Shell osteochondral allografts of the knee: comparison of mr imaging findings and immunologic responses.

PURPOSE: To define the magnetic resonance (MR) imaging appearance of shell osteochondral allografts of the knee and compare the MR findings with antibody responses. MATERIALS AND METHODS: Thirty-six grafts were evaluated with a 1.5-T unit with T1-, intermediate-, and T2-weighted, and three-dimensional spoiled gradient-recalled MR imaging at 3, 6, 12, 24, and/or 36 months after surgery. Nineteen patients underwent imaging serially. Two osteoradiologists scored by consensus host marrow edema, thickness of graft-host interface, signal intensity of graft marrow, cyst formation, joint effusion, articular cartilage defects, and surface collapse. Patients were divided into antibody-positive (AP) (n = 11) and antibody-negative (AN) (n = 25) groups evenly distributed across the different time points on the basis of results of anti-human leukocyte antigen antibody screening. MR findings for the two groups were compared. RESULTS: AP patients demonstrated greater mean edema (P<.002), thicker interface (P<.03), and more abnormal graft marrow (P<.04) than AN patients, and they had a higher proportion of surface collapse (P<.03). CONCLUSION: Humoral immune responses were associated with more inflammation and less complete incorporation after allograft placement. MR imaging shows promise as a surrogate biomarker for success of shell osteochondral allograft implantation.

Polydioxanone biodegradable pins in the knee: MR imaging.

OBJECTIVE: Biodegradable solid implants have been developed as an alternative to metallic orthopedic fixation. In animal models, implants degrade within and are replaced by bone. This study documents the resorption of these devices in human patients with MR imaging. SUBJECTS AND METHODS: One hundred seventy-five 1.3-mm biodegradable pins made of polydioxanone were used to secure a total of 59 osteochondral allografts of the knee. Patients with the pins underwent scanning on a 1.5-T unit with 3.3- to 4-mm contiguous T1-weighted spin-echo (TR/TE, 600/15), fat-saturated proton density-weighted (3000/40), T2-weighted fast spin-echo (3000/63), and three-dimensional spoiled gradient-recalled (47/7; flip angle, 60 degrees ) sequences at 3, 6, 12, 24, or 36 months after surgery. Eighty-nine pins were imaged on multiple occasions. Two osteoradiologists interpreted the MR examinations. RESULTS: More than 80% of the pin channels were visible at 3 and at 6 months after surgery. By 24 months, only 20% of the pin channels were visible, with the remainder having been replaced by bone. At 3 months, nearly 40% of the pins were associated with adjacent marrow edema. Edema generally diminished, involving less than 20% of pins at later time points. Focal cartilage defects were evident at 32% of the pin insertion sites during the first 6 months, but these defects were present in only 4% of the insertion sites thereafter. CONCLUSION: Biodegradable polydioxanone pins usually resorb completely by 24 months. Marrow edema, presumably representing inflammation related to pin resorption, is infrequent and tends to resolve. Cartilage defects related to pin placement heal spontaneously.

Calcium pyrophosphate dihydrate crystal deposition in and around the atlantoaxial joint: association with type 2 odontoid fractures in nine patients.

PURPOSE: To investigate the histopathologic anatomy of calcium pyrophosphate dihydrate (CPPD) crystal deposition in and around the atlantoaxial joint and the association between CPPD crystal deposition and subchondral cysts, erosions, and fracture involving the odontoid process of the axis. MATERIALS AND METHODS: One adult cadaver demonstrating calcification in the retro-odontoid area at computed tomography (CT) was selected for further radiography, CT, and magnetic resonance (MR) imaging at the C1-2 level. Anatomic sectioning and histologic evaluations were performed in the specimen. For clinical study, radiographs (n = 5), CT scans (n = 8), and MR images (n = 6) in nine patients (mean age, 74.4 years) with odontoid process fractures and CPPD crystal deposits in and around the atlantoaxial joint were reviewed. RESULTS: In the cadaveric specimen, radiography and CT demonstrated calcifications in the transverse ligament; histologic evaluation confirmed that these calcifications were CPPD crystal deposits. In all nine patients, radiography (n = 5) and CT (n = 8) also showed calcification in areas adjacent to the odontoid process, which included the transverse ligament. T1- and T2-weighted MR imaging showed a retro-odontoid mass of low signal intensity that compressed the cervical cord in six patients. CT, MR imaging, or both demonstrated subchondral cysts, osseous erosions, or a type 2 odontoid fracture in all patients. CONCLUSION: CPPD crystal deposition disease involving the C1-C2 articulation can be a clinically important entity that may place affected patients at increased risk of pathologic fracture of the odontoid process.

