Wartenberg's Sign refers to the slightly greater abduction of the fifth digit, due to paralysis of the abducting palmar interosseous muscle and unopposed action of the radial innervated extensor muscles (digiti minimi, digitorum communis ).This should not be confused with Wartenberg's Syndrome which is described as the entrapment of the superficial branch of the radial nerve  with only sensory manifestations and no motor deficits. Wartenberg's Syndrome
The first literature regarding this sign appears to be the Letter to the Editor By Robert Wartenberg himself at 1939. In this ,he emphasize the diagnostic importance of this sign in ulnar nerve neuropathy which is not documented. The author further describes "this sign consists of position of abduction assumed by the little finger. Sometimes the fourth finger too has a tendency to assume a position of abduction, but usually it is only the little that is found in abnormal position. It was found to be most conspicuous when the patient was asked to extend his finger at the proximal joints. The importance of this sign has become increasingly evident from numerous experiences which indicate that this tendency of the little finger to be abducted may constitute an early (in some cases the first) and also a late sign of ulnar palsy".
"From the physiological standpoint , this sign is easily understandable. Adduction of the little finger is performed by the interosseous and abduction by the hypothenar muscles. Both groups of the muscles are innervated by the ulnar nerve. However, in abduction of the little finger, the extensor digiti minimi and the branch to the little finger of extensor digitorum communis also play a definite part.These both are innervated by radial nerve. If the muscles innervated by the ulnar nerve are weak, those innervated by the intact radial nerve predominate in strength and abduct the little finger. Thus it is understandable why this abduction of the little finger is best seen when extensor digitorum communis comes into action and extends the fingers and the hand. In cases with the combined palsy of ulnar nerve and radial nerve ,this sign would not be present" explains the author.
Wartenburg’s sign is a test used for assessing integrity of the motor innervations of hand intrinsics in cases of suspected ulnar neuropathy. The inability to perform adducted digital extension is due to weakness in ulnar innervated intrinsic muscles, and the unopposed action of the slightly medially attached extensor digiti minimi results in extension and abduction of the 5th digit. A positive test indicates ulnar nerve neuropathy but does not determine site of compression (Guyon’s canal, cubital tunnel, arcade of Struthers).
It is seen that the author (Robert Wartenberg) had not prescribed a specific technique to assess the sign. The literature describes few techniques of assessment based on the explanation given by the author.
- A study by Goldman et al (2009)  adopted the technique to assess Wartenberg's Sign - The patient is placed with wrist in neutral position and forearm fully pronated and instructed to perform full extension of all the fingers. Once digits are extended patient is asked to fully abduct all fingers and then adduct all fingers. A positive sign is indicated with the observation of abduction of the 5th digit, with inability to adduct the 5th finger when extended.
- David J Magee  propose another technique with minor variation - The patient sits with his or her hand resting on the table. The examiner passively spreads the finger apart and asks the patient to bring them together again. Inability to squeeze the little finger to the remainder of the hand indicates positive test for ulnar neuropathy.
Really Ulnar Neuropathy ????
The mere presence of this sign doesn’t warrants ulnar neuropathy as the various studies reported abducted posture of little finger in patients without ulnar nerve involvement or even without neurological involvement. A study by Kilgus et al (2003)  analysed the aetiology of the Wartenberg sign. In this study five cases suffering from bothersome permanent abduction of the small finger and referred under the diagnosis of ulnar nerve paresis are presented. The authors commented that the Clinical, electrodiagnostic and imaging evaluation of three neurogenic cases disclosed a lesion of the ramus profundus distal to the branches innervating hypothenar muscles in one case, ulnar nerve injury with neuromuscular hyperactivity of the abductor digiti minimi muscle following split repair in another case and syringomyelia in the third case. Two patients revealed an abduction posture of the little finger of nonneurogenic origin. One of them showed closed ligament injuries.
The other patient revealed necrosis, scarring and contracture of hypothenar muscles and atrophy of the third palmar interosseous muscle following compression in a tight cast.
As there is no general consensus regarding the aetiology of the Wartenberg's sign, managment cannot be attempted for the sign alone. Hene it would be optimal to analyse the reason for the abducted posture of the little finger and can be managed accordingly. There are few surgical procedures documented for the correction of abduction deformity of the little finger.
A cadaveric study investigated the impact of the radialization of the extensor digiti minimi (EDM) at the level of the fifth metacarpophalangeal (MCP) joint and reroutes it from the fifth to fourth extensor compartment. The tudy was done in 16 freshly frozen cadaver hands sectioned at mid forearm.The authors concluded that the The key to correct abduction deformity of the little finger is radialization of the EDM, which can be done through a solitary incision at the level of the MCP joint. Rerouting alone does not correct the abduction deformity, and in combination with radialization it does not predictably enhance the correction.
The Physiotherapy management may include
- Electrical stimulation
- Exercise program
Recent Related Research (from Pubmed)
- A.J. Larner; A Dictionary of Neurological Signs; Springer Science & Business Media, 12-Nov-2010; page 369
- Tosun N, Tuncay I, Akpinar F. Entrapment of the sensory branch of the radial nerve (Wartenberg's syndrome): an unusual cause ;Tohoku J Exp Med. 2001 Mar;193(3):251-4.
- Robert Wartenberg, M.D ;A SIGN OF ULNAR PALSY ;JAMA. 1939;112(17):1688. doi:10.1001/jama.1939.62800170002011a.
- Dutton, M. (2008). Orthopaedic: Examination, evaluation, and intervention (2nd ed.). New York: The McGraw-Hill Companies, Inc.
- Goldman SB, Brininger TL, Schrader JW, Curtis R, Koceja DM. Analysis of clinical motor testing for adult patients with diagnosed ulnar neuropathy at the elbow. Arch Phys Med Rehabil 2009;90:1846-52
- David J. Magee:Orthopedic Physical Assessment: chapter 6-elbow ;sixth edition;Elsevier Health Sciences, 2008
- Kilgus M , Burg D, Loss M, Weishaupt D, Meyer VE.: Wartenberg's Sign of Ulnar Nerve Lesion. A Contribution to Pathophysiology and to the Differential Diagnosis; Handchir Mikrochir Plast Chir. 2003 Jul;35(4):2518.
- Jan van Aaken, Jin Zhu, Jean H. D. Fasel, Jean-Yves Beaulieu ; Investigation of radialization and rerouting of the extensor digiti minimi (EDM) in the abduction deformity of the little finger: a cadaver study ; HAND June 2011, Volume 6, Issue 2, pp 202-205