MRI of the cartilaginous epiphysis of the femoral head in the piglet hip after ischemic damage

T1ρ and T2 mapping detect acute ischemic injury in a piglet model of Legg-Calvé-Perthes disease

This study investigated the sensitivity of T1ρ and T2 relaxation time mapping to detect acute ischemic injury to the secondary ossification center (SOC) and epiphyseal cartilage of the femoral head in a piglet model of Legg-Calvé-Perthes disease. Six piglets underwent surgery to induce global right femoral head ischemia and were euthanized 48 h later. Fresh operated and contralateral-control femoral heads were imaged ex vivo with T1, T2, and T1ρ mapping using a 9.4T magnetic resonance imaging scanner. The specimens were imaged a second time after a freeze/thaw cycle and then processed for histology. T1, T2, and T1ρ measurements in the SOC, epiphyseal cartilage, articular cartilage, and metaphysis were compared between operated and control femoral heads using paired t tests. The effects of freeze/thaw, T1ρ spin-lock frequency, and fat saturation were also investigated. Five piglets with histologically confirmed ischemic injury were quantitatively analyzed. T1ρ was increased in the SOC (101 ± 15 vs. 73 ± 16 ms; p = 0.0026) and epiphyseal cartilage (84.9 ± 9.2 vs. 74.3 ± 3.6 ms; p = 0.031) of the operated versus control femoral heads. T2 was also increased in the SOC (28.7 ± 2.0 vs. 22.7 ± 1.7; p = 0.0037) and epiphyseal cartilage (57.4 ± 4.7 vs. 49.0 ± 2.7; p = 0.0041). No changes in T1 were detected. The sensitivities of T1ρ and T2 mapping in detecting ischemic injury were maintained after a freeze/thaw cycle, and T1ρ sensitivity was maintained after varying spin-lock frequency and applying fat saturation. In conclusion, T1ρ and T2 mapping are sensitive in detecting ischemic injury to the SOC and epiphyseal cartilage of the femoral head as early as 48 h after ischemia induction.

Aetiology of Legg-Calvé-Perthes disease: A systematic review

BACKGROUND

Legg-Calvé-Perthes disease (LCPD) is a clinical condition affecting the femoral head of children during their growth. Its prevalence is set to be between 0.4/100000 to 29.0/100000 children less than 15 years of age with a peak of incidence in children aged from 4 years to 8 years. LCPD aetiology has been widely studied, but it is still poorly understood.

AIM

To analyse the available literature to document the up-to-date evidence on LCPD aetiology.

METHODS

A systematic review of the literature was performed regarding LCPD aetiology, using the following inclusion criteria: studies of any level of evidence, reporting clinical or preclinical results and dealing with the aetiology or pathogenesis of LCPD. Two reviewers searched the PubMed and Science Direct databases from their date of inception to the 20th of May 2018 in accordance with the Preferred Reporting Items for Systemic Reviews and Meta-Analyses guidelines. To achieve the maximum sensitivity of the search strategy, we combined the terms: ‘‘Perthes disease OR LCPD OR children avascular femoral head necrosis” with “pathology OR aetiology OR biomechanics OR genetics” as either key words or MeSH terms.

RESULTS

We include 64 articles in this review. The available evidence on LCPD aetiology is still debated. Several hypotheses have been researched, but none of them was found decisive. While emerging evidence showed the role of environmental risk factors and evidence from twin studies did not support a major role for genetic factors, a congenital or acquired predisposition cannot be excluded in disease pathogenesis. One of the most supported theories involved mechanical induced ischemia that evolved into avascular necrosis of the femoral head in sensible patients.

CONCLUSION

The literature available on the aetiology of LCPD presents major limitations in terms of great heterogeneity and a lack of high-profile studies. Although a lot of studies focused on the genetic, biomechanical and radiological background of the disease, there is a lack of consensus on one or multiple major actors of the etiopathogenesis. More studies are needed to understand the complex and multifactorial genesis of the avascular necrosis characterizing the disease.

[Experimental induction of Perthes disease in lambs]

OBJECTIVE

To establish a simple, reproducible and safe experimental model, for the development of ischemic vascular necrosis of the hip in the lamb.

