Orthopedic Biomechanics

Orthopedic Biomechanics Indian Medical PG Question 1: Which of the following is not a ball and socket type of joint?

• A. Incudostapedeal joint
• B. Talocalcaneonavicular joint
• C. Calcaneocuboid joint (Correct Answer)
• D. Shoulder joint

Orthopedic Biomechanics Explanation: ***Calcaneocuboid joint*** - The calcaneocuboid joint is a **saddle joint** (or modified plane joint), which allows for movement primarily in gliding motions, but not the multi-axial movement characteristic of a ball-and-socket joint. - Its structure, specifically the **reciprocally saddle-shaped articular surfaces** of the calcaneus and cuboid bones, limits its range of motion to primarily inversion and eversion during foot movements. *Talocalcaneonavicular joint* - This joint functions as a **modified ball-and-socket joint**, allowing for complex movements like pronation and supination of the foot. - It involves the head of the talus acting as the 'ball' articulating with the navicular anteriorly and the sustentaculum tali of the calcaneus posteriorly, forming a socket. - This unique configuration allows for multi-axial movement essential for foot adaptation to terrain. *Incudostapedial joint* - This is a **synovial saddle-type joint** (not a ball-and-socket joint) found in the middle ear, connecting the lenticular process of the incus and the head of the stapes. - It allows for limited rocking motion to efficiently transmit sound vibrations through the ossicular chain. - The joint permits only small amplitude movements necessary for auditory function, not the multi-axial freedom of a ball-and-socket joint. *Shoulder joint* - The shoulder joint, also known as the **glenohumeral joint**, is a classic example of a **ball-and-socket joint**, offering the widest range of motion in the human body. - The **head of the humerus** (ball) articulates with the **glenoid fossa** of the scapula (socket), allowing for flexion, extension, abduction, adduction, rotation, and circumduction.

Orthopedic Biomechanics Indian Medical PG Question 2: 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.

Orthopedic Biomechanics 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.

Orthopedic Biomechanics Indian Medical PG Question 3: Buttressing bone formation is the periodontal tissue response to an increase in occlusal forces seen in

• A. Stage I injury
• B. Stage II repair (Correct Answer)
• C. Stage III repair
• D. None of the options

Orthopedic Biomechanics Explanation: **_Stage II repair_** - In response to increased occlusal forces, buttressing bone formation is a reparative mechanism where the **alveolar bone thickens** to better withstand these forces. - This adaptive change is characteristic of the **Stage II repair phase**, aiming to reinforce the supportive structures around the tooth. *Stage I injury* - This stage typically involves the **initial damage** to the periodontal tissues, such as widening of the periodontal ligament space or increased vascularity. - **Buttressing bone formation** is a reparative, not an initial injury, response. *Stage III repair* - Stage III repair is usually associated with more **severe or chronic injury**, often involving a more pronounced remodeling or even degenerative changes if the forces are persistent and overwhelming. - While repair continues, buttressing bone formation is most characteristic of the **active phase of adaptation** in Stage II. *None of the options* - Buttressing bone formation is a well-documented biological response to increased occlusal forces and is particularly relevant in the context of **periodontal adaptation and repair**. - Therefore, one of the provided stages is the correct answer.

Orthopedic Biomechanics Indian Medical PG Question 4: Antalgic hip gait is related to which of the following?

• A. Painful hip gait (Correct Answer)
• B. Trendelenberg gait
• C. Waddling gait
• D. Short leg gait

Orthopedic Biomechanics Explanation: ***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.

Orthopedic Biomechanics Indian Medical PG Question 5: Which of the following movements is typically restricted in Perthes disease?

