Measuring contact area, force, and pressure for bioengineering applications: Using Fuji Film and TekScan systems

Load Distribution After Serial Resection of the Posterior Horn of the Lateral Meniscus and Subsequent Meniscal Allograft Transplant: A Biomechanical Study

BACKGROUND

Data are lacking as to when a meniscal allograft transplant (MAT) may be biomechanically superior to a partially resected lateral meniscus.

HYPOTHESIS

Lateral MAT using a bone bridge technique would restore load distribution and contact pressures in the tibiofemoral joint to levels superior to those of a partial lateral meniscectomy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eleven fresh-frozen human cadaveric knees were evaluated in 5 lateral meniscal testing conditions (native, one-third posterior horn meniscectomy, two-thirds posterior horn meniscectomy, total meniscectomy, MAT) at 3 flexion angles (0°, 30°, and 60°) under a 1600-N axial load. Pressure sensors were used to acquire contact pressure, contact area, and peak contact pressure within the tibiofemoral joint.

RESULTS

Limited (one-third and two-thirds) partial lateral posterior horn meniscectomy showed no significant increase in mean and peak contact pressures as well as no significant decrease in contact area compared with the intact state. Total meniscectomy significantly increased mean contact pressure at 0° and 30° (P = .008 and P < .001, respectively), increased peak contact pressure at 30° (P = .04), and decreased mean contact area in all flexion angles compared with the native condition (P < .01). Lateral MAT significantly improved mean contact pressure compared with total meniscectomy at 0° and 30° (P = .002 and P = .003, respectively) and increased contact area at 30° and 60° (P = .003 and P = .009, respectively), although contact area was still significantly smaller (24.1%) after MAT relative to the native meniscus (P = 0.015). However, allograft transplant did not result in better tibiofemoral contact biomechanics compared with limited partial meniscectomy (P > .05).

CONCLUSION

The peripheral portion of the lateral meniscus provided the most important contribution to the distribution of contact pressure across the tibiofemoral joint in the cadaveric model. Total meniscectomy significantly increased mean and peak contact pressure in the cadaveric model and decreased contact area. Lateral MAT restored contact biomechanics close to normal but was not superior to the partially meniscectomized status.

CLINICAL RELEVANCE

Surgeons should attempt to preserve a peripheral rim of the posterior lateral meniscus. Meniscal allograft transplant appears to improve but not normalize mean contact pressure and contact area relative to total lateral meniscectomy.

An ex vivo sequential ligament transection model of flatfoot

BACKGROUND

The ligaments implicated in the earliest stages of developing a progressive collapsing foot deformity are poorly understood. Commonly employed cadaveric flatfoot models are created from simultaneous transection of multiple ligaments, making it difficult to assess early changes in pressure distribution from ligaments critical for maintaining load distribution. A serial transection of ligaments may provide insight into changes in pressure distribution under the foot to identify a potential combination of ligaments that may be involved in early deformities.

METHODS

Specimens were loaded using a custom designed axial and tendon loading system. Plantar pressure data for the forefoot and hindfoot were recorded before and after six sequential ligament complex transections.

FINDINGS

Sectioning the plantar fascia (first) and short/long plantar ligaments (second) failed to generate appreciable differences in load distribution. Dividing the spring ligament (third) led to changes in hindfoot load distribution with a shift towards the lateral column indicative of hindfoot valgus angulation. All subsequent conditions resulted in similar patterns in hindfoot plantar load distribution. An anterior shift in the center of pressure only occurred after transection of all six ligament complexes.

INTERPRETATION

Loss of the plantar fascia and short/long plantar ligaments are not critical in maintaining plantar load distribution or contact area. However, the additional loss of the spring ligament caused notable changes in hindfoot load distribution, indicating the combination of these three ligament complexes is particularly critical for preventing peritalar subluxation. Minimal changes in load distribution occurred when performing additional transections to reach a complete flatfoot deformity.

Proximal Row Carpectomy Does Not Alter Contact Pressures of the Lunate Fossa: A Cadaveric Study

BACKGROUND

Previous studies have suggested that proximal row carpectomy (PRC) results in increased contact pressures and decreased contact areas in the radiocarpal joint. Such experiments, however, used older technologies that may be associated with considerable measurement errors. The purpose of this study was to determine whether there was a significant difference in contact pressure and contact area before and after PRC using Tekscan, a newer pressure sensing technology.

METHODS

Ten nonpaired cadaveric specimens were dissected proximal to the carpal row and potted. An ultra-thin Tekscan sensor was secured in the lunate fossa of the radius. The wrists were loaded with 200 N of force for 60 seconds to simulate clenched-fist grip; contact pressure and area was assessed before and after PRC.

RESULTS

Performing a PRC did not significantly increase mean contact pressure at the lunate fossa compared to the native state (mean increase of 17.4 ± 43.2 N/cm2, P = .184). Similarly, the PRC did not significantly alter peak contact pressures at the lunate fossa (intact: 617.2 ± 233.46 N/cm2, median = 637.5 N/cm2; PRC: 707.8 ± 156.6 N/cm2, median = 728.5 N/cm2; P = .169). In addition, the PRC (0.46 ± 0.15 cm2, median = 0.48 cm2) and intact states (0.49 ± 0.25 cm2, median = 0.44 cm2) demonstrated similar contact areas (P = .681).

CONCLUSIONS

In contrast to prior studies that demonstrated significant increases in contact pressure and decreases in contact area after PRC, our findings propose that performing a PRC does not significantly alter the contact pressures or area of the lunate fossa of the radiocarpal joint.

Experimental Methods for Studying the Contact Mechanics of Joints

Biomechanics researchers often experimentally measure static or fluctuating dynamic contact forces, areas, and stresses at the interface of natural and artificial joints, including the shoulders, elbows, hips, and knees. This information helps explain joint contact mechanics, as well as mechanisms that may contribute to disease, damage, and degradation. Currently, the most common in vitro experimental technique involves a thin pressure-sensitive film inserted into the joint space; but, the film's finite thickness disturbs the joint's ordinary articulation. Similarly, the most common in vivo experimental technique uses video recording of 3D limb motion combined with dynamic analysis of a 3D link-segment model to calculate joint contact force, but this does not provide joint contact area or stress distribution. Moreover, many researchers may be unaware of older or newer alternative techniques that may be more suitable for their particular research application. Thus, this article surveys over 50 years of English-language scientific literature in order to (a) describe the basic working principles, advantages, and disadvantages of each technique, (b) examine the trends among the studies and methods, and (c) make recommendations for future directions. This article will hopefully inform biomechanics investigators about various in vitro and in vivo experimental methods for studying the contact mechanics of joints.

Commercially available pressure sensors for sport and health applications: A comparative review

Pressure measurement systems have numerous applications in healthcare and sport. The purpose of this review is to: (a) describe the brief history of the development of pressure sensors for clinical and sport applications, (b) discuss the design requirements for pressure measurement systems for different applications, (c) critique the suitability, reliability, and validity of commercial pressure measurement systems, and (d) suggest future directions for the development of pressure measurements systems in this area. Commercial pressure measurement systems generally use capacitive or resistive sensors, and typically capacitive sensors have been reported to be more valid and reliable than resistive sensors for prolonged use. It is important to acknowledge, however, that the selection of sensors is contingent upon the specific application requirements. Recent improvements in sensor and wireless technology and computational power have resulted in systems that have higher sensor density and sampling frequency with improved usability - thinner, lighter platforms, some of which are wireless, and reduced the obtrusiveness of in-shoe systems due to wireless data transmission and smaller data-logger and control units. Future developments of pressure sensors should focus on the design of systems that can measure or accurately predict shear stresses in conjunction with pressure, as it is thought the combination of both contributes to the development of pressure ulcers and diabetic plantar ulcers. The focus for the development of in-shoe pressure measurement systems is to minimise any potential interference to the patient or athlete, and to reduce power consumption of the wireless systems to improve the battery life, so these systems can be used to monitor daily activity. A potential solution to reduce the obtrusiveness of in-shoe systems include thin flexible pressure sensors which can be incorporated into socks. Although some experimental systems are available further work is needed to improve their validity and reliability.

