Alphonsus K. S. Chong

Bone marrow-derived mesenchymal stem cells influence early tendon-healing in a rabbit achilles tendon model.

BACKGROUND A repaired tendon needs to be protected for weeks until it has accrued enough strength to handle physiological loads. Tissue-engineering techniques have shown promise in the treatment of tendon and ligament defects. The present study tested the hypothesis that bone marrow-derived mesenchymal stem cells can accelerate tendon-healing after primary repair of a tendon injury in a rabbit model. METHODS Fifty-seven New Zealand White rabbits were used as the experimental animals, and seven others were used as the source of bone marrow-derived mesenchymal stem cells. The injury model was a sharp complete transection through the midsubstance of the Achilles tendon. The transected tendon was immediately repaired with use of a modified Kessler suture and a running epitendinous suture. Both limbs were used, and each side was randomized to receive either bone marrow-derived mesenchymal stem cells in a fibrin carrier or fibrin carrier alone (control). Postoperatively, the rabbits were not immobilized. Specimens were harvested at one, three, six, and twelve weeks for analysis, which included evaluation of gross morphology (sixty-two specimens), cell tracing (twelve specimens), histological assessment (forty specimens), immunohistochemistry studies (thirty specimens), morphometric analysis (forty specimens), and mechanical testing (sixty-two specimens). RESULTS There were no differences between the two groups with regard to the gross morphology of the tendons. The fibrin had degraded by three weeks. Cell tracing showed that labeled bone marrow-derived mesenchymal stem cells remained viable and present in the intratendinous region for at least six weeks, becoming more diffuse at later time-periods. At three weeks, collagen fibers appeared more organized and there were better morphometric nuclear parameters in the treatment group (p < 0.05). At six and twelve weeks, there were no differences between the groups with regard to morphometric nuclear parameters. Biomechanical testing showed improved modulus in the treatment group as compared with the control group at three weeks (p < 0.05) but not at subsequent time-periods. CONCLUSIONS Intratendinous cell therapy with bone marrow-derived mesenchymal stem cells following primary tendon repair can improve histological and biomechanical parameters in the early stages of tendon-healing.

Flexor tendon tissue engineering: acellularized and reseeded tendon constructs.

Background: Tissue engineering of flexor tendons requires scaffolds with adequate strength and biocompatibility. The biomechanical properties of acellularized and reseeded flexor tendon scaffolds are unknown. Acellularized tendons and reseeded constructs were tested to determine whether the treatment process had altered their biomechanical properties. Methods: Rabbit flexor tendons were acellularized using a freeze-thaw cycle followed by trypsin and Triton-X treatment. Complete acellularization of the tendon samples was confirmed by histology and by attempting to obtain viable cells by trypsin treatment of acellularized tendon. Reseeded constructs were obtained by incubating acellularized tendons in a tenocyte suspension. Tensile testing was performed to compare the ultimate tensile stress and elastic modulus of acellularized tendons and reseeded flexor tendon constructs to control flexor tendons. Results: The treatment protocol successfully acellularized flexor tendons. No cells were seen within the tendon on histologic assessment, and no viable cells could be obtained from acellularized tendon. Acellularized tendon was successfully reseeded with tenocytes, although cell adhesion was limited to the surface of the tendon scaffold. Tensile testing showed that acellularized tendon had the same ultimate stress and elastic modulus as normal tendons. Reseeded tendons had the same elastic modulus as normal tendons, but hind-paw tendon constructs showed a decrease in ultimate stress compared with normal tendons (50.09 MPa versus 66.01 MPa, p = 0.026). Conclusions: Acellularized flexor tendons are a potential high-strength scaffold for flexor tendon tissue engineering. This approach of acellularization and reseeding of flexor tendons may provide additional intrasynovial graft material for hand reconstruction.

