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No Difference Unicompartmental Knee Arthroplasty for Medial Knee Osteoarthritis With or Without Anterior Cruciate Ligament Deficiency: A Systematic Review and Meta-analysis

  • Genfa Du
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Hongtao Qiu
    Affiliations
    Department of Orthopedics, Shenzhen Bao'an Traditional Chinese Medicine Hospital, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Jianzong Zhu
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Hongbo Wang
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Qinghua Xiao
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Zhen Zhang
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Xiaosheng Lin
    Correspondence
    Address correspondence to: Xiaosheng, Lin, MD, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, 3 Shajing Street, Shenzhen, 518104, China.
    Affiliations
    Department of Orthopedics, Shenzhen Hospital of Integrated Chinese and Western Medicine, Guangzhou University of Chinese Medicine, Shenzhen, China
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  • Guangming Zheng
    Correspondence
    Address correspondence to: Guangming, Zheng, MM, Shunde Hospital Guangzhou University of Chinese Medicine, 12 Jinsha Avenue, Foshan, 528329, China.
    Affiliations
    Department of Orthopedics, Shunde Hospital Guangzhou University of Chinese Medicine, Foshan, China
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Open AccessPublished:October 16, 2022DOI:https://doi.org/10.1016/j.arth.2022.10.018

      Abstract

      Background

      A functional intact anterior cruciate ligament (ACLI) is considered to be a prerequisite for unicompartmental knee arthroplasty (UKA). However, UKA has been shown to have good clinical efficacy in ACL-deficient (ACLD) knees at 3 to 10 years follow-up. Therefore, the role of ACLD in UKA remains controversial, and more evidence is needed to clarify the role of ACLD in UKA.

      Methods

      PubMed, the Web of Science, EMBASE, and Cochrane Central were queried for articles comparing the results of the ACLD and ACLI groups after UKA. Outcomes of interest included the Tegner Activity Scale, the Oxford Knee Score (OKS), postoperative slope of the implant (PSI), the Knee Injury and Osteoarthritis Outcomes Score (KOOS), the Lysholm score, and revision rate. There were eight studies included. The mean age was 66 years (range 49 to 87 year old) and the mean follow-up time was 6.9 years (range 1.3 to 16.6 years). There was baseline comparability regarding mean age, duration of follow-up, and body mass index (P > .5) between the ACLD and ACLI groups.

      Results

      The ACLD and ACLI groups had improved postoperative functional indicators, and that postoperative revision rate (mean difference [MD], 1.24; 95% confidence interval [CI], 0.75 to 2.04; P = .4), Tegner score (MD, −0.1; 95% CI, −0.26 to 0.05; P = .19), and Lysholm score (95% CI, −2.46 to 7.32; P = .33) were similar between the groups, with no significant differences; however, the ACLD groups had significantly better KOOS Activities of Daily Living scores, with a significant difference (MD, 4.53; 95% CI, 1.75 to 7.3; P = .001). Also, there were no significant differences between two groups in the PSI, OKS, KOOS.

      Conclusion

      ACL deficiency is not always a contraindication for UKA. With correct patient selection, UKA could be considered for medial knee osteoarthritis with ACL deficiency without antero-posterior instability, especially these people over 60 years of age.

