While a number of studies have successfully used bisphosphonate therapy to counter structural bone weakening in ONFH [1, 2], recent studies evaluating the effectiveness of core decompression in early stage ONFH remains controversial. To our knowledge, this is the first study that attempts to evaluate both treatment strategies to determine whether one results in greater improvements in clinical outcomes and a delayed progression of the disease.
In our study, 21/40 (52.5%) hips with a mean follow-up of 25.3 months following BP treatment, required a THA compared to 5/22 (22.73%) hips with a mean follow-up of 22.7 months treated with BP + CD + MSC. After adjusting for baseline Ficat stage, age, and sex, a hip treated with BP + CD + MSC had between a 17 and 46% reduction in risk of progressing to the next stage and a 58% reduction in risk of THR compared to a hip treated with BP only, but this finding was not statistically significant. Previous studies have reported that collapse of Steinberg stage II and III femoral heads typically occurs within the first 16–21 months after diagnosis without treatment [16]. Earlier studies have reported rates of collapse of the femoral head of 75 and 80% at 2 and 3 years, respectively [2]. In our present study, our results show that BP treatment alone and BP + CD + MSC treatment resulted in collapse rates and need for THR at 2 years in 43 and 21% of hips, respectively. Although there were no statistically significant differences, our results demonstrate that BP alone and BP + CD + MSC prevented or delayed THA in the first 24 months in 57 and 79% of hips, respectively. These results indicate both treatment options, BP alone and BP + CD + MSC, decrease the risk of collapse as well as the risk of the need for THR. The decision to proceed with a THR is multivariate and dependent on a careful discussion between the patient and their surgeon. While patients may choose to delay THR when presented with an alternate and less invasive option, our results show that both interventions decrease the risk of collapse and thus absolute need for THR. Even though there is no statistical difference between BP alone and BP + CD + MSC, the variations seen in the results between the treatment groups warrants prospective studies to evaluate possible differences in efficacy in delaying the progression of collapse in ONFH. These results indicate that both BP alone and BP + CD + MSC may postpone surgical intervention. This may be complicated by the fact that the treating physician is already providing an alternative therapy. The indications for THR are not entirely objective.
The data from this study also demonstrates no significant difference in clinical outcomes between the two treatment groups when evaluating MHHS, VAS, ROM, and support system. These results may indicate that clinically, there is no difference between the two treatment strategies, thereby questioning CD as necessary surgical intervention. In the BP group, a mean score of 0 (range 0–4) for support system was calculated. In contrast, a mean score of 2.5 (range 0–5) was calculated for the BP + CD + MSC group. Standardized evaluation with larger sample sizes along with the differentiation of the diagnosed stage is necessary to determine a more accurate determination of clinical functional outcomes.
Bisphosphonate therapy has been shown to counter the structural bone weakening caused by reparative osteocytic necrosis and apoptosis through anti-resorptive and anti-inflammatory actions [26]. Bisphosphonates function by inhibiting osteoclast activity, thereby curtailing bone resorption. Recent studies have demonstrated improvement and a reduction in patient disability scores, as well as an overall reduction in the rate of collapse in patients when compared to a control [1, 2, 17]. Lai et al. found that at a minimum of 24 months, only two of the 25 hips in the bisphosphonate group had loss of femoral head integrity compared with 19 of the 25 hips in the control group [17]. Although these results have been promising, the role of bisphosphonates still has remained controversial. Chen et al. reported no significant difference in disease progression, functional outcomes, and radiologic outcomes. In addition, the optimal dosage of bisphosphonate therapy has not yet been established. Therefore, these drugs should be carefully administered. The dosage regimens used in this present study were chosen because they are currently recommended in the standard of care for the treatment of ONFH.
