Orthopedic Biomechanics — MCQs

Orthopedic Biomechanics Indian Medical PG Practice Questions and MCQs

Question 11: Trendelenburg sign is positive due to the involvement of:

A. Gluteus maximus
B. Psoas major
C. Gluteus medius (Correct Answer)
D. Adductor magnus

Explanation: ***Gluteus medius*** - The **Trendelenburg sign** indicates weakness or paralysis of the hip abductor muscles, primarily the **gluteus medius** and **gluteus minimus**. - When standing on one leg, these muscles contract on the supported side to keep the pelvis level; if they are weak, the unsupported side of the pelvis drops. *Gluteus maximus* - This muscle is the primary **extensor of the hip** and is crucial for activities like climbing stairs or standing up from a seated position. - Its weakness would primarily affect hip extension, not the ability to keep the pelvis level during single-leg stance. *Psoas major* - The **psoas major** is a powerful **hip flexor** and contributes to lumbar spine stability. - Weakness of this muscle would impair hip flexion, making it difficult to lift the leg forward, but it is not directly involved in stabilizing the pelvis in the frontal plane during standing. *Adductor magnus* - The **adductor magnus** is an important **hip adductor** and also functions as an extensor in certain positions. - Its primary role is to bring the leg towards the midline, and its weakness would not cause the characteristic pelvic drop seen in a positive Trendelenburg sign.

Question 12: Wolff's law is:-

A. Epiphyseal centre which appears first unites last with diaphysis
B. None of above.
C. Osteogenesis is directly proportional to stress and strain. (Correct Answer)
D. Epiphyseal centre which appears first unites first with diaphysis.

Explanation: ***Osteogenesis is directly proportional to stress and strain.*** - **Wolff's Law** states that **bone adapts to the loads** under which it is placed. This means bone will remodel and strengthen in response to increased mechanical stress and strain. - Increased weight-bearing exercise or physical activity leads to **increased bone density** and strength, while lack of stress (e.g., bed rest, immobility) results in bone resorption and weakening. *Epiphyseal centre which appears first unites last with diaphysis* - This statement describes **Ritter's law**, which pertains to the sequence of epiphyseal fusion rather than bone's response to mechanical stress. - Ritter's law is a concept in anatomy related to the order of **epiphyseal plate ossification** and closure. *None of above.* - This is incorrect because one of the provided options accurately defines Wolff's Law. - The third option precisely articulates the principle behind **bone remodeling** in response to mechanical forces. *Epiphyseal centre which appears first unites first with diaphysis.* - This statement is generally not a recognized law in bone development and is inconsistent with the principles of epiphyseal fusion, often contradicting Ritter's law. - The timing of epiphyseal fusion is complex and influenced by various factors, but not simply an "appears first, unites first" rule.

Question 13: During an autopsy, a pathologist finds a transverse fracture of the femur. Which type of force is most likely responsible for this fracture?

A. Tensile force
B. Shear force
C. Bending force (Correct Answer)
D. Compressive force

Explanation: ***Bending force*** - A **transverse fracture** results from a force applied perpendicular to the long axis of the bone, causing it to bend and fracture at the point of maximum stress. - This typically happens when the bone is **bent beyond its elastic limit**, leading to a clean break across its width. *Tensile force* - **Tensile force** involves pulling on the bone, which tends to cause **avulsion fractures** or **spiral fractures** if combined with twisting. - It would result in the bone being stretched apart, not a clean transverse break from bending. *Shear force* - **Shear force** occurs when forces are applied parallel to the surface of the bone but in opposite directions, causing one part to slide over another. - This typically leads to **oblique fractures** or **dislocations**, not a transverse fracture. *Compressive force* - **Compressive force** involves pushing the bone together, which can result in **crush fractures** or **impacted fractures**. - This force would typically shorten the bone or create multiple fragments, unlike a distinct transverse break.

Question 14: Increased Q angle predisposes to

A. Medial patellar subluxation
B. Lateral patellar subluxation (Correct Answer)
C. Superior patellar subluxation
D. Inferior patellar subluxation

Explanation: ***Lateral patellar subluxation*** - An increased **Q angle** signifies a greater lateral pull on the patella due to the alignment of the quadriceps muscle and the patellar ligament. - This increased lateral force disproportionately stresses the **medial patellofemoral ligament** (MPFL) and can lead to the patella moving out of its trochlear groove laterally. *Medial patellar subluxation* - This is a rare condition, typically associated with **iatrogenic causes** (e.g., overcorrection during surgery) or congenital anomalies, not an increased Q angle. - An increased Q angle would exert a **lateral pull** on the patella, making medial subluxation less likely. *Superior patellar subluxation* - This usually results from patella alta (high-riding patella) or a **quadriceps tendon rupture**, which allows the patella to migrate proximally. - An increased Q angle directly influences the **medial-lateral stability** of the patella, not its superior-inferior position. *Inferior patellar subluxation* - This is often due to patella baja (low-riding patella) or conditions like **infrapatellar contracture syndrome**, where the patella is pulled distally. - The Q angle is a measure of the angle between the quadriceps femoris muscle and the patellar tendon, primarily affecting **transverse plane stability**.

