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. Author manuscript; available in PMC: 2015 Jul 20.
Published in final edited form as: Spine (Phila Pa 1976). 2012 Apr 1;37(7):612–622. doi: 10.1097/BRS.0b013e318228f32d

Disparities in Rates of Spine Surgery for Degenerative Spine Disease Between HIV Infected and Uninfected Veterans

Joseph T King Jr 1, Adam J Gordon 2, Melissa F Perkal 3, Stephen Crystal 4, Ronnie A Rosenthal 3, Maria C Rodriguez-Barradas 5, Adeel A Butt 2, Cynthia L Gibert 6, David Rimland 7, Michael S Simberkoff 8, Amy C Justice 9
PMCID: PMC4507821  NIHMSID: NIHMS312760  PMID: 21697770

Abstract

Study Design

Retrospective analysis of nationwide Veterans Health Administration (VA) clinical and administrative data.

Objective

Examine the association between HIV infection and the rate of spine surgery for degenerative spine disease.

Summary of Background Data

Combination anti-retroviral therapy (cART) has prolonged survival in patients with HIV/AIDS, increasing the prevalence of chronic conditions such as degenerative spine disease that may require spine surgery.

Methods

We studied all HIV infected patients under care in the VA from 1996–2008 (n=40,038) and uninfected comparator patients (n=79,039) matched on age, gender, race, year, and geographic region. The primary outcome was spine surgery for degenerative spine disease defined by ICD-9 procedure and diagnosis codes. We used a multivariate Poisson regression to model spine surgery rates by HIV infection status, adjusting for factors that might affect suitability for surgery (demographics, year, comorbidities, body mass index, cART, and laboratory values).

Results

Two-hundred twenty eight HIV infected and 784 uninfected patients underwent spine surgery for degenerative spine disease during 700,731 patient-years of follow-up (1.44 surgeries per 1,000 patient-years). The most common procedures were spinal decompression (50%), and decompression and fusion (33%); the most common surgical sites were the lumbosacral (50%), and cervical (40%) spine. Adjusted rates of surgery were lower for HIV infected patients (0.86 per 1,000 patient-years of follow-up) than for uninfected patients (1.41 per 1,000 patient-years; IRR 0.61, 95% CI: 0.51, 0.74, P<0.001). Among HIV infected patients, there was a trend towards lower rates of spine surgery in patients with detectable viral loads levels (IRR 0.76, 95% CI: 0.55, 1.05, P=0.099).

Conclusion

In the VA, HIV infected patients experience significantly reduced rates of surgery for degenerative spine disease. Possible explanations include disease prevalence, emphasis on treatment of non-spine HIV-related symptoms, surgical referral patterns, impact of HIV on surgery risk-benefit ratio, patient preferences, and surgeon bias.

Keywords: disparities, HIV/AIDS, spine, surgery, outcomes

Introduction

In the era of combined antiretroviral treatment (cART), HIV/AIDS has been transformed into a chronic disease with survival measured in decades, and HIV infected patients survival long enough to develop chronic conditions that can require elective surgical intervention. Degenerative spine disease is a chronic progressive condition with a high prevalence in the general population, and the majority of adults will experience related symptoms such as low back pain at some time during their lives.1 Most symptomatic episodes are self-limited and effectively treated with non-surgical modalities such as analgesics, physical therapy, and manipulation.2 When these treatments fail, it is appropriate to consider surgical intervention in selected patients. Spine surgery for degenerative spine disease has become increasingly common in the United States3;4 and is the subject of numerous academic publications, yet there are few publications describing outcomes of spine surgery for degenerative disease in HIV infected individuals.5;6 The low United States population prevalence of HIV infection (estimated at 0.4%)7 complicates the study of surgical procedures in HIV positive patients – single institutions or even consortia may have insufficient numbers of HIV infected surgical patients to power meaningful analyses.

The Veterans Health Administration (VA) is the largest single provider of health care in the United States, with over 5 million veterans under care.8 Between 1996 and 2008, the VA provided care to 40,594 HIV positive veterans, one of the largest cohorts of HIV infected patients under care in the world. The VA utilizes an electronic medical record and central data repositories containing nationwide clinical and administrative data, including diagnosis and procedure codes that permit the identification of surgical procedures and accompanying medical conditions. We used VA databases to perform a population-based study of the rate of spine surgery for degenerative spine disease in all HIV positive patients under care in the VA and in matched uninfected comparator patients.

Materials and Methods

The Veterans Aging Cohort Study Virtual Cohort (VACS-VC) uses VA administrative and clinical databases and a validated algorithm9 to identify all HIV infected veterans that have received care within the VA from October 1, 1996 – September 30, 2008. VACS-VC contains detailed subject data from date of enrollment in the VA on 121,782 patients: 40,594 HIV infected Veterans, and on two uninfected comparator Veterans (n=81,188) matched to each HIV infected patient on age, gender, race, geographic region, and year of enrollment for care in the VA. VACS-VC data includes demographics, date of HIV diagnosis, combined anti-retroviral therapy (cART), survival, alcohol and drug use, comorbid conditions, body mass index (BMI), laboratory values, pharmacy data, hospital admissions and outpatient treatment encounters, and diagnosis and procedure codes.

