Spontaneous Osteonecrosis of Knee After Arthroscopy Is Not Necessarily Related to the Procedure.

Reports in the literature have suggested a causal relationship between knee arthroscopy and spontaneous osteonecrosis of the knee (SONK). We conducted a study to determine if there are imaging characteristics associated with SONK and if there is a relationship between arthroscopy and SONK. In this retrospective review, we compared preoperative and postoperative findings in 11 patients (12 joints) who developed SONK after arthroscopy with findings in 11 age- and sex-matched controls who did not develop SONK after arthroscopy. There were no significant preoperative radiologic differences between the SONK and control groups. All 12 SONK lesions seen on magnetic resonance imaging were in the medial femoral condyle. Six SONK knees developed the lesion after arthroscopy, and 6 had SONK lesions before arthroscopy. Eleven of the 12 SONK knees had a medial meniscal tear, compared with 8 medial meniscal tears and 3 lateral meniscal tears in the control group. Eight SONK knees and 5 control patients had medial meniscal extrusion of more than 3 mm. A causal relationship between knee arthroscopy and SONK is questionable.

Review of three magnetic resonance arthrography related infections.

We report three cases of intra-articular infection which followed injection for magnetic resonance arthrography. In an effort to reduce the risk of arthrogram related infection, representatives from radiology, infectious disease medicine, and microbiology departments convened to analyze the contributing factors. The proposed source was oral contamination from barium swallow studies which preceded the arthrogram injections in the same room. We propose safety measures to reduce incidence of arthrogram related infections.

Ultrasound of the postoperative hip.

Imaging of the postoperative hip with ultrasound can be difficult and challenging. The primary role of ultrasound is to help determine whether or not there is infection. It is difficult at times to differentiate between complex fluid and synovium. Whether fluid is infected or not cannot be determined by ultrasound criteria and aspiration, and laboratory analysis is required. Particle disease and infection cannot be reliably differentiated by ultrasound criteria. In the setting of possible infection, any fluid collection/s around the hip should be treated with suspicion and, if possible, aspirated. The importance of sending part of the aspirated fluid for cell count is stressed; aspirated synovial fluid with a cell count >3000 white blood cells per milliliter of aspirated synovial fluid when combined with an elevated erythrocyte sedimentation rate and C-reactive protein level is highly predictive of infection.

Apophyseal injuries of the lesser tuberosity in adolescents: a series of five cases.

An isolated avulsion fracture of the lesser tuberosity is an uncommon injury. We present five cases in adolescent athletes which demonstrate the radiographic, ultrasound, and MR appearances of this injury. Clinically and radiologically, the diagnosis can be difficult. In a setting of trauma, careful review of the imaging studies can lead to early diagnosis and appropriate treatment.

Musculoskeletal ultrasound: elbow imaging and procedures.

Elbow injuries, both acute and chronic sports-related cases, have increased over the last decade. With one in every four members of a household participating in sports, both clinics and radiology departments are seeing more patients with elbow pain. High-resolution ultrasound is well suited for evaluating the elbow. Ultrasound is growing in popularity and fast becoming another modality that the radiologist can use to help diagnose elbow pathology. With advancing transducer technology and accessibility, ultrasound offers focused and real-time high-resolution imaging of tendons, ligaments, and nerve structures. Its advantages include the use of safe nonionizing radiation, accessibility, and cost effectiveness. Another unique advantage is its ability for dynamic assessment of tendon and ligament structures such as in cases of partial tears of the medial ulnar collateral ligament or ulnar nerve dislocation. It is also easy to assess the contralateral side as a control. Ultrasound is also useful in therapeutic guided injections for its multiplanar capability and clear visualization of major vessels and nerves. We discuss the unique application of ultrasound in evaluating common elbow pathology and in advanced ultrasound-guided treatments such as dextrose prolotherapy and platelet-rich plasma.

Complications in the use of rhBMP-2 in PEEK cages for interbody spinal fusions.

