Chapter 6 Elbow and Forearm

A forearm that passively supinates as the elbow is passively extended to its end range strongly suggests that biceps brachii (an elbow flexor and forearm supinator muscle) is excessively tight (stiff).

A patient has a 20-degree elbow flexion contracture that is assumed to originate from muscular tightness. As the clinician applies an extension stretch (torque) to the elbow near the end range of motion, the forearm passively "drifts" rather strongly toward supination. What clue does this observation provide as to which muscle or muscles are most tight (stiff)?

The only elbow flexor muscle that would potentially be paralyzed from a median nerve injury is the pronator teres. The other elbow flexor muscles would remain fully innervated. Overall loss of elbow flexion strength, therefore, would likely be minimal. Because of paralysis of essentially all pronator muscles, however, the forearm would be biased toward the position of supination. In time, the supinator muscles may shorten, thereby limiting the full extent of pronation

A patient has a median nerve injury at the level of the middle of the humerus. Would you expect any weakness in active flexion of the elbow? Over time, what deformity or "tightness pattern" is most likely to develop at the forearm?

Interosseous membrane

Along with the annular ligament the ________ provides critical passive stability to the Proximal Radial Ulnar Joint (PRUJ), and Distal Radial Ulnar Joint (DRUJ).

No, because the brachialis attaches distally to the ulna (rather than to the radius), the muscle does not cross the pronation-supination axis of rotation of the forearm. The muscle, therefore, cannot produce an active (or passive) torque on the forearm that could limit passive range of pronation or supination motion.

Assume you want to maximally stretch (elongate) the brachialis muscle by passively extending the elbow. Would the effectiveness of the stretch be enhanced by combining full passive pronation or supination of the forearm to the elbow extension?

The long head of the triceps, based on its physiologic cross-sectional area and internal moment arm length.

Based on data provided in Table 6-7, which head of the triceps produces the greatest elbow extension torque?

The dermis in the antecubital region has the longest moment arm length relative to the medial-lateral axis of rotation at the elbow. This relatively long moment arm length, in conjunction with marked resistance from this tissue, could contribute significantly to an elbow flexion contracture.

Based on moment arm alone, which tissue shown in Figure 6-18 A, could generate the greatest resistive torque opposing an elbow extension movement?

Falling onto an outstretched arm can cause a significant valgus-producing force to the elbow that injures the Medial collateral ligament (MCL). This same fall can also injure the LUCL if the valgus force also creates a large posterior-lateral rotational stress at the elbow. Such a rotational stress can injure the LUCL, which is naturally positioned to resist "external rotation" of the humeroradial joint

Describe a mechanism of injury at the elbow that could potentially injure the lateral (ulnar) collateral ligament (LUCL) from an excessive valgus-producing force applied to the elbow.

The broad triangular medial collateral ligament of the elbow allows for some of its fibers to pass anterior and posterior to the medial-lateral axis of rotation of the elbow. Consequently, at least some fibers are stretched and therefore relatively taut throughout the full range of flexion and extension. Taut fibers within the ligament provide a critical source of resistance against a valgus-producing force to the elbow

Describe how the different fibers of the medial collateral ligament of the elbow provide useful tension throughout the entire range of flexion and extension.

Arthrokinematics include a combined spin and a roll-and-slide in similar directions.

Describe the arthrokinematics at the humeroradial joint during a combined motion of elbow flexion and supination of the forearm.

No

During extension are they any articulating surface being contacted in the Humeroradial Joint?

The rim of the radial head slides in the capitulotrochlear groove entering the radial fossa

During flexion what occurs at the Humeroradial Joint?

Medial Collateral Ligament (MCL)

During the action of sequence of throwing or the action sequence of golfing the most amount of stress is placed on which elbow ligaments?

1. Arm in full supination 2. Radius is held firmly against the ground 3. Ulna is free to move on radius 4. Ulna perform ER to 90° this motion produces pronation at the weight bearing joint 5. Infraspinatus: Rotates humerus relative to fixed scapula 6. Pronator quadratus: Rotates ulnar relative to fixed radius 7. Collectively produce pronation torque at forearm

Explain the Osteokinematics of pronation in a closed chain environment.

Convex distal humerus will roll in posterior direction with a simultaneous anterior glide on Concave proximal ulna and radius Hack follow the shaft of the humerus toward the forearm

Explain the arthokinematics of closed chain elbow extension.

