Procedures Leading to Iatrogenic Injury of the Sural Nerve

Abstract

Background:

Iatrogenic sural nerve injuries can result in significant patient morbidity and functional impairment following surgical procedures involving the distal leg, ankle, or lateral foot. This study investigates the surgical procedures implicated and the clinical presentation of patients with iatrogenic sural nerve injuries.

Methods:

The authors completed a retrospective review of 9 patients with iatrogenic sural neuropathy following surgical procedures between 2010 and 2022 at the University of Miami Health System. Patient demographics, surgical details, symptom onset, imaging findings, and final neuropathy diagnosis were extracted and analyzed.

Results:

The average age of patients was 47 years. The ankle was the common site of sural nerve injury (88.9%). Most patients experienced pain, numbness, and tingling, with tenderness and loss of sensation in the sural nerve distribution. The average time between surgery and completion of imaging evaluation for sural nerve injury was 80.5 weeks. All patients underwent ultrasound (77.8%) and/or magnetic resonance imaging (77.8%) evaluation postoperatively. The most frequent resulting pathology was neuroma formation, followed by entrapment, neuropraxia, and complete transection. Four patients had surgical management of sural nerve neuropathy, with none experiencing complete resolution of symptoms after surgery.

Conclusions:

This study highlights the surgical procedures that can result in iatrogenic sural nerve injuries beyond Achilles tendon repair. Increased awareness of surgical causes and continued reporting of iatrogenic sural nerve injuries can contribute to improved patient outcomes in procedures involving the distal lower extremity.

Takeaways

Question: What surgical procedures are associated with iatrogenic sural nerve injury?

Findings: In this retrospective study of 9 patients with imaging-confirmed iatrogenic sural nerve injury, a range of procedures were implicated—most commonly Achilles and peroneal tendon repairs.

Meaning: Awareness of at-risk procedures and early use of ultrasound imaging can improve diagnosis and guide timely, tailored management of sural nerve injuries, potentially preventing long-term morbidity.

INTRODUCTION

The sural nerve provides cutaneous sensation to the posterolateral aspect of the distal leg and the lateral aspect of the foot and ankle (Fig. 1). Originating just inferior to the popliteal fossa, the nerve is formed by the union of cutaneous branches of the tibial and common peroneal nerves.^1–3 It then passes through the 2 heads of the gastrocnemius muscle and travels down the distal third of the leg, midway between the Achilles tendon and the lateral malleolus, before terminating as the lateral dorsal cutaneous nerve in the fifth digit.^4–6 Although this is the most frequent distribution, several sural nerve variants have been identified that vary in either origin or trajectory.^3,7–9

Fig. 1.

Anatomy of the sural nerve and its area of innervation. The sural nerve provides cutaneous sensation to the posterolateral aspect of the distal leg and the lateral foot and ankle. The nerve is derived from the union of cutaneous branches of the tibial and common peroneal nerves.

Due to the proximity of the sural nerve to the gastrocnemius muscle, peroneal tendons, the short saphenous vein, and the Achilles tendon, the nerve is at risk for iatrogenic injury during surgical procedures involving these structures.^10,11 Resulting symptoms can range from mild sensory disturbance, with complaints of paresthesia or numbness, to complete loss of sensation in the affected cutaneous distribution or impairment of functional surgical outcomes.^12–14 In cases of severe injury, transection, or entrapment, further surgical intervention and prolonged hospital stays may be required.¹⁵ Therefore, adequate knowledge of both the normal anatomy and its numerous variants is vital in decreasing the risk of intraoperative sural nerve injury.³

In addition to patient-specific anatomy, familiarity with the procedures that commonly lead to sural nerve morbidity can assist surgeons in developing techniques to avoid injury. Cases of iatrogenic sural nerve injury in the literature are primarily limited to Achilles tendon and calcaneal fracture repair procedures.^7,16–20 However, the authors of this study have noticed a pattern of iatrogenic sural nerve injury at our institution in patients who have undergone a wide variety of procedures involving the distal leg and ankle. This study aimed to increase the available information on surgical causes of sural nerve injury and to discuss the clinical presentations of iatrogenic sural nerve injury.