STUDY DESIGN: All patients of spinal interbody fusion using polyetheretherketone (PEEK) cages and recombinant human bone morphogenetic protein (rhBMP)-2 performed over a 16-month period were reviewed. OBJECTIVE: To determine the suitability of PEEK cages when used in conjunction with rhBMP-2 in interbody spinal fusion. SUMMARY OF BACKGROUND DATA: Bone morphogenetic proteins are increasingly being used in spinal fusion to promote osteogenesis. PEEK is a semicrystalline aromatic polymer that is used as a structural spacer to maintain the disc and foraminal height. Their use has led to increased and predictable rates of fusion. However, not many reports of the adverse effects of their use are available. METHODS: Fifty-nine consecutive patients of interbody spinal fusion in the cervical or lumbar spine using a PEEK cage and rhBMP-2 were followed for an average of 26 months after surgery. A clinical examination and a record of Oswestry Disability Index, Visual Analog Scale for pain, and a pain diagram were performed preoperatively and at every follow-up visit. All patients had plain radiographs carried out to assess fusion. Ten patients of lumbar spine fusion were additionally evaluated with a computed tomography scan. RESULTS: All cases demonstrated an appreciable amount of new bone formation by 6 to 9 months in the cervical spine and by 9 to 12 months in the lumbar spine. End plate resorption was visible radiologically in all cervical spine fusions and majority of lumbar fusions. Cage migration was observed to occur maximally in patients with transforaminal lumbar interbody fusion and posterior lumbar interbody fusion. Disc space subsidence was seen in both cervical and lumbar arthrodesis with the latter showing a lesser incidence, but with a greater degree of collapse. CONCLUSIONS: PEEK cages and rhBMP-2 when used in spinal fusion give consistently good fusion rates. However, the early role of BMP in the resorptive phase may cause loosening, cage migration, and subsidence.

Radiography and US of os peroneum fractures and associated peroneal tendon injuries: initial experience.

PURPOSE: To retrospectively evaluate the imaging features of os peroneum fractures and associated peroneus longus tendon injuries at radiography and ultrasonography (US) and to retrospectively compare these imaging features with those of multipartite os peroneum. MATERIALS AND METHODS: Institutional review board approval was obtained and informed consent was waived for this HIPAA-compliant study. Retrospective review of findings in nine patients (five men, four women; age range, 35-59 years) with os peroneum fracture at radiography and lateral foot pain after injury who had undergone US of the foot was performed. Three patients underwent magnetic resonance (MR) imaging, and two underwent surgery. Os peroneum fragment separation and displacement relative to the calcaneocuboid joint were measured on radiographs. Os peroneum fracture and peroneus longus tendon injuries were characterized with US and MR imaging. Review of 43 foot radiographs obtained in 36 control subjects (eight men, 28 women; age range, 18-84 years) who were found to have an os peroneum at radiography but were asymptomatic in that area was completed to measure os peroneum distance from the calcaneocuboid joint and bipartite os peroneum fragment distraction. RESULTS: Os peroneum fragment separation of 6 mm or more or displacement of the proximal fragment by 10 mm or more on a lateral radiograph or 20 mm or more on an oblique radiograph was associated with full-thickness peroneus longus tendon tear in seven of seven patients (100%). Os peroneum fragment separation of 2 mm or less or proximal displacement of 8 mm or less was associated with normal tendons, partial-thickness tears, or tendinosis. In the control subjects, os peroneum location ranged from 7 mm proximal to 8 mm distal to the calcaneocuboid joint on lateral radiographs and from 9 mm proximal to 8 mm distal to the joint on oblique radiographs. Bipartite os peroneum fragment separation was 2 mm or less. CONCLUSION: Os peroneum fragment separation of 6 mm or more suggests os peroneum fracture and associated full-thickness peroneus longus tendon tear. Separation of 2 mm or less may be seen with nondisplaced os peroneum fractures and bipartite os peroneum.

Three-tesla imaging of the knee: initial experience.

