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Clin Orthop Relat Res. 2010 September; 468(9): 2363–2371.
Published online 2010 April 29. doi:  10.1007/s11999-010-1354-0
PMCID: PMC2914297

Factors That Predict Short-term Complication Rates After Total Hip Arthroplasty

Abstract

Background

There remains uncertainty regarding the relative importance of patient factors such as comorbidity and provider factors such as hospital volume in predicting complication rates after total hip arthroplasty (THA).

Purpose

We therefore identified patient and provider factors predicting complications after THA.

Methods

We reviewed discharge data from 138,399 patients undergoing primary THA in California from 1995 to 2005. The rate of complications during the first 90 days postoperatively (mortality, infection, dislocation, revision, perioperative fracture, neurologic injury, and thromboembolic disease) was regressed against a variety of independent variables, including patient factors (age, gender, race/ethnicity, income, Charlson comorbidity score) and provider variables (hospital volume, teaching status, rural location).

Results

Compared with patients treated at high-volume hospitals (above the 20th percentile), patients treated at low-volume hospitals (below the 60th percentile) had a higher aggregate risk of having short-term complications (odds ratio, 2.00). A variety of patient factors also had associations with an increased risk of complications: increased Charlson comorbidity score, diabetes, rheumatoid arthritis, advanced age, male gender, and black race. Hispanic and Asian patients had lower risks of complications.

Conclusions

Patient and provider characteristics affected the risk of a short-term complication after THA. These results may be useful for educating patients and anticipating perioperative risks of THA in different patient populations.

Level of Evidence

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Introduction

THA is effective for decreasing pain and improving the function of patients with arthritis refractory to nonoperative treatment with antiinflammatory medications, activity modification, and weight loss. Despite the efficacy of THA, complications can occur which result in poor functional outcomes for a subset of patients. Given hip arthroplasty is a common and costly procedure, documenting and improving the quality of care and outcomes after THA remains a priority. Identifying risk factors that predict postoperative complications and, more specifically, being able to predict those patients at higher risk before surgery is an important step in searching for strategies that might reduce short-term complication rates.

The most common major complications include mortality, infection, dislocation, revision, and pulmonary embolism [46]. The rates of complication have been reported in international registries [2, 3, 8]. In addition, several papers have used administrative databases to evaluate complications in Medicare patients, with emphasis on the relationship between hospital and surgeon volume to rates of mortality and complications during the first 90 days after THA [4, 10]. The California Patient Discharge Database similarly contains data on mortality and complications. The database has the advantage of capturing complication rates of patients in the population of a state comparable in size to those covered in international registries. In addition, the age range is not limited by Medicare coverage. In the absence of a domestic joint replacement registry, the database provides a large alternative source of information on the rates and predictors of complication rates in a large group of patients from the United Stated including all age groups.

To confirm reported risk factors noted in the literature, we therefore identified patient and provider factors predicting complications after THA using the California database.

Patients and Methods

We obtained data for all hospitalizations in California during the years 1995 through 2005 from California’s Office of Statewide Health Planning and Development (OSHPD). The OSHPD database is compiled annually and includes discharge abstracts from all licensed nonfederal hospitals in California [11, 12]. Each discharge abstract reports demographic information that includes age, gender, insurance type, and the race or ethnicity of the patient. In addition, International Classification of Diseases, 9th Revision (ICD-9) codes are entered into the record for each patient; the number of codes entered is not prespecified and the maximum allowed is up to 20 inpatient procedures and 24 diagnoses per hospitalization (Table 1). Hospital characteristics are also reported, including the teaching status and whether a hospital is classified as rural in location. The OSHPD state inpatient database was initiated as a component of the Healthcare Cost and Utilization Project (HCUP) and is collected through mandatory reporting by all nonfederal hospitals in the state of California. Institutional Review Board approval was obtained for this study.

