Aims. The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position. Methods. A total of 16 fresh-frozen knees in eight human cadavers, without macroscopic anatomical defects, were selected. The knees from each cadaver were randomized to have the OUKA implanted in the HL or SL position. Results. Tibial base plate rotation was significantly more variable in the SL group with 75% of tibiae mal-rotated. Multivariate analysis of navigation data found no difference based on all kinematic parameters across the range of motion (ROM). However, area under the curve analysis showed that knees placed in the HL position had much smaller differences between the pre- and post-surgery conditions for kinematics mean values across the entire ROM. Conclusion. The sagittal tibia cut, not dependent on standard instrumentation, determines the tibial component rotation. The HL position improves accuracy of this step compared to the SL position, probably due to better visuospatial orientation of the hip and knee to the surgeon. The HL position is better for replicating native kinematics of the knee as shown by the area under the curve analysis. In the supine knee position, care must be taken during the sagittal tibia cut, while checking flexion balance and when sizing the tibial component

Introduction. The results of the mobile bearing Oxford unicompartmental knee replacement (UKR) in the lateral compartment have been disappointing with a five year survival of 82%. Therefore, it is recommended that mobile bearings should not be used for lateral UKR. This low survivorship is primarily due to high dislocation rate, all occurring in the first year. A detailed analysis of the causes of bearing dislocation confirmed the elevated lateral tibial joint line to be a contributory factor. A new surgical technique was therefore introduced in which care was taken neither to remove too much bone from distal femur nor to over tighten the knee and thus ensure that the tibial joint line was not elevated. Other modifications to the technique were also introduced including use of a domed tibial component. Aim. The aim of this study is to compare the outcome of these iterations: the original series [series I], Series II with improved surgical technique and the domed tibial component [Series III]. Method. The primary assessment of outcome was bearing dislocation at one year. One year was chosen as all the dislocations in the first series occurred within a year. In series I, there were 53 knees, in series II 65 knees and in series III 100 knees, all with a minimum of one year follow up. Results. In series I, there were 6 bearing dislocations (11%) and the average range of movement (ROM) was 110°. In the second series, there were 2 dislocations (3%) and the average ROM was 118°. In the third series, there were no primary dislocations and the average ROM was 125°, the difference between range of movement as well as dislocation rate being significant. Conclusions. The improved surgical technique and implant design have reduced the dislocation rate to an acceptable level and therefore a mobile bearing can now be recommended for lateral UKR

Introduction. Kozinn and Scott have made recommendations about contra-indications for unicompartmental knee replacement (UKR). They suggest that patients younger than 60, weight > 82 kilograms, patients with exposed bone in patella-femoral compartment or patients who are physically active/perform heavy labour should not be offered a UKR. In addition, chondrocalcinosis is a contra-indication. These strict selection criteria are based on the experience with fixed bearing UKAs and are more intuitive than evidence based. The Oxford UKR has a fully congruous mobile bearing and has been shown to have minimal wear. Over the past 25 years, the Oxford Group has followed a standardised protocol for patient selection for UKR. We ignore patella-femoral joint pathology, chondrocalcinosis, patient's age, weight and activity level when deciding the suitability for UKR. Methods. Using the standardised indications, more than 1100 Oxford UKRs have been performed to date over the last 10 years. These patients are assessed pre-operatively and at regular intervals post-operatively in a dedicated research clinic. We present the results of these consecutive cases. Patients were classified into two groups: group I (satisfy Kozinn-Scott recommendations) and group II (outside recommendations). Results. Overall 70% of patients were outside Kozinn and Scott's indications (27% < 60 years, 47% > 82 kg, 12% chondrocalcinosis and 21% with patellofemoral damage with exposed bone as an inter-operative finding, 10% Tegner score 5 or more). No significant difference was noted either in 10 year survivorship or in 5-year clinical outcome (mean 5 year Oxford Knee Score [range 0 -48] for group I is 41 and 40.5 for group II). Discussion and Conclusion. These results suggest that the indications for UKR proposed by Kozinn and Scott are too narrow. Probably four times as many patients are appropriate for the mobile bearing Oxford Unicompartmental Knee Replacement than suggested

