MR imaging of patellar dislocation and relocation.

Patellar dislocation and relocation (PDR) typically occurs suddenly after trauma or torsional stress on the extensor mechanism. Clinical evaluation after patellar dislocation/relocation usually reveals a swollen knee that is difficult to examine. Radiographs may show hemathroses and a minority of patients will have a chip fracture of the patella. Magnetic resonance (MR) imaging features seen with PDR include disruption or sprain of the medial retinaculum, lateral patellar tilt or subluxation, lateral femoral condylar and medical patellar osseous contusions, osteochondral injury, damage to Hoffa's fat pad, and joint effusion. Up to one third of patients will also show concomitant injury to the major ligaments of the knee or menisci. Without repair of the primary injury, redislocation occurs in greater than one half of patients. Consequently, surgical correction is often advocated. This article reviews the factors predisposing to PDR, the activities associated with PDR, the clinical, radiographic, and MR imaging features of PDR, and (briefly) therapy for this injury.

The role of hip arthroscopy in the evaluation of avascular necrosis.

This prospective study evaluated the correlation between plain radiographs, magnetic resonance imaging (MRI), and diagnostic arthroscopy in the staging of avascular necrosis of the femoral head. Fifty-two hips in 46 patients were prospectively staged using radiographic and MRI staging systems. Patients subsequently underwent hip arthroscopy to visualize the articular surface prior to considering salvage of the femoral head and debride delaminated osteochondral fragments. Weighted Kappa analysis revealed only moderate correlation between MRI and plain radiographs (K=.11), MRI and arthroscopy (K=.21), and plain radiographs and arthroscopy (K=.19). Six (46%) of 13 patients with a radiographically apparent subchondral fracture demonstrated collapse of the articular surface at arthroscopy. Four (24%) of 17 hips with >2 mm of collapse of the femoral head on plain radiographs demonstrated fragmentation of the osteochondral surface of the femoral head at arthroscopy. In 5 patients with flattening of the femoral head, 3 patients had delamination of both the femoral and acetabular surfaces. In regard to labral pathology, 5 of 22 post-collapse hips also had large bucket handle tears of the labrum. Arthroscopy of the hip revealed osteochondral degeneration that was not detected by plain radiographs or MRI in 36% of post-collapse femoral heads.

Neurologic dysfunction in patients with rheumatoid arthritis of the cervical spine. Predictive value of clinical, radiographic and MR imaging parameters.

The aim of this study was to evaluate if subjective symptoms, radiographic and especially MR parameters of cervical spine involvement, can predict neurologic dysfunction in patients with severe rheumatoid arthritis (RA). Sequential radiographs, MR imaging, and neurologic examination were performed yearly in 46 consecutive RA patients with symptoms indicative of cervical spine involvement. Radiographic parameters were erosions of the dens or intervertebral joints, disc-space narrowing, horizontal and vertical atlantoaxial subluxation, subluxations below C2, and the diameter of the spinal canal. The MR features evaluated were presence of dens and atlas erosion, brainstem compression, subarachnoid space encroachment, pannus around the dens, abnormal fat body caudal to the clivus, cervicomedullary angle, and distance of the dens to the line of McRae. Muscle weakness was associated with a tenfold increased risk of neurologic dysfunction. Radiographic parameters were not associated. On MR images atlas erosion and a decreased distance of the dens to the line of McRae showed a fivefold increased risk of neurologic dysfunction. Subarachnoid space encroachment was associated with a 12-fold increased risk. Rheumatoid arthritis patients with muscle weakness and subarachnoid space encroachment of the entire cervical spine have a highly increased risk of developing neurologic dysfunction.

Are magnetic resonance flexion views useful in evaluating the cervical spine of patients with rheumatoid arthritis?

OBJECTIVE: To determine whether MR imaging in flexion adds value relative to imaging in the neutral position with respect to displaying involvement of the subarachnoid space, brainstem and spinal cord. DESIGN AND PATIENTS: T1-weighted MR images of the cervical spine in 42 rheumatoid arthritis patients with cervical spine involvement were obtained and analyzed prospectively. We assessed changes between images obtained in the neutral position and following active flexion, especially horizontal atlantoaxial and subaxial motion, presence or absence of brainstem compression, subarachnoid space involvement at the atlantoaxial and subaxial level and the cervicomedullary angle. Vertical atlantoaxial subluxation and the amount of pannus were correlated with motion and change in subarachnoid space. RESULTS: The flexion images showed horizontal atlantoaxial motion in 21 patients and subaxial motion in one patient. The flexion view displayed brainstem compression in only one patient. Involvement of the subarachnoid space increased at the atlantoaxial level in eight (19%) patients (P=0.004) and at the level below C2 in five (12%) patients (P=0.03). There were no patients with a normal subarachnoid space in neutral position and compression in the flexed position. The cervicomedullary angle changed significantly with flexion. Vertical atlantoaxial subluxation and the amount of pannus did not show a significant correlation with motion or subarachnoid space involvement. CONCLUSION: MR imaging in the flexed position shows a statistically significant narrowing of the subarachnoid space at the atlantoaxial level and below C2. Cord compression is only observed on flexion views if the subarachnoid space in neutral position is already decreased. MR imaging in the flexed position might be useful, since subarachnoid space involvement may be an indicator for the development of neurologic dysfunction.