Evaluation of the postoperative meniscus of the knee: a study comparing conventional arthrography, conventional MR imaging, MR arthrography with iodinated contrast material, and MR arthrography with gadolinium-based contrast material.

OBJECTIVE: To compare four imaging methods in the evaluation of the postoperative meniscus: conventional arthrography, conventional MR imaging, MR arthrography with iodinated contrast material, and MR arthrography with gadolinium-based contrast material. DESIGN AND PATIENTS: Thirty-three patients referred for knee MR examinations with a history of meniscal surgery were studied prospectively. At the first patient visit, conventional MR examination was followed by an MR arthrogram with gadolinium-based contrast material. At the second visit, a conventional arthrogram with iodinated contrast material was followed immediately by an MR examination. Imaging examinations were interpreted by a masked reader, and then compared with the results of repeat arthroscopic surgery in 12 patients. RESULTS: The correct evaluation of the status of postoperative menisci was allowed in 12 of 13 patients (92%) by MR arthrography using gadolinium-based contrast agent, 10 of 13 patients (77%) by conventional MR examination, 9 of 12 patients (75%) by MR arthrography, and 7 of 12 patients (58%) by conventional arthrography. CONCLUSION: Intra-articular fluid is advantageous in the evaluation of patients with a suspected meniscal retear. MR arthrography with gadolinium-based contrast material is the most accurate imaging method for the diagnosis of meniscal retears.

Extensive intraosseous gas associated with lymphangiomatosis of bone: report of three cases.

Asymptomatic pneumatosis may be found in patients with lymphangiomatosis of bone. The authors report three cases from three institutions in which development of intraosseous gas in association with lymphangiomatosis of bone was found incidentally at imaging. Soft-tissue emphysema also developed in two cases. In all three cases, intraosseous gas developed after biopsy or surgery in the areas involved with lymphangiomatosis.

Pseudarthrosis: US evaluation after posterolateral spinal fusion: work in progress.

PURPOSE: To determine the value of ultrasound (US) in evaluation of pseudarthrosis after posterolateral spinal fusion. MATERIALS AND METHODS: In 10 patients who had undergone bilateral posterolateral thoracic or lumbar fusion with autologous bone graft and instrumentation more than 9 months previously, US was performed within 1 week before second-look surgery. A total of 20 sites each side of midline were evaluated for the presence of bone graft, solid fusion, clefts, fluid collections, and hardware visibility. US findings were compared with those at surgery. In three patients, standard radiographs were reviewed before US; blinded US evaluation was performed in the remaining seven patients. RESULTS: At US, all 10 sites of pseudarthrosis seen at surgery were identified correctly. Of 10 sites with solid fusion at surgery, US depicted six. At four sites (two patients), fusion was mistaken for or obscured by hardware. Overall, sensitivity was 100%, specificity was 60%, and accuracy was 80%. CONCLUSION: US can play a valuable role in the detection of posterolateral bone graft pseudarthrosis, especially when hardware is present.

Magnetic resonance imaging in pachydermoperiostosis.

