Complete extensor digitorum profundus complex: a deep hand extensor muscle to the medial four digits

An accessory head of the extensor indicis: a rare case report

PURPOSE

A deep knowledge of the variations of the posterior forearm musculature is crucial for assessing and diagnosing conditions in this region. Extensor indicis (EI) is one of the muscles in this region, which exhibits diverse anatomical variations. This report documents an extremely unusual form of the EI with an accessory head on the dorsum of the hand.

METHODS

During routine dissection, an extremely rare presentation of the EI was found in the left forearm of a 94-year-old female cadaver.

RESULTS

This unusual EI consisted of two muscle bellies. The traditional belly originated from the distal two-thirds of the ulna. The muscle became tendinous around the carpal area, distal to the extensor retinaculum. The tendon was subsequently joined by an accessory muscle belly originating from the distal radioulnar ligament. The EI tendon inserted onto the dorsal expansion of the index finger, ulnar to that of the extensor digitorum. The posterior interosseous nerve innervated the muscle.

CONCLUSION

Herein, we report an extremely rare form of the EI. To our knowledge, EI with an accessory head has only been reported rarely over the past 200 years. Moreover, our report appears to be the first case with photographic details of this anatomical variation. Clinicians should be aware of this variation for proper diagnosis and treatment.

Accessory extensor pollicis longus from the extensor digitorum: a rare case report and review of the literature

PURPOSE

Variations of the extensor pollicis longus are rare. When present, these include a separate extensor pollicis longus muscle, tendon or an intertendinous connection with nearby tendons within the deep extensor compartment of the forearm. Here, we report an extremely rare variation of an accessory extensor pollicis longus originating from the extensor digitorum.

METHODS

An unusual muscle was found during the routine dissection forearm of a 71 year-old at death male cadaver.

RESULTS

This variant muscle originated from part of the extensor digitorum muscle belly that supplies the index finger. It became tendinous and entered the third extensor compartment of the wrist before joining the ulnar side of the extensor pollicis longus tendon. Traction on the muscle belly resulted in simultaneous extension of both the thumb and the index finger.

CONCLUSION

This study documents an extremely rare extensor tendon to the thumb originating from the extensor digitorum, with a unique attachment to the normal extensor pollicis tendon. There have been minimal accounts of this variation, and the present report adds to the limited literature. Furthermore, the report suggests a new subtype, 1f, be included in the existing classification system. Surgeons should be aware of this rare variant for proper evaluation, diagnosis and surgical treatment. Further anatomical studies are needed to study the prevalence of this variant.

A reverse form of Linburg-Comstock variation with comments on its etiology and demonstration of interactive 3D portable document format

Purpose

Two most common variations of flexor pollicis longus include its accessory head and its connection with the flexor digitorum profundus of the index (Linburg–Comstock variation). In addition, while three-dimensional (3D) screening has widely been used in anatomical education, its use as reporting tool in anatomical research is still limited. The objective of this study is to report a previously unrecognized form of the accessory head of flexor pollicis longus, discuss the potential etiology of Linburg–Comstock variation, and pilot the 3D scanning of a large-scale anatomical structure.

Methods

An unusual tendon slip was discovered during a routine dissection in the anterior compartment of the right forearm of a 54-year-old male cadaver. A 3D scanner was used to capture the surface topography of the specimen and an interactive portable document format (PDF) was created.

Results

An anomalous tendon was found originating from the lateral aspect of the flexor digitorum profundus muscle. This variant tendon then inserted onto the medial surface of the flexor pollicis longus tendon before entering the carpal tunnel. The variation resembles a reverse form of Linburg–Comstock variation, because pulling this variant tendon resulted in simultaneous flexion of the interphalangeal joint of thumb.

Conclusion

Surgeons should be aware of the reverse Linburg–Comstock variation, because it may not be detectable by the conventional provocative testing. Linburg–Comstock variation may be classified as an anatomical variant or a secondarily acquired condition depending on its type. Our demonstration of interactive 3D-PDF file highlights its potential use for delivering anatomical information in future cadaveric studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00276-021-02858-8.

Bilateral anatomical variations in the extensor compartment of forearm and hand

An unusual variation of the extensor muscles was found during the routine dissection of the posterior compartment of the forearm. The left forearm presented an extensor medii proprius muscle, the tendon of which had an unusual trajectory. It passed through the second extensor compartment between the tendons of the extensor carpi radialis longus and extensor carpi radialis brevis muscles. The right forearm presented two muscles for the index finger: one, the extensor indicis et medius communis, the tendon of which was split into three tendons, one radial and one ulnar for the index finger and a rudimentary tendon for the middle finger; the second muscle for the index finger had an unusual origin, common with the extensor carpi radialis brevis, and its tendon ran superficially to the tendon of the extensor indicis et medius communis muscle. Knowledge goes tendon variations can be significant not only for clinicians to misdiagnose a debilitating wrist extensor pain syndrome but also for surgeons to avoid iatrogenic injuries in hand surgery.