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Published online before print November 24, 2004, 10.1148/radiol.2341031653
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(Radiology 2005;234:206-210.)
© RSNA, 2004

Musculoskeletal Imaging

Chronic Plantar Fasciitis: Acute Changes in the Heel after Extracorporeal High-Energy Shock Wave Therapy—Observations at MR Imaging1

Fang Zhu, MD, PhD, Jeffrey E. Johnson, MD, Christopher B. Hirose, MD and Kyongtae T. Bae, MD, PhD

1 From the Mallinckrodt Institute of Radiology (F.Z., K.T.B.) and Department of Orthopedic Surgery (J.E.J., C.B.H.), Washington University School of Medicine, 510 S Kingshighway Blvd, CB 8131, St Louis, MO 63117. Received October 10, 2003; revision requested December 30; final revision received March 31, 2004; accepted May 12. Address correspondence to K.T.B. (e-mail: baet@mir.wustl.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To prospectively evaluate with magnetic resonance (MR) imaging the acute changes in the heel associated with extracorporeal shock wave therapy (ESWT).

MATERIALS AND METHODS: Institutional clinical study review board approved the study, and informed consent was obtained. MR imaging was performed within 24 hours before and after ESWT on 18 feet of 12 patients (eight women and four men; age range, 33–63 years; average, 49.9 years) with chronic plantar fasciitis. ESWT was applied to the most painful point on the plantar surface of the heel, with a total of 1500 shocks at 18 kV. The MR imaging protocol consisted of sagittal and coronal T1- and T2-weighted images with and without fat saturation. The images were reviewed to assess the post-ESWT changes in soft-tissue and bone marrow edema, the thickness of the proximal plantar fascia, and the presence of a heel spur. Paired t test was used for the statistical analysis.

RESULTS: Soft-tissue edema, which was present in 16 (89%) of 18 heels before ESWT, had increased in severity in 12 (75%) heels after ESWT. Calcaneus bone marrow edema at the insertion site was observed in eight heels before ESWT. After ESWT, the extant of bone marrow edema had increased in one heel and had newly developed in another heel. The heel spur seen in nine (50%) feet was not affected by ESWT. In 17 (94%) heels, the proximal plantar fascia was abnormally thick, with thickness not significantly changed with use of ESWT (P > .05).

CONCLUSION: Increase in soft-tissue edema is the most common acute response associated with ESWT.

© RSNA, 2004


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Plantar fasciitis is one of the most common causes of heel pain (1). Nonsurgical management of plantar fasciitis includes plantar fascia and gastrocnemius-soleus muscle stretching, cushioned-sole footwear, night splints, foot orthoses, application of a short leg cast, and steroid injection. Surgical treatments such as plantar fasciotomy have been advocated when nonsurgical managements fail (1,2). Recently, the development of extracorporeal shock wave therapy (ESWT) for the plantar surface of the heel has added a new dimension to the treatment of plantar fasciitis (3–8). The success rate of ESWT, which is based on subjective symptomatic relief of heel pain, remains variable (9–13). Objective measures from a physical examination are difficult to quantify; therefore, imaging modalities are desirable to assess the effectiveness of ESWT and to potentially optimize the treatment.

Magnetic resonance (MR) imaging has been used to diagnose and characterize plantar fasciitis (14–17). To date, to our knowledge no findings of an imaging study have been published in which the responses associated with ESWT have been evaluated. Thus, the purpose of this study was to prospectively evaluate with MR imaging the acute changes in the heel associated with ESWT.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Patients
This study was approved by the institutional clinical study review board, and all subjects gave informed consent. From July 2002 to May 2003, MR imaging was performed on 18 feet (six bilateral and six unilateral) of 12 patients with chronic plantar fasciitis. The patients consisted of eight women and four men (age range, 33–63 years; average, 49.9 years). The diagnosis of chronic proximal plantar fasciitis was established by means of clinical criteria as follows: localized tenderness at the plantar fascia insertion site, start-up pain after rest, negative work-up results on radiographs (and electromyogram and/or nerve conduction study in two patients) to rule out other sources of heel pain, and failure of nonsurgical treatment for at least 6 months.

