Model for assessment of mobility of toes and healing of tendons in rabbits

Repair of a transected flexor tendon will, despite careful technique and early rehabilitation, usually result in a restricted range of movement. This is mainly because adhesions form between the tendon and the surrounding structures. Our aim was to establish an experimental model in rabbits for future studies on new techniques to reduce the formation of adhesions after zone II repair of flexor tendons. In rabbits' hind paws the metatarsal bones II, IV, and V were removed and the flexor tendon was freed to the metatarsophalangeal (MTP) joint. The digits were secured in a specifically-designed biomechanical testing device comprising a servo-hydraulic actuator that was designed to apply controlled force or displacement. The tests were videotaped with a digital force-monitor behind the tested digit. Paper printouts from the recordings were obtained for 0, 0.5, 1, 2, 3, 4, and 5 Newton (N) and metatarsophalangeal, proximal interphalangeal, and distal interphalangeal, angles and distances between metatarsophalangeal joints and claws were measured. The tensile strength of the tendon was evaluated by a load-to-failure test. The continuous data obtained from the experiments were used to calculate functional stiffness at the selected forces. The model allows for unique continuous recordings of mobility of toes, thereby indirectly quantifying the presence of adhesions and the assessment of tensile strength. The data are reproducible, and there is little variation between the digits tested. The model is primarily intended to compare data among treated and non-treated digits of methods to limit the formation of adhesions after tendons have been repaired.     

Comparison of modified Kessler and Yotsumoto-Dona suture: A biomechanical study on porcine tendons

Abstract

There is a need for a strong suture technique that allows early active mobilisation after repair of flexor tendons, but the best method has not yet been found. The aim of this study was to compare the modified Kessler suture biomechanically with a newer, two–strand suture. Eighteen porcine tendons were cut and repaired according to either the grasping modified Kessler suture or the combined side-locking loop technique (Yotsumoto) and interlocking horizontal mattress suture (Dona). The specimens were tested linearly to failure. The 2 mm gap force, yield force, ultimate force, stiffness, energy to yield, and energy to failure were all significantly higher (p value = 0.005, 0.003, <0.001, 0.001, 0.004, and 0.001, respectively) in the Yotsumoto-Dona group (median values (IQR): 30.9 (28.1-39.5) N, 82.7 (64.9-114.1) N, 82.7 (76.6-114.1) N, 12.5 (10-14.5) N/mm, 0.45 (0.2-0.5) J, and 0.45 (0.35-0.5) J) than in the modified Kessler group (25.8 (12.2-28.1) N, 35 (24.6-54.4) N, 50.9 (34.4-55.1) N, 7 (5.8-91) N/mm, 0.09 (0.06-0.18) J, and 0.21 (0.18-0.28) J). All Yotsumoto-Dona specimens had a yield force exceeding 35 N, while in the Kessler group only four did. The early yielding rate was 6/9 and 2/9 in the modified Kessler and the Yotsumoto-Dona groups, respectively (p = 0.15). Most of the core sutures failed by breakage, but three Yotsumoto knots loosened. All the simple running and six of the Dona epitendinous sutures failed predominantly by pulling-out, and by breakage at the intersections in three of the latter. The relatively easy two-strand Yotsumoto-Dona suture is likely to withstand the loads of active finger flexion, whereas the modified Kessler suture is probably not.     

Comparative biomechanic performances of locked cruciate four-strand flexor tendon repairs in an ex vivo porcine model

PURPOSE: To investigate the effects of 3 different locking configurations on repair strength when used in a cruciate four-strand repair. METHODS: Sixty fresh porcine flexor tendons were transected and repaired with cruciate four-strand core suture repairs with 3 different locking configurations: simple locks (a modification of the Pennigton method), circle locks, and cross locks. Half of the repairs in each locking group were reinforced with a peripheral suture. The tendon repairs were subjected to linear load-to-failure testing. Outcome measures were 2-mm gap force and ultimate tensile strength. RESULTS: The cross lock repair had significantly greater 2-mm gap force and ultimate tensile strength than the simple lock repair, both with and without a peripheral suture. The cross lock repair showed significantly greater 2-mm gap force without a peripheral suture and significantly greater ultimate tensile strength with a peripheral suture than the circle lock repair. With peripheral reinforcement, the cross lock cruciate repair had a mean 2-mm gap force of 92 N and ultimate tensile strength of 119 N. The cross lock cruciate repair consistently produced the strongest biomechanic performance in all outcome measures. CONCLUSIONS: Locking configuration influences the biomechanic performance of cruciate four-strand flexor tendon repairs. Our results suggest that the cruciate repair with cross locks is stronger than repairs with simple locks or circle locks. Whether the results of this ex vivo porcine linear model can be translated to the clinical arena is unknown, because the factors of tendon/sheath friction, tendon healing, and compromised tendon viability from the lock were not addressed.     

