Objectives

To investigate psychosocial and biomedical outcomes following total hip replacement (THR) and to identify predictors of recovery from THR.

A prospective cohort of 222 patients who underwent revision hip replacement between April 2001 and March 2004 was evaluated to determine predictors of function, pain and activity level between one and two years post-operatively, and to define quality of life outcomes using validated patient reported outcome tools. Predictive models were developed and proportional odds regression analyses were performed to identify factors that predict quality of life outcomes at one and two years post-operatively. The dependent outcome variables were the Western Ontario and McMaster Osteoarthritis Index (WOMAC) function and pain scores, and University of California Los Angeles activity scores. The independent variables included patient demographics, operative factors, and objective quality of life parameters, including pre-operative WOMAC, and the Short Form-12 mental component score. There was a significant improvement (t-test, p < 0.001) in all patient quality of life scores. In the predictive model, factors predictive of improved function (original regression analyses, p < 0.05) included a higher pre-operative WOMAC function score (p < 0.001), age between 60 and 70 years (p < 0.037), male gender (p = 0.017), lower Charnley class (p < 0.001) and aseptic loosening being the indication for revision (p < 0.003). Using the WOMAC pain score as an outcome variable, factors predictive of improvement included the pre-operative WOMAC function score (p = 0.001), age between 60 and 70 years (p = 0.004), male gender (p = 0.005), lower Charnley class (p = 0.001) and no previous revision procedure (p = 0.023). The pre-operative WOMAC function score (p = 0.001), the indication for the operation (p = 0.007), and the operating surgeon (p = 0.008) were significant predictors of the activity assessment at follow-up. Predictors of quality of life outcomes after revision hip replacement were established. Although some patient-specific and surgery-specific variables were important, age, gender, Charnley class and pre-operative WOMAC function score had the most robust associations with outcome

The aim of the study was to evaluate radiological and clinical outcomes of surgical treatment of developmental dysplasia of the hip (DDH) with Periacetabular Osteotomy (PAO) and to determine the values of radiological parameters allowing us to obtain an optimal clinical result.

Radiological evaluation included a standardized AP digital radiograph of the hip joints. Centre edge angle (CEA), medialization, distalization, femoral head coverage (FHC) and ilioischial angle were measured. Clinical evaluation based on HHS, WOMAC, Merle d'Aubigne-Postel scales and Hip Lag Sign. Radiological and clinical evaluation was performed preoperatively and approximately 12 months after the surgery.

Statistically significant (p<0.05) differences in radiological measurements and all clinical scales have been observed pre- and postoperatively for all of the parameters. The results of PAO presented decreased medialization by 3.4mm (range: 3 to 3.7), distalization by 3.5mm (range: 3.2 to 3.8) and the ilioischial angle by 2.7° (range: 2.2 to 3.7). There was also an improvement in the femoral head bone coverage: CEA increased by 16.3° (range: 12.1˚ to 20.5˚) and FHC by 15.2% (range: 10.8 to 19.8). Clinically we observed an increase in HHS by 22 points (range: 15.8 to 28.2) and M. Postel d'Aubigne by 3.5 points (range: 2.0 to 4.4) and a decrease in WOMAC by 24% (range: 22.6 to 25.8). HLS improvement of gluteal muscles’ efficiency has been observed in 67% of patients postoperatively.

This study revealed that the qualification of patients with DDH for an elective PAO is more justified due to the predicted optimal clinical outcomes based on three parameters: CEA <25 degrees, FHC <75%, and ilioischial angle >85.9 degrees. Accordingly, to achieve better clinical results for all scales, it is necessary to increase the average CEA value by 11˚, the average FHC by 11%, and reduce the average ilioischial angle by 3˚.

In-hospital length of stay (LOS) and discharge disposition following arthroplasty could act as surrogate measures for improvement in patient pathways, and have major cost saving implications for healthcare providers. With the ever-growing adoption of robotic technology in arthroplasty, we wished to evaluate its impact on LOS. The objectives of this study were to compare LOS and discharge disposition following robotic-arm assisted (RO THA) versus conventional technique Total Hip Arthroplasty (CO THA).