Tactile Pressure Sensors Calibration with the Use of High Pressure Zones

A simple and cost-effective calibration procedure for piezoresistive ink tactile pressure sensors is crucial for their use in geotechnical research applications. Such a procedure should be applicable in field conditions and require a minimum amount of equipment. The paper describes a new method for calibrating tactile pressure sensors with 8-bit sensels' output. The method is based on the approximation of a single sensel output and consideration of multiple calibration patches. The advantage of the developed method is using local high-pressure zones in calibration patches. The developed method has been successfully applied in calibration of two 5051-350 Tekscan sensors by means of three dead weights: 2 kg, 5 kg and 10 kg. One calibrated sensor was new, and another one had been previously used in the harsh environment of the ice tank in the experiment with model ice. The calibration curves for these two sensors did not reveal a significant difference. For 72% of the 150 obtained load patches in calibration, the absolute discrepancy of actual and calibrated load occurred to be less than 5%.

Experimental investigation on ball plate contact using ultrasonic reflectometry: From static to dynamic

Machine elements such as rolling element bearings are widely used in engineering and transportation areas. The life of a bearing is closely related to the stress state in the constituent components. Determining the stress state experimentally is difficult since the contact region is hidden inside the contacting bodies, making it difficult to characterize without altering the contact itself. This paper presents an experimental study to monitor static and dynamic ball-on-flat contacts, by using an ultrasonic reflectometry measuring technique, to demonstrate the concept of monitoring operating ball-bearing conditions in a non-invasive manner. By using an ultrasonic focusing probe and a 64-element ultrasonic array, contacts between a nitrile ball and a Perspex plate as well as contact between a steel ball and a grooved steel plate were characterised under both static and dynamic conditions. Both contact size and distribution of contact stress can be visualized in 2-dimensional plots. In this paper, the capability of ultrasonic reflectometry for non-invasive characterisation of contact conditions are demonstrated, and more importantly the development of multiple measuring mechanisms to realize real-time contact monitoring from static to dynamic conditions is illustrated. The proposed technique in the study is expected to characterise dynamic contacts of bearings in various scenarios from small mechanical systems (e.g., micro motors) to large civil infrastructures (e.g., wind turbines).

3DKnITS: Three-dimensional Digital Knitting of Intelligent Textile Sensor for Activity Recognition and Biomechanical Monitoring

We present an approach to develop seamless and scalable piezo-resistive matrix-based intelligent textile using digital flat-bed and circular knitting machines. By combining and customizing functional and common yarns, we can design the aesthetics and architecture and engineer both the electrical and mechanical properties of a sensing textile. By incorporating a melting fiber, we propose a method to shape and personalize three-dimensional piezo-resistive fabric structure that can conform to the human body through thermoforming principles. It results in a robust textile structure and intimate interfacing, suppressing sensor drifts and maximizing accuracy while ensuring comfortability. This paper describes our textile design, fabrication approach, wireless hardware system, deep-learning enabled recognition methods, experimental results, and application scenarios. The digital knitting approach enables the fabrication of 2D to 3D pressure-sensitive textile interiors and wearables, including a 45 x 45 cm intelligent mat with 256 pressure-sensing pixels, and a circularly-knitted, form-fitted shoe with 96 sensing pixels across its 3D surface both with linear piezo-resistive sensitivity of 39.4 for up to 500 N load. Our personalized convolutional neural network models are able to classify 7 basic activities and exercises and 7 yoga poses in-real time with 99.6% and 98.7% accuracy respectively. Further, we demonstrate our technology for a variety of applications ranging from rehabilitation and sport science, to wearables and gaming interfaces.

Discharging the medial knee compartment: comparison of pressure distribution and kinematic shifting after implantation of an extra-capsular absorber system (ATLAS) and open-wedge high tibial osteotomy-a biomechanical in vitro analysis

PURPOSE

Young and active patients suffering early degenerative changes of the medial compartment with an underlying straight-leg axis do face a therapeutical gap as unloading of the medial compartment cannot be achieved by high tibial osteotomy. Extracapsular absorbing implants were developed to close this existing therapeutical gap. Purpose of the present cadaveric biomechanical study was to compare the unloading effect of the knee joint after implantation of an extra-articular absorber system (ATLAS) in comparison to open-wedge high tibial osteotomy (OW-HTO) under physiological conditions. The hypothesis of the study was that implantation of an extra-capsular absorber results in an unloading effect comparable to the one achievable with OW-HTO.

METHODS

Eight fresh-frozen cadaveric knees were tested under isokinetic flexion-extension motions and physiological loading using a biomechanical knee simulator. Tibiofemoral area contact and peak contact pressures were measured using pressure-sensitive film in the untreated medial compartment. The tibiofemoral superior-inferior, latero-medial translation and varus/valgus rotation were measured with a 3D tracking system Polaris. Pressures and kinematics changes were measured after native testing, ATLAS System implantation and OW-HTO (5° and 10° correction angles) performed with an angular stable internal fixator (TomoFix).

RESULTS

The absorber device decreased the pressure in the medial compartment near full extension moments. Implantation of the ATLAS absorbing system according to the manufacturers' instruction did not result in a significant unloading effect. Deviating from the surgery manual provided by the manufacturer the implantation of a larger spring size while applying varus stress before releasing the absorber resulted in a significant pressure diminution. Contact pressure decreased significantly Δ0.20 ± 0.04 MPa p = 0.044. Performing the OW-HTO in 5° correction angle resulted in significant decreased contact pressure (Δ0.25 ± 0.10 MPa, p = 0.0036) and peak contact pressure (Δ0.39 ± 0.38 MPa, p = 0.029) compared with the native test cycle. With a 10° correction angle, OW-HTO significantly decreased area contact pressure by Δ0.32 ± 0.09 MPa, p = 0.006 and peak contact pressure by Δ0.48 ± 0.12 MPa, p = 0.0654 compared to OW-HTO 5°. Surgical treatment did not result in kinematic changes regarding the superior-inferior translation of the medial joint section. A significant difference was observed for the translation towards the lateral compartment for the ATLAS system Δ1.31 ± 0.54 MPa p = 0.022 and the osteotomy Δ3.51 ± 0.92 MPa p = 0.001. Furthermore, significant shifting varus to valgus rotation of the treated knee joint was verified for HTO 5° about Δ2.97-3.69° and for HTO 10° Δ4.11-5.23° (pHTO 5 = 0.0012; pHTO 10 = 0.0007) over the entire extension cycle.

CONCLUSION

OW-HTO results in a significant unloading of the medial compartment. Implantation of an extra-capsular absorbing device did not result in a significant unloading until the implantation technique was applied against the manufacturer's recommendation. While the clinical difficulty for young and active patients with straight-leg axis and early degenerative changes of the medial compartment persists further biomechanical research to develop sufficient unloading devices is required.

Radiocarpal Contact Pressures Are Not Altered after Scapholunate Ligament Tears

Background  The scapholunate interosseous ligament (SLIL) couples the scaphoid and lunate, preventing motion and instability. Prior studies suggest that damage to the SLIL may significantly alter contact pressures of the radiocarpal joint. Questions/Purposes  The purpose of this study was to investigate the contact pressure and contact area in the scaphoid and lunate fossae of the radius prior to and after sectioning the SLIL. Methods  Ten cadaveric forearms were dissected distal to 1-cm proximal to the radiocarpal joint and a Tekscan sensor was placed in the radiocarpal joint. The potted specimen was mounted and an axial load of 200 N was applied over 60 seconds. Results  Sectioning of the SLIL did neither significantly alter mean contact pressure at the lunate fossa ( p  = 0.842) nor scaphoid fossa ( p  = 0.760). Peak pressures were similar between both states at the lunate and scaphoid fossae ( p  = 0.301-0.959). Contact areas were similar at the lunate fossa ( p  = 0.508) but trended toward an increase in the SLIL sectioned state in the scaphoid fossa ( p  = 0.055). No significant differences in the distribution of contact pressure ( p  = 0.799), peak pressure ( p  = 0.445), and contact area ( p  = 0.203) between the scaphoid and lunate fossae after sectioning were observed. Conclusion  Complete sectioning of the SLIL in isolation may not be sufficient to alter the contact pressures of the wrist. Clinical Relevance  Injury to the secondary stabilizers of the SL joint, in addition to complete sectioning of the SLIL, may be needed to induce altered biomechanics and ultimately degenerative changes of the radiocarpal joint.

Assessing Increased Activities of the Forearm Muscles Due to Anti-Vibration Gloves: Construct Validity of a Refined Methodology

OBJECTIVE

The primary aim was to test the construct validity of a surface electromyography (EMG) measurement protocol, indirectly assessing the effects of anti-vibration (AV) gloves on activities of the forearm muscles.

BACKGROUND

AV gloves impose a relatively higher grip demand and thus a higher risk for musculoskeletal disorders. Consequently, activities of the forearm muscles should be considered when assessing AV glove performance.