Pachydermoperiostosis is a rare inherited disorder that is manifest clinically by digital clubbing, extremity enlargement, painful and swollen joints, hypertrophic skin changes, and periosteal bone formation. This report illustrates the skeletal findings that may be seen with long-standing disease as evaluated with conventional radiography and with magnetic resonance (MR) imaging, with emphasis on the MR appearance of periosteal reaction in this disorder. There are features that suggest pachydermoperiostosis may represent a generalized enthesopathy.

Denervation hypertrophy of muscle: MR features.

OBJECTIVE: Denervation hypertrophy is an entity well recognized in the neurology literature, but with little mention in the radiology literature. Denervation hypertrophy occurs when a muscle paradoxically enlarges rather than atrophies in response to loss of innervation. The purpose of this report is to describe the MR appearance of true hypertrophy and pseudohypertrophy of muscle following denervation. MATERIALS AND METHODS: The clinical data and MRI findings in three patients with muscle enlargement due to denervation hypertrophy are reviewed retrospectively. Two women and one man aged 19-80 years were included. Denervation resulted from spinal stenosis in one patient, a herniated thoracic disc in another, and spina bifida with a tethered cord in the third. RESULTS: True hypertrophy of a single muscle was seen in one patient and pseudohypertrophy of two muscles was present in one patient. One patient had one muscle with true hypertrophy and one muscle with pseudohypertrophy. Electromyographic examination was performed and was consistent with denervation in two patients. Biopsy confirmation of denervation was obtained in two patients. All five abnormal muscles exhibited increased volume, well defined margins, and normal contour. In true hypertrophy the enlarged muscle was isointense with normal muscle on all MRI sequences. In pseudohypertrophy the MRI appearance was consistent with an excessive amount of fat interspersed throughout normal muscle. CONCLUSION: Magnetic resonance in these cases established muscle hypertrophy rather than neoplasm as the cause of a palpable mass. If muscle hypertrophy or pseudohypertrophy is seen on an MR examination of an enlarged extremity, the possibility of an underlying neurologic process should be considered.

Thoracolumbar burst fractures: evaluation with MR imaging.

PURPOSE: To determine the frequency of posterior ligamentous injury that occurs in patients with thoracolumbar burst fractures and to correlate ligamentous disruption with radiographic appearance. MATERIALS AND METHODS: Magnetic resonance (MR) imaging examinations of 21 patients with 25 thoracolumbar burst fractures were retrospectively evaluated to determine spinal ligament integrity. Radiographic and computed tomographic (CT) examinations were evaluated for interpediculate widening, midsagittal canal narrowing, posterior element fractures, and kyphosis; a radiographic assessment of posterior ligamentous integrity was made. These findings were then correlated with the status of the spinal ligaments. RESULTS: The patients were divided into two groups on the basis of the status of their supraspinous ligament (SSL). Six patients had disrupted SSLs, and 15 had intact SSLs. Radiographic and CT findings did not correlate with supraspinous ligament disruption. Radiographic indicators of posterior ligamentous disruption were present in only 33% of patients with SSL disruption. CONCLUSION: SSL disruption is a frequent occurrence in patients with burst fractures. No radiographic features of burst fractures correlate with SSL disruption, and radiographic signs of posterior ligamentous disruption are insensitive.

Complete dislocation of the knee: spectrum of associated soft-tissue injuries depicted by MR imaging.