Influence of core suture purchase length on strength of four-strand tendon repairs

PURPOSE: Recently the length of core suture purchase has been identified as a variable affecting the strength of tendon repairs. The influence of the length of the core suture purchase on the strength of multistrand locking and grasping suture repairs, however, has not been studied extensively in transversely lacerated tendons. We assessed the effects of the length of the core suture purchase on the strength of three 4-strand grasping or locking repair techniques. METHODS: Seventy-four fresh adult pig flexor tendons were cut transversely and repaired with 1 of 3 methods: double-modified Kessler, locking cruciate, and modified Savage. Each method was assessed using 2 different lengths of core suture purchase (1.0 and 0.4 cm). The tendons were subjected to a linear noncyclic load-to-failure test in a tensile testing machine. We recorded the forces required for gap formation, ultimate strength, stiffness of the tendon, and the mode of repair failure. RESULTS: The resistance to gap formation, the ultimate strength of all 3 repairs, and the stiffness of the tendons with the double-modified Kessler and modified Savage repairs decreased significantly as the length of core sutures decreased from 1.0 to 0.4 cm. Locking and grasping repairs had a similar decrease in strength when the purchase was decreased from 1.0 to 0.4 cm. All tendons with modified Savage repairs with 1.0-cm purchase failed by suture breakage and tendons with 0.4-cm purchase failed predominantly by pullout. CONCLUSIONS: The length of core suture purchase significantly affects the strength of these 4-strand tendon repairs. The forces required for gap formation and the ultimate failure of repairs with 0.4-cm purchase were 20% to 45% lower than those of the repairs with 1.0-cm purchase. Locking repairs did not show a greater capacity to offset the decrease in strength than grasping repairs when the length of core suture purchase was decreased from 1.0 to 0.4 cm. Our study indicates that the length of suture purchase directly influences the strength of both locking and grasping core tendon repair methods.     

Effects of superficialis tendon repairs on lacerated profundus tendons within or proximal to the A2 pulley: an in vivo study in chickens

PURPOSE: In a flexor tendon injury model in chickens we undertook a study to evaluate effects of the flexor digitorum superficialis (FDS) tendon repairs on excursions, work of flexion, and adhesions of the repaired flexor digitorum profundus (FDP) tendon after their injuries within or proximal to the equivalent of the A2 pulley and early tendon motion. METHODS: Thirty-five leghorn chickens were divided into 3 groups. In group 1 the FDS and FDP tendons of the long toes on both sides were transected in the area covered by the pulley. In group 2 the tendons were transected proximal to the pulley. In the first 2 groups, both tendons were repaired on the left feet, and only the profundus was repaired with superficialis excision on the right. The operated toes underwent simulated passive flexion for 3 weeks and results were evaluated 8 weeks after surgery. Chickens in group 3 were unoperated and served as the controls. RESULTS: When the tendons were cut within the pulley the FDP excursions and work of flexion were significantly better in the toes in which the FDS was excised than in those with both tendon repairs. When they were cut proximal to the pulley the repairs of both tendons had outcomes similar to that with excision of the FDS. Adhesions were more severe when both tendons were repaired under the pulley as compared with those after repair of a single tendon. CONCLUSIONS: This study showed different effects of the surgical repair or excision of the FDS on the FDP tendon within or proximal to a major pulley. Repair of both tendons worsens the gliding of the FDP tendon and increases adhesions within the major pulley; however, repair of both tendons yields outcomes equivalent to that after repair of only the FDP tendon proximal to the pulley.     

Tissue reactions of adenoviral, adeno-associated viral, and liposome-plasmid vectors in tendons and comparison with early-stage healing responses of injured flexor tendons

