Value of 3D CT in Defining Skeletal Complications of Orthopedic Hardware in the Postoperative Patient

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1 Musculoskelet al Imaging Pictorial Essay Musculoskeletal Imaging Pictorial Essay Laura M. Fayad 1 janta Patra Elliot K. Fishman Fayad LM, Patra, Fishman EK Keywords: CT, nonunion, orthopedic hardware, osteolysis, postoperative complications DOI: /JR Received February 19, 2009; accepted after revision March 23, ll authors: The Russell H. Morgan Department of Radiology and Radiological Science, 601 N Caroline St., altimore, MD ddress correspondence to L. M. Fayad (lfayad1@jhmi.edu). CME This article is available for CME credit. See for more information. JR 2009; 193: X/09/ merican Roentgen Ray Society Value of 3D CT in Defining Skeletal Complications of Orthopedic Hardware in the Postoperative Patient OJECTIVE. Conventional CT of the postoperative patient with metal hardware is frequently limited by beam-hardening artifacts. With the evolution of 3D CT, CT is an increasingly effective means of examining the postsurgical patient for the integrity of their hardware and the course of their healing. CONCLUSION. Potential postsurgical complications such as nonunion, osteolysis, infection, and heterotopic ossification are all well assessed by 3D CT. ecause of severe beam-hardening artifacts, evaluating the skeleton of a postsurgical patient with metal hardware is challenging with conventional CT. Metals, which have high Hounsfield unit values (usually 1,000 4,000 HU), result in the attenuation of x-rays, producing gaps in CT projection data and significant starburst artifacts or streaking [1]. The degree of artifact is related to several factors, including the composition of the metal, the orientation and shape of the hardware, the thickness of the metal, and the intrinsic scanning parameters [1 4]. With the optimization of CT parameters and the evolution of 3D CT, metal-related artifacts can be diminished, allowing diagnostic examinations in most clinical scenarios [5 8]. In this article, the technical aspects and benefits of generating 3D CT images in the postoperative setting will be reviewed, highlighting the role of 3D CT in diagnosing post operative complications of the skeleton. Optimal CT Technique and Reconstruction lgorithms The CT technique must be optimized in the setting of metal. Modifications to standard CT protocols include using a lower pitch setting, a higher tube current ( ms), and higher peak kilovoltage (140 kvp) during acquisition. Soft-tissue image reconstruction filters, rather than edge-enhancing algorithms, are used to reduce the appearance of metal artifacts. Finally, at the time of display, the use of wide window settings (width, 3,000 4,000 HU; level, 800 HU) is advocated [1 8]. Many of the modified acquisition parameters will increase radiation dose to the patient. However, as was the case with the introduction of the 16-MDCT, the use of 64- MDCT with volume visualization and postprocessing (3D CT) limits radiation exposure by offering single-plane acquisitions with isotropic data sets. These data sets may be subsequently manipulated to view the imaged body part in any perspective of choice at the same resolution as the initial acquisition. fter the axial acquisition, the data sets are reconstructed at 3-mm thickness for axial viewing and at the thinnest possible thickness (0.75 mm on a 16-MDCT) for reconstruction into multiplanar (MPR) and 3D CT views. In general, 3D CT images provide a comprehensive view of the postoperative site, displaying the relationship of the hardware to the skeleton and soft tissues, while drastically minimizing artifacts associated with the metal hardware observed on traditional axial and MPR views (Figs. 1 4). Using the volume-rendering technique, the data sets can be reconstructed to show the skeleton alone, the soft tissues alone, or their relationship, a decided advantage over MPR views [6, 7] (Figs. 4 and 5). Postoperative Complications of the Skeleton Nonunion Evaluation of fracture healing is generally assessed by evaluating the amount of osseous JR:193, October

