Anatomical snuff box is a triangular depression on the lateral aspect of the dorsum of the hand bounded laterally by the tendons of Abductor pollicis longus (AbPL), Extensor pollicis brevis (EPB) and medially by the tendon of Extensor pollicis longus (EPL) muscle.¹(Fig. 1) It is most easily visible when the thumb is in an extended position. The main content of the anatomical snuff box is the radial artery, and the roof contains the cephalic vein and the superficial branch of the radial nerve.        

The tendon of the Abductor Pollicis Longus (AbPL) typically divides into two slips and inserts onto the lateral aspect of the base of the first metacarpal bone and sometimes to the trapezium.¹ The Extensor Pollicis Brevis (EPB) and Extensor Pollicis Longus (EPL) generally have single tendons that insert onto the dorsal aspect of the base of the proximal phalanx and the base of the distal phalanx of the thumb, respectively. The number and sites of insertion of these tendons, forming the boundaries of the anatomical snuff box, show variations among different populations. Multiple tendinous slips (approx. 2-5) of the AbPL most commonly insert onto the base of the first metacarpal and occasionally to the trapezium.² Two tendinous slips of Extensor Pollicis Brevis (EPB) and Extensor Pollicis Longus (EPL) insert onto the dorsal aspect of the base of the proximal phalanx and distal phalanx of the thumb, respectively.⁵

These tendons play a crucial role in the movement of the thumb. Inflammation of these tendons due to overuse can lead to pain around the thumb, as seen in De Quervain’s tenosynovitis. Variations in these tendons forming the boundaries of the anatomical snuff box are probably responsible for recurrence and unilateral affection in de Quervain’s disease⁵. In severe cases, surgical decompression of the affected tendons may be required. A thorough understanding of the variations in the number and site of insertion of these tendons is essential for orthopaedic surgeons in the diagnosis and management of conditions such as De Quervain’s tenosynovitis, first carpometacarpal arthritis, and trapeziometacarpal subluxation.⁴Another important clinical application of multiple tendinous slips of the Abductor Pollicis Longus (AbPL) is their use as grafting material for tendon reconstruction following rupture.⁵

Although a few studies have reported data on the number or sites of insertion of the tendons forming the boundaries of the anatomical snuff box in the Indian population, comprehensive data addressing both parameters simultaneously is limited. Therefore, the present study was undertaken to observe and document the number and sites of insertion of Abductor Pollicis Longus (AbPL), Extensor Pollicis Brevis (EPB) and Extensor Pollicis Longus (EPL) tendons in the North Indian population

After obtaining ethical and institutional approval, the present observational study was conducted in the Dissection Hall of the Department of Anatomy at the University College of Medical Sciences (UCMS), Delhi, India. A total of 55 formalin-fixed cadaveric upper limbs (28 right and 27 left) of either gender, aged between 30 and 70 years, available in the department from November 2022 to November 2025, were included in the study, excluding any damaged or deformed limbs.

Routine dissection of all the upper limbs was carried out according to Cunningham’s Manual of Practical Anatomy (14th edition). The posterior compartment of the forearm and the dorsum of the hand were dissected, the extensor retinaculum was incised, and the tendons forming the boundaries of the anatomical snuff box were examined for variations in the number and site of insertion. Photographic documentation was conducted using a digital camera, and all observations were recorded in accordance with the study protocol.

Fig. 1: Image showing the tendons forming the lateral (AbPL, EPB) and medial (EPL) boundaries of the Anatomical snuff box (dashed outline) in the right upper limb

• AbPL: Abductor Pollicis Longus tendon
• EPB: Extensor Pollicis Brevis tendon
• EPL: Extensor Pollicis Longus tendon, RA: Radial Artery
• S= Superior, I= Inferior, M= Medial, L= Lateral

Fig. 2: Image showing tendinous slips of AbPL in the upper limbs

• AbPL (1,2,3,4,5,6,7): Abductor Pollicis Longus tendons
• EPB: Extensor Pollicis Brevis tendon
• EPL: Extensor Pollicis Longus tendon
• S= Superior, I= Inferior, M= Medial, L= Lateral

