The effect of the patellar tendon-bearing cast on loading

Assessment of compression forces in a digitally modified short leg cast for pressure injury risk monitoring in healthy children

Introduction

Casting is an essential treatment for neuro-orthopedic conditions in children with cognitive, sensory, and communicational disabilities. However, a main side-effect is the development of pressure injuries resulting in additional (wound) therapies and prolongation of the hospital stay. The primary aim of our study was to investigate the potential of objective pressure measurements in casts to assess the risk for pressure injury development.

Methods

Five pediatric healthy participants were included in this study. We measured the global and the local compression force at body sites prone to pressure injury development for different body positions and the transfer in-between in a cast equipped with pressure sensors. These conditions resulted in partial or full body weight loading.

Results and discussion

The global maximum compression force was affected significantly by body postures with partial and full loading of the cast and during transfer. The local compression force significantly correlated with the global compression force at the heel and instep area. In conclusion, the integration of sensing technologies into casts bears a high potential for early recognition of critical conditions inside the cast and inducing preventive measures in the at-risk population.

Passive Articulated and Non-Articulated Ankle-Foot Orthoses for Gait Rehabilitation: A Narrative Review

The aim of this work was to study the different types of passive articulated and non-articulated ankle-foot orthoses for gait rehabilitation in terms of working principles, control mechanisms, features, and limitations, along with the recent clinical trials on AFOs. An additional aim was to categorize them to help engineers and orthotists to develop novel designs based on this research. Based on selected keywords and their composition, a search was performed on the ISI Web of Knowledge, Google Scholar, Scopus, and PubMed databases from 1990 to 2022. Forty-two studies met the eligibility criteria, which highlighted the commonly used types and recent development of passive articulated and non-articulated ankle-foot orthoses for foot drop. Orthotists and engineers may benefit from the information obtained from this review article by enhancing their understanding of the challenges in developing an AFO that meets all the requirements in terms of ease of use, freedom of movement, and high performance at a relatively low cost.

Biomechanical Comparison of a New Dynamic Ankle Orthosis to a Standard Ankle-Foot Orthosis During Walking

Patients who sustain irreversible cartilage damage or joint instability from ankle injuries are likely to develop ankle osteoarthritis (OA). A dynamic ankle orthosis (DAO) was recently designed with the intent to offload the foot and ankle using a distractive force, allowing more natural sagittal and frontal plane ankle motion during gait. To evaluate its efficacy, this study compared ankle joint kinematics and plantar pressures among the DAO, standard double upright ankle-foot orthosis (DUAFO), and a nonorthosis control (CON) condition in healthy adults during walking. Ten healthy subjects (26 ± 3.8 yr; 69.6 ± 12.7 kg; and 1.69 ± 0.07 m) walked on a treadmill at 1.4 m/s in three orthosis conditions: CON, DAO, and DUAFO. Ankle kinematics were assessed using a three-dimensional (3D) motion capture system and in-shoe plantar pressures were measured for seven areas of the foot. DAO reduced hallux peak plantar pressures (PPs) compared to CON and DUAFO. PPs under toes 2–5 were smaller in DAO than DUAFO, but greater in DUAFO compared to CON. Early stance peak plantarflexion (PF) angular velocity was smaller in DAO compared to CON and DUAFO. Eversion (EV) ROM was much smaller in DUAFO compared to CON and DAO. Early stance peak eversion angular velocity was smaller in DAO and much smaller in DUAFO compared to CON. This study demonstrates the capacity of the DAO to provide offloading during ambulation without greatly affecting kinematic parameters including frontal plane ankle motion compared to CON. Future work will assess the effectiveness of the DAO in a clinical osteoarthritic population.

Ankle Motion and Offloading in Short Leg Cast and Low and High Fracture Boots

BACKGROUND

Short leg casts (SLCs) and fracture boots are used to treat foot and ankle injuries, but the decision to use one device over the other is often subjective. This study compared the impact of SLCs and low and high fracture boots on ankle motion and offloading.