Table 1
Demographics of patient sample

We identified 138,399 patients undergoing their first THA using the ICD-9 procedure code for primary THA (81.51) who met inclusion and exclusion criteria. A previously published coding algorithm was modified and used to exclude 20,291 patients with infection, pathologic fracture, or undergoing revision arthroplasty [4, 10] (Appendix 1). We also excluded 3,848 patients with a non-California zip code to decrease the probability of the patient having prior admissions meeting exclusion criteria or experiencing a subsequent complication treated outside of the state. The unit of analysis was hospital discharge for each patient. All patients had basic demographic data as mandated by the state reporting requirements so no patients were excluded for missing data. Baseline patient characteristics were recorded in the database and analyzed. The mean age of the patient sample was 66 years with 85% being white. The population was diverse with 4% being black, 7% Hispanic, and 2% Asian. Complicated diabetes is defined as diabetes associated with end-organ damage; uncomplicated diabetes was noted in 8%, whereas less than 1% of patients had complicated diabetes. A diagnosis of rheumatoid arthritis was noted in 4% of patients (Table 1).

We selected the primary patient-based predictors: the Charlson comorbidity index [1, 9], age, race, gender, and income using zip code as a proxy as reported in the OSHPD database crossreferenced to US Census data. The Charlson comorbidity index assesses 19 comorbid conditions and has been validated for use in administrative database studies [1, 9]. This study uses the approach of Deyo et al. that adapted the Charlson index by defining the 19 comorbid conditions using ICD-9-CM coding and subsequently determining if the relevant codes are included in a patient record [1, 9]. In addition to the Charlson score, individual comorbidities were included for separate analysis consisting of diabetes, peripheral vascular disease, and rheumatoid arthritis.

Hospitals characteristics included surgical volume of THA, rural location, and teaching status. Teaching status and rural location are self-reported by the participating hospitals. Surgical volume was defined as the average number of primary THAs performed yearly during the study period. Hospitals were classified by their annual average volume as high-, intermediate-, or low-volume hospitals. Hospitals were categorized as low-volume if they were in the lowest 40th percentile by annual volume among hospitals where THA was performed. Intermediate-volume hospitals were defined as the next 40th percentile; high-volume hospitals were defined as the highest 20th percentile.

The outcomes analyzed as the dependent variables were the aggregate rate of short-term complications as well as the separately analyzed rates of individual complications, including mortality or readmission for the specific complications of infection, dislocation, revision surgery, perioperative fracture, neurologic injury, and thromboembolic disease at 90 days postoperatively. Previously published algorithms [4, 5] were adapted to detect codes consistent with a complication. The coding algorithms use ICD-9 nomenclature to identify patients undergoing total hip replacement using the 81.51 procedure code. Additional associated diagnoses, exclusion criteria, and complications are defined based on ICD-9 procedure and diagnoses codes judged by the authors to be consistent with the diagnoses or complications of interest. These algorithms were modified to correct for coding changes made during the study period [7, 11] (Appendix 1). Mortality was identified by the linkage of the California State Death Statistical Master File to the OSHPD database. This allowed us to identify hospital deaths occurring after discharge and the time elapsed before death in patients undergoing primary THA. The DSMF is a database of death certificates for all individuals dying in California and of those California residents who die outside of California’s borders but within the United States [13].

We used multiple variable logistic regression models to determine the role of the patient and provider characteristics as independent variables in predicting the occurrence of the complications selected as dependent variables. This method allows us to report the odds ratio for each patient and provider independent variable adjusted for all of the other variables included in the model. The regression models included the patient characteristics of race/ethnicity, age, gender, income, specific comorbidities, and modified Charlson comorbidity index and the provider characteristics of hospital volume, rural location, and teaching status as independent variables. The strength of association between the risk of a complication and the patient and provider characteristics is reported as the odds ratio in relation to a reference group adjusted for all the other variables included in the model. P-values and 95% confidence intervals are reported with the odds ratios. All statistical analyses were conducted using Stata/SE 8.0 (Stata Corp, College Station, TX).

