Double Crush Syndrome in the Lower Extremity. A Case Report

Abstract

Upton and McComas first described double crush syndrome in 1973. The theory behind double crush syndrome postulated that a proximal lesion in a nerve would make that same nerve more vulnerable to additional distal lesions. Many of the studies investigating the possibility of the double crush syndrome involve lesions in the upper extremity with very few articles written specifically about double crush syndrome in the lower extremity. We present the case of a 33-year-old massage therapist who uses her feet to provide therapy to clients who presented to our clinic with symptoms consistent with tarsal tunnel syndrome. Her failure to progress in a satisfactory manner after a variety of therapies made us search for additional etiologies for her foot pain. In cases where tarsal tunnel persists after surgical therapy, the treating physician should search for more proximal lesions along the course of the nerve.

Upton and McComas first described double crush syndrome in 1973 [1]. The double crush theory postulated that a proximal lesion in a nerve would make that same nerve more vulnerable to additional distal lesions. Further addition of lesions could lead to partial or complete denervation evidenced with electrophysiology studies [2–4]. This theory has been explored in many previous studies [2,4–7]. Although most research into the double crush phenomenon involves the upper extremity and the carpal tunnel, studies have begun to prove a cross-over between the two entrapment neuropathies in patients [8,9].

Studies performed on nerves attempting to demonstrate the pathophysiology of double crush syndrome have demonstrated that at 20 mm Hg, the extraneural blood flow was effectively terminated, and at 80 mm Hg intraneural blood flow was terminated [10]. Additionally, pressures of 30 mm Hg on a nerve were sufficient enough to inhibit all anterograde and retrograde axonal transport [11]. By removing all sources of energy and waste transport systems, the nerve is in a compromised situation. While in this state, the damaged nerves have shown to have lower threshold to produce clinical symptoms [7]. Although the nerve will not undergo permanent degeneration during short-term experiments, long-standing compression can lead to Wallerian degeneration of the compressed nerve [12].

Tarsal tunnel syndrome was a term first presented in the literature in 1962 by Keck [13] and Lam [14], but descriptions of the disease were published previously. The tarsal tunnel is a fibro-osseous structure bounded by the sustentaculum tali, medial calcaneous, and medial talus deep; the flexor retinaculum or laciniate ligament superficially and the abductor hallucis inferiorly. Structures passing through the tarsal tunnel are the posterior tibialis tendon, flexor hallucis longus (FHL) tendon, flexor digitorum longus (FDL) tendon, posterior tibial artery and vein, and the posterior tibial nerve [15,16].

Patients presenting with tarsal tunnel symptoms may complain of paresthesias or dysesthesia along the distribution of the tibial nerve. A detailed history may indicate increased severity of symptoms with increased standing, long periods of walking, or sleeping when the foot takes on a plantarflexed position. On physical examination, greater than 50% of patients with a compression neuropathy of the tarsal tunnel will have a positive Tinel’s sign of the posterior tibial nerve, but of those that are negative, an additional 15% may still be discovered by using the dorsiflexion-eversion test [16,17]. Additional palpation and compression of the nerve trunk may yield paresthesias (Valleix Phenomenon) [13,18]. Functional deficits or increased severity of symptoms may be noticed in patients with a long-standing history of tarsal tunnel symptoms. The examining physician should be suspicious of an absent Tinel’s sign, as a false-negative result can be present in patients with late-stage nerve entrapment.

Attention should be paid to those with comorbid conditions such as diabetes mellitus or metabolic syndrome as these conditions can act as the first ‘crush’ on the nerve and patients may have more severe symptoms [19]. Patients with metabolic disease should be offered surgery at the onset of verified, reproducible symptoms because of the higher likelihood of success of decompression [20,21].

Nerve conduction studies can provide the physician with a numerical value of the severity of disease. However nerve conduction studies may be normal in patients with mild compression of the tarsal tunnel as the nerve can regain function at rest, even when axonal loss is present [22,23].

Studies have shown that small amounts of inflammatory cytokines (IL-6, IL-1β, TNF-α) are released and remain in the surrounding tissues when a tear in the annulus fibrosis is present. The actual substance of the nucleus pulposus is highly concentrated in prostaglandin E2, which is an inflammatory substance. When applied to nerve roots, the cytokines not only act as an irritant increasing the discharge rate of nerves, but also provide for a positive feedback loop resulting in an increase in the production of additional prostaglandin E2. These cytokines can induce structural, and in time, functional deficits in the nerve [24–27].

Case report

A 33-year-old female massage therapist presented to her primary care physician with burning sensation around her bilateral medial ankles with numbness and tingling radiating to her toes after performing seven deep barefoot compression massages in 2 days time—a technique that involves the therapist standing on the client’s back. She was diagnosed with bilateral Achilles tendonitis and placed on light duty by the family physician. She denied any previous trauma or surgery to the affected area. Her past medical history was negative for any endocrine, cardiovascular, rheumatologic, osteoarthritis, or crystal deposition diseases.

After 9 weeks of no improvement, the patient was referred to Southern Nevada Foot and Ankle Center. The patient still complained of bilateral burning, numbness, and tingling sensations arising from the posterior medial ankle. She also stated that she has required the use of a cane for ambulation due to muscle atrophy and decreased sensation.