PURPOSE: Delivery of growth factor genes that may substantially increase the healing rate of injured digital flexor tendons is a new application of gene therapy. Adenoviral, adeno-associated viral (AAV), and liposome-plasmid vectors have been used to deliver genes to tendons, but the tendon reactions to these vectors--particularly in contrast to the healing responses in the injured tendons--were unknown. This study was designed to compare the tissue reactions of the earlier-mentioned vectors in tendons with the healing responses of injured flexor tendons. METHODS: Forty-two flexor digitorum profundus tendons of 6 New Zealand white rabbits were used. Eighteen tendons were divided into 3 groups of 6 each and injected with different vectors: adenoviral vector, AAV2-luciferase vector, or pCMV-beta vector with liposome. Another 12 tendons were cut and repaired. At 3, 7, and 14 days, the tendons were harvested and stained with hematoxylin and eosin. Normal flexor tendons were harvested as controls. RESULTS: The tissue reactions of the liposome-plasmid vector in tendons were the most prominent among the 3 vectors tested. The adenoviral vector elicited a moderate degree of tissue reaction. The AAV2 vector caused remarkable reactions in epitenon but almost no reactions in endotenon. Early-stage tissue reactions were more robust in the injured tendons. Compared with early-stage inflammatory and healing responses, the reactions elicited by these vectors were less severe. CONCLUSIONS: The 3 gene delivery systems tested elicit less severe tissue reactions in flexor tendons compared with early-stage inflammatory changes in injured tendons. Adenoviral and AAV vectors elicit less severe tissue reactions than liposome-plasmid vectors. The AAV2 vector appears to cause almost no reaction in endotenon. In terms of tissue reactions, the adenoviral and AAV2 vectors, in particular AAV2, are suitable gene delivery systems for future gene transfer to the tendon in vivo.     

The tensile strength of various peripheral circumferential repair techniques in canine flexor tendons

The purpose of this study was to evaluate the tensile strength of six peripheral circumferential suture techniques, using a variable number of suture strands. Transverse lacerations were made in 184 fresh frozen canine flexor profundus tendons and repaired using only a 6-0 Prolene circumferential suture. The six running suture techniques were: Simple, Simple-locking, Lembert, Halsted, Cross-stitch and Lin-locking, and 6, 10, 14, and 20 suture strands were used. For each technique, the tensile strength gradually increased with the increased number of suture strands. The tensile strength of the Lin-locking technique (19–34 N) was greater than that of the other techniques, followed by Cross-stitch (16–33 N), Halsted (10–25 N), Lembert (8–23 N), Simple (6–12 N), and Simple-locking (5–8 N). The Lin-locking had the best holding power, but it was technically the most complicated to place. The Cross-stitch had good tensile strength values. The Simple and the Simple-locking had the lowest tensile strengths. From the viewpoints of tensile strength and technical skill, the Cross-stitch may be preferable to other suture techniques.     

Resistance to motion of flexor tendons and digital edema: An in vivo study in a chicken model

PURPOSE: Tissue edema contributes to resistance to motion of flexor tendons during postsurgical exercises. We assessed edema formation and resistance of injured subcutaneous tissue and sheath to motion of the digital flexor tendon in a chicken model. METHODS: Ninety-four toes of 47 white Leghorn chickens were divided into 6 surgical groups and 1 nonsurgical control. Subcutaneous tissue and the sheath were incised, and the skin incision and the subcutaneous tissue were closed surgically. The toes were evaluated morphologically for severity of edema and tested for the force and work required to move the tendon. The evaluation time points were 1, 2, 3, 4, 5, and 7 days after surgery. Edema in the toes was scored according to severity and extent. The force and energy required to move the tendon were measured at the first and sixth cycles after cyclic loading in a testing machine with customized software and were statistically analyzed. RESULTS: The force and work increased progressively for the first 4 days, and were relatively consistent from days 4 to 7. The severity of edema peaked at the third and fourth days. At each postsurgical day, edema scores corresponded to increases in the force and work. The force and work were reduced drastically (30%-50%) after the first 6 cycles of toe motion. CONCLUSIONS: Resistance to tendon motion increased for the initial 4 days after surgery and remained comparatively consistent from the fourth to the seventh days. The severity of digital edema peaks at the third and fourth postoperative days. Motion of the digits for several cycles greatly reduces the resistance to the subsequent movement. We believe that tendon mobilization should not necessarily be started within the initial postoperative days, the optimum time to begin probably is the period from the fourth to the seventh day after surgery, and that judgment of edema helps to determine how aggressive exercise should be.     

Effect of helium-neon and infrared laser irradiation on wound healing in rabbits

We examined the biostimulating effects of helium-neon laser radiation (HeNe; 632.8 nm), pulsed infrared laser radiation (IR; 904 nm), and the two combined on skin wound healing in New Zealand white rabbits. Seventy-two rabbits received either 1) no exposure, 2) 1.65 J/cm2 HeNe, 3) 8.25 J/cm2 pulsed IR, or 4) both HeNe and IR together to one of two dorsal full-thickness skin wounds, daily, for 21 days. Wound areas were measured photographically at periodic intervals. Tissue samples were analyzed for tensile strength, and histology was done to measure epidermal thickness and cross-sectional collagen area. Significant differences were found in the tensile strength of all laser-treated groups (both the irradiated and nonirradiated lesion) compared to group 1. No differences were found in the rate of wound healing or collagen area. Epidermal growth was greater in the HeNe-lased area compared to unexposed tissue, but the difference was not significant. Thus, laser irradiation at 632.8 nm and 904 nm alone or in combination increased tensile strength during wound healing and may have released tissue factors into the systemic circulation that increased tensile strength on the opposite side as well.     

