Fractures and Dislocations: Forearm
Seth D. Dodds
David C. Ring
Forearm
I. Introduction
The rotary movements (pronation/supination) provided by the unique two bone, dual intra-articulation structure of the forearm greatly expand the variety of ways in which objects can be positioned and manipulated by the hand.
Loss of this motion as a result of malunion, prolonged immobilization, and/or proximal or distal radioulnar joint (DRUJ) incongruity following trauma to the adult forearm can be disabling.
The gradual improvement in functional outcomes and decrease in the rate of complications associated with the management of forearm fractures during this century parallel the history of the development of sound, stable techniques of internal skeletal fixation, which permit mobility while assuring the maintenance of skeletal alignment during fracture union.
Forearm fractures are often the sequelae of high-energy injury and a relatively large percentage are open fractures.
Injury and treatment-related complications include compartment syndrome, neurovascular injury, soft tissue loss, bone loss, refracture after plate removal, and posttraumatic radioulnar synostosis. Infection is unusual, even in the case of an open fracture due in part to the relative ease of wound debridement as well as the well-perfused forearm musculature.
II. Anatomy
There is a slight apex posterior bow along the entire length of the ulna as seen on a lateral radiograph.
The ulna is triangular in cross section through the majority of its midportion, becoming cylindrical distally. The laterally directed apex of the triangle corresponds with the insertion of the interosseous ligament. The posterior apex remains essentially subcutaneous as it divides the flexor and extensor musculature on the ulnar border of the forearm, and is palpable along the entire length of the bone.
The radius has a double curvature in both the anteroposterior and lateral planes.
The large ulnar concavity of the distal curvature of the radius allows for overriding of the ulna without restriction of pronation. Loss of this “radial bow” is associated with limitation in both forearm rotation and grip strength.
The radius rotates about the relatively stationary ulna along an axis that passes roughly through the center of the radial head proximally and the fovea of the ulnar head distally.
Rotation of the radius occurs via axial rotation of the radial head at the proximal radioulnar joint (PRUJ), whereas distally, the motion is a combination of axial rotation and translation of the radius relative to the ulna.
The association of the radius and ulna is maintained by ligamentous structures at the proximal and DRUJs as well as by the interosseous ligament, a ligamentous sheet interconnecting the two bones along their midportion that extends from radial-proximal to ulnar-distal.
The PRUJ is stabilized by the annular and quadrate ligaments proximally, and the interosseous ligament.
The distal radioulnar articulation is stabilized by the triangular fibrocartilage complex (TFCC). The complex represents a combination of structures that are inseparable in anatomic dissections including the articular disc, the dorsal and volar radioulnar ligaments, the ulnar collateral ligament, and the sheath of the extensor carpi ulnaris.
III. Operative Exposures
Ulna
The posterior apex of the ulnar shaft defines the plane between the extensor forearm musculature innervated by the radial nerve and the flexor musculature innervated by the ulnar nerve.
Elevate the muscle, extraperiosteally from only one side of the bone. Extraperiosteal means that you leave the periosteum on the bone, only elevate the muscle.
Radius
Dorsal or thompson exposure
The dorsal (or Thompson) approach has waned in popularity as a result of the potential of injury to the posterior interosseous nerve, which must be dissected from the substance of the supinator and protected.
A straight longitudinal skin incision is made along the line connecting the lateral epicondyle at the elbow with Lister tubercle at the wrist while the elbow is at 90 degrees of flexion and the forearm is in neutral rotation.
The internervous interval between the extensor digitorum communis (supplied by the posterior interosseous nerve) and the extensor carpi radialis brevis (supplied by the radial nerve) is most easily identified by locating the point at which the abductor pollicis longus and extensor pollicis brevis emerge from between the mobile wad and dorsal compartment musculature in the distal half of the forearm.
The deep fascia is incised directly adjacent to this interval and the muscles are separated in a distal to proximal direction until their common aponeurosis is encountered. The supinator muscle covering the proximal radius is thereby exposed.
Utilization of the proximal portion of the dorsal surface of the radius for plate fixation requires identification and mobilization of the posterior interosseous nerve as this nerve may lie almost directly adjacent to the bone at this level and could potentially be trapped beneath a plate. The posterior interosseous nerve emerges from between the superficial and deep heads of the supinator muscle approximately 1 cm proximal to the distal limit of this muscle. It can be identified at this point and then dissected free from the muscle being careful to preserve its muscular branches. Following
sufficiently proximal mobilization of the nerve, exposure of the radial shaft can be performed by rotating the radius into full supination and detaching the insertion of the supinator from the anterior aspect of the radius.
Exposure of the midportion of the bone is facilitated by mobilization and retraction of the crossing abductor pollicis longus and extensor pollicis brevis muscles. Exposure of the radius distal to the extensor pollicis brevis is performed in the interval between the radial wrist extensors (extensor carpi radialis brevis and longus muscles) and the extensor pollicis longus muscle, which ultimately produce the tendons occupying the third and second dorsal extensor compartments, respectively.
Anterior or Henry exposure
Exposure of the anterior surface of the radius is both safer and more extensile than a dorsal exposure.
A straight longitudinal incision along a line between the lateral margin of the biceps tendon at the elbow and the radial styloid process at the wrist will afford access to the plane between the mobile wad and the flexor musculature of the forearm.
The deep fascia is incised adjacent to the medial border of the brachioradialis and a plane is developed between this radial nerve-innervated muscle and the median nerve-innervated flexor carpi radialis and pronator teres muscles. Dissection is initiated distally and proceeds proximally following the course of the radial artery.
Arterial branches to the brachioradialis and the recurrent radial artery arising near the elbow are ligated and the radial artery is mobilized and retracted medially with the flexor carpi radialis muscle.
The superficial radial nerve is encountered on the undersurface of the brachioradialis and remains lateral with this muscle.
Deep dissection is initiated proximally where the biceps tendon is followed toward its insertion on the bicipital tuberosity of the radius. Full supination of the forearm displaces the posterior interosseous nerve laterally and brings the insertion of the supinator muscle anterior. The insertion of the supinator muscle is identified by deepening the muscular plane along the lateral aspect of the biceps tendon. Here one may encounter a bursa between the biceps tendon and the supinator, which further facilitates this dissection.
The posterior interosseous nerve remains well protected within the substance of the supinator muscle during elevation of its insertion from the radius, provided that excessive lateral traction is not applied and the forearm is held in supination.Related posts:
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