Projections of Single-level and Multilevel Spinal Instrumentation Procedure Volume and Associated Costs for Medicare Patients to 2050

Abstract

Background:

Instrumented spinal fusions can be used in the treatment of vertebral fractures, spinal instability, and scoliosis or kyphosis. Construct-level selection has notable implications on postoperative recovery, alignment, and mobility. This study sought to project future trends in the implementation rates and associated costs of single-level versus multilevel instrumentation procedures in US Medicare patients aged older than 65 years in the United States.

Methods:

Data were acquired from the Centers for Medicare & Medicaid Services from January 1, 2000, to December 31, 2019. Procedure costs and counts were abstracted using Current Procedural Terminology codes to identify spinal level involvement. The Prophet machine learning algorithm was used, using a Bayesian Inference framework, to generate point forecasts for 2020 to 2050 and 95% forecast intervals (FIs). Sensitivity analyses were done by comparing projections from linear, log-linear, Poisson and negative-binomial, and autoregressive integrated moving average models. Costs were adjusted for inflation using the 2019 US Bureau of Labor Statistics' Consumer Price Index.

Results:

Between 2000 and 2019, the annual spinal instrumentation volume increased by 776% (from 7,342 to 64,350 cases) for single level, by 329% (from 20,319 to 87,253 cases) for two-four levels, by 1049% (from 1,218 to 14,000 cases) for five-seven levels, and by 739% (from 193 to 1,620 cases) for eight-twelve levels (P < 0.0001). The inflation-adjusted reimbursement for single-level instrumentation procedures decreased 45.6% from $1,148.15 to $788.62 between 2000 and 2019, which is markedly lower than for other prevalent orthopaedic procedures: total shoulder arthroplasty (−23.1%), total hip arthroplasty (−39.2%), and total knee arthroplasty (−42.4%). By 2050, the number of single-level spinal instrumentation procedures performed yearly is projected to be 124,061 (95% FI, 87,027 to 142,907), with associated costs of $93,900,672 (95% FI, $80,281,788 to $108,220,932).

Conclusions:

The number of single-level instrumentation procedures is projected to double by 2050, while the number of two-four level procedures will double by 2040. These projections offer a measurable basis for resource allocation and procedural distribution.

The number of individuals aged 65 years and older in the United States is projected to increase from 54 million in 2014 to 80 million by 2050.¹ With this increase, there has been a corresponding rise in the prevalence of degenerative spinal disorders.² This is expected to lead to increased demand for spine surgery in the coming years.² Posterior instrumentation is used in the management of a variety of spinal disorders, including degenerative disk disease, spondylolisthesis, deformity, and spinal trauma.³ Advanced spinal fusion techniques, such as pedicle screw fixation and interbody fusions, have further contributed to the rising rates of posterior instrumented procedures.^3-5 In a report published in 2021, spinal fusion accounted for the highest aggregate hospital costs ($14.1 billion across 455,500 procedures in 2018) of any surgical procedure performed in US hospitals.⁶ The increased utilization of lumbar spinal fusion procedure in the United States is drawing interest from a variety of stakeholders, including patients, physicians, payers, and policymakers.

Several studies have attempted to measure past trends in the utilization and cost of spinal procedures.^7-10 Rajaee et al.⁷ reported that the annual number of spinal fusion discharges increased 137% between 1998 and 2008 in the United States. By contrast, during the same period, laminectomy, hip replacement, and knee arthroplasty yielded smaller increases of 11.3%, 49.1%, and 126.8%, respectively.⁷ In another study based on the National Inpatient Sample, Sheikh et al.¹¹ reported an 88% increase in spinal fusion procedures from 1998 to 2014. Despite recent works that sought to characterize past trends in orthopaedic spinal procedures, there is a paucity of research that projects future volume and associated costs. There are only two studies that have projected utilization of spinal fusions, which stands in stark contrast to the large bodies of work that project utilization of other orthopaedic procedures, such as total joint arthroplasty.^12,13 Heck et al.⁹ reported that the utilization of posterior spinal fusions is projected to increase between 82% and 102% in 2060, with women and patients aged older than 75 years most likely to see increases in rate of fusion. Neifert et al.⁸ further projected increases to 2040 in anterior and posterior cervical decompression and fusion of 13.3% and 19.3%, respectively.

