SUMMARY Rationale: Delayed union is a problem in adolescent idiopathic scoliosis (AIS) surgery, especially at the distal end of the construct. Surgeons therefore use local autograft or bone graft substitutes to prevent loss of correction and/or anchor failure and additionally restrict patients' activities during the first year. The concept of this study was developed after the promising results of the MaxA study (METC 18-311), where we compared the efficacy of BCP<μm ceramic granules (MagnetOs™ Granules) to autograft in posterolateral fusion (PLF). This randomized intra-patient-controlled trial indicated superior spinal fusion rates for the BCP<μm condition. The current investigational product (MagnetOs™ Putty) is made of the same MagnetOs™ Granules embedded in a fast-resorbing polymeric binder to improve surgical handling. If MagnetOs™ Putty allows better and faster fusion in scoliosis patients, it is possible to mobilize them faster and even abandon post-operative activity restrictions.

Objective: The primary objective is to demonstrate superiority and safety of MagnetOs™ Putty compared to autograft regarding the posterolateral spinal fusion rate, in instrumented PLF in AIS patients. The secondary objectives encompass comparisons of posterolateral spinal fusion rates on different levels at various points in time, monitoring the changes in trunk rotation, evaluating quality of life and patient's experiences as well as improving the reliability of Hounsfield unit measurements.

Study design: Multicenter, randomized, controlled superiority trial with intra-patient comparisons over a 1-year follow-up.

Study population: 140 patients between 12 to 30 years with AIS qualified for scoliosis surgery with lowest instrumented vertebrae T12-L4.

Intervention: According to a randomization scheme, one side of the caudal PLF will be grafted with the MagnetOs™ Putty and the other side with local bone. The rest of the surgical procedure will be according to standard care.

Main study parameters/endpoints: The fusion rate of MagnetOs™ Putty compared to standard fusion with local autograft, assessed locally and centrally through a three plane assessment tool at the caudal segment on CT scans at 3 or 6 months. The complication rate will be compared to the rate in control populations from literature.

Nature and extent of the burden and risks associated with participation, benefit, and group relatedness: The study population includes AIS patients between 12 to 30 years with an indication for PLF. Patient burden and risks are expected to be minimal. The post-operative follow-up will be according to standard care. Additional study procedures include the completion of patient-reported outcome measures (PROM) at four time points and a limited CT scan. Based on pre-clinical investigations and the results of the MaxA study, we expect MagnetOs™ Putty to perform better than the current treatment. This may benefit the patient as currently about 5% experience problems of delayed union in our own series.

SUMMARY Rationale: Delayed union is a problem in adolescent idiopathic scoliosis (AIS) surgery, especially at the distal end of the construct. Surgeons therefore use local autograft or bone graft substitutes to prevent loss of correction and/or anchor failure and additionally restrict patients' activities during the first year. The concept of this study was developed after the promising results of the MaxA study (METC 18-311), where we compared the efficacy of BCP<μm ceramic granules (MagnetOs™ Granules) to autograft in posterolateral fusion (PLF). This randomized intra-patient-controlled trial indicated superior spinal fusion rates for the BCP<μm condition. The current investigational product (MagnetOs™ Putty) is made of the same MagnetOs™ Granules embedded in a fast-resorbing polymeric binder to improve surgical handling. If MagnetOs™ Putty allows better and faster fusion in scoliosis patients, it is possible to mobilize them faster and even abandon post-operative activity restrictions.

Objective: The primary objective is to demonstrate superiority and safety of MagnetOs™ Putty compared to autograft regarding the posterolateral spinal fusion rate, in instrumented PLF in AIS patients. The secondary objectives encompass comparisons of posterolateral spinal fusion rates on different levels at various points in time, monitoring the changes in trunk rotation, evaluating quality of life and patient's experiences as well as improving the reliability of Hounsfield unit measurements.

Study design: Multicenter, randomized, controlled superiority trial with intra-patient comparisons over a 1-year follow-up.

Study population: 140 patients between 12 to 30 years with AIS qualified for scoliosis surgery with lowest instrumented vertebrae T12-L4.

Intervention: According to a randomization scheme, one side of the caudal PLF will be grafted with the MagnetOs™ Putty and the other side with local bone. The rest of the surgical procedure will be according to standard care.

Main study parameters/endpoints: The fusion rate of MagnetOs™ Putty compared to standard fusion with local autograft, assessed locally and centrally through a three plane assessment tool at the caudal segment on CT scans at 3 or 6 months. The complication rate will be compared to the rate in control populations from literature.

Nature and extent of the burden and risks associated with participation, benefit, and group relatedness: The study population includes AIS patients between 12 to 30 years with an indication for PLF. Patient burden and risks are expected to be minimal. The post-operative follow-up will be according to standard care. Additional study procedures include the completion of patient-reported outcome measures (PROM) at four time points and a limited CT scan. Based on pre-clinical investigations and the results of the MaxA study, we expect MagnetOs™ Putty to perform better than the current treatment. This may benefit the patient as currently about 5% experience problems of delayed union in our own series.

AIS indicated for sugical treatment