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Evaluation of complex carpal trauma: Thin-section direct longitudinal computed tomography scanning through a plaster cast
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY 1985; 9:107-109
107
EVALUATION OF COMPLEX CARPAL TRAUMA: THIN-SECTION DIRECT LONGITUDINAL COMPUTED TOMOGRAPHY SCANNING THROUGH A PLASTER CAST RAMESH B. PATEL,
MD
Direct longitudinal computed tomography of the wrist, with a plaster cast on the forearm, is described. In a case of complex carpal injuries, the advantages of this method are compared with those of conventional radiographic studies. KEY WORDS:
Computed tomography, skeletal; wrist trauma; Longitudinal computed tomography
In recent years, there has been increasing interest in obtaining direct coronal and sagittal sections of various parts of the body for evaluation of gross morphologic abnormalities by computed tomography (CT). Although most scanner computer systems have software to allow reconstruction of sagittal and coronal scans from data gathered during axial scanning, direct sagittal and coronal scans offer several advantages. Among the advantages is avoidance of degradation of the image caused by slight patient movement in between axial scans. Better reconstructed images, free from partial volume averaging and step margins, require thinner axial cuts initially. Thus, a larger dose of radiation is received by the patient when reconstructed coronal and sagittal images are obtained from initial thin axial cuts. Often a longer examination time is required for the
initial study with thin axial sections as compared with a study for direct sagittal or coronal scans. Direct sagittal and coronal CT scans have been found to be useful in cranial and orbital studies, for evaluation of facial trauma, and, more recently, to study abdominal and pelvic structures (1). The upper extremity has also been studied with direct longitudinal scanning for preoperative evaluation in a case of tumor of the forearm (2). With improved design of scanner gantry, resulting in a wider aperture, larger portions of the upper extremity can be scanned in a longitudinal plane. Newer software programs reduce computer artifacts, allowing the upper extremity to be advantageously studied with increasing frequency, even in compromised situations such as a limb with a plaster cast. Such an application may be found to be particularly useful in cases of trauma to small and multiple bones, such as the wrist joint, where routine radiography may require multiple projections and additional studies, such as tomography with thin sections, to accurately diagnose fractures and dislocations. Described is a case of complex carpal injury. While the patient’s arm was immobilized in an orthopedic plaster cast, the injury was studied by obtaining direct longitudinal scans with subsequent computerreconstructed sagittal and axial scans. CASE REPORT
From the Department of Radiology, University of Mississippi Medical Center, Jackson, Mississippi. Address reprint requests to: Ramesh B. Patel, MD, Radiology Department, University of Mississippi Medical Center, 2500 N. State Street, Jackson, Mississippi 39216. Received June 1984. 0 1985 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., 0149-936X/851$3.30
New York, NY 10017
A young man in his mid-20s sustained injuries to his left forearm and wrist in a motor vehicular accident. Initial radiographs of the forearm and wrist included a posteroanterior, lateral, and oblique view. The study showed fracture of the distal ulna, ventral ulnar subluxation, a cornminuted fracture of scaphoid, and dorsal lunate dislocation. The study
108
PATEL
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 9 NO. 2
FIGURE 1. (A-C) SG = sagittal; AX = axial; LG = longitudinal; R = radius; L = lunate; C = capitate; U = ulna; T = triquetrum; H = hamate; S = scaphoid; M L = lesser multangular; MG = greater multangular; white arrow = fracture fragment from capitate; open black arrow = fracture of ulna; white arrowhead = radioulnar dislocation; black arrowhead = fracture of base of third metacarpal; open white arrowhead = triquetrolunate dislocation.
