Intra- and post-operative accuracy assessments of two different patient-specific instrumentation systems for total knee replacement.
OBJECTIVE
The aim of this study is to assess and compare the accuracy of two different patient-specific instrumentation (PSI) systems for total knee replacement, both intra-operatively for bone preparation and post-operatively for final component alignment.


METHODS
Twenty-five patients were treated according to a computer tomography (CT)-based PSI system (group A) and 25 to a magnetic resonance imaging (MRI)/X-ray-based system (group B). Alignments on the three anatomical planes and resection thickness at the cutting blocks and at the resulting bone cuts were recorded intra-operatively by a standard surgical navigation system. Alignments of the prosthetic components and mechanical axis were also measured post-operatively on radiographs. These measurements at both the femur and tibia were compared with those of the corresponding pre-operative planning, considering discrepancies larger than 3° as outliers.


RESULTS
In both groups, the mean absolute differences between pre-operatively planned alignments and corresponding intra- and post-operative measurements ranged from a minimum of 1.2° to a maximum of 2.9° in all three anatomical planes. In both groups and in both femur and tibia, the plane with the smallest percentage of outliers was the coronal, maximum 17%. The comparison between two groups was statistically significant (p = 0.02) in the femoral sagittal plane, where group B showed smaller alignment discrepancies at the cutting blocks.


CONCLUSIONS
Both PSI systems showed good alignments in the coronal plane in all stages. For a few measurements, a better performance was observed in the MRI/X-ray-based system than in the CT-based system.


METHODS
I.
Department of Orthopaedic Surgery, Istituto Ortopedico Rizzoli, Via Pupilli 1, 40136, Bologna, Italy.
Andrea
A
Ensini
Antonio
A
Timoncini
Francesco
F
Cenni
Claudio
C
Belvedere
Francesca
F
Fusai
Alberto
A
Leardini
Sandro
S
Giannini
D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007432:Intraoperative Period; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging; D020370:Osteoarthritis, Knee / Q000601:surgery*; D011184:Postoperative Period; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome