The clinical syndrome of enthesopathy of the plantar fascia presents as pain on the inferior posteromedial surface of the heel, which is characterized by amplified morning discomfort usually aggravated by walking and running ( [9]Figure 1 [10]). This syndrome of unknown cause may produce significant disability for many months and possibly years, even though it is generally self-resolving.[1-3]

Diagnosis is based on clinical presentation and tenderness over the medial calcaneal tubercle. Radiological examination may reveal a calcaneal spur at the medial calcaneal tubercle, but this is also found in up to 21% of asymptomatic patients (Figure 2 [11]). Ultrasound may reveal thickening of the plantar fascia near the medial calcaneal tubercle.[3] However, some investigators have found that there is no reliable clinical correlation between positive ultrasound findings and patient symptoms.[3,4]

The examining physician must consider that seronegative spondyloarthropathies and rheumatoid arthritis may present as plantar fasciitis. One identified complication involves entrapment of the calcaneal branch of the tibial nerve by the postinflammatory scar. Treatment is mainly symptomatic and includes rest, ice, physiotherapy, oral anti-inflammatories, shock-absorbing heel pads, orthotic foot devices, night splints, casting, and treatment with corticosteroids topically or by injection.[5] Open or endoscopic surgery is reserved for cases where time and all conservative means have not produced satisfactory results. Significant risks of surgery include postoperative complications, prolonged healing, and altered foot biomechanics. The resistant nature of plantar fasciitis creates a need for a safe and effective intervention beyond conservative therapy that makes the risks of surgery unnecessary.[5,6]

Extracorporeal shock wave therapy

The use of externally applied acoustic shock waves was established in the 1980s for the treatment of calculi in the urinary, renal, biliary, and salivary systems. It was found that short pulses in water create a fast pressure rise leading to a high-pressure maximum that can be focused on a target (Figure 3 [12]) such as the kidney system, causing disintegration of calculi and avoiding the need for surgery. By 1991 Valchanow and Michailov had initiated the use of these high-energy shock waves for delayed union of bone fractures and pseudoarthroses. In the next decade the application of extracorporeal shock wave therapy (ESWT) to a wide variety of musculoskeletal disorders stimulated technological changes to the generation and type of shock waves.[7]

The mechanism by which ESWT may have a positive effect on enthesopathies is unknown. The following possible effects have been suggested:

Cellular. Creates extracellular cavitations, ionized molecules, increased membrane permeability, and neovascularization.

Analgesic. Creates hyperstimulation analgesia by nerve stimulation through a pathway that inhibits transmission.

Acoustic shock waves can be generated in three ways (Figure 4 [13]), each with distinct focal characteristics:

• Electrohydraulic—large focus
• Electromagnetic—medium focus
• Piezoelectric—small focus
ESWT may be delivered in two ways:
• High energy—energy-flux density >0.60 mJ/mm²
• Low energy—energy-flux density 0.04-0.28 mJ/mm²
The ESWT devices in use today include the following:
• OssaTron. This high-energy device uses an electrohydraulic method for ESWT generation. Anesthesia and physician supervision are required. Usually one treatment of less than 1500 pulses is administered.
• Dornier Epos. Another high-energy device, this machine uses an electromagnetic method for ESWT generation. Anesthesia and physician supervision are required. Usually a single treatment is given. 
• Sonocur. This low-energy machine uses the electromagnetic method of shock wave generation. Usually three treatments of under 3000 pulses at weekly intervals are administered under physician supervision. Treatments are applied without the use of anesthesia and delivered to the site of maximal tenderness.

Rationale for a literature review

In the past decade there have been hundreds of references in the medical literature to the use of ESWT for musculoskeletal conditions. The enthesopathic conditions treated with EWST include:

• Plantar fasciitis
• Lateral epicondylitis
• Supraspinatus tendinitis 
• Patellar tendinitis

This has led to a variety of review articles and meta-analyses.[7-9] The wide range in the quality of the research methods combined with the different applications of ESWT in divergent medical diagnoses have produced challenges to reliable conclusions. The use of the low-energy Sonocur device includes clinical focusing of the electromagnetic shock head on the point of maximum tenderness with feedback from the patient to the operator of the device. This differs from the use of high-energy devices such as OssaTron and Dornier Epos Ultra, which require anesthesia with focusing of the acoustic energy on a location guided by fluoroscopy or ultrasound to assumed pathological points. Consequently, when comparing the research using these two distinct approaches, we must acknowledge these differences.

Results

The review was limited to prospective, randomized, placebo-controlled, peer-reviewed, and published research studies in which ESWT was the therapeutic intervention in patients with plantar fasciitis. Seven studies involving a total of 748 cases met these criteria (see the Table).[1,2,6,9-12] Aspects of the studies analyzed include the following:

Number of subjects. The number of subjects in each study ranged from 30 to 260.

Duration of symptoms. Most studies included subjects not helped by conservative therapy, with symptoms persisting between 26 weeks and 52 weeks. The one exception was the Buchbinder study, which included subjects with only 6 weeks of symptoms.

Device and energy level. All studies used low-energy devices, with the exception of Ogden and colleagues who utilized the high-energy OssaTron.

Total number of pulses. This ranged from 1500 to 6300 pulses.

Anesthesia. This was necessary only with the use of the high-energy OssaTron.