Fig. 3: Image showing the sites of insertion of AbPL in the left and right upper limbs

• AbPL1: First tendinous slip inserting into the AbPB muscle
• AbPL2: Second tendinous slip inserting onto the base of 1^st metacarpal bone of the hand, AbPL1,2,3: three tendinous slips of Abductor Pollicis Longus muscle inserting onto the trapezium.
• AbPB: Abductor Pollicis Brevis muscle
• FPB: Flexor Pollicis Brevis muscle, TPZ: Trapezium

Fig. 4: Image showing two tendinous slips, each of the EPB and EPL tendons in the right upper limb

• EPB1, EPB2: Extensor Pollicis Brevis tendons
• EPL1, EPL2: Extensor Pollicis Longus tendons
• AbPL: Abductor Pollicis Longus tendon
• S= Superior, I= Inferior, M= Medial, L= Lateral

A total of fifty-five upper limbs (28 right, 27 left) from 28 cadavers (22 male and 6 female) were dissected for this study. In each limb, the tendons of the Abductor Pollicis Longus (AbPL), Extensor Pollicis Brevis (EPB), and Extensor Pollicis Longus (EPL) were identified, and the number of tendons and their site of insertion were documented.

Abductor Pollicis Longus:

The number of tendons of the Abductor Pollicis Longus (AbPL) varied from two to seven, of which five, six and seven tendons were the least common, each occurring in 6, 6 (10.90%) & 5 (9.09%) limbs, respectively. Four tendons were the most frequent, observed in 17 (30.90%) limbs. Multiple slips (2 to 7) were more common on the right side (R: L = 24:21) (Fig. 2) (Table 1).

Table 1:  The number of tendons of the Abductor Pollicis Longus (AbPL) in the upper limbs:

In all upper limbs examined, the primary insertion of the Abductor Pollicis Longus (AbPL) tendon was at the base of the first metacarpal (MCP) bone (Fig.8). Additional sites of insertion were the fleshy fibers of the Abductor Pollicis Brevis (APB) muscle in 35 limbs (63.63%) and the trapezium in 15 limbs (27.27%). Out of the total tendinous slips, 66.66% inserted on the base of the 1^st metacarpal, 26.48% into the Abductor Pollicis Brevis and 6.84% were inserted on the trapezium bone. (Fig. 3) (Table 2)

Table 2. Insertion Sites of Abductor pollicis longus APL Tendon Slips.

Extensor Pollicis Brevis:

The tendon of the Extensor Pollicis Brevis muscle (EPB), located in the first extensor compartment along with the tendons of the Abductor Pollicis Longus (AbPL), is usually single; however, it was found to be doubled in 11 (20%) limbs. (Fig. 4) All tendinous slips were inserted onto the base of the dorsal aspect of the proximal phalanx of the thumb. (Table 3)

Table 3:  The number of tendons of the Extensor Pollicis Brevis (EPB) muscle in the upper limbs:

Extensor Pollicis Longus:

The tendon of the Extensor Pollicis Longus (EPL), located in the third extensor compartment, had a single slip in 21 (38.18%) upper limbs and double slips in 34 (61.82%) upper limbs. (Fig. 4) These tendons were inserted into the capsule of the interphalangeal joint before joining the extensor expansion. (Table 4)  

Table 4: The number of tendinous slips of the Extensor pollicis longus (EPL) muscle in the upper limbs:

The boundaries of the anatomical snuff box show great variability. Many studies have described these variations, but few conclusions exclude each other. Awareness of variations in the tendons of Abductor Pollicis Longus (AbPL), Extensor Pollicis Brevis (EPB) and Extensor Pollicis Longus (EPL) is essential for planning treatment of de Quervain’s disease.

