Ulnar Nerve Entrapment at the Cubital Tunnel Successfully Treated with Ultrasound-Guided Peripheral Nerve Hydrodissection: A Case Report and Further Evidence for a Developing Treatment Option

In Brief

Ulnar nerve entrapment at the cubital tunnel successfully treated with ultrasound-guided hydrodissection with dextrose solution.

Introduction

Ulnar nerve entrapment is the second most common peripheral nerve entrapment of the upper extremity, second only to median nerve entrapment at the carpal tunnel (^1,2). The estimated annual incidence of ulnar nerve entrapment is about 0.8% per person-year (³). The ulnar nerve is composed of the C8 and T1 cervical nerve roots. As the ulnar nerve extends distally down the upper extremity, it passes deep to the Arcade of Struthers, enters the ulnar sulcus, and then courses posterior to the medial epicondyle and medial to the olecranon before entering the cubital tunnel. The cubital tunnel is defined by the arcuate ligament of Osbourne, the medial collateral ligament of the elbow, the elbow joint capsule, and the olecranon. Upon exiting the cubital tunnel, the ulnar nerve passes between the ulnar and humeral heads of the flexor carpi ulnaris and into the forearm. Entrapment may occur at several locations along the path of the nerve with the most common site being at the elbow within the cubital tunnel, known as cubital tunnel syndrome (^1,2). Compression of the ulnar nerve at the sight of entrapment results in proliferation of the endoneurial and perineurial microvasculature, edema in the epineurial space, fibrotic changes, myelin sheath thinning, and axonal degeneration, if prolonged (²).

Patients suffering from ulnar nerve entrapment often present with numbness and paresthesias in the fifth digit and ulnar half of the fourth digit (⁴), hand strength and grip problems secondary to intrinsic muscle weakness (^1,2), and occasionally a vague sense of clumsiness within the hand (¹). Patients with intermittent symptoms often have difficulty localizing their symptoms (¹). Ill-defined pain within the upper extremity may localize to the medial aspect of the elbow (^5,6), but this is less common (⁴). Physical examination of patients with cubital tunnel syndrome may reveal an increased carrying angle of the elbow. Symptoms may be provoked by elbow flexion, cubital tunnel compression testing, or Tinel's sign at the cubital tunnel (^1,2). Decreased two-point discrimination, monofilament detection, and vibration sense in the ulnar digits may be noted on sensory testing along with grip and pinch strength on motor testing (²). In severe cases, Duchenne's and/or Wartenberg's sign may be present secondary to paralysis of the lumbrical and interosseous muscles (¹).

A variety of diagnostic tests may aid in the evaluation. Electromyography (EMG) can display spontaneous action potential muscle fibrillations and decreased interference patterns in advanced compression neuropathy with muscular denervation. Motor nerve conduction studies may show focal slowing of nerve conduction velocity in the ulnar nerve segment crossing the elbow (²). However, in patients with clinical findings of cubital tunnel syndrome, EMG and nerve conduction studies may have a greater than 10% false-negative rate (¹). Additionally, electrodiagnostic testing is likely unnecessary to predict outcomes (⁷). Ultrasound has been implemented as a diagnostic tool with studies suggesting an increased ulnar nerve cross-sectional area in the cubital tunnel with distal flattening when compared with controls (^8,9). Ultrasound also has been shown to be at least equivalent to electrodiagnostic studies in the diagnosis of cubital tunnel syndrome (¹⁰). Advanced imaging with magnetic resonance imaging (MRI) or magnetic resonance arthrogram may be considered to evaluate for compression secondary to mass effect or an articular loose body, if clinically suspected.

Conservative nonsurgical management for mild to moderate cubital tunnel syndrome, defined as having only intermittent symptoms, consists of night splinting with 45 degrees of elbow flexion, nonsteroidal anti-inflammatory drugs (NSAIDs), occupational therapy, and activity modification (^1,2). According to one study, as high as 89.5% of patients with mild to moderate presentations benefit from conservative management (¹¹). However, in patients with constant symptoms or muscle atrophy, conservative management is less beneficial, and surgical interventions have generally been recommended (^1,2). A variety of surgical techniques have been studied with varying rates of success, relapse, and complications. The specifics of these techniques are beyond the scope of this case report and have been extensively reviewed within the orthopedic surgery literature.

In this case report, we illustrate a patient with ulnar nerve entrapment at the cubital tunnel with constant symptoms that was managed successfully with peripheral nerve hydrodissection. This case suggests that ultrasound-guided peripheral nerve hydrodissection may provide an effective treatment option that is significantly less invasive than surgical interventions.

