High Tibial Osteotomy (HTO) Versus Unicompartmental Knee Arthroplasty (UKA) in Medial-Compartment Knee Osteoarthritis (KOA): A Critical Narrative Review of Comparative Costs and Cost-Effectiveness

Abstract

Background: Medial-compartment knee osteoarthritis (KOA) carries substantial disability and long-term cost. High tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA) are key joint-preserving or joint-replacing options for selected patients, but their comparative economic ranking remains uncertain. Methods: This critical narrative review synthesized comparative economic evidence on HTO versus UKA for isolated medial-compartment KOA. PubMed and Web of Science were searched as primary sources for English-language studies published from 1 January 2000 to 15 January 2026, while Google Scholar and citation tracking were used supplementarily to identify potentially missed records. Eligible studies were direct economic evaluations or comparative cost/resource studies with clear decision relevance to the HTO–UKA choice. Burden and cost-of-illness studies were used for contextual framing only and were not included in the core comparative synthesis. Results: The direct evidence base was small and methodologically heterogeneous and was dominated by decision-analytic models that differed in perspective, time horizon, utility metric, and assumptions regarding reoperation, revision, and conversion to total knee arthroplasty (TKA). These structural differences largely explain why a U.S. lifetime societal model favored HTO, a UK age-stratified 10-year model produced age-dependent findings, and a recent Canadian public-payer model favored UKA. Observational studies suggest that UKA episode costs can fall substantially in outpatient or ambulatory pathways, whereas HTO costs may rise when reoperations and technique-specific resource use are explicitly captured. Conclusions: Current evidence does not support a context-free economic ranking of HTO and UKA. Because the available studies are heterogeneous and incremental utility differences are often small, the findings should be interpreted cautiously and as scenario-dependent rather than definitive. Future comparative analyses should use contemporary pathway data, transparent and standardized costing, and explicit downstream event definitions for both procedures.

1. Introduction

In patients with isolated medial-compartment knee osteoarthritis who remain symptomatic despite nonoperative care, the central “value” question is often not whether to operate, but which mid-stage strategy delivers better economic value: high tibial osteotomy (HTO) or unicompartmental knee arthroplasty (UKA). These procedures address the same compartmental pathology via different mechanisms—realignment and joint preservation (HTO) versus compartment resurfacing (UKA)—and therefore generate distinct cost trajectories over time. The relevant economic endpoint is rarely the index episode alone; rather, it is the cumulative pathway cost required to sustain function until (and if) conversion to total knee arthroplasty (TKA) or revision becomes necessary.

Head-to-head economic evidence is dominated by decision-analytic models, because large prospective cohorts with directly measured preference-based utilities and long-horizon costs remain uncommon. In a U.S. probabilistic state-transition model (societal perspective; lifetime horizon; 3% discounting), Konopka et al. reported nearly identical discounted quality-adjusted life years (QALYs) for HTO and UKA (14.62 vs. 14.63), while discounted direct medical costs favored HTO ($20,436 vs. $24,637 in 2012 USD). At a willingness-to-pay (WTP) threshold of $50,000/QALY, HTO had the highest probability of being cost-effective (57%), and the authors emphasized that the cost-effectiveness of both HTO and UKA hinges on the conversion rate and outcomes to TKA [1]. In a UK 10-year Markov model, Smith et al. similarly found that cost-effectiveness is age-stratified—HTO tending to dominate in younger cohorts and UKA becoming more attractive with increasing age—while functional utility assumptions were the primary determinant of incremental cost-effectiveness [2]. However, transferability is limited: in a recent Canadian public-payer Markov model, Ruangsomboon et al. concluded that UKA was the most cost-effective strategy for young patients at a specified WTP threshold (expressed per quality-adjusted life-month), while HTO was dominated under their base case, underscoring how jurisdictional costing structures, model architecture, and WTP conventions can flip conclusions [3]. These three models are not directly interchangeable. Konopka et al. used a lifetime societal perspective and placed substantial weight on conversion-to-TKA pathways and post-conversion outcomes; Smith et al. used a 10-year age-stratified Markov framework in which utility inputs had the greatest leverage on incremental cost-effectiveness; and Ruangsomboon et al. used a Canadian public-payer framework, quality-adjusted life months rather than quality-adjusted life years, and a different decision architecture in which HTO was evaluated alongside additional surgical alternatives. Accordingly, differences in perspective, time horizon, effectiveness metric, costing basis, and downstream state structure are sufficient to explain why these models do not converge on a single preferred strategy. The principal analytical differences across these three direct model-based studies are summarized in

Table 1. Analytical features of the principal direct HTO–UKA economic models that explain divergent conclusions.

