GUIDed Growth of the Proximal Femur to Prevent Further Hip MigrAtion in CErebral Palsy Patients

The Primary study outcome is treatment failure, defined as:

• Need for secondary bony hip surgery to the affected hip or progression to hip migration > 50% at 5-year follow-up . An indication for secondary bony surgery will be defined as;
• Migration percentage > 50% at a minimum of 1 year after surgery, OR
• An increased migration > 10% in 1 year during follow-up
• Increase in Acetabular index to > 30 degrees or an increase of more than 5 degrees during follow-up

Standardized conventional radiographs, AP and Lauenstein view (frog leg lateral) Pelvic radiographs will be performed according to the standardized protocol as defined by AACPDM

• Migration percentage (%), change in migration percentage per treatment arm (on baseline and follow-up)
• Head Shaft angle (HSA) in degrees
• Acetabular index
• Melbourne hip classification
• Pelvic obliquity
• Positioning of the hemi epiphysiodesis screw in the intervention group

CT-scans of the hip will be performed in the intervention group directly postoperative, at 2-year follow-up and 5-year follow-up. On these scans the following measurements will be performed:

• Positioning of the hemi epiphysiodesis screw
• 3-dimensional proximal femoral shape analysis regarding (change in) sphericity, congruency and head-neck orientation will be performed in patients at 2-year follow-up and at 5-year follow-up.
• The direction of migration of the hip and acetabular morphology will be determined according to the method described by Brunner et al.
• Sphericity of the femoral head will be determined by the Mose technique.

"Caregivers Priorities and Child Health Index of Life with Disabilities"

The CPCHILD™ is a parent completed questionnaire and was developed to help clinicians to identify areas that are impairing a child's quality of life, determine what is most important to the child and caregiver, and monitor the child's progress in a way that is meaningful to the family.

Minimum value is 0 and maximum value is 100, the higher the score the better the outcome.

CPG = "Checklist Pijn Gedrag" (Dutch for Checklist Pain behaviour) A mean pain score will be calculated.

A minimum value of 0 with a maximum value of 10. Higher scores mean more pain.

Screw revision ▪ The following will be used as indications for screw revision in the intervention group throughout the study period:

• < 1 thread of the screw remaining in the epiphysis, and
• HSA > 100 degrees

Repeated soft tissue release.

▪ The following will be used as indications for repeated soft tissue releases (adductor and/or psoas tenotomy) in both the intervention and control group throughout the study period:

• Abduction < 30 degrees, and
• No indication for bony surgery

Other patient related measurements that will be obtained at baseline include

• Age
• Weight
• Height
• GMFCS classification
• Change in Migration Percentage in the year prior to the adductor tenotomy
• Use of tone regulation; Baclofen, Artane, Baclofen pump, Selective Dorsal Rhizotomy (SDR