Biomedical Engineering Reference
In-Depth Information
The analysis of the morphofunctional adaptations of the thrower athlete cannot
be circumscribed to the glenohumeral joint, and should be extended to the other
joints of the shoulder complex, particularly the scapulothoracic joint.
During the throwing cycle it is suppose that athletes, such as volleyball or
handball players, keep their scapula stable while the arm is fastly moved from
a full external position to a full internal position. Scapular stabilization could be
challanged when the arm motion is to fast. Therefore, an innadequate scapular
position at the end-range of glenohumeral motion will lead to shoulder dysfunction
and pathology [
21
].
The results showed that throwers demonstrated a scapula more in retraction
(acromion backwards) when compared with non-throwers. This seems to work
as a protective mechanism for the glenohumeral joint. In fact, the inability to
retract the scapula, appears to impart several negative biomechanical effects on the
shoulder, including narrowing of the subacromial space, increased strain on the
anterior-inferior glenohumeral ligament, reduced impingement-free arc of upper
limb elevation, reduced isometric elevation strength tested in the sagital plane.
Concerning this, throwers on our study seem to have developed an adaptation
towards stability.
While in clinical trial these kinds of patterns are important to evaluate, to
allow a better rehabilitation, with the traditional methods this does not seem
possible. Using 3D kinematic analysis, scapular positioning could be recorded and
morphofunctional adaptations could be identified, and also the specific movement
of throwers. While using traditional goniometry this cannot be possible.
Concerning axial shoulder rotation, scapular contribution is crucial as it is well
recognized that the external rotation needed to perform the throwing motion occurs
not only at the glenohumeral joint but also with the participation of the scapula [
21
].
Excessive motion is required at the shoulder joint during throwing, yet the
glenohumeral joint must remain stable to resist injury. We found that volleyball
players show a more posterior tilted scapula when arm is positioned more in external
rotation, while the control group showed less posterior scapula tilt. This seems to
demonstrate that shoulder adaptation on volleyball players, while throwing, does
not occur only at the glenohumeral joint, as it is commonly assumed in clinical
practice, but instead it is supported by the trunk where the scapula in retraction and
posterior tilt gives the necessary stability to achieve best performance. This seems
the reason why proper 3D position of the scapula relative to the humerus and trunk is
so relevant for muscle function. The scapula acts as the common point of attachment
of the rotator cuff and primary humeral movers such as the biceps, deltoid and
triceps, as well as several scapular stabilizers. Poor position of the scapula can lead
to alterations to the relationship between length and tension of each muscle, thus
adversely affecting muscle force generation [
45
]. An imbalance in external rotators
will lead to alterations in scapular tilt. Concerning the movement, clinical trials use
passive and active motion. But the active motion used is usually a slow motion [
26
],
and not simulating the sports practice. In our study we looked for active motion. We
have used an elevated arm position as the testing position, however the calibration
one, was the same proposed in the ISB protocol [
50
] as mentioned in methods, with
