Thumb Saddle Joint Arthritis
The thumb’s base (saddle) joint is the joint that connects the base of the thumb to the wrist. Its “saddle-like” shape and the complex set of ligaments surrounding it allow for very good mobility. These properties make a significant contribution to the thumb, in effect giving us our essential gripping function. Osteoarthritis of a joint means nothing more than the wear and tear of the joint cartilage, which normally enables the joint surfaces to glide smoothly and without pain. If the cartilage is worn out so much that bare bone surfaces rub against each other, pain occurs. Rhizarthrosis is often associated with arthritic changes in other finger joints and affects women more often than men, probably because of their tendency to have more ligament laxity.
Due to the saddle joint’s large range of motion, which inevitably goes hand in hand with a certain amount of instability, it seems to be particularly sensitive to the development of osteoarthritis. In addition, the shape of the joint’s surface is a predisposing factor, as the repetitive, movement dependent load peaks of the connecting joint sections generate greater force on the thumb. Hereditary factors also seem to play a role in the development of osteoarthritis. It can also develop as a result of an accident involving the joint.
Pain is felt in the area of the thumb root, occurring especially when gripping forcefully, and is exacerbated by an additional rotation component (typically when opening twist locks or wringing out textiles). Initially, the pain only exists when under load, later also at rest. Rhizarthrosis is already visible from the outside in advanced stages – the thumb’s saddle joint appears to be clearly arched, the first metacarpal bone can no longer be spread completely by the hand and the neighboring thumb base joint can often be stretched out considerably in a compensatory manner.
In addition to the above-mentioned, typical visible and palpable changes, there is often tenderness on the flexor side over the thumb saddle joint and compression pain. Later noticeable by both the patient and the examiner is a painful rubbing of the worn joint surfaces. To confirm the diagnosis X-rays of the thumb are taken, which depending on the stage, initially show a narrowing of the joint space of the thumb saddle joint, later also bone cysts below the (damaged) joint surfaces and reactive bone nodes on the edges of the joint surfaces.
Conservative measures that provide pain relief should be used as a first step when symptoms are predominately moderate and only minor changes are seen on the X-ray image, even though they cannot stop the progression of osteoarthritis in the long term.
A bandage or splint can be worn to stabilize and thus relieve the damaged joint. As part of joint protection instruction by a hand therapist, heavily stressful activities can be carried out alternatively, possibly using aids, in order to reduce the load on the thumb saddle joint. Furthermore, local pain relieving and anti-inflammatory measures should be used as part of an electrotherapy or ultrasound treatment. Under certain circumstances, X-ray guided cortisone injections, can help to alleviate the symptoms for a certain time.
As soon as the above-mentioned measures no longer lead to sufficient pain reduction and the affected hand can no longer be used fully in everyday life, surgical treatment should be considered.
The operation is usually carried out under inpatient conditions (normally 2 nights) with an anesthetic of the arm nerve network (plexus anesthesia). The joint capsule of the thumb saddle joint is opened and exposed via a slightly curved skin incision on the extensor side. The large polygonal leg (Trapezium), which forms the thumb saddle joint, together with the base of the 1st metacarpal bone, is released from its ligament connections and completely removed. One of the “joint partners” is thus missing and the painful rubbing of the worn bone surfaces against each other is no longer possible. However, so that the thumb can continue to function as the most important gripping instrument, the abutment that is now missing should be replaced and the thumb connected again to the wrist. For this purpose, a narrow strip of the wrist tendon on the radius side of the wrist is separated and placed in the middle of the forearm via an additional small cut. This tendon strip, which is now still attached to the base of the 2nd metacarpal bone, is pulled through a drilled channel in the base of the 1st metacarpal bone (and thus through the thumb root). Finally, it is inserted into the cavity created by the removal of the large polygonal leg and sutured to itself. The opened joint capsule is then closed again and the skin is sutured after inserting a small drain. The procedure takes about 60 minutes.
It is not uncommon for (painful) swelling of the hand to occur immediately after the operation, so that a consistent elevation of the arm and an adequate supply of pain relievers are absolutely necessary. There may also be some loss of pinching strength compared to the healthy side. Compared to the pain-related reduction in strength before the operation, however, this is usually negligible. In rare cases it is observed that the new position of the thumb is not stable enough and collapses, in which case follow-up interventions are necessary.
If a drain has been inserted, it can usually be removed after 2 days; the stitches can be removed after 2 weeks. The thumb, including the wrist, is immobilized in a splint for 6 weeks after the procedure; under the guidance of a hand therapist, non-weight bearing mobility exercises may be carried out. After 6 weeks, a “short” splint (which leaves the wrist free) is worn, especially during strenuous activities – this is usually necessary for a further 6 weeks. A complete return of function can therefore be expected 3 months after the surgical intervention. The final phase in terms of strength and mobility is often only reached after 5-6 months.