The VA uses ICD-9 procedure codes to classify all inpatient procedures, and ICD-9 diagnosis codes to describe all inpatient and outpatient encounters.10 VACS-VC utilizes ICD-9 codes dated from 12 months before until 6 months after starting care in the VA and validated algorithms to determine a broad spectrum of baseline comorbidities prevalent at study enrollment. Our analysis incorporated a subset of these comorbidities that might impact on surgical referral or selection for surgery, including significant cardiovascular, respiratory, hepatobiliary, renal, endocrine, rheumatologic, neoplastic, infectious, and psychiatric disease, alcohol use disorders, and drug abuse.

We excluded from the analysis patients with zero follow-up time (n=2,705), i.e., whose only contact with the VA healthcare system was on their date of enrollment. We used ICD-9 procedure and diagnosis codes to identify all remaining patients in the database who underwent an inpatient surgical procedure for degenerative spine disease between October 1996 and September 2008 (Appendix). Dates of enrollment for care in the VA healthcare system were grouped into tertiles with similar number of patients: 1996–2000, 2001–2004, and 2005–2008. Inclusion criteria encompassed procedures on the vertebral bodies, intervertebral discs, and spinal ligaments and supporting structures. We excluded spinal diagnostic procedures, spine injections, procedures not directly related to treatment of degenerative spine disease (spinal pumps, spinal neurostimulators, spinal cerebrospinal fluid shunts or drains, spine biopsies, spine foreign body removals, spinal cord procedures), and procedures associated with a diagnosis of spinal tumor, congenital spine disorder, spine trauma, spine infection, inflammatory spinal condition, or spinal vascular disorder (Appendix). Eligible procedures were grouped using ICD-9 procedure codes and categorized as decompression, fusion, decompression and fusion, and motion preservation (Appendix). ICD-9 procedure and diagnostic codes were also used to classify the location of spine procedures (i.e., cervical, thoracic, lumbosacral, combined, or unspecified), and to identify spine diagnoses during the surgical admission.

Appendix.

Inclusion Criteria
ICD-9 Procedure Codes Description
Decompression
 03.02  Reopening of laminectomy site
 03.09  Other exploration and decompression of spinal canal
 80.5x  Excision, destruction of intervertebral disc, unspecified
Fusion
 81.0x  Spinal fusion
 81.3x  Refusion of spine
 81.62  Fusion or refusion of 2–3 vertebrae
 81.63  Fusion or refusion of 4–8 vertebrae
 81.64  Fusion or refusion of 9 or more vertebrae
 84.51  Insertion of interbody spinal fusion device
Motion preservation
 84.59  Insertion of other spinal devices
 84.6x  Replacement of spinal disc
 84.8x  Insertion, replacement, and revision of posterior spinal motion preservation device(s)
Exclusion Criteria
ICD-9 Procedure Codes Description
03 Operations on spinal cord and spinal canal structures
 03.01  Removal of foreign body from spinal canal
 03.1  Division of intraspinal nerve root
 03.2x  Cordotomy
 03.3x  Diagnostic procedures on spinal cord and spinal canal structures
 03.4  Excision or destruction of lesion of spinal cord or spinal meninges
 03.5x  Plastic operations on spinal cord structures
 03.6x  Lysis of adhesions of spinal cord and nerve roots
 03.7x  Shunt of spinal theca
 03.8  Injection of destructive agent into spinal canal
 03.9x  Other operations on spinal cord and spinal canal structures
81.6 Other procedures on spine
 81.65  Percutaneous vertebroplasty
 81.66  Percutaneous vertebral augmentation
ICD-9 Diagnosis Codes Description
013 Tuberculosis of meninges and central nervous system
 013.4x  Tuberculoma of spinal cord
 013.5x  Tuberculous abscess of spinal cord
015 Tuberculosis of the bones and joints
 015.0  Vertebral column
324 Intracranial and intraspinal abscess
 324.1  Intraspinal abscess
192 Malignant neoplasm of other and unspecified parts of nervous system
 192.2  Spinal cord
 192.3  Spinal meninges
198 Secondary malignant neoplasm of other unspecified sites
 198.3  Brain and spinal cord
 198.4  Meninges (cerebral) (spinal)
 198.5  Bone and bone marrow
225 Benign neoplasm of brain and other parts of nervous system
 225.3  Spinal cord
 225.4  Spinal meninges
336 Other diseases of spinal cord
 336.1  Vascular myelopathies
720 Ankylosing spondylitis and other inflammatory spondylopathiess
 720.0  Ankylosing spondylitis
 720.1  Spinal enthesopathy
 720.2  Sacroiliitis, not elsewhere classified
 720.8x  Other inflammatory spondylopathies
 720.9  Unspecified inflammatory spondylopathy
721 Spondylosis and allied disorders
 721.6  Ankylosing vertebral hyperostosis
 721.7  Traumatic spondylopathy
722 Intervertebral disc disorders
 722.9  Other and unspecified disc disorder (calcification of intervertebral cartilage or disc, discitis)
733 Other disorders of bone and cartilage
 733.13  Pathologic fracture of vertebrae */
741 Spina bifida
 741.0x  With hydrocephalus
 741.9x  Without mention of hydrocephalus
742 Other congenital anomalies of the nervous system
 742.5x  Other specified anomalies of spinal cord
747 Other congenital anomalies of circulatory system
 747.82  Spinal vessel anomaly
756 Other congenital musculoskeletal anomalies
 756.1x  Anomalies of spine
805 Fracture of vertebral column without mention of spinal cord injury
 805.0x  Cervical, closed
 805.1x  Cervical, open
 805.2  Dorsal [thoracic], closed
 805.3  Dorsal [thoracic], open
 805.4  Lumbar, closed
 805.5  Lumbar, open
 805.6  Sacrum and coccyx, closed
 805.7  Sacrum and coccyx, open
 805.8  Unspecified, closed
 805.9  Unspecified, open
806 Fracture of vertebral column with spinal cord injury
 806.0x  Cervical, closed
 806.1x  Cervical, open
 806.2  Dorsal [thoracic], closed
 806.3  Dorsal [thoracic], open
 806.4  Lumbar, closed
 806.5  Lumbar, open
 806.6  Sacrum and coccyx, closed
 806.7  Sacrum and coccyx, open
 806.8  Unspecified, closed
 806.9  Unspecified, open
839 Other, multiple, and ill-defined dislocations
 839.0x  Cervical vertebra, closed
 839.1x  Cervical vertebra, open
 839.2x  Thoracic and lumbar vertebra, closed
 839.3x  Thoracic and lumbar vertebra, open
 839.4x  Other vertebra, closed
 839.5x  Other vertebra, open
905 Late effects of musculoskeletal and connective tissue injuries
 905.1  Late effect of fracture of spine and trunk without mention of spinal cord lesion
 952.9  Unspecified site of spinal cord
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Our analysis incorporated baseline cART, body mass index (BMI), and laboratory values for serum hemoglobin, serum albumin, CD4 cell count, and viral load. We defined cART as any multi-drug antiretroviral therapy administered between 90 days before and 1 year after enrollment into the VACS-VC. For laboratory results we used the value closest to the date of enrollment and collected from 12 months before until 6 months after enrollment. Laboratory and biometric data with non-normal distributions were categorized. Serum hemoglobin was trichotomized as normal (> 12 g/dl), mild anemia (10–12 g/dl), or severe anemia (< 10 g/dl). Serum albumin was dichotomized into normal (≥ 3.5 g/dl) or hypoalbuminemia (< 3.5 g/dl). CD4 cell count was stratified into five levels: ≥ 500, 350 – 499, 200 – 349, 50 – 199, and < 50 cells/mm3. Viral load was categorized as undetectable (<500 copies/ml) or detectable (≥ 500 copies/ml). We used the closest BMI to the date of enrollment obtained within 12 months of enrollment. BMI was categorized as underweight (< 18.5 kg/m2), normal (18.5 – 24.9 kg/m2), overweight (25 – 29.9 kg/m2) and obese (≥ 30 kg/m2). The most recent BMI and preoperative laboratory values within 1 year of surgery and cART status at the time of surgery were also tabulated for all surgical patients. Excluding cases with missing values may bias results,11 thus missing values for laboratory data and BMI were imputed using multiple imputation by chained equations implemented by the Stata v12.0 (Stata Corporation, College Station, Texas) ice command.12–14 The imputation model included the outcome and all covariates, undertook 10 switching procedures, and generated five datasets. Imputed dataset results were combined using Rubin’s rules.15 No patient had more than five missing data values requiring imputation. Results, tables, and figures include imputed data.

