Associations Between Time to Reduction and Complications in Patients With Dislocated Total Hip Arthroplasty - A Protocol for an Observational Cohort Study
Conditions: Closed Reduction, Arthroplasty, Replacement, Hip, Length of Stay
Sponsor: Nordsjaellands Hospital

1 
 
Cover page 
 
Title: 
Associations between time to reduction and complications in patients 
with dislocated total hip arthroplasty: A protocol for an observational 
cohort study 
 
NCT number:  
Not available 
 
Date: 
4th March 2025 
 
 
 
 
 
 
 

2 
 
Associations between time to reduction and 
complications in patients with dislocated total 
hip arthroplasty:  
A protocol for an observational cohort study 
 
Rikke Helene Frølund. Bjulf1, Rasmus Linnebjerg. Knudsen1, Aurelien Xuan Rosendal. Bahuet1, Mathias 
Therkel Steensbæk1, Anne-Sofie Linde Jellestad1, Tazio Maleitzke3, Kai Henrik Wiborg Lange1,2, Markus 
Harboe Olsen4,5, Anders Peder Højer Karlsen2,6 Lars Hyldborg Lundstrøm1,2, Anders Kehlet Nørskov1,2 
 
1Department of Anesthesiology, Copenhagen University Hospital – North Zealand, Hillerød, Denmark 
2Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark 
3 Department of Orthopaedic Surgery Copenhagen University Hospital Hvidovre University of Copenhagen  
4Department of Neuroanaesthesiology, The Neuroscience Centre, Copenhagen University Hospital-Rigshospitalet, Denmark  
5Copenhagen Trial Unit, Centre for Clinical Intervention Research, The Capital Region, Copenhagen University Hospital - 
Rigshospitalet, Copenhagen, Denmark 
6Department of Anesthesiology and Intensive Care Medicine, Copenhagen University Hospital- Bispebjerg, Denmark 
 
Correspondence: Rikke Helene Frølund Bjulf, Department of Anesthesiology, Copenhagen University Hospital – North Zealand, 
Hillerød, Dyrehavevej 29, 3400 Hillerød, Denmark. Email: rikke.helene.froelund.bjulf.01@regionh.dk 
 
 
 

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Table of contents 
Background ....................................................................................................................................................... 4 
Objective ............................................................................................................................................................ 5 
Methods ............................................................................................................................................................. 5 
Study design .................................................................................................................................................. 5 
Setting and Population ................................................................................................................................... 5 
Inclusions Criteria ......................................................................................................................................... 6 
Exclusion Criteria .......................................................................................................................................... 6 
Exposure and Outcomes ................................................................................................................................ 6 
Exposure variables. .................................................................................................................................... 6 
Outcome measures ..................................................................................................................................... 6 
Variables .................................................................................................................................................... 7 
Data collection ............................................................................................................................................... 7 
Data handling................................................................................................................................................. 7 
Statistical Analysis ......................................................................................................................................... 8 
Strengths and limitations .................................................................................................................................. 9 
Publications ...................................................................................................................................................... 9 
References ....................................................................................................................................................... 10 
Appendix ......................................................................................................................................................... 11 
Appendix 1: Variable table .......................................................................................................................... 11 
 
  
 
 
 
 
 
 
 