2 bridging present [3]. Signs of nonhealing on CT include the lack of bony bridging, persistent cortical defects, and bone sclerosis. Early bridging may be subtle because immature osteoid is not as dense as mature bone, thereby making detection easier on CT than on radiography. Predisposing factors to nonunion include the displacement of fragments, open fractures, and inadequate immobilization. The treatment of nonunion includes open reduction and internal fixation using plates and screws, with the option for bone grafting across the fracture site in some cases [9, 10] (Figs. 6 and 7). Loosening and Particle Disease (Osteolysis) Loosening is a general term that describes aseptic hardware relaxation manifested on CT as greater than 2 mm of radiolucency surrounding the hardware [3]. Such features overlap with those of infection; typically, the entities must be differentiated by clinical means or other tests. In implants, the polyethylene liner can erode, with debris causing a granulomatous reaction in the nearby bone that is termed particle disease, a specific cause of aseptic loosening. Imaging may show lobulated expansile radiolucencies in the bone and a periosteal reaction [2, 11, 12] (Fig. 8). Occasionally, CT may also show associated soft-tissue masses that can mimic malignancy [11]. Treatments for osteolysis include surgical revision with cement, bone graft, or metallic augmentation. Infection When areas of focal erosions or regions of periosteal reaction are identified on CT, infection should be ruled out (Fig. 9). Other signs of infection include joint effusions and fluid collections surrounding the hardware [4]. In later stages, sclerosis of the bone may occur. cute infection is generally managed aggressively with débridement and replacement of the hardware [13]. New Fracture Secondary fracture may occur in postoperative patients from weakened bone or altered weight-bearing. These are easily recognized on postoperative 3D CT that show reduced metal artifact (Fig. 10). Malplacement Malplacement is the postoperative scenario in which the hardware is not positioned in the expected location or when the hardware impinges on an adjacent vital structure such as a nerve or vessel. In these cases, IV contrast material with CT angiography may be useful for the detection of vascular complications (Figs ). Hardware Fracture Hardware fracture occurs when the hardware experiences abnormal stresses because of malpositioning or migration or as a result of nonhealing at the original fracture site. This scenario is well evaluated by 3D CT (Fig. 14) because 3D CT images are superior to axial and MPR views for the detection of hardware fracture [1]. Heterotopic Ossification Heterotopic bone formation may develop around hardware and limits movement around the joint. The presence of heterotopic ossification is easily detected on CT. Heterotopic ossification after joint replacement in the lower limb occurs in 3 90% of cases [2]. Prophylaxis options for patients at high risk for the development of heterotopic ossification include radiotherapy and treatment with indomethacin [14] (Fig. 15). Conclusion For the evaluation of the postoperative skeleton, 3D CT carries an advantage over traditional axial and MPR views by markedly diminishing artifact associated with the presence of hardware. References 1. White LM, uckwalter K. Technical considerations: CT and MR imaging in the postoperative orthopedic patient. Semin Musculoskelet Radiol 2002; 6: Sofka CM, Potter HG, dler RS, Pavlov H. Musculoskeletal imaging update: current applications of advanced imaging techniques to evaluate the early and long-term complications of patients with orthopedic implants. HSS J 2006; 2: uckwalter K, Parr J, Choplin RH, Capello WN. Multichannel CT imaging of orthopedic hardware and implants. Semin Musculoskelet Radiol 2006; 10: erg V, Malghem J, Maldague, Lecouvet F. Multi-detector CT imaging in the postoperative orthopedic patient with metal hardware. Eur J Radiol 2006; 60: Robertson DD, Magid D, Poss R, Fishman EK, rooker F, Sledge C. Enhanced computed tomographic techniques for the evaluation of total hip arthroplasty. J rthroplasty 1989; 4: Neyman EG, Corl FS, Fishman EK. 3D-CT evaluation of metallic implants: principles, techniques, and applications. Crit Rev Computed Tomogr 2002; 43: Pretorius ES, Fishman EK. Volume-rendered three-dimensional spiral CT: musculoskeletal applications. RadioGraphics 1999; 19: Douglas-kinwande C, uckwalter K, Rydberg J, Rankin JL, Choplin RH, Multichannel CT: evaluating the spine in postoperative patients with orthopedic hardware. RadioGraphics 2006[suppl 1]; 26:S97 S Lorenzen M, Wedegärtner U, Weber C, Petersen JP, dam G, Lorenzen J. Clinical relevance of multislice CT of the spine after osteosynthesis [in German]. Rofo 2005; 177: Ebraheim N, Mekhail O, Ortho MS, Darwich M. Open reduction and internal fixation with bone grafting of clavicular nonunion. J Trauma 1997; 42: Park JS, Ryu KN, Hong HP, Park YK, Chun YS, Yoo MC. Focal osteolysis in total hip replacement: CT findings. Skeletal Radiol 2004; 33: Maloney W, Rosenberg. What is the outcome of treatment for osteolysis?; Impant Wear Symposium 2007 Clinical Work Group. J m cad Orthop Surg 2008; 16[suppl 1]:S26 S Haddad FS, ridgens. Infection following hip replacement: solution options. Orthopedics 2008; 31: oard TN, Karva, oard RE, Gambhir K, Porter ML. The prophylaxis and treatment of heterotopic ossification following lower limb arthroplasty. J one Joint Surg r 2007; 89-: JR:193, October 2009

3 Fig year-old woman with transolecranon fracture dislocation of left elbow after motor vehicle collision requiring open reduction and internal fixation., Coronal multiplanar reformatted image provides limited evaluation because of streak artifact., Sagittal 3D CT image shows satisfactory alignment of fracture fragments and hardware. Fig year-old boy with right mid-diaphyseal femur fracture after motor vehicle collision. CT was requested in immediate postoperative period to assess hardware position relative to fracture and its relationship to soft tissues, although detection of complications in immediate perioperative period is often fulfilled with radiography., xial CT image from immediate postoperative examination is limited because of streak artifact. Fracture line is difficult to visualize in axial plane., Coronal 3D CT image shows intramedullary rod and screw fixation with good postoperative alignment. lso note fracture of posterior roof of acetabulum (arrow). JR:193, October