Study	Setting and Model	Perspective/Metric	Main Driver(s)	Interpretation for HTO vs. UKA
Konopka et al. [1]	United States; probabilistic state-transition model; patients aged 50–60 years; lifetime horizon	Societal perspective; discounted QALYs and direct medical costs; 2012 USD; 3% discounting	Conversion-to-TKA rate, post-conversion outcomes, and very small incremental utility difference	Favored HTO economically when lifetime downstream pathways were emphasized. QALYs were nearly identical, but discounted costs were lower for HTO.
Smith et al. [2]	United Kingdom; Markov model; age-stratified cohorts aged 40, 50, 60, and 70 years; 10-year horizon	UK health-system setting; costs and outcomes estimated over 10 years	Functional utility assumptions dominated sensitivity analysis; costs were secondary; 10-year revision risk was least influential	No universal winner. HTO was more likely to be cost-effective in cohorts younger than 60 years, whereas UKA was more likely to be cost-effective in cohorts aged 60 years and older.
Ruangsomboon et al. [3]	Ontario, Canada; probabilistic Markov cost-utility model; base-case 45-year-old cohort; lifetime horizon	Ontario public-payer perspective; QALMs, discounted lifetime costs, and NMB; 2023 CAD; 1.5% discounting	Public-payer costing, QALM rather than QALY outcome metric, and three-strategy model architecture	UKA was favored within the model. HTO was dominated in the full three-strategy framework, while direct HTO–UKA costs were close, but modeled effectiveness favored UKA.

Note. The Canadian study was a three-strategy model (TKA, UKA, HTO), so “HTO dominated” refers to the full model architecture rather than a simple isolated pairwise HTO–UKA comparison. HTO = high tibial osteotomy; UKA = unicompartmental knee arthroplasty; TKA = total knee arthroplasty; QALY = quality-adjusted life years; QALM = quality-adjusted life-month; NMB = net monetary benefit.

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Understanding why models disagree requires explicit attention to procedure-specific “failure architectures” and the cost items they generate. For HTO, a major and often under-modeled driver is reintervention: hardware irritation, delayed union, and other complications can lead to additional procedures, thereby increasing costs even when the osteotomy successfully delays arthroplasty. In a large HTO series with approximately 10-year follow-up, Yapici et al. reported that complications prompting additional surgery occurred in 20.3% of treated knees, although serious complications requiring surgery were uncommon (2.6%) [4]. For UKA, implant costs and facility costs dominate the index episode, while long-run value is driven by revision or conversion pathways and their associated utility decrements. Importantly, UKA costs are increasingly setting-dependent: in a matched cost study, Cozzarelli et al. found that mean direct facility costs were substantially lower when UKA was performed in an ambulatory surgery center ($9025) compared with hospital outpatient ($12,032) or inpatient care ($14,542), implying that older inpatient-based economic conclusions may overestimate contemporary UKA costs [5].

Because incremental QALY differences between HTO and UKA are often small, downstream event rates can dominate incremental cost-effectiveness. In a large matched U.S. claims analysis, Serbin et al. reported higher long-term conversion-to-TKA rates after UKA than after HTO (10-year conversion 9.2% vs. 4.5%), while early medical and mechanical complications were more frequent after HTO—illustrating the core economic trade-off between early pathway intensity and longer-term durability [6]. Therefore, a focused synthesis of HTO versus UKA economics must be explicit about analytic perspective, time horizon, discounting, site of service, and—critically—how reoperations, revisions, and conversions are defined and costed.

Objective and scope. The aim of this review is to critically synthesize the comparative economic evidence on high tibial osteotomy (HTO) versus unicompartmental knee arthroplasty (UKA) for isolated medial-compartment knee osteoarthritis, and to identify the assumptions that most strongly drive divergent conclusions across studies. The core synthesis is limited to direct economic evaluations and comparative real-world cost/resource studies relevant to the HTO–UKA decision. Broader clinical outcomes are considered only when they inform utilities, transition probabilities, or downstream costs within economic analyses.

2. Results

2.1. Study Identification and Evidence Map

The structured search identified the small, methodologically heterogeneous literature directly relevant to the HTO–UKA economic question. Most core references were decision-analytic economic models or comparative claims/cost analyses; directly measured head-to-head studies that collected both cost and preference-based utility data were scarce. The final included reference set comprised of 28 records. Of these, 15 references formed the core comparative economic synthesis, and 13 were retained only for contextual interpretation in the Introduction and Discussion. A narrative-review evidence map of literature identification and study classification is shown in Figure 1.