Background. The cemented mobile bearing metal backed low contact stress patellofemoral arthroplasty (LCS PFA) is a newer design belonging to the second generation of inlay type implant, based on the more successful knee arthroplasty model. The advantage is the patella can articulate with the trochlear implant as well as the femoral component of a total knee replacement (TKR). Patients. This series is a cohort of 21 patients who underwent 24 (3 bilateral) unicompartmental PFA replacements for isolated patellofemoral osteoarthritis. We have used the mobile bearing LCS PFA in all of them. There were 3 males and 18 females. Average age was 51(40-58) years. The Oxford Knee score was used to assess the results. Results. At the latest follow-up averaging 2.7 (0.5 to 4) years, 9 patients showed excellent improvement in their knee scores, 5 patients showed fair improvement and 7 patients very little. There were 9 revisions in 7 patients either due to mechanical problems or with persistent symptoms. We had 4 patients with mechanical complications who underwent revision and 4 patients had a conversion to TKR. The revision rate at 2 years was 33%. There were no infections or loosening of trochlear implants. Conclusion. The revision rate for this implant seems to be very high and mainly with the patellar implant (at the metal polyethylene interface). The Australian Orthopaedic association annual joint registry report 2008 reported a higher revision rate for the same implant at 5% from a pool of 1057 patients. The young active patient having a patellofemoral replacement may put extreme force on their patellar implant. We strongly advocate patellofemoral arthroplasties to be analysed separately from the unicompartmental knees in the National Joint Registries to highlight any persistent issues with this implant

Introduction. Mobile-bearing TKRs allow some axial rotation and may provide a more natural patellar movement. The aim was to compare patellar kinematics among the normal knee, fixed-bearing and mobile-bearing TKR. Methods. Optical computer navigation (Brainlab) was used to track the position of the femur, tibia and patella in 9 whole lower extremities (5 fresh cadavers) in the natural knee, in the same knee with the trial components of a posterior stabilised fixed-bearing TKR (FB) (Sigma PFC, Depuy) and a posterior stabilised mobile-bearing TKR (MB) (Sigma RP Stabilised). The patellae were not resurfaced. Values: mean+/−one standard deviation. Statistical analysis: two tailed paired Student's T-test. Results. M/L shift: There was a tendency for the patella to track 2mm more laterally with a FB or MB TKR compared to the natural knee, but this did not reach significance. Tilt: The patella in the natural knee tilted progressively laterally from extension to flexion, plateauing at 50° of flexion (20°: 1.9+/−2.7°, 40°: 5.6+/−5.4°, 60°: 6.2+/−6.4°, 80°:6.5+/−7.3°, 90°: 6.4+/−7.7°). With a FB or MB TKR the patellae also tilted laterally up to 50 degree of flexion, but then started to tilt back medially, reaching the neutral position at 90° again. There was no difference between the FB and MB TKRs. (Fixed bearing: 20°: 2.5+/−7.2° p=0.30, 40°: 3.7°+/−6.5° p=0.15, 60°: 3.1+/−5.8° p=0.02, 80°:1.2+/−6.5° p=0.001, 90°: 0.3+/−7.2° p=0.001, Mobile bearing: 20°: 0.3+/−5.5° p=0.27, 40°: 3.6+/−5.2° p=0.08, 60°: 2.1°+/−5.8 p=0.01, 80°: 0.2+/−6.8 p=0.003, 90°: -0.6+/−7.3 p=0.002; vs. natural). Trochlea position: The centre of the patellar groove of the femur component was more lateral than the trochlea by 2-5mm, it also extended 10mm further proximally. Conclusion. There are kinematic differences in patellar tracking between the natural knee and a FB/MB TKR. Compared to the FB TKR the patellar kinematics of the MB TKR is not more natural

Aims. 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. Patients and Methods. 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). Conclusion. 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

Polyethylene particulate wear debris continues to be implicated in the aetiology of aseptic loosening following knee arthroplasty. The Oxford unicompartmental knee arthroplasty employs a spherical femoral component and a fully congruous meniscal bearing to increase contact area and theoretically reduce the potential for polyethylene wear. This study measures the in vivo ten-year linear wear of the device, using a roentgenstereophotogrammetric technique.