Hip arthroscopy in staging avascular necrosis of the femoral head.

The purposes of this study were to evaluate how accurately current imaging modalities predict the quality of the articular surface in avascular necrosis (AVN) of the femoral head and to provide arthroscopic correlation to current staging modalities. An arthroscopic classification system, derived from the work of Marcus et al, was used to prospectively stage the articular surface in 23 hips with AVN using plain radiographs, magnetic resonance imaging (MRI), and arthroscopy. There was little correlation between all three diagnostic modalities. These findings were not statistically significant. Patients with stage IV disease had the widest variation in the appearance of the articular surface. This study shows poor correlation in the staging of AVN using current imaging techniques. Magnetic resonance imaging has been shown to be inadequate at assessing the articular cartilage. Therefore, either arthroscopy or direct visualization is required for accurate evaluation and staging, especially in stage IV disease.

Magnetic resonance imaging of the musculoskeletal system. Part 9. Primary Tumors.

Magnetic resonance imaging, because of its exquisite soft tissue contrast, has dramatically improved the ability to preoperatively stage primary osseous and soft tissue neoplasms. This technique also has allowed the monitoring of the effects of chemotherapy and the screening for recurrence of neoplasms. The role of magnetic resonance imaging in the preoperative evaluation of the patient with a suspected primary osseous or soft tissue neoplasm is outlined, instances where magnetic resonance imaging potentially may make a specific diagnosis are outlined, the importance of gadolinium enhancement as an adjunct to native magnetic resonance imaging is stressed, and an algorithm for followup of patients after chemotherapy or definitive surgical treatment is presented. In all cases, the magnetic resonance images should be correlated with the plain film, which is still an important aspect of the diagnosis of osseous lesions.

Usefulness of radiography in differentiating enchondroma from central grade 1 chondrosarcoma.

OBJECTIVE: The purpose of this study was to evaluate clinical symptoms and radiographic features that allow radiologists to differentiate between enchondroma and central grade 1 chondrosarcoma. Such differentiation is important because of differences in management. MATERIALS AND METHODS: Clinical symptoms and location and size of 35 enchondromas and 43 central grade 1 chondrosarcomas were analyzed. Radiographic features were assessed independently by three observers. The chi-square test and linear discriminant analysis were used to identify features with discriminating strength. Kappa values were calculated to validate the consistency of observations among observers. A consensus diagnosis made by histology and long-term follow-up was used as the standard. RESULTS: No statistically significant correlation was found between clinical symptoms and the benign or malignant nature of the neoplasms. Grade 1 chondrosarcomas were more likely to be found in the axial skeleton and in flat bones. Also, chondrosarcomas were significantly larger than enchondromas (p < .001). Ill-defined margins and lobulated contours were the only morphologic features seen on radiographs that allowed significant discrimination (p = .004 and .009, respectively). An optimal combination of four radiographic features still left 72 of the 78 lesions with a 10-90% probability of malignancy, indicative of poor discriminating power. Kappa values generally showed poor to fair agreement. CONCLUSION: Location in the axial skeleton and size greater than 5 cm are the most reliable predictors of central grade 1 chondrosarcoma. Morphologic features seen on radiographs and clinical symptoms do not improve the ability to differentiate between enchondromas and central grade 1 chondrosarcomas.

Dedifferentiated chondrosarcoma in patients with multiple osteochondromatosis: report of a case and review of the literature.

Multiple osteochondromatosis (MOS) is a familial disorder of autosomal dominant transmission characterized by the development of multiple exostoses and often derangements of epiphyseal cartilage, sometimes resulting in long bone growth retardation. Patients with the disorder appear to be at increased risk for developing secondary chondrosarcomas. Rarely, dedifferentiated chondrosarcomas may also occur. We report a single case of a 27-year-old man with multiple osteochondromatosis who developed a fatal dedifferentiated chondrosarcoma. Radiographically, the neoplasm arose from the pelvis completely destroying the left pubic ramus. Subsequently, the patient underwent preoperative chemotherapy followed by a left external hemipelvectomy. On pathologic examination, the tumor was characterized by high-grade pleomorphic sarcoma sharply juxtaposed to a low-grade chondrosarcoma. The patient ultimately died of widespread metastatic sarcoma.

