Can Ultrasound Predict the Need for Carpal Tunnel Surgery?

While corticosteroid injections may be given to carpal tunnel syndrome patients to help prevent the need for surgical intervention, the risk factors for the conversion to surgical management for carpal tunnel are not well understood.

Could ultrasound be used to predict a patient’s progression to surgical management for carpal tunnel after receiving the injection?

In their 2022 study published in Plastic and Reconstructive Surgery, Wessel et al. examined patients with moderate carpal tunnel syndrome who were indicated to undergo a carpal tunnel steroid injection to determine whether sonographic measurements could be associated with progression to surgical management.

Their study identified that decreased cross-sectional area of the medial nerve over time was more likely to progress to operative intervention.

Carpal Tunnel Management: Determining Whether Surgery Is Needed

All 76 patients (96 wrists) included in the study underwent sonographic evaluation with measurement of the median nerve cross-sectional area by one of two musculoskeletal radiologists at the Division of Hand and Upper Extremity Surgery at the Hospital for Special Surgery in New York and then received a corticosteroid injection.

Wessel et al. followed up with patients for a minimum of one year after the injection and recorded their progression to surgical management for carpal tunnel. They hypothesized that change in the cross-sectional area of the median nerve along the carpal tunnel would be associated with conversion to surgical treatment.

They noted the following key takeaways:

• • 54% of the 96 wrists examined converted to surgical management for carpal tunnel at a minimum of one year follow-up.
  • The cross-sectional area of the median nerve decreased over the course of the carpal tunnel between the pisiform and the hamate bone in 81 of 96 wrists, and this reduction was significantly higher in patients whose conservative treatment had failed.
  • The average change in cross-sectional area was -5.01mm² in those who progressed to surgery compared to just -2.97 mm² in those who did not.
  • The study authors found that a 2 mm² decrease in cross-sectional area along the tunnel was associated with a 76% sensitivity for progression to surgical release.
    • This suggests that measuring the cross-sectional area of the median nerve using ultrasound could aid physicians in counseling their patients about the likelihood of success of an intervention before doing it.

While their patients had similar clinical symptoms, duration of symptoms, physical exam findings, Levine-Katz symptom severity and functional severity scores and six-item carpal tunnel syndrome symptom scale scores, ultrasound findings differed between groups and therefore can assist in preoperative counseling in ways that these other metrics cannot. Wessel et al. noted that neither nerve conduction study nor electromyographic findings were associated with progression to surgical management for carpal tunnel.

Important to note a possible limitation of the study that there could have been selection bias in the cohort, as all patients had moderate carpal tunnel syndrome disease severity based on clinical presentation assessed by a single hand surgeon.

Further research is needed to determine whether sonographic measurements could also be useful in predicting clinical response to surgical intervention as well as whether any posttreatment changes in the cross-sectional area could be indicative of clinical improvement.

How Else is Ultrasound Used in Carpal Tunnel Management?

In recent years, ultrasound has also garnered attention as an alternative way to diagnose carpal tunnel syndrome as opposed to the painful and costly electromyography (EMG) or nerve conduction studies procedures.

In their 2021 study, Charles et al. examined 132 patients who had been admitted to the University of Pittsburg Medical Center with numbness and tingling in their hands to determine whether diagnosing their carpal tunnel syndrome using ultrasound would decrease their time to surgery and the number of office visits needed.

Ultrasound was used to confirm carpal tunnel diagnosis in 34 patients and EMG and nerve conduction studies were used in 98 patients, yet the study authors found that the average time to surgery was much shorter in the ultrasound group—nearly three weeks difference. The ultrasound group also had a smaller number of office visits prior to surgery compared to the EMG group as well.

Charles et al. acknowledged that the patients within their study were assigned to a diagnostic method based on surgeon’s preference and therefore the outcomes may not be generalizable to all patients with carpal tunnel syndrome symptoms. Despite that limitation, their study highlights that ultrasound may have utility to confirm the diagnosis of carpal tunnel syndrome and could improve the efficiency of patient care.