HRJ - spin of the radial notch of ulna and annular ligament around radius PRUJ - spin of the radial notch of ulna and annular ligament around radius DRUJ - Convex distal ulna rolls anterior and simultaneously slides/glides posteriorly upon the concave radius

Explain the arthokinematics of the forearm during pronation in a closed chain environment where the arm is already in supination.

HRJ (Humeroradial joint) - spin of the fovea (radial head) on the Capitulum PRUJ (Proximal Radial Ulnar Joint) - internal rotation of the radial head within the annular ligament and radial notch DRUJ (Distal Radial Ulnar Joint) - Concave distal radius rolls anteriorly and simultaneously slides/glides anteriorly upon the convex ulnar head

Explain the arthorkinematics of Pronation in an open chain environment.

Concave proximal ulna and radius simultaneously roll and slide posteriorly on the convex distal humerus. Hack follow the hand as is moves posteriorly

Explain the arthorkinematics of elbow extension in an open chain environment.

HRJ - spin of the radial head on the capitulum PRUJ - external rotation of the radial head within the annular ligament and radial notch DRUJ - Concave distal radius rolls posteriorly and simultaneously slides/glides posteriorly upon the convex ulnar head.

Explain the arthrokinematics of Supination in an open chain environment.

Convex distal humerus will roll in anterior direction with a simultaneously posterior glide on Concave proximal ulna and radius Hack follow the shaft of the humerus toward the forearm

Explain the arthrokinematics of elbow flexion in a closed chain environment.

Concave proximal ulna and radius simultaneously roll and slide anterior on the convex distal humerus. HACK follow the hand as it moves anteriorly

Explain the arthrokinematics of elbow flexion in a open chain environment

One, Flexion and Extension (Sagittal)

How many DOF are at the Humeroulnar Joint?

One, Pronation and Supination

How many DOF can occur at the Proximal Radioulnar Joint?

Three: The musculocutaneous nerve innervates the brachialis, the radial nerve innervates the brachioradialis (and part of the brachialis), and the median nerve innervates the pronator teres.

How many nerves innervate muscles that flex the elbow?

biceps muscle functions as the primary supinator of the forearm. With paralysis of the triceps (due to a radial nerve lesion) the biceps would flex the elbow, possibly pulling the screwdriver away from the screw.

How would a radial nerve lesion in the axilla affect the task depicted in the figure ?

From a weight-bearing position (and radius fixed), any muscle that can internally rotate the shoulder—such as the latissimus dorsi—can indirectly rotate the ulna to a position parallel with the radius. Such a position is defined as supination of the forearm. Full supination may be limited by tightness in the forearm pronators, extrinsic digital flexors, shoulder external rotators, posterior capsule of the shoulder, palmar capsule of the distal radio-ulnar joint, or central band of the interosseous membrane; as well as a painful Triangular Fibrocartilage Complex (TFCC).

In a weight-bearing position similar to that shown in Fig. 6.30 explain how, from a starting position of pronation, the latissimus dorsi could contribute to active supination of the forearm. Which tissues could restrict this active movement?

Muscular tissues capable of resisting a distal pull on the radius include the brachioradialis and biceps (or any muscle with a distal attachment onto the radius). Nonmuscular tissues include the annular ligament, oblique cord, or distal oblique fibers of the interosseous membrane

List both muscular and nonmuscular tissues that are able to resist a distal pull (distraction) of the radius

A relatively taut interosseous membrane provides longitudinal stability throughout the forearm and a firm connection for the attachments of many muscles that act on the digits.

List some biomechanical benefits of the near-isometric behavior of the central band of interosseous membrane during pronation and supination

Convex

The Capitulotrochlear Groove is convex or concave?

Triangular Fibrocartilage Complex (TFCC), Interosseous Membrane

The Distal Radial Ulnar Joint is made up of what ligaments?

disc that is a continuation of articular cartilage of the distal radius. Usually described as a shelf

The Triangular Fibrocartilage Complex (TFCC) is a ____?

attached to the edge of the ulna notch of the radius

The base of the Triangular Fibrocartilage Complex (TFCC) is ?

articulates with the carpal bones and is concave

The distal surface (inferior) of the Triangular Fibrocartilage Complex (TFCC) ______

Annular Ligament, Quadrate Ligament, Oblique Cord

The proximal radial ulnar joint is made up of what ligaments ?

concave at the distal radioulnar joint, it is deepened to accommodate the ulna head

The proximal surface (superior) of the Triangular Fibrocartilage Complex (TFCC) is _______

Oblique Cord Ligament

What acts as a shock absorber at the wrist for nonweight bearing activities ?

