Codman's Paradox, Shoulder Motion PDF

 Codman's paradox It is a sequential movements about the two axes of the shoulder, bring about a mechanical and involuntary movement about the longitudinal axis of the upper limb. This conjunct rotation occurs only during sequential movements Automatic rotation occurs in...

 Codman's paradox It is a sequential movements about the two axes of the shoulder, bring about a mechanical and involuntary movement about the longitudinal axis of the upper limb. This conjunct rotation occurs only during sequential movements Automatic rotation occurs in biaxial joint or triaxial joint when only two of these axes are in use. Codman's paradox refers to a specific pattern of motion at the shoulder joint. It asked how a mysterious axial rotation about the longitudinal axis of the arm occurred during two or three sequential arm rotations that did not involve rotation about the long-axis. ……………………………………………………………………………………. Apply ………………………………  AXES OF MOTION AND MOVEMENTS PERMITTED Movements of the glenohumeral joint are occurring about three axes perpendicular to each other, all of which pass through the center of the head of the humerus; - Flexion takes place in the sagittal plane about a transverse axis through the head of the humerus. Approximately 90 degrees of motion is permitted. At this instant the coracohumeral ligaments become taut and limit further motion. -Extension is the reverse of flexion. When the arm passes behind the body, the movement is called hyperextension. The range of motion is 40 to 60 degrees and is limited again by the coracohumeral ligaments.  AXES OF MOTION AND MOVEMENTS PERMITTED - Abduction occurs in the frontal plane. The amount of abduction permitted depends on rotation at the glenohumeral joint. When the joint is in full internal rotation, active abduction is limited to approximately 60 degrees, because the greater tubercle strikes the acromion process and the coracoacromial ligament With external rotation, active abduction increases to 90 degrees as the greater tubercle goes behind and under the acromion. Here le limiting structures are the glenohumeral ligaments. -Adduction is the reverse of abduction. When performed strictly in the frontal plane and the arm is lowered to the side, adduction is arrested by contact with the body. With the arm slightly in front or in back of the body, the movement range increases is functionally important, but is not classified as pure adduction. The term horizontal abduction is often used to indicate a movement in the horizontal plane, starting with 90 degrees flexion and moving laterally to 90 degrees abduction. Horizontal adduction is the reverse movement.  AXES OF MOTION AND MOVEMENTS PERMITTED - External (lateral) rotation takes place about an axis longitudinally through the head d the shaft of the humerus in the horizontal plane. If the arm is hanging a: the side of the body, external rotation causes the medial epicondyle of the humerus to move posteriorly. When the glenohumeral joint is placed in the standard goniometric position of 90 degrees of shoulder abduction and 90 degrees of elbow flexion the normal range of external rotation is ap- proximately 90 degrees. Functionally, full range of external rotation is needed to place the hand behind the neck. - Internal (medial) rotation occurs in the same plane as external rotation. "When the arm is at the side of the body, the medial epicondyle of the humerus moves posteriorly Conventionally, internal rotation is considered to be..90 degrees.-When, however, shoulder girdle movements are prevented, internal rotation is usually found to be approximately 70 to 80 degrees.  AXES OF MOTION AND MOVEMENTS PERMITTED - External (lateral) rotation takes place about an axis longitudinally through the head d the shaft of the humerus in the horizontal plane. If the arm is hanging a: the side of the body, external rotation causes the medial epicondyle of the humerus to move posteriorly. When the glenohumeral joint is placed in the standard goniometric position of 90 degrees of shoulder abduction and 90 degrees of elbow flexion the normal range of external rotation is approximately 90 degrees. Functionally, full range of external rotation is needed to place the hand behind the neck. - Internal (medial) rotation occurs in the same plane as external rotation. "When the arm is at the side of the body, the medial epicondyle of the humerus moves posteriorly Conventionally, internal rotation is considered to be..90 degrees.-When, however, shoulder girdle movements are prevented, internal rotation is usually found to be approximately 70 to 80 degrees. A functional check for maximum range of internal Ration is the ability to place the hand behind the back and touch the opposite scapula Summary of Active Arthrokinematics Resisting Shear  Glenohumeral joint stability Depends on: 1- A glenoid cavity of an adequate sides. 2- A posteriorly titled glenoid fossa. 3- A post tilted humeral head. 4- An intact capsule & labrum glenoid 5- Tensile force of the ligaments. 6- Functional muscles controlling the anteroposterior position of the humeral head (rotator cuff; supraspinatus - subscapularis - infraspinatus - teres minor).  