METHOD

Effects of AV gloves on activities of the forearm muscles (ECR: extensor carpi radialis longus; ED: extensor digitorum; FCR: flexor carpi radialis; FDS: flexor digitorum superficialis) were measured via EMG, while gripping a handle with two grip force levels. Fifteen subjects participated with 11 glove conditions, including one with bare hand.

RESULTS

Activities of ECR, FCR, mean of ECR and FCR (ECR_FCR), and mean of all four muscles were sensitive to wearing gloves. Compared with bare hand, combined ECR_FCR activities increased by 22%-78% (mean = 48%, SD = 28%) with gloves. The correlation coefficient (r) of ECR_FCR activities with glove thickness and manual dexterity scores were 0.74 (p < .05) and 0.90 (p < .001), respectively.

CONCLUSIONS

A refined EMG methodology was the most sensitive to AV gloves with specific forearm muscles (ECR and FCR) and the 50-N handgrip force. Its construct validity was further substantiated by correlations with glove thickness and manual dexterity.

APPLICATION

Assessment of the effect of AV gloves on activities of the forearm muscles can yield design guidance for AV gloves to reduce grip exertion by the gloved hand.

The Effect of Axial Compression and Distraction on Cervical Facet Cartilage Apposition During Shear and Bending Motions

During cervical spine trauma, complex intervertebral motions can cause a reduction in facet joint cartilage apposition area (CAA), leading to cervical facet dislocation (CFD). Intervertebral compression and distraction likely alter the magnitude and location of CAA, and may influence the risk of facet fracture. The aim of this study was to investigate facet joint CAA resulting from intervertebral distraction (2.5 mm) or compression (50, 300 N) superimposed on shear and bending motions. Intervertebral and facet joint kinematics were applied to multi rigid-body kinematic models of twelve C6/C7 motion segments (70 ± 13 year, nine male) with specimen-specific cartilage profiles. CAA was qualitatively and quantitatively compared between distraction and compression conditions for each motion; linear mixed-effects models (α = 0.05) were applied. Distraction significantly decreased CAA throughout all motions, compared to the compressed conditions (p < 0.001), and shifted the apposition region towards the facet tip. These observations were consistent bilaterally for both asymmetric and symmetric motions. The results indicate that axial neck loads, which are altered by muscle activation and head loading, influences facet apposition. Investigating CAA in longer cervical spine segments subjected to quasistatic or dynamic loading may provide insight into dislocation and fracture mechanisms.

The effect of hemiarthroplasty implant modulus on contact mechanics: an experimental investigation

BACKGROUND

Hemiarthroplasties cause damage to the cartilage that they articulate against, which is a major limitation to their use. This study investigated the use of lower-stiffness materials to determine whether they improve hemiarthroplasty contact mechanics and thus reduce the risk of cartilage damage.

METHODS

Eleven fresh-frozen cadaveric upper extremities were disarticulated and fixed in a custom-built jig that applied a static load of 50 N to the radiocapitellar joint. Flexion angles of 0°, 45°, 90°, and 135° were tested with radial head implants made of cobalt-chrome (CoCr) and ultrahigh-molecular-weight polyethylene (UHMWPE) compared with the native radial head. A Tekscan thin-film sensor was used to measure the contact area and contact pressure between the radius and capitellum.

RESULTS

UHMWPE and CoCr were too stiff in the application of hemiarthroplasty, resulting in lower contact areas and higher contact pressures relative to the native joint. The native contact area was, on average, 42 ± 20 mm² larger than that of UHMWPE (P < .001) and 55 ± 24 mm² larger than that of CoCr (P < .001). UHMWPE had a contact area 13 ± 10 mm² greater than that of CoCr (P = .014).

DISCUSSION AND CONCLUSION

This study shows that even though UHMWPE has a stiffness several times lower than CoCr, the use of this material in hemiarthroplasty led to only a minor improvement in contact mechanics. Neither implant restored contact similar to the native articulation. Investigations into new materials to improve the contact mechanics of hemiarthroplasty should focus on materials with a lower stiffness than UHMWPE.

Estimating Facet Joint Apposition with Specimen-Specific Computer Models of Subaxial Cervical Spine Kinematics

Computational models of experimental data can provide a noninvasive method to estimate spinal facet joint biomechanics. Existing models typically consider each vertebra as one rigid-body and assume uniform facet cartilage thickness. However, facet deflection occurs during motion, and cervical facet cartilage is nonuniform. Multi rigid-body computational models were used to investigate the effect of specimen-specific cartilage profiles on facet contact area estimates. Twelve C6/C7 segments underwent non-destructive intervertebral motions. Kinematics and facet deflections were measured. Three-dimensional models of the vertebra and cartilage thickness estimates were obtained from pre-test CT data. Motion-capture data was applied to two model types (2RB: C6, C7 vertebrae each one rigid body; 3RB: left and right C6 posterior elements, and C7 vertebrae, each one rigid body) and maximum facet mesh penetration was compared. Constant thickness cartilage (CTC) and spatially-varying thickness cartilage (SVTC) profiles were applied to the facet surfaces of the 3RB model. Cartilage apposition area (CAA) was compared. Linear mixed-effects models were used for all quantitative comparisons. The 3RB model significantly reduced penetrating mesh elements by accounting for facet deflections (p = 0.001). The CTC profile resulted in incongruent facet articulation, whereas realistic congruence was observed for the SVTC profile. The SVTC profile demonstrated significantly larger CAA than the CTC model (p < 0.001).

Assessment of Stress in the Soil Surrounding the Axially Loaded Model Pile by Thin, Flexible Sensors

Foundation piles transfer the applied vertical load to the surrounding soil by skin friction and base resistance. These two components induce stress in the soil. The load transfer is still not fully recognized, and some pile load tests analyses have raised many doubts. The present paper aimed to measure the stress levels during pile load tests in laboratory conditions. This research examined the possibilities of using thin, flexible sensors in measuring the stress in soil. Two sensors were used: tactile pressure sensor with mapping system and color film pressure sensors with digital analyzing. Calibration and preliminary tests of the sensors have been described. This calibration proved that this kind of sensor could measure the stress in the soil in laboratory conditions. The results of stress distribution in the soil, shown as pressure maps, have been presented. Significant stress changes were observed in pile load tests. Rough and smooth piles were compared in the analyses. Stress distribution was the result of simultaneous interaction of pile skin and base. The knowledge about stresses surrounding the pile allows us to carry out a deeper analysis of the pile–soil interaction.

Effects of implant rotational malposition on contact surface area after implantation of the augmented glenoid baseplate in the setting of glenoid bone loss

AIM OF THE STUDY

Augmented glenoid baseplates are utilized in reverse total shoulder arthroplasty in the setting of glenoid bone loss. These implants permit lateralization of the joint line and correction of bony version abnormalities. To allow bone preservation in the setting of abnormal bony version or deficiency, the backside of the augmented glenoid baseplate is not perpendicular to the axis of the central post/screw. Thus, if the baseplate is implanted with any rotational malposition, this could affect the backside contact area available for ingrowth. The purpose of this study was to assess if rotational malpositioning of a full-wedge augmented baseplate alongside the axis of the central screw significantly affects the glenoid implant backside contact area.

METHODS

Seven synthetic scapulas (Sawbones, Vashon, WA) were used to implant a 15° full-wedge glenoid baseplate (Wright Medical, Memphis, TN) according to the manufacturer's technique. The contact pressure between the baseplate and the glenoid surface at rotational positions 5°, 10°, and 15° clockwise (CW) and counterclockwise (CCW) from the central axis was measured with Extreme Low Fujifilm Prescale (Tekscan, Boston, MA). The data was analyzed digitally to obtain a percentage of contact surface area. To evaluate gross contact, a computed tomography (CT) scan was performed and manual measurements of contact between the glenoid and the baseplate were conducted using a standardized axial CT slice.

RESULTS

The average contact area at zero degrees of malrotation was 37.26 ± 3.27%. Average contact areas for the simulated malposition cases were 13.99 ± 9.39% at 15° CCW, 24.89 ± 5.11% at 10° CW, and 19.32 ± 3.13% at 15° CW. Each of these results was significant (p < 0.003). On computed tomography, at 15° CCW, the contact area decreased by 39%; at 15° CW, the contact area decreased by 38%.