Clinical focusing. Used in all studies except Buchbinder’s, where treatment was ultrasound-guided, and Ogden’s, where treatment demanded anesthesia and prevented applying ESWT to the site of greatest tenderness.

Primary outcome variable. The studies used patient satisfaction, subjective pain, walking ability, tenderness, and morning pain as outcome measures.

Follow-up examination. Evaluation of status and possible improvement ranged from 6 to 52 weeks.

Statistical significance. All studies except Buchbinder’s showed statistical significance.

Discussion

In 1996, Rompe and colleagues reported on two studies using rest pain, night pain, local tenderness to manual pressure at rest, and walking ability assessed by tolerance to distance as primary and secondary outcome measures. Statistically significant differences were found between the ESWT group and the placebo group (treated with an inactive or dummy ESWT machine) after a 12-week follow-up. Further follow-up at 24 weeks may be confounded by the application of further therapy to both ESWT and placebo groups.[10,11] In 1998, Kirschek and colleagues reported on 50 subjects, using pain-free walking and manual pressure while walking as outcome variables. Kirschek found statistical significance comparing low-energy ESWT with placebo intervention.[11]

In 2001, Ogden reported on the use of high-energy ESWT with the result that after 12 weeks, 56% more of the treated patients had a successful result when compared with those treated with a placebo.[6]

In 2002, Buchbinder and colleagues studied 166 patients using overall pain, morning pain, activity pain, walking ability, and two scoring forms as primary and secondary outcome measures. No significant differences were found between the ESWT and placebo groups. This outcome stands alone against the other six studies, which each demonstrated consistent and statistically significant improvement comparing ESWT and placebo intervention.[12] The protocols used by Buchbinder differ in two areas when compared with Rompe’s methods. Patient selection allowed a minimum duration of symptoms of 6 weeks compared with 26 weeks to 52 weeks in the other studies. In fact, the median duration of symptoms for the ESWT group was 38 weeks and for the placebo group was 43 weeks. Six weeks is a relatively short duration for a condition that may spontaneously resolve in many patients within 52 weeks of diagnosis. Patient selection also included ultrasound-confirmed plantar fascia thickening, which can be found in asymptomatic individuals. This criterion has not been used by any other reported study. Rompe used clinical focusing of the ESWT by using patient feedback of maximal tenderness of the heel while applying the shock waves. Buchbinder used ultrasound-guided direction to the point of maximal thickening of the plantar fascia but makes no mention of using clinical focusing to identify the point of maximum tenderness.

In 2002 and 2003, Rompe and colleagues reported on two further studies. The first study indicated a 47% greater improvement in the EWST group compared with the placebo group at 24 weeks follow-up.[2] The most recent study on 45 running athletes used an increased low-energy flux density with more than double the total number of pulses. Pain on walking in the morning was used as the primary outcome measure and was assessed by the visual analog scale (VISA). At 52 weeks follow-up the ESWT group dropped from 6.9 points to 1.5 points compared with 7.0 to 4.4 points in the placebo group. The P value was >0.0001.[1]

Ogden and colleagues conducted a meta-analysis of shock wave therapy for chronic plantar fasciitis in 2002. They found 8 of 20 published studies up to 2001 met their criteria for acceptable studies. Their conclusion shows that the directed application of shock waves to the enthesis of the plantar fascia at the inferior calcaneus to be a safe and effective nonsurgical method for treating refractory plantar fasciitis. They suggest that the use of ESWT be considered before any surgical intervention and that ESWT may be preferable to cortisone injection, which may rupture the plantar fascia and lead to frequent recurrence of symptoms.[8]

In 2002, Chung and Wiley reviewed 60 abstracts, 25 case series, and 40 randomized controlled studies in which ESWT was utilized in supraspinatus tendinitis, patellar tendinitis, lateral epicondylitis, and plantar fasciitis. They concluded that although no specific mechanism has been identified by which ESWT acts, the pain-relieving effect of shock waves on tendinopathies has been consistently observed in both case series and prospective, randomized, placebo-controlled studies in the published literature. There are no reports of severe adverse effects with the use of ESWT. Controversy exists regarding specific ESWT protocols in terms of energy density, number of sessions, and use of high-or low-energy machines.[7]

Treatment is available in Vancouver with the low-energy ESWT machine, Sonocur. Cost is $895 for the expected three-treatment protocol at Sonorex Inc.

In the US, coverage of EWST by Medicare, workers’ compensation plans, and private insurers is increasingly common at a cost of US$1500 to US$2100 for three treatment sessions.

Conclusion

A review of seven studies on the effects of extracorporeal shock wave therapy on plantar fasciitis resistant to conservative intervention shows convincing and statistically significant improvement. The single contradictory study differed in patient selection and methodology, which may account for the difference in reported results. The clinical use of ESWT should, therefore, be considered after conservative therapy has failed and before surgical intervention for chronic plantar fasciitis is contemplated.

Competing interests

Drs Clement and Taunton are partners in Sonorex Inc. BCMJ editorial board members Drs Wilson and Day hold nominal shares in Sonorex Inc.

Table. Studies assessing treatment of plantar fasciitis with ESWT.

D.B. Clement, CM, MD and J.E. Taunton, MD

Dr Clement is professor emeritus in the Department of Family Practice and School of Human Kinetics at the University of British Columbia. Dr Taunton is a primary care sports medicine physician and director of the Allan McGavin Sports Medicine Centre, as well as professor in the Department of Family Practice and School of Human Kinetics at the University of British Columbia.