1 Introduction

Osteoarthritis (OA) represents a mounting global health challenge, with its prevalence surging over recent decades. In 2020, an estimated 7.6% of the world's population—roughly 595 million individuals—were affected by OA, a stark rise from the 4.8% (approximately 256 million people) recorded in 1990, marking a more than 132% escalation in cases.¹ Projections from systematic analyses indicate that knee OA incidence could climb by nearly 75% by 2050, reaching 59.4 to 89.9 cases per 100,000 individuals¹. This escalating burden underscores the urgent need for effective interventions, particularly as aging demographics amplify demand for knee arthroplasty procedures. Life expectancy at birth in India is currently estimated at approximately 72 years, which remains considerably lower than that of high-income Western nations, where average life expectancy commonly exceeds 78–80 years across OECD member countries.^2,3 As a result, individuals aged 75 years and above in India represent a comparatively older segment of the population, having already surpassed the national average lifespan. Evaluating outcomes of knee arthroplasty in Indians aged ≥75 years is therefore particularly important, as this group occupies the extreme upper end of the national life-expectancy distribution and is often perceived as high risk for surgical intervention.

Epidemiological data on total knee arthroplasty (TKA) in the United States, as outlined by Kurtz et al., forecast a dramatic uptick in procedural volumes: primary TKA cases are expected to hit 1.37 million annually by 2020 and soar to 3.48 million by 2030.⁴ Paralleling this trend, the population aged 80 and older is projected to double by 2035,⁵ driving a parallel surge in arthroplasty needs within this demographic.⁶ However, elderly patients in this cohort often contend with multifaceted comorbidities and diminished physiological reserves, rendering surgical interventions more complex and fraught with risks.⁷ Following TKA, these individuals face heightened vulnerabilities, including extended hospital stays, elevated readmission frequencies, and a greater incidence of perioperative adverse events.^8,9

In response to these challenges, unicondylar knee arthroplasty (UKA) emerges as a compelling therapeutic avenue for individuals with isolated unicompartmental knee degeneration, such as medial compartment arthritis. As a minimally invasive, bone- and soft tissue-preserving technique, UKA confers substantial advantages, including abbreviated hospital durations, diminished complication profiles, and lower readmission likelihoods postoperatively.^10,11 These attributes position UKA as an especially pragmatic choice for geriatric patients harbouring unicompartmental disease, mitigating the deconditioning hazards associated with TKA, such as those stemming from extended immobilization, hospitalization, or reduced mobility. These can precipitate functional decline and dependency in vulnerable older adults.^12–14

We aim to answer the following reserch questions in this study:RQ1What are the mid-term improvements in functional outcomes, as measured by the American Knee Society Score—Functional subscale (AKSS-F), following mobile-bearing unicompartmental knee arthroplasty (MB-UKA) in Indian patients aged ≥75 years?RQ2What levels of patient-reported satisfaction and joint awareness, assessed via the Forgotten Joint Score-12 (FJS-12), are achieved at 3 years post-MB-UKA in this multimorbid elderly population?RQ3What is the incidence of major perioperative complications, revisions, or readmissions in elderly Indian patients undergoing MB-UKA?RQ4How does the prevalence of common comorbidities (e.g., hypertension and diabetes) influence the overall functional and satisfaction outcomes in this cohort?

2 Materials and methods

Following institutional review board approval (IEC no. IAH-BMR/063/11-25), we conducted a retrospective analysis of data from patients aged 75 years or older who underwent primary unilateral or bilateral medial mobile-bearing unicondylar knee arthroplasty (MB-UKA), using Zimmer Biomet Oxford® Partial Knee Microplasty® Implants between January 2018 and December 2023. All procedures were executed by a single senior surgeon at a high-volume tertiary care centre, ensuring procedural consistency and expertise.

For this study, the age cut-off of 75 years was deliberately chosen as this threshold exceeds the current average life expectancy of 72 years in India and thus represents an advanced elderly cohort within the national demographic context. Patient selection adhered to rigorous inclusion criteria to optimize outcomes in this cohort. Eligible individuals presented with isolated Kellgren-Lawrence (KL) grade IV OA confined to the medial compartment, varus deformity <10°, and flexion contracture <10°. Inclusion required clinical stability of cruciate and collateral ligaments, preserved full-thickness cartilage in the lateral tibiofemoral compartment, and ≤grade III OA changes in the lateral patellofemoral compartment, confirmed via intraoperative inspection. Exclusion criteria encompassed prior complex knee surgery, significant trauma, inflammatory arthritis, body mass index >40 kg/m², ligamentous instability, or grade IV cartilage loss in the lateral compartments. Preoperatively, all patients underwent comprehensive medical optimization per the institution's standardized joint arthroplasty pathway, minimizing perioperative risks.

