Summary Background Total knee replacement (TKR) or unicompartmental knee replacement (UKR) are options for end-stage osteoarthritis. However, comparisons between the two procedures are confounded by ...differences in baseline characteristics of patients undergoing either procedure and by insufficient reporting of endpoints other than revision. We aimed to compare adverse outcomes for each procedure in matched patients. Methods With propensity score techniques, we compared matched patients undergoing TKR and UKR in the National Joint Registry for England and Wales. The National Joint Registry started collecting data in April 1, 2003, and is continuing. The last operation date in the extract of data used in our study was Aug 28, 2012. We linked data for multiple potential confounders from the National Health Service Hospital Episode Statistics database. We used regression models to compare outcomes including rates of revision, revision/reoperation, complications, readmission, mortality, and length of stay. Findings 25 334 UKRs were matched to 75 996 TKRs on the basis of propensity score. UKRs had worse implant survival both for revision (subhazard ratio SHR 2·12, 95% CI 1·99–2·26) and for revision/reoperation (1·38, 1·31–1·44) than TKRs at 8 years. Mortality was significantly higher for TKR at all timepoints than for UKR (30 day: hazard ratio 0·23, 95% CI 0·11–0·50; 8 year: 0·85, 0·79–0·92). Length of stay, complications (including thromboembolism, myocardial infarction, and stroke), and rate of readmission were all higher for TKR than for UKR. Interpretation In decisions about which procedure to offer, the higher revision/reoperation rate of UKR than of TKR should be balanced against a lower occurrence of complications, readmission, and mortality, together with known benefits for UKR in terms of postoperative function. If 100 patients receiving TKR received UKR instead, the result would be around one fewer death and three more reoperations in the first 4 years after surgery. Funding Royal College of Surgeons of England and Arthritis Research UK.
Abstract Objectives To present estimates of clinically meaningful or minimal important changes for the Oxford Hip Score (OHS) and the Oxford Knee Score (OKS) after joint replacement surgery. Study ...Design and Setting Secondary data analysis of the NHS patient-reported outcome measures data set that included 82,415 patients listed for hip replacement surgery and 94,015 patients listed for knee replacement surgery was performed. Results Anchor-based methods revealed that meaningful change indices at the group level minimal important change (MIC), for example in cohort studies, were ∼11 points for the OHS and ∼9 points for the OKS. For assessment of individual patients, receiver operating characteristic analysis produced MICs of 8 and 7 points for OHS and OKS, respectively. Additionally, the between group minimal important difference (MID), which allows the estimation of a clinically relevant difference in change scores from baseline when comparing two groups, that is, for clinical trials, was estimated to be ∼5 points for both the OKS and the OHS. The distribution-based minimal detectable change (MDC90 ) estimates for the OKS and OHS were 4 and 5 points, respectively. Conclusion This study has produced and discussed estimates of minimal important change/difference for the OKS/OHS. These estimates should be used in the power calculations and the interpretation of studies using the OKS and OHS. The MDC90 (∼4 points OKS and ∼5 points OHS) represents the smallest possible detectable change for each of these instruments, thus indicating that any lower value would fall within measurement error.
High-volume surgeons attain the best results following unicompartmental knee replacement (UKR), but the exact relationship between caseload and outcome is not clear. It is not known whether this ...effect is due to patient selection or surgical skill nor whether a similar effect is seen in total knee replacement (TKR). The aim of this study was to quantify the effect of surgical caseload on survival of both TKR and UKR.
This study was based on 459,280 patient records (422,149 TKRs and 37,131 UKRs) from the National Joint Registry for England and Wales. The caseload-outcome relationship was characterized graphically and quantified using regression techniques. Patient selection was compared among high, medium, and low-volume surgeons. Prosthetic survival was compared between UKRs (performed by high, medium, and low-volume surgeons) and matched TKRs.