      Keywords

      Knee osteoarthritis (OA) is the most common degenerative joint disease in the elderly, affecting 3.8 to 16% of the population [
      • Wallace I.J.
      • Worthington S.
      • Felson D.T.
      • Jurmain R.D.
      • Wren K.T.
      • Maijanen H.
      • et al.
      Knee osteoarthritis has doubled in prevalence since the mid-20th century.
      ,
      • Cross M.
      • Smith E.
      • Hoy D.
      • Nolte S.
      • Ackerman I.
      • Fransen M.
      • et al.
      The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study.
      ]. Only the unilateral compartment is affected in approximately one-third of these patients [
      • Ledingham J.
      • Regan M.
      • Jones A.
      • Doherty M.
      Radiographic patterns and associations of osteoarthritis of the knee in patients referred to hospital.
      ,
      • O'Connor J.J.
      • Goodfellow J.W.
      • Dodd C.A.
      • Murray D.W.
      Development and clinical application of meniscal unicompartmental arthroplasty.
      ,
      • Longo U.G.
      • Loppini M.
      • Trovato U.
      • Rizzello G.
      • Maffulli N.
      • Denaro V.
      No difference between unicompartmental versus total knee arthroplasty for the management of medial osteoarthtritis of the knee in the same patient: a systematic review and pooling data analysis.
      ], which can influence the choice of treatment. Unicompartmental knee arthroplasty (UKA) is considered an effective alternative to total knee arthroplasty in isolated unicompartmental knee arthritis [
      • Calkins T.E.
      • Hannon C.P.
      • Fillingham Y.A.
      • Culvern C.C.
      • Berger R.A.
      • Della V.C.
      Fixed-bearing medial unicompartmental knee arthroplasty in patients younger than 55 Years of age at 4-19 Years of follow-up: a concise follow-up of a previous report.
      ]. UKA is characterized by minimal invasiveness and the preservation of joint kinematics and proprioception. These benefits have been attributed in part to the fact that UKA allows for retention of the nonarthritic compartments and the native structures of the joint, especially the anterior cruciate ligament (ACL) [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ].
      In the native knee, the intact ACL (ACLI) plays an important role in knee kinematics and joint stability [
      • McLean S.G.
      • Mallett K.F.
      • Arruda E.M.
      Deconstructing the anterior cruciate ligament: what we know and do not know about function, material properties, and injury mechanics.
      ,
      • Sutter E.G.
      • Liu B.
      • Utturkar G.M.
      • Widmyer M.R.
      • Spritzer C.E.
      • Cutcliffe H.C.
      • et al.
      Effects of anterior cruciate ligament deficiency on tibiofemoral cartilage thickness and strains in response to hopping.
      ,
      • Defrate L.E.
      • Papannagari R.
      • Gill T.J.
      • Moses J.M.
      • Pathare N.P.
      • Li G.
      The 6 degrees of freedom kinematics of the knee after anterior cruciate ligament deficiency: an in vivo imaging analysis.
      ]. Goodfellow et al [
      • Goodfellow J.W.
      • Kershaw C.J.
      • Benson M.K.
      • O'Connor J.J.
      The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases.
      ] in a series of medial UKA procedures performed on 103 knees, reported that the incidence of implant failure was closely related to ACL deficiency (ACLD). A later study of 301 knees also reported reduced survivorship at 6 years in knees without an ACL [
      • Goodfellow J.
      • O’Connor J.
      The anterior cruciate ligament in knee arthroplasty. A risk-factor with unconstrained meniscal prostheses.
      ]. This UKA failure in ACLD was primarily attributable to aseptic loosening of the tibial components [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ]. Bohm et al [
      • Bohm I.
      • Landsiedl F.
      Revision surgery after failed unicompartmental knee arthroplasty: a study of 35 cases.
      ] reported that the use of fixed-bearing implants led to a greater incidence of failure in patients who did not have an ACL. Therefore, ACLD has traditionally been considered a contraindication for UKA. However, evidence has emerged more recently that UKA can be successful in ACLD knees. Both Engh et al [
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ] and Boissonneault et al [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ] showed that component survivorship rates between UKA recipients who did and did not have intact ACLs were similar at mean 5 years follow-up (range 2.9 to 10 years). Moreover, growing evidence supports this view. Kikuchiet al [
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ] performed an analysis between the ACID (32 knees) and ACLI (369 knees) groups who had undergone mobile UKA, and no significant difference between the groups existed in the component survival rate (100% in the ACLD and 98.9% in the ACLI group) at mean 5 years. Plancheret al [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ] in a series of medial UKA procedures performed on 32 ACLD knees and 99 ACLI knees, reported that the combined survivorship for both the two groups was 96% at 10 years. This is different from the results of previous studies, a trend which may be related to the improvements in prosthesis design, operative technologies, and patient selection.
      The effect of ACLD in UKA remains controversial [
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ], and there is currently no consensus on whether the ACL is a necessary prerequisite for a successful procedure. More studies are needed to compare ACLD and ACLI in terms of multiple outcomes. The purpose of this study was to conduct a systematic review and meta-analysis to compare the clinical outcomes between the ACID and ACLI patients who had undergone medial UKA. Specifically, our goal was to compare the following: (1) functional outcomes; (2) rates of revision; and (3) postoperative activity between the 2 groups. In addition, to guide clinical practice, we sought to conduct an analysis of whether the ACLD and ACLI groups who experienced UKA could achieve the same clinical efficacy.

      Materials and Methods

      Search Strategy

      This present meta-analysis was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines [
      • Moher D.
      • Liberati A.
      • Tetzlaff J.
      • Altman D.G.
      Preferred reporting items for systematic reviews and meta-analyses: the PRISMA Statement.
      ].The protocol for this review has been registered in the International Prospective Register of Systematic Reviews (identifier CRD42021278475).

