Variable epidemiologic data are available concerning femoral head osteonecrosis. In the United States it is expected that approximately 10,000 to 20,000 patients will have this disorder develop annually. 22 Osteonecrotic lesions in adults usually have similar pathomorphologic changes. 2,12 Frequently, the underlying condition is a circulatory disorder accompanied by the progressive destruction of bone cells. However, direct damage caused by inflammation, radiation, or high-dosage cortisone therapy also may cause metabolic disorders that adversely affect bony tissue. The onset of the disease is heralded by micromorphologic changes that are not visible on standard radiographic studies. However, disorders of bone metabolism may be visualized at an early stage by angiography, magnetic resonance imaging (MRI), or bone scans. 16,26,27,33,36,40,44
In the joint-preserving surgical treatment of femoral head necrosis, the choice of method still is controversial. The procedures that now are available are recommended primarily on the basis of the stage of the disease. Treatment methods include: (1) decompression of the medullary space of the femur with and without the transplantation of spongiosa material 13–15,25,32 to cause new ingrowth of blood vessels; (2) a large number of conversion osteotomy procedures aimed at rotating the necrotic focus out of the zone of loading 4,18,43,44; (3) bone transplants with vascular pedicles 8,15,20,31; and (4) endoprosthetic joint replacement after the failure of head-preserving methods.
The published results for surgical treatment of patients with femoral head necrosis, with a followup of 4 to 18 years, show that total hip replacement could be delayed in only 22.6% of cases. 28 Surgical procedures preserved the current stage of the osteonecrosis before surgical treatment for some time, but none led to recovery of the femoral head necrosis to a restitutio ad integrum.
To the authors’ knowledge, no therapy has been developed that addresses the cause of femoral head necrosis. In most patients, conservative therapy succeeds only in postponing implantation of a hip prosthesis. The conservative methods used to date consist only of symptomatic measures that usually succeed only in alleviating the patient’s symptoms but not in halting the progress of the disease. The promotion of new bone formation observed in patients with posttraumatic pseudarthrosis (a condition marked by bone deterioration and the absence of new bone formation) after high-energy shock wave therapy led the current authors to hope that this therapy also might stimulate the formation of new bone in patients with osteonecrosis. To date there are no known scientific reports on the use of high-energy shock waves to treat femoral head necrosis. 11
After the initial publication by Heinrichs et al in 1993, 10 four papers on the use of extracorporeal shock waves to treat patients with pseudarthrosis were published. 9,29,40,41 All authors reported excellent therapeutic success and new bond formation. As a result, the current authors began their prospective study on the treatment of femoral head necrosis in adults with extracorporeal shock wave therapy in 1998.
Shock wave therapy offers several important advantages over conventional surgical treatment. It is a noninvasive treatment with a substantially reduced incidence of complications. 34 Moreover, should the implantation of a total endoprosthesis become necessary, it can be replaced in bone that has not been altered by surgery. Additionally followup treatment and rehabilitation is shortened considerably for patients who have received extra-corporeal shock wave therapy.
The objective of the current study was to test the efficacy of shock wave therapy for patients with femoral head necrosis.
MATERIALS AND METHODS
The study population consisted of 10 women and 12 men who ranged in age from 33 to 79 years. The left hip was affected in nine patients and the right hip was affected in 13. The age distribution produced almost a normal distribution curve with a mean value of 54.9 (± 12.3) years.
At the beginning of the study, five hips were classified as Stage I on the Association Research Circulation Osseous (ARCO) scale. 37 In these patients femoral head necrosis was evident only on magnetic resonance imaging (MRI) or bone scans. The hips in all the patients were classified according to the ARCO scale; the results showed eight hips with Stage II disease, eight with Stage III, and one with Stage IV disease. The hip with Stage IV disease was included, because the patient had Stage III necrosis involving the contralateral side and requested treatment of both hips with extracorporal shock wave therapy. For repetitive followups, MRI was proven to be the most practical imaging technique. 17,37 For this reason, radiography and MRI were used to classify the lesions on the ARCO scale throughout the current study.
