This cadaveric study measures how inferior tuberosity malpositioning during fracture hemiarthroplasty affects glenohumeral joint forces. Eight shoulders were tested at anatomic height and with 10 mm and 20 mm of inferior tuberosity displacement. The question: does lowering the tuberosities explain the poor function seen clinically after these reconstructions?
When you are seating a fracture prosthesis, restoring humeral height is necessary for component stability, but over-reducing the head lowers the tuberosities relative to the articular surface. This study shows that dropping the tuberosities 10 mm or more shifts the joint reaction force superiorly during abduction, forcing the deltoid and cuff to work against their own mechanical disadvantage.
That biomechanical penalty is the likely reason patients with a radiographic head-to-tuberosity height over 20 mm have significantly worse function. Aim for the normal 7 to 8 mm.
A practical decision rule: if the greater tuberosity sits more than roughly 1 cm below the head apex, the reconstruction is over-reduced and function will suffer. There is also a stability cost, since half of specimens dislocated posteriorly at 20 mm in external rotation.
The limitation to weigh: this is static loading in 8 cadavers with no active or scapulothoracic motion, so it explains a mechanism rather than proving a clinical threshold.
This cadaveric study measures how inferior tuberosity malpositioning during fracture hemiarthroplasty affects glenohumeral joint forces. Eight shoulders were tested at anatomic height and with 10 mm and 20 mm of inferior tuberosity displacement. The question: does lowering the tuberosities explain the poor function seen clinically after these reconstructions?
When you are seating a fracture prosthesis, restoring humeral height is necessary for component stability, but over-reducing the head lowers the tuberosities relative to the articular surface. This study shows that dropping the tuberosities 10 mm or more shifts the joint reaction force superiorly during abduction, forcing the deltoid and cuff to work against their own mechanical disadvantage.
That biomechanical penalty is the likely reason patients with a radiographic head-to-tuberosity height over 20 mm have significantly worse function. Aim for the normal 7 to 8 mm.
A practical decision rule: if the greater tuberosity sits more than roughly 1 cm below the head apex, the reconstruction is over-reduced and function will suffer. There is also a stability cost, since half of specimens dislocated posteriorly at 20 mm in external rotation.
The limitation to weigh: this is static loading in 8 cadavers with no active or scapulothoracic motion, so it explains a mechanism rather than proving a clinical threshold.