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Anatomy of the Limbs

Anatomy of the Limbs

LCRS Year 2

Anil Chopra

Contents

1Limbs 1a - Bone Growth, organisation and repair

6Limbs 1b - Overview of Anatomy of Upper and Lower Limbs

10Limbs 2 Shoulder and Arm

24Limbs 3 Elbow, Forearm and Wrist

33Limbs 4 Hand

42Limbs 5 Brachial Plexus

44Limbs 6 - Hip, Buttock and Thigh

58Limbs 7 Knee, Popliteal Fossa, Leg and Foot

74Limbs 8 - Lower limb Nerves and Vessels

Limbs 1a - Bone Growth, organisation and repairAnil Chopra1 Outline the process of longitudinal growth of long bones making appropriate use of the following terms: cartilage model; primary ossification centre; diaphysis; secondary ossification centre; epiphysis; epiphyseal plate; calcification; vascularisation; ossification

2 Suggest possible advantages of epiphyseal growth over simple appositional growth at the bone extremities.

3 Suggest reasonable dates for the appearance of primary and secondary centres of ossification for long bones.

4 Recognise ossification centres in radiographs of growing limbs and use this information to estimate the age of a child.

5 Explain how bones grow in diameter and are remodelled.

6 Describe the sequence of events in the repair of a fracture.

7 List the main risk factors for fracture of the femoral neck.

8 Identify anatomical and other factors that may compromise satisfactory repair of fractures of the femoral neck.

9 Explain the principles of management of simple fractures of limb bones.

10 List the main dangers of limb fractures and of their mismanagement.

Functions of Bone: support

storage of minerals

protection

levers for movement site of blood cell productionTypes of Bone:

Woven immature, in growing skeletons or in fractures. Weaker and more flexible than lamellar bone.Lamellar - mature, in normal skeletons. There are two types (usually arranged as layers compact on the outside and cancellous on the inside): Cortical (compact): 80% of skeleton, high resistance to torsion and bending. Normally on the outside of the lamellar bone. Here the functional unit is the Haversian system, which has osteocytes round the outside and a Haversian canal on the inside. They are arranged into concentric layers of matrix called lamellae. Cancellous (trabecular): less dense, spicules of marrow in between; has high turnover rate. Normally on the inside of the lamellar bone. There are no lamellae in cancellous bone, only a network of rods called trabeculae.Adaptability in Bone: Can grow without compromising its support functions redundancy

Increases or decreases bulk and density in response to pattern of use

Can alter its shape both internally and externally in response to the pattern of use remodelling

Can repair when fractured

Cells in BoneOsteocytes: mature bone cells that lie within a lacunae (each lacunae contains one osteocyte). The lacunae are connected by canaliculi. Their role is to maintain bone matrix and repair bone. When bone is damaged, osteocytes are no longer bound to the lacunae and so they differentiate into osteoblasts and osteoprogenitor cells.Osteoblasts: produce bone matrix. They eventually become osteocytes.

Osteoprogenitor cells: stem cells that differentiate into osteoblasts. Involved in fracture and repair.Osteoclasts: (giant cells) remove bone matrix. They are derived from monocytes. This results in a constant turnover of bone matrix with the osteoblasts producing bone and the osteoclasts removing bone. This is known as remodelling and occurs as a result of different physical stresses put on the bone. Around 20% of the adult skeleton is remodelled each year.Bone Matrix

The combination of substances in the bone matrix gives bone its mechanical properties. It consists of:

Collagen fibres: strong, flexible, good at resisting tension, twisting, bending, and provide a lattice for the hydroxyapatite crystals. They are not good for resisting compression.

Inorganic Ions: mainly calcium phosphate, calcium hydroxyapatite, and calcium hydroxide. The calcium phosphate crystals are hard but inflexible and brittle but good at resisting compression. PeriosteumThe periosteum is a thin layer of dense, irregular connective tissue membrane that covers the outer surface of a bone in all places except at joints. The outer layer is fibrous and the inner layer is cellular. Its job is to protect the bone from the surrounding tissues and also allows blood vessels and nerves into the bone. It is also very important for growth and repair.Endosteum

The endosteum is a thin layer of connective tissue which lines the surface of the bony tissue that forms the medullary cavity (or marrow cavity) of long bones. It is very active in bone growth and repair. Blood Supply in Bones

Periostial Arteries: enter bone via the periosteum. Stripping the periostium in a fracture can result in disruption of the blood supply from the bone and can also lead to bone infection and death.Nutrient Arteries: enters near the middle of the bone, passing obliquely through the cortical bone and supplies the cancellous bone. Metaphyseal and epiphyseal arteries: supply the ends of the bones. These are only present in a growing skeleton.

