Radius and Ulna

Radius and Ulna

Vidyadhar Upasani

Henry Chambers


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.

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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).


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.

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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Nov 17, 2018 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Radius and Ulna

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