Three-Dimensional Planning and Patient-Specific Drill Guides for Repair of Spondylolysis/L5 Pars Defect.

BACKGROUND: Incomplete ossification of the pars interarticularis will result in a pars defect, a common cause of low back pain in youth and strongly associated with participation in high-impact sports. If left untreated, it can result in spondylolisthesis, causing dynamic canal stenosis, low back pain, and radiculopathy. The treatment of pars defect was first described by Bucks in 1970, who used screws in the lamina placed through an upward and outward direction. However, because of the multiple inclusion and exclusion criteria and narrow margin of error, the Bucks pars repair technique is not commonly performed. METHODS: A 28-year-old woman had with low back pain that she had been experiencing since mid-adolescence. Computed tomography revealed a bilateral L5 pars defect without spondylolisthesis. Her L5 vertebra was reconstructed virtually. The screw trajectories, a 3-dimensional (3D) model of the vertebra, and a patient-specific drill guide (PSDG) were designed and printed using positioning guide software (MySpine MC Guides [Medacta International SA, Castel San Petro, Switzerland]). A modified Bucks procedure using cannulated compression screws and the PSDG was performed. RESULTS: Follow-up computed tomography revealed accurate placement of the compression screws, mirroring the planned trajectory. The patient was pain free at 3 months postoperatively, and early union across the defect was visualized on the 5-month radiographic imaging study. CONCLUSION: Using 3D planning software, complex surgical procedures can be planned using the patient's anatomy and computed tomography. With the aid of 3D-printed PSDGs, screw placement in narrow corridors, such as was shown in our case, is safe, efficient, and achievable.

Three-Dimensional Patient-Specific Guides for Intraoperative Navigation for Cortical Screw Trajectory Pedicle Fixation.

BACKGROUND: Cortical bone trajectory (CBT) technique for pedicle fixation has been proposed and adopted in recent years. This technique involves a mediolateral direction and a caudocephalad path to maximize screw purchase in cortical bone. Various techniques have been proposed to increase the accuracy of screw placement. A novel technique for CBT screw placement using a three-dimensional printed patient-specific drill guide (PSDG) is presented. METHODS: CBT screw fixation combined with posterior lumbar interbody fusion was performed for reduction of an L4-5 spondylolisthesis in a 71-year-old woman. PSDGs (MySpine MC Guides) were designed and printed based on the patient's preoperative computed tomography scan. PSDGs were used intraoperatively to facilitate screw trajectory and placement. RESULTS: Postoperative imaging performed at 6 weeks and 3 months revealed accurate screw trajectory with excellent reduction of spondylolisthesis. The patient improved clinically with minimal mechanical pain and claudication at 3-month follow-up. CONCLUSIONS: PSDG for CBT screw fixation offers significant benefits, including preoperative planning; improved screw placement accuracy while minimizing cortical breach; reduction of operative time; and lower cost compared with intraoperative computed tomography-based neuronavigation, thus expanding the availability of this technique. Drawbacks include time required for PSDG planning and learning curve for surgeons.

Cortical pedicle screw placement in lumbar spinal surgery with a patient-matched targeting guide: A cadaveric study.

BACKGROUND: Cortical pedicle screw placement is an attractive technique in terms of both fixation strength and less invasiveness. However, to insert the screw with penetrating cortical bone on the ideal trajectory is technically demanding. The use of three-dimensional (3D) patient-matched guides may facilitate the use of this technique. PURPOSE: To examine the accuracy of cortical screw placement using a patient-matched targeting guide with a cadaveric study assessing the accuracy. METHODS: The 3D planning of the pedicle screw placement, including the location at which the screw would pass through the center of the pedicle, sagittal/transverse trajectory (angle), length, and diameter, was developed using 3D CAD design software. Three-dimensional guides based on the preoperative planning were created for three cadaveric specimens (L1 to S1, 36 pedicles). Screws (n = 18) and pins (n = 18) were placed using K-wire or drill-based guides, without X-ray exposure. Actual positioning was compared to the preoperative plan by superimposing the inserted screws/pins based on postoperative CT. The placement accuracy was graded based on the degree of perforation of the pedicle by the pedicle screw or pin using an acceptance criterion (no perforation; Grade A, 0-2 mm; Grade B, 2-4 mm; and Grade C, >4 mm). The mean deviation between the planned and inserted screw positions on the coronal plane at the midpoint of the pedicle was compared to the accuracy of screw guide for traditional pedicle screw trajectory (0.70 mm). RESULTS: Of 35 evaluated screws and pins, 32 (91.4%) were inserted completely inside the pedicle. All pedicle perforation was within 2 mm. The mean deviation from the plan at the midpoint of pedicle was 0.66 mm; thus, the accuracy was within the predefined criteria. CONCLUSIONS: Cortical pedicle screw placement using 3D-patient matched guides is accurate. Further clinical studies are required to confirm the radiographic and clinical effects.

Pedicle screw placement accuracy in thoracic and lumbar spinal surgery with a patient-matched targeting guide: a cadaveric study.

PURPOSE: Pedicle screw placement is an increasingly common procedure for the correction of spine degenerative disease, deformity and trauma. However, screw placement is demanding, with complications resulting from inaccurate screw placement. While several different techniques have been developed to improve accuracy, they all have their limitations. METHODS: We examined the MySpine (Medacta International SA, Castel San Pietro, CH) patient-matched pedicle targeting guide in three cadaveric spine specimens operated on by three surgeons. A three-dimensional (3D) preoperative plan was constructed from spinal computed tomography scans, from which individualised guides were developed for the placement of Medacta Unconstrained Screw Technology pedicle screws. Following screw placement, the 3D positioning of the screws was compared to the preoperative plan against a series of pre-defined criteria. RESULTS: Of 46 inserted screws eligible for assessment, 91.3 % were fully inside the pedicle. There were no cases of Grade B (2-4 mm) or C (>4 mm) pedicle perforation. The mean deviation between the planned and actual screw position at the midpoint of the pedicle was 0.70 mm, the mean horizontal deviation was 0.60 mm and the mean vertical deviation was 0.77 mm. The mean angular deviation in the sagittal plane was 1.74°, versus 1.32° in the transverse plane. The mean deviation in screw depth was 1.55 mm. On all measures, the accuracy of screw placement was within the predefined criteria. CONCLUSIONS: Our cadaver study indicates that pedicle screw placement with the system is accurate and should be investigated in larger in vitro and in vivo studies.