Plain Radiographs Underestimate the Asymmetry of the Posterior Condylar Offset of the Knee Compared With MRI

Abstract

Background Restoration of posterior condylar offset (PCO) during total knee arthroplasty is essential to maximize range of motion, prevent impingement, and minimize flexion instability. Previously, PCO was determined with lateral radiographs, which could not distinguish the asymmetries between the femoral condyles. MRI can independently measure both medial and lateral PCO. Questions/purposes The purpose of this study is to determine the normal PCO of the knee, to establish the differences in medial and lateral PCO, and to compare PCO measurements obtained from radiographs versus those obtained from MRI. Methods We identified 32 patients without a history of prior knee pathology who had both plain radiographs and MRI scans of the same knee performed. The PCO was measured on lateral radiographs and compared with MRI measurements using a novel three-dimensional protocol.Results By MRI, the mean medial PCO was 29 (± 3) mm and the mean lateral PCO was 26 (± 3) mm; both values were greater (p \ 0.001 and p = 0.03, respectively) than the mean radiographic PCO of 25 (± 2) mm. The medial PCO, as measured by MRI, was significantly greater than the lateral PCO (p \ 0.001). Conclusions Plain radiographs underestimate PCO as well as the asymmetry of the medial and lateral PCO compared with MRI. This discrepancy is the result of both articular cartilage thickness and the anatomic differences between medial and lateral condyles. Designers of knee prostheses and instrumentation should take these differences into account.

Posterior Condylar Cartilage Thickness and Posterior Condylar Offset of the Femur: A Magnetic Resonance Imaging Study

“…In a study measuring femoral PCC thickness in 111 individuals, 7 the lateral PCC was thicker than the medial PCC (2.15 vs. 1.95 mm), but the results were not stratified in terms of gender. In a study evaluating the difference between PCO measured by radiography and MRI in 32 individuals, 8 the mean medial and lateral PCO was 29 and 26 mm, respectively, and the medial PCC was thicker than the lateral PCC (2.3 vs. 1.9 mm). In our study, males had thicker PCC in the medial and lateral sides than females.…”

“…Based on the protocols for MRI measurement of PCC thickness, 8 the deepest part of the medial and lateral posterior condyles was identified in the sagittal plane. These points were then viewed in the coronal plane to ensure that they were centred in their respective condyles.…”

No Sex Differences Exist in Posterior Condylar Offsets of the Knee

“…1) [22]. In brief, the technique was performed using multiplanar reformatted images created from isovoxel 3-D sampling perfection with application optimized contrasts using different flip angle evolutions (3-D SPACE) proton density-weighted fat-suppressed MRI sequences.…”

“…In contrast, three-dimensional (3-D) MRI can show articular cartilage and eliminate imprecisions related to magnification and obliquity, allowing for more accurate measurements. We previously developed a protocol to determine the posterior condylar offset of the medial and lateral femoral condyles using 3-D MRI reconstruction sequences designed to coordinate axial, coronal, and sagittal MR images [22]. Therefore, the purpose of our study was to determine if sex differences exist in (1) absolute posterior condylar offset size, (2) relative posterior condylar offset size with relation to total condylar height, and (3) posterior condylar articular cartilage thickness.…”

Important Differences Exist in Posterior Condylar Offsets in an Osteological Collection of 1,058 Femurs

“…2) In the second technique, measurements were taken along the anatomic transepicondylar axis (TEA) and measured from the deepest point of the intercondylar fossa along the TEA, as has been similarly reported in studies utilizing MRI [6,15]. For both measuring techniques, a virtual TEA was created by determining the most medial and lateral aspects of the femoral condyles.…”