Before the start of shock wave therapy, each patient underwent radiographic examination in two planes, MRI examination with a standardized method, clinical examination, and questioning to elicit information allowing the authors to rank the patients using the Harris hip scale, 7 the Brougham Scale, 3 and the Ficat assessment scheme. 6 None of the patients had transient osteoporosis of the hip. 38 In addition, the patients ranked themselves on the visual pain analog scale.
The scoring systems used in the current study take into account clinical and radiologic criteria with different subjective and objective parameters and have been used to facilitate comparisons with studies on invasive therapeutic methods. The Harris hip score is one of the most commonly used scores for evaluating hip disease. It originally was developed for evaluating degenerative arthritis of the hip. However, it has proven to be of value for a wide range of hip disorders and has been used to document the clinical course of femoral head necrosis.
In the Harris hip score the parameter with the highest weighting is pain. Consumption of painkillers and subjective restriction of activity are included in the ranking. Other factors taken into account are type of gait, walking radius, objective restriction of activity, mobility, and ability to do everyday activities.
The ranking system developed by Ficat 5,6 and Brougham et al 3 includes radiologic and clinical criteria and has been developed especially for assessing femoral head necrosis. The visual pain analog scale also was applied.
The ARCO system was used to classify femoral head necrosis on the basis of MRI findings. The development of the MRI findings were evaluated by members of the study team according to defined criteria using a standardized approach (Table 1).
The acoustic parameters of the shock wave therapy subsequently administered with an OssaTron unit (HMT Company, Lengwil, Switzerland) are shown in Table 2. Studies of anatomic human specimens were done by the authors to determine the most favorable position for the ultrasonic head and the patients during extracoporeal shock wave therapy. To date, 35 patients with femoral head necrosis have been treated. However, the 1-year results were only available for 22 patients, who were assessed subsequently.
A clinical examination was done 2 weeks, 6 weeks, 3 months, 6 months, and 1 year after the administration of shock wave therapy. If the results of the first shock wave treatment were unsatisfactory after 6 weeks, a second shock wave treatment was administered.
To date, the 1-year results obtained from 22 patients with femoral head necrosis have been evaluated. One of these patients was excluded because of very poor compliance and failure to report for the followups. Six patients have had core decompression (two patients) or total hip replacement (four patients) after the 6-month results had been evaluated. All patients, however, have been included in the data analysis.
Analysis of the Harris hip scores obtained at the first examination before shock wave therapy revealed a mean value of 43.3 (± 10.9) points of a maximum possible score of 100 points. The mean value attained on the visual pain analog scale was 8.5 (± 1.3) points. On this scale, 10 points are given for unbearable pain and one point is given for freedom from pain. On the Ficat scale, in contrast, one point was assigned for very good results and a lowest value of four points for very poor results. The mean values obtained for pain and mobility on this scale were 3.6 and 2.5, respectively.
Patients initially reported a distinct improvement in pain after extracorporeal shock wave therapy. During the subsequent period, this improvement stabilized at 14 patients (66.6%) for the entire followup. After 2 to 6 weeks, seven patients (33.3%) complained that their previous symptoms had returned. None of the patients reported noticeable worsening of their initial condition.
Distinct therapeutic success was observed in 14 patients. This success manifested as an improvement of the pain symptomatology and mobility and in higher scores on the Harris hip scale. For patients who did not undergo subsequent surgery, the score on the visual pain analog scale decreased to 1.2 (± 1.1) and the score on the Harris hip scale increased to 92.0 (± 7.5) at the 1-year examination (Fig 1). The pain and mobility values on the Ficat scale decreased to 0.7 (± 0.6) and 0.9 (± 0.8), respectively. All of these improvements in results proved to have a high statistical significance (p < 0.001).
Separating the study population into groups characterized by therapeutic success and therapeutic failure, the mean values of the 6-month results showed that the visual pain analog scale of patients who did not respond to therapy improved only slightly from 8.7 (± 1.3) to 8.4 (± 1.3) whereas the values of patients whose therapy was successful improved from 8.4 (± 1.4) to 2.0 (± 1.2) (p < 0.001).