Baseline demographics, comorbidities, cART, BMI, and laboratory values were tabulated and compared using the Wilcoxon sign-rank test for continuous variables and Chi squared or Fischer’s exact test for categorical variables. A similar comparison on the subset of patients who underwent surgery for degenerative spine disease also incorporated surgical procedure and location, and spine diagnoses.

Simple and multivariate Poisson regressions were used to compare rates of surgery per 1,000 person-years of follow-up for HIV infected and uninfected patients. Poisson regression provides incidence rate ratios (IRR) showing the ratio of event rates (i.e., spine surgery) between different levels of a variable (e.g., HIV status). Patients were considered “at risk” for surgery from enrollment for care in the VA healthcare system (and thus enrollment into the VACS-VC) until death or the last known date of treatment within the VA through September 30, 2008. When patients had multiple dates of surgery for degenerative spine disease, only the first procedure was used in the analysis. Rates of surgery stratified by HIV status were calculated using simple Poisson regression. Kaplan-Meier plots and the log rank test were used to examine rates of surgery stratified by HIV status. Multivariate Poisson regression was used to examine overall rates of surgery for HIV infected versus uninfected patients after adjusting for demographics, year of enrollment, co-morbid conditions, BMI, and serum hemoglobin and albumin values. A second multivariate Poisson model analyzing rates of surgery among HIV infected patients used a simple comorbidity score in lieu of individual comorbid disease variables because of power limitations, and also incorporated cART, CD4 cell count, and viral load. Simple Poisson regressions were used to identify individual comorbidities that were associated with surgery with a P value <0.200 (i.e., alcohol abuse, cancer, COPD, diabetes, drug abuse, hypertension, major depression, osteoarthritis, PTSD), and the number of these conditions was tabulated for each patient to generate the comorbidity score. The data met the assumptions of a Poisson model (goodness of fit Chi square = 9,489; P=1.000). Analyses were performed using Stata version 12, StataCorp, College Station, Texas.

Results

Study Population

After excluding 2,705 patients lacking follow up data, there were 119,077 eligible VACS-VC study patients eligible for analysis: 40,038 HIV infected, and 79,039 uninfected. The exclusions produced asymmetry in 2,679 matched patient triads, leading to slight differences in baseline demographics across the HIV infected and uninfected groups (Table 1). Among all 1,012 patients (0.85%) undergoing surgery for degenerative spine disease, there were no significant baseline differences between HIV infected and uninfected surgical patients in age, gender, race, or in the prevalence of most comorbid conditions (Table 2).

