Derik L. Davis

Hip Arthroplasty Pseudotumors: Pathogenesis, Imaging, and Clinical Decision Making

Pseudotumors are a complication of hip arthroplasty. The goal of this article is to review the clinical presentation, pathogenesis, histology, and the role of diagnostic imaging in clinical decision making for treatment, and surveillance of pseudotumors. We will discuss the multimodal imaging appearances, differential diagnosis, associated complications, treatment, and prognosis of pseudotumors, as an aid to the assessment of orthopedic prostheses at the hip.

Evaluation of Epiphyses in the Skeletally Immature Knee Using Magnetic Resonance Imaging A Pilot Study to Analyze Parameters for Anterior Cruciate Ligament Reconstruction

Background: Questions have been raised concerning the height of the tibial epiphysis as an important factor related to the safety of intra-articular anterior cruciate ligament (ACL) reconstruction in skeletally immature knees. However, normal values for this parameter have yet to be established on cross-sectional magnetic resonance imaging (MRI). Purpose: To determine normal values for the height of the tibial epiphysis and width of the lateral femoral condylar epiphysis in children and adolescents by use of MRI. Study Design: Cross-sectional study; Level of evidence, 3. Methods: An electronic search was conducted for pediatric knee MRI examinations at the authors’ institution from August 2007 to July 2011. The height of the tibial epiphysis was determined on the sagittal T1-weighted image best containing the ACL footplate. Lateral femoral condylar width was recorded on coronal proton-density-weighted images. The intraclass correlation coefficient (ICC) was calculated to determine interobserver agreement. Knees were stratified by age into 2 groups based on potential risk of iatrogenic growth plate injury: Group 1 consisted of boys younger than 13 years (range, 7-12 years) and girls younger than 12 years (range, 10-11 years); group 2 consisted of boys between the ages of 13 and 16 years and girls between the ages of 12 and 14 years. Each cohort was further stratified by sex. Results: Group 1 consisted of 17 boys (mean age, 10.4 years) and 5 girls (mean age, 10.8 years), and group 2 contained 23 boys (mean age, 14.4 years) and 14 girls (mean age, 13.7 years). There was a total of 59 knees. No difference was found for average tibial epiphyseal height between group 1 (15.26 ± 1.25 mm) and group 2 (15.01 ± 2.14 mm). However, there was a statistically significant difference related to sex in each cohort: boys versus girls in group 1 (15.63 ± 1.15 mm vs 14.00 ± 0.62 mm, respectively; P = .007) and boys versus girls in group 2 (16.00 ± 1.88 mm vs 13.40 ± 1.47 mm, respectively; P = .0001). The average femoral condylar width for both cohorts was greater than 28 mm where femoral tunnel location would be expected. The ICC was strong (>0.7) at tibial and femoral locations where tunnel placement would be expected. Conclusion: The average height of the tibial epiphysis in both children and adolescents is 15 mm. Girls had shorter tibial epiphyses than boys, but further studies are necessary to determine whether this difference is clinically relevant. Lateral femoral condylar width in children and adolescents can be expected to be greater than 28 mm.

Analysis of the Tibial Epiphysis in the Skeletally Immature Knee Using Magnetic Resonance Imaging: An Update of Anatomic Parameters Pertinent to Physeal-Sparing Anterior Cruciate Ligament Reconstruction

