Richard A. Freiberg

Extensive localized bone resorption in the femur following total hip replacement.

Extensive localized bone resorption within the femur was observed after four total hip replacements. The amount and location of the resorption suggested the presence of infection or tumor, but there was no evidence of either condition and the roentgenographic appearance differed from that associated with a loose uncemented endoprosthesis or a grossly loose femoral component of a total hip replacement. At reoperation the femoral components were not rigidly fixed but were only slightly loose. Histologically there were sheets of macrophages, a few giant cells, and multiple small fragments of a birefringent material, but no inflammatory cells. While the exact mechanism of this serious complication is unclear, the findings suggest that a benign, non-inflammatory, adverse tissue response can occur in relation to the femoral components of total hip replacements that are not rigidly fixed. In all four hips, reimplantation of a new total hip replacement was successful after follow-up of thirteen to eighteen months.

Hypofibrinolysis, thrombophilia, osteonecrosis.

In the context of additional characterization of the pathoetiologic associations of heritable hypofibrinolysis and thrombophilia with osteonecrosis of the hip, the authors assessed 15 women and 21 men at entry to a 12-week treatment study of the amelioration of Ficat Stages I or II osteonecrosis by low molecular weight heparin (Enoxaparin). All 36 patients had osteonecrosis of the hip; four patients had unifocal osteonecrosis, 25 patients had two joints affected, five had three affected joints, and two had four affected joints. In 11 of 15 women (73%), hyperestrogenemia of pregnancy (20%) or exogenous estrogen supplementation (53%) were associated with the development of osteonecrosis. Five gene mutations affecting coagulation and nine serologic coagulation tests were studied. Compared with control subjects, patients were more likely to have heterozygosity and homozygosity for the hypofibrinolytic 4G polymorphism of the plasminogen activator inhibitor-1 gene. Moreover, the plasminogen activator inhibitor-1 gene product, plasminogen activator inhibitor activity, the major determinant of hypofibrinolysis, was 10 times more likely to be high (> 21.1 U/mL) in patients than in control subjects (31% versus 3%), with a median of 15.7 versus 6.3 U/mL. Compared with controls, patients were more likely to have the thrombophilic methylenetetrahydrofolate reductase gene mutation. In addition, the thrombophilic methylenetetrahydrofolate reductase gene product, homocysteine, was four times more likely to be high (> 13.5 umol/L) in patients than in control subjects (20% versus 5%), with a median of 9.1 versus 7 umol/L. Twenty-three percent of patients had low levels (< 65%) of the thrombophilic free protein S versus 3% of control subjects. Patients were more likely than control subjects to have hypofibrinolytic high lipoprotein (a) (≥ 35 mg/dL), 33% versus 13%. Median lipoprotein (a) was higher in patients than in control subjects, 15 versus 5 mg/dL. Heritable hypofibrinolysis and thrombophilia, often augmented in women by hyperestrogenemia, seem to be major pathoetiologies of osteonecrosis. If the association between coagulation disorders and osteonecrosis reflects cause and effect, as postulated, then anticoagulation with Enoxaparin should be a promising therapy for patients with osteonecrosis.

Thrombophilia and hypofibrinolysis : pathophysiologies of osteonecrosis

In 31 patients with osteonecrosis (primarily of the hip), 74% had 1 or more primary coagulation disorders. In 18 patients, 15 (83%) who had coagulation disorders, the osteonecrosis was initially identified as idiopathic and was not associated with known underlying drugs (glucocorticoids) or diseases (alcoholism, sickle cell disease, Gauchers disease). In 13 patients, 8 (62 %) who had coagulation disorders, the osteonecrosis was initially identified as secondary, and was associated with glucocorticoids in 12 patients, and with alcoholism in 1. The coagulation disorders included thrombhophilia (increased tendency to intravascular thrombosis) and hypofibrinolysis (reduced ability to lyse thrombi). Of the 18 patients initially thought to have idiopathic osteonecrosis, thrombophilia alone was found in 12% (resistance to activated protein C in 6%, low protein C in 6%), hypofibrinolysis alone was found in 50% (high lipoprotein(a) in 44%, low stimulated tissue plasminogen activator activity was found in 6%), and mixed thrombophilia hypofibrinolysis was found in 22%. Resistance to activated protein C was more common in these 18 patients than in healthy controls (11% versus 0%), as was high lipoprotein(a) (67% versus 20%). Of the 13 patients with secondary osteonecrosis, thrombophilia alone was found in 8% (low protein C), hypofibrinolysis alone was found in 30% (high Lp(a) in 15%, low tissue plasminogen activator activity in 15%), and mixed thrombophilia hypofibrinolysis was found in 23%. Low tissue plasminogen activator activity was more common in the 13 patients with secondary osteonecrosis than in controls (27% versus 7%), as was low protein C (23% versus 0%). In aggregate, these findings lead us to the speculation that primary, heritable thrombophilia or hypofibrinolysis causes thrombotic venous occlusion in the head of the femur, leading to venous hypertension and hypoxic death of bone (osteonecrosis).

