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Does Routine Postoperative Computerized Tomography After Acetabular Fracture Fixation Affect Management?

Elnahal, Walid A., MBBHc, FRCS (Orth)*,†; Ward, Anthony J., BMBS, FRCS*; Acharya, Mehool R., MBChB, FRCS (Orth)*; Chesser, Timothy J. S., MBBS, FRCS (Orth)*

doi: 10.1097/BOT.0000000000001405
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Introduction and Aims: The use of routine postoperative computerized tomography (CT) scan after acetabular fracture reconstruction remains controversial. CT scan may provide more accurate detail regarding metalwork position, retained intra-articular fragments, and quality of reduction but does expose the patient to additional radiation dosage and incurs increased cost. The aim of this study was to evaluate a protocol of routine postoperative CT scan for all acetabular fractures after surgical fixation and assess the effect this has on patient management.

Patients and Methods: The perioperative fluoroscopic images and postoperative plain radiographs of 122 patients who underwent surgical stabilization of a displaced acetabular fracture were reviewed and categorized into 3 groups: (1) safe, when there was no suspicion of metalwork malposition or intra-articular fragments; (2) inconclusive, when it was not possible to exclude malposition; or (3) definite malposition or intra-articular penetration of implants. The findings were compared with postoperative CT scans. The quality of reduction of the acetabular fracture was graded on plain radiographs using the Matta criteria and compared with the CT scan using a standardized technique.

Results: Fractures that were categorized as safe on plain radiographs were confirmed to have no metalwork malposition on CT scan in 94% of the cases, with the other 6% having insignificant findings that did not require revision surgery. When plain radiographs were inconclusive (n = 17), 4 patients had metalwork malposition documented on CT scan and 2 of these required revision surgery. There was an increased risk of implant malposition with use of spring plates for posterior wall stabilization. There was significant variation between the quality of reduction when assessed with plain radiographs as compared with CT scans (P < 0.001). In 42% of the patients who were thought to have anatomic reduction on plain radiographic assessment, the reduction was either imperfect or poor based on CT assessment.

Conclusions: CT scans were more accurate than plain radiographs in detecting metalwork malposition and in assessing quality of reduction of the acetabular fracture. The use of postoperative CT scans may be restricted to a group of fractures that have inconclusive or definite malpositioning of implants on perioperative or postoperative radiographs, especially with use of spring pates or to those patients in whom quality of reduction needs more accurate assessment for quality assurance or prognostic reasons.

Level of Evidence: Level IV; Diagnostic -Investigating a diagnostic test.

*North Bristol NHS Trust, Bristol, United Kingdom; and

Cairo University, Giza Governorate, Egypt.

Reprints: Anthony J. Ward, BMBS, FRCS, Department of Trauma and Orthopaedic Surgery, Brunel Building, Southmead Hospital, Bristol BS10 5NB, United Kingdom (e-mail: anthony.ward@nbt.nhs.uk).

The authors report no conflict of interest.

This project has been approved and registered as a quality improvement project at our local institution review board.

Accepted November 08, 2018

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INTRODUCTION

Letournel and Judet1 emphasized the importance of anatomic reduction and stable fixation of displaced acetabular fractures and the importance of the evaluation of outcome of surgical fixation with detailed radiographic and clinical assessments.

Postoperative computerized tomography (CT) imaging after acetabular fracture surgery may play an important role in detecting metalwork malposition or retained intra-articular fracture fragments and in assessing the quality of reduction of the articular surface. The role of CT scanning as a routine screening tool after pelvic and acetabular surgery is debatable due to the additional cost and the radiation exposure to the patient.2–4

As part of a pelvic and acetabular fracture treatment protocol, all patients are screened with fluoroscopy intraoperatively and before terminating the surgical fixation procedure, including standard anteroposterior (AP) view, oblique (Judet) views, and additional projections as judged necessary to exclude implant malposition and fracture malreduction, with the images being stored in our radiology PACS system. Postoperative standard plain x-rays and axial CT scans of the pelvis and acetabulum are obtained for all patients.

The aims of this study were to assess the clinical value of routine postoperative CT imaging in all patients undergoing acetabular fracture fixation, to determine the accuracy of plain radiographs in detecting metalwork malposition and in assessing quality of reduction, and the clinical effect of the postoperative CT scan findings on patients' management.