DISCUSSION

The use of augmented glenoid baseplates presents a technical challenge. It is difficult to avoid implant malrotation along the axis of the central peg/screw, because the final rotation of the baseplate must be chosen while the implant is several centimeters away from the bone. This study found that 10° and 15° malrotation about the glenoid baseplate's central axis leads to significant decreases in the implant-bone contact area.

CONCLUSIONS

When implanting an augmented baseplate for total shoulder arthroplasty, it is important to minimize baseplate malrotation to decrease the risk of baseplate loosening.

Different effects of the lateral meniscus complete radial tear on the load distribution and transmission functions depending on the tear site

PURPOSE

To compare the effect of the lateral meniscus (LM) complete radial tear at different tear sites on the load distribution and transmission functions.

METHODS

A compressive load of 300 N was applied to the intact porcine knees (n = 30) at 15°, 30°, 60°, 90°, and 120° of flexion. The LM complete radial tears were created at the middle portion (group M), the posterior portion (group P), or the posterior root (group R) (n = 10, each group), and the same loading procedure was followed. Finally, the recorded three-dimensional paths were reproduced on the LM-removed knees. The peak contact pressure (contact area) in the lateral compartment and the calculated in situ force of the LM under the principle of superposition were compared among the four groups (intact, group M, group P, and group R).

RESULTS

At all the flexion angles, the peak contact pressure (contact area) was significantly higher (lower) after creating the LM complete radial tear as compared to that in the intact state (p < 0.01). At 120° of flexion, group R represented the highest peak contact pressure (lowest contact area), followed by group P and group M (p < 0.05). The results of the in situ force carried by the LM were similar to those of the tibiofemoral contact mechanics.

CONCLUSION

The detrimental effect of the LM complete radial tear on the load distribution and transmission functions was greatest in the posterior root tear, followed by the posterior portion tear and the middle portion tear in the deep-flexed position. Complete radial tars of the meniscus, especially at the posterior root, should be repaired to restore the biomechanical function.

Maximum Bridging Suture Tension Provides Better Clinical Outcomes in Transosseous-Equivalent Rotator Cuff Repair: A Clinical, Prospective Randomized Comparative Study

BACKGROUND

Some studies reporting clinical outcomes after transosseous-equivalent (TOE) repair have attributed type II rotator cuff failure to excessive bridging suture tension, as it can cause overloading on the medial row. In a previous biomechanical cadaveric study, increasing bridging suture tension over 90 N did not improve the contact area and ultimate failure load of the TOE construct, despite increasing the contact force and contact pressure.

PURPOSE

To compare the clinical outcomes of different bridging suture tensions after TOE rotator cuff repair based on the results of a previous biomechanical study.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

A total of 78 patients who underwent arthroscopic rotator cuff repair for medium- to large-sized tears were prospectively enrolled and randomly divided into 2 groups according to the applied bridging suture tension: optimum tension group (96.3 ± 4.9 N) and maximum tension group (199.0 ± 20.3 N). Bridging suture tension was measured with a customized tensiometer, as used in the previous biomechanical study. The functional outcome was measured at the final follow-up (27.4 ± 5.9 months [range, 24-45 months]) using the visual analog scale for pain, American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and Constant score, and the anatomic outcome was evaluated using magnetic resonance imaging or ultrasonography at least 12 months after surgery.

RESULTS

Overall, 64 patients (32 in each group) were analyzed. The functional outcomes improved significantly compared with preoperative values (all P < .05) but did not show significant differences between the 2 groups (all P > .05). Regarding the anatomic outcomes, the maximum tension group (n = 1; 3.1%) had a significantly lower healing failure rate than the optimum tension group (n = 9; 28.1%) (P = .013). One patient in the maximum tension group had a type II failure.

CONCLUSION

Maximum bridging suture tension in TOE repair for medium- to large-sized rotator cuff tears provided better anatomic healing with less risk of medial rotator cuff failure, which differs from the results of a previous time-zero biomechanical study.

Computational Model Validation of Contact Mechanics in Total Ankle Arthroplasty

Revision rates in total ankle arthroplasty (TAA) are nearly double compared with hip or knee arthroplasty procedures. Contact mechanics for metal-polyethylene articulation in TAA is critical due to the reduced size of the implant and higher expected load, compared with a hip or knee joint. This study was focused on developing a validated computational model to predict contact area in a polyethylene tibial bearing articulating with a metallic talar component in a bicondylar TAA design. Contact area was evaluated at five different flexion angles in an experimental test and in a computational model, per ASTM F2665. The overall contact area values predicted in the computational model matched closely (within 8%) with that measured in the comparator; well within the range reported in the literature. The credibility of the model to sufficiently predict the outputs relative to the experimental data was discussed using the guidelines provided by the recently published ASME V&V 40-2018 standard. Various sensitivities associated with both the model and the comparator, were explored. It was concluded that the validated modeling approach presented in this study demonstrated sufficient accuracy to support the use of modeling for evaluation of contact area of TAA designs. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1063-1069, 2020.

Stress Measurements on the Articular Cartilage Surface Using Fiber Optic Technology and In-Vivo Gait Kinematics

It has been hypothesized a change in stress on the cartilage of a joint is a significant factor in the initiation and progression of post-traumatic osteoarthritis. Without a reliable method for measuring stress, this hypothesis has largely gone untested. In this study, a novel, repeatable, and reliable method for measuring stress on the surface of articular cartilage in articular joints is presented. Small Fiber Bragg Grating (FBG) sensors capable of measuring normal stress between contact surfaces in diarthrodial joints were developed and validated. The small size of these sensors (diameter of 125-300 μm and sensing length of 1 mm) allows them to be inserted into the joint space without the removal of biomechanically relevant structures. In-vitro stresses on the surface of the cartilage for both healthy and surgically damaged joints were measured after implantation of the FBG sensors using in vivo generated gait kinematic data and a 6-degrees of freedom parallel robot. Along with our capability to reproduce in vivo motions accurately and the improvements in fiber optic technology, this study describes the first direct measurement of stress in a joint using in vivo gait kinematics.

Plantar Tactile Feedback for Biped Balance and Locomotion on Unknown Terrain

This work introduces a new sensing system for biped robots based on plantar robot skin, which provides not only the resultant forces applied on the ankles but a precise shape of the pressure distribution in the sole together with other extra sensing modalities (temperature, pre-touch and acceleration). The information provided by the plantar robot skin can be used to compute the center of pressure and the ground reaction forces. This information also enables the online construction of the supporting polygon and its preemptive shape before foot landing using the proximity sensors in the robot skin. Two experiments were designed to show the advantages of this new sensing technology for improving balance and walking controllers for biped robots over unknown terrain.

Biometric Data Comparison Between Lewis and Sprague Dawley Rats

Introduction: Pressure mapping systems are often used for indirect assessment of kinematic gait parameter differences after repair of critical peripheral nerve defects in small animal models. However, there does not appear to be any literature that studies the differences in normal gait pattern of Sprague Dawley rats compared to Lewis rats using a Tekscan VH4 pressure mat system. The purpose of this study is to assess the gait profile of Lewis and Sprague Dawley rats generated by Tekscan's VH4 system to detect similarities and/or differences in gait parameters involving both force and temporal variables. Materials and Methods: The gait profile of 14 Lewis and 14 Sprague Dawley rats was recorded using a Tekscan VH4 pressure map system with two successful walks per animal and gait parameter data was normalized for mean variance between the two rodent strains. Results: The results showed that temporal and normalized force parameters were not significantly different between the two types of rats. Maximum force, contact area, stride length, and adjusted pressure variables were significantly different between the two strains, likely attributed to the body size and weight differential between the strains. Variation in some of these parameters were considered due to differences in overall body size between the two strains, variations in gait kinematics between individual rodent subjects, and the limitations of the current experimental design. Conclusion: For future in vivo models, either Sprague Dawley or Lewis rat strains would be acceptable animal models when comparing base-line gait profiles using the Tekscan VH4 pressure map system when assessing critical defect repairs of peripheral nerves.

Bone-Plug Versus Soft Tissue Fixation of Medial Meniscal Allograft Transplants: A Biomechanical Study

BACKGROUND

It is controversial whether soft tissue fixation only and bone-plug techniques for medial meniscal allograft transplantation provide equivalent fixation and restoration of load distribution. Prior studies on this topic did not re-create the clinical situation with use of size-, side-, and compartment-matched meniscal transplants.