Enoxaparin prevents progression of stages I and II osteonecrosis of the hip.

In a prospective pilot study, we hypothesized that enoxaparin (60 mg/day for 12 weeks) would prevent progression of Stages I and II osteonecrosis of the hip associated with thrombophilia or hypofibrinolysis or both over ≥ 108 weeks of followup versus untreated historic controls, with different treatment responses in primary versus corticosteroid-associated secondary osteonecrosis. Patients with one or more thrombophilic-hypofibrinolytic disorder and Ficat Stages I or II osteonecrosis of at least one hip were included. A blinded committee interpreted anteroposterior and frog-leg lateral radiographs at entry in the study and every 36 weeks to ≥ 108 weeks. Maintenance of the disease at Stages I and II versus progression of the osteonecrosis to Stages III and IV requiring total hip replacement was the major end point. Sixteen patients had primary osteonecrosis (25 hips; 13 Stage I, 12 Stage II), and 12 had secondary osteonecrosis (15 hips; five Stage I, 10 Stage II). With no Enoxaparin-related complications, 19 of 20 hips (95%) with primary osteonecrosis were unchanged from Stages I and II osteonecrosis at ≥ 108 weeks; 12 of 15 hips (80%) with secondary osteonecrosis progressed to Stages III and IV osteonecrosis. In primary osteonecrosis at ≥ 108 weeks, survival of 95% hips, or 76% (19/25 hips, based on intent to treat), compared favorably with untreated historical controls (approximately 20% 2-year survival), comparable to 20% survival in secondary hip osteonecrosis. Enoxaparin may prevent progression of primary hip osteonecrosis, decreasing the incidence of total hip replacement. Level of Evidence: Therapeutic study, II-1 (prospective cohort study)

Association of Antithrombotic Factor Deficiencies and Hypofibrinolysis with Legg-Perthes Disease*

Thirty-three (75 per cent) of forty-four unselected children who had Legg-Perthes disease were found to have coagulation abnormalities. Twenty-three children had thrombophilia (a deficiency in antithrombotic factor C or S, with an increased tendency toward thrombosis); nineteen of the twenty-three children had protein-C deficiency and four had protein-S deficiency. Seven children had a high level (0.25 gram per liter or more) of lipoprotein(a), a thrombogenic, atherogenic lipoprotein associated with osteonecrosis in adults. Three children had hypofibrinolysis (a reduced ability to lyse clots). The mean age of the children when the Legg-Perthes disease was first diagnosed was 5.8 ± 2.7 years, and the mean age at the time of the present study was 10.1 ± 4.4 years. At least one of the first-degree relatives of eleven of the nineteen probands who had a low protein-C level had a low protein-C level as well; all of these low levels represented previously undiagnosed familial protein-C deficiency. The eleven probands who had familial protein-C deficiency were more likely to have early onset of Legg-Perthes disease (at or before the age of five years) than the eleven children who had normal levels of protein C, protein S, and lipoprotein(a) as well as normal fibrinolytic activity (chi-square = 6.6; p = 0.01). At least one first-degree relative of one of the four probands who had a low protein-S level had a low protein-S level and previously undiagnosed familial protein-S deficiency. At least one first-degree relative of six of the seven probands who had a high level of lipoprotein(a) had a familial high level of lipoprotein(a). Six of the seven children who had a high level of lipoprotein(a) also had a low level of stimulated tissue-plasminogen activator activity, the major initiator of fibrinolysis. At least one first-degree relative of one of the three probands who had normal levels of protein C, protein S, and lipoprotein(a) but low stimulated tissue-plasminogen activator activity also had low stimulated tissue-plasminogen activator activity (familial hypofibrinolysis). Legg-Perthes disease, thrombophlebitis, premature myocardial infarction, and stroke, which are ramifications of the familial thrombophilic-hypofibrinolytic disorders, were common in the first and second-degree relatives of the thirty-three children with Legg-Perthes disease who also had thrombophilic-hypofibrinolytic disorders. CLINICAL RELEVANCE: Protein-C or S deficiency, hypofibrinolysis, or a high level of lipoprotein(a) may result in thrombotic venous occlusion of the femur, which leads to the venous hypertension and osteonecrosis of the femoral head characteristic of Legg-Perthes disease. When Legg-Perthes disease develops in a child, the levels of proteins C and S, lipoprotein(a), and stimulated fibrinolysis should be measured. Early diagnosis of protein-C or S deficiency, hypofibrinolysis, or a high level of lipoprotein(a) in such children may open avenues for pharmacological preventive therapy to reduce thrombophilia, stimulate fibrinolysis, or lower the level of lipoprotein(a), potentially ameliorating the Legg-Perthes disease process.

