Minimally invasive total knee replacement: techniques and results

Minimally invasive medial femoral approach to total knee arthroplasty improves short-term outcomes compared to the standard medial parapatellar approach: a systematic review and meta-analysis

OBJECTIVE

The aim of this study is to conduct a comprehensive evaluation of the effectiveness of the medial parapatellar approach via the vastus medialis obliquus muscle in comparison with the standard medial parapatellar approach for total knee arthroplasty, using a systematic approach.

METHODS

A computer search was conducted on PubMed, EMBASE, Medline, Cochrane libraries, and Web of Science databases to comprehensively collect randomized controlled studies on minimally invasive (MMV) approaches for knee arthroplasty, specifically the vastus and medial parapatellar (MP) approaches. Two authors independently screened the literature based on inclusion and exclusion criteria, evaluated the quality of the included studies using the Cochrane systematic review method, and performed a meta-analysis using RevMan 5.3 software.

RESULTS

A total of twelve randomized controlled studies were ultimately included, comprising 788 knees. The small incision medial femoral muscle approach (MMV) group consisted of 398 cases, while the traditional parapatellar approach (MP) group consisted of 390 cases. Data analysis showed that in the comparison of KSS, VAS, and ROM score at 3 months after surgery, MMV approach was superior to MP approach [MD = 2.89, 95%CI (0.33, 5.46), P = 0.03], [MD = - 0.22, 95%CI (- 0.36, - 0.09), P = 0.001], and [MD = 1.08, 95%CI (0.04, 2.12), P = 0.04]. However, there was no significant difference in the postoperative KSS, VAS, and ROM score between the MMV and MP approaches at 6 and 12 months after surgery. The operation time of the MMV group was longer than that of the MP group [MD = 8.98, 95%CI (4.64, 13.32), P < 0.0001], and the number of days of straight leg raising after surgery was shorter in the MMV group than in the MP group [MD = - 1.91, 95%CI (- 3.45, - 0.37), P = 0.01], with statistically significant differences. There was no significant difference in the lateral support band release rate [OR = 0.72, 95%CI (0.23, 2.28), P = 0.58], length of hospital stay [MD = 0.07, 95%CI (- 0.18, 0.31), P = 0.58], postoperative complications [MD = 0.62, 95%CI (0.33, 1.18), P = 0.15], and intraoperative blood loss [MD = 70.50, 95%CI (- 57.51, 198.72), P = 0.28].

CONCLUSION

Most of the approaches have similar length of stay and incidence of complications compared to standard approaches. However, the minimally invasive midvastus approach has shown potential to improve short-term outcomes.

STUDY REGISTRATION

PROSPERO registration number CRD42023410583.

Comparison of postoperative pain, anxiety, and sleep quality in robotic-assisted and manual total knee replacement surgery

This study aimed to comparatively evaluate postoperative pain, anxiety, and sleep quality in patients after robotic-assisted and manual total knee replacement surgery. Patients who underwent either robotic or manual total knee replacement (TKR) surgery were analyzed in this cross-sectional observational study. Volunteers who were conscious, mentally healthy, without primary sleep disorders, without chronic uncontrolled diseases, 18 years of age or older, able to understand verbal warnings, and who agreed to participate in the study after being informed about the purpose of the study were included in the study. A total of 80 patients who underwent robotic-assisted TKR and 87 patients who underwent manual TKR were participated in the study. Data were collected using the "Patient Description Form" Visual Analog Scale, Richards-Campbell Sleep Scale, and State Anxiety Scale. All patients were operated on by the same physicians and received standard perioperative care. In the study, a statistically significant difference was found between the education level of the patients and the type of surgery (p = 0.007). According to the average scores, it was observed that the patients in the robotic group had higher pain levels, better sleep quality, and higher anxiety levels compared to the manual group. There was a significant correlation between the level of pain felt on the 1st and 2nd day (p =  < 0.001) and state anxiety levels with gender (p = 0.010) in the robotic group. For the robotic group, pain on day 2 was mostly affected by pain on day 1 and state anxiety. For the manual group, pain on day 2 was mostly affected by pain on day 1. According to our results, patients who underwent robotic-assisted TKR had higher pain levels, better sleep quality, and higher anxiety levels than patients who underwent manual TKR.

Effects of general anesthesia and epidural anesthesia on deep vein thrombosis and perioperative cognitive function of patients undergoing total knee arthroplasty

OBJECTIVE

To explore the effects of general anesthesia and epidural anesthesia on deep vein thrombosis (DVT) and perioperative cognitive function of patients undergoing total knee arthroplasty.