Table 1.

HIV Infected and Uninfected Study Patients at Baseline

HIV Infected (n=40,038) Uninfected (n=79,039) P value
Age (years) Mean (SD) 46.3 (10.2) 46.6(10.3) <0.001
Gender Male 39,102 (98%) 77,185 (98%) 0.951
Race White 15,019 (38%) 30,927 (39%) <0.001
African American 19,340 (48%) 36,978 (47%)
Hispanic 2,985 (7.5%) 6,019 (7.6%)
Other 2,694 (6.7%) 5,115 (6.5%)
Comorbidities Alcohol abuse 6,456 (16%) 11,496 (15%) <0.001
Atrial fibrillation 308 (0.8%) 793 (1.0%) <0.001
CAD 1,422 (3.6%) 4,861 (6.2%) <0.001
Cancer 2,035 (5.1%) 2,554 (3.2%) <0.001
CHF 647 (1.6%) 1,299 (1.6%) 0.735
Cirrhosis 418 (1.0%) 474 (0.6%) <0.001
COPD 1,733 (4.3%) 3,129 (4.0%) 0.003
Depression, major 2,651 (6.6%) 4,625 (5.9%) <0.001
Diabetes 2,926 (7.3%) 9,640 (12%) <0.001
Drug abuse 7,484 (19%) 9,827 (12%) <0.001
Hepatitis B, chronic 1,191 (3.0%) 302 (0.4%) <0.001
Hepatitis C 3,716 (9.3%) 2,354 (3.0%) <0.001
Hypertension 7,020 (18%) 21,039 (27%) <0.001
Hyperlipidemia 2,306 (5.8%) 10,666 (13%) <0.001
Osteoarthritis 1,059 (2.6%) 5,380 (6.8%) <0.001
PTSD 1,896 (4.7%) 6,120 (7.7%) <0.001
PVD 412 (1.0%) 1,050 (1.3%) <0.001
Renal insufficiency 1,621 (4.1%) 1,325 (1.7%) <0.001
Schizophrenia 1,367 (3.4%) 4,880 (6.2%) <0.001
Stroke 628 (1.6%) 1,349 (1.7%) 0.080
TIA 75 (0.2%) 181 (0.2%) 0.146
cART 20,997 (52%) n/a n/a
BMI, kg/m2 <18.5 2,464 (5.0%) 1,052 (1.1%) <0.001
18.5–24.9 19,834(48%) 20,324 (22%)
25–29.9 12,590 (33%) 29,850 (37%)
≥30 5,150 (14%) 27,813 (40%)
Hemoglobin, g/dl >12 30,658 (77%) 72,920 (92%) <0.001
10–12 6,393 (16%) 4,660 (5.9%)
<10 2,987 (7.5%) 1,458 (1.9%)
Albumin, g/dl ≥3.5 27,393 (68%) 69,499 (88%) <0.001
<3.5 12,645 (32%) 9,540 (12%)
CD4 cell count, cells/mm3 ≥ 500 9,748 (24%) n/a n/a
350 – 499 7,303 (18%) n/a
200 – 349 8,640 (22%) n/a
50 – 199 8,807 (22%) n/a
<50 5,540 (14%) n/a
Viral load, copies/ml <500 11,154 (28%) n/a n/a
≥ 500 28,884 (72%) n/a
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SD = Standard deviation; CAD = Coronary artery disease; CHF = Congestive heart failure; COPD = chronic obstructive pulmonary disease; PTSD = post-traumatic stress disorder; PVD = peripheral vascular disease; TIA = Transient ischemic attack

cART = Combination anti-retroviral therapy

BMI = Body mass index

Table 2.

