residual pain of the knee remains a concern and the TiN coating in combination with the mobile bearing does not seem to be the simple solution to this problem. Future research will have to show that the coating gives a better survival than the cobalt chrome version.

Results with nine years mean follow up on one hundred and three KAPS® uni knee arthroplasties: eighty six medial and seventeen lateral.

The purpose of this study was to present the results of the KAPS® uni knee arthroplasty system, both mobile and fixed bearing with reference to function, alignment and complications in 103 implants with a mean follow-up of nineyears. This was a retrospective study of 103 unicompartimental knee arthroplasties in 89 patients operated on between March 2005 and March 2010. The population was composed of 50 males and 39 females, with a mean age of 70.5 ± 7.5years (41 - 90). Eighty-seven patients had a genu varum deformity (84.5%), one of whom had an osteoid osteoma of the lateral tibial plateau and 16 patients had a genu valgum (15.5%). Eighty-six medial prostheses were implanted (82 mobile bearings and 4 fixed bearings) and 17 lateral prostheses (all fixed bearings) including the osteoid osteoma. At a mean follow-up of 107.5months (73-138), 72 knees (58 patients) were reviewed (70%). The mean IKS score was of 173 ± 31 points (58 - 200). The mean Oxford knee score was 21 ± 8 points (12 - 50). The cumulated survival rate at a follow up of 132months was 98.2%. The KAPS® unicompartmental knee arthroplasty gives efficacious and safe outcomes in the majority of cases at a mean follow-up of nineyears. The availability of both fixed and mobile bearings with the same instrumentation, allowing to choose the right implant intra-operatively, is a great advantage in order to avoid the occurrence of some complications, specific to mobile bearing prostheses (dislocation and over-correction).

Cementless knee arthroplasty.

Total knee replacement is a common treatment for advanced knee osteoarthritis. The most common and widespread method is cemented arthroplasty. As in the prosthetic hip a gradual transition from cemented to uncemented fixation techniques occurred over time, increasing interest is growing also around cementless knee fixation, with the theoretical advantages of preserving the bone stock and obtaining a biological fixation avoiding cement fragmentation. On the basis of the actual knowledge, the uncemented knee prosthesis represents an interesting alternative especially for the patient under 65 years of age, with viable bone quality, in which a biological bone-prosthesis fixation is desirable, while avoiding the drawbacks of cement fragmentation and of the possible future revision of a cemented implant. However the weak link remains the tibial fixation, so that technical tips are important to avoid micromovements with subsequent lack of osteointegration. In our experience, gap balancing, mobile bearings and no haemostatic tourniquet well combine with this kind of implant.

Eight Hundred Twenty-Five Medial Mobile-Bearing Unicompartmental Knee Arthroplasties: The First 10-Year US Multi-Center Survival Analysis

BackgroundFDA approval for the Oxford phase III device was approved for use in the United States in 2004. This study seeks to provide the first long-term, large patient sample size, Oxford phase III multi-site survivorship study in the United States, investigating patient reported outcomes of pain and function, while also providing an in-depth analysis of causes for revision, and finally addressing recent advancements that can help aid the unicompartmental knee arthroplasty (UKA) process and further improve partial knee survivorship. MethodsBetween July 2004 and December 2006, 5 surgeons from around the United States performed medial UKA through the minimally invasive surgical approach, on 825 knees in 695 patients. This was a consecutive series of primary UKAs using the phase III mobile bearing; cemented Oxford Knee (Zimmer Biomet, Warsaw, IN), implanted utilizing phase III instrumentation. UKA survivorship considered all revisions as the end point. Implant survivorship eliminated revisions at which the original Oxford implant was determined to be well fixated and functional intra-operatively. ResultsA total of 93 knees were revised in this study. Mean follow-up was 9.7 years (6-12). Implant survivorship at year 10 was 90% (confidence interval 2.7%). UKA survivorship at year 10 was 85% (confidence interval 3.8%). Average preoperative American Knee Society Score (knee score) was 49 and rose to 90 postoperatively (standard deviations 16 and 18, respectively). Average preoperative American Knee Society Score (function score) was 55 and rose to 77 postoperatively (standard deviations 15 and 28, respectively). ConclusionThis was the first large-scale, 10-year, multi-site follow-up of the Oxford mobile-bearing medial UKA undertaken in the United States, displaying good survivorship and excellent patient outcomes.