METHODS

Twenty healthy adults were prospectively studied. High-speed dynamic radiography was utilized to determine tibiotalar range of motion in the sagittal plane during nonweightbearing (NWB) and weightbearing (WB) gait in a shoe (control), SLC, and low and high fracture boots. Sensors captured peak plantar surface forces to determine ankle offloading.

RESULTS

In NWB, the low fracture boot (2.2 ± 2.0 degrees), high fracture boot (2.3 ± 1.6 degrees), and SLC (2.3 ± 1.5 degrees) had significantly less motion compared with the control (3.6 ± 2.1 degrees; P ≤ .026). During WB, the SLC (3.4 ± 1.4 degrees) and high fracture boot (4.8 ± 2.0 degrees) had less motion compared with the low fracture boot (7.8 ± 3.4 degrees; P < .001). Finally, the SLC (172.6% ± 48.3% body weight [BW]) and low fracture (165.1% ± 36.2% BW) and high fracture (154.5% ± 32.9% BW) boots were associated with less peak plantar surface force compared with the control (195.0% ± 43.8% BW; P ≤ .087).

CONCLUSION

The SLC and high fracture boot immobilized the ankle in NWB and offloaded and immobilized the ankle in WB. The low fracture boot also immobilized the ankle in NWB, but in WB, the low fracture boot only offloaded the ankle and did not immobilize it.

CLINICAL RELEVANCE

The low fracture boot may be more suited for NWB or possibly immobilizing the foot in WB.

Total contact cast wall load in patients with a plantar forefoot ulcer and diabetes

BACKGROUND

The total contact cast (TCC) is an effective intervention to reduce plantar pressure in patients with diabetes and a plantar forefoot ulcer. The walls of the TCC have been indirectly shown to bear approximately 30 % of the plantar load. A new direct method to measure inside the TCC walls with capacitance sensors has shown that the anterodistal and posterolateral-distal regions of the lower leg bear the highest load. The objective of this study was to directly measure these two regions in patients with Diabetes and a plantar forefoot ulcer to further understand the mechanism of pressure reduction in the TCC.

METHODS

A TCC was applied to 17 patients with Diabetes and a plantar forefoot ulcer. TCC wall load (contact area, peak pressure and max force) at the anterodistal and posterolateral-distal regions of the lower leg were evaluated with two capacitance sensor strips measuring 90 cm(2) (pliance®, novel GmbH, Germany). Plantar load (contact area, peak pressure and max force) was measured with a capacitance sensor insole (pedar®, novel GmbH, Germany) placed inside the TCC. Both pedar® and pliance® collected data simultaneously at a sampling rate of 50Hz synchronised to heel strike. The magnitude of TCC wall load as a proportion of plantar load was calculated. The TCC walls were then removed to determine the differences in plantar loading between the TCC and the cut down shoe-cast for the whole foot, rearfoot, midfoot and forefoot (region of interest).

RESULTS

TCC wall load was substantial. The anterodistal lower leg recorded 48 % and the posterolateral-distal lower leg recorded 34 % of plantar contact area. The anterodistal lower leg recorded 28 % and the posterolateral-distal lower leg recorded 12 % of plantar peak pressure. The anterodistal lower leg recorded 12 % and the posterolateral-distal lower leg recorded 4 % of plantar max force. There were significant differences in plantar load between the TCC and the cut down shoe-cast for the whole foot, rearfoot, midfoot and forefoot (region of ulcer). Contact area significantly increased by 5 % beneath the whole foot, 8 % at the midfoot and 6 % at the forefoot in the shoe-cast (p < 0.05). Peak pressure significantly increased by 8 % beneath the midfoot and 13 % at the forefoot in the shoe-cast (p < 0.05). Max force significantly increased 6 % beneath the midfoot in the (shoe-cast p < 0.05).

CONCLUSION

In patients with diabetes and a plantar forefoot ulcer, the walls of the TCC bear considerable load. Reduced plantar contact area in the TCC compared to the shoe-cast suggests that the foot is suspended by the considerable load bearing capacity of the walls of the TCC which contributes mechanically to the pressure reduction and redistribution properties of the TCC.