Despite the frequent citation of past trends in healthcare policy formulation,¹² there is no available literature on future spinal instrumentation volume and associated costs,¹¹ which necessitates the development of projections based on national data. This study aimed to project single-level and multilevel spinal instrumentation procedure volume and associated costs until 2050. We used an alternative model based on past utilization data from the Centers for Medicare & Medicaid Services (CMS) Medicare/Medicaid Part B National Summary¹² and a novel time-series forecasting methodology, Prophet.¹⁴ We hypothesized that the demand for both single-level and multilevel spinal instrumentation in the United States will increase substantially over the next three decades.

Methods

CMS Medicare/Medicaid Data and CPT Codes

This study used data acquired from the CMS Medicare/Medicaid Part B National Summary in patients aged 65 years or older.¹² Data included annual procedure counts from 2000 to 2019 and the combined procedural terminology (CPT) codes that were used to identify whether the procedure used spinal instrumentation.¹² CPT codes were divided into four categories: single-level, two-four–level, five-seven–level, and eight-twelve–level. CPT codes were also identified for total shoulder arthroplasty, total hip arthroplasty, and total knee arthroplasty to establish a baseline for comparing trends in mean inflation-adjusted reimbursement for spinal instrumentation procedures. The regressions were formed using annual data from the CMS and included data on Medicare Fee-for-Service (FFS) beneficiaries. As each instrumentation category was likely to exhibit a unique trend over time, this study modeled them separately. Data from 2020 were excluded because of COVID-19–related confounding.

Volume and Cost Adjustments

Procedure counts only included FFS patients. To account for this, we normalized the procedure counts using a ratio of FFS to Medicare Advantage patients provided by the Kaiser Family Foundation, as previously reported in the literature.¹² We adjusted the total procedure counts for each CPT code using the proportions reported in Table 1. In addition to the primary analysis, we adjusted the volume counts by CMS population data on Medicare beneficiaries. This allowed us to consider potential confounding factors such as increased spinal trends that may have been influenced by changes in Medicare beneficiaries over time. To compare costs across different time periods, we adjusted the costs for inflation using the US Bureau of Labor Statistics' 2019 Consumer Price Index as a reference.¹⁵ Finally, we used annual primary total procedure counts for spinal instrumentation volume to generate Prophet time series forecasts between 2020 and 2050.¹⁴

Table 1.

Spinal Instrumentation Volume Between 2000 and 2019, Adjusted to Include Medicare Advantage Patients

Year	Proportion of Medicare Advantage Patients $\left(r\right)$	Adjusted Volume and Level $\frac{\left(Volume\right)}{\left[1–r\right]}$
		Single	APC	Two-Four	APC	Five-Seven	APC	Eight-Twelve	APC
2000	17%	7,342	—	20,319	—	1,218	—	193	—
2001	15%	10,431	42.07%	22,864	12.53%	1,559	28.00%	195	0.01%
2002	14%	12,907	23.74%	26,163	14.43%	1,558	−0.04%	223	14.32%
2003	13%	15,441	19.64%	29,633	13.26%	1,970	26.44%	217	−2.69%
2004	13%	18,493	19.76%	32,855	10.87%	2,224	12.89%	224	12.17%
2005	13%	21,215	14.72%	36,113	9.91%	2,662	19.69%	330	35.38%
2006	16%	23,925	12.77%	38,360	6.22%	3,168	19.00%	430	30.28%
2007	19%	26,133	9.23%	40,993	6.86%	3,793	19.72%	431	0.26%
2008	22%	31,251	19.58%	45,737	11.57%	4,269	12.57%	483	12.18%
2009	23%	36,238	15.96%	51,025	11.56%	4,904	14.87%	579	19.84%
2010	24%	40,303	11.22%	53,992	5.68%	5,541	13.00%	692	19.49%
2011	25%	42,763	6.10%	56,231	4.28%	6,089	9.90%	701	1.33%
2012	26%	45,631	6.71%	59,504	5.82%	7,043	15.67%	869	23.90%
2013	28%	49,371	8.20%	62,742	5.44%	7,962	13.05%	1,085	24.84%
2014	30%	54,670	10.73%	67,110	6.96%	9,113	14.45%	1,289	18.80%
2015	31%	57,172	4.58%	70,936	5.70%	9,819	7.75%	1,255	−2.60%
2016	31%	59,972	4.90%	75,946	7.06%	10,672	8.69%	1,378	9.82%
2017	33%	59,469	−0.84%	79,190	4.27%	11,685	9.49%	1,469	6.56%
2018	35%	62,608	5.28%	83,832	5.86%	13,380	14.51%	1,492	1.61%
2019	36%	64,350	2.78%	87,253	4.08%	14,000	4.63%	1,620	8.58%

