Biomechanics of Fracture Fixation — MCQs
Which of the following is false regarding clavicle?
Healing of bone is affected by:
False about fracture of vertebrae
The PRIMARY mechanisms that cause increased bone density (sclerosis) on X-ray include: a) Increased thickening of trabeculae b) Fracture & Collapse of cancellous bone c) Defective mineralization d) Myositis ossificans
What should be done as an immediate measure for ongoing bleeding in a patient with pelvic bone fracture?
During fixation of Bennett's fracture, which muscle hinders it
A 6-year-old child is suspected with supracondylar fracture of right hand, complaining of pain and swelling. X-ray of right elbow was not significant. What is the next best step in this case?
During fixation of Bennett's fracture, which muscle hinders it?
During fixation of Bennett's fracture, which muscle hinders it :
Locking compression plating is commonly indicated in which of the following fracture types?
Biomechanics of Fracture Fixation Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is false regarding clavicle?
- A. First bone to ossify
- B. Membranous ossification
- C. Fracture can be treated with figure of 8 bandage
- D. Non-union is the commonest complication of clavicle fractures (Correct Answer)
Explanation: ***Non-union is the commonest complication of clavicle fractures*** - While clavicle fractures are relatively common, **malunion** (healing in an imperfect position) is more frequent than non-union. - **Non-union** typically occurs in less than 5% of all clavicle fractures, making it a rare complication rather than the commonest. *First bone to ossify* - The clavicle is indeed the **first bone to ossify** in the human embryo, beginning around the 5th to 6th week of gestation. - This characteristic highlights its unique developmental pathway compared to most other bones. *Membranous ossification* - The clavicle develops primarily through **intramembranous ossification**, which involves direct ossification of mesenchymal tissue without a cartilaginous precursor. - It's one of the few bones in the body, along with some bones of the skull, that ossifies this way. *Fracture can be treated with figure of 8 bandage* - A **figure-of-eight bandage** was historically used for clavicle fractures to provide reduction and immobilization. - However, current evidence suggests that a **simple sling** is equally effective and often more comfortable, with less risk of complications like neurovascular compression.
Question 2: Healing of bone is affected by:
- A. Hypoxia
- B. Micromovement
- C. Muscle interposition
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Hypoxia**, **micromovement**, and **muscle interposition** are all factors known to impede or negatively affect the normal healing process of a bone fracture. - The successful healing of a bone fracture relies on a series of biological events that can be disrupted by these adverse conditions, leading to delayed union or non-union. *Hypoxia* - **Hypoxia**, or insufficient oxygen supply, impairs the metabolic activity of cells essential for bone healing, such as osteoblasts and chondrocytes. - It interferes with **angiogenesis**, the formation of new blood vessels, which is critical for delivering nutrients and oxygen to the healing bone. *Micromovement* - Excessive **micromovement** at the fracture site prevents the formation of a stable callus and can stimulate the development of fibrous tissue or cartilage instead of bone. - While some motion is beneficial, uncontrolled or excessive micromotion can lead to a **non-union** or pseudarthrosis, as it constantly disrupts the delicate tissue bridges attempting to form. *Muscle interposition* - **Muscle interposition** refers to muscle tissue becoming trapped between the bone fragments, physically separating them and preventing direct bone-to-bone contact. - This physical barrier inhibits the formation of the **fracture hematoma** and subsequent callus, thus mechanically hindering the healing process.
Question 3: False about fracture of vertebrae
- A. Fracture dislocation is common in flexion rotation injury
- B. Chance fracture occurs due to flexion distraction injury
- C. Wedge compression causes flexion injury
- D. Anterior longitudinal ligament runs along the posterior surface of vertebral bodies (Correct Answer)
Explanation: ***Anterior longitudinal ligament runs along the posterior surface of vertebral bodies*** - The **anterior longitudinal ligament (ALL)** runs along the **anterior aspect** of the vertebral bodies, preventing hyperextension. - The **posterior longitudinal ligament (PLL)** runs along the posterior surface of the vertebral bodies, within the vertebral canal. *Fracture dislocation is common in flexion rotation injury* - **Flexion-rotation injuries** are highly unstable and frequently lead to **fracture-dislocations** of the vertebral column. - The combined forces cause significant disruption of both bony and ligamentous structures, increasing the likelihood of displacement. *Chance fracture occurs due to flexion distraction injury* - A **Chance fracture** (or seatbelt fracture) is caused by a **flexion-distraction injury**, typically seen in individuals wearing lap belts during deceleration. - This mechanism results in a horizontal splitting of the vertebral body and posterior elements. *Wedge compression causes flexion injury* - A **wedge compression fracture** is the most common type of vertebral fracture and results from a **flexion injury** (hyperflexion). - The anterior portion of the vertebral body collapses, creating a wedge shape, while the posterior column remains intact.
