Focal osteolysis in total hip replacement: CT findings

Femoral defects in revision hip arthroplasty: a therapy-oriented classification

INTRODUCTION

The complex field of femoral defects in revision hip arthroplasty displays a lack of standardized, intuitive pre- and intraoperative assessment. To address this issue, the femoral defect classification (FDC) is introduced to offer a reliable, reproducible and an intuitive classification system with a clear therapeutic guideline.

MATERIALS AND METHODS

The FDC is based on the integrity of the main femoral segments which determine function and structural support. It focuses on the femoral neck, the metaphysis consisting of the greater and lesser trochanter, and the femoral diaphysis. The four main categories determine the location of the defect while subcategories a, b and c are being used to classify the extent of damage in each location. In total, 218 preoperative radiographs were retrospectively graded according to FDC and compared to intraoperatively encountered bone defects. To account for inter-rater and intra-rater agreement, 5 different observers evaluated 80 randomized cases at different points in time.

RESULTS

A Cohens kappa of 0.832 ± 0.028 could be evaluated, accounting for excellent agreement between preoperative radiographs and intraoperative findings. To account for inter-rater reliability, 80 patients have been evaluated by 5 different observers. Testing for inter-rater reliability, a Fleiss Kappa of 0.688 could be evaluated falling into the good agreement range. When testing for intra-rater reliability, Cohens Kappa of each of the 5 raters has been analyzed and the mean was evaluated at 0.856 accounting for excellent agreement.

CONCLUSION

The FDC is a reliable and reproducible classification system. It combines intuitive use and structured design and allows for consistent preoperative planning and intraoperative guidance. A therapeutic algorithm has been created according to current literature and expert opinion. Due to the combination of the FDC with the recently introduced Acetabular Defect Classification (ADC) a structured approach to the entire field of hip revision arthroplasty is now available.

Value of multidetector computed tomography for the differentiation of delayed aseptic and septic complications after total hip arthroplasty

OBJECTIVE

The differentiation between delayed aseptic and septic complications of total hip arthroplasty is crucial to allow appropriate surgical planning and timely antimicrobial treatment. The aim of this study was to investigate the utility of multidetector computed tomography (CT) findings to diagnose aseptic mechanical loosening, granulomatous reaction, and periprosthetic joint infection in patients who underwent total hip arthroplasty before revision surgery.

MATERIALS AND METHODS

Ninety-six consecutive patients with a clinical suspicion of periprosthetic complications underwent revision surgery over an 8-year period. All patients had been evaluated preoperatively using multidetector CT without contrast media. Two blinded musculoskeletal radiologists reviewed multidetector CT images, including periprosthetic soft-tissue accumulation, prosthetic acetabular malposition, periprosthetic osteolysis, enlarged iliac lymph nodes, and heterotopic ossification. Risk factors for aseptic and septic loosening were identified using multivariate analysis.

RESULTS

Multidetector CT-related variables independently associated with periprosthetic joint infection were high periprosthetic soft-tissue accumulation, periprosthetic osteolysis without expansile periosteal reaction and enlarged iliac lymph nodes. On the other hand, the absence of the following radiological signs: low or high periprosthetic soft-tissue accumulation, mild or severe periprosthetic osteolysis, and enlarged iliac lymph nodes, were predictors of aseptic mechanical loosening. Low periprosthetic soft-tissue accumulation, severe periprosthetic osteolysis with expansile periosteal reaction, and mild acetabular malposition were significant variables associated with granulomatosis.

CONCLUSION

Multidetector CT findings are useful to differentiate between aseptic and septic complications before revision surgery. The presence of osteolysis with expansile periosteal reaction appeared to be a time-dependent variable.

An exploratory study into measuring the cortical bone thickness from CT in the presence of metal implants

PURPOSE

The aim of this study was to develop and evaluate a method for measuring the cortical bone thickness from computed tomography (CT) scans with metallic implants and to assess the benefits of metal artefact removal software.

METHODS

A previously validated technique based on the fitting of a cortical model was modified to also model metal structures when required. Cortical thickness measurements were taken over intact bone segments and compared with the corresponding contralateral bone segment. The evaluation dataset includes post-operative CT scans of a unipolar hemi-arthroplasty, a dynamic hip screw fixation, a bipolar hemi-arthroplasty, a fixation with cannulated screws and a total hip arthroplasty. All CT scans were analysed before and after processing with metal artefact removal software.

