Imaging orthopedic hardware with an emphasis on hip prostheses

Case report: Total knee arthroplasty polyethylene liner disengagement identified by arthrography

We report a case of total knee arthroplasty polyethylene liner disengagement identified by plain film arthrography and CT arthrography.

Imaging of soft tissues adjacent to orthopedic hardware: comparison of 3-T and 1.5-T MRI

OBJECTIVE

The purpose of this study was to compare metal artifact reduction techniques at 1.5-T and 3-T MRI.

MATERIALS AND METHODS

A titanium plate with steel screws was placed in a freshly harvested pig leg. The leg was imaged with 1.5-T and 3-T MRI. A T2-weighted turbo spin-echo sequence was used with echo-train lengths of 8, 16, 32, and 64 and a constant readout bandwidth of 31.2 kHz. The images were compared qualitatively, and the optimal echo-train length was selected. Images were acquired at the optimal echo-train length with four different readout bandwidths. Artifact was measured quantitatively, and image quality was ranked qualitatively. The qualitatively best image acquired at 1.5 T was compared with the qualitatively highest-ranked image acquired at 3 T.

RESULTS

At both 1.5 T and 3 T, optimal images of equal quality were produced at echo-train lengths of 8 and 16. At higher readout bandwidths, there was quantitatively less artifact. The qualitatively best images were acquired at a readout bandwidth of 31.2 kHz at 1.5 T and 62.5 kHz at 3 T (Cronbach's alpha=1.00). The optimal image at 3 T was qualitatively superior to that at 1.5 T.

CONCLUSION

Optimizing image acquisition parameters in this phantom model resulted in similar quantitative susceptibility artifact at 3 T and 1.5 T and better qualitative images at 3 T than at 1.5 T.

MRI as a problem-solving tool in unexplained failed total hip replacement following conventional assessment

OBJECTIVE

To evaluate MRI as a problem-solving tool for patients with an unexplained failed total hip replacement following conventional radiological assessment.

METHODS AND MATERIALS

Patients' informed consent was obtained in all cases. Institutional review board approval was obtained. Twenty-eight patients with unexplained failed total hip replacements following conventional radiological assessment underwent additional MR imaging with an optimised turbo-spin echo sequence. Images were reviewed by two musculoskeletal radiologists by consensus and compared with findings at surgery, or following response to image-guided intervention or clinical follow-up.

RESULTS

Of the 28 patients, MRI revealed an unsuspected diagnosis explaining the cause of prosthesis failure in 15 patients. In eight of 15 patients in this group, subsequent minimally invasive image-guided intervention obviated the need for revision total hip replacement. No cause for prosthesis failure was identified in 13 patients.

DISCUSSION

MRI may be successfully undertaken in patients following total hip replacement, and, when performed, it frequently leads to an unsuspected diagnosis, allowing informed patient treatment. In this study it allowed the identification of an unsuspected diagnosis in over 50% of cases.

Postoperative imaging of the hip

The number and type of operative procedures involving the hip continue to increase, placing a greater emphasis on characterizing patient postoperative condition accurately. Optimal postoperative imaging evaluation may involve multiple modalities, including conventional radiography, radionuclide scintigraphy, and cross-sectional imaging. Many of the surgical procedures involve the placement of metallic joint replacements or fixation that can make the imaging evaluation of the postoperative anatomy challenging. Clinical examination of patients combined with the type of procedure performed direct the appropriate imaging evaluation; adequate clinical knowledge of these procedures and how to optimally image them provide an opportunity to attain the most accurate evaluation possible.

Orthopedic Hardware Complications Diagnosed with Multi–Detector Row CT

PURPOSE

To retrospectively evaluate multi-detector row computed tomography (CT) for the depiction of orthopedic hardware complications in the spine and appendicular skeleton.

MATERIALS AND METHODS

This HIPAA-compliant study had institutional review board approval; patient informed consent was not required. Results of 114 multi-detector row CT studies performed because of possible hardware complications in 109 patients (57 men, 52 women; mean age, 44 years; age range, 12-82 years) were available for analysis. The CT studies were retrospectively reviewed and compared with clinical or surgical outcomes, which were used as the reference standard. In another experiment, detection of hardware complications on radiographs and multi-detector row CT images was compared between two readers for selected cases (18 positive and 26 negative) by using receiver operating characteristic (ROC) methods.

RESULTS

For 91 (80%) of 114 multi-detector row CT studies, the complication status could be determined on the basis of clinical or surgical outcomes. Twenty-three multi-detector row CT studies were confirmed to be positive (revealing 10 cases of nonunion, five cases of hardware malplacement, three cases of hardware loosening, three perihardware fractures, and two chronic infections), and 57 were confirmed to be negative. There were three false-positive and eight false-negative multi-detector row CT studies. With clinical or surgical outcomes as the reference standard, the sensitivity, specificity, and positive and negative predictive values of multi-detector row CT were 74% (23 of 31 studies), 95% (57 of 60 studies), 88% (23 of 26 studies), and 88% (57 of 65 studies), respectively. Results of ROC analysis indicated that detection of hardware complications was much lower with radiography than with multi-detector row CT (area under ROC curve, 0.84 vs 1.00; F = 4.69, df = 1, 43; P < .05).