In this in vivo study, seven medial Oxford unicompartmental prostheses, which had been implanted ten years previously were studied. Stereo pairs of radiographs were acquired for each patient and the films were analysed using a roentgen stereophotogrammetric analysis calibration and a computer-aided design model silhouette-fitting technique. Penetration of the femoral component into the original volume of the bearing was our estimate of linear wear. In addition, eight control patients were examined less than three weeks post-insertion of an Oxford prosthesis, where no wear would be expected. The control group showed no measured wear and suggested a system accuracy of 0.1 mm. At ten years, the mean linear wear rate was 0.02 mm/year.

The results from this in vivo study confirm that the device has low ten-year linear wear in clinical practice. This may offer the device a survival advantage in the long term.

This single-blinded randomised controlled trial investigated whether one design of mobile-bearing (MB) total knee replacement (TKR) has any advantage over a fixed-bearing (FB) design on long-term fixation as measured by radiostereometry. The amount of wear underneath the mobile bearing was also evaluated. A series of 42 knees was randomised to MB or FB tibial components with appropriate polyethylene inserts and followed for between ten and 12 years, or until the death of the patient. The polyethylene in the MB group was superior in that it was gamma-irradiated in inert gas and was calcium-stearate free; the polyethylene in the FB group was gamma-irradiated in air and contained calcium stearate. In theory this should be advantageous to the wear rate of the MB group. At final follow-up the overall mean migration was 0.75 mm (. sd. 0.76) in the MB group and 0.66 mm (. sd. 0.4) in the FB group, with the FB group demonstrating more posterior tilt and the MB group more internal rotation. In the FB group there was one revision for aseptic loosening, but none in the MB group. There were no significant differences in clinical or radiological scores. . For the MB group, the mean linear wear rate on the under-surface was 0.026 mm/year (. sd.  0.014). This was significantly smaller than the wear rate of 0.11 mm/year (. sd. 0.06) in the MB between femur and polyethylene (p < 0.001). Nevertheless, even in a best-case setting the mobile bearings of this TKR design had no apparent advantage in terms of fixation over the FB knee prosthesis at ten to 12 years. The wear underneath the mobile bearing was small and is unlikely to be clinically relevant

There is conflicting evidence about the merits of mobile bearings in total knee replacement, partly because most randomised controlled trials (RCTs) have not been adequately powered. We report the results of a multicentre RCT of mobile versus fixed bearings. This was part of the knee arthroplasty trial (KAT), where 539 patients were randomly allocated to mobile or fixed bearings and analysed on an intention-to-treat basis. The primary outcome measure was the Oxford Knee Score (OKS) plus secondary measures including Short Form-12, EuroQol EQ-5D, costs, cost-effectiveness and need for further surgery.

There was no significant difference between the groups pre-operatively: mean OKS was 17.18 (sd 7.60) in the mobile-bearing group and 16.49 (sd 7.40) in the fixed-bearing group. At five years mean OKS was 33.19 (sd 16.68) and 33.65 (sd 9.68), respectively. There was no significant difference between trial groups in OKS at five years (-1.12 (95% confidence interval -2.77 to 0.52) or any of the other outcome measures. Furthermore, there was no significant difference in the proportion of patients with knee-related re-operations or in total costs.

In this appropriately powered RCT, over the first five years after total knee replacement functional outcomes, re-operation rates and healthcare costs appear to be the same irrespective of whether a mobile or fixed bearing is used.

Cite this article: Bone Joint J 2013;95-B:486–92.

