Continuing Education Activity

Carpal tunnel injections are performed because of the extremely high prevalence of carpal tunnel syndrome in the general population. Carpal tunnel syndrome is the most common peripheral nerve entrapment syndrome, and therapies, both conservative and more invasive, are routinely performed. This activity reviews common injection techniques for carpal tunnel syndrome, evaluates the risk factors for the development of the condition, and describes the common presentation of symptomatology. It also reviews the role of the interprofessional team in this procedure.

Objectives:

• Describe the technique of carpal tunnel injections.
• Review of the pain distribution seen in carpal tunnel based on the anatomy of the median nerve.
• Outline the major risk factors for the development of carpal tunnel syndrome.
• Summarize the appropriate treatment strategy for patients with symptoms of carpal tunnel syndrome.

Introduction

Carpal tunnel syndrome (CTS) is a common ailment affecting the general patient population. It is the most common cause of peripheral nerve compression, with an incidence of 99 in 100,000 people. CTS is most commonly seen in patients over 40 years of age and has a greater prevalence in females. Females comprise approximately 65% to 75% of all reported cases [1]. CTS results from compression of the median nerve within the carpal tunnel in the wrist.[2] Typically the pressure within the carpal tunnel in these patients can be 32 to 110 mm Hg compared to 2 to 31 mm Hg in normal patients.[3] The compression of the median nerve causes the classic pain distribution and/or parathesiass seen in CTS on the palmar aspect of the hand. The classic distribution invloves the area innervated by the median nerve to include the volar aspect of the thumb, index finger, long finger, and the radial volar half of the ring finger.  Risk factors for the development of CTS include obesity, pregnancy (especially later in pregnancy), age, trauma to the wrist, and inflammatory rheumatic disorders.[4] Controversy exists whether or not overuse is a contributing factor (such as daily typing). Conservative treatment options include keeping the wrist immobile using wrist splints, physiotherapy, and pain medications, both topically and systemically.[5] More invasive options include local steroid injections to the carpal tunnel and surgical decompression of the space. This article will focus on injection techniques for CTS.

The exact etiology of CTS is not completely known, but the condition is largely assumed to be idiopathic or multifactorial. Some of the suspected risk factors for CTS include diabetes mellitus type 1 or 2, hypothyroidism, menopause, obesity, arthritis, and age.[6] Diabetes seems to have the greatest association with CTS with a prevalence rate of 30% in patients with diabetic neuropathy and 14% in patients without neuropathic symptoms.[7] Hormonal changes may be a contributing factor since pregnancy, menopause, and hypothyroidism are associated with CTS. Mechanical risk factors, including inflammation, thickening, arthritic deformity, and bony irregularities, contribute to median nerve compression.

Anatomy and Physiology

The carpal tunnel is located in the volar aspect of the wrist between the carpal bones and flexor retinaculum.[8] The boundaries of the carpal tunnel include the floor of carpal bones and the roof formed by the flexor retinaculum. The carpal tunnel contains the median nerve as well as 9 tendons (flexor pollicis longus, 4 flexor digitorum superficialis, and 4 flexor digitorum profundus). Increased pressure within the tunnel causes pain in the distribution of the median nerve within the hand. The median nerve is formed by a confluence of the medial and lateral cords of the brachial plexus. The nerve supplies motor innervation to the thenar muscles and sensory innervation to the radial 3.5 fingers. The median nerve supplies sensation to the radial half of the fourth finger. The ulnar nerve supplies sensation to the ulnar (or medial) half of the fourth finger.

Indications

Most patients are indicated for a carpal tunnel injection after failure of conservative therapies, including wrist immobilization, physical therapy, and oral analgesic medications. Carpal tunnel injections may also be considered preoperatively to confirm the diagnosis of carpal tunnel syndrome when EMG/NCV results are equivacal.

Contraindications

Some of the contraindications to carpal tunnel injections include patient refusal, infection over the injection site, and edema at the injection site. Patients on anticoagulation may undergo carpal tunnel injections, but with careful evaluation for bleeding. 

