Transhumeral prosthesis use affects upper body kinematics and kinetics.

BACKGROUND: Transhumeral (TH) limb loss leads to loss of body mass and reduced shoulder range of motion. Despite most owning a prosthesis, prosthesis abandonment is common. The consequence of TH limb loss and prosthesis use and disuse during gait may be compensation in the upper body, contributing to back pain or injury. Understanding the impact of not wearing a TH prosthesis on upper body asymmetries and spatial-temporal aspects of gait will inform how TH prosthesis use and disuse affects the body. RESEARCH QUESTION: Does TH limb loss alter upper body asymmetries and spatial-temporal parameters during gait when wearing and not wearing a prosthesis compared to able-bodied controls? METHODS: Eight male TH limb loss participants and eight male control participants completed three gait trials at self-selected speeds. The TH limb loss group performed trials with and without their prosthesis. Arm swing, trunk angular displacement, trunk-pelvis moment, and spatial-temporal aspects were compared using non-parametric statistical analyses. RESULTS: Both TH walking conditions showed greater arm swing in the intact limb compared to the residual (p≤0.001), resulting in increased asymmetry compared to the control group (p≤0.001). Without the prosthesis, there was less trunk flexion and lateral flexion compared to the control group (p≤0.001). Maximum moments between the trunk and pelvis were higher in the TH group than the control group (p≤0.05). Spatial-temporal parameters of gait did not differ between the control group and either TH limb loss condition. SIGNIFICANCE: Prosthesis use affects upper body kinematics and kinetics, but does not significantly impact spatial-temporal aspects of gait, suggesting these are compensatory actions. Wearing a prosthesis helps achieve more normative upper body kinematics and kinetics than not wearing a prosthesis, which may help limit back pain. These findings emphasize the importance of encouraging at least passive use of prostheses for individuals with TH limb loss.

Extended physiological proprioception is affected by transhumeral Socket-Suspended prosthesis use.

The objective of this study was to define targeted reaching performance without visual information for transhumeral (TH) prosthesis users, establishing baseline information about extended physiological proprioception (EPP) in this population. Subjects completed a seated proprioceptive targeting task under simultaneous motion capture, using their prosthesis and intact limb. Eight male subjects, median age of 58 years (range 29-77 years), were selected from an ongoing screening study to participate. Five subjects had a left-side TH amputation, and three a right-side TH amputation. Median time since amputation was 9 years (range 3-54 years). Four subjects used a body-powered prosthetic hook, three a myoelectric hand, and one a myoelectric hook. The outcome measures were precision and accuracy, motion of the targeting hand, and joint angular displacement. Subjects demonstrated better precision when targeting with their intact limb compared to targeting with their prosthesis, 1.9 cm2 (0.8-3.0) v. 7.1 cm2 (1.3-12.8), respectively, p = 0.008. Subjects achieved a more direct reach path ratio when targeting with the intact limb compared to with the prosthesis, 1.2 (1.1-1.3) v. 1.3 (1.3-1.4), respectively, p = 0.039 The acceleration, deceleration, and corrective phase durations were consistent between conditions. Trunk angular displacement increased in flexion, lateral flexion, and axial rotation while shoulder flexion decreased when subjects targeted with their prosthesis compared to the intact limb. The differences in targeting precision, reach patio ratio, and joint angular displacements while completing the targeting task indicate diminished EPP. These findings establish baseline information about EPP in TH prosthesis users for comparison as novel prosthesis suspension systems become more available to be tested.

Strain-mode-specific mechanical testing and the interpretation of bone adaptation in the deer calcaneus.

