New parameter of flexion after posterior stabilized total knee arthroplasty: posterior condylar offset ratio on X-ray photographs

Abstract

In cruciate-retaining (CR) type TKA, the increase in posterior condylar offset (PCO) is considered to be correlated to flexion angle acquired postoperatively according to the article reported by Bellemans (J Bone Joint Surg Br 84:50-53, 2002). However, the significance of PCO seems to differ according to the size of joints. We therefore have defined a new parameter of posterior condylar offset ratio (PCOR) on the lateral view of plain X-ray photographs and studied the relationship between PCOR and postoperative flexion status in posterior-stabilized (PS) type TKA. Flexion status includes two parameters, such as postoperative flexion angle (FA) and flexion achievement rate (AR). The subjects of this study were 160 knees (16 males and 144 females, average 75 years.) with PS type TKA for osteoarthritic knees between 1999 and 2003 at our institution, more than at least 1 year postoperative follow-up. In the study of FA, patients with FA of less than 100 degrees were divided into Group L (n = 28), patients with FA of 130 degrees and greater were divided into Group H (n = 58). In the study of AR, patients with AR of less than 100% were divided into Group P (n = 46), patients with AR of 120% and greater were divided into Group G (n = 22). PCOR was statistically compared in each group, respectively. In FA, PCOR in Group L (0.385) was significantly lower (P = 0.027) than that in Group H (0.428). In AR, PCOR in Group P (0.376) was significantly lower (P = 0.0018) than that in Group G (0.456). We have concluded, though there are many factors influencing the range of movement after TKA, our newly defined PCOR could possibly serve as a parameter of postoperative flexion status of PS type TKA on plain X-ray photographs.

The Posterior Condylar Offset Ratio

“…The importance of the posterior condylar offset has been studied by several investigators, with some having observed a correlation between the posterior condylar offset and final range of movement in cruciate-retaining knees [4,5] and also posterior-stabilized knees [6]. However, others have reported no correlation in posterior-stabilized knees [5] or cruciate-sacrificing rotating platform knees [8,9].…”

“…Soda et al [6] proposed an alternative method of assessing a Posterior Condylar Ratio on post-operative radiographs. They suggested dividing the posterior condylar offset by the maximum antero-posterior diameter of the femoral component.…”

“…They defined the posterior condylar offset as the maximal thickness of the posterior condyle projecting posteriorly to the tangent of the posterior cortex of the femoral shaft on a true lateral radiograph. The role of posterior condylar offset in the eventual range of motion, and particularly deep flexion, after primary TKA has been a topic of great interest and controversy, with some authors showing a significant association [1][2][3][4][5][6][7] and others not [8,9]. Restoring posterior condylar offset by means of femoral component size or use of offsets, is the means by which flexion gaps are frequently balanced in revision TKA, but the importance of restoring the posterior offset versus the importance of restoring joint line or just balancing the flexion and extension spaces, has not been proven.…”

Prospective study of posterior condylar offset ratio and its influence on maximal flexion angle of knee in posterior cruciate ligament substituting total knee arthroplasty

“…Theoretically the value of PCO differs with the body type of the patient especially the size of the knee joint. Hence the study on posterior clearance cannot be done with just by PCO for which a ratio had to considered as described by Soda et al [27] i.e., PCOR which according to him had correlation with the maximum flexion angle on cruciate substituting knee. But our results came to be contrary as per the study by Soda et al and our study results were similar to the study done by Kim et al Moreover, maximum flexion angle after TKA is a multivariate hence PCO and PCOR cannot be used as an independent variable for the quantification of functional outcome of TKA [28] .…”

The posterior condylar offset ratio and femoral anatomy in anterior versus posterior referencing total knee arthroplasty

“…Being dimensionless, the PCOR corrects the bias introduced by normal joint size distribution naturally occurring in patients and the non-standardized magnification of each radiograph [15]; in addition, it offers a fast and reproducible way, independent of referencing system, for gauging alterations in condylar offset resulting from implant fit [16].…”