HYPOTHESIS

Both techniques will provide equivalent fixation of the meniscal transplant and restore load distribution and contact pressures similar to those of the native knee.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine fresh-frozen human cadaveric knees underwent mean contact pressure, mean contact area, and peak contact pressure evaluation in 4 medial meniscal testing conditions (native, total meniscectomy, bone-plug fixation, and soft tissue fixation) at 3 flexion angles (0°, 30°, and 60°) using Tekscan sensors under a 700-N axial load.

RESULTS

Medial meniscectomy resulted in significantly decreased contact area and increased contact pressure compared with the native condition at all flexion angles (P < .0001). Compared with the native state, soft tissue fixation demonstrated significantly higher mean contact pressure and lower mean contact area at 0° and 30° of flexion (P < .05), while bone-plug fixation showed no significant difference. There was no significant difference in peak contact pressure between study conditions.

CONCLUSION

Total medial meniscectomy leads to significantly worsened load distribution within the knee. Medial meniscal allograft transplantation can restore load parameters close to those of the native condition. The bone-plug technique demonstrated improved tibiofemoral contact pressures compared with soft tissue fixation.

CLINICAL RELEVANCE

Medial meniscal allograft transplantation with bone-plug fixation is a viable option to restore biomechanics in patients with meniscal deficiency.

Evaluation of laparoscopic forceps jaw contact pressure and distribution using pressure sensitive film

In this study, the authors used the Fujifilm Prescale Pressure Measuring System to measure the contact pressure and distribution at the jaws of laparoscopic grasping forceps. This data was then correlated with measured pressures at the forceps handles to understand the relationship between the surgeon's actuating pressure and that on the organ being manipulated. The purpose of this study is to create a database of tactile information to provide guidelines in defining minimally invasive surgery (MIS). This is expected to be important as today's society continues to progress in the use of automation, IoT, AI and MIS. In order to achieve the above, the authors developed an experimental device consisting of an actuator, a load cell and an MCU to stably actuate and control the handle side of grasping forceps. Target organs were simulated using triangular prisms of various silicone rubber materials. The experimental method involved actuating the handle side with preset pressure values for fixed time periods and using sensitive film to measure the pressure at the forceps tip. The film data was then scanned, processed and analyzed.

Biomechanical Properties of Nitinol Staples: Effects of Troughing, Effective Leg Length, and 2-Staple Constructs

PURPOSE

Nitinol memory compression staples are a recent addition to carpal bone fixation. Compared with traditional staples, they have been shown to have superior compression at the far cortex relative to standard and traditional compression staples. The purpose of this study was to (1) determine the effective leg length of different nitinol staples, (2) confirm the effect of 1 versus 2 staples on biomechanical compression, and (3) determine the effect of troughing (countersinking the staple into bone) the bone on staple biomechanical properties.

METHODS

Three commonly used nitinol staples of various bridge and leg lengths were used in a bicortical sawbones block construct. There were 3 separate constructs tested, which included single staple, double staple, and troughed. We measured compression force, stiffness, and bending strength for each construct before and after cyclical 4-point bending. Compression mapping was used to determine the effective leg length of each staple, which included the distance that compression extended beyond the tips of the staple legs.

RESULTS

Effective leg length for each staple construct extended 2 mm distal to the tip of the shortest staple leg. Two staple constructs more than doubled compressive force and increased bending strength by greater than 90% in all staple types. There was no loss of compressive force before or after loading for single, double, or troughed constructs with any staple type.

CONCLUSIONS

This study supports that nitinol staples do not have to be placed bicortically to achieve adequate compression; placing staples 2 mm short of the far cortex has the same compression as bicortical placement; and troughing of the bone will not significantly diminish the biomechanical properties of the construct.

CLINICAL RELEVANCE

Better understanding of the effective leg length of nitinol staples provides support that bicortical placement is not necessary for adequate compression. This study supports troughing bone to minimize implant prominence.

Biomechanical Evaluation of Interfragmentary Compression of Lag Screw Versus Positional Screw at Different Angles of Fixation

OBJECTIVES

To compare the compressive force achieved and retained with the lag versus positional screw technique at various angles of screw application.

METHODS

Sixty humeral sawbones were stratified into 6 groups based on the technique (lag or positional) and fixation angle (30, 60, or 90 degrees relative to the fracture plane). A sensor was placed between fragments to record compressive force. Absolute screw force is the final screw force. Normalized force is the final screw force minus force generated by reduction forceps. Retained force is the quotient of absolute force relative to reduction forceps force.

RESULTS

Lag screws attained higher force than positional at 60 degrees (absolute force 41% higher, P = 0.041; normalized force 1300% higher, P = 0.008; retained force 60% higher, P = 0.008) and 90 degrees (absolute force 86% higher, P = 0.006; normalized force 730% higher, P = 0.005; retained force 70% higher, P = 0.011), but not at 30 degrees. For lag screws, compressive force was similar at 60 and 90 degrees (absolute force P = 0.174, normalized force P = 0.364, and retained force P = 0.496), but not 30 degrees. For positional screws, no difference was found between the 3 angles of fixation for absolute force (P = 0.059). Normalized force and retained force were similar at 60 and 90 degrees (P = 0.944 and P = 0.725, respectively), but not 30 degrees.

CONCLUSIONS

Lag screw technique compressive force was superior to positional screw technique at 60 and 90 degrees. Comparison of force at angles of 60 and 90 degrees showed no significant difference for both techniques. Indicating 30 degrees deviation from perfect technique is tolerated without significant decrease in compressive force.

Sectioning of the Anterior Intermeniscal Ligament Changes Knee Loading Mechanics

PURPOSE

The purpose of this cadaver research project was to describe the biomechanical consequences of anterior intermeniscal ligament (AIML) resection on menisci function under load conditions in full extension and 60° of flexion.

METHODS

Ten unpaired fresh frozen cadaveric knees were dissected leaving the knee joint intact with its capsular and ligamentous attachments. The femur and tibia were sectioned 15 cm from the joint line and mounted onto the loading platform. A linear motion x-y table allows the tibial part of the joint to freely translate in the anterior-posterior direction. K-scan sensors were used to define contact area, contact pressure, and position of pressure center of application (PCOA). Two series of analysis were planned: before and after AIML resection, mechanical testing was performed with specimens in full extension (1,400 N load) and in 60° of flexion (700 N load) to approximate heel strike and foot impulsion during the gait.

RESULTS

Sectioning of the AIML produced mechanical variations below the 2 menisci when specimens were at full extension and loaded to 1,400 N: increasing the mean contact pressure (delta 0.4 ± 0.2 MPa, +15% variation P = .008) and maximum contact pressure (delta 1.50 ± 0.8 MPa, 15% variation P < .0001) and decreasing of tibiofemoral contact area (delta 71 ± 51 mm², -15% variation P < .0001) and PCOA (delta 2.1 ± 0.8 mm). At 60° flexion, significant differences regarding lateral meniscus mechanical parameters were observed before and after AIML resection: mean contact pressure increasing (delta 0.06 ± 0.1 MPa, +21% variation P = .001), maximal contact-pressure increasing (delta 0.17 ± 0.9 MPa, +28% variation P = .001), mean contact area decreasing (delta 1.84 ± 8 mm², 4% variation P = .3), and PCOA displacement to the joint center (mean displacement 0.6 ± 0.5 mm).

CONCLUSIONS

The section of the intermeniscal ligament leads to substantial changes in knee biomechanics, increasing femorotibial contact pressures, decreasing contact areas, and finally moving force center of application, which becomes more central inside the joint.

CLINICAL RELEVANCE

AIML resection performed ex vivo in this study, might potentially be deleterious in vivo. Clinical studies focusing on preserving or even repairing the AIML are needed to evaluate those ex vivo elements.

Pressure Distribution in the Ankle and Subtalar Joint With Routine and Oversized Foot Orthoses

BACKGROUND

Foot orthoses are used to treat many disorders that affect the lower limb. These assistive devices have the potential to alter the forces, load distribution, and orientation within various joints in the foot and ankle. This study attempts to quantify the effects of orthoses on the intra-articular force distribution of the ankle and subtalar joint using a cadaveric testing jig to simulate weight bearing.

METHODS

Five lower-limb cadaveric specimens were placed on a custom jig, where a 334-N (75-lb) load was applied at the femoral head, and the foot was supported against a plate to simulate double-leg stance. Pressure-mapping sensors were inserted into the ankle and subtalar joint. Mean pressure, peak pressure, contact area, and center of force were measured in both the ankle and subtalar joints for barefoot and 2 medial foot orthosis conditions. The 2 orthosis conditions were performed using (1) a 1.5-cm-height wedge to simulate normal orthoses and (2) a 3-cm-height wedge to simulate oversized orthoses.

