Kosuri Kalyan Chakravarthi

Professor, Department of Anatomy, Varun Arjun Medical College and Rohilkhand Hospital, Banthra-Shahjahanpur - 242307, Uttar Pradesh, INDIA.

Email: kalyankosuric@gmail.com

Figure 1                                                        Figure 2

Figure 3                                                                      Figure 4                                                          Figure 5

Figure 1: Showing higher origin (in the lower part of forearm) of anomalous lumbricals in a right hand( A, B, C, D- First, second, third (bipinnate) and fourth (unipennate) lumbricals; 1, 2, 3, 4- medial four tendons of FDP); Figure 2: Showing higher origin (in the lower part of forearm) of anomalous lumbricals in a right hand with congenital absence of FDP tendon to the little finger (A, B, C, D- First, second, third (unipennate) and fourth (unipennate) lumbricals; 1, 2, 3 - tendons of FDP); Figure 3: Showing higher origin (in the lower part of forearm) of anomalous lumbricals in a left hand with congenital absence of FDP tendon of little finger (A, B, C, D- First, second (bulky bipinnate), third (bulky bipinnate) and fourth (bulky bipinnate) lumbricals; 1, 2, 3 - tendons of FDP); Figure 4: Showing anomalous lumbricals in a left hand (Yellow circle-- First lumbrical(bipinnate); 1- tendon of FDS; 2 - tendon of FDP); Figure 5: Showing higher origin of anomalous lumbricals in a left hand with anomalous muscle (Black circle- Anomalous muscle in the lower part of forearm; Black arrows- Bulky second, third and fourth lumbricals)

DISCUSSION

Anatomically lumbricals take origin distal to the flexor retinaculum form the four tendons of flexor digitorum profundus muscle. Many studies reported higher origin of first and second lumbricals in the carpal tunnel. Chakravarthi et al. reported origin of all unipennate lumbricals from the four tendons of FDP muscle beneath the flexor retinaculum in the carpal tunnel of right hand of a middle-aged male cadaver. ¹In another study by Tintu et al. reported two additional bellies in the right hand of a male cadaver, one additional belly for first lumbrical originated from the radial side of the tendon of FDS of the index finger and another additional belly for second lumbrical originated from the ulnar side of the tendon of FDP of the index finger, deep to the flexor retinaculum. ² In this study, in eight cadavers (7 male and 1 female) all lumbricals were originated proximal to the flexor retinaculum in the anterior part of the forearm and extending in to then palm through carpal tunnel. Out of eight cadavers in seven male cadavers all lumbricals were found unipennate except second which is bipinnate in origin and in one female cadaver all lumbricals were found as unipennate in origin. Such higher origin of lumbricals in the anterior part of forearm proximal to the flexor retinaculum noted in this study have not seated in the modern medical literature. Benny et al. reported bilateral carpal tunnel syndrome in a 73-year-old male retired army veteran. ³ In which hypertrophied first and second lumbricals in the right hand of carpal tunnel, and abnormal ring finger lumbricals originated from the tendons of FDP and FDS in the left hand of carpal tunnel as well as in the forearm were observed. Where as in the present study in a left hand of middle-aged male cadaver, hypertrophied bipinnate first lumbrical in the carpal tunnel as well as in the forearm and hypertrophied bipinnate second and third lumbricals in the carpal tunnel were observed. Such anomalous or accessory or hypertrophic bellies in and around the carpal tunnel noted in this study may reduce the anatomical capacity of carpal tunnel and leads to carpal tunnel syndrome. Anomalous or accessory muscles or tendons in the upper limb are quite common, may lead to confusion during surgical procedures which results in errors in both diagnosis and treatment. Different accessory or anomalies or abnormal muscles of upper limb have been described in the literature. ^4-7 Although many anatomical variations in the forearm were reported in the past, Chakravarthi et al.reported a rare case of an accessory muscle of forearm originated from the middle of the medial surface of the ulna, when traced distally deep to the flexor retinaculum in the carpal tunnel it merged with the tendon of the index finger of FDS. ⁸ In this study also a rare accessory muscle of forearm originated from the tendon of the index finger of FDP, when traced distally deep to the flexor retinaculum in the carpal tunnel it merged with the second lumbrical. As per review of literature such accessory muscle noted in this study, first of kind, have not been reported in the literature till date. Such accessory muscles may alter or interfere the biomechanics of second lumbrical and FDP muscle. Accessory muscle belly appearance in the carpal tunnel is clinically important because it may reduce the capacity or volume of narrow carpal tunnel which results in entrapment neuropathy of the medial nerve. Congenital absence of FDP tendon to the little finger is very rare and is of high clinical importance for physicians examining patients for tendon lacerations and especially for hand surgeons operating tendon injuries. Santosh et al. reported congenital bilateral absence of FDP tendon to the little finger with abnormal lumbrical insertion to the little finger. ⁹ Furrer et al. reported absence of the FDP tendon to the little finger of a nine-year-old boy by ultrasound and magnetic resonance imaging. ¹⁰ Kisner et al. also reported absence of the profundus tendon to the little finger on the left hand of a 15-year-old boy during surgery. ¹¹ In another study by Yılmaz A et al. reported a double FDS tendon to the little fingers in a left forearm of a 32-year-old female cadaver, in which one tendon connected with the index finger tendon of FDP muscle and acted as the FDP tendon to the little finger. ¹² Where as in the present study, absence of FDP tendon to the little finger was noted and there was no muscle or supportive tendon substituting for the flexor digitorum profundus tendon to the little finger. Moreover, unipennate third and fourth lumbricals were taken origin from the tendon of FDP of the index finger in the carpal tunnel made this study very unique. Little finger tendon of FDP only the muscle for flexion of little finger at distal interphalangeal joint, it also helps in flexion at proximal interphalangeal joints of little finger. Congenital absence of FDP of tendon of little finger noted in this study leads to loss of flexion of little finger at distal interphalangeal joint. It also leads to flexion deformity at proximal interphalangeal joints of little finger due to imbalance between the flexor and extensor forces acting upon the proximal interphalangeal joint. Such non traumatic congenital flexion deformity at proximal interphalangeal joints of little finger is known as Camptodactyly. Dupuytren’s contracture, congenital absence of the extensor mechanism, a trigger finger and boutonniere deformity are also fall under the flexion deformities of fingers. Hence, such congenital anatomical knowledge is very important to radiologists, physiotherapists and orthopedic surgeons to avoid complications during radiodiagnostic procedures or surgeries of flexor deformities of fingers. Accessory muscles or tendons in the hand may lead to confusion during surgical procedures which results in errors in both diagnosis and treatment. There are many studies describing the anatomical variations in the origin and insertion of lumbricals, Kurzumi M et al. revealed that the lumbrical muscles originated from the intermediate tendon of the deep layer of the flexor digitorum superficialis of the index finger. ¹³ In this study bipinnate first lumbrical arising from the radial side of FDS and FDP tendons of index finger was noted. Such anatomical variations may interfere or disturb the biomechanics of FDS. Moreover, presence of hypertrophied lumbricals noted in this study can cause compression of the radial and ulnar digital arteries leading to chronic ischemia, hence a complete knowledge of lumbricals is essential during various surgical procedures of hand.