2.2. Comparative Economic Evidence Landscape (HTO vs. UKA)

Across the included literature, direct HTO–UKA economic comparisons are dominated by decision-analytic cost-utility models, while procedure-specific cost studies (within HTO or within UKA) provide important context on how local practice patterns can materially shift the “HTO vs. UKA” cost conclusion. The head-to-head models consistently report very small incremental health-utility differences between HTO and UKA, which makes comparative value conclusions highly sensitive to (i) cost inputs (index episode + follow-up) and (ii) downstream event structures—particularly reoperations after HTO (e.g., hardware-related procedures) and revision or conversion pathways after UKA. Key model-based head-to-head comparisons were reported from the United States (lifetime, societal), the United Kingdom (10-year, age-stratified), and Canada (lifetime, public-payer), supplemented by earlier European cost analyses [1,2,3,7,8].

2.3. Model-Based Cost-Utility Findings: HTO vs. UKA

United States (lifetime; societal perspective): HTO lower cost, essentially equivalent QALYs.

In a probabilistic state-transition (Markov) model evaluating patients aged 50–60 years with medial unicompartmental OA, discounted QALYs were nearly identical for HTO and UKA (14.62 vs. 14.63), while discounted direct medical costs differed meaningfully: $20,436 for HTO vs. $24,637 for UKA (2012 USD). In probabilistic sensitivity analysis, at a $50,000/QALY willingness-to-pay threshold, HTO had the highest probability of being cost-effective (57%), compared with UKA (19%). Notably, the authors emphasized that relative value is driven by the rate of conversion to TKA and outcomes after conversion, reinforcing that small modeled QALY gaps shift attention toward downstream pathway assumptions [1].

United Kingdom (10-year; age-stratified): age-dependent “winner,” utility dominates sensitivity. A 10-year Markov model simulating cohorts aged 40, 50, 60, and 70 reported HTO as most likely to be cost-effective under age 60, while UKA was most likely cost-effective at ages 60 and above. Importantly, probabilistic results did not identify a single intervention as decisively superior across simulations; the model was described as “exquisitely sensitive” to utility (functional outcome), more sensitive to changes in cost, and least sensitive to assumptions about 10-year revision risk. This again indicates that when utility differences are small or uncertain, modest shifts in health-state utilities can flip the cost-effectiveness ordering between HTO and UKA [2].

Canada (lifetime; Ontario public-payer): UKA favored; HTO dominated by an alternative strategy, but remains cost-close to UKA. A lifetime probabilistic Markov model (base case: 45-year-old cohort) from a Canadian public-payer perspective reported mean discounted lifetime costs of $9238 (HTO) and $9419 (UKA) (2023 CAD). UKA produced higher quality-adjusted life months (290.53 QALMs) than HTO (270.88 QALMs). Within the model’s decision framework, HTO was absolutely dominated by another strategy (more costly and less effective), while UKA emerged as the most cost-effective option in 55.27% of probabilistic simulations at the specified threshold. For the specific HTO–UKA comparison, the key result is that cost differences were small in absolute terms (≈$181 CAD), yet modeled effectiveness differences favored UKA—highlighting again how assumptions about durability and downstream states dominate incremental results when costs cluster tightly [3].

Earlier model-based evidence (10-year horizon): UKA is generally less costly than HTO, based on reported expected costs. A 10-year economic analysis comparing UKA and HTO (among other strategies) reported cost-effectiveness ratios of approximately $5150/QALY (UKA) and $6754/QALY (HTO) versus no treatment, and 10-year expected total costs of $17,570 (UKA) versus $22,825 (HTO) (values as reported in the abstract). While this work is not a contemporary, jurisdiction-specific payer model, its directionality is consistent with the concept that HTO can accrue substantial downstream costs (reoperations, conversions, complications) that erode any index-cost advantage unless those events are minimized and/or valued within a broader societal framework [7].

Why the Head-to-Head Models Reach Different Conclusions

Table 1 compares the structural assumptions that most plausibly explain the divergent conclusions of the principal direct HTO–UKA economic models. The divergence across the U.S., UK, and Canadian models is explainable rather than contradictory. The U.S. model used a lifetime societal perspective and placed substantial economic weight on downstream conversion-to-TKA pathways; the UK model used a 10-year age-stratified framework in which utility inputs were the dominant sensitivity driver; and the Canadian model used a public-payer perspective, quality-adjusted life months rather than quality-adjusted life years, and a different decision architecture. When incremental health gains are small, these differences in perspective, time horizon, effectiveness metric, costing base, and downstream state definitions are sufficient to reverse the preferred strategy. The comparative literature should therefore be interpreted as showing assumption-sensitive scenario dependence rather than a stable universal ranking.

