A study of structures which obstruct reduction of hip dislocation was performed on 15 hips by magnetic resonance imaging (MRI). Before treatment started, MRI studies were performed on 10 patients, six of whom were treated conservatively, after which further MRI studies helped to establish a concentric reduction. In the other four conservative treatment failed and they were operated on; in them the MRI studies were compared with arthrographic and surgical findings. In all but one of these 10 patients, MRI enabled us to differentiate between an everted and an inverted limbus. In five other patients with unsatisfactory development of the hip following closed reduction, MRI was compared with earlier arthrographic studies. MRI provided accurate anatomical information which would not have been obtained by arthrography. It clearly has great potential in assisting the surgeon to select the appropriate form of treatment.

1. Screw fixation of clavicle to coracoid process, with subsequent calcification and ossification along the conoid and trapezoid ligaments, creates an extra-articular fusion of the acromio-clavicular joint.

2. Though the follow-up is admittedly early, excellent results can be obtained in the young healthy adult. It is possible to return an athlete to competitive sports and a heavy labourer to full work in a surprisingly short time.

3. The operation is of doubtful value in older patients.

4. A precise operative technique is most important in producing a successful result.

5. Screw fixation introduces a new movement into the abduction mechanism of the shoulder: synchronous scapulo-clavicular rotation.

1. It is suggested that the obstruction causing delayed reduction of the congenitally dislocated hip is the infolded limbus.

2. An operation is described by which the infolding limbus may be easily and safely removed.

3. The early results of the operation are reported.

4. The evidence for the original assumption is discussed.