METHODS

This study received institutional review board approval for the use of retrospective, de-identified patient data. No additional patient consent for inclusion in this study was necessary due to protocols at our institution that collect patient consent for the sharing of their de-identified data and photographs before surgery. The authors completed a retrospective chart review of all patients in the electronic medical record system at the University of Miami Health System who had sural nerve pathology identified on ultrasound or magnetic resonance imaging (MRI) imaging between January 2010 and January 2018. Resulting patients were screened for sural nerve pathology that was attributed to iatrogenic injury from a prior surgical procedure, with other etiologies of sural nerve morbidity excluded. Patient notes without specific mention of the sural nerve, despite complaints of pain, paresthesia, and/or numbness in the sural nerve distribution following a surgical procedure, were also included for further assessment.

Nine patients met all inclusion criteria. Demographic information, including age, sex, comorbidities (hypertension, diabetes mellitus, smoking status), and body mass index of patients, was extracted from a retrospective review of prior documentation. Surgical information included the procedure attributed to the injury, the time between the procedure and symptom onset, the character and severity of resulting symptoms, available imaging reports, and the final diagnosis and management.

RESULTS

Nine patients underwent postoperative imaging following iatrogenic injury to the sural nerve in a prior surgical procedure. Most patients were female (n = 8, 88.9%). The average patient age was 45.8 years (range 20–87 y), and body mass index was 28.1 kg/m² (range 21.6–41.6 kg/m²).

The most common site of initial injury was the ankle (n = 8, 88.9%). Etiologies leading to surgery included ankle impingement (n = 1, 11.1%), Achilles injury (n = 2, 22.2%), ankle fracture (n = 2, 22.2%), peroneal tendon injury (n = 2, 22.2%), and calcaneofibular ligament injury (n = 1, 11.1%). Patients underwent a variety of procedures leading to sural nerve injury, the most frequent being peroneal tendon repair (n = 2, 22.2%). (See table, Supplemental Digital Content 1, which shows a summary of postoperative sural nerve pathologies by procedure, symptoms, and time to imaging evaluation, https://links.lww.com/PRSGO/E903.) Of the patients seen early (within 6 mo of original surgery date) in the postoperative period (n = 4, 44.4%), symptoms related to sural neuropathy were reported at an average of 7.9 weeks following surgery (range 4.3–13.1 wk). Most commonly, patients complained of pain, numbness, and tingling in the ankle. Frequent physical examination findings included tenderness to palpation along the ankle joint (n = 7, 77.8%), loss of sensation in the sural nerve distribution (n = 9, 100.0%), and a positive Tinel sign (n = 5, 55.6%).

The mean time between surgical sural nerve injury and assessment of sural neuropathy through imaging was 80.5 weeks (range 109–2920 wk). Three patients underwent the operation leading to injury at an outside hospital, resulting in a longer interval before imaging was completed. For patients who reported an estimated onset of symptoms (n = 4), the average time from sural nerve symptom onset to the completion of postoperative imaging for evaluation of sural nerve pathology was 24.4 weeks (range 15.7–42.7 wk). Two patients underwent MRI, another 2 patients underwent ultrasound neurography, and the remaining 5 patients received both MRI and ultrasound evaluations postoperatively (77.8%). (See table, Supplemental Digital Content 2, which shows a summary of imaging and management outcomes of patients with sural nerve injury, https://links.lww.com/PRSGO/E904.) The final diagnosis based on imaging was most often sural nerve neuroma (n = 4), followed by sural nerve entrapment (n = 3), sural neuritis (n = 1), and sural nerve scarring (n = 1) (Figs. 2, 3).

Fig. 2.

Sural nerve entrapment. Axial T1-weighted MRI of right ankle demonstrating postsurgical changes of the peroneal tendons (A–D), with surrounding scar tissue just above (B, arrow) and extending below the lateral malleolus. The proximal and mid portions of the sural nerve are of normal course and caliber; however, the nerve appears entrapped (E–G, arrow) below the lateral malleolus scar tissue.

