Sonography of polyethylene liners used in total knee arthroplasty

ACR Appropriateness Criteria® Imaging After Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the most commonly performed joint replacement procedure in the United States and annual demand for primary TKA is expected to grow by 673% by 2030. The first part provides an overview of imaging modalities (radiographs, CT, MRI, ultrasound, and various nuclear medicine studies) and discusses their usefulness in the imaging evaluation of TKA. The second part focuses on evidence-based imaging and imaging-guided intervention algorithms for the workup of TKA and its complications, including routine follow-up, component wear, periprosthetic infection, aseptic loosening, granulomas/osteolysis, conventional and rotational instability, periprosthetic fracture, patellar complications, and a variety of periprosthetic soft tissue abnormalities. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

The measurement of medial knee gap width using ultrasound

INTRODUCTION

Medial knee instability is a key clinical parameter for assessing ligament injury and arthroplasty success, but current methods for measuring stability are typically either qualitative or involve ionizing radiation. The purpose of this study was to perform a preliminary analysis of whether ultrasound (US) could be used as an alternate approach for quantifying medial instability by comparing an US method with an approach mimicking the current gold standard fluoroscopy method.

MATERIALS AND METHODS

US data from the medial knee were collected, while cadaveric lower limbs (n = 8) were loaded in valgus (10 Nm). During post-processing, the US gap width was measured by identifying the medial edges of the femur and tibia and computing the gap width between these points. For comparison, mimicked fluoroscopy (mFluoro) images were created from specimen-specific bone models, developed from segmented CT scans, and from kinematic data collected during testing. Then, gap width was measured in the mFluoro images based on two different published approaches with gap width measured either at the most medial or at the most distal aspect of the femur.

RESULTS

Gap width increased significantly with loading (p < 0.001), and there were no significant differences between the US method (unloaded: 8.7 ± 2.4 mm, loaded: 10.7 ± 2.2 mm) and the mFluoro method that measured gap width at the medial femur. In terms of the change in gap width with load, no correlation with the change in abduction angle was observed, with no correlation between the various methods. Inter-rater reliability for the US method was high (0.899-0.952).

CONCLUSIONS

Ultrasound shows promise as a suitable alternative for quantifying medial instability without radiation exposure. However, the outstanding limitations of existing approaches and lack of true ground-truth data require that further validation work is necessary to better understand the clinical viability of an US approach for measuring medial knee gap width.

MRI of Polyethylene Tibial Inserts in Total Knee Arthroplasty: Normal and Abnormal Appearances

OBJECTIVE

The purpose of this study was to describe the normal and abnormal MRI appearances of polyethylene tibial inserts. Subjects who underwent MRI before revision total knee arthroplasty were identified. The polyethylene tibial insert's shape was categorized on MRI, and the presence of abnormalities was noted.

CONCLUSION

The shape of the polyethylene tibial insert varied with the design. Polyethylene tibial insert abnormalities seen on MRI included displacement and fracture. MRI distinguishes various designs of polyethylene tibial inserts and can show associated abnormalities.

The tram track sign: a characteristic sonographic feature of polyethylene liner dissociation after total-hip arthroplasty

OBJECTIVES

Polyethylene liner dissociation from an acetabular component is a complication of total-hip arthroplasty (THA) caused by slippage of the liner, which causes pain and requires a revision. The aim of this study was to evaluate sonographic features of liner dissociation and detect useful sonographic findings compared to conventional radiography and computed tomography (CT).

METHODS

Among a total of 226 patients who underwent revision THA at our institution between September 2008 and June 2012, 10 patients (6 male and 4 female; mean age, 56.2 years) who showed severe narrowing of the superior joint space on the THA side and underwent sonography were retrospectively reviewed by evaluating radiographic, CT, and sonographic findings. In evaluation of the images, we put more emphasis on the "radiographic crescent sign," "CT crescent sign," and "sonographic tram track sign."

RESULTS

At surgery, 7 patients showed liner dissociation, and 3 showed severe liner wear. On radiography, 8 of 10 patients (80%) had a correct diagnosis of the presence or absence of liner dissociation; on sonography, all 10 patients (100%) had a correct diagnosis. The sensitivity, specificity, and accuracy for diagnosis of liner dissociation by pelvic radiography and sonography were 100% (7 of 7), 33% (1 of 3), and 80% (8 of 10) and 100% (7 of 7), 100% (3 of 3), and 100% (10 of 10), respectively.

CONCLUSIONS

Liner dissociation can be easily and well visualized by sonography, especially compared to pelvic radiography and CT. The sonographic tram track sign should be a very useful feature in the early diagnosis of liner dissociation.