A similar trend was observed in the Harris hip score, which remained practically unchanged, with an increase from 33.3 (± 7.1) to 34.7 (± 10.0) in the group of patients who did not respond to therapy. In the patients whose therapy was successful, the average score increased from 48.3 (± 8.8) to 88.9 (± 8.8). The group of patients who did not respond to therapy also had poorer baseline values.
The two groups also scored differently on the ARCO scale. On this scale, the group of patients who did not respond to therapy achieved a mean value of 2.7; this was a stage higher than the mean value of 1.9 measured in the group of patients whose therapy was successful. Figure 2 shows that patients with lower ARCO stages at the beginning of extracorporeal shock wave therapy obtained higher scores 1 year after treatment. A comparison of the age distribution in the two groups revealed that the average age of the patients who did not respond to therapy was 58.4 (± 15.8) years, which was not significantly different than the average age of patients (51.8 (± 9.6) years) whose therapy was successful (p > 0.05).
Analysis of the MRI results obtained in the patients whose therapy was successful showed complete healing in four patients (Fig 3), a significant decrease in the size of the area of poor circulation in six patients, and unchanged findings in comparison with the initial examination in four patients.
Analysis of the MRI results obtained from the patients who did not respond to therapy showed unchanged findings in six patients and a slight increase in the size of the area of poor circulation in one patient.
A review of studies on the use of shock wave therapy for orthopaedic indications only revealed one published prospective study on the treatment of patients with femoral head necrosis. 21 This review found several articles on the treatment of delayed bone healing with the direct application of shock wave therapy to bony tissue, 9,10,29,41,42 and a report on an in vivo study on the osteogenic potency of extracorporeal shock wave therapy. 24 One report describes the use of magnetic field therapy to treat patients with femoral head avascular necrosis. 19
A comparison of the medium-term results achieved by the commonly used surgical methods reveals widely varying success rates. Although relatively uniform results are reported for the pedicled bone transplants, with good and very good results attained in between 62% and 89% of patients, 32,39 surgical techniques involving drilling into the femoral head or intertrochanteric flexion osteotomy produced less satisfactory results. The success rates reported for these procedures ranged from 35.2% to 65%. 23,32,35 These studies emphasize the high rate of late sequelae and the technical difficulties associated with the performance of rotation osteotomies. 1,30
The analysis of the authors’ results 1 year after treatment is encouraging. Nevertheless, medium-term and long-term results are necessary before it is possible to determine whether this method can prevent recurrence or progression of this disease.
In particular, the reduction of pain experienced by some patients who had an unchanged zone of necrosis on MRI raises questions as to the mechanism responsible for this pain alleviation. In the current study, a sclerotic margin around the zone of necrosis revealed by MRI has gained acceptance as a criterion for therapeutic failure. The study shows that the success rate depends on the ARCO stage at the beginning of extracorporeal shock wave therapy, which is shown clearly in Figure 2. In addition to the higher success rates among the patients with Stage I and Stage II disease, a conclusion congruent with the surgical results published in the literature, patient age seems to have a corresponding impact on the clinical and radiologic results, although there is no statistically significant difference. This may be explained by the increasingly poor circulation of older patients. To date, the 1-year results have not shown a poorer outcome in patients treated with this method than in patients treated with surgical methods. Another possible explanation for the poor results obtained with the use of shock waves to treat femoral head necrosis after medial fracture of the femoral neck may be damage to the medial branch of the circumflex femoral artery. To clarify this question, future studies will have to include angiographic MRI studies.
The good results obtained with the use of high-energy shock wave therapy in patients with femoral head necrosis confirm the authors’ suspicion that this procedure offers a potentially viable alternative to invasive methods for treating this disease. If the current results are verified by the 2-year results, a noninvasive economically sound method may be offered to patients.
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John A. Ogden, MD; and Richard R. Alvarez, MD, Guest Editors