Reappraisal of the anatomical diversities of the pyramidalis muscle with their potential clinical applicability: cadaveric analysis.

INTRODUCTION: The present study examined the morphology and morphometric parameters of the pyramidalis muscle (PM) in detail with their potential applicability in making midline infra-umbilical incisions and biomechanics of the linea alba. METHODS: PM was examined in 51 formalin-fixed cadavers (36 males and 15 females), and based on the mode of insertion or the level of apex, the formation or shape of the muscle was classified into nine types (Mori's classification). RESULTS: Bilateral PM was more prevalent (39.21%) than unilateral (1.96%) (p = 0.001). All the cases showed side symmetry except one. Mori's type 7 (right PM is higher apex and the left PM with elongated origin) was the most common form. The mean length of PM in males and females was 4.51 ± 0.14 and 3.33 ± 0.12 cm on the right and 4.51 ± 0.11 and 3.26 ± 0.16 cm on the left side. The mean width of right-sided PMs in males and females was 1.90 ± 0.17 and 1.58 ± 0.13 cm and left-sided 1.88 ± 0.14 and 1.55 ± 0.38 cm. The mean of pyramidalis-pubo-umbilical index (PPI) in males and females was 32.82 ± 1.65 and 27.50 ± 1.08, respectively. The mean insertion angle was 24.56 ± 3.07 on right side and 23 ± 2.03 on the left side (p = 0.03). Male predominance existed on right- and left-sided PM length (p < 0.001 and p < 0.001), width (p = 0.001) and PPI (p = 0.001). The strong positive correlation (r = 0.83) between length and width indicates a symmetrical muscle augmentation in the two dimensions. CONCLUSION: PM is an inconsistent anatomical structure with persistent morphology. The level and angle of insertion into the linea are crucial in the biomechanics of linea alba. PPI, determining the termination level would be useful to surgeons making midline infra-umbilical incisions.

Anatomical variations of the pyramidalis muscle: a systematic review and meta-analysis.

PURPOSE: To provide a comprehensive evidence-based assessment of the anatomical characteristics of the pyramidalis muscle (PM). MATERIALS AND METHODS: A thorough systematic search of the literature through August 31st 2020 was conducted on major electronic databases PubMed, Scopus and Web of Science (WOS) to identify studies eligible for inclusion. Data were extracted and pooled into a meta-analysis using MetaFor package in R and MetaXL. A random-effects model was applied. The primary outcome of interest was the prevalence of PM. The secondary outcomes were the dimensions (length and width) of the PM. RESULTS: A total of 11 studies (n = 787 patients; 1548 sides) were included in the meta-analysis. The multinomial pooled prevalence estimate (PPE) for a bilateral absence of the PM was 11.3% (95% CI [7.2%, 16.2%], 82.3% (95% CI [76.2%, 87.6%]) for a bilateral presence, and 6.3% (95% CI [3.3%, 10.2%]) for a unilateral presence. Of four studies (n = 37 patients) that reported the side of a unilateral presence, the PPE of a unilateral right-side presence was 42.2% (95% CI [23.0%, 62.3%]) compared to 57.8% for a unilateral left-side presence (95% CI [37.7%, 77.0%]). The mean length of the PM displayed high levels of heterogeneity, ranging from 3.12 to 12.50 cm. CONCLUSION: The pyramidalis muscle is a rather constant anatomical structure being present in approximately 90% of individuals.

Prevalence and pubo-umbilical index of pyramidalis muscle in a select Kenyan population.

PURPOSE: Pyramidalis is a lower anterior abdominal wall muscle that is considered vestigial and shows variations in prevalence and size. It's been utilized as an anatomical landmark and harvested for use in various surgical procedures. Despite knowledge of its clinical importance, data on the prevalence of pyramidalis remain absent from the Kenyan population with few studies globally reporting on its pubo-umbilical index. We therefore aimed to determine the prevalence and relative lengths (pubo-umbilical index) of pyramidalis muscle in a sample Kenyan population. MATERIALS AND METHODS: Fifty-two cadavers (41 males, 11 females) from the Department of Human Anatomy, University of Nairobi were used. Prevalence and length of the muscle (l) were established, and the distance between pubic symphysis and umbilicus (L) measured and used to calculate pubo-umbilical index (l/L ×100%). Independent and paired T tests were done, using SPSS® version 22. A p value of ≤ 0.05 was considered statistically significant at a 95% confidence interval. RESULTS: Pyramidalis was present in 84% (44) of cadavers; 83% (43) bilaterally, 2% (1) unilaterally, and 85.4% (35) in males, 81.8% (9) in females. Mean length in males and females was 71.8 ± 35 mm and 63.5 ± 37.5 mm, respectively. Mean pubo-umbilical index was 38% ± 18 (39 % ± 18 males, 35% ± 19 females). No statistically significant difference was found. CONCLUSION: Pyramidalis is a highly prevalent muscle in the Kenyan population and, hence, could be exploited for its clinical and surgical utilities. The muscle terminates largely within the 2nd quarter (25-50%) of the infra-umbilical linea alba measured from pubic symphysis. Its pubo-umbilical index would be useful to surgeons making midline infra-umbilical incisions and performing procedures involving the muscle.