On physical exam, the patient demonstrated point tenderness at the insertion of the posterior tibialis tendon. A positive Tinel’s sign was noted for the posterior tarsal tunnels bilaterally and the anterior tarsal tunnel on the left. There was pain upon palpation over sinus tarsi bilateral. During gait analysis, the patient exhibited an antalgic gait pattern with hyperpronation. Magnetic resonance imaging (MRI) of the bilateral lower extremities was obtained that demonstrated bilateral subtalar synovitis with mild fluid in ankles and tenosynovitis of the posterior tibial tendon sheath.

Because of the unusual finding of an antalgic gait requiring a cane in an otherwise healthy young patient, additional concerns of proximal neurological involvement were brought up. Typically, a 33-year-old with tarsal tunnel or localized pedal complaints should not have proximal limb weakness, which was quite evident on her gait analysis. The podiatric physician ordered an MRI of the lower back, which revealed degenerative disc disease at the L4-5 and L5-S1 levels with desiccation, disc height loss, and annular tears with ventral chondral defects at these levels.

The patient was first treated conservatively with orthoses, nonopioid pain medication, and injections. Additional referrals to our local neurologist and orthopedic spine surgeon proved uneventful with no mention of the possibility of double crush syndrome. During this period, the patient underwent a nerve conduction study that showed some abnormalities within the tarsal tunnel, but no specific findings. Due to the persistence on the part of the patient and podiatric physician, she was seen at a well-known tertiary academic center that concluded she did fit the criteria of double crush syndrome. Despite the MRI being positive with findings demonstrating intervertebral disc disease at L4-L5 and L5-S1 levels with desiccation and tears of the annulus, there were no abnormalities discovered in subsequent nerve conduction velocities or electromyography studies.

Fifteen months after initial presentation, the patient underwent a staged bilateral subtalar arthroscopy with partial synovectomy. These procedures resulted in a 30% subjective reduction in joint pain. However, the patient continued to report pain over the dorsum of the left foot with pain radiating proximally from the ankle.

A subsequent anesthetic block of the L5 and S1 nerve roots relieved all leg and ankle pain for the duration of the block. Thirty months after initial presentation, the patient underwent a laminectomy, discectomy, and foraminotomy at the L4-S1 levels. At 3 months postoperation, the patient reported an 80% reduction in subjective pain. Additionally, she is able to walk 1.5 miles without assistance and only has recurrence of positional tarsal tunnel pain upon long periods of standing. She is seeing a physical therapist and considers her back surgery successful. As the pain at the dorsal aspects of both feet has resolved, she no longer requires the use of a cane to walk. On clinical exam her abnormal gait pattern has since resolved.

She is currently being considered a candidate for a subtalar arthroeresis procedure with possible tarsal tunnel release following her course of therapy. This was proposed because it has been shown that placing the patient into neutral position maximizes volume and decreases internal pressures of the tarsal tunnel [28–30].

Discussion

Although the patient presented with prominent symptoms of tarsal tunnel syndrome, ankle, and subtalar pain, performing a complete physical exam with gait analysis demonstrated signs of a more involved problem not specifically isolated to the lower extremity. In our case, with a young, active, otherwise normally healthy female, an antalgic gait pattern requiring the use of a cane was a rather concerning finding. The significant finding of the gait abnormality required that we determine a possible contributing etiology of our patient’s symptoms.

Additionally, the patient’s uneventful improvement with conservative treatment and partial improvement with surgical arthroscopy further solidified our hypothesis that she had additional nerve involvement more proximally. Her rather significant improvement in symptoms and functional capacity after spinal decompression solidified our speculation that her complaints were attributable to double crush syndrome with the first ‘crush’ occurring at the level of the spine, where the nerve root was being irritated by mechanical compression and inflammatory cytokines, and the second in the tarsal tunnel.

Conclusions

Double crush syndrome is not widely reported in the literature, and for cases in which it is an attributable cause, nearly all are documented in the upper extremity. For patients who present with symptoms consistent with tarsal tunnel syndrome that fail to resolve with conservative measures as well as surgical intervention, double crush syndrome should be considered in the differential and investigated.

An appropriate history and physical encompassing all possible endocrine dysfunction as well as any previous trauma to the back or activities that could lead to a back injury is vital. A full physical examination including gait analysis and appropriate laboratory studies to rule out metabolic, endocrine, or rheumatologic abnormalities should be performed. A work-up of low-back pain beginning with palpation, active and passive range of motion, and the straight leg raise test should be performed in the office. Imaging including plain radiography, nerve conduction studies, and MRI of the spine can determine the level of the nerve lesion and assist the treating physician in the creation of a plan.

When a mechanical compression of the nerve root is determined to be present in addition to a tarsal tunnel syndrome, it may be prudent for the treating surgeon to have the patient treated for more central problems antecedent to any peripheral surgical treatment for tarsal tunnel. Questioning patients about their hypothesis of the etiology of their pain is also a consideration, because they may be able to describe both central and distal areas as problematic, helping guide the physician to the diagnosis of double crush syndrome.

With the double crush syndrome, the concern is with antegrade damage along the course of the nerve with worsening and possible permanent dysfunction of distal structures. With resolution of the proximal lesion, the severity of the distal lesions can be lessened. It is also possible that surgical alleviation of a distal entrapment may decrease the severity of the proximal lesion.