Physician’s Corner ––

Thumbs Up

 By Ron Ripps, MD

Much has been written about the wonders of the human thumb. Anthropologists say our thumb is what differentiates us from the apes and other primates. Why so? Because it is “opposable.” What that means is that our thumb is not in the same plane as the rest of our fingers. Our ability to move the thumb away from the plane of the fingers is one of the important features that allow us to grasp things. Another important feature is that the thumb is rotated. It is rotated at a right angle to the plane of the fingers such that the pad of thumb contacts the pads of the fingers. In fact, the thumb is a post around which the other fingers are arranged for “opposition.” The base of the post, just above the wrist, is called the “basilar” joint of the thumb.

The basilar joint is unique in that it is shaped like a saddle. The thumb post acts like a rider, sitting on the saddle and rotating up and down, toward and away from the plane of the hand. The basilar joint has more mobility than all the other joints of the thumb combined, which permits us to make a sweeping circle with the thumb, even when the rest of the hand is kept rigid.

When we grasp an object, enormous force is generated between the thumb and the fingers, force that is transmitted down the thumb post as a compressive load to the basilar joint. Anyone who has spent her life working with her hands, especially heavy hand work such as assembly, can testify that given sufficient force, time, and frequency, work activity will wear the basilar joint out.

Arthritis of the basilar joint of the thumb can be very painful and disabling. It is characterized by aching pain over the entire thumb side of wrist and is often mistaken for tendonitis of the wrist. Longstanding basilar arthritis reveals itself as a large painful knob at the base of the thumb, and people so afflicted tend to protect the basilar joint by grasping things with a side to side pinch rather than pulp to pulp (as we normally do). X-rays of the arthritic thumb not only show narrowing of the joint space, but slippage as well. It is the slip, or “subluxation,” that causes the prominent bump.

Preventative measures include job modification and splinting. There are a variety of small, comfortable splints that serve to limit the motion of the arthritic joint and reinforce its role as an anchor to the thumb post. Sometimes a corticosteroid injection is required, and often anti-inflammatory pills are helpful. The theory of conservative management is that if one were to wait long enough, the thumb would become stiffer, but less painful.

 When conservative measures no longer control night pain, and when pain hinders function, surgery becomes a consideration. Over the last century a number of techniques were developed to resurface or replace the joint. For people who do very heavy work, like some machinists or road construction crews, fusion of the joint provides a stable thumb post and a predictable outcome. The downside to a fused joint is that its neighboring joints, which can then also wear out, must pick up the duties of the fused basilar joint.

 The most popular procedure today involves tendon “interposition” where a tendon is used as a spacer. After the arthritic joint is removed, the surgeon takes one of the “extra” tendons in the wrist, rolls it up like an anchovy, and sutures it into the place where the joint used to be. Although there is some thumb shortening, and some have reported diminished grip strength, results are consistently satisfactory.

The procedure I prefer is an implant arthroplasty. Here only part of the joint is removed and replaced with a small titanium hemispherical button. The button is attached to the thumb post and sits in a depression in the saddle, mimicking the real joint. Although technically more demanding than the other two procedures described, I believe the results are closest to the “real thing.” Regardless of the procedure your surgeon might select, it is important to recognize that the joint above the basilar joint, the first “knuckle” of the thumb, may have to be fused or fixed so to correctly position the thumb post rider in its new saddle. Fortunately this may all be done as outpatient surgery, and all three methods roughly require six weeks’ immobilization in a cast, followed by a month of rehab.

As with so many things in medicine, prompt preventive measures can often put off surgery. If your thumb is sore from all that holiday gift-wrapping, cooking, and computer games, let your orthopedist know.

Dr Ripps is one of seven orthopedic surgeons comprising Connecticut Family Orthopedics with offices in Danbury and Ridgefield.