Secondhand smoke, hypofibrinolysis, and Legg-Perthes disease

In 39 children with Legg-Perthes disease who were nonsmokers, the specific aim was to assess relationships among parental cigarette smoking during pregnancy, household smoking before diagnosis of Legg-Perthes disease, hypofibrinolysis, and thrombophilia. Fifteen (38%) children had no secondhand smoke exposure; 24 (62%) had secondhand smoke exposure before their diagnosis. Seventeen (71%) of these 24 children were exposed while in utero to smoking by a parent or live in relative and also had exposure to household smoke during childhood; seven (29%) had only household smoke exposure in childhood. In the full cohort of 39 children, secondhand smoke exposure correlated inversely with the major stimulator of fibrinolysis, stimulated tissue plasminogen activator activity. Of the children exposed to smoking, 48% had low stimulated tissue plasminogen activator activity (< 2.19 IU/ml) compared with 7% of the children without secondhand smoke exposure and 14% of 22 healthy control children. Secondhand smoke exposure had no significant effects on other measures of coagulation. Secondhand smoke exposure while in utero and during childhood appears to lower stimulated tissue plasminogen activator activity and additionally may depress heritable low stimulated tissue plasminogen activator activity, leading to hypofibrinolysis. Hypofibrinolysis may facilitate thrombotic venous occlusion in the head of the femur, leading to venous hypertension and hypoxic bone death, Legg-Perthes disease.

Thrombophilia, Hypofibrinolysis, the eNOS T-786C Polymorphism, and Multifocal Osteonecrosis

BACKGROUND We examined the hypothesis that thrombophilia, hypofibrinolysis, and the endothelial nitric oxide synthase (eNOS) T-786C polymorphism are common, potentially treatable, and similar pathophysiologic causes of multifocal (three sites or more) and unifocal (single-site) osteonecrosis. METHODS We prospectively evaluated twenty-six consecutively referred adults with multifocal osteonecrosis, who included thirteen with idiopathic multifocal osteonecrosis and thirteen with secondary multifocal osteonecrosis (resulting from steroid therapy in ten and alcoholism in three). We compared these patients with race, sex, and age-matched normal control subjects and with patients with idiopathic unifocal and secondary unifocal osteonecrosis, respectively. Using polymerase chain reaction and serologic measures, we studied thrombophilic and hypofibrinolytic mutations and the eNOS T-786C polymorphism. RESULTS The total number of polymerase chain reaction and serologic thrombophilic-hypofibrinolytic abnormalities and the eNOS T-786C polymorphism did not differ between patients with idiopathic (p > 0.5) or secondary (p > 0.5) multifocal and unifocal osteonecrosis. The frequency of low free protein-S levels (<66%) in patients with secondary multifocal osteonecrosis (four of eleven patients) was higher than that in the control subjects (one of fifty-nine) (risk ratio = 21.5; 95% confidence interval, 2.6 to 174; p = 0.0016, Benjamini-Hochberg adjusted p [Bp] = 0.004). Factor-V Leiden heterozygosity was present in two of thirteen patients with secondary multifocal osteonecrosis compared with none of sixty-four control subjects (p = 0.027, Bp = 0.008). For eleven patients with secondary multifocal osteonecrosis, the eNOS T-786C polymorphism was present in nine of twenty-two alleles compared with eight of forty-four alleles in twenty-two normal control subjects (risk ratio = 2.3; 95% confidence interval, 1.0 to 5.0; p = 0.047, Bp = 0.016). The frequency of homocystinemia (>13.5 mumol/L) was higher in patients with idiopathic multifocal osteonecrosis (two of thirteen patients) than in normal controls (none of fifty-one) (p = 0.039, Bp = 0.004). A high level of factor VIII (>150%) was seen in four of eight patients with idiopathic multifocal osteonecrosis and in seven of forty-eight normal controls (risk ratio = 3.4; 95% confidence interval, 1.3 to 9.1; p = 0.04, Bp = 0.008). The eNOS T-786C mutant allele was present in seven of twelve alleles in the six patients with idiopathic multifocal osteonecrosis who were tested, compared with twenty-five of 108 alleles in fifty-four control subjects (risk ratio = 2.5; 95% confidence interval, 1.4 to 4.5; p = 0.015, Bp = 0.008). CONCLUSIONS Limited by the small numbers of patients with multifocal osteonecrosis, this exploratory study suggested that thrombophilia was associated with both idiopathic multifocal osteonecrosis and secondary multifocal osteonecrosis, as was the eNOS T-786C polymorphism. Multifocal and unifocal osteonecrosis are similarly associated with thrombophilia, hypofibrinolysis, and the eNOS T-786C polymorphism, which are potentially treatable pathophysiologic conditions, requiring further study.