4 
 
Background 
Total hip arthroplasty (THA) is one of the most performed surgical procedures worldwide, with 
well-established efficacy in relieving joint pain and enhancing patient mobility..1-4 Between 1995 
and 2023, around 241,000 primary THA’s were recorded in Denmark, averaging over 8,000 
procedures annually.3 An increasing number of THAs are performed in Denmark, with, 
approximately 14,000 in 2023, caused by a growing elderly population.3,5,6 In Denmark, the 
proportion of patients experiencing a dislocation of their primary THA is around 3%, and 23% of 
1,400 THA revision surgeries performed in 2023 were due to dislocation.3,7 
Dislocation of THA is painful and can result in neurovascular damage, making immediate reduction 
essential. Furthermore recurrent dislocations, can lead to a decrease in quality of life.8,9 Patients are 
usually elderly and frail with multiple comorbidities, making them susceptible to perioperative 
complications. 10 Delirium is a common postoperative complication in elderly patients and can lead 
to increased length of stay, admission to Intensive care unit and incidence of other complications 
such as pneumonia and death.11-13  
In Denmark, the standard treatment for dislocated THA is closed reduction, mostly performed in the 
operating theatre under general anesthesia and with potential additional use of a neuromuscular 
blocking agent.14 However, general anesthesia presents both logistical and clinical challenges. It 
requires the availability of an operating theatre and experienced personnel, consideration of fasting 
regimes, and carries an increased risk of cardiovascular and respiratory complications.14,15  Despite 
the widespread use of general anesthesia, there is currently a lack of consensus on how to provide 
anesthesia for patients with THA dislocations in Denmark.14 
Outside of Denmark, closed reduction of dislocated THA is increasingly being performed in the 
emergency department under sedation.9,16 This strategy presents potential advantages of reducing 
time to reduction along with hospital costs and length of stay, while freeing  up resources in 
operating theatres.17-21 However, sedation may induce complications such as, respiratory 
depression, apnea, aspiration, and other adverse events, that can be safely avoided in an operating 
theatre using general anesthesia.16,22,23 

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It remains unclear whether time to reduction, type of anesthesia and strategy for airway 
management are associated with increased risks of postoperative complications after closed 
reduction of dislocated THA. 
Objective 
The aim of the study is to investigate the impact of time to closed reduction on both patient related 
and organizational factors. These include, length of stay, hospitalization, admission to intensive care 
unit, rehospitalizations, delirium, all-cause mortality, infection requiring hospital contact, and 
cardiovascular complications. We also intend to investigate whether different anesthetic strategies 
and airway management are associated with different complication rates.  
We hypothesize that longer waiting time until reduction increase the post procedure length of stay, 
readmissions, and risk of complications. 
 
Methods 
This protocol is developed in accordance with the principles outlined in STROBE (Strengthening 
the Reporting of Observational Studies in Epidemiology).24 
Study design  
We will conduct a retrospective cohort study based on prospectively collected clinical data on 
patients presenting with THA dislocations who were treated with closed reduction in an operating 
theatre.  
Setting and Population  
The cohort contains all adults presenting with a dislocated THA, who underwent closed reduction in 
an operating theatre with anesthesiology being involved, in public hospitals in the Capital and 
Zealand Regions of Denmark.  
The study population is extracted from a dataset retrieved from the Electronic Health Record (EHR) 
system ‘Sundhedsplatformen’ (Epic Systems Corporation, WI, USA) from 1 January 2017 to 31 
December 2024, including granular data from approximately 1.1 million anesthetic procedures.   

6 
 
Inclusions Criteria  
Patients are eligible for inclusion if they are 18 years of age or above, presented in the emergency 
department with a dislocated THA, and underwent subsequent closed reduction in the operating 
theatre with the involvement of anesthesiology.  
Exclusion Criteria  
Patients are excluded if they: 
- 
Were primarily booked for open surgical reduction.  
- 
Did not have a complete case log (i.e. time of admission; referral to the operation theatre; 
anesthesia induction; discharge, etc.) and we were unable to recreate the log using simple 
code rules. 
 
Exposure and Outcomes  
Exposure variables. 
- 
Time in minutes from admission to closed reduction. 
- 
Time of day  
- 
Weekday vs. weekend  
- 
Airway management 
- 
Anesthesia method(s)  
- 
Neuromuscular blocking agent (Yes/No) 
Outcome measures 
Primary outcome  
- 
Post procedure length of stay in minutes from closed reduction until discharge from the 
hospital.  
Secondary outcomes  
- 
All-cause mortality at 90 days.  (Y/N) 
- 
Post procedure admission to the intensive care unit within 30 days (Y/N) 
- 
Readmissions to hospital within 30 days (Y/N) 
- 
Diagnosis with delirium or administration of haloperidol, olanzapine, risperidone, or 
quetiapine (as a surrogate for new onset delirium) (Y/N) 