The artiodactyl (deer and sheep) calcaneus is a model that helps in understanding how many bones achieve anatomical optimization and functional adaptation. We consider how the dorsal and plantar cortices of these bones are optimized in quasi-isolation (the conventional view) versus in the context of load sharing along the calcaneal shaft by "tension members" (the plantar ligament and superficial digital flexor tendon). This load-sharing concept replaces the conventional view, as we have argued in a recent publication that employs an advanced analytical model of habitual loading and fracture risk factors of the deer calcaneus. Like deer and sheep calcanei, many mammalian limb bones also experience prevalent bending, which seems problematic because the bone is weaker and less fatigue-resistant in tension than compression. To understand how bones adapt to bending loads and counteract deleterious consequences of tension, it is important to examine both strain-mode-specific (S-M-S) testing (compression testing of bone habitually loaded in compression; tension testing of bone habitually loaded in tension) and non-S-M-S testing. Mechanical testing was performed on individually machined specimens from the dorsal "compression cortex" and plantar "tension cortex" of adult deer calcanei and were independently tested to failure in one of these two strain modes. We hypothesized that the mechanical properties of each cortex region would be optimized for its habitual strain mode when these regions are considered independently. Consistent with this hypothesis, energy absorption parameters were approximately three times greater in S-M-S compression testing in the dorsal/compression cortex when compared to non-S-M-S tension testing of the dorsal cortex. However, inconsistent with this hypothesis, S-M-S tension testing of the plantar/tension cortex did not show greater energy absorption compared to non-S-M-S compression testing of the plantar cortex. When compared to the dorsal cortex, the plantar cortex only had a higher elastic modulus (in S-M-S testing of both regions). Therefore, the greater strength and capacity for energy absorption of the dorsal cortex might "protect" the weaker plantar cortex during functional loading. However, this conventional interpretation (i.e., considering adaptation of each cortex in isolation) is rejected when critically considering the load-sharing influences of the ligament and tendon that course along the plantar cortex. This important finding/interpretation has general implications for a better understanding of how other similarly loaded bones achieve anatomical optimization and functional adaptation.

Exploration of the synergistic role of cortical thickness asymmetry ("Trabecular Eccentricity" concept) in reducing fracture risk in the human femoral neck and a control bone (Artiodactyl Calcaneus).

The mechanobiology of the human femoral neck is a focus of research for many reasons including studies that aim to curb age-related bone loss that contributes to a near-exponential rate of hip fractures. Many believe that the femoral neck is often loaded in rather simple bending, which causes net tension stress in the upper (superior) femoral neck and net compression stress in its inferior aspect ("T/C paradigm"). This T/C loading regime lacks in vivo proof. The "C/C paradigm" is a plausible alternative simplified load history that is characterized by a gradient of net compression across the entire femoral neck; action of the gluteus medius and external rotators of the hip are important in this context. It is unclear which paradigm is at play in natural loading due to lack of in vivo bone strain data and deficiencies in understanding mechanisms and manifestations of bone adaptation in tension vs. compression. For these reasons, studies of the femoral neck would benefit from being compared to a 'control bone' that has been proven, by strain data, to be habitually loaded in bending. The artiodactyl (sheep and deer) calcaneus model has been shown to be a very suitable control in this context. However, the application of this control in understanding the load history of the femoral neck has only been attempted in two prior studies, which did not examine the interplay between cortical and trabecular bone, or potential load-sharing influences of tendons and ligaments. Our first goal is to compare fracture risk factors of the femoral neck in both paradigms. Our second goal is to compare and contrast the deer calcaneus to the human femoral neck in terms of fracture risk factors in the T/C paradigm (the C/C paradigm is not applicable in the artiodactyl calcaneus due to its highly constrained loading). Our third goal explores interplay between dorsal/compression and plantar/tension regions of the deer calcaneus and the load-sharing roles of a nearby ligament and tendon, with insights for translation to the femoral neck. These goals were achieved by employing the analytical model of Fox and Keaveny (J. Theoretical Biology 2001, 2003) that estimates fracture risk factors of the femoral neck. This model focuses on biomechanical advantages of the asymmetric distribution of cortical bone in the direction of habitual loading. The cortical thickness asymmetry of the femoral neck (thin superior cortex, thick inferior cortex) reflects the superior-inferior placement of trabecular bone (i.e., "trabecular eccentricity," TE). TE helps the femoral neck adapt to typical stresses and strains through load-sharing between superior and inferior cortices. Our goals were evaluated in the context of TE. Results showed the C/C paradigm has lower risk factors for the superior cortex and for the overall femoral neck, which is clinically relevant. TE analyses of the deer calcaneus revealed important synergism in load-sharing between the plantar/tension cortex and adjacent ligament/tendon, which challenges conventional understanding of how this control bone achieves functional adaptation. Comparisons with the control bone also exposed important deficiencies in current understanding of human femoral neck loading and its potential histocompositional adaptations.

