The distance to the posterior crural intermuscular septum (PS) and the depth of each named nerve in the posterolateral calf were calculated.
Cadaveric specimen showing the lateral sural cutaneous nerve (medium-sized arrows), the peroneal communicating nerve (thin arrow), and the common peroneal nerve (thick arrow). The popliteal fossa is to the right and the posterior crural intermuscular septum spans the inferior aspect.
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Dolan RW, McAvoy DW, Carr M. Anatomical Variations of the Sensory Nerves to the Fibular Osteocutaneous Flap. Arch Facial Plast Surg. 2000;2(4):252–255. doi:
Copyright 2000 American Medical Association. All Rights Reserved.
Applicable FARS/DFARS Restrictions Apply to Government Use.2000
Objective To describe the anatomical relationship of the sural sensory nerve complex to the posterior crural intermuscular septum (PS), the key anatomical structure for the osteoseptocutaneous fibula skin paddle.
Design Anatomical study.
Subjects Twenty-two legs from 11 cadavers (7 females and 4 males).
Results The lateral sural cutaneous (LSC) nerve, present in 20 of 22 legs, divides into lateral and medial branches near the head of the fibula. The LSC nerve and its medial branch course away from the PS, whereas the lateral branch tends to course toward the PS. The lateral branch courses nearest to the PS at a median distance of between 4 cm proximally and 3 cm distally. The medial branch of the LSC nerve terminates approximately in the middle of the leg, and the lateral branch of the LSC nerve terminates within 7 cm below the head of the fibula. The peroneal communicating branch is thicker than the LSC nerves; however, it is further from the PS in the upper leg.
Conclusions The LSC nerve is the most consistent and accessible donor sensory nerve in the posterior leg for harvest with the osteoseptocutaneous fibula free flap. Results of this study will assist the surgeon in harvesting a sensory nerve with the osteoseptocutaneous fibula free flap, bringing this potentially sensate flap into more common use.
THE osteoseptocutaneous fibula free flap1-2 is rapidly becoming the workhorse for anterior mandibular composite defects. Recent advances in harvesting the flap with a sensory nerve will add to its popularity because the anterior oral cavity is the only area within the head and neck in which maintaining sensation has shown a clear benefit.3-5 Sadove et al6 were the first to describe successfully incorporating a sensory nerve with the osteoseptocutaneous fibula free flap for penile reconstruction. However, Sadove et al6 and others3, 7-8 noted that the anatomical features of the sensory nerve are inconsistent. Further study into the anatomical features of these nerves is necessary to bring this potentially sensate flap into more common use.
This article describes the anatomical relationship of the sural nerve complex to the posterior crural intermuscular septum (PS), the key anatomical structure for skin paddle harvest. Also described are the thickness, subcutaneous depth, and length of the sensory nerves.
Twenty-two legs from 11 cadavers (7 females and 4 males) were placed in a prone position to expose the posterior and lateral portions of the lower legs. The cadavers were fixed with formaldehyde and did not receive vascular dye injections. The head of the fibula (HF) and the lateral malleolus were identified by palpation, and an incision was made between these structures down to the peroneal muscles. The PS was identified, and tick marks 1 cm apart were placed from the fibular head (level 0) caudally to 31 cm (near the lateral malleolus) along the PS (Figure 1). A subdermal flap was created from the PS over the entire posterior calf, leaving the entire subcutaneous layer intact. The incision along the PS was continued superiorly, and a subdermal flap was created to expose the popliteal fossa. The peroneal and posterior tibial nerves were identified as they entered the popliteal fossa, and they were followed inferiorly to the lateral sural cutaneous (LSC) nerve, the peroneal communicating (PCOM) nerve, and the medial sural nerve (Figure 2). The common branch of the LSC (cLSC) nerve was followed inferiorly to the origin of the lateral branch of the LSC (lLSC) nerve and the medial branch of the LSC (mLSC) nerve. The PCOM nerve joined the medial sural cutaneous nerve to form the sural nerve in the lower leg. The superficial peroneal nerve is known to course within the lateral compartment of the leg, and the level at which this sensory nerve emerged into the subcutaneous tissue was noted.
