Current evidence on medial unicompartmental knee arthroplasty in patients 60 and younger: a narrative review

Introduction

Background

Knee osteoarthritis (OA) is a progressive degenerative joint disease significantly affecting quality of life and functional mobility. In the United States, symptomatic knee OA affects over 14 million adults, with a median age of diagnosis at approximately 55 years. Furthermore, 10% of adults 60 years and older will experience symptomatic knee OA (1). Knee OA is associated with substantial economic costs, with annual per-patient expenses ranging from $1,442 to $21,335, a figure steadily increasing (1). Total knee arthroplasty (TKA) remains the gold standard treatment for end-stage OA in older adults, offering implant survivorship exceeding 15 years (2). However, concerns regarding implant durability, activity limitations, and future revisions have led to the exploration of joint-preserving procedures for younger, active patients.

Effective management of knee OA requires an understanding of knee anatomy and biomechanics. The knee primarily functions as a hinge joint, composed of the distal femur, tibial plateau, patella, and fibular head. It moves along three primary axes: flexion-extension in the sagittal plane, internal-external rotation of the tibial plateau in the axial plane, and patellar tracking within the trochlear groove (3). Stability is maintained primarily by the anterior and posterior cruciate ligaments (ACL, PCL), and medial and lateral collateral ligaments (MCL, LCL). Patellar alignment is supported by the medial patellofemoral ligaments, patellar tendon, trochlear groove and tibial tubercle. Specifically, the integrity and tensioning of the MCL is important for stability of the medial compartment and durability of implants (4). Coronal plane alignment, defined by a mechanical axis extending from the femoral head to the tibial plafond, significantly influences load distribution within the joint. The natural varus alignment of the knee, results in medialization of the mechanical axis, increasing mechanical stress and accelerating medial compartment cartilage degeneration (5). As a result, isolated medial compartment OA has been reported to be the most prevalent form of knee OA (5).

Initial management of isolated medial compartment OA typically involves conservative interventions such as activity modification, nonsteroidal anti-inflammatory medications, physical therapy, corticosteroid injections, and viscosupplementation. While effective for symptom relief, these treatments do not alter disease progression (6,7).

For mild to moderate arthritis with focal cartilage defects, cartilage-preserving procedures including microfracture, mesenchymal stem cells, matrix-induced autologous chondrocyte implantation and osteochondral autograft/allograft transplantation are available. Osteochondral allograft (OCA) transplantation, is often considered for patients with osteochondral lesions larger than 2 cm × 2 cm. While often regarded as a salvage procedure, OCA has demonstrated promising results, with Nielsen et al. reporting survivorship rates of 91% and 89% at 5 and 10 years, respectively, with over 75% returning to sport (8,9).

Treatment options such as high tibial osteotomy (HTO) and implantable shock absorbers (ISAs) function to alter load distribution for symptomatic relief in young patients with isolated medial compartment OA (10,11). HTO is a well-established procedure aimed at redistributing load away from the medial compartment through realigning the mechanical axis of the knee (12). Survival rates of HTO have been reported to be 95%, 79%, and 56% at 5, 10, and 15 years respectively (13). Guarino et al. reported approximately 13% of HTO patients underwent subsequent TKA within 12 years (14). Though HTO demonstrates good medium-term results, it involves a prolonged rehabilitation period which may not be suitable for young patients wanting a quick return to activity. ISA is newer approach to managing isolated medial knee OA in younger patients, by reducing compressive forces to the medial compartment. Gomoll et al. demonstrated an 85% survival rate at 5 years in patients with ISA implants, without requiring conversion to knee arthroplasty or HTO (10). Though this has expanded the treatment landscape it remains constrained by selective patient factors and calls for more comprehensive research.

Unicompartmental knee arthroplasty (UKA) is a good surgical option for isolated medial compartment OA. UKA offers greater bone preservation, more closely replicates normal knee kinematics through preservation of ligaments, such as the ACL and PCL, and offers faster post-operative recovery when compared to TKA (15). UKA has been shown to have a survivorship of 98% and 91% at 10 and 20 years respectively (16,17). Modern UKA implants include fixed-bearing and mobile-bearing designs. Fixed-bearing implants secure the polyethylene insert to the tibia, whereas mobile-bearing implants allow polyethylene mobility, potentially enhancing range of motion (ROM) and reducing wear (18).