METHODS

A retrospective analysis was conducted on 110 orthopedic patients who underwent total knee arthroplasty at Zhangzhou Affiliated Hospital of Fujian Medical University from March 2018 to March 2021. According to different anesthesia schemes, 56 cases with epidural anesthesia were included in the observation group and 54 patients with general anesthesia were assigned to the control group. The following items were recorded and compared between the two groups: postoperative coagulation indicators; operation duration, total dosage of anesthetics; postoperative recovery time; heart rate (HR) and mean arterial pressure (MAP) before anesthesia induction (T0), intubation (T1), and completion of the operation (T2); cognitive function before surgery and 1 d and 3 d after surgery; postoperative incidence of DVT; pain at postoperative 24 h; stress-related factors before and 2 h after surgery, and incidence of adverse reactions during hospitalization.

RESULTS

Compared to the control group, the levels of fibrinogen (Fbg) and platelets (PLC) in the observation group 24 hours after surgery were significantly lower, with longer thrombin time (TT) and prothrombin time (PT) (all P<0.05); no significant difference was found in operation duration between the two groups (P>0.05). Total dosage of anesthetics and postoperative recovery time were less in the observation group (P<0.05); the HR and MAP fluctuations were lower in the observation group (P<0.05). The postoperative cognitive function score of patients in the observation group was significantly higher (P<0.05), with a lower incidence of postoperative DVT (P<0.05) and better relief of pain (P<0.05). The expression levels of stress-related factors 2 h after surgery and the incidence of adverse reactions were lower in the observation group compared to the control group (P<0.05).

CONCLUSION

In total knee arthroplasty, epidural anesthesia, compared with general anesthesia, can reduce the incidence of DVT in patients and has less impact on patients' cognitive function and stress state with a higher safety profile.

Does Application of Lymphatic Drainage with Kinesiology Taping Have Any Effect on the Extent of Edema and Range of Motion in Early Postoperative Recovery following Primary Endoprosthetics of the Knee Joint?

Background: The surgery of knee replacement due to degenerative changes is the last step of the treatment. After surgery, a major problem in patients is pain, swelling, intraarticular hematoma, and the restriction of the mobility of the joint. The aim of this work was to determine the effect of Kinesio Taping (KT) on reducing edema of the subcutaneous tissue and improving the range of motion in the joint. Methods: 82 patients were qualified for the study. After surgery, 42 patients received postoperative edema treatment with KT bands, and 40 patients did not receive the treatment. The swelling thickness and range of mobility were measured on the third and eighth days after the operation. Results: A statistical difference between the longitudinal measurements of the KT group and the group without KT application was shown at the level of the fibula head, 25 mm below the fibula neck, and 50 mm below the fibular neck. There were no statistically significant differences in the change in knee angle between the applied and non-applied patients. Conclusion: The lymphatic application technique KT influences the absorption of subcutaneous edema after primary knee joint replacement surgery but has no influence on mobility.

Development of a decision analytical framework to prioritise operating room capacity: lessons learnt from an empirical example on delayed elective surgeries during the COVID-19 pandemic in a hospital in the Netherlands

OBJECTIVE

To develop a prioritisation framework to support priority setting for elective surgeries after COVID-19 based on the impact on patient well-being and cost.

DESIGN

We developed decision analytical models to estimate the consequences of delayed elective surgical procedures (eg, total hip replacement, bariatric surgery or septoplasty).

SETTING

The framework was applied to a large hospital in the Netherlands.

OUTCOME MEASURES

Quality measures impacts on quality of life and costs were taken into account and combined to calculate net monetary losses per week delay, which quantifies the total loss for society expressed in monetary terms. Net monetary losses were weighted by operating times.

RESULTS

We studied 13 common elective procedures from four specialties. Highest loss in quality of life due to delayed surgery was found for total hip replacement (utility loss of 0.27, ie, 99 days lost in perfect health); the lowest for arthroscopic partial meniscectomy (utility loss of 0.05, ie, 18 days lost in perfect health). Costs of surgical delay per patient were highest for bariatric surgery (€31/pp per week) and lowest for arthroscopic partial meniscectomy (-€2/pp per week). Weighted by operating room (OR) time bariatric surgery provides most value (€1.19/pp per OR minute) and arthroscopic partial meniscectomy provides the least value (€0.34/pp per OR minute). In a large hospital the net monetary loss due to prolonged waiting times was €700 840 after the first COVID-19 wave, an increase of 506% compared with the year before.

CONCLUSIONS

This surgical prioritisation framework can be tailored to specific centres and countries to support priority setting for delayed elective operations during and after the COVID-19 pandemic, both in and between surgical disciplines. In the long-term, the framework can contribute to the efficient distribution of OR time and will therefore add to the discussion on appropriate use of healthcare budgets. The online framework can be accessed via: https://stanwijn.shinyapps.io/priORitize/.

