Levator ani muscle (LAM) plays a fundamental role in the pathophysiology of female pelvic floor disorders. Due to its complex anatomical and functional structure, a wide range of terminology has been used to describe it. Each bundle interfaces with adjacent structures and has a specific orientation and function. Most studies have focused on the puborectalis bundle. However, as the LAM is not a ring but rather a concave, tubular structure, a comprehensive evaluation along its entire caudal-to-cranial axis may provide additional insights.
The primary objective was to assess LAM contractility along its entire length. Secondary objectives included a subgroup analysis of participants with LAM avulsion and/or levator hiatus overdistension during the Valsalva manoeuvre.

This was a pilot study with a cross-sectional design. A total of 28 patients were recruited from the pelvic floor unit outpatient clinic at our centre to undergo transperineal ultrasound. A rendered axial image of the levator hiatus was obtained. Tomographic slices of 2.5 mm were acquired from the most caudal to the most cranial region. The levator hiatus area (cm²) was measured at rest and during maximal contraction across eight tomographic images. The percentage reduction in area was calculated.
For each participant, a graphical representation of the levator hiatus areas was created. The x-axis represented the eight LAM levels assessed. The positive y-axis represented hiatus area at rest and during contraction, while the negative y-axis represented the percentage reduction in area during contraction. Subgroup analyses were also performed, generating equivalent graphs for patients with LAM avulsion and for those with levator hiatus overdistension  (>25 cm²).

The mean age was 45.7 years. A total of 64.3% of participants presented with urinary incontinence, while 7.8% had pelvic organ prolapse. Twenty-one participants (75%) had an intact levator ani muscle (LAM), whereas 3 (10.7%) had bilateral avulsion and 4 (14.2%) had unilateral LAM injury. Fifteen participants (53.6%) demonstrated levator hiatus overdistension during the Valsalva manoeuvre.
Figure 1 shows representative graphs from three participants: (A) a patient without LAM injury or hiatal overdistension; (B) a patient with right-sided LAM avulsion; (C) a patient with hiatal overdistension without LAM avulsion.
Figure 2 shows the mean data from all 28 patients (A), from LAM avulsion group (B), and from hiatal overdistension group (C).

In Figure 1, the red area represents the levator hiatus at rest, which was larger in patient B and similar in A and C. The green area represents the hiatus during contraction, showing a similar trend. The purple area represents the percentage reduction in hiatus area across the eight tomographic slices. A marked reduction in contractility was observed in the central slices in the patient with LAM avulsion. In contrast, this reduction was not significant in the patient with hiatal overdistension, although overall contraction amplitude was lower compared to the patient without injury. 
Figure 2A  shows three peaks of maximal contraction corresponding to slices 2, 4, and 7. These likely correspond to the three muscle bundles from caudal to cranial, as histological studies have shown lower muscle density and increased connective tissue between bundles.  Figure 2B (LAM avulsion subgroup) demonstrates preserved contraction peaks with reduced amplitude and more pronounced depressions between bundles. In contrast, Figure 2C (hiatal overdistension subgroup) shows loss of the characteristic contraction peaks, while maintaining a contraction amplitude similar to the overall cohort.

A dynamic evaluation along its entire length may provide a better understanding of LAM function. This approach may serve as a starting point to better characterise in vivo LAM behaviour, including the function of individual muscle bundles and the interaction between them, where both functional and histological properties differ.

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