Abductor Pollicis Longus (AbPL)

In this study, multiple tendinous slips of the Abductor Pollicis Longus (AbPL) were found, ranging from 02 to 07 slips, in the fifty-five dissected upper limbs.  Similar findings have been reported by Bonczar et al.⁷, whereas up to 14 tendinous slips of Abductor Pollicis Longus have been reported by Thwin SS et al.⁴. Less than 07 tendinous slips of the Abductor Pollicis Longus (AbPL) were reported by Gautam A et al¹, P karauda P et al,² Tewari S et al,³ Roy A et al⁵, Chentanez et al⁶ and Palatty et al^8, respectively, which is lower in number than the present study. (Table 5)

Table 5:  The number of tendons of the AbPL in different studies.

In the present study, the most common site of insertion of the tendon of the Abductor Pollicis Longus (AbPL) was onto the dorsal aspect of the base of the first metacarpal (MCP) bone in all upper limbs examined. This finding aligns with those reported by earlier authors.¹-⁶,⁹–¹²

The second most common site of insertion was in the fleshy fibres of the Abductor Pollicis Brevis (APB) muscle, observed in 35 upper limbs (63.63%). This is comparable to the 60% reported by El-Beshbishy et al⁹. However, Bravo et al.¹⁰ and Vollala et al.¹¹ noted this insertion less frequently, in 22% and 44% of limbs, respectively.

The third site of insertion reported was the trapezium bone, identified in 15 limbs (27.27%). This frequency is lower than that previously reported by Deivasigamani et al.¹² (63%) and El-Beshbishy et al.⁹ (80%), but higher than the 10% observed by Karauda P et al.² (Table 6).

Table 6.  Sites of insertion of Tendinous slips of AbPL in different studies.

Extensor Pollicis Brevis (EPB)

One to two tendons of the Extensor Pollicis Brevis (EPB) were found in all specimens included in the present study, which is consistent with the findings of Pallaty et al.⁸ and Roy et al.⁵. Three tendinous slips of EPB muscle were reported by Bonczar et al.⁷, Nayak et al.¹³, and Ravi et al.¹⁴, whereas Gautam et al.¹ and Thwin et al.⁴ observed only a single EPB tendon. These variations may be related to developmental differences or differences in sample size.

In the present study, a single EPB tendon was present in 80% of specimens, a finding consistent with that of Nayak et al. Two EPB tendons were observed in 20% of specimens, which is consistent with the variation described by Roy et al.⁵ (Table 7). 

Table 7. Number of Tendinous Slips of Extensor Pollicis Brevis (EPB) in different studies.

Extensor Pollicis Longus (EPL)

Thwin SS. et al.⁴, Gnanasekaran D. et al¹⁵, and Pallaty et al⁸ documented the presence of two tendons of the Extensor Pollicis Longus (EPL) in their studies, findings that are comparable to the observations in the present investigation. In the present study, a single EPL tendon was identified in 38% of the limbs, whereas two EPL tendons were observed in 62% of the limbs. According to Thwin S. et al⁴, Gnanasekaran D. et al¹⁵, and Palatty et al.⁸, two EPL tendons were present in 80% to 95% of the upper limbs examined. This variation in the incidence of EPL tendons may be attributed to developmental factors and different sample sizes (Table 8).

Table 8. Number of Tendinous Slips of Extensor Pollicis Longus (EPL) in different studies.

Multiple variations, including supernumerary tendinous slips of the muscles forming the boundaries of the anatomical snuff box, were observed in the present study. The Abductor Pollicis Longus (AbPL) frequently demonstrated multiple tendinous slips, which inserted variably onto the base of the first metacarpal, the abductor pollicis brevis muscle, or the trapezium.

Understanding these tendinous variations holds significant clinical importance, particularly in the management of De Quervain’s tenosynovitis. Detailed anatomical knowledge of these variations is also essential in interventional radiology for accurate diagnosis of tendon rupture, and in orthopaedic surgery, especially while performing tendon transfer procedures.

Furthermore, awareness of variations in number and site of attachment is crucial for orthopaedic surgeons when evaluating and managing conditions such as De Quervain’s tenosynovitis, first carpometacarpal arthritis, and trapeziometacarpal subluxation. Such anatomical insights can directly influence diagnostic accuracy and treatment outcomes.

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