The role of electrical stimulation in the management of avascular necrosis of the femoral head in adults: a systematic review

In the two retrospective studies, a total of 117 patients or 146 hips with symptomatic, non-collapsed avascular necrosis of the femoral head were included [2, 3]. In both studies, patients were treated with PEMF for 8 h a day for 6 months. Cebrian et al. demonstrated that electromagnetic stimulation in femoral heads of ARCO stages I and II led to a survival percentage of 88.57% of the heads on radiographic assessment [3]. Similarly, the paper by Cadossi et al. revealed that PEMF preserved 90% of the femoral heads of Ficat I, 75% of Ficat II and 50% of Ficat III; there were even improvements in the staging of 45% of Ficat I hips to stage 0 and 35% of Ficat II hips to stage I. Functionally, 46% of patients achieved normal hip function and 39% achieved sufficient hip joint function at the end of treatment. As for pain scores, the study found that 53% of patients were pain free after treatment with PEMF while 26% had pain of moderate intensity [2]. Likewise, Cebrian et al. also noted improvement on the D’Aubigne pain scale in 78.57% of the hips [3]. Nevertheless, in both studies, there were some hips that eventually progressed to collapse. Cebrian’s study had a total of eight femoral head collapses, all of which were of ARCO stage II (n = 50) whereas Cadossi found that 15 (three Ficat II and 12 Ficat III initially) of the 76 hips had radiographic progression that led to the development of severe osteoarthritis requiring hip arthroplasty [2, 3].

Steinberg et al. conducted several studies comparing the outcome of hips that received electrical stimulation, and those that did not [11, 14, 15]. In one paper, he looked at two groups of patients, one who received direct current (DC) stimulation and one who had capacitive coupling (CC) [11], both in addition to core decompression and grafting. The results of the former group showed radiographic progression in 70% compared to 79% in control hips; there was a mean 5 point improvement in the Harris Hip score whereas the control group had a mean 3 point drop instead; however, 41% of hips treated with DC required THA compared to 37% of control hips. The CC group showed less promising results, with 42% of hips either clinically and radiographically improving or remaining unchanged compared to 50% in the control group; 25% of stimulated hips eventually needed THA versus 20% of unstimulated hips [11].

Steinberg et al. also compared non-operative management with core decompression and grafting alone, and with DC as adjunct. They found that electrical stimulation showed an improvement in number of hips and average extent of roentgenographic progression, albeit not a significant difference. Electrical stimulation also gave better Harris scores, with 64% showing improvement or remained unchanged, versus 43% in the core decompression alone group. Requirement for hip replacement was similar with or without electrical stimulation. Both groups were superior in all aspects compared to non-operative management [15].

In another similar study, Steinberg et al. compared non-operative management, core decompression with grafting, and CC as adjunct to decompression and grafting. They found that no significant difference was found when CC was used, based on roentgenographic progression, clinical evaluation, and hips requiring replacement. However both groups were superior to non-operative management [14].

In the present review, studies examining the effect of PEMF, whether alone or in combination with other treatments, generally showed some benefit when PEMF was administered. As a treatment used on its own, PEMF was shown to preserve majority of femoral heads (80.2% by Cadossi (2), 88.57% by Cebrian [3], 83.9% by Bassett [10] with these benefits being more pronounced in hips of earlier stages, namely Ficat I and II and Steinberg II and III, and decreasing as severity increased. Remarkably, PEMF has also been shown to reverse the disease progression across 2 of these studies; Bassett et al. found 9 hips demonstrated improvements with 3 of these even returning to normal [10], while Cadossi et al. showed improvements in Ficat stages [2].

Additionally, it was found that PEMF was also effective in improving symptoms of osteonecrosis. Cebrian and Cadossi both found that significant proportions of patients who received PEMF therapy eventually experienced an improvement in pain or even became pain free [2, 3]. Moreover, Massari et al. found that though the efficacy of PEMF decreased overall with increased Steinberg staging, there was greater clinical than radiographic benefit seen in those with Steinberg IV hips [4], further reinforcing the potential of PEMF to alleviate pain in these patients. Conversely, Windisch et al. showed that there was no difference in clinical outcomes between patients who received PEMF and those who didn’t. However, unlike the other papers, the method of inducing the electromagnetic field in this study was an invasive one via a bipolar induction screw through the femoral head [5]. This may have contributed to the discrepancy, as discussed later in the section on DC therapy.

