Impacted bone allograft personalised by a novel 3D printed customization kit produces high surgical accuracy in medial opening wedge high tibial osteotomy: a pilot study

Abstract

Purpose: Contemporary medial opening wedge high tibial osteotomy (MOWHTO) still seems to struggle with inconsistent accuracy outcomes. Our objective was to assess surgical accuracy and short-term clinical outcomes when using 3D planning and a patient-specific instrumentation (PSI) kit to prepare customized bone allografts.

Methods: Thirty subjects (age 48y ± 13) were included in a double-center prospective case series. A low-dose CT-scan was performed to generate 3D bone models, a MOWHTO was simulated, and PSI was designed and 3D printed based on the complementary negative of the planned osteotomy gap. Clinical outcome was assessed at two, four, 12 weeks and one year using NRS, KOOS, UCLA activity score, EQ-5D and anchor questions. A linear-mixed model approach was implemented for data analysis.

Results: Preoperative 3D values were 175.0° ± 2.2 mechanical tibiofemoral angle (mTFA), 85.0° ± 3.0 medial proximal tibial angle (MPTA), and 94.1° ± 3.4 medial posterior tibial slope (MPTS). Target planning ranged from slight varus to the lateral tibial spine (slight valgus). Postoperative 3D analysis showed an accuracy of 1.1° ± 0.7 ΔMPTA (p = 0.04) and 1.2° ± 1.2 ΔMPTS (p = 0.11). NRS decreased from baseline 6.1 ± 1.9 to 2.7 ± 1.9 at four weeks (p < 0.001) and 1.7 ± 1.9 at one year (p < 0.001). KOOS increased from 31.4 ± 17.6 to 50.6 ± 20.6 at 12 weeks (p < 0.001) and to 71.8 ± 15.6 at one year (p < 0.001).

Conclusion: The study suggests that 3D printed instrumentation to personalize structural bone allograft is a viable alternative method in MOWHTO that has the benefit of optimizing surgical accuracy while providing early and consistent pain relief after surgery.

Keywords: 3D planning; Accuracy; High tibial osteotomy; Joint preservation; Patient-specific instrumentation.

Fig. 1

3D preoperative osteotomy simulation using (A) the planning angles MPTA in the coronal plane and (B) the tibial slopes in the sagittal plane. (C) The negative of the planned osteotomy gap (red) is embodied and exported with the hinge axis (blue) to design the 3D printed customization kit for bone graft preparation

Fig. 2

Design of the customized bone graft preparation kit: (a) a winged nut, (b) an adjustable upper fixation part, (c) a cutting block, (d) a backed platform and (e) a sliding cast of the required gap opening. Cutting block (c) is marked with patients’ initials, side of surgery, correction size and anteroposterior graft orientation

Fig. 3

Intraoperative preparation of structural impacted bone allograft with the customized 3D printed kit. (A) The femoral head is placed on the platform and fixed with two 1.8 mm Kirschner pins through the cutting block, without full engagement to the bottom. (B) The anterior and posterior borders of the graft are cut perpendicular to the platform. (C) The medial contour of the graft is trimmed, which identically matches the curvature of the medial cortex of the patient. Correct graft positioning can hereby later controlled. (D) The desired result after graft shape contouring with an oscillating saw. (E) Next, the designated cast is pushed to the graft, again matching the prepared medial curvature of the graft. (F) The upper surface of the cast is used as guiding plane to obtain (G) the desired bone wedge. (H) Finally, the intended structural bone allograft can safely be removed from the guide and is ready for introduction in the osteotomy gap

Fig. 4

3D matching of the pre-and postoperative proximal tibia plateaus, above the osteotomy level. Average distance error between bone models was 0.0716 ± 0.0019 mm

Fig. 5

Postoperative 3D accuracy analysis by matching the pre-and postoperative proximal tibia plateaus

Fig. 6

The Numeric Rating Scale (NRS), KOOS, UCLA and EQ-5D outcomes up to one year after surgery. (*significant difference compared to baseline; **significant difference compared to baseline and first postoperative timepoint)