Aims. The primary objective of this registry-based study was to compare patient-reported outcomes of cementless and cemented medial unicompartmental knee arthroplasty (UKA) during the first postoperative year. The secondary objective was to assess one- and three-year implant survival of both fixation techniques. Methods. We analyzed 10,862 cementless and 7,917 cemented UKA cases enrolled in the Dutch Arthroplasty Registry, operated between 2017 and 2021. Pre- to postoperative change in outcomes at six and 12 months’ follow-up were compared using mixed model analyses. Kaplan-Meier and Cox regression models were applied to quantify differences in implant survival. Adjustments were made for patient-specific variables and annual hospital volume. Results. Change from baseline in the Oxford Knee Score (OKS) and activity-related pain was comparable between groups. Adjustment for covariates demonstrated a minimally greater decrease in rest-related pain in the cemented group (β = -0.09 (95% confidence interval (CI) -0.16 to -0.01)). Cementless fixation was associated with a higher probability of achieving an excellent OKS outcome (> 41 points) (adjusted odds ratio 1.2 (95% CI 1.1 to 1.3)). The likelihood of one-year implant survival was greater for cemented implants (adjusted hazard ratio (HR) 1.35 (95% CI 1.01 to 1.71)), with higher revision rates for periprosthetic fractures of cementless implants. During two to three years’ follow-up, the likelihood of implant survival was non-significantly greater for cementless UKA (adjusted HR 0.64 (95% CI 0.40 to 1.04)), primarily due to increased revision rates for tibial loosening of cemented implants. Conclusion. Cementless and cemented medial UKA led to comparable improvement in physical function and pain reduction during the initial postoperative year, albeit with a greater likelihood of achieving excellent OKS outcomes after cementless UKA. Anticipated differences in early physical function and pain should not be a decisive factor in the choice of fixation technique. However, surgeons should consider the differences in short- and long-term implant survival when deciding which implant to use. Cite this article: Bone Jt Open 2024;5(5):401–410

Aims

The aim of this study was to describe the pattern of revision indications for unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) and any change to this pattern for UKA patients over the last 20 years, and to investigate potential associations to changes in surgical practice over time.

Aims. Total knee arthroplasty (TKA) with a highly congruent condylar-stabilized (CS) articulation may be advantageous due to increased stability versus cruciate-retaining (CR) designs, while mitigating the limitations of a posterior-stabilized construct. The aim was to assess ten-year implant survival and functional outcomes of a cemented single-radius TKA with a CS insert, performed without posterior cruciate ligament sacrifice. Methods. This retrospective cohort study included consecutive patients undergoing TKA at a specialist centre in the UK between November 2010 and December 2012. Data were collected using a bespoke electronic database and cross-referenced with national arthroplasty audit data, with variables including: preoperative characteristics, intraoperative factors, complications, and mortality status. Patient-reported outcome measures (PROMs) were collected by a specialist research team at ten years post-surgery. There were 536 TKAs, of which 308/536 (57.5%) were in female patients. The mean age was 69.0 years (95% CI 45.0 to 88.0), the mean BMI was 32.2 kg/m. 2. (95% CI 18.9 to 50.2), and 387/536 (72.2%) survived to ten years. There were four revisions (0.7%): two deep infections (requiring debridement and implant retention), one aseptic loosening, and one haemosiderosis. Results. Kaplan-Meier analysis demonstrated no difference in implant survival according to sex, age, or obesity status. Ten-year PROMs were available for 196/387 (50.6%) surviving patients and were excellent: mean Oxford Knee Score 34.4 (95% CI 32.7 to 36.1); mean Forgotten Joint Score (FJS) 51.2 (95% CI 16.1 to 86.3); mean EuroQol five-dimension five-level questionnaire score 69.9 (95% CI 46.8 to 93.0); 141/196 (71.9%) achieved the 22-point FJS patient-acceptable symptom state (PASS); and 156/196 (79.6%) were “very satisfied or satisfied”. Conclusion. This is the only large study reporting ten-year implant survival and functional outcomes of TKA using a cemented single-radius design and with a CS tibial bearing construct. The findings of excellent implant survival, safety, and functional outcomes indicate that this combination is a safe and effective option in routine TKA. Further investigation of this single-radius design TKA with CS tibial bearings with well-matched patient study groups will allow further insight into the performance of these implants. Cite this article: Bone Joint J 2024;106-B(8):808–816

