Summary

Distance from fibular insertion of the LCL to the CPN in cadaveric specimens proves fibular tunnels can be drilled safely without CPN neurolysis

Abstract

Introduction

The most popular knee posterolateral corner (PLC) reconstruction techniques nowadays are the ones described by Robert LaPrade and Robert Arciero. Both authors describe that a common peroneal nerve (CPN) neurolysis has to be done to safely address the posterolateral aspect of the knee. Measurement of the distances from the fibular tip to the CPN and from the fibular tip to the lateral collateral ligament (LCL) fibular insertion have been described. There is scarce evidence on the distance between de CPN and the fibular LCL insertion or the fibular tunnel holes in PLC reconstructions.

Objective

Our objective was to measure the distance between the CPN and the fibular insertion of the LCL in different degrees of knee flection in cadaveric specimens, to identify if tunnel drilling could be done anatomically and safely without a common peroneal nerve neurolysis.

Methods

Considering an alpha error of 0.05, measurement precision of 2.5mm and a variance of 3.6mm, a sample size of 10 knees was estimated.
Knees were dissected and the LCL fibular insertion was identified. A 2mm K-wire was inserted at the centre of the fibular insertion and directed towards the distal half of the popliteofìbular ligament insertion. The CPN was then carefully identified to avoid displacing it from its original position. Measurements were performed from the K-wire to the CPN posteriorly and distally at 90º, 60º, 30º and 0º of knee flection. The edge of the tunnel was estimated for a 6mm drill bit. To have a worst case scenario situation, the tunnel diameter estimation was oversized to 8.48mm, assuming a 45º angle between the drill bit and the bone surface. Distances between this theoretical tunnel edge and the CPN were also estimated.
Measurements between different flexion angles were compared using Mann-Whitney U Test and correlation between knee flexion angle and distance was identified using Spearman's test.

Results

At 0º of knee flexion, median distance from the LCL fibular insertion to de CPN (LCL-CPN distance) was 8.75mm (range 3.4mm - 18mm) posteriorly and 9.5mm (range 5mm - 14mm) distally. At 90º of knee flexion, median LCL-CPN distance was 21.5mm (range 9.8mm - 31mm) posteriorly and 11.75mm (range 8.9mm - 19mm) distally. LCL-CPN distance is greater at 90º than at 0º of knee flection both posteriorly (p=0.001) and distally (p=0.02). There is a strong correlation between LCL-CPN distance posteriorly and knee flexion angle (r=0.61 p<0.001), there is a moderate correlation between LCL-CPN distance distally and knee flexion angle (r=0.41 p=0.008).

Conclusions

Distance from the LCL fibular insertion to the CPN is modified by knee flexion angle, being greater at 90º than at 0º of knee flexion. When performing a posterolateral corner reconstruction, at 90º of knee flexion angle, an anatomically positioned 6mm fibular tunnel is safe without a common peroneal nerve neurolysis.