Results

Overall, the 90-day complication rate after primary THA was 3.8%. The most common complication identified was dislocation (1.4%). The mortality rate was 0.68%. The rates of infection, thromboembolic disease (including pulmonary embolism and deep venous thrombosis), neurovascular injury, perioperative fracture, and revision surgery were each below 1% (Table 2).

Table 2
90-day complication rates following total hip arthroplasty

Increased age was associated with a higher risk of a short-term complication as was a higher Charlson comorbidity index (Table 3). One of the stronger predictors of an increased aggregate risk of a complication within 90 days was the presence of complicated diabetes (odds ratio [OR], 1.94; 95% confidence interval [CI], 1.49–2.53; p < 0.001) as a result of increased risks of mortality and infection. Relative to white patients, black patients had an increased risk of complications (OR, 1.19; 95% CI, 1.05–1.35; p = 0.007), whereas Hispanic (OR, 0.75; 95% CI, 0.67–0.85; p < 0.001) and Asian patients (OR, 0.54; 95% CI, 0.42–0.69; p < 0.001) had a lower risk. Patients’ quintile of income was not associated with the aggregate risk of a complication. Hospital volume was the strongest predictor of a complication with both low-volume (OR, 2.00; 95% CI, 1.82–2.20; p < 0.001) and intermediate-volume (OR, 1.33; 95% CI, 1.22–1.45; p < 0.001) hospitals having an increased OR in relation to high-volume hospitals (Table 3). Teaching status and rural location were not associated with increased risks for most complications (Table 4).

Table 3
Odds ratios for a complication within 90-days according to patient and hospital characteristics
Table 4
Odds ratios for specific complications at 90-days according to patient and hospital characteristics

Discussion

Many reports from various registries and individual papers report risk factors predicting complication rates after total hip arthroplasty (THA). However, the findings vary and there remains uncertainty regarding the relative importance of patient factors such as comorbidity and provider factors such as hospital volume in predicting complications. The California Office of Statewide Health Planning and Development (OSHPD) database provides a large alternate source of information. To confirm information in the literature, we therefore identified patient and provider factors predicting complications after THA using this alternate database. We specifically report the role of a variety of patient and hospital characteristics in predicting rates of mortality, infection, revision, dislocation, and thromboembolic disease after THA.

There are several limitations of studies examining administrative databases. First, this study was performed using a database of all patients in California over an 11-year period; this population may be less prone to selection bias than those studies looking at isolated Medicare populations. However, one potential bias in this population stems from patients having had surgery in California and sustaining a complication elsewhere, which would go unrecorded. More research is needed to determine if there is substantial bias in groups moving or receiving care outside of California. Another potential source of bias comes from relying on administrative registries. There can be substantial discrepancies between administrative data and audited and validated clinical data [10]. Second, the use of readmission and death records may underestimate morbidity and mortality if complications are not coded properly or do not require hospitalization. Third, the OSHPD statewide database does not include information on long-term functional outcomes. As a result, we could not evaluate the relationship of the predictor variables to functional outcome. Fourth, we were limited in our ability to identify confounding variables such as surgeon volume and training. Information on surgeon volume was not available and could not be evaluated separately from hospital volume. The studies by Katz et al. suggest both surgeon volume and hospital volume are independently associated with complication rates after THA [4]. Fifth, the California database includes hospital identifier but not surgeon identifiers, so we could not identify information on the relative importance of hospital and surgeon volume. Despite these limitations, the California discharge database has the advantage of being mandated by the state to include all admissions [13]. In addition, California is a large state with a diverse population allowing for the analysis of large numbers of patients from a variety of socioeconomic categories. In the absence of a formal domestic registry, the complication rates reported in this study provide an initial estimate of complication rates using population-based data on a large group of patients in the United States of all groups.