APC = annual percentage change

Prophet Time-series Modeling

We used the time-series analysis method, Prophet, developed by Taylor et al.,¹⁴ to predict the procedural counts and costs of single-level versus multilevel spinal instrumentation until the year 2050. For a detailed mathematical description, refer to the original paper.¹⁴ The Prophet model is a state-of-the-art time-series algorithm created by Facebook that has been shown to generate reliable and high-quality forecasts in a variety of healthcare settings.^16,17 To ensure an appropriate modeling approach, we applied the default setting for the number of change point parameters in the Prophet model. This involves Prophet identifying 25 potential change points, which were uniformly distributed within the first 80% of the accessible data.¹⁴ In cases where the data set is relatively small, Prophet automatically adjusts the number of change points to effectively capture notable changes in the time-series trend.

Each Prophet model used a Bayesian framework that relied on past distributions of the parameters for posterior inference to address the uncertainties associated with the projections.¹⁴ The Prophet model substitutes τ with a variance inferred from the data, and the model simulates future rate adjustments that mirror those observed in the past. The parameter τ directly influences the model's flexibility in modifying its rate. As τ increases, the model becomes more flexible in fitting the historical data, resulting in a reduction in training error.¹⁴ Point forecasts were generated, and the width of the forecast intervals (FIs) for all models was set to 95% to account for the uncertainties in the projections. To mitigate the potential effect of higher variance associated with smaller sample sizes, we used bootstrapping by maintaining 1,000 uncertainty samples.¹⁴ This resampling technique allowed us to simulate a larger number of samples from the available data, thereby facilitating more robust estimates of uncertainty in the FIs.

Model Performance, Sensitivity Analyses, and Statistical Methods

To assess the overall goodness of fit of the Prophet time-series models, the period was partitioned into training (first 15 years) and validation data sets (last 5 years), and the value of the normalized root mean square error (NRMSE) was calculated. NRMSE is a widely used measure of the lack of fit between model and data.^18-21 The Prophet model projections were compared with alternative model specifications: generalized linear model methods in the form of Poisson and negative binomial regressions, ordinary least squares linear and log-linear regressions, and autoregressive integrated moving average, all of which have been used extensively in the literature to project Orthopaedic procedure volume (Supplemental Table 1, http://links.lww.com/JG9/A337).^12,13,21-23 Sensitivity analyses were conducted, and past and future trends were characterized through compound annual growth rates (CAGRs) for both the Prophet and alternative models (Supplemental Tables 2, http://links.lww.com/JG9/A338 and 3, http://links.lww.com/JG9/A339).^12,13,21-23 Analysis of variance (ANOVA) tests were conducted to compare the trend components among the four Prophet models (single-level, two-four–level, five-seven–level, and eight-twelve–level) for volume and cost, respectively, and to characterize past (2000 to 2019) and future (2020 to 2050) trends. Statistical analysis was done with the use of the R programming environment (version 4.6.5; R Core Team 2023).

