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Patient-specific vs. conventional instrumentation TKA: similar effect on implant rotation
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January 2014
Patient-specific vs. conventional instrumentation TKA: similar effect on implant rotation
Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:2
Rotation in total knee arthroplasty: no difference between patient-specific and conventional instrumentation
Knee Surg Sports Traumatol Arthrosc. 2013 Oct;21(10):2213-9Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here
Synopsis
40 patients, between the ages of 50 and 85, who were unresponsive to conservative treatment and were scheduled to receive total knee arthroplasty (TKA), were randomly assigned into 1 of 2 groups to test the effect of patient-specific instrumentation (PSI) on accuracy and rotational alignment in TKA. Patients received treatment with PSI or through a conventional TKA. Results indicated that PSI did not have a significant effect on the rotational alignment in patients following TKA.
Publication Funding Details
+
Funding:
Not Reported
Conflicts:
None disclosed
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.
3/4
Randomization
4/4
Outcome Measurements
2/4
Inclusion / Exclusion
4/4
Therapy Description
3/4
Statistics
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?
Implant malposition has been reported to be as high as 20-40% when using conventional instrumentation in total knee arthroplasty. To reduce the likelihood of implant malposition patient-specific instrumentation (PSI) was introduced with the goal of improving implant positioning and reducing the overall cost and surgery time needed to complete the procedure. Previous studies have shown that PSI can successfully restore the mechanical axis, but very little information has been gathered regarding the role of PSI in the rotation of the tibial and femoral implants. This study was brought forward to assess the matching of preoperative planning and postoperative position of the TKA implants, and to closely analyze the femoral rotation of implants positioned with or without PSI.
What was the principal research question?
Does the use of patient-specific instruments improve the accuracy of the rotational alignment in TKA?
Study Characteristics
-
Population:
40 patients, between the ages of 50 and 85, who had failed nonoperative intervention and who were scheduled to receive total knee arthroplasty
Intervention:
PSI Group: Patients in this group received an MRI 6-8 weeks prior to the surgery. The MRI included image acquisition on the hip and knee (between 80 and 120 cuts) and on the angle). Following segmentation, a group of engineers performed the planning of the TKA and submitted it to the participating surgeon. Based on clinical examination and on standing full-length X-rays, an edition of the planning was performed by the surgeon concerning the depth of the distal femoral and tibial cuts. Following the edition, the extension spaces were checked and planning approved. Rapid-prototyping, computer assisted, technology created the PSI jigs and a PSI guide was carefully positioned over the articular surface. A standard TKA procedure was then performed. All patients received the same high-flex mobile bearing TKA (NexGen LPS-Flex mobile, Zimmer, Warsaw) (n=20).
Comparison:
Control Group: Patients in this group were operated according to a previously described technique using an extra-medullary guide for the tibia and intra-medullary guide for the femur. All patients received the same high-flex mobile bearing TKA (NexGen LPS-Flex mobile, Zimmer, Warsaw) (n=20).
Outcomes:
Outcomes assessed were obtained through: X-ray and CT-scan results, which were used to calculate the three-dimensional angle of the implants. Rotation and alignment following treatment were also analyzed.
Methods:
RCT: Single Center: Single Blinded
Time:
Radiological assessments and CT-Scans were performed 3 days after surgery completion, and weight-bearing full-length X rays were performed 3 months after treatment
What were the important findings?
- Patients in the PSI group experienced <2 degrees or mm of difference between the planned position of the femoral implant and the obtained position in all femoral measurements except distal cut flexion angle (Mean difference of 2.6 degrees, 95% CI= 0.9)
- Patients in the PSI group experienced <2 degrees of difference between the planned position of the tibial implant and the obtained position when analyzing average tibial proximal cut (1.2 degrees), but not when looking at mean tibial slope angle (Mean difference of 2.2 degrees, 95% CI= 0.8), and tibial rotation (Mean difference of 6.8 degrees, 95% CI= 2.1).
- A total of 90% of all patients in the PSI group experienced less than 2 degrees or less than 2 mm of difference between the planned position of the femoral and tibial implants and their obtained positions, expect for when measuring tibial rotation, where the variations were much higher.
- No difference was observed between the two groups when analyzing weight-bearing full length X-rays 3 months after surgery. Mean HKA was 179 degrees in the PSI group with 4 outliers compared to 178.3 degrees with 2 outliers in the control group (p>0.05).
- No difference was found between the two groups concerning frontal and sagittal position of implants measured through Ml and AP X-rays (FFC, FTC, LFC, and LTC angle, and tibial slope, p>0.05 for all measurements).
- No significant difference in femoral rotation was observed between the two groups with a mean of 0.4 degrees begin expressed in the PSI group compared to 0.2 degrees in the control group (p>0.05).
- Mean tibial rotation was 8 degrees of internal rotation in the PSI group compared to 15 degrees of internal rotation in the control (p>0.05).
What should I remember most?
90% of all patients in the PSI group experienced less than 2 degrees or less than 2 mm of difference between the planned position of the femoral and tibial implants and their obtained positions, expect for when measuring tibial rotation, where the variations were much higher. No difference was observed between the two groups when analyzing weight-bearing full length X-rays 3 months after surgery or when concerning frontal and sagittal position of implants measured through Ml and AP X-rays. No difference in femoral rotation was found between the groups. Average tibial rotation was also similar between the two groups.
How will this affect the care of my patients?
The results of this study indicate that PSI does not improve rotation/ rotational alignment in TKA. Further research must be completed on the topic of patient-specific instrumentation to fully understand the effect it has on outcomes following TKA.
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