Category: Biomechanics

Arize, Hewlett Packard’s digital foot orthotic business, exemplifies a significant innovation in healthcare technology, integrating advanced 3D printing with cloud-based workflows to deliver custom orthotic solutions for foot health. Arize was officially announced in July 2021, marking HP’s expansion from its well-known printing and computing portfolio into the medical and biomechanical field. The Arize solution offers podiatrists and orthotists a revolutionary platform to prescribe custom orthoses tailored to specific patient needs—streamlining clinic operations and elevating standards for comfort, function, and patient satisfaction.

Origins and Industry Context

HP’s entry into foot orthotics came in response to a significant medical challenge: an estimated 77% of Americans suffer from foot pain at some point, impacting productivity and quality of life. Traditionally, producing custom orthotic insoles required time-consuming manual manufacturing, intensive labor, and could be prone to variability. HP leveraged its legacy in 3D printing—particularly its Multi Jet Fusion technology—to disrupt the orthotics sector and create a more efficient, scalable system for personalized care

Arize is now part of the Edser group of orthotic labs, further consolidating expertise and resources in digital healthcare. This partnership has helped Arize stay at the forefront of the market’s digital transformation, ensuring rapid adoption in podiatric clinics

The Arize Technology Platform

At its core, Arize features an end-to-end workflow leveraging HP’s integrated 3D laser scanning hardware, proprietary cloud-based software, and centralized 3D printing facilities. The process begins with a clinic capturing a high-resolution 3D scan of a patient’s foot—quickly building an exact digital model using laser-triangulation and detailed imaging. This model is then uploaded to HP’s cloud system, where software tools help providers visualize, annotate, and prescribe modifications according to each patient’s anatomy and clinical needs.

One of Arize’s strengths lies in its automated detection of anatomical landmarks and ergonomically relevant features. Providers can easily fine-tune the design, ensuring form, fit, and function are optimized for outcomes ranging from alleviating pain to supporting postural correction. The final digital prescription is sent to HP’s centralized production facilities, where the orthoses are fabricated on demand. HP’s Multi Jet Fusion 3D printers allow for five core styles: functional, sports, stability, everyday comfort, and dress/low-profile.

Business Model and Clinical Benefits

Arize’s business model targets both the economic and workflow pain points in clinical orthotics. By digitizing and automating the design and ordering process, HP reduces labor costs, minimizes errors inherent in manual production, and offers a predictable flat-rate pricing structure—covering modifications and shipping. For clinics, this translates into efficiency gains, streamlined patient intake, and fewer logistical hurdles, as reordering and patient tracking are managed via a unified interface.

Clinicians have highlighted improved productivity and patient outcomes. Digital scans and 3D visualization not only facilitate precision but can be used as a tool for patient education, improving buy-in and compliance with prescribed orthoses. Clinics benefit from highly consistent orthoses and a straightforward reordering process, helping maintain continuity and patient satisfaction.

Collaborative and Clinical Validation

HP worked closely with an independent advisory council comprising podiatrists, biomechanics experts, and physical therapists to ensure clinical validity and practical application. Notable consultants included Dr. Bruce Williams DPM and Dr. Gavin P. Ripp; both report increased efficiency and improved patient outcomes since the adoption of Arize. HP’s continued collaboration with podiatric specialists ensures the solution adapts dynamically to real-world clinic needs and reflects the evolving science of foot biomechanics.

Market Impact and Sustainability

Arize’s market impact is notable, coming at a time of robust growth in the orthotic insoles sector, driven by population aging and greater awareness of foot health. The adoption of 3D printing for orthotic production not only enhances customization but also fosters sustainability; production is done near the point of consumption, reducing logistical waste and allowing for more circular manufacturing practices.

Arize’s emphasis on digital workflows brings production closer to the patient and may help reduce supply chain inefficiencies, carbon emissions, and material waste—a key advantage over traditional, more resource-intensive methods.

Conclusion: The Future of Foot Health

HP’s Arize orthotic business stands at the intersection of technology and personalized medical care, reshaping the way clinics diagnose, prescribe, and deliver custom foot support. By deploying digital scanning, cloud-based prescription, and next-generation 3D printing, Arize advances the vision of accessible, high-quality orthotics for millions suffering from foot pain—while making clinics more efficient and operations more sustainable. As digital health ecosystems evolve, Arize signifies how legacy tech companies like HP can drive innovation in wellness, using their engineering expertise to address real medical needs.

The study of human gait is crucial in understanding lower limb function and diagnosing pathomechanical abnormalities. One such abnormality observed during gait analysis is the Abductory Twist. This essay discusses the definition, biomechanics, underlying causes, clinical implications, diagnosis, and management of abductory twist, providing a thorough, evidence-based overview of this unique gait phenomenon.

Definition of Abductory Twist

Abductory Twist, also referred to as a medial heel whip, is an observable moment during the stance phase of walking gait when the heel rapidly moves in a medial or abducted direction as the heel lifts off the ground. This sudden movement occurs just as weight transitions off the heel, leading to a visible “twist” or whip of the heel inward. Despite being commonly observed in clinical practice, especially among podiatrists, abductory twist is not a diagnosis or disease but a gait manifestation indicating underlying biomechanical issues.

