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  • Systematic Review
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Comparison of the clinical efficacy of lateral versus medial unicondylar replacement for unicompartmental osteoarthritis of the knee: a meta-analysis

Journal of Orthopaedic Surgery and Research volume 20, Article number: 12 (2025) Cite this article

Abstract

Objective

This meta-analysis evaluates the comparative efficacy of lateral unicompartmental arthroplasty (UKA) versus medial UKA in treating unicompartmental knee osteoarthritis (KOA).

Methods

We systematically searched Cochrane, PubMed, Embase, and Web of Science databases from January 2000 to September 2024. Literature screening, quality assessment, and data extraction were conducted based on predefined inclusion and exclusion criteria. Review Manager 5.4 software was used to analyze postoperative functional scores, pain scores, aseptic loosening, progression of contralateral arthritis, and prosthesis survival.

Results

Fifteen cohort studies, encompassing 2,592 knees with medial UKA and 614 knees with lateral UKA, were included. The analysis showed no statistically significant differences in functional scores [SMD = 0.11, 95% CI (− 0.10, 0.33), I2 = 64%, P = 0.31], pain scores [SMD = 0.23, 95% CI: (− 0.22, 0.67), I2 = 91%, P = 0.32], aseptic loosening [OR = 1.33, 95% CI: (0.31, 5.78), I2 = 0%, P = 0.70], progression of contralateral arthritis [OR = 0.37, 95% CI: (0.07, 1.91), I2 = 0%, P = 0.23], short- to intermediate-term survival [OR = 1.40, 95% CI: (0.84, 2.35), I2 = 0%, P = 0.20], and long-term survival [OR = 1.12, 95% CI: (0.61, 2.05), I2 = 0%, P = 0.70].

Conclusion

Our findings indicate no significant differences in functional outcomes, pain relief, aseptic loosening, progression of contralateral arthritis, or prosthesis survival between lateral and medial UKA. Thus, both approaches are reliable options for patients with unicompartmental KOA.

Introduction

Unicompartmental knee arthroplasty (UKA) is a surgical procedure that selectively addresses the damaged area of the knee joint while preserving the cruciate ligaments, effectively treating unicompartmental knee osteoarthritis (KOA) [1, 2]. UKA primarily includes medial and lateral approaches, with medial UKA being more commonly performed in clinical settings [3]. Its efficacy has been well-documented through numerous studies following technological advancements [4, 5]. In contrast, lateral UKA is less frequently applied due to significant anatomical and kinematic differences between the lateral and medial compartments [6, 7], making it technically more challenging [8, 9].

Several studies have compared the therapeutic efficacy of medial and lateral UKA, but results have been inconsistent and often based on small sample [10,11,12,13]. A 2020 meta-analysis by Seung-Beom Han included eight studies, suggesting that both medial and lateral UKA can be equally effective [14], though the findings now lack timeliness. This study incorporates additional outcome indicators, such as aseptic loosening and postoperative progression of contralateral arthritis, and integrates recent literature on medial and lateral UKA. The aim is to verify efficacy more comprehensively and accurately, providing robust evidence-based support for the clinical development of unicompartmental knee arthroplasty.

Literature search

The search strategy for this study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [15]. The study protocol was registered in the PROSPERO database (registration number: CRD42024554969). We conducted computerized searches in Cochrane, PubMed, Embase, and Web of Science, covering the period from January 2000 to September 2023 to ensure the inclusion of current prosthesis types and data. For instance, in Embase, search terms included “medial,” “lateral,” “survival,” “unicondylar knee arthroplasty,” “partial knee arthroplasty,” among others.

Inclusion and exclusion criteria

Two reviewers independently assessed the full texts to gather sufficient evidence for review. Inclusion criteria were: (1) Study population: patients who underwent medial or lateral UKA, regardless of gender and age; (2) Follow-up duration of more than 1 year; (3) Availability of data needed for this study, such as functional scores, pain scores, aseptic loosening, progression of postoperative contralateral arthritis, and prosthesis survival, analyzed with appropriate statistical methods. Exclusion criteria included: (1) Lack of separate reporting for medial and lateral UKA cases; (2) Absence of separate reporting for unicondylar prosthesis survival or clinical outcomes of medial and lateral UKA; (3) Missing mean and standard deviation data that could not be obtained by other means; (4) Animal studies, reviews, conference abstracts, and studies with incomplete data.

Literature screening and data extraction

Two reviewers independently extracted data using a predefined form and verified the information. Any discrepancies were resolved through discussion or by consulting a third reviewer. Extracted data included the author’s name, publication date, study type, postoperative pain scores, functional scores, aseptic loosening, progression of contralateral arthritis, and survival rates in patients undergoing medial or lateral UKA. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) was the preferred tool for assessing clinical outcomes. If WOMAC scores were unavailable, other relevant scales were utilized.

