Between August 2014 and May 2016, 39 patients with unstable ITF were treated at the Nangjing Medical University, Nanjing Hospital and were divided into two groups based on patient preference. The 3DP-RP assisted surgery group consisted of 19 patients (11 men and 8 women; mean age of 66.2 years; age range, 55–74 years). In the control group, 20 patients (11 males and 9 females; mean age, 65.9 years; age range, 52–73 years) with unstable ITF were treated using a traditional PFNA technique with the reduction and PFNA implantation under fluoroscopic guidance. All patients were treated by the same surgical team using the same type of PFNA implant (Weigao Orthopedic Device Co., Ltd., Weihai, China). All cases were classified as Müller Arbeitsgemeinschaft für Osteosynthesefragen Classification of fracture types II and III (18). Patients presenting with any of the following were excluded from the present study: Subtrochanteric, pathologic, open, or multiple fractures; isolated fracture of the greater or lesser trochanter; revision hip surgeries; and walking disability before injury caused by paraplegics, severe osteoarthritis, rheumatoid arthritis, lumbar stenosis or lumbar disc herniation. There were no significant differences in patient demographics between the 3DP-RP assisted surgery and traditional surgery groups (Table I). Ethical approval for the present study was granted by the Institutional Medical Ethical Committee of Nanjing Medical University, Nanjing Hospital (Nanjing, China). Informed consent was obtained from each patient prior to the current study.

Anatomical data obtained by computed tomography (CT) scanning (volume thickness, 1 mm, matrix 512×512; SOMATOM Sensation; Siemens AG, Munich, Germany) were transferred to the planning workstation (M3D; Medical Graphics, Gloucester, UK) using a Digital Imaging and Communications in Medicine interface and a 3D upper femoral model was reconstructed on the screen (Fig. 1). The surgeon then performed the planning using a preoperative planning program (MedGraphics 5.0; MGC Diagnostics, Saint Paul, MN, USA). The software allowed the surgeon to ‘navigate’ the prosthetic components into the correct positions following fracture reduction using computer aided design (CAD; Boholo 5.0; Boholo, Shanghai, China) (Fig. 2). The surgeon selected the appropriate sizes of components and recorded them. This model was stored as a stereolithography (STL) file, which was subsequently sent to a 3D printer (Songsun N2, Songsun Medical Technology Co., Ltd., Nanjing, China). The STL file stored the information of actual size, as a 1:1 scale was achieved by CT scanning, due to the design of the scanner and software. The printing procedure was repeated layer by layer until the life-size 3D model was completed (Fig. 3A-C). Simulated fracture reduction was conducted on the model with the femoral neck-shaft angle, size and displacement of fragments measured preoperatively.

Fracture reduction in the 3DP-RP model allowed simulation of the procedure under direct vision (Fig. 3D-F); optimum reduction ensures good contact and apposition of the internal and posterior cortical bone. The nail and screw blade selected by the M3D software were checked to ensure that the screw blade was located in the ideal position on the femoral head and neck (i.e., central or inferior on the anteroposterior radiograph and central on the lateral radiograph). The tip-apex distance (TAD) was measured using a standard method (19). In the conventional surgery group, the preoperative traction for fracture reduction was performed using the same traction devices under fluoroscopic guidance (OEC FlexiView 8800, GE Healthcare, Chicago, IL, USA).

Next, each fracture reduction and implantation of the PFNA in the two group was performed on a traction table under the same fluoroscopic guidance with the orientation of traction designed based on the CAD data and the 3DP-RP model. All tractions were performed under general anesthesia by continuous intravenous injection of propofol (4–12 mg/kg/h; Fresenius SE & Co., Bad Homburg, Germany).

A 5 cm skin incision was made, the fascia and gluteus medius were isolated and a 3.2 mm guide wire was inserted from the trochanteric peak. With the soft tissue protected, the proximal femur was manually opened using a bone reamer. The appropriate nail was selected and manually introduced into the femur. Subsequently, the guide wire for the screw blade was inserted through a 2 cm lateral incision, ensuring the central position in the femoral head in anterior-posterior and lateral fluoroscopic views (20). Final distal locking in the two groups were performed by the navigation of manufacturer's supplementary guiding instruments and fluoroscopy (21).

All patients received antibiotic prophylaxis (2.0 g twice a day, intravenous; cefathiamidine, Baiyunshan Pharmaceutical Co., Ltd., Guangzhou, China) for 24 h. For thromboprophylaxis, low molecular weight heparin (2,500 U once a day, hypodermic; Fraxiparine, GlaxoSmithKline Co., Ltd., Tianjin, China) was administered subcutaneously until the patients recovered to full mobilization. Supervised weight bearing was allowed as tolerated.

The parameters of PFNA measured according to the 3DP model, including nail diameter, nail length, screw blade length and TAD, were compared with the actual values obtained during surgery (Table I). Duration of surgery, intraoperative blood loss, postoperative drainage volume and length of hospital stay were recorded and compared with the corresponding values in control patients undergoing conventional PFNA procedures. The volume of postoperative blood loss was calculated as the sum of blood collected in the gauzes (size of each gauze: 45×26 cm, blood volume in each gauze calculated as 15 ml). Patients were reviewed clinically and radiologically at 3 days post-surgery and followed up for 6 months, with physical evaluations and hip X-rays performed at 1, 3 and 6 months post-surgery. All patients were followed up successfully and no patients were lost.

All data are presented as the mean ± standard deviation. Fisher's exact test and the Student's t-test were used to compare data. Comparison of variables between the groups was performed using the independent sample t test. P<0.05 was considered to indicate a statistical significant difference. SPSS version 13.0 software (SPSS Inc., Chicago, IL, USA) was used for statistical analysis.

For the 19 patients in the 3DP-RP group, preoperative planning was performed using CAD and 3DP technology. During surgery, the operative approach, the diameter and length of the nail, the length and position of the screw blade were all consistent with the preoperative plan (Table II).

Surgical duration, intraoperative and postoperative blood loss were significantly lower in the 3DP-RP group compared with the patients undergoing conventional surgery (P<0.01, P=0.02 and P=0.03, respectively; Table III). There was no significant difference between the two groups in the mean hospital stay duration. At review 3 days post-surgery, radiography revealed satisfactory reductions of all fractures in the two groups, with the implants positioned correctly (Fig. 4). The postoperative follow-up indicated that patients in the 3DP-RP group had a shorter time to ambulation compared with patients that underwent the conventional procedure (4.8±2.2 vs. 6.7±2.6 days; P<0.05; Table II).

At the 6-month follow-up, bone healing was satisfactory in all cases in the two groups, without the screw cut out of the head or obvious displacement of fracture segments. All patients in the two groups exhibited good hip function with no varus/vague hip deformities observed (Fig. 5).