2.4. Direct (Non-Model) Cost Comparisons: HTO vs. UKA

Historical inpatient cost analysis (Germany). In an inpatient/outpatient cost comparison drawn from patients treated between 1988 and 1993, the reported average total costs were 9487 for HTO versus 11,687 for unicompartmental arthroplasty (UKA) (units as presented in the abstract). The authors concluded that, for total operative treatment costs, HTO (with or without hardware removal) was the least expensive of the operative options. Because these estimates reflect an older reimbursement and care-delivery era (and likely different implant pricing and length-of-stay norms), their main contribution to this review is conceptual: HTO can appear economically favorable when evaluated primarily on index and near-term episode costs, but transferability to modern pathways requires careful adjustment for current outpatient migration (especially for UKA) and contemporary reintervention patterns [8].

2.5. Within-Procedure Cost Variability That Materially Shifts HTO–UKA Conclusions

HTO: index cost and cost-effectiveness vary sharply across techniques and costing perspectives.

Cost variability within HTO is large enough to change conclusions in any HTO–UKA comparison.

Technique-driven cost differences. In a Spanish public health system evaluation comparing opening-wedge HTO (OW-HTO) versus closing-wedge HTO (CW-HTO), total costs were substantially higher for OW-HTO (€4612 ± 766) than CW-HTO (€1827 ± 702), with OW-HTO showing a worse cost-effectiveness ratio per KOOS-12 MCID achieved. This magnitude of difference (≈€2785) is large enough to offset or reverse modeled differences between HTO and UKA in settings where UKA is delivered efficiently [9].

Perspective-driven reversals. In an economic evaluation of locking vs. nonlocking plate fixation in medial opening-wedge HTO, the locking plate strategy was not cost-effective from a healthcare payer perspective within 12 months, but became cost-effective (and cost-saving) from a societal perspective when indirect costs (time off work) were included. For HTO–UKA comparisons that include working-age populations, this finding is critical: whether HTO “wins” on cost can depend on whether the analysis captures productivity and return-to-work effects [10].

UKA: Site-of-service is a dominant cost lever. Modern cost studies show that UKA costs can vary by thousands of dollars depending on where the procedure is performed, directly affecting any HTO–UKA comparison.

Facility cost differentials across settings. In a matched three-cohort analysis, mean direct facility costs were $14,542 (inpatient hospital), $12,032 (outpatient hospital), and $9025 (ambulatory surgery center) for UKA—demonstrating a roughly $5500 spread between inpatient and ASC delivery [5].

Charges and reimbursement signals. In an analysis comparing inpatient versus outpatient UKA, mean outpatient UKA charges were reported as ~$20,500 lower per patient than inpatient charges, driven primarily by facility charges; outpatient reimbursement was also lower than inpatient reimbursement, reflecting system-level payment differences that influence economic conclusions depending on whether “cost” is measured as charges, reimbursements, or micro-costed resources [11].

System-level pathway redesign. A large NHS observational analysis of a day-surgery pathway for unicompartmental knee replacement reported mean per-patient savings ranging from £577 to £1429, depending on the costing approach, alongside reduced length of stay. These data reinforce that UKA costs are not fixed; they depend heavily on pathway engineering and accounting method [12].

These within-procedure studies should not be interpreted as independent evidence of overall HTO or UKA superiority; rather, they indicate that intra-procedural heterogeneity may be large enough to reverse the direction of HTO–UKA cost comparisons in specific settings.

2.6. Downstream Events That Act as “Cost Multipliers” in HTO vs. UKA Comparisons

Because modeled QALY differences between HTO and UKA are often extremely small, revision/conversion trajectories and reoperations become first-order cost drivers.

HTO reoperations are common enough to require explicit costing.

In a 10-year follow-up study of medial open-wedge HTO, the overall complication rate was high, and 20.3% required additional surgery; while serious-complication reoperations were uncommon, the frequency of additional procedures is economically relevant because even “minor” reoperations can substantially increase cumulative costs over a 10-year horizon [4].

Conversion/revision patterns differ across datasets and follow-up windows, introducing structural uncertainty. In a U.S. propensity-matched claims analysis, UKA showed higher 5- and 10-year conversion-to-TKA rates than HTO (UKA 9.2% at 10 years vs. HTO 4.5%), while early (1-year) medical complications were more frequent after HTO for several endpoints [6]. Conversely, other claims-based analyses have reported lower infection and lower conversion-to-TKA risk after UKA, compared with HTO in earlier time windows, emphasizing that short-term adverse events and longer-term durability may point in different directions and must be modeled explicitly rather than assumed [13]. A large Korean national claims analysis likewise found differences in revision and adverse-event profiles between UKA and HTO over longer observation periods, reinforcing that jurisdictional practice patterns and coding definitions can materially shift the apparent failure architecture that drives costs [14].

