The pathology of total joint arthroplasty.II. Mechanisms of implant failure

Although the clinical results of total joint arthroplasty are usually excellent, some implants develop loosening and require revision. Implants usually fail by a combination of mechanisms, but different basic designs tend to show different dominant mechanisms of failure. Infection causes failure of about 1-5% of cases of primary arthroplasty. Clues to the presence of infection include clinical signs, a periosteal reaction, a positive culture of aspirated joint fluid, and acute inflammation identified in tissue around the implant. There are several different mechanisms and modes of implant wear, and perhaps the most important cause of aseptic loosening is an inflammatory reaction to particles of wear debris. Abrasive, adhesive, and fatigue wear of polyethylene, metal and bone cement produces debris particles that induce bone resorption and implant loosening. Particles can cause linear, geographic, or erosive patterns of bone resorption (osteolysis), the distributions of which are influenced by the implant design. Micromotion of implants that did not achieve adequate initial fixation is another important mechanism of loosening. Fatigue failure at the bone/cement and bone/implant interface may cause aseptic loosening, and may be especially important for implants with relatively smooth surfaces. Stress shielding can influence local bone density, but is rarely an isolated cause of implant loosening. Elevated hydrodynamic pressure has been associated with bone resorption in the absence of implants, and may also play a role in implant loosening.

The pathology of total joint arthroplasty. I. Mechanisms of implant fixation

The clinical results of total joint arthroplasty are usually excellent, but surgeons, radiologists, and pathologists are often called upon to evaluate, in one way or another, the stability of the implants. These evaluations are aided by an understanding of the basic pathophysiology of total joint arthroplasty. The first part of this two-part review, will summarize the mechanisms whereby total joint implants achieve fixation. The second part will describe and illustrate the most important mechanisms of implant loosening. The "gold standard" for hip and knee arthroplasty is to use polymethylmethacrylate bone cement to anchor the implant to bone, but the optimal surface texture of cemented implants is controversial. Some surgeons advocate a rough implant texture to facilitate bonding between implant and cement; other surgeons prefer a smooth, polished implant to minimize abrasion of cement. Implant loosening can be initiated by particles of cement generated at either the implant/cement, or cement/bone interface. Uncemented implants with porous metal surfaces achieve a variable amount of bone ingrowth, but some designs have excellent clinical results. Maximal bone ingrowth usually occurs along surfaces that are relatively close to cortical bone. Implants with bioactive coatings, such as hydroxyapatite achieve rapid bone apposition. The amount of bone that persists on uncemented implants long-term is determined by many variables, inlcuding the quality of the coating, the overall implant design, and factors that influence local bone remodeling.

MR imaging of spinal infections

In the appropriate clinical situation, MR imaging is a powerful tool in the diagnosis of spinal infection. Imaging of spinal infections requires the use of a combination of T1-weighted and T2-weighted or STIR sequences. Contrast enhancement is useful and helps to define paraspinal and epidural disease. Knowledge of potential pitfalls with MR imaging and of normal marrow conversion is required. With these points in mind, MR imaging will be beneficial in the care of patients with spinal infections.

Imaging modalities for study of the distal ulnar region

Judicious use of diagnostic imaging maximizes the diagnostic capabilities of the surgeon treating the distal radio-ulnar joint (DRUJ). A good clinical history and clinical examination are necessary to direct the selection of appropriate imaging studies. Plain radiographs are almost always the first imaging examination. More advanced imaging techniques are costly and may provide only limited information. This article discusses imaging modalities useful for assessment of the DRUJ and the area around it.

Acute calcific tendinitis of the hip: case report with magnetic resonance imaging findings

The clinical presentation of acute calcific tendinitis can be quite dramatic. This report describes a patient with this entity who had calcification in an unusual area, accompanied by abnormalities seen on radiography and magnetic resonance imaging. Clinical aspects of acute calcific tendinitis are also reviewed. With recognition of this entity, treatment can be initiated promptly, with dramatic resolution.