OBJECTIVE: Complete knee dislocation is a rare injury. The purpose of this study was to evaluate the spectrum of injuries that are depicted by MR imaging in patients with a dislocation of the knee and to determine if there is any predictive factor that might indicate those patients who may be at risk for popliteal nerve injury. MATERIALS AND METHODS: A retrospective search for patients sustaining traumatic knee dislocations who had radiographs and an MR imaging examination of the knee as part of their initial evaluation was done at three level I trauma centers for the period between 1989 and 1993. Each MR examination was independently reviewed by three osteoradiologists for ligamentous, tendinous, meniscal, and osseous injuries. Equivocal diagnoses were decided by consensus. Only patients who underwent surgery were selected. MR imaging findings were confirmed at the time of surgery. Seventeen patients (15 men, two women; age range, 14-62 years; mean age, 29 years) were studied. Motor vehicle accident, fall from a height, a vehicle striking a pedestrian, and football injury were common mechanisms of injury. Posterior dislocation (seven patients) and anterior dislocation (five patients) were the most common injuries. RESULTS: At the time of surgery, all patients had complete tears of the anterior cruciate ligament, 15 had complete tears of the posterior cruciate ligament, nine had complete tears of the medial collateral ligament, and 12 had tears of the fibular collateral ligament (nine tore both the fibular collateral ligament and the biceps femoris tendon). Popliteal tendon tears occurred in eight patients (six complete, two partial). Of the six patients with complete tears of the popliteal tendon, five occurred at the musculotendinous junction; all were the result of either posterior or posterolateral dislocations. Four patients had injuries to the peroneal nerve; three of the four also had tears of the popliteal tendon. On MR imaging, the integrity of the anterior cruciate and lateral collateral ligaments was correctly depicted in all 17 patients; evaluation of the posterior cruciate ligament resulted in one false-positive and one false-negative diagnosis of a tear; evaluation of the medial collateral ligament resulted in one false-positive diagnosis of a tear; and one false-positive diagnosis of a tear occurred with evaluation of the popliteal tendon. CONCLUSION: Knee dislocations cause extensive disruption of the ligaments that stabilize the knee and the surrounding soft-tissue structures, including the popliteal artery. Nearly all will result in disruption of the cruciate ligments and, often, injury of the collateral ligaments. An injury to the popliteal tendon denotes a more severe injury. The mechanism of injury that results in a popliteal tendon tear may also increase the possibility of a peroneal nerve injury. Recognition of this pattern of injuries on MR imaging enables precautionary observation for ischemic changes of the foot to be instituted in patients that otherwise may not be considered at risk for acute vascular compromise.

Magnetic resonance imaging of the shoulder.

MRI has rapidly become a commonly used technique for evaluation of the shoulder. It provides a wealth of information regarding the entire shoulder girdle, and it is the most accurate noninvasive method available for imaging the rotator cuff. There have been numerous technical improvements in MRI in the relatively short time that clinical MRI has been in existence. Further refinements in design, new imaging sequences, and additional clinical experience should help to increase the accuracy and flexibility of this imaging modality.

Acute calcific retropharyngeal tendinitis. Clinical presentation and pathological characterization.

Acute calcific retropharyngeal tendinitis is an underrecognized cause of pain and stiffness in the neck associated with odynophagia and retropharyngeal soft-tissue swelling. We report on five patients in whom an initial misdiagnosis of this entity as a retropharyngeal or nasopharyngeal abscess, a neoplasm, or a fracture-dislocation of the cervical spine led to interventions such as admission to the hospital and parenteral administration of antibiotics. An open biopsy was performed in one patient because of a suspected neoplasm. Evaluation of the tissue specimen with routine and polarized light microscopy, scanning electron microscopy, and energy-dispersive spectrometry demonstrated a foreign-body inflammatory response to deposited crystals of hydroxyapatite. In all five patients, the correct diagnosis was established only after retrospective review of the radiographic studies by a physician who was familiar with acute calcific retropharyngeal tendinitis. The computed tomographic findings of acute calcific retropharyngeal tendinitis are distinctive and consist of prevertebral calcification localized to the insertion of an edematous tendon of the longus colli muscle. Symptomatic relief was provided with anti-inflammatory and analgesic medications. The symptoms resolved, without sequelae, within one to two weeks for all of the patients. We hope that an increased awareness of hydroxyapatite deposition in the tendon of the longus colli muscle will result in improved early diagnosis of acute calcific retropharyngeal tendinitis.

MR imaging of injuries of the extensor mechanism of the knee.