Case Presentation

A 15-year-old otherwise healthy female competitive swimmer presented with a 2-month history of worsening pain on the medial aspect of the left elbow with numbness and tingling radiating distally down the forearm and into the hand in an ulnar nerve distribution that had progressed from episodic with swimming workouts to constant paresthesia. Her physical examination was notable for cubitus valgus deformity bilaterally and positive Tinel's sign at the left cubital tunnel. A thorough examination of the bilateral upper extremities and cervical spine was otherwise normal. Conservative management with relative rest, physical therapy, nocturnal splinting, and NSAIDs recommended by her primary care physician was unsuccessful in alleviating her symptoms.

Subsequent MRI of the left elbow displayed swelling of the ulnar nerve as it crossed behind the medial humeral epicondyle, as well as a flattened morphology of the ulnar nerve (Fig. 1A) as it exited the cubital tunnel and passed through the two heads of the flexor carpi ulnaris muscle. Upon presentation to the sports medicine clinic, the patient underwent ultrasound-guided hydrodissection of the ulnar nerve at the distal cubital tunnel using a 5% dextrose solution as detailed in the Methods/Procedure section.

Figure 1: T1 MRI of the left elbow obtained before hydrodissection demonstrating flattening of the ulnar nerve (A). T1 MRI of the left elbow obtained 2 months after hydrodissection, demonstrating restoration of normal architecture of the ulnar nerve (B).

The patient reported 90% resolution of her paresthesia, but persistence of medial elbow pain with no adverse effects at 72-h follow-up. At 1-month follow-up, the patient reported complete resolution of her paresthesia without relapse and had returned to full swimming competition. At 2-month follow-up, the patient continued to report resolution of her paresthesia, and a repeat MRI at that time displayed the return of normal nerve architecture (Fig. 1B). At 3-month follow-up, her neuropathy symptoms remained absent; however, her medial elbow pain persisted with examination notable for pain with resisted pronation and wrist flexion. Of note, she had not taken any breaks from her training after the competition, which had been advised. The patient then began to work with her swim coach to identify errors in her stroke form, which were putting excess stress on the flexor-pronator muscle complex. At 5-month follow-up, after undertaking activity modification and relative rest during her swim practices, her medial elbow pain was improved but not yet resolved.

Methods/Procedure

Before the procedure, the patient and her mother were thoroughly counseled on the potential risks, benefits, and alternatives to peripheral nerve hydrodissection. Conservative measures were again discussed, but there was a strong desire by the mother and patient to provide treatment that might allow the patient to compete in an upcoming regional tournament. They expressed a desire to delay changes in her training until after this competition. The patient provided verbal consent, and her mother provided verbal and written informed consent to proceed with the intervention. Due to her lack or response to conservative management and desire to avoid surgery, the patient, her mother, and the physician team accepted the known minimal risks of the procedure to include pain, bleeding, infection, damage to surrounding structures, and possible intraneural injection, as well as any unforeseen adverse events given the minimal data available on ulnar nerve hydrodissection at the cubital tunnel.

The patient was placed in the supine position on the examination table with the left elbow at 90 degrees of flexion with the shoulder externally rotated and abducted. The ulnar nerve was visualized with a 12-MHz high frequency linear transducer (General Electric LOGIQ e) from the Arcade of Struthers to several centimeters distal to its path deep to the flexor carpi ulnaris muscle. The morphology of the ulnar nerve on ultrasound was noted to be swollen as it exited the cubital tunnel (Fig. 2A) and then flattened distally (Fig. 2B), consistent with the MRI findings as above.

Figure 2: Cross-sectional short axis ultrasound view of the ulnar nerve at the cubital tunnel demonstrating nerve swelling (A). Cross-sectional short axis ultrasound of the ulnar nerve demonstrating nerve flattening distally (B).

The procedural area just proximal to the cubital tunnel was then prepped by cleaning the skin overlying the path of the nerve with a single-use chlorhexidine sponge followed by application of sterile ultrasound gel. The transducer was cleansed with appropriate bactericidal wipes.

The ulnar nerve was then visualized in the short axis just before entering the cubital tunnel, where the nerve is fairly superficial and easy to visualize. The overlying skin was anesthetized using lidocaine 1% with epinephrine. Using a two-provider technique, the first provider used ultrasound guidance to advance a 21-gauge ultrasound needle to a point just superficial and lateral to the ulnar nerve in the surrounding connective tissue (Fig. 3). The needle was attached to connector tubing, which was attached to a 60-mL syringe held by the second physician. The syringe was loaded with 5% dextrose in water (D5W) solution as the sole injectate for this procedure. As the needle entered the perineural connective tissue, the D5W was slowly injected to bluntly dissect the surrounding connective tissue from the ulnar nerve. Using fluid to maintain distance between the needle and the nerve, the needle was maneuvered superficially, deep, and essentially circumferentially around the nerve until a complete hypoechoic ring of fluid was visualized in both the short and long axes (Fig. 4). At this point, the nerve was visualized in long axis and further injectate was pushed through the syringe along the superficial aspect of the nerve, traveling along the length of the nerve and extending the area of hydrodissection through the cubital tunnel. A total of 40 mL of D5W was injected.