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- 
Serum creatinine increase of more than 25 μmol/L within a period of less than 48 hours (as a 
surrogate for acute kidney failure) (Y/N) 
- 
Infection requiring hospital contact. 
- 
Cardiovascular complications (diagnosed arrythmia, myocardial infarction, cerebral 
ischemia or hemorrhage, pulmonary embolism or deep venous thrombosis) 
Variables 
Patient demographics like age, sex, weight, height, BMI, American Society of Anesthesiology 
(ASA) classification, location (hospital), first-time dislocation/recurrent dislocation and 
comorbidity (diagnose codes at admission) will be retrieved for baseline statistics and adjustment in 
our multivariate statistical analyses.  
A detailed list of variables is provided in Appendix 1.  
Data collection  
The data is extracted from the EHR-system Sundhedsplatformen validated and cleaned. The 
patients are recorded when they are admitted to a public hospital in the Capital and Zealand Regions 
of Denmark, which contains one or more operations CSN-ID linked to an anesthesia CSN-ID 
(indicating that a procedure was performed with anesthesia).  
The initial database extraction has been approved by ’Team for journaldata, videnskabsetik og 
forskningsstøtte, Region Hovedstaden’ (Approval number R-23038250; 14 July 23). Furthermore, 
approval has been granted for the transfer of medical record data from the database to this research 
project (Approval number R-24079695; 13 December 24).  
Data handling  
The dataset will undergo preprocessing and validation before analysis, including checks for missing 
values, duplicates, and errors. Only validated data will be used in the analysis to ensure accuracy 
and reliability. 
Data will be stored in a secure database with restricted access. The dataset will be retained for a 
period and will be deleted once the study is completed. 
 

8 
 
Statistical Analysis 
Baseline data will be presented using descriptive statistics.  For continuous variables, means and 
standard deviations (SDs) will be used to summarize data with normal distributions, and medians 
and interquartile range (IQR) for non-normally distributed data. Counts and percentages will 
represent categorical variables. 
Linear regression models will be applied to assess the primary outcome of post procedure length of 
stay and other continuous outcomes.  
Logistic regressions models with corresponding odds ratios (ORs) will be applied to assess the 
dichotomous secondary outcomes. To mitigate bias, we will adjust for relevant confounders in our 
statistical models and ensure data validation for the key variables, age, BMI, ASA-classification, 
comorbidities, site etc. 
For all analyses we will present statistical tests as two-sided and consider a p value less than 0.05 
statistically significant. For precision 95% confidence intervals will be presented.  
For exposure variables with more than 10% missing data, multiple imputation will be employed to 
reduce potential bias. We will use baseline demographics (age, sex, BMI, ASA-classification, first-
time dislocation/recurrent dislocation, site, and comorbidity) for imputation  
In cases where a patient undergoes multiple closed reductions during the observation period, we 
will conduct two analyses. The primary analysis will be based on each patient’s first reduction 
event. A secondary analysis will utilize a linear mixed model for all reduction events regardless of 
multiple events by the same patient. In this latter analysis, patients will be included for each 
hospitalization that involves a dislocation requiring closed reduction.  
In cases where missing data on outcome variables exceed 10%, we will impute worst-case and best-
case scenarios and conduct sensitivity analyses to assess the impact of these imputations on our 
findings.  
Statistical analyses will be performed using latest available stable version of R (R Core Team, 
Vienna, Austria).  
 