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PATIENTS AND METHODS

One hundred sixty-eight patients underwent acetabular fracture reconstruction in a Level 1 Trauma Center between January 2010 and December 2015. Forty-six patients were excluded from study as 40 underwent acute total hip arthroplasty and 6 had missing fluoroscopic images, radiographs, or CT scan. The medical records, perioperative fluoroscopic images, postoperative plain radiographs, and CT scans of the remaining 122 patients were assessed by 2 independent assessors (pelvic consultant surgeon and pelvic trauma fellow). The acetabular fracture type was classified according to Letournel and Judet.1

The AP, Judet, and additional views recorded on per-operative fluoroscopy and postoperative plain radiographs were scrutinized for implant position and retained intra-articular fracture fragments for each patient. Patients were categorized into 1 of 3 groups: “Safe”—radiographs showed no suspicion of metalwork malposition, intra-articular penetration, or retained fracture fragments; “Inconclusive”—radiographs cannot exclude metalwork malposition or retained intra-articular fragment; and “Definite” malposition—radiographs seem to show definite metalwork malposition or retained intra-articular fracture fragment.

Separately, the immediate postoperative CT scans were then assessed, using axial (1 or 2 mm slice thickness), coronal, and sagittal reconstructions and graded in to the same 3 groups. The findings were compared with those of the plain radiographs and fluoroscopy for each patient. Metalwork malposition was defined as intra-articular penetration of the acetabulum or screws protruding more than 10 mm into the soft tissues (Figure 1).

FIGURE 1

FIGURE 1

The quality of reduction of the acetabular fracture was assessed on the postoperative AP and Judet radiographs using the Matta criteria,5 graded as anatomic (0–1 mm displacement), imperfect (2–3 mm displacement), or poor (greater than 3 mm displacement). The gap and step measurements of the fracture displacement at the articular surface were measured using a standardized measurement technique.3,6 The postoperative CT scans were reviewed for quality of reduction using a similar technique to that described by Verbeek et al.7 Any fracture line gap or step in the subchondral bone was measured on the axial, coronal, and sagittal reconstructed views (if available) and the location noted (anterior wall, anterior column, dome, posterior wall, or posterior column). The vertical distance of the maximum step/gap from the most proximal level of the weight-bearing dome was noted. The weight-bearing dome was defined as the region of subchondral bone or arc in the proximal 1 cm vertical height as previously identified by Verbeek et al.7 The site of the largest gap/step was documented, regardless of its distance from the weight-bearing dome or level in the posterior wall (Figure 2). The quality of reduction was graded as anatomic, imperfect, or poor based on the maximum documented gap or step measurement on the CT scan.

FIGURE 2

FIGURE 2

Data were coded and entered using the statistical package SPSS (Statistical Package for the Social Sciences) version 25. Data were summarized using mean, minimum, and maximum in quantitative data and using frequency (count) and relative frequency (percentage) for categorical data. For comparing categorical data, χ2 test was performed. Exact test was used instead when the expected frequency was less than 5. A P value less than 0.05 was considered as statistically significant.

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RESULTS

The study included 101 male and 21 female patients, of mean age 42.5 years (range: 16–83 years) at the time of injury. Trauma was caused by road traffic accidents (52%), fall from height (30%), and other modalities of injury (18%), included bicycle accidents, falls from horse, and sports injuries. The acetabular fracture classifications are shown in Table 1, with the majority being associated both column fractures (30%) or posterior wall fractures (28%).

TABLE 1

TABLE 1

After examining the perioperative fluoroscopy images and postoperative plain radiographs, 104 patients were categorized into the “safe” group, with no suspicion of hardware malposition or intra-articular fragments. Seventeen patients were categorized “inconclusive” and 1 with “definite” implant malposition.

In the “safe” group (n = 104), CT scan detected 6 patients with metalwork malposition (5.7%), 5 of which were screws protruding more than 10 mm into soft tissues and 1 was a spring plate with pointed tines in the labrum. None of these patients required revision surgery.

In the “inconclusive” group (n = 17), the CT scan showed safe positioning of hardware and excluded intra-articular fragments in 13 patients but detected metalwork malposition in 4 patients. Two of these patients underwent revision surgery: one had both an intra-articular penetration by a screw and a spring plate potentially impinging on the femoral head, both requiring removal; and the other patient had intra-articular penetration by a screw, requiring removal. The remaining 2 patients had a spring plate with tines potentially in the labrum without apparent impingement on the femoral head and neither underwent revision surgery.

The “definite” group (n = 1) comprised of 1 patient with a long screw protruding more than 10 mm into the soft tissues, which was confirmed by CT scan. No revision surgery was required.

Overall, perioperative fluoroscopy and postoperative plain radiographs showed an accuracy of 94% in detecting safe metalwork position in this series. Of the 104 patients deemed to be safe, 98 were confirmed safe by CT scan. Furthermore, none of the 6 malpositioned implant cases that were missed on plain radiographs were clinically significant and none required revision surgery for this reason. None of the patients were documented to have retained intra-articular fracture fragments or underwent revision for this reason.