Aims. Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs. Methods. A total of 21,610 medial UKAs from 2007 to 2018 were selected from the Dutch Arthroplasty Register. Multivariate Cox regression analyses were used to compare uncemented mobile bearings with cemented mobile and fixed bearings. Adjustments were made for patient and surgical factors, with their interactions being considered. Reasons and type of revision in the first two years after surgery were assessed. Results. In hospitals performing less than 100 cases per year, cemented mobile bearings reported comparable adjusted risks of revision as uncemented mobile bearings. However, in hospitals performing more than 100 cases per year, the adjusted risk of revision was higher for cemented mobile bearings compared to uncemented mobile bearings (hazard ratio 1.78 (95% confidence interval 1.34 to 2.35)). The adjusted risk of revision between cemented fixed bearing and uncemented mobile bearing was comparable, independent of annual hospital volume. In addition, 12.3% of uncemented mobile bearing, 20.3% of cemented mobile bearing, and 41.5% of uncemented fixed bearing revisions were for tibial component loosening. The figures for instability were 23.6%, 14.5% and 11.7%, respectively, and for periprosthetic fractures were 10.0%, 2.8%, and 3.5%. Bearing exchange was the type of revision in 40% of uncemented mobile bearing, 24.3% of cemented mobile bearing, and 5.3% cemented fixed bearing revisions. Conclusion. The findings of this study demonstrated improved survival with use of uncemented compared to cemented mobile bearings in medial UKA, only in those hospitals performing more than 100 cases per year. Cemented fixed bearings reported comparable survival results as uncemented mobile bearings, regardless of the annual hospital volume. The high rates of instability, periprosthetic fractures, and bearing exchange in uncemented mobile bearings emphasize the need for further research. Cite this article: Bone Joint J 2021;103-B(7):1261–1269

Aims

It has been suggested that mobile-bearing total knee arthroplasty (TKA) might lead to better outcomes by accommodating some femorotibial rotational mismatch, thereby reducing contact stresses and polyethylene wear. The aim of this study was to determine whether there is a difference between fixed- and mobile-bearing versions of a contemporary TKA with respect to durability, range of movement (ROM) and function, ten years postoperatively.

Aims. To report mid- to long-term results of Oxford mobile bearing domed lateral unicompartmental knee arthroplasty (UKA), and determine the effect of potential contraindications on outcome. Methods. A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and the presence of full-thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results. Median follow-up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%); 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing, and 12 (4%) were revised for medial osteoarthritis (OA). Ten-year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion. Domed lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. It is recommended that the stability of the bearing is assessed intraoperatively. If the bearing can easily be displaced, the fixed rather than the mobile bearing version of the Oxford lateral tibial component should be inserted instead. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications. Cite this article: Bone Joint J 2020;102-B(8):1033–1040