9 
 
Strengths and limitations 
This study offers several strengths. First, the retrospective design allows for a quick and cost-
effective study, as data are already available. This allows for analysis of a large cohort of patients 
with dislocated THA and explores the impact of timing on outcomes such as length of stay, 
readmissions, and complications. Additionally, the use of an extensive patient database increases 
statistical power, enabling assessment of multiple outcomes across a broad sample. 
Several limitations should be considered. 
Selection bias may arise since the study relies on existing patient records potentially resulting in 
incomplete or non-representative data particularly for specific patient groups, e.g. those treated in 
emergency settings outside an operating theatre. This could limit the generalizability of the findings 
to a broader patient population. 
Information bias may be present as clinical documentation might be inconsistent or incomplete, 
particularly regarding timing of reduction or complications. Additionally, patient identification 
relied on specific procedural codes for orthopedic surgery, which may have led to misclassification 
and potentially eligible patients being not correctly registered.  
Confounding factors, such as comorbidities, may influence both the timing of reduction and clinical 
outcomes. Confounding by indication may occur if patients with more severe conditions are either 
delayed in receiving treatment or receive specific types of airway management, which may in turn 
affect both the timing of reduction and clinical outcomes. As an example, more frail or acute 
patients may experience shorter waiting times or specific airway interventions, while more healthy 
patients might face delays in treatment due to the less urgent nature of their condition. This could 
falsely appear to influence outcomes, when in fact, their poorer prognosis is due to their underlying 
condition rather than the treatment provided.  
Publications 
Findings will be submitted for publication in an international, peer-reviewed journal relevant to the 
field of study. 
 
 

10 
 
References 
 
 
1. 
Stibolt, R.D., Jr., et al. Total hip arthroplasty for posttraumatic osteoarthritis following acetabular 
fracture: A systematic review of characteristics, outcomes, and complications. Chin J Traumatol 21, 
176-181 (2018). 
2. 
Dainty, J.R., et al. Trajectories of pain and function in the first five years after total hip and knee 
arthroplasty : an analysis of patient reported outcome data from the National Joint Registry. Bone 
Joint J 103-b, 1111-1118 (2021). 
3. 
(DHR), T.D.H.A.R. National Annual Report.  (2023). 
4. 
Price, A.J., et al. The use of patient-reported outcome measures to guide referral for hip and knee 
arthroplasty. Bone Joint J 102-b, 941-949 (2020). 
5. 
Kurtz, S., Ong, K., Lau, E., Mowat, F. & Halpern, M. Projections of primary and revision hip and knee 
arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 89, 780-785 (2007). 
6. 
Rasmussen, M.B., El-Galaly, A., Daugberg, L., Nielsen, P.T. & Jakobsen, T. Projection of primary and 
revision hip arthroplasty surgery in Denmark from 2020 to 2050. Acta Orthop 93, 849-853 (2022). 
7. 
Kirurgi, D.O.S.D.S.f.H.-o.K. Total Hoftealloplastik , Referenceprogram (2006). 
8. 
Kotwal, R.S., Ganapathi, M., John, A., Maheson, M. & Jones, S.A. Outcome of treatment for 
dislocation after primary total hip replacement. The Journal of Bone & Joint Surgery British Volume 
91-B, 321-326 (2009). 
9. 
Germann, C.A., Geyer, D.A. & Perron, A.D. Closed reduction of prosthetic hip dislocation by 
emergency physicians. Am J Emerg Med 23, 800-805 (2005). 
10. 
Hopkins, T.J., et al. Associations between ASA Physical Status and postoperative mortality at 48 h: a 
contemporary dataset analysis compared to a historical cohort. Perioper Med (Lond) 5, 29 (2016). 
11. 
Inouye, S.K., Westendorp, R.G. & Saczynski, J.S. Delirium in elderly people. Lancet 383, 911-922 
(2014). 
12. 
Schubert, M., et al. A hospital-wide evaluation of delirium prevalence and outcomes in acute care 
patients - a cohort study. BMC Health Serv Res 18, 550 (2018). 
13. 
Inouye, S.K., et al. A multicomponent intervention to prevent delirium in hospitalized older patients. 
N Engl J Med 340, 669-676 (1999). 
14. 
Holler, C.P., Lohse, N. & Foss, N.B. Anaesthesia practice in Denmark for relocation of the dislocated 
hip after total hip arthroplasty. Dan Med J 65(2018). 
15. 
Harris, M. & Chung, F. Complications of general anesthesia. Clin Plast Surg 40, 503-513 (2013). 
16. 
Waseem, S., Ngu, A. & Patel, J. Emergency Department closed reduction of dislocated THR: the 
REDDTHR Prospective Multi-centre Study. Hip Int 34, 633-640 (2024). 
17. 
Dilbone, E.S., et al. Location of Initial Closed Reduction Attempt Significantly Increases Cost and 
Length of Stay in Total Hip Arthroplasty. Arthroplast Today 15, 102-107 (2022). 
18. 
Lawrey, E., Jones, P. & Mitchell, R. Prosthetic hip dislocations: is relocation in the emergency 
department by emergency medicine staff better? Emerg Med Australas 24, 166-174 (2012). 
19. 
Gagg, J., et al. Door to relocation time for dislocated hip prosthesis: multicentre comparison of 
emergency department procedural sedation versus theatre-based general anaesthesia. Emerg Med 
J 26, 39-40 (2009). 
20. 
Blokland, A., Van Den Akker, V., Van Der Poort, C., Somford, M. & Holkenborg, J. Results of 
Reduction of Dislocated Prosthetic Hips in the Emergency Department. J Emerg Med 62, 462-467 
(2022). 
21. 
Sanchez-Sotelo, J., Haidukewych, G.J. & Boberg, C.J. Hospital cost of dislocation after primary total 
hip arthroplasty. J Bone Joint Surg Am 88, 290-294 (2006). 
22. 
Mathieu, N., et al. Is propofol a safe and effective sedative for relocating hip prostheses? Emerg 
Med J 26, 37-38 (2009). 

