Basal Thumb Joint Osteoarthritis

01.04.2020

Definition

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 function, in effect giving us our essential gripping function. Basal thumb joint 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.

Causes

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 resulting tendency of subluxation generates greater force on the joint surfaces. Hereditary factors also seem to play a role in the development of osteoarthritis. It can also develop as a result of an injury involving the joint Cartilage.

Symptoms

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. In advanced stages the joint is thickened and deformed and the first metacarpal bone can no longer be spread away from the hand. The more distal thumb  joint can be stretched out/hyper-extended considerably in a compensatory manner.

Examination

In addition to the above-mentioned, typical visible and palpable changes, there is often tenderness on the flexor side over the thumb basal joint and compression pain. Later noticeable by both the patient and the examiner is a painful grinding 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 spurs on the edges of the joint surfaces.

Treatment

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 basal joint. Furthermore, local pain relieving and anti-inflammatory measures should be used like an electrotherapy or ultrasound treatment. Under certain circumstances, X-ray guided cortisone injections, can help to alleviate the symptoms for a certain time.

If 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.

Surgical Procedure

The operation is usually carried out under inpatient conditions (normally 2 nights) with an anesthesia of the arm nerves (plexus anesthesia). The joint capsule of the basal thumb joint is opened and exposed via a slightly curved skin incision on the extensor side. The large polygonal bone (Trapezium),  is removed and the base of the 1st metacarpal bone, is released from its ligament connections. One of the “joint partners” is thus missing and the painful grinding 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 thumb metatarsal has to be stabilised. For this purpose, a narrow strip of the wrist flexor tendon is harvested up to 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 tunnel in the base of the 1st metacarpal bone (and thus through the thumb root) and sutured to the intact tendon left. Finally, it is inserted into the cavity  removing  large polygonal bone.  The  joint capsule is then closed again and the skin is sutured after inserting a small drain. The procedure takes about 60 minutes.

Risks/Temporary Limitations

Painful swelling of the hand if frequent 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 as compared to the healthy side. Reduction in strength is most often already present before the operation. In rare cases however,  the new position of the thumb is not stable enough and collapses, in which case follow-up interventions may be necessary.

Follow-up Treatment

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 operation. 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.

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