Testing Precision and Accuracy of an Upper Extremity Proprioceptive Targeting Task Assessment.

Objective: To develop and test an assessment measuring extended physiological proprioception (EPP). EPP is a learned skill that allows one to extend proprioception to an external tool, which is important for controlling prosthetic devices. The current study examines the ability of this assessment to measure EPP in a nonamputee population for translation into the affected population. Design: Measuring precision and accuracy of an upper extremity (UE) proprioceptive targeting task assessment. Participants completed 2 sessions of a targeting task while seated at a table. The targeting was completed with the dominant and nondominant hand and with eyes open and eyes closed during the task. Participants completed 2 sessions of the clinical test with a 1-week washout period to simulate reasonable time between clinical visits. Setting: Research laboratory. Participants: Twenty right-handed participants (N=20) with no neurologic or orthopedic deficits that would interfere with proprioception, median age of 25 years (range, 19-33 years), completed the assessment (10 men, 10 women). Interventions: Not applicable. Main Outcome Measures: Precision (consistency in targeting) and accuracy (distance between the intended target and participant result) in UE targeting task using EPP; test-retest repeatability between sessions. Results: Both precision and accuracy were significantly decreased in the eyes-closed condition compared with the eyes-open condition regardless of targeting with dominant or nondominant hand (all P<.001). In the eyes-open condition, there was a dominance effect relating to the accuracy; however, in the eyes-closed condition, accuracy between dominant and nondominant hands was statistically equivalent. Based on minimum detectable change with 95% confidence, there was no change in either metric between the first and second sessions. Conclusions: The results of this study support the feasibility of using this assessment to measure EPP-based on the definition of EPP as a learned skill that indicates control over an external, simple tool-because they demonstrate reliance on proprioception in the eyes-closed condition, symmetry in proprioceptive accuracy between hands for within-participant control, and test-retest reliability for longitudinal measurements. The results also establish normative values for this assessment in young, healthy adults. Further research is required in a clinical population to evaluate the UE proprioceptive targeting task assessment further and collect objective data on EPP.

Clinical Basis for Creating an Osseointegrated Neural Interface.

As technology continues to improve within the neuroprosthetic landscape, there has been a paradigm shift in the approach to amputation and surgical implementation of haptic neural prosthesis for limb restoration. The Osseointegrated Neural Interface (ONI) is a proposed solution involving the transposition of terminal nerves into the medullary canal of long bones. This design combines concepts of neuroma formation and prevention with osseointegration to provide a stable environment for conduction of neural signals for sophisticated prosthetic control. While this concept has previously been explored in animal models, it has yet to be explored in humans. This anatomic study used three upper limb and three lower limb cadavers to assess the clinical feasibility of creating an ONI in humans. Anatomical measurement of the major peripheral nerves- circumference, length, and depth- were performed as they are critical for electrode design and rerouting of the nerves into the long bones. CT imaging was used for morphologic bone evaluation and virtual implantation of two osseointegrated implants were performed to assess the amount of residual medullary space available for housing the neural interfacing hardware. Use of a small stem osseointegrated implant was found to reduce bone removal and provide more intramedullary space than a traditional implant; however, the higher the amputation site, the less medullary space was available regardless of implant type. Thus the stability of the endoprosthesis must be maximized while still maintaining enough residual space for the interface components. The results from this study provide an anatomic basis required for establishing a clinically applicable ONI in humans. They may serve as a guide for surgical implementation of an osseointegrated endoprosthesis with intramedullary electrodes for prosthetic control.

