Can the TrueLok Hexapod System™ Be Used to Accurately Correct Lower Limb Deformity in Children?

Introduction: Progressive bone lengthening in children can be done using an external fixator, a lengthening nail, or plate with screws. The TrueLok Hexapod System™ (TL-HEX™) is the newest hexapod external fixator on the market. We hypothesized that the TL-HEX™ can accurately correct lower limb deformities in children. The goal of this study was to evaluate the clinical and radiographic outcomes after correcting lower limb deformities in children using the TL-HEX™ system.

Material And Methods: Data from 58 limbs that underwent bone lengthening with the TL-HEX™ were analyzed for this retrospective, single-center study. The average patient age was 11.4 years. The femur was lengthened in 23 limbs and the tibia in 35. The outcomes were evaluated using long leg standing radiographs preoperatively and at the final assessment. The variables of interest were the mechanical axis deviation (MAD), mechanical lateral distal femoral angle (mLDFA), mechanical lateral proximal tibia angle (mMPTA), healing index (HI) and accuracy of the correction. The complications were graded on a 4-point scale summarizing three broad goals: planned correction, duration of treatment and sequelae. The accuracy of the correction was defined as the difference between the planned correction and the actual correction achieved.

Results: The mean HI was 37 days/cm. Significant correction was achieved for leg length discrepancy (LLD) (60 mm vs. 20 mm; p<0.01) and mLDFA (88.6° vs. 89.9°; p=0.04) but not the MAD (17.7 vs. 14.7; p= 0.17) or mMPTA (87.3 vs. 88.1; p=0.08). In the entire cohort, the difference from planned was 12.5 mm (p<0.01) for lengthening, 1.3° for the mLDFA (p=0.5) and 3° for the mMPTA (p=0.02). Relative to the initial goal, the mean lengthening achieved was 118%. In the sub-group where the plan did not need to be modified, the accuracy of the correction was better. There were 40 complications (69%).

Conclusion: The TL-HEX™ is an effective and accurate system. The complication rate associated with its use is the same as other hexapod external fixators. Surgeons and patients must be aware of the high complication rate, which may require the plan to be modified and could potentially compromise the outcome.