The following data were gathered for the cLSC, lLSC, mLSC, and PCOM nerves: (1) distance to nerve origins around the HF, (2) length of the nerve above and below the HF (level 0) to arborization, (3) distance from the PS to the nerve at all levels to arborization, (4) nerve diameter at all levels to arborization, and (5) depth of the nerve from the skin.
The cLSC nerve was present at or below the HF in 55% (12/22) of the legs, an lLSC nerve was present in 59% (13/22), and an mLSC nerve was present in 68% (15/22). There were no identifiable LSC nerves (common, lateral, or medial branch) in only 2 legs (9%, both in the same cadaver). A PCOM nerve was present in 64% (14/22) of the legs, including the 2 legs without LSC nerves. The distance above the HF that the cLSC nerve originated from the common peroneal nerve was 0 to 13 cm (median, 9 cm). The point at which the cLSC nerve divided into the lLSC and mLSC nerves was 5 cm above to 8 cm below the HF (median, 0 cm, or at the HF). The distance above the HF that the PCOM nerve originated from the cLSC nerve was 1 to 14 cm (median, 7.5 cm).
The median length below the HF of the lLSC nerve was 6 cm (range, 2-17 cm) and including the cLSC nerve was 7 cm (range, 2-19 cm), of the mLSC nerve was 10 cm (range, 3-27 cm) and including the cLSC nerve was 13 cm (range, 7-27 cm), and of the PCOM nerve was 22 cm (range, 15-29 cm).
The distances of the nerves from the PS are presented in Table 1. The medial sural nerve was in the midleg and deep to the crural fascia. The sural nerve coursed toward the PS in the lower leg, and the median distance at level 21 was 5.0 cm (range, 3.5-8.5 cm). The superficial peroneal nerve emerged subcutaneously very low in the leg (median, 25 cm; range, 22-30 cm) and was not accessible as a donor sensory nerve for the osteoseptocutaneous fibula free flap.
Nerve diameters and depths are presented in Table 2 and Table 3, respectively.
The LSC nerve is the most consistent and accessible donor sensory nerve in the posterior leg for harvest with the osteoseptocutaneous fibula free flap. The origin of the cLSC nerve from the peroneal nerve is at or above the HF. Clinical harvest of the LSC nerve might involve identification of the common branch first by following the peroneal nerve superiorly from the HF. The cLSC nerve usually divides into an mLSC nerve and an lLSC nerve below the HF; however, the level of the division is inconsistent, ranging from 5 cm above to 8 cm below the HF. Identifying the LSC nerves at the HF from a medial to posterolateral approach avoids popliteal fossa dissection; however, the surgeon must be aware of the anatomical inconsistencies, including where the cLSC nerve divides. The cLSC and mLSC nerves course away from the PS, whereas the lLSC nerve tends to course toward the PS after branching from the cLSC nerve near the HF. The mLSC nerve terminates approximately in the midleg, and the lLSC nerve terminates within 7 cm below the HF. The mLSC and lLSC nerves course approximately 5 and 3 cm, respectively, from the PS. Nerve diameters approaching 3 mm at the HF make nerve identification straightforward. However, their depths of approximately 1 cm in the subcutaneous tissues require more dissection than might be anticipated in harvesting a sensory nerve.
The PCOM nerve, found in a majority of legs (14 of 22), including those without identifiable LSC nerves, courses more posterolaterally than the LSC nerves. The PCOM nerve joins the medial sural cutaneous nerve in the lower half of the leg to form the sural nerve. Rarely does the PCOM nerve originate directly off the peroneal nerve, taking origin from the cLSC nerve in the majority of legs (12 of 14). The PCOM nerve consistently extends into the lower leg but courses approximately 1 cm further from the PS in the upper leg compared with the mLSC nerve. In the lower half of the leg, the PCOM nerve tends to be closer to the PS than the mLSC nerve but still more than 5 cm away from the PS. The diameter of the PCOM nerve remains consistent at approximately 2 mm throughout its course, and its depth is about 1 cm.
