Sujee Jeyapalina

New extensometer to measure in vivo uniaxial mechanical properties of human skin

Biomechanical properties of skin are important for clinical decision making as well as clinical intervention. Measuring these properties in vivo is critical for estimating dimensional behaviour of skin flap or graft after harvest. However, existing methodologies and devices often suffer from lack of standardisation and unwanted peripheral force contribution due to the deformation of surrounding tissues during measurement. This naturally leads to measurement inaccuracies and lack of reproducibility. In order to improve the measurement accuracy, a new portable extensometer, which measures the non-invasive in vivo biomechanical properties of skin, has been designed and constructed. This design incorporates three pads that attach to the skin, including a C-shaped pad to shield the force sensor from peripheral forces. Such design produces data that are significantly closer to in vitro measurements. The results have been verified by finite element analysis, and experiments on rubber sheets and pig skins. This device can be used to obtain biomechanical properties of skin that will aid doctors in measuring skin elasticity and surgical planning, especially in skin flap surgery.

Efficacy of a Porous-Structured Titanium Subdermal Barrier for Preventing Infection in Percutaneous Osseointegrated Prostheses

Infections of percutaneous osseointegrated prostheses (POP) cause prolonged morbidity and device failure because once established, they are refractory to antibiotic therapy. To date, only limited translational animal studies have investigated the efficacy of POP designs in preventing infections. We developed an animal model to evaluate the efficacy of a porous‐coated titanium (Ti) subdermal barrier to achieve skin–implant integration and to prevent periprosthetic infection. In a single‐stage “amputation and implantation” surgery, 14 sheep were fitted with percutaneous devices with an attached porous‐coated Ti subdermal barrier. Nine sheep were implanted with a smooth Ti subdermal barrier construct and served as controls, with one control sheep removed from the study due to a fractured bone. Clinical, microbiological, and histopathological data showed that the porous Ti barrier prevented superficial and deep tissue infections in all animals (14/14, 100%) at the 9‐month endpoint. In contrast, animals with the smooth Ti implant construct had a 25% (2/8) infection rate. Survival analysis indicated a significant difference between the groups (log‐rank test, p = 0.018). Data also indicated that although skin marsupialization was evident in both implant types, animals in the control group had a four times greater marsupialization rate. We concluded that osseointegrated implants incorporating porous‐coated Ti subdermal barriers may have the ability to prevent infection by maintaining a healthy, biologically attached epithelial barrier at the skin–implant interface in load‐bearing animals up to a 9‐month terminus.

Fifteen years of experience with Integral-Leg-Prosthesis: Cohort study of artificial limb attachment system.

Integral-Leg-Prosthesis (ILP) is a comparatively new attachment system that allows direct skeletal docking of artificial limbs. Between January 1999 and December 2013, 69 patients with transfemoral amputation were fitted with ILPs by a single German surgeon. Device design iterations and surgical techniques evolved during these years. For the purposes of comparison, patients receiving the first two designs and procedure iterations were placed in group 1 and the patients fitted with the final design were placed in group 2. Infection rate and planned and unplanned surgical interventions were statistically compared using Fisher exact test. Data demonstrated that the high rate of stoma-associated infections seen in group 1 was dramatically reduced in group 2. Of the 39 patients with 42 implants in group 2, none had operative interventions secondary to infection. All group 2 patients remained infection-free without the use of antibiotics by following a simple but defined wound-hygiene protocol. We concluded that the final iteration of the osseointegrated intramedullary device with a low energy surface at the soft tissue and prosthesis interface allowed a biologically stable skin stoma that remained infection-free without chronic use of antibiotics. The reduction in the infection rate was attributed to the clinically based, empirically driven changes in design and surgical techniques.