There was a significant association between the use of spring plates in posterior wall fractures and metalwork malposition (P = 0.015). Malpositioning of spring plates was documented in 4 (28.5%) of 14 patients, in which spring plates were used as part of the acetabular fracture fixation, with tines extending beyond the rim of the acetabular wall and in the labrum, one of which required revision. However, there was no association of metalwork malposition with the use of anterior column screws, posterior column screws, or the type of acetabular fracture.

The quality of reduction of the acetabular fractures, graded as anatomic, imperfect, or poor, documented on plain radiographs and on CT scan are shown in Table 2. There were significant differences between both modalities (P < 0.001), with anatomic reduction in 107 of 122 (88%) fractures assessed with plain radiographs but only in 62 of 122 (51%) cases assessed with CT scan. Of the 107 fractures documented to be anatomic reductions on plain radiographs, CT scan showed that 37 of these were imperfect and 8 were poor reductions. Similarly, imperfect reduction was documented in 10 of 122 (8%) cases on plain radiograph assessment but was increased to 45 of 122 (37%) cases with CT scan assessment.

TABLE 2

TABLE 2

Measurements of residual fracture displacement on plain radiographs showed a mean fracture line gap of 0.35 mm (range: 0–6.5 mm) at the articular surface, with 87% of the gaps in the dome region and 13% below the dome. Plain radiographs also demonstrated a mean step in the articular surface of 0.24 mm (range: 0–13 mm), with 55% of the steps situated in the dome region and 45% below the dome. Measurements of residual fracture displacement on CT scan showed that the mean fracture line gap was 1 mm (range: 0–13 mm), with 34% at the level of the dome and the remainder being at a mean of 20 mm below the level of the dome, including 21% in the posterior wall region. The CT scan documented a mean step in the articular surface of 0.4 mm (range: 0–5.5 mm), with 43% of the steps being in the dome region and the remainder being outside the dome, at a mean of 18 mm below the dome, including 7% in the posterior wall.

There was no significant association between fracture classification type and quality of reduction.

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DISCUSSION

Previous studies have shown that postoperative CT scan imaging provides more accurate information than fluoroscopy and plain radiographs in detecting metalwork malposition, retained intra-articular fragments, and quality of reduction.2–4,7–10 This information may be helpful in deciding patient management, for prediction of clinical outcome,5,8,10,11 for audit, quality assurance, and research purposes. A disadvantage of CT scan is the additional exposure to radiation in a group of patients who have already undergone radiologic imaging during their initial trauma assessment and intraoperative fracture fixation. The amount of radiation from conventional radiography may vary but is estimated to be 0.32 millisievert (mSv)12 as compared with 2.5 mSv for CT scan of the pelvis4 or 0.79 mSv for low-dose CT.12 The cost of the investigative procedure may be an additional concern, with an estimated cost of $93 USD (£71 GBP) for a CT scan of a single area without a radiologist's report in the National Health Service in the United Kingdom.13

The aim of this study was to audit the institution's protocol of routine postoperative CT imaging in all patients who undergo acetabular fracture fixation surgery to investigate whether the postoperative CT findings changed the subsequent management of these patients. A comparison of the perioperative fluoroscopy and postoperative radiographic and CT scan images in a consecutive series of operatively treated patients was performed to detect metalwork malposition, joint penetration, or retained intra-articular fracture fragments. Radiographs suggested that 104 of 122 cases were deemed “safe.” However, in this group, CT scan identified 6 patients with implant malposition and no retained fracture fragments or potential femoral head impingement. None of the 6 patients required revision surgery. The accuracy of plain radiographs was 94% in detecting malposition, meaning that when plain radiographs and fluoroscopy showed no suspicion of malposition, this was correct in 94% of the cases and in the other 6% was not clinically significant. The extra information gained by CT scan in the “safe” radiographic group was not important as it did not change the patients' management, suggesting CT scan was not indicated in this group.

It is worth noting that the radiographs were only deemed safe if all the metalwork could be clearly seen outside the acetabular joint space using the standard AP and Judet views. If there were any doubts, such as detail obscured by overlying implants, then the radiographs would be categorized as “inconclusive”. In the “inconclusive” group, comprising 17 patients, CT scan did identify 4 cases with metalwork malposition, 2 of which were significant and required revision. Thus, the postoperative CT scan findings resulted in a change of management with surgical intervention in 12% of patients in the “inconclusive” radiographic group, suggesting CT scan is indicated in this group.

There were no risk factors associated with malposition except for the use of spring plates for posterior wall reconstruction. The main problem was positioning the spring plate too close to or overlapping the acetabular wall rim so that the tines on the end of the plate penetrated into the labrum or capsule and potentially impinged on the femoral head. Additional perioperative measures to ensure correct positioning of the spring plate, such as use of a syringe needle to mark the osseous-labral junction during plate application and fluoroscopic screening, are recommended now. It is recognized that visualization of the posterior wall of the acetabulum may be inadequate with plain radiographs, and CT scan is advantageous.10 As a result, we recommend patients treated with spring plate fixation are now selected for postoperative CT scan assessment.