11 
 
23. 
Saiz, A.M., Lum, Z.C. & Pereira, G.C. Etiology, Evaluation, and Management of Dislocation After 
Primary Total Hip Arthroplasty. JBJS Rev 7, e7 (2019). 
24. 
von Elm, E., et al. The Strengthening the Reporting of Observational Studies in Epidemiology 
(STROBE) statement: guidelines for reporting observational studies. J Clin Epidemiol 61, 344-349 
(2008). 
Appendix 
Appendix 1: Variable table 
 
Exposure variables  
Variable  
Measurement  
Definition  
When  
Time to reduction  
Minutes, as a continuous 
variable  
From arriving time in 
the emergency 
department until the 
start of procedure in 
the operating theater.  
From arriving time at the 
hospital until start of 
procedure 
Time of day  
Nominal categorical 
variable, defined as 08-
16, 16-00 or 00-08 
At arriving time at the 
hospital defined as 
Day (08-16), evening 
(16-00) or nightshift 
(00-08) 
At arriving time at the 
hospital 
Weekday vs weekend  
Nominal categorical 
variable 
Defined as weekday 
from Monday 08 to 
Friday 00 and 
weekend Friday 00 to 
Monday 08.  
At arriving time at the 
hospital   
Airway management  
Categorical variable, 
defined as spontaneous 
breathing, mask 
ventilation, elective 
intubation, rapid 
sequence induction, or 
laryngeal mask. 
The type of airway 
management 
categorized as 
spontaneous 
breathing, mask 
ventilation, elective 
intubation, rapid 
At anesthesia induction 

12 
 
sequence induction, or 
laryngeal mask. 
Anesthesia method(s) 
Categorical variable, 
defined as propofol, 
etomidate, thiopental, 
midazolam, ketamine, 
sevoflurane, and 
desflurane. 
Anesthesia method(s) 
categorized as 
propofol, etomidate, 
thiopental, 
midazolam, ketamine, 
sevoflurane, and 
desflurane. 
At anesthesia induction 
Neuromuscular blocking 
agents 
Categorical variable  
Rocuronium, 
suxamethonium or non.  
Neuromuscular 
blocking agent 
categorized as 
Rocuronium, 
suxamethonium or 
non. 
At anesthesia induction 
Primary outcomes  
Post-reduction length of stay  
Minutes, as a continuous 
variable.  
Post procedure length 
of stay. 
From procedure start until 
hospital discharge up to 30 
days after discharge.  
Secondary outcomes  
All-cause mortality  
Binary variable (Y/N) 
90 days all-cause 
mortality  
90 days after closed 
reduction 
Admissions to Intensive care 
unit 
Binary variable (Y/N) 
Admissions to the 
intensive care unit 
within 30 days after 
the closed reduction.  
30 days after the closed 
reduction 
Readmission 
Binary variable (Y/N) 
Readmission within 
30 days after 
discharge  
30 days after discharge  
Delirium  
Binary variable (Y/N) 
Defined as diagnose 
of delirium (F05.x, 
obtained from the 
Post procedure, during 
admission up to 30 day after 
closed reduction.  