Rationale and knowledge gap

In younger, active patients, joint-preserving alternatives such as HTO or cartilage restoration procedures often involve prolonged rehabilitation, restricted weight-bearing, and inconsistent return to preoperative activity levels (19). UKA, however, allows for immediate postoperative weight-bearing, shorter rehabilitation periods, and greater preservation of bone stock compared to TKA, presenting significant advantages for younger athletic populations (19,20). Despite these clinical benefits, concerns persist regarding the longevity of UKA implants and their performance under the high functional demands typical in younger patients (19). Although contemporary studies demonstrate favorable short- to mid-term functional outcomes and high return-to-sport rates, uncertainties regarding long-term survivorship and suitability for high-impact activities remain, highlighting the necessity for ongoing research in this specific patient demographic (21).

Objective

The objective of this study is to provide a comprehensive review of the current literature focusing on outcomes for patients ≤60 years who underwent medial UKA for symptomatic knee OA. We present this article in accordance with the Narrative Review reporting checklist (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-29/rc).

Methods

A literature review was conducted on February 28, 2025 and again on June 20, 2025, to identify current studies examining outcomes of medial UKA specifically in younger patient populations. For the purposes of this review, “young” was defined as patients aged 60 years or younger, consistent with the focus requested in the editorial invitation and aligned with common age cutoffs used in relevant orthopedic literature. Though a narrative review does not require a complete review of all literature available a structured approach was carried out to provide an up to date and comprehensive review.

The electronic database PubMed, MEDLINE, and SPORTDiscus was searched using the following Boolean search terms: (medial) AND (unicompartmental) AND (knee) AND (arthroplasty) AND (young OR ≤60 OR under 60 OR age 60). The search was limited to English-language articles published between January 1, 2015, and June 20, 2025. Titles and abstracts were screened for relevance. Selected studies were then reviewed by full texts to ensure that included studies met the following inclusion criteria: (I) original research studies evaluating outcomes of medial UKA; (II) patients aged ≤60 years or studies that provided separate age-stratified data for this subgroup; and (III) indications limited to medial compartment knee OA.

Studies were excluded if they were review articles, case reports, technical notes, studies involving concomitant procedures (e.g., ACL reconstruction), or if they focused on lateral UKA, patellofemoral arthroplasty, or patients older than 60 years without distinct stratification for the ≤60 years subgroup. A total of 19 studies met the final inclusion and exclusion criteria. The primary outcome variables extracted from each study included: Implant survivability, statistically significant postoperative patient-reported outcome measures (PROMs) (P<0.05), postoperative ROM at final follow-up, return-to-activity or return-to-sport rates, sample size, implant type, and mean follow-up duration. These methods are demonstrated in Table 1.

Results

Patient demographics and cohort characteristics

Across the 19 included studies, a total of 2,510 patients (2,687 knees) underwent medial UKA. The majority of studies specifically targeted younger patients under the age of 60 years (21-32). Several investigations focused more narrowly on subgroups under age 50 or 55 years, reflecting growing interest in the viability of medial UKA in increasingly active and younger populations (33-39). Although inclusion criteria varied slightly, nearly all studies selected patients with isolated medial compartment OA, preserved ACL, and correctable varus deformity—often less than 15 degrees. Most excluded patients with inflammatory arthritis or lateral/patellofemoral joint involvement (31,33,35).

