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Case Reports |
MJ Mueller, PhD, PT, is Assistant Professor, Program of Physical Therapy, Washington University School of Medicine, Box 8502, 4444 Forest Park Blvd, St Louis, MO 63108 (USA) (muellerm{at}medicine.wustl.edu).
KE Smith, AAS, is Engineer, Mallinckrodt Institute of Radiology, Washington University School of Medicine
PK Commean, BEE, is Engineer, Mallinckrodt Institute of Radiology, Washington University School of Medicine
DD Robertson, MD, PhD, is Assistant Professor, Mallinckrodt Institute of Radiology, Washington University School of Medicine
JE Johnson, MD, is Associate Professor, Department of Orthopaedic Surgery, Washington University School of Medicine
Address all correspondence to Dr Mueller
Submitted March 10, 1998;
Accepted September 3, 1998
 | Abstract |
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Key Words: Computed tomography • Diabetes • Neuropathy • Pressure • Spiral x-ray • Ulcer
| Introduction |
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 TopAbstract Introduction Case DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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Pecoraro et al3 found that 72% of amputations include an identifiable causal sequence of minor trauma, skin ulceration, and wound-healing failure. Many factors contribute to skin breakdown on the diabetic foot, but the primary etiology is thought to be excessive, repeated pressure on the insensitive foot.1–3,10,12 Structural changes and deformities within the foot as a result of complications of DM, particularly peripheral neuropathy, contribute to excessive local pressures.1,2
Advances in technology have led to improved methods of measuring plantar pressures during walking. Several reports have described the benefits of in-shoe pressure measurement for managing patients with DM, peripheral neuropathy, and plantar ulcers.2,13,14 A critical benefit of this technology is the ability to obtain measurements of pressure distribution on the feet of patients who are insensitive to pressure and pain.
Spiral x-ray computed tomography (SXCT) is a recent technology for investigating internal structural characteristics.15,16 Spiral x-ray computed tomography scanners are widely available, and virtually all new computed tomography scanners incorporate spiral (also known as helical) capability. The spiral scanner is practical and advantageous15–17 due to improved image quality, minimal x-ray dose, and relatively low cost when compared with other methods for volumetric imaging, especially magnetic resonance methods. Spiral x-ray computed tomography scanning of the extremities avoids exposure of reproductive organs to radiation and is considered a low-risk noninvasive technique.
Although SXCT and plantar pressure measurement have been described separately, we are aware of no reports of simultaneous use of the methods. Images obtained with SXCT have been shown in investigations of patients with transtibial amputation18–22 to be geometrically accurate and highly reproducible. Spiral x-ray computed tomography provides high resolution and 3-dimensional (3-D) data of the foot, which can be used to gather geometric, tissue composition, mass properties,23 and bone densitometry information in a single session. Because the data are digital, SXCT offers rapid acquisitions and extensive processing capabilities. The advantage of combining pressure measurement with SXCT imaging is to determine quantitatively how the internal structure of the foot is related to plantar pressures on the foot during walking.
The purposes of this case report are (1) to describe how data from plantar pressure measurement and SXCT were used to treat a patient with recurrent plantar ulcers and (2) to discuss the potential future benefits of this technology in managing patients who are at high risk for skin breakdown and subsequent amputation.
| Case Description |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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| Previous Treatment and Outcomes |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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measuring approximately 1 cm thick.
The patient was treated with total contact casting during his initial visit using methods that have been described in detail previously.26,27 The ulcer was covered with one thin layer of gauze. Stockinette was applied to the lower leg (from the knee to the toes), with 0.32-cm (
-in) felt pads applied to the malleoli and anterior tibia and a foam pad placed around the toes. A total contact plaster shell then was molded around the lower leg. The shell was reinforced with plaster splints, and a walking heel was attached to the plantar surface. A fiberglass roll was applied around the plaster for extra durability and to allow weight bearing sooner than would be allowed with plaster alone. The patient was provided with crutches, given a written list of precautions (ie, keep cast dry, call therapist if any problem is noticed), and instructed to limit ambulation to one third of his usual amount.
Seven days later, when the cast was changed, the wound was healed, as defined by complete skin coverage and lack of drainage. He was provided with instructions regarding foot care (eg, visually inspect skin daily) and advised to obtain extra-depth shoes, custom-made inserts, and a rigid rocker-bottom sole. This footwear has been shown to reduce forefoot pressures during walking and is often used for patients with a history of forefoot ulcer.28 The patient, however, refused to obtain the recommended footwear, expressing a concern over the appearance of the shoes. Although he was advised to use an assistive device to help protect the foot from trauma during walking as the wound continued to mature,2 the patient stated that he had a busy week scheduled at his clinic.
