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Abstract
Background and Aims The saphenous nerve (SN) is described as innervating the anteromedial knee area, the medial part of the lower leg and the medial malleolus (MM), sometimes extending to the medial foot1. However, it has been shown that the anteromedial knee area is most often innervated by the medial femoral cutaneous nerve (MFCN)2. Furthermore, a sub-study of data from a recent volunteer trial showed that the MFCN (anterior or posterior branch (MFCN-A, MFCN-P)) often innervates part of the “classical saphenous nerve territory” on the medial lower leg, sometimes including the MM3. This knowledge is important for correct diagnosis and treatment of chronic neuropathic pain in this area. The primary aim was to explore the distal cutaneous innervation of the MFCN.
Methods Post-hoc analysis was performed on photographic material from a recently concluded randomized, double-blind volunteer trial.3 Extensive photo documentation of the areas of cutaneous anesthesia after SN block and MFCN block or selective MFCN-A block was reviewed in order to characterize the sensory distribution of the MFCN.3 The medial lower leg (MLL) was defined as the anteromedial crus distal to the tibial tuberosity.
Results The non-selective MFCN block anesthetized part of the MLL in 67% and the MM in 28%. Selective MFCN-A block anesthetized part of the MLL in 67% and the MM in 13% (figure 1–3).
Shows an example of MFCN innervation of the medial lower leg. The left leg of a volunteer is shown in medial (1A) and anterior view (1B). The tibial tuberosity is marked with a red line. Areas of cutaneous anesthesia after SN block (magenta area) and MFCN block (green area) are seen in both views. The MFCN innervates part of the medial lower leg, however, the SN innervates the very distal part including the medial malleolus. Photographic material from trial (3) approved by the Central Denmark Region Committee on Health Research Ethics (1–10-72–266-20) and Danish Medicines Agency (EudraCT 2020–004942-12). MFCN, medial femoral cutaneous nerve; SN, saphenous nerve. Printed with permission from Siska Bjørn.
Shows an example of MFCN innervation of the medial lower leg including the medial malleolus. The left leg of a volunteer is shown in medial (2A) and anterior view (2B). The tibial tuberosity is marked with a red line. Areas of cutaneous anesthesia after SN block (magenta area) and MFCN block (green area) are seen in both views. Photographic material from trial (3) approved by the Central Denmark Region Committee on Health Research Ethics (1–10- 72–266-20) and Danish Medicines Agency (EudraCT 2020–004942-12). MFCN, medial femoral cutaneous nerve; SN, saphenous nerve. Printed with permission from Siska Bjørn.
Shows three examples of cutaneous anesthesia after SN block (magenta areas). 3A, 3B and 3C are anteromedial views of three right legs from different volunteers. The tibial tuberosity is marked with a red line. The cutaneous area innervated by the SN was often found to be smaller and more anterolateral than the classical description (3B, 3C). In 3A a more classical distribution is seen, however, the SN innervation area does not include the MM. The MM was only innervated partly or completely by the SN in half of the cases. Photographic material from trial (3) approved by the Central Denmark Region Committee on Health Research Ethics (1–10-72–266-20) and Danish Medicines Agency (EudraCT 2020–004942-12). MM, medial malleolus; SN, saphenous nerve. Printed with permission from Siska Bjørn.
Conclusions In the majority of cases, the MFCN seems to innervate part of the classical saphenous nerve territory on the medial lower leg. This knowledge is important for correct diagnosis and treatment of acute pain or chronic neuropathic pain.