Biomechanics of Foot and Ankle — MCQs
In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?
A 41-year-old man is admitted to the emergency department with a swollen and painful foot. Radiographic examination reveals that the head of the talus has become displaced inferiorly, thereby causing the medial longitudinal arch of the foot to fall. What is the most likely cause in this case?
Which of the following ligaments is injured in an ankle inversion injury?
Ruptured tendons are most commonly seen in
Injury at which of the following marked sites on the leg causes failure of dorsiflexion?
Sudden dorsiflexion of the foot may lead to which of the following injuries?
Comment on the diagnosis:
When Class III elastics are used, what movement will the maxillary first molars exhibit?
A high crural index is typically observed in which of the following groups?
Which posture is associated with the greatest lumbar intradiscal pressure?
Biomechanics of Foot and Ankle Indian Medical PG Practice Questions and MCQs
Question 1: In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?
- A. Adductor muscles
- B. Quadriceps
- C. Gluteus medius and minimus (Correct Answer)
- D. Gluteus maximus
Explanation: ***Gluteus medius and minimus*** - The **gluteus medius** and **gluteus minimus** are essential **abductors** of the hip, primarily responsible for stabilizing the pelvis during the **single-limb support phase of gait**. - When one leg is lifted during walking, these muscles on the **stance leg side** contract to prevent the pelvis from tilting downwards on the unsupported swing leg side. *Adductor muscles* - **Adductor muscles** (adductor longus, brevis, magnus, pectineus, gracilis) primarily function to bring the thigh toward the midline of the body. - While they play a role in gait stability, their main action is not to prevent the lateral pelvic tilt described. *Quadriceps* - The quadriceps femoris group (rectus femoris, vastus lateralis, medialis, intermedius) are powerful **extensors of the knee**. - They are crucial for weight acceptance and propulsion during walking but do not directly prevent lateral pelvic tilt [1]. *Gluteus maximus* - The **gluteus maximus** is the largest and most powerful muscle of the hip, primarily responsible for **hip extension** and **external rotation**. - It is crucial for activities like climbing stairs or running, but its main role in normal walking is not to prevent lateral pelvic tilt; that function is more specific to the gluteus medius and minimus.
Question 2: A 41-year-old man is admitted to the emergency department with a swollen and painful foot. Radiographic examination reveals that the head of the talus has become displaced inferiorly, thereby causing the medial longitudinal arch of the foot to fall. What is the most likely cause in this case?
- A. Tearing of the plantar calcaneonavicular (spring) ligament (Correct Answer)
- B. Fracture of the navicular bone
- C. Tearing of the deltoid ligament
- D. Sprain of the calcaneocuboid ligament
Explanation: ***Tearing of the plantar calcaneonavicular (spring) ligament*** - The **plantar calcaneonavicular ligament**, also known as the **spring ligament**, is crucial for supporting the head of the talus and maintaining the **medial longitudinal arch** of the foot. - Tearing of this ligament leads to the **inferior displacement of the talar head** and subsequent collapse of the arch, consistent with the symptoms described. *Fracture of the navicular bone* - A fracture of the **navicular bone** would typically cause localized pain and tenderness over the navicular, and while it could contribute to arch instability, it wouldn't primarily cause the **talar head** to *inferiorly displace* in this specific manner. - While a navicular fracture might lead to secondary arch collapse, the primary issue described is the displacement of the **talar head**, which is more directly related to spring ligament integrity. *Tearing of the deltoid ligament* - The **deltoid ligament** is located on the medial side of the ankle and primarily stabilizes the **talocrural joint**, preventing excessive eversion of the foot. - Its rupture would lead to ankle instability and pain, but it doesn't directly support the **medial longitudinal arch** in the same way the spring ligament does, nor would its tearing directly cause the talar head to displace inferiorly as described. *Sprain of the calcaneocuboid ligament* - The **calcaneocuboid ligament** is a component of the **lateral longitudinal arch** of the foot and connects the calcaneus to the cuboid bone. - A sprain of this ligament would primarily affect the *lateral* foot stability and lead to pain in that region, not the described collapse of the **medial longitudinal arch** or inferior displacement of the talar head.
Question 3: Which of the following ligaments is injured in an ankle inversion injury?