This large-scale, single institution study included patients of any age undergoing primary THA (N = 1,732) for any cause between May 2019 and January 2023. Data extracted included patient demographics, LOS, need for Post Anaesthesia Care Unit (PACU) admission, anaesthesia type, readmission within 30 days and discharge dispositions. Univariate and multivariate logistic regression models were also employed to identify factors and patient characteristics related to delayed discharge.

The median LOS in the RO THA group was 54 hours (34, 78) versus 60 (51, 100) in the CO THA group, p<0.001. Discharge disposition was comparable between the two groups. In the multivariate model, age, need for PACU admission, ASA score > 2, female gender, general anaesthesia and utilisation of the conventional technique were significantly associated with LOS > 2 days.

Our study showed that robotic-arm assistance was associated with a shorter LOS in patients undergoing primary THA and no difference in discharge destination. Our results suggest that robotic-arm assistance could be advantageous in partly addressing the upsurge of hip arthroplasty procedures and the concomitant health care burden; however, this needs to be corroborated by long-term cost effectiveness analyses and data from randomised controlled studies.

Periprosthetic femoral fractures are increasingly seen in recent years, adding considerable burden to the National Health Service. These require complex revision or fixation and prolonged post-operative care, with significant morbidity with associated costs. The purpose of this study was to assess whether the size of femoral cement mantle is associated with periprosthetic femoral fractures (PPF).

This retrospective study was carried out on a cohort of 49 patients (Fracture Group - FG) who previously had a revision procedure following a proximal PPF between 2010 and 2021. Inclusion criteria – all primary cemented total hip replacements (THR). Exclusion criteria – complex primary THR, any implant malposition that required early revision surgery or any pre-fracture stem loosening. The antero-posterior (AP) radiographs from this cohort of patients were assessed and compared to an age, sex, time since THR-matched control group of 49 patients without PPF (Control Group - CG). Distal cement mantle area (DCMA) was calculated on an AP radiograph of hip; the position of the femoral stem tip prior to fracture was also recorded: valgus, varus or central. Limitations: AP radiographs only. Statistical analyses were performed using Microsoft® Excel.

Chi-square test demonstrated statistically significant difference in DCMA between FG and CG. DCMA of 700 to 900 mm² appeared to be protective when compared to DCMA of 0 to 300 mm². Also, a valgus position observed in 23% in FG Vs 4 % in CG increased the risk, with a smaller area of DCMA.

This study demonstrates and recommends that a size of 700 – 900 mm² of the DCMA is protective against periprosthetic fractures, which are further influenced by the positioning of the distal stem tip. This could be due to the gradual decrease in the stiffness gradient from proximal to distal around the stem tip than steep changes, thereby decreasing possibility of a stress riser just distal to the cement mantle or restrictor. Further biomechanical research specific to this finding may be helpful to validate the observation, progressing to suggest a safe standardised surgical technique.

Total hip arthroplasty has been constantly evolving with technological improvements to achieve the best survival rates. Although the new implants are under closer surveillance through processes such as Beyond Compliance, orthopaedic surgeons generally tend to look out for the latest implants with good short-term results and hope for better long-term results for these. We questioned whether such an assumption or bias is valid.

We analysed the data of Kaplan-Meier estimates of cumulative revisions of primary hip replacement by fixation, stem/cup brand and bearing combinations from the NJR 19th Annual Report published in September 2022. We performed a univariate linear regression analysis to predict the 10- and 15-year revision rates for these different hip implant combinations from the 3- and 5-year revision rates.

Thirty-seven implant combinations had their 15-year revision rates reported and 67 had the 10-year revision rates. The correlation co-efficients were 0.43 and 0.58 for the 3-year and 5-year revision rates against 15-year revision rates. Only 17% of the variance in 15-year revision rates could be predicted by a linear regression model from the 3-year revision rate and 32% from the 5-year revision rate. Corresponding values for the 10-year revision rates were 46% and 67%.

95% prediction intervals for the 15-year revision rate were +/− 3.1% from the 3-year revision rate and +/− 2.8% from the 5-year revision rate. Corresponding values for the 10-year revision rates were +/− 1.3% and +/− 1%.

19 of 37 implant combinations showed 15-year revision rate of more than 4%. Average 3-year and 5-year revision rates for this cohort was 1.0% and 1.42% compared to 1.4% and 1.9% for the rest and the difference was statistically significant.

