Hip dysplasia is a common orthopedic condition, defined as an abnormality in the shape, size and orientation of the femoral head, acetabulum or both. The most frequent presentation of hip dysplasia is the maldevelopment of the acetabulum, resulting in insufficient superior coverage of the femoral head, defined as a lateral center-edge angle (Wiberg) of less than 20 degrees. Patients suffer from groin pain, an abnormal gait, decreased strength, and an increased rate of degenerative hip disease.

The possible treatments affecting the shape of the acetabulum once the patient reaches adolescence are all surgical. The PAO is regarded as the current gold standard in the treatment of symptomatic adult hip dysplasia. The 3-dimensional orientation of the acetabulum is changed with the use of 3 osteotomies around the acetabulum and a refixation in the obtained position. However, the PAO is a difficult operation and is associated with a large number of major complications (up to 37%), and the surgery is associated with a long rehabilitation period.

Hence, a strong unmet need exists for an effective but less invasive solution that enhances the quality of life of adult hip dysplasia patients. The treatment gap can be filled with a 3-dimensional (3D) shelf procedure. This custom-made implant (called the 3D-Shelf implant) was developed with the goal to be more predictable in terms of containment and fit than the old autologous shelf-acetabuloplasty, and less invasive and easier to perform than the PAO.

This study aims to study the safety and evaluate the early performance in terms of the clinical outcomes after implantation of the 3D-Shelf implant in patients with adult hip dysplasia, to show that the 3D-Shelf procedure is safe, has lower complication rates, and shows no inferiority in clinical outcomes compared to the current treatment of a peri-acetabular osteotomy.

Inclusion Criteria:

• Hip dysplasia based on AP x-ray with a LCEA of <25°
• Groin pain and/or gait abnormalities, with no other explanatory hip pathology
• Aged at least 18 years and maximal 45 years at time of surgery (indicated age for PAO(19))
• Willing to comply with the study visit schedule during 12 month follow-up
• Able and willing to provide informed consent

Exclusion Criteria:

• Previous acetabular surgery >10yr of age
• Signs of osteoarthritis on x-ray (Tonnis classification >1),
• Body mass index of more than 35
• Large labral tears visible on non-contrast MRI
• Pre-consultation known titanium allergy
• Pre-consultation known medical histories of diseases that per the investigator possibly affect the outcome: neuromuscular disease affecting the stability of the hip, diseases affecting bone ingrowth and fixation strength of the implant like rheumatoid arthritis and metabolic bone diseases, e.g. osteomalacie, osteoporosis, hyperparathyroidism, hypercalcemia.
• Pre-consultation known pregnant women or women who are planning to become pregnant during the duration of the study.
• Part of vulnerable population (e.g. Mentally disabled with cognitive impairment or mental disease)
• Currently participating in another investigational clinical trial.
• Unable to provide informed consent (e.g. insufficient language skills)

To be determined.