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The Journal of Arthroplasty Vol. 26 No. 1 2011

Complications After Minimally Invasive TotalKnee Arthroplasty as Compared With

Traditional Incision Techniques

A Meta-Analysis

RajivGandhi,MD,MS,FRCSC,*HollySmith,*KellyA.Lefaivre,MD,MSc,FRCSC,yJ. Rod Davey, MD, FRCSC,* and Nizar N.Mahomed, MD, ScD, FRCSCz§||b

Abstract: The primary objective of our meta-analysis was to compare the incidence ofcomplications between minimally invasive surgery and standard total knee arthroplasty (TKA)approaches. We reviewed randomized controlled trials comparing minimally invasive TKA tostandard TKA. After testing for publication bias and heterogeneity, the data were aggregated byrandom effects modeling. Our primary outcome was the number of complications. Our secondaryoutcomes were alignment outliers, Knee Society Function scores, and Knee Society Knee scores.The combined odds ratios for complications for the minimally invasive surgery group andalignment outliers were 1.58 (95% confidence interval, 1.01-2.47; P b .05) and 0.79 (95%confidence interval, 0.34-1.82; P = .58), respectively. The standard difference in means for KneeSociety scores was no different between groups. Minimally invasive knee surgery should beapproached with caution. Keywords: minimally invasive, knee, complications.© 2011 Elsevier Inc. All rights reserved.

Minimally invasive knee arthroplasty surgery hasexperienced a recent surge in popularity, driven by thepatient concerns of a faster recovery time and a shorter,more cosmetic scar [1]. After first being successfullyapplied to unicompartmental knee arthroplasty [2,3],the principles of minimally invasive surgery (MIS) werethen expanded to total knee arthroplasty (TKA). Thelimited incision approaches to TKA include the mini-midvastus [4], the subvastus [5], and mini-arthrotomytechniques [6]. Possible advantages of MIS TKA includeless postoperative pain [7], a faster functional recovery

the *Division of Orthopaedic Surgery, Department of Surgery,Health Network, University of Toronto, Toronto, Canada;

ent of Orthopaedic Surgery, University of British Columbia,lumbia, Canada; zDivision of Orthopaedic Surgery, Universityetwork, Toronto Western Research Institute, Toronto, Canada;of Health Care and Outcomes Research and Arthritis Communitynd Evaluation Unit, Toronto Western Research Institute, Toronto,||Department of Health Policy, Management and Evaluation,of Toronto, Toronto, Canada; and bDepartment of Surgery,of Toronto, Toronto, Canada.tted July 6, 2009; accepted November 25, 2009.nefits or funds were received in support of the study.t requests: Rajiv Gandhi, MD, MS, FRCSC, Toronto WesternUniversity Health Network, 399 Bathurst St, EastWing 1-439,Ontario, Canada M5T-2S8.1 Elsevier Inc. All rights reserved.403/2601-0005$36.00/0.1016/j.arth.2009.11.022

29

[8,9], decreased length of hospital stay [9], and lessblood loss [6,10].The evaluation of any new medical therapy must

include a detailed evaluation of both efficacy and safetyoutcomes. Postoperative complication rates after MISTKA have been documented in many studies; some havereported more complications in MIS TKA comparedwith the standard technique, whereas others reportfewer or no significant difference. Potential drawbacks ofMIS TKA include longer tourniquet times [11-13], poorcomponent placement [11,14] and early implant failure[15]. It is important to note that no published studycomparing the MIS technique with the standardtechnique is adequately powered to report any statisticalcomparison of complication rates.The literature evaluating the outcomes of MIS TKA

consists mainly of nonrandomized prospective andretrospective cohort studies. In many cases, the authorsimposed strict eligibility criteria for patients undergoingMIS TKA, limiting the generalizability of their findings. Inaddition,manyof the studies are conducted by individualswho have developed the surgical techniques and must beinterpreted with caution. Randomized controlled trials(RCTs) represent the best available data because they limitthe potential confounding between treatment groups.We performed a systematic review and meta-analysis

of RCTs to compare the complication rates between MIS

30 The Journal of Arthroplasty Vol. 26 No. 1 January 2011

TKA and standard TKA. Our secondary objective was tocompare the outcomes of Knee Society scores (KSS) andoutliers from the acceptable range of alignment for these2 treatment groups.

