Body alignment positioning during 3D scanning for foot orthotics
Arguably the most important component of an effectively manufactured foot orthotic is the cast taken of the foot. An orthotic laboratory can only work with the data it is provided – an optimally positioned body during the foot scan and increased scan resolution will lead to improved outcomes.
Footcare specialists (Pedorthists, Chiropodists, Podiatrists, & Orthotists) must consider a plethora of factors when determining best patient outcomes. With the increased prevalence of 3D scanning technology, many footcare specialists have spent the last 10+ years learning to work with these various types of scanners to get the same outcomes as traditional foot casting methods (plaster, biofoam, impression wax). Today, 3D scanning technology has become so precise that it is now outperforming these traditional casting methods; however, this technology is still just a tool, and its efficacy is highly dependent on the techniques and protocols implemented in its execution by the clinician.
Let us start with the patient position during scanning and the theory behind it. Do you scan seated, standing, or lying down? We know that muscle and fascial tension as well as skeletal posture and soft tissue, changes between these 3 positions so, which is best for the patient?
Considering the biomechanics when seated, the hip is flexed at 90 degrees and the posterior kinetic chain is under increased tension, the pelvis rotates posteriorly, impacting lumbar spine alignment. Extending the knee while seated further increases tension in the hamstrings and therefore the pull on the ischial tuberosity increases the posterior rotation of the pelvis beyond what the seated position has already influenced; we are now left in a compromised body alignment position. The hip and pelvis position are especially important to consider when many biomechanical ailments presenting at the foot stem from poor hip and/or pelvic function. Foot orthotics offer little efficacy with patients in a seated position as they are only functional while weight-bearing where the torso is erect, the pelvis has a slight anterior pelvic tilt, and the posterior kinetic chain is unloaded. Therefore, doesn't it make sense to scan the feet in a position that best replicates the body’s functional behaviour?
Fully weight bearing in perfect body alignment may be more ideal when considering the limitations of seated casting, however; it is often very challenging for the clinician to guide the pelvis and lower extremity into this neutral alignment (inclusive of hip, knee, ankle, foot) while under such load, and often even more challenging for the patient to be able to understand and maintain this position.
If we are in agreement so far that both seated and fully weight bearing positions have limitations in reliability for capturing optimal posture for precise foot orthotic casting, then how do we decide between the remaining two options of lying prone or supine?
Whether prone or supine, we find the pelvis, hip and the rest of the lower extremity in an unloaded position that allows easy manipulation of the body into its ideal anatomical alignment (an interesting conversation on its own) vs a seated or fully weight-bearing position for scanning. In a prone position you may find it easier to palpate the subtalar and talocrural joints while evaluating calcaneal alignment as well as rearfoot to forefoot alignment, yet supine may be more comfortable for some patients. Of course, this is only valuable and important if the assessment conducted is inclusive of the patient’s posture and biomechanics above the ankle.
So, assuming we are scanning with the patient lying prone with the spine, hip and knee in a neutral and unloaded position, how does one position the foot? Calcaneal vertical, sub-talar neutral, locked lateral column? Following the same principles of ideal anatomical alignment, optimizing the foot position based the best range of motion in all directions - the foot has optimal movement through pronation and supination, dorsi-flexion and plantarflexion, inversion and eversion, mid-foot torsional rotation internally and externally, and equal 1st ray mobility in dorsiflexion and plantarflexion. This often requires careful testing of fascial limitations up the kinetic chain and ensuring a neutral pelvic and hip position so that fascial tension is not influencing the foot’s ideal alignment.
Considering the functional behaviour of the body when foot orthoses will be used can also be helpful when positioning the foot. For example, a golfer who is having trouble loading their hallux of their rear foot during the terminal stage of their swing may benefit from a slightly plantarflexed 1st ray during the scan vs a neutral alignment that may be more conducive to walking the course. These subtle positioning differences during scanning can have considerable output improvements in the accuracy and efficacy of your patient’s custom foot orthotics. The more aligned the body and foot is during the scan, the less CAD alternations required post processing, the more accurate the foot orthotics will function on the patient’s feet.
So, if the clinician is spending all of this time carefully positioning the patient's body into optimal alignment, who is taking the scan? Laser scanning technology is more accurate when multiple passes are made from different angles - you simply get more data. Good data in, good data out, more precise foot orthotics. The depth of the scans is also better, giving one more to work with during the design phase. It is therefore clear that assistance from a colleague (even non-medical) to move a hand-held scanner around the foot with the patient lying prone while the assessing clinician is guiding the patient into ideal anatomical alignment of the body will provide the best cast of the patient’s feet.
There is still one limitation with this approach of optimal body alignment positioning for 3D scanning the feet – we have not accounted for the fact that when weight bearing, changes in soft tissue expansion and skeletal foot structure may influence the design and technical accommodations added to the foot orthotic. The addition of a supplementary fully weight-bearing scan (with the foot and ankle corrected as best as possible to a neutral alignment) offers increased accuracy and enables precise placement of forefoot accommodations, which is instrumental in the success and comfort of the foot orthotic for your patient.
Technology has offered many advancements in the healthcare field; however, it is still up to the healthcare provider to effectively utilize the technology to its full potential. Careful body alignment positioning and recruiting assistance to aid in the foot scan of your patients can provide considerably better outcomes in your orthotic design – maximizing the potential from this technology.
If you are interested to learn more about the Align Clinician Program including body alignment, gait and custom fitting footwear, reach out and connect with us – we would love to hear from you.