Fascial topography of the posterior forearm
In the posterior region of the forearm, the muscle mass is divided into two main levels: the first (superficial) and the second (deep) layers. The delimitation of these layers is provided by dense fascial sheets. Topographically, the fasciae are distributed as follows: one sheet lines the deep (anterior) surface of the muscles of the first layer, while the second sheet covers the superficial (posterior) surface of the muscles of the second layer.
A slit-like fascial space is formed between the indicated fascial sheets. The main contents of this intermuscular space are the neurovascular bundle, which passes in transit, being protected by fascial sheaths on both sides.
Scapula and subscapular space
The subscapularis muscle (m. subscapularis) occupies the anterior surface of the scapula. It is located in an isolated osteofascial compartment formed by the fusion of the subscapular fascia with the bone margins of the scapula.
The tendon of this muscle extends into the subdeltoid space and attaches to the lesser tubercle of the humerus. On its way to the insertion site, the tendon lies closely against the anterior aspect of the capsule of the shoulder joint. Directly beneath the tendon lies a large synovial bursa (bursa synovialis subscapularis). It is important to remember that this bursa continuously communicates with the cavity of the shoulder joint capsule.
Along with its fascia, m. subscapularis performs an important topographic function:
- Forms the posterior wall of the axillary fossa.
- Forms the posterior wall of the prescapular fascial space (which serves as the dorsal continuation of the axillary space). The anterior wall of this space is formed by the serratus anterior muscle (m. serratus anterior), covered by its own thoracic fascia (fascia thoracica).
Deep muscle layer of the gluteal region
The muscles of the deep layer of the gluteal region are concealed beneath the muscle mass of the middle layer. Two key structures are distinguished in this layer:
- Gluteus minimus muscle (m. gluteus minimus). Occupies the superior position. Originates from the external surface of the iliac wing. Topographically, it is completely overlapped by the gluteus medius muscle. Both of these muscles are enclosed in a single enclosed osteofibrous fascial space.
- Obturator externus muscle (m. obturatorius externus). Located in the inferior section. Originates from the outer surface of the circumference of the obturator foramen and obturator membrane. The muscle curves around the hip joint inferiorly, extends posteriorly into the gluteal region, and attaches to the trochanteric fossa (fossa trochanterica).
Fascial spaces of the gluteal region
Knowledge of the fascial spaces of the gluteal region is essential for understanding the pathways of purulent infection spread.
Subgluteal fascial space An extensive zone between the gluteus maximus muscle and the muscles of the middle layer. Boundaries of the space:
- Anterior wall: fascia covering the muscles of the middle layer.
- Posterior wall: deep layer of the own fascia of the gluteus maximus muscle.
- Superiorly: the space is closed due to the attachment of the own fascia to the iliac crest.
- Internally (medially): the space is closed by the line of attachment of the fascia to the sacrum and coccyx.
The subgluteal space contains all major neurovascular bundles emerging through the suprapiriform and infrapiriform foramina.
Osteofibrous space of the gluteus medius and minimus muscles The gluteus minimus muscle is completely covered by the gluteus medius, and together they are enclosed in an isolated osteofibrous sheath. The closed nature of this space causes high tissue pressure during purulent processes, which leads to an extremely severe clinical course of phlegmons in this localization.
To memorize the boundaries of the subgluteal space, imagine a "pocket": the posterior wall is the fascia of the gluteus maximus muscle (the outer side of the pocket), the anterior is the fascia of the middle layer (the bottom), and superiorly and medially the pocket is tightly sewn to the bones (iliac crest, sacrum, and coccyx).
Class and exam questions
Where does the neurovascular bundle run on the posterior surface of the forearm?
It is located in the fascial space between the first (superficial) and second (deep) muscle layers, positioned between their fascial linings.
What does the synovial bursa of the subscapularis muscle communicate with?
The subscapular bursa (bursa synovialis subscapularis) continuously communicates with the cavity of the shoulder joint capsule.
Why do deep gluteal space phlegmons have a severe clinical course?
The gluteus minimus and medius muscles are enclosed in an absolutely closed osteofibrous space. In purulent inflammation, the exudate has nowhere to escape, causing a sharp rise in pressure and severe intoxication.
What forms the anterior wall of the prescapular fascial space?
The anterior wall is formed by the serratus anterior muscle (m. serratus anterior), which is covered by its own thoracic fascia (fascia thoracica).
What else to study on this topic
- Topography of the supra- and infrapiriform foramina of the pelvis
- Course and branching of the neurovascular bundles of the gluteal region
- Boundaries and contents of the axillary fossa
- Topography of the subdeltoid cellular space
- Fascial compartments of the anterior forearm
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