71THIEME

Original Article

A Study of Variations in Radial Wrist ExtensorsStelin Agnes Michael1 Gaddam Vijaya Lakshmi1

1Department of Anatomy, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India

Address for correspondence Stelin Agnes Michael, Department of Anatomy, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla 689101, Kerala, India (e-mail: stelinagnes@gmail.com).

Background and Aim Supernumerary muscles and tendons from extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB) are sometimes encoun-tered during hand surgery. They include accessory muscles like extensor carpi radialis intermedius (ECRI), intertendinous slips (ITS) between the two muscles, or simple birfurcated tendons. Awareness of these variations is crucial for preoperative planning for tendoplasty. This study was conducted with the aim of studying their prevalence since there is limited literature on its variations.Materials and Methods The study was carried out on 80 free upper limbs from the human cadavers, in the Anatomy Department of Pushpagiri Institute of Medical Sci-ences and Research Centre, Thiruvalla, Kerala. The radial carpal extensors were studied in detail. The length and width of the accessory muscles and tendons were measured. The percentage of different variations was also calculated.Results ITS from ECRL were seen in 20 of the limbs. ECRI was identified in 7 cases. Bifurcated tendon from ECRB was observed in two limbs. Absent ECRB was also noted in a specimen. In one specimen, ECRL and ECRB fused to form a single muscle and tendon, that later split into two for insertion into second and third metacarpal. The proximal attachment of both radial extensors was normal in all cases.Conclusion A total of 37.5% of variations was observed, among which supernumerary tendons accounted for 35%. Knowledge of these variations is essential in planning for tendon grafting and finger deformity correction surgeries.

Abstract

Keywords ► ITS ► accessory ► supernumerary ► bifurcated tendon

Natl J Clin Anat 2019;8:71–76

DOI https://doi.org/ 10.1055/s-0039-1688901 ISSN 2277-4025.

©2019 Society of ClinicalAnatomists

Introduction

The radial wrist extensors (RWE) include extensor carpi radialis longus (ECRL) and extensor carpi radialis brevis (ECRB). Supernumerary tendons of ECRL and ECRB have been recognized since 1867, when they were first described by Wood.1 He classified the tendons into three types: (1) clefts or bifurcated tendons, (2) tendons belonging to super-numerary muscles, and (3) intermediate tendon slips (ITS) connecting ECRL and ECRB.2,3 Supernumerary muscles include extensor carpi radialis accessories (ECRA), extensor carpi radialis intermedius (ECRI), and extensor carpi radialis tertius (ECRT).4–6

ECRA has its origin along with ECRL and inserted into the first metacarpal, the abductor pollicis brevis or the first

dorsal interosseous.7–9 ECRI has origin from the belly of ECRL/ ECRB and is inserted into the base of second or third meta-carpal. ECRT takes origin between ECRL and extensor digito-rum communis, and bifurcates for insertion into the base of second and third metacarpal bone.6,10

Variations in these muscles are encountered during sur-gical procedures. The presence of additional bellies/tendons can mislead the surgeons. They can be misdiagnosed as a soft tissue swelling such a ganglion, synovial nodule, or cyst.11 Additional tendons can also reduce the space in the extensor retinaculum, thereby increasing the risk for tenosynovitis.12 Similarly, additional muscle belly can cause posterior inter-osseous nerve compression within the radial tunnel, which is bounded medially by brachialis and tendon of biceps brachii, and laterally by forearm extensors.13

Published online: 2019-06-26

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These additional tendons can be utilized for tendon graft, tendon transfers and hand reconstructive surgeries.14–17 ECRL and ECRB tendons have been used to restore thumb opposition with excellent postoperative results.18,19 ECRL tendon was found to be effective to correct finger clawing deformity with flexor muscle loss.20,21 Taking these facts into consideration, present study has been undertaken for a better diagnosis and treatment outcome in the ante brachial and carpal region.

Materials and MethodsThis study was performed on 80 free upper limbs specimens in the Department of Anatomy of Pushpagiri Medical College, Thiruvalla, Kerala. Deformed upper limbs and those with any soft tissue pathology were excluded. The posterior compart-ment of forearm and hand were carefully dissected as per the standard dissection protocol. The topographic details of the radial carpal extensors were examined and the presence of any accessory muscles/tendons was recorded and photo-graphed. Measurements of the additional muscle bellies and the tendons were taken with the help of thread, ruler, and Vernier caliper in centimeters (cm). Data were entered on to Microsoft Excel and analyzed.

ResultsOut of the 80 upper limbs, ECRI was noticed in a total of 7 (4 right and 3 left) upper limbs. In all of them, it took origin as a small muscle belly from ECRB. Six of them inserted as a separate tendon into the base of third metacarpal, whereas the last one inserted onto the base of second metacarpal bone, medial to the ECRL tendon. We observed two cases of double ECRI. In each of them, accessory muscle bellies took origin separately from ECRL and ECRB. Their tendons crossed one another to get inserted into the third metacarpal and second metacarpal, respectively (►Fig.  1). We did not observe any

ECRI taking origin from ECRL. The length and width of the muscle bellies and their tendons are given in ►Table 1.

