Extensor tendons and variations of the medial four digits of hand: a cadaveric study

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.

Cosimulation of the index finger extensor apparatus with finite element and musculoskeletal models

Musculoskeletal modeling has been effective for simulating dexterity and exploring the consequences of disability. While previous approaches have examined motor function using multibody dynamics, existing musculoskeletal models of the hand and fingers have difficulty simulating soft tissue such as the extensor mechanism of the fingers, which remains underexplored. To investigate the extensor mechanism and its impact on finger motor function, we developed a finite element model of the index finger extensor mechanism and a cosimulation method that combines the finite element model with a multibody dynamic model. The finite element model and cosimulation were validated through comparison with experimentally derived tissue strains and fingertip endpoint forces respectively. Tissue strains predicted by the finite element model were consistent with the experimentally observed strains of the 9 postures tested in cadaver specimens. Fingertip endpoint forces predicted using the cosimulation were well aligned in both force (difference within 0.60 N) and direction (difference within 30°with experimental results. Sensitivity of the extensor mechanism to changes in modulus and adhesion configuration were evaluated for ± 50% of experimental moduli, presence of the radial and ulnar adhesions, and joint capsule. Simulated strains and endpoint forces were found to be minimally sensitive to alterations in moduli and adhesions. These results are promising and demonstrate the ability of the cosimulation to predict global behavior of the extensor mechanism, while enabling measurement of stresses and strains within the structure itself. This model could be used in the future to predict the outcomes for different surgical repairs of the extensor mechanism.

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.

Surgical Management of Extensor Digitorum Brevis Manus Anomaly with a Dorsal Ganglion Cyst

Background  The most common soft tissue tumor of the hand is the dorsal ganglion cyst and often is an indication for surgical excision. The differential diagnoses for dorsal hand masses include but are not limited to tenosynovitis, epidermoid cyst, abscess, lipoma, xanthoma, rheumatoid nodule, tophus, carpal boss, myositis ossificans, foreign body granuloma, neoplasm, and anomalous muscles. Case Description  Our case report reflects the latter, a 33-year-old female who presented with a 3-year history of a symptomatic dorsal ganglion cyst of her left wrist. She is a female in her 30s, with progressive, worsening pain on wrist extension. Intraoperatively, it was determined that an anomalous extensor digitorum brevis manus (EDBM) was present and may have contributed to her pain and was excised. Literature Review  The literature is sparse with the surgical management of EDBM. This case study aims to explore algorithms for managing simultaneous EDBM with a dorsal wrist ganglion, which is clinically relevant for any hand surgeon, when faced with a similar intra-operative management situation.

Finger abduction as a novel function of the extensor digitorum brevis manus muscle

A 25-year-old female presented with a chronic scapho-lunate ligament injury with development of carpal instability requiring reconstruction. During a standard dorsal longitudinal mid-line approach to the carpus, an extensor digitorum brevis manus (EDBM) muscle was found taking its origin from the dorsal wrist capsule overlying the lunate with innervation from the posterior interosseous nerve (PIN). Electrical stimulation of the muscle belly demonstrated abduction of the middle finger. The EDBM is a rare anatomical variant of the extensor compartment of the wrist and may be encountered during surgical approaches. Where possible these variant muscles should be carefully dissected off underlying structures, preserved and repaired at the conclusion of a procedure to ensure no perceived functional deficit to the patient. We present a case of a previously undescribed EDBM muscle function of pure finger abduction with no extension and a surgical technique of preserving its origin. We propose that the middle finger variant of the EDBM should be re-named the extensor digitorum brevis medius to reflect our findings.

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.

The forearm and hand musculature of semi-terrestrial rhesus macaques (Macaca mulatta) and arboreal gibbons (Fam. Hylobatidae). Part I. Description and comparison of the muscle configuration