also indicated a possible fracture of distal, dorsal radius, and the capitate. Following closed reduction of the wrist anteroposterior and lateral views of the wrist were obtained through the plaster cast. The second radiographic study redemonstrated the fracture of the scaphoid and again raised the possibility of a fracture of the capitate. Loss of parallelism between the triquetrum and lunate, and between the lunate and scaphoid, was suggested (3). Slight overlap of the lunate over the capitate was noted. As expected, radiographic details were obscured by the overlying orthopedic plaster cast. Subsequently, a CT scan of the forearm and wrist was obtained through the plaster cast. In order to obtain direct longitudinal scans, the patient was placed prone on the table. The left arm was abducted at the shoulder and flexed at the elbow. The arm was raised above the patient’s head and placed in a pronated position against the table. It was comfortably immobilized by surgical adhesive tape
over the forearm and the fingers. With laser lights in the scanner gantry, the long axis of the forearm and wrist were aligned with the x-ray beam. On the scout view, scan lines were annotated; 130 kV and 125 mA were used. Field size was 29 cm and scan time was 2 seconds for each section. Twomillimeter thick, contiguous sections were obtained. The acquired data was processed through a high-resolution algorithm. Images were reconstructed with a matrix of 256 x 256. Additionally, sagittal and axial reconstructed images were obtained over the wrist. The complete study was examined at appropriate window and level settings to bring out bony details (window level, 575, with a width of 1800; + 2000 to - 1000 Hounsfield units). The CT study was interpreted as showing absence of radial fracture; fracture of the distal ulna with persistent wide radioulnar joint; a comminuted fracture of the scaphoid; fracture of capitate; and scapholunate dislocation, as indicated by loss of parallelism between the scapholunate joint and widening of the joint space proximally. In the reconstructed axial section through the proximal carpal row, widening and asymmetry of the joint space
APRIL 1985
COMPLEX CARPAL TRAUMA, LONGITUDINAL CT
between the triquetrum and lunate were noted, indicating persistent partial dislocation at this joint. A fracture of the dorsal surface of the base of the third metacarpal was also seen. Dorsal angulation of the lunate was noted, with the angulation measuring about 15”. The distal carpal row showed normal intercarpal as well as metacarpo-carpal alignment (Figure lA-C).
without overlap of bones. Hence, the same principles used for interpretation of routine radiographs of a traumatized wrist could be used without hindrance from the overlying plaster cast or from other carpal bones. High-resolution images reconstructed from thin sections allowed a very high spatial resolution. This led to detection of two additional fractures, one of the capitate, that could only be suspected from the results of the two prior radiographic studies. The other newly detected fracture, that of the base of the third metacarpal bone, was seen on the reconstructed axial section. The computerized study was done without any additional discomfort to the patient. A scanning time of 2 seconds allowed completion of the study in a reasonable time, about 20 minutes. In addition to trauma, other possible indications for direct thin-section longitudinal CT of the wrist include cases of osteomyelitis and prosthetic joint replacements.
DISCUSSION Carpal dislocations and fracture-dislocations are considered diagnostic and therapeutic challenges. Traditional radiographic views for evaluation of carpal trauma have been posteroanterior and lateral projections. The lateral view is analyzed for a variety of angles between the radiocarpal, intercarpal, and carpometacarpal articulations (4). The posteroanterior view is mainly used to assess articulations between the two rows of carpal bones and between the radiocarpal and carpometacarpal joints. The most useful parameters of normal radiocarpal and intercarpal alignment in the posteroanterior view are the three parallel arcs (3,s). Parallelism between the articular surfaces of adjacent bones and lack of overlap of the articular surfaces have been described as indications of normal alignment (3). Several advantages were noted when the postreduction radiographic study was compared with direct longitudinal CT. The small bones of the wrist were visualized with much more clarity, as degradation of the image detail in the radiographic study due to the plaster cast was obviated. Alignment of the carpal bones could be studied in three planes
109
REFERENCES 1. van Waes, Paul FGM, Zonneveld FW: Direct coronal body computed tomography. J Comput Assist Tomogr 1982;6:58-66. 2. Nesbit D, Levine E, Neff JR: Direct longitudinal computed tomography of the forearm. J Comput Assist Tomogr 1981; 5:144-6. 3. Gilula LA: Carpal injuries: Analytical approach and case exercises. Am J Roentgen01 1979;133:503-17. 4. Linscheid RL, Dobyns JH, Beabout JW, et al.: Traumatic instability of the wrist: Diagnosis, classification, and pathomechanits. J Bone Joint Surg 1972;54A:1612. 5. Wright RD: A detailed study of movement of the wrist joint, J Anat 1935;70:137-42.