Caseload affected survival of TKR and, more strongly, of UKR. The revision rate following UKR dropped steeply until the volume reached ten cases per year, plateauing at thirty cases. For surgeons performing fewer than ten UKRs per year, the mean eight-year rate of survival of the UKRs was 87.9% (95% confidence interval CI = 86.9% to 88.8%) compared with 92.4% (95% CI = 90.9% to 93.6%) for those who performed thirty UKRs or more per year. Analysis of the TKRs showed a linear decrease in revision rate as caseload increased (hazard ratio HR for revision = 0.99 95% CI = 0.98 to 0.99 for every five-case increase in caseload). Surgeons who performed a lower volume of UKRs tended to operate on younger and healthier patients and were more likely to perform revisions to treat loosening and pain. After matching of patients who had undergone UKR with those who had undergone TKR, the surgeons who performed a high volume of UKRs were found to have an eight-year revision/revision rate similar to that seen after TKR (HR for revision or reoperation = 1.10 95% CI = 0.99 to 1.22 favoring TKR).
This study confirmed the importance of surgical caseload in determining the survival of UKR and, to a lesser extent, TKR. The reasons for this effect are complex and not fully explained by variables recorded in the National Joint Registry; however, the patient selection and revision threshold of lower-volume surgeons may be a factor. Examination of matched patients in this study demonstrated that high-volume surgeons can achieve revision/reoperation rates similar to those observed following TKR.
Background and purpose - There is debate as to the relative merits of unicompartmental and total knee arthroplasty (UKA, TKA). Although the designer surgeons have achieved good results with the ...Oxford UKA there is concern over the reproducibility of these outcomes. Therefore, we evaluated published long-term outcomes of the Oxford Phase 3 UKA.
Patients and methods - We searched databases to identify studies reporting ≥10 year outcomes of the medial Oxford Phase 3 UKA. Revision, non-revision, and re-operation rates were calculated per 100 component years (% pa).
Results - 15 studies with 8,658 knees were included. The annual revision rate was 0.74% pa (95% CI 0.67-0.81, n = 8,406) corresponding to a 10-year survival of 93% and 15-year survival of 89%. The non-revision re-operation rate was 0.19% pa (95% CI 0.13-0.25, n = 3,482). The re-operation rate was 0.89% pa (95% CI 0.77-1.02, n = 3,482). The most common causes of revision were lateral disease progression (1.42%), aseptic loosening (1.25%), bearing dislocation (0.58%), and pain (0.57%) (n = 8,658). Average OKS scores were 40 at 10 years (n = 3,417). The incidence of medical complications was 0.83% (n = 1,443).
Interpretation - Very good outcomes were achieved by both designer and non-designer surgeons. The PROMs, medical complication rate, and non-revision re-operation rate were better than those found in meta-analyses and publications for TKA but the revision rate was higher. However, if failure is considered to be all re-operations and not just revisions, then the failure rate of UKA was less than that of TKA.
Background and purpose - Unicompartmental knee replacement (UKR) offers advantages over total replacement but has higher revision rates, particularly for aseptic loosening. The cementless Oxford UKR ...was introduced to address this. We undertook a registry-based matched comparison of cementless and cemented UKRs.
Patients and methods - From 40,552 Oxford UKRs identified by the National Joint Registry for England, Wales, Northern Ireland and Isle of Man (NJR) we propensity score matched, based on patient, surgical, and implant factors, 7,407 cemented and 7,407 cementless UKRs (total = 14,814).
Results - The 10-year cumulative implant survival rates for cementless and cemented UKRs was 93% (95% CI 90-96) and 90% (CI 88-92) respectively, with this difference being significant (HR 0.76; p = 0.002). The risk of revision for aseptic loosening was less than half (p < 0.001) in the cementless (0.42%) compared with the cemented group (1.00%), and the risk of revision also decreased for unexplained pain (to 0.46% from 0.74%; p = 0.03) and lysis (to 0.04% from 0.15%; p = 0.03). However, the risk of revision for periprosthetic fracture increased significantly (p = 0.01) in the cementless (0.26%) compared with the cemented group (0.09%). 10-year patient survival rates were similar (HR 1.2; p = 0.1).
