Unicompartmental arthroplasty for knee osteoarthritis

  • Protocol
  • Intervention


  • Brigitte M Jolles,

    Corresponding author
    1. Centre Hospitalier Universitaire Vaudois and University of Lausanne, Department of Orthopaedic Surgery and Traumatology, Lausanne, Switzerland
    • Brigitte M Jolles, Department of Orthopaedic Surgery and Traumatology, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Site Hôpital Orthopédique, 4 Avenue Pierre Decker, Lausanne, 1011, Switzerland.

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  • Antoine F Eudier,

    1. Centre Hospitalier Universitaire Vaudois and University of Lausanne, Department of Orthopaedic Surgery and Traumatology, Lausanne, Switzerland
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  • Estelle Lécureux

    1. Centre Hospitalier Universitaire Vaudois / University of Lausanne, Direction médicale, Lausanne, CH, Switzerland
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This is the protocol for a review and there is no abstract. The objectives are as follows:

To assess the benefits and harms of unicompartmental knee arthroplasty in the treatment of knee osteoarthritis in adults in terms of decreasing pain, increasing knee function, and postponing the need for a total knee arthroplasty.


Description of the condition

Knee osteoarthritis (OA) is a clinical syndrome in which cartilage is affected by progressive breakdown and eventual loss and destruction. It is caused by abnormal wearing of the cartilage and reduction of the zones where the synovial fluid lubricates the knee joint and feeds the cartilage. Absence of bone surface protection may cause pain upon weight bearing, including walking and standing. Numerous OA risk factors have been identified, such as family history, advancing age, obesity, overuse of or injury to the joint, lower limb malalignment, and suffering from another form of arthritis (e.g. rheumatoid arthritis) (Bierma-Zeinstra 2007). OA classified as primary is most often related to aging, and secondary OA is caused by another preexistent disease or condition. Osteoarthritis of the knee or gonarthrosis can be uni-, bi-, or tricompartmental, whether medial and lateral femorotibial compartments and/or the femoropatellar compartment is affected or not. Gonarthrosis location induces a varus/valgus malalignment whether the mechanical axis of the lower limbs passes inside the medial or the lateral knee compartment because lost cartilage is not replaced. This intra-articular malalignment will progressively increase loads on only one compartment of the knee, leading to further cartilage loss and increased OA. Standard knee radiographs will show decreased joint space in only one compartment of the knee (schuss weight-bearing view) and the position of the mechanical axis of the lower limb (full-length weight-bearing radiograph); and magnetic resonance imaging (MRI) will delineate the absence of cartilage lesions in the other knee compartments.

OA is treated primarily by medication, bracing, and physiotherapy (Bartels 2007; Bellamy 2006; Brosseau 2009; Brouwer 2005; Fransen 2009; Hulme 2002; Rutjes 2009; Rutjes 2010; Scott 2007). As the disease progresses and treatment shows its limits, surgery can be proposed according to the location and cause of the knee OA. Surgical treatment can consist of conservative surgery or replacement surgery. Bi- and tricompartimental knee OA is currently treated with total knee arthroplasty. Options for femorotibial unicompartmental OA of the knee include tibial or femoral osteotomy (conservative surgery) (Brouwer 2007), unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) (replacement surgeries) (Jacobs 2001; Price 2010). Treatment options are influenced by age, co-morbidities, and level of activity. New techniques such as mosaicplasty and cartilage grafts (conservative surgeries) are emerging (Jakobsen 2005; Vasiliadis 2010).

Description of the intervention

Femorotibial UKA replaces the missing bearing surface of one compartment of the knee-the medial or lateral compartment-with an implant. The implant may have a fixed-bearing or a mobile-bearing surface. The tibial component may have two different shapes in the lateral and medial compartments. This surgery implies healthy knee cruciate ligaments and no extra-articular cause of malalignment. It should allow preservation of bone stock and minimization of soft tissue disruption, including preservation of the central pivot, which ought to ensure a better kinematic. Indications for femorotibial UKA in unicompartmental OA have gradually become more aggressive over the past decade, in part because of the exponential demand for early recovery and the unwillingness of young patients to cope with the weight-bearing restrictions imposed by a high tibial osteotomy (HTO).

How the intervention might work

In UKA the damaged cartilage surfaces of the knee compartment are replaced allowing the patient to bear more weight on the resurfaced compartment. It helps the remaining articular cartilage of the other knee compartment to behave as normally as possible mechanically by restoring the normal alignment of the knee, and helps the knee to go back close to a normal kinematic pattern. It can be performed through a minimal access approach with lower perioperative morbidity and earlier recovery (Brown 2012).