4 Fig year-old woman with right distal clavicle fracture several months previously after open reduction and internal fixation. CT examination was performed to evaluate for nonunion., xial CT image is limited by streak artifact., Coronal 3D CT image shows bony bridging across fracture site with no evidence of nonunion. Fig year-old man with comminuted fracture of distal left tibia after trauma who subsequently underwent placement of external fixation hardware., Full assessment of hardware placement is difficult on axial CT image alone., Coronal 3D CT image comprehensively depicts external fixation hardware alignment and its relationship to skeleton JR:193, October 2009

5 Fig year-old man with history of bladder cancer and right hip pain. C, Coronal volume-rendered 3D CT images: rendered to show right hip prosthesis (), rendered to show relationship of prosthesis screws to skeleton and adjacent iliac arteries (), and rendered to show relationship of prosthesis screws to skeleton and right ureter (C). Note bladder mass, patient s known bladder cancer (arrow). lthough surgical screws traversed cortex and extended into adjacent pelvic soft tissues, no symptoms were directly attributable to this abnormality. Fig year-old man who sustained traumatic tibial fracture. Coronal 3D CT image taken 8 months after fracture shows fracture in middistal tibia with intramedullary rod in place. Note evidence of nonunion with no evidence of bony bridging across fracture line and sclerotic fracture margins. C JR:193, October

6 Fig year-old man with history of osteosarcoma of mid left tibia after resection and allograft placement. Plate and screw fixation was performed to augment healing. Three-dimensional CT was performed 6 months later to assess healing. and, Coronal 3D CT images show no evidence of bony bridging at allograft host junction. Fig. 8 Two patients with osteolysis demonstrated by 3D CT imaging.,43-year-old woman with history of bilateral hip replacement and increasing right hip pain. nteroposterior radiograph of pelvis shows hip prostheses bilaterally. Note radiolucency about right hip prosthesis., However, degree of osteolysis in patient shown in is better appreciated on CT. Coronal multiplanar reformatted CT image shows large lytic component (arrow) in inferior right acetabulum representing osteolysis or particle disease. Note asymmetry of right femoral head component in acetabular component, consistent with polyethylene wear. Note also that acetabular component is rotated clockwise from its expected position. C, 62-year-old man with volume-rendered 3D depiction of osteolysis in left hip (arrow). C 1160 JR:193, October 2009

7 Fig year-old man after hip replacement who has history of right femur fracture after motor vehicle collision 20 years earlier. Patient presented with draining ulcer near right hip (arrow). Coronal 3D CT image shows cortical irregularity and lytic area in right ischium adjacent to ulceration, suggestive of osteomyelitis, which was subsequently proven at biopsy. Fig year-old boy with history of bilateral hip resurfacing for avascular necrosis who presented with right hip pain after motor vehicle collision. and, Coronal 3D CT images show fracture of right ischium () and acetabulum () with displacement (arrow, ). JR:193, October

8 Fig year-old woman with history of spinal fusion with increasing back pain. C, Sagittal (), axial (), and coronal (C) 3D CT images show that one screw at S1 level on right extends through foramen into pelvic soft tissues. C Fig year-old woman who underwent posterior fusion of L5 S1 vertebrae with laminectomy at L5., Sagittal 3D CT image provides comprehensive view of hardware in spine. and C, Sagittal oblique () and coronal (C) 3D CT images show that L5 pedicle screw tip protrudes anterior to L5 vertebral body, with tip contacting left common iliac artery (arrows, and C). C 1162 JR:193, October 2009

9 Fig year-old woman after left hip hemiarthroplasty performed for fracture, who presented with left hip pain., Coronal 3D CT image shows superior dislocation of left hip prosthesis., xial multiplanar reformatted CT image, shown for comparison, does not provide comprehensive view of regional anatomy and is limited by streak artifact. Fig year-old girl with Marfan syndrome who underwent surgical treatment of scoliosis. Coronal 3D CT image shows disconnection of horizontal bar and surgical screw (arrow). Note that for detection of hardware fracture, 3D CT retains particular advantage over axial and multiplanar reformatted CT. Fig year-old woman with left intertrochanteric femur fracture who underwent open reduction and internal fixation. Coronal 3D CT image shows dynamic hip screw traversing femoral neck. t medial aspect of femoral diaphysis, note development of heterotopic ossification (arrow). s ossification increases, range of motion of hip may become compromised. FOR YOUR INFORMTION This article is available for CME credit. See for more information. JR:193, October