Physeal bar resection using a patient-specific guide with intramedullary endoscopic assistance for partial physeal arrest of the distal radius

The patient-specific surgical guide was created on the basis of 3-D information attained preoperatively from CT data. The 3-D surface model of the radius was created using commercially available software (Bone-Viewer™ and Bone Simulator™; Orthree, Osaka, Japan). In addition, the computer model of the physeal bar was created by manually segmenting the bridging regions connecting the epiphysis to the metaphysis to target the spatial location. The 1.0-mm expansion of the physeal bar was defined as a target to avoid both inadequate removal of the bar and excessive removal of the healthy physeal cartilage. Merging the physeal bar model onto the radius model could help attain spatial information on the physeal bar (Fig. 1). Subsequently, a patient-specific guide was created as a surgical guide in accordance with patients’ bone surface to facilitate the multiple pinning through the guide to surround the target physeal bar (Fig. 2a–e); the guide was manufactured by Teijin Nakashima Medical Co., Ltd. (Okayama, Japan) using the plastic laser sintering system [Formiga P110; Electro-Optical Systems (EOS), Munich, Germany] with a medical grade polymer (PA2200).

Patients were placed in the supine position with the operative limb, with tourniquet, placed on an arm board, using the modified Henry (radio-palmar) approach. Retracting the flexor tendons to the ulnar side, the pronator quadratus muscle on the radial side was elevated by subperiosteal dissection to expose the palmar surface of the distal radius. The patient-specific guide was fitted onto the palmar surface under the fluoroscopic guidance of a K-wire designed to indicate the radial styloid tip as a reference, allowing the confirmation of the precise guide position. Next, multiple pinning with 1.0-mm K-wires was performed through the holes created on the patient-specific guide. The insertion depth of these K-wires was determined under fluoroscopic guidance using block pins designed to avoid penetration into the radiocarpal joint as points of reference. After that, the patient-specific guide was removed leaving the K-wires, which were cut at the bone surface (Fig. 3a–d). An osseous window of approximately 10 mm × 10 mm enclosed by the wires was created using an osteotome through which resection of the physeal bar was performed by advancing curettes under fluoroscopic guidance until the block pins were encountered. Finally, a 1.7-mm endoscope was used under saline-solution perfusion to verify the thoroughness of the bar excision for direct visualization (intramedullary endoscopically assisted technique). Once the normal physeal cartilage was identified, the residual bar inside the epiphysis was debrided carefully with a motorized shaver until a complete ring of the physeal cartilage was identified by alternately introducing and removing the scope and shaver (Fig. 4a–c). After nearly 360° of the “physeal cartilage ring” was observed around the border of the bar (Fig. 5) [13], some interposition material, such as autogenous body fat or surgical bone wax, was packed into the resection cavity and secured with sutures through the surrounding soft tissues as necessary.

Postoperatively, a short arm cast was applied for approximately 2 weeks. After cast removal, the range of motion exercise was gradually started.

In the first operation, closed-wedge osteotomy was used to correct the distal radius, and lengthening was started using an external fixator (Orthofix MiniRail Fixator™; Orthofix Inc., Verona, Italy). Before the operation, 3-D computer models of the bilateral radius and ulna were created from the CT data. Referring to the standard mirror image of the contralateral counterparts, the spatial position of the planes for osteotomy was estimated. Additionally, precise information on screw positions and directions for the external fixator was gained followed by computational lengthening of the distal fragment of the radius by 25 mm (Fig. 8). The operation was performed according to this preoperative planning and the osteotomy site was lengthened from 1 week postoperatively to 7 weeks (total lengthening, 25 mm; as planned). The external fixator was removed 18 weeks postoperatively when adequate maturation of the callus at the bone interval and complete correction of the deformities were confirmed through plain radiographs (Fig. 9a–c).

To plan the second operation, the affected radius was rescanned on CT after lengthening was complete. The scan revealed that the area of the osseous bar was approximately 20% of the growth plate. At this time, the patient was 11 years old with the predicted growth of approximately 25 mm in the distal ulna [15]. The 3-D computer models of the radius and the physeal bar were created using these data. In addition, the patient-specific guide was designed as a surgical guide to target the physeal bar model surrounded by multiple K-wires. PBR was performed using this patient-specific guide as described previously, and with careful debridement with a motorized shaver, confirmed the thoroughness of the bar excision for direct visualization using the 1.7-mm endoscope once the “physeal cartilage ring” was observed [13]. After that, the surgical bone wax was interposed into the space. Postoperatively, the affected limb remained immobilized for 2 weeks. After 2 years of PBR, no recurrence of the wrist deformities was observed, and the patient did not complain of any pain and restriction of the motion. Furthermore, radiographs demonstrated no growth disturbance and restoration of normal length of forearm bones, which remained constant since the first operation (Fig. 10a, b). The patient regained full activity of her wrist and was able to participate in athletics.