Implant survivorship

Survivorship outcomes for medial UKA in patients ≤60 years reported in the past decade generally indicate favorable mid-term (3–5 years) to long-term (>7 years) results. Mid-term survivorship was consistently high, with rates exceeding 96%. Wang et al. reported a 99% survival rate at 3 years (28), Lo Presti et al. reported 100% at four years (23), and Streit et al. noted 97% at 5 years (26). Long-term outcomes were also favorable, with eight of the 19 studies reporting survivorship greater than 90% at 10 years (21,24,25,30,31,33,38,39). Walker et al. demonstrated a survival rate of 96.6% at 6.5 years and 91.7% at 10 years in patients under 50 receiving mobile-bearing implants (39). In a cohort of 183 UKAs in active patients under 55 years old, Krych et al. observed 94% survivorship at a mean of 5.8 years, reinforcing durability even in active populations (37). Comparable outcomes were reported by Martín et al. with a 95% survival rate at 12 years (24), and by Kim et al., who reported survivorship rates of 97.4% at 7 years and 94.7% at 10 years (21).

Fixed-bearing implants also demonstrated robust long-term performance: Mannan et al. reported 92.9% survival at 10 years (25), and Calkins et al. observed 90.4% at 10 years, though survivorship decreased to 75.1% at 19 years, highlighting reduced longevity with extended follow-up (33). Similarly, Koch et al. reported declining survival rates in 119 knees—86.7% at 15 years and 81.7% at 17.5 years (22). Collectively, these findings suggest that both mobile-bearing and fixed-bearing medial UKA can achieve strong mid- to long-term durability.

Functional outcomes

Functional improvement following medial UKA was consistently demonstrated across all studies, measured through standardized outcome scores. Wang et al. reported significant gains in Oxford Knee Score (OKS) (14.4 to 40.0), Hospital for Special Surgery (HSS) score (56.0 to 85.7), and Visual Analog Scale (VAS) pain score (5.2 to 1.1) at a mean follow-up of 3 years, all with P values <0.05(28). Walker et al. observed a similar mean OKS improvement from 26.7 to 40.9 at 3.4 years (39). Other studies echoed these findings: Koch et al. and Kennedy et al. both reported significant gains in Knee Society Scores (KSS) at long-term follow-up (22,31). Faour Martín et al. found American Knee Society Knee Score increased from 53.4 to 91.6 and Function Score from 51.6 to 89.2 at 12 years postoperatively (P<0.01), underscoring consistent symptomatic relief and functional enhancement (24).

Functional results were similar between mobile-bearing and fixed-bearing implants. Kim et al. demonstrated significant improvement in mean KSS at a mean of 8.9 years postoperatively for patients ≤60 years who underwent mobile-bearing UKA (60.4 vs. 94.2; P<0.001) (21). Similarly, Greco et al. observed mean KSS improvement from 37.3 to 86.5 at 6 years (P<0.001), further supporting medial UKA’s effectiveness in younger populations (35). Fixed-bearing implants showed comparable results: Mannan et al. reported that 97% of patients were pleased or very pleased at 15 years postoperatively (25), and Calkins et al. demonstrated an increase in mean KSS from 51.9 to 88.6 at a mean follow-up of 11.2 years (P<0.001) (33).

ROM

ROM at final follow-up ranged from 116° to 137.9° across the included studies (21,22,24,26,28,32-35,39). Streit et al. reported a statistically significant increase from 113.3° preoperatively to 129° postoperatively (26). Wang et al. found similar gains from 103.7° to 116°, and Walker et al. observed improvement from 118° to 125° (28,39). These results demonstrate consistent improvement in knee motion following medial UKA, reinforcing its suitability in active younger patients.

Return to activity

Return to physical activity strongly influences patient satisfaction and perceived success of medial UKA, particularly in younger, active cohorts. Two studies examined return-to-sport rates at mid-term follow-up (mean 4–4.4 years), reporting high overall resumption rates (23,27). Walker et al. reported a 93% return-to-activity rate, with approximately two-thirds of patients aged ≤60 years achieving high postoperative activity levels [University of California Los Angeles (UCLA) score ≥7] (27). However, there was a marked shift toward low-impact activities (e.g., cycling, swimming, hiking), while participation in high-impact sports—such as soccer, skiing, tennis, and jogging—significantly decreased. This reduction was primarily attributed to precautionary behavior to preserve the prosthesis. Pain or ROM limitations were rarely reported as reasons for reduced participation (27).

