• Orthopaedic Pediatrics

Rotational deformities of long bones in children, while often resolving spontaneously, can sometimes persist, leading to functional disturbances like joint pain, instability, or gait issues. Traditionally, surgical correction involves osteotomies, which are major procedures. Guided growth, a less invasive technique successfully used for correcting angular deformities and limb length discrepancies in growing children, presents a potential alternative. This concept involves temporarily tethering the growth plate (physis) to modulate growth direction. Inspired by this, the concept of rotational guided growth emerged, proposing that obliquely placed tethers spanning the physis could induce controlled rotation as longitudinal bone growth occurs.
This PhD thesis aimed to comprehensively evaluate the concept of rotational guided growth. The primary objectives were threefold:

1. To systematically map the existing preclinical and clinical literature on rotational guided growth, identifying surgical methods, research models, reported outcomes, adverse effects, and knowledge gaps.

2. To investigate the efficacy and safety of a novel, rigid, z-shaped titanium plate (Rotos Plate™), specifically designed for rotational guided growth, in a large animal preclinical model.

3. To evaluate the efficacy and safety of a surgical technique using flexible tethers comparing its outcomes and potential complications to the rigid tether approach.

Methods:
The research comprised a scoping review and two preclinical in vivo studies using a porcine model.

Study I (Scoping Review): A systematic search across multiple databases was conducted following JBI methodology and a predefined protocol. Studies describing the use of guided growth for rotational deformities were included, screened, and data regarding methods, models, outcomes, and adverse effects were extracted.

Studies II & III (Preclinical): Skeletally immature female pigs underwent surgery on the distal left femur, with the right femur serving as a control. In Study II the rigid Rotos Plate™ was implanted and in study III flexible tethers using separated Hinge Plates and Fibertape were implanted. Tethers were oriented to induce external rotation during growth over a 12-13 week period. Rotational changes, limb length discrepancy and angular changes were assessed using CT scans (pre- and post-intervention) analyzed with both traditional 2D and novel 3D surface registration-based techniques, alongside direct bone measurements post-euthanasia.

Results:
Study I: The scoping review identified 14 relevant studies, revealing significant heterogeneity in surgical techniques (rigid vs. flexible tethers), animal models (mostly rabbit), outcome reporting, and measurement methods. While preclinical and preliminary clinical studies reported successful rotation induction (ranging from 9.6° to 30°), the evidence base was limited and highlighting a lack of standardization.

Study II: The rigid Rotos Plate™ successfully induced external rotation in all subjects, with a mean ∆Rotation of 8.1° (2D) and 5.7° (3D). No significant limb length discrepancy was observed. However, minor, randomly directed angular deformities occurred, and concerning changes in knee joint morphology, including trochlear groove alterations, were noted.

Study III: The flexible tethers also induced external rotation (mean ∆Rotation 7.3° (2D), 7.2° (3D)) without causing limb length discrepancy. Crucially, this method led to consistent secondary valgus deformities (mean 7.8° in the coronal plane) and alterations in the sagittal plane. Similar to Study II, changes in joint morphology were observed.

Discussion & Conclusion: This thesis confirms that rotational guided growth is a viable concept capable of inducing torsional changes in long bones during growth. The scoping review underscored the growing stage of this field, characterized by methodological diversity and limited high-quality evidence. The preclinical studies demonstrated the feasibility of inducing rotation using both specially designed rigid plates and adapted flexible tethers in a large animal model.
While both tether types achieved rotation, significant challenges and potential adverse effects were identified.
A critical finding across both in vivo studies was the alteration of distal femoral joint morphology, an adverse effect sparsely reported previously, highlighting a crucial area for future investigation. Other reported concerns like rebound rotation and histological physeal changes require further study.
In conclusion, while rotational guided growth holds promise as a less invasive alternative to osteotomy for pediatric rotational deformities, it is currently an experimental technique. Significant refinements are needed to improve predictability, standardize methods, and mitigate adverse effects. Until robust clinical evidence demonstrating safety and efficacy comparable or superior to osteotomy is available, its application should be approached with caution.

Principal supervisor: Ole Rahbek, Professor, MD, PhD, Aalborg University Hospital
Principal co-supervisor: Søren Kold, Professor, MD, PhD, Aalborg University Hospital
Co-supervisor: Jan Duedal Rölfing, MD, PhD, Aarhus University Hospital
Co-supervisor: Ahmed A. Abood, MD, PhD, Aarhus University Hospital

Assessment committee:
Chairman: Thomas Starch-Jensen, Professor
Department of Oral and Maxillofacial Surgery
Aalborg University Hospital, Denmark

Danish representative: Andreas Peter Balslev-Clausen, Associate Professor
Department Orthopaedics
Rigshospitalet, Denmark

International representative: Rune Bruhn Jakobsen, Associate Professor
Department of Orthopaedics,
Akershus University Hospital, Norway