Although average early revision rates showed small but significant difference between the groups with lower and higher 15-year revision rates, the prediction intervals for 15-year revision rates for individual hips based on their 3-year and 5-year revision rates are very wide. Three- and 5-year revision rates for primary total hip replacements are poor predictors of 15-year revision rates.

Introduction

With the removal of total hip arthroplasty (THA) from the Centers for Medicare & Medicaid Services (CMS) inpatient-only list, understanding predictors of length of stay (LOS) after THA is critical. Thus, we aimed to determine the influence of patient- and procedure-related risk factors as predictors of >1-day LOS after THA.

The purpose of this study was to examine a cohort of patients with minor acetabular dysplasia features in order to identify the preoperative clinical characteristics and imaging findings that differentiate patients with hip instability from patients with impingement.

A retrospective cohort study of patients with borderline acetabular dysplasia was performed. All patients were identified by prospective radiographic evaluation with an LCEA between 20° and 25°. Multivariate statistical analyses were used to identify independent predictors of disease type.

Of the 143 hips in the cohort, 39.2% (n=56) had the diagnosis of instability, while 60.8% (n=87) had the diagnosis of impingement. The cohort included 109 females (76.2%) and 34 males (23.8%).

Hips with instability had a lower LCEA (21.8° vs. 22.8°; p<0.001), lower ACEA (23.3° vs. 26.6°; p=0.002), a higher AI (11.8° vs. 8.5°; p<0.001), and a lower maximum alpha angle (54.4° vs. 61.1°; p=0.001). The odds of instability increased 1.7 times for each one-degree decrease in LCEA, 1.4 times for each one-degree decrease in ACEA, and 1.1 times for each one-degree increase in acetabular inclination (all p0.003). Female sex was strongly associated with instability.

The instability subgroup had greater range of motion (IRF, 22.7° vs. 12.4°, p<0.001) and total arc of motion (IRF+ERF, 61.2° vs. 47.4°, p<0.001). We identified predictors of diagnosis including: acetabular inclination (1.49, p<0.001), ACEA (0.89, p=0.007), crossover sign (0.27, p=0.014), preoperative mHHS (0.96, p=0.014), IRF (1.10, p=0.001), and age (0.88, p=0.001).

Patients with symptomatic instability tend to have increased acetabular inclination, decreased ACEA, greater functional limitations, younger, greater IRF, while hips with impingement demonstrate the opposite trends.

Introduction

Intraoperative periprosthetic femoral fractures (IOPFF) lead to reduced implant survival. A deeper understanding of predictors enables surgeons to modify techniques and patient selection to reduce the risk of IOPFF. The aim of this study was to estimate predictors of IOPFF and each anatomical subtype (calcar crack, trochanteric fracture, femoral shaft fracture) during primary THA.

We undertook a retrospective cohort study to determine clinical outcomes following the revision of metal-on-metal (MoM) hip replacements for adverse reaction to metal debris (ARMD), and to identify predictors of time to revision and outcomes following revision. Between 1998 and 2012 a total of 64 MoM hips (mean age at revision of 57.8 years; 46 (72%) female; 46 (72%) hip resurfacings and 18 (28%) total hip replacements) were revised for ARMD at one specialist centre. At a mean follow-up of 4.5 years (1.0 to 14.6) from revision for ARMD there were 13 hips (20.3%) with post-operative complications and eight (12.5%) requiring re-revision.

The Kaplan–Meier five-year survival rate for ARMD revision was 87.9% (95% confidence interval 78.9 to 98.0; 19 hips at risk). Excluding re-revisions, the median absolute Oxford hip score (OHS) following ARMD revision using the percentage method (0% best outcome and 100% worst outcome) was 18.8% (interquartile range (IQR) 7.8% to 48.3%), which is equivalent to 39/48 (IQR 24.8/48 to 44.3/48) when using the modified OHS. Histopathological response did not affect time to revision for ARMD (p = 0.334) or the subsequent risk of re-revision (p = 0.879). Similarly, the presence or absence of a contralateral MoM hip bearing did not affect time to revision for ARMD (p = 0.066) or the subsequent risk of re-revision (p = 0.178).

Patients revised to MoM bearings had higher rates of re-revision (five of 16 MoM hips re-revised; p = 0.046), but those not requiring re-revision had good functional results (median absolute OHS 14.6% or 41.0/48). Short-term morbidity following revision for ARMD was comparable with previous reports. Caution should be exercised when choosing bearing surfaces for ARMD revisions.

