Low-dose CT: A safe and effective imaging modality in post-operative pelvic & acetabular fixation.

INTRODUCTION: Post-operative pelvic & acetabular fixation patients are conventionally imaged using 3-view radiographs (AP, inlet and outlet). The efficacy of such radiographs is inconsistent due to technical difficulties capturing an adequate view, often necessitating repeat radiographs and therefore increasing radiation exposure. Radiographs can be difficult to interpret, limiting the assessment of fracture reduction and fixation, especially with respect to metalwork positioning around articular surfaces. Traditionally, post-operative pelvic & acetabular fixation patients undergo repeat 3-view radiographs post-operatively, at 6 weeks, followed by at 3, 6, 12, 18 and 24 months. We propose a new pathway, in which patients have one low-dose pelvic CT immediately post-operatively, followed by one radiograph (AP pelvis) at the same time points. METHODS: A new pelvic CT protocol was created to provide high quality 3D imaging whilst delivering a 5 times lower radiation dose (compared to normal pelvic CT). Data for all pelvic radiographs and CTs between January 2021 and March 2022 was exported. Using dose area product values, effective radiation dose and attributable lifetime cancer risk were calculated. RESULTS: There were 42 patients included in the analysis (age range 15 to 87).The average effective dose for the 3-view pelvic X-rays was 0.6mSv (range 0.2 to 2.8mSv), and 1.1mSv (range 0.5 to 2.2mSv) for the low-dose pelvic CT. Traditional 7 × 3-view post-operative radiographs: 7 × 0.6mSv = 4.2mSv (corresponding to 1 in 11,000 cancer risk) Low dose post-operative CT and 6 × 1-view radiographs: 1.1mSv + (6 × 0.6mSv / 3) = 2.3mSv (corresponding to 1 in 20,000 cancer risk) CONCLUSION: Low-dose CT scanning (in conjunction with 1-view radiographs) is an effective and safe imaging modality in the post-operative assessment of pelvic & acetabular fracture fixation, conferring a lower radiation burden, easier logistics, and higher quality images when compared to the traditional pathway of 3-view radiographs.

The accuracy of computer-assisted percutaneous iliosacral screw placement.

The benchmark fluoroscopic technique of iliosacral screw insertion is disadvantaged by its reliance on ionizing radiation and presentation of dynamic information in only one plane. Multiplane targeting requires interpolation, which may be associated with inherent errors. Computer-assisted surgery enables surgeons to monitor their screw trajectory in 3-D space. The clinical application of computer-assisted surgery requires validation of its accuracy when tested against a benchmark technique. We simulated surgical implantation of cannulated screws in 10 embalmed human cadavers. Two specimens had sacral dysplasia. We inserted 20 screws into the S1 body, the left side by the benchmark fluoroscopic technique and the right side by a fluoroscopically registered computer-assisted surgery technique. All specimens were intact with no simulated injuries. A postoperative high-definition computed tomography scan showed the screw track. The actual track was compared with the intended screw track by a graphical technique. There was no deviation from the intended screw path in any of the simulated screw paths. With both techniques, two of the 10 tracks penetrated the sacral cortex in dysplastic pelvices. A fluoroscopic computer-assisted surgery technique appears as accurate as the standard fluoroscopic technique but no more so. Caution is recommended in dysplastic pelvices.

Proposed mechanisms of lower urinary tract injury in fractures of the pelvic ring.

OBJECTIVE: To investigate whether the observation of particular pelvic fracture patterns enables the clinician to predict the presence and type of injuries to the lower urinary tract, as the mechanisms of injury to the lower urinary tract in association with fractures of the pelvic ring are unclear. PATIENTS AND METHODS: The case-notes and radiographs of 168 patients with either pelvic ring or acetabular fractures were reviewed; 108 pelvic ring fractures (81 men, 27 women) and 60 acetabular fractures (46 men, 14 women). The pelvic fractures were classified according to the system described by Tile and were correlated with the incidence and type of lower urinary tract injury (LUTI). RESULTS: Overall, of the 108 men and women with pelvic ring fractures, 27 (25%) had a LUTI documented either radiologically or as an intraoperative finding. Of the 81 men with pelvic ring fractures, 24 (30%) had a LUTI, of whom six (7%) had an isolated bladder laceration, 14 (17%) a partial urethral injury (PUI) and four (5%) a complete urethral disruption (CUD). Five of the 18 men with urethral injuries also had bladder injuries and in three of these, the bladder neck was also injured. Three of 27 women (11%) had a LUTI, all of whom had isolated bladder lacerations. Of the 46 men with an acetabular fracture, one (2%) had a CUD, and three (7%) had a PUI. One of 14 of women with an acetabular fracture sustained a bladder laceration. None of the three men with a Tile Type-A pelvic ring fracture sustained a LUTI. Of the 28 men with 'open-book' (Tile Type-B1) fractures, 21 (75%) had no associated LUTI and seven (25%) had a LUTI (five partial urethral injuries and two bladder lacerations). Of the 10 men with 'lateral compression' (Tile Type-B2) fractures, six had no LUTI and four had a LUTI (two partial urethral injuries and two bladder lacerations). Of the 40 men with 'vertical shear' (Tile Type-C) fractures, 27 (68%) had no LUTI and 13 (32%) a LUTI (four complete urethral disruptions, seven partial urethral injuries, and two bladder lacerations) including all of the combined bladder and urethral injuries and all of the bladder neck injuries. CONCLUSION: The pelvic fracture pattern alone does not predict the presence of a LUTI. When it occurs, the type of LUTI appears to be related to the fracture mechanism. The pattern of injury to the soft tissue envelope and specifically to the ligaments supporting the lower urinary tract offers the best correlation with the observed LUTI. We propose a mechanism for this.

Emergency management of pelvic fractures.

Pelvic fractures are relatively uncommon, accounting for 1-3% of all fracture. Around 60% occur in men. This article discusses the multidisciplinary management of pelvic ring disruptions resulting from high energy transfer.