Six days after the wound healed, the patient walked into the clinic without assistive devices. His foot had an ulcer in the same location. We speculated that high pressures encountered during walking and standing caused the wound to reopen. Due to his busy work schedule, the patient chose to delay casting and to treat the ulcer using dressing changes. The ulcer did not heal, however, and the patient was referred back to the physical therapy clinic 4 months later (Table) for treatment with total contact casting. A cast was applied, and 11 days later at the scheduled cast change, the ulcer was healed. This time, the patient agreed to obtain extra-depth shoes and a custom-molded pink (#1) Plastazote and PPT insert, but he refused the rigid rocker-bottom sole, still expressing objections about the appearance of the rocker soles. The benefits of pressure distribution from the extra-depth shoe with an accommodative insert without a rocker-bottom sole is comparable to walking in athletic shoes with an insert.29,30
Due to his history of recurrent ulceration, an in-shoe pressure test (F-Scan In-shoe Pressure System
) was conducted to determine whether the new footwear reduced plantar pressures at the ulcer site compared with his old shoes. Methods of calibration and testing have been described elsewhere, and measurements obtained with these methods have been shown to be reliable.31 The sensor was cut to fit inside the shoe and was placed between his sock and the shoe insole. Data were collected at 50 Hz as the patient walked across the room at his normal, self-selected speed.
Plantar pressures were highest at the location of his ulcer and measured approximately 311 kPa, equivalent to 45 psi, while wearing his tennis shoes and old insert. Although good data on in-shoe plantar pressures to identify a threshold of injury are not available, we attempt to keep forefoot pressures evenly distributed, with a peak pressure below 207 kPa (30 psi), in our practice. After several modifications to his new insole, peak pressures were reduced to 207 kPa. The modifications were the addition of a larger metatarsal pad that extended across metatarsal shafts 2 to 5, beginning in the midfoot and continuing immediately proximal to the metatarsal heads. The patient was instructed to use crutches with approximately 30% weight bearing on the right lower extremity for the next 2 weeks and then to resume his normal activity level slowly.
The ulcer recurred a second time 14 weeks later (Table). The patient was seen 1 week later with a referral from his physician to evaluate his footwear for proper fit. Visual inspection indicated the pink Plastazote in his insoles was worn and "bottomed out," meaning that the Plastazote had become compressed, thin, and nonaccommodating in regions of high plantar pressure. The in-shoe pressure system indicated a peak plantar pressure during walking of 332 kPa (48 psi) at the ulcer site. The high pressures appeared to be due to his worn orthoses and shoes. Another layer of pink Plastazote (0.64 cm [
in]) was added to the insole, and the thickness of the metatarsal pad was increased approximately 0.32 cm ( in). A repeated pressure measurement indicated a peak pressure of 262 kPa (38 psi) at the ulcer site. We applied a temporary rigid rocker-bottom sole (20° angle) to the patient's shoes, with the apex of the rocker immediately proximal to the metatarsal heads. Repeated testing indicated pressures were reduced to 207 kPa. The patient agreed to wear the rigid rocker-bottom soles in his house, but not in the community.
The patient was not seen again for physical therapy until 9 months later. The ulcer had increased in size (1.5 x 1.5 cm, 0.5 cm deep). A total contact cast was applied and changed twice, with progressive healing (Table). Four weeks later, the patient called to report "a vague pain" at the anterior mid tibia, and the cast was removed that day. Redness was observed at the anterior mid tibia, but there was no skin breakdown or drainage in this area. The ulcer size was unchanged, and the patient chose to discontinue use of the cast.
The patient was seen 1 and 2 weeks later to monitor his progress and to suggest alternative treatments to total contact casting, with the goal of lowering plantar pressures, protecting the wound site, and allowing the wound to heal. In-shoe pressure measurement was conducted and showed good distribution of pressures over the forefoot (<207 kPa) while the patient walked without an assistive device in his extra-depth shoes with Plastazote/PPT inserts and rocker-bottom soles. He also was instructed to use crutches and allow only partial weight bearing (about 30%) on the right foot.
The patient was seen in the clinic 2 weeks later, and the ulcer was healed. Although the patient reported wearing his shoes and using crutches "all the time," wearing time when getting up during the night to go to the bathroom was not addressed specifically. In-shoe pressure analysis revealed good pressure distribution (ie, no sharp peaks at the second metatarsal head and pressures less than 210 kPa) during walking. He was instructed to continue to use a cane for the next 2 weeks and to increase his activity gradually.