Results

In 2019, the most recent year for which Medicare Part B procedural data were included, a total of 29,072 spinal instrumentation procedures were done nationally in the United States among Medicare patients aged older than 65 years, with associated costs of $33,976,785. Between 2000 and 2019, the prevalence and cost of single-level and multilevel spinal instrumentation procedures all increased substantially (P < 0.0001). Analysis of variance tests indicated a statistically significant difference in the trend components among the four volume models (F (3, 200) = 104.2, P < 0.0001) and the four cost models (F (3, 200) = 67.46, P < 0.0001).

From 2000 to 2019, the CAGRs for spinal instrumentation volume and cost were 11.61% and 9.31% for single-level, 7.64% and 5.67% for two-four–level, 13.18% and 10.89% for five-seven–level, and 14.83% and 11.14% for eight-twelve–level, respectively. From 2020 to 2050, the CAGRs for spinal instrumentation volume and cost are projected to change as follows: 2.04% and 1.86% for single-level, 2.78% and 2.32% for two-four–level, 3.72% and 3.47% for five-seven–level, and 3.40% and 3.29% for eight-twelve–level, respectively. The projected CAGRs for all of the Prophet models indicated that the growth rate for spinal instrumentation volume is expected to increase more markedly compared with costs. This trend suggests that the demand and utilization of spinal instrumentation are anticipated to rise at a faster pace than the corresponding costs associated with the procedures across all levels, from single-level to eight-twelve–level surgeries.

The overall goodness of fit of the Prophet time-series models on the validation data set was measured by the NRMSE and averaged 0.0856 for spinal instrumentation volume (range, 0.0248 for two-four–level spinal instrumentation to 0.1189 for single-level procedures) and 0.0681 for spinal instrumentation cost (range, 0.0117 for two-four–level spinal instrumentation to 0.1189 for single-level procedures), indicating good-to-excellent quality of fits (Supplemental Table 1, http://links.lww.com/JG9/A337). The Prophet, autoregressive integrated moving average, and ordinary least squares-linear models all achieved lower NRMSE compared with ordinary least squares log-linear, generalized linear model Poisson and negative binomial models, and projected more conservative CAGRs.

Tables 1 and 2 summarize spinal instrumentation volume and costs, respectively, between 2000 and 2019 after adjusting for Medicare advantage patients and inflation. Between 2000 and 2019, the adjusted annual spinal instrumentation volume increased by 776% (from 7,342 to 64,350 cases) for single level, by 329% (from 20,319 to 87,253 cases) for two-four levels, by 1049% (from 1,218 to 14,000 cases) for five-seven levels, and by 739% (from 193 to 1,620 cases) for eight-twelve levels. The adjusted cost of spinal instrumentation procedures increased by 502% (from $8,429,736 to $50,747,629) for single-level, by 206% (from $22,704,431 to $69,404,647) for two-four levels, by 670% (from $1,545,433 to $11,893,724) for five-seven levels, and by 459% (from $297,185 to $1,662,171) for eight-twelve levels.

Table 2.

Spinal Instrumentation Cost Between 2000 and 2019, Adjusted to Include Medicare Advantage Patients and the Cost of Inflation

