Can three-phase skeletal scintigraphy predict the outcome and determine the timing of removal of bone distracters in avascular necrosis of femur using a novel corticostomy technique?

Introduction: ^99mTc-Methylene diphosphonate (^99mTc-MDP) three phase bone scintigraphy (TPS) is beneficial to evaluate the success of femoral head revascularization using novel distraction osteogenesis techniques with bone muscle pedicle grafts. This pilot study was undertaken to evaluate the feasibility and utility of ^99mTc-MDP three phase bone scintigraphy in predicting outcome in patients with femoral avascular necrosis (Ficat staging 2 or 3) using a new surgical technique and external fixator device as part of the distraction osteogenesis technique. We also wanted to find out if bone scan can determine the timing of removal of bone distracters and thus improve the clinical outcome.
Methods: 39 newly diagnosed patients with femoral AVN underwent a new modified Iliazaro technique in a nearby specialised Orthopaedic centre. 40 hips with Ficat and Arlet stage II and III in the age group of 18 to 33 years were included (Male: Female = 38: 01). Necessary clearance from institutional review board was obtained. Patients were assessed both subjective and objectively for the presence of pain (Harris Hip score), range of movements, radiological and TPS findings of the affected hip joints. TPS of hip joints was performed pre and postoperatively using 15 mCi of ^99mTc-MDP intravenously. Patients who did not show improvement in bone scan at 6^th week had follow up scans at 10^th and 14^th week respectively. Radiographic correlation was also obtained.
Results:Clinical and TPS imaging data were analysed.Clinical scoring (Harris hip score, HHS) was done pre and postoperatively in all patients. TPS demonstrated good improvement in cortical blood flow to the femoral head after revascularization at 6 weeks in 30 out of 40 hips ( i.e. 75%) using this new surgical technique and fixator device. 7 patients showed improvement at 10th week and remaining 2 patients showed no improvement even at 14^th week post-surgery. Quantitation was also performed to substantiate the visual findings using perfusion index(PI), initial uptake ratio (IUR) in soft tissue phase image and delayed uptake ratio (DUR) in skeletal phase image in all patients. Patients demonstrated significant improvement in Postop DUR when compared to preop. DUR values. HHS improved from 57 to 83 in 75% patients postoperatively indicating a good success of this surgical technique. All the data was analysed using SPSS software version. Statistical significance was accepted when p<0.05.
Conclusion: TPS is a simple, reliable and cost effective investigation in the non-invasive assessmentof distraction osteogenesis in AVN patients using this novel technique of corticostomy and gluteus medius pedicle graft at greater trochanter.It is a good tool to assess new bone formation. Intensity of MDP uptake at affected femoral head is a marker of restored metabolism and can be effectively used in timing the removal of bone distracters which is usually 6 weeks in majority of cases.