MR imaging of vertebral osteomyelitis revisited

OBJECTIVE

The purpose of this study was to reevaluate previously reported MR imaging findings for vertebral osteomyelitis that include decreased signal intensity in the disk and adjacent vertebral bodies on T1-weighted images, increased signal intensity in the disk and adjacent vertebral bodies on T2-weighted images, loss of endplate definition on T1-weighted images, and contrast enhancement of the disk, adjacent vertebral bodies, and involved paraspinal and epidural soft tissues.

MATERIALS AND METHODS

Medical records, radiographs, and MR scans of 37 patients with vertebral osteomyelitis with 41 levels of involvement were reviewed for agreement with reported MR imaging findings.

RESULTS

Ninety-five percent of the levels (39/41) showed decreased vertebral body signal intensity on T1-weighted images; 95% (39/41) had loss of endplate definition; 95% (37/39) had increased disk signal intensity on T2-weighted images; and 56% (22/39) had increased vertebral body signal intensity on T2-weighted images. Eighty-five percent of the levels (35/41) and 84% of patients (31/37) had both signal intensity changes of the vertebral body on T1-weighted images and signal intensity changes of the disk on T1-and T2-weighted images. Only 46% of the levels (19/41) and 49% of patients (18/37) had both vertebral body and disk changes on T1- and T2-weighted images. Contrast enhancement of the disk and vertebral body was seen in 94% of patients (17/18). Ring enhancement of paraspinal and epidural processes was found to correlate at surgery with abscess, and homogeneous enhancement was found to correlate with phlegmon.

CONCLUSION

Hypointense signal intensity in the vertebral body on T1-weighted images, abnormal disk signal intensity on both T1- and T2-weighted images, and contrast enhancement are the findings that indicate spinal infection most reliably.

Transient osteoporosis of the hip: clinical and imaging features

Transient osteoporosis of the hip is a form of reflex sympathetic dystrophy characterized by pain, limping, limitation of hip joint motion, and delayed radiographic patchy osteoporosis of the proximal femur. Spontaneous resolution is usually paralleled by radiographic recovery, usually within a few months. We present clinical and imaging features in seven cases of unilateral transient osteoporosis of the hip. In the appropriate clinical setting, conventional radiography will support the diagnosis. The role of more sensitive imaging techniques such as bone scintigraphy and magnetic resonance imaging in the early diagnosis of this disease has yet to be defined.

Diagnostic efficacy of digitized images vs plain films: a study of the joints of the fingers

Four hundred fifteen finger joints from 30 patients were evaluated for the presence of joint-space erosion, narrowing, and degenerative spurring on plain films, low-resolution digitized images (1024 x 840 bytes x 12 bit matrix), and high-resolution digitized images (2048 x 1680 bytes x 12 bit matrix). Three hundred four joints were abnormal. Low- and high-resolution digital images were displayed on a 1K x 1K monitor with the ability to change level, window, orientation, and brightness. Five radiologists interpreted images. The presence or absence of each abnormality was determined by consensus of two skeletal radiologists who did not otherwise participate in the study. Receiver-operating-characteristic analysis was used to obtain an area and a true-positive rate at a 0.10 false-positive rate for each interpreter. Randomized block analysis of variance with interpreters as blocks was used to compare areas and true-positive rates among imaging techniques for each type of abnormality; no statistically significant differences were found. In conclusion, the efficacy of display of digitized images on high- and low-resolution modes is not significantly different from that of plain films in the detection of erosions, joint-space narrowing, or degenerative spurring in small joints of the hands.

