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Survivorship Analysis of Hips Treated with Core Decompression for Nontraumatic Osteonecrosis of the Femoral Head*

KEVIN J. BOZIC, M.D., DAVID ZURAKOWSKI, PH.D. and THOMAS S. THORNHILL, M.D.§, BOSTON, MASSACHUSETTS

Investigation performed at the Department of Orthopaedic Surgery, Brigham and Women's Hospital and Harvard Medical School, Boston

	Abstract

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We reviewed the long-term results of core decompression for the treatment of nontraumatic osteonecrosis of the femoral head, performed in thirty-four patients (fifty-four hips) between January 1, 1981, and June 30, 1995. Twenty patients (59 percent) had bilateral involvement. The mean age of the patients at the time of presentation was thirty-eight years (range, twenty-two to eighty-three years). The presumed risk factors were use of corticosteroids (thirty-seven hips), excessive in take of alcohol (eight hips), and use of adrenocorticotropic hormone for the treatment of multiple sclerosis (two hips); the remaining seven hips had idiopathic osteonecrosis. According to a modification of the classification system of Ficat and Arlet in combination with the system of Steinberg et al., thirteen hips were stage I (normal radiographs) preoperatively; seven, stage IIA sclerotic; sixteen, stage IIA cystic or sclerocystic; ten, stage IIB (transitional stage, with a crescent sign); and eight, stage III (collapse). The mean duration of follow-up after the core decompression was 120 months (range, twenty-four to 196 months). The result was considered successful if the patient was asymptomatic, with no progression of the disease, and unsuccessful if there was radiographic failure (progression to stage III [collapse]) or clinical failure (the need for a subsequent operation), or both. The Kaplan-Meier product-limit method was used to estimate clinical and radiographic survival. Overall, twenty-six hips (48 percent) had a satisfactory clinical result and twenty (37 percent) survived according to radiographic criteria. Radiographic or clinical failure, or both, were seen in four of the thirteen stage-I hips, none of the seven stage-IIA sclerotic hips, thirteen of the sixteen stage-IIA cystic or sclerocystic hips, nine of the ten stage-IIB hips, and all eight stage-III hips. On the basis of the Cox proportional-hazards regression model, significant predictors of overall failure included an advanced preoperative radiographic stage (p < 0.0001), a shorter duration of symptoms (p < 0.05), and use of corticosteroids (p < 0.05). No association was found between age, gender, excessive intake of alcohol, or renal transplantation and the overall outcome. Two patients (two hips; 4 percent) had a postoperative complication. One patient had a fracture of the femoral neck, and the other had a hematoma. Our findings suggest that core decompression is a safe and effective procedure for the treatment of stage-I or stage-IIA sclerotic disease. These data also demonstrate the importance of differentiating between stage-IIA sclerotic disease and stage-IIA cystic or sclerocystic disease. We believe that core decompression has a limited role in the operative management of patients who have evidence of cystic changes in the femoral head on plain radiographs.

	Introduction

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Nontraumatic osteonecrosis of the femoral head is an important cause of morbidity in young patients and can lead to early destruction of the hip joint^30,58. Despite advances in the understanding of the pathogenesis and etiology of this disease, nontraumatic osteonecrosis remains a challenging diagnostic and therapeutic dilemma^51,75. The natural history of nontraumatic osteonecrosis has been well documented^{7,45,58,59,82}, and a high rate of progression has been reported when nonoperative treatment alone has been used for symptomatic patients^1,45,55,58. Given the relatively young age at the time of presentation and the poor long-term results that have been reported after total hip arthroplasty in this population of patients^11,67,68,91, preservation of the joint is recommended for patients who have early-stage disease.

Core decompression, one of several joint-preserving operations for the treatment of nontraumatic osteonecrosis, has been widely reported during the last two decades^{1,9,17,19,27,28,42-44,53,55,63,65,70,76,77,79,85,89}. In 1964, Arlet and Ficat⁴ hypothesized that core decompression acts to decompress the rigid intraosseous chamber, thus improving venous drainage and promoting revascularization of the femoral head. Initially, Ficat²⁰ as well as Hungerford and Lennox²⁹ reported high rates of success with use of this procedure. However, their results have not been duplicated by other investigators, and enthusiasm for core decompression has recently waned^9,27,44.