- A. Calcaneofibular ligament
- B. Posterior talofibular ligament
- C. Deltoid ligament
- D. Anterior talofibular ligament (Correct Answer)
Explanation: ***Anterior talofibular ligament*** - The **anterior talofibular ligament (ATFL)** is the most commonly injured ligament in an **ankle inversion sprain** due to its position and weaker structure. - It connects the **fibula** to the **talus** anteriorly, and when the foot inverts, this ligament is stretched and often torn first. *Calcaneofibular ligament* - The **calcaneofibular ligament (CFL)** is also an important lateral ankle ligament that can be injured in **severe inversion sprains**. - It is often damaged in conjunction with the ATFL, but typically only after the ATFL has already been compromised through an ankle inversion injury. *Posterior talofibular ligament* - The **posterior talofibular ligament (PTFL)** is the strongest of the **lateral collateral ligaments** and is rarely injured in isolation. - Injury to the PTFL usually occurs in cases of **severe, high-grade ankle dislocations** or very forceful inversion injuries, often involving other ligaments. *Deltoid ligament* - The **deltoid ligament** is a strong, fan-shaped ligament located on the **medial side of the ankle**. - It resists **eversion** of the ankle, meaning it is more commonly injured in **eversion sprains**, not inversion sprains.
Question 4: Ruptured tendons are most commonly seen in
- A. Overuse (Correct Answer)
- B. Direct trauma from injury
- C. Structural abnormalities from birth
- D. Tumor-related structural changes
Explanation: ***Overuse*** - Chronic **overuse** leads to **microtrauma and degeneration** within the tendon, weakening it over time and making it susceptible to rupture even with minimal acute stress. - This is particularly common in tendons that experience **repetitive strain**, such as the Achilles tendon, rotator cuff, and patellar tendon. *Direct trauma from injury* - While acute, high-impact **direct trauma** can cause tendon ruptures, it is not the most common mechanism overall. - Many traumatic ruptures occur in tendons already weakened by **chronic degeneration**, rather than purely healthy tendons. *Structural abnormalities from birth* - **Congenital structural abnormalities** are relatively rare causes of primary tendon rupture. - These conditions usually present earlier in life with functional limitations rather than sudden rupture in adulthood. *Tumor-related structural changes* - **Tumors** can, in rare cases, weaken tendons and lead to rupture, but this is a far less common cause compared to overuse. - Tendon compromise due to a tumor usually involves direct invasion or pressure, which is not the predominant etiology for the majority of tendon ruptures.
Question 5: Injury at which of the following marked sites on the leg causes failure of dorsiflexion?
- A. Anterior aspect of the thigh (site 1)
- B. Medial aspect of the leg (site 4)
- C. Lateral aspect of the leg (site 3) (Correct Answer)
- D. Posterior aspect of the thigh (site 2)
Explanation: ***Lateral aspect of the leg (site 3)*** - Site 3 points to the **fibula head** and the adjacent region on the lateral aspect of the leg. This is the anatomical location where the **common fibular nerve (peroneal nerve)** wraps around. - The common fibular nerve innervates the muscles responsible for **dorsiflexion** and eversion of the foot. Damage to this nerve, often due to trauma at the fibular neck, leads to **foot drop** and an inability to dorsiflex the foot. *Anterior aspect of the thigh (site 1)* - Site 1 points to the distal femur, which is part of the thigh. Nerves in the anterior thigh (e.g., **femoral nerve**) primarily control hip flexion and knee extension. - Damage here would affect movements of the hip and knee, not directly causing failure of dorsiflexion of the foot. *Medial aspect of the leg (site 4)* - Site 4 points to the medial tibia. This area is associated with the **tibial nerve** and saphenous nerve, which primarily innervate muscles for plantarflexion and inversion of the foot, or provide sensory innervation. - Injury to the tibial nerve would result in an inability to plantarflex and invert the foot, not dorsiflexion. *Posterior aspect of the thigh (site 2)* - Site 2 points to the posterior aspect of the thigh, which is the region for the hamstrings. The **sciatic nerve** and its branches (tibial and common fibular) pass through this region. - While the common fibular nerve originates from the sciatic nerve in the posterior thigh, an injury at this level would likely cause more widespread motor and sensory deficits than isolated dorsiflexion failure, and site 3 is a more common and specific site for common fibular nerve injury isolated to foot drop.
Question 6: Sudden dorsiflexion of the foot may lead to which of the following injuries?