The overall 90-day complication rate of 0.68% for mortality, 0.64% for pulmonary embolus, and 1.39% for hip dislocation was lower than previously reported rates in the Medicare population of 1.0%, 0.9%, and 3.1%, respectively [6]. The Swedish Registry reported a similar 90-day mortality rate of 0.76% while the readmission rate was 3.9% within 30 days [3] (Table 5). The Australian and Finnish registries annual reports do not detail complication rates over periods shorter than 1-year so direct comparison to our study is not available [2, 8]. The higher rates of complication in Medicare analyses may demonstrate the selection bias in the Medicare population toward older and potentially sicker patients. Interestingly, our population had a higher wound infection rate of 0.9% than that previously reported in the Medicare population of 0.2% [6]. Further research is needed to elucidate the potential causes for this with respect to potential differences in the prevalence of diabetes, nosocomial infections, regional variations in pathogens, or intrinsic differences in our California population. Our dislocation rate of 1.39% was similar to previously published data in the Medicare population for those treated by surgeons who performed more than 50 THAs per year, 1.5%; however, this is notably different from the dislocation rate in those treated by surgeons who performed five or fewer per year, which has been reported as 4.2% [6]. Our study demonstrated similar increased risks of dislocation at lower-volume hospitals after adjusting for patient and provider characteristics. These observations may be useful for targeting interventions with a goal to decrease dislocation and complication rates at lower-volume centers.

Table 5
Short-term complication rates compared to Swedish Registry and Medicare Database analyses

Age, comorbidity, and race/ethnicity had an effect on the risk of short-term complications similar in magnitude to that of hospital volume. These findings are similar to those reported by Katz et al. who found age, gender, comorbidity, race, and income were associated with a higher risk of complications in the Medicare population [4]. Confirmation of these observations suggests the need for further study on the relative importance and underlying causes of these differences among populations. Future studies of these predictive factors would benefit from enriched data sources that include functional outcomes. Identifying these differing risks may be useful in counseling patients regarding the risks of surgery. The causes of these differences between populations warrant additional study to determine if they should play a role in patient selection or result in different approaches to perioperative care in patients at increased risk of complications.

This study reports short-term complication rates following total hip arthroplasty and the role of some patient and provider factors in predicting the occurrence of complications. The elucidation of these factors is useful in patient education and discussion of the perioperative risks of THA in different patient population.

Open Access

This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

Appendix 1

Inclusion Diagnosis codes -- to be flagged

715
degenerative disease
7150
degenerative disease
71500
degenerative disease
71509
degenerative disease
7151
degenerative disease
71510
degenerative disease
71515
degenerative disease
7152
degenerative disease
71520
degenerative disease
71525
degenerative disease
7153
degenerative disease
71530
degenerative disease
71535
degenerative disease
718
degenerative disease
71580
degenerative disease
71585
degenerative disease
71589
degenerative disease
7159
degenerative disease
71590
degenerative disease
71595
degenerative disease
714
rheumatoid arthritis, JRA, and RA with systemic involvement
7140
rheumatoid arthritis, JRA, and RA with systemic involvement
7143
rheumatoid arthritis, JRA, and RA with systemic involvement
71430
rheumatoid arthritis, JRA, and RA with systemic involvement
71431
rheumatoid arthritis, JRA, and RA with systemic involvement
71432
rheumatoid arthritis, JRA, and RA with systemic involvement
71433
rheumatoid arthritis, JRA, and RA with systemic involvement
7334
AVN
73340
AVN
73342
AVN
7310
Pagets
73300
osteoporosis
73301
osteoporosis
73302
osteoporosis
73303
osteoporosis
73309
osteoporosis
27800
obesity - NOS
27801
obesity - morbid
27802
obesity - overweight
V850
obesity - BMI<19
V851
obesity - BMI 19-24
V8521
obesity - BMI 25-30
V8522
obesity - BMI 25-30
V8523
obesity - BMI 25-30
V8524
obesity - BMI 25-30
V8525
obesity - BMI 25-30
V8530
obesity - BMI 30-40
V8531
obesity - BMI 30-40
V8532
obesity - BMI 30-40
V8533
obesity - BMI 30-40
V8534
obesity - BMI 30-40
V8535
obesity - BMI 30-40
V8536
obesity - BMI 30-40
V8537
obesity - BMI 30-40
V8538
obesity - BMI 30-40
V8539
obesity - BMI 30-40
V854
obesity - BMI>40

