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doi: 10.1227/NEU.0000000000000062
Research-Human-Clinical Studies: Editor's Choice

Clinical Results of Transferring a Motor Branch of the Tibial Nerve to the Deep Peroneal Nerve for Treatment of Foot Drop

Flores, Leandro Pretto MD, PhD†,‡; Martins, Roberto Sérgio MD, PhD§; Siqueira, Mario Gilberto MD, PhD§

Free Access
Editor's Choice
CNS University of Neurosurgery
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Author Information

Unit of Neurosurgery, Hospital de Base do Distrito Federal, Brasília, Distrito Federal, Brazil;

Hospital Santa Helena, Brasília, Distrito Federal, Brazil;

§Peripheral Nerve Unit, Department of Neurosurgery, University of São Paulo Medical School, São Paulo, Brazil

Correspondence: Leandro Pretto Flores, SHIN QL 07 Conjunto 01 Casa 18, Lago Norte, Brasília, Distrito Federal, Brazil 71515015. E-mail:

Received November 21, 2012

Accepted June 20, 2013

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BACKGROUND: Foot drop is a very debilitating condition affecting patients' daily activities, and its treatment has been a challenge for neurosurgeons. Grafting the peroneal or sciatic nerve usually results in poor outcomes. Our previous anatomic study demonstrated the feasibility of transferring a motor branch of the tibial nerve to the deep peroneal nerve at the level of the popliteal fossa.

OBJECTIVE: To demonstrate the outcomes obtained after the transfer of a branch of the tibial nerve to the peroneal nerve for recovery of foot drop.

METHODS: A retrospective review of 13 patients with foot drop caused by injuries to a lumbar root or the sciatic or peroneal nerve, who underwent a transfer of the nerve of the soleus muscle to the deep peroneal nerve. The results were evaluated using the British Medical Research Council grading system.

RESULTS: Three patients were lost to follow-up. Of the remaining 10 patients, the outcomes were considered good (Medical Research Council grade M3 or M4) in 2 patients (20%) concerning ankle dorsiflexion and in 2 patients concerning toe extension (20%). One patient reported a reduced calf circumference.

CONCLUSION: The transfer of the nerve of the soleus muscle to the deep peroneal nerve demonstrated poor results in most of the patients, although favorable outcomes were observed in a few subjects. Due to the inconsistency of the results, we do not favor the routine use of this technique for the treatment of foot drop.

ABBREVIATION: MRC, Medical Research Council

Foot drop is characterized by the inability to or difficulty with movement of the ankle and toe dorsally and is a very debilitating condition. A myriad of mechanisms and etiologies can be responsible for the development of this problem, such as metabolic, oncologic, degenerative, iatrogenic, and traumatic conditions.1 Traumatic lesions resulting in foot drop are more frequently secondary to injuries to the peroneal or sciatic nerve. The treatment of this condition is usually a challenge for most neurosurgeons. Although nerve reconstruction is indicated in some cases, poor outcomes are frequently associated with such procedures, especially if long grafts are needed.2 Tendon transfers, such as the transfer of the posterior tibialis tendon to the dorsum of the foot, have been suggested as the best surgical option for these cases. However, there are descriptions of high morbidity rates associated with such techniques, and the results are not consistently excellent.3 Therefore, the search for an ideal method for the treatment of foot drop deformity remains.

Recently, nerve transfer has been used as a reliable and effective technique to treat injuries to nerves for which direct reconstruction has not historically yielded good results, such as for the ulnar nerve.4 One of the most important advantages offered by this technique is the possibility to shorten the distance between the site of the suture and the target muscle, thus decreasing the time for reinnervation.5 We previously demonstrated the feasibility of transferring a motor branch from the tibial nerve to the deep peroneal nerve at the level of the proximal calf in cadavers.6 We proposed that this technique would theoretically be useful for the treatment of foot drop if the motor fascicle of the common peroneal nerve could be proximally isolated by means of intraneural dissection. This maneuver may increase the length of the deep peroneal nerve, allowing a tensionless direct suture between the donor and recipient nerves. The surgical indications for this technique include injuries to the peroneal division of the sciatic nerve and also some restricted injuries of the common peroneal nerve at the level of the head of the fibula, if proximal dissection and isolation of its motor component are feasible.