Year	Proportion of Medicare Advantage Patients $\left(r\right)$	Consumer Price Index $\left(c\right)$	Adjusted Cost and Level $\frac{\left(Cost*[1+C]\right)}{\left[1–r\right]}$
			Single	APC	Two-Four	APC	Five-Seven	APC	Eight-Twelve	APC
2000	17%	+53%	$8,429,736	—	$22,704,431	—	$1,545,433	—	$297,185	—
2001	15%	+47%	$12,550,457	48.89%	$26,650,778	17.38%	$2,056,502	33.07%	$314,528	5.84%
2002	14%	+46%	$13,658,468	8.83%	$28,634,258	7.44%	$1,844,009	10.33%	$325,604	3.52%
2003	13%	+42%	$16,487,373	20.71%	$31,530,017	10.11%	$2,240,882	21.52%	$314,471	−3.42%
2004	13%	+39%	$20,075,344	21.76%	$36,006,166	14.20%	$2,558,450	14.17%	$349,275	11.07%
2005	13%	+35%	$22,974,739	14.44%	$39,334,947	9.25%	$3,067,441	19.89%	$479,887	37.40%
2006	16%	+30%	$25,031,776	8.95%	$40,526,977	3.03%	$3,543,012	15.50%	$592,202	23.40%
2007	19%	+27%	$24,642,085	−1.56%	$39,132,449	−3.44%	$3,824,296	7.94%	$524,361	−11.46
2008	22%	+22%	$27,563,001	11.85%	$40,664,869	3.92%	$4,007,477	4.79%	$555,067	5.86%
2009	23%	+22%	$32,406,942	17.57%	$45,996,129	13.11%	$4,674,692	16.65%	$667,899	20.33%
2010	24%	+19%	$35,845,504	10.61%	$48,382,232	5.19%	$5,241,612	12.13%	$771,751	15.55%
2011	25%	+17%	$38,524,605	7.47%	$51,064,083	5.54%	$5,825,555	11.14%	$796,631	3.22%
2012	26%	+14%	$39,447,998	2.40%	$51,776,749	1.40%	$6,462,321	10.93%	$939,380	17.92%
2013	28%	+12%	$41,555,435	5.34%	$53,141,865	2.64%	$7,071,442	9.43%	$1,116,147	18.82%
2014	30%	+10%	$46,458,031	11.80%	$57,290,168	7.81%	$8,206,592	16.05%	$1,361,269	21.96%
2015	31%	+9%	$48,826,975	5.06%	$60,943,729	6.38%	$8,936,888	8.90%	$1,342,583	−1.37%
2016	31%	+6%	$49,453,811	1.28%	$63,161,897	3.64%	$9,447,866	5.72%	$1,462,652	8.94%
2017	33%	+4%	$48,255,815	−2.42%	$64,876,563	2.71%	$10,222,941	8.20%	$1,544,224	5.58%
2018	35%	+2%	$49,940,944	3.49%	$67,455,460	3.98%	$11,486,343	12.36%	$1,550,829	0.43%
2019	36%	—	$50,747,629	1.62%	$69,404,647	2.89%	$11,893,724	3.55%	$1,662,171	7.18%

APC = annual percentage change

Tables 3 and 4 summarize spinal instrumentation volume and cost projections between 2020 and 2050, after adjusting for Medicare advantage patients and inflation. From 2000 to 2019, the mean inflation-adjusted reimbursement for single-level spinal instrumentation procedures decreased 45.6% from $1,148.15 to $788.62. The mean inflation-adjusted reimbursement for other prevalent orthopaedic procedures decreased as follows: total shoulder arthroplasty $1,941.46 to 1,492.19 (−23.1%), total hip arthroplasty $2,312.01 to 1,406.14 (−39.2%), and total knee arthroplasty $2,439.81 to 1,406.20 (−42.4%). The mean inflation-adjusted reimbursement for single-level spinal instrumentation procedures is projected to decrease an additional 4.2% by 2050, to $756.89. By 2050, the number of single-level spinal instrumentation procedures performed yearly is projected to be 124,061 (95% FI, 87,027 to 142,907, Figure 1), with an associated cost of $93,900,672 (95% FI, $80,281,788 to $108,220,932), and the number of two-four level spinal instrumentation procedures performed yearly is projected to be 214,517 (95% FI, 191,425 to 237,425), with an associated cost of $146,323,437 (95% FI, $135,874,961 to $157,427,669). Figure 2 shows volume trends from 2000 to 2019, after adjusting for the changing Medicare population. Figure 2 is not meant to present the true national volume counts of spinal instrumentation procedures but to more accurately assess trends in utilization after adjusting for Medicare beneficiaries as a potential cofounder. Notably, two-key inflection points can be visualized: a rapid increase in single-level instrumentation beginning in 2008 and a plateau of single-level instrumentation beginning in 2017 (Figure 3).

Table 3.