The patient was not seen again for 5 months, when he was again referred by his orthopedist for evaluation of his footwear using the in-shoe pressure measurement. He reported that the ulcer had recurred for the third time about 2 months previously. He reported concerns about the fit of his shoes and requested help in identifying anything else that could be done to help heal the ulcer. Visual inspection of his shoes showed the heel counter was soft and distorted into a varus position. The lateral posterior aspect of the sole was worn away in a wedge shape by about 1.5 cm. The in-shoe pressure measurement revealed a moderately high peak of pressure (
242 kPa [35 psi]) at the ulcer site.
Because the old shoes were worn and he showed high pressures at the forefoot, new shoes of the same design were prescribed. Two weeks later, he wore his new shoes and insoles to the clinic and repeated in-shoe pressure testing. After several minor modifications to the metatarsal pad as described before, the peak plantar pressure was 186 kPa (27 psi) at the ulcer site. He was seen a final time 3 months later, and the ulcer showed no change in size. The patient was instructed to walk slower and decrease his push-off during walking. Such gait changes have been shown to reduce forefoot pressures.32 Whether the patient was able to permanently adjust his walking pattern is not known.
At his final clinic visit, the patient was discharged from physical therapy because there did not appear to be other treatment options to heal the ulcer. His orthopedic surgeon had suggested additional surgery to correct the severe foot deformity (ie, prominent metatarsal and hammertoe deformity), but because of the poor outcome of his previous foot surgery, the patient refused additional surgery. Total contact casting was considered, but the patient and the therapist believed that although the ulcer might heal inside the cast, it would recur when he resumed his normal activity schedule. Walking with crutches also was considered, but the patient did not want to use crutches permanently. We speculated some sort of severe structural problem was related to the recurrent ulcer, but we had exhausted all possible traditional evaluation and treatment techniques that we were aware of.
| SXCT and Concurrent Plantar Pressure Measurement |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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Plantar pressure data were collected during barefoot walking and during SXCT data acquisition using the F-Scan In-shoe Pressure System (software version 3.847). The foot was loaded during SXCT data acquisition to simulate peak plantar pressures during walking. The methods had been developed and tested on a volunteer who did not have diabetes or a foot deformity.33 Three lead markers were placed on the forefoot portion of the sensor to enable precise localization and identification of a sensor on the plantar surface of the foot during SXCT. The sensor was attached to the patient's foot with tape, and a thin sock was placed over the foot to secure the sensor. The F-Scan sensor was calibrated using the patient's body weight according to manufacturer recommendations and previous research.31 After allowing the patient to adjust to the hardware during walking, data during 3 walking trials were collected. Location and surface area of peak plantar pressure were recorded and printed to help train the patient during the next set of simulated loading conditions.
After acquisition of data during walking, the patient was positioned on the loading device to practice loading his forefoot (Fig. 1a). The patient was seated with his hips flexed to about 90 degrees, the knees flexed to about 40 degrees, and the ankles in slight plantar flexion (10°). Only the forefoot was in contact with a digital scale placed on the base of the loading device (Fig. 1a). The patient practiced pushing against the loading device with 25% to 75% of his body weight. The amount of weight bearing was confirmed using the digital scale and the F-Scan system located on the base of the loading device. We determined whether peak plantar pressures on the forefoot during walking corresponded to the peak plantar pressure during simulated loading of the forefoot by assessing peak plantar pressure location, magnitude, and contact area.
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The SXCT raw data and images were archived on an optical disk. The archived data and images were copied to a Siemens satellite computed tomography console
and reconstructed at 1 mm resolution. The SXCT image data were imported into the ANALYZE software program|| operating on an interactive workstation for resizing, segmenting, and measuring the 3-D data.
For the purposes of this case report, we focus on a parsimonious number of variables taken from the SXCT data that were most relevant to the patient's problem. Hammertoe deformity was defined as the angle between the metatarsal and the proximal phalanx. Soft tissue under the midshaft of the metatarsal was used as an indication of the intrinsic muscle size. The length of each metatarsal was measured, and the midpoint was calculated. The amount of soft tissue, relative to the plantar skin surface, was measured orthogonal to the metatarsal shaft. Soft tissue thickness also was measured orthogonal to the loading surface under the distal second metatarsal.
