Radius and Ulna
Vidyadhar Upasani
Henry Chambers
INTRODUCTION
Forearm fractures, especially about the wrist, are among the most common pediatric injuries. When a child falls off a bike, scooter, or skateboard, the upper extremity bears most of the force, particularly the forearm and wrist, because the arms are often used to brace one’s fall: this is a variation of the parachute reflex (Fig. 10-1). The parachute reflex protects the vital organs, often at the expense of the forearm.
“Learning is not attained by chance, it must be sought for with ardor and attended to with diligence.”
—Abigail Adams
 Figure 10-1 Children of every age enjoy a variety of sports. This junior bull rider suffered bilateral distal radius fractures from this fall. (Photo courtesy of R. Knudson.) |
 Figure 10-2 Malrotation limits movement. Ninety degrees of pronation deformity, as shown here, limits pronation to the mid-position, because the proximal radioulnar joint has reached the limit. |
In many ways, these fractures are different from those of adults:
Shattering injuries of the articular surfaces of each end of the radius are less common.
The bones may bend or plastically deform without a complete fracture.
Non-union is rare.
Fractures of the shafts of both bones of the forearm can usually be managed closed, therefore requiring reduction and casting skills.
Forearm fractures in children have remodeling potential, which does not exist in adult forearm fractures.
Anatomy and Pathology
The forearm bones are subcutaneous in the lower half of the forearm. The quality of reduction can be appreciated, not only by the surgeon but also by the patient when the cast comes off.
Forearm rotation has a range of 180 degrees, perhaps the greatest range of rotation of any joint in the body. Although a decrease of rotation by 50% may go unnoticed for most activities, fractures should be reduced well so that patients will re-gain adequate rotation.
Fractures have been produced in cadavers and plated with various types of malunion to determine the effects of each.
Ten degrees of malrotation limits rotation by 10 degrees (Fig. 10-2).
Ten degrees of angulation limits rotation by 20 degrees (Fig. 10-3).
Bayonet apposition does not limit rotation.
Pure narrowing of the interosseous distance is important in proximal fractures. (Narrowing impedes rotation by causing the bicipital tuberosity to impinge on the ulna.)
Malalignment of fractures of the ulnar metaphysis increases the tension on the articular disc so that the head of the ulna is not free to rotate (Fig. 10-4).
Clinical Examination
Some injuries to the forearm are more obvious than others. First observe the extremity to see how the child holds it and if there is deformity. With severe deformity, the child will be difficult to examine due to pain and/or fear. The joints above and below the suspected site of injury are examined to rule out other injuries. The Monteggia injury should not be missed. Supracondylar fractures are often seen along with a distal radius fracture.
 Figure 10-3 Angulation malunion limits rotation, because the interosseous membrane cannot widen and narrow. |
 Figure 10-4 Angulation of the distal ulna prevents rotation of the ulna. |
Distal pulses, nerve function, and forearm compartment status are noted. As always, it is important to only document what you can confirm. Look at the forearm in its position of displacement. You should be able to tell from the shape of the arm how the distal fragment lies in relation to the proximal part.
It sometimes helps if first part of the arm below the fracture is blocked off from vision with a hand and then the part above. If the upper part of the arm lies in supination, and the distal part looks as if it is pronated, a simple supination force on the hand will reduce the fracture. The first person who sees the child has a great advantage, because he or she are the only one who can see the limb as it lies (Fig. 10-5). Prior vigorous splinting may make this analysis problematic.
The skin exam is critical. Often there is a small puncture wound where a bone end stuck through the skin and then retracted back. The spike of bone may have pulled debris and bacteria back inside with it. If you can visualize subcutaneous fat or express hematoma through a puncture hole, it should be considered an open fracture and treated appropriately.
Despite the presence of closed fascial spaces in the forearm, the risk of ischemic contracture is low if a well-padded splint or split cast is used. Nerve injuries are also rare but can occur from stretch or laceration.