A total of twenty (25%) specimens showed ITS from ECRL to ECRB. Sixteen of them arose as small bellies from the radial side of ECRL. Their tendons passed deep to ECRB and inserted into ECRB tendon prior to its entry into the second compart-ment (►Fig. 2). In the other four, ITS arose directly as tendons from ECRL muscle and were inserted into ECRB tendon in three cases, and in one case into the belly of ECRI. We did not observe any ITS from ECRB into ECRL. The length and width of the muscle bellies and their tendons are given in ►Table 2.

Tendon bifurcation was observed in two specimens in ECRB only. ECRB tendon bifurcated into two slips within the compartment, which were inserted into bases of the second and third metacarpal bones (►Fig. 3). In three other speci-mens, ECRB tendon bifurcated into two in the middle of the forearm, rejoined proximal to the retinaculum, and had nor-mal insertion onto base of third metacarpal.

We also noted the absence of ECRB in one limb. In one specimen, ECRL and ECRB muscle bellies were fused, and the common tendon bifurcated deep to the retinaculum to get inserted into bases of the second and third metacarpal bones (►Fig. 4). No ECRA or ECRT were found in our study.

Fig. 1 Double extensor carpi radialis intermedius (ECRI). (A) Extensor carpi radialis brevis (ECRB). (B) ECRI from ECRB. (C) Extensor carpi radi-alis longus (ECRL). (D) ECRI from ECRL. Arrow showing crossing of the tendons of ECRI muscles.

Table 1 Extensor carpi radialis intermedius (ECRI)No. Side Muscle

length (cm)

Muscle width (cm)

Tendon length (cm)

Tendon width (cm)

1. L 4.5 0.5 15.5 0.2

2. R 3.5 0.4 19 0.2

3. L 2.5 0.6 15 0.3

4. R 3.7 0.3 15.5 0.1

5. R 2 0.2 18 0.1

6. R 2.5 0.3 14 0.1

7. L 1.4 0.3 14 0.2

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Fig. 2 (A) Extensor carpi radialis longus (ECRL). (B) Extensor carpi radialis brevis (ECRB). Arrow showing intermedius tendinous slip from ECRL to ECRB.

Table 2 Intermedius Tendinous Slips (ITS)No. Side Muscle length (cm) Muscle width (cm) Tendon length (cm) Tendon width (cm)

1. R 3.5 0.1 15 0.1

2. L 2.7 0.45 14.5 0.4

3. R 4.5 0.4 17 0.1

4. L 5 0.5 16 0.2

5. L 5 1.2 13.5 0.3

6. L 4.5 0.6 17 0.2

7. R 5 0.4 14.5 0.1

8. L 3 0.6 13 0.2

9. L 2 0.5 11 0.3

10. L 3.6 0.6 13.6 0.4

11. L 3.5 0.4 16 0.2

12. L 3 0.4 12 0.2

13. L 2 0.5 10 0.4

14. L 3.8 0.6 13 0.3

15. R 1.4 0.3 14 0.2

16. R 4 0.4 12 0.3

17. R – – 10 0.3

18. L – – 11 0.2

19. L – – 11 0.4

20. R – – Very short tendons to measure

No variations were found in the proximal attachment of the radial carpal extensors. The percentage of different types of variations is shown in ►Table 3.

DiscussionHand is the most complex organ in human body next to the brain. Preserving the function of a traumatized hand is of importance. Extensors of the hand are liable to undergo deformity as in rheumatoid arthritis,22 atrophy in quadriplegic

patients,23 or rupture following a trauma.20 Tendon transfer plays a significant role in restoring hand function. An accu-rate knowledge on the variations of radial extensors and their frequency will provide the clinicians a broader perspective in the treatment protocol.

ITS from ECRL to ECRB was found to be the commonest variation among RWE.24 Its frequency was found to be 25% in our study, similar to that (26%) obtained by Albright and Lin-burg.25 Lower frequencies were reported by Wood4 (9.3%) and Young et al5 (13.8%). ITS from ECRB to ECRL has been reported by several authors,2,25,26 but we did not notice this variation in our study.

In the present study, we noticed ECRI in 7 (8.75%) spec-imens. This variation was first observed by Wood1 in 1867, but the frequency reported by him was 1.4%. Other frequen-cies reported include 5% by Young et al5 and 24% by Albright and Linburg.25 All the ECRI took origin from ECRB in our study, similar to the finding of Wood and Young et al. We observed

double ECRI in one specimen, tendons of which crossed each other for insertion into the third and second metacarpal. Similar finding has also been documented earlier.27 Other accessory muscles like ECRA1,8,9,28 and ECRT6 have also been described by other authors but we did not observe any such variation.

ECRB tendon bifurcation has been observed in 2 cases (2.5%) in our study. This has been described by Kosugi et al26 in 1.1% cases, Wood2 in 2.2%, and Young et al5 in 2.5% cases. We did not notice bifurcated tendon from ECRL which has been

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Fig. 4 Fused extensor carpi radialis longus and extensor carpi radialis brevis. (A) Fused muscle mass. (B) Fused tendon. Arrow showing splitting of tendon just prior to insertion into base of second and third metacarpal.