Why it is important to do this review

Femorotibial UKA has been evolving and expanding over past decades, but some aspects of these techniques such as the longevity of the results, the age of patients, the level of activity, the patellofemoral OA, and the presence of obesity are still controversial (Berger 2010; Donell 2010). Some have argued that UKA might not be appropriate in cases of knee OA secondary to conditions such as rheumatoid arthritis and crystal deposition disease (e.g., chondrocalcinosis) that could cause progression of cartilage loss and extension of OA changes to other compartments (Schindler 2010). TKA is considered a relatively heavy surgery for unicompartmental OA (Saccomanni 2010). Femoral or tibial osteotomy has contraindications and is often reserved for relatively young people. An osteotomy does not halt the progression of OA but may delay the need for knee arthroplasty by shifting the excessive load from one compartment of the knee to the other. Cartilage transplantation techniques, such as autologous chondrocyte or osteochondral graft implantation, are often reserved for focal cartilage defects in the absence of angular defects (e.g., varus or valgus). They serve as very promising solutions but are compromised by the fixation method required to secure them in place. Thus careful selection of patients for these methods is crucial (Sgaglione 2010).

Clear guidelines regarding selection of the most appropriate treatment for the unicompartmental OA are needed.


To assess the benefits and harms of unicompartmental knee arthroplasty in the treatment of knee osteoarthritis in adults in terms of decreasing pain, increasing knee function, and postponing the need for a total knee arthroplasty.


Criteria for considering studies for this review

Types of studies

To assess benefit, randomised controlled trials (RCTs) and controlled clinical trials (CCTs) will be searched. If no RCTs or CCTs are identified, we will include controlled before and after studies (CBAs) and interrupted time series (ITS). Registries will be searched for survival rate evaluations.

Types of participants

Participants will be adult patients with unicompartmental OA of at least grade 2 according to Ahlbäck radiologic criteria (Ahlbäck 1968) or grade 4 according to the Kellgren and Lawrence grading system (Petersson 1997).

Types of interventions

Intervention: unicompartmental knee arthroplasty.

Control: no intervention (usual care) or any other surgical techniques currently available for treating unicompartmental knee OA, particularly tibial osteotomy, TKA, or mosaicplasty.

Types of outcome measures

SF-36 (Short-Form 36) or EQ-5D (EuroQoL in 5 dimensions), VAS (visual analogue scale) pain and stiffness, WOMAC (Western Ontario and McMaster Osteoarthritis Index), and clinical and radiologic KSS (Knee Society Score) will be searched as standardized outcomes measures. Follow-ups of 6 months, 1 year, 5 years, 10 years, and 15 years or longer will be searched.

Major outcomes
  • Survival rate of the implant-femoral and tibial loosening (aseptic loosening).

  • Serious adverse events.

  • Mortality.

  • Failure of treatment rate-time to revision (any complication that needed surgical intervention).

 These major outcomes will be part of the summary of findings table.

Minor outcomes
  • Global assessment (patient).

  • Range of motion.

  • Length of hospital stay.

Search methods for identification of studies

Electronic searches

Studies will be searched in the following electronic databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, current issue); MEDLINE (1966 to present); CINAHL (1982 to present); EMBASE (1988 to present); and Web of Science (1900 to present). No language restriction will be applied. We will also search databases of ongoing trials: Current Controlled Trials ( links to other databases of ongoing trials).

For full details of the search strategy, please see Appendix 1.

Searching other resources

We will try to identify additional studies by searching the reference lists of included trials.

Data collection and analysis

Two authors will independently assess all potential abstracts and published reports that will be identified by the literature search strategy. Consensus will be reached through discussion of any disagreements. Reasons for excluded studies will be noted. These two authors will be blinded to authors and institution but will not be blinded to the journal of the publication.

Selection of studies

With the use of reference management software program, search results will be merged, and duplicate records of the same report will be removed. Each author will examine titles and abstracts independently to remove obviously irrelevant reports (authors would be over inclusive at this stage). Full text of potentially relevant reports will be retrieved, and multiple reports of the same study will be linked together (author names, location and setting, specific details of the interventions, numbers of participants and baseline data, date and duration of the study). Full-text reports will be examined for compliance of studies with eligibility criteria. Final decisions on study inclusion will be made after comparison of selected studies by each author. Discrepancies will be resolved by consensus of two authors.

A kappa statistic will be calculated for measuring agreement between the two authors who are making simple inclusion/exclusion decisions. Values of kappa between 0.40 and 0.59 will be considered to reflect fair agreement, between 0.60 and 0.74 to reflect good agreement, and 0.75 or higher to reflect excellent agreement.