Aims. Unicompartmental knee arthroplasty (UKA) has a higher risk of revision than total knee arthroplasty (TKA), particularly for younger patients. The outcome of knee arthroplasty is typically defined as implant survival or revision incidence after a defined number of years. This can be difficult for patients to conceptualize. We aimed to calculate the ‘lifetime risk’ of revision for UKA as a more meaningful estimate of risk projection over a patient’s remaining lifetime, and to compare this to TKA. Methods. Incidence of revision and mortality for all primary UKAs performed from 1999 to 2019 (n = 13,481) was obtained from the New Zealand Joint Registry (NZJR). Lifetime risk of revision was calculated for patients and stratified by age, sex, and American Society of Anesthesiologists (ASA) grade. Results. The lifetime risk of revision was highest in the youngest age group (46 to 50 years; 40.4%) and decreased sequentially to the oldest (86 to 90 years; 3.7%). Across all age groups, lifetime risk of revision was higher for females (ranging from 4.3% to 43.4% vs males 2.9% to 37.4%) and patients with a higher ASA grade (ASA 3 to 4, ranging from 8.8% to 41.2% vs ASA 1 1.8% to 29.8%). The lifetime risk of revision for UKA was double that of TKA across all age groups (ranging from 3.7% to 40.4% for UKA, and 1.6% to 22.4% for TKA). The higher risk of revision in younger patients was associated with aseptic loosening in both sexes and pain in females. Periprosthetic joint infection (PJI) accounted for 4% of all UKA revisions, in contrast with 27% for TKA; the risk of PJI was higher for males than females for both procedures. Conclusion. Lifetime risk of revision may be a more meaningful measure of arthroplasty outcomes than implant survival at defined time periods. This study highlights the higher lifetime risk of UKA revision for younger patients, females, and those with a higher ASA grade, which can aid with patient counselling prior to UKA. Cite this article: Bone Joint J 2022;104-B(6):672–679

Aims. The purpose of this study was to compare the clinical outcomes, mortalities, implant survival rates, and complications of total knee arthroplasty (TKA) in patients with or without hepatitis B virus (HBV) infection over at least ten years of follow-up. Methods. From January 2008 to December 2010, 266 TKAs were performed in 169 patients with HBV (HBV group). A total of 169 propensity score–matched patients without HBV were chosen for the control group in a one-to-one ratio. Then, the clinical outcomes, mortalities, implant survival rates, and complications of TKA in the two groups were compared. The mean follow-up periods were 11.7 years (10.5 to 13.4) in the HBV group and 11.8 years (11.5 to 12.4) in the control group. Results. The mean Knee Society scores in the HBV and control groups improved from 37.1 (SD 5.6) and 38.4 (SD 5.4) points preoperatively to 78.1 (SD 10.8) and 81.7 (SD 10.2) points at final follow-up (p = 0.314), while the mean function scores in the HBV and control groups improved from 36.2 and 37.3 points preoperatively to 77.8 and 83.2 points at final follow-up (p = 0.137). Nine knees in the HBV group required revision surgery, including seven due to septic loosening and two due to aseptic loosening. Four knees in the control group required revision surgery, including three due to septic loosening and one due to aseptic loosening. Kaplan–Meier survivorship analysis with the revision of either component as an endpoint in the HBV and control groups estimated 96.6% and 98.5% chances of survival for ten years, respectively (p = 0.160). Conclusion. TKA in patients with HBV infection resulted in good clinical outcomes and survivorship. However, there was a higher revision rate over a minimum ten-year follow-up period compared to TKA in patients without HBV infection. Cite this article: Bone Jt Open 2022;3(6):470–474

