Fibula head is a useful landmark to predict the location of posterior cruciate ligament footprint prior to total knee arthroplasty

Abstract

Purpose: The hypothesis of our study is that a routine tibial cut during cruciate retaining TKA may result in a partial or a total removal of the PCL footprint. Therefore providing a reliable landmark is essential to estimate the probability of PCL damage with a tibial cut and to enable the surgeon to decide pre-operatively whether a cruciate retaining implant design is suitable.

Methods: In a case series of 175 cruciate retaining TKA, the routinely made standing postoperative AP-view radiographs were evaluated to determine the distance between fibula head and tibial cutting plane. In a second case series knee MRI of 223 subjects were consecutively used to measure the vertical distance between tibial attachment of PCL and fibula head. The probability of partial or total PCL damage was calculated for different vertical distances between tibial cut and fibula head.

Results: The vertical distance between the tibial cut and the most proximal point of the fibula head averaged 6.1 mm ±4.8 mm. The mean vertical distance from fibula head to proximal and to distal PCL footprint revealed to be 11.4 mm ±3.7 mm and 5.4 mm ±2.9 mm, respectively. The location of the insertion was not significantly different between subgroups such as age (<50 or >50 years), gender and side. Based on our results 11 (7%) knees were considered at high risk of an entire PCL removal after implantation of a cruciate retaining TKA design.

Conclusions: Currently available routine tibial preparation techniques result in partial or total posterior cruciate ligament detachment. Fibula head as a landmark aids to predict the PCL location and to estimate its disruption pre- and postoperatively on AP-view radiographs.

Fig. 1

a 1 horizontal line perpendicular to tibial mechanical axis, 2 medial and 3 lateral vertical distances between femur condyles and fibula head. b 2 medial and 3 lateral distances between tibial cutting plane and femur condyles which corresponds to height of tibial component

Fig. 2

a The horizontal line defines the level of the fibula head. b The distance between the most proximal and the most distal point of the PCL footprint to fibula head were measured as illustrated

Fig. 3

Distribution of the vertical distance between fibula head and tibial cutting surface (+ cutting surface above fibula head, − cutting surface below fibula head)

Fig. 4

Distribution of the vertical distance between fibula head and proximal (blue) or distal (red) aspect of the PCL footprint (+ insertion point above fibula head, - insertion point below fibula head)

Fig. 5

This diagram was obtained after calculating the relative frequency of distances between proximal, distal PCL footprint and fibula head. The probability (0 to 1) of partial (blue) or total (red) PCL damage depends on the distance between fibula head and level of tibial osteotomy (+ tibial cutting plane above fibula head, − tibial cutting plane below fibula head)