Simplifying the upper limb peripheral motor screen: Proposing the "K" sign.

The well-recognized erosion of pathoanatomic correlations in basic medical training, combined with the increasing everyday pressures of time-efficacy in patient examination, continue to place strain on junior clinicians. Over the years, many refinements to tried-and-true basic physical examination techniques have been described, allowing improvement in diagnostic yield. A multitude of "screening" techniques are available for physical assessment; however, such approaches are often nonstandardized and inconsistently taught and applied in the clinical realm. Great interexaminer inconsistency in the documentation of many forms of screening techniques also substantively undermines their respective clinical value. The current work presents a novel refinement/combination of previously described examination approaches for the assessment of peripheral upper limb (UL) motor function--the "K" sign. Having been successfully applied in both the acute and ambulatory clinical settings for several years, we feel that the technique has a useful role as a rapid and specific screening technique that is easily taught, learnt, and applied. Arguably, its employment serves to improve time efficacy in the screening examination, and may even improve diagnostic yield through its reliable reproducibility and provision of direct bilateral comparison. Its inherent simplicity also lends itself well to high levels of uptake (and retention) by medical students and junior clinicians alike. On top of presenting the simple screening test itself, we offer a simple means of subsequent notation for the patient's case note record, again in the hope of standardization and endurance of clinical value beyond the time of patient examination.

Introduction

Medical and clinical curricula continue to expand at a rapid rate.[1] The pressures on junior clinicians to learn, retain, and apply a growing body of knowledge and understanding have never been greater. With recognized graduate deficiencies in core anatomical knowledge,[23] the expectation of a clear extrapolation of pathologic findings by junior doctors to anatomic bases is becoming less accepted. Screening assessment approaches to aid rapid patient evaluation have merit whereby such approaches minimize the risk of gross oversight while providing a platform for “abnormality” identification, prompting deeper and targeted inquisition. A multitude of “screening” techniques are available for physical assessment; however, such approaches are often nonstandardized and inconsistently taught and applied in the clinical realm. Great interexaminer inconsistency in the documentation of many forms of screening techniques also potentially and substantively undermines their respective clinical value.[45]

Neuromuscular disorders effecting the upper limb (UL) are encountered with high frequency[6] in many domains from the general practitioner (GP) clinic to the busy emergency department (ED) to the refined specialist ambulatory outpatient clinic. The goal of this paper is to present a quick and reliable screening tool—a refinement and culmination of several previously-described techniques—which can be employed by clinical personnel at any level, with a high degree of reproducibility and specificity. The tool's simple nature negates the need to commit extensive series of complex clinical tests to memory.

The Test

Rather than progressing through a series of cumbersome individual screening tests to appraise the function of the three principle peripheral motor nerves of the UL (namely, the radial, median, and ulnar), we propose the employment of a simple “one-step” test, the “K” sign. The technique allows a rapid, simultaneous evaluation of the motor function of these nerves bilaterally.

The patient is assessed facing the examiner (i.e., seated opposite the examiner or perhaps from the end of the bed). He/she is asked to oppose the tips (not pulps) of his/her thumb and index finger on both hands [Figure 1] and then touch the two thumbs together at the interphalangeal joints [Figure 2]. The remaining three fingers (i.e., middle, ring, and little) on each hand are then extended and fully abducted [Figure 3]. Finally, the wrists are maximally extended (maintaining the previous hand/finger positioning, as seen in Figure 4).

Figure 1

Performing the “K” sign — step 1. Index to thumb tip-to-tip opposition. This should create a circle. Note: Not pad-to-pad opposition. This demonstrates the median nerve motor function contribution to the sign

Figure 2

Performing the “K” sign — step 2. Maintaining the positioning from step 1, the hands are brought together in the midline until thumb interphalangeal joint contact is achieved

Figure 3

Performing the “K” sign — step 3. The ulna-sided three fingers (middle, ring, and little) are maximally abducted. This demonstrates the ulnar nerve motor function contribution to the sign

Figure 4

Performing the “K” sign — step 4. Both wrists (and the ulna-sided three fingers) are maximally extended. This demonstrates the radial nerve motor function contribution to the sign

The three critical elements of the test include:

Tip opposition of the first and second digits (not pulp);

Full splaying of the medial three fingers in the interphalangeal and metacarpophalangeal joint extensions;

End-of-range extension of both wrists.

The examiner looks for apparent deficiencies of the three principal movements, and for asymmetry (directly comparing left versus right) — which, if detected — would deem the test “positive.”

