Bone ninja mobile app for reverse planning method in internal limb deformity and lengthening surgery

Abstract

Aim: To report whether Bone Ninja (BN) is a reliable tool to teach the reverse planning method (RPM) for implantable intramedullary (IM) limb-lengthening devices and for deformity correction surgery. Background: Motorised fully implantable implantable intramedullary (IM) lengthening devices have been gaining popularity all over the world for limb-lengthening procedures. Multiple advantages have been demonstrated over external fixator-controlled lengthening. Mechanical axis deviation may result if careful preoperative planning and surgical intervention are not completed for femur cases. The RPM proposed by Baumgart has been shown to be an accurate means of arriving at the desired end point. The RPM addresses the ideal correction position accounting for length, angulation, and translation created during lengthening along the nail axis. The original description calls for the use of life-size paper tracings of the bone and large light boxes to allow planning. We propose an alternative method using a digital tool that is readily available. The BN mobile app was developed for patient/physician education and is available for the Apple iPad platform. Bone Ninja has been shown to have similar accuracy for measurements of the limb length and deformity angles when compared to the gold standard picture archiving and communication systems (PACSs). Technique: We used BN (version 4.2) on an iPad mini to perform the same RPM steps, using the same terminology originally described by Baumgart. Conclusion: Bone Ninja is a simple validated deformity correction tool with accuracy comparable to PACS. It is a reasonable alternative to paper/ pencil cutouts for applying RPM for IM limb lengthening and deformity correction surgery. Clinical significance: We proposed a digitised RPM for internal limb-lengthening surgeries, which is highly feasible and practical to use conveniently without the need for the traditional tedious paper-cutting procedure and related equipment.