2.7. Synthesis of the Comparative Cost Signal (HTO vs. UKA)

Across jurisdictions, no stable HTO–UKA economic ranking emerged. Instead, the apparent preferred strategy shifted with analytic perspective, time horizon, utility assumptions, site of service, and the treatment of reoperations, revisions, and conversion-to-TKA events. The comparative signal is therefore best interpreted as conditional and assumption-sensitive rather than as evidence of a universal cost winner: the U.S. lifetime societal model favored lower-cost HTO with essentially identical QALYs, the UK 10-year model suggested an age-stratified preference (HTO younger, UKA older) with high utility sensitivity, and the Canadian payer model favored UKA with small absolute cost differences but higher modeled utility [1,2,3]. Real-world cost studies show that UKA costs can drop substantially with outpatient/ASC delivery, while HTO costs can rise materially if reoperations and technique-specific resource use are not minimized and explicitly costed [4,5,9,10,11,12]. Collectively, the comparative economic evidence indicates that HTO–UKA cost conclusions are scenario-dependent, driven primarily by: site-of-service and episode costing for UKA, and reoperation/conversion accounting plus technique/perspective choices for HTO [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. As summarized in Table 1, the apparent instability of the preferred strategy is driven mainly by analytic perspective, time horizon, effectiveness metric, and downstream-state architecture, rather than by large intrinsic differences in index utility.

3. Discussion

The available evidence does not support a single, universal economic “winner” between high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA). Reported cost and cost-effectiveness differences are primarily a function of (i) the analytic frame (payer vs. societal perspective; short vs. long horizon), (ii) the care pathway (inpatient vs. outpatient/ambulatory/day-case delivery), and (iii) whether downstream events are comprehensively captured (complications, reoperations/hardware removal, revision, and conversion procedures). Consequently, HTO-versus-UKA findings should be interpreted as conditional on context rather than as generalizable ranking statements [1,2,3].

Model-based cost-utility analyses illustrate how easily conclusions can flip when quality-adjusted health gains are small and close together. In a U.S. probabilistic state-transition model of 50–60-year-old patients, discounted direct medical costs were lower for HTO than UKA, while discounted QALYs were nearly identical; at common willingness-to-pay thresholds, HTO therefore had the highest probability of being cost-effective, and the authors highlighted sensitivity to conversion rates and post-conversion utilities [1]. An age-stratified Markov model over a 10-year horizon suggested that HTO is more likely to be cost-effective in cohorts < 60 years, whereas UKA is more likely in cohorts ≥ 60 years, and explicitly reported that functional utility inputs dominate model outputs by a much greater margin than revision risk [2]. In contrast, a recent Canadian public-payer lifetime model found that UKA generated the highest quality-adjusted life months and that HTO was “absolutely dominated” in the base case [3]. These analyses are not inherently contradictory; they embed different health system cost structures (e.g., Medicare-anchored reimbursement vs. Canadian case-costing), different time horizons, and different utility assumptions—each of which can change the incremental net monetary benefit when outcome differences are marginal. This interpretation is also consistent with the broader comparative clinical literature, in which UKA often provides statistically better early pain and satisfaction scores while HTO more directly addresses malalignment and may preserve a slightly greater range of motion; importantly, several reported between-procedure differences are small and frequently fall below established minimal clinically important difference thresholds. When clinically perceived utility differences are modest, model outputs become highly sensitive to how utilities are sourced, mapped, and extrapolated over time, which helps explain why otherwise credible economic models can reach different conclusions [1,2,3,15]. Small absolute cost differences also require careful interpretation. A modest incremental cost may be economically meaningful in high-volume systems if it is paired with a robust difference in downstream durability or revision burden; however, when both incremental costs and incremental utilities are small, incremental cost-effectiveness ratios become unstable, and preference rankings become highly threshold-dependent. For that reason, the present literature is more informative about the drivers of value than about a fixed universal price advantage of one procedure over the other.

A second, often underappreciated, source of heterogeneity is what “cost” actually represents. Older inpatient-era hospital cost analyses reported lower average costs for HTO than for UKA, but these estimates reflect historical implant pricing, length-of-stay norms, and reimbursement rules that are unlikely to map directly onto contemporary pathways [8]. More recent U.S. work underscores that charges, reimbursements, and true costs can diverge substantially; studies that report “charges saved” (or reimbursement fractions) can be decision-relevant for some stakeholders, but they should not be interpreted as interchangeable with payer costs or hospital cost accounting [11].