 Figure 10-5 Typical deformity in a forearm fracture. A fracture with this deformity (apex dorsal, ulnar angulation) often is most easily reduced by supination. |
 Figure 10-6 A change in the diameter of the radius, the width of the cortex, and the smooth curve of the radius indicate malrotation. |
 Figure 10-7 Angulation is usually associated with rotation. Use a strip of paper to prove this yourself. |
RADIOGRAPHIC ISSUES
Standard AP and lateral views of the forearm are the usual films performed when a child has a forearm injury. A separate elbow film may be needed to evaluate the relationship between the radial head and the capitellum (Monteggia injury). Beware the forearm film that does not clearly show the radial head-capitellar relationship or because the x-ray technician has placed the name-plate over this vital area.
Radius
The radius is a curved bone that is pear-shaped in cross section. Malrotation of the radius is recognized by a break in the smooth curve of the bone and by a sudden change in the width of the cortex (Fig. 10-6).
Angulation
Angulation that produces a volar apex or prominence is conventionally described as volar angulation or bowing. Some describe the distal fragment as being dorsally displaced or tilted. If the distal fragment is tipped in the palmar direction, a dorsal angulation is created. This is worth stating clearly because telephone conversations about fractures are often plagued by semantic ambiguities.
Rotation
X-rays are two-dimensional, so it is difficult to recognize and understand rotational deformity. A supination or pronation force causes most fractures. For example, when a child extends the hand to break a fall, the pronated thenar eminence hits the ground first and an immediate supination force is applied. The radiographic appearance of this fracture seems to be apex volar angulation, but the displacement is usually rotational. Test this for yourself with a strip of paper, as shown in Figure 10-7. If the surgeon considers only the angulation and corrects it, the rotational deformity will remain uncorrected. An apex volar fracture is often more accurately reduced by applying a pronation force to the hand, whereas an apex dorsal fracture is usually better reduced with a supination force to the hand. It may help to remember that when reducing these fractures, the thumb is rotated toward the apex of the deformity.
Position of Bicipital Tuberosity
The bicipital tuberosity is a good landmark for understanding rotation. It normally lies medially when the arm is fully supinated, posteriorly in mid-position, and laterally in full pronation (Fig. 10-8). This method is better applied in older children who have a more prominent tuberosity.
 Figure 10-8 The bicipital tuberosity as a guide to the rotation of the proximal radius. If you cannot remember where the bicipital tuberosity should be, put an ink mark on your palm at the site indicated. The prominence of the tuberosity always points in this direction. |
In complete fractures, the rotational position of the proximal fragment can be identified by this method to aid in reduction. The distal fragment is lined up in the same degree of rotation as the proximal fragment, which usually maintains its normal position.
Application
The above theories must be applied when reducing forearm fractures. Although useful in achieving reduction, casting in distorted positions of rotation makes x-ray analysis difficult. Except for extreme cases (Monteggia or Galeazzi fractures), we apply a long arm (above elbow) cast with the forearm in neutral rotation (after using rotational theory to achieve reduction). Follow-up x-rays are much easier to analyze (clear AP and lateral views).
Ultrasound Assisted Management
Point-of-care ultrasounds are gaining popularity in assessing pediatric forearm fractures. This has been considered as a potential alternative that avoids exposure to ionizing radiation. A prospective, nonrandomized, interventional diagnostic study was recently completed demonstrating that after a short training program, inexperienced physicians could appropriately diagnose pediatric forearm fractures with ultrasonography. Although this technique has been popularized by emergency department physicians, it will likely take time to infiltrate orthopedic offices that are more comfortable with traditional radiographs.
