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12 Articles in Volume 7, Issue #8
A Clinical Guide to Weaning Off Intrathecal Opioids
Avoiding the Pitfalls of Opioid Reversal with Naloxone
Central Role of Dopamine in Fibromyalgia
CES in the Treatment of Insomnia: A Review and Meta-analysis
Combined Phrenic Nerve Palsy and Cervical Facet Joint Pain
Dextrose Prolotherapy for Unresolved Neck Pain
Low Level Laser Therapy - Part 1
Mistakes Made by Chronic Pain Patients
Near-infrared Therapeutic Laser and Pain Relief
Patulous Eustachian Tube: Part 2
The “Promise” of Pain Medicine: Profession, Oaths, and the Probity of Practice
Three Dimensional Imaging of the Foot

Three Dimensional Imaging of the Foot

The use of force plate technology provides new insight into potential sources of foot and/or leg pain by providing pathoanatomical visualization of foot pressure patterns, foot velocity, and motion characteristics.

Foot pain and dysfunction may be treated in many different ways depending on what type of clinician is performing the treatment. There are a multitude of conditions that—both directly and indirectly—influence, modify, and/or cause foot pain. Foot disorders are known to be associated with functional limitations and disability among community-dwelling older adults.1 The Women’s Health and Aging Study has confirmed that severe foot pain is associated with walking difficulty and disabilities in activities of daily living among older women.2

Medical doctors and podiatrists use medication, surgery, and injection procedures to eliminate or control foot pain while alternative medicine and manual physical therapists use manual techniques to adjust, mobilize, or manipulate the various joints in the foot to achieve a pain-free state. There are numerous other alternative therapies that are also commonly sought out by the public to alleviate foot pain including acupuncture, massage, reflexology, chiropody, and orthotic insertion.

The use of foot orthotics utilizes a biomechanical approach in treating foot and ankle pain. Many practitioners view chronic foot pain as the result of mechanical or structural faults that can be corrected with a mechanical intervention. In the absence of any specific foot pathology or definable lesion, biomechanists view chronic foot pain/problems as typically being caused by an ankle joint that is out of balance. Rather than the primary ankle joint (talo-crural joint), the subtalar joint is the joint of interest and upon which practitioners focus their corrections.

Orthotic correction has been an evolving art and science for many years and the best method of orthotic evaluation and correction is heatedly debated even today. Orthotic correction for foot disorders is another one of those areas where research has not fully validated the procedures involved in the foot assessment and orthotic construction process, yet, despite conflicting data, the use of foot orthoses for correcting subtalar misalignments and intrinsic foot disorders and deformities continues to grow. Increasing demand has also fueled technology growth in this area including the use of three dimensional imaging to assess foot/ankle mechanics. This data can be used for a variety of reasons including balance assessment, gait analysis, and foot orthotic construction.

The Biomechanical Model of the Foot

Below the ankle joint there is the joint complex called the subtalar joint. This very complex joint moves through all 3 body planes simultaneously. It’s movement and range of motion is translated up into the leg in the form of tibial rotation and into the foot distally causing the locking and unlocking of another joint complex called the midtarsal joint. When the subtalar joint functions abnormally, the locking and unlocking of the midtarsal joint also functions abnormally and results in a number of foot pathologies.3 The abnormal subtalar joint is also thought to contribute to other joint problems such as:

  • knee pain (e.g., chondromalacia patella and patella-femoral syndrome)
  • leg pain (e.g., shin splints)
  • foot pain (e.g., posterior tibial tendonitis, bunions, neuromas, and plantar fasciiti)

In the knee, an abnormally functioning subtalar joint will cause excessive internal or external tibial rotation and, in turn, cause a change in the orientation of the patella and patellar tendon. In subtalar non neutral, the tibia is excessively rotated and causes a faulty force vector to be generated on the patella by the pull of the patellar tendon which then causes it to increase it’s contact pressure in the femoral groove. The excessive contact pressure is thought to irritate and inflame the chondral tissue resulting in patella-femoral syndrome (retro-patellar irritation) and/or chondromalacia patella (retro-patellar degradation).4

It is estimated that many conditions typically seen in orthopedic offices have a biomechanical basis and that just treating the acute symptoms will not address the underlying biomechanical faults. Recently, the use of digital 3-dimensional imaging has added a new and missing component in the differential diagnosis of foot and ankle related pain. The use of 3D imaging can enhance the clinician’s current understanding of foot pain and dysfunction by providing relevant biomechanical kinetic and kinematic data.