30-Year Survival of the Oxford Mobile Bearing Unicompartmental Knee Arthroplasty

30-Year Survival of the Oxford Mobile Bearing Unicompartmental Knee Arthroplasty

Kinematics of mobile-bearing unicompartmental knee arthroplasty compared to native: results from an in vitro study.

Fixed-bearing unicompartmental knee arthroplasty (UKA) closely replicates native knee kinematics. As few studies have assessed kinematics following mobile-bearing (MB) UKA, the current study aimed to investigate whether MB UKA preserves natural knee kinematics. Seven fresh-frozen full-leg cadaver specimens were prepared and mounted in a kinematic rig that allowed all degrees of freedom at the knee. Three motion patterns, passive flexion-extension (0°-110° flexion), open-chain extension (5°-70° flexion) and squatting (30°-100° flexion), were performed pre- and post-implantation of a medial MB UKA and compared in terms of rotational and translational knee joint kinematics in the different anatomical planes, respectively. In terms of frontal plane rotational kinematics, MB UKA specimens were in a more valgus orientation for all motion patterns. In the axial plane, internal rotation of the tibia before and after UKA was consistent, regardless of motion task, with no significant differences. In terms of frontal plane, i.e., inferior-superior, translations, the FMCC was significantly higher in UKA knees in all flexion angles and motor tasks, except in early flexion during passive motion. In terms of axial plane, i.e., anteroposterior (AP), translations, during open-chain activities, the femoral medial condyle center (FMCC) tended to be more posterior following UKA relative to the native knee in mid-flexion and above. AP excursions of the FMCC were small in all tested motions, however. There was substantial AP translation of the femoral lateral condyle center during passive motion before and after UKA, which was significantly different for flexion angles >38°. Our study data demonstrate that the kinematics of the unloaded knee following MB UKA closely resemble those of the native knee while relative medial overstuffing with UKA will result in the joint being more valgus. However, replacing the conforming and rigidly fixed medial meniscus with a mobile inlay may successfully prevent aberrant posterior translation of the medial femoral compartment during passive motion and squatting motion.

Spinout/Dislocation in Mobile-Bearing Total Knee Arthroplasty: A Report of 26 Cases

BackgroundExcellent medium-term to long-term results for function and survivorship have been shown with mobile-bearing (MB) total knee arthroplasty (TKA). One of the key arguments against its use is the risk of “spinout” or dislocation of the MB.The aim of this study is to discuss the etiology, prevention, incidence, management, and outcome of spinout. MethodsBetween October 1993 and February 2016, 8373 consecutive primary MB TKAs were performed irrespective of preoperative deformity.Before 2001, soft-tissue knee balancing was achieved by release of collateral ligaments and all spinouts were treated by open reduction. Thereafter, soft-tissue balancing was achieved without ligament release and with the use of a higher conformity MB and all spinouts were reduced closed, giving 2 comparative cohorts. ResultsTwenty-six spinouts occurred in 8373 (0.31%) patients. In the first cohort up until May 2001, there were 14 spinouts of 2379 (0.58%) cases. There were 12 in cohort 2, in those patients having surgery after May 2001, thus giving an incidence of 12 of 5994 (0.2%), which was significantly lower than in cohort 1 (P < .01). Spinout was associated with the valgus knee (P < .01) and most (73%) occurred within the first 6 months. There was 1 arthrodesis in cohort 1 and 1 both-component revision in cohort 2. ConclusionThe etiology of spinout is flexion gap instability. It can normally be reduced closed with recurrence being uncommon. Focus on soft-tissue balance necessary with an MB TKA can reduce the incidence of revision for instability as compared to a fixed-bearing TKA. Therefore, the risk of spinout should not be used as an argument against the MB TKA.