MATERIAL AND METHODS

We used 15 lambs (10 males and 5 females) aged four weeks, divided into a control group (7 animals) and an experimental group (8 animals) producing ischemia in the proximal femur. Standard radiography and MRI were performed. The animals were euthanised at the 4th, 8th and 12th weeks after surgery. The femoral heads were extracted and measured and a histological analysis was performed with hematoxylin-eosin staining.

RESULTS

Decreased height and increased width of the femoral head was observed in the X-Rays, particularly after the 4th week. We did not observe any changes in the height of the lateral pillar or trochanteric distance. The experimental group showed macroscopical hypertrophy and progressive flattening of the head. At 4 weeks necrotic areas in articular cartilage were observed, bone marrow was dense and the growth cartilage height was lower. The vessels were thickened by proliferation of the medial and adventitia layers. At 8 weeks, we found fibrosis in the subchondral bone with thinned and devitalized angiogenesis fat areas. The articular cartilage showed irregularities. At 12 weeks the closure of the physis was noted, as well as chondral areas in the trabecular bone and fat cells in the methaphysis.

CONCLUSION

Although the histological changes are consistent with necrosis of the femoral head, the images obtained did not resemble Perthes disease, so we do not advise this experimental model for the study of this disease.

Femoral head deformation and repair following induction of ischemic necrosis: a histologic and magnetic resonance imaging study in the piglet

BACKGROUND

Ischemic necrosis of the femoral head can be induced surgically in the piglet. We used this model to assess femoral head deformation and repair in vivo by sequential magnetic resonance imaging and by correlating end-stage findings with histologic assessments.

METHODS

Ischemic necrosis of the femoral head was induced in ten three-week-old piglets by tying a silk ligature around the base of the femoral neck (intracapsular) and cutting the ligamentum teres. We used magnetic resonance imaging with the piglets under general anesthesia to study the hips at forty-eight hours and at one, two, four, and eight weeks. Measurements on magnetic resonance images in the midcoronal plane of the involved and control sides at each time documented the femoral head height, femoral head width, superior surface cartilage height, and femoral neck-shaft angle. Histologic assessments were done at the time of killing.

RESULTS

Complete ischemia of the femoral head was identified in all involved femora by magnetic resonance imaging at forty-eight hours. Revascularization began at the periphery of the femoral head as early as one week and was underway in all by two weeks. At eight weeks, magnetic resonance imaging and histologic analysis showed deformation of the femoral head and variable tissue deposition. Tissue responses included (1) vascularized fibroblastic ingrowth with tissue resorption and cartilage, intramembranous bone, and mixed fibro-osseous or fibro-cartilaginous tissue synthesis and (2) resumption of endochondral bone growth. At eight weeks, the mean femoral head measurements (and standard error of the mean) for the control compared with the ligated femora were 10.4 +/- 0.4 and 4.8 +/- 0.4 mm, respectively, for height; 26.7 +/- 0.8 and 31.2 +/- 0.8 mm for diameter; 1.1 +/- 0.1 and 2.3 +/- 0.1 mm for cartilage thickness; and 151 degrees +/- 2 degrees and 135 degrees +/- 2 degrees for the femoral neck-shaft angle. Repeated-measures mixed-model analysis of variance revealed highly significant effects of ligation in each parameter (p < 0.0001).

CONCLUSIONS

Magnetic resonance imaging allows for the assessment of individual hips at sequential time periods to follow deformation and repair. There was a variable tissue response, and histologic assessment at the time of killing was shown to correlate with the evolving and varying magnetic resonance imaging signal intensities. Femoral head height on the ischemic side from one week onward was always less than the initial control value and continually decreased with time, indicating collapse as well as slowed growth. Increased femoral head width occurred relatively late (four to eight weeks), indicating cartilage model overgrowth concentrated at the periphery.

Biophysical stimulation with pulsed electromagnetic fields in osteonecrosis of the femoral head

BACKGROUND

Osteonecrosis of the femoral head is the end point of a disease process that results in bone necrosis, joint edema, and cartilage damage. It leads to joint arthritis that necessitates total hip arthroplasty in many patients. Because of its positive effects on osteogenesis and its chondroprotective effect of articular cartilage, pulsed electromagnetic field stimulation has been proposed as a method to prevent or delay the progression of osteonecrosis.