Diffuse pigmented villonodular synovitis in a college football player.

In retrospect, it is evident that our patient had signs of PVS on initial presentation: suprapatellar pouch effusion and swelling out of proportion to discomfort. In addition, his first MRI scan showed characteristics of PVS: thickening and enhancement. Difficulty in reaching the diagnosis of PVS was aided by his asymptomatic return to football. Further confusing the issue, his initial presentation was directly associated with trauma, which is not pathognomonic for PVS. In conclusion, diffuse pigmented villonodular synovitis can be recognized early on MRI scans, which should be carefully examined, especially in the presence of large suprapatellar effusions. Diffuse PVS can be successfully treated with arthroscopic subtotal synovectomy.

Intraosseous pneumatocyst of the iliac bone.

Intraosseous pneumatocyst of the iliac bone is usually an innocuous incidental finding with characteristic radiographic features. Because this entity is uncommon and has not been described in the orthopaedic literature, many orthopaedic surgeons are unfamiliar with the entity. Three cases of intraosseous pneumatocyst of the iliac bone are presented to illustrate some of the imaging features to assist in recognizing it for what it is: an innocuous incidental finding that should not prompt invasive procedures such as a biopsy.

Magnetic resonance imaging of the musculoskeletal system. Part 4. The knee.

Since its introduction to musculoskeletal imaging in the early 1980s, magnetic resonance imaging has proven to be an excellent technique for evaluating patients with knee problems. Studies have shown it to be accurate in the identification of abnormalities of the menisci, ligaments, patellofemoral joints, and other soft tissue and osseous structures in the knee. The main advantages of magnetic resonance imaging are its noninvasive nature and its high accuracy and negative predictive value in evaluating the menisci and anterior cruciate ligament. Magnetic resonance imaging has been shown to be useful in the detection and diagnosis of various traumatic and nontraumatic knee abnormalities. It has also proved useful in the diagnosis of occult or unsuspected bone lesions. Magnetic resonance imaging can therefore help in the selection of those patients who need therapeutic arthroscopy. There is evidence that magnetic resonance imaging of the knee is a cost effective screening technique when used in conjunction with the clinical findings in patients who are candidates for arthroscopy. Magnetic resonance imaging of the knee is still a relatively expensive modality.

Medial collateral ligament injuries of the knee: ultrasonographic findings.

The aims of our study were (1) to describe the ultrasonographic findings of the injured medial collateral ligament of the knee and (2) to assess the usefulness of ultrasonography in both evaluating the presence and location of the medial collateral ligament injuries and predicting the prognoses for the patients. The study group consisted of 16 patients with the clinical diagnosis of medial collateral ligament injury. We also examined 20 knee joints in 10 volunteers who had no history of injury to the knee. To predict prognoses, we divided the patients into two groups on the basis of the location of medial collateral ligament injuries. A thickened and heterogeneously hypoechoic appearance of the medial collateral ligament was considered abnormal. The normal medial collateral ligament was a thin and moderately homogeneous hypoechoic band with an average thickness of 4.3 mm (range, 3.3 to 5.6 mm) at the femoral attachment and of 2.3 mm (range, 1.3 to 3.2 mm) at the tibial attachment. All injured medial collateral ligament structures were thickened and heterogeneously hypoechoic. According to the criteria for grading of medial collateral ligament injury with stress view, 10 patients had grade III medial collateral ligament tears, three had grade II tears, and none had grade I injuries. In 15 (94%) of 19 knees, a correct diagnosis could be made with ultrasonography. Ultrasonography is useful in evaluating isolated medial collateral ligament injuries and in predicting patient outcome on the basis of the location of the medial collateral ligament injuries.

Change in trabecular architecture as measured by fractal dimension.

The objective of this work was to expose dried trabecular bone material to a decalcifying environment and to quantify the change in the spatial distribution of the bone with a fractal measure. Digitized radiographic images were produced from four separate slices of human vertebral bone as they dissolved within a solution of nitric acid. Pixel data from a region of interest (ROI) within the trabecular bone were used to estimate the time-dependent change in fractal dimension of the ROI as the bone dissolved. Results demonstrated that a change in the spatial distribution of trabecular material may be expressed in terms of a concurrently changing estimate of the fractal dimension.