Virtual implantation technique to estimate endoprosthetic contact of percutaneous osseointegrated devices in the tibia.

Percutaneous osseointegrated (OI) devices have an endoprosthesis attached to the residual bone of an amputated limb, then pass permanently through the skin to be connected to the distal prosthetic componentry outside of the body. Whether the bone-anchoring region of current OI endoprostheses are cylindrical, and/or conical, they require intimate bone-endoprosthesis contact to promote stabilizing bone attachment. However, removing too much cortical bone to achieve more contact leads to thinner and, subsequently, weaker cortical walls. Endoprostheses need to be designed to balance these factors, namely maximizing the contact, while minimizing the volume of bone removed. In this study, 27 human tibias were used to develop and validate a virtual implantation method. Then, 40 additional tibias were virtually implanted with mock cylindrical and conical bone-anchoring regions at seven residual limb lengths to measure resultant bone-endoprosthesis contact and bone removal. The ratio of bone-endoprosthesis contact to bone volume removed showed the conical geometry had more contact area per volume bone removed for all amputation levels (p ≤ 0.001). In both mock devices, cortical penetration of the endoprosthesis at 20% residual length occurred in 74% of cases evaluated, indicating that alternative endoprosthesis geometries may be needed for clinical success in that region of bone.

Finite Element Analysis of Transhumeral and Transtibial Percutaneous Osseointegrated Endoprosthesis Implantation.

Cadaveric mechanical testing of a percutaneous osseointegration docking system (PODS) for osseointegration (OI) prosthetic limb attachment revealed that translation of the exact system from the humerus to the tibia may not be suitable. The PODS, designed specifically for the humerus achieved 1.4-4.8 times greater mechanical stability in the humerus than in the tibia despite morphology that indicated translational feasibility. To better understand this discrepancy, finite element analyses (FEAs) modeled the implantation of the PODS into the bones. Models from cadaveric humeri (n = 3) and tibia (n = 3) were constructed from CT scans, and virtual implantation preparation of an array of endoprosthesis sizes that made contact with the endosteal surface but did not penetrate the outer cortex was performed. Final impaction of the endoprosthesis was simulated using a displacement ramp function to press the endoprosthesis model into the bone. Impaction force and maximum first principal (circumferential) stress were recorded to estimate stability and assess fracture risk of the system. We hypothesized that the humerus and tibia would have different optimal PODS sizing criteria that maximized impaction force and minimized first principal stress. The optimal sizing for the humerus corresponded to implantation instructions, whereas for the tibia optimal sizing was three times larger than the guidelines indicated. This FEA examination of impaction force and stress distribution lead us to believe that the same endoprosthesis strategy for the humerus is not suitable for the tibia because of thin medial and lateral cortices that compromise implantation.

Cortical and medullary morphology of the tibia.

Bone resorption caused by stress shielding and insufficient bone-implant contact continues to be problematic for orthopedic endoprostheses that utilize osseointegration (OI) for skeletal fixation. Morphologic analyses have helped combat this issue by defining anatomic parameters to optimize endoprosthesis loading by maximizing bone-implant contact. These studies have not typically included diaphyseal medullary morphology, as this region is not pertinent to total joint replacement. To the contrary, percutaneous OI endoprostheses for prosthetic limb attachment are placed in the diaphysis of the long bone. This study examined the cortical and medullary morphology of 116 fresh-frozen human cadaveric tibia using computed tomography. Anatomic landmarks were selected and custom MATLAB scripts were used to analyze the cross-sectional cortical and medullary morphology normalized to biomechanical length (BML). BML measured the distance between the tibial plateau and the tibial plafond. Properties such as cortical thickness, medullary diameter, and circularity of the medullary canal were quantified. We tested the influence of sex and laterality on morphology, and examined variations along the length of the bone. Results showed that while both sex and laterality impacted the location of anatomic landmarks, only sex influenced cross-sectional morphology. Overall, morphology significantly affected shape along the length of the bone for all examined properties except medullary circularity. This analysis found that distal to 35% BML, the canal is conducive to a circular implant, with medullary diameter ranging from 13 to 32 mm between 20 and 80% BML. A large size range is necessary for sufficient implant contact in order to accommodate residual limb length after amputation.