Radiology image interpretation system: modified observer performance study of an image interpretation expert system

Application of computer-based expert systems to diagnostic medical problems has been described in many areas including clinical diagnosis and radiology. Expert systems are computer programs that contain encoded expert knowledge to provide expert advice. A modified observer-performance study was done comparing the efficacy of the Radiology Image Interpretation System (RIIS), an expert system that diagnoses focal bone abnormalities, and radiology residents on a known set of 44 abnormal and 10 normal cases. Modified receiver operating characteristic curves for four inexperienced residents, five experienced residents, and RIIS were generated using the set of known radiographs. The true-positive rates of RIIS and the residents at false-positive rates of 0.05, 0.15, and 0.20 were estimated using the modified receiver operating characteristics curve and were compared using a paired t test. On the average, the RIIS system was less accurate when compared with experienced and inexperienced residents but the difference was only significant for experienced residents at a false-positive rate of 0.05. RIIS performed better than inexperienced residents when RIIS was used by experienced residents but this difference was not significant.

Total knee replacement: radiologic findings in failure of porous-coated metal-backed patellar component

One technique for replacing the articular surface of the patella in total knee replacement is the use of a cementless porous-coated metal-backed polyethylene component. Anteroposterior, lateral, and Merchant or skyline radiographs in 10 cases of porous-coated metal-backed components that failed were evaluated for component alignment, component displacement, radiolucencies, loose beads, and integrity of the patellar component. Component failure was documented by surgery in all 10 cases. Seven cases of failure involved the patellar pegs or junction of the pegs with the metal backing and three cases involved the polyethylene portion. In the seven cases of peg-metal backing failure, three cases showed loose beads before failure and seven cases showed displacement of the metal backing at time of failure. All three cases of polyethylene failure showed narrowing or displacement of the polyethylene portion. Our experience shows that displacement of the metal backing, displacement of the polyethylene, and disruption of patellar pegs are seen in failed porous-coated metal-backed patellar components. Loose beads may be seen before peg-metal backing failure.

Skeletal involvement in sarcoidosis: a case report

A patient is described in whom sarcoidosis caused a pathological fracture of the middle phalanx of the little finger. A bone scan showed increased uptake. She was treated by resection of the diseased area and bone grafting, which led to bone healing. The bony manifestations of sarcoidosis are reviewed.

Skeletal Involvement in Sarcoidosis: A Case Report

A patient is described in whom sarcoidosis caused a pathological fracture of the middle phalanx of the little finger. A bone scan showed increased uptake. She was treated by resection of the diseased area and bone grafting, which led to bone healing. The bony manifestations of sarcoidosis are reviewed.

Antenatal diagnosis of pulmonary tumours: report of two cases

We report two cases of antenatal diagnosis of pulmonary tumours. In one case a bronchogenic cyst was connected with the bronchopulmonary tree and grew rapidly after birth. Thanks to the antenatal diagnosis, it was resected before any complication appeared. In the second case, congenital cystic adenomatoid malformation of the lung was associated with fetal anasarca. Initially cyst aspiration was carried out; then long-term drainage was attempted. These cases illustrate the impact of antenatal diagnosis on perinatal management.

Sonographic monitoring of biliary endoprostheses

Biliary drainage by endoprosthesis, inserted either transcutaneously or endoscopically, is as effective and better supported than percutaneous drainage, but harder to control. Forty-four patients with biliary or pancreatic carcinoma treated by endoprostheses were followed up by ultrasound. Sonography was effective in the demonstration of the drainage effectiveness and the detection of prosthetic dysfunction or eventual complications. Consequently, it may be considered a valuable method to complement the biochemical tests in the monitoring of endoprostheses.

[Radiologic and hemodynamic studies of sexual impotence of vascular origin]

Vascular pathology is responsible for about 25% of male impotence, the arterial investigation is now classical. In our experience a great number of patients showed a normal arterial condition, requiring further venous exploration. Cavernographies and pressure flow dynamics were used to evaluate 45 patients. The cavernograms allowed visualization of structural abnormalities within the cavernous tissues and their venous drainage. The heparinized and diluted contrast medium is infused at 80 to 120 ml/minute until the appearance of an erection, in normal condition the intracavernous pressure rise at greater than or equal to 80 mmHg as long as the erection last. The venous leak is characterized by the absence of erection, no increase of the intra-cavernous pressure and a rapid opacification of venous plexus under a normal perfusion flow.