Question at position 6 Which biomechanical mechanism is primarily responsible for maintaining dynamic stabilization of the humeral head during arm elevation?Ligamentous tension of the coracoclavicular ligamentsStructural rigidity of the acromionCompression generated by the rotator cuff musclesPassive tension of the joint capsule aloneClear my selection单项选择题
A
Ligamentous tension of the coracoclavicular ligaments
B
Structural rigidity of the acromion
C
Compression generated by the rotator cuff muscles
D
Passive tension of the joint capsule alone

Question

Question at position 6 Which biomechanical mechanism is primarily responsible for maintaining dynamic stabilization of the humeral head during arm elevation?Ligamentous tension of the coracoclavicular ligamentsStructural rigidity of the acromionCompression generated by the rotator cuff musclesPassive tension of the joint capsule aloneClear my selection单项选择题

A

Ligamentous tension of the coracoclavicular ligaments

B

Structural rigidity of the acromion

C

Compression generated by the rotator cuff muscles

D

Passive tension of the joint capsule alone

BlackTom AI · Accepted Answer

Compression generated by the rotator cuff muscles (the concavity‑compression mechanism) is the principal biomechanical mechanism that dynamically stabilizes the humeral head during arm elevation.

1) Relevant knowledge points and concepts
- The glenohumeral joint is inherently mobile and relies on both static (capsule, labrum, ligaments) and dynamic (muscle) stabilizers.
- The rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis) produces a compressive force that centers the humeral head into the glenoid fossa; this is called concavity‑compression.
- During elevation, large movers (e.g., deltoid) create superior or translational shear forces that must be countered to keep the joint congruent.

2) Step‑by‑step reasoning
- As the arm elevates, the deltoid generates a large upward resultant force on the humerus.
- Without counteraction, this would translate the humeral head superiorly and cause instability or impingement.
- The rotator cuff contracts concentrically, pulling the humeral head medially and slightly inferiorly into the glenoid and increasing compressive joint reaction force.
- The increased compression into the concave glenoid surface resists translation and maintains joint centering throughout motion.

3) Intermediate steps (force balance shown conceptually)
- Deltoid force vector → upward shear on humeral head.
- Rotator cuff force vectors → medial/inferior components + compression.
- Net effect → resultant joint reaction directed into glenoid center → stability.

4) Why the correct answer is correct
- Dynamic stabilization during movement requires active muscle compression; experimental and clinical data show rotator cuff activity is essential for centering and resisting translational forces during elevation.

5) Why other options are incorrect
- Ligamentous tension of the coracoclavicular ligaments: these stabilize the clavicle–scapula relationship (AC joint), not primary for glenohumeral dynamic centering during elevation.
- Structural rigidity of the acromion: provides a roof and can limit superior migration but is passive and not the primary mechanism keeping the humeral head centered during active motion.
- Passive tension of the joint capsule alone: capsule contributes at extremes of motion, but passive structures cannot provide the active, adjustable centering force required during elevation.

6) Conclusion
The dynamic, active compressive force produced by the rotator cuff muscles is the primary mechanism maintaining humeral head stability during arm elevation, confirming the correct answer: Compression generated by the rotator cuff muscles.