How does forearm rotate

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You can also search for this author in PubMed Google Scholar. Correspondence to A. Van Der Vaart. Reprints and Permissions. Van Der Vaart, A. Point A indicates pronator teres distal enthesis just at the apex of radial curvature. Planes P 1 , P 2 and P 3 are parallel to each other and perpendicular to the forearm axis. P 1 passes through point B, P 2 passes through the most proximal point of the radial head and P 3 passes through point A.

Point X is the intersection between humeral axis and a plane perpendicular to the humeral axis that passes through point B. Point C is the most distal humeral point of the humeral axis. Point O is the intersection between plane P 3 and the forearm axis. The dashed circle indicates the zoomed-in area of the right image. B: Detail of the left image.

Distance l 1 is the sum of and Figs. Then, the distance l 1 in maximum elbow extension can be calculated as follows:. A static radius yellow is represented with the humerus in the three positions blue. Planes P 1 , P 2 and P 3 are represented.

Distance l pr is the distance between planes P 2 and P 3. The distance between planes P 1 and P 2 depends on the elbow position. The square indicates the zoomed-in area of the right image. B: Change in the position of point B and in the distance as a function of the elbow angle.

The position of point B for the three elbow angles is represented. Point B is positioned in a coordinates system x , y which center is the flexion-extension axis from a lateral point of view.

R c is the radius of the humeral condyle. Distance is the curvature of the radius, measured on dry bone [4] , [15]. Then, and can be respectively calculated from and by determining distance [4]. Knowing the position of point B and its projection on plane P 3 Fig. Point A is the radial attachment site of pronator teres. S1 and it is assessed with regards to the horizontal axis by angle. Figure 4 shows PT E rot throughout the flexion-extension and the pronation-supination ranges.

A: Three-dimensional surface showing efficiency values at each forearm and elbow angles. B: Projection of the three-dimensional surface on XY plane showing efficiency ranges at each forearm and elbow angles. The points connected by a continuous line indicate the forearm positions where efficiency is maximal for each elbow angle.

The dashed line indicates the neutral position of the forearm. The force that PT exerts on the radius is represented by Fig. The projection of this vector on the axial plane P 3 is represented by Fig. This component increases as the forearm pronates, regardless of the elbow position. It is also slightly greater in extension than in flexion of the elbow. These values decrease as the forearm pronates, reaching negatives values in pronation. Therefore, this component reaches lower negative values, i.

Several simulations were carried out to assess how E rot and components are modified by changes in some osteometric parameters. From the mathematic expression to calculate E rot see Materials and Methods and Figures 1 , 2 and 3 , it is easily inferable that a greater curvature of the radius , and so a greater rotational radius , leads to a proportional increase in the E rot values Fig. Hence, the moment of force can be improved by rising either the tangential force or the curvature of the radius.

Although both scenarios would cause an increase in E rot , they are related to different structural characteristics. All this information is summarized in Table 2. Simulations are shown throughout the flexion-extension range.

A: Simulations of an increase in. B: Simulations of a decrease in l pr. The effect caused by an increase in is similar to the effect caused by the decrease in l pr shown here. C: Simulations with different coordinates of point B cm. Conversely to the abovementioned simulations, the direction of the change in E rot and modulus increase or decrease caused by a change in the position of point B depends on the elbow angle Fig. When coordinate x increases, maximal E rot and modulus rise in flexion of the elbow and decrease in extension.

When this coordinate is lower, the values for these parameters decrease in flexion and rise in extension. When coordinate y is closer to 0, E rot and modulus increase in flexion and fall in extension, whereas when this coordinate is lower, these parameters decrease in flexion and rise in extension.

In the current study, PT E rot has been assessed throughout the entire flexion-extension range using three-dimensional technology. The variation of E rot obtained from our innovative biomechanical model is in agreement with the results of kinematic studies using cadaveric specimens [16] , [17] and virtual and resin models of the upper-limb skeleton [18] — [20] , as well as with analysis on forearm discomfort [21] and on electromyographic signals of the forearm pronators [7].

