Our patient was 16 years old and he was a student with no particular medical history. The patient and his parents gave their informed consent to report this case. He presented a left upper limb trauma when he was 12 years old that was orthopedically treated by a cast during 3 weeks. Since then, he presented pain in his wrist, especially at sport and when he was leaning on his left hand. His pain was quoted at 7/10 (visual analog scale) and he reported a severe handicap at sport. Clinical examination showed a normal range of motion of his wrist with a normal but painful pronosupination motion. It revealed distal radioulnar instability with a protrusion of the ulnar head (Fig. 1) without instability of the extensor carpi ulnaris tendon. The radioulnar ballottement test of the radioulnar joint, the fovea sign, and the chair test were positive. The clunk test was negative. The symptomatology was marked by a severe functional concern when leaning on his hand during gym classes or when playing basketball. The patient-rated wrist evaluation (PRWE) score was at 51/100 (pain = 31, function = 20), the QuickDASH score was at 43/100. The pain was specifically localized on the ulnar side of the wrist by the patient. No nerve compression or vascular signs were detected. X-rays of the wrist revealed a shortening of the radius with a high radioulnar index (11mm on the anteroposterior view) and an ulnocarpal impingement (Fig. 2). This was highlighted on the magnetic resonance imaging T1sequence of the wrist that revealed overpressure cysts of the triquetrum (Fig. 3). The radioulnar joint surface on the radial side was flat. A lengthening of the radius with an iliac crest autograft was indicated as a reconstructive surgery to recover the normal length of the radius. A bilateral wrist computed tomographyscan was performed with a 3D reconstruction to evaluate the needed lengthening according to the contralateral side. The position and the orientation of the metaphyseal osteotomy were also calculated. A lengthening of 10mm in the longitudinal axis was calculated. The final position of the plate, the length of its screws, and the dimensions of the graft were also generated (Fig. 4). A patient-specific guide was 3Dprinted (Allians Radius , Newclip) to guide the osteotomy during the surgery. The 3D-printed material of the guide was done in PA2200 uspcl6 (polyamide). Under locoregional anesthesia and with a tourniquet, a volar Henry approach was performed to expose the distal radius. The distal part of the brachioradialis tendon was released at its radial insertion. The guide was applied on the metaphysis of the radius; a K-wire was positioned to evaluate the good position of the guide on the metaphysis with a fluoroscopy control. The holes of the plate were drilled previously. The osteotomy was performed with a 0.8mm saw blade and completed with an osteotome. A specific distractor with 1.8 pins was used to spread the two fragments. To avoid the buckling of the wire and the rotation of the fragment under the distraction stress, a Meary distractor was used and left in place. This allowed the stretching of the soft tissues during the iliac crest taking and it facilitated the insertion of the graft. A tricortical iliac crest bone graft of 10mm length was then taken on the homolateral side. The tricortical graft was then positioned into the osteotomy site flush to the anterior radial surface. The plate was screwed on the radius using the previously drilled holes (Fig. 5). The tourniquet was deflated (50 min). A cautious hemostasis was done and the approach was closed as usual. A removable sling was used to immobilize the patient during 1 month and a passive mobilization of the wrist was started the day after surgery. At 6-month post-operative(Fig. 6), the radius was consolidated with no more clinical deformation. The radioulnar index was improved (5mm on the anteroposterior view) with no more ulnocarpal impingement. The extension was symmetric at 65 , the flexion was at 80  versus 90  on the contralateral side, the radial and ulnar inclinations were at 5  and 40 , respectively, on both sides. The PRWE was at 2/100 (pain = 2/50, function = 0/50), the Quick DASH score was at 2/100. The patient presented no more pain on the ulnar side and was back to sport. No neurologic symptoms were found.