Surgical and Non-Surgical Patients at Baseline

Patients Undergoing Degenerative Spine Surgery (n=1,102) Non-Surgery Patients (n=118,065)
HIV Infected (n=228) Uninfected (n=784) P value HIV Infected (n=39,810) Uninfected (n=78,255) P value
Age (years) Mean (SD) 45.3 (8.4) 45.4 (8.2) 0.694 46.3 (10.2) 46.6 (10.3) <0.001
Gender Male 222 (97%) 767 (98%) 0.621 38,880 (98%) 76,418 (98%) 0.919
Race White 104 (46%) 370 (47%) 0.823 14,915 (37%) 30,57 (39%) <0.001
African American 110 (48%) 357 (46%) 19,230 (48%) 36,621 (47%)
Hispanic 12 (5.3%) 44 (5.6%) 2,973 (7.5%) 5,975 (7.6%)
Other 2 (0.9%) 13 (1.7%) 2,692 (6.8%) 5,102 (6.5%)
Comorbidities Alcohol abuse 48 (21%) 130 (17%) 0.138 6,408 (16%) 11,366 (15%) <0.001
Atrial fibrillation 1 (0.4%) 5 (0.6%) 1.000 307 (0.8%) 788 (1.0%) <0.001
CAD 6 (2.6%) 55 (7.0%) 0.011 1,416 (3.6%) 4,806 (6.1%) <0.001
Cancer 12 (5.3%) 17 (2.2%) 0.022 2,023 (5.1%) 2,537 (3.2%) <0.001
CHF 0 (0%) 7 (0.9%) 0.360 647 (1.6%) 1,292 (1.7%) 0.753
Cirrhosis 0 (0%) 2 (0.3%) 1.000 418 (1.1%) 472 (0.6%) <0.001
COPD 11 (4.8%) 33 (4.2%) 0.712 1,722 (4.3%) 3,096 (4.0%) 0.003
Depression, major 28 (12%) 85 (11%) 0.551 2,623 (6.6%) 4,540 (5.8%) <0.001
Diabetes 21 (9.2%) 85 (11%) 0.540 2,905 (7.3%) 9,555 (12%) <0.001
Drug abuse 53 (23%) 114 (15%) 0.003 7,431 (19%) 9,713 (12%) <0.001
Hepatitis B, chronic 6(2.6%) 4 (0.5%) 0.011 1,185 (3.0%) 298 (0.4%) <0.001
Hepatitis C 14 (6.1%) 24 (3.1%) 0.045 3,702 (9.3%) 2,330 (3.0%) <0.001
Hypertension 37 (16%)) 209 (27%) 0.001 6,983 (18%) 20,830 (27%) <0.001
Hyperlipidemia 8 (3.5%) 85 (11%) <0.001 2,298 (5.8%) 10,581 (14%) <0.001
Osteoarthritis 15 (6.6%) 109 (14%) 0.003 1,044 (2.6%) 5,271 (6.7%) <0.001
PTSD 16 (7.0%) 96 (12%) 0.030 1,880 (4.7%) 6,024 (7.7%) <0.001
PVD 2 (0.9%) 9 (1.2%) 1.000 410 (10%) 1,041 (1.3%) <0.001
Renal insufficiency 5 (2.2%) 4 (0.5%) 0.032 1,616 (4.1%) 1,321 (1.7%) <0.001
Schizophrenia 6 (2.6%) 26 (3.3%) 0.830 1,361 (3.4%) 4,854 (6.2%) <0.001
Stroke 2 (0.9%) 18 (2.3%) 0.277 626 (1.6%) 1,331 (1.7%) 0.106
TIA 0 (0%) 8 (1.0%) 0.210 75 (0.2%) 173 (0.2%) 0.254
cART 113 (50%) n/a n/a 20,884 (52%) n/a n/a
BMI, kg/m2 <18.5 14 (6.1%) 10 (1.3%) <0.001 2,450 (6.2%) 1,042 (1.3%) <0.001
18.5 – 24.9 122 (54%) 244 (31%) 19,712 (50%) 20,080 (26%)
25 – 29.9 62 (27%) 302 (38%) 12,528 (31%) 29,548 (38%)
>30 29 (13%) 228 (29%) 5,120 (13%) 27,585 (35%)
Hemoglobin, g/dl >12 183 (80%) 720 (92%) <0.001 30,475 (77%) 72,200 (92%) <0.001
10 – 12 33 (15%) 44 (5.7%) 6,359 (16%) 4,616 (6.0%)
<10 12 (5.1%) 20 (2.5%) 2,975 (7.5%) 1,439 (1.8%)
Albumin, g/dl ≥3.5 154 (668%) 663 (85%) <0.001 27,239 (68%) 68,835 (88%) <0.001
<3.5 74 (32%) 121 (15%) 12,571 (32%) 9,420 (12%)
CD4 cell count, cells/mm3 ≥ 500 74 (32%) n/a n/a 9,675 (24%) n/a n/a
350 – 499 47 (21%) n/a 7,256 (18%) n/a
200 – 349 50 (22%) n/a 8,591 (22%) n/a
50 – 199 35 (15%) n/a 8,772 (22%) n/a
<50 23 (10%) n/a 5,517 (14%) n/a
Viral load, copies/ml <500 81 (36%) n/a n/a 11,073 (28%) n/a n/a
≥ 500 147 (64%) n/a 28,737 (72%) n/a
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SD = Standard deviation; CAD = Coronary artery disease; CHF = Congestive heart failure; COPD = chronic obstructive pulmonary disease; PTSD = post-traumatic stress disorder; PVD = peripheral vascular disease; TIA = Transient ischemic attack

cART = Combination anti-retroviral therapy

BMI = Body mass index

The 1,012 surgical procedures for degenerative spine disease occurred during 700,731 person-years of follow-up, the equivalent of 1.44 procedures per 1,000 person-years. The most common surgical procedures were spinal decompression (50%) and decompression and fusion (33%), the most common surgery locations were the lumbosacral (50%) and cervical (40%) spine, and the most common spine diagnoses were ICD9 722.10 lumbar disc displacement (22%) and ICD9 724.02 lumbar spinal stenosis (17%) (Table 3). At the time of surgery, 68% of HIV positive patients were receiving cART, 25% had a CD4 cell count < 200 cells/mm3, and 47% had a viral load > 500 copies/ml. Simple Poisson regression showed a significant difference in the unadjusted rate of surgery between HIV infected (1.13 per 1,000 person-years) and uninfected patients (1.57 per 1,000 person years; IRR 0.72, 95% CI: 0.62, 0.83, P<0.001) (Figure 1). After adjustment for demographics, year of enrollment, comorbidities, BMI, and serum hemoglobin and albumin, the multivariate Poisson model showed that HIV infected patients had significantly lower rates of surgery for degenerative spine disease (0.86 per 1,000 person years) compared to uninfected patients (1.41 per 1,000 person-years; IRR 0.61, 95% CI: 0.51, 0.74, P<0.001) (Table 4). Restricting the multivariate Poisson model to HIV infected patients, there was a trend towards less frequent surgery in patients with detectable viral load levels (IRR 0.76, 95% CI: 0.55, 1.05, P=0.099) (Table 5). Baseline cART and CD4 cell counts were not independent predictors of altered rates of spine surgery for degenerative disease in HIV infected patients (for all, P≥0.306).