Inclusion Procedure codes

8151
total hip replacement

Exclusion Codes --

Procedures
7905
fracture - femur
7915
fracture - femur
7925
fracture - femur
7935
fracture - femur
8153
revision hip replacement
786
removal of implanted device
7860
removal of implanted device
7865
removal of implanted device
800
arthrotomy for removal of prosthesis
8000
arthrotomy for removal of prosthesis
8005
arthrotomy for removal of prosthesis
8153
 

Diagnosis
820
fracture of neck, shaft, or unspecified - femur
8200
fracture of neck, shaft, or unspecified - femur
8200
fracture of neck, shaft, or unspecified - femur
82001
fracture of neck, shaft, or unspecified - femur
82001
fracture of neck, shaft, or unspecified - femur
82003
fracture of neck, shaft, or unspecified - femur
82009
fracture of neck, shaft, or unspecified - femur
8201
fracture of neck, shaft, or unspecified - femur
82010
fracture of neck, shaft, or unspecified - femur
82011
fracture of neck, shaft, or unspecified - femur
82012
fracture of neck, shaft, or unspecified - femur
82013
fracture of neck, shaft, or unspecified - femur
82019
fracture of neck, shaft, or unspecified - femur
8202
fracture of neck, shaft, or unspecified - femur
82020
fracture of neck, shaft, or unspecified - femur
82021
fracture of neck, shaft, or unspecified - femur
82022
fracture of neck, shaft, or unspecified - femur
8203
fracture of neck, shaft, or unspecified - femur
82030
fracture of neck, shaft, or unspecified - femur
82031
fracture of neck, shaft, or unspecified - femur
82032
fracture of neck, shaft, or unspecified - femur
8208
fracture of neck, shaft, or unspecified - femur
8209
fracture of neck, shaft, or unspecified - femur
821
fracture of neck, shaft, or unspecified - femur
8210
fracture of neck, shaft, or unspecified - femur
82100
fracture of neck, shaft, or unspecified - femur
82101
fracture of neck, shaft, or unspecified - femur
8211
fracture of neck, shaft, or unspecified - femur
82110
fracture of neck, shaft, or unspecified - femur
82111
fracture of neck, shaft, or unspecified - femur
8080
acetabulum, closed
8081
acetabulum, open
8082
pubis, closed
8083
pubis, open
80841
ilium, closed
80842
ischium, closed
80843
multiple pelvic, closed
80849
pelvic, other
80851
ilium, open
80852
ischium, open
80853
multiple pelvic, open
80850
other pelvic, open
8088
unspecified, pelvic, closed
71105
infection - hip
71165
infection - hip
71195
infection - hip
7300
infection - hip
73000
infection - hip
73005
infection - hip
7301
infection - hip
73010
infection - hip
73015
infection - hip
7302
infection - hip
73020
infection - hip
73025
infection - hip
7309
infection - hip
73090
infection - hip
73095
infection - hip
170
malignancy or pathoalogic fracture
1706
malignancy or pathoalogic fracture
1707
malignancy or pathoalogic fracture
1709
malignancy or pathoalogic fracture
1953
malignancy or pathoalogic fracture
1955
malignancy or pathoalogic fracture
198
malignancy or pathoalogic fracture
1985
malignancy or pathoalogic fracture
1990
malignancy or pathoalogic fracture
7331
malignancy or pathoalogic fracture
73314
malignancy or pathoalogic fracture
V540
aftercare for removal of fracture plate or other fixation device
9964
complications of implant
9966
complications of implant
99660
complications of implant
99666
complications of implant
99667
complications of implant
9967
complications of implant
99670
complications of implant
99677
complications of implant
99678
complications of implant