The care setting is arguably the most time-sensitive driver of current HTO versus UKA economics. UKA has rapidly migrated to outpatient, ambulatory surgery center (ASC), and day-case pathways, which can materially reduce facility costs through shorter stays and different resource use. Direct facility-cost comparisons demonstrate lower mean costs when UKA is performed in an ASC compared with hospital outpatient or inpatient settings [5]. In parallel, UK NHS observational data show that day-case UKA pathways can reduce the mean length of stay and yield per-patient savings (with the magnitude dependent on the costing method used) [12]. Any analysis that benchmarks UKA to an inpatient pathway risks overstating UKA costs relative to modern practice; updated economic models should therefore use contemporary site-of-service distributions and corresponding costs [5,11,12].

Downstream event costing is the other economic axis on which HTO and UKA trade places. For HTO, the “true” pathway cost is not only the index osteotomy; complication management, reoperations, and elective or symptomatic hardware removal may add meaningful cost over time. Long-term observational data have reported high overall complication rates after medial open-wedge HTO, with a substantial proportion requiring additional surgery, even if surgery for serious complications is less frequent [4]. For UKA, downstream costs are driven primarily by revision and conversion to total knee arthroplasty (TKA); these events are expensive and therefore heavily weighted in cost-utility models [1,2,3,6,13,14]. If an evaluation omits common HTO reoperations, underestimates UKA conversion risk, or assumes overly favorable post-conversion utility, the incremental cost-effectiveness result can shift materially [1,2,6].

Real-world database studies also show that the time profile of adverse events matters for economic interpretation. In a U.S. matched-claims analysis, HTO patients had a higher risk of several early complications, while UKA demonstrated conversion rates that accumulated over longer follow-up; the authors concluded that HTO may be converted to TKA later than UKA in short- to mid-term follow-up [6]. Conversely, another large database study reported lower infection odds and lower 1-year conversion risk for UKA versus HTO [13]. A nationwide Korean claims analysis in 50–70-year-old patients found a higher long-term revision risk after HTO, but a higher incidence of certain perioperative adverse outcomes after UKA [14]. Short-term registry data adds nuance: NSQIP-based comparisons in patients ≤ 60 years showed broadly similar 30-day complication and reoperation rates, with higher superficial surgical-site infection after HTO [16]. Economically, these discrepancies imply that models should not assume a single, constant “failure rate” for either procedure; rather, early complication hazards and late conversion/revision hazards should be distinguished and costed within their respective budget windows [6,13,14,16].

Contextual economic burden and indirect costs. Knee osteoarthritis (KOA) represents a major and growing global burden; Global Burden of Disease (GBD) 2019 analyses estimate approximately 364.6 million prevalent cases and 29.5 million incident cases worldwide in 2019, underscoring the scale at which value-based surgical decisions can influence health-system spending and societal costs [17]. Beyond direct medical expenditures, cost-of-illness evidence indicates substantial non-healthcare and productivity-related losses in osteoarthritis, which are particularly relevant to the working-age cohorts commonly considered for HTO or UKA. As a result, economic comparisons between HTO and UKA can be meaningfully affected by whether analyses adopt a payer versus societal perspective and whether time away from work is treated as a material cost component [18,19].

UKA economic context relevant to HTO–UKA comparisons. Although the present synthesis focuses on HTO versus UKA, the interpretation of the UKA cost profile is informed by broader economic evidence on partial-versus-total knee replacement. Registry-based cost-effectiveness analyses suggest that unicompartmental replacement can be cost-effective compared with total knee replacement under common willingness-to-pay thresholds, particularly when local revision rates are favorable [20]. Randomized trial evidence from TOPKAT similarly supports the clinical and economic competitiveness of partial replacement strategies in appropriately selected medial-compartment osteoarthritis [21,22]. However, longer-horizon matched-cohort data demonstrate that early perioperative savings may narrow over time as revision-related resource use accumulates, reinforcing the importance of the time horizon when translating UKA cost findings into HTO–UKA comparisons [23].

Revision thresholds and age dependence as key economic parameters. Economic evaluations consistently show that the value proposition of UKA is sensitive to age, implant survivorship, and revision thresholds. Decision-analytic work indicates that UKA’s cost-effectiveness relative to TKA varies across age strata, reflecting differences in baseline revision risks, competing mortality, and expected QALY gains [24]. Meta-analytic thresholds for annual revision rates that preserve UKA cost-effectiveness have also been proposed, highlighting that local registry performance and revision propensity can be decisive in real-world value assessments [25]. These observations align with the heterogeneity seen in HTO–UKA models, where assumptions regarding revision probabilities, time-to-failure, and post-revision utilities can materially shift long-term cost-effectiveness rankings.

HTO reintervention burden and pathway costs. For HTO, short-term and mid-term costs may be influenced by secondary procedures, particularly hardware removal. Contemporary series of medial opening-wedge HTO with locking plate constructs report low rates of serious adverse events but comparatively high rates of subsequent implant removal, which can add operative costs and recovery-related indirect costs that vary across regions and practice patterns [26]. These downstream events should be considered when extrapolating costs between healthcare systems with different implant choices, follow-up protocols, and thresholds for elective removal.