      Literature Search

      We conducted a literature screening for original articles published before January 3, 2022. Two independent authors accessed PubMed, the Web of Science, Embase, and the Cochrane Central Register of Controlled Trials to identify relevant articles. Only published articles written in English were included, and the following search terms were used in combination to locate studies: unicompartmental knee arthroplasty, unicondylar knee arthroplasty, partial knee arthroplasty, unicompartmental knee replacement, unicondylar knee replacement, partial knee replacement, compartment replacement, compartment arthroplasty, UKA, UKR, anterior cruciate ligament Injury, anterior cruciate ligament tear, anterior cruciate ligament defect, anterior cruciate ligament damage, anterior cruciate ligament rupture, ACL injury, ACL tear, knee osteoarthritis, knee arthritis, KOA, and OA. The same reviewers screened the articles of interest and accessed their full-text versions. Disagreements between these authors were solved by a third author.

      Eligibility Criteria

      All clinical studies of patients who had knee osteoarthritis with or without ACLI were considered for inclusion. Two independent authors reviewed the full texts of identified articles, and studies were included in this analysis according to the listed criteria as follows: (1) original material was presented in English; (2) a comparative study (randomized control, cohort, comparison) of intact versus deficient ACL in patients with knee osteoarthritis after medial UKA was performed; (3) there was an absence of evident antero-posterior instability by examination preoperatively or intraoperatively, and the status of the ACL was confirmed intraoperatively (functionally intact or normal ACL/partial, near-complete tear or absent ACL); (4) ACL injury was caused by long-term impingement and wear; and (5) the postoperative mean follow-up period was ≥3 years. During the article-selection process, the following exclusion criteria were applied: (1) ACL deficiency was caused by trauma; (2) patients underwent ACL reconstruction combined with UKA; (3) original data were incomplete; (4) the articles was a review, letter, case report, conference abstract, or editorial; and (5) the study involved animal, in vitro, cadaveric, or biomechanics experiments. The references of all included articles were also reviewed by 2 authors to ensure relevant studies were not missed.

      Study Selection

      A total of 319 studies were initially identified from the 4 aforementioned literature databases. After removing 64 duplicate articles, 255 articles underwent title and abstract screening; from there, we subsequently identified 20 articles closely related to the research content. However, after reviewing their full-text version, 12 papers were soon excluded that did not meet the inclusion criteria. Finally, 8 original articles [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ,
      • Pegg E.C.
      • Mancuso F.
      • Alinejad M.
      • van Duren B.H.
      • O'Connor J.J.
      • Murray D.W.
      • et al.
      Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.
      ] (2,516 knees) matched the inclusion and exclusion criteria (See Figure1).

      Data Extraction

      Two independent reviewers extracted the following data of the included studies: author, year of publication, study design, type of prosthesis, and length of follow-up. In addition, we gathered certain baseline data, such as the number of patients, number of knees, mean age, sex, and mean body mass index (BMI). Outcomes of interest included the Tegner Activity Scale, Oxford Knee Score (OKS), postoperative slope of the implant (PSI), Knee Injury and Osteoarthritis Outcomes Score (KOOS) Pain, Activities of Daily Living (KOOS-ADL), Quality of Life (KOOS-QOL), and Symptoms subscales, the Lysholm score, and revision rate.

