Properties of the two neuromuscular compartments in a split bipennate muscle

Architectural properties of the neuromuscular compartments in selected forearm skeletal muscles

The purposes f this study were to (i) explore the possibility of splitting the selected forearm muscles into separate compartments in human subjects; (ii) quantify the architectural properties of each neuromuscular compartment; and (iii) discuss the implication of these properties in split tendon transfer procedures. Twenty upper limbs from 10 fresh human cadavers were used in this study. Ten limbs of five cadavers were used for intramuscular nerve study by modified Sihler's staining technique, which confirmed the neuromuscular compartments. The other 10 limbs were included for architectural analysis of neuromuscular compartments. The architectural features of the compartments including muscle weight, muscle length, fiber length, pennation angle, and sarcomere length were determined. Physiological cross-sectional area and fiber length/muscle length ratio were calculated. Five of the selected forearm muscles were ideal candidates for splitting, including flexor carpi ulnaris, flexor carpi radials, extensor carpi radialis brevis, extensor carpi ulnaris and pronator teres. The humeral head of pronator teres contained the longest fiber length (6.23 ± 0.31 cm), and the radial compartment of extensor carpi ulnaris contained the shortest (2.90 ± 0.28 cm). The ulnar compartment of flexor carpi ulnaris had the largest physiological cross-sectional area (5.17 ± 0.59 cm(2)), and the ulnar head of pronator teres had the smallest (0.67 ± 0.06 cm(2)). Fiber length/muscle length ratios of the neuromuscular compartments were relatively low (average 0.27 ± 0.09, range 0.18-0.39) except for the ulnar head of pronator teres, which had the highest one (0.72 ± 0.05). Using modified Sihler's technique, this research demonstrated that each compartment of these selected forearm muscles has its own neurovascular supply after being split along its central tendon. Data of the architectural properties of each neuromuscular compartment provide insight into the 'design' of their functional capability. In addition to improving our understanding of muscle anatomy and function, elucidation of forearm neuromuscular compartments architecture may ultimately provide information useful for selection of muscle subdivisions used in tendon transfer.

The architecture and contraction time of intrinsic foot muscles

Although critical for effective human locomotion and posture, little data exists regarding the segmentation, architecture and contraction time of the human intrinsic foot muscles. To address this issue, the Abductor Hallucis (AH), Abductor Digiti Minimi (ADM), Flexor Digitorum Brevis (FDB) and Extensor Digitorum Brevis (EDB) were investigated utilizing a cadaveric dissection and a non-invasive whole muscle mechanomyographic (wMMG) technique. The segmental structure and architecture of formaldehyde-fixed foot specimens were determined in nine cadavers aged 60-80 years. The wMMG technique was used to determine the contraction time (Tc) of individual muscle segments, within each intrinsic foot muscle, in 12 volunteers of both genders aged between 19 and 24 years. While the pattern of segmentation and segmental -architecture (e.g. fibre length) and -Tc of individual muscle segments within the same muscle were similar, they varied between muscles. Also, the average whole muscle Tc of FDB was significantly (p < 0.05) shorter (faster) (Tc = 58 ms) than in all other foot muscles investigated (ADM Tc = 72 ms, EDB Tc = 72 ms and ABH Tc = 69 ms). The results suggest that the architecture and contraction time of the FDB reflect its unique direct contribution, through toe flexion, to postural stability and the rapid development of ground reaction forces during forceful activities such as running and jumping.

Posterior elbow coverage using whole and split flexor carpi ulnaris flaps: a cadaveric study

PURPOSE

The purpose of this study is to evaluate the coverage patterns of whole and split flexor carpi ulnaris (FCU) pedicle muscle flaps for posterior elbow soft-tissue defects.

METHODS

Seventeen fresh-frozen cadaveric upper extremities were used. The whole FCU was raised to the dominant vascular pedicle and transposed proximally over the olecranon. The widths of coverage at 2-cm distances about the posterior elbow were measured. Widths were also measured after making 3 longitudinal cuts in the fascia and after suturing the muscle to adjacent soft tissue under tension. The FCU was also split into its ulnar and humeral heads along the central tendon. The larger ulnar head was transposed and the widths again measured. Mid-forearm circumference, elbow circumference, and ulnar length were assessed for ability to predict flap width.

RESULTS

The whole muscle under no tension provided an average of 2.7 cm width coverage at the tip of the olecranon process. Cutting the fascia provided approximately 15% additional width and suturing the muscle to the surrounding soft tissue an additional 25%, to approximately 4 cm. The isolated FCU ulnar head provided approximately 75% of the width of the entire muscle. Mid-forearm circumference was the most predictive of flap width, and divisors were generated that improved the accuracy of predicting the width for outlier specimens. The dominant pedicle was a consistent distance relative to the end of the central tendon and the olecranon tip.

CONCLUSIONS

The whole and split FCU pedicle flaps provide predictable coverage for 2- to 4-cm posterior elbow soft-tissue defects. For especially large and small arms, the divisors improve accuracy in predicting flap width. Consistent locations of the olecranon tip and the end of the central tendon in relation to the dominant pedicle make them useful surgical landmarks.