Rupture of the extensor mechanism of the knee must be diagnosed early in order to be successfully treated. However, the clinical signs of this condition may be concealed by hematoma or hemarthrosis. The noninvasiveness and accuracy of magnetic resonance (MR) imaging make it useful in detection of such ruptures. Normal quadriceps tendons have a laminated appearance on MR images. The normal patella has signal intensity similar to that of bone marrow and cortex, while normal patellar tendons have homogeneous low signal intensity with all sequences. Patellar fractures, bone bruises, and avulsion of the tibial tubercle manifest as changes in marrow signal intensity. The laminated configuration of the quadriceps tendon allows distinction between partial and complete tears; both may be accompanied by edema and hemorrhage, which manifest as increased signal intensity on T2-weighted images. Ruptures of the patellar tendon also manifest as increased signal intensity on T2-weighted images.

Hill-Sachs lesion and normal humeral groove: MR imaging features allowing their differentiation.

PURPOSE: To present a method of differentiating Hill-Sachs lesions from the anatomic groove in the posterolateral humeral head with use of magnetic resonance imaging. MATERIALS AND METHODS: A 360 degrees reference about the humeral head was established to define the locations of Hill-Sachs lesions and the anatomic groove on transaxial images. The extension of each finding along the longitudinal humeral axis was noted. Eight cadaveric specimens were sectioned and similarly analyzed. RESULTS: The locations of Hill-Sachs lesions and the anatomic groove in the circular reference frame were statistically significantly different (P < .001), yet their respective ranges overlapped. Along the longitudinal humeral axis, there was no overlap between the respective ranges of location (P < .001). CONCLUSION: A Hill-Sachs lesion is best differentiated from the anatomic groove by means of its more cephalic position along the longitudinal humeral axis.

The fate of anterior vertebral bone grafts in patients irradiated for neoplasm.

Perioperative irradiation is often used with anterior decompression and vertebral interbody fusion for the treatment of spinal neoplasms, yet little is known regarding the healing potential of these grafts. This review of 25 patients with neoplasm who had anterior vertebrectomy, bone strut insertion, and perioperative irradiation was performed to look specifically for evidence of radiographic fusion as determined by plain radiographs, tomograms, or computed tomography reconstruction. Four of 25 patients (16%) were judged to have a pseudarthrosis. All four pseudarthrosis patients but only four of 21 fusion patients had 4000 cg or more of irradiation, a statistically significant difference. There was a trend for lumbar lesions to have a higher risk for nonunion. Concomitant posterior stabilization did not necessarily prevent pseudarthrosis. Two iliac strut grafts with a pseudoarthrosis developed late fracture and one went on to collapse into kyphosis. The pseudarthrosis rate of anterior vertebral strut grafts in the face of irradiation for tumor is relatively high, and late graft fracture can occur if pseudarthrosis develops. Probable risk factors include irradiation greater than 4000 cg and lumbar lesions. Posterior stabilization to protect the graft may be warranted in the highest-risk patients.

Hyperostosis of ribs: association with vertebral ossification.

OBJECTIVE: Costal hyperostosis occurring with vertebral disorders, although not well known, has been described in patients with diffuse idiopathic skeletal hyperostosis (DISH). Our purpose was to examine the possible association of similar hyperostosis in other spinal conditions. METHODS: We investigated the frequency of hyperostotic rib changes on routine radiographs in 191 patients with various spinal disorders, including DISH (51 cases), ankylosing spondylitis (AS) (58 cases), psoriasis (21 cases) and quadriplegia (61 cases), and in a healthy control group (191 cases). RESULTS: Results showed that the frequency of rib hyperostosis was significantly higher in DISH (21.6%), AS (10.3%) and quadriplegia (6.6%) than in the healthy control group (0.5%). There was no significant difference in the frequency of right and left-sided involvement. The main radiographic features were a short segment of cortical thickening and sclerosis, which predominated in the medial aspect of the posterior portion of the rib. Some patients had a long segment of bone enlargement and extensive sclerosis. The resulting radiographic features simulated the appearance of Paget's disease. Osseous excrescences of adjacent costovertebral articulations were significantly related to the rib hyperostosis, seen in 73% of instances of rib involvement. CONCLUSION: Our observations suggest that diseases that lead to bone formation and resultant hypomobility of costovertebral articulations are associated with rib hyperostosis.

