Visit our Evidence-Based Covid-19 Website and Stay Up to Date with the latest Research.
Volume:2 Issue:4 Number:161 ISSN#:2563-5476
Author Verified
ACE Report #4359

MIS not better than conventional technique for unicompartmental knee arthroplasty

How to Cite

OrthoEvidence. MIS not better than conventional technique for unicompartmental knee arthroplasty. ACE Report. 2013;2(4):161. Available from: https://myorthoevidence.com/AceReport/Report/4359

Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A

Minimally invasive surgery did not improve outcome compared to conventional surgery following unicompartmental knee arthroplasty using local infiltration analgesia: a randomized controlled trial with 40 patients

Acta Orthop. 2012 Dec;83(6):634-41. doi: 10.3109/17453674.2012.736169. Epub 2012 Oct 8

Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here


40 patients undergoing unicompartmental knee arthroplasty with local anaesthetic infiltration were randomized to receive a minimally invasive or conventional surgical procedure to determine if minimally invasive surgery (MIS) would result in earlier postoperative home-readiness, as well as improved pain and functional outcomes. Follow-up was conducted over 6 months postoperatively. The results indicated that there were no benefits to using MIS techniques over conventional techniques as there were no differences in the outcomes.

Publication Funding Details +
Not Reported
None disclosed

Risk of Bias


Reporting Criteria


Fragility Index


Was the allocation sequence adequately generated?

Was allocation adequately concealed?

Blinding Treatment Providers: Was knowledge of the allocated interventions adequately prevented?

Blinding Outcome Assessors: Was knowledge of the allocated interventions adequately prevented?

Blinding Patients: Was knowledge of the allocated interventions adequately prevented?

Was loss to follow-up (missing outcome data) infrequent?

Are reports of the study free of suggestion of selective outcome reporting?

Were outcomes objective, patient-important and assessed in a manner to limit bias (ie. duplicate assessors, Independent assessors)?

Was the sample size sufficiently large to assure a balance of prognosis and sufficiently large number of outcome events?

Was investigator expertise/experience with both treatment and control techniques likely the same (ie.were criteria for surgeon participation/expertise provided)?

Yes = 1

Uncertain = 0.5

Not Relevant = 0

No = 0

The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.




Outcome Measurements


Inclusion / Exclusion


Therapy Description



Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65

The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.

Why was this study needed now?

Many studies have investigated procedures that focused on improving postoperative pain and mobilization in patients following knee arthroplasty. Minimally invasive surgery (MIS) with local infiltration analgesia (LIA) was developed with respect to these criteria in unicompartmental knee arthroplasty on the basis that it caused less trauma to the soft tissue surrounding the knee and improved patient outcomes. However, the MIS technique is more demanding than conventional methods, and some surgeons hesitate to use it due to its longer learning curve. Moreover, there has been recent interest in the investigation of the importance of MIS with local anaesthetic infiltration, indicating the need for this study.

What was the principal research question?

Did the use of minimally invasive surgery with local infiltration analgesia in unicompartmental knee arthroplasty lead to improved postoperative outcomes in pain management and mobilization when compared to conventional surgery, assessed over a 6 month period?

Study Characteristics -
40 patients undergoing unicompartmental knee arthroplasty (UKA) with local infiltration analgesia technique. (n=38 completed follow-up, 2 patients converted to total knee arthroplasty intraoperatively)
Minimally Invasive Surgery (MIS) Group: Patients underwent UKA using a minimally invasive technique. The knee was exposed via an 8 to 10 cm medial parapatellar skin incision from the medial pole of the patella distally to the medial side of the tibial tuberosity, and a medial parapatellar arthrotomy was carried from the base of the patella distally to the medial side of the tibial tuberosity (2-3cm below joint line). A retractor was then placed behind the patella tendon for visualization of the lateral compartment. (n=20)
Conventional (CON) Surgery Group: Patients underwent a medial UKA using a conventional technique. The knee was exposed via a 15 to 20 cm midline incision, followed by medial parapatellar arthrotomy from the base of the patella distally to medial side of the tibial tuberosity, and extended 5 to 10 cm proximally into the rectus tendon of the quadriceps for evertion and dislocation of the patella. (n=18)
Primary outcome measure was postoperative home-readiness based on criteria necessary for discharge. Secondary endpoints were length of hospital stay, postoperative pain (VAS-pain), analgesic consumption, functional outcome (patient satisfaction, Oxford Knee Score, EQ-5D questionnaire, knee extension and knee flexion), mobilization (Time to up and go (TUG) test), and adverse events.
Primary outcome follow-up conducted 21 hours postoperatively and subsequently 3 times daily thereafter until discharge. Follow-up of analgesic consumption and patient satisfaction was conducted at 1, 2, 3, and 7 days postoperatively. Follow-up of knee extension, knee flexion, and TUG test was conducted at 24h, discharge, 3, 7, 14 days, 3, and 6 months postoperatively. Follow-up of Oxford knee score was conducted at 14 days, 3 and 6 months, and EQ-5D questionnaires at 3 and 6 months.

What were the important findings?

  • Time of fulfillment for discharge criteria (home-readiness) did not statistically differ between groups (p=0.6), with the median discharge 24 (21-71) hours in the MIS group and 24 (21-46) hours in the CON group. Length of hospital stay also did not significantly differ (p=0.7).
  • VAS-pain scores at rest and 60 degrees flexion did not significantly differ between groups at any time.
  • There was no significant difference in analgesic consumption between groups at any time during follow up. (1 day p=0.2, 2 days p=0.6, 3 days p=0.3, 7 days p=0.2)
  • Postoperative functional outcomes of patient satisfaction, Oxford Knee Score, and EQ-5D questionnaire did not significantly differ at any point during follow-up (p>0.05).
  • There were numerical differences indicating better maximum knee extension and knee flexion in the MIS group, however these did not reach statistical significance (p>0.05).
  • Postoperative mobilization assessed by the "time to up and go" (TUG) test showed no difference between groups at any point during follow up (p>0.05).
  • Incidences of adverse events on the first postoperative were similar between groups, but nausea was significant higher in MIS patients on the second postoperative day (p=0.006). No postoperative complications were encountered in either group during the 6-month follow up period

What should I remember most?

MIS technique for medial unicompartmental knee arthroplasty with local anaesthetic infiltration did not provide any advantages over a conventional surgical technique with respect to postoperative home-readiness, pain, functional outcome, mobilization and adverse events.

How will this affect the care of my patients?

The operating surgeon should decide whether to use a conventional or an MIS technique for medial unicompartmental knee arthroplasty based on preference and the individual patient characteristics, as both procedures provide similar outcomes. Further clinical assessments with extended follow-up periods may prove useful in examining any differences in long-term outcomes.

CME Image

Continuing Medical Education Credits

You could be earning 0.5 CME credits for each report you read.

For Reprints and Permissions, click here

Please Login or Join to leave comments.