107
EVALUATION OF COMPLEX CARPAL TRAUMA: THIN-SECTION DIRECT LONGITUDINAL COMPUTED TOMOGRAPHY SCANNING THROUGH A PLASTER CAST RAMESH B. PATEL,
MD
Direct longitudinal computed tomography of the wrist, with a plaster cast on the forearm, is described. In a case of complex carpal injuries, the advantages of this method are compared with those of conventional radiographic studies. KEY WORDS:
Computed tomography, skeletal; wrist trauma; Longitudinal computed tomography
In recent years, there has been increasing interest in obtaining direct coronal and sagittal sections of various parts of the body for evaluation of gross morphologic abnormalities by computed tomography (CT). Although most scanner computer systems have software to allow reconstruction of sagittal and coronal scans from data gathered during axial scanning, direct sagittal and coronal scans offer several advantages. Among the advantages is avoidance of degradation of the image caused by slight patient movement in between axial scans. Better reconstructed images, free from partial volume averaging and step margins, require thinner axial cuts initially. Thus, a larger dose of radiation is received by the patient when reconstructed coronal and sagittal images are obtained from initial thin axial cuts. Often a longer examination time is required for the
initial study with thin axial sections as compared with a study for direct sagittal or coronal scans. Direct sagittal and coronal CT scans have been found to be useful in cranial and orbital studies, for evaluation of facial trauma, and, more recently, to study abdominal and pelvic structures (1). The upper extremity has also been studied with direct longitudinal scanning for preoperative evaluation in a case of tumor of the forearm (2). With improved design of scanner gantry, resulting in a wider aperture, larger portions of the upper extremity can be scanned in a longitudinal plane. Newer software programs reduce computer artifacts, allowing the upper extremity to be advantageously studied with increasing frequency, even in compromised situations such as a limb with a plaster cast. Such an application may be found to be particularly useful in cases of trauma to small and multiple bones, such as the wrist joint, where routine radiography may require multiple projections and additional studies, such as tomography with thin sections, to accurately diagnose fractures and dislocations. Described is a case of complex carpal injury. While the patient’s arm was immobilized in an orthopedic plaster cast, the injury was studied by obtaining direct longitudinal scans with subsequent computerreconstructed sagittal and axial scans. CASE REPORT
From the Department of Radiology, University of Mississippi Medical Center, Jackson, Mississippi. Address reprint requests to: Ramesh B. Patel, MD, Radiology Department, University of Mississippi Medical Center, 2500 N. State Street, Jackson, Mississippi 39216. Received June 1984. 0 1985 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., 0149-936X/851$3.30
New York, NY 10017
A young man in his mid-20s sustained injuries to his left forearm and wrist in a motor vehicular accident. Initial radiographs of the forearm and wrist included a posteroanterior, lateral, and oblique view. The study showed fracture of the distal ulna, ventral ulnar subluxation, a cornminuted fracture of scaphoid, and dorsal lunate dislocation. The study
108
PATEL
CT: THE JOURNAL OF COMPUTED TOMOGRAPHY VOL. 9 NO. 2
FIGURE 1. (A-C) SG = sagittal; AX = axial; LG = longitudinal; R = radius; L = lunate; C = capitate; U = ulna; T = triquetrum; H = hamate; S = scaphoid; M L = lesser multangular; MG = greater multangular; white arrow = fracture fragment from capitate; open black arrow = fracture of ulna; white arrowhead = radioulnar dislocation; black arrowhead = fracture of base of third metacarpal; open white arrowhead = triquetrolunate dislocation.
