The past, present, and future of podiatric biomechanics

Thick shells and medially wedged posts increase foot orthoses medial longitudinal arch stiffness: an experimental study

BACKGROUND

Foot orthoses (FOs) are commonly prescribed devices to attenuate biomechanical deficits and improve physical function in patients with musculoskeletal disorders. It is postulated that FOs provide their effects through the production of reaction forces at the foot-FOs interface. An important parameter to provide these reaction forces is their medial arch stiffness. Preliminary results suggest that adding extrinsic additions to FOs (e.g., rearfoot posts) increases their medial arch stiffness. A better understanding of how FOs medial arch stiffness can be modulated by changing structural factors is necessary to better customise FOs for patients. The objectives of this study were to compare FOs stiffness and force required to lower the FOs medial arch in three thicknesses and two models (with and without medially wedged forefoot-rearfoot posts).

METHODS

Two models of FOs, 3D printed in Polynylon-11, were used: (1) without extrinsic additions (mFO), and (2) with forefoot-rearfoot posts and a 6^o medial wedge (FO6MW). For each model, three thicknesses (2.6 mm, 3.0 mm, and 3.4 mm) were manufactured. FOs were fixed to a compression plate and vertically loaded over the medial arch at a rate of 10 mm/minute. Two-way ANOVAs and Tukey post-hoc tests with Bonferroni corrections were used to compare medial arch stiffness and force required to lower the arch across conditions.

RESULTS

Regardless of the differing shell thicknesses, the overall stiffness was 3.4 times greater for FO6MW compared to mFO (p < 0.001). FOs with 3.4 mm and 3.0 mm thicknesses displayed 1.3- and 1.1- times greater stiffness than FOs with a thickness of 2.6 mm. FOs with a thickness of 3.4 mm also exhibited 1.1 times greater stiffness than FOs with a thickness of 3.0 mm. Overall, the force to lower the medial arch was up to 3.3 times greater for FO6MW than mFO and thicker FOs required greater force (p < 0.001).

CONCLUSIONS

An increased medial longitudinal arch stiffness is seen in FOs following the addition of 6^o medially inclined forefoot-rearfoot posts, and when the shell is thicker. Overall, adding forefoot-rearfoot posts to FOs is significantly more efficient than increasing shell thickness to enhance these variables should that be the therapeutic aim.

Lower Extremity Biomechanical Examination of Athletes

A comprehensive lower extremity examination is a critical examination component for any type of injury in an athlete but should also be part of a preseason or preventive care program. Identification and treatment of biomechanical abnormalities and association with evidence-based risk factors for lower extremity disorders can be incorporated to potentially reduce risk or prevent acute and chronic injuries.

Specialisation versus special interest - the Australian podiatry experience

Background

Ensuring efficient and effective delivery of health care to an ageing population has been a major driver for a review of the health workforce in Australia. As part of this process a National Registration and Accreditation Scheme (NRAS) has evolved with one goal being to improve workforce flexibility within a nationally consistent model of governance. In addition to increased flexibility, there have been discussions about maintaining standards and the role of specialisation. This study aims to explore the association between practitioners’ self-perceptions about their special interest in musculoskeletal, diabetes related and podopaediatric foot care and the actual podiatry services they deliver in Australia.

Methods

A cross sectional on-line survey was administered on behalf of the Australasian Podiatry Council and its’ state based member associations. Self-reported data were collected over a 3-week interval and captured information about the practitioners by gender, years of clinical experience, area of work by state, work setting, and location. For those participants that identified with an area of special interest or specialty, further questions were asked regarding support for the area of special interest through education, and activities performed in treating patients in the week prior to survey completion. Queensland University of Technology Human Research Ethics approval was sought and confirmed exemption from review.

Results

218 podiatrists participated in the survey. Participants were predominately female and worked in private practices.

The largest area of personal interest by the podiatrists was related to the field of musculoskeletal podiatry (n = 65), followed closely by diabetes foot care (n = 61), and a third area identified was in the management of podopaediatric conditions (n = 26).

Conclusions

Health workforce reform in Australia is in part being managed by the federal government with a goal to meet the health care needs of Australians into the future. The recognition of a specialty registration of podiatric surgery and endorsement for scheduled medicines was established with this workforce reform in mind. Addition of new subspecialties may be indicated based on professional development, to maintain high standards and meet community expectations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13047-015-0127-0) contains supplementary material, which is available to authorized users.

The subtalar joint axis palpation technique part 2: reliability and validity results using cadaver feet

BACKGROUND

Clinically locating the point of no rotation to determine the subtalar joint axis location by applying pressure on the plantar surface of the foot was described by Kirby in 1987 but was never validated. We sought to extend a previously validated mechanical model to cadaver feet and to examine the intratester and intertester reliability.

