NCBTMB Exam Kinesiology and Biomechanics 6

Question 1

During closed-chain knee extension, which of the following accurately describes the arthrokinematic behavior of the tibiofemoral joint?

Accepted Answer

The femoral condyles roll anteriorly and slide posteriorly on the fixed tibia

Answer

In closed-chain knee extension (e.g., standing up from a chair), the tibia is fixed and the femur moves. The femoral condyles roll anteriorly (in the direction of femoral motion) while simultaneously sliding posteriorly (opposite to roll) to maintain joint congruency. This concave-on-convex rule governs all synovial joint arthrokinematics.

Question 2

A massage therapist notices a client has a unilateral anterior pelvic tilt. Which combination of muscle imbalances most precisely explains this pattern according to Janda's lower crossed syndrome?

Accepted Answer

Shortened hip flexors and erector spinae; inhibited gluteus maximus and rectus abdominis

Answer

Janda's lower crossed syndrome describes a predictable pattern where the hip flexors (iliopsoas, rectus femoris) and lumbar erector spinae are overactive/shortened, while the gluteus maximus and deep abdominals (not rectus abdominis) are inhibited and lengthened. This imbalance produces anterior pelvic tilt and increased lumbar lordosis.

Question 3

The screw-home mechanism of the knee joint involves terminal external tibial rotation during open-chain extension. Which structure is primarily responsible for initiating UNLOCKING of this mechanism at the start of flexion?

Accepted Answer

Popliteus muscle

Answer

The popliteus muscle is classically described as the 'key' that unlocks the screw-home mechanism. At the initiation of knee flexion from full extension, the popliteus internally rotates the tibia (or externally rotates the femur in closed-chain) to disengage the locked position, allowing flexion to proceed. The ACL and LCL provide passive stability but do not actively unlock the joint.

Question 4

A client presents with weakness during resisted shoulder abduction between 60° and 120° with pain localized to the acromion region. Applying the biomechanical concept of the painful arc syndrome, which rotator cuff structure is MOST likely being compressed during this range?

Accepted Answer

Supraspinatus tendon and subacromial bursa

Answer

The painful arc (60°–120° of abduction) corresponds to the supraspinatus tendon and subacromial bursa passing beneath the coracoacromial arch. Below 60° and above 120°, these structures are not impinged. The infraspinatus, subscapularis, and teres minor occupy different anatomical positions that do not produce this specific arc pattern under the acromion.

Question 5

When analyzing gait biomechanics, excessive contralateral pelvic drop (Trendelenburg sign) during single-leg stance on the right limb indicates weakness in which muscle group on which side?

Accepted Answer

Right hip abductors (gluteus medius and minimus)

Answer

During right single-leg stance, the right hip abductors must contract eccentrically to prevent the unsupported (left) pelvis from dropping. If the right gluteus medius and minimus are weak, they cannot stabilize the pelvis against the body weight, causing contralateral (left) pelvic drop. The weakness is ipsilateral to the stance leg, not contralateral.

NCBTMB Exam Practice Test

NCBTMB Exam Practice Test

NCBTMB Exam Kinesiology and Biomechanics 6