3 Results

This study encompassed a cohort of 23 Indian cohorts (75 years and above) who underwent a total of 32 primary MB-UKA between 2018 and 2023. The mean age at the time of surgery was 76.9 ± 2.0 years (75-82years), with a near-equitable gender distribution comprising 12 males (52.2%) and 11 females (47.8%). The average body mass index (BMI) stood at 26.6 ± 3.4 kg/m², indicative of a moderately overweight. Regarding surgical laterality, procedures were distributed as follows: nine (39.1%) on the right knee, five (21.7%) on the left, and, notably, nine patients (39.1%) received bilateral simultaneous MB-UKAs, highlighting the feasibility of staged or concurrent interventions in appropriately selected individuals without escalating risks.

Comorbidity profiling revealed a predictable burden of age-related conditions. Hypertension emerged as the predominant comorbidity, affecting 14 patients (60.9%), a prevalence reflective of cardiovascular vulnerabilities in this age group. Diabetes mellitus followed in seven patients (30.4%), consistent with rising metabolic syndrome trends in urban Indian settings. Less frequent were hypothyroidism in three patients (13.0%) and coronary artery disease in one (4.3%), collectively illustrating a multimorbid yet optimized population that tolerated the procedure well.

3.1

3.1 Clinical outcomes

The analysis of this study demonstrated robust and sustained enhancements in knee function and patient satisfaction, affirming UKA's efficacy in mitigating age-related functional decline. Functional performance, as measured by the AKSS-F, exhibited marked progressive improvement across all postoperative intervals, a trajectory that not only achieved statistical significance but also translated to clinically meaningful gains. Preoperatively, the cohort's mean AKSS-F was 47.8 ± 2.4, emblematic of severe functional limitation due to medial compartment osteoarthritis, with patients reporting substantial pain, stiffness, and ambulatory restrictions. By the 6-month mark, this had ascended to 57.2 ± 3.5, signalling early recovery in daily activities such as walking and stair navigation. Momentum persisted, yielding 65.4 ± 2.8 at 1 year, 71.3 ± 2.9 at 2 years, and culminating in a mean of 77.1 ± 3.0 at 3 years, representing a net 61.3% uplift from baseline. Every paired comparison (preoperative versus each follow-up) yielded p < 0.001, indicating the reliability and consistency of these gains, attributable to UKA's tissue-sparing nature that facilitates rapid rehabilitation and neuromuscular retraining in elderly patients.

These temporal dynamics are presented in Table 1. There was a stepwise progression, with low variability (SD ranging from 2.4 to 3.5) attesting to uniform responses across the cohort. Notably, the repeated listings for 6-month, 1-year, and 2-year intervals (each paired with preoperative) emphasize the robustness of early and mid-term improvements, while the 3-year versus preoperative pairing highlights long-term durability.

Table 1 Functional outcomes assessment using the American Knee Society Score (AKSS-F) showing significant improvement at each postoperative follow-up, compared to preoperative scores.

Parameters	Mean	Standard Deviation (SD)	p-value
AKSS - Preoperative	47.8	2.4	<0.001
AKSS - 6 months	57.2	3.5
AKSS - 6 months	57.2	3.5	<0.001
AKSS - 1 year	65.4	2.8
AKSS - 1 year	65.4	2.8	<0.001
AKSS - 2 year	71.3	2.9
AKSS - 2 year	71.3	2.9	<0.001
AKSS - 3-year	77.1	3.0
AKSS - Preoperative	47.8	2.4	<0.001
AKSS - 3-year	77.1	3

At the 3-year endpoint, AKSS-F scores spanned a tight range of 70–82 (mean 77.1 ± 3.0), classifying outcomes as excellent per Knee Society criteria (>80 ideal, 70–79 good), with minimal dispersion indicating equitable benefits irrespective of baseline comorbidities or bilaterality. Complementing this objective metric, PROMs via the FJS-12 illuminated subjective dimensions, revealing a mean of 87.8 ± 2.8 (range 84–94). This high FJS-12 threshold, well above the 70-point benchmark for "forgotten" joint perception, evidences profound satisfaction and negligible awareness of the implant during routine activities, a testament to UKA's kinematic fidelity in restoring near-native knee mechanics (Table 2). The compact format confirms the cohort's homogeneity: tight ranges (AKSS-F: 12-point span; FJS-12: 10-point span) and low SDs (<3.0) suggest that even frail cohorts achieved "excellent" joint function.

Table 2 Functional and Patient-Reported Outcome Measures (PROMs) at three-year follow-up showing high American Knee Society Score (AKSS) and forgotten joint score (FJS).