One shortcoming of the previously reported studies on this subject has been the limited duration of follow-up. Lee et al.⁴⁵ as well as Jergesen and Khan³² stressed the importance of long-term follow-up in order to accurately describe the natural history of hips affected with nontraumatic osteonecrosis. In our review of the literature, we found only three studies that had a mean duration of follow-up of more than five years^17,20,57.

We previously reported our short-term experience (mean duration of follow-up, sixteen months) with core decompression for the treatment of nontraumatic osteonecrosis in twenty-five patients⁸⁹. The purpose of the present study was to provide a long-term survivorship analysis of hips that had core decompression for the treatment of nontraumatic osteonecrosis of the femoral head at our institution and to identify the independent risk factors that were associated with poor results.

	Materials and Methods

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Preoperative Evaluation and Demographic Data
Core decompression was performed between January 1, 1981, and June 30, 1995, in thirty-four patients (fifty-four hips) for the treatment of nontraumatic osteonecrosis of the femoral head. All procedures were carried out by one of us (T. S. T.) at the same institution. Patients who had advanced disease and were managed with femoral osteotomy or arthroplasty were excluded from the study.

Each patient was evaluated preoperatively on the basis of the medical history, the results of physical examination, and anteroposterior and lateral radiographs. The data that were recorded included the age at presentation, gender, duration of symptoms before presentation, and associated risk factors. Preoperative technetium-99 bone scans were performed for twenty-six patients, and magnetic resonance imaging studies were done for fourteen. The initial stage and extent of radiographic involvement of the disease were assessed quantitatively with use of a modification of the staging system of Ficat and Arlet¹⁸ in combination with the system of Steinberg et al.⁷².

Twenty-one patients were men and thirteen were women. The age at the time of the index procedure was a mean (and standard deviation) of 38 ± 13.7 years (range, twenty-two to eighty-three years). Twenty patients (59 percent) had bilateral involvement. The mean duration of the symptoms before the core decompression was 10.3 ± 17.6 months (range, one to eighty-four months). According to the systems of Ficat and Arlet¹⁸ as well as Steinberg et al.⁷², thirteen hips (24 percent) were stage I (normal radiographs); seven (13 percent), stage-IIA sclerotic; sixteen (30 percent), stage-IIA cystic or sclerocystic; ten (19 percent), stage IIB (transitional stage, with a crescent sign); and eight (15 percent), stage III (collapse).

The presumed risk factors included use of corticosteroids (thirty-seven hips; 69 percent), excessive intake of alcohol (eight hips; 15 percent), and use of adrenocorticotropic hormone for the treatment of multiple sclerosis (two hips; 4 percent). The remaining seven hips (13 percent) were classified as having idiopathic osteonecrosis as no specific risk factors were identified. The group that used steroids was subdivided further according to whether the patients had a history of steroid use or were chronic users (that is, continued to use steroids after the core decompression). Corticosteroids were used by six patients (ten hips; 19 percent) who had had a renal transplantation because of end-stage renal disease. Other reasons for the use of steroids included ulcerative colitis (five hips), Crohn disease (four hips), asthma (four hips), head injury (four hips), non-Hodgkin lymphoma (four hips), Hodgkin lymphoma (two hips), infertility (two hips), systemic lupus erythematosus (one hip), and an orbital tumor (one hip). Forty-nine (91 percent) of the fifty-four hips were symptomatic at the time of the core decompression. The diagnosis of osteonecrosis was confirmed in all hips by histological identification of extensive marrow and trabecular necrosis in the core of bone that had been removed.

Operative Technique
Before the core decompression was carried out, thirty-three patients had intraoperative functional diagnostic tests (baseline bone-marrow-pressure measurements, stress-testing, and intramedullary venography) with use of the methods described by Ficat²⁰.

The core decompression was performed as was described previously⁸⁹. A seven-centimeter mid-lateral longitudinal incision was made over the flare of the greater trochanter. The fascia lata and vastus lateralis were split in the direction of their fibers, and the lateral aspect of the metaphysis was exposed subperiosteally. The lateral cortex of the femur was entered with a drill-bit, and an eight-millimeter trephine was guided into the osteonecrotic segment with use of biplanar image intensification. The core of bone up to the subchondral level was removed, was labeled for orientation, and was sent for histopathological analysis. The incision then was closed in layers over a single Hemovac drain.

Only partial weight-bearing was permitted for at least six weeks after the procedure.

Review of the Data
Follow-up consisted of serial radiographs, a review of the office charts and the operative and pathology reports, interviews, and clinical examination. Contact was made with all thirty-four patients who were enrolled in the study. All patients were still alive, and none had been lost to follow-up.

