Anatomy and Kinesiology Flashcards

During passive knee flexion, a massage therapist notices a hard end-feel at approximately 120° rather than the expected soft tissue approximation end-feel. Which clinical finding most accurately explains this presentation?

Answer: Osteophyte formation or intra-articular loose body blocking joint mechanics

A hard end-feel during passive knee flexion — where a soft tissue approximation (soft end-feel) is expected — indicates bony obstruction such as osteophytes or an intra-articular loose body. Hypertonic hamstrings would produce a firm/muscular end-feel and affect active rather than passive ROM. Quadriceps passive insufficiency would restrict flexion with a firm/muscular quality. Capsular pattern at the knee is a greater limitation of flexion than extension, but produces a firm/leathery end-feel, not hard.

The obturator internus muscle performs lateral rotation of the hip when the hip is extended. When the hip is flexed beyond approximately 90°, its mechanical line of pull shifts and it becomes a primary contributor to which movement?

Answer: Hip abduction

The obturator internus is unique because its function changes with hip position. When the hip is extended, it laterally rotates the femur. However, when the hip is flexed beyond ~90°, the muscle's line of pull shifts relative to the joint's axis of rotation, converting its action to hip abduction. This functional duality is a classic advanced kinesiology concept tested on certification exams.

A client presents with weakness in resisted shoulder abduction between 60° and 120° (the 'painful arc'), normal strength below 60° and above 120°, and no neurological deficits. Which structure is most likely compressed during this arc?

Answer: Supraspinatus tendon and subacromial bursa

The painful arc between 60°–120° of glenohumeral abduction is the hallmark of subacromial impingement, where the supraspinatus tendon and subacromial bursa are compressed beneath the coracoacromial arch. Below 60° the structures are not yet impinged; above 120° the greater tubercle rotates past the arch, relieving compression. The inferior glenohumeral ligament is a capsuloligamentous structure not involved in impingement. The biceps tendon produces a painful arc but typically at a different ROM and reproduces with Speed's test. The subscapularis is located anteriorly and is not a subacromial structure.

Which spinal ligament is the primary restraint against excessive anterior translation of one vertebral body on another (anterior shear), and is also the structure most commonly torn in whiplash-type hyperflexion injuries?

Answer: Posterior longitudinal ligament

The posterior longitudinal ligament (PLL) runs along the posterior aspect of the vertebral bodies inside the spinal canal. It resists anterior shear (forward sliding of a superior vertebra on the one below) and is placed under maximal tension during flexion. Hyperflexion injuries can rupture the PLL, potentially compromising the anterior wall of the spinal canal. The anterior longitudinal ligament resists hyperextension and distraction. The ligamentum flavum connects laminae and resists flexion but is not the primary anterior-shear restraint. The interspinous ligament connects spinous processes and is a secondary flexion restraint.

A muscle that crosses two joints is said to exhibit 'active insufficiency' when it reaches its shortest functional length. For the rectus femoris, active insufficiency occurs when the muscle attempts to:

Answer: Simultaneously flex the hip and extend the knee maximally

Active insufficiency occurs when a two-joint muscle is shortened across both joints simultaneously, preventing it from generating adequate tension. The rectus femoris is both a hip flexor and a knee extensor. Attempting to fully flex the hip AND fully extend the knee at the same time shortens the muscle at both ends simultaneously, rendering it actively insufficient — it cannot develop meaningful force in this position. This is why full knee extension becomes difficult when the hip is already maximally flexed (e.g., sitting with the thigh pressed to the chest). Option D describes the action of the hamstrings, the rectus femoris's functional antagonist.

The 'screw-home mechanism' of the knee joint involves terminal lateral rotation of the tibia relative to the femur during the final degrees of knee extension in the open kinetic chain. Which muscle is primarily responsible for 'unlocking' the knee from this close-packed position to initiate flexion?

Answer: Popliteus

The popliteus is the key muscle responsible for 'unlocking' the screw-home mechanism. In the open kinetic chain (non-weight-bearing), it medially rotates the tibia on the femur to reverse the terminal lateral rotation that occurred during full extension, allowing knee flexion to begin. In the closed kinetic chain (weight-bearing), it laterally rotates the femur on the fixed tibia to achieve the same unlocking effect. This unique role makes the popliteus a frequent topic in advanced kinesiology. The biceps femoris actually contributes to the external rotation component of the screw-home mechanism. The semimembranosus and sartorius are knee flexors but do not primarily serve the unlocking function.