Alan J. Melvin

Fiber technology for reliable repair of skeletal muscle

Conventional soft-tissue reclosure methods-sutures and staples-require substantial organized-collagen content. Some tissues lack extensive intrinsic collagenous content. Wound disruption consequences range from newly closed abdominal wounds bursting open, to post-cesarean wombs splitting at delivery, to heart valves loosening. Although sutures do approach the theoretical limit of normal force transfer-cross-sectional area times compressive strength, a different paradigm-shear force transfer across the far greater surface attainable by fine fibers parallel to the potential disruptive force could exceed that theoretical limit. Capacity is now the product of frictional coefficient, existing tissue pressure, and contact area. Using a device comprising bundles of poly(ethylene terephthalate) fibers through tissue, we previously coupled muscles to devices and bones. Here we tested an analogous device for reclosing fascia-stripped abdominal wall muscles. In 28 rabbits, fascia-deprived rectus abdominus muscles were reclosed, using the experimental device or conventional sutures. Testing muscles from the 21 three-week survivors, (with closure devices retained-the usual clinical practice) demonstrated experimental failure strength which exceeded that of controls by 58%. Histologically, solid tissue elements did in-grow between fibers for an extensive tissue-prosthetic interface. Both histology and mechanical performance suggest the fiber technology presented herein surpasses conventional sutures in closure of collagen-deficient tissues.

An artificial tendon with durable muscle interface

A coupling mechanism that can permanently fix a forcefully contracting muscle to a bone anchor or any totally inert prosthesis would meet a serious need in orthopaedics. Our group developed the OrthoCoupler™ device to satisfy these demands. The objective of this study was to test OrthoCouplers performance in vitro and in vivo in the goat semitendinosus tendon model. For in vitro evaluation, 40 samples were fatigue‐tested, cycling at 10 load levels, n = 4 each. For in vivo evaluation, the semitendinosus tendon was removed bilaterally in eight goats. Left sides were reattached with an OrthoCoupler, and right sides were reattached using the Krackow stitch with #5 braided polyester sutures. Specimens were harvested 60 days postsurgery and assigned for biomechanics and histology. Fatigue strength of the devices in vitro was several times the contractile force of the semitendinosus muscle. The in vivo devices were built equivalent to two of the in vitro devices, providing an additional safety factor. In strength testing at necropsy, suture controls pulled out at 120.5 ± 68.3 N, whereas each OrthoCoupler was still holding after the muscle tore, remotely, at 298 ± 111.3 N (mean ± SD) (p < 0.0003). Muscle tear strength was reached with the fiber–muscle composite produced in healing still soundly intact. This technology may be of value for orthopaedic challenges in oncology, revision arthroplasty, tendon transfer, and sports‐injury reconstruction.

An Artificial Tendon to Connect the Quadriceps Muscle to the Tibia

No permanent, reliable artificial tendon exists clinically. Our group developed the OrthoCoupler™ device as a versatile connector, fixed at one end to a muscle, and adaptable at the other end to inert implants such as prosthetic bones or to bone anchors. The objective of this study was to evaluate four configurations of the device to replace the extensor mechanism of the knee in goats. Within muscle, the four groups had: (A) needle‐drawn uncoated bundles, (B) needle‐drawn coated bundles, (C) barbed uncoated bundles, and (D) barbed coated bundles. The quadriceps tendon, patella, and patellar tendon were removed from the right hind limb in 24 goats. The four groups (n = 6 for each) were randomly assigned to connect the quadriceps muscle to the tibia (with a bone plate). Specimens were collected from each operated leg and contralateral unoperated controls both for mechanical testing and histology at 90 days post‐surgery. In strength testing, maximum forces in the operated leg (vs. unoperated control) were 1,288 ± 123 N (vs. 1,387 ± 118 N) for group A, 1,323 ± 144 N (vs. 1,396 ± 779 N) for group B, 930 ± 125 N (vs. 1,337 ± 126 N) for group C, and 968 ± 109 N (vs. 1,528 ± 146 N) for group D (mean ± SEM). The strengths of the OrthoCoupler™ legs in the needled device groups were equivalent to unoperated controls (p = 0.6), while both barbed device groups had maximum forces significantly lower than their controls (p = 0.001). We believe this technology will yield improved procedures for clinical challenges in orthopaedic oncology, revision arthroplasty, tendon transfer, and tendon injury reconstruction. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1775–1782, 2011

A soft-tissue coupling for wound closure

Wounds often cannot be successfully closed by conventional means of closure such as sutures or staples. Our group developed the FiberSecure™ device to close soft tissue wounds reliably, surpassing native tissue strength. We closed cross-fiber muscle incisions, to evaluate (1) four different configurations of FiberSecure™ for 30 days, then (2) the resulting preferred configuration for 180 days. The four treatment groups each placed 21,504 polyester (PET) 12-μm fibers (cross-sectional area 1% of muscle) traversing the incision, in the form of (A) Four large (No.7 suture) non-textured bundles, (B) Eight small (No.2 suture) non-textured, (C) Four large textured, or (D) Eight small textured. Four incisions were closed in the external oblique muscle of 16 Sinclair minipigs. At 30 days, specimens were removed for biomechanics, histology, and total collagen content. Group (B) was selected for 180-day evaluations in the same wound model in eight animals, four closures each (n = 32), again with biomechanics and histology. In strength testing, every specimen tore through muscle remotely, while the repair region remained intact. Maximum forces were (A) 37.8 ± 3.9 N, (B) 37.1 ± 4.7 N, (C) 39.0 ± 5.3 N, and (D) 32.4 ± 3.4 N at 30 days, and 37.2 ± 11.3 N at 180 days (mean ± SEM). No significant difference was observed among the groups or time points (p > 0.05).

Extended Healing Validation of an Artificial Tendon to Connect the Quadriceps Muscle to the Tibia: 180-day Study

Whenever a tendon or its bone insertion is disrupted or removed, existing surgical techniques provide a temporary connection or scaffolding to promote healing, but the interface of living to non‐living materials soon breaks down under the stress of these applications, if it must bear the load more than acutely. Patients are thus disabled whose prostheses, defect size, or mere anatomy limit the availability or outcomes of such treatments. Our group developed the OrthoCoupler™ device to join skeletal muscle to prosthetic or natural structures without this interface breakdown. In this study, the goat knee extensor mechanism (quadriceps tendon, patella, and patellar tendon) was removed from the right hind limb in 16 goats. The device connected the quadriceps muscle to a stainless steel bone plate on the tibia. Mechanical testing and histology specimens were collected from each operated leg and contralateral unoperated control legs at 180 days. Maximum forces in the operated leg (vs. unoperated) were 1,400 ± 93 N (vs. 1,179 ± 61 N), linear stiffnesses were 33 ± 3 N/mm (vs. 37 ± 4 N/mm), and elongations at failure were 92.1 ± 5.3 mm (vs. 68.4 ± 3.8 mm; mean ± SEM). Higher maximum forces (p = 0.02) and elongations at failure (p = 0.008) of legs with the device versus unoperated controls were significant; linear stiffnesses were not (p = 0.3). We believe this technology will yield improved procedures for clinical challenges in orthopedic oncology, revision arthroplasty, tendon transfer, and tendon injury reconstruction.