Table 3.

HIV Infected and Uninfected Patients at Surgery

HIV Infected (n=228) Uninfected (n=784) P value
Procedure* Decompression 134 (59%) 377 (48%) 0.060
Fusion 32 (14%) 122 (16%)
Decompression and Fusion 60 (26%) 277 (35%)
Motion preservation 2 (0.88%) 8 (1.0%)
Location* Cervical 87 (38%) 320 (41%) <0.001
Thoracic 3 (1.3%) 7 (0.90%)
Lumbosacral 104 (46%) 404 (52%)
Combined 7 (3.1%) 23 (2.9%)
Unspecified 27 (12%) 30 (3.8%)
Spine Diagnoses** 722.10 Lumbar disc displacement 56 (25%) 169 (23%) 0.366
724.02 Lumbar spinal stenosis 34 (15%) 138 (18%) 0.369
721.1 Cervical spondylosis with myelopathy 29 (13%) 93 (12%) 0.729
722.71 Cervical disc displacement without myelopathy 19 (8.3%) 6 (8.4%) 1.000
722.0 Cervical disc displacement 17 (7.5%) 69 (8.8%) 0.890
723.0 Cervical spinal stenosis 11 (5.3%) 77 (9.8%) 0.016
721.0 Cervical spondylosis 7 (3.1%) 38 (4.8%) 0.360
721.3 Lumbosacral spondylosis 7 (3.1%) 34 (4.3%) 0.451
cART 155 (68%) n/a n/a
BMI, kg/m2 <18.5 7 (3.0%) 14 (1.8%) <0.001
18.5 – 24.9 104 (45%) 200 (26%)
25 – 29.9 85 (37%) 303 (39%)
>30 32 (14%) 267 (34%)
Hemoglobin, g/dl >12 196 (86%) 743 (95%) <0.001
10 – 12 24 (11%) 37 (4.7%)
<10 8 (3.6%) 5 (0.59%)
Albumin, g/dl ≥3.5 178 (78%) 721 (92%) <0.001
<3.5 50 (22%) 63 (8.1%)
CD4 cell count, cells/mm3 ≥ 500 86 (38%) n/a n/a
350 – 499 47 (21%) n/a
200 – 349 39 (17%) n/a
50 – 199 28 (12%) n/a
<50 29 (13%) n/a
Viral load, copies/ml <500 120 (53%) n/a n/a
≥ 500 108 (47%) n/a
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*

Based on ICD9 procedure and diagnosis codes from surgical admission

**

ICD9 diagnosis codes from surgical admission

cART = Combination anti-retroviral therapy

BMI = Body mass index

Figure 1.

Figure 1

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Kaplan-Meier plot of surgery for degenerative spine disease in HIV-infected and uninfected patients. HIV-infected patients have significantly lower rates of surgery (P < 0.001).

Table 4.

Multivariate Poisson Regression Model of 1,012 Spine Surgeries in 111,047 HIV Infected and Uninfected Patients

Variable IRR 95% CI P value
HIV infected 0.61 0.51, 0.74 <0.001
Age
< 40 1.00 n/a n/a
40 – 49 1.25 1.06, 1.47 0.007
50 – 59 1.06 0.89, 1.29 0.567
60 – 69 0.69 0.49, 0.97 0.034
≥ 70 0.15 0.06, 0.42 <0.001
Race
White 1.00 n/a n/a
Black 0.74 0.64, 0.85 <0.001
Hispanic 0.56 0.42, 0.73 <0.001
Other 0.31 0.19, 0.53 <0.001
Selected Comorbidities Alcohol abuse 1.00 0.81, 1.24 0.998
CHF 0.54 0.25, 1.18 0.121
Diabetes 1.17 0.93, 1.46 0.176
Drug abuse 1.03 0.83, 1.28 0.795
Hepatitis C 0.94 0.63, 1.33 0.716
Hypertension 1.25 1.06, 1.48 0.009
Osteoarthritis 2.28 1.96, 2.90 <0.001
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Note: Regression also adjusted for gender, year, additional baseline comorbidities (atrial fibrillation, cancer, chronic obstructive pulmonary disease, cirrhosis, coronary artery disease, hepatitis B, hyperlipidemia, major depression, peripheral vascular disease, post-traumatic stress disorder, renal insufficiency, schizophrenia, stroke, transient ischemic attack), baseline BMI, and baseline serum albumin and serum hemoglobin.

IRR = Incidence rate ratio

CI = Confidence interval

CHF = Congestive heart failure

Table 5.