A Biomechanical Comparison of 3 Loop Suture Materials in a 6-Strand Flexor Tendon Repair Technique

PURPOSE The braided polyblend (FiberWire) suture is recognized for its superiority in tensile strength in flexor tendon repair. The purpose of this study was to compare the biomechanical performance of 3 loop-suture materials used in a locking 6-strand flexor tendon repair configuration: braided polyblend (FiberLoop 4-0), cable nylon (Supramid Extra II 4-0), and braided polyester (Tendo-Loop 4-0). We hypothesized that, using this technique, the braided polyblend suture would give superior tensile strength compared with the other 2 suture materials. METHODS We divided 30 fresh porcine flexor tendons transversely and repaired each with 1 of the 3 suture materials using a modified Lim-Tsai 6-strand suture technique. We loaded the repaired tendons to failure using a materials testing machine and collected data on the mechanism of failure, ultimate tensile strength, gap strength, and stiffness. RESULTS Failure mechanisms for the repaired specimens were as follows: the braided polyblend had 50% suture breakage and 50% suture pullout; the cable nylon had 100% suture breakage; and the braided polyester had 80% suture breakage and 20% suture pullout. Specimens repaired with the braided polyblend suture had the highest mean ultimate tensile strength (97 N; standard deviation, 22) and the highest mean gap force (35 N; standard deviation, 7). CONCLUSIONS This study supports the findings of previous studies showing superior strength of the braided polyblend suture. CLINICAL RELEVANCE We were able to achieve up to 124 N in ultimate tensile strength and 48 N of gap force with this suture in porcine tendons. This gives greater confidence in starting immediate controlled passive or active rehabilitation after repair of flexor tendon injuries.

Optimization of flexor tendon tissue engineering with a cyclic strain bioreactor.

PURPOSE Mechanical manipulation of cultured tendon cells can enhance cell proliferation and matrix production. This study aims to determine the bioreactor strain patterns (amplitude, frequency, and on/off ratio) that favor cellular proliferation, promote collagen production, and maintain morphology in candidate cell lines cultured for flexor tendon tissue engineering, including multipotent stromal cells. METHODS We studied epitenon tenocytes (Es), sheath fibroblasts (Ss), bone marrow-derived mesenchymal stem cells (BMSCs), and adipoderived stem cells (ASCs). We examined the effects of 3 patterns of cyclic uniaxial strain on cell proliferation, collagen I production, and cell morphology. RESULTS Adipoderived stem cells (33% adhesion) and Ss (29%) adhered more strongly to bioreactor membranes than did Es (15%) and BMSCs (7%), p=.04. Continuous cyclic strain (CCS, 8%, 1 Hz) inhibited cell proliferation (p=.01) and increased per-cell collagen production (p=.04) in all cell types. Intermittent cyclic strain (4%, 0.1 Hz, 1 hour on/5 hours off) increased proliferation in ASCs (p=.06) and Ss (p=.04). Intermittent cyclic strain (4%, 0.1 Hz, 1 hour on/2 hours off) increased total collagen production by 25% in ASCs (p=.004) and 20% in Ss (p=.05). Cyclic strain resulted in cell alignment perpendicular to the strain axis, cytoskeletal alignment, and nuclear elongation. These morphological characteristics are similar to those of tenocytes. CONCLUSIONS These results demonstrate that intermittent cyclic strain can increase cell proliferation, promote collagen I production, and maintain tenocyte morphology in vitro. Use of a cell bioreactor might accelerate the in vitro stage of tendon tissue engineering.

Mesenchymal stem cells and tendon healing.

Tendons transmit forces generated by muscle to move the joints they cross. Tendon problems are complicated by slow and incomplete healing as well as re-injury. Mesenchymal stem cell based therapies show promise in improving outcomes. Much of the work has been experimental, although early clinical use in equine strain-induced tendon injury supports the efficacy of this strategy. While much has been studied about the mechanisms of action of implanted MSCs, the relative importance of the various mechanisms is still unknown. Key areas of research that could prove pivotal in the clinical use of MSCs include the use of allogeneic cells, optimization of MSC culture, gene therapy, and mechanical stimulation techniques.