- A. Anterior talofibular ligament injury
- B. Tendo Achilles avulsion injury (Correct Answer)
- C. Rupture of deltoid ligament
- D. Tarsal tunnel syndrome
Explanation: ***Tendo Achilles avulsion injury*** - **Sudden dorsiflexion** of the foot, especially if forced or excessive, can cause extreme stretch on the **Achilles tendon**, potentially leading to its avulsion or rupture. - This mechanism often occurs during activities requiring a forceful push-off or landing with the foot in dorsiflexion, placing significant tensile stress on the tendon. *Anterior talofibular ligament injury* - This injury typically results from an **inversion sprain** of the ankle, where the foot is forcefully turned inward, causing damage to the lateral ankle ligaments. - **Dorsiflexion** alone is not the primary mechanism for injury to the **anterior talofibular ligament**. *Rupture of deltoid ligament* - The **deltoid ligament** is located on the medial side of the ankle and is most commonly injured with an **eversion sprain**, where the foot rolls outward. - While extreme dorsiflexion can put some strain on anterior fibers, it is not the primary mechanism, and a concomitant eversion force would likely be required for rupture. *Tarsal tunnel syndrome* - This condition involves **compression of the tibial nerve** as it passes through the tarsal tunnel, typically causing pain, numbness, and tingling in the sole of the foot. - It is often caused by chronic factors such as swelling, repetitive stress, or structural abnormalities, rather than an acute traumatic event like sudden dorsiflexion.
Question 7: Comment on the diagnosis:
- A. Jones fracture (Correct Answer)
- B. March fracture
- C. Shepherd's fracture
- D. Cotton's fracture
Explanation: ***Jones fracture*** - The image indicates a fracture located at the **proximal metaphyseal-diaphyseal junction of the fifth metatarsal**, which is characteristic of a **Jones fracture**. - This fracture involves the **base of the fifth metatarsal** and is often associated with a higher risk of nonunion due to limited blood supply. *March fracture* - A **March fracture** is a type of stress fracture, typically affecting the **shaft of the second, third, or fourth metatarsals**, often seen in military recruits or those who engage in prolonged walking or running. - It results from repetitive stress rather than an acute injury, and its location is distinct from the proximal fifth metatarsal. *Shepherd's fracture* - A **Shepherd's fracture** refers to an avulsion fracture of the **posterolateral tubercle of the talus**, also known as an os trigonum fracture. - This fracture is located in the ankle region, distinct from the metatarsals. *Cotton's fracture* - A **Cotton's fracture** is a trimalleolar fracture of the ankle, involving the **medial malleolus**, **lateral malleolus**, and the **posterior malleolus** of the tibia. - This is a complex ankle injury, entirely unrelated to fractures of the metatarsals.
Question 8: When Class III elastics are used, what movement will the maxillary first molars exhibit?
- A. Move distally and intrude
- B. Move mesially and extrude (Correct Answer)
- C. Move mesially and intrude
- D. Move only mesially; there will be no vertical movement
Explanation: **Explanation:** In orthodontic biomechanics, the direction of force determines the displacement of teeth. **Class III elastics** are stretched from the **mandibular anterior region** (usually the canines) to the **maxillary posterior region** (usually the first molars). **1. Why Option B is correct:** The force vector of a Class III elastic on the maxillary molar acts in a **downward and forward** direction. * **Mesial Movement:** The horizontal component of the force pulls the maxillary molar forward (mesially). * **Extrusion:** Because the elastic is attached to the lower arch (which is inferior to the maxilla), the vertical component of the force pulls the molar downward, leading to extrusion. **2. Why the other options are incorrect:** * **Option A & C:** Distal movement is characteristic of **Class II elastics**, where the force pulls the maxillary teeth backward. Intrusion would require a superiorly directed force (like a high-pull headgear), which elastics do not provide to the maxillary molars. * **Option D:** This ignores the vertical vector. In clinical practice, elastics rarely exert a purely horizontal force; the "line of action" always creates a vertical component that results in either extrusion or intrusion. **Clinical Pearls for NEET-PG:** * **Class II Elastics:** Cause **distalization and extrusion** of maxillary incisors/molars and **mesialization and extrusion** of mandibular molars. * **Side Effects:** A common side effect of Class III elastics is the steepening of the occlusal plane and a potential increase in the lower anterior facial height due to molar extrusion. * **Center of Resistance:** If the force does not pass through the center of resistance, rotation (tipping) will occur alongside translation.
