Some nerves of the lower extremity are superficial in nature and are susceptible to damage after a traumatic injury or surgical intervention. Peripheral nerve injury can result in neuroma formation, in which the damaged nerve undergoes an inflammatory reaction followed by unorganized regeneration of the distal segment, forming a bulbous ending.1 The milieu of the neuroma increases nerve fiber sensitivity through a decreased threshold for excitability.2 Thus, neuromas can be a significant source of pain and often require multiple therapeutics for symptom management. First-line management of neuromas consists of pharmacological modalities to decrease nerve excitation with other adjunctive treatments added for persistent symptoms.

In cases refractory to pharmacologic management, surgical intervention may be required. Common surgical interventions described include targeted muscle reinnervation and regenerative peripheral nerve interfaces. Both of these have been reported on in the literature as successful management techniques for traumatic neuromas. The theory, during surgical management of neuromas, of transferring the proximal nerve segment into an adjacent structure such as muscle or bone is widely supported. This process protects the nerve from mechanical stressors that can trigger neuropathic pain. For some neuromas of the foot and ankle, as will be described in this case, transfer into an adjacent structure is not feasible as there is limited anatomic space and surrounding musculature for adequate burial and nerve immobilization.3 A solution for treating neuromas in areas of limited space is neuroma excision with the placement of the proximal nerve segment into a collagen conduit. This enables the proximal end of the nerve to remain protected and independent of the surrounding anatomy.

Gould and colleagues published the largest cohort of foot and ankle neuromas treated with excision and collagen nerve-conduit placement. In a retrospective review of 69 nerve-conduit constructs, patients reported significant improvement in 59/69 cases (85%). The nerves involved included the 2,3 intermetatarsal (28), 3,4 intermetatarsal (26), tibial (2), lateral plantar (1), a middle branch of the lateral plantar nerve (1), dorsomedial hallucal (medial branch of the superficial peroneal nerve) (2), lateral hallucal (1), superficial peroneal (1), a calcaneal branch of the tibial (4), deep peroneal (1), common peroneal (1), and sural (1).3

In this report, we use the technique described by Gould and colleagues for the excision and transposition of the saphenous nerve into the periosteum under the protection of a collagen conduit for the treatment of a symptomatic neuroma. To our knowledge, this is the first case describing this technique for the surgical treatment of a distal saphenous nerve neuroma.

CASE PRESENTATION

This is a 22-year-old girl who presented to our clinic with a year-long history of painful and burning sensations on the “top of her foot” and a progressively enlarging nodule just anterior to the medial malleolus. In addition, she reported occasional sharp pains with walking over the “inside” aspect of her foot. Patient’s surgical history was significant for a right-sided gastrocnemius recession, posterior tibial tendon (PTT) debridement, and flexor digitorum longus transfer to the navicular due to PTT dysfunction. Medical history was insignificant. However, the patient had been seeing a rheumatologist for diffuse joint pain throughout her upper and lower extremities for the past year. Subsequent test results were negative and signs were pointing to a seronegative arthropathy. Per the rheumatologist, her diagnosis is uncertain at this time and is still being worked up. Based on further questioning and physical examination, the occasional sharp pains overlying the medial aspect of her ankle were attributed to her remote surgical history on the PTT. In regards to the enlarging nodule and the neuropathic sensations on the anteromedial aspect of her foot, the patient could call no recent trauma or injury. Physical examination yielded a positive Tinel sign as direct manual compression over the mass reproduced her symptoms throughout the saphenous nerve distribution of her foot. Based on available evidence, suspicion of an iatrogenic saphenous neuroma was high. Further imaging was obtained with magnetic resonance imaging and revealed bulky granulation tissue and surgical bed scarring affecting the saphenous nerve. A diagnostic lidocaine injection was performed and provided transient relief of the neuropathic symptoms while, in addition, providing confirmatory diagnostic value. The patient underwent a trial of conservative measures with anti-inflammatories and a walking boot, which failed to resolve her symptoms. As the symptoms progressed, surgical treatments were discussed, and after discussing the risks and benefits of surgical intervention, the patient consented to the operation.

Surgical Technique Preoperative Surgical Site Localization and Preparation

The medial aspect of the distal right lower extremity was percussed along the course of the saphenous nerve, distal to proximal, and the patient was asked to report sensations of pins and needles or pain to localize the area of nerve damage. The patient was placed under general anesthesia and kept in the supine position for the duration of surgery. A bump was placed under the right leg to elevate the foot and ankle. A tourniquet was placed on the right thigh and later inflated to 300 mm Hg. A time-out was performed.

Saphenous Nerve Identification and Neuroma Excision

A marking pen was used to draw a 5 cm line over the localized nodule and a 4 cm skin incision was made with a 15-blade. Surgical scissors were used to dissect the subcutaneous fat until the underlying periosteum was visible. Care was taken to identify the saphenous nerve, which was appreciated directly below the thin plane of subcutaneous fat. The nerve was isolated and dissected ~1 to 2 cm proximally and distally, freeing it from the surrounding tissue. The neuroma was identified and then excised by cutting its proximal and distal attachment (Fig. 1) and was sent to the pathologist, where the definitive diagnosis of neuroma was confirmed.

FIGURE 1:

Intraoperative photograph demonstrating neuroma (marked with purple marking pen) with the distal end of the saphenous nerve transected.