Fig. 3.

Sural nerve neuroma. Proton dense–weighted axial MRI of the left ankle demonstrating a 4-mm neuroma (A, B, arrow) involving the distal aspect of the sural nerve at the level of the peroneal tubercle, immediately posterior to the calcaneal anchor for calcaneal fibular ligament reconstruction. C, Corresponding sagittal T1-weighted MRI of the left ankle demonstrating the 4-mm neuroma involving the distal aspect of the sural nerve.

Five patients underwent an ultrasound-guided anesthetic injection procedure: 3 were for the diagnosis and treatment of sural nerve neuropathy, 1 for diagnostic evaluation only, and 1 for treatment only. All 4 patients who underwent the procedure for therapeutic purposes experienced temporary relief. These patients were treated with a mixture of corticosteroid and lidocaine injections, using combinations of Kenalog or Depo-Medrol (40 mg) with 1% lidocaine (1–5 mL, with or without epinephrine). One patient reported up to 6 months of relief before the pain recurred. Four patients underwent surgery, which included sural nerve neurolysis with amnion graft placement (n = 2), sural nerve neurolysis with neuroma resection and grafting (n = 1), and neurectomy with neurolysis and removal of a symptomatic implant (n = 1). One patient who underwent sural nerve neurolysis with graft placement for sural neuritis required reoperation 12 months later for perineural cyst drainage, amnion graft removal, sural nerve resection, and implantation of the proximal stump into an adjoining muscle. None of the patients who received surgical treatment for sural neuropathy experienced resolution of symptoms. All 4 patients continued to report pain postintervention, and 1 patient was eventually lost to follow-up.

DISCUSSION

Iatrogenic sural nerve injury is an infrequent sequela of surgery involving the distal leg, ankle, or lateral foot. Nonetheless, it can result in significant patient morbidity and impairment of functional outcomes.^12–14,21 This study demonstrates a wide variety of surgical procedures that pose a risk of iatrogenic sural neuropathy, many of which are uncommonly reported in the literature. Our analysis revealed that procedures involving the foot and ankle, more so than those involving the distal leg or knee, appeared to place the sural nerve at greater risk for injury. Patients also experienced numerous differing injuries as a result. Notably, the patients in this study often had substantial delays between symptom onset and completion of ultrasound or MRI imaging, resulting in late intervention and a prolonged duration of neurogenic symptoms. It is hypothesized that early intervention in peripheral nerve injuries can reduce the risk of pain centralization.²² When a peripheral nerve trigger persists for too long, it can lead to pain centralization that is not responsive to surgical interventions. Instead, centralized neuropathic pain is best managed nonsurgically through pain management and desensitization therapy.²² Increased awareness of procedures leading to sural nerve injury, along with ultrasound imaging preoperatively to map the nerve and postoperatively to determine the mechanism of injury, may improve patient outcomes following surgical procedures involving the distal lower extremity. It may also allow for more appropriate patient education on the risks of the initial procedure. For example, patients can and should be educated on the symptoms associated with sural nerve injury to more efficiently and effectively address any complications.

Achilles tendon repair is among the most frequently implicated causes of iatrogenic sural nerve injury in the literature.^7,18,19,23 Anatomical studies have found that the sural nerve intersects the lateral border of the Achilles tendon at approximately one-half the length of the tendon, though this can vary considerably among patients.^{3,21,24–26,} A few decades ago, iatrogenic sural nerve injury was reported in as many as 60% of patients undergoing Achilles tendon repair.^16,27–29 However, continued meticulous evaluation of sural nerve anatomy and subsequent improvements in surgical technique over the years have led to a substantial reduction in this rate.^{16,23,27,30,31} A systematic review and meta-analysis found the rate of sural nerve injury in more recent years to be less than 4% with minimally invasive techniques, highlighting the importance of identifying procedures that lead to morbidity.¹⁶ Nonetheless, rates of sural neuropathy may remain elevated for other surgical procedures of the distal lower extremity, such as open reduction and internal fixation of various ankle fractures, in which injury is reported in up to 55% of patients undergoing this procedure.^17,25 Additionally, peripheral nerve grafts are considered the gold standard for autograft harvest in peripheral nerve gap repair, and the sural nerve is the most frequently used for this purpose. Approximately 16% of patients develop neuroma formation, likely due to variability in operative or biopsy techniques.³²

