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Fracture

Axial Computed Tomography of Pilon Fractures

Tornetta, Paul; Gorup, John

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Clinical Orthopaedics and Related Research: February 1996 - Volume 323 - Issue - p 273-276
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Abstract

Computed tomography (CT) scans are useful in the evaluation of complex intraarticular fractures.2,7 They are particularly helpful in identifying fractures in the sagittal and coronal planes, which are difficult to see on standard anteroposterior (AP) and lateral radiographs.5

The value of any test that is done is its ability to affect treatment. This study examined the use of axial CT scans for pilon fractures. The authors were interested in what information is gained from the scan, rather than from the plain films alone, and in the subsequent changes in the operative plan based on this additional information.

MATERIALS AND METHODS

The senior author (PT) has used CT scans for the preoperative planning of selected pilon fractures for 4 years.8 For a prospective period of 2 years, all closed Ruedi types 2 and 3 pilon fractures were evaluated with AP, lateral, oblique, and traction AP radiographs, and with axial CT scans. Twenty-two patients were studied.

In each patient, the plain films were reviewed first, then the CT scans. The fracture pattern, number of fragments, presence of comminution, impaction, and Ruedi classification were documented based on only the plain films and then based on the plain films in conjunction with the CT scans. Changes based on the information from the CT scans were documented. An increased number of fragments was documented if additional fracture lines were seen on the CT scans, even if they were not displaced. Additional comminution was defined as small fragments at the edge of major fractures or additional displaced fragments not visible on the plain films. Impaction on the CT was considered present if a portion of the articular surface was displaced superiorly and not attached to the peripheral cortex. The fracture angle was measured on the CT scans as the angle from the tibiofibular axis to the major fracture line (Fig 1). By definition, the angles could range from 0 ° to 179 °, with higher angles indicating a more medial fracture. The location of the major fracture line was measured at 3 positions: the level of the joint, 1 cm above the joint, and 2 cm above the joint.

Changes in the operative plan based on the information from the CT scan were recorded in a prospective manner. These included the placement of percutaneous screws before the incision, the location of the operative incision, and the planned location of lag screws. The surgeon's subjective opinion of whether or not the scan saved operative time also was documented prospectively.

RESULTS

Based on the plain films alone, there were 15 Ruedi type 2 and 7 type 3 injuries. With the addition of the CT scan, 4 fractures were upgraded from a type 2 to a type 3 (Fig 2). Additional information gained from the scans included increased number of fragments (12 patients), impaction (6 patients), and increased comminution (11 patients).

The angle of the major fracture line from the tibiofibular axis (fracture angle) averaged 90 °. However, there were clearly 2 distinct groups of patients. In 12 patients, the fracture angle was <90 °, indicating a lateral position (Fig 2). In the other 10 patients, the fracture was directed medially, and the angle was >90 ° (Fig 3). The fracture angle was not different when measured at the level of the joint compared with measurements taken 1 cm or 2 cm above the joint.

The location of the major fracture line dictated the operative approach in all patients.8 Ten patients were operated on through a standard anteromedial incision based over the tibialis anterior. In the other 12 patients, the location of the major fracture line was more lateral (angle <90 °), and a more lateral incision was used. This incision was made between the extensor digitorum communis and peroneus tertius. In 5 patients, nondisplaced fracture lines visible only on the CT scan were fixed percutaneously before the operative incision was made.

Thus, the operative plan was influenced by information obtained from the CT scan in 14 (64%) patients. In addition, the operative surgeons thought that the CT scan added to their understanding of the fracture pattern in 18 (82%) patients. Subjectively, it was thought that the information obtained from the CT scans shortened operative time for 17 (77%) patients.

DISCUSSION

Careful preoperative planning of intraarticular distal tibia fractures is a prerequisite to successful operative treatment.1,3,4,6,8 Plain radiographs are helpful in identifying fracture fragments, impaction, and associated injuries. In particular, translations and rotational displacements in the sagittal and coronal plane are clearly visualized. However, fracture lines may be missed if they are not in the plane of the x-ray beam. Computed tomography scanning has been shown to visualize vertical fractures off the sagittal and coronal planes better than do plain films.4 Nondisplaced fractures also are seen more clearly on CT scans.

This study evaluated the routine use of CT scans for the preoperative assessment of pilon fractures. In a series of 22 consecutive patients, it was found that the CT scan added information regarding the number of fragments, the degree of comminution, and the presence of impaction in 18 of the patients.