PURPOSE: To assess 3-T imaging of the knee. MATERIALS AND METHODS: We reviewed 357 3-T magnetic resonance images of the knee obtained using a dedicated knee coil. From 58 patients who had arthroscopy we determined the sensitivity and specificity for anterior cruciate ligament (ACL) tear and medial and lateral meniscal tear. RESULTS: A chemical shift artifact showed prominently at 3 T even after improvements had been made by increasing the bandwidth. For complete ACL tear the sensitivity was 100% (95% confidence interval, CI, 75.30-100.00), and the specificity was 97.9% (95% CI 87.7-99.9). For the medial meniscus the sensitivity was 100.00% (95% CI 90.0-100.00), and the specificity was 83.3%(95% CI 66.6-95.3). For the lateral meniscus the sensitivity was 66.7% (95% CI 38.4-88.2), and the specificity was 97.6% (95% CI 87.1-99.9). CONCLUSIONS: In general 3-T imaging allows a favorable display of anatomy and pathology. The lateral meniscus was assessed to be weaker than the other anatomic structures. Three-tesla imaging allows increased signal-to-noise ratio, increased resolution, and faster scanning times.

The distal femoral and proximal tibial growth plates: MR imaging, three-dimensional modeling and estimation of area and volume.

OBJECTIVE: To explore how the size of the growth plate changes with age using three-dimensional (3D) models of the distal femoral and proximal tibial growth plates in pediatric patients. DESIGN AND PATIENTS: We retrospectively created 3D models of the normal unaffected distal femoral (n=20) and proximal tibial (n=10) growth plates in 14 patients (9 males, 5 females) age range 3.8-15.6 years who were referred for evaluation of premature partial closure of the growth plate or hyaline cartilage abnormality. All patients had one or more 3D fat-suppressed spoiled GRASS sequence from which models were made of normal growth plates. Total projected area was estimated from standardized maximum intensity projection (MIP) views, and volume was computed from the entire model. We also included the total projected area of the distal femur (n=7) or proximal tibia (n=8) in 11 patients (8 males, 3 females, 5-13 years) who had previously been evaluated for bone bridging. RESULTS: The 3D femoral and tibial growth plate anatomy was displayed. Femoral growth plate area varied from 804 mm2 to 3,463 mm2. Femoral physeal cartilage volume varied from 2.1 cm3 to 12.6 cm3. Tibial growth plate area varied from 736 mm2 to 3,026 mm2. Tibial physeal cartilage volume varied from 1.9 cm3 to 13.2 cm3. The growth plate area values appear to increase linearly with increasing age. CONCLUSIONS: The distal femoral and proximal tibial physeal plates have complex anatomy. Both area and volume of the growth plates appeared to follow a linear increase with age and reached a plateau in adolescence, although there was some scatter. Area appears to have less measurement variability than volume, and may be a more reliable predictor of growth plate tissue quantity.

Calcium sulfate used as bone graft substitute in acetabular fracture fixation.

The purpose of this study was to determine the natural history of calcium sulfate pellets implanted during acetabular fracture surgery. The study group consisted of patients sustaining an acetabular fracture with intraarticular comminution or marginal impaction or both in whom calcium sulfate pellets were implanted in lieu of autologous bone graft. Between 1997 and 1999, 32 fractures were treated. Followup adequate to delineate pellet outcome, including radiographs and computed tomography, was obtained in 31 patients. Evaluation of plain radiographs showed that the calcium sulfate pellets became undifferentiated from the surrounding bone at an average of 7 weeks postoperatively. In no case was a residual bony deficit seen. Computed tomography analysis showed that in 22 patients, the pellets essentially had been (> 90%) replaced by bone and in four patients, the majority (> 50%-90%) of the pellets had been replaced by bone. However, in five patients, less than 50% of the pellets had been replaced by bone, including one showing no bony replacement. The common finding in patients with an extensive residual deficit was direct communication of the pellets with the joint space shown on the postoperative computed tomography scan. Patients with the best results had complete containment of the pellets within bone. Therefore, it seems that implanted calcium sulfate pellets in contact with joint synovial fluid are at risk for resorption without significant bony response. If calcium sulfate pellets are to be implanted in a periarticular location, complete bony containment is desirable. Evaluation of the periacetabular bony response requires computed tomography scans, as plain radiographs are inadequate for this purpose.

