por He flexor pollicis longus It is a muscle whose purpose is to cause the flexion of the thumb and indirectly contributes to the movement of the hand. It is even, flat and, as the name implies, long. Its name comes from the Latin muscle flexor pollicis longus.
The flexor pollicis longus muscle can be injured by trauma. The symptoms are mainly due to injury or compression of the interosseous nerve that innervates this muscle.
This type of injury causes muscle weakness or difficulty grasping objects with the fingers. Especially the ability to pinch the thumb and index finger together is affected. There is also pain in the forearm.
Another important factor that has been related to interosseous nerve compression is the finding of unusual muscular anatomical variants at the level of the nerve pathway. Such is the case of the presence of the accessory fascicle of the flexor pollicis longus muscle that affects a small group of individuals.
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Characteristics
It is a paired, long and flat muscle. It lies lateral to the flexor digitorum profundus muscle. It runs from the tuberosity of the radius, passes in front of the pronator quadratus muscle, until it reaches the thumb. The fibers of the flexor pollicis longus muscle are oriented obliquely.
Origin
The flexor pollicis longus muscle originates from the proximal third of the forearm, from the anterior aspect of the radius (tuberosity), and from the interosseous membrane.
Insertion
The flexor pollicis longus muscle inserts on the base of the distal or nail phalanx of the thumb, on its anterior or palmar face.
Function
The flexor pollicis longus muscle flexes the distal phalanx of the first finger (thumb). This folds on the proximal phalanx and the latter on the first metacarpal, that is, it moves the metacarpophalangeal joint, the proximal and distal interphalangeal joint.
It also has an indirect or accessory function in the movement of the wrist.
This muscle is very useful in our daily life, since it allows fine tweezers to hold small objects, such as holding a pencil, etc., as well as thick tweezers, that is, larger objects grasped with the thumb and index finger. , being an example of this grabbing a glass.
innervation
This muscle is innervated by the anterior interosseous nerve, whose function is purely motor. This nerve comes from the trunk of the median nerve.
Irrigation
The flexor pollicis longus muscle is supplied by the anterior interosseous artery.
Pathologies and related disorders
Anterior interosseous nerve compression
This pathology is characterized by the appearance of pain in the anterior face of the forearm, specifically at the level of the proximal third. The patient finds it difficult to grasp things using the fingers as tweezers, as well as there may be difficulty in pronation.
All of this is caused by compression of the interosseous nerve, affecting the mobility of the muscles it innervates, that is, the long flexor of the thumb, the deep flexor of the index and medial muscles, and the pronator quadratus.
If the median nerve is affected in compression, the patient complains of radiating pain to the wrist.
The source of compression may be due to forearm fractures, puncture wounds, or from long-range firearms.
Treatment in most cases is non-invasive, that is, the arm is immobilized for 8 to 12 weeks and non-steroidal anti-inflammatory drugs are placed.
Accessory fascicle of flexor pollicis longus
It should be noted that there is another cause that can compress the interosseous nerve, since some people may present an anatomical variant called the accessory fascicle of the flexor pollicis longus muscle.
The presence of anatomical variants can lead to the formation of additional fibrous arches that compress the anterior interosseous nerve. This muscular variant can present unilaterally or bilaterally.
Restrictive tenosynovitis of the flexor pollicis longus and flexor digitorum profundus (Lindburg syndrome)
It was first described in 1978 by Lindburg. This syndrome is characterized by the patient’s inability to flex the interphalangeal joint of the thumb in isolation, since doing so also flexes the distal interphalangeal joint of the index finger.
Another finding that confirms the diagnosis is the appearance of pain when the patient flexes the thumb and the examiner tries to resist the action.
This syndrome is caused by the abnormal presence of anatomical communications, which interconnect the flexor pollicis longus muscle and the flexor muscle of the index finger. This anomaly can present unilaterally or bilaterally.
This condition is usually associated with carpal tunnel syndrome. Treatment is almost always surgical.
Diagnosis
The flexor tendons together cause the hand to assume a characteristic position when it is completely at rest. This position resembles a waterfall, hence this position is called «normal waterfall of the fingers.»
In this position, the thumb and index finger show a little flexion. It increases as you move to the following fingers, that is, the middle finger will be a little more flexed than the index finger and the little finger more arched than the middle finger.
Knowledge of this physiological behavior is of the utmost importance for hand surgeons, since when they perform surgery on an injured finger, it must adopt this form after the procedure has been performed.
If a flexor tendon is injured, its function, which is to stress in order to bend the finger, is lost; therefore, the extensor tendon dominates, leaving the finger permanently extended. In this case, the damage to the flexor muscle is evident and no exploratory procedure is necessary.
If the lesion is partial and at the level of the deep flexors, the following exploration maneuver is described:
The proximal interphalangeal joint of the injured finger must be immobilized to later instruct the patient to try to flex the finger (distal phalanx). If you can do this, it means that the deep flexors are working well.
Rehabilitation
In order to achieve complete rehabilitation of the injured flexor muscle, a correct surgical technique must be followed, plus an adequate number of therapeutic sessions with a professional trained in hand injuries.
References
De Santolo A. The hand numbed by nerve compressions. Gac Med Caracas 2005; 113(4):485-499. Available at: scielo.org
Pacheco-López R. Acute repair of flexor tendons. plastic iberolatinoam. 2017; 43 (Suppl 1): s27-s36. Available at: sky.
“Flexor pollicis longus muscle.” Wikipedia, The Free Encyclopedia. Oct 2, 2019 13:55 UTC. Oct 11, 2019 04:32
Riveros A, Olave E, Sousa-Rodrigues C. Anatomical Study of the Accessory Fascicle of the Flexor Pulgrim Longus Muscle and its Relationship with the Anterior Interosseous Nerve in Brazilian Individuals. Int. J. Morphol.2015; 33(1):31-35. Available in: sky
Ramírez C, Ramírez C, Ramírez M, Ramírez N. Hand trauma: diagnosis and initial management. Magazine of the Industrial University of Santander. Health, 2008; 40(1) 37-44. Available at: redalyc.org
Delgado M, Moreno J, Vilar J, Recio R, Criado C, Toledano R, Collantes F. Restrictive tenosynovitis of the long flexor pollicis and deep flexor index (Lindburg syndrome). About a case. Magazine of the Andalusian Society of Traumatology and Orthopedics, 1999; 19(1):91-94. Available from: Elsevier.