Quadriceps muscle group function and after total knee arthroplasty-asystematic narrative update

BACKGROUND

This article systematically summarizes the present evidences, published in the last 20 years, regarding the pre- and post-operative factors, which may influence recovery of the function of the quadriceps muscle group following total knee arthroplasty (TKA). We following the PRISMA methodology, including meta-analyses and high-level evidence studies (prospective trials, and, when unavailable, retrospective studies).

SOURCES OF DATA

Pubmed and Cochrane databases: 582 articles were identified and 54 of them were selected.

AREAS OF AGREEMENT

Tourniquets inflated at high pressure exert a detrimental effect on the quadriceps muscle group. Faster quadriceps recovery takes place using mini-invasive approaches, an eight-week rehabilitation period including balance training and the use of nutraceuticals.

AREAS OF DISAGREEMENT

Pre-habilitation and pre-operative factors, analgesic methods and different TKA implants.

GROWING POINTS AND AREAS TIMELY FOR DEVELOPING RESEARCH

Telerehabilitation seems a cost-effective tool for rehabilitation after TKA. Patients' optimization protocols before TKA should include standardized nutraceuticals intake.

Minimally invasive surgery total knee arthroplasty is less popular, but the prosthesis designed specifically for MIS provides good survival and PROMs with a minimum follow-up of 10 years

BACKGROUND

The concept of minimally invasive surgery (MIS) was introduced in total knee arthroplasty (TKA) in the late 1990s. The number of MIS TKAs has clearly decreased in recent years. An implant designed specifically for MIS TKA has been used all over the world, but there are no reports of long-term postoperative results. The purpose of this study was to characterize long-term clinical results with a minimum follow-up of 10 years.

METHODS

This retrospective study included 109 consecutive patients with 143 NexGen CR-Flex prostheses, which are MIS tibial component prostheses designed specifically for MIS TKA. Twelve-year survival analysis was performed using Kaplan-Meier method. Revision surgery for any reason was the endpoint. Long-term clinical and radiographic results of 74 knees (55%) in 60 patients with more than 10 years of follow-up were analyzed.

RESULTS

The cumulative survival rate of the single-radius posterior-stabilized TKA of 74 knees was 94.7% (95% confidence interval, 90-99%) at 12 years after surgery. Seven knees (9%) required additional surgery during the 10-year follow-up because of periprosthetic infections. Mean postoperative Knee Society knee score and functional score were 91 and 74 points, respectively. There were no cases of prosthesis breakage, polyethylene wear, or aseptic loosening of the prosthesis.

CONCLUSION

The prosthesis designed specifically for MIS TKA is associated with good survival and clinical results with a minimum follow-up of 10 years, even though MIS TKA has become less popular.

LEVEL OF EVIDENCE

III.

Better outcomes after minimally invasive surgeries compared to the standard invasive medial parapatellar approach for total knee arthroplasty: a meta-analysis

PURPOSE

Minimally invasive surgery (MIS) for total knee arthroplasty (TKA) is often marketed as being able to speed up healing times over standard invasive surgery (SIS) through the medial parapatellar approach. The advantages of these minimally invasive approaches, however, are not yet definitively established. A meta-analysis of studies comparing peri-operative and post-operative differences and long-term complications of MIS versus SIS for TKA was conducted.

METHODS

This meta-analysis was conducted following the PRISMA guidelines. The Pubmed, Google Scholar, Scopus, and Embase databases were accessed in September 2020. All clinical trials comparing minimally-invasive versus standard approaches for TKA were considered. Only studies reporting quantitative data under the outcomes of interest were included. Methodological quality assessment was performed using the PEDro appraisal score.

RESULTS

This meta-analysis covers a total of 38 studies (3296 procedures), with a mean 21.3 ± 24.3 months of follow-up. The MIS group had shorter hospitalization times, lower values of total estimated blood loss, quicker times of straight-leg raise, greater values for range of motion, higher scores on the Knee Society Clinical Rating System (KSS) and its related Function Subscale (KSFS). Pain scores, anterior knee pain and revision rate were similar between MIS and SIS. SIS allowed a quicker surgical duration.

CONCLUSION

The present meta-analysis encourages the use of minimally invasive techniques for total knee arthroplasty. However, MIS TKA is technically demanding and requires a long learning curve.

LEVEL OF EVIDENCE

III, meta-analysis of clinical trials.

Does mini-midvastus approach have an advantageous effect on rapid recovery protocols over medial parapatellar approach in total knee arthroplasty?