Literature quality assessment

Two reviewers evaluated the quality of the included studies using the Newcastle–Ottawa Scale (NOS) [16], focusing on three areas: cohort selection, comparability, and outcomes. The scale has a maximum score of 9. Any disagreements were resolved through discussion or by consulting a third reviewer.

Statistical analysis

In this study, we analyzed postoperative functional scores, pain scores, aseptic loosening, progression of contralateral arthritis, and prosthesis survival in patients who underwent medial and lateral UKA. Prosthesis survival was divided into two subgroups: short- to intermediate-term and long-term survival, with a 10-year threshold.

For dichotomous variables, the odds ratio (OR) was used as the effect size. For continuous variables like pain and functional scores, the standardized mean difference (SMD) was employed to account for variations across different rating scales. Their corresponding 95% confidence interval (CI) will also be calculated.

Inter-study heterogeneity was assessed using the chi-square test and I2. When P > 0.05 and I2 ≤ 50%, indicating low heterogeneity, a fixed-effects model was applied. When P ≤ 0.05 and I2 > 50%, indicating high heterogeneity, a random-effects model was used. If sensitivity analysis identified the source of heterogeneity, a fixed-effects model could be applied after addressing the cause. Otherwise, the random-effects model remained in use.

All statistical analyses were conducted using Review Manager version 5.4. P ≤ 0.05 was considered statistically significant.

Results

Literature search results

A total of 8,953 relevant studies were retrieved using the developed search strategy. After removing duplicates, 4,608 articles remained. Excluding reviews, systematic evaluations, animal studies, and conference abstracts further narrowed this down to 4,396 articles. By screening titles and abstracts for relevance, 131 articles were selected, and finally, 15 articles were included after excluding those with incomplete endpoint indicators [17,18,19,20,21,22,23,24,25,26,27,28,29,30,31]. These studies encompassed a total of 3,206 knees, with 614 in the lateral UKA group and 2,592 in the medial UKA group. The literature screening process is illustrated in Fig. 1.

Fig. 1
figure 1

PRISMA flow diagram of literature search

Full size image

Basic types of research and assessment of the quality of the literature

A total of 15 cohort studies were included, all of which were of high quality. Seven studies [22, 23, 26,27,28,29, 31] scored 8, while eight studies [17,18,19,20,21, 24, 25, 30] scored 7. The general information and quality assessment of the included literature are presented in Table 1.

Table 1 Basic characteristics and quality assessment of the included studies
Full size table

Meta-analysis results

Function score

A total of seven studies reported function scores for the medial (n = 1,482) and lateral (n = 378) groups. There was significant heterogeneity among the included studies (I2 = 64%, P = 0.31). Since the heterogeneity could not be reduced through sensitivity analysis, a random effects model was used. The results indicated an SMD of 0.11 (95% CI − 0.10 to 0.33, I2 = 64%, P = 0.31), showing no statistically significant difference (Fig. 2).

Fig. 2
figure 2

Comparison of function score between the medial UKA and lateral UKA

Full size image

Pain score

A total of six studies reported pain scores for the medial (n = 1,450) and lateral (n = 319) groups. There was significant heterogeneity among the studies (I2 = 91%, P = 0.32). As the heterogeneity could not be reduced through sensitivity analysis, a random effects model was applied. The results showed an SMD of 0.23 (95% CI − 0.22 to 0.67, I2 = 91%, P = 0.32), indicating no statistically significant difference (Fig. 3).

Fig. 3
figure 3

Comparison of pain score between the medial UKA and lateral UKA

Full size image

Aseptic loosening

A total of four studies analyzed aseptic loosening in the medial (n = 1,016) and lateral (n = 107) groups. The heterogeneity was not statistically significant (I2 = 0%, P = 0.70), so a fixed-effects model was used. The results showed an OR of 1.33 (95% CI: 0.31 to 5.78, I2 = 0%, P = 0.70), indicating no statistically significant difference (Fig. 4).

Fig. 4
figure 4

Comparison of aseptic loosening between the medial UKA and lateral UKA

Full size image

Progression of postoperative contralateral arthritis

Three studies analyzed aseptic loosening in the medial (n = 1,016) and lateral (n = 107) groups. The heterogeneity was not statistically significant (I2 = 0%, P = 0.23), so a fixed-effects model was used. The results showed an OR of 0.37 (95% CI 0.07 to 1.91, I2 = 0%, P = 0.23), indicating no statistically significant difference (Fig. 5).