Materials and MethodsEligibility CriteriaWe included articles relevant to the following: (1)

patients underwent primary TKA; (2) the comparisonwas between minimally invasive TKA and standardTKA; (3) the outcome measures included postoperativecomplications, Knee Society Knee scores, Knee SocietyFunction scores, and alignment outliers; and (4) thestudy was a published or unpublished RCT. Studiesevaluating the intervention of computer navigation–assisted MIS TKA were excluded.

Study IdentificationTwo of the authors (RG and HS) independently

completed a computerized search of the onlinedatabases PubMed MEDLINE and OVID MEDLINE(1950 to May 2009) and EMBASE (1950 to 2009)with the following search terms: (total knee arthroplastyOR total knee replacement OR knee prosthesis) AND(minimally invasive OR mini-incision OR less invasive)AND (postoperative complications OR post-op complicationsOR treatment outcome OR joint instability OR recovery offunction). We also searched the Cochrane Database ofSystematic Reviews, the Cochrane Central Register ofControlled Trials, and www.clinicaltrials.gov. Wesearched the archives of orthopedic meetings forpotential abstracts to minimize publication bias. Wereviewed the American Academy of Orthopedic Sur-geons (2001-2009), Knee Society (2001-2009), Cana-dian Orthopedic Association (2003-2009), and BritishOrthopedic Association (2002-2009) meetings.

Fig. 1. Funnel plot of studies indicati

The bibliographies of articles that met the inclusioncriteria were also reviewed for relevant studies.

Assessment of Study QualityEach RCT was independently assessed by 2 of the

authors to grade the quality of the study design with useof a 21-point scale [16]. Both reviewers were blinded toeach article's title, authors, and institution of origin.Conflicts were resolved through consensus. Intraclasscorrelations were calculated to assess the level ofagreement between reviewers.

Data ExtractionFor all studies, 2 of us extracted relevant data including

demographics, relevant outcomes, details of implantsand surgical technique, loss to follow-up, and method ofrandomization. Complications of surgery were defined asany adverse event that was directly related to thesurgical procedure. These included categories of deep/superficial infections, fracture, manipulation, femoralnotching, ligament rupture, implant subsidence, exten-sor mechanism disruption, thromboembolic disease, andmedical complications such as cardiovascular events.For the outcome of the KSS, we extracted data on the 2

components individually: the Knee score and theFunction score. A greater score on both scales representsbetter function. We evaluated the scores at 3 months offollow-up. Radiographic outliers from the acceptablealignment range were taken as a ratio from each study.Studies consistently applied the criteria of deviation of 2°to 3° of varus or valgus from a neutral mechanical axis asan outlier.

Statistical AnalysisHeterogeneity describes between-study variability,

which can be related to differences in the treatmenteffects between studies [17]. We used 2 strategies toassess statistical heterogeneity between studies for all of

ng no evidence of publication bias.

Tab

le1.

SummaryDataforRCTsIncluded

inAnalysis

Study

Subjects

MIS

Typ

eMea

nAge

(y)