Replicating dynamic humerus motion using an industrial robot.

Transhumeral percutaneous osseointegrated prostheses provide upper-extremity amputees with increased range of motion, more natural movement patterns, and enhanced proprioception. However, direct skeletal attachment of the endoprosthesis elevates the risk of bone fracture, which could necessitate revision surgery or result in loss of the residual limb. Bone fracture loads are direction dependent, strain rate dependent, and load rate dependent. Furthermore, in vivo, bone experiences multiaxial loading. Yet, mechanical characterization of the bone-implant interface is still performed with simple uni- or bi-axial loading scenarios that do not replicate the dynamic multiaxial loading environment inherent in human motion. The objective of this investigation was to reproduce the dynamic multiaxial loading conditions that the humerus experiences in vivo by robotically replicating humeral kinematics of advanced activities of daily living typical of an active amputee population. Specifically, 115 jumping jack, 105 jogging, 15 jug lift, and 15 internal rotation trials-previously recorded via skin-marker motion capture-were replicated on an industrial robot and the resulting humeral trajectories were verified using an optical tracking system. To achieve this goal, a computational pipeline that accepts a motion capture trajectory as input and outputs a motion program for an industrial robot was implemented, validated, and made accessible via public code repositories. The industrial manipulator utilized in this study was able to robotically replicate over 95% of the aforementioned trials to within the characteristic error present in skin-marker derived motion capture datasets. This investigation demonstrates the ability to robotically replicate human motion that recapitulates the inertial forces and moments of high-speed, multiaxial activities for biomechanical and orthopaedic investigations. It also establishes a library of robotically replicated motions that can be utilized in future studies to characterize the interaction of prosthetic devices with the skeletal system, and introduces a computational pipeline for expanding this motion library.

Upper extremity prosthetic selection influences loading of transhumeral osseointegrated systems.

Percutaneous osseointegrated (OI) implants are increasingly viable as an alternative to socket suspension of prosthetic limbs. Upper extremity prostheses have also become more complex to better replicate hand and arm function and attempt to recreate pre-amputation functional levels. With more functionality comes heavier devices that put more stress on the bone-implant interface, which could be an issue for implant stability. This study quantified transhumeral loading at defined amputation levels using four simulated prosthetic limb-types: (1) body powered hook, (2) myoelectric hook, (3) myoelectric hand, and (4) advanced prosthetic limb. Computational models were constructed to replicate the weight distribution of each prosthesis type, then applied to motion capture data collected during Advanced Activities of Daily Living (AADLs). For activities that did not include a handheld weight, the body powered prosthesis bending moments were 13-33% (range of means for each activity across amputation levels) of the intact arm moments (reference 100%), torsional moments were 12-15%, and axial pullout forces were 30-40% of the intact case (p≤0.001). The myoelectric hook and hand bending moments were 60-99%, torsional moments were 44-97%, and axial pullout forces were 62-101% of the intact case. The advanced prosthesis bending moments were 177-201%, torsional moments were 164-326%, and axial pullout forces were 133-185% of the intact case (p≤0.001). The addition of a handheld weight for briefcase carry and jug lift activities reduced the overall impact of the prosthetic model itself, where the body powered forces and moments were much closer to those of the intact model, and more complex prostheses further increased forces and moments beyond the intact arm levels. These results reveal a ranked order in loading magnitude according to complexity of the prosthetic device, and highlight the importance of considering the patient's desired terminal device when planning post-operative percutaneous OI rehabilitation and training.

Estimated forces and moments experienced by osseointegrated endoprostheses for lower extremity amputees.