Although there is general agreement in the literature that core decompression is effective in earlier stages of the disease, evidence of its efficacy in preventing collapse has been controversial with the overall rate of success varying from as low as 40% to as high as 89% [5,7, 8] A meta-analysis of 24 studies analyzing 1206 hips demonstrated that the best results of CD were in the treatment of early-stage lesions [18]. Eighty-four percent of patients with Ficat and Arlet stage I disease and 65% of patients with stage II disease had successful results [18]. The pathological mechanism underlying osteonecrosis has been associated with premature conversion of the red marrow to the fatty marrow resulting in an overall diminished number of progenitor cells in the affected bone [10, 16]. There has been documentation of decreased osteogenic stem cell concentrations beneath the sequestrum and in the inter-trochanteric region of the femoral head [12]. Therefore, the addition of autologous bone marrow along with core decompression may enhance repair of bone after osteonecrosis. Previous studies have demonstrated therapeutic effects of bone marrow implantation through marrow stromal cell secretion of angiogenic cytokines increasing both angiogenesis and osteogenesis. Hernigou et al. reported better outcomes in patients who had greater numbers of progenitor cells transplanted in their hips during CD procedures [13]. The addition of autologous mesenchymal stem cells as an adjunctive therapy may offer a potential safe and effective alternative in the treatment of ONFH.
Given the complex and variable nature of the pathogenesis of ONFH, it is not surprising that the variety of treatment modalities remain a controversial issue. The novel therapeutic approach of combining BP + CD + MSC may not only provide stability to the affected hip, but also may aid in reversing the disease process. CD reduces intra-medullary pressure, thereby increasing femoral head perfusion. This procedure allows for substitution to the necrotic area by bringing blood supply through the drill channel [
20]. The mesenchymal stem cells augment osteogenic potential and when combined with CD, create an environment that enhances bone growth and delays disease progression. Furthermore, the addition of bisphosphonate therapy reduces marrow edema and the rate of remodeling, ultimately halting bone resorption. Our results were similar to some of the more recent studies evaluating CD in the treatment of ONFH in a comparable patient population (Table
4). Hernigou and Gangji pioneered the instillation of using MSCs along with CD in the treatment of ONFH. Our overall success rate of 77% for patients treated with BP + CD + MSC is comparable to the results reported by both Hernigou et al. and Gangji et al [
9,
11]. A recent study by Kang et al. demonstrated an 83.6% overall success rate after treatment with BP + CD and reported a mean onset of progression of collapse at 23 months post-operatively [
15]. The results of the current study, in addition to the evidence reported in the literature, support the belief that future prospective clinical trials are warranted to determine the efficacy and compare the outcomes of operative, medical, and conservative care in delaying the progression of ONFH. The data from this study can be used to help direct and inform hypotheses and power analyses for such studies.
Table 4
Review of the current literature
This study has several limitations. Our study was retrospective and thus maintains the biases inherent to such a study design. Although this current study suggests that treatment with either BP or BP + CD + MSC are effective in delaying collapse within the first 24 months after diagnosis, the lack of long-term follow-up data makes it difficult to determine whether this effect can be maintained over longer periods of time. Future prospective studies are critical in determining whether these treatment strategies can prevent THR in the long term. While there is clinical and radiologic improvement, delaying THR in the younger, active population may not ultimately be the best option. Assuming that 50% of patients treated with BPs alone will undergo THR within 2 years post-treatment initiation, 109 patients per group (218 total) would be required to obtain 80% power at a two-sided alpha level of 0.05 to detect a 20 percentage point decrease in THR within 2 years post-treatment initiation in the BP + CD + MSC group using logistic regression. The sample size estimate includes an adjustment for the assumption that a multiple regression of treatment group on the other predictors would produce a pseudo R2 of 0.15.
The lack of clinical evidence in the literature makes it difficult to identify optimal treatment protocols to manage patients with pre-collapse AVN of the femoral head. Our results demonstrate that treatment with BP alone or BP + CD + MSC have the potential to delay the need for THA in the first 24 months in patients with ONFH. Future prospective studies are warranted to determine the efficacy of these treatment strategies in the long term. Prospective studies should attempt to compare operative, medical, and conservative care in the treatment of ONFH to establish conclusive evidence.