Lo Presti et al. similarly found a 90% return-to-sport rate, with no cases of implant failure or revision (23). While patients maintained preoperative activity frequency and duration, a clear shift toward lower-impact sports was again observed. High-impact participation decreased, largely due to patient preference rather than functional limitations. These findings suggest medial UKA is appropriate for younger active patients, though continued caution around high-impact sports was carried out due to theoretical risks of accelerated polyethylene wear and implant loosening.

Complications and revision rates

Despite favorable survivorship and outcomes, complications and revision risk remain relevant considerations. Revision rates were generally low, typically below 10% at mid- to long-term follow-up. The most common indication for revision was unexplained persistent pain. Calkins et al. reported a 14.3% revision rate at approximately 14 years, with unexplained pain accounting for 7 of 11 revisions (33). Walker et al. observed a 9.2% revision rate, primarily due to progression to lateral compartment OA and persistent pain (39). Wang et al. reported a 0.9% revision rate at 3 years, also due solely to unexplained pain (28). Faour Martín et al. and Streit et al. similarly identified unexplained pain as a leading cause of revision, underscoring the need for careful patient selection and vigilant postoperative follow-up (24,26).

Other reported reasons for revision included aseptic loosening, bearing dislocation, and medial joint collapse. Greco et al. reported a 5.8% revision rate, mainly from aseptic loosening (35). Kim et al. identified bearing dislocation and tibial collapse as primary revision causes, though the overall revision rate remained low (6.1%) (21). These findings highlight the importance of understanding UKA-specific risks to optimize outcomes and improve preoperative counseling.

The findings of the 19 studies selected for review are summarized in Table 2.

Discussion

Indications

The use of medial UKA in younger patients has long been controversial. Historically, medial UKA was indicated primarily for older, lower-demand patients (age >60 years) presenting with symptomatic isolated medial tibiofemoral OA, intact knee ligaments, minimal (<5°) and correctable varus deformity, no lateral joint line tenderness, and body weight under 82 kilograms due to concerns about implant durability and mechanical failure (39). However, patient selection criteria for medial UKA have expanded in recent years. Contemporary studies have demonstrated favorable outcomes in more active patients younger than 60 years, individuals with a BMI up to 35 kg/m², patients with ACL deficiency, those with concomitant patellofemoral OA, and patients with varus deformity up to 10 degrees (15). These broadened indications are supported by advances in surgical technique, improvements in implant design, enhanced durability, and accumulating evidence supporting successful outcomes in populations that were traditionally considered contraindicated. While mobile-bearing implants theoretically offer advantages such as increased ROM and reduced polyethylene wear, studies have shown comparable survivorship and patient-reported outcomes relative to fixed-bearing implants—even among younger and active patient groups (21,25,26,33,39). Collectively, the studies included in this review suggest that, when performed in appropriately selected patients, medial UKA offers durable outcomes, substantial functional improvement, and a low complication profile—even in patients younger than 60 years, and in some cases, younger than 50 years.

Reassessing longevity and implant survival in the young

UKA modes of failure include polyethylene wear, instability, fracture, infection, and osteolysis leading to loosening. A failure mode specific to UKA (compared to TKA) is progression of OA in the untreated compartments (15). Over time, implant design and surgical technique have improved significantly. Enhancements in polyethylene crosslinking, in particular, have reduced early failures previously attributed to wear (15). One of the most frequently cited arguments against UKA in young patients has been the concern for early implant failure due to increased activity levels and higher functional demands. Yet, several contemporary studies now report survivorship rates for medial UKA that rival those observed in older populations. In patients ≤50 years, Walker et al. demonstrated a 10-year survivorship of 91.7% (39), and Lee et al. reported 96% survival at 10 years in patients under ≤55 years (38). Similar figures were reported by Kim et al., who found 94.7% survivorship at 10 years (21), and by Hamilton et al., who observed 94.8% survivorship at 15 years—a particularly impressive figure in a younger population (30). The consistency of these findings across institutions, implant designs, and geographic regions suggests that longevity in UKA may depend more on surgical technique and patient selection than on age alone (38).