Cite this article: Bone Joint J 2014;96-B:1600–9.

Introduction

The vast majority of intertrochanteric fractures treated with cephalomedullary nails (CMN) will heal. Occasionally even though bony union occurs excessive lag screw sliding can cause persistent pain and soft tissue irritation and return to surgery for hardware removal. The purpose of this study was to evaluate if fracture stability, lag screw tip-apex distance (TAD), and quality of reduction have any impact excessive lag screw sliding and potential cutout.

The purpose of this study was to identify factors that predict implant cut-out after cephalomedullary nailing of intertrochanteric and subtrochanteric hip fractures, and to test the significance of calcar referenced tip-apex distance (CalTAD) as a predictor for cut-out.

We retrospectively reviewed 170 consecutive fractures that had undergone cephalomedullary nailing. Of these, 77 met the inclusion criteria of a non-pathological fracture with a minimum of 80 days radiological follow-up (mean 408 days; 81 days to 4.9 years). The overall cut-out rate was 13% (10/77).

The significant parameters in the univariate analysis were tip-apex distance (TAD) (p <  0.001), CalTAD (p = 0.001), cervical angle difference (p = 0.004), and lag screw placement in the anteroposterior (AP) view (Parker’s ratio index) (p = 0.003). Non-significant parameters were age (p = 0.325), gender (p = 1.000), fracture side (p = 0.507), fracture type (AO classification) (p = 0.381), Singh Osteoporosis Index (p = 0.575), lag screw placement in the lateral view (p = 0.123), and reduction quality (modified Baumgaertner’s method) (p = 0.575). In the multivariate analysis, CalTAD was the only significant measurement (p = 0.001). CalTAD had almost perfect inter-observer reliability (interclass correlation coefficient (ICC) 0.901).

Our data provide the first reported clinical evidence that CalTAD is a predictor of cut-out. The finding of CalTAD as the only significant parameter in the multivariate analysis, along with the univariate significance of Parker’s ratio index in the AP view, suggest that inferior placement of the lag screw is preferable to reduce the rate of cut-out.

Cite this article: Bone Joint J 2014; 96-B:1029–34.

Although the association between femoroacetabular impingement and osteoarthritis is established, it is not yet clear which hips have the greatest likelihood to progress rapidly to end-stage disease. We investigated the effect of several radiological parameters, each indicative of a structural aspect of the hip joint, on the progression of osteoarthritis. Pairs of plain anteroposterior pelvic radiographs, taken at least ten years apart, of 43 patients (43 hips) with a pistol-grip deformity of the femur and mild (Tönnis grade 1) or moderate (Tönnis grade 2) osteoarthritis were reviewed. Of the 43 hips, 28 showed evidence of progression of osteoarthritis. There was no significant difference in the prevalence of progression between hips with initial Tönnis grade 1 or grade 2 osteoarthritis (p = 0.31). Comparison of the hips with and without progression of arthritis revealed a significant difference in the mean medial proximal femoral angle (81° vs 87°, p = 0.004) and the presence of the posterior wall sign (39% vs 7%, p = 0.02) only. A logistic regression model was constructed to predict the influence of these two variables in the development of osteoarthritis.

Mild to moderate osteoarthritis in hips with a pistol-grip deformity will not progress rapidly in all patients. In one-third, progression will take more than ten years to manifest, if ever. The individual geometry of the proximal femur and acetabulum partly influences this phenomenon. A hip with cam impingement is not always destined for end-stage arthritic degeneration.

Introduction

Within the field of arthroplasty, the use of patient-reported outcome measures (PROMs) is becoming increasingly ubiquitous in an effort to employ more patient-centered methods of evaluating success. PROMs may be used to assess general health, joint-specific pain or function, or mental health. General and joint-specific questionnaires are most often used in arthroplasty research, but the relationship between arthroplasty and mental health is less well understood. Furthermore, longitudinal reports of PROM changes after arthroplasty are lacking in the literature.

Our primary aim was to quantify the improvement in general, joint-specific, and mental health PROMs following total hip arthroplasty (THA) as well as the extent of any deterioration through the 7 years follow-up. Our secondary aim was to identify predictors of clinically significant PROM decline.