The results were classified as successful (no symptoms or radiographic progression) or as a radiographic failure (progression of the disease to stage III¹⁸, with collapse) or a clinical failure (performance of a subsequent operation), or both. All patients were followed for a minimum of two years or until the performance of a subsequent operation (clinical failure). Twelve patients (seventeen hips) had a subsequent operation less than two years after the index procedure. Twenty patients (twenty-seven hips) had progression to stage-III disease¹⁸, with collapse, less than two years after the index procedure.

The duration of follow-up (including that of the patients who were followed after failure) was a mean (and standard deviation) of 120 ± 57 months (range, twenty-four to 196 months).

Statistical Methods
The primary outcomes of the study were clinical and radiographic failure. The preoperative radiographic stages were compared for each outcome with use of Kaplan-Meier survivorship analysis³⁶. The significance of the differences among the stages was tested with use of the log-rank test.

Two subgroups were defined preoperatively on the basis of a modification of the staging system of Ficat and Arlet¹⁸ and the system of Steinberg et al.⁷² for the radiographic classification of osteonecrosis. Group A included hips with stage-I involvement or stage-IIA sclerotic involvement, and Group B included those with stage-IIA cystic or sclerocystic, stage-IIB, or stage-III involvement. Survival curves were calculated for these subgroups according to the product-limit method and were compared with use of the log-rank test³⁶. Standard errors and 95 percent confidence intervals of the estimated survival function were derived with use of Greenwood's formula⁴⁶. Multivariate analysis was performed with use of the Cox proportional-hazards model with censoring to identify the independent prognostic factors with regard to clinical and radiographic failure¹².

Hazard ratios and 95 percent confidence intervals were used to assess the importance of the duration of symptoms, renal transplantation, use of corticosteroids, excessive intake of alcohol, and the preoperative radiographic stage for Group A compared with Group B. The models were fitted with use of the backward elimination (stepdown) procedure, and the likelihood ratio test was used to select the variables that were included in the final model⁴⁶. A two-sided p value of less than 0.05 was considered significant. Survival analysis was performed with use of Proc Lifetest and NLIN (nonlinear regression) (version 6.12; SAS Institute, Cary, North Carolina). Power calculations were performed with use of nQuery Advisor software (version 2.0; Statistical Solutions, Boston, Massachusetts).

	Results

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Overall, twenty-six hips (48 percent) had a successful clinical result and twenty hips (37 percent) survived radiographically. The mean duration of clinical survival for all hips was ninety-seven months (95 percent confidence interval, seventy-seven to 117 months), and the mean duration of radiographic survival was seventy-three months (95 percent confidence interval, fifty-four to ninety-two months). The median duration of clinical survival was eighty-five months, and the median duration of radiographic survival was twenty-two months.

The procedure was a clinical success for twelve of the thirteen stage-I hips, all seven stage-IIA sclerotic hips, five of the sixteen stage-IIA cystic or sclerocystic hips, two of the ten stage-IIB hips, and none of the eight stage-III hips. The Kaplan-Meier curves, as compared with use of the log-rank test, showed significantly longer durations of survival for the stage-I and stage-IIA sclerotic hips than for the stage-IIA cystic or sclerocystic, stage-IIB, and stage-III hips (p < 0.01 for all comparisons) (Fig. 1). The clinical survivorship curves for the stage-I and stage-IIA sclerotic hips were not found to be significantly different, with the numbers available (p = 0.46). Furthermore, no significant differences were found among the hips that had stage-IIA cystic or sclerocystic, stage-IIB, or stage-III involvement (p > 0.10 for all comparisons).

View larger version (16K): [in this window] [in a new window]   FIG1: Fig. 1 Kaplan-Meier survivorship curves36 depicting clinical failure (defined as the performance of a subsequent operation) of core decompression for the treatment of nontraumatic osteonecrosis of the femoral head. Censored observations (the observations of each hip at the end of the study) are denoted by open circles. Error bars showing the 95 percent confidence intervals are provided for the sixty and 120-month follow-up intervals.

View larger version (15K): [in this window] [in a new window]   FIG2: Fig. 2 Kaplan-Meier survivorship curves36 depicting radiographic failure (defined as progression to stage-III disease18,72, characterized by collapse of the femoral head) of core decompression for the treatment of nontraumatic osteonecrosis of the femoral head. Censored observations (the observations of each hip at the end of the study) are denoted by open circles. Error bars showing the 95 percent confidence intervals are provided for the sixty and 120-month follow-up intervals.