Gait Cycle: Where Does Abductory Twist Occur?

In the standard gait cycle, the stance phase is when the foot is in contact with the ground, supporting body weight. The abductory twist typically occurs during the later part of midstance and the onset of the propulsion phase—precisely, at the instant of heel-off, when the heel leaves the ground but before the toes push off.

Biomechanics Behind Abductory Twist

The occurrence of an abductory twist involves a complex interplay of transverse plane motions and inadequate biomechanical compensation within the lower limb. At late midstance:

• The pelvis and swing leg externally rotate, exerting an external rotational force on the stance limb.
• If the stance foot is overpronated or unable to supinate adequately, excessive internal rotation of the tibia persists.
• This results in a buildup of elastic strain energy due to unmatched rotational forces between the upper and lower segments.
• When the friction of the ground no longer restrains the heel at heel-off, this pent-up energy discharges as a rapid medial twist of the heel.

Pathomechanical Explanations

Two main biomechanical scenarios contribute to abductory twist:

1. Persistent Pronation and Rotational Discrepancy

• In individuals with overpronated feet, the foot remains pronated (and the tibia internally rotated) longer than it should.
• Meanwhile, the opposite leg (the swing limb) externally rotates the pelvis and stance leg.
• Unable to convert to a supinated, rigid lever, the stance foot is “caught” between opposing torque forces.
• When the heel lifts, the external rotation driven from above is released abruptly through the twist motion in the heel.

2. First Metatarsophalangeal (MTP) Joint Block

• If the big toe joint (first MTP) is restricted (due to hallux rigidus, osteoarthritis, or functional hallux limitus), it cannot dorsiflex as needed during propulsion.
• The body compensates by forcing the foot to roll off the medial side of the forefoot, resulting in a medial whip or abductory twist at the heel.
• Shoes with excessively stiff forefeet can also mimic this mechanism, further hindering first ray dorsiflexion.

Additional Causes and Contributing Factors

Other anatomical or functional abnormalities can predispose or contribute to abductory twist:

• Loss of ankle joint dorsiflexion range
• Short or tight calf-Achilles complex
• Weakness in tibialis anterior or extensor toe muscles
• Excessive subtalar pronation
• Limited hip extension or swayback biomechanics
• Flexion contracture at the knee
• Poorly fitting or inappropriate footwear

Clinical Presentation and Observation

Clinically, the abductory twist manifests as a small, sudden medial movement of the heel at the moment of heel-off. Observers may note concentrically worn patterns in the medial forefoot area of footwear—a sign that repeated rotational twists are present during walking. In many cases, the twist is subtle and best observed from behind as the subject walks away from the examiner.

Significance and Consequences

The abductory twist is not inherently pathological but indicates abnormal loading and compensation in the kinetic chain. Its presence points to:

• Increased muscular effort: Muscles must compensate for inefficient energy transfer.
• Maladaptive tissue loading: Tissues may sustain loads they were not designed for, increasing risk for overuse injuries in the foot, ankle, or proximal structures.
• Footwear wear patterns: Can provide supportive evidence for the abnormal movement.

Ultimately, while the abductory twist itself does not cause pain, it is a marker of ineffective gait mechanics and a risk factor for injury if the primary biomechanical issue is not addressed.

Diagnosis

Diagnosis relies on gait analysis—preferably with video slow-motion replay—and careful observation of heel motion during walking. Accompanying assessments may include:

• Range of motion (ankle dorsiflexion, first MTP joint)
• Muscle testing (calf flexibility, tibialis anterior strength)
• Assessment for overpronation, hallux limitus, or other noted abnormalities

Management Approaches

Management of abductory twist targets the underlying biomechanical dysfunction rather than the twist itself. Evidence-based approaches include:

• Orthotic therapy: Foot orthoses can address excessive pronation or offload restricted joints.
• Physical therapy: Targeted exercises to improve ankle dorsiflexion, calf flexibility, and muscle strength.
• Footwear modification: Prescription of appropriate shoes with flexible forefoot and good motion control.
• Surgical intervention (in select cases): For fixed contractures or severe hallux rigidus, surgical options may be explored if conservative therapies fail.

Prognosis

With correct identification and addressing of the root biomechanical cause, the abductory twist can be minimized or eliminated. This, in turn, improves functional gait and reduces injury risk.

The abductory twist during gait is a unique movement characterized by a sudden medial movement of the heel as it leaves the ground. It signals underlying biomechanical inefficiency—most commonly persistent pronation, rotational discrepancies, or obstruction at the first MTP joint. Recognizing the abductory twist provides valuable clinical insight for podiatric and physical therapy professionals. Correct management hinges on addressing the primary biomechanical abnormality through orthoses, physical therapy, and individualized footwear recommendations, ensuring optimal gait efficiency and reduced injury risk for affected individuals.