In Vitro Investigation of Column Fixation Constructs for Periacetabular Osteotomy: Which Provide the Greatest Stiffness and Strength?

Background: Periacetabular osteotomy (PAO) is an effective surgical procedure for managing acetabular dysplasia. The purpose of this study was to analyze the biomechanical properties of novel PAO constructs that incorporate orthopaedic trauma techniques. We hypothesize that these fixation methods will create a stiffer construct that tolerates higher loads to failure. Methods: Twenty bio-composite hemi-pelvises underwent PAO with the following fixation configurations: Group A: 4 iliac crest (IC) screws; Group B: 3 IC screws; Group C: 2 IC screws, 1 retrograde anterior column (AC) screw, and 1 lateral compression type-2 (LC2) screw directed from the anterior inferior iliac spine to the posterior inferior iliac spine; Group D: 1 AC screw, 1 LC2 screw, 1 posterior column screw; Group E: 2 LC2 screws, 1 AC screw. Constructs were loaded to failure on a material testing hydraulic press, and ultimate strength, stiffness, and osteotomy displacement were measured. Results: The highest load to failure was seen in group D (2511 N), which was significantly more than groups A (1528 N, P = .0114) and B (1348 N, P < .0001). The stiffest construct was group E (602 N/mm) compared to groups A (315 N/mm, P = .0439) and B (243 N/mm, P = .0008). Failure occurred most often with a fracture in the posterior column. Conclusions: This study supports column fixation methods used in orthopaedic trauma for PAO as biomechanically advantageous to traditional fixation techniques. These constructs may be beneficial to patients with weight-bearing concerns or early rehabilitation needs.

Biomechanical Comparison of 4 Transsacral Fixation Constructs in a Type 61C, Zone II Pelvic Fracture Model.

OBJECTIVES: OTA/AO 61C pelvic ring injuries are vertically unstable because of complete sacral fractures combined with anterior ring injury. The objective of this study was to compare the biomechanical characteristics of 4 transsacral screw constructs for posterior pelvic ring fixation, including one that uses a novel fixation method with a pair of locked washers with interdigitating cams. METHODS: Type C pelvic ring disruptions were created on 16 synthetic pelvis models. Each pelvis was fixated with an S2 screw in addition to being allocated to 1 of 4 transsacral constructs through S1: (1) 8.0-mm screw, (2) 8.0-mm bolt, (3) 8.0-mm screw locked with a nut, and (4) 8.00-mm screw locked with a nut with the addition of interdigitating washers between the screw head and ilium on the near cortex, and ilium and nut on the far cortex. The anterior ring fractures were not stabilized. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. The anterior and posterior osteotomy sites were instrumented with pairs of infrared (IR) light-emitting markers, and the relative displacement of the markers was monitored using a three-dimensional (3D) motion capture system. Displacement measurements at 25,000; 50,000; 75,000; and 100,000 cycles and failure force were recorded for each pelvis. RESULTS: The novel washer design construct performed better than the screw construct with less posterior ring motion at 75,000 ( P = 0.029) and 100,000 cycles ( P = 0.029). CONCLUSIONS: The novel interdigitating washer design may be superior to using a screw construct alone to achieve rigid, locked posterior ring fixation in a synthetic pelvis model with a Type C pelvic ring disruption.

Thoracoscopic discectomy and fusion in an animal model: safe and effective when segmental blood vessels are spared.

STUDY DESIGN: Disc-endplate excision and spine fusion were compared in animals randomly assigned to segmental vessel-spared and segmental vessel-ligated groups in an in vivo goat model of anterior spine discectomy and fusion using thoracoscopic techniques. OBJECTIVES: To compare safety and completeness of disc and endplate excision, and to perform a histologic and biomechanical comparison between fusion masses when the segmental vessels are spared and when they are ligated using thoracoscopic techniques. SUMMARY OFF BACKGROUND DATA: Because thoracoscopy is relatively new and technically demanding, many surgeons ligate the segmental blood vessels to enhance spine exposure and limit the risk of injury during discectomy and fusion. Although rare, spinal cord compromise secondary to segmental vessel ligation has been reported. METHODS: This study was divided into two phases. In Phase 1, 10 mature goats were randomly assigned to either the segmental vessel-ligated or the segmental vessel-spared group. Disc and endplate excision was performed at six consecutive thoracic levels in each animal (30 levels per group). The animals were killed, and the depth of disc excision was measured in the transverse and sagittal planes. The vertebral bodies then were separated through the disc space; photographic images of the endplates were digitized, and the area of endplate excision was calculated. In Phase 2, 12 mature goats were randomly assigned to the segmental vessel-ligated or vessel-spared group, and five noncontiguous thoracic segments were fused using autologous iliac crest graft. At 4 months the animals were killed, and the spines were harvested. At each disc level, the three-dimensional rotational and translational motions were analyzed and histomorphometric analysis was performed. RESULTS: Phase 1: Each animal survived the operative procedure, and no surgical complications occurred. No difference was found between vessel-ligated and vessel-spared groups in operative time (21.8 vs 22.7 minutes per disc), blood loss (97 vs 159 mL), or transverse (81% vs 74%) or sagittal (85% vs 85%) disc excision. The total area of endplate excision was 70% in the vessel-ligated group and 67% in the vessel-spared group (P > 0.1). Phase 2: Biomechanical testing demonstrated no difference in stiffness of the fused segments between the two groups in flexion-extension or axial rotation. However, greater flexibility in lateral bending was found in the specimens whose vessels were ligated (P < 0.05). The percentage of trabecular bone volume was similar between the two groups. CONCLUSIONS: The segmental vessels in the thoracic spine can be effectively spared without injury during disc excision and fusion. Although slightly more disc area was excised with ligation of the vessels, this was not statistically significant, and the fusion mass was similar between the two groups. Sparing the segmental vessels may provide blood supply that aids fusion mass, and the result may be greater spine stiffness in the coronal plane. Sparing the segmental vessels during thoracoscopic anterior disc excision and fusion can be safe. It should be considered in patients with a high risk for neurologic injury because of decreased spinal cord perfusion in revision surgery, severe kyphosis, congenital anomalies. Because the neurologic risk of vessel ligation has not been clearly established for idiopathic scoliosis, the surgeon will have to consider the risk-benefit ratio of adopting these methods when deciding not to ligate vessels in these patients.