 Figure 10-9 Typical SH I fracture. A. Diagram illustrating bleeding and swelling but without displacement. B. X-ray at injury (normal). C. Treatment—either a cast or splint (if patient is cooperative) can be used. |
 Figure 10-10 The typical SH II fracture of the distal radius can be reduced with a hematoma block or conscious sedation. |
DISTAL FRACTURES—PHYSEAL
Salter-Harris Type I Injuries
Type I injuries are seen in younger children, are seldom much displaced, and are diagnosed on clinical suspicion more than by radiographic findings (Fig. 10-9). Swelling and tenderness at the growth plate, despite normal radiographs, are grounds for making the diagnosis. The radiograph may demonstrate a slight widening of the physis. Protection for 3 weeks in a cast or removable splint provides adequate treatment. You may consider this over-treatment, but the entity is common, real, and painful. A cast relieves the symptoms and stops the parents worrying. On follow-up exam, callus formation may be seen on the radiograph confirming the diagnosis. In general, only cases with more severe trauma would have follow-up to rule out occult physeal injury.
Salter-Harris Type II Injuries
Type II injuries are the most common, usually associated with posterior displacement (volar angulation) and are frequently accompanied by a chip off the ulnar styloid (Fig. 10-10).
This angulation pattern is often referred to as a Colles type fracture (although Colles described it in adults). For typical volarly angulated Type II fractures, wrist flexion alone may not maintain the reduction, because the wrist joint flexes easily to 80 degrees before the capsule tightens enough to exert any influence on the distal fragment. Thus, in addition to moderate wrist flexion, three-point molding must be optimized.
Several studies have evaluated long arm (above elbow) versus short arm casts to manage these fractures, demonstrating minimal differences in clinical outcome. At our institution, a well-molded (excellent molding required—Fig. 10-11) short arm cast is usually selected to maintain alignment yet allow early elbow motion (if the fracture is in the distal third of the forearm). Exceptions include severely displaced fractures and “chubby forearms” that pre-dispose to a cast “sliding off.”
Distal physeal fractures can also be seen with anterior displacement (dorsal angulation—Smith variant) because of a fall from a bike, scooter, etc. These Smith-variant fractures are easily reduced by direct pressure (with appropriate anesthesia). The reduction maneuver and molding are reversed (from Colles pattern) when the cast is applied (Fig. 10-12).
In 4-6 weeks, the fracture will be united and the cast can be removed. If a reduction was performed, the child should return to clinic in 1 week for an x-ray check to ensure maintenance of reduction. Severe loss of reduction, up to 10 days after the original injury, is usually
re-reduced under general anesthesia. If more than 10-14 days past injury, this re-reduction may damage the physis; thus, the fracture is left in its mal-reduced position with hope for remodeling. In rare cases, a late osteotomy will be required.
re-reduced under general anesthesia. If more than 10-14 days past injury, this re-reduction may damage the physis; thus, the fracture is left in its mal-reduced position with hope for remodeling. In rare cases, a late osteotomy will be required.
 Figure 10-11 Hyndman et al. studied the ratio of the cast width for maintaining fracture reduction. The lateral diameter (A) must be significantly less than the AP diameter (B) to maximize molding and stability. |
It is important to discuss the risks of physeal closure with the family. We follow these children at 6 months and even 1 year after the fracture has healed to assess for premature closure. X-rays of both wrists are taken at follow-up visits, and if there is suspicion of early closure, a CT or MRI can help to further evaluate possible closure.
Salter-Harris Type III and IV Injuries
Injuries that involve the joint surface are less common in children and can be difficult to see on the radiograph. For these injuries, the stepoff, depression, or gap at the joint surface as well as physeal congruity are best evaluated with a CT scan.
If significant displacement is seen (greater than 2 mm in any direction), reduction is required to minimize joint incongruity and risk for physeal closure. This can be performed arthroscopically, or more typically with a dorsal or volar incision, depending on where the joint damage is located. Plan your incision to get maximum exposure of the joint injury. When possible, we try to minimize internal fixation and use percutaneous pins that are removed after 3-4 weeks, prior to starting motion. If more permanent fixation is required to maintain the reduction, all fixations must be countersunk (or very low profile) to prevent injury to the tendons as they glide over the implants.
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