Aims. This prospective study reports longitudinal, within-patient, patient-reported outcome measures (PROMs) over a 15-year period following cemented single radius total knee arthroplasty (TKA). Secondary aims included reporting PROMs trajectory, 15-year implant survival, and patient attrition from follow-up. Methods. From 2006 to 2007, 462 consecutive cemented cruciate-retaining Triathlon TKAs were implanted in 426 patients (mean age 69 years (21 to 89); 290 (62.7%) female). PROMs (12-item Short Form Survey (SF-12), Oxford Knee Score (OKS), and satisfaction) were assessed preoperatively and at one, five, ten, and 15 years. Kaplan-Meier survival and univariate analysis were performed. Results. At 15 years, 28 patients were lost to follow-up (6.1%) and 221 patients (51.9%) had died, with the mean age of the remaining cohort reducing by four years. PROMs response rates among surviving patients were: one-year 63%; five-year 72%; ten-year 94%; and 15-year 59%. OKS and SF-12 scores changed significantly over 15 years (p < 0.001). The mean improvement in OKS was 18.8 (95% confidence (CI) 16.7 to 19.0) at one year. OKS peaked at five years (median 43 years) declining thereafter (p < 0.001), though at 15 years it remained 17.5 better than preoperatively. Age and sex did not alter this trajectory. A quarter of patients experienced a clinically significant decline (≥ 7) in OKS from five to ten years and from ten to 15 years. The SF-12 physical component score displayed a similar trajectory, peaking at one year (p < 0.001). Patient satisfaction was 88% at one, five, and ten years, and 94% at 15 years. In all, 15-year Kaplan-Meier survival was 97.6% (95% CI 96.0% to 99.2%) for any revision, and 98.9% (95% CI 97.9% to 99.9%) for aseptic revision. Conclusion. Improvements in PROMs were significant and maintained following single radius TKA, with OKS peaking at five years, and generic physical health peaking at one year. Patient satisfaction remained high at 15 years, at which point 2.4% had been revised. Cite this article: Bone Jt Open 2023;4(10):808–816

Aims. The optimal bearing surface design for medial unicompartmental knee arthroplasty (UKA) remains controversial. The aim of this study was to compare outcomes of fixed-bearing (FB) and mobile-bearing (MB) UKAs from a single high-volume institution. Methods. Prospectively collected data were reviewed for all primary cemented medial UKAs performed by seven surgeons from January 2006 to December 2022. A total of 2,999 UKAs were identified, including 2,315 FB and 684 MB cases. The primary outcome measure was implant survival. Secondary outcomes included 90-day and cumulative complications, reoperations, component revisions, conversion arthroplasties, range of motion, and patient-reported outcome measures. Overall mean age at surgery was 65.7 years (32.9 to 94.3), 53.1% (1,593/2,999) of UKAs were implanted in female patients, and demographics between groups were similar (p > 0.05). The mean follow-up for all UKAs was 3.7 years (0.0 to 15.6). Results. Using revision for any reason as an endpoint, five-year survival for FB UKAs was 97.2% (95% CI 96.4 to 98.1) compared to 96.0% for MB (95% CI 94.1 to 97.9; p = 0.008). The FB group experienced fewer component revisions (14/2,315, 0.6% vs 12/684, 1.8%; p < 0.001) and conversion arthroplasties (38/2315, 1.6% vs 24/684, 3.5%; p < 0.001). A greater number of MB UKAs underwent revision due to osteoarthritis progression (FB = 21/2,315, 0.9% vs MB = 16/684, 2.3%; p = 0.003). In the MB group, 12 (1.8%) subjects experienced bearing dislocations which required revision surgery. There were 15 early periprosthetic tibia fractures (0.6%) in the FB group compared to 0 for MB (p = 0.035). Conclusion. In similar patient populations, FB UKAs demonstrated slightly higher survival than a commonly used MB design. Adverse event profiles differed by bearing type, with an increased risk of bearing dislocation and OA progression with MB designs, and early periprosthetic tibia fractures for FB designs. Cite this article: Bone Joint J 2024;106-B(9):916–923

