A Landmark-Based Technique for Determining an Isometric Femoral Attachment Site for Lateral Extraarticular Tenodesis is Inaccurate

Abstract

Purpose: To evaluate the reliability and accuracy of a method of placing the femoral fixation location for lateral extra-articular tenodesis (LET) within a safe isometric area using anatomic landmarks.

Methods: Using a pilot cadaveric specimen, the center of the radiographic safe isometric area for femoral fixation of LET, defined as a 1 cm (proximal-distal) area located proximal to the metaphyseal flare and posterior to the posterior cortical extension line (PCEL), was located using fluoroscopy and found to be 20 mm directly proximal to the center of the fibular collateral ligament (FCL) origin. Using 10 additional specimens, the center of the FCL origin and a location 20 mm directly proximal was identified. K-wires were placed at each location. A lateral radiograph was obtained, and distances of the proximal K-wire relative to the PCEL and metaphyseal flare were measured. The location of the proximal K-wire relative to the radiographic safe isometric area was assessed by 2 independent observers. Intrarater and inter-rater reliability was calculated for all measurements using intraclass coefficients (ICCs).

Results: There was excellent intrarater and inter-rater reliability for all radiographic measurements (.908 to .975 and .968 to .988, respectively). In 5/10 specimens, the proximal K-wire was outside of the radiographic safe isometric area, with 4/5 anterior to the PCEL. Overall, the mean distance from the PCEL was 1 mm ± 4 mm (anterior), and the mean distance from the metaphyseal flare was 7.4 mm ± 2.9 mm (proximal).

Conclusion: A landmark-based technique referencing the FCL origin was inaccurate in the placement of femoral fixation within a radiographic safe isometric area for LET. Therefore intraoperative imaging should be considered to ensure accurate placement.

Clinical relevance: These findings may help to decrease the likelihood of misplacement of femoral fixation during LET by showing that landmark-based methods without intraoperative image guidance may be unreliable.

Fig 1

Pilot cadaveric specimen for determining center of safe isometric femoral attachment area during lateral extra-articular tenodesis (LET). (A) Fibular collateral ligament (FCL) outlined on left knee with purple marking pen. Central aspect of femoral insertion visualized and palpated, and 0.045″ K-wire placed at that location (red arrow and label). (B) For pilot specimen, second 0.045″ K-wire placed 15 mm directly proximal along the long axis of the femur into lateral femur. Metal wire placed along femoral shaft to guide placement of proximal K-wire. G, Gerdy’s tubercle; F, Fibular head.

Fig 2

Lateral radiograph of pilot cadaveric specimen for confirmation of safe isometric area of femoral attachment site during lateral extra-articular tenodesis (LET). Posterior cortical extension line (PCEL) labeled on left knee. Proximal condylar line drawn perpendicular to the PCEL where the posterior femoral condyle intersects the posterior femoral cortex. Yellow box indicates radiographic safe isometric area as described by Jaecker et al., an area 1 cm from distal to proximal that is located on or posterior to the PCEL and on or proximal to the proximal condylar line. A K-wire was placed at the center of the FCL origin on the femur. A second K-wire was placed 15 mm directly proximal along the long axis of the femur and was located at the distal aspect of the radiographic safe isometric area.

Fig 3

Experimental specimen radiographic measurements. (A) Green line indicates the Blumensaat line (labeled) on left knee. Red lines indicate posterior cortical extension line (PCEL) and proximal condylar line (both labeled). K-wires are clamped at the level of the lateral femoral cortex. Distance between K-wires is 20 mm in all specimens. The distance along the Blumensaat line, from the anterior aspect of the femoral condyle to the posterior aspect of the femoral condyle, as well as the distance proximal or distal to the Blumensaat line, was measured. The distance from the PCEL to the proximal K-wire was measured. The distance from the proximal condylar line to the proximal K-wire was measured. (B) Yellow box indicates radiographic safe isometric area for femoral fixation during lateral extra-articular tenodesis (LET). In this specimen, the proximal K-wire is located within this safe isometric area.

Fig 4

Schematic radiograph containing a point cloud of tunnel positions for all 10 specimens relative to radiographic safe isometric area. The white box indicates the safe isometric area posterior to the posterior cortical extension line (PCEL) and proximal to the proximal condylar line. Five of 10 (50%) specimens fell within the radiographic safe isometric area.