Conduit Placement and Saphenous Nerve Transposition

A 2 cm periosteal flap was created along the tibia with a 15-blade along the course of the saphenous nerve, and a freer was used to elevate the periosteum off the bone. The nerve was then prepared for placement into the collagen conduit. The diameter of the conduit was selected for the closest approximation of the nerve diameter and then it was soaked in normal saline. Typically, the nerve conduit is buried into an appropriate muscle belly. But, given the lack of surrounding musculature and soft tissue coverage in this specific location, a periosteal flap was created to decrease the prominence of the conduit and prevent any excess irritation that would occur if the nerve was placed directly into the bone and remained proud. A 4-0 silk suture was passed through the free end of the transected nerve (Fig. 2A). A Hewson suture passer was placed through the presoaked conduit. The silk ends of the suture were placed through the loop of the passer and the suture limbs were pulled through, sliding the conduit onto the nerve (Fig. 2B). The distal end of the conduit was secured to the epineurium using a 4-0 silk suture. The conduit-encased nerve was placed into the periosteal pocket (Fig. 3). The sutures were cut, and the periosteal flap was closed. The wound was then closed in a layered manner and sterile dressings were applied (Supplemental Digital Video, Supplemental Digital Content 1, https://links.lww.com/TIO/A52, which demonstrates the described technique in its entirety). Postoperatively, a short leg splint was placed, and the patient was non-weight bearing for 2 weeks to facilitate wound healing. At 2 weeks the patient was transferred to a tall boot and began weight bearing as tolerated. Physical therapy began at 2 weeks and consisted of deep massaging, desensitization techniques, and various modalities for pain control.

FIGURE 2:

A, 4-0 silk passed through the end of the transected portion of the saphenous nerve (marked in purple) before conduit placement. B, Sutures used to slide collagen conduit over the proximal segment of the saphenous nerve.

FIGURE 3:

Open periosteal pocket containing conduit-encased nerve before wound closure.

Outcomes

We have described the first reported case utilizing a collagen conduit for an iatrogenic saphenous nerve neuroma resection and transposition into nearby tibial periosteum. Our patient was followed at 2, 6, 12, 24, and 52 weeks and was found to have complete resolution of burning and tingling symptoms. Symptom resolution started at the 2-week follow-up, with complete resolution at 24 weeks. Currently, the patient experiences numbness in the saphenous nerve distribution, which was an expected outcome discussed before surgery. The patient has full range of motion about the ankle and lower extremities without any Tinel sign along the saphenous nerve distribution. The wound has healed nicely. Overall, outcomes for this case were excellent and consistent with previously reported patient outcomes from Gould et al,3 which demonstrated an 85% satisfaction rate after neuroma resection and transposition with a collagen conduit.

For nerves with purely sensory function, it is understood that resecting the neuroma with the transfer of the nerve to a tissue bed, such as muscle, is an appropriate strategy.4 The anatomy of the foot and ankle are unique in that there are limited options for nerve transposition within the muscle, especially in areas along the distal saphenous nerve at the ankle. Studies have concluded that transposing the superficial peroneal nerve into bone results in significantly better outcomes than transposition into muscle, however, this is not always the best option.5 This specific technique described is advantageous due to the fact that it does not transpose the nerve directly into the bone and risks leaving the nerve unprotected as a result of inadequate soft tissue coverage. The use of the collagen conduit and periosteal flap allows the nerve end to be placed more parallel to the distal tibia in an attempt to prevent any excess irritation from direct bone transposition at a location with minimal surrounding musculature. In addition, the combination of the collagen conduit and periosteal flap prevents the need for drilling into the bone while simultaneously providing a similar environment to direct bone transposition. This described technique, for distal saphenous neuromas, is feasible with a small incision, which also limits any cosmetic concerns associated with procedures requiring transposition to a location with more suitable soft tissue coverage. Further proof of the utility of a collagen conduit for neuroma management can be found when analyzing the studies by Thomsen et al.6,7 In a retrospective study of 10 cases of neuromas of the digital nerves, they concluded that collagen conduits offer effective treatment based on the recovery of 2-point discrimination, Semmes-Weinstein monofilament testing, Quick-Dash survey scores, and convergence insufficiency symptom survey (CISS) scores. In all cases, there was no recurrence of pain.6 In a more expansive prospective study, Thomsen and his colleagues isolated 185 traumatic nerve defects. The nerves were sutured end to end and wrapped in a type I collagen tube. At the 6-month follow-up, there was no neuroma formation in the 185 nerves analyzed.7 Gould and Thomsen, through their studies, have shown the obvious utility of the use of a collagen conduit for nerve injuries and recurrent neuromas.

Complications

Complications possibly encountered after neuroma resection and nerve transposition with collagen conduits are surgical site infections, persistent pain, complex regional pain syndrome, neuroma recurrence, and stump neuroma. Superficial surgical site infections can be treated with a short course of oral antibiotics if clinically indicated. Persistent, unresolved pain and complex regional pain syndrome can first be addressed with warm compresses, over-the-counter pain medication, and/or topical analgesics such as lidocaine or capsaicin. Prescribed medications or nerve block injections can be considered in cases refractory to conservative treatment. Neuroma recurrence and stump neuromas can be managed with the aforementioned conservative management or more surgical intervention if encountered.

CONCLUSION

The technique described in this study, consisting of neuroma resection with collagen conduit encasement of the nerve and transposition into the periosteum, is an elegant approach to the treatment of neuromas of the foot and ankle that are lacking adequate surrounding soft tissue. We have demonstrated successful treatment of a distal saphenous neuroma of the ankle using this technique and have had great success utilizing this in our practice. Overall, our colleagues have treated 79 recurrent neuromas of the foot and ankle over the last 10 years. Of these 79 patients, 67 (85%) have reported satisfactory outcomes, which implies significantly diminished pain and return to normal function. Of these 79 neuromas, 2 have involved the saphenous nerve. Both cases reported complete resolution of symptoms following the procedure at a minimum follow-up of 9 months. We believe that the use of a collagen conduit for recurrent neuromas of the foot and ankle is an important, affordable, and technically practical technique that offers significant patient relief.

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