Three Dimensional Imaging of the Foot
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.
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: