Biomechanical tests and finite element analyses of pelvic stability using bilateral single iliac screws with different channels in lumbo-iliac fixation

CT-based Anatomic and Clinical Analysis of Iliac Screw Placement During Spinopelvic Fixation

BACKGROUND/AIM

Iliac screws provide strong caudal anchorage for both long spinal fusions as well as short lumbopelvic fixations. However, anatomic based placement can be challenging, and complication rates are often underestimated.

PATIENTS AND METHODS

We analysed 47 iliac screws being placed in 24 patients. Using postoperative computed tomography (CT), iliac screw placement was analysed with reference to anatomic landmarks. Iliac narrowings were described with regard to their relevance for iliac screw placement. Moreover, we analyzed clinical records for clinical complications. The latter were classified as intraoperative, postoperative, and radiological.

RESULTS

From starting points, described by distance to the posterior superior iliac spine (PSIS), the average iliac screw length was 71.2±13.7 mm, and the diameter was as wide as 7.9±0.7 mm. Divergence was 30.7±12.6° (transverse plane) and caudal orientation was 34.2±13.0° (sagittal orientation). General pelvic dimensions correlated significantly with each other, and certainly with the length of implanted screws. Different adverse events and complications occurred. A total of 20% of patients were found with at least partial extracortical malpositioning. The main group of complications were postoperative with painful prominence in 20% of cases, wound infection in 8.9% and wound healing disorders in 6.7%. Further complications were radiological screw loosening (11.1%). No complications were detected in 33.3% of patients.

CONCLUSION

Optimal iliac screw size relative to the individual anatomy in general is not achieved. In most cases compared to the literature, iliac screw dimensions could be both longer and thicker. Perfect anatomic placement can be challenging, which highlights the need for individual preoperative CT-based surgical planning to achieve a strong caudal anchorage in lumbopelvic fixations. In general, the diameter seems to be more important than the screw length.

Finite Element Analysis of a 3D-Printed Acetabular Prosthesis for an Acetabular Defect According to the Paprosky Classification

The treatment of Paprosky Type III acetabular defects is a significant challenge in orthopedic surgery, as standard components often do not fit properly. This study aims to evaluate the biomechanical efficacy of a custom 3D-printed PEEK acetabular prosthesis compared to a conventional titanium implant. A 3D model of the pelvis was created using a computed tomography scanner and a custom-made acetabular implant was designed. Finite element analysis (FEA) was performed using Ansys Workbench to evaluate the stress and strain distribution of two materials on the pelvic bone. The results showed that the titanium prosthesis model had less strain transmitted to the bone, while the PEEK model had better stress transmission and bone stimulation. The use of custom implants reduced the risk of stress shielding, potentially improving long-term bone health. Three-dimensional-printed acetabular prostheses therefore offer significant advantages over traditional implants, suggesting improved implant stability and reduced failure rates.

Salvage of Iatrogenic Sciatic Nerve Injury Caused by Operatively Treated Acetabular Fractures: Two Cases and Literature Review

BACKGROUND

While sciatic nerve injury has been described as a complication of acetabular fractures, iatrogenic nerve injury remains sparsely reported. This study aims to assess iatrogenic sciatic nerve injuries occurring during acetabular fracture surgery, tracking their neurological recovery and clinical outcomes, and investigating any correlation between recovery and the severity of neurologic injury to facilitate physicians in providing prediction of prognosis.

CASE PRESENTATION

We present two cases of male patients, aged 56 and 22, who developed sciatic palsy due to iatrogenic nerve injury during acetabular fracture surgery. Iatrogenic sciatic nerve injury resulted from operatively treated acetabular fractures. Surgical exploration, involving internal fixation removal and nerve decompression, successfully alleviated symptoms in both cases postoperatively. At the latest follow-up, one patient achieved full recovery with excellent function, while the other exhibited residual deficits at the L5/S1 root level along with minimal pain.

CONCLUSION

Sciatic nerve injury likely stemmed from reduction techniques and internal fixation procedures for the posterior column, particularly when performed with the hip flexed, thereby placing tension on the sciatic nerve. Our case reports underscore the significance of liberal utilization of electrophysiologic examinations and intraoperative monitoring for the prediction of prognosis. Surgical exploration, encompassing internal fixation removal and nerve decompression, represents an effective intervention for resolving sciatic palsy, encompassing both sensory neuropathy and motor symptoms.

Finite element analysis of sacral-alar-iliac screw fixation for sacroiliac joint dislocation

The percutaneous sacroiliac (SI) screw is a common fixation option for posterior ring disruption in pelvic fractures. However, SI screw placement is difficult and can injure adjacent neurovascular structures. The sacral-alar-iliac screw (SAI) is a safe, reliable free-hand sacral pelvic fixation technique. To investigate the biomechanical stability of SAI for SI joint dislocation, finite element analysis was performed in unstable Tile-Type B and C pelvic ring injuries. The displacement in S1 (fixation of a unilateral S1 segment with one SI screw), TS1 (fixation of the S1 segment with a transsacra 1 screw), TS2 (fixation of the S2 segment with a transsacra 2 screw), S1AI, and S2AI exceeded the normal SI joint mobility. Sufficient stability after SI joint dislocation was obtained with (TS1 + TS2), (TS2 + S1), (S1AI + S2AI + rod), (S1AI + S2AI), and (S1 + S2AI + S1 pedicle) fixation. The TS1 + TS2 group had the smallest displacement and lowest peak screw stress, followed by (S1 + S2AI + S1 pedicle) placement. Our findings suggest that SAI screws are a valuable option for SI joint dislocation.