In the thumb saddle joint, the first metacarpal bone sits like a “saddle” on the large polygonal bone of the wrist. To give the thumb its mobility, the saddle joint only has a weak bony support. Muscles and ligaments give it stability. The saddle joint of the thumb is relatively small, but it is also one of the most stressed joints in the body, as it enables the gripping and holding function of the hand.
The main causes are permanent overload and imbalances in the position of the joints. If ligaments and muscles are weakened, the thumb saddle joint has too much play. This leads to incorrect loading.
As would be expected with a wear-and-tear disease, the risk of rhizarthrosis increases with age. According to estimates, one in four women and one in twelve men over 70 are affected, but many younger people are also affected. The disease occurs more frequently within families and in women after menopause. This suggests that both genetics and hormonal causes play a role.
The loss of cartilage caused by overloading and incorrect joint positioning manifests itself in joint pain for those affected. Attempting to stabilize the joint muscularly results in uneven stress, which in turn causes muscle pain. Over time, muscle shortening and changes in the joint capsule can occur, which result in restricted movement.
The symptoms are particularly noticeable during holding and turning movements, for example when turning a key or opening a screw cap.
The diagnosis of rhizarthrosis is made by the doctor. The first assumption is confirmed by an x-ray.
Prevention is the motto when it comes to rhizarthrosis. In order to avoid progression of cartilage loss, prevention and therapy for rhizarthrosis largely have the same content.
It is important, especially under stress, that the joint partners are positioned as optimally as possible in relation to each other. This means the pressure is evenly distributed throughout the joint. Imbalances in the joint position must be corrected – the sooner the better.
Excessive and incorrect stress in everyday life should be avoided. As a rule, rhizarthrosis is initially treated conservatively, which means that surgery is usually not necessary in the early stages.
A doctor decides on the treatment of rhizarthrosis depending on the extent of joint wear and the intensity of the symptoms.
Special thumb splints (ortheses) can be used to relieve and stabilize the diseased joint. Lighter models specifically stabilize the thumb saddle joint under stress without restricting the mobility of the hand. If the rhizarthrosis is more advanced, an orthosis is recommended, which offers the saddle joint even more stability and prevents hyperextension in the metatarsophalangeal joint of the thumb.
Cooling with ice, taking anti-inflammatory painkillers and local application of ointments can be used to relieve acute pain.
Further therapy options include cortisone injections, hand, occupational and physiotherapy, acupuncture, etc.
Surgery and aftercare
If all conservative treatment options are unsuccessful or if the rhizarthrosis is already in an advanced stage, there are surgical approaches. An operation for rhizarthrosis is a rescue operation after other measures have been exhausted. Doctors decide individually which procedure makes the most sense.
A common procedure is the removal of the polygonal bone (trapezium bone). The first metacarpal bone is fixed with a tendon so that it does not slip into the resulting hole. After the operation, the thumb is initially immobilized for three weeks. It will take around twelve weeks before he can bear full weight again. Since a joint partner is now missing, it is also advisable to stabilize the saddle joint under load.
Of course, there are other surgical procedures that can be used, for example stiffening the saddle joint of the thumb (arthrodesis) or inserting an artificial joint.
To ensure that your thumb remains usable for as long as possible, you will find useful tips on preventing rhizarthrosis in the “Fokus Thumb” brochure.
OA Dr. Kathrin Sekyra, MScFA for orthopedics and orthopedic surgery, FA for trauma surgery