Prophet, Bayesian Inference, Volume Projections (2020-2050) for Spinal Instrumentation

Year (5-yr Intervals)	Spinal Instrumentation (No. of Procedures)
	Single (95% FI)	Two-Four (95% FI)	Five-Seven (95% FI)	Eight-Twelve (95% FI)
2020	66,408 [56,488-56,702]	91,819 [91,127-92,406]	14,965 [14,817-15,121]	1,747 [1,672-1,814]
2025	76,049 [63,994-68,553]	112,464 [110,657-114,347]	20,257 [19,512-20,976]	2,307 [2,214-2,390]
2030	85,691 [70,303-81,667]	132,558 [128,053-137,384]	25,587 [23,796-27,438]	2,815 [2,668-2,956]
2035	95,267 [75,546-95,561]	152,992 [144,967-161,006]	30,790 [27,622-33,934]	3,330 [3,097-3,572]
2040	104,778 [80,435-110,818]	173,782 [161,636-186,468]	35,867 [31,314-40,975]	3,852 [3,508-4,197]
2045	114,419 [83,913-126,754]	194,427 [177,376-212,372]	41,159 [34,621-48,120]	4,412 [3,954-4,881]
2050	124,061 [87,027 142,907]	214517 [191,425-237,425]	46,489 [37,771-55,152]	4,920 [4,326-5,528]

FI = forecast interval

Table 4.

Prophet, Bayesian Inference, Cost Projections (2020-2050) for Spinal Instrumentation

Year (5-yr Intervals)	Spinal Instrumentation (No. of Procedures)
	Single (95% FI)	Two-Four (95% FI)	Five-Seven (95% FI)	Eight-Twelve (95% FI)
2020	$53,070,839 [$51,606,906-$54,723,613]	$71,712,721 [$70,254,581-$73,166,687]	$12,610,829 [$12,461,322-$12,767,108]	$1,792,121 [$1,714,303-$1,872,135]
2025	$60,137,759 [$58,202,500-$62,211,625]	$84,835,009 [$83,157,192-$86,512,370]	$16,633,497 [$16,177,164-$17,213,341]	$2,351,571 [$2,264,409-$2,447,348]
2030	$66,922,404 [$63,646,329-$70,157,054]	$97,022,339 [$94,350,320-$99,826,626]	$20,625,135 [$19,403,863-$21,988,590]	$2,843,564 [$2,710,948-$2,982,480]
2035	$73,559,445 [$68,293,773-$78,925,770]	$109,081,793 [$104,679,562-$113,250,796]	$24,499,108 [$22,303,575-$26,806,195]	$3,339,665-[$3,105,871-$3,564,476]
2040	$80,049,108 [$72,240,696-$87,850,414]	$121,013,818 [$114,923,281-$127,164,025]	$28,255,531 [$25,031,366-$31,727,823]	$3,839,901 [$3,494,318-$4,155,291]
2045	$87,116,028 [$76,151,846-$98,271,898]	$134,136,106 [$125,856,737-$142,547,335]	$32,278,198 [$27,821,008-$37,096,086]	$4,399,351 [$3,932,775-$4,839,014]
2050	$93,900,672 [$80,281,788-$108,220,932]	$146,323,437-[$135,874,961-$157,427,669]	$36,269,836 [$30,480,091-$42,644,181]	$4,891,344 [$4,252,894-$5,470,979]

FI = forecast interval

Figure 1.

A, Graph showing that the x-axis represents the year, and the y-axis represents the total projected volume of spinal instrumentation procedures, stratified by the combined procedural terminology code. B, The x-axis represents the year, and the y-axis represents the total projected cost of spinal instrumentation procedures, stratified by the combined procedural terminology code. The colors and codes reflect the following: red/22,840 is single level, blue/22,842 is two-four levels, green/22,843 is five-eight levels, and purple/22,844 is eight-twelve levels.

Figure 2.

A, Graph showing that the x-axis represents the year, and the y-axis represents the projected volume of spinal instrumentation procedures, stratified by the combined procedural terminology code, and adjusted by the growing Medicaid Part B population. This adjusted case volume is not meant to represent the true national volume counts of spinal instrumentation procedures, but instead to assess trends more accurately in utilization after adjusting for Medicare beneficiaries as a potential cofounder. The colors and codes reflect the following: red/22,840 is single level, blue/22,842 is two-four levels, green/22,843 is five-eight levels, and purple/22,844 is eight-twelve levels.