BACKGROUND: Percutaneous osseointegrated (OI) docking of prosthetic limbs returns loading directly to the residual bone of individuals with amputations. Lower limb diaphyseal biomechanics have not been studied during the wide range of daily activities performed by individuals with lower extremity amputations; therefore, little is known about the loads experienced at the bone-endoprosthetic interface of a percutaneous OI device. RESEARCH QUESTION: Does residual limb length and/or gender influence loading magnitudes in the diaphysis of the femur or tibia during daily activities? METHODS: This observational study used motion capture data from 40 non-amputee volunteers performing nine activities ranging from low to high demand, to virtually simulate residual limbs of amputees. To simulate diaphyseal bone loading in individuals with lower limb amputations, virtual joints were defined during post-processing at 25, 50, and 75 % of residual limb length of both the femur and the tibia, representing six clinically relevant residual limb lengths for OI device placement. Peak axial distractive and compressive forces, torsional moments, and bending moments were calculated for each activity. Comparisons were made between genders and between different levels of the simulated residual limb. RESULTS: For simulated above and below knee amputations, short residual limbs showed the highest average bending, torsion, and axial distractive loads, while axial compressive loads were highest for long residual limbs. Absolute maxima for all subjects showed this same trend, except in below knee torsion, where 75 % residual tibia length showed the maximum. The highest demand activities yielding peaks in all directions were cutting with right leg planted, jump, run, and fall. SIGNIFICANCE: Overall, individuals with shorter residual limbs experienced higher diaphyseal forces. This should be taken into consideration during surgical implantation of percutaneous OI devices where residual limb length can potentially be shortened, and during rehabilitation of percutaneous OI patients.

Evaluation of soft-tissue response around laser microgrooved titanium percutaneous devices.

Percutaneous devices are prone to epidermal downgrowth and sinus tract formation, which can serve as a nidus for bacterial colonization and increase the risk of peri-prosthetic infection. A laser microgrooved topography has been shown to limit gingival epidermal downgrowth around dental implants. However, the efficacy of this laser microgrooved topography to limit epidermal downgrowth around nongingival percutaneous devices is yet to be investigated. In this study, devices with a porous-coated subdermal component and a percutaneous post were designed and manufactured. The proximal 2 mm section of the percutaneous post were left smooth, or were textured with either a porous coating, or with the laser microgrooved topography. The smooth and porous topographies served as controls. The devices were tested in a hairless guinea pig back model, where 18 animals were randomly assigned into three groups, with each group receiving one implant type (n = 6/group). Four weeks postimplantation, the devices with surrounding soft-tissues were harvested and processed for histological analyses. Results indicated that the laser microgrooved topography failed to prevent epidermal downgrowth (23 ± 4%) around percutaneous posts in this model. Furthermore, no significant differences (p = 0.70) in epidermal downgrowth were present between the three topographies, with all the groups exhibiting similar measures of downgrowth. Overall, these findings suggest that the laser microgrooved topography may not halt downgrowth around percutaneous devices for dermal applications.

Epidermal growth factor receptor genes are overexpressed within the periprosthetic soft-tissue around percutaneous devices: A pilot study.

Epidermal downgrowth around percutaneous devices produce sinus tracts, which then accumulate bacteria becoming foci of infection. This mode to failure is epidermal-centric, and is accelerated by changes in the chemokines and cytokines of the underlying periprosthetic granulation tissue (GT). In order to more fully comprehend the mechanism of downgrowth, in this 28-day study, percutaneous devices were placed in 10 Zucker diabetic fatty rats; 5 animals were induced with diabetes mellitus II (DM II) prior to the surgery and 5 animals served as a healthy, nondiabetic cohort. At necropsy, periprosthetic tissues were harvested, and underwent histological and polymerase chain reaction (PCR) studies. After isolating GTs from the surrounding tissue and extracting ribonucleic acids, PCR array and quantitative-PCR (qPCR) analyses were carried-out. The PCR array for 84 key wound-healing associated genes showed a five-fold or greater change in 31 genes in the GTs of healthy animals compared to uninjured healthy typical skin tissues. Eighteen genes were overexpressed and these included epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR). Thirteen genes were underexpressed. When GTs of DM II animals were compared to healthy animals, there were 8 genes overexpressed and 25 genes underexpressed; under expressed genes included EGF and EGFR. The qPCR and immunohistochemistry data further validated these observations. Pathway analysis of genes up-regulated 15-fold or more indicated two, EGFR and interleukin-10, centric clustering effects. It was concluded that EGFR could be a key player in exacerbating the epidermal downgrowth, and might be an effective target for preventing downgrowth.

