Orthopedic Biomechanics Practice Questions

Q: What is the primary mechanism of fixation provided by an intramedullary K nail (Kirschner wire) in orthopedic surgery?

Three-point fixation. ***Three-point fixation*** - Intramedullary K nails utilize **three-point fixation** by engaging two points of contact in the wider metaphyseal bone and one point at the apex of the fracture. - This mechanism allows the nail to be inserted into the medullary canal and act as an internal splint, providing stability against bending and shear forces. *Two-point fixation* - **Two-point fixation** is generally insufficient for long-bone fractures, as it only resists bending in one plane and offers limited rotational stability. - While intramedullary nails have two main points of contact at the ends, the additional contact at the fracture site creates a three-point system for enhanced stability. *Compression* - While some intramedullary nails can provide **compression** through dynamization or specific locking mechanisms, this is not their primary or inherent mechanism of fixation as a simple K nail. - Compression is more typically achieved with plates, screws, or external fixators directly apposing fracture fragments. *Weight concentration* - **Weight concentration** is not a biomechanical principle of fracture fixation; rather, it refers to the distribution of forces over a surface. - Intramedullary nails aim to redistribute forces and provide structural support, but not primarily by "weight concentration."

Q: What is the shape of the indenter used in the Knoop hardness test?

Rhomboid. ***Rhomboid*** - The Knoop indenter is designed with a **rhombic-based pyramidal shape**, which creates an elongated, diamond-shaped indentation. - This specific shape allows for a more precise measurement of hardness in brittle materials or thin layers by minimizing damage to the surrounding material. *Square* - A square indenter is characteristic of the **Vickers hardness test**, not the Knoop test. - The Vickers test produces a square indentation and is commonly used for a wide range of materials due to its versatility. *Oval* - An oval shape is not typically used for standard microhardness testing indenters. - Hardness testing indenters generally have pyramidal or conical shapes to provide distinct, measurable impressions. *Diamond* - While the Knoop indenter is made of diamond material, its actual shape is **rhomboid** (elongated pyramid), not a simple diamond cut. - The term "diamond" on its own is ambiguous as various hardness tests use diamond indenters of different shapes.

Q: Trendelenburg's sign is positive in injury to which structure?

Gluteus medius. ***Gluteus medius*** - A positive **Trendelenburg's sign** indicates weakness or paralysis of the **gluteus medius** muscle, or problem with its innervation or hip joint. - This muscle is crucial for **abduction** and **stabilization** of the pelvis during gait; its dysfunction causes the unsupported side of the pelvis to drop. *Gluteus maximus* - The **gluteus maximus** is primarily involved in **hip extension** and external rotation, not hip abduction or pelvic stability during single-leg stance. - Weakness in this muscle would manifest more as difficulty with climbing stairs or rising from a seated position. *Quadriceps femoris* - The **quadriceps femoris** muscles are responsible for **knee extension**, essential for walking and standing. - Injury to these muscles would primarily affect the ability to **straighten the leg** and bear weight on it, not cause pelvic drop. *Quadratus lumborum* - The **quadratus lumborum** is a deep abdominal muscle involved in **lateral flexion of the trunk** and stabilization of the lumbar spine. - Dysfunction of this muscle would lead to **trunk instability** or pain, but not the specific pelvic drop seen in Trendelenburg's sign.

Q: What deformity is likely to occur following the removal of the head of the radius?

Valgus deformity. ***Valgus deformity*** - Removal of the **radial head** destabilizes the **elbow joint**, particularly affecting its resistance to **valgus stress**. - Without the radial head, the **ulna** may deviate laterally relative to the humerus, leading to a **valgus angulation**. *Varus deformity* - A varus deformity involves medial deviation of the forearm, which typically results from injuries or conditions affecting the **medial collateral ligament** or **humeral trochlea**, not radial head excision. - The radial head's primary role in stability is against valgus forces, making a varus deformity an unlikely outcome of its removal. *Flexion deformity* - A flexion deformity, or **flexion contracture**, refers to a limited extension of the joint. - While elbow surgery can sometimes result in stiffness, the direct consequence of radial head removal is primarily related to **stability**, not a fixed flexion posture. *None of the options* - Removing the radial head significantly affects the **biomechanics** and **stability** of the elbow joint. - Due to the loss of a key restrictor of valgus motion, a **deformity is highly probable**, specifically a valgus angulation.