Parameters	Minimum	Maximum	Mean	Standard Deviation (SD)
AKSS (3 year)	70	82	77.1	3.0
FJS (3 year)	84	94	87.8	2.8

Fig. 1 demonstrates an obvious ascent in functional recovery as a line graph plotting the mean AKSS-F against time points from preoperative to 3 years. The upward trajectory, starting at ∼48 and plateauing near 77, mirrors a classic learning curve of postoperative adaptation, with steeper inclines in the first year reflecting accelerated gains from minimized surgical trauma, followed by gentler stabilization indicative of enduring stability. Error bars (implied by SDs) would further affirm precision, rendering the figure an intuitive narrative of resilience.

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Fig. 1 Mean American Knee Society Score (AKSS), at preoperative and follow-up of six months, one year, two years and three years, showing progressive improvement.

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4 Discussion

The findings of this mid-term analysis affirm the efficacy of MB-UKA as a transformative intervention for isolated medial compartment OA in septuagenarian and octogenarian Indian cohorts, a demographic often deemed high-risk due to advanced age and comorbid burdens. Over a 3-year follow-up, our cohort of 23 cases (mean age 76.9 years) demonstrated substantial, progressive enhancements in functional outcomes, with the AKSS-F) surging from a preoperative mean of 47.8 ± 2.4 to 77.1 ± 3.0 at final assessment (p < 0.001), alongside exemplary PROMs via the FJS-12, averaging 87.8 ± 2.8 (range 84–94). This trajectory not only signifies a 61% relative improvement but also reflects clinical excellence, with scores surpassing "good" thresholds (>70) and evoking minimal joint awareness during activities of daily living. Critically, the absence of major perioperative complications, revisions, or readmissions implies MB-UKA's favourable safety profile, mitigating the fears inherent to more invasive alternatives.

These results resonate strongly with global literature, reinforcing UKA's superiority over TKA in elderly cohorts, particularly regarding expeditious recovery and reduced morbidity. Newman et al.'s randomized trial of 102 knees with unicompartmental arthritis reported lower perioperative blood loss, shorter hospital stays, and diminished complication rates with UKA versus TKA at 5 years, advantages amplified in older patients susceptible to postoperative frailty.¹⁸ Echoing this, Lombardi et al. documented accelerated ambulation and superior early functional scores in MB-UKA recipients, attributing gains to preserved ligaments and kinematics that expedite neuromuscular adaptation. These benefits are pivotal for septuagenarians and octogenarians who are vulnerable to immobility-induced decline.¹⁸ Our observed AKSS-F plateau at 77.1 aligns closely with Berend et al.'s mid-term scores of 72–80 in elderly medial UKA patients, where tissue-sparing design similarly curbed rehabilitation demands.¹⁹ In contrast, TKA studies in those over 75 years often reveal protracted recovery and score stagnation, linked to extensive dissection and higher insult [⁸,²⁰]. On patient-centered metrics, our elevated FJS-12 corroborates Behrend et al.'s validation of the tool, wherein UKA yielded markedly higher scores than TKA, denoting "forgotten" joint perception and heightened satisfaction.¹⁷ Wilson et al.'s meta-analysis further substantiates this, highlighting UKA's edge in joint proprioception and quality-of-life gains over matched TKA groups.²¹

Implant durability in the elderly, a perennial concern, finds robust validation here: zero revisions at 3 years concurs with Pandit et al.'s 95% + 10-year survivorship in MB-UKAs, where advanced age emerged as protective rather than prognostic for failure, owing to subdued activity demands.²² Zuiderbaan et al. similarly discerned no age-stratified revision disparities in medial UKA, emphasizing indication adherence over chronology.²³ Complication sparsity mirrors registry data; Liddle et al.'s analysis of 101,330 matched cases showed UKA's halved risk of thromboembolism, infection, and medical events versus TKA,²⁴ while Hunt et al. pegged 45-day mortality at <0.1% post-UKA.²⁵ Brown et al.'s multicenter review echoed our nil major events, reporting 30-day readmissions <1% in elderly UKA versus 3–5% for TKA.²⁶

Within the Indian context, where OA burdens are escalating amid demographic aging and metabolic comorbidities, UKA data remain sparse, particularly for those ≥75 years. An important contextual factor in interpreting our findings is the disparity in life expectancy between India and Western countries. While a 75-year-old patient in many OECD nations lies close to the average expected lifespan, an Indian patient of the same chronological age has already exceeded national life expectancy by several years [²,³]. Consequently, Indian patients aged ≥75 years may be considered biologically older relative to their Western counterparts and are more likely to present with accumulated comorbidities and reduced physiological reserve. Despite this demographic disadvantage, our cohort demonstrated excellent functional outcomes, high patient satisfaction, and an absence of major complications following MB-UKA. These findings suggest that chronological age alone should not be viewed as a contraindication to UKA and highlight the need for population-specific interpretation of age thresholds in arthroplasty decision-making, particularly in low- and middle-income countries (LMIC) with lower life expectancy benchmarks [²⁷,²⁸].

