arm pathology

Five Stages of Fracture Healing

  • Stage 1: Haematoma Formation

    • Mechanism: A fracture results in the breaking of blood vessels crossing the fracture line. This leads to bleeding in the fractured bone, the medullary cavity, and the periosteum.

    • Timing: A fracture haematoma, or blood clot, forms between the ends of the bone fragments, in the medullary cavity, and under the periosteum approximately 6−86 - 8 hours after the fracture occurs.

    • Necrosis: Bone and periosteal cells die at the fracture site because torn blood vessels are unable to deliver nutrients to that specific area of the bone.

    • Fibrin Network: The haematoma serves as a fibrin network that facilitates two critical processes:

      • Angiogenesis (formation of new blood vessels).

      • Invasion of cells.

  • Stage 2: Cellular Proliferation and Inflammation

    • Inflammatory Response: This stage involves an influx of inflammatory cells and cellular invasion.

    • Cell types: Neutrophils and macrophages arrive at the site.

    • Phagocytic Activity: An influx of phagocytic cells removes debris from the fracture site.

    • Cytokines and Growth Factors involved in the Inflammation/Granulation Tissue stage:

      • Platelets: Release IL−1IL-1, IL−6IL-6, TNF−αTNF-α, FDGFFDGF, and TGF−BTGF-B.

      • Neutrophils: Release IL−1IL-1, IL−6IL-6, IL−10IL-10, TNF−aTNF-a, MCP−1MCP-1, MIP−1MIP-1, and CXCL−1aCXCL-1a.

      • Macrophages: Release IL−1IL-1, IL−6IL-6, IL−10IL-10, TNF−aTNF-a, MIP−1MIP-1, MCP−1MCP-1, TGF−BTGF-B, BMP−2BMP-2, and VEGFVEGF.

    • Involved Cells: Mesenchymal Stem Cells (MSCs), NK Cells, and the formation of capillary buds.

  • Stage 3: Callus Formation

    • Differentiation: Mesenchymal stem cells differentiate into chondrocytes and fibroblasts.

    • Product: These cells produce a fibrocartilaginous callus, also known as a procallus. This stage consists of cartilage and osteoid.

    • Duration: This stage lasts approximately 33 weeks.

    • Immune Interaction: T-Lymphocytes are active here, releasing TNF−aTNF-a, IFN−YIFN-Y, CXCL−7CXCL-7, RANKLRANKL, and IL−17IL-17.

  • Stage 4: Ossification

    • Bone Deposition: Osteoblasts invade the area and deposit new bone tissue.

    • Replacement: The fibrocartilaginous callus is mineralized and replaced with woven bone (primary bone).

    • Duration: This stage lasts up to approximately 66 weeks.

    • Immune Interaction: B-Lymphocytes release IL−17IL-17 and OPGOPG.

  • Stage 5: Remodelling

    • Process: Cellular proliferation decreases. Osteoclasts dissolve excess bone tissue to smooth out irregularities and reorganize the bone.

    • Bone Types: Osteoblasts lay down lamellar bone.

    • Structural Alignment: The reorganization of newly formed bone occurs along the lines of mechanical stress.

    • Cycles: Continuous cycles of resorption and formation occur until the bone regains its normal appearance.

    • Duration: Remodelling can take months to years.

Supracondylar Fracture

  • Epidemiology and Mechanism: This fracture is common in children, typically occurring around 6−76-7 years of age. It is often caused by a Fall On Outstretched Hand (FOOSH).

  • Anatomy:

    • Typically extra-articular in children, involving the thin bone between the coronoid fossa and the olecranon fossa.

    • In adults, these fractures may be intra-articular.

    • The fracture line usually angles from an anterior distal point to a posterior proximal site.

  • Gartland Classification:

    • Type I: Undisplaced fracture.

    • Type II: Displaced fracture with an intact posterior cortex. This may (Type IIb) or may not (Type IIa) include a rotational deformity.

    • Type III: Characterized by complete displacement.

  • Complications:

    • Malunion or misalignment (such as cubitus varus).

    • Volkmann’s contracture.

    • Nerve damage.

Humeral Shaft Fracture

  • Mechanisms and Fracture Patterns:

    • Bending Force: Produces a transverse fracture of the shaft.

    • Torsion Force: Results in a spiral fracture.

    • Bending + Torsion: Leads to an oblique fracture, which may or may not include a butterfly fragment.

    • Compression Forces: Typically fracture either the proximal or distal ends of the bone.

  • Specific Types:

    • Short Oblique Fractures: Displaced fractures through the distal shaft are difficult to reduce and maintain in a reduced position. These may be associated with delayed healing.

    • Long Spiral Fractures: These include spiral, comminuted, and oblique fractures, which tend to heal rapidly.

  • Potential Issues:

    • Muscle Interposition: If a displaced fracture has a gap that does not close when rotational alignment is restored, muscle tissue may be trapped between fragments.

    • Atrophic Nonunion: If there is good alignment but a significant gap remains between fracture fragments, the injury will likely develop into an atrophic nonunion.

Proximal Humeral Fracture

  • Anatomical Neck Fracture:

    • The fracture plane passes through the anatomical neck rather than the surgical neck.

    • Significant chondral defects and minimally separated fragments may not be visible on plain films.

    • There is a much higher incidence of Avascular Necrosis (AVN) compared to surgical neck fractures.

    • Even if soft tissue is detached from the humeral head, undisturbed blood supply transmitted through the tuberosities may prevent osteonecrosis of the articular segment.

  • Surgical Neck Fracture:

    • The most common type of fracture of the proximal humerus.

    • It is extracapsular and usually maintains an adequate blood supply, resulting in a relatively low incidence of AVN.

    • Deformity: The upper fragment is usually abducted and externally rotated by muscles inserting onto the greater tubercle. The lower fragment is adducted and internally rotated by the internal rotator muscles.

  • Greater Tuberosity (GT) Fractures:

    • Commonly associated with anterior shoulder dislocations.

    • Isolated, displaced GT fractures account for less than 2%2\% of proximal humeral fractures.

    • Displaced fractures of the GT are associated with longitudinal rotator cuff tears.

  • Hill-Sachs Lesion:

    • The magnitude of a fracture defect in the humeral head can be over-estimated if a Hill-Sachs lesion is present but unrecognized.

    • Definition: A fracture in the posterolateral head of the humerus caused by impaction against the glenoid rim.