Fig. 5
figure 5

Comparison of postoperative contralateral arthritis progression between the medial UKA and lateral UKA

Full size image

Prosthesis survival rate

A total of 14 studies analyzed survival in the medial and lateral groups, with 7 studies reporting short- to intermediate-term (< 10 years) prosthetic survival and 7 reporting long-term (≥ 10 years) survival. In the short- to intermediate-term subgroup, heterogeneity was not statistically significant (I2 = 0%, P = 0.20), so a fixed-effects model was used. For the long-term subgroup, there was significant heterogeneity (I2 = 48%, P = 0.01). A sensitivity analysis revealed that the studies by Argenson [17] and John [24] had a large impact on the heterogeneity. After removing these studies, heterogeneity was no longer significant (I2 = 0%, P = 0.70), allowing for a fixed-effects model to be used. For the short- to intermediate-term subgroup, the results showed an OR of 1.40 (95% CI: 0.84 to 2.35, I2 = 0%, P = 0.20), indicating no statistically significant difference (Fig. 6). Similarly, for the long-term subgroup, the results showed an OR of 1.12 (95% CI 0.61 to 2.05, I2 = 0%, P = 0.70), also indicating no statistically significant difference (Fig. 7).

Fig. 6
figure 6

Comparison of short- to medium-term survival rates between the medial UKA and lateral UKA

Full size image
Fig. 7
figure 7

Comparison of long-term survival rates between the medial UKA and lateral UKA

Full size image

Discussion

This meta-analysis included 15 cohort studies comparing the prosthetic survival and clinical outcomes of patients with unicompartmental osteoarthritis of the knee treated with lateral and medial UKA. The study involved 614 cases in the lateral UKA group and 2,592 cases in the medial UKA group.

The results indicated no statistically significant differences between lateral and medial UKA in terms of functional scores, pain scores, aseptic loosening, postoperative progression of contralateral arthritis, and prosthesis survival rates. This suggests that both treatment options achieve similar efficacy, consistent with a study by Filippo Migliorini in 2023 [19].

Although lateral and medial KOA present different pain patterns—lateral KOA often causes significant pain during knee flexion [32], while medial KOA results in pain during knee extension due to cartilage damage in the anterior and middle portions [33]. Both UKA types can restore the natural alignment and structure of the knee joint post-surgery [34]. Therefore, achieving similar postoperative scores in both groups is expected.

Regarding aseptic loosening, all cases in our study occurred in medial UKAs, consistent with Tay’s findings [35]. This study indicated that imprecise postoperative implant positioning in medial UKAs increases the likelihood of aseptic loosening [36, 37]. However, the authors concluded that imprecise implant positioning could equally affect both lateral and medial UKAs, resulting in no statistically significant difference in aseptic loosening between the two. The absence of aseptic loosening in the lateral UKA group may be due to the small sample size, suggesting a need for larger comparative studies.

For the progression of postoperative contralateral arthritis, it has been suggested that intraoperative overcorrection is a contributing factor [31, 38]. Tong Zheng recommended maintaining more than 3° of valgus alignment after lateral UKA [39] and 1°–4° of slight valgus for medial UKA [40,41,42] to achieve optimal functional outcomes and survival rates. However, overcorrection is typically related to surgical technique rather than the type of UKA, leading to no significant difference in contralateral arthritis progression between the two groups.

In this study, we found no statistically significant difference in postoperative prosthetic survival between the medial and lateral UKA groups. Both groups demonstrated high prosthetic survival rates: in the short- to intermediate-term, 96.0% in the medial group and 93.2% in the lateral group; in the long-term, 90.5% in the medial group and 90.3% in the lateral group.

The question of which prosthesis (medial or lateral UKA) has a better survival rate remains controversial. Some studies report higher survival rates for medial UKA, others for lateral UKA, while some suggest little difference between the two [18, 19, 26, 27]. Clinically, lateral UKA is used less frequently than medial UKA because the incidence of isolated lateral knee osteoarthritis is only one-tenth that of medial osteoarthritis [43]. Additionally, there are significant anatomical and biomechanical differences between the compartments: the lateral tibial plateau is convex, whereas the medial is concave [44]. As a result, implants and surgical techniques effective for the medial compartment cannot be directly applied to the lateral compartment [45, 46].

Surgeons typically have more experience and refined techniques for medial UKA. However, the authors suggest that the results of this meta-analysis may be attributed to improvements in the design of lateral UKA implants, enhanced surgical techniques, and better patient selection, leading to increased survival rates for lateral UKA prostheses.

Regarding improvements in implant design for posterolateral UKA, several advancements have been made, such as the introduction of cementless components and redesigned polyethylene (PE) bearings [47,48,49]. In a 2010 study [13], Pandit used a new domed tibial plateau implant, reducing the rate of active spacer dislocation to 1.7%, compared to 10% in a 1996 study [50]. By 2018, Walker et al. demonstrated that a lateral unicondylar prosthesis with a mobile spacer had a survival rate of 90.1% at three years and 85.0% at five years [51]. After switching to fixed spacers in 2020, Walker et al. reported 100% survival at two years in 51 patients [52], significantly improving lateral prosthesis survival.