Dynamic ultrasonography: a cadaveric model for evaluating aseptic loosening of total ankle arthroplasty

Aseptic loosening is the primary method of failure in total ankle replacements. Currently, loosening is defined by morphologic changes in osseous architecture determined by plain radiography. The loss of bone noted at diagnosis presents difficulties in future ankle revisions. A method by which early aseptic loosening could be detected before bony deformation or reaction could lead to improved patient outcomes. A cadaveric fresh frozen ankle specimen (mid-tibia to include the foot) was used in the present study. An anterior approach to the ankle was performed. A total ankle prosthesis was implanted in the standard fashion (Salto Talaris, Tornier). The initial cuts were made for a size 1 ankle, and a size 1 ankle was implanted. Dynamic ultrasonography was used to evaluate the bone-implant interface. The prosthesis was removed, and sequential removal of bone was performed at the interface of the medial tibial tray until visible motion was seen with flexion and extension. The reimplanted prosthesis was then re-evaluated using dynamic ultrasonography and dynamic and static fluoroscopy. In the loose prosthesis model, dynamic ultrasonography was able to determine the motion at the bone-prosthesis interface. Dynamic ultrasonography might be a useful tool in the evaluation of early loosening in a total ankle arthroplasty model.

The radiological assessment of total and unicompartmental knee replacements

Radiological assessment of total and unicompartmental knee replacement remains an essential part of routine care and follow-up. Appreciation of the various measurements that can be identified radiologically is important. It is likely that routine plain radiographs will continue to be used, although there has been a trend towards using newer technologies such as CT, especially in a failing knee, where it provides more detailed information, albeit with a higher radiation exposure. The purpose of this paper is to outline the radiological parameters used to evaluate knee replacements, describe how these are measured or classified, and review the current literature to determine their efficacy where possible.

Snapping knee: imaging findings with an emphasis on dynamic sonography

OBJECTIVE

The purpose of this article is to illustrate the causes of snapping knee. The value of imaging techniques is discussed with an emphasis on dynamic sonography in light of the available surgical and radiologic literature.

CONCLUSION

Because of its dynamic capabilities, dynamic sonography provides real-time visualization of snapping knee syndrome and may be used as a first-line modality.

PAIN FOLLOWING TOTAL KNEE ARTHROPLASTY - A SYSTEMATIC APPROACH

Total knee arthroplasty (TKA) is known to be a successful procedure. The aging of the population and the growing demand for quality of life have greatly increased the indications for the procedure. Nonetheless, TKA presents some complications that still lack definitive resolution. Pain after TKA is caused by a myriad of reasons that need to be systematically studied in order to reach the correct diagnosis and treatment. History, physical examination, laboratory tests and imaging examinations must all be included in the workup and repeated until a plausible reason has been identified, since if pain is the only indication for TKA revision, the results may be catastrophic.

Radiographic assessment of the thickness lost from polyethylene tibial inserts that had been sterilized differently

BACKGROUND

Archived serial radiographs of knee replacements provide indirect evidence of the clinical performance of ultra-high molecular weight polyethylene tibial bearings. Our purpose was to determine the loss of thickness in polyethylene tibial inserts that were of the same design but had been sterilized differently.

METHODS

Four hundred and sixteen knees with an Anatomic Modular Knee primary total knee replacement had five to eighteen years of follow-up and a posterior cruciate ligament-retaining polyethylene tibial insert that had been sterilized with either gamma radiation in air (from 1987 to 1993) or gamma radiation in an inert gas (from 1993 to 1995), or by means of a nonirradiation gas-plasma method (from 1995 to 2001). Readings were taken from 1975 weight-bearing anteroposterior radiographs of the knee on which the top surface of the metal tibial tray had nearly projected as a line. In each tibiofemoral compartment, loss of polyethylene thickness was calculated as the standard thickness of the insert minus the measured magnification-corrected thickness. For each sterilization method, thickness loss was plotted versus the corresponding follow-up time, and a mixed linear regression model was used to quantify the change in thickness over time. Multiple linear regression analysis was used to determine whether loss of thickness was associated with implant factors, patient variables, and early postoperative limb alignment.

RESULTS

According to the mixed model regression coefficients, loss of medial compartment thickness was greatest for inserts that had been sterilized with gamma radiation in air (0.15 mm/yr), least for those sterilized with gamma radiation in an inert gas (0.02 mm/yr), and of an intermediate magnitude for those sterilized with a nonirradiation method (0.06 mm/year); loss of lateral compartment thickness ranged from 0.03 to 0.06 mm/yr. Notably, no insert irradiated in an inert gas showed a loss of thickness of >1 mm, and no nonirradiated insert showed a loss of >2 mm. Loss of medial compartment thickness in inserts sterilized with radiation in air increased significantly with a greater polyethylene shelf age, lesser patient age, and more varus alignment of the limb in the early postoperative period (p < 0.01).