Revision Total Hip Arthroplasty in the Setting of a Well-Fixed Cup: Early Report on the Cup-in-Cup Technique

AbstractWhen faced with a well-fixed acetabular component during revision total hip arthroplasty (THA) in the setting of recurrent instability, reconstructive options are limited, and consequences can prove dire if removal leads to severe bone loss or pelvic discontinuity. Our aims are to report the surgical technique, early survivorship, radiographic improvements, and complications on a consecutive, retrospective series of 13 hips in 12 patients who were treated with a cup-in-cup surgical technique to address multiply recurrent dislocations in the setting of a well-fixed cup. If determined to be stable and acceptably positioned upon intraoperative assessment, the acetabular component is retained, a second shell is cemented into the preexisting cup, and a dual mobility or standard polyethylene liner bearing is utilized. At 2-year minimum follow-up, the cup-in-cup arthroplasty exhibited an overall 85% survivorship. Two subjects required subsequent revisions: one for infection and one for ongoing instability in the setting of general noncompliance. No revisions were performed for loosening of the cup-in-cup interface. The median affected leg length was increased by 2.8 mm (p = 0.04) and horizontal offset improved by an average of 6.9 mm (p &lt; 0.001). There were a total of four dislocations in two subjects after cup-in-cup revision arthroplasty with no failures at the cup–cup cement interface. Our series demonstrates acceptable early outcomes in terms of improved stability and decreasing the need for further revision surgery while utilizing the cup-in-cup revision arthroplasty technique in situations of recurrent dislocations.

CORR Insights®: Are There Differences in Gait Mechanics in Patients With A Fixed Versus Mobile Bearing Total Ankle Arthroplasty? A Randomized Trial.

Where Are We Now? Queen and colleagues performed a randomized trial to determine whether fixed- or mobile-bearing total ankle arthroplasty (TAA) results in better clinical and biomechanical improvement at 1-year followup. Similar to the results of previous studies [2, 3, 5, 8], the authors found no substantial differences between the 15 patients with fixed-bearing implants and the 18 patients with mobile-bearing implants. However, analysis of TAA survivorship based on high-quality national arthroplasty registries show less-favorable results than those following total hip or knee replacements, including a high revision rate (10% at 5 years, of which 40% is from aseptic loosening) [4]. The majority of TAAs included in national arthroplasty registries are mobile-bearing implants, which theoretically offer biomechanical advantages, but are also associated with polyethylene concerns [7, 9]. Fixed-bearing implants may be more reliable and improve TAA survivorship. Prior research reports a slight superiority favoring fixed-bearing prostheses over mobile-bearing designs in terms of clinical outcomes [3], risk of revision [7], and joint biomechanics [5]. Where Do We Need To Go? Although no important differences were found, the current study confirms the necessity of objectively comparing fixed- and mobile-bearing TAA designs, and emphasizes the importance of using both clinical and biomechanical criteria for this comparison. Even so, several unanswered questions remain: (1) To what extent can we tolerate a difference between implant designs in order to determine the superiority of either the mobile or the fixed-mobile concept? (2) What is the best way to assess clinical outcomes? (3) What are the minimal requirements for a comprehensive and sensitive biomechanical assessment? Biomechanical assessment offers the potential to detect factors that can help predict outcomes. However, comprehensive clinical assessment is a priority because we need to know the treatment's efficacy from the patient's perspective in terms of functional performance. Regarding biomechanical comparisons, although the authors of the current study performed a comprehensive gait assessment evaluating temporal distance, kinematics, and kinetics data, the biomechanical differences between the fixed- and mobile-bearing TAAs may be subtle and perhaps require foot-and-ankle-specific gait analysis focusing on longer walking distances than currently available in gait laboratories and daily living conditions [1, 6]. How Do We Get There? In order to compare fixed- versus mobile-bearing implants, researchers generally examine implants from different manufacturers. Only the Salto® ankle system (Integra Life Sciences, Plainsboro, NJ, USA) has both fixed-bearing (Salto Talaris®) and mobile-bearing (Salto®) options. Comparing fixed- and mobile-bearing implants from different manufacturers is a challenge because there are several possible biases resulting from the differences in the design of the prostheses, including the anatomic or nonanatomic shape of the articulating surfaces, the amount of mediolateral talar resurfacing, and the degree of congruence between the polyethylene and the metal. This could be overcome by including a larger number of patients and several fixed- and mobile-bearing prosthesis designs from the data in national arthroplasty registries—just one more reason to support their systematic and high-quality implementation. Beside a high number of patients, registry data are objective, offer long-term followup, and can provide relatively precise estimates of revision risk in different patient populations. Unfortunately, registries do not allow us to evaluate biomechanical parameters, and of course, they do not gather gait-analysis data. As demonstrated in the present study, where only 40 of 185 potentially eligible patients could be included, developing a large prospective and randomized database that compares gait analysis after the implantation of a fixed- or mobile-bearing TAA is a major challenge. However, in order to recruit enough patients for a sufficiently powered randomized trial, a multicenter design will be needed. I note, though, that since implant problems typically occur between 5 to 10 years after surgery, studying mid- and long-term results, including clinical and biomechanical assessment, may be even more important than randomization. Finally, gait analysis usually requires specialized facilities, even if modern, wearable systems have been validated to assess the patient during activities of daily living [6]. Defining a set of important gait parameters and validating them as the gold standard for TAA-assessment would be an important research goal because it would favor a more systematic use of gait analysis in the assessment of TAAs and facilitate comparison of the results, even between different studies. Of course, these assessments need to be performed in combination with clinical evaluation using validated and comprehensive outcome tools.