Plantar loading forces while walking in a below-knee cast with an attached loadbearing frame

BACKGROUND

We measured loading forces across different points of the plantar foot surface to examine how different types of casts affect load distribution through the foot and ankle. The patella tendon-bearing (PTB) or Sarmiento cast is the current "gold-standard" casting method for offloading force through the foot and ankle. We aimed to determine if a rocker bottom frame attached to a below-knee cast (Beagle Böhler Walker) would be as effective or better at reducing load distribution during full weightbearing.

METHOD

We applied TekScan FlexiForce A201 force sensors to the first and fifth metatarsal heads and the plantar surface of the calcaneus of 14 healthy volunteers. All volunteers had force measurements taken without a cast applied and then with a traditional Sarmiento cast, a standard below-knee cast, and a below-knee cast with the Böhler Walker frame fitted.

RESULTS

Compared with a standard below-knee cast, the Böhler Walker frame reduced the mean peak force through the head of the first metatarsal by 58.9% (P < .0001), 73.1% through the head of the fifth metatarsal (P < .0001), and 32.2% (P < .0001) through the calcaneus. The Sarmiento cast demonstrated a mean percentage reduction in peak force of 8.6% (P = .39) and 4.4% (P = .87) through the first and fifth metatarsal heads, respectively, but increased the mean peak force by 5.9% (P = .54) through the calcaneus.

CONCLUSION

Using a Böhler Walker frame applied to a below-knee cast significantly reduced weight transfer through the foot compared with a Sarmiento cast or standard below-knee cast.

CLINICAL RELEVANCE

This reduction in force through the foot could mean early weightbearing would be safer in patients with a wide variety of foot and ankle pathologies such as ankle fractures or operative fixations. This may reduce the incidence of immobility-dependent morbidity.

Patellar tendon bearing brace: combined effect of heel clearance and ankle status on foot plantar pressure

BACKGROUND

Heel clearance and ankle status (free or locked) are of major determinants affecting peak plantar pressures and contact area in patellar tendon bearing brace and have been separately studied by many researchers. This study investigated the combined effect of ankle status and heel clearance on contact area and peak plantar pressure in different areas of foot (hindfoot, midfoot, and forefoot).

STUDY DESIGN

Before-after repeated measurement trial.

METHODS

Nine healthy male volunteers walked 8 m with normal shoe and four conditions of patellar tendon bearing brace wear. Repeated-measure analysis of variance test was used to compare contact area and plantar pressure changes in three areas of the foot.

RESULTS

Application of patellar tendon bearing brace significantly reduced overall plantar pressure and contact area (p < 0.01). Although both contact area and plantar pressure significantly decreased in hindfoot and midfoot, plantar pressure increased in forefoot area (p < 0.05).

CONCLUSIONS

Application of the patellar tendon bearing brace can reduce the overall peak plantar pressure in the foot but increases focal plantar pressure in forefoot. Excessive lifting of the heel seems to minimize the contact area, thus increase focal pressure in forefoot. Overall, plantar pressure seems to be more effectively off-loaded by combining maximum heel clearance and restriction of the ankle joint.

CLINICAL RELEVANCE

Although effective parameters of patellar tendon bearing brace have been separately addressed in previous studies, no study was found that investigated the combined effect of ankle status and heel clearance. This study investigates the combined effect of these parameters and provides detailed information on clinical application of the patellar tendon bearing brace.

A novel approach to mapping load transfer from the plantar surface of the foot to the walls of the total contact cast: a proof of concept study

Background

Total contact casting is regarded as the gold standard treatment for plantar foot ulcers. Load transfer from the plantar surface of the foot to the walls of the total contact cast has previously been assessed indirectly. The aim of this proof of concept study was to determine the feasibility of a new method to directly measure the load between the cast wall and the lower leg interface using capacitance sensors.