A previous study comparing postoperative radiographs and CT scans reported that CT scan identified 14 patients (2.5%) with malpositioned hardware requiring revision surgery in a series of 563 patients in which fluoroscopy images and postoperative radiographs were deemed satisfactory.2 The authors concluded that postoperative CT scan was only beneficial in a small percentage of patients undergoing acetabular reconstruction. Another study concluded that postoperative CT scans could be reserved for complex cases of acetabular fracture fixation but did not recommend criteria on which CT scans can be targeted.14 A recent study comparing 3-dimensional (3D) CT with conventional CT scan in 20 patients after acetabular fracture fixation identified limitations in 3D imaging due to artifacts caused by implant material that can lead to missed malreduction and impairment of clinical outcome, recommending that postoperative CT should be considered in these cases.15

The findings of this study support the restricted use of postoperative CT to detect implant malposition. In an effort to reduce radiation exposure, the use of CT can be targeting on selected patients whose plain radiographs are inconclusive or show definite implant malposition or in which spring plates are used for posterior wall fixation.

The other major use of postoperative CT scan after acetabular fracture fixation surgery is in the assessment of the quality of fracture reduction, especially in the weight-bearing dome and posterior wall of the acetabulum. This information may be clinically useful in determining the prognosis and predicting the clinical outcome of surgical treatment.1,5,7–10,16–18 Difficulties arise in determining the most reliable method of measurement of residual fracture displacement, the most important site, and type of displacement, especially if involving multiple areas of the acetabulum.19,20 The residual displacement is often rotational, which is difficult to measure on axial cuts and may be better appreciated on 3D CT scan with femoral head subtraction, though still difficult to quantify.20 Furthermore, the quality of reduction of the acetabular fracture is only one factor in determining the outcome. Other factors include the fracture type, age of the patient (>50 years), posterior wall involvement, marginal impaction, dome impaction, and femoral head damage.8,10,11,18,20–22

In this study, there were significant differences in the grading of the quality of reduction of the acetabular fracture comparing postoperative plain radiographs with CT. CT scans detected greater displacement in more patients than radiographs, resulting in downgrading of reduction from perfect in 88% to 51% of patients and an increase of imperfect from 8% to 37% of patients. Similar findings have been reported in previous studies of postoperative CT scan.2–4,7,9,10,12 The value of using a standardized method of CT assessment, documenting any fracture step or gap displacement in the 3 axial, coronal, and sagittal planes and the site of displacement in the dome or middle third of the posterior wall if involved, has been highlighted in recent studies.7–9 The degree of displacement in the dome region has been shown to correlate with outcome, with critical values of 1 mm of step and 5 mm of gap, increasing the risk of later conversion to total hip replacement.11,22 Other sites of displacement were not taken into consideration and their relevance is uncertain. In acetabular fractures involving the posterior wall, the accuracy of surgical reduction as assessed by postoperative CT assessment has been shown to be highly predictive of clinical outcome.10 In the present study, the findings identified that only 34% of maximum fracture gaps and 43% of maximum step displacements were in the dome region but the importance of displacement in the other areas could not be determined without long-term clinical outcome review. The CT scan findings did not affect patient management but were useful for surgeon education purposes.

Postoperative CT scan may be useful for quality assurance, audit, and research purposes, but routine use remains controversial. If the emphasis is on reducing radiation dosage associated with postoperative imaging, CT scan may be restricted to assessment of (1) quality of reduction of fractures involving the dome region or posterior wall impaction or comminution and (2) implant placement or retained fracture fragments when plain radiographs are inconclusive or show definite malposition and in cases involving the use of spring plates on the posterior wall. However, the authors continue to recommend the continued use of postoperative CT scan in all cases to maximize the information gained on both implant fixation and quality of fracture reduction for the additional reasons discussed earlier, using a restricted field, low-dose CT protocol where possible.

The limitations of the study include the retrospective design and absence of long-term clinical outcome data to correlate with the quality of fracture reduction determined by the CT scan assessment method used.

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CONCLUSIONS

Postoperative CT scan imaging provides more information when compared with plain radiographs in assessing metalwork malposition and quality of reduction after acetabular fracture reconstruction. The accuracy of plain radiographs in detecting metalwork malposition was approximately 94%. Use of CT scans to detect malpositioned implants can be restricted to those patients with inconclusive or definite malpositioned appearances on plain radiographs and to those treated with spring plate fixation of the posterior wall. CT scans are more accurate in assessing residual fracture displacement, are useful for prognostic and quality assurance purposes, but rarely affect management decisions for reoperation.

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REFERENCES

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Keywords:

acetabular fractures; postoperative CT scan

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