Imaging and Treatment
All subjects underwent two MR imaging sessions: first imaging within 24 hours before and the second imaging within 24 hours after ESWT. Before the first MR imaging, each symptomatic heel was manually palpated by a study coordinator nurse to locate the point of the maximal intensity of heel pain. A circle of 2–3 cm in diameter was drawn, centered at the point of the maximal intensity of heel pain. Within 24 hours of the initial scan, each patient underwent ESWT (OssaTron; Health Tronics Surgical Services, Atlanta, Ga) for the affected heel(s), which was performed by the same orthopedic surgeon (J.E.J). The patients were treated in a hospital outpatient surgical suite by using general anesthetic with either a face mask or a laryngeal mask airway. ESWT was applied on the heel at the point of maximal intensity of heel pain to deliver a total of 1500 shock waves at a frequency of four shocks per second and a power setting of 18 kV. This power setting is defined as a high-energy treatment protocol (9). Each heel treatment required approximately 10 minutes of anesthesia time.

MR imaging (Sonata; Siemens Medical System, Iselin, NJ) of each affected foot was performed at 1.5 T by using a knee coil. Prior to each MR session, a vitamin E capsule was taped to the heel, where the point of the maximal intensity of heel pain was delineated with a permanent marker. Vitamin E was in oil form and could be readily seen on MR images corresponding to the location of the point of maximal intensity of heel pain for the MR image interpretation. The following MR sequences were performed: T1-weighted spin-echo (SE) (repetition time msec/echo time msec, 450/13), T2-weighted fast SE (4000/108), and T2-weighted fat-saturated fast SE (4000/108) sequences in the sagittal plane and T1-weighted SE (500/13) and T2-weighted fat-saturated fast SE (4200/108) sequences in the coronal plane. The section thickness was 3 mm with 20% gap for sagittal images and 5 mm with zero gap for coronal images. The choice of section thickness was made with the consideration that imaging in the coronal plane required larger scan coverage than did imaging in the sagittal plane. The scan time was reduced by using 5-mm section thickness for the coronal images. First, the sagittal plane was selected parallel to the long axis of the plantar fascia on the transverse scout image. Then, the coronal plane was determined perpendicular to the sagittal plane.

Image Review
MR images were evaluated in consensus by two observers (K.T.B., F.Z. with more than 10 and 5 years of experience, respectively, in interpreting MR images). The images were reviewed to assess the presence and severity of soft-tissue and calcaneal bone marrow edema, the presence of a heel spur, and the thickness and signal intensity of plantar fascia. The observers evaluated qualitatively subcutaneous soft-tissue and perifascial edema on T2-weighted fat-saturated fast SE images and compared pre- and posttreatment MR images side by side. The appearance of subcutaneous soft-tissue and perifascial edema was characterized as a poorly circumscribed area of high signal intensity beneath the fat pad and around the plantar fascia. Calcaneal bone marrow edema was also assessed on T2-weighted fat-saturated fast SE images and compared with that on pre- and posttreatment MR images. The morphology of bone marrow edema was classified into linear or diffuse type, as suggested in previous studies (18,19). The presence of a heel spur was assessed on T1-weighted images. The spur has the same signal intensity as calcaneus bone and arises from the inferior aspect of the calcaneus. The thickness of the plantar fascia was measured on both sagittal and coronal T2-weighted images at the thickest part of the plantar fascia by using the method described in previous studies (14,18). The point of maximal thickness is usually located in the proximal section of the fascia, which is within 5 cm of the calcaneus insertion point. We also compared the possible signal intensity change of the plantar fascia on both T1-weighted SE and T2-weighted fast SE images before and after ESWT.

Statistical Analysis
Plantar fascia thickness measurements before and after ESWT were compared. The data were tested for statistical significance with a three-way repeated-measures analysis of variance. The side of the foot (left or right) was a between-subject factor, and scan position (coronal or sagittal) and scan time (before or after ESWT) were within-subject factors. Up to three-way interactions were tested for statistical significance, and {alpha} was set at .05. All statistical analyses were performed by using statistical software (JMP version 5; SAS Institute, Cary, NC).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
No complications associated with ESWT were observed in our study population.

