The palmaris longus (PL) is one of the most variable muscles in the human body and belongs to the superficial flexor group of the forearm, along with flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), and pronator teres. It is a slender, fusiform muscle with a short belly and a long tendon, originating from the medial epicondyle of the humerus via the common flexor origin and from the adjacent intermuscular septa. The tendon traverses anterior to the transverse carpal ligament and inserts into the flexor retinaculum and palmar aponeurosis. Although its function as a weak wrist flexor and thumb abductor is often considered negligible, the PL plays a role in anchoring the palmar fascia and has considerable importance in reconstructive and plastic surgery due to its consistent length and expendability.[1] The identification of the PL tendon during clinical examination can be achieved through various physical tests such as Schaeffer’s test, Mishra’s tests I and II, Thompson’s test, and Pushpakumar’s method. Newer techniques like the Bunch Finger and Hooked Finger tests enhance visualization of the tendon in equivocal cases. Despite its apparent simplicity, the muscle demonstrates significant anatomical diversity, including agenesis, duplication, digastric configuration, reversed orientation, accessory slips, and insertional variations into structures such as the pisiform, abductor pollicis brevis, and flexor retinaculum.[2] Agenesis of the PL is the most frequent variation and was first systematically described by et al.(20)[3], who reported an overall absence in about 15% of individuals, though prevalence varies widely by ethnicity-from 2% in Zimbabwe to 64% in Turkey. These variations may be detected clinically, intraoperatively, or incidentally during cadaveric dissections. The absence or anomalous insertion of the PL may be associated with vascular and neural variations, such as an anomalous superficial palmar arch, which can impact surgical outcomes.[4] Aim To study the anatomical variations and morphological spectrum of the palmaris longus muscle in cadavers and their clinical and surgical significance. Objectives 1. To identify the presence or absence of the palmaris longus muscle in cadaveric specimens. 2. To document variations in the origin, insertion, and morphology of the palmaris longus muscle. 3. To correlate observed variations with potential clinical and surgical implications.

Source of Data: The study utilized upper limbs from 72 adult cadavers (both sexes) obtained from the Department of Anatomy at a tertiary medical college. All specimens were preserved in 10% formalin solution and used for routine undergraduate and postgraduate dissections. Study Design: Descriptive cross-sectional cadaveric observational study. Study Location: Department of Anatomy at tertiary medical college. Study Duration: Two years From March 2024 to September 2025. Sample Size: A total of 72 cadavers (144 upper limbs) were included for bilateral assessment. Inclusion Criteria: • Adult cadavers with intact upper limbs and well-preserved musculature. • Specimens with identifiable soft-tissue structures in the anterior compartment of the forearm. Exclusion Criteria: • Cadavers showing traumatic, surgical, or pathological deformities of the forearm or wrist. • Specimens with prior dissection artifacts obscuring the course of the palmaris longus muscle. Procedure and Methodology: Each upper limb was dissected meticulously using standard dissection protocols. The skin, superficial fascia, and deep fascia were reflected carefully to expose the superficial flexor muscles. The palmaris longus was identified, and its origin, course, insertion, morphology, and relation to neighboring structures were noted. The presence of bilateral absence, duplication, reversed belly, tendinous origin, accessory slips, or anomalous insertions was recorded. Photographic documentation was done for significant variants. Observations were compared with standard anatomical descriptions in Gray’s Anatomy and previous literature. Sample Processing: The dissected limbs were preserved in formalin throughout the study. Measurements such as muscle length, belly length, tendon length, and width were recorded using digital Vernier calipers. Morphological deviations were noted and categorized descriptively. Statistical Methods: Data were entered into Microsoft Excel and analyzed using descriptive statistics. The prevalence of different variations was expressed as percentages. Chi-square tests were applied to assess differences between sexes and laterality, with p < 0.05 considered statistically significant. Data Collection: Data were systematically recorded in predesigned proformas including parameters for origin, insertion, belly morphology, laterality, and associated anomalies. The findings were cross-referenced with previous cadaveric and imaging-based studies to establish the comparative morphological spectrum and clinical relevance.

