Clinical Applications of Biomechanics — MCQs

10 questions

In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?

Russell and Taylor classification is used for:

All of the following factors affect osseointegration EXCEPT:

The kinetic energy of the body is least in one of the following phases of the walking cycle

What is the biomechanical principle involved in symphyseal fracture with lag screw fixation?

Locking compression plating is commonly indicated in which of the following fracture types?

False about fracture of vertebrae

79 yrs old lady had fall, the following X-ray was taken. Which of the following is treatment?

The following gait is seen due to weakness of:

Q10

Open reduction (OR) is not required in which fracture?

Clinical Applications of Biomechanics 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: Russell and Taylor classification is used for:

A. Shaft of tibia fracture
B. Subtrochanteric femoral fracture (Correct Answer)
C. Humerus shaft fracture
D. Fracture of neck of femur

Explanation: ***Subtrochanteric femoral fracture*** - The **Russell and Taylor classification** system is specifically designed to classify **subtrochanteric femoral fractures**. - It categorizes these fractures based on the involvement of the **lesser trochanter** and the extension into the **piriformis fossa**, guiding treatment decisions. *Shaft of tibia fracture* - **Shaft of tibia fractures** are typically classified using other systems, such as the **AO/OTA classification**, which focuses on bone segment, morphology, and comminution. - The Russell and Taylor system is not applicable to lower leg fractures. *Humerus shaft fracture* - **Humerus shaft fractures** are commonly classified by systems that describe the **location (proximal, middle, distal third)**, **morphology (transverse, oblique, spiral)**, and **displacement**. - The Russell and Taylor classification does not apply to upper limb fractures. *Fracture of neck of femur* - **Fractures of the neck of the femur** are usually classified by the **Garden classification** (based on displacement) or the **Pauwels classification** (based on angle of fracture line). - These classifications determine the risk of **avascular necrosis** and guide treatment, which is distinct from the Russell and Taylor system.

Question 3: All of the following factors affect osseointegration EXCEPT:

A. Biocompatibility of implant material.
B. Implant design.
C. Patient's blood type (Correct Answer)
D. Status of the host bed.

Explanation: ***Patient's blood type*** - A patient's **blood type** (e.g., A, B, AB, O) is determined by antigens present on red blood cells and plays no direct role in the biological processes of bone healing or the integration of a dental implant with bone. - While systemic factors can influence osseointegration, blood type itself does not affect the cellular and molecular mechanisms required for direct bone-to-implant contact. *Biocompatibility of implant material* - The **biocompatibility** of the implant material (e.g., **titanium**) is crucial for osseointegration, as it must not elicit adverse reactions and must permit host bone growth on its surface. - Materials that are cytotoxic or inflammatory will prevent bone apposition and lead to fibrous encapsulation rather than direct bone contact. *Implant design* - **Implant design**, including features like **surface roughness**, thread pitch, and macro-geometry, significantly influences the initial stability and long-term success of osseointegration. - A greater surface area and appropriate surface treatments can enhance bone cell attachment and differentiation, promoting faster and stronger bone integration. *Status of the host bed* - The **status of the host bone bed** refers to its quality and quantity (e.g., bone density, vascularity), which are critical for the biological processes of osseointegration. - Adequate bone volume and good bone quality provide a stable foundation and sufficient blood supply for bone regeneration around the implant.

Question 4: The kinetic energy of the body is least in one of the following phases of the walking cycle

A. Double support
B. Mid-stance (Correct Answer)
C. Toe-off
D. Heel strike

Explanation: ***Mid-stance*** - During **mid-stance**, the body's center of gravity is at its **highest point**, and the vertical velocity is near zero as the body transitions from upward to downward motion, contributing to **reduced kinetic energy**. - At this phase, forward velocity is relatively constant but the body is at the apex of its vertical trajectory, representing a point of **minimal total kinetic energy** in the sagittal plane. - The body transitions from deceleration to acceleration, with the limb providing stable support as weight passes over the stance foot. *Double support* - In **double support**, both feet are on the ground during the weight transfer phase, and the body's center of gravity is at a lower position compared to mid-stance. - While some energy is dissipated during weight transfer, this phase involves active muscular work and forward momentum maintenance, with kinetic energy being variable. - This represents a transition phase between single support periods, with complex energy exchanges occurring. *Toe-off* - At **toe-off**, the propulsive phase of gait, the body is generating forward momentum with peak forward velocity, meaning there is **significant kinetic energy** as the foot pushes off the ground. - The body's center of gravity is moving upwards and forwards, indicating a higher kinetic energy state. - Ankle plantarflexors are actively propelling the body forward, maximizing kinetic energy output. *Heel strike* - **Heel strike** is a moment of initial contact where the body's forward velocity is still considerable, possessing **significant kinetic energy**. - The limb is preparing to absorb impact forces while the body's center of mass continues moving forward, representing high kinetic energy just before the deceleration phase. - This marks the beginning of the stance phase with substantial horizontal velocity maintained from the swing phase.

Question 5: What is the biomechanical principle involved in symphyseal fracture with lag screw fixation?