      Patient and Study Characteristics

      A total of 2,516 knees were included, including 416 knees with ACLD and 2,100 knees with ACLI. Among the included articles, the pooled mean follow-up time was >6 years. Also, the pooled mean age of patients in both the ACLD and ACLI groups was 66 years, with no significant difference in the meta-analysis (mean difference (MD), −0.62; 95% confidence interval (CI), −2.09 to 0.84; P = .4); Considering the available Body Mass Index (BMI) data [
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ], the meta-analysis also showed that there were no significant differences between the ACLD and ACLI groups (MD, 0.54; 95% CI, −1.22 to 0.14; P = .12). The patient characteristics of included papers are summarized in Table 1. The present meta-analysis included 1,287 fixed-bearing and 1,229 mobile-bearing implants, respectively (See Appendix 1).
      Table 1Patient Characteristics of the Included Studies.
      AuthorYearDesignACL TypeParticipantsPts/KneesM/FAge(years)BMI(kg/m2)Prosthesis TypesMean Follow-up
      Pegg et al [
      • Pegg E.C.
      • Mancuso F.
      • Alinejad M.
      • van Duren B.H.
      • O'Connor J.J.
      • Murray D.W.
      • et al.
      Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.
      ]
      2016Prospective cohortdeficiencyUKA14/1612/267 (50-87)
      Values are presented as mean (range).
      NRPhase III Oxford (Biomet)6.3 (1.3-12.8)
      Values are presented as mean (range).
      yrs
      intactUKA13/1612/168.3 (49-86)
      Values are presented as mean (range).
      NRPhase III Oxford (Biomet)6.0 (2.6-11.0)
      Values are presented as mean (range).
      yrs
      Kikuchi et al [
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ]
      2021Retrospective comparative studydeficiencyUKA32/326/2671.9 ± 7.025.8 ± 3.9mobile-bearing (Zimmer)66.1 ± 15.2 mo
      intactUKA369/36990/27972.7 ± 8.425.5 ± 3.7mobile-bearing (Zimmer)63.8 ± 15.0 mo
      Plancher et al [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ]
      2021Prospective cohortdeficiencyUKANR/32NR65 ± 12NRfixed-bearing (Zimmer)8.9 ± 3 y
      intactUKANR/99NR65 ± 9NRfixed-bearing (Zimmer)7.8 ± 4 y
      Hamilton et al [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ]
      2016Prospective cohortdeficiencyUKANR/13987/NR69.1 ± 9.2NRPhase 3 Oxford10.3 (5.3-16.6)
      Values are presented as mean (range).
      yrs
      intactUKANR/565271/NR66.1 ± 9.7NRPhase 3 Oxford10.3 (5.3-16.6)
      Values are presented as mean (range).
      yrs
      Liu Shaohua et al [
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ]
      2021Retrospective cohortdeficiencyUKA45/4517/2863.52 ± 10.4822.53 ± 3.12fixed-bearing (Link sled)(48-72)
      Values are presented as mean (range).
      mo
      intactUKA223/22394/12964.22 ± 11.0123.15 ± 2.99fixed-bearing (Link sled)(48-72)
      Values are presented as mean (range).
      mo
      Boissonneault et al [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ]
      2013Retrospective cohortdeficiencyUKA42/4632/1065 ± 11NRmobile-bearing (Biomet)4.9 ± 2.7 y
      intactUKA45/4635/1065 ± 11NRmobile-bearing (Biomet)4.8 ± 1.5 y
      Engh et al [
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ]
      2014Retrospective comparative study with prospectively collected datadeficiencyUKA60/6831/2965 ± 1228.4 ± 6fixed bearing (DePuy)6 ± 1.6 y
      intactUKA561/706223/33866 ± 1029.5 ± 6fixed bearing (DePuy)6 ± 1.6 y
      Plancher K. D.et al [
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ]
      2021Prospective cohortdeficiencyUKA38/3819/1965 ± 1028 ± 5fixed-bearing (ZUK)9 ± 3.5 y
      intactUKA76/7638/3865 ± 1029 ± 5fixed-bearing (ZUK)9 ± 3 y
      ACL, anterior cruciate ligament deficiency; Pts, patients; NR, no record; M, male; F, female; BMI, body mass index; yrs, years; mo, month.
      a Values are presented as mean (range).

      Data Transformation

      Some studies reported outcomes data (eg, the Tegner Activity Scale, OKS) using the median and the minimum and maximum values, or the median and first and third quartiles. In order to be able to use these data in our meta-analysis, we estimated the mean of the sample using the method presented by Luo et al [
      • Luo D.
      • Wan X.
      • Liu J.
      • Tong T.
      Optimally estimating the sample mean from the sample size, median, mid-range, and/or mid-quartile range.
      ], and the standard deviation of the sample based on the method presented by Wan et al [
      • Wan X.
      • Wang W.
      • Liu J.
      • Tong T.
      Estimating the sample mean and standard deviation from the sample size, median, range and/or interquartile range.
      ]. This method of estimating mean and standard deviation values has been proven to be reliable [
      • Ow Z.
      • Cheang H.
      • Koh J.H.
      • Koh J.
      • Lim K.K.
      • Wang D.
      • et al.
      Does the choice of acellular scaffold and augmentation with bone marrow aspirate concentrate affect short-term outcomes in cartilage repair? A systematic review and meta-analysis.
      ,
      • Zwiers R.
      • Miedema T.
      • Wiegerinck J.I.
      • Blankevoort L.
      • van Dijk C.N.
      Open versus endoscopic surgical treatment of posterior ankle impingement: a meta-analysis.
      ,
      • Lex J.R.
      • Edwards T.C.
      • Packer T.W.
      • Jones G.G.
      • Ravi B.
      Perioperative systemic dexamethasone reduces length of stay in total joint arthroplasty: a systematic review and meta-analysis of randomized controlled trials.
      ,
      • Fenelon C.
      • Murphy E.P.
      • Fahey E.J.
      • Murphy R.P.
      • O'Connell N.M.
      • Queally J.M.
      Total knee arthroplasty in hemophilia: survivorship and outcomes-A systematic review and meta-analysis.
      ].