Question 4: The PRIMARY mechanisms that cause increased bone density (sclerosis) on X-ray include: a) Increased thickening of trabeculae b) Fracture & Collapse of cancellous bone c) Defective mineralization d) Myositis ossificans
- A. ac
- B. ab (Correct Answer)
- C. bc
- D. ad
Explanation: ***ab*** - Increased **thickening of trabeculae** directly leads to more bone substance per unit volume, which appears as increased density or sclerosis on X-rays due to greater attenuation of radiation. - **Fracture and collapse of cancellous bone** results in impaction and compaction of bone tissue, increasing its density and thus appearing sclerotic on imaging. *ac* - While **increased thickening of trabeculae** contributes to sclerosis, **defective mineralization** (option c) actually leads to **osteomalacia** or **rickets**, characterized by **decreased bone density**, not increased density. *ad* - **Increased thickening of trabeculae** causes sclerosis. However, **myositis ossificans** (option d) involves the formation of ectopic bone within muscle tissue—a specific condition causing localized calcification/ossification outside the normal bone structure, not a primary mechanism for generalized bone density increase or sclerosis of existing bone. *bc* - **Fracture and collapse of cancellous bone** can contribute to sclerosis. However, **defective mineralization** (option c) would lead to **reduced bone density**, making this combination incorrect for explaining increased bone density.
Question 5: What should be done as an immediate measure for ongoing bleeding in a patient with pelvic bone fracture?
- A. Use Pelvic Binders (Correct Answer)
- B. Rapid blood transfusion
- C. External fixation
- D. Internal definitive fixation
Explanation: **Use Pelvic Binders** - **Pelvic binders** apply circumferential compression, which helps to stabilize the fracture and reduce the pelvic volume. - This mechanical stabilization significantly reduces ongoing hemorrhage from venous and bone surface bleeding in unstable pelvic fractures. *Rapid blood transfusion* - While critically important for managing **hemorrhagic shock**, blood transfusion alone does not address the source of ongoing bleeding. - It is a supportive measure, not an immediate means to stop the bleeding from an unstable pelvic fracture. *Internal definitive fixation* - **Internal definitive fixation** is a surgical procedure aimed at permanently stabilizing the fracture and would typically be performed after initial resuscitation and bleeding control. - It is not an immediate measure for **ongoing life-threatening hemorrhage** and carries procedural risks. *External fixation* - **External fixation** can stabilize an unstable pelvic fracture and helps in controlling bleeding, but applying a **pelvic binder** is a quicker and less invasive initial step. - External fixation is usually performed by a surgeon in a controlled environment, not as the very first immediate bedside measure to stop bleeding.
Question 6: During fixation of Bennett's fracture, which muscle hinders it
- A. Flexor pollicis longus
- B. Flexor pollicis brevis
- C. Extensor pollicis brevis
- D. Abductor pollicis longus (Correct Answer)
Explanation: ***Abductor pollicis longus*** - The **abductor pollicis longus (APL)** muscle attaches to the base of the first metacarpal and, due to its pull, causes the **proximal fragment of the metacarpal to subluxate dorsally and radially**, thus hindering reduction and fixation. - This muscle's action creates a **deforming force that pulls the metacarpal shaft proximally**, making it difficult to maintain reduction of the fracture. *Flexor pollicis longus* - The **flexor pollicis longus (FPL)** primarily flexes the **interphalangeal joint of the thumb** and does not exert a significant deforming force on the base of the first metacarpal in Bennett's fracture. - Its action does not directly hinder the reduction of the **fractured first metacarpal base**. *Flexor pollicis brevis* - The **flexor pollicis brevis (FPB)** flexes the **metacarpophalangeal joint of the thumb** and also does not directly pull on the fracture site to cause displacement. - Its fibers are mainly involved in **thumb flexion and opposition**, not in the displacement seen in Bennett's fracture. *Extensor pollicis brevis* - The **extensor pollicis brevis (EPB)** extends the **metacarpophalangeal joint of the thumb** and is involved in extending the thumb. - While it acts on the thumb, its pull is not the primary deforming force responsible for the characteristic displacement in **Bennett's fracture**.
Question 7: A 6-year-old child is suspected with supracondylar fracture of right hand, complaining of pain and swelling. X-ray of right elbow was not significant. What is the next best step in this case?
- A. Cast
- B. Closed reduction with K wire fixation
- C. Compare with X-ray of left hand (Correct Answer)
- D. Closed reduction and slab
Explanation: ***Compare with X-ray of left hand*** - In pediatric elbow injuries, a seemingly **normal X-ray** in the presence of strong clinical suspicion (pain, swelling, suspected supracondylar fracture) often warrants a comparison view of the contralateral unaffected limb. - This helps identify subtle findings like **epiphyseal separations** or **minimally displaced fractures** that might otherwise be missed due to the developing osseous structures in children. *Cast* - Applying a cast without definitive diagnosis or clear radiographic evidence of a fracture can lead to **unnecessary immobilization** and potential complications if no fracture is present, or inadequate treatment if a specific type of fracture requires reduction. - While immobilization is appropriate for confirmed fractures, it's not the **initial diagnostic step** when X-rays are inconclusive. *Closed reduction with K wire fixation* - This is an **invasive procedure** reserved for **displaced or unstable fractures** after a clear diagnosis has been established. - Performing this without a confirmed and characterized fracture is inappropriate and carries risks of **iatrogenic injury** and complications. *Closed reduction and slab* - Similar to casting, this is a treatment for **confirmed fractures**, typically for acute, stable, or minimally displaced fractures that can be managed non-surgically after a reduction. - It is not a diagnostic step and should not be performed when initial imaging is **inconclusive** and the exact nature of the injury is unknown.