Diagnosis of osteomyelitis: utility of fat-suppressed contrast-enhanced MR imaging.

PURPOSE: To assess the value of fat-suppressed contrast material-enhanced magnetic resonance (MR) imaging in the diagnosis of osteomyelitis. MATERIALS AND METHODS: T1- and T2-weighted MR imaging was performed in 51 cases of suspected osteomyelitis. Nonenhanced and contrast-enhanced T1-weighted fat-suppressed MR images were also obtained. Three-phase bone scan results were available for 30 cases. Complicating clinical factors, including chronic osteomyelitis (n = 26), postoperative state (n = 17), and neuropathic disease of the foot (n = 5), were identified in 73% of cases. RESULTS: In the diagnosis of osteomyelitis, scintigraphy demonstrated a sensitivity of 61% and specificity of 33%. For nonenhanced MR imaging, sensitivity was 79% and specificity was 53%. For fat-suppressed contrast-enhanced imaging, sensitivity was 88% and specificity was 93%. CONCLUSION: In diagnosing osteomyelitis in patients with complicating clinical factors, fat-suppressed contrast-enhanced MR imaging was significantly more sensitive than scintigraphy (P = .04) and significantly more specific than nonenhanced MR imaging (P = .02) or scintigraphy (P = .008).

MR appearance of idiopathic synovial osteochondromatosis.

OBJECTIVE: A retrospective review of the MR examinations in 21 patients with idiopathic synovial osteochondromatosis (ISO) was performed to determine its MRI characteristics. MATERIALS AND METHODS: Twenty-one patients diagnosed with ISO had undergone MRI prior to surgery. The MR images were retrospectively evaluated for configuration and extent of lesion as well as for signal characteristics. RESULTS: Three distinct MR patterns were seen in ISO: A--lobulated homogeneous intraarticular signal isointense to slightly hyperintense to muscle on T1-weighted images and hyperintense on T2-weighted images (n = 3); B--pattern A plus foci of signal void on all pulse sequences (n = 17); and C--features of pattern A and B plus foci of peripheral low signal surrounding central fat-like signal (n = 2). The foci of signal void in pattern B and C corresponded to areas of calcification and the foci of peripheral low signal surrounding central fat-like signal in pattern C corresponded to areas of ossification. CONCLUSION: The MR appearance of ISO appears sufficiently unique to allow its differentiation from other causes of intraarticular pathology.

Patterns of vertebral ossification and pelvic abnormalities in paralysis: a study of 200 patients.

To clarify the characteristics, extent, and frequency of spinal ossification and abnormalities of the sacroiliac joint, symphysis pubis, and hip in paralysis, routine radiographs of the lumbar spine, pelvis, and abdomen were retrospectively evaluated in 95 quadriplegic, 105 paraplegic, and 100 age-matched control patients, with attention to age and race and to spinal level and duration of paralysis. The spinal radiographs were evaluated for presence of osteophytes, syndesmophytes, paravertebral ossification, and flowing hyperostosis characteristic of diffuse idiopathic skeletal hyperostosis (DISH); the pelvic radiographs were used to measure the widths of the sacroiliac joint, hip, and symphysis pubis articulations and evaluate for presence of enthesopathy. Bone formation around vertebral bodies was often seen in quadriplegic (n = 41 [43%]) and paraplegic (n = 46 [44%]) patients. In quadriplegic patients, four distinct vertebral ossification patterns were evident: osteophytosis, paraspinal ossification resembling that found in psoriasis, syndesmophytosis, and flowing ossification similar to that in DISH. In paraplegic patients, osteophytosis was most frequent. Vertebral ossification in quadriplegic patients was significantly associated with age (P < .01) and increased in frequency and severity with increasing age.