Background: Physeal-sparing anterior cruciate ligament (ACL) reconstruction is being performed increasingly in skeletally immature knees. Purpose: To determine normal values for the maximum oblique length and “safe” physeal-sparing length and their corresponding angular trajectories across the tibial epiphysis on reconstructed magnetic resonance images (MRIs) in children and adolescents. Study Design: Cross-sectional study; Level of evidence, 3. Methods: An electronic search for pediatric knee MR examinations from April 2003 to April 2013 was performed at our institution. A 3-dimensional system viewer was used to measure the maximum oblique length, physeal-sparing length, and their corresponding angular trajectories on reconstructed MRIs. Knees were stratified by age into 2 groups: group 1 consisted of boys <13 years and girls <12 years and group 2 consisted of older boys (13-14 years) and girls (12-14 years). Each cohort was further stratified by sex. Group 1 consisted of 36 knees (mean age, 10.9 years) and group 2 consisted of 59 knees (mean age, 13.6 years). Results: Significant differences existed for the maximum oblique length and its angular trajectory for the younger versus older cohort (22.2 ± 2.7 vs 23.8 ± 2.7 mm, P = .007; 42.0° ± 4.0° vs 39.4° ± 4.2°, P = .003) and for the physeal-sparing length and its angular trajectory (19.4 ± 2.8 vs 21.3 ± 2.9 mm, P = .001; 30.1° ± 4.1° vs 28.2° ± 4.5°, P = .042). In group 2, females had shorter maximal oblique length and physeal-sparing length than boys (22.7 ± 2.3 vs 25.0 ± 2.7 mm, P < .001; 20.3 ± 2.6 vs 22.4 ± 2.9 mm, P = .004). Conclusion: The maximum oblique length across the tibial epiphysis is shorter than previously believed, measuring approximately 22 mm and approximately 24 mm for high- and intermediate-risk knees, respectively. However, “safe” physeal-sparing lengths were only approximately 19 mm and 21 mm for the younger and older cohorts, respectively. The angles corresponding to the maximum and safe lengths are more acute than commonly thought, measuring approximately 40° and 30°, respectively. All prepubescent knees and intermediate-risk females should receive careful attention before ACL reconstruction due to the relative smaller size of their tibial epiphyses. Clinical Relevance: Physeal-sparing ACL reconstruction is gaining acceptance as a surgical option for complete ACL tear in skeletally immature knees. Iatrogenic growth disturbance after violation of an open growth remains a real concern for surgeons tasked with providing operative management for the unstable pediatric knee. Inadvertent iatrogenic growth plate injury to the tibial physis has been shown to occur more commonly than surgeons would intend during physeal-sparing ACL reconstruction.

A Study of Epiphyses in the Young Prepubescent Knee Using Magnetic Resonance Imaging: Evaluation of Parameters for Anterior Cruciate Ligament Reconstruction

Background: Questions have been raised concerning the safety of intra-articular anterior cruciate ligament (ACL) reconstruction in prepubescent children aged <7 years. However, normal values for the width of the lateral femoral condylar epiphysis and height of the tibial epiphysis have yet to be established through the use of magnetic resonance imaging (MRI). Purpose: To determine normal values for the width of the lateral femoral condylar epiphysis and height of the tibial epiphysis at the knee in prepubescent children aged <7 years by use of MRI and to compare this age group with an older cohort of prepubescent children aged <10 years. Study Design: Cross-sectional study; Level of evidence, 3. Methods: An electronic search was conducted for pediatric knee MRI examinations at the authors’ institution from March 2003 to March 2013. The total and ossified lateral femoral condylar widths were determined on coronal proton density–weighted images. The total and ossified tibial epiphyseal heights were recorded on the sagittal T1-weighted image best containing the ACL footplate. The intraclass correlation coefficient (ICC) was calculated to determine interobserver agreement. Knees were stratified by age into 2 groups: children between the ages of 3 and 6 years (group 1) and children between the ages of 7 and 9 years (group 2). Each cohort was further stratified by sex. Results: Group 1 consisted of 10 children (mean age, 4.3 years) and group 2 consisted of 10 children (mean age, 8.5 years). There were a total of 20 knees. There was a statistically significant difference between groups 1 and 2 for the ossified lateral femoral condylar width where femoral tunnel location would be expected (20.00 ± 4.20 vs 26.27 ± 4.12 mm, respectively; P = .0035) and for total lateral femoral condylar width (25.57 ± 3.47 vs 29.43 ± 4.04 mm, respectively; P = .0339). No difference was found for total tibial epiphyseal height between the 2 groups. However, there was a difference between groups 1 and 2 for ossified tibial epiphyseal height (13.20 ± 1.63 vs 15.27 ± 0.94 mm, respectively; P = .0028). No difference was found for average ossified tibial epiphyseal height or ossified lateral femoral condylar width between boys and girls in the younger or older cohorts. The ICC was strong (>0.7) at femoral and tibial locations where tunnel placement would be expected. Conclusion: Prepubescent children <7 years old have smaller knee epiphyses than older prepubescent children, and on average, present with an osseous bone stock of 20 mm for lateral femoral condylar width and 13 mm for tibial epiphyseal height. Study results suggest that children aged <7 years possess enough osseous bone stock at the lateral femoral condyle to support transepiphyseal ACL reconstruction. However, future studies will be necessary to determine the safety and effectiveness of this procedure in children aged <7 years. Clinical Relevance: ACL tears in children are more frequently being recognized by the orthopaedic community. The trend toward increasing participation in competitive and recreational sports has contributed to this phenomenon. Young patients with complete ACL tears and open growth plates often provide a management dilemma for surgeons who wish to perform reconstructive surgery.