Association between the T-786C eNOS polymorphism and idiopathic osteonecrosis of the head of the femur.

BACKGROUND Nitric oxide regulates bone turnover by osteoblasts and osteoclasts. Nitric oxide production is impaired by the T-786C eNOS single nucleotide polymorphism, with a substitution of the nucleotide thymine by cytosine at a locus 786 base pairs upstream of the eNOS gene. This leads to vasoconstriction, platelet aggregation, reduced angiogenesis, and reduced bone formation, all of which may be associated with osteonecrosis of the hip. We studied relationships between the T-786C eNOS polymorphism and idiopathic and secondary necrosis of the head of the femur in order to better understand the pathophysiology of osteonecrosis. METHODS With use of polymerase chain reaction methodology, the T-786C eNOS polymorphism was compared in ninety-five patients with femoral head necrosis (including thirty-six nonsmokers with idiopathic necrosis and fifty-nine patients with secondary necrosis) and seventy-two healthy normal adult controls. RESULTS Homozygosity for the mutant eNOS allele (TT) was present in eight (22%) of thirty-six patients with idiopathic osteonecrosis as compared with one (3%) of thirty-six race, gender, and age-matched controls; heterozygosity (TC) was present in nineteen patients (53%) as compared with ten controls (28%); and the wild-type normal genotype (CC) was present in nine patients (25%) as compared with twenty-five controls (69%) (p = 0.0004). Logistic regression revealed that the T-786C eNOS mutant allele was positively associated with idiopathic osteonecrosis of the femoral head (odds ratio, 6.0; 95% confidence interval, 2.51 to 14.4). The fifty-nine patients with secondary osteonecrosis did not differ from fifty-two race, gender, and age-matched controls in terms of the distribution of the T-786C eNOS polymorphism (p = 0.19) or in terms of mutant allele frequency (30% compared with 21%; p = 0.15). The thirty-six patients with idiopathic osteonecrosis differed from the fifty-nine patients with secondary osteonecrosis in that they were more likely to have mutant eNOS genotypes (p = 0.033) and to have a higher mutant T allele frequency (49% compared with 30%; p = 0.009). CONCLUSIONS The T-786C eNOS polymorphism and resultant reduction of nitric oxide production is associated with, and may contribute to, the pathogenesis of idiopathic osteonecrosis of the femoral head. LEVEL OF EVIDENCE Prognostic Level III. See Instructions to Authors for a complete description of levels of evidence.

The Role of the Factor V Leiden Mutation in Osteonecrosis of the Hip

We examined the hypothesis that the factor V Leiden (FVL) and G20101A prothrombin gene mutations are commonly associated with hip osteonecrosis. We prospectively evaluated 244 consecutively referred adults with osteonecrosis (ON), 161 idiopathic and 83 secondary. Cases (n = 244) did not differ from 104 normal controls by race. Of the 244 patients, 23 (9.4%) were FVL heterozygotes versus 2 of 104 controls (1.9%), P = .013, risk ratio (RR) = 4.90, 95% confidence interval (CI) 1.18 to 20.4. Of the 161 patients with idiopathic ON, 15 (9.3%) were FVL heterozygotes versus 2 of 104 normal controls (1.9%), P = .017, RR = 4.84, 95% CI 1.13 to 20.8. Of the 83 patients with secondary ON, 8 (9.6%) FVL heterozygotes versus 2 of 104 normal controls (1.9%), P = .024, RR = 5.01, 95% CI 1.09 to 23.0. Prothrombin gene heterozygosity in normal controls (2.9%) did not differ from ON cases (3.4%), P = 1.0. The thrombophilic FVL mutation is commonly associated with and may be pathoetiologic for hip osteonecrosis.

Anticoagulant therapy for osteonecrosis associated with heritable hypofibrinolysis and thrombophilia.

Osteonecrosis develops as the end-result of reduced blood flow to the femoral head. We postulate that venous thrombosis leads to increased intraosseus venous pressure, reduced arterial flow and hypoxic bone death. Hypofibrinolysis (reduced ability to lyse thrombi) and thrombophilia (increased tendency to form thrombi) appear to play an important role in osteonecrosis. If coagulation disorders cause osteonecrosis, then anticoagulation might ameliorate osteonecrosis. In subjects with coagulation disorders and osteonecrosis of the hip, provided that anticoagulant therapy is started before irreversible segmental collapse of the head of the femur, osteonecrosis may be arrested or, speculatively, sometimes reversed. This has the potential of preventing femoral head collapse which usually leads to total hip replacement.