RESULTS

Cortical thickness validity and accuracy were improved through the use of a modified metalwork-optimised model and metal artefact removal software. For the proximal femoral segments of the aforementioned cases, the cortical thickness was measured with a mean absolute error of 0.55, 0.39, 0.46, 0.53 and 0.69 mm. The hemi-pelvis produced thickness errors of 0.51, 0.52, 0.52, 0.47 and 0.67 mm, respectively.

CONCLUSIONS

The proposed method was shown to measure cortical bone thickness in the presence of metalwork at a sub-millimetre accuracy. This new technique might be helpful in assessing fracture healing near implants or fixation devices, and improve the evaluation of periprosthetic bone after hip replacement surgery.

Management of severe femoral bone loss in revision total hip arthroplasty

Femoral bone loss is a complex problem in revision total hip arthroplasty. The Paprosky classification is used when determining the degree and location of bone loss. Meticulous operative planning is essential where severe bone loss is a concern. One must correctly identify the bone loss pattern, safely remove the existing components, and proceed with the proper reconstruction technique based on the pattern of bone loss. This article discusses the etiology and classification of bone loss, clinical and radiographic evaluation, components of effective preoperative planning, and clinical results of various treatment options with a focus on more severe bone loss patterns.

Cross-sectional imaging of metal-on-metal hip arthroplasties. Can we substitute MARS MRI with CT?

BACKGROUND AND PURPOSE

Metal artifact reduction sequence (MARS) MRI is widely advocated for surveillance of metal-on-metal hip arthroplasties (MOM-HAs). However, its use is limited by susceptibility artifact at the prosthesis-bone interface, local availability, patient compliance, and cost (Hayter et al. 2011a). We wanted to determine whether CT is a suitable substitute for MARS MRI in evaluation of the painful MOM-HA.

PATIENTS AND METHODS

50 MOM-HA patients (30 female) with unexplained painful prostheses underwent MARS MRI and CT imaging. 2 observers who were blind regarding the clinical data objectively reported the following outcomes: soft tissue lesions (pseudotumors), muscle atrophy, and acetabular and femoral osteolysis. Diagnostic test characteristics were calculated.

RESULTS

Pseudotumor was diagnosed in 25 of 50 hips by MARS MRI and in 11 of 50 by CT. Pseudotumors were classified as type 1 (n=2), type 2A (n=17), type 2B (n=4), and type 3 (n=2) by MARS MRI. CT did not permit pseudotumor classification. The sensitivity of CT for diagnosis of pseudotumor was 44% (95% CI: 25-65). CT had "slight" agreement with MARS MRI for quantification of muscle atrophy (κ=0.23, CI: 0.16-0.29; p<0.01). Osteolysis was identified in 15 of 50 patients by CT. 4 of these lesions were identified by MARS MRI.

INTERPRETATION

CT was found to be superior to MRI for detection of osteolysis adjacent to MOM-HA, and should be incorporated into diagnostic algorithms. CT was unable to classify and failed to detect many pseudotumors, and it was unreliable for assessment of muscle atrophy. Where MARS MRI is contraindicated or unavailable, CT would be an unsuitable substitute and other modalities such as ultrasound should be considered.

Risk factors for periacetabular osteolysis and wear in asymptomatic patients with uncemented total hip arthroplasties

Osteolysis is a silent disease leading to aseptic loosening. This has not been studied in a cohort of asymptomatic patients. The aim of this study was to detect factors that might be associated with the development of periacetabular osteolysis and wear around an uncemented cup. We assessed 206 patients with an uncemented cup, measuring wear and periacetabular osteolysis using computed tomography with a median follow-up of 10 years after surgery (range 7–14 years). EQ5D, pain from the hip, and satisfaction were assessed. The association between periacetabular osteolysis and wear, age, gender, activity, BMI, cup type, cup age, positioning of the cup, and surface coating was investigated with a proportional odds model. Wear and male gender were associated with an increased risk for periacetabular osteolysis. There was no association with periacetabular osteolysis for time from operation, patient age, UCLA Activity Score, liner thickness at time of operation, BMI, cup positioning, and type of implant. A thin liner at time of operation is correlated to increased wear. Linear wear rate was 0.18 mm/year and 46 of 206 patients had large periacetabular osteolysis. Asymptomatic patients with these implants should be followed up on a regular basis with a sensitive method such as CT in order to detect complications early.