This study aimed to evaluate the outcomes obtained after the transfer of a healthy motor branch of the tibial nerve (the nerve of the soleus muscle) to the motor fascicle of the peroneal nerve responsible for the innervation of ankle dorsiflexion (the deep peroneal nerve) when the transfer was used to treat patients with foot drop due to injuries to a lumbar root or the sciatic or the peroneal nerve.

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We conducted a retrospective follow-up study of 13 patients with sustained foot drop due to different causes, who underwent a transfer of 1 motor branch of the tibial nerve to the deep peroneal nerve as the surgical treatment of choice between April 2009 and September 2011. Patients from 3 centers were included: the Units of Neurosurgery at the Hospital de Base do Distrito Federal and at the Hospital Santa Helena, both located in Brasilia, Brazil, and the Peripheral Nerve Surgery Unit, Department of Neurosurgery, University of São Paulo Medical School, located in São Paulo, Brazil.

The preoperative evaluation included serial clinical examination of the foot strength and electromyography, which invariably showed complete paralysis and denervation of the muscles controlled by the common peroneal nerve, along with normal or near-normal function of the tibial nerve. The plantar flexion was graded as M4 or M5 according the Medical Research Council (MRC) grading system in all of the patients of this series. Surgery was indicated for patients presenting with closed injury to the peroneal nerve in which no sign of recovery had been noted 8 months after the trauma and for patients with sciatic nerve injuries (the peroneal division) admitted 6 months after the trauma. Contraindications for the use of this technique included paralysis or dysfunction of the tibial nerve, muscle denervation time longer than 1 year, and the presence of neuromuscular or metabolic disorders affecting the function of the limbs.

Serial postoperative reviews were recorded, and the outcomes were evaluated in terms of the power of the muscles for ankle dorsiflexion (deep peroneal nerve), ankle eversion (lateral tilting of the foot, superficial peroneal nerve), and toe extension (deep peroneal nerve), according to the MRC grading system. The results were categorized as poor, when the power was M2 or lower (active joint motion present with gravity eliminated) and as good when the power was M3 (muscle can move joint through full range of motion against gravity) or M4 (full range of motion against gravity and some resistance). Informed consent was obtained from each patient, and the study was carried out in accordance with the second revision of the Declaration of Helsinki.

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Surgical Technique

The patient was placed in prone position, and the procedure was performed with the patient under general anesthesia without the use of muscle relaxants or tourniquet inflation on the affected limb (Figure 1). A curvilinear incision was made in the posterior leg, starting at the level of the upper popliteal fossa, continuing to the insertion of the gastrocnemius muscle, and then turning in the direction of the head of the fibula, ending 2 or 3 cm below it (Figure 2A). Initially, we proceeded with the identification of the common peroneal nerve as well as its distal divisions (ie, the deep and superficial peroneal nerves). The peroneal tunnel (ie, the tunnel created by the 2 heads of the peroneus longus muscle) was released, aiming to allow proper axonal regrowth (Figure 2B). The epifascicular epineurium of the distal common peroneal nerve was opened, and an intraneural individualization of the deep (mainly motor) and superficial (mainly sensory) fascicles of the nerve was carried out. The cleavage plane between these fascicular groups was easily located; however, as the dissection proceeded proximally, a number of interconnections between the fascicles were found, preventing further fascicular individualization due to the risk of damaging the nerves. Generally, it was possible to separate the deep and the superficial components of the common peroneal nerve for a mean distance up to 70 mm proximally to the head of the fibula (Figure 2C). The deep peroneal fascicle was then sectioned as proximally as possible. In the 2 patients with peroneal nerve injury at the level of the knee, the viability of the distal stump was checked based only on the supposed healthy aspect of the fascicles as they were observed under microscopic visualization, after retrograde intraneural dissection. Next, a surgical plane was created between the 2 heads of the gastrocnemius muscle to identify the tibial nerve and its motor branches (Figure 2D). We previously described the patterns of distribution of these branches at the proximal level of the calf, observing that the nerve of the soleus muscle is usually the most suitable branch for the transfer due to its consistent pattern of branching and its length.6 Hence, the nerve of the soleus muscle was isolated, electrically stimulated (nerve stimulator; Aesculap, Tuttlingen, Germany) to confirm its normal function, sectioned as distally as possible, and finally sutured to the deep peroneal nerve (Figure 2E). This technique allowed a direct tensionless cooptation, using two 10.0 microsutures and fibrin glue. The limb was kept immobilized for 2 to 3 weeks, which was followed by an intensive program of physiotherapy, including motor re-education and strengthening exercises.