• A. Abduction & internal rotation (Correct Answer)
• B. Abduction & external rotation
• C. Adduction & internal rotation
• D. Adduction & external rotation

Orthopedic Biomechanics Explanation: ***Abduction & internal rotation*** - **Perthes disease** affects the femoral head, leading to pain and stiffness that most commonly restricts **abduction** and **internal rotation** of the hip. - This restriction is an early and consistent clinical finding, often accompanied by a ** Trendelenburg gait** due to gluteal muscle weakness or pain avoidance. *Abduction & external rotation* - While abduction can be restricted, a primary restriction in **external rotation** is less typical in early Perthes disease. - Reduced external rotation is more characteristic of conditions like **slipped capital femoral epiphysis (SCFE)**, especially in older children. *Adduction & internal rotation* - **Adduction** is generally preserved or even increased in Perthes disease as the hip seeks a position of comfort due to pain, making it an unlikely primary restriction. - While internal rotation is restricted, the combination with adduction restriction is not the classical presentation. *Adduction & external rotation* - Neither **adduction** nor **external rotation** are typically the primary hip movements restricted in Perthes disease. - Restriction in adduction is rare, and external rotation is often compensatory or less affected than internal rotation.

Orthopedic Biomechanics Indian Medical PG Question 6: A patient came with complaints of lower limb weakness. Examiner places one hand under the patient's heel and patient is asked to raise his other leg against downward resistance. What is the name of this test?

• A. O'Donoghue test
• B. McBride test
• C. Waddell's test
• D. Hoover test (Correct Answer)

Orthopedic Biomechanics Explanation: ***Hoover test*** - This specific maneuver is used to detect **malingering or non-organic weakness** in the lower limbs [1]. The examiner expects an involuntary downward thrust from the heel of the seemingly weak leg when the patient attempts to lift the contralateral leg. - Absence of this expected downward pressure on the examiner's hand when the patient is asked to lift the "strong" leg suggests the patient is not genuinely attempting to lift the affected leg. *O'Donoghue test* - The O'Donoghue test assesses for **meniscal or ligamentous injury** in the knee joint by combining passive and resisted motions of the knee. - It involves motions like resisted flexion, extension, and rotation to elicit pain, which is different from the described procedure. *McBride test* - The McBride test is used to evaluate the integrity of the **collateral ligaments of the knee**, particularly after injury. - It involves specific manipulations of the knee and ankle to assess stability and pain, which is not what the question describes. *Waddell's test* - Waddell's signs are a set of five physical signs that indicate **non-organic or psychological components to low back pain**. - These signs include superficial tenderness, simulated axial loading pain, distraction signs, regional weakness/sensory disturbance, and overreaction during examination, none of which involve the specific maneuver for detecting lower limb motor weakness described in the question.

Orthopedic Biomechanics Indian Medical PG Question 7: A 52-year-old female complains of increasing pain in the right shoulder. She is also finding it increasingly difficult to do overhead abduction of the affected joint. She had been diagnosed as a diabetic 20 years back and is on treatment since then. What is the most likely cause of her clinical condition?

• A. Frozen shoulder (Correct Answer)
• B. Bacterial arthritis
• C. Osteoarthritis
• D. Rotator cuff tear

Orthopedic Biomechanics Explanation: ***Frozen shoulder*** - The patient's presentation with **increasing pain** and **difficulty with overhead abduction** of the shoulder, especially in the context of long-standing **diabetes**, is highly characteristic of **adhesive capsulitis** (frozen shoulder). - This condition is marked by **progressive stiffness** and **restricted range of motion** in the shoulder joint due to inflammation and fibrosis of the joint capsule. *Bacterial arthritis* - **Bacterial arthritis** typically presents with an **acutely painful**, **swollen**, and **erythematous joint**, often accompanied by systemic symptoms like **fever** and **malaise**. - The chronic, progressive nature of the patient's symptoms and the absence of acute inflammatory signs or fever make bacterial arthritis less likely. *Osteoarthritis* - While **osteoarthritis** can cause shoulder pain and stiffness, it usually presents with **pain that worsens with activity** and is relieved by rest, often with **crepitus** and a more gradual loss of range of motion. - The pronounced restriction in **overhead abduction** in this patient, particularly given the diabetic history, points away from primary osteoarthritis as the most likely cause. *Rotator cuff tear* - A **rotator cuff tear** typically presents with pain and weakness, especially during **abduction** or **external rotation**, and may have a specific mechanism of injury. - While abduction can be difficult, the classic presentation of a frozen shoulder with severe, global restriction of both active and passive range of motion is a stronger fit for the described symptoms.