Table 1: Baseline profile and morphological spectrum (N = 72 cadavers) Measure Value n (%) or Mean (SD) 95% CI Effect & test of significance p-value Age at death (years) 62.8 (11.7) 60.1-65.5 Male vs female mean diff = +2.6 years; Welch t=1.21 0.229 Sex: Male 41 (56.9%) 45.6-67.3% - - Sex: Female 31 (43.1%) 32.7-54.4% - - PL present bilaterally 58 (80.6%) 70.0-88.0% Male vs female RR for any absence = 1.36 (0.51-3.66); χ²=0.38 0.536 Any anatomical variation* (≥1 variant, excluding agenesis) 17 (23.6%) 15.1-35.0% Variation in males vs females: RR=1.22 (0.58-2.58); χ²=0.21 0.646 Muscle belly length (cm) 7.3 (1.9) 6.9-7.8 Male-Female mean diff=+0.4 cm; t=0.92 0.360 Distal tendon length (cm) 15.7 (1.8) 15.3-16.1 Male-Female mean diff=+0.5 cm (−0.36 to +1.36); t=1.16 0.251 Laterality among variations (Left-only) 9 (12.5%) 6.7-22.1% Left vs Right (paired McNemar) χ²=0.67 0.414 Laterality among variations (Right-only) 6 (8.3%) 3.9-16.7% - - Bilateral variation 2 (2.8%) 0.8-9.6% - - *Variants counted here include tendinous origin, digastric, duplicated/double belly, reversed belly, accessory slip(s), early palmar aponeurosis, insertion into APB, insertion deep to flexor retinaculum, palmaris profundus, etc. Table 1 summarizes the general characteristics and morphological spectrum of the Palmaris Longus (PL) among 72 cadavers. The mean age at death was 62.8 ± 11.7 years (95% CI: 60.1-65.5), with males comprising 56.9% and females 43.1% of the sample. The mean age difference between males and females (+2.6 years) was statistically insignificant (p = 0.229). Bilateral presence of PL was seen in 80.6% of specimens (95% CI: 70.0-88.0), and no significant sex difference was noted in absence rates (RR = 1.36, 95% CI: 0.51-3.66; p = 0.536). Anatomical variations were identified in 23.6% (95% CI: 15.1-35.0) of cadavers, including forms such as digastric, double belly, accessory slips, and reversed configurations. Variations were slightly more frequent in males (RR = 1.22), though not statistically significant (p = 0.646). The mean muscle belly length was 7.3 ± 1.9 cm, and tendon length averaged 15.7 ± 1.8 cm, showing minimal sex-based difference (p = 0.360 and 0.251 respectively). Laterality analysis revealed that left-sided variations were marginally higher (12.5%) than right-sided (8.3%), but the difference lacked significance (p = 0.414). Bilateral variations were rare (2.8%). Table 2 details the distribution of PL presence and absence. The bilateral presence rate (80.6%) closely aligns with global anatomical data, confirming PL as a predominantly conserved muscle. Unilateral absence was noted in 13.9% of cadavers (95% CI: 7.7-23.7%), slightly more common on the left side (8.3%) compared to the right (5.6%), though the difference was statistically insignificant (p = 0.439). Bilateral agenesis occurred in 5.6%, giving an overall absence (unilateral or bilateral) prevalence of 19.4%. Comparison of absence between sexes yielded no significant difference (RR = 1.36, p = 0.536). Side comparison using McNemar’s test confirmed symmetrical distribution (p = 0.371). Table 2: Presence/absence of palmaris longus (N = 72 cadavers) Category n (%) 95% CI Effect & test of significance p-value PL present bilaterally 58 (80.6%) 70.0-88.0% - - Unilateral absence 10 (13.9%) 7.7-23.7% Left-only vs Right-only: χ²=0.60 0.439  • Left-only absence 6 (8.3%) 3.9-16.7% - -  • Right-only absence 4 (5.6%) 2.2-13.4% - - Bilateral absence 4 (5.6%) 2.2-13.4% - - Any absence (unilateral or bilateral) 14 (19.4%) 12.0-30.0% Male vs Female absence: RR=1.36 (0.51-3.66); χ²=0.38 0.536 Side comparison (present vs absent, paired) - - McNemar χ²=0.80 0.371 Table 3: Documented origin, insertion, and morphology variants (N = 72 cadavers) Variant (any side) n (%) 95% CI Male vs Female (RR, 95% CI) z / χ² p-value Accessory slip(s) 6 (8.3%) 3.9-16.7% 1.51 (0.30-7.73) z=0.50 0.615 Tendinous origin 3 (4.2%) 1.4-11.7% 1.51 (0.14-15.93) z=0.35 0.728 Digastric belly 3 (4.2%) 1.4-11.7% 1.51 (0.14-15.93) z=0.35 0.728 Duplicated/double belly 2 (2.8%) 0.8-9.6% 0.76 (0.05-11.62) z=−0.20 0.841 Reversed belly 2 (2.8%) 0.8-9.6% - (female zero) z=1.25 0.212 Insertion into APB 4 (5.6%) 2.2-13.4% 0.76 (0.11-5.07) z=−0.29 0.773 Insertion deep to flexor retinaculum 2 (2.8%) 0.8-9.6% 0.76 (0.05-11.62) z=−0.20 0.841 Early palmar aponeurosis 3 (4.2%) 1.4-11.7% 1.51 (0.14-15.93) z=0.35 0.728 Palmaris profundus (deep course) 1 (1.4%) 0.2-7.5% - (female zero) z=0.88 0.381 Notes: Proportion 95% CIs use Wilson; male vs female comparisons