METHODS

A retrospective analysis of the results of treatment with pulsed electromagnetic field stimulation of seventy-six hips in sixty-six patients with osteonecrosis of the femoral head was performed. Patients with Ficat stage I, II, or III osteonecrosis of the femoral head were treated with pulsed electromagnetic field stimulation for eight hours per day for an average of five months. Clinical and diagnostic imaging information was collected at the start of the treatment and at the time of follow-up. The primary end point analyzed was the avoidance of hip surgery, and the secondary end point was limiting the radiographic progression (according to Ficat stage) of osteonecrosis of the femoral head.

RESULTS

Fifteen hips required a total hip arthroplasty; twelve of these hips were in patients with Ficat stage-III disease. The need for total hip arthroplasty was significantly higher in patients with Ficat stage-III disease than in patients with Ficat stage-I (p < 0.0001) or II (p < 0.01) disease at the beginning of treatment. Pulsed electromagnetic fields preserved 94% of Ficat stage-I or II hips. Furthermore, radiographic progression (according to Ficat stage) occurred in twenty hips (26%). Pain, present in all patients at the start of the treatment, disappeared after sixty days of stimulation in thirty-five patients (53%) and was of moderate intensity in seventeen patients (26%).

CONCLUSIONS

The results of this study confirm that pulsed electromagnetic field treatment may be indicated in the early stages of osteonecrosis of the femoral head (Ficat stages I and II). Pulsed electromagnetic field stimulation may be able to either preserve the hip or delay the time until surgery. The authors hypothesize that the short-term effect of pulsed electromagnetic field stimulation may be to protect the articular cartilage from the catabolic effect of inflammation and subchondral bone-marrow edema. The long-term effect of pulsed electromagnetic field stimulation may be to promote osteogenic activity at the necrotic area and prevent trabecular fracture and subchondral bone collapse.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

Deformity of the femoral head following vascular infarct in piglets

BACKGROUND

In Legg-Calvé-Perthes disease (LCPD), 4 major patterns (coxa plana, coxa magna, coxa vara, subluxation) of the femoral head are commonly observed. However, direct observation of pathological specimens is rarely possible. An animal model of LCPD may clarify the pathogenesis of femoral head deformity.

ANIMALS AND METHODS

In 26 piglets, we interrupted the vascular supply to the capital femoral epiphysis by cutting the ligamentum teres and ligating the femoral neck containing the epiphyseal artery. 6-7 piglets in each experimental group were killed at early (2 and 4 weeks: P2 and P4), intermediate (12 weeks: P12), and late (20 weeks: P20) periods. We examined the extracted femoral heads macroscopically and radiographically.

RESULTS

The mean decrease in epiphyseal height was 1.5 mm, 4.1 mm, 5.0 mm, and 7.5 mm in P2, P4, P12 and P20, respectively (rs = 0.76, p = 0.002). The mean increase of diameter was 4.1 mm, 6.9 mm, and 6.8 mm in P4, P12 and P20, respectively. Decrease of the articulotrochanteric distance was mild in P2 and P4, and severe in P12 and P20. Subluxation of the femoral head was observed only in P12 and P20 piglets.

INTERPRETATION

The piglet model of LCPD was useful in the early stage of devascularization for investigation of the developmental pattern of femoral head deformity. However, when the piglets had grown to 20 weeks old or more--that is, to full skeletal maturity--the femoral head and acetabulum showed severe deformities that were most likely caused by heavy body weight.

Developmental pattern of femoral shortening following devascularization of the capital femoral epiphysis in piglets

To investigate the developmental pattern of femoral shortening in Legg-Calve-Perthes disease, the authors made an experimental model of the disease in piglets by devascularizing the capital femoral epiphysis and following the piglets to skeletal maturity. The discrepancy first increased in the postoperative 0 to 8 weeks (1.2-1.9 mm of shortening per week), then decelerated for a considerable period during the postoperative 8 to 16 weeks (0.2-0.6 mm per week), and then increased again toward the end of the growth period of the postoperative 20 weeks (1.2 mm per week). The developmental pattern of femoral shortening showed an upward slope/plateau/upward slope pattern, as in type IV of the Shapiro classification. As the mechanism of the observed pattern, the authors presumed reduced epiphyseal height and growth retardation in the physis during the initial upward slope, a repair process at the plateau phase, and premature physeal closure during the second upward slope.