Fixed and mobile-bearing total ankle prostheses: Effect on tibial bone strain

BackgroundTotal ankle replacement is associated to a high revision rate. To improve implant survival, the potential advantage of prostheses with fixed bearing compared to mobile bearing is unclear. The objective of this study was to test the hypothesis that fixed and mobile bearing prostheses are associated with different biomechanical quantities typically associated to implant failure. MethodsWith a validated finite element model, we compared three cases: a prosthesis with a fixed bearing, a prosthesis with a mobile bearing in a centered position, and a prosthesis with mobile bearing in an eccentric position. Both prostheses were obtained from the same manufacturer. They were tested on seven tibias with maximum axial compression force during walking. We tested the hypothesis that there was a difference of bone strain, bone-implant interfacial stress, and bone support between the three cases. We also evaluated, for the three cases, the correlations between bone support, bone strain and bone-implant interfacial stress. FindingsThere were no statistically significant differences between the three cases. Overall, bone support was mainly trabecular, and less effective in the posterior side. Bone strain and bone-implant interfacial stress were strongly correlated to bone support. InterpretationsEven if slight differences are observed between fixed and mobile bearing, it is not enough to put forward the superiority of one of these implants regarding their reaction to axial compression. When associated to the published clinical results, our study provides no argument to warn surgeons against the use of two-components fixed bearing implants.

Comparison of fixed and mobile-bearing total knee arthroplasty in terms of patellofemoral pain and function: a prospective, randomised, controlled trial

BackgroundDespite growing evidence in the literature, there is still a lack of consensus regarding the use of the mobile-bearing (MB) design total knee arthroplasty (TKA).MethodsIn a prospective, comparative, randomised, single centre trial, 106 patients with end-stage osteoarthritis of the knee were randomised to either an MB or fixed-bearing (FB) group to receive posterior stabilised (PS)-TKA using a standard medial parapatellar approach and patellar resurfacing with follow-up (FU) for 5 years. The primary outcome was anterior knee pain (AKP) during the chair rise test and the stair climb test 5 years after surgery. The secondary outcome was the ability to rise from a chair and to climb stairs, range of motion (ROM), Knee Society Score (KSS), RAND-36 scores and radiological analysis of the patellar tilt.ResultsNo statistically significant difference was found between the two groups at 5 years FU in terms of median AKP during the chair rise test and the stair climb test (p = 0.5 and p = 0.8, respectively). There was no significant difference in any of the other secondary outcome parameters between the groups at 5 years FU.ConclusionA mobile-bearing TKA does not decrease AKP compared to fixed bearings.Trial registration numberClinicalTrials.gov NCT02892838.Level of evidenceII

A novel flexible capacitive load sensor for use in a mobile unicompartmental knee replacement bearing: An in vitro proof of concept study