RESULTS

The contact area experienced in the subtalar joint significantly decreased during 3-cm orthotic posting of the medial arch, but neither orthosis had a significant effect on the spatial mean pressure or peak pressure experienced in either joint.

CONCLUSION

The use of an oversized orthosis could lead to a decrease in the contact area and alterations in the distribution of pressure within the subtalar joint.

CLINICAL RELEVANCE

The use of inappropriate orthoses could negatively impact the force distribution in the lower limb.

A Brief Review of Handgrip Strength and Sport Performance

Cronin, J, Lawton, T, Harris, N, Kilding, A, and McMaster, DT. A brief review of handgrip strength and sport performance. J Strength Cond Res 31(11): 3187-3217, 2017-Tests of handgrip strength (HGS) and handgrip force (HGF) are commonly used across a number of sporting populations. Measures of HGS and HGF have also been used by practitioners and researchers to evaluate links with sports performance. This article first evaluates the validity and reliability of various handgrip dynamometers (HGD) and HGF sensors, providing recommendations for procedures to ensure that precise and reliable data are collected as part of an athlete's testing battery. Second, the differences in HGS between elite and subelite athletes and the relationships between HGS, HGF, and sports performance are discussed.

Double row equivalent for rotator cuff repair: A biomechanical analysis of a new technique

Introduction

There are numerous configurations of double row fixation for rotator cuff tears however, there remains to be a consensus on the best method. In this study, we evaluated three different double-row configurations, including a new method. Our primary question is whether the new anchor and technique compares in biomechanical strength to standard double row techniques.

Methods

Eighteen prepared fresh frozen bovine infraspinatus tendons were randomized to one of three groups including the New Double Row Equivalent, Arthrex Speedbridge and a transosseous equivalent using standard Stabilynx anchors. Biomechanical testing was performed on humeri sawbones and ultimate load, strain, yield strength, contact area, contact pressure, and a survival plots were evaluated.

Results

The new double row equivalent method demonstrated increased survival as well as ultimate strength at 415N compared to the remainder testing groups as well as equivalent contact area and pressure to standard double row techniques.

Conclusions

This new anchor system and technique demonstrated higher survival rates and loads to failure than standard double row techniques. This data provides us with a new method of rotator cuff fixation which should be further evaluated in the clinical setting.

Level of Evidence

Basic science biomechanical study.

Techniques of Force and Pressure Measurement in the Small Joints of the Wrist

BACKGROUND

The alteration of forces across joints can result in instability and subsequent disability. Previous methods of force measurements such as pressure-sensitive films, load cells, and pressure-sensing transducers have been utilized to estimate biomechanical forces across joints and more recent studies have utilized a nondestructive method that allows for assessment of joint forces under ligamentous restraints.

METHODS

A comprehensive review of the literature was performed to explore the numerous biomechanical methods utilized to estimate intra-articular forces.

RESULTS

Methods of biomechanical force measurements in joints are reviewed.

CONCLUSIONS

Methods such as pressure-sensitive films, load cells, and pressure-sensing transducers require significant intra-articular disruption and thus may result in inaccurate measurements, especially in small joints such as those within the wrist and hand. Non-destructive methods of joint force measurements either utilizing distraction-based joint reaction force methods or finite element analysis may offer a more accurate assessment; however, given their recent inception, further studies are needed to improve and validate their use.

Biomechanical Measurement Error Can Be Caused by Fujifilm Thickness: A Theoretical, Experimental, and Computational Analysis

This is the first study to quantify the measurement error due to the physical thickness of Fujifilm for several material combinations relevant to orthopaedics. Theoretical and experimental analyses were conducted for cylinder-on-flat indentation over a series of forces (750 and 3000 N), cylinder diameters (0 to 80 mm), and material combinations (metal-on-metal, MOM; metal-on-polymer, MOP; metal-on-bone, MOB). For the scenario without Fujifilm, classic Hertzian theory predicted the true line-type contact width as W_O = {(8FD_cyl)/(πL_cyl)[(1 − ν_cyl²)/E_cyl + (1 − ν_flat²)/E_flat]}^1/2, where F is compressive force, D_cyl is cylinder diameter, L_cyl is cylinder length, ν_cyl and ν_flat are cylinder and flat Poisson's ratios, and E_cyl and E_flat are cylinder and flat elastic moduli. For the scenario with Fujifilm, experimental measurements resulted in contact widths of W_F = 0.1778 × F^0.2273 × D^0.2936 for MOM tests, W_F = 0.0449 × F^0.4664 × D^0.4201 for MOP tests, and W_F = 0.1647 × F^0.2397 × D^0.3394 for MOB tests, where F is compressive force and D is cylinder diameter. Fujifilm thickness error ratio W_F/W_O showed a nonlinear decrease versus cylinder diameter, whilst error graphs shifted down as force increased. Computational finite element analysis for several test cases agreed with theoretical and experimental data, respectively, to within 3.3% and 1.4%. Despite its wide use, Fujifilm's measurement errors must be kept in mind when employed in orthopaedic biomechanics research.

Evaluation of Flexible Force Sensors for Pressure Monitoring in Treatment of Chronic Venous Disorders

The recent use of graduated compression therapy for treatment of chronic venous disorders such as leg ulcers and oedema has led to considerable research interest in flexible and low-cost force sensors. Properly applied low pressure during compression therapy can substantially improve the treatment of chronic venous disorders. However, achievement of the recommended low pressure levels and its accurate determination in real-life conditions is still a challenge. Several thin and flexible force sensors, which can also function as pressure sensors, are commercially available, but their real-life sensing performance has not been evaluated. Moreover, no researchers have reported information on sensor performance during static and dynamic loading within the realistic test conditions required for compression therapy. This research investigated the sensing performance of five low-cost commercial pressure sensors on a human-leg-like test apparatus and presents quantitative results on the accuracy and drift behaviour of these sensors in both static and dynamic conditions required for compression therapy. Extensive experimental work on this new human-leg-like test setup demonstrated its utility for evaluating the sensors. Results showed variation in static and dynamic sensing performance, including accuracy and drift characteristics. Only one commercially available pressure sensor was found to reliably deliver accuracy of 95% and above for all three test pressure points of 30, 50 and 70 mmHg.

Can mechanical imaging increase the specificity of mammography screening?

Objectives

This study aimed to investigate the effects of adding adjunct mechanical imaging to mammography breast screening. We hypothesized that mechanical imaging could detect increased local pressure caused by both malignant and benign breast lesions and that a pressure threshold for malignancy could be established. The impact of this on breast screening was investigated with regard to reductions in recall and biopsy rates.

Methods

155 women recalled from breast screening were included in the study, which was approved by the regional ethical review board (dnr 2013/620). Mechanical imaging readings were acquired of the symptomatic breast. The relative mean pressure on the suspicious area (RMPA) was defined and a threshold for malignancy was established.

Results

Biopsy-proven invasive cancers had a median RMPA of 3.0 (interquartile range (IQR) = 3.7), significantly different from biopsy-proven benign at 1.3 (IQR = 1.0) and non-biopsied cases at 1.0 (IQR = 1.3) (P < 0.001). The lowest RMPA for invasive cancer was 1.4, with 23 biopsy-proven benign and 33 non-biopsied cases being below this limit. Had these women not been recalled, recall rates would have been reduced by 36% and biopsy rates by 32%.

Conclusions

If implemented in a screening situation, this may substantially lower the number of false positives.

Key Points

• Mechanical imaging is used as an adjunct to mammography in breast screening.

• A threshold pressure can be established for malignant breast cancer.

• Recalls and biopsies can be substantially reduced.

Polydimethylsiloxane pressure sensors for force analysis in tension band wiring of the olecranon

BACKGROUND

Several different surgical techniques are used in the treatment of olecranon fractures. Tension band wiring is one of the most preferred options by surgeons worldwide. The concept of this technique is to transform a tensile force into a compression force that adjoins two surfaces of a fractured bone. Currently, little is known about the resulting compression force within a fracture.

OBJECTIVE

Sensor devices are needed that directly transduce the compression force into a measurement quality. This allows the comparison of different surgical techniques. Ideally the sensor devices ought to be placed in the gap between the fractured segments.

METHODS

The design, development and characterization of miniaturized pressure sensors fabricated entirely from polydimethylsiloxane (PDMS) for a placement within a fracture is presented. The pressure sensors presented in this work are tested, calibrated and used in an experimental in vitro study.