Objectives

This study aims to compare the effects of mini- midvastus (MMV) versus medial parapatellar (MPP) approach on rapid recovery protocols during total knee arthroplasty (TKA).

Patients and methods

This prospective, randomized, single- blinded study was performed in 54 patients (4 males, 50 females; mean age 64.1±6.4 years) diagnosed as primary knee osteoarthritis and planned for unilateral TKA between May 2018 and March 2019. Patients were randomly assigned as MMV (1 male, 26 females; mean age 65±6.4 years) and MPP (3 males, 24 females; mean age 63.2±6.3 years) groups. Rapid recovery TKA protocol and discharge criteria were assembled and all patients were evaluated preoperatively, and at postoperative first and third months. Length of hospital stay (LOS) was recorded for all patients. Hemoglobin and hematocrit values, radiologic assessment of alignment, knee range of motion (ROM), quadriceps muscle strength, Visual Analog Scale (VAS), 30-sec chair-stand test, stair-climb test, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), and Short Form-36 (SF-36) were used for evaluations by blinded observers.

Results

There was no significant difference in demographic variables between two groups. Operative time in MMV Group (78.1±2.7 min) was significantly longer than the MPP Group (65.9±2.6 min) (p<0.0005). LOSs in the MMV and MPP Groups were 27.6±3.1 hours and 29.1±6.7 hours with no significant difference. There was no statistically significant difference in postoperative measurements between groups in hemoglobin and hematocrit values, radiologic alignment of components, knee ROM, VAS, 30-sec chair-stand test, stair-climb test, WOMAC, KOOS, and SF-36 evaluations (p>0.05). In terms of quadriceps muscle strength gain, we could not find any difference between groups in pre- and postoperative difference of changes (p>0.05).

Conclusion

With the use of contemporary rapid recovery protocols during TKA, MMV approach had no superiority over MPP approach when quadriceps muscle strength, LOS, pain, function, and quality of life were assessed. Longer operative time in the MMV approach compared to MPP approach may be considered as a disadvantage.

A matched comparison of revision rates of cemented Oxford Unicompartmental Knee Replacements with Single and Twin Peg femoral components, based on data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

Background and purpose - Registries report high revision rates after unicompartmental knee replacement (UKR) due, in part, to aseptic loosing. In an attempt to improve Oxford UKR femoral component fixation a new design was introduced with a Twin rather than a Single peg. We used the National Joint Registry (NJR) to compare the 5-year outcomes of the Single and Twin Peg cemented Oxford UKRs.Patients and methods - We performed a retrospective observational study using NJR data on propensity score matched Single and Twin Peg UKRs (matched for patient, implant and surgical factors). Data on 2,834 Single Peg and 2,834 Twin Peg were analyzed. Cumulative implant survival was calculated using the Kaplan-Meier method and comparisons between groups performed using Cox regression models.Results - In the matched cohort, the mean follow up for both Single and Twin Peg UKRs was 3.3 (SD 2) and 3.4 years (SD 2) respectively. The 5-year cumulative implant survival rates for Single Peg and Twin Peg were 94.8% (95% CI 93.6-95.8) and 96.2% (CI 95.1-97.1) respectively. Implant revision rates were statistically significantly lower in the Twin Peg (hazard ratio [HR)] = 0.74; p = 0.04). The revision rate for femoral component aseptic loosening decreased significantly (p = 0.03) from 0.4% (n = 11) with the Single Peg to 0.1% (n = 3) with the Twin Peg. The revision rate for pain decreased significantly (p = 0.01) from 0.8% (n = 23) with the Single Peg to 0.3% (n = 9) with the Twin Peg. No other reasons for revision had significant differences in revision rates.Interpretation - The revision rate for the cemented Twin Peg Oxford UKR was 26% less than the Single Peg Oxford UKR. This was mainly because the revision rates for femoral loosening and pain more than halved. This suggests that the Twin Peg component should be used in preference to the Single Peg design.

Computer assisted orthopaedic surgery: Past, present and future

Computer technology is ubiquitous and relied upon in virtually all professional activities including neurosurgery, which is why it is surprising that it is not the case for orthopaedic surgery with fewer than 5% of surgeons using available computer technology in their procedures. In this review, we explore the evolution and background of Computer Assisted Orthopaedic Surgery (CAOS), delving into the basic principles behind the technology and the changes in the discussion on the subject throughout the years and the impact these discussions had on the field. We found evidence that industry had an important role in driving the discussion at least in knee arthroplasty-a leading field of CAOS-with the ratio between patents and publications increased from approximately 1:10 in 2004 to almost 1:3 in 2014. The adoption of CAOS is largely restrained by economics and ergonomics with sceptics challenging the accuracy and precision of navigation during the early years of CAOS moving to patient functional improvements and long term survivorship. Nevertheless, the future of CAOS remains positive with the prospect of new technologies such as improvements in image-guided surgery, enhanced navigation systems, robotics and artificial intelligence.