Aims. The success of total knee arthroplasty (TKA) is usually measured using functional outcome scores and revision-free survivorship. However, reporting the lifetime risk of revision may be more meaningful to patients when gauging risks, especially in younger patients. We aimed to assess the lifetime risk of revision for patients in different age categories at the time of undergoing primary TKA. Methods. The New Zealand Joint Registry database was used to obtain revision rates, mortality, and the indications for revision for all primary TKAs performed during an 18-year period between January 1999 and December 2016. Patients were stratified into age groups at the time of the initial TKA, and the lifetime risk of revision was calculated according to age, sex, and the American Society of Anesthesiologists (ASA) grade. The most common indications for revision were also analyzed for each age group. Results. The overall ten-year survival rate was 95.6%. This was lowest in the youngest age group (between 46 and 50 years) and increased sequentially with increasing age. The lifetime risk of requiring revision was 22.4% in those aged between 46 and 50 years at the time of the initial surgery, and decreased linearly with increasing age to 1.15% in those aged between 90 and 95 years at the time of surgery. Higher ASA grades were associated with increased lifetime risk of revision in all age groups. The three commonest indications for revision were aseptic loosening, infection, and unexplained pain. Young males, aged between 46 and 50 years, had the highest lifetime risk of revision (25.2%). Conclusion. Lifetime risk of revision may be a more meaningful measure of outcome than implant survival at defined time periods when counselling patients prior to TKA. This study highlights the considerably higher lifetime risk of revision surgery for all indications, including infection, in younger male patients. Cite this article: Bone Joint J 2022;104-B(2):235–241

Aims. This study compares the PFC total knee arthroplasty (TKA) system in a prospective randomized control trial (RCT) of the mobile-bearing rotating-platform (RP) TKA against the fixed-bearing (FB) TKA. This is the largest RCT with the longest follow-up where cruciate-retaining PFC total knee arthroplasties are compared in a non-bilateral TKA study. Patients and Methods. A total of 167 patients (190 knees with 23 bilateral cases), were recruited prospectively and randomly assigned, with 91 knees receiving the RP and 99 knees receiving FB. The mean age was 65.5 years (48 to 82), the mean body mass index (BMI) was 29.7 kg/m. 2. (20 to 52) and 73 patients were female. The Knee Society Score (KSS), Knee Society Functional Score (KSFS), Oxford Knee Score (OKS), Western Ontario and McMaster Universities Arthritis Index (WOMAC), and 12-Item Short-Form Health Survey Physical and Mental Component Scores (SF-12 PCS, SF-12 MCS) were gathered and recorded preoperatively, at five-years’ follow-up, and at ten years’ follow-up. Additionally, Knee Injury and Osteoarthritis Outcome Scores (KOOS) were collected at five- and ten-year follow-ups. The prevalence of radiolucent lines (RL) on radiographs and implant survival were recorded at five- and ten-year follow-ups. Results. At the ten-year follow-up, the RP group (n = 39) had a statistically significant superior score in the OKS (p = 0.001), WOMAC (p = 0.023), SF-12 PCS (p = 0.019), KOOS Activities of Daily Living (ADL) (p = 0.010), and KOOS Sport and Recreation (Sport/Rec) (p = 0.006) compared with the FB group (n = 46). The OKS, SF-12 PCS, and KOOS Sport/Rec at ten years had mean scores above the minimal clinically important difference (MCID) threshold. There was no significant difference in prevalence of radiolucency between groups at five-years’ follow-up (p = 0.449), nor at ten-years’ follow-up (p = 0.08). Implant survival rate at 14 years postoperative was 95.2 (95% CI 90.7 to 99.8) and 94.7 (95% CI 86.8 to 100.0) for the RP and FB TKAs, respectively. Conclusion. At ten-year follow-up, the mobile-bearing knee joint arthroplasty had statistically and clinically relevant superior OKS, SF-12 PCS, and KOOS (Sport/Rec) than the fixed-bearing platform. No difference was seen in prevalence of radiolucent lines. There was a greater than 94% implant survival rate for both cohorts at 14 years. Cite this article: Bone Joint J 2018;100-B:1336–44