Importantly, studies of military or highly active cohorts—such as Rodkey et al., which showed 86.3% survivorship at 6.3 years in patients under 55—reinforce the notion that UKA can tolerate significant physical stress when implanted in a well-aligned, well-functioning knee (36). These outcomes challenge the notion that age is an independent contraindication to UKA and instead promote a more nuanced, indication-driven approach to surgical decision-making.

Functional recovery and return to activity

Improvement in pain and function following UKA in young patients was uniformly reported across the studies included in this review. Wang et al. observed large, statistically significant gains in OKS, ROM, and VAS pain scores (28)—findings consistent with those of Walker et al. (39), Koch et al. (22), and others. Notably, Walker et al. documented an improvement in Objective American Knee Society Score from 48.3 to 87.8 postoperatively, highlighting the potential for functional restoration even in high-demand individuals ≤50 years (39).

Return to athletic and impact-loading activities is an especially important benchmark in younger patients. Lo Presti et al. and Walker et al. found that many patients resumed running, hiking, and other activities after UKA without a measurable increase in complications or failure rates during follow-up (23,27). These findings contrast with the traditional view that UKA may necessitate lifestyle limitations and suggest that such restrictions may be unnecessarily conservative in properly selected patients.

This restoration of function is not merely academic. Younger patients with medial OA often remain employed, physically active, and socially engaged—factors that influence surgical expectations. The ability to return to a high level of function without the stiffness or recovery burden associated with TKA represents a significant advantage of UKA (23,27).

UKA vs. HTO and TKA in the young adult

While UKA offers clear advantages in recovery time and function, its role must be weighed against alternative surgical options, particularly HTO and TKA. Comparative data in this review highlight that both UKA and HTO can yield successful outcomes in young patients, though with differing risk-benefit profiles.

Yadav et al. found that UKA provided superior OKS and International Knee Documentation Committee scores compared to HTO using external fixation, while maintaining a lower complication rate (2% vs. 5%) (29). Similarly, Rodkey et al. reported a significantly lower reoperation rate due to lower complication rates in patients who underwent UKA compared to HTO (2.2% vs. 21.2%, P<0.01), though a higher rate of conversion to TKA at 5 years for UKA compared to HTO (13.7% vs. 3.5%) (36). Krych et al. reported that UKA patients returned to activity more quickly at 3 months, 1 year, 2 years, and final follow-up, and that HTO had higher failure rates compared to UKA (22.8% vs. 6%) (37). These findings are consistent with earlier studies suggesting that while HTO is joint-preserving, it often requires longer rehabilitation, can carry a higher complication profile, and may limit activity during the healing phase. Although the literature presents mixed results regarding conversion rates of UKA versus HTO to TKA, HTO may remain preferable in cases of metaphyseal varus deformity or in patients with high occupational loading where preservation of native bone and joint proprioception is prioritized.

The comparison to TKA is more complex. Goh et al. reported no significant differences in KSS, OKS, or Short Form-36 measures, and the same revision rate (2.2%) between UKA and TKA in patients younger than 55 years (34). UKA was associated with significantly greater flexion at both 6 months and 2 years postoperatively. Although Goh et al. found no differences in short-term function, quality of life, or satisfaction, TKA may present a higher risk of stiffness and more technically challenging revisions in younger patients—who are more likely to outlive their implants (34). Finally, Kyriakidis et al. conducted a systematic review of medial UKA in patients under 60 years of age, demonstrating good improvements in KSS and implant survivorship rates of up to 96.5% at 10 years—reinforcing the viability of medial UKA in younger, active patients (40). Taken together, these findings suggest that UKA is a good option in young patients with isolated medial compartment disease.

Radiographic OA progression and clinical outcomes

Recent literature underscores the safety and efficacy of medial UKA across diverse patient populations and phenotypes. In a large single-center study, Royon et al. found no significant differences in clinical or radiographic outcomes, complication rates, or survivorship based on gender, indicating that sex should not be a limiting factor in selecting patients for medial UKA (41). Complementing this, Bayoumi et al. demonstrated that anteromedial OA exhibits substantial phenotypic variation, identifying 76 distinct coronal alignment phenotypes preoperatively and 58 postoperatively—suggesting that individualized alignment strategies may better address anatomical diversity in this patient population (42).