A notable limitation to these studies is the lack of comparison to pain outcomes in non-operative management, hence making it difficult to ascertain the actual degree of improvement. However, Aaron et al. found that more patients who received PEMF alone experienced less pain than patients who received core decompression alone [6]. This is significant as it is the only study that directly compared outcomes of PEMF therapy to the current most widely-accepted conservative treatment method, and it showed a clear advantage of PEMF over core decompression.

These findings show that PEMF therapy is a promising technique, especially for the management of early stage disease.

Two studies examined the effect of electrical stimulation as an adjunct to core decompression and grafting with varying results. One study showed improvements in Harris Hip scores and less roentgenographic progression in electrically stimulated hips via DC, although the percentage of patients needing THA in both groups was the same [15]. Similarly, in another study, femoral heads that were treated with DC had better radiological and clinical outcomes than the control group, with an average progression of two thirds a stage compared to one and a third a stage respectively [11]. However, surprisingly, more hips from the DC group eventually required THA (41% vs 37%) [11]. Although there appears to be a small benefit with DC stimulation, its efficacy should be considered in the context of it being an invasive procedure. Due to the study designs, DC application was only evaluated as an adjunct therapy to core decompression and grafting, where it showed no extra benefit. Therefore, more research is required to assess its efficacy as a technique alone. Yet, randomised double-blind controlled trials may not be suitable in this instance, as the control group would likely have to receive insertion of a placebo device, which is ethically problematic [22]. As such, future trials should compare DC therapy alone to other techniques alone, or vary the protocols used in terms of voltage and length of stimulation.

Patients who received CC fared worse than those who did not. In one study, hips that were stimulated showed poorer outcomes in all parameters: roentgenographic progression, HHS and Steinberg staging [14]. The other study also revealed comparable findings with unstimulated hips faring better [11]. This is noteworthy because CC is another non-invasive method of applying electric fields, yet the results yielded are significantly worse than those of PEMF. One interesting difference we identified between the PEMF and CC groups is the duration of stimulation: all the patients who were treated with PEMF had it administered 8 h a day whereas those who received CC in one of the studies had their affected hips stimulated nearly 24 h a day [14]. This may explain the large discrepancy in results between the two modalities; it may be that CC would have similar effects to PEMF if the protocols used were more similar. This difference also makes it difficult to directly compare these studies, hence, more controlled clinical trials are needed before any concrete conclusion can be made about the effectiveness of CC compared to PEMF, with emphasis on evaluating the optimal protocol for CC application.

In the paper by Cebrian et al., it was noted that in addition to the presence of certain radiological features, having a femoral head with a greater than 15% necrotic area influenced the likelihood of progression as well. Moreover, they identified that all of the femoral heads that went on to have roentgenographic progression had predominantly lateral involvement [3]. Similarly, Steinberg et al. noted that hips with small lesions fared significantly better than those with intermediate and large lesions [11]. As such, lesion size and its location may be important prognostic markers, and are parameters that haven’t been addressed in other papers.

Finally, another important point to note is that many of these papers either did not take into consideration the aetiologies of the disease, or did not evaluate the outcomes according to aetiologies. With regards to PEMF therapy, Bassett et al. noted that corticosteroid use as an aetiology may have influenced response [10], while Cadossi et al. proposed that idiopathic lesions may be more sensitive [2]. Steinberg et al. mentioned that patients who have had alcohol and steroid use as disease aetiologies may have had poorer outcomes, although the difference was not statistically significant [11]. Causes of the disease may be a confounding factor; secondary lesions may be less responsive to treatment due to their ongoing nature, for example steroid use for treatment of another disease should not be interrupted [4]. Studies to date on this topic are limited in number, size, and quality of research methodology. There is heterogeneity in the methodology used (eg: dosage of electrical stimulation and follow up period) so a meta-analysis would not yield any meaningful data on the outcomes of interest. Hence this article shows the best available evidence on electrical stimulation in the management of AVN in the femoral head. Therefore, it is recommended that future research investigate the relationship between treatment outcomes and disease aetiologies.