Introduction

As orthopaedics shifts towards value-based models of care, methods of evaluating the value of procedures such as a total hip arthroplasty (THA) will become crucial. Patient reported outcome measures (PROMs) can offer a meaningful way for patient-centered input to factor into the determination of value.

Despite their benefits, PROMs can be difficult to interpret as statistically significant, but not clinically relevant, differences between groups can be found. One method of correcting this issue is by using a minimal clinically important improvement (MCII), defined as the smallest improvement in a PROM determined to be important to patients.

This study aims to find demographic and surgical factors that are independently predictive of failing to achieve a MCII in pain and physical function at 1-year following THA.

Objectives. Few studies have assessed outcomes following non-metal-on-metal hip arthroplasty (non-MoMHA) revision surgery performed for adverse reactions to metal debris (ARMD). We assessed outcomes following non-MoMHA revision surgery performed for ARMD, and identified predictors of re-revision. Methods. We performed a retrospective observational study using data from the National Joint Registry for England and Wales. All non-MoMHAs undergoing revision surgery for ARMD between 2008 and 2014 were included (185 hips in 185 patients). Outcome measures following ARMD revision were intra-operative complications, mortality and re-revision surgery. Predictors of re-revision were identified using Cox regression. Results. Intra-operative complications occurred in 6.0% (n = 11) of the 185 cases. The cumulative four-year patient survival rate was 98.2% (95% CI 92.9 to 99.5). Re-revision surgery was performed in 13.5% (n = 25) of hips at a mean time of 1.2 years (0.1 to 3.1 years) following ARMD revision. Infection (32%; n = 8), dislocation/subluxation (24%; n = 6), and aseptic loosening (24%; n = 6) were the most common re-revision indications. The cumulative four-year implant survival rate was 83.8% (95% CI 76.7 to 88.9). Multivariable analysis identified three predictors of re-revision: multiple revision indications (hazard ratio (HR) = 2.78; 95% CI 1.03 to 7.49; p = 0.043); selective component revisions (HR = 5.76; 95% CI 1.28 to 25.9; p = 0.022); and ceramic-on-polyethylene revision bearings (HR = 3.08; 95% CI 1.01 to 9.36; p = 0.047). Conclusions. Non-MoMHAs revised for ARMD have a high short-term risk of re-revision, with important predictors of future re-revision including selective component revision, multiple revision indications, and ceramic-on-polyethylene revision bearings. Our findings may help counsel patients about the risks of ARMD revision, and guide reconstructive decisions. Future studies attempting to validate the predictors identified should also assess the effects of implant design (metallurgy and modularity), given that this was an important study limitation potentially influencing the reported prognostic factors. Cite this article: G. S. Matharu, A. Judge, D. W. Murray, H. G. Pandit. Outcomes following revision surgery performed for adverse reactions to metal debris in non-metal-on-metal hip arthroplasty patients: Analysis of 185 revisions from the National Joint Registry for England and Wales. Bone Joint Res 2017;6:405–413. DOI: 10.1302/2046-3758.67.BJR-2017-0017.R2

Aims. To determine the outcomes following revision surgery of metal-on-metal hip arthroplasties (MoMHA) performed for adverse reactions to metal debris (ARMD), and to identify factors predictive of re-revision. Patients and Methods. We performed a retrospective observational study using National Joint Registry (NJR) data on 2535 MoMHAs undergoing revision surgery for ARMD between 2008 and 2014. The outcomes studied following revision were intra-operative complications, mortality and re-revision surgery. Predictors of re-revision were identified using competing-risk regression modelling. Results. Intra-operative complications occurred in 40 revisions (1.6%). The cumulative five-year patient survival rate was 95.9% (95% confidence intervals (CI) 92.3 to 97.8). Re-revision surgery was performed in 192 hips (7.6%). The cumulative five-year implant survival rate was 89.5% (95% CI 87.3 to 91.3). Predictors of re-revision were high body mass index at revision (subhazard ratio (SHR) 1.06 per kg/m. 2 . increase, 95% CI 1.02 to 1.09), modular component only revisions (head and liner with or without taper adapter; SHR 2.01, 95% CI 1.19 to 3.38), ceramic-on-ceramic revision bearings (SHR 1.86, 95% CI 1.23 to 2.80), and acetabular bone grafting (SHR 2.10, 95% CI 1.43 to 3.07). These four factors remained predictive of re-revision when the missing data were imputed. Conclusion. The short-term risk of re-revision following MoMHA revision surgery performed for ARMD was comparable with that reported in the NJR following all-cause non-MoMHA revision surgery. However, the factors predictive of re-revision included those which could be modified by the surgeon, suggesting that rates of failure following ARMD revision may be reduced further. Cite this article: Bone Joint J 2017;99-B:1020–7