3D Imaging

The essential component of three dimensional imaging of the foot is the foot pad that a patient stands or walks on (see Figure 1). The imaging pad is, in essence, a force plate consisting of multiple force sensors covered by a comfortable walking pad. The 3DO® system used in our facilities has over 1500 24-carat gold sensors that relay information to the imaging software via hardware circuitry. Gold is known to be a highly conductive metal and so is used as the conducting material of choice to eliminate data errors.5 The exam itself usually consists of a static (standing) and dynamic (walking) test and only takes a matter of seconds to complete. The 3DO system will analyze several motion and force parameters including mass displacement, velocity analysis, pressure analysis, and three dimensional plantar surfacing of the feet. These data are valuable for:

  • defining construction parameters in the manufacturing of foot orthotics
  • static and dynamic balance analysis
  • quantifying weight bearing status in orthopedic post surgical patients
  • quantifying unilateral lower extremity load characteristics in chronic pain patients who tend to manifest with biomechanically-induced pathology as a result of months and years of asymmetrical loading in the lower extremities

Injury, trauma, surgery, disease, faulty posture, and simply “favoring” (dominance) of one side vs the other can also lead to mechanical overuse, breakdown, and eventually cause pain, inflammation, and impairment.6

The 3DO system of three dimensional imaging utilizes high resolution graphics to demonstrate plantar foot surface contouring while the patient is on the imaging pad. The clinician can observe and evaluate how foot pressure migrates from different parts of the foot and compare these patterns to normal. Deviant patterns can be identified with proper interventions directed to the specific problem. Prior to purchasing our system we evaluated the data capture reliability of this system to ensure that data was being generated by the force plate in a consistent manner. Calibrated load measurements were repeatedly tested on the force plate on several occasions with the 3DO unit consistently yielding identical values using 5, 10, and 20 lb plate increments. The system appears highly responsive (ability to detect change) and is very precise at small increments of change. This is very important when minimal detectable change levels (MDC) have been identified for a specific variable.

Multidimensional foot scanning or imaging examines four key movement related properties, namely:

  • mass displacement
  • motion analysis
  • pressure analysis
  • 3D plantar surfacing or contouring

Mass Displacement

Mass displacement analyzes anterior shifting of the body mass or evaluation of equines. Mass displacement analysis also examines other key variables such as propulsion patterns (toe off) when the foot pushes off to create locomotion and the stability of the first ray (great toe) in the midstance of gait when the leg rocks over the foot. The rearfoot to forefoot load patterns are indicators of how the foot behaves when there is ground contact. The ability of the foot to react in a biomechanically correct manner when under load (weight bearing) is crucial to proper locomotion or ambulation.

Motion Analysis

There are several important motion analysis measures that are also assessed by the 3DO system including the velocity of pronation and supination in the rear-foot and mid-foot areas. This is an important parameter to evaluate since research has shown that there needs to be sufficient re-supination of the foot to occur after midstance to stabilize or “lock” the midtarsal area in sagittal plane for effective propulsion. Motion analysis also examines the first ray plantar flexion capability and general hyper/hypo mobility since both can be problematic.

Pressure Analysis

Three dimensional imaging emphasizes pressure characterization of the foot contacting the ground in both static and dynamic modes, allowing for real time pressure analysis. This is invaluable information that cannot be directly measured in any other manner at this time. This mode of evaluation allows the practitioner to see how the 3 sections of the foot, rear, mid and forefoot plantar areas are mechanically behaving. As well, metatarsalphalangeal (MTP) joint pressures can also be assessed for orthotic intervention through appropriate posting or pad support.

Figure 1. 3DO foot pad consisting of a covered force plate having multiple force sensors. Figure 2. 3DO static analysis report format with 2D foot image.

3D Plantar Foot Surface Contouring

The 3DO system of three dimensional imaging utilizes high resolution graphics to demonstrate plantar foot surface contouring while the patient is on the imaging pad. The clinician can observe and evaluate how the foot pressure migrates from different parts of the foot and compare these patterns to normal. Deviant patterns can be identified with proper interventions directed to the specific problem. Prior to purchasing our system we evaluated the data capture reliability of this product to ensure that data was being generated by the force plate in a consistent manner. Calibrated load measurements were repeatedly tested on the force plate on a single, and several occasions with the 3DO unit consistently yielding identical values using 5, 10, and 20 lb plate increments. The system appears highly responsive (ability to detect change) and is very precise at small increments of change. This is very important when minimal detectable change levels (MDC) have been identified for a specific variable.

3D Imaging Advantages

The sheer volume of data that can be captured using a 3D imaging system can be overwhelming and not all the data will be used in a clinically meaningful manner for every patient. As foot/ankle research continues to evolve, there are new parameters being discovered that will undoubtedly lead to some breakthroughs in what we deem important as we evaluate the mechanics of the foot. In the meantime, for those practitioners who are interested in foot orthotic construction for their patients, this system of data capture will be difficult to ignore.