METHODS

Four testers with different levels of experience determined the subtalar joint axis location and moved the subtalar joint through its range of motion, capturing the movement using kinematic analysis. The comparison of the spatial subtalar joint axis location as determined by palpation between and within testers determined the intertester and intratester reliability. The helical axis method was performed to validate the model.

RESULTS

The intrarater reliability varied from a high of α = 0.96 to a low of α = 0.26 for the slope and was, in general, high (α = 0.78-0.95) for the intersection. The interrater reliability scored moderate to high, depending on the specific cadaver specimen. Concerning the exact location of the subtalar joint axis, no significant difference was found between the results determined by different testers and the helical axis method.

CONCLUSIONS

The palpation technique as part of the subtalar joint axis location and rotational equilibrium theory proposed by Kirby is a reliable and valid clinical tool. Experience in performing the palpation technique has a positive influence on the accuracy of the results. In the context of evidence-based practice, this technique could be a standard tool in the examination of patients with lower-limb-related pathologic disorders.

The subtalar joint axis palpation technique-part 1: validating a clinical mechanical model

BACKGROUND

Locating the position of the subtalar joint axis can be a predictive clinical variable in biomechanical analysis and a valuable tool in the design of functional foot orthoses. Before testing Kirby's palpation technique to locate the subtalar joint axis in cadavers, it was important to develop and test the experimental methods in a mechanical model in which the exact location of the hinge joint can be controlled.

METHODS

Four testers determined the hinge joint location and moved it through its range of motion, capturing the movement of the joint axis using a kinematic model. The joint axis location was determined and validated by comparing the actual hinge joint location on the mechanical model with the location determined by the palpation technique described by Kirby in 1987 and the location determined by the helical joint axis method using three-dimensional kinematic data.

RESULTS

The overall angles result in mean slopes and intersections of 87° and 92 mm, 86° and 97 mm, 85° and 92 mm, and 88° and 91 mm for testers 1, 2, 3, and 4, respectively. Testers 1 and 3 were able to determine the location to 1° and 1 mm accuracy, tester 2 to 0° and 4 mm, and tester 4 to 2° and 2 mm compared with the kinematic data.

CONCLUSIONS

The technique of determining the points of no rotation as described by Kirby could be validated by using a three-dimensional kinematic model to determine the helical axis.

Intratest reliability in determining the subtalar joint axis using the palpation technique described by K. Kirby

BACKGROUND

Exact determination and classification of the spatial position of the subtalar joint axis could be a predictive clinical variable in biomechanical analysis and a valuable tool in the design of functional foot orthoses.

METHODS

Three clinicians with different levels of experience determined and classified the subtalar joint axis location, three times, on 52 individuals, using the clinical palpation, allocation and interpretation technique, as described by K. Kirby.

RESULTS

High intratester precision (ICC 0.72 to 0.93) was found for determining the axis location (SEM, 3.72° for angle/0.27 cm for X-axis); however, classification of the spatial position of the axis has large intertester variation (κ = 0.243 to 0.494)

CONCLUSIONS

The clinical palpation technique itself is reliable; the consistent attribution of a classification, in other words, interpretation, is weak.

The efficacy of foot orthoses in the treatment of individuals with patellofemoral pain syndrome: a systematic review

Patellofemoral pain syndrome (PFPS) is a highly prevalent condition, often reducing functional performance and being linked to osteoarthritis development later in life. Prescribing foot orthoses is often advocated, although the link between foot mechanics and PFPS development remains unclear. This systematic review was conducted to summarize and critique the existing evidence for the efficacy of foot orthoses in individuals with PFPS and to provide guidance for future research evaluating foot orthoses in individuals with PFPS. A comprehensive search of MEDLINE, EMBASE, CINAHL and Current Contents revealed 138 citations for review. Two of the authors independently reviewed and assessed each citation for inclusion and quality using a modified version of the quality assessment scale for randomized controlled trials in PFPS designed by Bizzini and colleagues. A total of seven studies were included in the final review. The review found limited evidence that prefabricated foot orthoses may reduce the range of transverse plane knee rotation and provide greater short-term improvements in individuals with PFPS compared with flat inserts. Findings also indicated that combining physiotherapy with prefabricated foot orthoses may be superior to prefabricated foot orthoses alone. Further research is now needed to establish the mechanisms behind the efficacy of foot orthoses and to identify individuals with PFPS who are most likely to benefit from prescription of foot orthoses. A comparison of the efficacy between prefabricated and customized foot orthoses is also needed.

Foot orthoses: how much customisation is necessary?

The relative merit of customised versus prefabricated foot orthoses continues to be the subject of passionate debate among foot health professionals. Although there is currently insufficient evidence to reach definitive conclusions, a growing body of research literature suggests that prefabricated foot orthoses may produce equivalent clinical outcomes to customised foot orthoses for some conditions. Consensus guidelines for the prescription of customised foot orthoses need to be developed so that the hypothesised benefits of these devices can be thoroughly evaluated.