Male(%

)Mea

nBMI

ImplantTyp

eNo.of

Complications

Mean

Knee

Score

Mea

nFunctionScore

No.of

Outliers

Boergeret

al,2005

M S60

60

MS

69

68

23

25

28

29

LPS

MB&

LPS-flex

13

12

NR

NR

1 0Kim

etal,2007

M S120

120

QS

65.4

65.4

22.5

22.5

28.1

28.1

LPS

16 7

91

92

85

83

NR

Kolisek

etal,2007

M S40

40

MID

67

70

72.5

60

32

30

PS

9 581

77

74

73

0 0Chin

etal,2007

M S60

30

MID

,QS

68.2

63.4

20

10

28.02

29.44

PFC

-FB,LPS

3 2NR

NR

12 3

Tashiroet

al,2007

M S24

25

MID

,QS

76.1

73.9

10 9.5

NR

MB,LPS

-flex&

LPS

1 090

92

92

91

18 14

Karachalioset

al,2008

M S50

50

MID

71.1

70.8

38

30

32

31.5

Gen

esisII

15 13

97

93.8

97

84

3 9Han

etal,2008

M S30

30

MP

66

64

6.7

6.7

26.9

26.4

MB,LPS

-flex

0 0NR

NR

NR

Luringet

al,2008

M S30

30

MP

69

69

NR

31

32

PFC

0 083

86

82

83

5 2Karpman

etal,2008

M S40

19

MID

,QS

73.5

73

37.5

47

29

29

FB,CR

2 0NR

NR

NR

BMIindicates

bodymassindex

;M,minim

ally

inva

sive

;S,stan

dard;

QS,quad

ricepssparing;

MID

,mini-midva

stus;MP,mini-med

ialparap

atellar;MS,mini-subv

astus;FB,fixed

bearing;

MB,

mobile

bearing;

CR,cruciateretaining;

PS,cruciatesubstituting;

PFC

,press-fitcondylar;NR,notreported

.

Complications After MIS TKA and Traditional Techniques � Gandhi et al 31

our outcome measures. Firstly, we used the methods ofHedges and Olkin [18]. A P value b .1 was consideredsuggestive of statistical heterogeneity because these testsare traditionally underpowered. Secondly, we calculatedthe I2 statistic that describes the percentage of totalvariation across studies that is attributable to heteroge-neity rather than chance [19]. A value of less than 25% isconsidered low heterogeneity; 50%, moderate hetero-geneity; and 75%, high heterogeneity [19]. Beforeanalyzing the data, we developed hypotheses of potentialsources of heterogeneity including implant manufactur-er, implant type (fixed bearing vs mobile bearing etc),minimally invasive surgical technique, and study quality.To assess for publication bias, the potential for

negative studies to not be published, we constructed afunnel plot for our primary outcome. This plotdemonstrates the relationship between the sample sizeof the studies and the precision in estimating thetreatment effect (Fig. 1). The x-axis represents the logsodds ratio (OR) as a measure of treatment effect,whereas the y-axis represents a measure of study size.Bias can be seen if the plots are asymmetric about thepooled log OR vs a plot resembling an inverted funnel,which represents no bias [20].For both the categorical outcomes of complications

and radiographic outliers, we used the OR as thesummary statistic. This ratio represents the odds ofcomplications in the MIS group over the odds ofcomplications in the standard group. An OR of greaterthan 1 indicates a greater incidence of complications inthe MIS group, and the point estimate of the OR isconsidered statistically significant if the 95% confidenceinterval (CI) does not include the null value 1. For thosestudies that had a zero in a cell for the number ofcomplications in 1 of the 2 groups, we applied the Yatescorrection, as these cells otherwise create problems withcomputing ratio measures and standard errors oftreatment effects. This problem is resolved by addingthe value 0.5 to each cell in the 2 × 2 table for that study[21]. We used the Mantel-Haenszel method to combinethe ORs for the outcomes of interest. For the continuousoutcome of KSS, we pooled data across studies by usingweighted mean differences (and 95% CIs). For thestudies in which the standard error for a mean differencein KSS was not reported, we calculated for the standarderror by converting the P value to a z score and solvingfor the standard error from the formula z = meandifference/standard error.All data were combined with the random effects model

because there was moderate evidence of heterogeneitybetween studies for the outcome of KSS [22]. Therandom effects model is a more conservative approachbecause it assumes that an effect may vary across studiesbecause of differences between studies [22].The analysis was carried out by using Comprehensive

Meta-analysis version 2.0 (Englewood, NJ).

Table 2. Summary of Complications Reported in the TrialsIncluded in This Analysis

Complications MIS Standard

Local surgical complicationsPatellar tendon injury (partial/complete)- 2 0Deep peroneal nerve palsy 2 0Fracture/notching 9 6Gross component malposition/subsidence 4 1Popliteus tendon injury 2 0Stiffness requiring manipulation 1 1Skin necrosis/delayed wound healing 9 3Superficial wound infection 3 1Deep infection 3 1Nonprogressive radiolucent lines 6 8Subtotal 41 21

Systemic complicationsDVT 15 17Systemic medical (MI, CHF, delirium, sciatica) 3 1Subtotal 18 18Grand total 59 39

DVT indicates deep vein thrombosis; MI, myocardial infarction; CHF,congestive heart failure.