Percutaneous bone cement refixation of aseptically loose hip prostheses: the effect of interface tissue removal on injected cement volumes

OBJECTIVE

To quantify whether injected cement volumes differed between two groups of patients who underwent experimental minimally invasive percutaneous cement injection procedures to stabilize aseptically loose hip prostheses. One patient group was preoperatively treated using gene-directed enzyme prodrug therapy to remove fibrous interface tissue, while the other group received no preoperative treatment. It was hypothesized that cement penetration may have been inhibited by the presence of fibrous interface tissue in periprosthetic lesions.

MATERIALS AND METHODS

We analyzed 17 patients (14 female, 3 male, ages 72-91, ASA categories 2-4) who were treated at our institution. Osteolytic lesions and injected cement were manually delineated using 3D CT image segmentation, and the deposition of injected cement was quantified.

RESULTS

Patients who underwent preoperative gene-directed enzyme therapy to remove fibrous tissue exhibited larger injected cement volumes than those who did not. The observed median increase in injected cement volume was 6.8 ml. Higher cement leakage volumes were also observed for this group.

CONCLUSION

We conclude that prior removal of periprosthetic fibrous interface tissue may enable better cement flow and penetration. This might lead to better refixation of aseptically loosened prostheses.

Altered load transfer in the pelvis in the presence of periprosthetic osteolysis

Periprosthetic osteolysis in the retroacetabular region with cancellous bone loss is a recognized phenomenon in the long-term follow-up of total hip replacement. The effects on load transfer in the presence of defects are less well known. A validated, patient-specific, 3D finite element (FE) model of the pelvis was used to assess changes in load transfer associated with periprosthetic osteolysis adjacent to a cementless total hip arthroplasty (THA) component. The presence of a cancellous defect significantly increased (p &lt; 0.05) von Mises stress in the cortical bone of the pelvis during walking and a fall onto the side. At loads consistent with single leg stance, this was still less than the predicted yield stress for cortical bone. During higher loads associated with a fall onto the side, highest stress concentrations occurred in the superior and inferior pubic rami and in the anterior column of the acetabulum with larger cancellous defects.

Does computed tomography add information on radiographic analysis in detecting periprosthetic osteolysis after total ankle arthroplasty?

BACKGROUND

The major longer term complications of ankle arthroplasty are periprosthetic osteolysis and aseptic loosening. Follow-up studies of total hip arthroplasties show that measurements of periprosthetic osteolytic lesions on radiographs underestimate the size compared with those made on computed tomography (CT), and some of the lesions may even remain undetected on radiographs. However, it is unclear whether the same applies to total ankle arthroplasty (TAA).

METHODS

We retrospectively reviewed the radiographs of 123 patients who had undergone TAA with the Ankle Evolutive System (AES) implant. Of these, 43 (34.9%) had at least 1 large (greater than 10 mm) osteolytic lesion on radiographs at a minimum follow-up of 14 months (mean, 43.1 months; range, 14-85 months). Forty of the 43 patients underwent helical CT imaging.

RESULTS

Computed tomography showed more osteolytic lesions than radiographs around both tibial and talar components. CT also showed larger lesions than radiographs in 9 of 10 zones around prosthetic components. The difference was highly significant in 3 zones around the talar component.

CONCLUSION

Computed tomography showed more and larger periprosthetic lesions than radiographs around an ankle prosthesis. Because osteolysis is progressive in nature, it presumably leads to component failure. Considering our results, we recommend adding CT imaging to postoperative follow-up after TAA for patients with suspected or known periprosthetic lucencies on radiographs.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Metal-on-metal bearings: the evidence so far

Lately, concerns have arisen following the use of large metal-on-metal bearings in hip replacements owing to reports of catastrophic soft-tissue reactions resulting in implant failure and associated complications. This review examines the literature and contemporary presentations on current clinical dilemmas in metal-on-metal hip replacement.

Various tumor-mimicking lesions in the musculoskeletal system: causes and diagnostic approach

Tumor-mimicking lesions in the musculoskeletal system can be defined as lesions mistaken as tumors due to the presence of palpation upon physical examination or a tumor-like appearance upon radiological examination. Moreover, tumor-mimicking lesions show diverse etiologies and anatomic locations. We illustrated the various tumor-mimicking lesions involving bone and soft tissue. In this review, the tumor-mimicking lesions were classified into those based on clinical examination and those based on radiological examination in musculoskeletal radiology. Awareness of the various causes of tumor-mimicking lesions, correctly obtaining clinical information, and the proper selection of imaging modality are important for the differentiation of tumor-mimicking lesions from true neoplasms.