Data extraction and management

Each author will extract data independently using predesigned standardized data abstraction forms (in accordance with the checklist Table 7.3.a of the Cochrane Handbook for Systematic Reviews of Interventions; Higgins 2011a). One author will enter data into RevMan, and the other will cross-check the printout against his or her own data extraction forms. We will resolve discrepancies by consensus of two authors. We will obtain information from the primary author when the published article provides inadequate information for the review.

Assessment of risk of bias in included studies

The risk of bias of included trials will be assessed independently by two authors using the 'Risk of bias' tool of The Cochrane Collaboration (Higgins 2011b). Risk of bias will be categorized as low, uncertain, or high for each of the included studies (Table 1). Disagreements will be resolved through discussion (a third author will be asked to adjudicate if necessary). The biases listed in the table below will be assessed.

Table 1. Risk of bias tool of the Cochrane Collaboration
Domain Support for judgement Review authors’ judgement
Selection bias.  
Random sequence generation.Describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.Selection bias (biased allocation to interventions) due to inadequate generation of a randomised sequence.
Allocation concealment.Describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrolment.Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment.
Performance bias.  
Blinding of participants and personnel Assessments should be made for each main outcome (or class of outcomes). Describe all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Provide any information related to whether the intended blinding was effective.Performance bias due to knowledge of the allocated interventions by participants and personnel during the study.
Detection bias.  
Blinding of outcome assessment Assessments should be made for each main outcome (or class of outcomes).Describe all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provide any information related to whether the intended blinding was effective.Detection bias due to knowledge of the allocated interventions by outcome assessors.
Attrition bias.  

Incomplete outcome data

Assessments should be made for each main outcome (or class of outcomes). 

Describe the completeness of outcome data for each main outcome, including attrition and exclusions from the analysis. State whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomised participants), reasons for attrition/exclusions where reported, and any re-inclusions in analyses performed by the review authors.Attrition bias due to amount, nature, or handling of incomplete outcome data.
Reporting bias.  
Selective reporting.State how the possibility of selective outcome reporting was examined by the review authors and what was found.Reporting bias due to selective outcome reporting.
Other bias.  
Other sources of bias.

State any important concerns about bias not addressed in the other domains in the tool.

If particular questions/entries were prespecified in the review’s protocol, responses should be provided for each question/entry.

Bias due to problems not covered elsewhere in the table.
Random sequence generation (selection bias)
Allocation concealment (selection bias)
Blinding of outcome assessment (detection bias)
Blinding of participants and personnel (performance bias)
Incomplete outcome data (attrition bias)
Selective reporting (reporting bias)


Measures of treatment effect

For each study, we will calculate risk ratio, except in the cases of rare events when the Peto odds ratio (OR) is most appropriate along with 95% confidence limits for dichotomous outcomes, and we will compute standardised mean differences (SMDs) and 95% confidence limits for continuous outcomes according to the method described by Rutjes (Rutjes 2010). For continuous outcomes such as pain, measured on the same scale, mean differences will be calculated.

Unit of analysis issues

Authors will consider whether in each study, a unit-of-analysis issue arises: if groups of individuals were randomly assigned together to the same intervention (i.e., cluster-randomised trials); if individuals undergo more than one intervention (e.g., in a cross-over trial, or simultaneous treatment of multiple sites on each individual [i.e., multiple joint prothesis]); or if multiple observations have been reported for the same outcome (e.g., repeated measurements, recurring events, measurements on different body parts).

Dealing with missing data

When possible, the authors will contact the original investigators to request missing data. Authors will make explicit the assumptions of any methods used to cope with missing data, for example, that the data are assumed missing at random, or that missing values were assumed to have a particular value such as a poor outcome. Sensitivity analyses will be performed to assess how sensitive results are to reasonable changes in the assumptions that are made. In the Discussion section, we will address the potential impact of missing data on the findings of the review.

Assessment of heterogeneity

Where statistical evidence of heterogeneity is found (a Chi2 test with P < 0.10 or an I2 test with a percentage of variability in effect estimates > 50%), we will use a random-effects model. Forest plots will be visually inspected for identification of heterogeneity.

Assessment of reporting biases

Funnel plots will be used to assess for the potential existence of small study bias for primary outcomes. A number of explanations for the asymmetry of a funnel plot are known. For continuous outcomes, we will use Egger’s test for asymmetry. Therefore, we will carefully interpret results (Rutjes 2010; Sterne 2011).