The progression of OA in untreated compartments remains a theoretical concern following UKA, particularly in younger individuals with longer life expectancy. However, multiple studies in this review found that radiographic deterioration did not necessarily translate to clinical failure. For instance, Walker et al. observed radiographic progression in nearly 40% of patients, yet functional outcomes remained favorable (39). Faour Martín et al. reported similar findings, suggesting that minor degenerative changes in the lateral or patellofemoral compartments do not automatically necessitate revision or correlate with symptomatic decline (24). Streit et al. reported 5% of knees with progressive OA in the lateral compartment, and 2% with full joint space loss at 5 years postoperatively, which led to failure (26). These data reinforce the importance of patient counseling and shared decision-making when considering UKA for highly active individuals.

Limitations and future directions

This narrative review has several limitations. Although the search strategy was structured and targeted, it does not meet the formal criteria of a systematic review and is therefore subject to potential selection bias. The editorial focus on studies reporting outcomes in patients aged 60 years or younger may have excluded high-quality studies that did not stratify by age, thereby limiting the comprehensiveness of this synthesis. Furthermore, most included studies were retrospective or observational, introducing inherent risks of reporting bias and limiting causal inference. Variability in implant type, surgical technique, surgeon experience, rehabilitation protocols, and outcome measures further reduces the generalizability of findings across diverse practice settings.

Another limitation is the relative paucity of long-term data. While midterm follow-up results are promising, only a few studies reported outcomes beyond 15 years, leaving questions regarding implant performance as patients age into their 60s and 70s. Additionally, although radiographic progression of OA in untreated compartments was frequently reported, it was not consistently correlated with clinical outcomes, underscoring the need for standardized imaging and symptom correlation. Further supporting the need for individualized assessment, Ten Noever de Brauw et al. applied the coronal plane alignment of the knee (CPAK) classification to 1,000 knees and found that only 45.1% of patients maintained their preoperative phenotype postoperatively, highlighting the dynamic nature of coronal alignment in UKA and the importance of phenotype-aware surgical planning (43).

Future investigations should focus on large, prospectively collected datasets that stratify outcomes by age, activity level, and surgical volume. Randomized controlled trials or well-powered registry studies comparing medial UKA to HTO and TKA in younger patients would provide higher-level evidence to guide treatment selection. Long-term studies are also essential to clarify appropriate activity recommendations, thresholds for revision, and the impact of polyethylene wear or implant design on survivorship.

Advancements in implant materials, computer-assisted navigation, and patient-specific instrumentation also merit further study, as they may improve the precision, consistency, and long-term success of UKA. Collectively, these efforts will enhance patient counseling, refine surgical indications, and inform postoperative management strategies tailored to the needs of younger, active individuals.

Conclusions

This narrative review of 19 contemporary studies reveals that medial UKA can offer good functional outcomes, high mid-term and long-term survivorship, a high rate of short-term return to activity, and relatively low complication rates in carefully selected young patients. Despite these positive findings, common risks of revision—particularly related to unexplained pain or disease progression in adjacent compartments—necessitate thorough patient selection and careful clinical follow-up. UKA appears particularly favorable when compared to HTO or TKA in terms of recovery time or proprioception. While challenges remain, including technical demands and the need for long-term data, these findings support an evolving paradigm in which age alone should not be considered a contraindication to UKA. Instead, surgical decision-making should be grounded in anatomic alignment, disease pattern, and patient-specific goals, with surgeon experience playing a critical role in optimizing outcomes. Continued prospective studies and larger registry analyses are warranted to better define optimal patient selection criteria and further improve long-term outcomes.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Brian Waterman, Alan Reynolds and Kevin Collon) for the series “The Medial Knee at Risk” published in Annals of Joint. The article has undergone external peer review.

Reporting Checklist: The authors have completed the Narrative Review reporting checklist. Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-29/rc

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-29/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-25-29/coif). The series “The Medial Knee at Risk” was commissioned by the editorial office without any funding or sponsorship. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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