Initial stability of a percutaneous osseointegrated endoprosthesis with proximal interlocking screws for transhumeral amputees.

BACKGROUND: Percutaneous osseointegrated devices for skeletal fixation of prosthetic limbs have the potential to improve clinical outcomes in the transhumeral amputee population. Initial endoprosthesis stability is paramount for long-term osseointegration and safe clinical introduction of this technology. We evaluated an endoprosthetic design featuring a distally porous coated titanium stem with proximal slots for placement of bicortical interlocking screws. METHODS: Yield load, ultimate failure load, and construct stiffness were measured in 18 pairs of fresh-frozen and thawed cadaver humeri, at distal and proximal amputation levels, without and with screws, under axial pull-out, torsion, and bending loads. Paired statistical comparisons were performed without screws at the two resection levels, and at distal and proximal levels with and without screws. FINDINGS: Without screws, the location of the amputation influenced the stability only in torsional yield (p = 0.032) and torsional ultimate failure (p = 0.033). Proximally, the torsional yield and the torsional ultimate failure were 44% and 47% of that distally. Screws improved stability. In axial pull-out, screws increased the distal ultimate failure 3.2 times (p = 0.003). In torsion, screws increased the yield at the proximal level 1.9 times (p = 0.035), distal ultimate failure load 3.3 times (p = 0.016) and proximal ultimate failure 6.4 times (p = 0.013). In bending, screws increased ultimate failure at the proximal level 1.6 times (p = 0.026). INTERPRETATION: Proximal slots and bicortical interlocking screws may find application in percutaneous osseointegrated devices for patients with amputations, especially in the less stable proximal bone of a short residual limb.

Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques.

BACKGROUND: Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury. OBJECTIVE: To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy. METHODS: Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested. RESULTS: The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension. CONCLUSION: Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

Variation in bone response to the placement of percutaneous osseointegrated endoprostheses: A 24-month follow-up in sheep.

Percutaneous osseointegrated (OI) devices for amputees are metallic endoprostheses, that are surgically implanted into the residual stump bone and protrude through the skin, allowing attachment of an exoprosthetic limb. In contrast to standard socket suspension systems, these percutaneous OI devices provide superior attachment platforms for artificial limbs. However, bone adaptation, which includes atrophy and/or hypertrophy along the extent of the host bone-endoprosthetic interface, is seen clinically and depends upon where along the bone the device ultimately transfers loading forces to the skeletal system. The goal of this study was to determine if a percutaneous OI device, designed with a porous coated distal region and an end-loading collar, could promote and maintain stable bone attachment. A total of eight, 18 to 24-month old, mixed-breed sheep were surgically implanted with a percutaneous OI device. For 24-months, the animals were allowed to bear weight as tolerated and were monitored for signs of bone remodelling. At necropsy, the endoprosthesis and the surrounding tissues were harvested, radiographically imaged, and histomorphometrically analyzed to determine the periprosthetic bone adaptation in five animals. Bone growth into the porous coating was achieved in all five animals. Serial radiographic data showed stress-shielding related bone adaptation occurs based on the placement of the endoprosthetic stem. When collar placement and achieved end-bearing against the transected bone, distal bone conservation/hypertrophy was observed. The results supported the use of a distally loading and distally porous coated percutaneous OI device to achieve distal host bone maintenance.

Biomimetic coatings and negative pressure wound therapy independently limit epithelial downgrowth around percutaneous devices.