The Effect of Surgeon Caseload on the Relative Revision Rate of Cemented and Cementless Unicompartmental Knee Replacements: An Analysis from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Comparison of the 10-year outcomes of cemented and cementless unicompartmental knee replacements: data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

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.

Geographical Variation in Outcomes of Primary Hip and Knee Replacement

IMPORTANCE

Little is known about variation in outcomes of surgery or about the factors associated with such variation.

OBJECTIVES

To evaluate variation in patient outcomes and costs for primary hip and knee replacement across health areas in England and to identify whether patient, surgical, or hospital factors are associated with such variation.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study used data from the National Joint Registry, linked to English Hospital Episode Statistics and Patient Reported Outcome Measures data sets, for 383 382 adult patients who underwent primary total hip replacement (THR) or primary total and unicompartmental knee replacement (TKR) surgical procedures from January 2014 to December 2016. Geographical Information Systems were used to display maps describing adjusted estimates of variation in outcomes across health areas. Data analysis took place from January 2018 to August 2019.

EXPOSURES

Patient characteristics (eg, age, sex, body mass index [BMI], and socioeconomic deprivation), surgical factors (eg, surgeon volume and grade), and hospital organizational factors (eg, number of operating theaters, number of specialist consultants, and hospital volume).

MAIN OUTCOMES AND MEASURES

Length of stay (LOS), bed-day costs, change in Oxford hip or knee scores 6 months after surgery, and complications 6 months after surgery.

RESULTS

A total of 173 107 patients (mean [SD] age, 69.3 [10.7] years; mean [SD] BMI, 28.9 [5.2]) underwent primary THR and 210 275 patients (mean [SD] age 69.7 [9.4] years; mean [SD] BMI, 31.1 [5.5]) underwent primary TKR, nested in 207 health areas. A number of factors were associated with longer LOS, higher bed-day costs, smaller changes in Oxford hip or knee scores, and a higher percentage of complications, including a workforce with a higher number of less experienced physicians (eg, LOS for less experienced surgeons, THR: regression coefficient, 0.02; 95% CI, 0.01 to 0.03; P < .001; TKR: regression coefficient, 0.01; 95% CI, 0.01 to 0.02; P < .001), public hospitals (eg, bed-day costs for private hospitals, THR: regression coefficient, -0.15; 95% CI, -0.15 to -0.14; P < .001; TKR: regression coefficient, -0.19; 95% CI, -0.19 to -0.19; P < .001), low volume of surgical procedures per surgeon (eg, change in Oxford hip or knee scores for lead surgeon with ≤10 vs >150 surgical procedures per year, THR: regression coefficient, -1.03; 95% CI, -1.47 to -0.58; P < .001; TKR: regression coefficient, -0.54; 95% CI, -1.01 to -0.06), and low volume of surgical procedures per hospital (eg, percentage of complications for hospitals with ≤200 vs ≥500 surgical procedures per year, THR: regression coefficient, 0.12; 95% CI, 0.04 to 0.21; P < .001; TKR: regression coefficient, 0.09; 95% CI, 0.01 to 0.18; P = .03). Although these factors did not attenuate the magnitude of variation across health areas, they had ecological correlations with the observed geographical variations in outcomes of surgery by health area. For example, the percentage of public and private hospitals was ecologically correlated at the health area level with longer and shorter stays, respectively (public hospital, THR: ρ, 0.41; public hospital, TKR: ρ, 0.44; private hospital, THR: ρ, -0.37; private hospital, THR: ρ, -0.38). Across health areas, estimated mean length of stay ranged from 3 to 7 days, and associated bed-day costs ranged from £4727 ($5827) to £8800 ($10 848) for both total hip and knee replacement. The absolute estimated mean change in Oxford hip score varied from 18.7 to 24.6 points and, for Oxford knee score, from 13.1 to 18.8. Estimated 6-month complications ranged from 2.9% to 5.8% for both THR and TKR.

CONCLUSIONS AND RELEVANCE

In this study, models indicated that higher surgical volume by surgeon and by hospital as well as private hospitals were associated with better patient outcomes, which could be explained by the changing case mix of public hospitals treating an increasing number of more complex patients. A higher proportion of less experienced physicians was associated with poorer outcomes. This variation was observed geographically.