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. Unicompartmental knee replacement (UKR) offers advantages over total knee replacement but has higher revision rates particularly for aseptic loosening. Cementless UKR was introduced in an attempt to address this. We used National Joint Registry (NJR) data to compare the 10-year results of cemented and cementless mobile bearing UKR whilst matching for important patient, implant and surgical factors. We also explored the influence of caseload on outcome. Methods. We performed a retrospective observational study using NJR data on 30,814 cemented and 9,708 cementless mobile bearing UKR implanted between 2004 and 2016. Logistic regression was utilised to calculate propensity scores allowing for matching of cemented and cementless groups for various patient, implant and surgical confounders, including surgeon's caseload, using a one to one ratio. 14,814 UKRs (7407 cemented and 7407 cementless) were propensity score matched. Outcomes studied were revision, defined as removal, addition or exchange of a component, and reasons for revision. Implant survival was compared using Cox regression models and groups were stratified according to surgeon caseload. Results. Based on raw unmatched data the 10 year survival for cementless and cemented UKR were 89% (95% CI 88%–90%) and 93% (CI 90%–96%), with cementless having a lower revision rate (Hazard ratio (HR)=0.59 (CI 0.52–0.68, p<0.001). However, there were differences between the cohorts in many potential confounding factors particularly surgeons caseload: Surgeons using cementless had a higher caseloads than those using cemented and for both cohorts the revision rate decreased with increasing caseload. Following matching, all potential confounders were well balanced and the 10-year survival for cementless and cemented were 90% (CI 88%–92%) and 93% (95% CI 90–96%) with cementless having a lower revision rate (HR 0.76; CI 0.64–0.91; p=0.003). This was due to rate of revision for aseptic loosening more than halving (p<0.001) in the cementless (n=31, 0.4%) compared to cemented (n=74, 1.0%) and the rate of revision for pain decreasing (p=0.03) in the cementless (n=34, 0.5%) compared to the cemented (n=55, 0.7%). However, the rate of peri-prosthetic fracture increased significantly (p=0.01) in the cementless (n=19, 0.3%) compared to the cemented (n=7, 0.1%). Following matching the decrease in revision rate with the cementless was similar for low (<10 cases/year; HR 0.74), medium (10–30 cases/year; HR 0.79) and high (>10 cases/year; HR 0.79) caseload surgeons. The 10- year survival for cementless and cemented were for low caseload 87% & 82%, medium caseload 94% & 92% and high caseload 98% & 94% respectively. Conclusions. This is the first study to compare the 10-year survival of the cementless and cemented mobile bearing UKR. We have demonstrated that the cementless device has a 24% reduced risk of revision and that this was independent of surgeon caseload and other important patient, surgical and implant confounders. This improvement was due to the rate of revision for aseptic loosening and pain halving. However, there was a small increase in rate of periprosthetic fracture. The results of both cemented and cementless UKR improved with increasing surgeon caseload. Low volume surgeons have poor results with both cemented and cementless UKR so should consider either stopping doing UKR or doing more. Medium and high volume surgeons should consider using the cementless. High volume surgeons using the cementless had particularly good results with a 10-year survival of 98%. For figures, tables, or references, please contact authors directly

Abstract. Introduction. Medial fix bearing unicompartmental knee replacement (UKR) designs are consider safe and effective implants with many registries data and big cohort series showing excellent survivorship and clinical outcome comparable to that reported for the most expensive and surgically challenging medial UKR mobile bearing designs. However, whether all polyethylene tibial components (all-poly) provided comparable results to metal-backed modular components during medial fix bearing UKR remains unclear. There have been previous suggestions that all-poly tibia UKR implants might show unacceptable higher rates of early failure due to tibial component early loosening especially in high body max index (BMI) patients. This study aims to find out the short and long-term survival rate of all-poly tibia UKR and its relationship with implant thickness and patient demographics including sex, age, ASA and BMI. Material and Methods. we present the results of a series of 388 medial fixed bearing all-polly tibia UKR done in our institution by a single surgeon between 2007–2019. Results. We found out excellent implant survival with this all-poly tibia UKR design with 5 years survival rate: 96.42%, 7 years survival rate: 95.33%, and 10 years survival rate: 91.87%. Only 1.28% had early revision within 2 years. Conclusion. Fixed bearing medial all-poly tibia UKR shows excellent survivor rate at 2, 5, 7 and 10 years follow up and the survival rate is not related with sex, age, BMI, ASA grade or implant thickness. Contrary to the popular belief, we found out that only 1.71% of all implants was revised due to implant loosening

Aims. For many designs of total knee arthroplasty (TKA) it remains unclear whether cemented or uncemented fixation provides optimal long-term survival. The main limitation in most studies is a retrospective or non-comparative study design. The same is true for comparative trials looking only at the survival rate as extensive sample sizes are needed to detect true differences in fixation and durability. Studies using radiostereometric analysis (RSA) techniques have shown to be highly predictive in detecting late occurring aseptic loosening at an early stage. To investigate the difference in predicted long-term survival between cemented, uncemented, and hybrid fixation of TKA, we performed a randomized controlled trial using RSA. Methods. A total of 105 patients were randomized into three groups (cemented, uncemented, and hybrid fixation of the ACS Mobile Bearing (ACS MB) knee system, implantcast). RSA examinations were performed on the first day after surgery and at scheduled follow-up visits at three months, six months, one year, and two years postoperatively. Patient-reported outcome measures (PROMs) were obtained preoperatively and after two years follow-up. Patients and follow-up investigators were blinded for the result of randomization. Results. RSA secondary stabilization did not show a significant difference between the three types of fixation. A maximum total point motion of less than 0.2 mm in the second postoperative year was shown in each group, which suggests stabilization of the implant. At 24 months after surgery, PROMs significantly improved compared to baseline in all treatment groups. No significant difference was observed between the three groups. Conclusion. Secondary stabilization measurements in this study demonstrated no significant difference between the groups. In all groups migration stabilized after initial settling of the implant. For this implant the long-term outcome is not expected to be influenced by the type of fixation to the bone. Cite this article: Bone Joint J 2021;103-B(1):98–104