It has been proposed that there are five main goals necessary to achieve a healthy gait:

  1. That the foot has the ability to re-supinate after midstance so as to lock out the tarsus and allow for propulsion to occur
  2. That the fore-foot contact the ground without a forced abnormal compensatory motion proximally or in any of the three planes
  3. That the first metatarsal be stable in muscular plantar flexion against the ground, during the rear-foot to forefoot loading cycle
  4. That the first metatarsal be able to accept 60% of the loading force
  5. That the first MTP joint must be able to dorsiflex sufficiently in forward gait progression, without compensation from other areas proximal or distal to the MTP joint7

These are the necessary conditions that need to be present for biomechanically-correct gait and proper locomotion. It is thought that we should have sufficient mechanical control over the tarsus of the foot with primary emphasis on the calcaneus and talus. The latter make up the subtalar joint which most hold out to be the control point for pronation/supination and is synonymous with unlocking and locking. It is necessary for the foot to unlock, or pronate, for shock absorption especially in uneven terrain; then it must re-supinate or lock, for proper MTP and fore-foot function leading to forward propulsion.7

Aside from both the quality and quantity of data involved in imaging systems there are some other advantages this type of system can bring to the clinic. The entire testing process utilizing the 3DO system takes approximately 1 to 2 minutes—this taking into account patient instruction time and relevant individual patient data entry (height, weight, age, foot length/width). The test is non invasive and requires the patient to perform a perfectly natural function (stand-walk) with minimal hands on interaction with the evaluator. This eliminates any evaluator-patient interaction error that inevitably creeps into other foot/ankle assessment methods.

Figure 2 presents the static analysis report format with a 2D image of the foot being examined as well. In the static test analysis the patient merely stands on the pad itself for approximately 5-10 seconds. The 3DO system captures both 2D and 3D images with color coordinated pressure points with red being the most pressure and blue-green the least pressure.

Figure 3 presents a three dimensional color coded rendering of a left foot graphically illustrating pressure zones of a foot. The data display columns also show the relative amounts of time that the person spends in each of the three phases of the gait cycle including contact, midstance, and propulsion or toe off. This is clinically useful data in helping to explain the effects of injury or trauma on the persons gait cycle. This—coupled with the fact that on average a person walks over 2.5 million steps in one year with a force roughly equal to that person’s weight multiplied by 2.5—helps patients understand how a 3-4 % weight asymmetry differential can eventually manifest as an inflammatory or degenerative problem at some point in time.6

In dynamic test mode, the patient actually steps onto the pad with each foot individually in reverse direction with the feet being displayed in full 3D animation with either foot being able to be rotated to any angle and speed of motion according to how the examiner wants to view the data. The common line of progression, along with normative values for each of the three phases of gait are displayed for comparison purposes. As well, the center of force is displayed as a blinking square which helps the examiner to identify any mechanical break down points during forward foot motion in dynamic test mode. Patients who have painful conditions of the feet tend to veer away from the traditional sigmoid shape line of progression commonly seen in the healthy foot, to more deviant patterns consistent with antalgia or painful gait.

Conclusion

The idea that painful feet will manifest as faulty biomechanics, and/or that faulty biomechanics will lead to painful feet—both of which can be effectively evaluated using 3D imaging—is not difficult to conceptualize, despite the paucity of research support in existence at this time. Like most other forms of imaging, the error lies mostly in the interpretation and conclusion of the examiner versus the actual technical measurement taking. There is little doubt as to the greater volume of musculo-skeletal information that can be generated using this technology than by manual examination of the foot alone. However, like other forms of imaging, the credo that… imaging should be used to confirm a diagnosis, but not establish one, should be adhered to. This means that 3D imaging provides another piece of the diagnostic puzzle and, in doing so, also provides us the new dimension of patho-anatomical visualization of such parameters as foot pressure, foot velocity, and motion characteristics (normal and abnormal) of a particular patient. This biomechanical approach to problem identification for foot pain and disorders lends itself well to a mechanical approach to treatment using such interventions as foot orthotics and various types of foot postings (wedges, lifts, and pads). The use of imaging using force plate technology is non invasive, reliable, has added precision over non image methods, and is relatively cost effective. n

Figure 3. Three dimensional color-coded rendering of a left foot graphically illustrating pressure zones of the foot.

Acknowledgement

Special thanks to Greg Armstrong of Rocky Mountain Orthotics and Brace Co. (RMOlink.com) for providing the images used in this article.

Last updated on: January 4, 2012
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