Promyelocytic sarcoma of the right humerus: an unusual clinical presentation with unique diagnostic and treatment considerations

Promyelocytic leukemia is a known medical emergency and requires rapid diagnosis and expedient therapy with differentiating agents. We present an unusual case in which the diagnosis is based on a fine needle aspirate of a humeral mass. Despite lack of systemic involvement, the sarcoma responded to traditional differentiation agents.

Case 229: Burn-related Global Ankylosis of Interphalangeal Joints with Associated Acroosteolysis

History A 50-year-old woman presented with a 6-month history of polyarthralgia involving the left and right hands, wrists, elbows, ankles, and knees. Her pain was not associated with morning stiffness but did worsen over the course of the day. She denied experiencing fevers, chills, or mouth ulcers. She did not report paresthesias or blue discoloration of her fingers when they were exposed to cold. Her family history was remarkable for an aunt who died of systemic lupus erythematosus and for a brother with arthritis. Her medical history was remarkable for vitamin D deficiency, hypertension, and rehabilitation for burns. At clinical examination, she had mild tenderness to palpation of her joints, without associated erythema, swelling, or crepitus. Healed skin grafts were also noted. Blood chemistry tests revealed a rheumatoid factor of 8.5 IU/mL (normal range, 0-13.9 IU/mL), an erythrocyte sedimentation rate of 2 mm/hr (normal range, 0-40 mm/hr), and a C-reactive protein value of 0.4 mg/L (3.8 nmol/L) (normal range, 0-4.9 mg/L [0-46.7 nmol/L]). Antinuclear antibodies test results were negative. Radiography of the right and left hands was performed.

Traumatic Extra-capsular and Intra-capsular Floating Fat: Fat-fluid Levels of the Knee Revisited

Floating fat is a sign of acute bone injury at the knee following trauma. The goal of this article is to review the etiology, patterns, and mimickers of extra-capsular and intra-capsular floating fat, with the major emphasis on knee trauma in the acute setting. We will discuss the spectrum of multimodal imaging findings for rare presentations of extra-capsular floating fat, and contrast these with common and atypical forms of intra-capsular lipohemarthrosis, as an aid to the assessment of acute bone trauma at the knee.