Introduction. Kneeling ability is better in unicompartmental than total knee arthroplasty. There is also an impression that mobile bearing knees achieve better functional outcome than their fixed bearing cousins in unicompartmental and to a lesser extent total joint arthroplasty. In the UK, the market leading unicompartmental replacement is mobile bearing. Aim. To analyse kneeling ability after total and unicompartmental knee replacement using mobile and fixed bearing inserts. Methods. In our department there are two prospective randomised studies (fixed versus mobile) in this area. For total knee arthroplasty, 207 TKR patients receiving the same prosthesis (Rotaglide, Corin, UK) were randomised into mobile bearing (102 patients, mean age of 53 years) or fixed bearing (105 patients, mean age of 55 years). Regarding unicondylar knees, data was collected on 352 UKR patients who received the same implant (Uniglide - previously known as AMC - Corin, UK). Within this group there was a randomised controlled trial of fixed v mobile bearings: 52 patients (mean age 62 years) had a mobile insert and 57 (mean age 65 yrs) had a fixed insert. Data was also collected on patients undergoing fixed bearing lateral unicondylar replacement (Uniglide). All patients completed the Oxford Knee Questionnaire preoperatively, 1 year and 2 years postoperatively, (where 0 = bad and 48 = good). There kneeling ability (question 7) and total Oxford scores were analysed. We are currently collecting objective data on post-operative kneeling ability with force plate analysis and subjective anterior knee-specific scoring systems. Results. Subjective kneeling ability: Oxford Knee Score Question 7 as range 0-4, where 4 = good. Conclusion. Both fixed and mobile UKR and TKR have good outcome. No group produced good kneeling ability, but there was a modest improvement in all groups from the preoperative kneeling scores. Fixed bearing knee replacement showed better outcome than mobile bearing knees, in both UKR and TKR groups

Aims. This study compared the cobalt and chromium serum ion concentration of patients treated with two different metal-on-metal (MoM) hinged total knee arthroplasty (TKA) systems, as well as a titanium nitride (TiN)-coated variant. Methods. A total of 63 patients (65 implants) were treated using either a MoM-coated (n = 29) or TiN-coated (n = 7) hinged TKA (GenuX mobile bearing, MUTARS; Implantcast, Germany) versus the BPKS (Brehm, Germany) hinged TKA (n = 27), in which the weight placed on the MoM hinge is diffused through a polyethylene (PE) inlay, reducing the direct load on the MoM hinge. Serum cobalt and chromium ion concentrations were assessed after minimum follow-up of 12 months, as well as functional outcome and quality of life. Results. No differences in mean age (69 years, 40 to 86), mean age adapted Charlson Comorbidity Index (3.1 (SD 1.4)), mean BMI (29.2 kg/m. 2. (SD 5.8)), or number of other implants were observed between groups. Significant improvements in outcome scores and pain levels were achieved for all groups, and there was no difference in quality of life (12-Item Short-Form Health Survey questionnaire (SF-12)). Mean cobalt and chromium ion levels were significantly higher for the GenuX versus the BPKS hinged TKA (GenuX vs BPKS: cobalt: 16.3 vs 9.4 µg/l; chromium: 9.5 vs 5.2 µg/l). The TiN-coated implants did not appear to confer improvement in the metal ion levels. Metal ion concentrations above 7 µg/l were detected in 81%(29/36) of GenuX patients versus 41% (11/27) in the BPKS group. No GenuX patients had normal levels under 2 µg/l, versus 22% of BPKS patients. No significant reduction in outcome scores was observed regardless of the metal ion levels, whereas higher work-related activity was correlated with higher chromium concentrations. Conclusion. Hinged TKA, using MoM hinges, resulted in critically high cobalt and chromium ion concentrations. The BPKS hinged TKA showed significantly lower metal ion concentrations compared with the GenuX TKA. No benefits were observed using TiN coating. The different weightbearing mechanics might influence the wear of the component materials. Higher workloads and physical activity could influence chromium levels. Cite this article: Bone Joint J 2022;104-B(3):376–385

