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/PELVIC GIRDLE AND LOWER LIMB/SKIN, FASCIA AND SOFT TISSUES

Section 9 – PELVIC GIRDLE AND LOWER LIMB

CHAPTER 79 – Pelvic girdle and lower limb: overview and surface anatomy

This chapter is made up of two sections. The first is an overview of the general organization of the lower limb, with particular emphasis on the fascial skeleton, distribution of the major blood vessels and lymphatic channels, and the branches of the lumbar and sacral plexuses: it is intended to complement the detailed regional anatomy described in Chapters 80 to 84 Chapter 81 Chapter 82 Chapter 83 Chapter 84. The second section describes the surface anatomy of the lower limb.

The structure of the lower limb is determined by its adaptations for weightbearing, locomotion and the maintenance of equilibrium (stability). Indeed, the adaptations for weightbearing and for stability, and the differing developmental histories of the limbs account for the major structural and functional differences between the upper and lower limbs. The inguinal (pelvicrural) and gluteal (buttock) regions are important anatomical junctional zones between the trunk and the lower limb through which longitudinally running nerves and vessels may pass in either direction. The inguinal region includes the junctional zones between the limb and abdominal cavity via the myopectineal orifice (the gap between the inguinal ligament and hip bone), and between the limb and pelvic cavity via the obturator foramen. The gluteal region includes the junctional zones between the limb and the abdominopelvic cavity via the greater sciatic foramen, and between the limb and the perineum via the lesser sciatic foramen (Fig. 79.1).

  

Fig. 79.1  Gateways from the abdomen, pelvis and perineum to the lower limb.
(From Drake, Vogl and Mitchell 2005.)

SKIN, FASCIA AND SOFT TISSUES

In the young adult the skin of the lower limb is generally stronger and thicker than that of the upper limb: weightbearing skin, e.g. of the sole of the foot, is particularly thickened. The skin of the buttocks and posterior thigh bears weight in the sitting position, and consequently is relatively thick. The skin over the anteromedial aspect of the lower leg is particularly fragile and vulnerable in the elderly. Body hair is usually well developed in all areas except the sole and posterior ankle.

Fascial skeleton

The ‘fascial skeleton’ (deep fascia) of the lower limb is well-defined and forms a tough circumferential ‘stocking-like’ structure that constrains the musculature (Fig. 79.2). Septa pass from the deep surface of this fascial sheath to the bones within, confining the functional muscle groups within osteofascial compartments. The tough fascia gives additional areas of attachment to the muscles and ensures that they work to maximal effect. Thickenings in the ensheathing layer may act as additional tendons (e.g. iliotibial tract). Elsewhere, thickenings in the fascial skeleton form fibrous retinacula where tendons cross joints. Although they are particularly prominent in the embalmed cadaver, these fascial layers are also readily demonstrable in the living, and are of considerable functional significance. The pattern of soft-tissue organization has a bearing on the physiological effects of the muscles and is crucial for efficient venous return from the limb. The fascial planes also control and direct the spread of pathological fluids (blood, pus) within the limb and play an important part in determining the degree and direction of displacement seen in long bone fractures.

  

Fig. 79.2  Deep fascia of the lower limb. A, Anterior view. B, Posterior view.
(From Sobotta 2006.)

Fasciocutaneous system

The fascial septa dictate the pathways of cutaneous arteries, which subsequently perforate and ramify on the fascial ‘stocking’ before supplying the skin.

Osteofascial compartments in the lower limb

The muscles of the thigh may be grouped into three compartments according to their function, namely anterior (extensor), posterior (flexor) and medial (adductor): only the anterior and posterior compartments possess distinct fascial boundaries. A very definite fascial separation into anterior (extensor), posterior (flexor) and lateral (evertor) compartments exists in the leg, and compartment syndrome is most common in this region (see below). Osteofascial compartments in the foot are described in Chapter 84.

Vessels and nerves run through all the osteofascial compartments and supply the muscles contained within them. The muscles acting within these closed compartments assist in maintaining the anti-gravity flow of venous blood.

Compartment syndrome

The fascial boundaries that limit the osteofascial compartments are largely inelastic, which means that any condition that leads to an increase in the volume of the compartmental contents, e.g. muscle swelling caused by trauma or unaccustomed overuse, haemorrhage and local infection, is likely to cause an increase in intracompartmental pressure. If unrelieved, this increased pressure will lead to compressive occlusion of the vessels in the compartment and consequent ischaemic damage to the nerves and muscles of the compartment, a phenomenon known as compartment syndrome.

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