Interpretation - The cementless UKR has improved 10-year implant survival compared with the cemented UKR, independent of patient, implant, and surgical factors. This improved survival in the cementless group was primarily the result of lower revision rate for aseptic loosening, unexplained pain, and lysis, suggesting the fixation of the cementless was superior. However, there was a small increased risk of revision for periprosthetic fracture with the cementless implant.
Spatial turnover in the composition of biological communities is governed by (ecological) Drift, Selection and Dispersal. Commonly applied statistical tools cannot quantitatively estimate these ...processes, nor identify abiotic features that impose these processes. For interrogation of subsurface microbial communities distributed across two geologically distinct formations of the unconfined aquifer underlying the Hanford Site in southeastern Washington State, we developed an analytical framework that advances ecological understanding in two primary ways. First, we quantitatively estimate influences of Drift, Selection and Dispersal. Second, ecological patterns are used to characterize measured and unmeasured abiotic variables that impose Selection or that result in low levels of Dispersal. We find that (i) Drift alone consistently governs ∼25% of spatial turnover in community composition; (ii) in deeper, finer-grained sediments, Selection is strong (governing ∼60% of turnover), being imposed by an unmeasured but spatially structured environmental variable; (iii) in shallower, coarser-grained sediments, Selection is weaker (governing ∼30% of turnover), being imposed by vertically and horizontally structured hydrological factors;(iv) low levels of Dispersal can govern nearly 30% of turnover and be caused primarily by spatial isolation resulting from limited exchange between finer and coarser-grain sediments; and (v) highly permeable sediments are associated with high levels of Dispersal that homogenize community composition and govern over 20% of turnover. We further show that our framework provides inferences that cannot be achieved using preexisting approaches, and suggest that their broad application will facilitate a unified understanding of microbial communities.
Periprosthetic fractures are serious complications of knee arthroplasty often requiring complex surgery. There is concern of increased periprosthetic fracture risk with cementless components given ...the reliance on interference fit for primary stability. It is unknown how the periprosthetic fracture risk compares between cemented and cementless total knee arthroplasties (TKAs).
A total of 22,477 cemented and 22,477 cementless TKAs from the National Joint Registry and Hospital Episodes Statistics database were propensity score matched on patient and surgical factors. Cumulative periprosthetic fracture rates were calculated using Kaplan-Meier analyses and compared with Cox regressions. Subgroup analyses were performed in different age, body mass index, and sex groups.
The 3-month fracture rate in the cemented and cementless TKA groups were 0.02% and 0.04%, respectively. At 10 years, the cumulative fracture rate after cemented TKA was 1.2%, and after cementless was 1.4%. During the study period, there were no significant differences in fracture rates between cemented and cementless TKAs with a hazards ratio 1.14 (confidence interval 0.94 to 1.37, P = .20) at 10 years postoperatively. There were no significant differences in fracture rates between fixation types on subgroup analyses of sex, body mass index, and age groups. Female sex was a risk factor for fracture in both cemented (odds ratio 2.35, P < .001) and cementless TKAs (odds ratio 2.97, P < .001).
The periprosthetic fracture rates following cemented and cementless TKA surgery are low being approximately 1.2% and 1.4%, respectively at 10 years. There were no significant differences in periprosthetic fracture rates requiring readmission between cemented and cementless TKAs.
III.
Unicompartmental knee replacement (UKR) offers substantial benefits compared with total knee replacement (TKR) but is associated with higher revision rates. Data from registries suggest that revision ...rates for cementless UKR implants are lower than those for cemented implants. It is not known how much of this difference is due to the implant or to other factors, such as a greater proportion of high-volume surgeons using cementless implants. We aimed to determine the effect of surgeon caseload on the revision rate of matched cemented and cementless UKRs.