Aims. Periprosthetic joint infection (PJI) is a devastating complication following total knee arthroplasty (TKA). Two-stage revision has traditionally been considered the gold standard of treatment for established infection, but increasing evidence is emerging in support of one-stage exchange for selected patients. The objective of this study was to determine the outcomes of single-stage revision TKA for PJI, with mid-term follow-up. Methods. A total of 84 patients, with a mean age of 68 years (36 to 92), underwent single-stage revision TKA for confirmed PJI at a single institution between 2006 and 2016. In all, 37 patients (44%) were treated for an infected primary TKA, while the majority presented with infected revisions: 31 had undergone one previous revision (36.9%) and 16 had multiple prior revisions (19.1%). Contraindications to single-stage exchange included systemic sepsis, extensive bone or soft-tissue loss, extensor mechanism failure, or if primary wound closure was unlikely to be achievable. Patients were not excluded for culture-negative PJI or the presence of a sinus. Results. Overall, 76 patients (90.5%) were infection-free at a mean follow-up of seven years, with eight reinfections (9.5%). Culture-negative PJI was not associated with a higher reinfection rate (p = 0.343). However, there was a significantly higher rate of recurrence in patients with polymicrobial infections (p = 0.003). The mean Oxford Knee Score (OKS) improved from 18.7 (SD 8.7) preoperatively to 33.8 (SD 9.7) at six months postoperatively (p < 0.001). The Kaplan-Meier implant survival rate for all causes of reoperation, including reinfection and aseptic failure, was 95.2% at one year (95% confidence interval (CI) 87.7 to 98.2), 83.5% at five years (95% CI 73.2 to 90.3), and 78.9% at 12 years (95% CI 66.8 to 87.2). Conclusion. One-stage exchange, using a strict debridement protocol and multidisciplinary input, is an effective treatment option for the infected TKA. This is the largest single-surgeon series of consecutive cases reported to date, with broad inclusion criteria. Cite this article: Bone Jt Open 2021;2(5):305–313

Aims. The purpose of this study was to compare the radiological outcomes of manual versus robotic-assisted medial unicompartmental knee arthroplasty (UKA). Methods. Postoperative radiological outcomes from 86 consecutive robotic-assisted UKAs (RAUKA group) from a single academic centre were retrospectively reviewed and compared to 253 manual UKAs (MUKA group) drawn from a prior study at our institution. Femoral coronal and sagittal angles (FCA, FSA), tibial coronal and sagittal angles (TCA, TSA), and implant overhang were radiologically measured to identify outliers. Results. When assessing the accuracy of RAUKAs, 91.6% of all alignment measurements and 99.2% of all overhang measurements were within the target range. All alignment and overhang targets were simultaneously met in 68.6% of RAUKAs. When comparing radiological outcomes between the RAUKA and MUKA groups, statistically significant differences were identified for combined outliers in FCA (2.3% vs 12.6%; p = 0.006), FSA (17.4% vs 50.2%; p < 0.001), TCA (5.8% vs 41.5%; p < 0.001), and TSA (8.1% vs 18.6%; p = 0.023), as well as anterior (0.0% vs 4.7%; p = 0.042), posterior (1.2% vs 13.4%; p = 0.001), and medial (1.2% vs 14.2%; p < 0.001) overhang outliers. Conclusion. Robotic system navigation decreases alignment and overhang outliers compared to manual UKA. Given the association between component placement errors and revision in UKA, this strong significant improvement in accuracy may improve implant survival. Level of Evidence: III. Cite this article: Bone Jt Open 2021;2-3:191–197

