The OK and W Signs in Pre-/Intraoperative Testing of Lacertus and Cubital Tunnel Syndrome

INTRODUCTION

Median and ulnar nerve compressions remain the most commonly found nerve pathologies in the upper extremity.¹ Although numerous clinical tests are described, we wish to present two novel and simple hand examinations for proximal median and ulnar nerve compressions, the OK and W signs, that allow pre-, intra-, and postoperative testing of muscle strength.

Lacertus syndrome, or proximal median nerve compression at level of the lacertus fibrosus in the elbow/proximal forearm, has recently seen increased diagnosis, often facilitated by patient history and the utilization of Hagert clinical triad, consisting of (1) muscle testing, (2) scratch collapse test, and (3) pain at compression site.²

Compression of the median nerve at the level of the lacertus fibrosus leads to weakness in the flexor carpi radialis, flexor pollicis longus (FPL), and flexor digitorum profundus II (FDPII). Similarly, compression of the ulnar nerve at the cubital tunnel results in weakness in the flexor digitorum profundus V (FDPV).

Decompression of the median and the ulnar nerve done under wide-awake local anesthesia with no tourniquet (WALANT) carries the advantage of the patient staying awake, providing subjective feedback throughout the procedure. This minimally invasive procedure enables continuous monitoring of intraoperative return of muscle power and the possibility of further release if required. Successful release of the compressed median and ulnar nerves at their respective sites typically results in an immediate intraoperative return of strength to the affected muscles,^3,4 with 99.2% improvement in strength seen following lacertus release in 250 patients.² This immediate improvement in muscle strength serves as a valuable indicator of the effectiveness of the surgical intervention.

This article describes the OK and W signs as clinical tools to simplify the manual muscle strength testing of specific muscles innervated by the median and ulnar nerves, pre-, intra-, and postoperatively.

OK SIGN

The OK sign is a clinical tool used to assess and monitor the strength of the FPL and FDPII. Here is how the test is performed.

Preoperative Assessment

In the outpatient and/or preoperative setting, the patient is asked to make an “OK” sign by touching their thumb to their index finger, forming a circle. The examiner stabilizes the patient’s wrist with one hand, then, using the opposite hand’s index finger, attempts to pull through the patient’s grip while the patient resists at maximum capability. If the patient is unable to maintain the OK sign and the clinician can easily separate the fingers, it suggests weakness in the FPL and FDPII due to compression of the median nerve, at the level of the anterior interosseous nerve or proximal thereof, clinically often at the level of the lacertus fibrosus. The test is repeated on the contralateral side to compare strength. In the case of unilateral nerve compression, the weakness will be apparent to examiner and patient both. [See Video (online), which illustrates the use of the OK and W signs in preoperative and intraoperative settings, to assess and monitor strength.]

Video 1. illustrates the use of the OK and W signs in preoperative and intraoperative settings, to assess and monitor strength.

Download video file ^{(19.9MB, mp4)}

Intraoperative Assessment

After releasing the compressed median nerve through an in situ or ultrasound-guided release under WALANT, the OK sign is repeated intraoperatively. The patient is instructed to hold the OK sign as strongly as possible, and the clinician once again attempts to pry open the fingers. If the patient can maintain the OK sign with resistance, it indicates a return of strength in the FPL and FDPII immediately following the nerve release [See Video (online)].

W SIGN

The W sign focuses on testing the FDPV, innervated by the ulnar nerve. Here is how the test is performed.

Preoperative Assessment

In the outpatient and/or preoperative setting, the patient is asked to make a “W” sign by touching their thumb to their little finger, forming a W shape with the extended index, middle and ring fingers. The distal interphalangeal joint of the little finger (DIP V) must be flexed during the test to ensure active testing of the FDPV. The clinician attempts to pry open the patient’s thumb-to-little finger grip while the patient resists as strongly as possible. If the patient is unable to maintain the W sign and the clinician can easily separate the fingers, it may indicate weakness in the FDPV due to compression of the ulnar nerve, often at the cubital tunnel [See Video (online)]. As with the OK sign, the test should be done on both hands to compare strength.

Intraoperative Assessment

After releasing the compressed ulnar nerve at the cubital tunnel under WALANT, the W sign is repeated intraoperatively. The patient is instructed to hold the W sign as strongly as possible, and the clinician once again attempts to pry open the fingers. If the patient can maintain the W sign with resistance, it indicates a full return of strength in the FDPV muscle immediately following the nerve release procedure [See Video (online)].

By comparing the patient’s ability to maintain these two hand signs before and after surgical intervention, clinicians can assess the effectiveness of the treatment in relieving proximal median and ulnar nerve compressions and restoring muscle strength.

DISCUSSION

The OK and W signs are proposed clinical tools for assessing and monitoring muscle strength in lacertus and cubital tunnel syndromes, especially in the context of wide-awake surgical treatment. They provide a simple and reproducible way for both clinicians and patients to observe the immediate improvement of muscle strength following surgical intervention. Both signs can also be used in combination with the lacertus antagonist test,⁵ whereby a strip of kinesiotape is wrapped around the proximal forearm to reduce the pressure on the nerves, momentarily giving increased power when testing the OK and W signs.

The limitation in new clinical assessments is the lack of structured data regarding sensitivity, specificity, and reliability. As such, the OK and W signs should be used as adjuncts to other clinical tests and examinations for median and ulnar nerve compression.¹ These tests are not meant to be solitary maneuvers in the diagnosis of peripheral nerve compressions. However, the simplicity and practicality of these two simple hand signs make them accessible tools for clinicians in various settings, from outpatient screening to intraoperative evaluation.

In summary, the OK and W signs offer a practical, simple, pain-free, and noninvasive way to assess and monitor muscle strength in instances of lacertus and cubital tunnel syndromes.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.