Figure 3.

Graph showing alternative scenario in which the expenditure of future spine surgeries plateaus. We utilize Prophet's logistic growth trend model with a specified carrying capacity. The carrying capacity is where the forecast might saturate, and it is some maximum achievable point (e.g., total market size, total population size, or in this case CMS and/or private insurers increasingly tight constraints on expenditures), where trend lines plateau. Using the 7.2% projected nominal return rate from the CMS 2022-2031 National Health Expenditure (NHE) report, and future projected inflation rates (acquired from the U.S. Congressional Budget Office's economic outlook report), we estimated the carrying capacity cap in 2030 to be $88,125,984.

Discussion

Our study aimed to project trends in spinal instrumentation utilization, costs, and reimbursement in the United States. The number of single-level spinal instrumentation procedures in Medicare beneficiaries is expected to double by 2050, while the number of two-four–level spinal instrumentation procedures is expected to double by 2040. We report that Medicare reimbursements to surgeons for spinal instrumentation procedures have either experienced a notable decline or failed to keep up with inflation. In addition, reimbursements for spinal instrumentation codes among surgeons have shown a disproportionate decrease compared with other commonly performed orthopaedic procedures. These drastic increases will place a heavy burden on the healthcare system and existing spinal surgeons.

We adjusted past spinal instrumentation volume trends for the increasing Medicare beneficiary population from 2000 to 2019. This allowed us to assess evolving spinal instrumentation volume utilization more accurately (Figure 2). We found two-key inflection points in our single-level spinal instrumentation data. In 2008 to 2009, we saw a rapid increase in spinal instrumentation volume, which may be a response to the 2007 landmark randomized, controlled Spine Patient Outcomes Research Trial (SPORT).^24,25 The SPORT trial showed that patients with laminectomy and fusion maintained substantially greater improvement in pain and function compared with those treated nonoperatively for the management of lumbar degenerative spondylolisthesis.^24,25 Beginning in 2017, we saw a large decrease in single-level and a simultaneous increase in two-four–level spinal instrumentation volume. These trends may be a response to the 2016 landmark randomized, controlled, Spinal Laminectomy versus Instrumented Pedicle Screw (SLIP) trial.²⁶ The SLIP trial shows that among patients with degenerative grade I spondylolisthesis, the addition of lumbar spinal fusion to laminectomy was associated with no clinical improvements in physical health-related quality of life compared with laminectomy at 1 year after surgery and only slightly greater improvements at 2, 3, and 4 years after surgery.²⁶ Several randomized controlled trials thereafter have shown equipoise between decompression/fusion and decompression alone in lumbar spinal stenosis both with and without degenerative spondylolisthesis.^27,28 This may explain the plateau in single-level instrumentation during the tail end of our time sample.

Our study adds to the literature by calculating changes in mean inflation-adjusted reimbursement of leading orthopaedic procedures to establish a baseline for comparing spinal instrumentation trends. We report that between 2000 and 2019, the mean inflation-adjusted reimbursement for single-level spinal instrumentation procedures decreased by 45.6% ($359.53), which is consistent with previous reports of decreases in per-procedure Medicare reimbursements for spinal fusions.^11,29 The decline in reimbursements during the same period has been previously reported for posterolateral fusion (−25.08%), anterior lumbar interbody fusion (−35.29%), and posterior lumbar interbody fusion (−0.11%).³⁰ Declining Medicare compensation trends are particularly evident in the diminishing allocation of reimbursements for spinal surgeons conducting instrumented construct procedures and illustrate the consequences of legislative changes favoring value-centric cost-cutting strategies. The surge in the adoption of value-based delivery models has shifted the burden of risk from entities such as Medicare to surgeons and medical facilities within novel shared-risk payment frameworks, designed to promote cost-effectiveness and value. Yet, the degree to which these value-based models have effectively curbed expenses while upholding or enhancing care quality remains uncertain.^31,32 Given the marked variations in complexity and associated risks of spinal instrumentation surgery, it is increasingly vital for value-based reforms to harmonize financial liabilities and corresponding incentives. This alignment should be directed at addressing the primary source of the bulk of expenses, which disproportionately affects spinal surgeries: hospital expenditures.

