Osteoarthritis of the joint between the forearm bones at the wrist (distal radioulnar joint, DRUJ) is a common sequel of fracture and ligament injuries or degenerative disease of the wrist. Intact DRUJ is important for normal load transfer from the hand to the forearm. DRUJ osteoarthritis leads to pain and decreased lifting capacity and rotation of the forearm. The standard treatment is resection of the ulnar head, known as the Darrach procedure. After the resection there is no longer contact in the affected joint, however, some patients can experience instability or impingement between the forearm bones. With ulnar head implant replacement may the load transfer and the stability between the forearm bones less affected. Studies with good long term results are published with both resection and replacement. However, these methods were never compared and thus it is not clear, which of the methods gives the best clinical result and less complications.

The aim of this study is to compare Darrach procedure with ulnar head replacement in a prospective randomized multicenter study. Several hand surgical centers form Norway would participate this study.

Individuals seeking treatment for their stable but painful DRUJ joints will be included and randomized to either Darrach procedure or ulnar head implant. Participants will be followed up to 5 years. Range of motion and grip strength measures and functional scores would be registered before operation, after 3 months, 1 and 5 years. Eventual complications and reoperations would be also registered.

Osteoarthritis of the joint between the forearm bones at the wrist (distal radioulnar joint, DRUJ) is a common sequel of fracture and ligament injuries or degenerative disease of the wrist. Intact DRUJ is important for normal load transfer from the hand to the forearm. DRUJ osteoarthritis leads to pain and decreased lifting capacity and rotation of the forearm. The standard treatment is resection of the ulnar head, known as the Darrach procedure. After the resection there is no longer contact in the affected joint, however, some patients can experience instability or impingement between the forearm bones. With ulnar head implant replacement may the load transfer and the stability between the forearm bones less affected. Studies with good long term results are published with both resection and replacement. However, these methods were never compared and thus it is not clear, which of the methods gives the best clinical result and less complications.

The aim of this study is to compare Darrach procedure with ulnar head replacement in a prospective randomized multicenter study. The study would be coordinated from Østfold Hospital Trust, and Oslo University Hospital, Haukeland University Hospital, Innlandet Hospital Trust, University Hospital of St Olav and University Hospital of North Norway would participate this study.

Participants would be included among individuals seeking treatment for their stable but painful DRUJ joints. Informed consent will be gained from every participant. The group size was calculated to 20 participants in both groups.

Participants will be randomized to either Darrach procedure or ulnar head implant. The procedures would be carried out standardized in every center. No further stabilization procedure for the ulna stump would be used in resection. Herbert UHP implant (Herbert Ulnar Head Prosthesis, KLS Martin, Germany) would be used for ulnar head replacement. Postoperative treatment and follow up would be identical between the groups.

Range of motion and grip strength measures and functional scores would be registered by an independent hand therapist before operation, after 3 months, 1 and 5 years. Eventual complications and reoperations would be also registered.

Patient related outcome measure scores, range of motion and grip strength would be registered as outcomes. The results would be checked for normal distribution and either parametric or non parametric statistical tests would be chosen for comparison of the two groups.

The null hypothesis is that Darrach procedure and ulnar head replacement with implant gives similar functional results, similar frequency of complication and reoperations.

Inclusion Criteria:

• painful osteoarthritis distal radioulnar joint
• stable DRUJ

Exclusion Criteria:

• activ inflammatory disease with significant destruction of the joint
• "low demand" persons
• significant instability i DRUJ
• active infections, poor soft tissue conditions
• accidental wound on the operated hand
• general contraindications for surgery

An independent hand therapist, who is not involved in the rehabilitation of the participants, will carry out the measurements.