From a group of 40,522 Oxford (Zimmer Biomet) UKR implants (30,814 cemented, 9,708 cementless) recorded in the National Joint Registry, 14,814 (7,407 cemented, 7,407 cementless) were propensity-score matched. Surgeons were categorized into 3 groups: low volume (<10 cases/year), medium volume (10 to <30 cases/year), and high volume (≥30 cases/year). The effect of caseload on the relative risk of revision was assessed with use of Cox regression.
The 10-year survival rates for unmatched cementless and cemented UKR implants were 93.3% (95% confidence interval CI = 89.8% to 95.7%) and 89.1% (95% CI = 88.6% to 89.6%), respectively, with the difference being significant (hazard ratio HR = 0.59; p < 0.001). Cementless UKR implants had a greater proportion of high-volume surgeon users than cemented implants (30.4% compared with 15.1%). Following matching, the 10-year survival rates were 93.2% (95% CI = 89.7% to 95.6%) and 90.2% (95% CI = 87.5% to 92.3%), which were still significantly different (HR = 0.76; p = 0.002). The 10-year survival rates for matched cementless and cemented UKR implants were 86.8% (95% CI = 73.6% to 93.7%) and 81.8% (95% CI = 73.0% to 88.0%) for low-volume surgeons, 94.3% (95% CI = 92.2% to 95.9%) and 92.5% (95% CI = 89.9% to 94.5%) for medium-volume surgeons, and 97.5% (95% CI = 96.5% to 98.2%) and 94.2% (95% CI = 90.8% to 96.4%) for high-volume surgeons. The revision rate for cementless implants was lower for surgeons in all 3 caseload groups (HR = 0.74, 0.79, 0.80, respectively).
Cementless fixation decreased the revision rate by about a quarter, whatever the surgeon caseload. Caseload had a profound effect on implant survival. Low-volume surgeons had a high revision rate with cemented or cementless fixation and therefore should consider either stopping or doing more UKR procedures. High-volume surgeons performing cementless UKR demonstrated a 10-year survival rate of 97.5%, which was similar to that reported in registries for the best-performing TKRs.
Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
Abstract Background The indications for unicompartmental knee arthroplasty remain controversial. Previously recommended contraindications include the following: age under 60 years, weight 180 lb (82 ...kg) or over, patients undertaking heavy labor, chondrocalcinosis, and exposed bone in the patellofemoral joint. This study explores whether these contraindications are valid in mobile-bearing unicompartmental knee arthroplasty. Methods Using a prospective series of 1000 consecutive medial unicompartmental knee arthroplasties in which the reported contraindications were not applied, the functional outcome and survival in patients with or without contraindications were compared. Results Of the 1000 consecutive unicompartmental knee arthroplasties (818 patients), 68% (678 knees) would be considered contraindicated based on published contraindications. At a mean follow-up of 10 years (5-17), there was no difference in American Knee Society (AKS) Objective Scores ( P = .05) or Oxford Knee Score ( P = .08) between groups. However, knees with contraindications had significantly ( P = .02) fewer poor outcomes and significantly better AKS Functional Scores ( P < .001) and Tegner Activity Scores ( P < .001). At 15 years, no difference in implant survival ( P = .33) was observed. The 3% of unicompartmental knee arthroplasties performed in young men (age <60) weighing 180 lb or over with high activity levels, who have been reported to have poor outcomes after fixed-bearing unicompartmental knee arthroplasty, had significantly better AKS Functional Scores ( P < .001), Oxford Knee Score ( P = .01), and Tegner Activity Score ( P < .001) at 10 years. No difference in AKS Objective Scores ( P = .54) at 10 years or implant survival at 15 years ( P = .75) was seen. Conclusion This large case series provides evidence that patients with the previously reported contraindications do as well as, or even better than, those without contraindications. Therefore these contraindications should not apply to mobile-bearing unicompartmental knee arthroplasty.
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