To provide a frame of reference, the data obtained from the patient were compared with data obtained from a 40-year-old subject matched for sex, height (1.8 m [6 ft]), weight (80.6 kg [185 lb]), and shoe size (USA size 11). Data collection methods were identical to those used for the subject without impairment, who also signed a consent form.
| Outcomes of SXCT and Pressure Testing |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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| Implications for Treatment of This Patient |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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The SXCT images also illustrated the resected second metatarsal head and confirmed that the greatest pressures were localized at this location (Figs. 3 and 4). Although other authors33 have reported decreased soft tissue thickness under the metatarsal heads in patients with DM and peripheral neuropathy, we did not observe decreased soft tissue thickness under the second metatarsal head in this patient compared with the foot of the comparison subject. The lack of difference in this patient may be due to the resection of the metatarsal head.
Repeated loading on the plantar surface of the foot during walking with this magnitude of pressure (886 kPa) likely would cause extreme pain to an individual with intact sensation, but this patient with peripheral sensory neuropathy was able to walk painlessly. The pressure of 886 kPa was reduced to 207 kPa when the patient wore his therapeutic footwear (described previously). When asked whether he ever walked barefoot at home, the patient said that he awoke 3 or 4 times a night and walked barefoot to the bathroom, a distance of about 12 m (40 ft).
We speculated that the extremely high plantar pressure while walking barefoot to the bathroom contributed to the patient's skin breakdown. Although Brand2 described a moderately high pressure (275 kPa) repeated hundreds or thousands of times during walking as the primary mechanism of injury, an extremely high pressure (886 kPa) may contribute to skin breakdown with fewer repetitions, for instance, walking 12 m to the bathroom 3 or 4 times a night. We instructed the patient to always wear his therapeutic shoes, even when he awoke during the night to go to the bathroom. We showed the patient the results of the barefoot plantar pressure measurement and the SXCT, and he was shown how the pressures were reduced when wearing his therapeutic shoes.
We also discussed with the patient how his current orthoses might be altered, given the pressure measurement and SXCT findings. The primary suggestion was to change his orthoses to increase the size of the metatarsal pad, especially under the second metatarsal. We speculated that a larger metatarsal pad would help to further stabilize the second metatarsal and shift weight bearing away from the area of the distal metatarsal. Because we believed the primary problem contributing to the patient's ulcer was his barefoot walking at night, we delayed changing his orthoses until we could evaluate the effect of wearing shoes at all times. No other change in treatment was initiated at that time.
The patient was seen 7 weeks later, and the ulcer was healed. He reported that he always wore his therapeutic shoes, even when going to the bathroom during the night. He ambulated without an assistive device and reported that he was "busier than ever" at work. The patient was seen 2 months later, and the ulcer remained healed.
| Discussion |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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Although we typically tell patients to always wear their shoes, adherence to this guideline can be difficult because patients lack sensory feedback.2 In addition, practitioners may not specify that shoes should be worn even if getting up during the night. The results of the SXCT and pressure testing provided the visible "proof" to this patient that he had extremely high plantar pressures that were related to his severe foot deformity. Although he was unable to sense these high pressures, the pressure and SXCT data allowed him to see the high pressures related to his foot deformity and ulcer when walking barefoot and how these pressures could be reduced by wearing his therapeutic shoes. Although we have not previously measured plantar pressures during barefoot walking because we usually want to measure pressures when patients wear footwear, perhaps measurements should be taken during barefoot walking to better demonstrate to patients the contribution of plantar pressures to ulceration and how therapeutic footwear reduces these high pressures. Research is needed to determine optimal methods for patient education to compensate for sensory neuropathy.
A number of questions and limitations arise regarding the evaluation and treatment for this patient. It is possible that the ulcer will reoccur.4–7 He continues to have the underlying risk factors of severe foot deformity and peripheral neuropathy. The wound, however, has been closed for greater than 3 months, and even this amount of time is important in terms of preventing infection and possible subsequent amputation.
Spiral x-ray computed tomography and pressure testing are not part of standard care for patients with neuropathic ulcers. We have used in-shoe pressure testing for several years to help optimize the pressure distribution of orthoses for patients with DM and peripheral neuropathy as described in this case report and as described elsewhere.13,14 A threshold of injury is unknown and likely is different from patient to patient, depending on a number of variables. Although we believe that in-shoe pressure testing is helpful to quantify pressure distribution, research is needed to define guidelines for use and to determine whether this technology can help to prevent skin breakdown.
