Background and purpose: Radiostereometric analysis (RSA) is the gold standard for migration analysis, but computed tomography analysis methods (CTRSA) have shown comparable results in other joints. We attempted to validate precision for CT compared with RSA for a tibial implant.Material and methods: RSA and CT were performed on a porcine knee with a tibial implant. Marker-based RSA, model-based RSA (MBRSA), and CT scans from 2 different manufacturers were compared. CT analysis was performed by 2 raters for reliability evaluation.Results: 21 double examinations for precision measurements for RSA and CT-based Micromotion Analysis (CTMA) were analysed. Mean (95% confidence interval) precision data for maximum total point motion (MTPM) using marker-based RSA was 0.45 (0.19–0.70) and 0.58 (0.20–0.96) using MBRSA (F-statistic 0.44 [95% CI 0.18–1.1], p = 0.07). Precision data for total translation (TT) for CTMA was 0.08 (0.03–0.12) for the GE scanner and 0.11 (0.04–0.19) for the Siemens scanner (F-statistic 0.37 [0.15–0.91], p = 0.03). When comparing the aforementioned precision for both RSA methods with both CTMA analyses, CTMA was more precise (p < 0.001). The same pattern was seen for other translations and migrations. Mean effective radiation doses were 0.005 mSv (RSA) (0.0048–0.0050) and 0.08 mSv (CT) (0.078–0.080) (p < 0.001). Intra- and interrater reliability were 0.79 (0.75–0.82) and 0.77 (0.72–0.82), respectively.Conclusion: CTMA is more precise than RSA for migration analysis of a tibial implant, has overall good intra- and interrater reliability but higher effective radiation doses in a porcine cadaver.

Purpose Ligament balancing is a prerequisite for good function and survival in total knee arthroplasty (TKA). Various balancing techniques exist, but none have shown superior results. The pie-crusting technique by Bellemans of the medial collateral ligament is commonly utilized; however, it can be difficult to achieve repeatable ligament lengthening with this technique. Therefore, we invented a novel instrument to standardize the pie-crusting technique of the superficial and deep medial collateral ligament (hereafter MCL). The purpose was to examine if pie-crusting with the instrument could produce repeatable ligament lengthening. Methods The MCL was isolated in 16 human cadaveric knees, and subjected to axial tension. The instrument was composed of a specific grid of holes in rows, used to guide sequential pie-crusting puncturing of the MCL with a Ø1.6 mm end-cutting cannula. Ligament lengthening was measured after each row of punctures. Regression analysis was performed on the results. Results Mean lengthening ± SD in human cadaveric MCL for puncturing of row 1 in the instrument was 0.06 ± 0.09 mm, 0.06 ± 0.04 mm for row 2, 0.09 ± 0.08 mm for row 3, 0.06 ± 0.05 mm for row 4 and 0.06 ± 0.04 mm for row 5, giving a mean total lengthening of 0.33 ± 0.20 mm. Linear regression revealed that MCLs were repeatably lengthened by 0.07 mm per row when punctured using the instrument. Conclusions MCLs showed linear lengthening in human cadavers for subsequent use of the instrument. Our instrument shows promising results for repeatable ligament lengthening.