Volar Plating for Unstable Proximal Interphalangeal Joint Dorsal Fracture-Dislocations

PURPOSE To report our results of open reduction internal fixation with volar mini plate and screw fixation for unstable dorsal fracture dislocations (DFDs) of the proximal interphalangeal (PIP) joint. METHODS We performed a retrospective review of 13 consecutive DFDs of the PIP joint treated with volar mini plate and screw fixation, measuring both clinical and radiological outcomes. RESULTS The age range of our patients was 15 to 56 years (average, 33 y). Six injuries were related to work, 5 to sports, and 2 to motor vehicle accidents. Of the 13 DFDs, 6 were comminuted. Articular involvement ranged from 30% to 70% (average, 44%). The average time to surgery was 7 days (range, 0-23 d). Patients had follow-up of 12 to 60 months (average, 25 mo). Four patients had a postoperative course complicated by plate and screw removal at an average of 4 months later, either as part of a secondary procedure to improve range of motion or owing to patient request. All patients returned to their original occupation. Of the 13 patients, 11 were satisfied with the result, and 12 of 13 had either no or mild pain. All 13 DFDs united in good alignment but 3 showed degenerative changes. Average grip strength was 85% of the unaffected side, and average active PIP joint and distal interphalangeal joint motion arcs were 75° and 65°, respectively. Average Quick Disabilities of Arm, Shoulder, and Hand score was 4 (range, 0-9). All patients had non-tender swelling of the proximal interphalangeal joints but no signs of flexor tenosynovitis or infection. CONCLUSIONS Fixation of unstable PIP joint DFDs via a volar approach is technically feasible with mini plates and screws. This treatment allows early active range of motion and provides good objective and subjective outcomes; however, noteworthy complications occurred in 39% of patients. TYPE OF STUDY/LEVEL OF EVIDENCE Therapeutic IV.

Flexor Tendon Tissue Engineering: Temporal Distribution of Donor Tenocytes versus Recipient Cells

Background: Tissue-engineered tendon material may address tendon shortages in mutilating hand injuries. Tenocytes from rabbit flexor tendon can be successfully seeded onto acellularized tendons that are used as tendon constructs. These constructs in vivo exhibit a population of tenocyte-like cells; however, it is not known to what extent these cells are of donor or recipient origin. Furthermore, the temporal distribution is also not known. Methods: Tenocytes from New Zealand male rabbits were cultured and seeded onto acellularized rabbit forepaw flexor tendons (n = 48). These tendon constructs were transplanted into female recipients. Tendons were examined after 3, 6, 12, and 30 weeks using fluorescent in situ hybridization to detect the Y chromosome in the male donor cells. One unseeded, acellularized allograft in each animal was used as a control. Results: The donor male tenocytes populate the epitenon and endotenon of the grafts at greater numbers than the recipient female tenocytes at 3 and 6 weeks. The donor and recipient tenocytes are present jointly in the grafts until 12 weeks. At 30 weeks, nearly all cells are recipient tenocyte-like cells. Conclusions: Donor male cells survive in decreasing numbers over time until 30 weeks. The presence of cells in tissue-engineered tendon grafts has been shown in prior studies to add to the strength of the constructs in vitro. This study shows that recipient cells can migrate into and repopulate the tendon construct. Cell seeding onto tendon material may create stronger constructs that will allow the initiation of motion earlier.

Bioactive Sutures for Tendon Repair: Assessment of a Method of Delivering Pluripotential Embryonic Cells

PURPOSE Pluripotential embryonic cells may be seeded onto sutures intended for tendon repair. These cells may be influenced to adhere to suture material using adhesion substrates, and furthermore, these cells may remain in culture attached to those sutures. These cell-impregnated sutures may be useful for promoting healing of tendon repairs. METHODS Ten-centimeter segments of 4-0 sutures (FiberWire) were coated overnight with 10 microg/mL fibronectin, 10 microg/mL poly-l-lysine, or phosphate-buffered saline. The sutures were placed in dishes and covered with a suspension of C3H10T1/2 cells at concentrations of 1 x 10(6), 2 x 10(6), or 4 x 10(6) cells for 24 hours. The sutures were then placed into low adhesion polypropylene tubes with Dulbeccos modified Eagles medium and 10% fetal bovine serum for 7 days. The presence of viable cells on these sutures was assessed by the colorimetric Alamar blue cell proliferation assay. Spectrophotometry was used to quantify the relative amount of cell proliferation across the experimental groups. The sutures were also visually inspected using phase-contrast light microscopy. RESULTS Our results show that at all seeding densities (1 x 10(6), 2 x 10(6), and 4 x 10(6) cells), the suture segments coated with poly-l-lysine and fibronectin showed a significant increase in C3H10T1/2 cell adhesion. Coating the suture with poly-l-lysine increased the adherent cell number to 17% of the initial seeding concentration compared with 2% for the control. Fibronectin coating increased the number of adherent viable cells present to 6.6%. CONCLUSIONS Pluripotential embryonic cells may be seeded onto sutures, adhere, and survive in culture. Coating sutures with poly-l-lysine and fibronectin offers significant improvement in retention of viable cells. This technique may be a useful adjunct for future tendon healing studies.