Multivariate Poisson Regression Model of 228 Spine Surgeries in 40,038 HIV Infected Patients

Variable IRR 95% CI P value
Age
< 40 1.00 n/a n/a
40 – 49 1.16 0.82, 1.61 0.394
50 – 59 1.13 0.76, 1.68 0.540
60 – 69 0.74 0.37, 1.48 0.395
≥ 70 0.42 0.10, 1.74 0.231
Race
White 1.00 n/a n/a
Black 0.72 0.54, 0.96 0.025
Hispanic 0.53 0.29, 0.97 0.041
Other 0.16 0.04, 0.67 0.012
Comorbidity Score 1.27 1.14, 1.41 <0.001
cART 0.90 0.68, 1.20 0.488
CD4 cell count ≥ 200 cells/mm3 1.26 0.80, 1.98 0.306
Viral load ≥ 500 copies/ml 0.76 0.55, 1.05 0.099
Open in a new tab
*

Regression also adjusted for gender, year, baseline BMI, and baseline serum albumin and serum hemoglobin.

IRR = incidence rate ratio

CI = Confidence interval

cART = Combination anti-retroviral therapy

Discussion

We studied rates of spine surgery for degenerative spine disease in patients selected from a cohort of all United States military Veterans with HIV infection under care from 1996 – 2008 (n=40,038) and matched uninfected controls (n=79,039). Our study focused on major procedures for degenerative spine disease intended to decompress neural structures (e.g., lumbar laminectomy) or stabilize spinal segments (e.g., cervical fusion), and we excluded minor procedures (e.g., injections), diagnostic procedures, procedures that did not address degenerative spine disease such as injections, percutaneous procedures, or surgeries performed for trauma, infection, tumors, and congenital defects. One thousand and twelve patients underwent spine surgery for degenerative spine disease, and after adjusting for demographics, an array of comorbidities spanning major organ systems and disease types, BMI, and laboratory values, HIV infected patients had a 39% lower rate of spine surgery for degenerative disease compared to uninfected patients.

In this study, we quantitate the end result of a process starting with degenerative spine symptoms and culminating in surgical intervention. Progression from symptoms to surgery is a multi-step process involving interactions between and decisions by patients, referring health care providers, and surgeons. Our data does not readily permit us to determine which of these steps is responsible for the disparity in rates of spine surgery for degenerative spine disease experienced by HIV positive patients. Perhaps our HIV infected population was less prone to develop symptomatic degenerative spine disease. The development of degenerative spine disease has been linked to increasing age,16;17 male gender,17 BMI,17;18 physical stress,19;20 height,21 weight,18;21 cigarette smoking,22;23 inflammatory factors,23;24 and genetics.25;26 We adjusted for age, gender, and BMI in our analysis, but the remaining factors were unmeasured and may play some role in our findings. Our study cohort was selected from patients seeking care from the VA healthcare system, and the iatrotrophic stimulus likely differed by HIV status. Some HIV infected patients were initiating care for HIV-related symptoms, and a thus smaller proportion may have had degenerative spine disease symptoms at enrollment.

Symptoms related to degenerative spine disease may be obscured by the array of symptoms associated with HIV infection. In a 20-item HIV symptom index developed by Justice et al. based on symptom frequency, bother, and expert opinion, common manifestations of degenerative spine disease such as low back pain, neck pain, sciatica, or radiculopathy did not merit inclusion.27 HIV infected patients and providers may be focusing on non-spine symptoms, with a corresponding reduction in attention to symptoms from spine disease. Specialty providers caring for HIV infected patients may be less effective at managing spine symptoms and less likely to refer patients for surgery. Many HIV infected patients are cared for in infectious disease clinics, and infectious disease specialists or physicians working in infectious disease clinics caring for HIV infected patients are not as comfortable as physicians in general medical clinics at treating common medical conditions like hypertension, diabetes, and hyperlipidemia.28 A lack of physician comfort may lead to less effective or efficient management, and this phenomenon may extend to the management of spine diagnoses and symptoms.

The disparity in rates of surgery for degenerative spine disease may be grounded in the perception that HIV infection adversely affects the outcomes of spine surgery. The decreased rate of surgery among HIV positive patients may reflect an “appropriate” weighing of HIV infection in the surgical decision making process. Before the development of cART, reports on surgical procedures on HIV infected patients described increased complication rates and higher mortality, and worse outcomes were associated with factors such as active opportunistic infection, low serum albumin, concurrent organ failure, CD4 cell count, and viral load.29–35 Since the adoption of cART in the developed world, declining rates of surgical complications and deaths in HIV infected patients may rival those experienced by uninfected individuals.36–40 In the largest surgical series published to date, Horber and colleagues found only small differences in complications and outcomes when comparing 322 HIV infected patients to contemporaneous matched uninfected controls undergoing the same surgical procedures.41 (None of the patients in the Horberg et al. report underwent spine surgery.) Indeed, despite the challenges of managing organ rejection in immunocompromised patients, successful solid organ transplants into HIV infected individuals are increasingly common.42–44 The development and dissemination of cART has improved survival and doubtless contributed to improved modern surgical outcomes for HIV infected patients.40 Referring providers and surgeons may also be selecting HIV infected patients for surgery that are likely to have better outcomes, accounting both for improved modern surgical outcomes and the disparity in rates of spine surgery seen in our study population.

The paucity of publications reporting on outcomes of surgery on HIV infected patients and their small sample sizes suggest that surgery on HIV infected individuals is still a relatively uncommon or unstudied event. Published reports of spine surgery on HIV infected patients are quite limited, and most do not deal with degenerative spine disease. 45–60 Only limited data are available on outcomes on HIV infected patients following spine surgery for degenerative spine disease. Eyenga and coworkers reported no complications after lumbar discectomy in nine HIV positive patients, improved sciatica symptoms in eight patients (89%) at three months follow-up, and no differences in outcomes when compared to a contemporaneous group of 68 uninfected patients undergoing the same procedure.6 Young et al. described improvement in five patients after surgery for degenerative spine disease with two minor complications (superficial infection, spontaneously resolving postoperative fever).5 Larger studies are required to accurately establish the outcomes of elective spine surgery for degenerative spine disease in HIV infected patients.