Question 8: During fixation of Bennett's fracture, which muscle hinders it?
- A. Flexor pollicis brevis
- B. Extensor pollicis brevis
- C. Abductor pollicis longus (Correct Answer)
- D. Flexor pollicis longus
Explanation: ***Abductor pollicis longus*** - In a Bennett's fracture, the **first metacarpal base** dislocates radially and proximally due to the pull of the **abductor pollicis longus** muscle. - This muscle inserts onto the base of the first metacarpal and is the primary deforming force that makes reduction and fixation challenging. *Flexor pollicis brevis* - This muscle primarily flexes and medially rotates the **thumb's metacarpophalangeal joint**. - While it contributes to thumb movement, its insertion and action do not directly create the deforming force characteristic of a Bennett's fracture. *Extensor pollicis brevis* - This muscle extends the **metacarpophalangeal joint** of the thumb. - Its action is primarily on the dorsal aspect of the thumb and does not contribute to the radial and proximal displacement seen in a Bennett's fracture. *Flexor pollicis longus* - This muscle is responsible for **flexing the interphalangeal joint** of the thumb. - Its tendon passes through the carpal tunnel and inserts on the distal phalanx, thus not directly implicated in the deforming forces at the metacarpal base in Bennett's fracture.
Question 9: During fixation of Bennett's fracture, which muscle hinders it :
- A. Flexor pollicis longus
- B. Flexor pollicis brevis
- C. Extensor pollicis brevis
- D. Abductor pollicis longus (Correct Answer)
Explanation: ***Abductor pollicis longus*** - The **abductor pollicis longus (APL)** attaches to the base of the first metacarpal and its **traction** causes the characteristic **proximal and radial displacement** of the fractured fragment in Bennett's fracture. - This muscle's pull makes manual reduction difficult to maintain, often necessitating surgical fixation with **K-wires** to stabilize the fracture. *Flexor pollicis longus* - The **flexor pollicis longus (FPL)** primarily flexes the **interphalangeal joint of the thumb** and does not directly attach to the base of the first metacarpal to cause fracture displacement. - While it contributes to thumb movement, its line of pull does not exert significant displacing force on the **Bennett's fracture fragment**. *Flexor pollicis brevis* - The **flexor pollicis brevis (FPB)** flexes the **metacarpophalangeal joint** of the thumb and is located more distally, not directly influencing the fracture displacement at the base of the metacarpal. - Its action is mainly on the phalanx, not the significant displacement of the **metacarpal base fragment**. *Extensor pollicis brevis* - The **extensor pollicis brevis (EPB)** extends the **metacarpophalangeal joint** of the thumb and runs along the dorsal aspect of the thumb. - Its attachment and action are primarily antagonistic to flexion and do not contribute to the typical **proximal and radial displacement** seen in Bennett's fracture.
Question 10: Locking compression plating is commonly indicated in which of the following fracture types?
- A. Periaicular fractures
- B. Transverse or oblique fractures of long bones (Correct Answer)
- C. Interochanteric fractures
- D. Fracture of long bones
Explanation: ***Transverse or oblique fractures of long bones*** - **Locking compression plates (LCPs)** are particularly well-suited for **transverse or oblique fractures of long bones** because they provide angular stability, preventing screw pullout even in compromised bone. - Their design allows for a **fixed-angle construct**, which helps maintain alignment and promotes biological healing by minimizing periosteal stripping. *Periaicular fractures* - While LCPs can be used in some **periarticular fractures**, their primary indication is not specifically these fractures, and their benefit is often related to the bone quality of the metaphysis rather than the articulation itself. - These fractures often require careful contouring of plates to conform to the complex anatomy, and sometimes require different fixation strategies. *Interochanteric fractures* - **Intertrochanteric fractures** of the femur are typically treated with intramedullary nails (e.g., trochanteric entry nails) or dynamic hip screws, which are better suited for load-sharing in this weight-bearing region. - Plates, especially LCPs, are generally not the first-line treatment for these fractures due to the high biomechanical forces and risk of cutout. *Fracture of long bones* - This option is too general; while LCPs are used for some **long bone fractures**, it is not indicated for all types. Many long bone fractures are better treated with intramedullary nailing or traditional non-locked plating. - The specific fracture pattern (e.g., comminuted, transverse, oblique) and location within the long bone determine the most appropriate fixation method.
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