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The atlas (C1) and axis (C2) have distinct morphologies to support the skull and facilitate head rotation and neck flexion. Congenital defects of C1 posterior arch are rare. We present a case of a 59-year-old man with both an absent C1 posterior arch with concomitant os odontoideum. The patient presented with neck crepitus, moderate neck pain and progressive worsening upper limbs paraesthesia and pain. Computed tomography (CT) revealed non-union between the odontoid process and body of axis as well as absence of C1 posterior arch. An occiput C0-C3 fusion was performed. The patient's symptoms improved significantly, and he is functioning well at 12 months. CT showed solid fusion without implant migration. Concomitant os odontoideum with aplastic C1 posterior arch is rare with limited evidence to guide management. Posterior fixation and fusion may be a potential solution to prevent dynamic compression, thereby preventing further myelopathy and related complications.

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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.

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OBJECTIVE: Anterior lumbar interbody fusion (ALIF) is a common spinal fusion option for different spinal pathologies. In the early years, implant migrations/expulsions were potential complications of ALIFs due to the lack of integral fixation. We present a historical vignette on the inception and development of the first stand-alone ALIF (SA-ALIF) implant-the Hartshill Horseshoe (HH). METHODS: A Preferred Reporting Items for Systematic Reviews and Meta-Analyses systematic search was carried out for 3 online databases focusing on implant development for ALIF, refining the search to before 1995. A personal communication with the original patent holders of the HH was used due to the lack of formal publication of the HH during its early years. RESULTS: Since 1932, the idea of anterior lumbar fusion was proposed and was carried out in 1933 using a tibial peg. Autografts were first reported in 1936 as interbody spacers for ALIF. Since then, bone grafts were commonly used for ALIF. However, ALIFs were not commonly performed due to variable reported outcomes. A pilot study in 1971 reported the use titanium mesh blocks as interbody implants in 6 patients. No articles reporting the use of integral fixation for SA-ALIF implants were found before the development of the HH in 1984. CONCLUSIONS: The HH was the first synthetic SA-ALIF implant developed. Since the HH, multiple SA-ALIF implants have been designed. The benefits of integral fixation in a SA-ALIF device include immediate implant stability, ability to reduce and correct deformity postimplantation, prevention of implant migration, and increased implant-bony endplate contact for early osseointegration.

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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.

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