also indicated a possible fracture of distal, dorsal radius, and the capitate. Following closed reduction of the wrist anteroposterior and lateral views of the wrist were obtained through the plaster cast. The second radiographic study redemonstrated the fracture of the scaphoid and again raised the possibility of a fracture of the capitate. Loss of parallelism between the triquetrum and lunate, and between the lunate and scaphoid, was suggested (3). Slight overlap of the lunate over the capitate was noted. As expected, radiographic details were obscured by the overlying orthopedic plaster cast. Subsequently, a CT scan of the forearm and wrist was obtained through the plaster cast. In order to obtain direct longitudinal scans, the patient was placed prone on the table. The left arm was abducted at the shoulder and flexed at the elbow. The arm was raised above the patient’s head and placed in a pronated position against the table. It was comfortably immobilized by surgical adhesive tape
over the forearm and the fingers. With laser lights in the scanner gantry, the long axis of the forearm and wrist were aligned with the x-ray beam. On the scout view, scan lines were annotated; 130 kV and 125 mA were used. Field size was 29 cm and scan time was 2 seconds for each section. Twomillimeter thick, contiguous sections were obtained. The acquired data was processed through a high-resolution algorithm. Images were reconstructed with a matrix of 256 x 256. Additionally, sagittal and axial reconstructed images were obtained over the wrist. The complete study was examined at appropriate window and level settings to bring out bony details (window level, 575, with a width of 1800; + 2000 to - 1000 Hounsfield units). The CT study was interpreted as showing absence of radial fracture; fracture of the distal ulna with persistent wide radioulnar joint; a comminuted fracture of the scaphoid; fracture of capitate; and scapholunate dislocation, as indicated by loss of parallelism between the scapholunate joint and widening of the joint space proximally. In the reconstructed axial section through the proximal carpal row, widening and asymmetry of the joint space
APRIL 1985
COMPLEX CARPAL TRAUMA, LONGITUDINAL CT
between the triquetrum and lunate were noted, indicating persistent partial dislocation at this joint. A fracture of the dorsal surface of the base of the third metacarpal was also seen. Dorsal angulation of the lunate was noted, with the angulation measuring about 15”. The distal carpal row showed normal intercarpal as well as metacarpo-carpal alignment (Figure lA-C).
without overlap of bones. Hence, the same principles used for interpretation of routine radiographs of a traumatized wrist could be used without hindrance from the overlying plaster cast or from other carpal bones. High-resolution images reconstructed from thin sections allowed a very high spatial resolution. This led to detection of two additional fractures, one of the capitate, that could only be suspected from the results of the two prior radiographic studies. The other newly detected fracture, that of the base of the third metacarpal bone, was seen on the reconstructed axial section. The computerized study was done without any additional discomfort to the patient. A scanning time of 2 seconds allowed completion of the study in a reasonable time, about 20 minutes. In addition to trauma, other possible indications for direct thin-section longitudinal CT of the wrist include cases of osteomyelitis and prosthetic joint replacements.
DISCUSSION Carpal dislocations and fracture-dislocations are considered diagnostic and therapeutic challenges. Traditional radiographic views for evaluation of carpal trauma have been posteroanterior and lateral projections. The lateral view is analyzed for a variety of angles between the radiocarpal, intercarpal, and carpometacarpal articulations (4). The posteroanterior view is mainly used to assess articulations between the two rows of carpal bones and between the radiocarpal and carpometacarpal joints. The most useful parameters of normal radiocarpal and intercarpal alignment in the posteroanterior view are the three parallel arcs (3,s). Parallelism between the articular surfaces of adjacent bones and lack of overlap of the articular surfaces have been described as indications of normal alignment (3). Several advantages were noted when the postreduction radiographic study was compared with direct longitudinal CT. The small bones of the wrist were visualized with much more clarity, as degradation of the image detail in the radiographic study due to the plaster cast was obviated. Alignment of the carpal bones could be studied in three planes
109
REFERENCES 1. van Waes, Paul FGM, Zonneveld FW: Direct coronal body computed tomography. J Comput Assist Tomogr 1982;6:58-66. 2. Nesbit D, Levine E, Neff JR: Direct longitudinal computed tomography of the forearm. J Comput Assist Tomogr 1981; 5:144-6. 3. Gilula LA: Carpal injuries: Analytical approach and case exercises. Am J Roentgen01 1979;133:503-17. 4. Linscheid RL, Dobyns JH, Beabout JW, et al.: Traumatic instability of the wrist: Diagnosis, classification, and pathomechanits. J Bone Joint Surg 1972;54A:1612. 5. Wright RD: A detailed study of movement of the wrist joint, J Anat 1935;70:137-42.