Abstract
BackgroundStudies of medial and lateral femoral posterior condylar offset have disagreed on whether posterior condylar offset affects maximum knee flexion angle after TKA.Questions/purposesWe asked whether posterior condylar offset was correlated with knee flexion angle 1 year after surgery in (1) a PCL-retaining meniscal-bearing TKA implant, or in (2) a PCL-substituting mobile-bearing TKA implant.MethodsKnee flexion angle was examined preoperatively and 12 months postoperatively in 170 patients who underwent primary TKAs to clarify the effect of PCL-retaining (85 knees) and PCL-substituting (85 knees) prostheses on knee flexion angle. A quasirandomized design was used; patients were assigned to receive one or the other implant using chart numbers. A quantitative three-dimensional technique with CT was used to examine individual changes in medial and lateral posterior condylar offsets.ResultsIn PCL-retaining meniscal-bearing knees, there were no significant correlations between posterior condylar offset and knee flexion at 1 year. In these knees, the mean (± SD) postoperative differences in medial and lateral posterior condylar offsets were 0.0 ± 3.6 mm and 3.8 ± 3.6 mm, respectively. The postoperative change in maximum knee flexion angle was −5° ± 15°. In PCL-substituting rotating-platform knees, similarly, there were no significant correlations between posterior condylar offset and knee flexion 1 year after surgery. In these knees, the mean postoperative differences in medial and lateral posterior condylar offsets were −0.5 ± 3.3 mm and 3.3 ± 4.2 mm, respectively. The postoperative change in maximum knee flexion angle was −2° ± 18°.ConclusionsDifferences in individual posterior condylar offset with current PCL-retaining or PCL-substituting prostheses did not correlate with changes in knee flexion 1 year after TKA. We should recognize that correctly identifying which condyle affects the results of the TKA may be difficult with conventional radiographic techniques.Level of EvidenceLevel II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Highlights
Postoperative maximum knee flexion is a primary functional outcome measure for TKA
The senior author (YI) [16] recently reported that changes in posterior condylar offset based on radiographic evaluations showed no significant correlation with the changes observed in CT evaluated medial and lateral posterior condylar offsets
In PCL-retaining meniscal-bearing knees, there were no significant correlations between the changes in the posterior condylar offsets and the post-TKA knee flexion angles (post-TKA knee flexion angle versus posterior condylar offset change in medial condyle: R = 0.049, p = 0.654 [Fig. 2A]; post-TKA knee flexion angle versus posterior condylar offset change in lateral condyle: R = À0.041, Fig. 1A–B Cross-sectional views in the sagittal plane of the femoral and tibial components of a prosthesis used in TKA are shown. (A) A digital model of the prosthesis complex is shown. (B) Measurement of the maximum condyle thickness is made from the farthest edge of the condyle to a line drawn tangent to the posterior femur shaft
Summary
Postoperative maximum knee flexion is a primary functional outcome measure for TKA. Previous studies [1, 3, 11, 12, 18, 19, 23, 24] using radiographic analyses showed contradictory findings regarding whether posterior condylar offset has an effect on knee flexion after TKA. The senior author (YI) [16] recently reported that changes in posterior condylar offset based on radiographic evaluations showed no significant correlation with the changes observed in CT evaluated medial and lateral posterior condylar offsets. Changes in posterior condylar offset should be examined individually for each condyle, as noted by previous studies [1, 3, 23, 24] that found significant correlations between posterior condylar offset and knee flexion angle after TKA. CT-based evaluations of medial and lateral posterior condylar offset were recommended when assessing the influence of posterior condylar offset on the knee flexion angle after TKA [16]. Studies of medial and lateral femoral posterior condylar offset have disagreed on whether posterior condylar offset affects maximum knee flexion angle after TKA. This work was performed at Ishii Orthopaedic and Rehabilitation Clinic, Gyoda, Saitama, Japan
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