We are aware of no reports using simultaneous SXCT and pressure testing. These evaluations were part of ongoing research to determine whether these procedures are useful to help heal or prevent plantar ulcers and prevent lower-extremity amputation. The combined results of the SXCT and pressure testing seemed to help convince this patient of the need to wear his shoes at all times. We do not know whether barefoot testing alone would have had the same results in this patient. We know that the SXCT data helped to confirm the location of high pressures to the location of the ulcer and to clearly identify this patient's structural deformities. Insights for orthosis modification were generated but were not pursued because the ulcer healed. We speculate that this testing may be helpful in the management of patients with recurrent plantar ulcers who are at high risk for infection and amputation,3,5 but additional research is needed. The results of this report further document the need to be aware of the mechanical factors that can contribute to skin breakdown.1–3,10,12–14 We believe that clinicians should question patients and assess footwear carefully for any factors that may contribute to trauma at the ulcer site, even if pressure testing and SXCT are not available.
Cost is another consideration for using the approach and the procedures that we chose. Cost is variable depending on the institution, the type of scan, and the patient's insurance carrier. Currently, the charge for a lower-extremity computed tomography scan at our institution is $669. We contend that this cost should be considered in comparison with the total cost of care for diabetic foot ulcers. One Swedish study showed the average costs of treating 274 patients with foot ulcers and DM over a 3-year period to be $16,100 if primary healing of the nonischemic wound occurred and $63,100 if a lower-limb amputation was required.11 Costs for a computed tomography scan could be justified, in our opinion, if the treatment can help to heal a plantar ulcer and prevent infection or an amputation. Additional research is needed to determine whether computed tomography and pressure testing are beneficial and cost-effective in the management of neuropathic foot ulcers.
| Potential Benefit of Procedures |
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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Another possible benefit of these methods is that they could lead to improved computer models of the foot to help design and fabricate orthoses. The computer model would require detailed, 3-D geometric knowledge of the soft tissue envelope surface location and the underlying skeletal framework. These 3-D geometric data, in addition to the load distribution and material properties, determine the transfer characteristics. Given 3-D geometric description of tissue displacements using SXCT, material properties reported in the literature and determined experimentally, and applied loading forces, the associated pressure distributions can be estimated using finite element analysis. Quantitative measurements relevant to orthosis design obtained using SXCT imaging, plantar pressure measurements, and finite element analysis tools can be modeled to determine which of the measured variables are most important to predictive orthosis evaluation. Contact areas between plantar soft tissues and the shoe or ground, stress, strain, and pressure distributions can be examined. Interventions, including use of orthoses or surgery, could be tested on the model before validation using patient populations. Although work has been reported using finite element analysis and a 2-dimensional model,35 we are aware of no reports using SXCT and 3-D imaging. Our initial work has indicated that it is possible to generate comprehensive 3-D geometric models that include bone, muscle, and fat from the SXCT data for use in finite element modeling and analysis (Fig. 5). More research is needed to develop these methods and implications.
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| Footnotes |
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Subjects signed a consent form approved by the Washington University School of Medicine Human Subjects Committee.
* Professional Protective Technology, 21 E Industry Ct, Deer Park, NY 11729. 
Bakelite Xylonite Ltd, London, England, distributed by Alimed Inc, 297 High St, Dedham, MA 02026.
Tekscan Inc, 307 W First St, South Boston, MA 02127.
Siemens Medical Systems Inc, 186 Wood Ave S, Iselin, NJ 08830-2770.
|| Mayo Foundation, Biomedical Imaging Resources, Rochester, MN 55905.
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TopAbstractIntroductionCase DescriptionPrevious Treatment and OutcomesSXCT and Concurrent Plantar...Outcomes of SXCT and...Implications for Treatment of...DiscussionPotential Benefit of ProceduresReferences |
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This article has been cited by other articles:
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  M. K. Hastings, J. Gelber, P. K Commean, F. Prior, and D. R Sinacore Bone Mineral Density of the Tarsals and Metatarsals With Reloading Physical Therapy, June 1, 2008; 88(6): 766 - 779. [Abstract] [Full Text] [PDF]
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M. J Mueller, D. J Lott, M. K Hastings, P. K Commean, K. E Smith, and T. K Pilgram Efficacy and Mechanism of Orthotic Devices to Unload Metatarsal Heads in People With Diabetes and a History of Plantar Ulcers Physical Therapy, June 1, 2006; 86(6): 833 - 842. [Abstract] [Full Text] [PDF]
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D. J Lott, K. S Maluf, D. R Sinacore, and M. J Mueller Relationship Between Changes in Activity and Plantar Ulcer Recurrence in a Patient With Diabetes Mellitus Physical Therapy, June 1, 2005; 85(6): 579 - 588. [Abstract] [Full Text] [PDF]
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