Downstream conversion-to-TKA assumptions after HTO. Long-term economic comparisons depend on how subsequent conversion to total knee arthroplasty is modeled after failure of joint-preserving surgery. Systematic review evidence suggests that total knee arthroplasty performed after prior high tibial osteotomy may carry a higher revision risk than primary total knee arthroplasty, an effect that could increase downstream costs and reduce QALYs if reflected in lower survivorship or a higher complication burden [27]. Where possible, models comparing HTO and UKA should therefore differentiate post-HTO TKA trajectories from primary TKA inputs rather than assuming identical revision and resource-use profiles.

This point is reinforced by Losina et al., whose U.S. Osteoarthritis Policy Model showed that expanding TKA eligibility increased OA-attributable discounted lifetime direct medical costs from $12,400 to $16,000 per patient and increased lifetime TKA uptake from 54% to 70%. In economic terms, conversion to TKA is therefore not a peripheral downstream event but a major structural cost driver. HTO–UKA models should consequently test conversion thresholds and post-conversion outcomes explicitly in sensitivity analyses rather than treat them as secondary background assumptions [28].

Finally, within-procedure variation can meaningfully change the HTO cost base, complicating cross-procedure comparisons if this heterogeneity is ignored. An economic evaluation from a Spanish public healthcare perspective reported substantially higher total cost and less favorable cost-effectiveness ratios for opening-wedge versus closing-wedge HTO, despite similar functional improvements [9]. Likewise, a Canadian example demonstrated that fixation choices in HTO can appear non-cost-effective from a payer perspective, yet become cost-effective from a societal perspective once indirect costs such as time off work are included, highlighting that “perspective” is not a technical footnote but a determinant of conclusions in working-age cohorts [10].

Taken together, the HTO-versus-UKA literature supports a pragmatic interpretation framework: (1) define the decision-maker and time horizon (hospital episode cost, payer budget impact, or lifetime cost-utility); (2) ensure UKA costs reflect contemporary outpatient/ASC/day-case delivery where applicable; (3) include the full downstream event set for both pathways (HTO reoperations/hardware removal as well as conversion; UKA revision and conversion) with time-dependent hazards; and (4) treat functional utility as a first-order parameter, because multiple models show it can dominate cost-effectiveness conclusions when costs and survivorship are close [1,2,3,5,6,9,10,11,12].

This review has important limitations. First, it is a narrative rather than a systematic review, and its purpose was a critical economic synthesis rather than an exhaustive meta-analytic aggregation. Second, the direct HTO–UKA economic literature is small and dominated by model-based studies rather than head-to-head studies that primarily collect both costs and preference-based utilities. Third, estimates are difficult to transfer across jurisdictions because studies differ in analytic perspective, time horizon, cost definition (true costs, charges, or reimbursement), utility metric, and definitions of reoperation, revision, and conversion to TKA. These limitations preclude any definitive universal ranking and support cautious interpretation of the findings. Finally, study selection and extraction were performed by one reviewer, which may have reduced reproducibility despite the use of prespecified criteria. Broader arthroplasty and osteoarthritis economic studies are cited here only to contextualize cost structure, perspective, and revision sensitivity; they are not presented as direct HTO–UKA comparative evidence.

4. Methods

4.1. Study Design and Scope

This article is a critical narrative review rather than a systematic review. A structured literature search was used to improve transparency in study identification, but the objective was an interpretive economic synthesis rather than an exhaustive systematic review or quantitative pooling. The review, therefore, focused on the studies most directly informative for the HTO–UKA economic question and on comparing the assumptions that determine their conclusions.

4.2. Data Sources and Search Coverage

PubMed and Web of Science were used as the primary bibliographic sources. Google Scholar was used only as a supplementary search tool to identify potentially missed records, ahead-of-print articles, and institution-hosted full texts not consistently indexed in the primary databases. Backward reference screening and forward citation tracking were also performed for influential economic studies. Because Google Scholar ranking and pagination are dynamic, it was not treated as a formal count-generating database for evidence mapping.

The formal database search was restricted a priori to English-language studies published between 1 January 2000 and 15 January 2026. This boundary was chosen to reflect contemporary surgical techniques, implant designs, fixation strategies, and health-economic methods. The structured search window for study identification extended through 15 January 2026, which served as the final cut-off date for study inclusion.