Quantification of shoulder muscle intramuscular fatty infiltration on T1-weighted MRI: a viable alternative to the Goutallier classification system

BackgroundQuantification of rotator cuff intramuscular fatty infiltration is important for clinical decision-making in patients with rotator cuff tear. The semi-quantitative Goutallier classification system is the most commonly used method, but has limited reliability. Therefore, we sought to test a freely available fuzzy C-means segmentation software program for reliability of the quantification of shoulder intramuscular fatty infiltration on T1-weighted MR images and for correlation with fat fraction by six-point Dixon MRI.Materials and methodsWe performed a prospective cross-sectional study to measure visible intramuscular fat area percentage on oblique sagittal T1 MR images by fuzzy C-means segmentation and fat fraction maps by six-point Dixon MRI for 42 shoulder muscles. Intra- and inter-observer reliability were determined. Correlative analysis for fuzzy C-means and six-point Dixon intramuscular fatty infiltration measures was also performed.ResultsWe found that inter-observer reliability for the quantification of visible intramuscular fat area percentage by fuzzy C-means segmentation and fat fraction by six-point Dixon MRI was 0.947 and 0.951 respectively. The intra-observer reliability for the quantification of visible intramuscular fat area percentage by fuzzy C-means segmentation and fat fraction by six-point Dixon MRI was 0.871 and 0.979 respectively. We found a strong correlation between fuzzy C-means segmentation and six-point Dixon techniques; r = 0.850, p < 0.001 by individual muscle; and r = 0.977, p < 0.002 by study subject.ConclusionQuantification of intramuscular fatty infiltration by fuzzy C-means segmentation on T1-weighted sequences demonstrates excellent reliability and strong correlation with fat fraction by six-point Dixon MRI. Quantitative fuzzy C-means segmentation is a viable alternative to the semi-quantitative Goutallier classification system.

Fatty Infiltration Is a Prognostic Marker of Muscle Function After Rotator Cuff Tear

Background: Massive rotator cuff tears (RCTs) begin as primary tendon injuries and cause a myriad of changes in the muscle, including atrophy, fatty infiltration (FI), and fibrosis. However, it is unclear which changes are most closely associated with muscle function. Purpose: To determine if FI of the supraspinatus muscle after acute RCT relates to short-term changes in muscle function. Study Design: Controlled laboratory study. Methods: Unilateral RCTs were induced in female rabbits via tenotomy of the supraspinatus and infraspinatus. Maximal isometric force and rate of fatigue were measured in the supraspinatus in vivo at 6 and 12 weeks after tenotomy. Computed tomography scanning was performed, followed by histologic analysis of myofiber size, FI, and fibrosis. Results: Tenotomy resulted in supraspinatus weakness, reduced myofiber size, FI, and fibrosis, but no differences were evident between 6 and 12 weeks after tenotomy except for increased collagen content at 12 weeks. FI was a predictor of supraspinatus weakness and was strongly correlated to force, even after accounting for muscle cross-sectional area. While muscle atrophy accounted for the loss in force in tenotomized muscles with minimal FI, it did not account for the greater loss in force in tenotomized muscles with the most FI. Collagen content was not strongly correlated with maximal isometric force, even when normalized to muscle size. Conclusion: After RCT, muscle atrophy results in the loss of contractile force from the supraspinatus, but exacerbated weakness is observed with increased FI. Therefore, the level of FI can help predict contractile function of torn rotator cuff muscles. Clinical Relevance: Markers to predict contractile function of RCTs will help determine the appropriate treatment to improve functional recovery after RCTs.

Computed Tomography Artifacts

Artifacts are commonly encountered pitfalls in musculoskeletal computed tomography (CT) which frequently reduce image quality. CT artifacts are manifestations of a divergence between actual attenuation coefficients and measured Hounsfield units of objects on a CT image. Unavoidable CT artifacts emanate from dense objects, while avoidable CT artifacts are outcomes of less than optimal protocol parameters affecting study acquisition and image reconstruction. Although unavoidable, several strategies exist to mitigate CT artifacts associated with metal. Utilizing protocol parameters specific for metal during CT acquisition and reconstruction, using metal artifact reduction software, and scanning with dual energy CT all play a role in improving CT image quality when dense objects are present. Attention to detail for protocol optimization regarding patient-specific factors and CT acquisition and reconstruction are effective techniques to reduce the amount of avoidable CT artifacts.