Increased VEGF expression in the epiphyseal cartilage after ischemic necrosis of the capital femoral epiphysis

Ischemic injury to the immature femoral head produces epiphyseal cartilage damage and cessation of endochondral ossification. This study suggests that VEGF facilitates the repair of the necrotic epiphyseal cartilage, which is essential for restoration of endochondral ossification and re-establishment of the growth of the immature femoral head after ischemic necrosis.

INTRODUCTION

Legg-Calve-Perthes disease (LCPD) is a childhood form of osteonecrosis that produces growth arrest of the secondary center of ossification. The cessation of growth is caused by ischemic damage to the hypertrophic zone of the epiphyseal cartilage where endochondral ossification normally occurs. The role of vascular endothelial growth factor (VEGF) in restoring endochondral ossification in the epiphyseal cartilage after ischemic necrosis was investigated in a piglet model of LCPD because the resumption of normal growth is important for maintaining the spherical shape of the femoral head.

MATERIALS AND METHODS

Piglet femoral heads were assessed 24 h to 8 weeks after the surgical induction of ischemia. Western blot analysis, ribonuclease protection assay (RPA), immunohistochemistry, and in situ hybridization were performed.

RESULTS

Western blot analysis and RPA showed increased VEGF protein and mRNA expression, respectively, in the epiphyseal cartilage of the infarcted heads compared with the contralateral normal heads. In the normal femoral heads, VEGF-immunoreactivity (VEGF-IR) and transcripts were observed in the hypertrophic zone of the epiphyseal cartilage. In the infarcted heads, VEGF-IR and transcripts were no longer observed in the hypertrophic zone because of diffuse cell death in that zone from ischemia. However, VEGF-IR and transcripts were observed in the proliferative zone above the necrotic hypertrophic zone. At 8 weeks, vascular granulation tissue invasion of the necrotic hypertrophic zone was observed with active resorption of the necrotic cartilage. In some areas where the necrotic cartilage was completely resorbed, restoration of endochondral ossification was observed. In these areas, VEGF transcripts were observed in the newly formed hypertrophic zone.

CONCLUSIONS

VEGF expression was increased, and its spatial expression was altered in the epiphyseal cartilage after ischemic necrosis of the immature femoral head. VEGF upregulation in the proliferative zone after ischemic damage may play a role in stimulating vascular invasion and granulation tissue formation in the necrotic hypertrophic zone of the epiphyseal cartilage. This may be an important step toward facilitating the resorption of the necrotic cartilage and restoration of endochondral ossification leading to further growth and development of the femoral head.

Age-Related Vascular Changes in the Epiphysis, Physis, and Metaphysis:Normal Findings on Gadolinium-Enhanced MRI of Piglets

OBJECTIVE

We sought to study the normal enhancement patterns seen on MRIs of the epiphysis, physis, and metaphysis and age-related vascular changes in piglets using gadoteridol, a nonionic gadolinium chelate.

MATERIALS AND METHODS

We quantitatively and qualitatively analyzed the normal changes on sequential T1-weighted images after the IV administration of gadoteridol. In an investigation approved by the research animal care committee at our hospital, we studied the proximal and distal femurs of 26 piglets 1-6 weeks old and correlated the enhanced images with findings on intermediate-weighted, T2-weighted, and gradient-recalled echo images and at histologic examination.

RESULTS

We observed early enhancement of the epiphyseal vascular canals, the main physis, the physis of the secondary ossification center, and a metaphyseal band adjacent to the physis. Enhancement of the epiphyseal and metaphyseal marrow and of the epiphyseal cartilage was slower. In the epiphyseal cartilage, we saw three phases of enhancement: vascular, canalicular, and cartilaginous. As the piglets matured, enhancement of the epiphyseal cartilage decreased, and the epiphyseal vascular canals were less conspicuous. Physeal enhancement was greatest during the first week of life, declined at 3 weeks, and subsequently increased again as the physis came to lie adjacent to a larger segment of the epiphyseal ossification center.

CONCLUSION

Gadoteridol-enhanced MRIs showed multiple cartilaginous and vascular structures of the growing skeleton. With maturity and progressive epiphyseal ossification, epiphyseal cartilage enhancement decreased, and physeal cartilage enhancement increased.