Interosseous Membrane

What acts as a shock absorber at the wrist for weight bearing activities?

Convex trochlea of the distal humerus articulates with the Concave trochlea notch of the proximal ulna

What are the arthokinematics of the Humeroulnar joint?

Oblique Cord Ligament, Annular Ligament, Brachioradialis

What are the main stabilizers that are able to resist applied forces distally?

Convex capitulum of the distal humerus articulates with the Concave head of the Radius

What is the arthokinematics of the Humeroradial joint?

Media-lateral

What is the axis of rotation at the Humeroulnar Joint?

Vertical

What is the axis of rotation of the Radioulnar joint?

The anterior deltoid has two roles in this action. First, the muscle flexes the shoulder to thrust the hand forward against the door. Second, the muscle produces a shoulder flexion torque that neutralizes the shoulder extension torque potential of the long head of the triceps

What is the kinesiologic role of the anterior deltoid during a "pushing" motion that combines elbow extension and shoulder flexion seen in the photo?

15 degrees, this angle results in lateral deviation of the ulna due to the medial angle of the trochlea extending more distally than does the lateral.

What is the normal carrying angle of the elbow also known as Cubitus (cubital) Valgus?

to resist Varus forces/stresses

What is the purpose of the Radial Collateral Ligament (Lateral Collateral Ligament LCL)?

to resist VaLgus forces/stresses

What is the purpose of the Ulnar Collateral Ligaments (Medial Collateral Ligaments MCL)?

Quadrate ligament

What ligament limits the spin of the radial head in supination/pronation?

Oblique cord

What ligament prevents the separation of the radius and ulna?

Infraspinatus, Pronator Quadratus

What muscle acts as a force couple in pronation in a closed chain environment?

The medial head of the triceps, based on its action and relative attachment site on the humerus

What muscle is the most direct antagonist to the brachialis muscle?

Shoulder extension, elbow extension, and forearm pronation.

What position of the upper extremity maximally elongates the biceps brachii muscle?

Biceps Brachii, Triangular Fibrocartilage Complex (TFCC)

What tissues are on tension during Pronation in an open chain environment?

~Triceps and triceps tendon, ~Posterior Joint Capsule, ~Certain fibers of the Radial Collateral Ligament (RCL) and Ulnar Collateral Ligament (UCL), ~Ulnar Nerve

What tissues are on tension during an open chain elbow flexion movement?

Dermis, Anterior Elbow Flexors (Biceps Brachii, Brachialis, Brachioradialis), Anterior Capsule, Anterior MCL

What tissues are on tension during elbow extension in an open chain environment?

Pronators, Triangular Fibrocartilage Complex (TFCC)

What tissues are on tension in supination in an open chain environment?

The extensor pollicis brevis attaches proximally on the radius and distally on the thumb. This muscle, therefore, does not cross the axis of rotation at the forearm and cannot produce a torque across the axis of rotation at the forearm

Why was the extensor pollicis brevis muscle not included in this chapter as a secondary supinator muscle of the forearm?

Even in the healthy extremity, the muscular action of active pronation (or even forming a tight grip) causes the radius to migrate proximally slightly, relative to the ulna. The amount of migration is limited by compression between the radial head and the capitulum and by increased tension in the central band of the interosseous membrane. Surgical resection of the head of the radius (due to a severe fracture, for example) creates a gap between the proximal radius and the capitulum. With a torn interosseous membrane, the radius would likely experience marked proximal migration, potentially creating a positive ulnar variance at the wrist. Increased positive variance can create damaging stress at the distal radio-ulnar joint and the wrist. The clinical scenario described above may also involve the implantation of a radial head arthroplasty. With a torn interosseous membrane, the proximal migration of the radius may cause excessive wear on the implanted radial head.

Why would a surgeon be concerned about the integrity of the interosseous membrane prior to a radial head resection?