Median-Ulnar nerve anomalies: a potential for incorrect diagnosis and treatment of upper limb neuropathies
The importance of knowledge of anatomical variants, whether it be muscular, neural, osseous, or vascular, cannot be overlooked for manual practitioners. Considering our lack of easy access to various diagnostic tools such as special imaging and electrodiagnostic testing procedures, these anomalies can often lead to incorrect diagnosis, which is subsequently followed by ineffective treatments.
Below is a review of one such scenario where various communications can occur between the median and ulnar nerve in the forearm and hand. This phenomenon can lead to confusing symptomatology in very common conditions such as carpal tunnel syndrome, or and cubital tunnel syndrome. As the direct effect on nerve conduction is not fully understood, it leads me to believe that patients complaining of “abnormal” sensory or motor symptoms, as often
occurs following motor vehicle accidents for example, may be unjustly diagnosed as having non-organic symptoms.
Martin–Gruber anastomosis (MGA), or median-to-ulnar nerve communication in the forearm, is not uncommon. The mean incidence is 20%, but incidence has been reported to be as high as 54%. This communication may be bilateral in up to 73.6% of cases. Research has sited the importance of MGA in clinical scenario’s. The intrinsic muscles of the hand can be completely unaffected by median lesions. A lesion of the median nerve situated proximal to the departure of the communicating branch would affect the median thenar muscles, whereas a lesion below that level would not. In addition an ulnar nerve lesion at the elbow may produce an unusual pattern of intrinsic muscle paralysis. Although some research claims the cross over to be purly motor in nature, other studies lend to the possibility that sensory fibers may be involved as well. Thus abnormal symptoms of sensory radiation may be produced.
Although the MGA is well known to many, it is not the only form of interneural communication in the upper extremity. It can even coexist with other communications. Ulnar-to-median nerve communication for example is not well known and are much less common. In the forearm, it is called Marinacci syndrome. This condition was first described by Marinacci when he described a patient with a forearm traumatic lesion of the median nerve showed preservation of the thenar muscles innervation both clinically and electrodiagnostically. Ulnar- to-median nerve communications in the forearm are again mostly motor, however sensory symptoms have also been described in the literature.
Ulnar-to-median nerve communication can also occur at the level of the palm in at least 2 forms. Riches-
Cannieu communication is a deep, motor communication. It is recognized when a patient presents with a lesion of the median nerve in the forearm but still shows some median nerve function. This can be erroneously interpreted as partial lesion of the median. The Berrettini branch, or superficial ulnar-to-median nerve communication in the palm, is a pure sensory communication that is present in up to 81% of cases. Its injury during carpal tunnel release results in alteration of middle and ring finger sensibility.
pictures from Unver Dogan, Uysal, Seker. Neuroanatomy  8: 15–19
Although uncommon, neural communications in the upper extremity should always be kept in mind. A thorough clinical examination of the peripheral nerves must be conducted where neurological symptoms exists and if possible should be completed with electrodiagnostic studies. In the same fashion, findings from electrodiagnostic studies alone should not exclude the possibility of pathology if findings are unable to explain unusual symptoms. Unusual presentations or discrepancies between the history and the physical examination should be considered clues to such entities, and suspicions should be communicated to the electrophysiologist so that they can look specifically for a recognizable pattern of variations.
In terms of manual care, such anomoalies re-inforce the importance of more dynamic tissue assessments; rather than simple manual muscle and nerve testing. Simply following “treatment protocols” (or “nerve release” protocols) as utilized in some soft tissue seminars will not suffice; as treating real anatomy, including the anatomic variants, does not lend itself well to ‘cookie-cutter’ approaches. Specific palpation of stuctures, as well as areas of fascial restriction, as is emphasized in FUNCTIONAL ANATOMIC PALPATION SYSTEMS™ seminars (including the Tissue Tension Technique™) must guide treatment approaches. Such dynamic assessment technique guides practitioners utilizing the FUNCTIONAL RANGE RELEASE™ system of myofascial release and conditioning.