Nerve Supply to BonesThe periosteum that surrounds bone is richly innervated with sensory (pain and proprioception) fibres. The blood vessels going to bone also have sympathetic supply.Growth of BonesBones grow from the 6th week of foetal life until 25 years of age. They grow via two different processes:Intramembranous OssificationThis forms directly from the mesenchyme, an embryonic connective tissue. It occurs mainly in bones that are directly beneath the skin e.g. skull, mandible and clavicle. It occurs as follows: Mesenchymal cells produce bone matrix (osteoid) containing collagen. Osteoid becomes mineralised with calcium salts.

Cells in the mesenchyme differentiate into osteoblasts.

These produce more matrix.

Some osteoblasts get trapped in lacunae and become osteocytes.

Blood vessels grow and maintain blood metabolism.

This forms cancellous bone

The cancellous bone eventually remodels into cortical bone.

Periosteum forms around the bone and traps the surface layer of osteoblasts

Endrochondral OssificationMost long bones ossify in this way and it involves the mesenchymal cells forming cartilage and then the cartilage ossifying. This allows them to support large forces while growing: Mesenchymal cells differentiate into chondroblasts (cells which form cartilage). These chondroblasts make cartilage models of the bone which expand by expansion of the cartilage matrix. In the middle of the bone the chondrocytes die as the cartilage is increasingly calcified and capillaries from the periosteum penetrate to the centre forming a periosteal bud. This differentiates into osteoblasts and forms a primary ossification centre. This grows outwards forming a diaphysis. Appositional growth increases the diameter of the diaphysis. Secondary ossification centres form at the epiphyses (ends) of the bone, usually around 2 years after birth. The area between the diaphysis and the epiphyses is the epiphyseal plate.

The bone grows by adding at each epiphysis and only stops when the epiphyses meet the diaphysis. This growth stops at puberty (increased hormone levels stop growth)

NB: calcification is not the same as ossification, ossification is vascular, calcification is not. Growth in bone diameter:

Apposition addition to the exterior of the periosteum

Osteoblasts and osteoclasts produce ridges and grooves on bone surface

Blood vessels align in grooves

Osteoblasts build new osteons around blood vessels

Osteoclasts remove bone from endosteal surfaceFracture Repair1) When bones are damaged, the vessels rupture producing a vessel haematoma.2) Active osteoblasts and osteoprogenitor cells migrate toward the fracture.3) They form a type bone and cartilage called external callus which bridges the ends of the bones and internal callus which forms between the bone ends. 4) Chondrocytes produce cartilage, which is calcified to woven bone and then cancellous bone, which eventually remodels into cortical bone (via osteoblasts and osteoclasts). Bone Remodelling:

Bone is not dead, it is continually remodelling

Process of remodelling mirrors bone growth and repair after fracture

It is affected by physical stresses placed on the bone and metabolic and hormonal factors

20% of the adult skeleton is remodelled every year

Limbs 1b - Overview of Anatomy of Upper and Lower Limbs

Anil Chopra

1 Explain briefly the embryological development of the limbs

2 Outline briefly the similarities and differences in the upper and lower limbs

3 Explain briefly the difference between the segmental and peripheral nerve supply of a limb

4 Describe the essential structure of the upper and lower limbs, noting the compartmentalised nature of the limbs and their neurovascular supply

5 Outline the muscular compartments of the upper limb

6 Describe the neurovascular patterns of the upper limb

7 Outline the muscular compartments of the lower limb

8 Describe the neurovascular patterns of the lower limb

9 Explain the neurological components of neurological supply to a limb: motor, sensory, reflex, autonomic and trophic

10 Describe a method whereby the neurological features of nerve injury can be evaluated using the pattern described above.

Embryology of the LimbsThe limbs grow out of the trunk along with the nerves that are going to supply them (C5-T1 for the arms