Instrumented knee replacements can provide in vivo data quantifying physiological loads acting on the knee. To date instrumented mobile unicompartmental knee replacements (UKR) have not been realised. Ideally instrumentation would be embedded within the polyethylene bearing. This study investigated the feasibility of an embedded flexible capacitive load sensor. A novel flexible capacitive load sensor was developed which could be incorporated into standard manufacturing of compression moulded polyethylene bearings. Dynamic experiments were performed to determine the characteristics of the sensor on a uniaxial servo-hydraulic material testing machine. The instrumented bearing was measured at sinusoidal frequencies between 0.1 and 10Hz, allowing for measurement of typical gait load magnitudes and frequencies. These correspond to frequencies of interest in physiological loading. The loads that were applied were a static load of 390N, corresponding to an equivalent body weight load for UKR, and a dynamic load of ±293N. The frequency transfer response of the sensor suggests a low pass filter response with a −3dB frequency of 10Hz. The proposed embedded capacitive load sensor was shown to be applicable for measuring in vivo loads within a polyethylene mobile UKR bearing.

Are There Differences in Gait Mechanics in Patients With A Fixed Versus Mobile Bearing Total Ankle Arthroplasty? A Randomized Trial.

Total ankle arthroplasty (TAA) is an alternative to arthrodesis, but no randomized trial has examined whether a fixed bearing or mobile bearing implant provides improved gait mechanics. We wished to determine if fixed- or mobile-bearing TAA results in a larger improvement in pain scores and gait mechanics from before surgery to 1year after surgery, and to quantify differences in outcomes using statistical analysis and report the standardized effect sizes for such comparisons. Patients with end-stage ankle arthritis who were scheduled for TAA between November 2011 and June 2013 (n=40; 16 men, 24 women; average age, 63years; age range, 35-81years) were prospectively recruited for this study from a single foot and ankle orthopaedic clinic. During this period, 185 patients underwent TAA, with 144 being eligible to participate in this study. Patients were eligible to participate if they were able to meet all study inclusion criteria, which were: no previous diagnosis of rheumatoid arthritis, a contralateral TAA, bilateral ankle arthritis, previous revision TAA, an ankle fusion revision, or able to walk without the use of an assistive device, weight less than 250 pounds (114kg), a sagittal or coronal plane deformity less than 15°, no presence of avascular necrosis of the distal tibia, no current neuropathy, age older than 35years, no history of a talar neck fracture, or an avascular talus. Of the 144 eligible patients, 40 consented to participate in our randomized trial. These 40 patients were randomly assigned to either the fixed (n=20) or mobile bearing implant group (n=20). Walking speed, bilateral peak dorsiflexion angle, peak plantar flexion angle, sagittal plane ankle ROM, peak ankle inversion angle, peak plantar flexion moment, peak plantar flexion power during stance, peak weight acceptance, and propulsive vertical ground reaction force were analyzed during seven self-selected speed level walking trials for 33 participants using an eight-camera motion analysis system and four force plates. Seven patients were not included in the analysis owing to cancelled surgery (one from each group) and five were lost to followup (four with fixed bearing and one with mobile bearing implants). A series of effect-size calculations and two-sample t-tests comparing postoperative and preoperative increases in outcome variables between implant types were used to determine the differences in the magnitude of improvement between the two patient cohorts from before surgery to 1year after surgery. The sample size in this study enabled us to detect a standardized shift of 1.01 SDs between group means with 80% power and a type I error rate of 5% for all outcome variables in the study. This randomized trial did not reveal any differences in outcomes between the two implant types under study at the sample size collected. In addition to these results, effect size analysis suggests that changes in outcome differ between implant types by less than 1 SD. Detection of the largest change score or observed effect (propulsive vertical ground reaction force [Fixed: 0.1±0.1; 0.0-1.0; Mobile: 0.0±0.1; 0.0-0.0; p=0.0.051]) in this study would require a future trial to enroll 66 patients. However, the smallest change score or observed effect (walking speed [Fixed: 0.2±0.3; 0.1-0.4; Mobile: 0.2±0.3; 0.0-0.3; p=0.742]) requires a sample size of 2336 to detect a significant difference with 80% power at the observed effect sizes. To our knowledge, this is the first randomized study to report the observed effect size comparing improvements in outcome measures between fixed and mobile bearing implant types. This study was statistically powered to detect large effects and descriptively analyze observed effect sizes. Based on our results there were no statistically or clinically meaningful differences between the fixed and mobile bearing implants when examining gait mechanics and pain 1year after TAA. Level II, therapeutic study.

