gms | German Medical Science

Objectives: Temporary Epiphysiodesis (TED) is an established procedure for correction of angular deformities (AD) of the knee and moderate leg length discrepancies (LLD) in growing children. Modern implants like the eight-Plate solved many problems that were observed using conventional staples for TED. Rather than creating rigid compression forces on the growth plate like conventional staples, the fulcrum of correction of the flexible eight-Plate is located extraphyseally for guided growth. The resulting tension band effect is appropriate for AD correction, but using the eight-Plate for LLD correction may lead to anatomical joint line deformation and iatrogenic AD. Implant-design, surgical technique and biomechanical alignment of the plate remain suboptimal leading to implant associated and biomechanical problems.

Methods: Therefore new devices for TED were developed consisting of anatomically preformed staples with cannulated legs to ensure the simple and precise implantation technique of the eight-Plate. Two different constructions were engineered to meet the divergent requirements for AD and LLD correction. Staples with flexible bar (FlexTack) are used for AD to constitute the extraphyseal tension band effect. To ensure a complete and evenly distributed arrest of the entire growth plate and therefore to prevent the mentioned complications, staples with rigid bar (RigidTack) are implanted in LLD.

Prospective cohorts with FlexTack and RigidTack implantations for AD and LLD, resp. were compared to a historical cohort with eight-Plate insertions for both indications (Table 1 [Tab. 1]).

Intraoperative parameters like operation time (cut-suture) and fluoroscopy time were assessed. Clinical-radiographic follow up examinations were performed every 3-6 months. Correction speed (MAD/LLD correction[mm]/ month / TED-site) was analysed. Complication rates were evaluated focusing implant associated and biomechanical problems. Statistical analysis was done using Mann Whitney U and Fisher's Exact Test.

Results and Conclusion: Operation time and fluoroscopy time were significantly shorter using the FlexTack. Earlier onset and faster speed of correction were measured using the FlexTack for valgus and varus correction and the RididTack for LLD equation. Common complications were comparable. However, only one FlexTack breakage (0.6 %) was observed compared to an implant associated complication rate of 10.8% using the eight-Plate (Table 2 [Tab. 2]). Using the eight-Plate iatrogenic AD occured in 15.8 % (varus or valgus) and 48.4 % (recurvation). In our short term follow up no iatrogenic AD had to be observed using the RigidTack so far.

The Flex-/RigidTack is a reasonable synthesis of staples and cannulated screw/plate devices. Due to the anatomical shape and biomechanical improvements faster corrections and lower rates of implant associated problems were achieved. The system offers the appropriate biomechanical effect for both, AD and LLD corrections.