Methods

Plantar load was measured with pedar® sensor insoles and cast wall load with pliance® sensor strips as participants (n=2) walked along a 9 m walkway at 0.4±0.04 m/sec. The relative force (%) on the cast wall was calculated by dividing the mean cast wall force (N) per step by the mean plantar force (N) per step in the shoe-cast condition.

Results

The combined average measured load per step upon the walls of the TCC equated to 23-34% of the average plantar load on the opposite foot. The highest areas of load on the lower leg were located at the posterior margin of the lateral malleolus and at the anterior ankle/extensor retinaculum.

Conclusions

These direct measurements of cast wall load are similar to previous indirect assessment of load transfer (30-36%) to the cast walls. This new methodology may provide a more comprehensive understanding of the mechanism of load transfer from the plantar surface of the foot to the cast walls of the total contact cast.

Optimizing the offloading properties of the total contact cast for plantar foot ulceration

AIMS

Total contact casting is the gold standard offloading treatment for plantar foot ulceration, but the optimal technique and preferred materials are poorly defined and not readily prescribed in daily practice. We investigated in-cast pressure offloading in two types of total contact casts vs. a control condition, in patients with plantar foot ulceration.

METHODS

In-cast walking pressures were collected using the Novel Pedar-X system in 20 participants with a plantar foot ulcer in two types of total contact casts: a conventional total contact cast and a cushion-modified total contact cast incorporating an inlay of 6 mm slow-rebound cellular urethane and 6 mm soft cellular urethane. Casts were compared with a canvas cast shoe to establish baseline pressure values.

RESULTS

Compared with the cast shoe, the conventional total contact cast significantly reduced peak pressure at the ulcer site by 44%, mean pressure by 47% and pressure-time integral by 37% (P<0.001), while the cushion-modified total contact cast significantly reduced peak pressure at the ulcer site by 70%, mean pressure by 60% and pressure-time integral by 69% (P<0.001). Plantar pressure across the entire foot and each region of the foot was also reduced with the conventional total contact cast compared with the cast shoe, and further reduced by the cushion-modified total contact cast (P<0.05).

CONCLUSIONS

The offloading properties of the total contact cast can be enhanced with a 12 mm cellular urethane cushion modification. Further well-designed trials are required to understand and validate this cast technique and to demonstrate healing rates and safety in different patient populations.

Unloading mechanism in the total contact cast

BACKGROUND

The effectiveness of total contact casts is postulated to be due to the reduction of plantar pressure. We investigated plantar loads to evaluate the mechanism by which total contact casts off-load the plantar surface of the foot to determine if it is the intimate molding of the weightbearing plantar surface or if a below-knee cast is necessary.

METHODS

Plantar pressures and forces in a total contact cast (TCC) were recorded in 12 healthy subjects, using the Pedar (Novel GmbH, Munich, Germany) pedobarographic system. The measurements were repeated after removal of the 'shank' portion of the cast (proximal to malleoli), leaving in effect, a well-molded shoe-cast (SC). Measurements included average force and peak pressure. All parameters were measured under two different loading conditions: single-leg standing balanced on the casted limb and over-ground walking. To assess the contribution of calf geometry, the 'calf ratio' was calculated by dividing the largest by the smallest circumferences of the calf. All parameters were compared between TCC and SC for each subject in each of the two conditions. Paired t-tests were used to evaluate significance, which was set at a level of p < 0.006 due to the Bonferroni Correction.

RESULTS

Removal of the shank portion of the TCC significantly increased the average plantar force by 31% during walking. The force only increased 9% during standing, which was not significant. Peak pressure increased 53% after removal of the shank portion of the TCC during walking. Peak pressure was not significantly different during standing on one limb. No correlation was found between the calf ratio and the magnitude of change in the measured values.

CONCLUSIONS

These results help to partially explain the widely recognized clinical observation that molded insoles and shoes, no matter how well conformed to the foot, do not reduce plantar loads as effectively as a total contact cast. The mechanism appears to be a critical unloading function of the proximal, 'shank' portion of the cast, presumably due to reduction in ankle motion.