Spinal fusion procedures already account for the most substantial collective hospital expenditures within the landscape of US hospitals,⁶ and the bulk of payer reimbursements comprises inpatient expenses.^33-36 Effectively reducing inpatient expenditures may require minimizing the length of hospital visits and shifting carefully selected low-acuity patients to ambulatory surgery centers.³¹ Notably, there has been a noticeable shift in recent years, where a rising proportion of spinal surgeries—including lumbar fusions and anterior cervical discectomy and fusions—have been relocated to ambulatory or outpatient settings.^34,37 These ambulatory surgery centers offer an alternative to the often-variable costs linked with hospital and inpatient services and have demonstrated comparable safety profile levels and superior cost-efficiency.³⁴ Advancements in surgical techniques and medical devices have played a role in refining protocols, particularly in the realm of minimally invasive surgery. This progress could potentially hasten the postoperative recovery process and lead to quicker discharges.³⁸ Moreover, the implementation of precise criteria for selecting suitable candidates for outpatient surgery, alongside optimized anesthesia and postoperative pain management protocols, has played a pivotal role in reducing the risks associated with readmissions and the associated financial expenditures.

Our model projects a more aggressive increase in the number of multilevel procedures that require posterior instrumentation than single-level instrumented procedures. Although the exact reason for these differences has not been elucidated, increasing provider confidence in surgical technique and advancements in technology may allow surgeons both preoperatively and intraoperatively to identify and then treat multilevel pathology.^3-5 The aging global population is leading to a rise in spinal disorders commonly associated with older age, such as osteoporotic compression fractures, lumbar spinal stenosis, and degenerative spinal deformity.³⁹ These conditions may subsequently necessitate the need for multilevel surgical treatment.³⁹ From 2020 to 2050, the growth rate for single-level and multilevel spinal instrumentation procedures is projected to outpace associated reimbursements. The decline in reimbursements may be attributed, in part, to the increasing costs associated with spinal instrumentation procedures. Between 1998 and 2006, the cost of primary fusion increased by 191%, reflecting a 408% increase in total spending, with $29.1 billion spent in 2006 alone.⁴⁰ In single-level lumbar fusions, implants account for most of the supply costs for these procedures (89%), while services contribute 38% of direct costs, which are highly dependent on surgical time and length of hospital stays.³⁴ Despite the ample evidence documenting the decreasing trend of spine surgery Medicare reimbursements, this is the first study to project future cost and reimbursement trends.

One major limitation of this study is its generalizability. The study used data from the Medicare database, which limits data to those patients aged 65 years or older and excludes private payer insurances. It is expected that the utilization of these procedures will increase in patients aged younger than 65 years as well, which may lead our model to underestimate volumes that may be seen in the coming years. Future research is needed to determine whether the trends described here extend to other demographic groups. There are also limitations to this work intrinsic to any projection study. In the span of three decades, various unforeseen events could arise, such as advancements in arthritis treatments, shifts in migration patterns, alterations in health financing, or changes in the structure of healthcare systems. These uncertainties cannot be fully captured or avoided in our predictive study or any other study. Furthermore, the decision to undergo a spinal instrumentation procedure is not solely influenced by the population size or the overall economic well-being of a country. For instance, changes in the prevalence of osteoarthritis and chronic obesity would affect the demand for spinal instrumentation procedures. The availability and acceptance of alternative treatment methods would also be unpredictable potentiality. However, it is impossible for any prediction model to account for all these potentialities.

Conclusion

This study describes a novel use of the time-series forecasting methodology, Prophet, and projects a notable increase in the demand and costs for single-level and multilevel spinal instrumentation to 2050 with a concomitant decrease in per procedure provider reimbursement. These projections are of utmost importance to a variety of stakeholders, including patients, physicians, payers, and health systems who must recruit and train personnel, budget time, and space in medical facilities, and procure implants to make sure the increased demand is adequately met.

Supplementary Material

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