Our outcomes harmonize with emerging evidence, advocating expanded utilization. Marya and Thukral's (2013) cohort of 45 octogenarians (mean age 83 years, 64 knees) with predominant medial involvement reported parallel KSS elevations (clinical: 46 to 81; functional: 24 to 73) and 96.4% implant survival at 72 months, with only 3.6% revisions for progression or fracture, mirroring our complication-free profile and affirming UKA's viability despite tricompartmental tendencies in Indian phenotypes.²⁹ More recently, Poudel et al.'s (2024) retrospective of 94 Indian patients (mean age 67.2 years) yielded KOOS improvements from 39.2 to 73.8 (p < 0.001) and FJS-12 of 75.7 at 5 years, alongside 92% survivorship; slightly tempered versus our figures, possibly due to broader age inclusion, yet substantiating consistent midterm gains in diverse Indian subgroups.³⁰ Kulshrestha et al.'s 2017 randomized trial, though in younger Indians (mean ∼60 years), still evidenced UKA's pain reduction and functional parity with TKA, suggesting scalability to elders.³¹ These studies align with our hypothesis, positing UKA's lower morbidity as a bulwark against India's rising geriatric arthroplasty needs, where TKA dominates but exacts higher tolls in multimorbid settings. A recent systematic review confirms that UKA in patients aged 80 years and older leads to significant improvements in pain relief and functional outcomes, with marked enhancement in knee performance. It further shows low complication and revision rates, with five-year implant survival exceeding 93%, supporting UKA as a safe and durable option for carefully selected octogenarians with isolated unicompartmental OA³².

This study's strengths lie in its targeted focus on an underrepresented Indian elderly niche, leveraging stringent selection (e.g., <10° varus, intact ligaments) and single-surgeon execution to minimize confounders, alongside standardized, prospective data capture for AKSS-F and FJS-12, enhancing internal validity and generalizability to similar resource-constrained, high-comorbidity contexts. The 39% bilateral rate further illustrates procedural tolerability, rare in global elderly reports. This study presents a unique perspective on UKA in elderly population of Indian subcontinent.

Notwithstanding, limitations temper extrapolation: the retrospective design, only Indian cohorts, single surgeon's cases, and modest sample (n = 23) curtail causal inference and power for subgroup analyses (e.g., by comorbidity). Absence of a contemporaneous TKA comparator precludes direct benchmarking, while omission of radiographic metrics (e.g., alignment, osteolysis) and extension beyond 3 years leaves long-term survivorship unprobed, given progression risks in Asians. Lastly, self-reported FJS-12, though validated, may undercapture subtle disparities in low-literacy cohorts.

Future directions should prioritize multicenter, prospective Indian trials with larger cohorts (n > 100) to dissect age-comorbidity interactions, incorporating TKA controls and advanced imaging (e.g., Computed Tomography (CT) for wear). Integrating cost-efficacy analyses could sway policy toward UKA in public health systems, while biomechanical studies on mobile-bearing kinematics in Indian anthropometrics might refine implants. Ultimately, these endeavors could destigmatize UKA in elders, offering equitable access amid India's osteoarthritis epidemic.

5 Conclusion

This mid-term analysis confirms the substantial benefits of mobile-bearing unicondylar knee arthroplasty (MB-UKA) in older Indian patients (75 years and above) with isolated medial compartment osteoarthritis, demonstrating marked improvements in functional scores and high patient satisfaction. The procedure's tissue-sparing design facilitated rapid recovery, with no major complications, revisions, or readmissions. These outcomes challenge chronological age as a barrier to UKA in carefully selected cases. Considering India's lower life expectancy, the excellent functional outcomes and safety profile of MB-UKA in patients aged ≥75 years underscore that advanced chronological age alone should not be considered a contraindication when patients are appropriately selected. Further prospective and multicentric studies on larger cohorts are needed to validate the conclusions of this study.

Ethical approval

We took the Institutional Ethical approval for this study ((IEC no. IAH-BMR/063/11-25).

Authors’ credit statement

•YG: Conceptualization, Literature Search, Methodology, Results, Manuscript writing, editing and final approval.•RV: Conceptualization, Literature Search, Methodology, Results, Manuscript writing, editing and final approval.•RS: Data Collection, Literature Search, Manuscript writing, editing and final approval.•VB: Literature Search and Analysis, Manuscript writing, editing, and final approval.•AV: Literature Search and Analysis, Manuscript writing, editing, and final approval.

Consent

All patients gave an informed consent regarding their anonymized data been used for publication. Moreover, an Institutional ethical approval was taken for this study.

Use of an AI tool

We used Grammarly to enhance the readability and improve the English grammar of the manuscript. However, the final version was rechecked, and the authors take full responsibility for its contents.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.