Application of the dorsal metacarpal artery perforator flap for resurfacing soft-tissue defects proximal to the fingertip.

Background: The dorsal metacarpal artery perforator flap is a versatile solution for resurfacing soft-tissue defects of fingers. The authors present their experience in applying this flap for a variety of finger wounds for which conventional means may not be amenable. Methods: Fifty-eight dorsal metacarpal artery perforator flaps were used to resurface 60 finger soft-tissue defects in 56 patients over a 5-year period. Fifty-two patients were men and their average age was 37 years. This flap was used to reconstruct soft-tissue defects after débridement of infected wounds in 28 patients, traumatic wounds in 26 patients, and electrical burns in two patients. Results: The average flap size was 4.6 × 2.3 cm; 34 flaps were based on the second dorsal metacarpal artery perforator, 14 were based on the third dorsal metacarpal artery perforator, and 10 were based on the fourth dorsal metacarpal artery perforator. Twenty-one flaps were used to resurface defects distal to the proximal interphalangeal joint, and 37 flaps were used to resurface defects over the proximal interphalangeal joint and proximal to it. Skin grafting was needed to close the donor defect in seven patients. Complications included venous congestion in six flaps and arterial insufficiency in three flaps, with total loss of two flaps and infection in one case. Conclusion: The dorsal metacarpal artery perforator flap is a thin, pliable flap that is simple to raise, has minimal donor-site morbidity, and can reliably cover soft-tissue defects up to the proximal half of the middle phalanx. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

An Analysis of the Pull-Out Strength of 6 Suture Loop Configurations in Flexor Tendons

PURPOSE New, stronger suture materials have been introduced for flexor tendon surgery. The advantage of these materials can be lost if the suture loop pulls out from the tendon. The aim of this study was to compare the ability of various locking loops to grip the tendon. METHODS We inserted 4 different standard and 2 experimental locking loops with 200-μm nitinol wire into human cadaveric flexor digitorum profundus tendons. The standard loops were: group 1, cruciate; group 2, Pennington modified Kessler; group 3, cross-stitch; and group 4, Lim-Tsai. The experimental loops were: group 5, a composition of Pennington modified Kessler with a cross-stitch loop; and group 6, a locking Kessler type of loop with a superficial transverse component. We loaded the loops until failure. We recorded the pull-out strength and stiffness and documented failure mechanisms during the pull-out test. RESULTS The cruciate loop had the weakest holding capacity, 20 N, which was significantly less than in groups 2 to 6. The cross-stitch loop, Lim-Tsai loop, and modified Kessler loop performed similarly (36 N, 37 N, and 39 N, respectively). The experimental loops had the highest pull-out strength (group 5, 59 N; and group 6, 60 N, both significantly greater than groups 1 to 4). The mode of failure was pull-out for all of the standard loops and 7 of the experimental loops. Of 20 experimental loops, 13 failed by suture rupture. CONCLUSIONS The 2 experimental loop configurations demonstrated higher pull-out strength and may have advantages when used with newer and stronger suture materials. The number of the locking components in the loops and the way the tension is transmitted to the tendon fibrils explain the results. CLINICAL RELEVANCE The loops presented in this study and that grip the tendon better may be useful with new materials that have high tensile strength.