The MR findings are summarized in the Table. Sixteen (89%) of 18 heels had subcutaneous soft-tissue and perifascial edema before ESWT. After ESWT, all 18 heels showed subcutaneous soft-tissue and perifascial edema. The degree and extent of edema increased with the treatment in 12 (75%) of 16 cases (Fig 1).


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  		MR Imaging Findings and Measurements in Each Heel before and after ESWT

 


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  		Figure 1. Sagittal (4000/108) (left) and coronal (4000/108) (right) T2-weighted fat-saturated fast SE images of the hind foot before (top) and after (bottom) ESWT. Mild soft-tissue and perifascial edema (arrow) and thickened plantar fascia (arrowhead) are clearly depicted on the pre-ESWT images; the perifascial and surrounding soft-tissue edema increased after ESWT. Thickness of the fascia was little affected (9.0 mm before and 9.2 mm after ESWT on sagittal and 9.1 mm both before and after ESWT on coronal images).

 
Calcaneus bone marrow edema at the plantar fascia insertion site was seen in eight heels (seven linear and one diffuse) before ESWT. After ESWT, the extent of bone marrow edema had increased in one heel and had newly developed in one additional heel. The remaining heels showed no interval change in bone marrow edema (Fig 2). A heel spur at the plantar fascia insertion site was present in nine (50%) of 18 heels and remained unchanged following ESWT (Fig 3).



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  		Figure 2. Sagittal T2-weighted fat-saturated fast SE images (4000/108) show the calcaneus bone marrow edema (arrow) at the insertion site before (left) and after (right) ESWT. There was no detectable change in bone marrow edema.

 


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  		Figure 3. Sagittal T1-weighted SE images (500/13) show the calcaneus bone spur (arrow) before (left) and after (right) ESWT. No apparent interval change was observed.

 
The accepted criterion for the upper limit of the thickness of normal plantar fascia is 4 mm (14). By using this criterion, 17 (94%) of 18 heels had an abnormally thickened plantar fascia. On sagittal images, the mean thickness of the plantar fascia on the right foot was 6.83 mm ± 1.44 (mean ± standard deviation) before and 7.42 mm ± 1.59 after ESWT; on the left foot, it was 6.76 mm ± 2.62 before and 6.64 mm ± 2.59 after ESWT. On coronal images, the mean thickness of the plantar fascia on the right foot was 6.55 mm ± 1.54 before and 6.55 mm ± 1.14 after ESWT; on the left foot, it was 6.26 mm ± 2.29 before and 6.25 mm ± 2.23 after ESWT. The thickness of plantar fascia was not significantly different between the right and the left foot. On both sagittal and coronal images obtained after ESWT, there was no significant interval change in the thickness on both feet. The thickened portion of the plantar fascia had a fusiform shape, and all of them were located at the proximal one-third of the fascia. The signal intensity of the thickened fascia was usually heterogeneous and was intermediate on T1- and intermediate to high on T2-weighted images, with little change after ESWT (Fig 4).



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  		Figure 4. Sagittal T2-weighted fat-saturated fast SE (4000/108) (left) and T1-weighted SE (500/13) (right) images of the hind foot before (top) and after (bottom) ESWT. The signal intensity (arrowhead on T2-weighted and arrow on T1-weighted images) of the plantar fascia was little affected by the therapy.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
REFERENCES
 
The plantar fascia is a multilayered fibrous aponeurosis with medial, central, and lateral cords (15). The central cord is the largest; it originates from the medial calcaneal tuberosity, extends forward along the plantar foot, and divides into five bands that connect to the base of the proximal phalanges. Plantar fasciitis usually occurs at the proximal portion of the central fascia, particularly near the insertion on the calcaneal tuberosity. The morphology and extent of plantar fasciitis, including commonly associated somatic changes such as soft-tissue edema, perifascial edema, calcaneal bone marrow edema, and plantar heel spur, can be accurately depicted with MR imaging (14–16,18–20). MR imaging is also useful to diagnose other disorders that would cause pain in the heel, such as calcaneal stress fracture, neoplasm of the plantar fascia, plantar fascia rupture, and tendonitis (15,21–26).