Biomimetic material coatings and negative pressure wound therapy (NPWT) have been shown independently to limit the epithelial downgrowth rates in percutaneous devices. It was therefore hypothesized that these techniques, in combination, could further limit the clinically observed epithelial downgrowth around these devices. In this study, we evaluated the efficacy of two biomimetic coatings, collagen and hydroxyapatite (HA), to prevent downgrowth when used with continuous NPWT. Using an established single-stage surgical protocol, collagen (n = 10) and HA (n = 10) coated devices were implanted subdermally on the back of hairless guinea pigs. Five animals from each group were subjected to continuous ~90 mmHg NPWT. Four weeks post-implantation, animals were sacrificed, and the devices and surrounding tissues were harvested, processed, and downgrowth was computed and compared to historical porous titanium coated controls. Data showed a significant reduction in downgrowth in NPWT treated animals (p ≤ 0.05) when compared to the untreated porous titanium controls. HA coated devices, without the NPWT treatment, also showed significantly decreased downgrowth compared to the untreated porous titanium controls.

Characterization and evaluation of fluoridated apatites for the development of infection-free percutaneous devices.

The wound healing process in the soft tissues adjacent to percutaneous implants induces "epithelial downgrowth", and subsequently, a sinus tract around the device. This provides an optimal environment for bacterial colonization and proliferation. In an attempt to arrest downgrowth and achieve epithelial attachment to a device surface, we have sought to mimic the most common and successful percutaneous organ, the tooth. Since teeth are composed of partially and fully fluoridated forms of hydroxyapatite (HA), it was hypothesized that the surface properties of fluoridated apatites, fluorohydroxyapatite (FHA) and fluorapatite (FA), would improve epithelial cellular adhesion and differentiation when compared to HA and titanium (Ti) surfaces. In this study, the apatites (HA, FHA, and FA) were synthesized and characterized. Following a high-temperature sintering treatment of these apatites, keratinocyte and fibroblast adhesion and differentiation properties were analyzed in vitro, revealing a statistically significant increase in keratinocyte adhesion and terminal differentiation on FA surfaces sintered at 1050-1150 °C as compared to Ti or HA. Moreover, fibroblasts displayed enhanced adhesion on FHA surfaces. This data suggests that percutaneous devices coated with, or fabricated from, fluoridated apatites may induce improved epithelial cellular adhesion and differentiation, potentially limiting deeply penetrating epithelial downgrowth and resultant bacterial ingress.

Sex and Laterality Differences in Medullary Humerus Morphology.

Percutaneous osseointegrated (OI) prosthetic limb attachment holds promise for transhumeral amputees. Understanding humeral medullary morphology is necessary for informed design of upper extremity OI systems, and is beneficial to the field of megaprosthetic reconstruction of the distal humerus where diaphyseal fixation is desired. The purpose of this study was to quantify the sex and laterality differences in humerus morphology, specifically over the diaphysis. Three-dimensional surface reconstructions of 58 pairs of cadaveric humeri (43 male, 15 female) were generated from CT data. Measures describing periosteal and medullary morphology were collected relative to an anatomic coordinate system. Sex and laterality differences in biomechanical length (BML) were observed (P ≤ 0.001 and 0.022, respectively). Head radius was larger in males than females (P ≤ 0.001). Retroversion was increased in right humeri relative to left (P ≤ 0.001). Canal orientation exhibited a conformational shift from anteversion to retroversion distally at approximately 65% BML. Right humeri exhibited larger medullary diameters than left in the 1st and 2nd principal directions (P ≤ 0.024). Males displayed larger diameter medullary canals proximally (P ≤ 0.029) and an increased rate of divergence of the endosteal cortex in the proximal diaphysis (P ≤ 0.009). Females exhibited higher canal aspect ratios at mid-shaft (P ≤ 0.014) and lower mean cortical thickness (P ≤ 0.001). Human humeral diaphysis morphology exhibits sex and laterality differences, which are dependent on position along the diaphysis. Understanding humeral morphology is necessary to achieve adequate primary stability and bone apposition in design of endoprosthetic stems for percutaneous OI implants, and distal humerus replacement. Anat Rec, 302:1709-1717, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association for Anatomy.