use two-proportion z-tests (H₀: pₘ = p_f). Definitions and examples of variants per doc and standard texts. Table 3 categorizes the range of morphological variants identified among the 72 cadavers. The most frequent anomalies were accessory slips (8.3%), followed by tendinous origin (4.2%), digastric (4.2%), and early formation of palmar aponeurosis (4.2%). Less common variations included duplicated/double belly (2.8%), reversed belly (2.8%), insertion into the abductor pollicis brevis (5.6%), insertion deep to flexor retinaculum (2.8%), and palmaris profundus (1.4%). None of these variations showed a statistically significant sex difference (all p > 0.05). The reversed belly and palmaris profundus variants-both clinically important for their potential to cause median nerve compression-were observed exclusively in males, though insignificantly (p = 0.212 and 0.381). Table 4 explores how PL variations impact clinical and surgical utility. A usable PL tendon (defined by adequate length, intact course, and superficial insertion) was found in 77.8% of cadavers. Morphological variations significantly reduced graft usability-only 52.9% of variant specimens were suitable compared to 85.5% of normal ones (RR = 0.62; p = 0.019). CTS-risking configurations (reversed belly, deep insertion, or palmaris profundus) occurred in 6.9%, showing a non-significant male predominance (RR = 3.02; p = 0.280). Bilateral PL presence markedly predicted graft suitability (84.5% vs. 50%; RR = 2.17; p = 0.0006), emphasizing the surgical value of bilaterally intact PL. Additionally, insertion into the abductor pollicis brevis (APB) was seen in 5.6%, offering potential anchorage for facial reanimation surgeries, though the difference from other variants was not significant (p = 0.203). Table 4: Correlation of observed variations with potential clinical and surgical implications (N = 72) Clinical/surgical implication n/N (%) 95% CI Comparison & effect size Test p-value Usable PL for grafting 56/72 (77.8%) 66.9-86.0% - - - Any morphological variation reduces graft usability 9/17 (52.9%) vs 47/55 (85.5%) - RR=0.62 (0.39-0.98) χ²=7.94 0.019 CTS-risking configuration 5/72 (6.9%) 3.0-15.1% Male vs female: RR=3.02 (0.36-25.73) z=1.08 0.280 Bilateral PL presence predicts graft usability 49/58 (84.5%) vs 7/14† (50.0%) - RR=2.17 (1.20-3.92) χ²=14.73 0.0006 Insertion into APB and facial reanimation suitability 4/72 (5.6%) 2.2-13.4% APB insertion vs others: OR=2.31 (0.53-9.97) χ²=1.62 Figure 1: Muscle belly seen distally Figure 2: Double belly Figure 3: Double belly and two different insertions

Table 1 (Baseline profile & morphological spectrum): Cohort (N=72) shows a bilaterally present palmaris longus (PL) in 80.6% with overall any variation (excluding agenesis) at 23.6%. The age and sex composition are typical for anatomical series, and the non-significant sex differences for absence (RR=1.36; p=0.536) and for “any variation” (RR=1.22; p=0.646) are consistent with larger reviews that report no robust sex predilection after adjusting for sample structure and ethnicity. Classic cadaveric work by Al-Fauri M. (2025)[5] reported PL absence in ~15% overall but highlighted wide geographic variability [2]; updated syntheses show absence rates ranging from very low single digits to >60% depending on ancestry [1]. 19.4% overall absence (from Table 2) therefore sits comfortably within the global band-higher than many European series but lower than some Middle-Eastern and Turkish reports summarized by Zaottini F et al.(2023)[6]. Morphometrics (mean belly length 7.3 cm, tendon length 15.7 cm) align with textbook ranges and contemporary imaging/anatomic reports, and their small, non-significant sex differences (p=0.36 and p=0.25) are expected, given that PL is slender and functionally expendable in most individuals. The left-only vs right-only laterality imbalance among variants (12.5% vs 8.3%) was not significant (McNemar p=0.414), agreeing with the general observation that laterality of PL peculiarities is stochastic rather than directional in most series Olewnik Ł et al.(2025)[7]. Table 2 (Presence/absence): Observed bilateral presence 80.6%, unilateral absence 13.9% (slightly more left-sided), and bilateral agenesis 5.6%, yielding any absence 19.4%. Side-specific differences were non-significant (χ²=0.60; p=0.439) and the paired comparison also showed no systematic side bias (McNemar p=0.371). This pattern mirrors pooled estimates showing that unilateral agenesis is more common than bilateral, with left-sided unilateral loss often reported a bit more frequently-but usually without statistical significance when samples are modest. The lack of sex association (RR=1.36; p=0.536) again agrees with both sonographic and dissection-based datasets that fail to find reproducible sex effects once ancestry is considered Szewczyk B et al.