      Quality Assessment

      The quality assessment of the included studies was performed by 2 independent authors. The risk of bias tool of the Newcastle-Ottawa Scale [
      • Elbardesy H.
      • Awad A.K.
      • McLeod A.
      • Farahat S.T.
      • Sayed S.
      • Guerin S.
      • et al.
      Does bicompartmental knee arthroplasty hold an advantage over total knee arthroplasty? Systematic review and meta-analysis.
      ] was used, focusing on the selection and comparability of cohorts, and the assessment of outcomes and follow-up. The risk of bias assessment revealed a low degree of bias in 4 studies [
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ] and a moderate bias in 4 studies [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Pegg E.C.
      • Mancuso F.
      • Alinejad M.
      • van Duren B.H.
      • O'Connor J.J.
      • Murray D.W.
      • et al.
      Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.
      ]. Therefore, the quality of the included articles was good.

      Data Analyses

      Statistical analyses were performed by one author using the Review Manager version 5.3 software (Cochrane, London, United Kingdom). Data were presented as mean ± standard deviations (SD). The assessment of continuous data adopted inverse variance methods, such as mean difference (MD) effect measures with a fixed-effects model; dichotomous outcome results were expressed using the Mantel-Haenszel method and risk ratios (RR) with a fixed-effects model. The confidence interval (CI) was set at 95% in all the comparisons, and a fixed model effect was set as the default. If moderate or severe heterogeneity was detected (the P value of heterogeneity test was <0.05 and I2 > 75%), a random model effect was used. Heterogeneity was quantified through the I2 statistic and P values. P < .05 was considered to be statistically significant. Sensitivity analyses were performed when necessary to evaluate the stability of the results. Subgroup analyses were performed to get some more concrete conclusions if data were available.

      Results

      Tegner Activity Scale

      Figure 2 shows that two UKA studies involving 493 knees analyzed Tegner scores during short-term follow-up (≤3 years) [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ], and showed no significant differences between the ACLD and ACLI groups (MD, 0.23; 95% CI, 0 to 0.45; P = .05). Six studies involving 1,611 knees did the same during mid-term follow-up (3 to 10 years) [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ,
      • Pegg E.C.
      • Mancuso F.
      • Alinejad M.
      • van Duren B.H.
      • O'Connor J.J.
      • Murray D.W.
      • et al.
      Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.
      ], and also revealed no significant differences between the ACLD and ACLI groups (MD, −0.1; 95%CI, −0.26 to 0.05; P = .19).
      Figure thumbnail gr2
      Fig. 2Subgroup analysis of the Tegner Activity Scale outcome by the length of follow-up.

      PSI

      Only 3 studies with 491 knees were examined with regard to postoperative slope of the implant (PSI), and no significant difference was found between the ACLD and ACLI groups (MD, −0.06; 95% CI, −0.51 to 0.4; P = .81) [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ].

      OKS

      Two independent studies examined OKS at 1, 3, and 5 years, respectively [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ]. No significant difference in OKS was found between the ACLD and ACLI groups during short-term follow up (≤3 years) (MD, −1.07; 95% CI, −2.22 to 0.07; P = .07). In addition, among 4 studies with 1,229 knees and mid-term follow up (3 to 10 years), no significant difference was found in this meta-analysis (MD, −0.78; 95% CI, −1.67 to 0.11; P = .09) [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Pegg E.C.
      • Mancuso F.
      • Alinejad M.
      • van Duren B.H.
      • O'Connor J.J.
      • Murray D.W.
      • et al.
      Sagittal kinematics of mobile unicompartmental knee replacement in anterior cruciate ligament deficient knees.
      ]. The forest plots are shown in Figure 3.
      Figure thumbnail gr3
      Fig. 3Subgroup analysis of the OKS outcome by the length of follow-up.

