Localization of the Lateral Retinacular Nerve for Diagnostic and Therapeutic Nerve Block for Lateral Knee Pain: A Cadaveric Study

Abstract

Background: The lateral retinacular nerve (LRN) is a branch of the superior lateral genicular nerve (SLGN) and is believed to contribute to anterolateral knee pain. The precise anatomical pathway of the LRN, however, has not been demonstrated as it relates to the performance of targeted nerve block procedures.

Objective: To describe the anatomical landmarks for localization of the LRN to facilitate diagnostic and therapeutic nerve blocks in the treatment of chronic anterolateral knee pain.

Design: Descriptive study.

Setting: Anatomy dissection laboratory in an academic institution.

Methods: Twenty lower extremities were dissected in 12 cadavers. The sciatic nerve was identified, and its branch to the posterior aspect of the knee, the SLGN, was dissected. The SLGN dissection was continued distally to identify its first branch, the LRN. Two measurements were taken from the branch point on the lateral knee deep to the distal biceps tendon in alignment with the fibular head. A validation study completed in 4 knees was performed as follows: 1 mL of colored dye was injected at the first and second measurements. The cadaveric knee was then dissected to assess the accuracy.

Main outcome measurements: Localization of the branch point of the LRN from the SLGN via dissection and then direct assessment of injected dye at the measurement points via dissection.

Results: The branch point of the LRN from the SLGN was, on average, 5.5 ± 0.66 cm (with a range of 4.5-7.0 cm) proximal to the lateral tibiofemoral joint line in line with the head of the fibula and 2.6 ± 0.62 cm (2.0-4.5 cm) proximal to the tip of the lateral femoral epicondyle. On assessment of the 2 measurements, the measurement 5.5 cm proximal to the lateral joint line accurately targeted the branch point in 100% (4/4) of the knees, whereas the measurement 2.6 cm proximal the tip of the lateral femoral epicondyle accurately targeted the branch point in 75% (3/4) of the knees.

Conclusion: The results of this study provide 2 dependable landmarks and a description of the path of the LRN, making it possible to accurately target the LRN to diagnose and alleviate lateral knee pain.

Figure 1

Figure 1A. Illustration of the nerve supply to the lateral retinaculum: posterior and lateral views. The SLGN branches from the SN. The LRN branches from the SLGN 5.5 cm proximal to the lateral joint line and 2.6 cm proximal to the tip of the lateral femoral epicondyle. The LRN then passes anteroinferiorly deep to the biceps femoris tendon to supply the lateral retinaculum. Note that the relative diameters of the SLGN and LRN in this image are increased to aid visibility. Figure 1B. Dissection showing the paths of the SLGN and LRN: lateral view. Abbreviations: LRN lateral retinacular nerve; SLGN superior lateral geniculate nerve; SN sciatic nerve.

Figure 2

Dissection of a cadaveric knee in the prone position. The red dye injected at the measurement 5.5 cm proximal to the lateral joint line and the blue dye injected 2.6 cm proximal to the tip of the lateral femoral epicondyle. Abbreviations: LRN lateral retinacular nerve; SLGN superior lateral geniculate nerve

Figure 3

Photograph of the right knee joint in full extension with the patient supine. With an imaginary line drawn parallel from the fibular head to the femur, a spinal needle is placed on the skin of the patient at 5.5 cm proximal to the lateral joint line at the branch point of the LRN from the SLGN. Abbreviations: LRN lateral retinacular nerve; SLGN superior lateral geniculate nerve

Figure 4

Flouroscopic image of a true anteroposterior view of the right knee joint in full extension. A spinal needle is placed on the skin of the patient at 5.5 cm proximal to the lateral joint line at the branch point of the LRN from the SLGN. Abbreviations: LRN lateral retinacular nerve; SLGN superior lateral geniculate nerve