Comment on "The Diagnostic Utility of Midcarpal Anesthetic Injection in the Evaluation of Chronic Wrist Pain."

The authors have proposed midcarpal injection of lidocaine as a diagnostic test to determine the presence or absence of intracarpal pathology in patients with chronic wrist pain and normal routine wrist x-rays by evaluating grip strength and pain relief after injection. The reference standard (the essential lesion) was the presence of intracarpal pathology on arthroscopic evaluation of the wrist. A 6-kg (28%) improvement of grip strength had 73% sensitivity (the proportion of patients with the disorder in whom the test result was positive) and 70% specificity (the proportion of patients without the disorder in whom the test results were negative) in association with arthroscopic evidence of intracarpal pathology. Tests with high sensitivities are useful for ruling out disease. Tests with high specificities are useful for ruling in disease. Likelihood ratios might provide more effective interpretation of diagnostic clinical tests than sensitivity and specificity values. [2, 3] Pain relief in this report did not correlate with intracarpal pathology and was therefore not considered a diagnostic discriminator. The methods for performing the test were described in detail with the exception of the amount of lidocaine that was injected into the midcarpal joint. The investigators used an appropriate reference standard in all of their patients with chronic wrist pain to determine if they had the target condition of intracarpal pathology, but not in their control patients. The investigators pointed out that their study was limited by the small number of control patients and of cohort patients with normal arthroscopic findings. In addition, selection of the control patients (known target negative patients) from a population separate from the patient cohort with chronic wrist pain and without accessing the reference standard may lead to overestimates of the power of the test. [2, 3] A lack of blinding may also result in overestimates of the power of the test. [2, 3, 5, 6] Investigators evaluating the test results should be blinded from the results of the reference standard and investigators evaluating the reference standard should be blinded from the results of the test. The investigators acknowledge uncertainty regarding the penetration of lidocaine into the radiocarpal joint. This fact alone may render the test validity and threshold values uncertain. [5, 6] An additional simultaneous injection of the radiocarpal joint would add little difficulty to the procedure and would seem more dependable than a midcarpal block alone in anesthetizing the radiocarpal, ulnocarpal, and midcarpal joints. [7] A combined anterior and posterior interosseous nerve block might provide another alternative. [1, 4, 7, 8] The value of a diagnostic test depends upon its reliability, applicability, and benefit to the patient by a change in management. The investigators are attempting to establish a threshold value beneath which future patients could be spared arthrogram, magnetic resonance imaging, and/or arthroscopy owing to a high probability that intracarpal pathology would not be present. A cost benefit would also accrue. Every journey starts with a single step. This report is a step in the right direction. The investigators have established a worthy goal, but more work is needed to provide a universally reliable diagnostic test and threshold values. [2, 3, 5, 6] A prospective double-blinded randomized controlled trial (RCT) with control patients embedded within the chronic wrist pain cohort, an improved assemblage of patients, and a pre-study power analysis to determine the number of patients necessary for validity might be the next step. [2, 3, 5, 6] A multicenter study may be necessary to obtain sufficient enrollment. The results of this study are valuable and intriguing, but must be considered preliminary.