Characterization of a novel active release coating to prevent biofilm implant‐related infections

Biofilm implant-related infections cost the US healthcare system billions of dollars each year. For several decades, device coatings have been developed that actively release antimicrobial compounds in an attempt to prevent these infections from developing. To date, few coatings have been put into clinical use. These have shown limited to no efficacy in clinical trials. Recent data have shown the in vitro and in vivo efficacy of a novel active release coating that may address the limitations of coatings that are used clinically. In this study, the novel active release coating was characterized to gain an understanding of the effects of combining an antimicrobial additive, cationic steroid antimicrobial-13 (CSA-13), to a medical grade polydimethylsiloxane (PDMS) material. Results indicated that the addition of CSA-13 did influence the physical properties of the PDMS, but not with adverse effects to the desired material properties. Furthermore, there was no indication of chemical reactivity. It was shown that CSA-13 was uniformly dispersed as small particles throughout the PDMS matrix. These particles were able to dissolve and elute out of the PDMS within a 30-day period. The results of this work suggested that the PDMS with CSA-13 was thermally, chemically and physically stable when used as a device coating to treat local infection and/or prevent biofilm implant-related infections from developing.

Immediate post‐implantation skin immobilization decreases skin regression around percutaneous osseointegrated prosthetic implant systems

A percutaneous, osseointegrated (OI) prosthetics are alternative docking systems for upper- and lower-extremity prostheses. Persistent inflammation and micro-motion are known to cause negative soft-tissue adaptation in wound healing and may also be detrimental to implant longevity. In this study, a unique single-stage sheep amputation and implantation model was developed to assess the efficacy of a porous coated sub-dermal fixation surface in the prevention of skin regression around a percutaneous osseointegrated prosthetic implant. Porous coated and smooth sub-dermal fixation surface prosthetics were implanted in the right forelimb of skeletally mature sheep for up to 12 months. Skin regression kinetics and sub-dermal fixation surface coverage were measured from histological samples. Quantitative measurements of porous coated surfaces yielded skin migration rates of 0.90 ± 0.23, 0.56 ± 0.15, 0.44 ± 0.22 mm/month for the 6, 9, and 12 month animals, respectively. In addition, three load dependent regions of skin adaptation were identified; an interface, a transition, and a stress absorbance region. Immediate post-implantation immobilization of the skin may foster improved load-bearing percutaneous device outcomes. The skin adaptations reported here will aid in informing the design and optimization of future percutaneous, OI devices intended for the treatment of upper- and lower-extremity amputees.

Progression of Bone Ingrowth and Attachment Strength for Stability of Percutaneous Osseointegrated Prostheses

BackgroundPercutaneous osseointegrated prosthetic (POP) devices have been used clinically in Europe for decades. Unfortunately, their introduction into the United States has been delayed, in part due to the lack of data documenting the progression of osseointegration and mechanical stability.Questions/purposesWe determined the progression of bone ingrowth into porous-coated POP devices and established the interrelationship with mechanical stability.MethodsAfter amputation, 64 skeletally mature sheep received a custom porous-coated POP device and were then randomized into five time groups, with subsequent measurement of percentage of bone ingrowth into the available pore spaces (n = 32) and the mechanical pullout force (n = 32).ResultsPostimplantation, there was an accelerated progression of bone ingrowth (~48% from 0 to 3 months) producing a mean pullout force of 5066 ± 1543 N. Subsequently, there was a slower but continued progression of bone ingrowth (~23% from 3 to 12 months) culminating with a mean pullout force of 13,485 ± 1855 N at 12 months postimplantation. There was a high linear correlation (R = 0.94) between the bone ingrowth and mechanical pullout stability.ConclusionsThis weightbearing model shows an accelerated progression of bone ingrowth into the porous coating; the amount of ingrowth observed at 3 months after surgery within the porous-coated POP devices was sufficient to generate mechanical stability.Clinical RelevanceThe data document progression of bone ingrowth into porous-coated POP devices and establish a strong interrelationship between ingrowth and pullout strength. Further human data are needed to validate these findings.

