Abstract
Background: Chronic ankle instability (CAI), resulting from repeated lateral ankle sprain (LAS), is a debilitating musculoskeletal condition that affects 20% of the general population and can limit physical activity and function. The lateral leg muscles, fibularis longus (FL) and brevis (FB) are important stablisers of the ankle joint and therefore may be implicated in CAI. However, the relationship between the architecture of these muscles and CAI remains poorly understood, and comprehensive anatomical data on the fibularis muscles are limited. An emerging method of recording neuromuscular parameters in dissection studies is through digitisation; however, the accuracy of digitisation measurements has not yet been compared to dissection measurements for any muscle.
Aims: The aim of this study was to define the detailed architecture and innervation patterns of FL and FB and to assess the accuracy of digitisation compared to dissection.
Methods: Ten cadaveric limbs (male; mean ± standard deviation (SD) age, 77.3 years ± 8.5 years) were dissected and whole musculotendon parameters measured. Pennation angle (PA), length and mass of individual fascicles were measured to determine muscle volume and physiological cross-sectional area (PCSA), and the number of nerve entry points per muscle were recorded. Muscles were digitised for post-dissection analysis, to obtain muscle belly length, musculotendinous junction (MTJ) length, fascicle length, PA, PCSA and the area of distal tendon attachment. Means and SDs were calculated for each parameter from dissection and digitisation. To explore the accuracy of digitisation compared to dissection, intraclass correlation coefficients (ICCs) were calculated, and paired Student’s t-tests were used to identify any systemic differences.
Results: Mean muscle belly length for FL was 27.2±2.5cm (dissection) and 25.8±2.6cm (digitisation), and for FB was 24.3±2.8cm (dissection) and 23.9±2.9cm (digitisation). Mean MTJ lengths were 23±2.9cm (dissection) and 21.3±3.4cm (digitisation) for FL, and 19.6±3.2cm (dissection) and 19.3±3.0cm (digitisation) for FB. Fascicle length was similar for both muscles by dissection (FL, 44±8.0mm; FB, 39±7.0mm) and digitisation (FL, 43.8±5.3mm; FB, 39.5±5.3mm). Pennation angle by dissection for FL was 7.8±4.4° and 9.5±5.2° for FB. By digitisation, a 3D PA was obtained (FL, 11.3±2.2°; FB, 12.6±2.3°). Fibularis longus (36.25±10.3g) was approximately twice as large as FB (17.3±6.0g), comparable to mean dissection PCSA (FL, 7.7 ±2.4cm2; FB, 4.1±1.8 cm2) and digitisation PCSA (FL, 6.1 ±2.1cm2; FB, 3.7 ±1.1cm2). Mean number of nerve entry points for FL and FB were 5.1±1.1 and 2.1±0.9, respectively. Overall, digitisation showed good accuracy, with eight of 12 parameters showing good or excellent validity (ICC>0.75) and no significant differences (p>0.05), when excluding 3D PA, which was expected to be different.
Conclusion: This investigation provides a better understanding of the anatomy of FL and FB. These baseline data will inform future studies focused on the cause and management of CAI. The finding that digitisation is an accurate way of recording the anatomy of FL and FB suggests that future dissection studies should integrate digitisation measurements, while continuing to refine this process, particularly for PA and PCSA.