Primates live in very diverse environments and, as a consequence, show an equally diverse locomotor behaviour. During locomotion, the primate hand interacts with the superstrate and/or substrate and will therefore probably show adaptive signals linked with this locomotor behaviour. Whereas the morphology of the forearm and hand bones have been studied extensively, the functional adaptations in the hand musculature have been documented only scarcely. To evaluate whether there are potential adaptations in forelimb musculature to locomotor behaviour, we investigated the forearm and hand musculature of the highly arboreal gibbons (including Hylobates lar, Hylobates pileatus, Nomascus leucogenys, Nomascus concolor, Symphalangus syndactylus) and compared this with the musculature of the semi-terrestrial rhesus macaques (Macaca mulatta) by performing complete and detailed dissections on a sample of 15 unembalmed specimens. We found that the overall configuration of the upper arm and hand musculature is highly comparable between arboreal gibbons and semi-terrestrial macaques, and follows the general primate condition. Most of the identified differences in muscle configuration are located in the forearm. In macaques, a prominent m. epitrochleoanconeus is present, which potentially helps to extend the forearm and/or stabilize the elbow joint during quadrupedal walking. The m. flexor carpi radialis shows a more radial insertion in gibbons, which might be advantageous during brachiation, as it can aid radial deviation. The fingers of macaques are controlled in pairs by the m. extensor digiti secondi et tertii proprius and the m. extensor digiti quarti et quinti proprius-a similar organization can also be found in their flexors-which might aid in efficient positioning of the hand and fingers on uneven substrates during quadrupedal walking. In contrast, extension of the little finger in gibbons is controlled by a separate m. extensor digiti minimi, whereas digits 2 to 4 are extended by the m. extensor digitorum brevis, suggesting that simultaneous extension of digits 2-4 in gibbons might be important when reaching or grasping an overhead support during brachiation. In conclusion, the overall configuration of the forelimb and hand musculature is very similar in gibbons and macaques, with some peculiarities which can be linked to differences in forelimb function and which might be related to the specific locomotor behaviour of each group.

Prevalence of the extensor digitorum, extensor digiti minimi and extensor indicis tendons and their variations

We aimed to investigate tendon variations of the extensor digitorum (ED), extensor digiti minimi (EDM), and extensor indicis proprius (EIP) muscles. Our study was performed on 43 fetal cadavers (86 extremities), aged between 17 and 40 weeks of gestation. The number of ED tendons varied from three to six, proximal to the extensor retinaculum (ER), and from three to eight, distal to the ER. The ED most often had four tendons, both proximally and distally from the ER. The ED tendons of the fourth finger were observed to be most frequently duplicated. The most common juncturae tendinum (JT) was type 1 in the second intermetacarpal space (IMCS), type 2 in the third IMCS, and type 3r in the fourth IMCS according to von Schroeder classification. The number of EIP and EDM tendons varied from one to two and from one to five, respectively. The EIP double tendons inserted both into the ulnar and palmar sides of the extensor digitorum of the second finger, which had not been reported in the literature. In our study, 7% of hands had variant muscles. In 4.7% of hands, the extensor indicis et medii communis was observed, while the extensor medii proprius and the extensor digitorum brevis manus were observed in 1.2% and 1.2% of hands, respectively. Knowing the prevalence of the ED, EDM and EIP tendons and their variations in the fetal period should help to treat partial loss of hand function or injury after birth and to correct congenital hand deformities.

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

PURPOSE

Anatomical variants in the posterior compartment of forearm and hand are not uncommon. Physicians should be aware of variations in this region for correct diagnosis and treatment of diseased hands.

METHODS

During a routine dissection at our department, an extremely rare case of deep hand extensor muscle was discovered.

RESULTS

A complete extensor digitorum profundus complex was found in the fourth extensor compartment in addition to the extensor indicis proprius. The complex consisted of two muscle bellies originating from the lateral aspect of distal ulna and the adjacent interosseous membrane. The first belly resembled the conventional extensor indicis proprius. The second belly gave off two tendon slips: one inserted to the index and middle fingers and the other formed aponeurosis before inserting to the ring and little fingers.

CONCLUSION

To our knowledge, a complete extensor digitorum profundus complex which inserts to all medial four digits has never been reported in humans. Awareness of variations in this region is critical for surgeons operating in the forearm and hand. The present case also provides insights into the evolutionary and developmental origin of these structures.

Variant Superficial Branch of Radial Artery along with Supplementary Tendons on the Dorsum of the Hand and Their Surgical Implications

Variations of radial artery, in both its course and branching pattern in the anatomical snuffbox, are clinically significant for the plastic surgeons, cardiologists, and radiologists. Reports on its abnormal high origin and subsequent superficial course have been well documented. Herein, we report an unusual superficial branch of the radial artery given off before its entry into the palm by passing between the two heads of first dorsal interosseous. It eventually divided into princeps pollicis and radialis indicis arteries at the first web space of palm as a unique vascular variation. Apart from this, in the present case, the tendon of extensor digiti minimi and of extensor indicis divided into two parts. The split tendons of extensor digiti minimi were inserted to the dorsal digital expansion of the digitus minimus. However, lateral tendon of split extensor indicis was inserted along with the tendon of extensor digitorum to the index finger and the medial one was inserted along with the tendon of extensor digitorum to the middle finger. Unusual superficial branch of radial artery on the dorsum of the hand is vulnerable for an iatrogenic injury during surgical approaches in the region. Supplementary extensor tendons on the hand are one of the potential causes for the tenosynovitis.