Table 3 Percentage of variations in the studyTypes of variations Number of limbs Percentage

ITS

 ECRL to ECRB 20 25%

 ECRB to ECRL Nil

ECRI 7 8.75%

Tendon bifurcation

 ECRL Nil

 ECRB 2 2.5%

Absent ECRB 1 1.25%

Fused bellies of ECRB and ECRL

1 1.25%

Abbreviations: ECRB, extensor carpi radialis brevis; ECRI, extensor carpi radialis intermedius; ECRL, extensor carpi radialis longus; ITS, intermedius tendinous slips.

Fig. 3 (A) Extensor carpi radialis longus (ECRL). (B) Extensor carpi radialis brevis (ECRB). Arrow showing bifurcation of ECRB tendon.

reported by several authors.1,5,25 ECRB tendon bifurcation was observed in another three cases, but they rejoined to form a single tendon prior to its insertion into the second metacar-pal. Similar findings were reported by Classen in 2002.7

Rare cases of tendon slip of ECRL attached to the fibrous flexor sheaths of fingers were documented. This variation has significant clinical relevance of hampering the biomechanics of the wrist.29 But we did not observe any such variation in our study.

Absence of ECRB was noted in one specimen in our study, and has been reported earlier.30,31 ECRL and ECRB are derived, along with brachioradialis, from the radial block of the dorsal muscle mass of upper limb bud that is destined to form the muscles of extensor compartment of the forearm. Failure of appearance of the muscle primordia of ECRB during embryo-logic development may account for the absence of the ECRB.32 Anomalous splitting of the radial muscle mass could account for the presence of accessory muscles and the different types

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of ITS between ECRB and ECRL.33 Failure of splitting may result in the formation of fused muscle belly and tendon of ECRL and ECRB, as was observed in one specimen. Brachiora-dialis was found to be normal in all specimens.

Radial carpal extensor tendon transfer has been used to restore thumb opposition in conditions of functional loss of thenar muscles following median nerve injury.18 It was found that ECRL and ERCB tendons produced better results compared to those of flexor digitorum superficial-is.18 Similar study done by Cooney et al concluded that 60% of ECRL tendons were effective in restoring thumb flexion and opposition, in both high and low median nerve palsy.19 Tendon transfers are very often used to restore elbow func-tion after obstetrical brachial plexus injuries.16

The tendon of extensor pollicis longus (EPL) is the most frequently affected tendon of the hand in cases of spon-taneous rupture in rheumatic patients or as a result of conservative management of distal forearm fractures. In such cases also, the ECRL have been used as a tendon trans-fer or intercalary graft.14 An alternative technique known as turnover graft using only the half-slip of the muscle has also been described.22

Tendon transfer using accessory tendons are safe alter-natives to ECRL, since they do not compromise the wrist movements. These accessory muscles could also be used effectively for restoring thumb opposition by motoring the flexor pollicis longus and extensor pollicis longus.4 The bifurcated ECRL tendon has been effectively used to correct finger clawing by Malaviya. It also reduces the operation time.20 Tendon transfer using these supernumerary tendons can also be considered in surgical rehabilitation of paralytic patients.23 Their presence can be confirmed by a preopera-tive MRI scan.

Surgeons treating tennis elbow with ERCB tendon length-ening must be aware of the variations in this region in order to avoid unwanted complications.34,35 Tennis elbow can also be treated by injecting autologous blood in to ECRB.36 Lately, ERCB has been shown to produce utility in “free functional muscle transfer” where a muscle with its motor nerve and vascular pedicle is transferred from one site of the body to another distant site, in order to restore the motor function. An awareness of variant muscle and tendon will be useful while ECRB is being harvested.15

Posterior interosseous nerve entrapment can also occur while it passes through the radial tunnel that is bounded by biceps muscle medially and forearm extensor muscles anterolaterally.13 The intimate relation of brevis muscle with the PIN can possibly cause neuropathy too.37 There-fore awareness of variations of RWE will help not only in planning for tendon transfer, but also in evaluating nerve compression.

LimitationsThe present study is confined to free upper limbs. Hence, sex preponderance and comparison between the sides cannot be determined.

ConclusionVariations of RWE occur with a frequency of 37.5%. Super-numerary tendons arising from ITS from ERCL was the commonest form of variation (25%). Among the accessory muscles described the commonest is ECRI (8.75%). ECRB ten-don bifurcation (2.5%), absence of ECRB (1.25%), and fused muscle and tendon of ECRL and ECRB (1.25%) were less com-monly observed variations. Other accessory muscles like ECRA or ECRT, ITS from ECRB, and ECRL tendon bifurcation were not observed in our study. Knowledge of these supernu-merary tendons is essential for planning tendon transfer and hand reconstructive surgeries, and in diagnostic approach to nerve compression syndrome.

FundingNone.

Conflicts of InterestNone.

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