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Comprehensive structural analysis of piriformis muscle and sciatic nerve in cadavers: potential implications for piriformis syndrome and OMT

Journal: Journal of Osteopathic Medicine Date: 2025/12, 125(12):Pages: A618–A619. doi: Subito , type of study: observational study

Full text    (https://www.degruyterbrill.com/document/doi/10.1515/jom-2025-2000/html)

Keywords:

anatomy [102]
body mass index [2]
cadaver [18]
observational study [217]
OMT [3746]
osteopathic manipulative treatment [3766]
piriformis syndrome [9]
sciatic nerve [7]

Abstract:

Context: Piriformis syndrome (PS) typically presents as lower back and upper buttock pain that radiates down the leg. It is estimated that 0.3%–6% of regional pain can be attributed to PS, amounting to approximately 2.4 million diagnoses annually.1 However, the actual prevalence is likely higher due to the condition’s vague presentation and the absence of clear diagnostic criteria, making it a diagnosis of exclusion.2 Previous studies have proposed etiologies such as lesions or chronic irritation of the sciatic nerve, leading to nerve entrapment by the piriformis muscle.3 Recent ultrasound studies have suggested structural differences in pathological versus non-pathological presentations.4-5 However, due to the deep anatomical location of both the sciatic nerve and the piriformis muscle, ultrasound sensitivity remains low. Currently, a combination of osteopathic manipulative treatment (OMT), physical exercises, and pharmacologic therapies is used in managing PS.6 Objective: To analyze the anatomical relationship between the sciatic nerve (SN), piriformis muscle (PM), body mass index (BMI), and other pelvic measurements to determine possible patterns supporting the entrapment theory in PS. Additionally, to identify anatomical features as potential predictive factors for PS and their implications for OMT targeting this region. Methods: The gluteal region of 20 formalin-embalmed cadavers (11 females, 9 males; mean [SD] age, 76.7 [10.5] years; mean [SD] BMI, 22.7 [4.2]) from the Kansas City University Gifted Body Program were dissected and examined. All measurements were independently repeated by the authors to ensure accuracy. PM length was measured across the muscle belly from its origin on the sacrum to its insertion on the greater trochanter. PM circumference was measured at the midpoint of its length using a marked string. SN diameter was measured at its exit from the infrapiriformis fossa. Statistical analysis was conducted using Microsoft Excel. Results: After excluding specimens due to quality issues or anatomical variations, 35 sciatic nerves were included in the final analysis. The mean (SD) circumferences of the SN and PM were 3.48 (0.53) cm and 4.41 (0.94) cm, respectively. No correlation was found between PM and SN circumference (R = 0.01). However, PM length showed a positive correlation with BMI (R = 0.36) and pelvic width (R = 0.42). Age was negatively correlated with both PM length (R = –0.25) and circumference (R = –0.19).Sex-based analysis revealed similar SN circumferences between males and females (Males: mean [SD], 3.62 [0.60] cm; Females: 3.43 [0.54] cm; p = 0.33). Males had a slightly greater PM circumference, although this was not statistically significant (Males: 4.78 [1.04] cm; Females: 4.22 [0.96] cm; p = 0.10). Individuals with BMI <25 had similar SN circumferences to those with BMI >25 (BMI <25: 3.51 [0.60] cm; BMI >25: 3.58 [0.55] cm; p = 0.72). PM circumference showed greater variability by BMI category (BMI <25: 4.34 [0.99] cm; BMI >25: 4.96 [0.95] cm; p = 0.08). Conclusion: This study is the first to use circumferential measurements of the piriformis muscle to better capture its three-dimensional structure. The relatively consistent dimensions of the SN, in contrast to the more variable PM, are consistent with previous findings and suggest the PM may play a larger role in the pathophysiology of PS. Therefore, it should continue to be a primary focus of physical therapy and OMT. When considering BMI, a weak inverse correlation between SN and PM in individuals with BMI >25 may indicate differing PS pathophysiology across BMI categories. The observed correlation of piriformis length with BMI and pelvic width underscores the importance of considering body morphology as a whole, although its direct contribution to PS remains uncertain. These findings may aid in optimizing the locations of local injections, surgical incisions, or other interventions targeting this region.


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