Figure 1
Figure 1
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Figure 2
Figure 2
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Thirteen patients who had sustained a nerve lesion resulting in foot drop underwent surgery to transfer the nerve of the soleus muscle to the deep peroneal nerve (Table 1). The mean age of the cohort was 36.7 years (range, 20-59 years), and there were 9 men and 4 women. The surgery was used to treat lesions of the sciatic nerve in 10 patients, for peroneal nerve injury in 2 patients, and for injury of the fourth lumbar root during a lumbar disk surgery in 1 patient. The injuries involved the proximal third of the sciatic nerve in 8 patients (61%), the middle third of the sciatic nerve in 2 patients (15%), the common peroneal nerve at the level of the knee in 2 patients (15%), and a lumbar root in 1 patient (7.5%). In those patients sustaining direct peroneal nerve injuries due to high-energy knee trauma, the surgical exploration revealed a nerve with a hard consistency near its branching point from the sciatic nerve and a normal appearance distally; moreover, the proximal intraneural dissection of deep peroneal nerve showed a normal fascicular pattern under microscopic visualization. No patients demonstrated fixed contracture of the ankle (pes equinovarus deformity), and only 1 patient reported the occurrence of compartment syndrome of the muscles of the calf after the trauma, which was not considered severe and did not result in marked muscle loss.

Table 1
Table 1
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The mean interval between trauma and surgery was 6.6 months (range, 3-10 months). Two patients were lost in the follow-up, and for 1 patient, the postoperative time frame was considered insufficient to determine the surgical result (6 months). Table 2 summarizes the outcomes observed for the 10 patients for whom the follow-up period (mean, 20.8 months; range, 12-31 months) was considered appropriate to draw definitive conclusions. The outcome was considered good in only 2 patients (20%) with respect to ankle dorsiflexion, in 3 patients (30%) with respect to ankle eversion, and in 2 patients with respect to toe extension (20%).

Table 2
Table 2
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Postoperatively, only 1 patient complained about the aesthetic aspect of the reduced calf circumference (due to denervation of the soleus muscle), and no other complications were observed. No patient reported decreased strength of the plantar flexion.

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The outcomes for the recovery of functional ankle dorsiflexion after injuries to the peroneal and sciatic nerves are usually considered poor.2,7-11 In contrast, satisfactory results have been reported associated with the use of the posterior tibialis tendon transfer for the recovery of ankle dorsiflexion. However, this technique usually provides only weak ankle dorsiflexion, and some controlled studies have demonstrated that it carries a 30% risk of complications, and satisfactory results cannot be obtained in all cases.3,12,13 Recently, nerve transfer has been used for the treatment of distal nerve injuries with increasing frequency. Examples include the transfer of the distal branch of the anterior interosseous nerve to the deep ulnar nerve14 or the transfer of motor branches of the median nerve to recover the function of the radial nerve.15 Our previous anatomic study in cadavers demonstrated the viability of transferring 1 motor branch from the tibial nerve to the deep peroneal nerve, and the nerve to the soleus muscle was determined to be the best donor for such a transfer. However, we noted that direct suture was possible only if the recipient nerve could be proximally lengthened to the level of the popliteal fossa, which was the case for 2 of our patients who had sustained closed injuries to the common peroneal nerve at the level of the head of the fibula due to high-energy trauma to the knee. We considered that this technique could be also useful for patients who had sustained injuries to the peroneal division of the sciatic nerve at the level of the buttocks or thigh and in whom the function of the tibial division remained preserved, which was the indication for surgery in most of our cases.