RESULTS

The pressure sensors are highly sensitive with an accuracy of approximately 3 kPa. A flexible fabrication process for various possible applications is described. The first in vitro study shows that using a single-twist or double-twist technique in tension band wiring of the olecranon has no significant effect on the resulting compression forces.

CONCLUSIONS

The in vitro study shows the feasibility of the proposed measurement technique and the results of a first exemplary study.

The role of fibular for supramalleolar osteotomy in treatment of varus ankle arthritis: a biomechanical and clinical study

Background

Supramalleolar osteotomy (SMOT) is a well-accepted treatment method for mid-stage varus ankle osteoarthritis (OA). However, few studies have examined the role of fibular osteotomy in SMOT. The objective of the current study was to compare the biomechanical and clinical outcomes of SMOT with and without fibular osteotomy.

Methods

Eight cadaveric lower legs with 10° varus/valgus SMOT models were tested using a Tekscan ankle sensor. Tibiotalar joint contact with and without fibular osteotomy conditions were compared. Forty-one varus ankle OA patients treated with SMOT were included; 22 underwent fibular osteotomy, and 19 did not. The Maryland foot score and radiological angles were used for clinical evaluation.

Results

The mean contact area and pressure did not differ significantly between normal and varus/valgus conditions with the fibula preserved. After fibular osteotomy, the mean contact area decreased and the mean contact pressure increased significantly in varus and valgus conditions (P < 0.01). The loading center moved to the opposite direction with and without fibular osteotomy in varus/valgus conditions. After a mean follow-up of 36.6 months (range 17–61), there was no significant difference in the Maryland scores of the two groups. However, in the fibular osteotomy group, the talar tilt angle decreased (P < 0.05), and the tibiocrural angle improved significantly (P < 0.01).

Conclusions

Fibular osteotomy facilitates the translation of tibiotalar contact pressure and is helpful for varus ankle realignment in patients with large talar tilts and small tibiocrural angles.

Biomechanical benefits of anterior offsetting of humeral head component in posteriorly unstable total shoulder arthroplasty: A cadaveric study

Restoration of joint stability during total shoulder arthroplasty can be challenging in the face of severe glenoid retroversion. A novel technique of humeral head component anterior-offsetting has been proposed to address posterior instability. We evaluated the biomechanical benefits of this technique in cadaveric specimens. Total shoulder arthroplasty was performed in 14 cadaveric shoulders from 7 donors. Complementary shoulders were assigned to either 10° or 20° glenoid retroversion, with retroversion created by eccentric reaming. Two humeral head component offset positions were tested in each specimen: The anatomic (posterior) and anterior (reverse). With loads applied to the rotator cuff and deltoid, joint contact pressures and the force and energy required for posterior humeral head translation were measured. The force and energy required to displace the humeral head posteriorly increased significantly with the anterior offset position compared to the anatomic offset position. The joint contact pressures were significantly shifted anteriorly, and the joint contact area significantly increased with the anterior offset position. Anterior offsetting of the humeral head component increased the resistance to posterior humeral head translation, shifted joint contact pressures anteriorly, and increased joint contact area, thus, potentially increasing the joint stability in total shoulder arthroplasty with simulated glenoid retroversion.

Safety and Effectiveness of SAF-R, a Novel Patient Positioning Device for Robot-Assisted Pelvic Surgery in Trendelenburg Position

PURPOSE

We found current robotic positioning devices to be inadequate and cumbersome. Furthermore, we realized there were no premarket well-designed studies to prove their safety and efficacy. In this prospective pilot study, we aimed to investigate the safety and effectiveness of a novel patient-positioning device (SAF-R) to secure the patient in Trendelenburg (T-burg) position for robot-assisted pelvic surgery.

PATIENTS AND METHODS

Sixteen patients undergoing robot-assisted pelvic operation in T-burg position were enrolled. Patients were positioned using SAF-R board. Pressure sensor mats were used for real-time monitoring of the contact pressures and contact area on the shoulders and calves throughout the surgery. Data collection included patients' body mass index (BMI), time needed for positioning, total time in the T-burg position, contact pressure and contact area readings from the sensor mats, and the patient shifting distance on the table. Patients were also followed for 1-month postoperatively for any position-related adverse event.

RESULTS

The median age of the patients was 56.5 years with median BMI of 27.3. The median positioning time was 6 minutes, duration of T-burg position was 3.5 hours, and patient shift on the table was 1 cm. The contact pressure over the shoulders was in the safe range (< 80 mm Hg) before and at the end of the surgery in all cases (right: 13.12 ± 1.12 vs 20.25 ± 1.56 mm Hg, left: 12.84 ± 1.05 vs 19.60 ± 1.09 mm Hg, p = 0.001). The changes in the mean contact pressure over the calves and the mean contact area for the shoulders and calves during the T-burg position were not significantly different. No significant position-related complication was detected during follow-up.

CONCLUSIONS

SAF-R surgical board is a safe, reliable, and timesaving positioning device for patients undergoing robotic pelvic surgery in the T-burg position.

Distal Radioulnar Joint Reaction Force Following Ulnar Shortening: Diaphyseal Osteotomy Versus Wafer Resection

PURPOSE

To compare how ulnar diaphyseal shortening and wafer resection affect distal radioulnar joint (DRUJ) joint reaction force (JRF) using a nondestructive method of measurement. Our hypothesis was that ulnar shortening osteotomy would increase DRUJ JRF more than wafer resection.

METHODS

Eight fresh-frozen human cadaveric upper limbs were obtained. Under fluoroscopic guidance, a threaded pin was inserted into the lateral radius orthogonal to the DRUJ and a second pin was placed in the medial ulna coaxial to the radial pin. Each limb was mounted onto a mechanical tensile testing machine and a distracting force was applied across the DRUJ while force and displacement were simultaneously measured. Data sets were entered into a computer and a polynomial was generated and solved to determine the JRF. This process was repeated after ulnar diaphyseal osteotomy, ulnar re-lengthening, and ulnar wafer resection. The JRF was compared among the 4 conditions.

RESULTS

Average baseline DRUJ JRF for the 8 arms increased significantly after diaphyseal ulnar shortening osteotomy (7.2 vs 10.3 N). Average JRF after re-lengthening the ulna and wafer resection was 6.9 and 6.7 N, respectively. There were no differences in JRF among baseline, re-lengthened, and wafer resection conditions.

CONCLUSIONS

Distal radioulnar joint JRF increased significantly after ulnar diaphyseal shortening osteotomy and did not increase after ulnar wafer resection.

CLINICAL RELEVANCE

Diaphyseal ulnar shortening osteotomy increases DRUJ JRF, which may lead to DRUJ arthrosis.

Effects of acetabular rim trimming on hip joint contact pressures: how much is too much?

BACKGROUND

In patients with femoroacetabular impingement (FAI), acetabular rim trimming removes the offending area of the acetabular deformity in patients with pincer-type and mixed-type FAI to improve hip joint kinematics. Although the rationale for arthroscopic acetabular rim trimming in patients with FAI is well established, the amount of rim resection has not been quantified, and the threshold at which excessive rim resection results in abnormal hip contact pressures has not been described.

PURPOSE

To investigate the changes in contact areas, contact pressures, and peak forces within the hip joint with sequential acetabular rim trimming.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six fresh-frozen, nondysplastic, human cadaveric hemipelvises were analyzed utilizing thin-film piezoresistive load sensors to measure the contact area, contact pressure, and peak force after anterosuperior acetabular rim trimming at depths of 0 mm (intact), 2 mm, 4 mm, 6 mm, and 8 mm. Each specimen was examined at 20° of extension and 60° of flexion. Analysis was performed on 2 regions of interest: the acetabular rim and the acetabular base (deep part of the acetabulum). After each experimental condition, the acetabulum was normalized with respect to the intact state to account for specimen variability. Statistical analysis was conducted through 1-way analysis of variance with post hoc Games-Howell tests.

RESULTS

At the acetabular base, there were significant increases in the contact area after 4-mm resection (60°: 169.12% ± 30.64%; P = .0138), contact pressure after 6-mm resection (60°: 292.76% ± 79.07%; P = .009), and peak force after 6-mm resection (60°: 166.00% ± 34.40%; P = .027). At the acetabular rim, there were significant decreases in the contact area after 6-mm resection (60°: 66.32% ± 18.80%; P = .0354) (20°: 65.47% ± 15.87%; P = .0127), contact pressure after 6-mm resection (60°: 50.77% ± 11.49%; P < .001) (20°: 58.01% ± 23.10%; P = .0335), and peak force after 6-mm resection (60°: 60.67% ± 9.29%; P < .001) (20°: 74.44% ± 9.84%; P = .007).