CONCLUSION

As per review of literature combination of multiple anatomical variation of lumbricals in and around the carpal tunnel noted in this study, have not been reported in the literature till date. Awareness of these variations is necessary to avoid complications during radiodiagnostic procedures or surgeries in the antebrachial and hand during various surgical procedures.

REFERENCES

1. Chakravarthi KK. Unusual Unilateral Muscular Variations of the Flexor Compartment of Forearm and Hand- A Case Report. Int J Med Health Sci 2012; 1(3): 93-8.
2. Tintu TS, Asha J Mathew. Numbers matter: Clinical significance of additional belly of first and second lumbrical muscles of the hand. Int J Anat Res 2014;2(3):459-61.
3. Benny E, Parminder GS, Nur Azuatul AK et al., Anatomical Variations of the Lumbrical Muscles Causing Carpal Tunnel Syndrome. Med and Health Jun 2019; 14(1): 197-202.
4. Chakravarthi KK. Gantzer’s muscle an accessory muscle of the forearm – Its Anatomical Variations and Clinical Insight. Int. J. Chemical and Life Sciences 2013; 2(7): 1199-1203.
5. Ramakrishna A, Chakravarthi KK. A study on morphology of the biceps brachii muscle. NUJHS 2012; 2 (3): 2-5.
6. Chakravarthi KK. An additional extensor carpi radialis longus muscle and its clinical significance. Int. J. Bioassays, 2013; 02 (06): 887-88.
7. Chakravarthi KK. Anatomical Variations of Brachioradialis Muscle in Relation to Radial Nerve. A cadaveric study. Int. J. Chemical and Life Sciences 2013; 2(4): 1156-58.
8. Chakravarthi KK. Unilateral accessory muscles of forearm-and its clinical implications. Asian Journal of Medical Sciences| Mar-Apr 2017; 8 (2): 94-96.
9. Santosh R, Haobijam N, Barad AK, Nepram SS. Absent flexor digitorum profundus (FDP): An unreported component of camptodactyly. J Med Soc 2014; 28:120-2.
10. Furrer M, Schweizer A, Meuli-Simmen C. Aplasia of the flexor digitorum profundus tendon of the small finger. J Hand Surg Eur 2007; 32(1):111- 2.
11. Kisner WH. Double sublimis tendon to fifth finger with absence of profundus. Plast Reconstr Surg. 1980; 65:229-30.
12. Yılmaz A, Cuneyt Bozer, Enis Ulucam, Oguz Taskınalp. An anomaly of flexor muscles of the fifth (little) finger of the hand: an anatomical case report. CLINICS 2009;64(11):1133-5.
13. Kurzumi M, Karwai K, Honma S, Kodama K. Anomalous lumbrical muscles arising from the deep surface of flexor digitorum superficialis muscles in man. Ann Anat. 2002; 184(4):387-92.