Data synthesis

If meta-analysis is possible, the Mantel Haenszel statistical method will be used. A fixed approach to the analysis will be undertaken unless evidence of heterogeneity is noted across studies, in which case the random-effects model will be used.

Subgroup analysis and investigation of heterogeneity

We will carry out subgroup analyses if one of the primary outcome parameters demonstrates statistically significant differences between intervention groups.

Subgroup analysis will be done in terms of patients' age (< 65 years or older), gender (female or male), and body mass index (< 30 kg/m2 or superior) and preoperative angular deformity in the frontal plane (mechanical axis deviation > 9°), and between lateral and medial unicompartmental arthroplasty.

Sensitivity analysis

A sensitivity analysis will be performed to compare studies in terms of their inclusion criteria, variations in treatment used, and study design. An analysis will be performed on study quality, which will be judged in terms of having low risk of bias as adequate allocation concealment, blinding, and limited loss to follow-up, with all trials contributing data to the review. For outcome instruments, we will compare effect size estimates and bootstrap confidence intervals when each subscale is considered independently or as a whole.

Grading the evidence

The grading system recommended by the Musculoskeletal Group and developed by the Grades of Recommendation, Assessment, Development and Evaluation Working Group (GRADE Working Group) will be used: The GRADE approach defines the quality of a body of evidence as the extent to which one can be confident that an estimate of effect or association is close to the quantity of specific interest (Schünemann 2011). The quality of a body of evidence involves consideration of within-study risk of bias (methodologic quality), directness of evidence, heterogeneity, precision of effect estimates, and risk of publication bias. The GRADE system entails an assessment of the quality of a body of evidence for each individual outcome. The GRADE approach specifies four levels of quality. The highest quality rating is used for randomised trial evidence. Review authors can, however, downgrade randomised trial evidence to evidence of moderate, low, or even very low quality, depending on the presence of the five factors. Usually, quality rating will fall by one level for each factor, up to a maximum of three levels for all factors. If very severe problems are noted for any one factor (e.g., when assessing limitations in design and implementation, all studies were unconcealed, were unblinded, and lost more than 50% of their patients to follow-up), randomised trial evidence may fall by two levels because of that factor alone (Table 2).

Table 2. Levels of quality of a body of evidence in the GRADE approach
Underlying methodology Quality rating
Randomised trials; or double-upgraded observational studiesHigh
Downgraded randomised trials; or upgraded observational studiesModerate
Double-downgraded randomised trials; or observational studiesLow
Triple-downgraded randomised trials; or downgraded observational studies; or case series/case reportsVery low

The authors will downgrade randomised trial evidence to evidence of moderate, low, or even very low quality, depending on the presence of the five factors that may decrease the quality level of a body of evidence:

1. Limitations in the design and implementation of available studies suggesting high likelihood of bias.

2. Indirectness of evidence (indirect population, intervention, control, outcomes).

3. Unexplained heterogeneity or inconsistency of results (including problems with subgroup analyses).

4. Imprecision of results (wide confidence intervals).

5. High probability of publication bias.


Angelina Poloni and Elizabeth Tanjong Ghogomu for administrative assistance.


Appendix 1. Search strategy

According to the Cochrane Collaboration strategy and in order to identify randomised controlled trials concerning UKA for treating knee osteoarthritis, we will combine our search strategy with the following search terms in MEDLINE:

1          Arthroplasty, Replacement, Knee/                                                              

2          Knee Prosthesis/                                                                                         

3          (knee arthroplast$ or knee replacement or knee prosthes$).tw.                 

4          (uka or unicompartmental knee arthroplast$).tw.                                      


6          4 or 1 or 3 or 2                                                                                             

7          6 and 5                                                                                                                   

8          Osteoarthritis, Knee/                                                                                   

9          Osteoarthritis/                                                                                                       

10        (osteoarthrit$ or osteoarthro$ or oa or degenerative joint disease

 or degenerative arthritis).tw.                                                                                  

11        10 or 9                                                                                                      

12        exp Knee Joint/                                                                                            

13        Knee/                                                                                                           


15        13 or 12 or 14                                                                                                        

16        11 and 15                                                                                                    

17        8 or 16                                                                                                         

18        6 and 17                                                                                                      

19        limit 18 to yr="1980 - 2010"                                                                              

20        7 and 17                                                                                                      

21        limit 20 to yr="1980 - 2010"               

Additional key words of relevance may be detected during the electronic searches. If this is the case, the search strategies will be modified to incorporate these terms.

Contributions of authors

BMJ: protocol draft, search strategy development.

AFE: protocol draft, search strategy development.

EM: protocol draft.

Declarations of interest

None known.