Question 15: What is the shape of the indenter used in the Knoop hardness test?

A. Diamond
B. Rhomboid (Correct Answer)
C. Oval
D. Square

Explanation: ***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.

Question 16: What is the primary advantage of titanium implants over stainless steel implants in orthopedic surgery?

A. V
B. Ti
C. Al, V
D. Al (Correct Answer)

Explanation: ***Al*** - **Aluminum (Al)** is a key component in **titanium alloys** (e.g., Ti-6Al-4V), contributing to increased **strength** and mechanical stability. - Adding aluminum to titanium enhances its ability to withstand significant loads and stresses, which is crucial for the longevity of orthopedic implants. *V* - **Vanadium (V)** is also used as an alloying element with titanium (e.g., Ti-6Al-4V) but primarily enhances **ductility** and workability, not the primary strength advantage over stainless steel. - While it contributes to overall mechanical properties, it's not the central element responsible for the superior strength characteristics in this context. *Ti* - **Titanium (Ti)** itself is the base metal, providing excellent **biocompatibility** and **corrosion resistance**, but its pure form has lower strength compared to its alloys. - The question asks for an *advantage* over stainless steel, implying a specific property enhanced by alloying rather than the base metal's inherent characteristics. *Al, V* - While both **aluminum (Al)** and **vanadium (V)** are components of common titanium alloys like Ti-6Al-4V, **aluminum** is particularly noted for its role in increasing the alloy's **strength**. - Combining them is essential for the alloy's overall profile, but aluminum's specific contribution to strength is often highlighted in material science for orthopedic applications.

Question 17: Trendelenburg's sign is positive in injury to which structure?

A. Gluteus maximus
B. Gluteus medius (Correct Answer)
C. Quadriceps femoris
D. Quadratus lumborum

Explanation: ***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.

Question 18: What deformity is likely to occur following the removal of the head of the radius?

A. Valgus deformity (Correct Answer)
B. Varus deformity
C. Flexion deformity
D. None of the options

Explanation: ***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.

Question 19: Deformation that is recovered upon removal of an externally applied force or pressure is known as what?

A. Elastic strain (Correct Answer)
B. Young's modulus
C. Plastic deformation
D. Bending strain

Explanation: ***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.

Question 20: Which property of Nitinol (NiTi) makes it particularly useful in orthopedic implants?

A. Stress
B. Both temperature and stress. (Correct Answer)
C. Temperature
D. None of the options.

Explanation: ***Both temperature and stress*** - **Nitinol** exhibits both **shape memory effect** (temperature-dependent phase transformation) and **superelasticity** (stress-induced phase transformation). - These unique properties allow it to undergo significant deformation and return to its original shape, making it ideal for **orthopedic implants** requiring adaptive and flexible materials. *Temperature* - While temperature is crucial for the **shape memory effect** in Nitinol, it is not the sole property that makes it useful. - The material's ability to recover its original shape upon heating is valuable, but its response to *stress* is also highly important for practical applications. *Stress* - Stress is a critical factor for **superelasticity** in Nitinol, allowing it to withstand large deformations without permanent damage. - However, relying solely on **stress-induced transformation** overlooks the significant therapeutic benefits derived from its **temperature-dependent shape memory** capabilities. *None of the options* - This option is incorrect as Nitinol's utility in orthopedic implants is directly attributable to its remarkable responses to both **temperature** and **stress**. - The combination of **shape memory** and **superelasticity** provides distinct advantages over traditional materials.

Practice by Chapter

Principles of Biomechanics

Practice Questions

Biomechanics of Fracture Fixation

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Biomechanics of Spine

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Biomechanics of Hip

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Biomechanics of Knee

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Biomechanics of Foot and Ankle

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Biomechanics of Upper Limb

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Gait Analysis

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Biomechanics of Arthroplasty

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Biomechanics of Sports Injuries

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Computational Modeling in Orthopaedics

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Clinical Applications of Biomechanics

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