Patient preferences may be contributing to disparities in rates of spine surgery by HIV infection. In 2003 the Agency for Healthcare Research and Quality first issued a report documenting disparities in health outcomes and access to care across race, ethnicity, and socioeconomic status.61 Differences in the rates of some procedures and treatments associated with race such as total knee replacement,62;63 surgery for early stage lung cancer,64;65 tooth extraction versus root canal therapy,66 and end of life care,67;68 can be explained in part by patient preferences. Our dataset does not contain data on patient preferences for spine surgery; however, it is possible that patient preferences may be contributing to reduced rates of spine surgery among HIV infected patients.

Concerns about personal safety may be influencing surgeons’ decisions to offer surgery to HIV positive patients. The discussions that were prevalent early in the AIDS epidemic about the ethical responsibilities of caring for HIV infected patients in the face of personal risk of disease transmission have faded.69;70 Subsequent epidemiologic studies showed extremely low rates of occupational HIV transmission to healthcare providers,71 and there have been no documented occupation HIV infections in surgeons.72 Additional evidence of occupational safety is provided by serosurveys showing very low rates of HIV seroconversion in the absence of non-occupational risk factors in orthopedic (0/3,267 = 0%) and general surgeons (1/740 = 0.14%).73;74 Major medical organizations, including the American Medical Association75 and the American College of Surgeons,76 have released statements affirming the ethical obligations of physicians to treat patients with HIV infection.

Notwithstanding organized medicine’s consensus about the ethical obligations of healthcare providers to care for HIV infected patients and the minimal personal risk involved, some physicians and dentists are reluctant to care for patients with HIV. The U.S. Department of Health and Human Services Office for Civil Rights reported a settlement in 2009 with a Texas orthopedic surgeon who declined to perform reconstructive knee surgery on an HIV infected Medicare beneficiary because blood spattering might expose them to the HIV virus, and referred the patient to another orthopedic surgeon 200 miles away.77 Recent surveys of HIV infected patients have reported discrimination by dentists78;79 and general practitioners.79 A 2008 anonymous international web-based survey of refractive ophthalmological surgeons found that 33% of respondents considered HIV infected status without definite AIDS to be a relative contraindication to refractive surgery, and 16% considered HIV infection an absolute contraindication.80 Follow-up surveys of respondents who declined to operate on HIV infected patients revealed that 51% were concerned with viral transmission to the surgeon or operating room staff. The data suggest that some Western healthcare providers limit care to HIV infected patients out of concern for personal safety. We do not know if these data generalize to spine surgeons and spine surgery in HIV infected patients.

Limitations

The selection, organization, and granularity of data within administrative and clinical databases are seldom designed to answer specific research questions and can limit analyses and conclusions; however, large databases provide significant advantages. VACS-VC uses multiple nationwide VA administrative and clinical databases, validated data extraction and cleaning algorithms, and a matched control population to assemble a rich database allowing for the investigation of complex research questions in the largest HIV infected cohort under treatment in the world. Non-VA surgical treatment options for degenerative spine disease are available, and some patients may have undergone surgery outside of the VA healthcare system, resulting in an underestimation of the rates of spine surgery. We have no a priori reason to suspect that HIV infected and uninfected patients would obtain surgery outside of the VA healthcare system at different rates, therefore the ratio of disparity in surgery rates between HIV infected and uninfected patients should be unaffected. We used baseline covariates in our multivariate regression models, and some of these values may have changed over time, affecting adjusted rates of surgery. There is conflicting evidence on the benefits of surgery for degenerative spine disease, and interpretation of our disparity findings is further complicated by the extensive regional and physician variation in rates of spine surgery. 81–84 It is impossible to say if either of the rates of surgery experienced by HIV infected or uninfected patients were appropriate.

Conclusion

HIV infected veterans experience significantly reduced rates of spine surgery for degenerative spine disease. Our data are insufficient to determine which step or steps in the progression from symptoms to surgery account for the disparity in surgical rates, and we can only speculate which patient, referring provider, surgeon, or system factors are contributing to the observed disparity. The incidence of spine disease, spine symptoms, referral patterns, the relationship between HIV infection and surgical outcomes, patient preferences, and surgeon bias may all play a role. There are no large studies on the impact of HIV infection on spine surgery outcomes. In the absence of reliable outcomes data and clear standards for undertaking spine surgery, we do not know whether the disparities in rates of spine surgery are affecting health outcomes in patients with HIV infection.

Acknowledgments

Funding/Support: National Institutes of Health: NIAAA (U10-AA13566), NIA (R01-AG029154), NHLBI (R01-HL095136; R01-HL090342; RCI-HL100347), NIAID (U01-A1069918), NIMH (P30-MH062294), and the Veterans Health Administration Office of Research and Development (VA REA 08-266) and Office of Academic Affiliations (Medical Informatics Fellowship).

Footnotes

IRB: This study was approved by the IRB of Yale University, and by the Human Subjects Subcommittee of the Research and Development Committee (i.e., IRB) of the VA Connecticut Healthcare System.

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