Figure 3: Positioning of patient in the supine position with the upper extremity externally rotated, abducted, and flexed at the elbow to best visualize the ulnar nerve under ultrasound at the cubital tunnel and advance a 21-gauge needle attached to a 60-mL syringe via connector tubing utilizing the two-provider technique.

Figure 4: Complete hypoechoic ring of fluid visualized under ultrasound after hydrodissection in both the short axis (A) and long axis (B).

The patient tolerated the procedure well with only minimal discomfort from the needle entering the skin and no immediate adverse effects. She returned home with her mother to return for clinic follow-up in 72 h.

Discussion

Nerve hydrodissection can be defined as the introduction of a solution under pressure between tissue planes to create separation and remove adhesions (¹²) with the goal of releasing a potential soft tissue adhesion or obstruction from an entrapped peripheral nerve (¹³). Hydrodissection has been suggested as a safe and proven procedural technique for the blunt dissection of tissue planes (¹²).

The use of hydrodissection in the treatment of peripheral nerve entrapment syndromes is a relatively new and emerging concept. However, the concept of hydrodissection itself has been used for many years in a variety of settings. Hydrodissection has been used in urologic oncology to preserve the neurovascular bundle during radical prostatectomy (¹⁴) and to prevent nerve damage during radiofrequency ablation of kidney tumors (¹⁵). It has been used to preserve perforating arteries during breast reconstruction (¹⁶), as well as to define surgical planes during ophthalmologic procedures (¹⁷).

The primary feared risk associated with peripheral nerve hydrodissection has been that of intraneural injection and resultant nerve damage. A study of 257 patients receiving peripheral nerve blocks before shoulder arthroscopy reported a 17% incidence of intraneural injection with zero patients experiencing postoperative neurologic complications (¹⁸). Another study evaluated 72 cases of apparent intraneural injection, none of which resulted in any permanent nerve injury (¹⁹). These findings suggest that the feared complication of intraneural injection does not pose a true significant risk of adverse outcomes.

The ability to successfully separate the ulnar nerve from the medial epicondyle and surrounding connective tissue under ultrasound guidance was demonstrated in one cadaver study (²⁰). While one small pilot study demonstrated decreased pain, ulnar nerve cross-sectional area, and improved electrodiagnostic measurements with ultrasound-guided corticosteroid injection (²¹), none are available investigating hydrodissection with only a dextrose solution without active components.

Case reports have been published reporting successful treatment of peripheral neuropathies using hydrodissection techniques, such as a case of meralgia paresthetica as described by Mulvaney in 2011 (²²), a case of foot drop as described by Tabor et al. in 2017 (²³), and several cases of carpal tunnel syndrome by Malone in 2010 (²⁴). However, these cases used local anesthetic or corticosteroid as part of the injectate solution. Improvement in radial nerve palsy signs and symptoms after ultrasound-guided perineural injection of D5W was noted in a single case report (²⁵). One recent study compared the use of corticosteroid injection vs. D5W perineural injections of the median nerve in carpal tunnel syndrome patients. This study showed increased benefit in the D5W group compared with the corticosteroid group at 4 to 6 months of follow-up (²⁶).

Conclusions

In this case, we present a patient with ulnar nerve entrapment with nerve architectural changes on MRI and ultrasound, which was refractory to conservative management. The technique of ultrasound-guided hydrodissection of the ulnar nerve at the cubital tunnel with a dextrose solution was used and resulted in resolution of the patient's neuropathy symptoms, as well as return of normal nerve architecture on follow-up MRI. Her medial epicondylitis symptoms persisted following the procedure, but improved with activity modification. Current available evidence, as outlined above, suggests that this technique is safe and carries minimal associated risk. While cases are present within the literature using similar techniques, none were found using hydrodissection with D5W only of the ulnar nerve at the cubital tunnel. While further investigation is warranted to evaluate the long-term effectiveness and applicability to a diverse patient population, this case suggests simple hydrodissection as a possible viable option for the management of peripheral nerve entrapment refractory to conservative management as an alternative to more invasive surgical techniques.