Morphometric variability of pyramidalis muscle and its clinical significance.

PURPOSE: The goal of the study is to analyze the morphometric diversity of the pyramidalis muscle (PM) and to evaluate how it is affected by gender and side of occurrence. MATERIALS AND METHODS: Ninety-six (50 male and 46 female) formalin-embalmed Greek cadavers were dissected. RESULTS: The PM was present in 93.8 %, usually bilaterally (79.2 %) than unilaterally (14.6 %) (p = 0.003) and more frequently in females (91.3 %) than in males (68 %) (p = 0.0001). Side symmetry was detected. The mean length of PM in males and females was 8.37 ± 2.80 and 6.18 ± 1.64 cm on the right and 7.50 ± 2.66 and 6.56 ± 1.68 cm on the left side. Male predominance existed on the right and left-sided PM lengths (p = 0.0001 and p = 0.054). The mean width of the right-sided PMs in males and females was 1.61 ± 0.55 and 1.50 ± 0.44 cm and the left-sided 1.56 ± 0.53 and 1.55 ± 0.38 cm without gender dimorphism. The positive correlation between the PM length and width indicates a symmetrical muscle augmentation on the two dimensions. CONCLUSIONS: The study demonstrates that the PM is almost constant in Greeks. Among populations the muscle morphometric variability, its clinical significance and its variable uses will help surgeons when intervening in the lower abdominal wall.

Pyramidalis muscle formation during human embryonic and early fetal periods.

The pyramidalis muscle (PM) is a paired small triangular muscle of the anterior abdominal wall; however, its physiological significance is unclear. Recent studies have failed to detect this muscle during embryonic period. Hence, the present study aimed to determine the time when PM is emerging and reveal its features using high-resolution magnetic resonance imaging. Fourteen embryos between Carnegie stage (CS)18 and CS23 and 59 fetuses (crown-rump length: 39.5-185.0 mm) were selected for this study. The PM was first detected in one of the three samples at CS20. It was detected in five of the seven samples (71.4%) between CS21 and CS23. Forty-eight samples (81.4%) at early fetal period had PMs on both the right and left sides, and 3 (5.1%) had it only on the right side. Eight samples (13.6%) had no PMs. No side-differences or sexual dimorphisms were detected. The PM length was larger than the width in most samples, although the length/width ratio varied among the samples. The PM/rectus abdominis muscle length and PM/umbilicus-pubic symphysis length ratios were almost constant, irrespective of the crown-rump length. The PM was located ventrally inferior to the rectus abdominis and closer to the medial muscle groups of the lower limb than the rectus abdominis. The present study demonstrated that PM formation occurred in the late embryonic period, and that the frequency, side differences, sex dimorphism, and spatial position of the PM in the early fetal period were similar to those in adults.

Morphometry and Frequency of the Pyramidalis Muscle in Adult Humans: A Pyramidalis Muscles Anatomical Analysis

OBJECTIVES: To verify the pyramidalis muscle's frequency (bilaterality, unilaterality, or absence) and morphometry (length of the medial border and width of its origin/base) in a sample of the Brazilian population and the anthropometric influence. METHODS: Dissection of 30 cadavers, up to 24h post-mortem. RESULTS: The pyramidalis muscle was present bilaterally and unilaterally in 83.33% and 3.33% of the cadavers, respectively, and absent in 13.33%. The muscles on the right and left sides were symmetrical in length but not in width; the pyramidalis muscles of men were longer, while those of the women were wider. We also found that there was greater variation in the dimensions (length and width) of the men's muscles. Finally, in this sample of the Brazilian population, the pyramidalis muscle's unilaterality was more prevalent than in other populations, and its complete absence was less prevalent. CONCLUSIONS: There were no cases of muscle duplication in one or both sides, as described in some studies. Despite all of its morphometric variation, the pyramidalis muscle maintained its triangular shape with longitudinal fibers in every case. Furthermore, no statistically significant correlation was noted between the muscles' dimensions and person's age, height, weight, or gender.