View larger version (15K): [in this window] [in a new window]   FIG3: Fig. 3 Kaplan-Meier survivorship curves36 depicting clinical and radiographic failure of core decompression for Groups A and B. The hips in Group A fared better than did those in Group B with regard to both clinical and radiographic survival (p < 0.0001 for both comparisons). Censored observations (the observations of each hip at the end of the study) are denoted by open circles. Error bars showing the 95 percent confidence intervals are provided for the sixty and 120-month follow-up intervals.

We previously reported the results of functional diagnostic evaluations (baseline measurements of bone-marrow pressure, stress-testing, and intramedullary venography) in this population of patients⁸⁹. Given the poor relationship between these results and both the diagnostic and the survivorship data reported in the literature^9,27, we discontinued the use of these tests after our previous report.

Two patients (two hips; 4 percent) had a postoperative complication. One patient sustained a fracture of the femoral neck when she fell down a flight of stairs eleven months after the core decompression and was managed with a bipolar hemiarthroplasty. The other patient had a hematoma, which resolved spontaneously.

	Discussion

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The natural history of symptomatic osteonecrosis of the femoral head is generally one of relentless progression to collapse and incongruity of the joint, ultimately leading to total hip arthroplasty if the initial treatment consisted of nonoperative measures only. In a prospective, randomized trial in which the results of core decompression were compared with those of nonoperative treatment at a mean of twenty-seven months, Stulberg et al. reported a clinically successful result for only two of twenty-three patients who had been managed nonoperatively⁷⁹. Steinberg et al. retrospectively reviewed the results of nonoperative treatment of fifty-five osteonecrotic hips and found radiographic progression in 92 percent (no numbers were given), with clinical progression in 84 percent, at a mean of twenty-one months⁷⁶. Musso et al. retrospectively reviewed the results for fifty osteonecrotic femoral heads that had been treated with modified weight-bearing, analgesics, and anti-inflammatory medications and found that forty-seven hips (94 percent) had progression of the disease, according to clinical or radiographic criteria, at a mean of sixteen months⁵⁸.

Despite the general consensus regarding the natural history of nontraumatic osteonecrosis in symptomatic hips, there is a great deal of controversy about the recommended treatment of so-called silent, or asymptomatic, hips with early-stage osteonecrosis. The reported rates of progression have ranged from as low as 17 percent (four of twenty-three in the series of Jergesen and Khan³²) to as high as 100 percent (fifteen of fifteen in the series of Bradway and Morrey⁷ as well as that of Lee et al.⁴⁵). In both reports^7,45, the authors emphasized the importance of long-term follow-up in order to determine the true rates of radiographic and clinical progression. Those results call into question the effectiveness of operative intervention for early-stage osteonecrosis in asymptomatic patients. However, most (forty-nine; 91 percent) of the fifty-four hips in our study were symptomatic at the time of the core decompression.

Given that many theories regarding the pathogenesis of osteonecrosis of the femoral head have been proposed, it is not surprising that a wide variety of treatment options have been advocated for this disease. These modalities have included nonoperative measures^{41,45,54,55,58}, corrective osteotomy^{5,6,16,24,56,66,69}, various vascularized^{26,31,34,49,86,88,90} and nonvascularized^52,64,73 bone-grafting techniques, electrical stimulation^{2,55,72,74,76}, core decompression^{1,9,17,19,27,28,41,43,44,53,55,57,63,70,76,77,79,85,89}, and endoprosthetic replacement^{11,21-23,40,62,67,68,80,83}. The long-term results of total hip arthroplasty in patients who have nontraumatic osteonecrosis are known to be worse than those in matched groups of patients who have other diseases involving the hip^{8,11,20,22,35,40,50,62,68,80}. Therefore, young, active patients should be managed with procedures that preserve the joint, such as core decompression.

There is general agreement in the literature that core decompression is most effective in the earlier stages of the disease^17,54,70. However, the overall rate of success of this procedure for the treatment of nontraumatic osteonecrosis has varied widely, from as low as 17 percent (seven of forty-one in the series reported by Learmonth et al.⁴⁴) to as high as 89 percent (119 of 133, as reported by Ficat²⁰) (Table I). Mont et al. reviewed the results in twenty-four reports of hips that had core decompression for the treatment of nontraumatic osteonecrosis and found an overall rate of clinical success of 64 percent (741 of 1166)⁵⁵. The 48 percent rate of clinical survival in the current study is slightly lower, possibly because of the longer mean duration of follow-up or the high (69 percent) proportion of hips in our study that had steroid-related disease, or both.