Orthopedic Biomechanics Indian Medical PG Question 8: A sportsman presented to you after injury during practice exercise. You performed the test given in the image, and it came out as positive. What is the diagnosis?

• A. Anterior cruciate ligament tear (Correct Answer)
• B. Posterior cruciate ligament tear
• C. Medial meniscus tear
• D. Medial collateral ligament tear

Orthopedic Biomechanics Explanation: ***Anterior cruciate ligament tear*** - The image depicts the **Lachman test**, a highly sensitive and specific clinical test for **ACL integrity**. - A positive Lachman test, characterized by *increased anterior tibial translation* and a *soft or absent endpoint*, confirms an **ACL tear**. *Posterior cruciate ligament tear* - A PCL tear is identified by tests like the **posterior drawer test** or **posterior sag sign**, which show *posterior tibial translation*. - The test shown in the image specifically assesses **anterior stability**, not posterior. *Medial meniscus tear* - Medial meniscus tears are typically diagnosed with tests like **McMurray's test** or **Apley's grind test**, which involve *rotation* and *compression* of the knee. - While a crucial knee structure, the meniscus does not primarily contribute to **anterior-posterior stability** in the way the ACL does. *Medial collateral ligament tear* - An MCL tear is detected by applying a **valgus stress** to the knee at various degrees of flexion. - This tear presents with *medial joint line pain* and *instability to valgus stress*, which is not assessed by the depicted test.

Orthopedic Biomechanics Indian Medical PG 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

Orthopedic Biomechanics 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.

Orthopedic Biomechanics Indian Medical PG Question 10: The compression fracture is commonest in

• A. Upper thoracic spine
• B. Cervical spine
• C. Lumbosacral region
• D. Lower thoracic spine (Correct Answer)

Orthopedic Biomechanics Explanation: ***Lower thoracic spine*** - The **thoracolumbar junction (T11-L2)** is the most common site for compression fractures due to its high biomechanical stress, transitioning from stiff thoracic spine to more flexible lumbar spine. - This area is particularly vulnerable to axial loading and flexion injuries because it's a zone of increased mobility and stress concentration. *Upper thoracic spine* - The upper thoracic spine has **rib cage support** and less mobility, making fractures here less common without significant traumatic force. - Fractures in this region often indicate a **high-energy injury** due to its inherent stability. *Cervical spine* - While cervical fractures can be serious, they typically result from **high-energy trauma** and are less commonly simple compression fractures compared to the thoracolumbar region. - The **cervical spine** is more prone to **burst fractures** or **dislocations** from flexion-distraction or extension injuries. *Lumbosacral region* - The **sacrum and coccyx** are relatively stable bone structures and are less prone to common compression fractures unless there is severe trauma or significant bone weakening (e.g., severe osteoporosis). - While lumbar compression fractures do occur, the **junctional region** between the thoracic and lumbar spine (lower thoracic/upper lumbar) is statistically more frequent.

Orthopedic Biomechanics Flashcard 1 of 3

Question: Cloverleaf shape of K-nail on the cross-section which provides good _____ stability.

Answer: rotational

Orthopedic Biomechanics Flashcard 2 of 3

Question: When the knee is extended, the _____ bundle of ACL is tight, and the AM bundle is moderately lax.

Answer: PL

Orthopedic Biomechanics Flashcard 3 of 3

Question: When _____ is weak, trunk lurches backward at heel-strike on weakened side to interrupt forward motion of the trunk

Answer: gluteus maximus