Technique or Treatment

Many patients turn to injections for their CTS when conservative therapies fail. Corticosteroid solutions are the predominant injectate used. Controversy exists over the safest injection site. A comparative study of several locations found that injecting within the flexor carpi radialis tendon proximal to the carpal tunnel might be the safest.[9] The in-plane ulnar approach has been shown to be superior to the proximal approach for improving symptom severity.[10]

The patient may be seated or supine during the injection. The affected wrist is supinated in slight dorsiflexion using a rolled-up towel and taping the fingers down. An ultrasound linear array probe can be used to scan the wrist for any anatomical variants such as volar ganglion cysts, flexor tendon tenosynovitis, and tumors.[11] The probe is then placed transversely at the proximal wrist crease by the entrance to the carpal tunnel. The goal is to have the pisiform, ulnar nerve, and ulnar artery in view as well as the median nerve. Doppler imaging can aid in determining vascular structures. The median nerve is identified and most often edematous. The injectate is targeted around the nerve in a target sign. The subsynovial tissue may also be injected, which has recently been implicated as the etiology of idiopathic CTS.[12]

Using sterile technique, the needle is introduced most commonly on the ulnar aspect of the carpal tunnel. The initial trajectory is shallow and superficial to the ulnar artery and nerve penetrating the flexor retinaculum.[13] The anterior aspect of the medial side of the nerve is injected first. The nerve should separate from the flexor retinaculum located anteriorly. This hydrodissection should reduce any adhesions, which may have caused entrapment. The needle is then redirected deeper on the ulnar side to inject the posterior aspect. The nerve should be completely surrounded by the injectate and “floating” in the solution.

Studies have shown that 75% of corticosteroid injections were accurately placed solely using landmarks, while 8.7% penetrated and damaged the median nerve.[14] Ultrasound guidance has been proven to reduce adverse events significantly. Meta-analysis also showed significant improvement in CTS severity using ultrasound guidance in 12 weeks compared to landmark-guided injections.[15]

Platelet-rich plasma (PRP) injections have recently risen as a new modality for long-lasting pain relief. PRP contains concentrated platelets and growth factors that have been shown to alleviate CTS symptomatology. PRP promotes axonal regeneration, thereby restoring the function of the median nerve. A systemic review of five studies, including three randomized controlled trials, one case-control, and one case report showed the efficacy of PRP for patients with mild CTS [16]. More extensive studies need to be performed to show the benefit of PRP injections for CTS.

Complications

• Bleeding

• Elevated blood glucose levels

• Infection

• Median nerve injury 

• Pain

• Paresthesias

Clinical Significance

The symptomatology of patients with CTS often develops insidiously over the course of months, years, or even decades. One of the most common symptoms is a “pins and needles” sensation in the first three fingers (thumb, index, and middle fingers) and nocturnal pain in the hand.[17] As the condition progresses, patients often experience intermittent pain and numbness in the affected area during daytime activities like driving, lifting, or using the computer.[17] Over time, patients complain primarily of constant pain and even swelling or the affected hand and thenar atrophy. On physical exam, practitioners may be able to see thenar wasting indicating extensive CTS.

Tinel’s and Phalen’s tests are in office maneuvers doctors may ask patients to perform to apply stress to the median nerve at the wrist.[17] A positive Tinel’s sign is elicited when percussing the carpal tunnel evokes the patient’s symptomatology. Phalen’s sign (or prayer sign) can be seen with forced wrist flexion or hyperextension for one minute. The diagnosis is most often made clinically, but many agree that nerve conduction studies are the gold standard for diagnosing.[18] The one drawback of nerve conduction testing is putting the patient through undue pain and stress.

Enhancing Healthcare Team Outcomes

Carpal tunnel syndrome poses a unique challenge to doctors in many specialties. As the most common peripheral nerve entrapment syndrome, it is extremely prevalent throughout the population. Wrist and hand pain, in general, can have a myriad of etiologies, including DeQuervain tenosynovitis, trigger finger, gout, carpal tunnel syndrome. Wrist and hand pain can even be referred from the neck in cervical radiculopathy or even from a cardiac condition like myocardial infarction. 

Usually, a primary care practitioner is the first person a patient sees with carpal tunnel syndrome. This provider may start conservative therapies, but for more advanced treatment options, proper coordination with a pain management doctor, rheumatologist, or orthopedist is needed. Radiologists play a vital role as well to rule out potential fractures or dislocations at the wrist after trauma. In the office setting, many pain physicians will need a team of nurse practitioners to help during the procedure to maintain sterility and help with ultrasound guidance throughout the injection. 

Proper coordination of care through different medical professionals gives patients with carpal tunnel syndrome the best chance at resolving their symptomatology.