Aims. The purpose of this study was to assess mid-term survivorship following primary total knee arthroplasty (TKA) with Optetrak Logic components and identify the most common revision indications at a single institution. Methods. We identified a retrospective cohort of 7,941 Optetrak primary TKAs performed from January 2010 to December 2018. We reviewed the intraoperative findings of 369 TKAs that required revision TKA from January 2010 to December 2021 and the details of the revision implants used. Kaplan-Meier analysis was used to determine survivorship. Cox regression analysis was used to examine the impact of patient variables and year of implantation on survival time. Results. The estimated survivorship free of all-cause revision was 98% (95% confidence interval (CI) 97% to 98%), 95% (95% CI 95% to 96%), and 86% (95% CI 83% to 88%) at two, five, and ten years, respectively. In 209/369 revisions there was a consistent constellation of findings with varying severity that included polyethylene wear and associated synovitis, osteolysis, and component loosening. This failure mode, which we refer to as aseptic mechanical failure, was the most common revision indication. The mean time from primary TKA to revision for aseptic mechanical failure was five years (5 months to 11 years). Conclusion. In this series of nearly 8,000 primary TKAs performed with a specific implant, we identified a lower-than-expected mid-term survivorship and a high number of revisions with a unique presentation. This study, along with the recent recall of the implant, confirms the need for frequent monitoring of patients with Optetrak TKAs given the incidence of polyethylene failure, osteolysis, and component loosening. Cite this article: Bone Joint J 2023;105-B(3):277–283

Limb alignment in total knee arthroplasty (TKA) influences periarticular soft-tissue tension, biomechanics through knee flexion, and implant survival. Despite this, there is no uniform consensus on the optimal alignment technique for TKA. Neutral mechanical alignment facilitates knee flexion and symmetrical component wear but forces the limb into an unnatural position that alters native knee kinematics through the arc of knee flexion. Kinematic alignment aims to restore native limb alignment, but the safe ranges with this technique remain uncertain and the effects of this alignment technique on component survivorship remain unknown. Anatomical alignment aims to restore predisease limb alignment and knee geometry, but existing studies using this technique are based on cadaveric specimens or clinical trials with limited follow-up times. Functional alignment aims to restore the native plane and obliquity of the joint by manipulating implant positioning while limiting soft tissue releases, but the results of high-quality studies with long-term outcomes are still awaited. The drawbacks of existing studies on alignment include the use of surgical techniques with limited accuracy and reproducibility of achieving the planned alignment, poor correlation of intraoperative data to long-term functional outcomes and implant survivorship, and a paucity of studies on the safe ranges of limb alignment. Further studies on alignment in TKA should use surgical adjuncts (e.g. robotic technology) to help execute the planned alignment with improved accuracy, include intraoperative assessments of knee biomechanics and periarticular soft-tissue tension, and correlate alignment to long-term functional outcomes and survivorship

Aims. It is not clear whether anterior knee pain and osteoarthritis (OA) of the patellofemoral joint (PFJ) are contraindications to medial unicompartmental knee arthroplasty (UKA). Our aim was to investigate the long-term outcome of a consecutive series of patients, some of whom had anterior knee pain and PFJ OA managed with UKA. Patients and Methods. We assessed the ten-year functional outcomes and 15-year implant survival of 805 knees (677 patients) following medial mobile-bearing UKA. The intra-operative status of the PFJ was documented and, with the exception of bone loss with grooving to the lateral side, neither the clinical or radiological state of the PFJ nor the presence of anterior knee pain were considered a contraindication. The impact of radiographic findings and anterior knee pain was studied in a subgroup of 100 knees (91 patients). Results. There was no relationship between functional outcomes, at a mean of ten years, or 15-year implant survival, and pre-operative anterior knee pain, or the presence or degree of cartilage loss documented intra-operatively at the medial patella or trochlea, or radiographic evidence of OA in the medial side of the PFJ. In 6% of cases there was full thickness cartilage loss on the lateral side of the patella. In these cases, the overall ten-year function and 15-year survival was similar to those without cartilage loss; however they had slightly more difficulty with descending stairs. Radiographic signs of OA seen in the lateral part of the PFJ were not associated with a definite compromise in functional outcome or implant survival. Conclusion. Severe damage to the lateral side of the PFJ with bone loss and grooving remains a contraindication to mobile-bearing UKA. Less severe damage to the lateral side of the PFJ and damage to the medial side, however severe, does not compromise the overall function or survival, so should not be considered to be a contraindication. However, if a patient does have full thickness cartilage loss on the lateral side of the PFJ they may have a slight compromise in their ability to descend stairs. Pre-operative anterior knee pain also does not compromise the functional outcome or survival and should not be considered to be a contraindication. Cite this article: Bone Joint J 2017;99-B:632–9