Normal and ischemic epiphysis of the femur: diffusion MR imaging study in piglets

PURPOSE

To evaluate normal diffusion characteristics in the femur in piglets and changes in diffusion with increasing duration of femoral head ischemia.

MATERIALS AND METHODS

Normal epiphyses, physes, and metaphyses of piglets were evaluated with line-scan diffusion imaging (n = 12) and diffusion-tensor imaging (n = 4). Apparent diffusion coefficient (ADC) differences between normal proximal and distal femoral structures, epiphyseal and physeal cartilage, and epiphyseal and metaphyseal marrow were compared (Mann-Whitney test). Short-term femoral ischemia was investigated after maximal abduction of the hips for 3 hours (n = 6); ADCs before and after abduction were compared (Wilcoxon signed rank test). Prolonged ischemia was investigated with placement of a ligature around the neck of a femur (n = 7); the ADC of the femur in this condition was compared (Wilcoxon signed rank test) with that of the normal contralateral femur. Changes in ADC ratios at three durations of ischemia (Kruskal-Wallis test) were compared.

RESULTS

ADC was greater in epiphyseal cartilage (mean +/- 1 SD, 1.62 x 10(-3) mm2/sec +/- 0.38) than it was in physeal cartilage (1.28 x 10(-3) mm2/sec +/- 0.31) (P <.007) and greater in epiphyseal marrow (1.26 x 10(-3) mm2/sec +/- 0.38) than it was in metaphyseal marrow (0.91 x 10(-3) mm2/sec +/- 0.35) (P <.001). There was columnar arrangement of tensors in the physis. ADC decreased 26% after 3 hours of maximal abduction. After femoral neck ligature, ADC increased a mean of 27% after 6 hours and a mean of 75% after 96 hours.

CONCLUSION

Normal line-scan diffusion imaging findings indicate relative restriction of diffusion in the metaphysis and parallel orientation of tensors in the physis. Diffusion is initially restricted with decreased blood flow but increases if ischemia lasts longer.

Histopathologic changes in growth-plate cartilage following ischemic necrosis of the capital femoral epiphysis. An experimental investigation in immature pigs

BACKGROUND

The developing capital femoral epiphysis consists of a secondary center of ossification surrounded by epiphyseal cartilage. Between the epiphyseal cartilage and the secondary center of ossification is a growth plate, which contributes to the circumferential increase in size of the secondary center of ossification during development. The main objective of this study was to describe the histopathologic changes that occur in the growth plate surrounding the secondary center of ossification during the early and reparative phases following the induction of ischemic necrosis of the capital femoral epiphysis in immature pigs.

METHODS

Ischemic necrosis of the capital femoral epiphysis was induced in eighteen piglets by placing a nonabsorbable suture ligature around the femoral neck following a capsulotomy and transection of the ligamentum teres. The animals were killed three days to eight weeks following the induction of ischemia, and visual, radiographic, and histologic assessments were performed.

RESULTS

Two to four weeks after the induction of ischemic necrosis, the growth plate surrounding the secondary center of ossification became necrotic. The observed histopathologic changes included chondrocyte death, loss of safranin-O staining of the matrix of the necrotic growth-plate cartilage, an absence of vascular invasion of terminal hypertrophic chondrocytes, and a decrease in the amount of primary spongiosa, indicating cessation of endochondral ossification. In the reparative phase, at four to eight weeks postoperatively, chondrocyte clusters and intense safranin-O staining were observed in the epiphyseal cartilage around the necrotic growth-plate cartilage. In the peripheral region of the femoral head, necrotic growth-plate cartilage surrounding the secondary center of ossification was resorbed by a fibrovascular tissue from the marrow space. By six weeks, new accessory centers of ossification with restored endochondral ossification were observed in the peripheral epiphyseal cartilage. New ossification centers contributed to the fragmented radiographic appearance of the secondary center of ossification. The physis appeared essentially normal in most animals, although five of the eighteen piglets showed mild or moderate histopathologic changes.

CONCLUSIONS

In this model, ischemic necrosis of the capital femoral epiphysis resulted in necrosis of the growth plate surrounding the secondary center of ossification. Small new ectopic centers of ossification appeared in the epiphyseal cartilage, explaining in part the fragmented radiographic appearance of the secondary center of ossification.