Congenital absence of LSC nerves is rare, occurring in 1.7% to 22.0% of legs9-10 (9.0% in the present study). Ortiguela et al7 noted that congenital absence of the PCOM nerve occurs in 20% of legs; however, 8 (36%) of the legs in our study lacked a PCOM nerve. The lengths of the cLSC, mLSC, and lLSC nerves in our study conform to those previously reported.7, 10 Overall, the results of our study are consistent with those of previous studies regarding the basic anatomical characteristics of these nerves. Woerdeman et al11 performed an anatomical study of the innervation pattern to the osteocutaneous flap using an operating microscope. They investigated the location of the LSC with respect to the PS. However, there were no detailed incremental measurements of distances, depths, or nerve diameters, as were presented in our study. Results regarding the presence of an lLSC nerve (88% in Woerdeman et al11 vs 91% in our study) and a PCOM nerve (52% in Woerdeman et al11 vs 64% in our study) was similar. They found that the LSC nerve divided into an mLSC nerve and an lLSC nerve in 79% of legs, and we found that there was an lLSC nerve in 59% and an mLSC nerve in 68% of legs. The distances of the lLSC and mLSC nerves from the PS were in good agreement between the 2 studies in the proximal leg. Measurements were provided for the distal nerve branches in their study, but nerve diameter and depth were omitted. As shown in our study, the size and depth of the nerves change dramatically as the LSC nerve courses inferiorly. Identification of these small branches in the clinical setting is difficult, and a more proximal dissection, while the nerve diameter is greater than 1 mm, is helpful to ensure that the nerve is harvested with the skin flap.
Wei et al,12 in applying the original description of Sadove et al6 of the sensate fibula flap to oromandibular reconstruction, commented that "further anatomical investigation of the lateral sural cutaneous nerve and its territory of innervation will be helpful to make the skin paddle of the fibula osteoseptocutaneous flap a reliable sensate surface." Other authors8 also noted the variability of the LSC, and electrophysiologic testing has demonstrated 2 patterns of innervation: the first limited to the upper lateral and posterior portions of the calf and the other demonstrating significant extension into the lower half of the calf. These patterns might have resulted from the underlying anatomical variability of the sensory nerves as demonstrated in our study; however, anatomical correlation with the electrophysiologic results was not performed. According to classic textbooks of anatomy, the LSC supplies cutaneous innervation to the upper and middle portions of the posterolateral leg.13 The PCOM and sural nerves typically supply cutaneous innervation outside the vascular angiosome of the peroneal artery, although should these nerves course through the skin paddle they can be used as vascularized cable grafts.
The typical design of the skin paddle might have to be altered to accommodate a sensory nerve. A defect of up to 6 cm across the midleg might allow for primary closure; however, all the sensate flaps reported by Wei et al12 were wider than 6 cm and required skin grafting of the donor site. The paddles were wider to accommodate the more posteriorly oriented sensory nerves. Along with a more posteriorly oriented approach, a skin flap located proximally has a better chance of being sensate. However, the majority of septocutaneous arterial perforators that supply the skin paddle originate in the middle third of the leg. The problem of maintaining vascularity while incorporating the predominately proximally located sensory nerves might be circumvented by harvesting a long skin paddle and discarding the excess skin after the anatomy is defined.12 Although administration of a local anesthetic might be useful for preoperative sensory nerve mapping, further studies are needed to determine whether preoperative electrophysiologic testing14 may be more accurate in predicting intraoperative neural anatomy.
Accepted for publication March 23, 2000.
Corresponding author: Robert W. Dolan, MD, Lahey Clinic, 41 Mall Rd, Burlington, MA 01805.