Introduction. Unidirectional mobile bearing knees (RP) were developed to optimise the tibio-femoral articulation in an effort to enhance function and reduce polyethylene wear. The self aligning bearing should also benefit the patello-femoral joint further improving outcome. This study was designed to assess whether these potential benefits are realised in the clinical setting. Methods. A total of 352 patients undergoing a PS PFC Sigma TKR were randomly allocated to receive either a Mobile Bearing (176 knees) or a Fixed Bearing (176 knees) tibial tray. Within each group a further randomisation for patella resurfacing versus retention was included. All knees were scored using standard tools (Oxford, AKSS, Patella Score) by independent nurse specialists. At 5 year review there had been 38 deaths (19 in each group), 5 revisions (4 fixed, 1 RP), 7 late patella resurfacings (4 fixed, 3 RP) and a small number of other patients had withdrawn, leaving 142 fixed bearing knees and 144 mobile bearing knees for evaluation. Results. The rotating platform TKR design had no impact on range of motion, Oxford Knee Score and American Knee Society knee and function scores when compared to its fixed bearing equivalent at minimum 5 year follow-up. Patella resurfacing, however, resulted in a greater improvement in knee function score from pre-op when compared to patella retention (25.5 vs 15.5, p=0.0015), with subsequent significant benefits seen in the SF-12 Physical and Total Scores (p=0.0004 and p=0.017 respectively). 5 year survivorship curves with revision for any cause as the endpoint were similar for both groups (fixed 96.2%, mobile 97.6%). This survivorship rises to 100% for both designs when considering aseptic loosening alone. Conclusion. There was no difference in performance between the fixed and RP groups. Patella resurfacing offered advantages over patella retention with this design and we would recommend its routine use

Introduction. Both mobile bearing and fixed bearing unicompartmental knee arthroplasty (UKA) have demonstrated clinical success. However, much debate persists about the superiority of a single design. Currently most clinical data is based on high volume centers data, however to reduce bias, we undertook a through review of retrospective national joint registries. In this study, we aim to investigate UKA implant utilization and survivorship between 2000 and 2018. Methods. Ten annual joint registry reports of various nations were reviewed. Due to the variable statistical methods of reporting implant use and survivorship we focused on three registries: Australia (AOANJRR), New Zealand (NZJR), United Kingdom (NJR) for uniformity. We evaluated UKA usage, survivorship, utilization and revision rates for each implant. Implant survivorship was reported in the registries and was compared within nations due to variation in statistical reporting. Results. UKAs accounted for 7.24–10.3% of all primary knee surgeries. The most popular implants were, in order of popularity, the Oxford (ZimmerBiomet, Warsaw IN), ZUK (Smith & Nephew, Memphis TN / LimaCorporate, Udine, Italy), Sigma HP (DePuy, Warsaw IN), Miller-Galante (ZimmerBiomet Warsaw IN), and Preservation (DePuy, Warsaw IN) models. UKA revision rates varied by nation and ranged from 8.22%–12.8%. The Sigma HP and ZUK designs had the lowest total percent revised in the registries-Australian (3.6% and 5.1%, respectively) and New Zealand (2.5% and 1.96%, respectively)-and demonstrated among the highest 10-year survivorship in the United Kingdom registry. The United Kingdom registry reports a greater number of mobile versus fixed bearing UKA undergoing revision for dislocation and/or subluxation and instability. Conclusion. Preference for implant design as well as survivorship rates varied significantly by nation. The fixed bearing ZUK and Sigma HP implants were among the highest performing implants across the three registries