      KOOS

      We were only able to include 2 studies (241 knees) for the statistical analysis of KOOS subscale results [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ]. No difference between the ACLD and ACLI groups was detected in scores for KOOS-Pain (MD, 2; 95% CI, −1.58 to 5.58; P = .27), KOOS Symptoms (MD, 1.0; 95% CI, −3.22 to 5.22; P = .64), KOOS Quality of Life (MD, −2.55; 95% CI, −7.5 to 2.04; P = .28), and KOOS Activities of Daily Living scores were significantly higher in the ACLD group compared to the ACLI group (MD, 4.52; 95% CI, 1.72 to 7.32; P = .002). A more detailed explanation is shown in Figure 4.
      Figure thumbnail gr4
      Fig. 4Forest plots of the comparison: KOOS Pain, Symptoms, ADL and QOL.

      Lysholm Score

      Two studies (241 knees) recorded Lysholm scores [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ]. The overall result for this continuous outcome scale was 2.43 (95% CI, −2.46 to 7.32; P = .33) in favor of the ACLI group. However, no significant differences in Lysholm scores was found between the ACLD and ACLI groups (P = .33).

      Revision Rate

      Seven studies with 2,484 knees reported revision rates [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Engh G.A.
      • Ammeen D.J.
      Unicondylar arthroplasty in knees with deficient anterior cruciate ligaments.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ,
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ,
      • Plancher K.D.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Patient-acceptable symptom state for reporting outcomes following unicompartmental knee arthroplasty : a matched pair analysis comparing UKA in ACL-deficient versus ACL-intact knees.
      ]. A total of 400 knees were involved in the ACLD group, there were 18 knees that required revision, with a revision rate of 4.5%; a total of 2,084 knees were involved, while 82 knees required revision in the ACLI group, with a revision rate of 3.9%. The pooled results showed no significant difference between the 2 groups in terms of the revision rates (MD, 1.24; 95% CI, 0.75 to 2.04; P = .4). The forest plots are shown in Figure 5.
      Figure thumbnail gr5
      Fig. 5Forest plots of the comparison: Revision Rate.