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diagnosis codes from 
the given admission) 
or the non-planned 
administration of 
haloperidol, 
olanzapine, 
risperidone, or 
quetiapine (as a 
surrogate for new 
onset delirium)  
Acute kidney failure  
Binary variable (Y/N) 
Defined as serum 
creatinine increase of 
more than 25 μmol/L 
within a period of less 
than 48 hours. or  an 
increase in serum 
creatinine >1.5 times the 
baseline value, with 
baseline defined as the 
most recent 
measurement within the 
past 12 months (As a 
surrogate for acute 
kidney failure) 
Post procedure until 30 days 
after discharge 
Infection requiring hospital 
contact  
Binary variable (Y/N) 
Defined as diagnosed 
infection 
(postoperative 
infection (T81.4), 
pneumonia (J13.x-
J18.x), Cystitis 
(N30.x, N39.0), sepsis 
Post procedure until 30 days 
after discharge 

14 
 
(R65.x A40.x, A41.x), 
C. difficile (A04.7) 
obtained from the 
diagnose codes from 
the given admission) 
or administration of 
antibiotic treatment 
(as a surrogate for in-
hospital infection 
Cardiovascular complications  Binary variable (Y/N) 
Defined as diagnosed 
arrythmia (I47.x, 
I48.x, I49.x), 
myocardial infarction 
(I21.x, I22.x), cerebral 
ischemia (I61.x, I63.x, 
I64.x), 
hemorrhage(T81), 
pulmonary 
embolism(I26.x) or 
deep venous 
thrombosis(I80.2) 
(obtained from the 
diagnosis codes from 
the given admission)   
From admission to 30 days 
after discharge.  
Baseline variables  
Age  
Years  
 
At admission  
Sex 
Male or female  
 
At admission 
Weight 
Kilograms  
 
At admission 
Height 
Centimeters  
 
At admission 
BMI 
Kg/m2 
 
At admission 
ASA-score 
ASA 1-6 
ASA I: Healthy 
patient, ASA II: Mild 
At admission 

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systemic disease, ASA 
III: Severe systemic 
disease, ASA IV: 
Severe systemic 
disease with constant 
threat to life, ASA V: 
Moribund patient, 
ASA VI: Declared 
brain-dead 
Comorbidity 
Diagnosis codes at 
admission  
Diagnose codes ad 
admission 
(Hypertension (I10, 
I11. I12, I13, I14, 
I15), Osteoporosis 
(M80, M81, M82, 
M83), Diabetes (E10, 
E11, E12, E13, E14), 
Congestive Heart 
failure (I50.x), 
Ischaemic heart 
disease (I21.x, I22.x, 
I24.x, I25.x), 
Arrythmia (I47.x, 
I48.x I49.x), Chronic 
Obst. Pulm. Disease 
(J44), Cancer (C00-
C97), Chronic kidney 
disease (N18), 
Cerebrovascular 
disease (I61.x, I63.x, 
I64.x), Mild liver 
disease (K70.x, K71.x, 
At admission 

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K73.x, K74.x, K76.x), 
Moderate/severe liver 
disease (K72.x, I85.x), 
Alcohol-related 
disease (F10.x), Drug-
related disease ( 
F11.x, F12.x, F13.x, 
F14.x, F16.x), 
Dementia (F00, F01, 
F02, F03), Parkinson 
disease (G20), 
Alzheimer (G30), 
Depression (F32.x-
F33.x), Anxiety 
(F40.x-F41.x), 
Schizophrenia (F20.x)    
Location (Hospital) 
OPIAD def.  
Locations categorized 
in The Capital Region 
(Site A-F) and 
Zealand Region (Site 
G-I)of Denmark. 
 
  
At admission. 
First-time 
dislocation/recurrent 
dislocation 
Binary variable, First 
time or recurrent 
dislocation.