A histologic analysis of the effects of stainless steel and titanium implants adjacent to tendons: an experimental rabbit study

PURPOSE: The current trend is to treat distal radius fractures with open reduction and internal fixation with either titanium or stainless steel plates. Both provide stable fixation; however, there is minimal evidence concerning the soft-tissue response to these materials. Our objective was to evaluate the response of adjacent extensor tendons to titanium and stainless steel in a rabbit in vivo model and to evaluate the influence of time. METHODS: Forty rabbits were divided into 5 groups of 8 rabbits each. Groups I and II had unilateral osteotomy of the distal radius followed by dorsal fixation with titanium and stainless steel plates, respectively. Groups III and IV had fixation with titanium and stainless steel, respectively, but without osteotomy. Group V had surgical dissection without osteotomy or plates. Two animals per group were killed at 1, 4, 12, and 24 weeks. The specimens (distal radius, plate, overlying soft tissue, and extensor tendon) were harvested en bloc for histologic analysis. For interface preservation between implant and tissues the specimens were embedded in methylmethacrylate, sectioned, and stained with hematoxylin-eosin. RESULTS: Histologic analysis showed a fibrous tissue layer formed over both implants between the plate and the overlying extensor tendons in the groups treated with plating independently of the material and the presence or absence of osteotomy. This fibrous layer contained the majority of debris. Metallic particles were not observed in the tendon or muscle substance of any animals; however, they were visualized in the tenosynovium. Hematoxylin-eosin-stained sections of groups I through IV showed proliferative fibroblasts and metallic particles; however, this layer was not observed in group V. Statistical analysis did not show differences between the groups regarding the number of cells or metallic particles. CONCLUSIONS: Our results indicate that both implants generated adjacent reactive inflammatory tissue and particulate debris. There was no difference in cell or particle number produced by both materials. There is a statistically significant increase in inflammatory cells with increasing time of implantation.     

Auto‐crosslinked hyaluronic acid gel accelerates healing of rabbit flexor tendons in vivo

This study's purpose was to assess the in vivo effect of auto‐crosslinked hyaluronic acid (HA) gel, a natural HA derivative with increased viscosity and tissue residence time, on adhesions and healing of injured and surgically repaired rabbit digital flexor tendons. The second and third right deep digital flexor tendons from 48 rabbits (n = 96 tendons) were cut and repaired with a modified Kessler and running peripheral suture. Animals were randomized to two groups, receiving either HA gel or saline injected around both freshly repaired tendons. After 2, 3, 6, and 12 weeks, six rabbits in each group were euthanized. Tendon pull‐out force and breaking strength were measured as a value for adhesion formation and tendon healing, respectively. A histological assessment of adhesions and healing was related to the mechanical results. A significantly faster increase in breaking strength was found in HA gel‐treated compared to saline‐treated tendons; this coincided with a significantly accelerated tissue repair response after injury. No significant difference in adhesion formation was found between the two groups at any time. Our results indicate a significant acceleration of in vivo healing of tendons treated with HA gel. Adhesion formation was unaffected. These results could have important clinical value in promoting rehabilitation after tendon injury. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:408–415, 2009     

Retrieval of the retracted flexor tendons for long fingers: New tip

Zone II flexor tendon injuries continue to be a challenge for hand surgeons. During the injury event, the tendon ends may retract towards the palm. Retrieval of these lacerated ends can be problematic because the tendon sheath is unstretchable. This demanding surgery requires a precise repair technique where the tendon stumps are handled in an atraumatic manner. Microtrauma to the tendon sheath must be avoided as this can induce adhesions and lead to poor functional outcomes. Several retrieval methods for retracted tendon ends have been described in published studies. In this technical note, we will describe a technical variation that streamlines the surgical procedure and uses commonly available materials. This simple trick makes the procedure easier and avoids having to suture the tendon to the tubing.     

Closed rupture of the flexor tendons of the thumb and index due to severe scaphotrapezoidal arthritis

We report a case of severe scaphotrapezoidal osteoarthritis with closed rupture of multiple flexor tendons. The thumb was treated with a tenodesis with the remaining flexor and the deep flexor of the index was reconstructed with a short cable graft, harvested from the superficial flexor.