General Structure and Interosseous Membrane
Throughout the forearm, the forearm fascia (fascia antebrachii) functions as a strong, dense "cuff." Deep connective tissue septa originate from its inner surface and attach directly to the crests of the radius and ulna.
Between these bones stretches the interosseous membrane of the forearm (membrana interossea antebrachii). Its structure includes the following key elements:
- Oblique cord (chorda obliqua) — an additional fibrous band reinforcing the union of the bones.
- Proximal aperture — allows the passage of vessels and nerves in the upper third of the forearm.
- Distal aperture — provides passage for neurovascular bundles in the lower third of the forearm.
Distal Fascia and Retinacula
Distally, as it transitions to the hand, the forearm fascia thickens significantly and forms specialized ligaments known as tendon retinacula. These are essential for preventing tendon displacement during muscle contraction.
- On the dorsal side: forms the extensor retinaculum (retinaculum extensorum).
- On the palmar side: forms the flexor retinaculum (retinaculum flexorum). This structure is also known as the transverse carpal ligament. It spans across the carpal bones to form the dense roof of the carpal tunnel, through which tendons and nerves pass.
Boundaries of Adjacent Spaces
When studying fascial compartments and the topography of the upper extremity, it is important to clearly understand the boundaries of connected anatomical regions (specifically, the axillary fossa, which transitions into the arm and forearm fascia).
According to classic descriptions, the following walls and boundaries are defined:
- Apex (aperture): located between the clavicle, the first rib, and the superior border of the scapula. Here, the cervicoaxillary canal (canalis cervicoaxillaris) is formed.
- Base: formed by skin, subcutaneous fat, and the axillary fascia.
- Anterior wall: formed by the pectoralis major and minor muscles, as well as the clavipectoral fascia.
- Posterior wall: includes the latissimus dorsi, teres major, and subscapularis muscles.
- Medial wall: formed by the serratus anterior muscle and the thoracic wall (ribs).
- Lateral wall: bounded by the intertubercular sulcus of the humerus (sulcus intertubercularis).