CONCLUSION

Resecting more than 4 to 6 mm of the acetabular rim during hip arthroscopic surgery to address a pincer deformity may dramatically increase contact pressures by 3-fold at the acetabular base. The study suggests that excessive rim resection may lead to increased loads in the hip joint and may predispose to premature joint degeneration.

CLINICAL RELEVANCE

Resecting more than 4 to 6 mm of the acetabular rim may significantly alter hip joint biomechanics, increasing joint reactive forces and subsequent chondrolabral degeneration.

Impact of Ulnar Collateral Ligament Tear on Posteromedial Elbow Biomechanics

Ulnar collateral ligament insufficiency has been shown to result in changes in contact pressure and contact area in the posteromedial elbow. This study used new digital technology to assess the effect of a complete ulnar collateral ligament tear on ulnohumeral contact area, contact pressure, and valgus laxity throughout the throwing motion. Nine elbow cadaveric specimens were tested at 90° and 30° of elbow flexion to simulate the late cocking/early acceleration and deceleration phases of throwing, respectively. A digital sensor was placed in the posteromedial elbow. Each specimen was tested with valgus torque of 2.5 Nm with the anterior band of the ulnar collateral ligament intact and transected. A camera-based motion analysis system was used to measure valgus inclination of the forearm with the applied torque. At 90° of elbow flexion, mean contact area decreased significantly (107.9 mm(2) intact vs 84.9 mm(2) transected, P=.05) and average maximum contact pressure increased significantly (457.6 kPa intact vs 548.6 kPa transected, P<.001). At 30° of elbow flexion, mean contact area decreased significantly (83.9 mm(2) intact vs 65.8 mm(2) transected, P=.01) and average maximum contact pressure increased nonsignificantly (365.9 kPa intact vs 450.7 kPa transected, P=.08). Valgus laxity increased significantly at elbow flexion of 90° (1.1° intact vs 3.3° transected, P=.01) and 30° (1.0° intact vs 1.7° transected, P=.05). Ulnar collateral ligament insufficiency was associated with significant changes in contact area, contact pressure, and valgus laxity during both relative flexion (late cocking/early acceleration phase) and relative extension (deceleration phase) moments during the throwing motion arc.

Cartilage and chondrocyte response to extreme muscular loading and impact loading: Can in vivo pre-load decrease impact-induced cell death?

BACKGROUND

Impact loading causes cartilage damage and cell death. Pre-loading prior to impact loading may protect cartilage and chondrocytes. However, there is no systematic evidence and understanding of the effects of pre-load strategies on cartilage damage and chondrocyte death. This study aimed at determining the effects of the pre-load history on impact-induced chondrocyte death in an intact joint.

METHODS

Patellofemoral joints from 42 rabbits were loaded by controlled quadriceps muscle contractions and an external impacter. Two extreme muscular loading conditions were used: (i) a short-duration, high intensity, static muscle contraction, and (ii) a long-duration, low-intensity, cyclic muscle loading protocol. A 5-Joule centrally-oriented, gravity-accelerated impact load was applied to the joints. Chondrocyte viability was quantified following the muscular loading protocols, following application of the isolated impact loads, and following application of the impact loads that were preceded by the muscular pre-loads. Joint contact pressures were measured for all loading conditions by a pressure-sensitive film.

FINDINGS

Comparing to cartilage injured by impact loading alone, cartilage pre-loaded by static, maximal intensity, short-term muscle loads had lower cell death, while cartilage pre-loaded by repetitive, low-intensity, long-term muscular loads has higher cell death. The locations of peak joint contact pressures were not strongly correlated with the locations of greatest cell death occurrence.

INTERPRETATION

Static, high intensity, short muscular pre-load protected cells from impact injury, whereas repetitive, low intensity, prolonged muscular pre-loading to the point of muscular fatigue left the chondrocytes vulnerable to injury. However, cell death seems to be unrelated to the peak joint pressures.

A nondestructive, reproducible method of measuring joint reaction force at the distal radioulnar joint

PURPOSE

To develop a nondestructive method of measuring distal radioulnar joint (DRUJ) joint reaction force (JRF) that preserves all periarticular soft tissues and more accurately reflects in vivo conditions.

METHODS

Eight fresh-frozen human cadaveric limbs were obtained. A threaded Steinmann pin was placed in the middle of the lateral side of the distal radius transverse to the DRUJ. A second pin was placed into the middle of the medial side of the distal ulna colinear to the distal radial pin. Specimens were mounted onto a tensile testing machine using a custom fixture. A uniaxial distracting force was applied across the DRUJ while force and displacement were simultaneously measured. Force-displacement curves were generated and a best-fit polynomial was solved to determine JRF.

RESULTS

All force-displacement curves demonstrated an initial high slope where relatively large forces were required to distract the joint. This ended with an inflection point followed by a linear area with a low slope, where small increases in force generated larger amounts of distraction. Each sample was measured 3 times and there was high reproducibility between repeated measurements. The average baseline DRUJ JRF was 7.5 N (n = 8).

CONCLUSIONS

This study describes a reproducible method of measuring DRUJ reaction forces that preserves all periarticular stabilizing structures. This technique of JRF measurement may also be suited for applications in the small joints of the wrist and hand.

CLINICAL RELEVANCE

Changes in JRF can alter native joint mechanics and lead to pathology. Reliable methods of measuring these forces are important for determining how pathology and surgical interventions affect joint biomechanics.

Measurement of hand/handrim grip forces in two different one arm drive wheelchairs

Purpose. The aim of this study was to explore the total and regional grip forces in the hand when propelling two different manual one arm drive wheelchairs: the Neater Uni-wheelchair (NUW) and a foot steered Action3 wheelchair. Methods. 17 nondisabled users were randomly assigned to each wheelchair to drive around an indoor obstacle course. The Grip, a multiple sensor system taking continuous measurement of handgrip force, was attached to the propelling hand. Total grip force in each region of the hand and total grip force across the whole hand were calculated per user per wheelchair. Results. The Action3 with foot steering only generated significantly greater total grip force in straight running compared to the NUW and also in the fingers and thumb in straight running. Conclusions. The results suggest that the Action3 with foot steering generated greater grip forces which may infer a greater potential for repetitive strain injury in the upper limb. Further work is required to explore whether the difference in grip force is of clinical significance in a disabled population.

Site-specific loading at the fifth metatarsal base in rehabilitative devices: implications for Jones fracture treatment

BACKGROUND

Fractures of the fifth metatarsal base are a relatively common injury. Whether treated surgically or nonsurgically, injury rehabilitation typically involves immobilization in a rigid sandal or short controlled ankle movement (CAM) walker boot.

OBJECTIVE

To determine the peak pressure, contact pressure, and impulse at the base of the fifth metatarsal in 3 common footwear devices during common gait activities.

DESIGN

This was a retrospective comparative study.

SETTING

Research was conducted in a sports performance laboratory at a university.

PARTICIPANTS

Twenty subjects without a recent history of foot injuries volunteered to participate.

METHODS

Each subject performed 3 common gait activities (walking, heel walking, and pivoting) in 3 footwear devices (short CAM walker boot, postoperative sandal, running shoe). Pressure data were sampled (100 Hz) using individually sized plantar pressure insoles and software (Tekscan). Walking trials were collected at 1.0 m/s ± 5% (FusionSport Timing Gates).

OUTCOME MEASUREMENTS

Peak pressure, contact pressure, and impulse at the fifth metatarsal base region were determined for all trials for all subjects. Mixed-effect regression models were used to compare pairwise differences in outcome variables between footwear devices.

RESULTS

The CAM walker boot resulted in significantly lower peak pressure at the fifth metatarsal during walking and heel-walking relative to the postoperative sandal (P < .01) and during heel-walking (P < .01) relative to the standard athletic shoe. The CAM walker boot significantly reduced contact pressures at the fifth metatarsal during walking and heel-walking relative to the postoperative sandal (P < .01), and during heel-walking relative to the standard athletic shoe (P < .001).

CONCLUSIONS

Our results suggest that the short CAM walker boot more effectively offloads the fifth metatarsal during common gait activities than a postoperative sandal or a standard athletic shoe. A short CAM walker boot may be a beneficial rehabilitative tool for patients undergoing rehabilitation after treatment of Jones fractures and other base of fifth metatarsal fractures.