Retrieval evidence of impingement at the third articulation in contemporary dual mobility cups for total hip arthroplasty

PurposeWe aimed to assess polyethylene liners of retrieved hips of one design of a dual mobility (DM) cup liner and two designs of femoral stems to better understand the role of femoral stem design on polyethylene impingement.MethodsThis was a case-control study involving 70 retrieved highly cross-linked polyethylene (X3) liners used with ABGII (n = 35) and Rejuvenate (n = 35) stems (Stryker). All polyethylene liners were assessed for evidence of rim deformation and the damage quantified using metrology methods.ResultsA total of 80% of polyethylene liners paired with ABGII necks had macroscopic evidence of neck impingement resulting in a raised lip whilst 23% of liners paired with Rejuvenate necks had evidence of a raised lip (p < 0.0001). The height of the raised rims of the DM cups paired with ABGII necks had a median (range) of 139 μm (72–255). The height of the raised rims of the DM cups paired with Rejuvenate necks had a median (range) of 52 μm (45–90) (p < 0.0001).ConclusionOur new findings from retrieved dual mobility bearings showed that polyethylene liner rim deformation resulting from impingement with the femoral neck occurs in early in-human function, is circumferential in distribution, and is affected by the stem neck design. We recommend the use of highly polished and non-edged neck designs when used in conjunction with DM cups.

Does low-constraint mobile bearing knee prosthesis give satisfactory results for severe coronal deformities? A five to twelve year follow up study.

Severe varus and valgus knee deformities traditionally are replaced with constrained implants, with a number of disadvantages. We present our results in this challenging group using a low constraint deep-dish mobile bearing implant design. One hundred fifty-four patients (170 arthroplasties) who underwent primary TKA using a deep-dish, mobile bearing posterior-stabilized implant for severe varus (HKA < 170°) or valgus (HKA > 190°) deformity between 2004 and 2009 were evaluated at a mean of 6.6years post-operatively (minimum of 5years). Alignment improved from a pre-operative mean (±SD) varus deformity of 167.4° (±2.6°) and a mean (±SD) valgus deformity of 194.1° (±4.0°) to an overall mean (±SD) post-operative mechanical alignment of 178.6° (±3.2°). Twenty-three patients had post-operative varus alignment, five patients had post-operative valgus alignment and 134 knees were in neutral alignment (within 3° spread). Clinical scores at final follow-up were excellent (IKS score 93.8 (±7.4) and function score 82.4 (±20.2)). Three patients were re-operated upon: one deep infection, one periprosthetic fracture and one revision at 144months for aseptic loosening of the femoral component. No patient was revised for instability or implant failure. The survival rate at fiveyears was 99.4% and at tenyears 98.6%. Satisfactory outcomes can be achieved in patients with substantial varus or valgus deformities using low constraint deep-dish mobile bearing implant, standard approach and appropriate soft tissue releases.

Superior long-term survival for fixed bearing compared with mobile bearing in ligament-balanced total knee arthroplasty.

Only few long-term data on ligament-balanced cruciate-retaining total knee arthroplasty (CR TKA) are currently available. Either a mobile- or fixed-bearing insert can be chosen, which showed good mid-term outcome and few complications and revisions. This multi-centre retrospective cross-sectional cohort study investigated the 12-year results of primary TKA using a balancing gap technique and compared survival and clinical outcome between fixed and mobile inserts. In this retrospective cross-sectional cohort study, 557 cases of three clinics (2 Swiss, 1 Dutch) operated between 1998 and 2003 with the first series of a TKA implanted with a balanced gap technique (433 (77.7%) fixed, 124 (22.3%) mobile (anterior-posterior gliding (7-9mm) and rotational (15°) degrees of freedom) inserts) were included for survival analysis (Kaplan-Meier, by insert type). At the 12-year follow-up (FU) examination of 189 cases, range of motion, knee society score (KSS), numeric rating scale (NRS) for pain and satisfaction were determined and radiographs were evaluated by median tests, by insert type. Of 521 cases available for analysis, 28 (5.4%; 11 fixed, 17 mobile bearing) were revised. Mean cumulative survival after 12.4years was 97.0% (95% CI 94.7-98.4) for fixed bearings and 85.4% (95% CI 77.5-90.7) after 12.2years for mobile bearings, p<0.0001. Patients' mean age at 11.0years FU (n=189) was 78.0 (range 54.5-97.3) years. Mean total KSS was 157.8 (24-200) points, and mean passive flexion was 114° (45-150); no clinical score differed significantly between fixed and mobile bearings. This study showed a superior survival for fixed bearing compared with mobile bearing in a CR TKA using a ligament-balanced technique after more than 12years. Clinical outcomes are excellent to good after long-term follow-up, and similar for fixed and mobile bearing. Therapeutic studies-retrospective cohort study, Level III.