32 The Journal of Arthroplasty Vol. 26 No. 1 January 2011

ResultsAs a result of our searches, 266 studies were identified.

Applying our eligibility criteria resulted in 7 articles forsystematic review and data analysis for our primaryoutcome. We excluded 184 studies based on the title orabstract, 40 because they were non-English publications,29 because they were nonrandomized trials, and 6because they were duplicate publications. Two addi-tional studies were identified through a review of thebibliographies of relevant studies, for a total of 9 studiesevaluating our primary outcome.All articles were published in English, and all were

prospective RCTs. The method of randomization variedamong studies. Two studies used computer-generatedrandomization and sealed envelopes [23,24]. Threestudies used sealed envelopes for allocation conceal-

Fig. 2. Forest plot of combin

ment and a randomization table for sequence genera-tion [25-27]. A table of randomized numbers was usedin 2 studies; however, allocation concealment was notdiscussed [12,28]. In 2 of the studies, the method ofrandomization was not discussed [13,29]. Postoperativeassessments were completed by blinded, independentreviewers in 5 of the 9 studies [13,23,24,26,28]. It hasbeen documented that there is a learning curveassociated with the optimal performance of MIS TKA[30]. Of the 9 studies we reviewed, 4 specificallyindicated that the surgeons performing MIS wereexperienced with the procedure and had performed aminimum of 25 MIS TKAs before beginning the study.Average follow-up time ranged from 3 to 28 months.The details of the studies are shown in Table 1.There were 59 total complications in the MIS group as

compared with 39 in the standard incision group. Whenconsidering just the local surgical complications, therewas a 95% greater number of complications in the MISgroup as compared with the standard incision group, 41vs 21, respectively (Table 2).The reviewers achieved good agreement on evaluation

of study quality (intraclass correlation, 0.83; 95% CI,0.11-0.97).Fig. 1 demonstrates a funnel plot of the 9 studies

reporting the logs OR of complications as a measure oftreatment effect. The plot demonstrates only minimalasymmetry, and all studies fall within the 95% CI axisfor a given standard error. The plot demonstrates noevidence of publication bias.The combined OR for complications for the MIS group

was 1.58 (95% CI, 1.01-2.47; P = .04). There was noevidence of statistical heterogeneity between studies (P =.96, I2 = 0.00). Fig. 2 shows a forest plot of the cumulativedata from the 9 studies included in the analysis.The standard difference in means for KSS-Function

scores was 0.17 (95% CI, −0.05 to 0.38; P = .12). Therewas evidence of moderate statistical heterogeneity

ed ORs for complications.

Fig. 3. Forest plot of clinical outcomes as measured by the KSS-Function scores.

Complications After MIS TKA and Traditional Techniques � Gandhi et al 33

between studies (P =.24, I2 = 27.1). Fig. 3 shows a forestplot of the cumulative data from the 5 studies includedin the analysis.The standard difference in means for KSS-Knee

scores was 0.10 (95% CI, −0.07 to 0.28; P = .23).There was no evidence of statistical heterogeneitybetween studies (P = .43, I2 = 0.00). Fig. 4 shows aforest plot of the cumulative data from the 5 studiesincluded in the analysis.The combined OR for outliers from the acceptable

range of alignment was 0.79 (95% CI, 0.34-1.82; P =.58). There was evidence of moderate statistical hetero-geneity between studies (P = .18, I2 = 33.9). Fig. 5 showsa forest plot of the cumulative data from the 6 studiesincluded in the analysis.We found no significant heterogeneity between

studies for our primary outcome; and as such, we didnot perform a sensitivity analysis.