CONCLUSION

Multi-detector row CT is an effective tool for depicting orthopedic hardware complications.

Infections Associated with Prosthetic Knee and Prosthetic Hip

Arthroplasty of the knee and hip is a common procedure. There is a risk of infection with primary arthroplasty, with an incidence of 1% to 2%. Significant cost and morbidity are associated with infection of the prosthetic joint. Most infections (60% to 70%) are caused by staphylococci, but approximately 10% are caused by streptococci and/or enterococci, whereas the remainder are caused by gram-negative enteric aerobes or anaerobic flora. Surgical revision is often required for cure because the biofilm that adheres to the infected prosthesis precludes antibiotic therapy from being effective. Biofilm formation occurs consistently as a consequence of host protein deposition on the prostheses, which serve as ligands for bacterial receptors. Once established, biofilm infections require removal of the prosthesis in order to effect a cure. Clinical and radiologic features are not specific for the diagnosis. Culture is specific but not sensitive enough to establish a pathogen in all cases. Surgical approaches are varied and range from debridement with retention of the prostheses to amputation of the limb. The most favored approach is the two-stage delayed reimplantation, in which patients receive specific antibiotic therapy for 6 weeks or more. Several additional antibiotics other than vancomycin are available for methicillin-resistant staphylococcal infection, but these are still unproven in the treatment of osteomyelitis or prosthetic joint infection.

Low-field-strength MR imaging of failed hip arthroplasty: association of femoral periprosthetic signal intensity with radiographic, surgical, and pathologic findings

PURPOSE

To investigate the association between periprosthetic signal intensity at low-field-strength magnetic resonance (MR) imaging after failed hip arthroplasty and radiographic, surgical, and pathologic findings.

MATERIALS AND METHODS

The study group comprised 22 consecutive women who underwent hip arthroplasty (mean age, 62 years; age range, 35-74 years). All patients underwent MR imaging prior to revision surgery. Coronal fast short inversion time inversion-recovery (STIR) images and spin-echo T1-weighted images were obtained with a 0.5-T MR imaging unit before and after administration of contrast material. The periprosthetic region was divided into the seven femoral Gruen zones. Two observers retrospectively analyzed signal intensity patterns. Association of signal intensity patterns with radiographic, surgical, and pathologic findings was determined with chi2 analysis and generalized estimating equations.

RESULTS

Diagnostic-quality images were obtained for 150 zones. Periprosthetic signal intensity was greater than that of bone marrow in the distal femur on the fast STIR images, and no contrast enhancement was seen on the T1-weighted images (type I signal intensity pattern) in 11 zones. Signal intensity was greater than that of bone marrow on the fast STIR images, and contrast enhancement was seen on the T1-weighted images (type II signal intensity pattern) in 45 zones. Signal intensity was less than or equal to that of bone marrow on the fast STIR images, and no contrast enhancement was seen on the T1-weighted images (type III signal intensity pattern) in 94 zones. Type I and II patterns were associated with focal or nonfocal lucency, an unstable stem, and fibrosis or granuloma. A type III pattern was associated with a normal radiographic appearance, a stable stem, and normal bone tissue. Significant association was demonstrated between periprosthetic signal intensity and radiographic (P <.001, chi2 test and generalized estimating equations), surgical (P <.05, Mantel-Haenszel chi2 test and generalized estimating equations), and pathologic findings (P <.05, chi2 test).

CONCLUSION

Low-field-strength MR imaging depicted periprosthetic tissue signal intensity that was significantly associated with radiographic, surgical, and pathologic findings.

MR imaging of sports-related hip disorders

Hip arthroscopy is being used increasingly for the diagnosis and treatment of hip disorders. MR imaging performed with appropriate technical considerations may aid not only in preoperative planning but in the appropriate selection of patients, which tends to lead to better postoperative results. Although the painful hip is imaged most commonly by radiography, MR imaging is considered the next imaging test of choice for evaluation of most common hip abnormalities in athletes, including labral injuries, ligament injuries, osteochondral injuries, fractures, bursitis, and musculotendinous injuries. MR arthrography can be a particularly useful technique for dedicated assessment of hip joint internal derangements.

Prosthetic joint infections: bane of orthopedists, challenge for infectious disease specialists

Prosthetic joint infections (PJIs) occur in approximately 1.5%-2.5% of all primary hip or knee arthroplasties. The mortality rate attributed to PJIs may be as high as 2.5%. Substantial morbidity is associated with a loss of mobility, although this is temporary. The costs associated with a single episode of PJI are approximately $50,000 per episode, exclusive of lost wages. Risk factors that increase the occurrence of PJI include revision arthroplasty, time in the operating room, postoperative surgical site infection, and malignancy. Pain is the most consistent symptom. Staphylococcus species are the most common organisms isolated from PJI sites. Two-stage revision is superior to single-stage revision or to debridement with prosthesis retention. Long-term antibiotic suppression and/or arthrodesis are useful for patients too frail to undergo extensive surgery. Using an optimal approach, recurrent infection occurs in <10% of previously infected joints.