Several studies have suggested that minimally invasive surgical techniques pose a greater risk of iatrogenic sural nerve injury than traditional open methods. This may partially be the result of surgeons being unable to directly visualize the nerves as they would in an open procedure.^16,23,27 Ultrasound neurography may have value in these cases to preoperatively map the trajectory of the nerve.^26,33–38 The high resolution, low cost, and widespread availability of ultrasound make it an excellent option for preoperative localization of small-caliber nerves compared with alternative options such as MRI.^34–36,38 Ultrasound also has the unique ability to trace the course of the sural nerve from its origin to its termination in the lateral foot, which can assist the operator in identifying anatomical variants that may differ from the measurements based on traditional body surface markers.^3,35,36

As previously mentioned, patients in this study frequently had a significant delay between the onset of neurogenic symptoms and the completion of imaging with appropriate intervention. In general, sural neuropathy is commonly diagnosed based on physical examination findings and electrodiagnostic studies. Although these measures can correctly identify the presence of sural neuropathy, they may fail to provide specific information related to the underlying etiology and severity of injury. Ultrasound neurography may again be advantageous in these cases by providing specific information on the mechanism of injury. Pathologies, including entrapment, neuroma formation, neuropraxia, and transection, can be easily identified on ultrasound.³⁸ Differentiation of underlying pathology is necessary to determine the next best steps in management, as the recommended treatment will vary according to the injury at hand. Low-grade neuropraxia usually does not require operative intervention. Alternatively, although only 1 patient underwent successful reoperative treatment, sural nerve entrapment can lead to permanent symptomatic relief with a simple neurolysis procedure.^39,40 Moreover, patients with neuroma formation can achieve substantial reduction or remission of symptoms with surgical excision and subsequent nerve grafting or rerouting. It is important to be aware of complications such as perineural cyst formation, as experienced by one of the patients. The perineural cyst likely developed secondary to fluid accumulation or an inflammatory reaction around the grafted sural nerve postoperatively. This may have resulted from the amnion graft acting as a barrier that trapped serous or axoplasmic fluid following neurolysis. However, a foreign-body reaction to the graft material could not be excluded, and thus, the initially placed amnion graft was removed.

Limitations of this study include its small sample size and retrospective design, as retrospective data collection does not capture the same detailed information as a prospective study design. Therefore, a prospective study would not be appropriate to further investigate iatrogenic sural nerve injury as a complication of surgery involving the distal lower extremity. Furthermore, several patients had the initial surgery leading to sural neuropathy at an outside institution, and thus, the study team was unable to extract information about specific surgical techniques from the operative notes of these patients. Despite these limitations, this study adds to the limited existing literature discussing the surgical causes of iatrogenic sural nerve injury and the utility of ultrasound both pre- and postoperatively. To improve patient outcomes, future studies should continue to report instances of iatrogenic sural neuropathy, including information on the surgical techniques that lead to patient morbidity.

CONCLUSIONS

Patients in this study underwent a wide array of surgical procedures involving the distal lower extremity that resulted in sural nerve injury, though injury most commonly followed repair of the Achilles or peroneal tendons. Resulting sural neuropathies ranged from entrapment to neuroma formation and complete transection, with several patients having a substantial delay from symptom development to imaging evaluation and intervention. Future studies should continue to report instances of iatrogenic sural nerve injury and the surgical techniques that lead to patient morbidity.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.

ACKNOWLEDGMENT

The authors thank medical illustrator Anabella Miki for her efforts in creating the illustrations in this article.

ETHICAL APPROVAL

Ethical approval was obtained from the institutional review board.