Anatomic Basis

It is certainly not the aim of this short paper to provide an extensive and exhaustive account of the neuromuscular innervation of the human UL. Readers requiring such revision are directed to any number of widely available anatomic texts. However, in keeping with the three critical elements of the proposed test as described above, the following brief summary is offered:

Digital opposition in the hand (i.e., the tip of the index finger versus the tip of the thumb) is provided by the median nerve, and largely made possible by terminal branches of the anterior interosseous [flexor pollicis longus (FPL), flexor digitorum profundus (FDP)], recurrent motor (opponens pollicis and abductor pollicis brevis), and palmar digital nerves (lateral two lumbricals);

Wide abduction of the medial fingers is facilitated by the distal motor branches of the ulnar nerve in the hand (especially dorsal interossei and abductor digiti minimi);

End-of-range extension of the wrist and fingers is permitted by intact radial nerve function [especially, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ERCB), extensor carpi ulnaris (ECU), extensor digitorum communis (EDC), extensor digiti minimi (EDM)].

Discussion

The aim of our presentation of this test is to neither replace appropriately detailed clinical examination teaching and supervised skill honing nor to ameliorate the need for pathoanatomic understanding but rather to provide a simple and reproducible tool to increase the standardization of UL peripheral motor function screening. On replacing the need to otherwise perform three (or more) individually performed screening tests (as had been advocated by previous teachings), we expect to also provide some improvement in time efficacy in screening time. Indeed, we have borne witness to this in our own clinical experiences having taught the technique to medical students and junior colleagues alike over several years. Those with whom we have shared the test have uniformly agreed on its simplicity, and we are heartened to have seen its employment slowly permeating in the clinical setting. Despite whispers around the hospital to the contrary, the term “K” sign bears its name not from reference to the authors’ surnames (i.e., “Kurmis” sign) but rather from the similarly postured (albeit anatomically less precise!) “OK” sign from everyday common gesturing. Regardless, the coined term “K” sign has been widely accepted and is easily remembered.

The test itself is certainly not without its clear and apparent limitations. It will not “diagnose” the underlying pathology (when present) or localize the site of a lesion (or lesions) present. If performed haphazardly or poorly, it will inevitably yield unreliable results. We suggest that the test demonstrates a high crude specificity (i.e., a “normal” test is unlikely to fail to identify significant neuromuscular deficit) but poor sensitivity (i.e., a “positive” test is unlikely to reveal the nature of the underlying abnormality itself). The test may under-appreciate subtle/subclinical lesions; however, these shortcomings are certainly not worse than could otherwise be anticipated using conventional methods, and may indeed be arguably better than previously employed approaches simply through the inclusion of direct bilateral comparison. We feel that this direct comparison of both sides (i.e., the left hand immediately adjacent to the right) adds significant clinical value, using the patient as his/her own control, and that this represents a progression/improvement to the ipsilateral test proposed in 2006 by Rajkumar and Tay.[7] The side-by-side visual appreciation of any deficits present reduces the likelihood of failure of appreciation of more subtle anomalies [Figure 5a and b].

Figure 5

Illustration of isolated right-sided (a) median (b) radial nerve dysfunction. Note: Any apparent/gross asymmetry thereafter prompts a more formal bilateral motor-sensory peripheral nerve screen

It is critical to stress that the proposed test is intended to serve as an easily remembered, simply executed screening tool. A “negative” result (as would have been the case having more laboriously performed three individual “traditional” movement tests, per side, with normal findings) would crudely exclude major peripheral neuromuscular deficiencies. This can simply be documented as “K sign negative” in the patient's case note record. A “positive” screen would serve to provide the impetus for more detailed nerve- or lesion-specific assessment (or may appropriately prompt clinical review by a more senior/experienced colleague). Such a screening result could be recorded in the patient's case note record in a standardized fashion as “K sign positive.”

Clearly, a multitude of other (i.e., nonnerve-related) pathologies may masquerade as a “false positive” test — one has to consider advanced wrist osteoarthritis or 1st MCP joint fusions — that will present, as would be the case with a genuine nerve-related positive result, as an indication for more detailed patient examination/history collection. As a screening tool, the “K” sign's value lies in its high specificity, rather than sensitivity.

Conclusion

The current paper presents the synergistic combination of a series of previously described examination approaches for UL peripheral motor function into a single, simple, clinical screening tool — the “K” sign. We have been employing the test and sharing its use with clinical colleagues for several years now and believe that this simple, yet highly specific, test could be incorporated into mainstream musculoskeletal examination teaching in the hope that it may facilitate a standardized approach to quick UL neurologic screening, ultimately improving the standard of frontline patient care. The test can be easily learnt, easily performed (in seconds), and likely yields specificity comparable to (or arguably better than) previous multicomponent screening approaches. Standardized documentation (i.e., “K” sign “negative” or “positive”) will allow immediate retrospective appreciation of crude UL peripheral motor function from patient case note records. As with most screening tools, test positivity provides the impetus for a deeper and more directed investigation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.