The idea of transferring some healthy branches of the tibial nerve to recover the function of the peroneal nerve is not completely new. Anatomic16,17 and clinical18-22 data have been published before, and the results have been highly contradictory. There have been studies suggesting very good outcomes associated with this type of nerve transfer, such as in the article by Gousheh and Babaei,18 reporting outcomes of M3 or better in 6 of 8 children with sciatic nerve injuries. Nath et al19 reported that good outcomes were achieved in 11 of the 14 adult patients treated with nerve transfers to the deep peroneal nerve, in which branches from the tibial nerve were used as donors in 9 participants. Conversely, Giuffre et al21,22 reported good recovery of ankle dorsiflexion in only 4 patients in a cohort of 11 patients in whom some branches or intraneural fascicles of the tibial nerve (branches destined to the flexor digitorum longus or the flexor hallucis longus muscle) were transferred to the branch to the tibialis anterior muscle for patients who have sustained high-energy injuries of the peroneal nerve at the level of the knee. Given the variability of donor nerves and outcomes that have been previously reported, it is difficult to determine the real potential of the technique, especially because all previously reported series enrolled a small number of patients. Our observations are more in line with the results noted by Giuffre et al,22 ie, the surgical outcomes obtained with the technique are frustrating in most of the cases (good results in only 20% of the patients with respect to ankle dorsiflexion), although some patients may benefit from it. Therefore, a question arises: who can benefit from this technique?

Kemp et al23 developed a rodent model of hind limb nerve transfer, evaluating the effect of selective tibial branch nerve transfer on behavioral recovery in animals after acute transection of the deep peroneal nerve. Their results indicated that not only could hind limb nerve transfers be successfully accomplished in a rat model, but also that these animals displayed a recovery of skilled locomotor function on a par with that of animals that underwent direct deep peroneal nerve repair. Terminal electrophysiological and myological assessments demonstrated similar levels of reinnervation, whereas retrograde labeling studies confirmed that the peroneal nerve–innervated muscles were reinnervated by neurons from the tibial nerve pool in the nerve transfer group. We can assume from this experimental study that the proposed transfer has the potential for powerful reinnervation of the muscles supplied by the peroneal nerve, and the good results observed in 2 of our patients confirm this idea. We tried to isolate parameters from these selected patients that could help to identify why they achieved better outcomes; however, the time between trauma and surgery, the mechanism of injury, and the age of patients did not demonstrate any differences with the other cases. Conversely, our best result was observed in a subject who had sustained an injury to the peroneal nerve at the level of the knee and in whom the function of the tibial nerve remained intact. Based on this observation, we propose that the quality of the donor might be an important parameter to obtain better results. In patients with sciatic nerve injury in whom the function of the tibial division is considered preserved, we cannot ensure that the axons of the tibial nerve and its branches are really normal. Trauma to nerves always induces cellular death in a number of motor neurons located in the anterior horn, and it also modifies the intracellular machinery of the remaining neurons.24 Therefore, we suggest that, due to the intracellular modifications after the trauma, the donor axons that we initially assumed to be normal had a decreased propensity to reinnervate distal targets. In extrapolating these ideas to the patient who reached grade MRC M4 for ankle dorsiflexion, we concluded the following: his tibial nerve function was intact because the injury was restricted to the peroneal nerve and hence the axons from the nerve to the soleus in this particular patient also had a better biochemical quality for the transfer. This hypothesis should be further studied in future animal models.

