Extension osteotomy of the first metacarpal is considered extra-articular (outside the joint) procedure. First refers to the thumb as the digits on the hand are numbered from one to five, starting with the thumb. The metacarpal bone is the long bone of the thumb from the base of the wrist to the first knuckle on the thumb.
An extension osteotomy is done by removing a wedge- or pie-shaped piece of bone from the metacarpal above the CMC joint. A wire is used to pull the opening (made by removing the bone) closed. This procedure changes the angle of the metacarpal bone where it connects with the wrist and brings it more into a neutral position (normal alignment).
Younger patients and anyone with less advanced disease can qualify for an extension osteotomy. The main advantage of this procedure is that it doesn’t mess with the joint itself. That means rather than jump right to a joint replacement, patients have a few options. They can still have joint reconstruction or joint replacement sometime in the future should they need it.
The extension osteotomy hasn’t been studied very closely. The few studies published haven’t followed the patients long-term. They also didn’t collect much information before and after about the patient (e.g., demographics such as age, gender, education, marital status and so on) or about the patients’ outcomes. A small study from the Mayo Clinic in Rochester, Minnesota offers some insight into the long-term results of this little used management technique for CMC arthritis.
In this study, one surgeon followed eight patients over a period of six to 13 years after surgery for thumb arthritis. Measures used to determine the benefits of this procedure included pain, grip strength, pinch strength (thumb to index finger), oppositional pinch strength (thumb to any other finger), and function (e.g., lifting, opening jars, turning doorknobs).
Patients included in the study were those with Eaton stage I to III disease. They were all treated by extension osteotomy after conservative (nonoperative) care failed to resolve pain or improve function. Eaton classification of CMC osteoarthritis uses X-rays to grade the disease as normal, mild, moderate, or severe. The classification is done without taking the patient’s symptoms into consideration.
Grade I is a normal appearing joint on X-ray. With grade II, there is a narrowing of the joint space (less than two millimeters) and the presence of bone spurs. Grade III has more than two millimeters of joint narrowing along with bone cysts, bone spurs, and bone sclerosis (hardening). Grade IV is referred to as pantrapezial arthritis. This means there is evidence of arthritic changes affecting the wrist bones (scaphoid, trapezium, trapezoid) around the CMC joint.
None of the eight patients were candidates for just ligament reconstruction. But joint replacement wasn’t needed yet either. So the extension osteotomy was an acceptable alternative.
Before surgery, pain levels were reported as moderate-to-severe in all eight patients. Moderate pain was defined as present with daily tasks. Severe pain was constant and occurred at rest as well as with daily activities. Half the patients reported instability in the CMC joint. Sometimes this type of instability is referred to as a subluxation or shifting of the joint causing a partial dislocation.
After surgery, pinch and grip strength improved more than 100 per cent when compared with the other hand. Five of the eight patients were able to maintain status quo. In other words, their joint did not get worse as measured by the Eaton stages. The osteotomy healed without problems. Pain was improved. Activities improved with only mild pain occasionally when lifting heavy objects. The two patients who needed additional surgery had a lag time of at least seven years before the next procedure was done.
The authors concluded that extension osteotomy is a safe and effective way to treat thumb osteoarthritis in patients with Eaton grade I, II, or III. The procedure can be done early before painful symptoms even develop. Stabilizing the joint sooner than later can reduce the load and compressive forces through the joint that later lead to osteoarthritis.