Dynamic stability of glenohumeral joint The requirement varies, throughout the range. Anterior stability is the function of the subscapularis muscle while the infraspinatus and teres minor protect the humeral head posteriorly. There must be equilibrium between muscular force (rotatory and stabilizing) and force of gravity. Scapulohumeral Rhythm "Scapulothoracic and Glenohumeral Contributions“  Dynamic stability of glenohumeral joint The scapulothoracic joint contributes to both flexion and abduction (elevation) of the humerus by upwardly rotating the glenoid fossa 60° from its resting position. If the humerus were fixed to the fossa, this alone would result in 60° of elevation of the humerus. The humerus is not fixed, of course, but can move independently on the glenoid fossa. The glenohumeral joint contributes 120° of flexion and anywhere from 90 to 120° of abduction (depending on individual structural variations and on one's philosophy of available glenohumeral abduction). The combination of scapular and humeral movement results in what is commonly held to be a maximum range of elevation to 180° and in an overall ratio of 2° of glenohumeral to 1 ° of scapulothoracic motion. When less maximum range is cited for the glenohumeral joint, the ratio may be close to 3° of glenohumeral movement to 2° of scapulothoracic.  The purpose of scapulohumeral rhythm is threefold 1- Distributing the motion between two joints permits a large ROM with less compromise of stability than would occur if the same range occurred at one joint. 2- Maintaining the glenoid fossa in an optimal position to receive the head of the humerus increases joint congruency while decreasing shear forces. 3- Permitting muscles acting on the humerus to maintain a good length-tension relationship minimizes or prevents active insufficiency of the GH muscles.  Scapulohumeral rhythm This term express the pattern of coordinated movement of different shoulder girdle articulation. The ratio, of glenohumeral articulation to scapular movement is generally 2 : 1 for arm elevation. This ratio changes according to: 1-Degree of arm elevation. 2-Addition of load during elevation. 3-Variation among subjects. The scapular movement is possible only because an equal amount of motion takes place at AC it and S.C.  Scapulohumeral rhythm Elevation of the arm through a full ROM normally requires 60° of scapulothoracic motion and 120° of GH motion. These motions occur concomitantly, not sequentially. Sideward elevation through scapulohumeral rhythm  Close and Loose Packed Position Close Packed position o Position where the articular surfaces of joint are in maximal congruency status, resulting in greatest mechanical stability. o Most ligament and capsule surrounding joint are taut. o 90° of glenohumeral abduction and full external rotation Loose Packed position o Position where the articular surface of joint are in minimal congruency status. o Supporting structures are most lax. o 55° of semi-abduction and 30° of horizontal adduction  KINETICS The involvement of a great many muscle complicate exact calculation of the loads acting on the shoulder joint complex. Also the unusual aspects of these muscle action adds to the problem. These aspects are: a- Since the glenohumeral joint lack rigid stability a muscle exerting an effect on the humerus must act in concert with other muscles to avoid producing a dislocating force in the joint b- The existence of multiple linkeage in the shoulder lead to the situation that a single muscle may span several joints, exerting an effect on each. e.g. lattismus dorsi muscle. c- The extensive range of shoulder motion cause muscle function to vary depending on the position of the arm in space.  KINETICS Forces generated by surrounding musculature to support the limb is approximately 10 times weight of the limb at 60 degrees of abduction while it reaches 8.2 times the weight of the limb at 90 degrees of abduction. Internal rotator strength exceed the external rotator strength by a ratio of 3 to 2. Extensor strength exceeds flexion strength by a ratio of 5 to 4 and adduction strength exceeds abduction strength by a ratio of 2 to 1.  Loading of glenohumeral joint The glenohumeral joint receives the largest portion of load of the shoulder joint complex. The joint reaction force is approximately 0.9 of body weight at 90 degrees of scapular plane elevation. The shear force is about 0.4 w at 60 degrees of elevation.  Pathomechanics of Shoulder Abnormal motion of the shoulder complex is often severe that may involves pain, soft tissue lesions or paralytic that may seek surgery. - Shoulder dislocation , anterior -inferior dislocation is common with laxity and weakness of this direction of the capsule. Predisposition may include muscle weakness with the importance of conditioning of rotator cuff. - Painful arc syndrome; pain referred to the lateral arm between 60 and 120 abduction with the impingement that aggravate the sense of pain. - Combined serratus anterior and trapezius paralysis , there is specific difficulty in raising the arm above head with loss of the scapular part of rotation (as a force couple). Impingement: Roll-Slide Kinematics Summary of Active Arthrokinematics Resisting Shear “Roll” created by abduction not countered with “Slide” action