Assessment of patient functional performance in different knee arthroplasty designs during unconstrained squat.

In this paper, squat named by Authors unconstrained because performed without constrains related to feet position, speed, knee maximum angle to be reached, was tested as motor task revealing differences in functional performance after knee arthroplasty. It involves large joints ranges of motion, does not compromise joint safety and requires accurate control strategies to maintain balance. Motion capture techniques were used to study squat on a healthy control group (CTR) and on three groups, each characterised by a specific knee arthroplasty design: a Total Knee Arthroplasty (TKA), a Mobile Bearing and a Fixed Bearing Unicompartmental Knee Arthroplasty (respectively MBUA and FBUA). Squat was analysed during descent, maintenance and ascent phase and described by speed, angular kinematics of lower and upper body, the Center of Pressure (CoP) trajectory and muscle activation timing of quadriceps and biceps femoris. Compared to CTR, for TKA and MBUA knee maximum flexion was lower, vertical speed during descent and ascent reduced and the duration of whole movement was longer. CoP mean distance was higher for all arthroplasty groups during descent as higher was, CoP mean velocity for MBUA and TKA during ascent and descent. Unconstrained squat is able to reveal differences in the functional performance among control and arthroplasty groups and between different arthroplasty designs. Considering the similarity index calculated for the variables showing statistically significance, FBUA performance appears to be closest to that of the CTR group. III a.

Clinical Results of Low Contact Stress Mobile Bearing Total Knee Arthroplasty in Patients with Rheumatoid Arthritis –More Than Five Years of Evaluation

Clinical Results of Low Contact Stress Mobile Bearing Total Knee Arthroplasty in Patients with Rheumatoid Arthritis –More Than Five Years of Evaluation

What have we learned from 100% success of press fit condylar rotating platform posterior stabilized knees?: A 5-10 years followup by a nondesigner.

Background:Total joint arthroplasties of the hip and knee represent a remarkable feat of modern medicine in terms of reducing pain and restoring function to millions of patients afflicted with severe arthritis. Oftentimes, the performance and longevity of new implants and devices are based on limited data. This is the first study by a non-designer on the press fit condylar rotating platform posterior stabilized (PFC-RP-PS) design with 100’ success. This has a relevance, vis-á -vis bias that one may have in terms of reproducibility of technique and funding from the manufacturer. We associate our excellent mid-term results to intra operative technical aspects and stringent intra operative exclusion criteria.Materials and Methods:Our study includes a cohort of 121 selected knees operated between January 2003 and October 2010. We used cemented, posterior stabilized (PS), mobile bearing (MB), and RP prosthesis from the same manufacturer in all these 121 knees. The patients were evaluated bi-annually with the calculation of their Knee Society Scores (KSS) and a radiological assessment for loosening/osteolysis.Results:120 knees were available for followup. The average Knee Society clinical and functional scores, respectively, were 27 points and 40 points preoperatively and 93 points and 95 points postoperatively. This indicates a mean increase of about 71’ in the clinical score and about 58’ in the functional score, which is statistically significant. The mean postoperative flexion was 124°, a mean increase of 23° from the preoperative flexion of 101°. There were no revisions (Kaplan-–Meier survivorship of 100’).Conclusions:We feel durable and reproducible results of PFC-RP-PS design knees are very technique sensitive. The way ahead with the PFC-RP-PS knees looks promising when the exclusion criteria for this design are strictly met. Coming from a non-designer, this study acquires a higher degree of relevance without any designer's or manufacturer's bias.