Improved surgical techniques have also contributed. According to Forster et al [53], the posterolateral approach reduces the risk of medial patellar subluxation compared to the medial approach. Regarding the rationalization of indications for lateral UKA, Berend et al [54] identified complete lateral cartilage loss and correctable medial joint deformity on stress radiographs as reasonable indications for lateral unicondylar arthroplasty.

Conversely, the actual prosthetic survival rate of medial UKA is often lower than ideal due to high surgical volumes, varying clinician skill levels, and inconsistencies in surgical approaches and prostheses. In summary, the increased survival rate of lateral UKA and the decreased survival rate of medial UKA have resulted in similar survival rates for both.

Our meta-analysis addresses a critical issue in current clinical practice: the choice of total knee arthroplasty for patients with posterolateral KOA, driven by uncertainty about the outcomes of posterolateral UKA. This trend may negatively impact future practice by limiting opportunities for physicians to develop expertise in posterolateral UKA and restricting patient access to advanced techniques. We advocate for the integration of posterolateral UKA into routine clinical care.

Lateral UKA is emerging as a valuable tool for treating posterolateral KOA. Although our study shows that posterolateral UKA can achieve results comparable to medial UKA, further research is necessary to investigate the impact of factors such as spacer type and material on the efficacy of posterolateral UKA.

However, our study faced several limitations. There was significant heterogeneity in the pain score data, as indicated by high I2 values, likely due to different rating scales. Unfortunately, we couldn’t perform subgroup analyses because too few studies used the same scale. Additionally, the included studies were cohort studies, lacking randomized controlled trials, which provide a higher level of evidence. We did not control for confounders such as age, BMI, gender, spacer type, and prosthesis type. Using data from original publications might have introduced biases inherent in observational studies. Furthermore, the mean follow-up time varied across the studies, and some of the prosthesis types examined were outdated.

Conclusion

This meta-analysis found no significant differences in functional scores, pain scores, aseptic loosening, postoperative progression of contralateral arthritis, or prosthesis survival between lateral and medial UKA. In short- to mid-term follow-up (< 10 years), the survival rate was 96.0% for the medial group and 93.2% for the lateral group. In long-term follow-up (> 10 years), the survival rates were 90.5% for the medial group and 90.3% for the lateral group. Thus, both lateral and medial UKA are reliable options for patients with unicompartmental knee osteoarthritis. However, further high-quality studies are needed to address uncertainties caused by confounding factors regarding the clinical benefits of the procedure.

Availability of data and materials

No datasets were generated or analysed during the current study.

Abbreviations

UKA:

Unicompartmental knee arthroplasty

KOA:

Knee osteoarthritis

PRISMA:

Preferred reporting items for systematic reviews and meta-analyses

NOS:

Newcastle‒Ottawa scale

CI:

Confidence interval

SMD:

Standardized mean difference

OR:

Odds ratio

WOMAC:

The Western Ontario and McMaster Universities Osteoarthritis Index

RCS:

Retrospective comparative study

PCS:

Prospective comparative study

AP:

All-polyethylene

MB:

Metal-backed

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Acknowledgements

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Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and publication of this article: This work was supported in part by grants from the Fund Program for the Basic Research Program of Shanxi Province (NO. 202203021221276) and the Research Grants for Returned Scholars of Shanxi Province (NO. 2023-189).

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  1. Haowei Bai and Pengyu Liu have contributed equally to this work, and both should be considered first author.

Authors and Affiliations

  1. Department of Orthopaedic Surgery, Shanxi Medical University Second Affiliated Hospital, Taiyuan, China

    Haowei Bai, Pengyu Liu, Jiaju Yang, Qidong Guo & Min Zhang

  2. Department of Orthopaedic Surgery, Tianjin Medical University General Hospital, Tianjin, China

    Hao Li

  3. Department of Endocrinology, Shanxi Bethune Hospital, Taiyuan, China

    Zhitong Li

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Contributions

HWB and PYL conceptualised the topic of this review, reviewed and identified studies that met the selection criteria, processed the data and drafted the manuscript. HL reviewed and identified studies that met the selection criteria. ZTL designed the article layout. JJY assessed the risk of bias and extracted the data. HWB extracted and checked the results and QDG discussed them with PYL. MZ designed the article layout, revised and approved the manuscript. All authors read and approved the final manuscript.

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Correspondence to Min Zhang.

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Bai, H., Liu, P., Li, H. et al. Comparison of the clinical efficacy of lateral versus medial unicondylar replacement for unicompartmental osteoarthritis of the knee: a meta-analysis. J Orthop Surg Res 20, 12 (2025). https://doi.org/10.1186/s13018-024-05404-5

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Keywords

Journal of Orthopaedic Surgery and Research

ISSN: 1749-799X