      Discussion

      The main findings of the study include that there was no significant difference in the implant survival rate at mid-term follow-up between ACLD and ACLI patients who had undergone UKA. Moreover, no significant differences were found between the 2 groups in terms of the Tegner Activity Scale, Lysholm score, PSI, OKS, and KOOS. Interestingly, the ACLD group had significantly better results compared to the ACLI group in terms of KOOS-ADL.
      Previous research has suggested that, owing to high failure rates, ACL deficiency is a contraindication for UKA surgery [
      • Goodfellow J.W.
      • Kershaw C.J.
      • Benson M.K.
      • O'Connor J.J.
      The Oxford Knee for unicompartmental osteoarthritis. The first 103 cases.
      ,
      • Goodfellow J.
      • O’Connor J.
      The anterior cruciate ligament in knee arthroplasty. A risk-factor with unconstrained meniscal prostheses.
      ]. However, with the improvement of various conditions, the short-to mid-term clinical results or survivorship rates of UKA in ACLD knees were similar to those in ACLI knees, and ACLD is not always a contraindication for medial UKA [
      • Hamilton T.W.
      • Pistritto C.
      • Jenkins C.
      • Mellon S.J.
      • Dodd C.A.
      • Pandit H.G.
      • et al.
      Unicompartmental knee replacement: does the macroscopic status of the anterior cruciate ligament affect outcome?.
      ,
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Kikuchi K.
      • Hiranaka T.
      • Kamenaga T.
      • Hida Y.
      • Fujishiro T.
      • Okamoto K.
      Anterior cruciate ligament deficiency is not always a contraindication for medial unicompartmental knee arthroplasty: a retrospective study in nondesigner's Japanese hospital.
      ]. There are many factors that may have caused these different results, such as improvements in prosthesis design, proficiency and improvement in surgical techniques, and patient selection. In the present study, the findings were similar to those of previous reports, with no significant differences in survival rate and clinical outcomes between the 2 groups. Notably, ACLD in the included studies was caused by long-term chronic impingement and wear, and the knee joint had no functional antero-posterior instability according to a physical examination performed preoperatively. This antero-posterior stability may be due to the presence of posterior osteophytes [
      • Mullis B.H.
      • Karas S.G.
      • Kelley S.S.
      Characterization of a consistent radiographic finding in chronic anterior cruciate ligament deficiency: the posteromedial osteophyte.
      ] and stiffness of the knee capsule, which contributes to the knee stability [
      • Mancuso F.
      • Dodd C.A.
      • Murray D.W.
      • Pandit H.
      Medial unicompartmental knee arthroplasty in the ACL-deficient knee.
      ]. Brage et al [
      • Brage M.E.
      • Draganich L.F.
      • Pottenger L.A.
      • Curran J.J.
      Knee laxity in symptomatic osteoarthritis.
      ] found that osteoarthritic knees tend to have less laxity than normal knees, and they thought that this trend may be due to a combination of knee ligament contracture and osteophyte stress on ligaments and other capsular structures. Later, Dayal et al reported a similar result, i.e., knees with severe OA had less antero-posterior laxity than knees with mild OA did [
      • Dayal N.
      • Chang A.
      • Dunlop D.
      • Hayes K.
      • Chang R.
      • Cahue S.
      • et al.
      The natural history of anteroposterior laxity and its role in knee osteoarthritis progression.
      ]. Thus, osteophyte production and soft-tissue contracture may serve as a compensatory mechanism to stabilize the knee joint in the absence of an ACL. On the other hand, the evolution of surgical instruments and techniques has altered the role of the ACL in UKA. For example, the phase 3 procedure differs from the phase 1 procedure in that it allows ligament tensions to be balanced intraoperatively, which facilitates more accurate restoration of the native muscle–tendon length and may allow the hamstring muscles to stabilize the tibia from subluxing anteriorly during heel strike [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ].
      Age and BMI are key factors that optimize clinical outcomes and survival in patients with UKA. Early indications for UKA included an age >60 years and weight <82 kilograms [
      • Kozinn S.C.
      • Scott R.
      Unicondylar knee arthroplasty.
      ]. However, in recent years, the standard has been extended. A study by Thompson et al showed that patients aged <60 years had higher KSS scores than those aged ≥60 years within 2 years, indicating that UKA can provide good clinical outcomes for younger patients [
      • Thompson S.A.
      • Liabaud B.
      • Nellans K.W.
      • Geller J.A.
      Factors associated with poor outcomes following unicompartmental knee arthroplasty: redefining the "classic" indications for surgery.
      ]. Wang et al suggested that Oxford UKA is a reliable and effective treatment for young patients with medial osteoarthritis aged ≤60 years [
      • Wang F.
      • Xue H.
      • Ma T.
      • Wen T.
      • Yang T.
      • Xue L.
      • et al.
      Short-term effectiveness of medial unicompartmental knee arthroplasty in young patients aged less than or equal to 60 years.
      ]. Despite this, compared to elderly patients, younger ones participate in more physical activity after surgery [
      • Witjes S.
      • Hoorntje A.
      • Kuijer P.P.
      • Koenraadt K.L.
      • Blankevoort L.
      • Kerkhoffs G.M.
      • et al.
      Goal setting and achievement in individualized rehabilitation of younger total and unicondylar knee arthroplasty patients: a cohort study.
      ] and have higher requirements for knee joint function in the postoperative period and longer prosthesis lives [
      • Wang F.
      • Xue H.
      • Ma T.
      • Wen T.
      • Yang T.
      • Xue L.
      • et al.
      Short-term effectiveness of medial unicompartmental knee arthroplasty in young patients aged less than or equal to 60 years.
      ]; thus, patient selection in UKA requires caution. Besides, some studies have suggested that a BMI >30 kg/m2 is a (relative) contraindication for UKA [