Outcome diagnosis of Interest

* Code descriptions ending in an * also require a V-code (to specify the joint)

41511
DVT/PE - iatrogenic pulmonary embolism and infarction
41519
DVT/PE - pulmonary embolism and infarction, other
45340
DVT/PE - deep venous thrombosis of lower extremity
45341
DVT/PE - DVT of proximal lower extremity
45342
DVT/PE - DVT of distal lower extremity
711
infection - arthropathy associated with infections
7110
infection - pyogenic arthritis
71100
infection - pyogenic arthritis, site unspecified
71105
infection - pyogenic arthritis, pelvic region and thigh
7116
infection - mycotic arthropathy
71160
infection - mycotic arthropathy, site unspecified
71165
infection - mycotic arthropathy, pelvic region and thigh
7119
infection - unspecified infective arthritis
71190
infection - unspecified infective arthritis, site unspecified
71195
infection - unspecified infective arthritis, pelvic region and thigh
7300
infection - acute osteomyelitis
73000
infection - acute osteomyelitis, site unspecified
73005
infection - acute osteomyelitis, pelvic region and thigh
7301
infection - chronic osteomyelitis
73010
infection - chronic osteomyelitis, site unspecified
73015
infection - chronic osteomyelitis, pelvic region and thigh
7302
infection - unspecified osteomyelitis
73020
infection - unspecified osteomyelitis, site unspecified
73025
infection - unspecified osteomyelitis, pelvic region and thigh
7309
infection - unspecified
73090
infection - unspecified unspecified site
73095
infection - unspecified infection of bone, pelvic region and thigh
99640
mechanical complication - unspecified mechanical complication of internal orthopedic device, implant, graft *
99641
mechanical complication - mechanical loosening of prosthetic joint *
99642
mechanical complication - dislocation of prosthetic joint *
99643
mechanical complication - prosthetic implant joint failure *
99644
mechanical complication - peri prosthetic fracture around prosthetic joint*
99645
mechanical complication - peri-prosthetic osteolysis *
99646
mechanical complication - articular bearing surface wear of prosthetic joint *
99647
mechanical complication - other mechanical complication of prosthetic joint implant *
99649
mechanical complication - other mechanical complication of other internal orthopedic device, implant, and graft *
99811
hemorrahge, hematoma, or seroma complicating a procedure
99812
hemorrahge, hematoma, or seroma complicating a procedure
99813
hemorrahge, hematoma, or seroma complicating a procedure
9982
neurovascular - accidental puncture or laceration during procedure on vessel, nerve, organ
9966
infection and inflammatory reaction due to joint prosthesis *
786
removal of implanted device from bone
7860
removal of implanted device from bone, site unspecified
7865
removal of implant device from bone, femur
800
arthrotomy for removal of prosthesis
8000
arthrotomy for removal of prosthesis, site unspecified
8005
arthrotomy for removal of prosthesis, hip
801
arthrotomy, other
8010
arthrotomy, other, site unspecified
8015
arthrotomy, other, hip
7975
closed reduction, hip
7985
open reduction, hip
8153
revision arthroplasty - Revision of hip replacement
8622
I and D - excisional debridement of wound, infection, burn
8628
I and D - nonexcisional debridement of wound, infection, burn
7765
I and D - local excision of lesion or tissue of bone, femur

Valid V codes -- only used for outcomes with a *
V4364
v - hip

Footnotes

One or more of the authors (NFS) received funding from the Orthopaedic Research and Education Foundation.

Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.

This work was performed at the UCLA School of Medicine.

References

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