Introduction. Historically, US arthroplasty revision rates are based on CMS data that cannot verify initial surgery date in patients under 65 years or laterality of revision. We calculated US one-year revision rates for primary total hip replacement (THR) using a representative cohort. Reasons for revision were documented. Methods. A multi-center cohort from US surgeons in 28 states collected sociodemographic data; medical, emotional, musculoskeletal comorbidities; BMI; and patient-reported pain and function (SF36, HOOS) for elective THR patients. Cases in 2011–2013 were matched with CMS data to ascertain 1 year revision through 2014. Predictors of revision were identified. Chart reviews to verify reasons for revision were performed. Results. Overall, 1.6% of 2926 primary THR surgeries were revised within 12 months. Mean age was 72 years, 59% female. No significant difference in pre-operative age, sex, BMI, pain, function, or emotional health was detected between revision and non-revision patients. Severe low back pain was twice as prevalent among revisions (23% vs. 11%; p<0.04) as was prior stroke (8.5% vs. 3%). Primary reasons for revision were infection (30%), mechanical failure including dislocation (26%), fracture (19%), metal ions (15%) and other (10%). In patients under 65 years of age, the distribution of reasons for revision are identical. Conclusion. The incidence of revision THR in the US within 12 months of the index procedure is 1.6%. Infection and mechanical failure, including dislocation, are the most common causes of early revision, followed by peri-prosthetic fracture. Patients with severe pre-op lumbar spine pain are at higher risk for early revision after THR. Abbreviations: total hip replacement (THR)

Aims

Hip arthroscopy has gained prominence as a primary surgical intervention for symptomatic femoroacetabular impingement (FAI). This study aimed to identify radiological features, and their combinations, that predict the outcome of hip arthroscopy for FAI.

Recent studies have reported on non-metal-on-metal hip arthroplasty (non-MoMHA) patients requiring revision surgery for adverse reactions to metal debris (ARMD). Although the outcomes following revision surgery for ARMD in MoMHA patients are known to generally be poor, little evidence exists regarding outcomes following non-MoMHA revision surgery performed for ARMD. We determined the outcomes following non-MoMHA revision surgery performed for ARMD, and identified predictors of re-revision. We performed a retrospective observational study using data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man. All primary non-MoMHA patients who subsequently underwent revision surgery for ARMD between 2008–2014 were included (n=185). Outcome measures following ARMD revision were intraoperative complications, mortality, and re-revision surgery. Predictors of re-revision surgery were identified using Cox regression analysis. Intra-operative complications occurred in 6.0% (n=11) of ARMD revisions. The cumulative 4-year patient survival rate was 98.2% (95% CI=92.9–99.5%). Re-revision surgery was performed in 13.5% (n=25) of hips at a mean time of 1.2 years (range 0.1–3.1 years) following ARMD revision. Infection (32%), dislocation/subluxation (24%), and aseptic loosening (24%) were the commonest re-revision indications. The cumulative 4-year implant survival rate was 83.8% (95% CI=76.7%-88.9%). Significant predictors of re-revision were: multiple revision indications (Hazard Ratio (HR)=2.78; 95% CI=1.03–7.49; p=0.043), incomplete revision procedures (including modular component exchange only) (HR=5.76; 95% CI=1.28–25.9; p=0.022), and ceramic-on-polyethylene revision bearings (HR=3.08; 95% CI=1.01–9.36; p=0.047). Non-MoMHA patients undergoing ARMD revision have a high short-term risk of re-revision. Infection, dislocation/subluxation, and aseptic loosening were the commonest re-revision indications. Furthermore, important and potentially modifiable predictors of future re-revision were identified. Although the poor prognostic factors identified require validation in future studies, our findings may be used to counsel patients about the risks associated with ARMD revision surgery, and guide decisions about the reconstructive procedure