Cortical Bone Response to the Presence of Load-Bearing Percutaneous Osseointegrated Prostheses

Although the current percutaneous osseointegrated (OI) prosthetic attachment systems are novel clinical treatments for patients with limb loss, there have only been limited translational studies undertaken to date. To bridge this knowledge gap, from a larger study group of 86 animals that were implanted with a novel percutaneous OI implant construct, 33 sheep were randomly selected from the 0‐, 3‐, 6‐, 9‐ and 12‐month groups for histomorphometric analyses of periprosthetic cortical bone tissue. At necropsy, implanted and nonimplanted limbs were harvested and processed for the evaluation of cortical bone porosity and mineral apposition rate (MAR). The data showed a maximum increase in bone porosity within the first 3 months following implantation and then a progressive reduction in porosity to the baseline steady‐state (“Time 0”) value by 12 months. The data further verified that the MAR increased during the first 6 months of implantation, reaching a plateau between 6 and 9 months, followed by a progressive decline to the baseline steady state. It was concluded that clinical load bearing and falls precautions, taken during the first 3–6 months following percutaneous OI device implantation surgery, could greatly limit bone fractures during this vulnerable time of increasing cortical bone porosity. Anat Rec, 2012.

Radiographic Evaluation of Bone Adaptation Adjacent to Percutaneous Osseointegrated Prostheses in a Sheep Model

BackgroundPercutaneous osseointegrated prostheses (POPs) are being investigated as an alternative to conventional socket suspension and require a radiographic followup in translational studies to confirm that design objectives are being met.Questions/purposesIn this 12-month animal study, we determined (1) radiographic signs of osseointegration and (2) radiographic signs of periprosthetic bone hypertrophy and resorption (adaptation) and (3) confirmed them with the histologic evidence of host bone osseointegration and adaptation around a novel, distally porous-coated titanium POP with a collar.MethodsA POP device was designed to fit the right metacarpal bone of sheep. Amputation and implantation surgeries (n = 14) were performed, and plane-film radiographs were collected quarterly for 12 months. Radiographs were assessed for osseointegration (fixation) and bone adaptation (resorption and hypertrophy). The cortical wall and medullary canal widths were used to compute the cortical index and expressed as a percentage. Based on the cortical index changes and histologic evaluations, bone adaptation was quantified.ResultsRadiographic data showed signs of osseointegration including those with incomplete seating against the collar attachment. Cortical index data indicated distal cortical wall thinning if the collar was not seated distally. When implants were bound proximally, bone resorbed distally and the diaphyseal cortex hypertrophied.ConclusionsHistopathologic evidence and cortical index measurements confirmed the radiographic indications of adaptation and osseointegration. Distal bone loading, through collar attachment and porous coating, limited the distal bone resorption.Clinical RelevanceSerial radiographic studies, in either animal models or preclinical trials for new POP devices, will help to determine which designs are likely to be safe over time and avoid implant failures.

Osseointegration: a review of the fundamentals for assuring cementless skeletal fixation

Direct skeletal fixation, termed osseointegration, has expanded in the last century and includes use in total joint replacements, the edentulous mandible and maxilla, and percu- taneous osseointegrated prosthetics. Although it is well known that titanium and bone have the ability to form a durable bone-implant interface, new applications have emerged in the field of orthopedics, which requires a more thorough assessment of the literature. This review aims to introduce the basic biological principles for attaining osseointegration and discusses the major factors for assuring successful cementless fixation.

Pig dorsum model for examining impaired wound healing at the skin-implant interface of percutaneous devices

Percutaneous medical devices are indispensable in contemporary clinical practice, but the associated incidence of low to moderate mortality infections represents a significant economic and personal cost to patients and healthcare providers. Percutaneous osseointegrated prosthetics also suffer from a similar risk of infection, limiting their clinical acceptance and usage in patients with limb loss. We hypothesized that transepidermal water loss (TEWL) management at the skin-implant interface may improve and maintain a stable skin-to-implant interface. In this study, skin reactions in a 3-month, pig dorsum model were assessed using standard histology, immunohistochemistry, and quantitative image analysis. Immunohistochemical analysis of peri-implant tissue explants showed evidence of: continuous healing (cytokeratin 6+), hypergranulation tissue (procollagen+), hyper-vascularity (collagen 4+), and the presence of fibrocytes (CD45+ and procollagen type 1+). Importantly, the gross skin response was correlated to a previous load-bearing percutaneous osseointegrated prosthetic sheep study conducted in our lab. The skin responses of the two models indicated a potentially shared mechanism of wound healing behavior at the skin-implant interface. Although TEWL management did not reduce skin migration at the skin-implant interface, the correlation of qualitative and quantitative measures validated the pig dorsum model as a high-throughput platform for translational science based percutaneous interface investigations in the future.