In our cohort, poor outcomes were observed in most of the patients, in contrast to some studies and in agreement with others. Several reasons could explain these failures. One of the explanations is the possibility that the same reasons that explain the unfavorable results associated with grafting the peroneal nerve would also explain the fair results observed with the nerve transfer. Extensive intraneural scar tissue, an increased amount of connective tissue, and a imbalance of the power of the muscles between the ventral and dorsal compartments of the leg are commonly described as possible reasons to explain such phenomena,25,26 and they cannot be ruled out as factors that may eventually have affected the final results of the proposed transfer. The use of a donor nerve that acts as an antagonist to the function that it is intended to recover may be another possible explanation, especially with respect to the postoperative physical relearning. Experimental studies in rodents have demonstrated that muscles that were targeted by antagonistic nerves showed electrophysiological and microscopic patterns of reinnervation, but functional recovery was only rarely observed.27 The same phenomenon may have occurred in our patients. The insufficient number of available donor axons could also be responsible for the poor outcomes: a study by Pirela-Cruz et al16 showed that the branch to the soleus muscle had a similar axonal count as that of the branch to the tibialis anterior muscle; however, it had less than half of the axonal count of the deep peroneal nerve. Considering this possibility, an increase in the number of available axons may theoretically improve the surgical results. The technique proposed by Gousheh and Babaei18 included the use of 2 motor branches as donors, which could explain the better results reported by those authors. Another way to increase the number of available motor fibers would be optimization of the target: Giuffre et al21,22 and Pirela-Cruz et al16 suggested the motor branch to the tibialis anterior muscle as the ideal target of the technique, a strategy adopted to avoid axonal dispersion. The role of these technical maneuvers can only be determined by future prospective studies enrolling larger patient cohorts. Finally, the mechanism of gait associated with central plasticity may also have a role in the capacity to control the movement of the ankle joint. A spinal network of motor neurons, known as the central pattern generator, controls the rhythmic motor patterns required for coordinated swimming, walking, and running in mammals.28 This mechanism is highly dependent on a perfect balance between the simultaneous activation of agonistic and inhibition of antagonistic motor neurons.29 By modifying the input and output to and from this central pool of neurons using the technique described here, we may have interfered with the fine-tuning necessary to control this mechanism, and the final result could have been a lack of voluntary function.

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The limitations of this study include the following: the small number of patients (although we operated on a total of 13 patients, we were only able to assess the outcome for 10 of them); the relatively short follow-up period in some of these cases; the variable patient population, such as different types of injuries, different sites of injury, and even different delays for surgery; and the fact that the patients were enrolled from 3 different centers, which could have potentially introduced technical and analytical biases.

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Given the inconsistency of the outcomes observed in our patients after the transfer of the soleus nerve to the deep peroneal nerve, we do not recommend the routine use of this technique as a treatment for foot drop, although favorable results can occasionally be obtained in some patients.

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The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.

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1. Stewart JD. Foot drop: where, why and what to do? Pract Neurol. 2008;8(3):158–169.

2. Murovic JA. Lower-extremity peripheral nerve injuries: a Louisiana State University Health Sciences Center literature review with comparison of the operative outcomes of 806 Louisiana State University Health Sciences Center sciatic, common peroneal, and tibial nerve lesions. Neurosurgery. 2009;65(suppl 4):A18–A23.

3. Steinau HU, Tofaute A, Huellmann K, et al.. Tendon transfers for drop foot correction: long-term results including quality of life assessment, and dynamometric and pedobarographic measurements. Arch Orthop Trauma Surg. 2011;131(7):903–910.

4. Battiston B, Lanzetta M. Reconstruction of high ulnar nerve lesions by distal double median to ulnar nerve transfer. J Hand Surg Am. 1999;24(6):1185–1191.

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6. Flores LP. Proximal motor branches from the tibial nerve as direct donors to restore function of the deep fibular nerve for treatment of high sciatic nerve injuries: a cadaveric feasibility study. Neurosurgery. 2009;65(suppl 6):218–224.

7. Kim DH, Murovic JA, Tiel R, Kline DG. Management and outcomes in 353 surgically treated sciatic nerve lesions. J Neurosurg. 2004;101(1):8–17.

8. Kim DH, Murovic JA, Tiel RL, Kline DG. Management and outcomes in 318 operative common peroneal nerve lesions at the Louisiana State University Health Sciences Center. Neurosurgery. 2004;54(6):1421–1428.

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10. Weil YA, Pearle AD, Palladas L, Liebergall M, Mosheiff R. Long-term functional outcome of penetrating sciatic nerve injury. J Trauma. 2008;64(3):790–795.

11. de Bruijn IL, Geertzen JH, Dijkstra PU. Functional outcome after peroneal nerve injury. Int J Rehabil Res. 2007;30(4):333–337.

12. Kremer T, Riedel K, Germann G, Heitmann C, Sauerbier M. Tendon transfers for peroneal palsy—functional outcome [in German]. Handchir Mikrochir Plast Chir. 2011;43(2):95–101.