Computed tomographic assessment of fractures of the posterior wall of the acetabulum after operative treatment.

BACKGROUND: The purpose of this study was to evaluate the results after operative treatment of fractures of the posterior wall of the acetabulum in relationship to the quality of the fracture reduction as assessed by postoperative two-dimensional computed tomography. METHODS: The functional results for sixty-seven patients who had open reduction and internal fixation of an unstable fracture of the posterior wall of the acetabulum and the findings of two-dimensional computed tomography performed postoperatively were analyzed. Sixty-one patients were followed for a mean of four years after the injury, and the remaining six patients who had poor early results necessitating reconstructive surgery were followed for less than two years. All patients were evaluated preoperatively and postoperatively with use of three standard plain radiographs (one anteroposterior and two Judet 45 degrees oblique pelvic radiographs) and a two-dimensional computed tomography scan. The functional outcome for the patients was evaluated with use of a modification of the clinical grading system described by Letournel and Judet. The radiographs were graded according to the criteria described by Matta. The two-dimensional computed tomography scans were used to determine fracture gap and offset measurements. RESULTS: The clinical outcome was graded as excellent in thirty-one patients (46%), very good in twenty (30%), good in eight (12%), and poor in eight (12%). The final radiographic results were graded as excellent in fifty-three hips (79%), good in four (6%), fair in three (5%), and poor in seven (10%). There was a strong association between clinical outcome and final radiographic grade. Fracture reductions were graded as anatomic in sixty-five and imperfect in two, as determined with use of plain radiography. However, postoperative computed tomography revealed an incongruency (offset) of >2 mm in eleven hips and fracture gaps of > or = 2 mm in fifty-two. Fracture gaps of > or = 10 mm in any dimension or a total gap area of > or = 35 mm(2) were associated with a poor result. The main risk factors for a poor result were a residual fracture gap width of > or = 10 mm and osteonecrosis of the femoral head. CONCLUSIONS: The degree of residual fracture displacement is detected more accurately on postoperative computed tomography scans than on plain radiographs. The accuracy of surgical reduction as assessed on postoperative computed tomography is highly predictive of the clinical outcome. LEVEL OF EVIDENCE: Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Longitudinal stress fracture: patterns of edema and the importance of the nutrient foramen.

DESIGN AND PATIENTS: We reviewed the MR appearances of six cases of longitudinal stress fracture of the lower extremity. RESULTS: One fracture was in the femur and five were in the tibia. Four of the tibial fractures showed edema starting in the mid-tibia at the level of the nutrient foramen with the fracture on the anteromedial cortex. The other tibial fracture started at the nutrient foramen. Three fractures (two tibial and the femur fracture) showed eccentric marrow edema; all fractures showed either eccentric periosteal reaction or soft tissue edema. CONCLUSION: Primary diagnosis of longitudinal stress fracture is made by finding a vertical cleft on one or more axial images. Secondary signs of position of the nutrient foramen and patterns of edema may be useful.

The utility of MR in assessing Blount disease.

OBJECTIVE: To review the MR appearances of Blount disease. DESIGN AND PATIENTS: The MR examinations of six knees in four patients (ages 6-7 years) with Blount disease were reviewed. RESULTS: All patients showed delay in ossification of the medial tibial epiphysis. A spectrum of changes was seen in and around the tibial growth plate including: widening and depression of the medial growth plate; small and deep intrusions of cartilage into the metaphysis; edema of the medial tibial epiphysis and medial and lateral metaphysis; varus deformity of the lower leg; widening of the lateral growth plate; osteochondral injury to the medial femoral condyle; hypertrophy of the medial meniscus; focal bone bridging. CONCLUSION: MR appearances are consistent with the primary abnormality in Blount disease, which is failure of endochondral ossification of the medial growth plate. MR examination is useful in surgical planning.