Although ESWT has been used to treat various chronic musculotendinous disorders for almost a decade (27–29), no MR imaging follow-up studies have been reported to describe the effect of ESWT in humans. Imaging evaluation of posttreatment somatic changes would further our understanding of ESWT and may prove valuable in patient assessment and selection and the treatment planning process. We postulate that objective measures such as MR imaging would clarify some of the controversies regarding the effectiveness and mechanism of action of ESWT (9–13).

The most common morphologic change related to ESWT was an increased severity and extent of soft-tissue and perifascial edema. The region of the edema became more apparent and larger, but the signal intensity and thickness of the fascia were minimally affected by ESWT. The increase in edema likely represents an acute posttraumatic and inflammatory response as a result of the ultrasound shock waves applied to the plantar surface of the heel.

Our MR findings demonstrated that bone marrow edema had increased in one case and had newly developed in another case. This relatively little effect on the bone marrow could be explained by the magnitude of the shock waves used in ESWT. The prevalence of plantar calcaneal bone spur in our study group was 50% (nine of 18), which is comparable to the prevalence of 52% (15 of 29) in a study by Tanz (30). After ESWT, no change was observed in the plantar heel spurs in this study.

With our current ESWT protocol, every patient received the same dose of shock wave energy. To increase the effectiveness of ESWT, tailoring the magnitude of the energy dose for each patient may be beneficial. For this application, preoperative MR imaging evaluation of the heel may help prescribe an appropriate dose of the shock wave energy; although the criteria for determining this dose have not been established.

Our study was limited to the acute response to ESWT and is part of our ongoing research to evaluate the effectiveness of this therapy. Further studies will include the clinical outcome of the patients and will evaluate any correlation between the MR findings and clinical data. For this purpose, long-term follow-up MR imaging at 1 year after ESWT may be also desirable. Further clinical and imaging studies are required to provide the data that can be used to optimize treatment protocols.

There were several limitations to our study. First, the sample size of the study was relatively small. Second, most of the MR imaging findings, except for plantar fascia thickness measurements, were assessed qualitatively. We attempted but found it very difficult to objectively measure the signal intensities of the images to quantify the posttreatment changes. We performed appropriate quality control procedures, including the use of uniform-display window settings, to ensure a reliable qualitative comparison of the pre- and post-ESWT MR images. Our comparison study was based on the evaluation of the pre- and post-ESWT images side by side. Third, the ESWT protocol used in the study was considered a high-energy protocol. The findings of our study should be interpreted in the context of this particular protocol.

In conclusion, the most common acute somatic change in the heel after ESWT was increased edema in the soft tissue of the heel around the plantar fascia. Preexisting bone marrow edema, the plantar heel spur, the thickness of the plantar fascia, and the signal intensity of the plantar fascia were affected minimally or not at all by ESWT. It is unknown if the MR findings will prove useful in the assessment of the treatment outcome when correlated with clinical data, as their long-term clinical importance has not yet been determined.


   FOOTNOTES
 
Abbreviations: ESWT = extracorporeal shock wave therapy, SE = spin echo

J.E.J. has an indirect financial interest through a partnership that owns and operates an extracorporeal shock wave device, OssaTron.

Author contributions: Guarantors of integrity of entire study, all authors; study concepts, all authors; study design, J.E.J., K.T.B., F.Z.; literature research, F.Z.; clinical studies, all authors; data acquisition, F.Z., C.B.H.; data analysis/interpretation, F.Z.; statistical analysis, F.Z.; manuscript preparation, F.Z.; manuscript definition of intellectual content and revision/review, F.Z., K.T.B., J.E.J.; manuscript editing, F.Z., K.T.B.; manuscript final version approval, all authors


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 

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