The precise direction of the major fracture line was easily measured on the CT scans. The fracture angle was the same when measured at or 2 cm above the joint, indicating its vertical nature distally. The location of this fracture determined the site of the incision in all patients. If the fracture angle was <90 °, a lateral incision was chosen. If the fracture angle was >90 °, a standard anteromedial incision was used. As described previously, placement of the incision directly over the major fracture line aids in reducing the joint with minimal periosteal stripping.8 The fracture angle was the most important factor affecting the operative plan. A lateral, rather than a standard, anteromedial incision was used in 12 of the 22 patients. It should be noted that the authors use an external fixator to stabilize the metaphyseal disruption in these injuries. This enables fixation of the distal tibia through the more lateral incision described because the fibula is not internally fixed, so only 1 incision is used.8 If fibular fixation is done, the described lateral incision cannot be used because of the risk of skin slough. In this case, a 7 cm skin bridge between the incisions for fibular fixation and tibial fixation should be maintained.

Changes in the operative plan also were made based on nondisplaced fractures, which were fixed before the incision was made in 5 patients. The precise location of impacted segments was more clearly shown on the CT scans than on the plain radiographs. This made locating and reducing impacted segments easier. Finally, the exact plane of screw placement was much easier to plan using the CT scans because of the exact definition of the direction of the fracture lines.

Overall, the operative plan was changed on the basis of the CT scan in 14 (64%) of the patients. The surgeons subjectively thought that the surgical time was decreased and that a better understanding of the fracture pattern was obtained based on the CT scan in most patients.

Many surgeons now use intraoperative fluoroscopy during the fixation of complex intraarticular fractures. In this series, all operations were done with the use of fluoroscopy. However, although intraoperative images were helpful in lag screw placement, intraoperative information cannot substitute for a careful and complete preoperative plan. Multiple authors have stressed the importance of a preoperative plan, including the location of lag screws and implants.4,8 This is especially true for surgeons who have less experience in treating these complicated injuries.

Although simple fractures with minimal displacement can be handled using standard radiographs, this study supports the use of CT scans for the preoperative assessment of displaced, intraarticular pilon fractures. Additional information was gained or a change in the operative plan was made in 18 of 22 consecutive patients. In addition, CT scans allowed for a more precise preoperative plan.

Fig 1
Fig 1:
. The fracture angle is defined as the angle between the tibiofibular axis and the direction of the major fracture line from the center of the joint. The angle in this patient is <90 °.
Fig 2A-C
Fig 2A-C:
. (A) Anteroposterior and (B) lateral radiographs of a pilon fracture. Based on the plain films, this was classified as a Ruedi 2. (C) The CT scans above the joint reveal increased comminution and impaction within the anterolateral fragment not seen on the plain radiographs. Based on this, the fracture was reclassified as a Ruedi 3. The major fracture line in this patient is <90 °. A lateral incision was chosen.
Fig 3
Fig 3:
. The major fracture line in this patient is >90 °, and an anteromedial incision was chosen.

References

1. Bourne RB: Pilon fractures of the distal tibia. Clin Orthop 240:42-46, 1989.
2. Harley JC, Mack LA, Winquist RA: CT of acetabular fractures: Comparison with conventional radiography. AJR 138:413-417, 1982.
3. Kellam JF, Waddell JP: Fractures of the distal tibial metaphysis with intraarticular extension. The distal tibial explosion fracture. J Trauma 19:593-601, 1979.
4. Mast JW, Speigel PG, Pappas JN: Fracture of the tibial pilon. Clin Orthop 230:68-82, 1988.
5. Olson SA, Matta JM: The computerized tomography subchondral arc: A new method of assessing acetabular articular continuity after fracture (a preliminary report). J Orthop Trauma 7:402-413, 1993.
6. Ruedi T, Allgower M: The operative treatment of intraarticular fractures of the lower end of the tibia. Clin Orthop 138:105-119, 1979.
7. Segal D, Marsh J, Leiter B: Clinical application of computerized axial tomography (CAT) scanning of calcaneus fractures. Clin Orthop 199:114-123, 1985.
8. Tornetta III P, Weiner L, Bergman M, et al: Pilon fractures: Treatment with combined internal and external fixation. J Orthop Trauma 7:489-496, 1993.

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SECTION II

ORIGINAL ARTICLES

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