Question 9: A high crural index is typically observed in which of the following groups?
- A. Jumping athletes (Correct Answer)
- B. Gymnasts
- C. Weight lifters
- D. Long-distance runners
Explanation: **Explanation:** The **Crural Index** is a biomechanical ratio used to describe the proportions of the lower limb. It is calculated as: **Crural Index = (Length of Tibia / Length of Femur) × 100** **1. Why Jumping Athletes is Correct:** A high crural index indicates a **longer tibia relative to the femur**. From a biomechanical standpoint, a longer distal segment (tibia) increases the "lever arm" of the lower limb. In jumping athletes (such as high jumpers or basketball players), this anatomical advantage allows for a faster rate of limb extension and greater velocity at the foot during takeoff. This "long-lever" system is more efficient for explosive power and vertical displacement. **2. Analysis of Incorrect Options:** * **Gymnasts:** Typically have a lower crural index and shorter stature. This provides a lower center of gravity and a smaller moment of inertia, which is advantageous for rotational stability and balance. * **Weight lifters:** Benefit from shorter limbs (lower crural index) because shorter levers reduce the torque required to lift heavy loads, providing a mechanical advantage for strength over speed. * **Long-distance runners:** While they often have lean limbs, they do not necessarily require the extreme distal elongation seen in explosive jumpers; their biomechanics favor metabolic efficiency over maximum vertical power. **3. Clinical Pearls for NEET-PG:** * **Evolutionary Note:** High crural indices are often seen in populations adapted to hot climates (to increase surface area for heat dissipation) and in cursorial (running/jumping) animals. * **Brachial Index:** A similar ratio for the upper limb (Radius length / Humerus length × 100). * **High-Yield Fact:** In orthopedics, limb length ratios are crucial for gait analysis and prosthetic design. A higher crural index generally correlates with a higher center of mass, which is beneficial for high-velocity movements.
Question 10: Which posture is associated with the greatest lumbar intradiscal pressure?
- A. Sitting with trunk flexed (Correct Answer)
- B. Sitting with trunk erect
- C. Standing with trunk flexed
- D. Standing with trunk erect
Explanation: This question is based on the classic biomechanical studies by **Nachemson**, which measured intradiscal pressure at the L3-L4 level in various positions. ### **Explanation** The intradiscal pressure is determined by the combination of **superincumbent body weight** and **muscle activity** required to maintain balance. 1. **Sitting vs. Standing:** When sitting, the pelvis tilts posteriorly, and the normal lumbar lordosis is flattened. This increases the lever arm of the upper body weight, requiring greater back muscle contraction to maintain the posture, which significantly increases the load on the discs compared to standing. 2. **Flexion vs. Extension:** Flexion (leaning forward) shifts the center of gravity further forward. This creates a large **flexion moment**, forcing the posterior spinal muscles and ligaments to exert a massive counter-traction force to prevent the trunk from falling. This "pincer effect" compresses the disc severely. Therefore, **Sitting with trunk flexed (Option A)** combines the high baseline pressure of sitting with the added mechanical disadvantage of flexion, resulting in the highest intradiscal pressure (approx. 185-200% of standing pressure). ### **Analysis of Other Options** * **B. Sitting with trunk erect:** While higher than standing, the vertical alignment reduces the flexion moment compared to leaning forward. * **C. Standing with trunk flexed:** Pressure is high (approx. 150%), but the lower limbs and pelvis help absorb some load that is otherwise transmitted directly to the spine when sitting. * **D. Standing with trunk erect:** This is used as the baseline (100%). The weight is distributed through the vertebral bodies and facets. ### **High-Yield Clinical Pearls for NEET-PG** * **Lowest Pressure:** **Supine (lying flat)** has the lowest intradiscal pressure (approx. 25%). * **Highest Overall Pressure:** Sitting or standing while **flexed and lifting a weight** (e.g., lifting a bucket) produces the absolute maximum pressure. * **Coughing/Straining:** These maneuvers significantly increase intradiscal pressure due to the Valsalva effect. * **Clinical Application:** Patients with acute disc prolapse are advised to avoid sitting and forward bending to minimize the risk of further herniation.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free