13. Mehling I, Lanz U, Prommersberger KJ, Fuhrmann RA, van Schoonhoven J. Transfer of the posterior tibialis tendon to restore an active dorsiflexion of the foot [in German]. Handchir Mikrochir Plast Chir. 2012;44(1):29–34.

14. Flores LP. Distal anterior interosseous nerve transfer to the deep ulnar nerve and end-to-side suture of the superficial ulnar nerve to the third common palmar digital nerve for treatment of high ulnar nerve injuries: experience in five cases. Arq Neuropsiquiatr. 2011;69(3):519–524.

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16. Pirela-Cruz MA, Hansen U, Terreros DA, Rossum A, West P. Interosseous nerve transfers for tibialis anterior muscle paralysis (foot drop): a human cadaver-based feasibility study. J Reconstr Microsurg. 2009;25(3):203–211.

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This retrospective analysis presents results of lower extremity nerve transfers, using antagonistic motor neurons in a diverse group of patients. It is interesting that ankle dorsiflexion never recovered without some recovery of ankle eversion (superficial peroneal nerve), raising the question of whether spontaneous (perhaps better) recovery may have occurred without intervention. It may also indicate that some degree of original innervation is needed to facilitate motor re-education of the soleus motor neurons to execute an originally antagonistic function. The spontaneous superficial peroneal functional recovery may also indicate that patient selection paradigms (timing) should be different for lower extremity nerve repairs due to longer regeneration distances compared with upper brachial plexus injuries. The use of intraoperative nerve action potential recordings of the deep peroneal nerve (with predominantly muscle innervation) at the time of exploration for nerve transfer may have identified spontaneous reinnervation and avoided unnecessary intervention. Postoperative electromyographic studies to assess reinervation and muscle activation patterns may help explain the lack of functional recovery in the majority of the patients. In the absence of good prospective studies, this paper supports the notion that this particular transfer generally yields poor results. Further exploration of the use of functionally agonistic donors may yield better results.

Jacob Alant

Calgary, Alberta, Canada

Foot drop is the most common nerve deficit in the lower limb, having a bad prognosis both for spontaneous recovery and after surgical treatment. Since the success of Oberlin's original report in 1994, numerous nerve transfer techniques have flooded the medical literature and changed the surgical management of upper limb nerve and brachial plexus injuries. In this scenario, it is surprising that scarce nerve transfer techniques were described for the lower limb. This paper has the merit of analyzing retrospectively a nerve transfer designed to treat foot drop. The described technique has not shown the positive results awaited by the authors, probably demonstrating that some concepts currently applied to upper limb injuries cannot be directly translated to the lower limb.

In our department, tibial nerve and tibial component of sciatic nerve injuries deserve all our efforts for reconstruction, primarily due to the important sensitive function that this nerve has at the sole of the foot. On the other hand, foot drop caused by severe closed stretching of the peroneal nerve, open wounds with nerve defects longer than 8 cm, or direct sciatic nerve injuries at the buttock or thigh affecting exclusively the peroneal division, receive no nerve treatment. We prefer to perform a posterior tibial tendon transfer; which is a simple, safer, and predictable technique. We believe that this tendon transfer still remains as the gold standard for the treatment of foot drop.

Mariano Socolovsky

Buenos Aires, Argentina

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CME Questions:

1. What is the best surgical option for patients with foot drop secondary to traumatic sciatic or peroneal nerve injury?

a. Nerve reconstruction with long grafts

b. Tibial to deep peroneal nerve transfer

c. Posterior tibial tendon to dorsum of the foot transfer

d. Soleus tendon to dorsum of the foot transfer

2. After how many months is it considered contraindicated to perform nerve transfer from the tibial nerve to the deep peroneal nerve in patients with foot drop?

a. 6

b. 8

c. 10

d. 12

e. 14

3. What factor is associated with poor outcomes following tibial nerve transfer to the deep peroneal nerve?

a. Age

b. Gender

c. Mechanism of injury

d. Extensive interneural scar tissue

e. Use of a donor nerve with agonist function


Foot drop; Nerve transfer; Peroneal nerve; Tibial nerve

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