CONCLUSIONS

In this total knee design, tibial polyethylene performance improved markedly after discontinuation of the gamma radiation in air sterilization technique. Future concerns are that bearings sterilized with radiation in an inert gas may oxidize in vivo and develop fatigue wear because of free radicals generated during sterilization with radiation and that nonirradiated bearings may undergo greater losses in thickness from routine burnishing since they lack the cross-linking that accompanies sterilization with radiation.

Current applications of advanced cross-sectional imaging techniques in evaluating the painful arthroplasty

Patients with a painful arthroplasty can present a clinical diagnostic dilemma. Aspirates are often negative for infection and alignment of the prosthesis on conventional radiographs is usually satisfactory. These patients can have a myriad of soft tissue as well as osseous pathologies, which may be clinically unsuspected or radiographically occult. The ability of advanced cross-sectional imaging to diagnose osseous and soft tissue injuries has been well documented, but applications to arthroplasty imaging are often limited by regional metallic artifacts. Adjustment of standard imaging parameters can make CT and MR imaging useful adjuncts in imaging the painful arthroplasty, especially in the setting of normal radiographs. Ultrasound can be used to evaluate the periprosthetic soft tissues and provide a real-time method of evaluating the dynamic relationship of the periprosthetic soft tissues to the arthroplasty components, and it also can be used as a guide for diagnostic and therapeutic interventions.

Optimizing Techniques for Musculoskeletal Imaging of the Postoperative Patient

Knowledge of imaging principles and parameter modifications of advanced imaging techniques--nuclear medicine, ultrasound, CT, and MR--aid musculoskeletal radiologists in selecting the appropriate examination for clinical questions; tailoring imaging parameters results in better image quality, thus more confident diagnoses. CT can evaluate for subtle fractures often better than conventional radiographs. Adjusting the area of interest, increasing the peak kilovoltage (kVp), and viewing images with postprocessing software allow better CT image quality. Proper modification of MR imaging parameters also provides useful information including visualizing the extent of osteolysis better than conventional radiographs. Fast spin echo imaging should be used, gradient echo avoided, and fast inversion recovery used instead of frequency-selective fat suppression.

Postoperative Imaging of the Knee

The knee is a frequently injured joint and, thus, a common focus of operative intervention. As operative techniques and imaging modalities evolve, radiologists must be aware of the expected postoperative appearance after knee surgeries that are performed commonly and also must be comfortable recognizing complications encountered commonly in the immediate and delayed postoperative period. Drawing on the large amount of attention this subject has received of late in the radiologic and orthopedic literature, this article reviews the knee surgeries performed most commonly and the expected normal and most frequently encountered abnormal postoperative imaging findings with an emphasis on MR imaging.

Musculoskeletal imaging update: current applications of advanced imaging techniques to evaluate the early and long-term complications of patients with orthopedic implants

Technical advances in imaging have increased their applicability to diagnosing conditions of the musculoskeletal system, especially in the postoperative setting, where traditionally metallic artifacts have hindered evaluation. Advances in computed tomography (CT), magnetic resonance (MR) imaging, ultrasound, and nuclear medicine have resulted in improved overall image quality. Specific modifications of imaging parameters, especially in CT and MRI, have improved the radiologist's ability to diagnose potential hardware complications such as loosening and osteolysis. Sonography can evaluate the periprosthetic soft tissues and enables both diagnostic information and therapeutic treatment at the same sitting. Lastly, diagnostic scintigraphic applications such as positron emission tomography (PET) have increased specificity in diagnosing potential infection in the arthroplasty setting. This review discusses some of the current applications of CT, MRI, ultrasound, and nuclear medicine in evaluating the postoperative orthopedic patient, concentrating on the appropriate imaging evaluation for the painful arthroplasty patient.

Imaging of knee arthroplasty

Knee replacement surgery, either with unicompartmental or total systems, is common. The purpose of this manuscript is to review the appearance of normal knee arthroplasty and the appearances of complications such as infection, polyethylene wear, aseptic loosening and particle-induced osteolysis, patellofemoral abnormalities, axial instability, and periprosthetic and component fracture. Knowledge of the potential complications and their imaging appearances will help the radiologist in the diagnostic evaluation of the patient with a painful knee arthroplasty.