The natural history of metallosis from catastrophic failure of a polyethylene liner in a total hip

We report on a case of metallosis initially presumed to be heterotopic ossification based on radiologic findings. A 68-year-old man with a total hip arthroplasty experienced failure of the polyethylene liner, resulting in articulation of the ceramic head with the titanium acetabular shell. During revision surgery, extensive metallic debris was evident macroscopically throughout the periprosthetic tissue and was confirmed histologically to be metallosis.

Algorithmic approach for reconstruction of proximal femoral bone loss in revision total hip arthroplasty

Reconstruction of the femur depends on the quantity of bone loss and the quality of the remaining bone stock. Multiple classifications and reporting systems can be used to characterize the bone defect. We present a simple algorithmic approach for proximal femoral bone loss reconstruction during revision total hip arthroplasty. Quantity of bone loss is assessed using radiographs based on different classification systems, whereas quality of the remaining bone stock is assessed intraoperatively. Based on the type of proximal bone loss and the quality of the available bone, we describe our preferred reconstruction technique. For minor bone loss, the metaphysis is expanded but intact with partially absent calcar. There is minimal bone loss anteriorly and posteriorly, and the diaphysis is intact. For significant bone loss, the metaphysis is compromised, and there is no calcar. There is minimal bone loss anteriorly and posteriorly. The available proximal bone may be thin, sclerotic, and incapable of support. However, the diaphysis is intact. For massive bone loss, there is complete circumferential bone loss in the metaphysis, extending to the diaphysis. The anterolateral bone and supporting subtrochanteric metaphyseal bone are absent. The metaphysis is not stable and will not offer rotational stability. There is massive bone loss anteriorly and posteriorly. The stability of the implant is dependent on distal diaphyseal fixation. For complete proximal bone loss, there is extensive circumferential segmental bone loss proximally and extensive cavitary loss involving the entire diaphysis. Additionally, there is extensive ectasia of the diaphysis.

Computed tomography assessment of pelvic osteolysis and cup-lesion interface involvement with a press-fit porous-coated acetabular cup

We used computed tomography to investigate the 3-dimensional pattern of expansile osteolysis that occurs with a modular cementless acetabular component incorporating a central hole. We measured pelvic osteolysis volume and evaluated how much of the porous-coated surface area was involved with osteolytic defects. Among the 34 total hip arthroplasties we studied, osteolysis almost always originated from the dome hole and typically expanded inferiorly or superiorly without involving the anterior or posterior surfaces of the cup. Larger-volume lesions generally involved greater amounts of the cup surface area, but the cup-lesion interface involvement plateaued at 40% for radiographically stable cups without clinical complications. We hypothesize that the plateauing surface area involvement may explain the absence of cup loosening among these cases despite the presence of large osteolytic lesions.

Particle-induced osteolysis in three-dimensional micro-computed tomography

Small-animal models are useful for the in vivo study of particle-induced osteolysis, the most frequent cause of aseptic loosening after total joint replacement. Microstructural changes associated with particle-induced osteolysis have been extensively explored using two-dimensional (2D) techniques. However, relatively little is known regarding the 3D dynamic microstructure of particle-induced osteolysis. Therefore, we tested micro-computed tomography (micro-CT) as a novel tool for 3D analysis of wear debris-mediated osteolysis in a small-animal model of particle-induced osteolysis. The murine calvarial model based on polyethylene particles was utilized in 14 C57BL/J6 mice randomly divided into two groups. Group 1 received sham surgery, and group 2 was treated with polyethylene particles. We performed 3D micro-CT analysis and histological assessment. Various bone morphometric parameters were assessed. Regression was used to examine the relation between the results achieved by the two methods. Micro-CT analysis provides a fully automated means to quantify bone destruction in a mouse model of particle-induced osteolysis. This method revealed that the osteolytic lesions in calvaria in the experimental group were affected irregularly compared to the rather even distribution of osteolysis in the control group. This is an observation which would have been missed if histomorphometric analysis only had been performed, leading to false assessment of the actual situation. These irregularities seen by micro-CT analysis provide new insight into individual bone changes which might otherwise be overlooked by histological analysis and can be used as baseline information on which future studies can be designed.

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.