Pronator teres E rot is dependent on the skeletal structure of the arm, elbow and forearm, which in turn can be modified by the usage of this muscle. In this regard, the analysis of E rot has enabled to study the effect of the components of PT force vector on the upper-limb skeleton.

The perpendicular component of this vector shows high relative values, which indicates that an important part of PT force is employed in a direction parallel to the rotational axis of the forearm, i. This compression is also produced during the contraction of other upper-limb muscles, such as biceps brachii and the wrist and fingers flexors. As regards PT, the compressive effect on the radius is higher in pronation than in supination and slightly decreases from elbow extension to maximum flexion.

Although the differences are slight, this indicates that pronated positions of the forearm enhance the curvature of the radius through radial compression in a greater degree than supinated positions. This effect is independent of the skeletal structure, as is broadly unaffected by changes in the parameters used to calculate E rot.

When the forearm is pronated, biceps brachii is reflexly inhibited and plays little if any role in flexion, because it would supinate the forearm during contraction [22] — [24].

As mentioned, the perpendicular component of PT force is greater on the prone forearm. This increase may partially compensate the lack of action of biceps brachiii, enhancing the assisting role of PT as elbow flexor and joint stabilizer in this position. The component , which directs to the rotation center, reaches negative values in forearm pronation. When this component is negative, the vector directs opposite to the rotational center, and so it enhances the curvature of the radius.

Negative values are reached in a position of the forearm that gets closer to the neutral position as the elbow flexes. Therefore, the curvature of the radius is enhanced during pronation in flexion rather than in extension of the elbow. In any case, the relative values for responsible for the curvature of the radius are low when compared to values for , which suggests that radii with marked curvatures are more probably associated to compression forces from PT, among other muscles, than to forces applied perpendicularly to the forearm axis.

These findings are in agreement with a previous empirical study that revealed that the pattern of muscular loading exerted on the apex of the radial shaft curvature by the PT muscle plays an important role as a mechanical stimulus involved in diaphyseal bowing [15]. The effect that the skeletal structure and form have on E rot and on the force vectors has also been assessed.

The results show that a greater bowing of the radius entails an increase of E rot. This is consistent with previous studies suggesting an enhancement of PT action and forearm rotational power by a markedly bowed radius [3] , [25] — [28]. An increase of the radial curvature also causes that becomes negative in a more pronated position of the forearm, and so its modulus reach lower values in full pronation. Therefore, the radius is more easily bowed when its curvature is low. The radial location of PT muscle also affects E rot : at any elbow angle, E rot increases when this enthesis is more proximally located, which is consistent with previous observations in full elbow extension [3].

Moreover, radii with a more proximal enthesis for PT muscle lead to the reach of negative values of closer to the neutral position of the forearm. Therefore, these radii entail lower negative values for this component, i. Concerning the humeral medial epicondyle, E rot also tends to increase in all elbow positions as this structure enlarges.

Even though the current analysis uses a different approach to quantify humeral medial epincondylar projection , the results are consistent with previous studies [3] , [5] , [29]. Moreover, an enlargement of the medial epicondyle has the same effect on than a more proximally located radial enthesis for PT, and therefore a more medially projected epicondyle enhances radial curvature. The orientation of the medial epicondyle is also relevant for the determination of E rot. The alteration of this orientation causes changes in that lead to changes in E rot.

A more posteriorly oriented epicondyle, i. Moreover, a more proximally oriented epicondyle enhances E rot in full flexion, whereas when it is more distally oriented, E rot increases in extension.

Along with several other muscles, it arises from the medial epicondyle. In addition it has a small deep head of origin which arises from this part of the ulna.

The median nerve passes between the two heads of pronator teres as it enters the forearm. Pronator teres inserts here, halfway down the lateral surface of the radius. The second pronator muscle is pronator quadratus, which arises from the anteromedial aspect of the ulna, and inserts here, on the anterior surface of the radius. Here it is. It arises from the lateral epicondyle, from the anular ligament, and from this ridge on the ulna, the supinator crest.

The deep branch of the radial nerve runs through the supinator. It enters here, and emerges under here. The other supinator muscle we know about already. The insertion of the biceps on the radial tuberosity gives it plenty of power to rotate the radius, especially when the elbow is flexed.