A. Load bearing
B. Load sharing (Correct Answer)
C. Compression osteosynthesis
D. Adaptation osteosynthesis

Explanation: **Load sharing** - Lag screw fixation allows for **interfragmentary compression** while still permitting some load to be borne by the surrounding bone and soft tissues, promoting a more physiological healing response. - This method provides a **stable environment** for bone healing by distributing forces across both the implant and the bone fragments. *Load bearing* - This principle implies that the **implant alone carries the majority of the load**, effectively shielding the fracture site from stress. - While a lag screw provides stability, it is not designed to be the sole load bearer; rather, it facilitates the bone's ability to bear load as it heals. *Compression osteosynthesis* - Although lag screws achieve compression, the term **compression osteosynthesis** is a broader concept that can include techniques like tension banding or plates, with the primary goal of creating stability through direct compression. - While **interfragmentary compression** is a part of lag screw fixation, "load sharing" more accurately describes the overall biomechanical outcome in symphyseal fractures where some physiological stress is beneficial for healing. *Adaptation osteosynthesis* - This refers to fixation designed primarily to **adapt or hold fragments in place** without providing significant compressive forces or the ability to share physiological loads directly with the bone during healing. - It’s typically used for non-weight-bearing fractures or where minimal stress is anticipated, which is not the case for symphyseal fractures.

Question 6: 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.

Question 7: 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 8: 79 yrs old lady had fall, the following X-ray was taken. Which of the following is treatment?

A. Hip spica
B. Nailing
C. Hemiahroplasty (Correct Answer)
D. Total Hip Replacement

Explanation: ***Hemiarthroplasty*** - The X-ray shows a **displaced femoral neck fracture** in an elderly patient, which typically has a high risk of **avascular necrosis** of the femoral head due to disruption of blood supply. - Hemiarthroplasty involves replacing only the **femoral head and neck** with a prosthetic component, leaving the acetabulum intact, which is suitable for elderly patients with good acetabular cartilage and less active lifestyles. *Hip spica* - A hip spica cast is primarily used for **pediatric femur fractures** or certain types of hip dislocations in children, not for displaced femoral neck fractures in elderly adults. - This method would not provide stable fixation or address the high risk of **avascular necrosis** associated with these fractures in older patients. *Nailing* - Nailing (intramedullary nailing) is typically used for **intertrochanteric fractures** or subtrochanteric fractures, where the fracture line is distal to the femoral neck. - For displaced femoral neck fractures, nailing alone may not provide adequate stability and carries a higher risk of **non-union** or **avascular necrosis** compared to arthroplasty in elderly patients. *Total Hip Replacement* - Total hip replacement involves replacing both the **femoral head and the acetabulum** with prosthetic components. - While an option for femoral neck fractures, it is generally reserved for younger, more active patients or those with pre-existing **acetabular pathology** like arthritis, as it is a more extensive and complex procedure than hemiarthroplasty.

Question 9: The following gait is seen due to weakness of:

A. Gluteus maximus
B. Gluteus medius (Correct Answer)
C. Psoas major
D. Tibialis anterior

Explanation: ***Gluteus medius*** - Weakness of the **gluteus medius** leads to a **Trendelenburg gait**, where the pelvis drops on the unsupported side during the swing phase of gait. - The image suggests pelvic tilting, which is characteristic of the body attempting to compensate for the inability of the gluteus medius to stabilize the pelvis. *Gluteus maximus* - Weakness of the gluteus maximus causes difficulty in **hip extension**, resulting in a **lurching gait** where the trunk is thrown backward at heel strike. - This is commonly known as a **gluteus maximus lurch**, which is not depicted in an obvious manner here. *Psoas major* - Weakness of the psoas major would primarily affect **hip flexion**, making it difficult to lift the leg off the ground (e.g., during the swing phase). - This would result in compensatory movements such as circumduction or hiking the hip, rather than the characteristic pelvic drop. *Tibialis anterior* - Weakness of the tibialis anterior causes **foot drop**, leading to a **steppage gait** where the knee is lifted high to avoid dragging the foot. - The image does not show a foot drop or high stepping, thus ruling out tibialis anterior weakness.

Question 10: Open reduction (OR) is not required in which fracture?

A. Fracture of the patella
B. Fracture of the outer one-third of the radius (Correct Answer)
C. Displaced fracture of the olecranon
D. Fracture of the condyle of the humerus

Explanation: ***Fracture of the outer one-third of the radius*** - Fractures of the **outer one-third of the radius** (distal radius fractures) often can be managed with **closed reduction and casting** if stable and adequately reduced. - While some unstable distal radius fractures require OR, many stable patterns, especially those with minimal displacement or good alignment after closed manipulation, do not. *Fracture of the patella* - Many patellar fractures lead to significant **extensor mechanism disruption**, necessitating OR with **tension band wiring** or screw fixation to restore quadriceps function. - Displaced patellar fractures, especially transverse ones, require surgical fixation to prevent extensor lag and **nonunion**. *Displaced fracture of the olecranon* - Displaced olecranon fractures disrupt the **triceps mechanism** and compromise elbow stability, almost always requiring **open reduction and internal fixation (ORIF)**, typically with tension band wiring. - Without surgical repair, a displaced olecranon fracture can lead to significant loss of extension strength and **nonunion**. *Fracture of the condyle of the humerus* - Fractures of the humeral condyle, particularly in children, often require OR due to the risk of **avascular necrosis** (especially lateral condyle) and the need for **precise anatomical reduction** to prevent joint incongruity and cubitus varus/valgus deformities. - Intra-articular and displaced condylar fractures almost invariably require surgical intervention to ensure harmonious joint function and prevent long-term complications like **stiffness and deformity**.

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