Influence of orthotic devices prescribed using pressure data on lower extremity kinematics and pressures beneath the shoe during running

BACKGROUND

Orthotic devices are frequently prescribed as a conservative treatment of lower extremity injury. The purpose of this study was to investigate the influence of orthotic devices prescribed using pressure data on lower extremity movement and loading patterns.

METHODS

Twenty-two subjects ran barefoot over a pressure plate for the prescription of orthotic devices. The influence of the prescribed orthoses on lower extremity kinematics and pressure beneath the shoe was assessed by collection of data for 10 running trials with a neutral shoe and 10 with the addition of the orthotic device. For each running trial, initial and peak angles were determined for rearfoot inversion-eversion, lower leg internal rotation, ankle dorsi-plantar flexion, knee flexion and rearfoot eversion velocity. In addition, the relative pressure on the lateral side to medial side of the shoe (pressure balance) was determined by dividing the foot into areas of medial and lateral heel and five metatarsals. Peak lateral and medial heel and foot balance were determined during early stance to indicate differences in balance during this phase.

FINDINGS

The orthotic devices resulted in a significant reduction in peak eversion and eversion velocity and a significant increase in the initial inversion angle (P<0.05). In addition, the peak ankle dorsi-flexion and initial dorsi-flexion angle were significantly increased (P<0.05). Consistent with the observed increase in initial inversion, the early pressure balance data revealed a significantly more lateral (less medial) concentration of pressure (P<0.05).

INTERPRETATION

It is concluded that the devices used in the present study have resulted in the production of shoe inserts that successfully lower peak eversion and eversion velocity by encouraging the foot to operate in a more inverted orientation throughout the initial stance phase of running. In addition, there is evidence that orthotic effects can be detected through the use of pressure data collected from beneath the shoe.

Comparison of foot orthoses made by podiatrists, pedorthists and orthotists regarding plantar pressure reduction in The Netherlands

Background

There is a need for evidence of clinical effectiveness of foot orthosis therapy. This study evaluated the effect of foot orthoses made by ten podiatrists, ten pedorthists and eleven orthotists on plantar pressure and walking convenience for three patients with metatarsalgia. Aims were to assess differences and variability between and within the disciplines. The relationship between the importance of pressure reduction and the effect on peak pressure was also evaluated.

Methods

Each therapist examined all three patients and was asked to rate the 'importance of pressure reduction' through a visual analogue scale. The orthoses were evaluated twice in two sessions while the patient walked on a treadmill. Plantar pressures were recorded with an in-sole measuring system. Patients scored walking convenience per orthosis. The effects of the orthoses on peak pressure reduction were calculated for the whole plantar surface of the forefoot and six regions: big toe and metatarsal one to five.

Results

Within each discipline there was an extensive variation in construction of the orthoses and achieved peak pressure reductions. Pedorthists and orthotists achieved greater maximal peak pressure reductions calculated over the whole forefoot than podiatrists: 960, 1020 and 750 kPa, respectively (p < .001). This was also true for the effect in the regions with the highest baseline peak pressures and walking convenience rated by patients A and B. There was a weak relationship between the 'importance of pressure reduction' and the achieved pressure reduction for orthotists, but no relationship for podiatrists and pedorthotists.

Conclusion

The large variation for various aspects of foot orthoses therapy raises questions about a consistent use of concepts for pressures management within the professional groups.

Instrumentation considerations of a clinical and a computerized technique for the measurement of foot angles

Measurement of the foot angles either directly from the patient, from video images, or from radiographs is integral to podiatric clinical practice to confirm diagnoses and to plan, prescribe, and monitor treatment protocols. The reliability, precision, and accuracy involved in any measured value limits the validity and usefulness of the measurement to optimal patient management. Studies are described that ensured the accuracy and validity of the standard clinical tool, the universal goniometer (UG), by applying a calibration protocol. These same calibration angles were then measured by a computer-assisted human movement analysis system, the Ariel Performance Analysis System (APAS). The APAS was found to overestimate consistently the UG angular measures by less than 1 degree and this amount of error was considered clinically irrelevant. The angular results obtained by a clinician and a technician using the APAS on two separate days were tested and were found to be comparable and reliable to within 1 degree, and thus the analysis was deemed to be of excellent reliability and precision. The study found that clinicians could establish the accuracy and validity of their instruments by means of simple calibration, and that computer measures could be repeated on patients by a clinical or a technician. The simple calibration procedure described will assist the clinician to ensure that the measures obtained in the clinical setting have minimal measurement error and that the values can be confidently used to make decisions and draw clinical inferences.