DiscussionThe results of this meta-analysis demonstrate a

statistically significant increase in complication rates

Fig. 4. Forest plot of clinical outcomes a

with MIS TKA when compared with standard TKA.There were no significant differences in postoperativealignment or KSS at 3 months between the 2 groups.Many experienced surgeons have reported serious

complications with MIS surgery including vascularinjury [31] and patellar tendon injury [32]. A recentreport examining a consecutive series of revision kneesdemonstrated a mean time to revision of less than 15months for the MIS cohort [15]. Our study shows asignificantly greater complication rate for minimallyinvasive techniques as compared with the standardsurgical approach. This greater complication rate maybe related to greater tension on wound edges, lessvisualization, or increased surgical times [10]. More-over, a recent report comparing the MIS and traditionalapproaches demonstrated no difference betweengroups in levels of muscle damage as measured byserum levels of muscle-related enzymes [33]. Thisfurther questions the utility of MIS techniques inknee arthroplasty surgery.For an adequately powered randomized trial to find a

difference in complication rates of 50% (eg, 6% in one

s measured by the KSS-Knee scores.

Fig. 5. Forest plot of combined ORs for the outliers from the acceptable range of alignment.

34 The Journal of Arthroplasty Vol. 26 No. 1 January 2011

group compared with 3% in another group) at 80%power and a type I error rate of 5%, it would require 749patients. An RCT of this size would be very difficult toorganize and expensive to perform, emphasizing theimportance of meta-analysis techniques. The 9 studieswe identified combined to give a total of 858 patients forour primary outcome, increasing the power of ourconclusion. Another meta-analysis was previously doneto evaluate the outcomes after MIS TKA and found nosignificant difference in complication rates betweengroups [34]. This group included 7 studies in theirmeta-analysis, of which 4 compared navigation-assistedMIS TKA to standard TKA. Only 2 of the 7 studies wereRCTs [25,29]. Moreover, their study demonstratedsignificant statistical heterogeneity across studies (I2 =83.7, P b .0001), which greatly limits the reliability oftheir results.Several cohort studies have reported that MIS TKA is

associated with a quicker functional recovery in theshort term [8,35,36]; however, the results of our pooledanalysis of the best available evidence shows nosignificant functional difference at 3-month follow-upas measured by the KSS. This finding is consistent withseveral other studies that showed no significant differ-ence in functional outcome, KSS, or range of motion at afollow-up of 3 months or greater [4,25,35,36]. Non-randomized data comparing the outcomes of 2 surgicaltechniques must be interpreted with caution becausethey have the potential of a selection bias that mayconfound the relationship between the intervention andthe outcome.Limited incision approaches raise concerns of less

visualization and the potential for component malposi-tion; however, we did not find this in our study. Otherauthors have shown that minimally invasive techniquesare related to poorer component alignment and thepotential for a poorer clinical outcome and subsequentlyearly revision [15,37,38].There are several strengths of our meta-analysis. First,

there was essentially no statistical heterogeneity for ourprimary outcome. Second, we conducted a thorough

search of the literature including unpublished abstracts,clinical trials, and non–English-language publications.We found no evidence of publication bias as we wouldsuspect because we are not reviewing the primaryoutcome of the studies, but rather the complication rate.Third, we included only RCT data for this analysis.Our study also has several limitations. The strength

and accuracy of our conclusions depend entirely on thestrength and extent of reporting of the primary studiesused for analysis. Although all studies were RCTs, not allof them commented on whether those collecting theoutcome measures were blinded to the surgical ap-proach used. In addition, the method of randomizationvaried greatly; and several studies did not comment onthe method at all.The results of our systematic review and meta-analysis

of the literature indicate that MIS TKA results in asignificantly higher complication rate when comparedwith standard TKA. There were no statistically signifi-cant differences between the 2 groups in alignmentoutliers or KSS at 3 months postoperation. The MIS TKAappears to cause unnecessary risk for the patient withoutdemonstrating any clinical benefit in the parametersexamined. For a surgical procedure to be used regularly,it must yield outcomes that are at least as good as thoseproduced by the standard technique [39]. Thus far,minimally invasive TKA has failed to demonstrateimproved outcomes; and as such, the indications forMIS TKA remain unclear. We advocate for an adequatesurgical exposure to ensure accurate component align-ment and soft tissue balancing. The role of computernavigation in complimenting these minimally invasivetechniques requires further study.

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