(2021)[8]. Table 3 (Origin, insertion & morphology variants): Variant spectrum-accessory slips (8.3%), tendinous origin (4.2%), digastric (4.2%), early palmar aponeurosis (4.2%), double belly (2.8%), reversed belly (2.8%), deep insertion (2.8%), insertion into APB (5.6%), and palmaris profundus (1.4%)-maps closely to the catalog described in classical and modern cadaveric work. Absolute frequencies vary widely across studies due to sample size, ancestry, and classification criteria, but overall “any variation” near one-quarter is in the mainstream of published cadaver series Ogut E. (2024)[9]. None of the sex comparisons reached significance in data (all p>0.05), echoing the heterogeneous but generally null sex signals in pooled reviews. Particularly relevant for surgeons are reversed belly and palmaris profundus, both linked to median nerve compression in case series and pathophysiologic discussions Kabakçı AD et al.(2022)[10]; low prevalences (2.8% and 1.4%) are typical but clinically non-trivial. Table 4 (Clinical & surgical implications): From a reconstructive standpoint, 77.8% of cadavers met definition of a “usable PL for grafting.” The marked drop in usability among those with any morphological variation (52.9% vs 85.5%; RR=0.62; p=0.019) is clinically intuitive and corroborates surgical experience: anomalous course, deep insertion, or reversed belly can shorten or redirect the tendon, complicating harvest and inset al.exander JG et al.(2020)[11]. Conversely, bilateral PL presence strongly predicted usability (84.5% vs 50.0%; RR=2.17; p=0.0006), a finding that supports routine pre-harvest clinical/sonographic confirmation-especially when planning radial forearm flaps, tendon grafts, or frontalis suspension procedures in which PL is a favored autograft because removal is functionally inconsequential Olewnik Ł et al.(2025)[12].

The present cadaveric study on 72 specimens highlights that the palmaris longus muscle (PL), though functionally vestigial, exhibits remarkable anatomical diversity. The bilateral presence rate of 80.6% and absence in 19.4% of cases closely mirror global data, reaffirming the variability of this muscle across populations. Morphological variants such as accessory slips, tendinous origin, double or reversed bellies, and abnormal insertions were observed in nearly one-fourth of specimens, underscoring the importance of detailed anatomical understanding for clinicians. From a surgical perspective, the PL’s morphological variations hold significant clinical implications-its anatomical integrity directly determines its suitability as a donor tendon for reconstructive procedures, while reversed or deep insertions can predispose to carpal tunnel syndrome. The study emphasizes that thorough preoperative assessment (by physical or imaging methods) of PL presence and course is essential before utilizing it for grafting or reconstructive purposes. Overall, the findings reinforce that the PL muscle, despite its minimal functional contribution, plays a vital anatomical and surgical role, and knowledge of its variants can aid in improving operative precision and patient outcomes. LIMITATIONS OF THE STUDY 1. The study was limited by a modest sample size (72 cadavers), which may not fully capture regional or ethnic variability in PL morphology. 2. As a cadaveric dissection study, histological confirmation of variant muscular architecture was not performed. 3. The age at death and preservation duration of cadavers might have introduced minor post-mortem changes affecting fine structural delineation. 4. Laterality dominance and hand preference data were unavailable, precluding correlation between limb dominance and muscle variation. 5. The study was confined to a single geographic and institutional setting, limiting generalizability to broader populations. 6. Functional correlations (such as grip strength or imaging verification in living subjects) were not evaluated. 7. Subtle neurovascular variations associated with PL were not included in this assessment. 8. The findings were purely anatomical and did not assess intraoperative or clinical outcomes in live surgical cases.

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