4.3. Search Strategy and Keywords

Database-specific search formulations, date limits, and supplementary identification rules used for the structured search are summarized in Supplementary Table S1. Search terms covered three concepts: (1) knee osteoarthritis, (2) HTO/UKA procedure terms and synonyms, and (3) economic evaluation and costing terms. For Google Scholar, simplified relevance-ranked queries were used because of platform limitations, and screening was limited a priori to the first 100 results per query on the search date. Supplementary Google Scholar records were subjected to the same eligibility criteria as records identified from the primary databases, but were not used as the basis for formal database-yield counts.

4.4. Eligibility Criteria

Studies were eligible for the core synthesis if they met all of the following criteria: (1) involved adults with medial-compartment knee osteoarthritis treated with HTO and/or UKA; (2) reported a direct economic comparison between HTO and UKA or comparative cost/resource-use data with clear decision relevance to the HTO–UKA choice (e.g., index episode costs, reoperations, revisions, or conversion-to-TKA pathways); and (3) reported at least one interpretable economic design element, such as analytic perspective or payer context, time horizon or follow-up window, costing basis, currency year, or explicit definitions of revision, conversion, or reoperation. Purely technical surgical studies without extractable economic or resource-use data were excluded. Burden and cost-of-illness studies were not included in the core comparative synthesis and were used only for contextual framing in the Introduction and Discussion.

4.5. Study Selection Process

Records identified from the primary database searches were deduplicated before screening. Title/abstract screening and full-text eligibility assessment were performed by one reviewer (F.Y.) using prespecified criteria. To improve consistency, all potentially eligible full texts underwent a second eligibility check after the extraction framework had been finalized. Google Scholar and citation-tracing records were subjected to the same full-text eligibility criteria but were handled as supplementary identification sources rather than formal database-yield records. Because the review was narrative and screening was single-author, inter-reviewer agreement statistics were not generated; this is acknowledged as a limitation.

4.6. Data Extraction and Data Items

From eligible studies, the following data were extracted when available:

Study identification: author, year, country/health system context;

Study design: model-based vs. trial-based vs. observational/claims/registry vs. cost-of-illness;

Population/indication: KOA definition (symptomatic vs. radiographic when provided), compartment phenotype (medial/lateral/patellofemoral), age/eligibility criteria;

Intervention/comparator details: HTO technique (opening-wedge vs. closing-wedge when specified), UKA type, revision/conversion definitions, setting (inpatient, hospital outpatient, or ambulatory surgery center (ASC);

Economic framework: perspective (payer/healthcare sector/societal), time horizon, discount rate, cost year/currency, and costing approach (micro-costing, time-driven activity-based costing (TDABC), reimbursement-based, charge-based, claims-based);

Outcomes: total and incremental costs, QALYs/QALMs/utility values, ICERs, cost-effectiveness acceptability results, and key sensitivity/threshold findings;

Drivers and assumptions: revision risk, conversion-to-TKA probabilities, complication profiles, utility mapping methods (e.g., KOOS/WOMAC to EQ-5D), and assumptions related to duration of benefit for nonoperative interventions.

When cost values were reported in different currencies and years, values were retained as presented in the source studies to avoid introducing misleading cross-country comparability. Currency year and costing basis were recorded where reported to support interpretability.

4.7. Synthesis Framework

Evidence was synthesized in two strata: (i) head-to-head economic evaluations directly comparing HTO and UKA, and (ii) comparative real-world cost/resource utilization studies describing major cost drivers that determine the HTO–UKA economic conclusion (site-of-service/episode costing for UKA; reoperations, complications, and conversion-to-TKA pathways for HTO). Due to heterogeneity in costing methods, follow-up windows, currencies, and endpoints, no quantitative pooling was performed.

4.8. Methodological Credibility Assessment

Given the heterogeneity of the included evidence (decision-analytic models, registry or claims studies, and comparative cost analyses), we did not apply a single aggregate risk-of-bias score or cross-design level-of-evidence ranking in the main synthesis. Instead, each study was interpreted across common credibility domains: analytic perspective, time horizon, discounting, costing basis, utility source or mapping method, definition of downstream events, and extent of sensitivity or uncertainty analysis. These domains were used to structure the comparative synthesis and to explain why superficially similar studies could reach different economic conclusions.

4.9. Ethics and Data Availability

Ethics approval was not required because the review was based exclusively on published literature. All data synthesized were derived from publicly available sources and are cited in the manuscript reference list.

5. Conclusions

HTO and UKA each appear economically attractive under specific and defensible conditions, but the current evidence base does not justify a universal ranking between them. The direction of preference changes with analytic perspective, time horizon, site of service, costing basis, and assumptions regarding reoperation, revision, and conversion to TKA. Accordingly, this review should be read as identifying the major drivers of comparative value rather than as establishing a single preferred procedure. Future comparative analyses should use contemporary pathway data from the target health system, explicit definitions of downstream events, and standardized costing and preference-based utility methods.