Harryman and colleagues studied whether passive glenohumeral motion is accompanied by humeral head translation on the glenoid, and how operative tightening of the posterior capsule changes that translation.
Cadaver study of 7 isolated fresh glenohumeral joints, with an eighth joint used for the opposing‑force test.
Glenohumeral translation results from locally tight capsular tissue, not from asphericity of the humeral head.
Methods
Model
7 isolated fresh cadaveric glenohumeral joints
1 further joint for the opposing‑force test
Constructs
Intact capsule
Capsule vented with an 18‑gauge needle
Posterior capsule tightened by 2 cm mattress‑suture overlap
Capsule fully excised (control, subtracted to give net translation)
Loading
Five passive motions: flexion, extension, internal rotation, external rotation, cross‑body
Torque 3000 N‑mm
Opposing force of 30 to 40 N against flexion translation
Outcome measures
Direction and magnitude of humeral head translation with passive glenohumeral motion
Six‑degrees‑of‑freedom position sensor
Six‑axis force and torque transducer
Key Findings
The humeral head translated anteriorly with passive flexion and posteriorly with extension, and these translations were reproducible and significant.
No significant translation occurred through the mid‑range arc (-35° to 55° in the shoulder reported), only when flexion or extension went beyond it.
Anterior translation with flexion was obligate: an opposing force of more than 30 N did not change it.
Posterior capsular tightening raised mean anterior translation with flexion to 7.27 mm, from 5.14 mm with the capsule vented (3.79 mm intact).
With the posterior capsule tightened, the head also moved superiorly during flexion, but only by a mean of 2.13 mm.
Excising the capsule eliminated the translation, so the capsule, not head shape, drove it.
Board pearl
The humeral head translates away from the tight side of the capsule (capsular constraint mechanism), so obligate translation signals asymmetric capsular tightness, not laxity.
Authors' conclusion
Awareness that glenohumeral translation is associated with passive motion of the shoulder is clinically important in attempts to maintain or restore normal kinematics of the shoulder.
Harryman and colleagues studied whether passive glenohumeral motion is accompanied by humeral head translation on the glenoid, and how operative tightening of the posterior capsule changes that translation.
Cadaver study of 7 isolated fresh glenohumeral joints, with an eighth joint used for the opposing‑force test.
Glenohumeral translation results from locally tight capsular tissue, not from asphericity of the humeral head.
Methods
Model
7 isolated fresh cadaveric glenohumeral joints
1 further joint for the opposing‑force test
Constructs
Intact capsule
Capsule vented with an 18‑gauge needle
Posterior capsule tightened by 2 cm mattress‑suture overlap
Capsule fully excised (control, subtracted to give net translation)
Loading
Five passive motions: flexion, extension, internal rotation, external rotation, cross‑body
Torque 3000 N‑mm
Opposing force of 30 to 40 N against flexion translation
Outcome measures
Direction and magnitude of humeral head translation with passive glenohumeral motion
Six‑degrees‑of‑freedom position sensor
Six‑axis force and torque transducer
Key Findings
The humeral head translated anteriorly with passive flexion and posteriorly with extension, and these translations were reproducible and significant.
No significant translation occurred through the mid‑range arc (-35° to 55° in the shoulder reported), only when flexion or extension went beyond it.
Anterior translation with flexion was obligate: an opposing force of more than 30 N did not change it.
Posterior capsular tightening raised mean anterior translation with flexion to 7.27 mm, from 5.14 mm with the capsule vented (3.79 mm intact).
With the posterior capsule tightened, the head also moved superiorly during flexion, but only by a mean of 2.13 mm.
Excising the capsule eliminated the translation, so the capsule, not head shape, drove it.
Board pearl
The humeral head translates away from the tight side of the capsule (capsular constraint mechanism), so obligate translation signals asymmetric capsular tightness, not laxity.
Authors' conclusion
Awareness that glenohumeral translation is associated with passive motion of the shoulder is clinically important in attempts to maintain or restore normal kinematics of the shoulder.