Aims. While medial unicompartmental knee arthroplasty (UKA) is indicated for patients with full-thickness cartilage loss, it is occasionally used to treat those with partial-thickness loss. The aim of this study was to investigate the five-year outcomes in a consecutive series of UKAs used in patients with partial thickness cartilage loss in the medial compartment of the knee. Patients and Methods. Between 2002 and 2014, 94 consecutive UKAs were undertaken in 90 patients with partial thickness cartilage loss and followed up independently for a mean of six years (1 to 13). These patients had partial thickness cartilage loss either on both femur and tibia (13 knees), or on either the femur or the tibia, with full thickness loss on the other surface of the joint (18 and 63 knees respectively). Using propensity score analysis, these patients were matched 1:2 based on age, gender and pre-operative Oxford Knee Score (OKS) with knees with full thickness loss on both the femur and tibia. The functional outcomes, implant survival and incidence of re-operations were assessed at one, two and five years post-operatively. A subgroup of 36 knees in 36 patients with partial thickness cartilage loss, who had pre-operative MRI scans, was assessed to identify whether there were any factors identified on MRI that predicted the outcome. Results. Knees with partial thickness cartilage loss had significantly worse functional outcomes at one, two and five years post-operatively compared with those with full thickness loss. A quarter of knees with partial thickness loss had a fair or poor result and a fifth failed to achieve a clinically significant improvement in OKS from a baseline of four points or more; double that seen in knees with full thickness loss. Whilst there was no difference in implant survival between the groups, the rate of re-operation in knees with partial thickness loss was three times higher. Most of the re-operations (three-quarters), were arthroscopies for persistent pain. Compared with those achieving good or excellent outcomes, patients with partial thickness cartilage loss who achieved fair or poor outcomes were younger and had worse pre-operative functional scores. However, there were no other differences in the baseline demographics. MRI findings of full thickness cartilage loss, subchondral oedema, synovitis or effusion did not provide additional prognostic information. Conclusion. Medial UKA should be reserved for patients with full thickness cartilage loss on both the femur and tibia. Whilst some patients with partial thickness loss achieve a good result we cannot currently identify which these will be and in this situation MRI is unhelpful and misleading. Cite this article: Bone Joint J 2017;99-B:475–82

Aims. The primary aim of the study was to perform an analysis to identify the cost per quality-adjusted life-year (QALY) of robot-assisted unicompartmental knee arthroplasty (rUKA) relative to manual total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) for patients with isolated medial compartment osteoarthritis (OA) of the knee. Secondary aims were to assess how case volume and length of hospital stay influenced the relative cost per QALY. Patients and Methods. A Markov decision analysis was performed, using known parameters for costs, outcomes, implant survival, and mortality, to assess the cost-effectiveness of rUKA relative to manual TKA and UKA for patients with isolated medial compartment OA of the knee with a mean age of 65 years. The influence of case volume and shorter hospital stay were assessed. Results. Using a model with an annual case volume of 100 patients, the cost per QALY of rUKA was £1395 and £1170 relative to TKA and UKA, respectively. The cost per QALY was influenced by case volume: a low-volume centre performing ten cases per year would achieve a cost per QALY of £7170 and £8604 relative to TKA and UKA. For a high-volume centre performing 200 rUKAs per year with a mean two-day length of stay, the cost per QALY would be £648; if performed as day-cases, the cost would be reduced to £364 relative to TKA. For a high-volume centre performing 200 rUKAs per year with a shorter length of stay of one day relative to manual UKA, the cost per QALY would be £574. Conclusion . rUKA is a cost-effective alternative to manual TKA and UKA for patients with isolated medial compartment OA of the knee. The cost per QALY of rUKA decreased with reducing length of hospital stay and with increasing case volume, compared with TKA and UKA. Cite this article: Bone Joint J 2019;101-B:1063–1070

