In this article, hand surgeons from the Philadelphia Hand Center at Jefferson University (Philadelphia, Pennsylvania) review injuries that cause forearm instability. They present normal anatomy and biomechanics of the forearm affected by these injuries and discuss treatment for forearm instability.
What is forearm instability? Forearm instability is the disruption of the joints of the two forearm bones where they join at the top (elbow) or bottom (wrist). Traumatic events strong enough to send a compression force through the forearm can result in bone fractures and tears of the soft tissues of the forearm. The specific areas of damage that cause a disruption of forearm stability affect the radial head, the triangular fibrocartilage complex (TFCC), and the interosseous membrane.
A quick look at normal forearm anatomy will help understand this injury. First, the forearm is made up of two major bones: the radius and the ulna. They are held together by joints at either end and ligaments and cartilage from one end to the other. The interosseous membrane connects the two bones together from top to bottom.
The triangular fibrocartilage complex (TFCC) is an articular disc where the radius and ulna meet at the wrist. This triangle-shaped structure binds the radius and ulna firmly together and prevents dislocation while still allowing free motion. The outside margins of the complex are attached to the ligaments of the wrist joint.
There are varying degrees of injury and disruption of forearm stability. Injuries range from fracture of the radial head without tearing of the supportive soft tissues to fracture plus complete rupture of the TFCC and interosseous membrane. Immediate surgical repair is needed for this type of injury. But the problem is, the extent of the injury might not be recognized and treatment is delayed. The longer the delay, the worse the final outcome.
Working together, these three anatomical structures make it possible for the forearm to remain stable while under various types of load from the wrist and hand up to the elbow. The interosseous membrane is especially good at transferring loads between the two bones of the forearm. That helps take some of the stress off the elbow.
What kind of trauma is powerful enough to disrupt these anatomical structures? Well, a fall from a height onto an outstretched hand with the elbow extended will do it. And if it’s so traumatic, why doesn’t it get properly diagnosed? The fracture is easy enough to see on X-ray.
Usually the head of the radius is either removed or replaced. Removal without replacement results in migration (movement) of the radius up slightly (toward the shoulder). Tears of the interosseous membrane have the same effect. Without the membrane holding the two bones together and without the head of the radius butting up against the epicondyle, the bone starts migrating. So it’s easy to think the changes occurred because of the radial migration without realizing there’s a problem with the interosseous membrane. And swelling in the forearm often limits motion as well, further confusing the picture.
It isn’t until the patient experiences continued pain at the elbow and wrist that the full extent of the injury is recognized. The interosseous membrane accounts for the majority of forearm stiffness. Without this important protective feature, the forearm can’t resist force from the wrist to the elbow. And for every one millimeter of radial migration that occurs, the load at the wrist increases by 10 per cent. You can see why wrist pain is the result.
What can be done? The patient must be re-evaluated. A more comprehensive diagnosis is determined. Additional X-rays, ultrasound studies, and MRIs will help pinpoint the area of damage and degree of soft tissue disruption. Once the injuries are fully identified, then a treatment plan can be determined.
Treatment options are broken down into two groups based on how much time has gone by since the injury occurred. Immediate recognition of the problem and treatment right away describes the acute phase of injury. As already mentioned, the fractured radial head is attended to first.
Sometimes the fractured pieces of bone can be wired back together. If the interosseous membrane and triangular fibrocartilage complex (TFCC) are okay, it’s best to try and save the radial head. If repair isn’t possible, then replacement is considered. A metal implant is used. For a while silicone radial head implants were tried, but they didn’t hold up under the load and force that is put through the wrist, forearm, elbow unit.
If the interosseous membrane and/or the TFCC can be repaired, there’s a better chance of maintaining forearm stability. The goal is to restore as normal of anatomy and biomechanical function as possible in order to prevent forearm instability. But these ideas for treatment come mostly from cadaver studies. Long-term results in live patients are fairly limited at this time.
What about treatment for chronic injuries? Results are slowly improving as our understanding of the way the forearm unit is put together and works increases. Surgeons are finding better ways to reconstruct the soft tissues. The interosseous membrane is a unique band of tissue. It’s natural construction as at an angle, not just straight across between the two bones. Tendon grafts from half a dozen different tendons have been tried with various results. Getting the right angle and tension to allow for normal loading patterns hasn’t been 100 per cent successful.
Another big challenge is to keep the radius and the ulna level with each other and prevent radial migration. Sometimes the surgeon has to cut out a piece of the longer (ulna) bone to match it up to the shorter (radius) bone. This procedure is called an ulnar-shortening osteotomy.
All of these surgical options have potential complications that make the procedures less than ideal. Patients can end up with a stable but painful wrist, forearm, and/or elbow. Loss of motion in any of these three areas can affect function. Sometimes there are issues with cosmesis (how the forearm looks) because of deformities caused by surgery.
Some surgeons are experimenting with a one-arm forearm. By removing one of the bones altogether, it’s possible to avoid some of the problems with migration, impaction, impingement, and instability. Despite the variable patient responses to surgery, there is general agreement among surgeons that the earlier the surgery is done, the better the results.
The authors conclude that we have a long way to go in the treatment of forearm stability at any phase (acute or chronic). Long-term studies are needed to document what happens with each of the more common treatment procedures. We are still far away from finding the best way to restore forearm stability after severe destabilizing injuries of this type.