Abstract
The modified Hedgehog technique was previously used to reattach pure chondral shear-off fragments in the pediatric knee. In the modified Hedgehog technique, the calcified side of chondral fragments is multiple times incised and trimmed obliquely for an interlocking fit in the defect site. Fibrin glue with or without sutures is subsequently applied to fix the fragment to the defect. This preliminary report further elucidates the potential of the technique by evaluation of its application in young adults using patient reported outcome measures (PROMs) and high-field Magnetic Resonance Imaging (MRI) as outcome measures. Three patients with a femoral cartilage defect (2 medial, 1 lateral), and a concomitant pure chondral corpus liberum were operatively treated by the modified Hedgehog technique. Age at surgery ranged from 20.6–21.2 years, defect size ranged from 3.8–6.0 cm2. Patients were evaluated at three months and one year after surgery by PROMs and 7.0T MRI. PROMs included the Internation Knee Documentation (IKDC), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Visual Analog Scale (VAS) questionnaires. 7.0T MRI (Magnetom, Siemens Healthcare, Erlangen, Germany) using a 28-channel proton knee coil (QED, Electrodynamics LLC, Cleveland, OH) included a proton density weighted turbo spin-echo sequence with fat suppression to assess morphological tissue structure andgagCEST imaging to measure the biochemical tissue composition in terms of glycosaminoglycans (GAG). Twelve months after surgery all patients reported no pain and showed full range of motion. While PROMs at three months showed large variability between patients, one year after surgery the scores were consistently improved. Over time, morphological MRI visualized improvements in integration of the cartilage fragment with the surrounding cartilage, which was supported by biochemical MRI showing increased GAG values at the defect edges. Statistics were not applied to the results because of the small sample size. The modified Hedgehog technique in young adults with an acute onset caused by a pure chondral corpus liberum can be considered promising. The improved PROM results over time were supported by 7.0T MRI that visualized improvements in tissue structure and biochemical composition. Inclusion of more patients in future studies would allow statistical analysis and more conclusive results. The etiology of loosening and time between onset of symptoms and surgery for successful graft integration may differ between pediatric and young adult patients and is subject for future studies.