Aims. Robotic-assisted unicompartmental knee arthroplasty (UKA) promises accurate implant placement with the potential of improved survival and functional outcomes. The aim of this study was to present the current evidence for robotic-assisted UKA and describe the outcome in terms of implant positioning, range of movement (ROM), function and survival, and the types of robot and implants that are currently used. Materials and Methods. A search of PubMed and Medline was performed in October 2018 in line with the Preferred Reporting Items for Systematic Review and Meta-Analysis statement. Search terms included “robotic”, “knee”, and “surgery”. The criteria for inclusion was any study describing the use of robotic UKA and reporting implant positioning, ROM, function, and survival for clinical, cadaveric, or dry bone studies. Results. A total of 528 articles were initially identified from the databases and reference lists. Following full text screening, 38 studies that satisfied the inclusion criteria were included. In all, 20 studies reported on implant positioning, 18 on functional outcomes, 16 on survivorship, and six on ROM. The Mako (Stryker, Mahwah, New Jersey) robot was used in 32 studies (84%), the BlueBelt Navio (Blue Belt Technologies, Plymouth, Minnesota) in three (8%), the Sculptor RGA (Stanmore Implants, Borehamwood United Kingdom) in two (5%), and the Acrobot (The Acrobot Co. Ltd., London, United Kingdom) in one study (3%). The most commonly used implant was the Restoris MCK (Stryker). Nine studies (24%) did not report the implant that was used. The pooled survivorship at six years follow-up was 96%. However, when assessing survival according to implant design, survivorship of an inlay (all-polyethylene) tibial implant was 89%, whereas that of an onlay (metal-backed) implant was 97% at six years (odds ratio 3.66, 95% confidence interval 20.7 to 6.46, p < 0.001). Conclusion. There is little description of the choice of implant when reporting robotic-assisted UKA, which is essential when assessing survivorship, in the literature. Implant positioning with robotic-assisted UKA is more accurate and more reproducible than that performed manually and may offer better functional outcomes, but whether this translates into improved implant survival in the mid- to longer-term remains to be seen. Cite this article: Bone Joint J 2019;101-B:838–847

Aims. This study reports on the medium- to long-term implant survivorship and patient-reported outcomes for the Avon patellofemoral joint (PFJ) arthroplasty. Patients and Methods. A total of 558 Avon PFJ arthroplasties in 431 patients, with minimum two-year follow-up, were identified from a prospective database. Patient-reported outcomes and implant survivorship were analyzed, with follow-up of up to 18 years. Results. Outcomes were recorded for 483 implants (368 patients), representing an 86% follow-up rate. The median postoperative Oxford Knee Score (0 to 48 scale) was 35 (interquartile range (IQR) 25.5 to 43) and the median Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, 0 to 100 scale) was 35 (IQR 25 to 53) at two years. There were 105 revisions, 61 (58%) for progression of osteoarthritis. All documented revisions were to primary knee systems without augmentation. The implant survival rate was 77.3% (95% confidence interval (CI) 72.4 to 81.7, number at risk 204) at ten years and 67.4% (95% CI 72.4 to 81.7 number at risk 45) at 15 years. Regression analysis of explanatory data variable showed that cases performed in the last nine years had improved survival compared with the first nine years of the cohort, but the individual operating surgeon had the strongest effect on survivorship. Conclusion. Satisfactory long-term results can be obtained with the Avon PFJ arthroplasty, with maintenance of patient-reported outcome measures (PROMs), satisfactory survival, and low rates of loosening and wear. Cite this article: Bone Joint J 2018;100-B:1162–7

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The aim of this study was to determine whether obesity had a detrimental effect on the long-term performance and survival of medial unicompartmental knee arthroplasties (UKAs).

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The aims were to assess whether joint-specific outcome after total knee arthroplasty (TKA) was influenced by implant design over a 12-year follow-up period, and whether patient-related factors were associated with loss to follow-up and mortality risk.