The Strümpell sign is a co-movement of the toes when the knee joint is flexed against resistance. This movement is physiologic in children under one year of age. However, in adults, it is evaluated as a pyramidal tract sign and refers to damage to the central motor neurons.
What is the Strümpell sign?
The Strümpell sign is a co-movement of the toes during flexion of the knee joint against resistance. The Strümpell sign is an extension of the big toe toward the foot. Flexion in the knee joint triggers dorsiflexion of the toe against resistance. The extension of the big toe towards the dorsum of the foot is realized by the extensor hallucis longus muscle. Simultaneously with the dorsal extension of the great toe, toes II to V often extend.
The Strümpell sign is physiological in infants under one year of age. On adults, the movement is pathological and is evaluated as a pyramidal trajectory sign. Along with Babinski, Gordon, Oppenheim, and Chaddock reflexes, the Strümpell sign is often included in the Babinski group. Pyramidal tract signs indicate neurological damage to the pyramidal tracts that connect the first and second motor neurons in the spinal cord. As part of the pyramidal system, the pyramidal tracts are involved in all voluntary and reflex motor activity. The Strümpell sign is named after its first describer, Adolf von Strümpell. The German internist first documented the movement at the end of the 19th century. The toe movement is also called Strümpel reflex or Strümpel’s sign with reference to his name. In a narrower sense, the Strümpell sign is not a reflex, but a moving along.
Function and task
In infants under one year of age, the neurological circuitry of the individual muscle groups is not yet differentiated. Therefore, they still move many muscle groups together, which can later be moved individually. In the Strümpell sign, such a joint movement is present with dorsal extension of the big toe and simultaneous spreading of the remaining toes. Sometimes there is also supination of the foot. In the first years of life, the central motor neurons slowly take over their function as superior control and switching centers of the motor system. As a result, the individual muscles no longer move in groups with the nearest muscles, but can be stirred individually. Reflex movements also reduce after the first year of life, which is also related to the higher control by the central motor neurons. The Strümpell sign thus normally regresses after the first year of life and therefore cannot be triggered in adulthood. If it can be triggered, the control by the central motoneurons is probably weakened or abolished. In adults, the Strümpell sign therefore corresponds to an obligatory pathological co-movement of the toes during flexion of the knee joint. Vigorous pressure is applied to the knee and the patient attempts knee flexion at the knee joint. The dorsal movement of the great toe, although extension by name, is part of the flexion synergy, so that knee flexion against resistance can trigger dorsal extension of the toes. The realizing extensor hallucis longus muscle is an extensor muscle of the lower leg musculature, whose surfaces of origin correspond to the facies anterior and the membrana interossea cruris. The tendon of the muscle runs under the retinaculum musculorum extensorum superius toward the forefoot. At the transition to the dorsum of the foot, the tendon crosses to the medial side of the anterior tibial artery and attaches to the dorsal surface of the big toe. The muscle is innervated by the profundus fibular nerve and attaches to the L4 to S1 nerve tracts.
Diseases and complaints
The Strümpell sign is relevant to neurologic diagnosis. If co-movement of the toes can be triggered, there is probably motoneuronal damage in the central nervous system if symptoms are present. However, the Strümpell sign alone is far from being a reliable diagnostic tool for such damage, since it can sometimes be triggered in healthy adults as well. The mere dorsal movement of the big toe is usually not evaluated as a characteristic pyramidal tract sign and thus has little diagnostic relevance. Only if the remaining toes spread simultaneously to the dorsal movement and, if necessary, an additional supination occurs, there is talk of a pyramidal trajectory sign.To strengthen the suspicion of pyramidal or motoneuronal damage, further examinations are necessary. For example, after a positive Strümpell sign, the patient is tested for other reflexes of the Babinski group. For example, evidence of the Babinski reflex, the Chaddock sign, the Gordon sign, and the Oppenheim sign may be helpful. Only when multiple pyramidal tract signs are present is damage to the central motor neurons suggested. Such damage may be accompanied by spastic or flaccid paralysis and can be detected by MRI of the skull and spine when contrast is administered. MRI can also be used to identify which motoneuron is affected by a lesion. The cause of motoneuronal damage can be neurological diseases such as ALS or MS. In MS, the patient’s immune system attacks central nervous tissue. In ALS, on the other hand, there is a degeneration of the motor nervous system in which damage to the central motoneurons is particularly characteristic. Cerebral infarction (stroke) due to vascular occlusion of the middle cerebral artery can also damage the upper motoneuron. In addition to disease-related damage, the lower motoneuron may experience traumatic damage or be affected by spinal cord infarction.