Q: Deformation that is recovered upon removal of an externally applied force or pressure is known as what?

Elastic strain. ***Elastic strain*** * **Elastic strain** describes a type of **deformation** where the material returns to its original shape once the applied stress or force is removed. * This temporary deformation is critical for the function of many biological tissues, such as cartilage and blood vessels, allowing them to withstand transient loads without permanent damage. * *Young's modulus* * **Young's modulus** is a measure of the **stiffness** of an elastic material, representing the ratio of stress (force per unit area) to strain (deformation) in a material. * It quantifies the material's resistance to elastic deformation under tension or compression, not the deformation itself. * *Plastic deformation* * **Plastic deformation** refers to **permanent changes** in a material's shape that remain even after the external force or pressure is removed. * This type of deformation occurs when the material's **yield strength** is exceeded, leading to irreversible structural changes. * *Bending strain* * **Bending strain** is a specific type of strain that occurs when a material is subjected to a **bending moment**, leading to compression on one side and tension on the other. * While it is a form of deformation that can be either elastic or plastic, it does not exclusively describe deformation that is fully recovered upon removal of the force.

Q: Antalgic hip gait is related to which of the following?

Painful hip gait. ***Painful hip gait*** - An **antalgic gait** is a deviation from a normal gait pattern caused by pain, most commonly experienced in the hip or knee. - The individual attempts to **minimize the time spent bearing weight** on the painful limb, resulting in a shortened stance phase on the affected side. *Waddling gait* - This gait is characterized by a **broad base** and a **swaying motion** from side to side, often due to weakness in the hip abductor muscles. - While sometimes seen in hip pathologies, it's not synonymous with an antalgic gait, which is specifically pain-driven. *Trendelenberg gait* - This gait occurs due to weakness of the **hip abductor muscles** (gluteus medius and minimus) on the stance leg, causing the pelvis to drop on the swing leg side. - It's a compensatory mechanism for muscle weakness, not directly caused by pain. *Short leg gait* - This gait arises from a **discrepancy in leg length**, leading to compensatory mechanisms like hip hiking or circumduction to clear the shorter limb during swing phase. - While it can lead to secondary pain, the primary cause is a structural difference, not acute pain influencing the weight-bearing phase.

Question 1

What is the primary mechanism of fixation provided by an intramedullary K nail (Kirschner wire) in orthopedic surgery?

Accepted Answer

Three-point fixation

Answer

Two-point fixation

Answer

Compression

Answer

Weight concentration

Question 2

What is the shape of the indenter used in the Knoop hardness test?

Accepted Answer

Rhomboid

Answer

Diamond

Answer

Oval

Answer

Square

Question 3

Trendelenburg's sign is positive in injury to which structure?

Accepted Answer

Gluteus medius

Answer

Gluteus maximus

Answer

Quadriceps femoris

Answer

Quadratus lumborum

Question 4

What deformity is likely to occur following the removal of the head of the radius?

Accepted Answer

Valgus deformity

Answer

Varus deformity

Answer

Flexion deformity

Answer

None of the options

Question 5

Deformation that is recovered upon removal of an externally applied force or pressure is known as what?

Accepted Answer

Elastic strain

Answer

Young's modulus

Answer

Plastic deformation

Answer

Bending strain

Question 6

Antalgic hip gait is related to which of the following?

Accepted Answer

Painful hip gait

Answer

Trendelenberg gait

Answer

Waddling gait

Answer

Short leg gait

Orthopedic Biomechanics — MCQs

Orthopedic Biomechanics — MCQs

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