      • Deschamps G.
      • Chol C.
      Fixed-bearing unicompartmental knee arthroplasty. Patients' selection and operative technique.
      ], and a meta-analysis revealed a significantly increased likelihood for revision in patients with a BMI ≥30 kg/m2 compared to those with a BMI <30 kg/m2, albeit without a significant difference between the 2 groups, and a lower improvement in clinical scores in the BMI ≥30 kg/m2 group [
      • Campi S.
      • Papalia G.F.
      • Esposito C.
      • Albo E.
      • Cannata F.
      • Zampogna B.
      • et al.
      Unicompartmental knee replacement in obese patients: a systematic review and meta-analysis.
      ]. Indications of age and BMI in UKA for isolated knee osteoarthritis remain controversial. In our study, the mean age of included patients was >66 years, while the mean BMI was <30 kg/m2, and this may be an important reason to ensure the comparability and reliability of the results in this meta-analysis.
      The adjustment of PSI is critical for survival rate and good clinical outcomes of the UKA in the absence of ligament stability [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ], because an increased tibial component slope in medial UKA can result in abnormal ligament strain, prosthesis loosening, and increased contact stresses [
      • Sekiguchi K.
      • Nakamura S.
      • Kuriyama S.
      • Nishitani K.
      • Ito H.
      • Tanaka Y.
      • et al.
      Effect of tibial component alignment on knee kinematics and ligament tension in medial unicompartmental knee arthroplasty.
      ,
      • Suzuki T.
      • Ryu K.
      • Kojima K.
      • Oikawa H.
      • Saito S.
      • Nagaoka M.
      The effect of posterior tibial slope on joint gap and range of knee motion in mobile-bearing unicompartmental knee arthroplasty.
      ]. The guideline for UKA recommends aiming for a 7° PSI. Hernigou et al also suggested a PSI of >7° of the tibial implant should be avoided, particularly in the absence of the ACL, because an increase in the PSI was associated with an increase in tibial translation [
      • Hernigou P.
      • Deschamps G.
      Posterior slope of the tibial implant and the outcome of unicompartmental knee arthroplasty.
      ]. In the present meta-analysis, preoperative tibial slope and PSI were documented in 3 studies [
      • Boissonneault A.
      • Pandit H.
      • Pegg E.
      • Jenkins C.
      • Gill H.S.
      • Dodd C.A.
      • et al.
      No difference in survivorship after unicompartmental knee arthroplasty with or without an intact anterior cruciate ligament.
      ,
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ,
      • Liu S.
      • Zhou G.
      • Chen X.
      • Xiao K.
      • Cai J.
      • Liu X.
      Influence of anterior cruciate ligament defect on the mid-term outcome of fixed-bearing unicompartmental knee arthroplasty.
      ]. In all, the PSI was significantly lower than the preoperative tibial slope and <7°, and a good survival rate of the implants and clinical efficacy were achieved accordingly. Recently, Kevin et al found that patients who had a PSI >7° had significantly worse postoperative pain [
      • Plancher K.D.
      • Shanmugam J.P.
      • Brite J.E.
      • Briggs K.K.
      • Petterson S.C.
      Relevance of the tibial slope on functional outcomes in ACL-deficient and ACL intact fixed-bearing medial unicompartmental knee arthroplasty.
      ]. Surgeons should be careful not to over-increase the PSI and thus affect the longevity of the implants and clinical efficacy. In the ACLD group, the KOOS-ADL outcomes were better, but this result may not represent the true functional outcomes of the knee joint due to a limited number of included studies.
      To our knowledge, this is the first comprehensive meta-analysis focusing on UKA with ACLD. We found that the ACLI and ACLD groups who experienced UKA can achieve the same survival rate and clinical efficacy at mid-term follow-up. However, several limitations must be recognized in this meta-analysis. There was a lack of good-quality data from randomized controlled trials in this meta-analysis. Also, in the included studies, patients on average were aged >66 years, and there was a lack of data for comparisons with 45 to 59 year old patients, because old people are less physically active, so we could not assess the role of ACLD-UKA in younger patients. Moreover, the lack of follow-up data with an average of more than 10 years in the present study needs to be resolved in future studies. In addition, there are many factors that maybe reduce a baseline balance values and could have influenced our results, such as the number of implants and implant type, surgical approach, and experience level of the operating surgeon. Also, different statistical methods were used in the original studies, and the data were transformed in some cases to facilitate the present meta-analysis, which may have led to data bias. In addition, given the limited numbers of available studies and the fact that some items offered incomplete data, the overall quality of our evidence may be affected. Despite limitations, however, this meta-analysis followed the appropriate methodology, and included some studies that reported data across multiple clinical outcomes from ACLD and ACLI groups. We aimed as best as possible to provide the most complete differences in outcomes between ACLD and ACLI patients. These results could provide reference for clinical treatment and better guide clinical practice.

      Conclusions

      In this meta-analysis, satisfactory clinical effectiveness was achieved in both ACLD and ACLI groups. Our results showed that the ACLD patients undergoing UKA can achieve survival rate and clinical efficacy of ACLI patients. Therefore, ACLD is not necessarily a contraindication for UKA, and especially middle-aged and elderly patients who have ACLD may be good candidates for UKA.

      Acknowledgments

      The research was supported by the key funds of hospital specialty.

      Appendix A. Supplementary Data

      Appendix 1.

      The using characteristics of UKA prosthesis .
      Figure thumbnail fx1
      Supplementary Figure 1The using characteristics of UKA prosthesis.

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