Many reports in the literature regarding the natural history of nontraumatic osteonecrosis and the results of core decompression have documented marked differences in prognosis between hips that have had collapse and those that have not^{17,47,53,57,70,73,75,85}. However, our results demonstrate the importance of distinguishing between patients who have cystic changes in the femoral head and those who have sclerotic changes only. Cystic changes in the femoral head as seen on plain radiographs (Group B) were associated with more than a fourfold increase in the rate of overall failure after core decompression. This observation is consistent with the findings of Lennox et al., who reported a combined rate of radiographic and clinical failure of 10 percent (two of twenty) in patients with stage-IIA sclerotic disease compared with seven of eleven patients with stage-IIA cystic or osteoporotic disease⁴⁷.

These findings should be viewed in conjunction with the histological data that have been reported regarding cystic and sclerotic changes in patients who have nontraumatic osteonecrosis. Mont and Hungerford reported that radiolucent or cystic areas on plain radiographs represented regions of resorption of bone and corresponded to the fibrous or granulation tissue seen in histological sections⁵⁴. Similarly, osteosclerotic changes bordering the necrotic area corresponded histologically to the region of repair, with newly formed bone laid down on dead trabeculae.

The current study also demonstrates the importance of identifying risk factors that are associated with the progression of osteonecrosis. We found an association between a shorter duration of symptoms and clinical failure, suggesting that patients who have an acute onset of symptoms may have a more rapidly progressive form of the disease, and this may be a predictor of an adverse outcome after core decompression. We also found an association between use of corticosteroids and radiographic progression, independent of the stage of the disease. Although other authors have suggested that outcomes are worse for patients who have steroid-related nontraumatic osteonecrosis^{10,13-15,33,48,57,65,85,87,89}, no previous study, to our knowledge, has demonstrated an independent statistical relationship between use of steroids and survival of the hip.

Although our study provides useful information regarding the success of core decompression for the treatment of nontraumatic osteonecrosis, it has certain limitations as well. Given the retrospective design of the study as well as the long duration of follow-up, we were unable to examine each patient in person. Therefore, our criterion for clinical failure was based on the performance of a subsequent operation rather than on an objective scoring system such as the Harris hip-scoring system²⁵. Although the inclusion of such data could alter our results, we believe that the performance of a subsequent operation is the ultimate factor in determining the clinical outcome. Moreover, both Smith et al.⁷¹ and Kay et al.³⁷ reported poor intraobserver and interobserver reliability with regard to the classification of osteonecrosis of the femoral head. Therefore, our results may have been affected by the subjective review of the preoperative radiographs. The use of magnetic resonance imaging or computed tomography, neither of which was routinely available at the beginning of this study, may improve the accuracy of preoperative staging. Finally, the small size of our series prevented us from making definitive causal inferences regarding patient-related factors and outcomes. However, given the long mean duration of follow-up (120 months), we were able to demonstrate significant differences that have not been found in previous studies.

Given the relatively young mean age of our patients at the time of presentation, we believe that preservation of the joint should be the goal of treatment of early-stage nontraumatic osteonecrosis. We demonstrated that patients who do not have cystic changes or collapse of the femoral head are most likely to benefit from core decompression. Furthermore, we found that both a rapid onset of symptoms and the use of corticosteroids are independently associated with a poor outcome. These data, used in conjunction with those from the many excellent reports in the literature on this subject, provide a useful framework for the management of patients who have nontraumatic osteonecrosis. Larger, prospective studies should be undertaken to evaluate the effect of the use of steroids and the duration of symptoms on the prognosis for patients who have this challenging, debilitating disease.

	Footnotes

 
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

Harvard Combined Orthopaedic Surgery, Harvard Medical School, 32 Fruit Street, Boston, Massachusetts 02114.

Department of Research Computing and Biostatistics, Children's Hospital, Department of Radiology, Harvard Medical School, 300 Longwood Avenue, Boston, Massachusetts 02115.

§Department of Orthopaedic Surgery, Brigham and Women's Hospital, 75 Francis Street, Boston, Massachusetts 02115. E-mail address: tthornhill@bics.bwh.harvard.edu.

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