Intrasynovial Flexor Tendon Repair

The effects of exogenous basic fibroblast growth factor on intrasynovial flexor tendon healing in a canine model

BACKGROUND

Studies have demonstrated that flexor tendon repair strength fails to increase in the first three weeks following suturing of the tendon, a finding that correlates closely with the timing of many clinical failures. The application of growth factors holds promise for improving the tendon-repair response and obviating failure in the initial three weeks.

METHODS

The effects of basic fibroblast growth factor on flexor tendon healing were evaluated with use of a canine model. Operative repair followed by the sustained delivery of basic fibroblast growth factor, at two different doses, was compared with operative repair alone. Histological, biochemical, and biomechanical methods were used to evaluate the tendons twenty-one days after repair.

RESULTS

Vascularity, cellularity, and adhesion formation were increased in the tendons that received basic fibroblast growth factor as compared with the tendons that received operative repair alone. DNA concentration was increased in the tendons that received 1000 ng of basic fibroblast growth factor (mean and standard deviation, 5.7 ± 0.7 μg/mg) as compared with the tendons that received 500 ng of basic fibroblast growth factor (3.8 ± 0.7 μg/mg) and the matched control tendons that received operative repair alone (4.5 ± 0.9 μg/mg). Tendons that were treated with basic fibroblast growth factor had a lower ratio of type-I collagen to type-III collagen, indicating increased scar formation compared with that seen in tendons that received operative repair alone (3.0 ± 1.6 in the group that received 500-ng basic fibroblast growth factor compared with 4.3 ± 1.0 in the paired control group that received operative repair alone, and 3.4 ± 0.6 in the group that received 1000-ng basic fibroblast growth factor compared with 4.5 ± 1.9 in the paired control group that received operative repair alone). Consistent with the increases in adhesion formation that were seen in tendons treated with basic fibroblast growth factor, the range of motion was reduced in the group that received the higher dose of basic fibroblast growth factor than it was in the paired control group that received operative repair alone (16.6° ± 9.4° in the group that received 500 ng basic fibroblast growth factor, 13.4° ± 6.1° in the paired control group that received operative repair alone, and 29.2° ± 5.8° in the normal group [i.e., the group of corresponding, uninjured tendons from the contralateral forelimb]; and 15.0° ± 3.8° in the group that received 1000 ng basic fibroblast growth factor, 19.3° ± 5.5° in the paired control group that received operative repair alone, and 29.0° ± 8.8° in the normal group). There were no significant differences in tendon excursion or tensile mechanical properties between the groups that were treated with basic fibroblast growth factor and the groups that received operative repair alone.

CONCLUSIONS

Although basic fibroblast growth factor accelerated the cell-proliferation phase of tendon healing, it also promoted neovascularization and inflammation in the earliest stages following the suturing of the tendon. Despite a substantial biologic response, the administration of basic fibroblast growth factor failed to produce improvements in either the mechanical or functional properties of the repair. Rather, increased cellular activity resulted in peritendinous scar formation and diminished range of motion.

Estimation of elbow flexion force during isometric muscle contraction from mechanomyography and electromyography

Mechanomyography (MMG) is the muscle surface oscillations that are generated by the dimensional change of the contracting muscle fibers. Because MMG reflects the number of recruited motor units and their firing rates, just as electromyography (EMG) is influenced by these two factors, it can be used to estimate the force exerted by skeletal muscles. The aim of this study was to demonstrate the feasibility of MMG for estimating the elbow flexion force at the wrist under an isometric contraction by using an artificial neural network in comparison with EMG. We performed experiments with five subjects, and the force at the wrist and the MMG from the contributing muscles were recorded. It was found that MMG could be utilized to accurately estimate the isometric elbow flexion force based on the values of the normalized root mean square error (NRMSE = 0.131 ± 0.018) and the cross-correlation coefficient (CORR = 0.892 ± 0.033). Although MMG can be influenced by the physical milieu/morphology of the muscle and EMG performed better than MMG, these experimental results suggest that MMG has the potential to estimate muscle forces. These experimental results also demonstrated that MMG in combination with EMG resulted in better performance estimation in comparison with EMG or MMG alone, indicating that a combination of MMG and EMG signals could be used to provide complimentary information on muscle contraction.

Technical and biological modifications for enhanced flexor tendon repair

Clinical outcomes after intrasynovial flexor tendon repair have been substantially improved over the past 2 decades through advances in tendon suture techniques and postoperative rehabilitation methods. Nevertheless, complications such as repair site elongation (i.e., gap formation) and rupture continue to occur frequently. Experimental studies have shown that repair site strength fails to increase in the first 3 weeks after tendon suture. After 3 weeks, the strength and rigidity of the repair site improve significantly, a process that continues for several months. Formation of a repair site gap during the early rehabilitation period has been shown to considerably delay the accrual of repair site strength over time. Thus, it is of prime importance that the method of tendon suture achieves and maintains a stiff and strong repair site during the early healing interval by maintaining close approximation of the tendon stumps and by stimulating, where possible, the intrinsic repair response. In this review, we describe recent efforts to enhance the integrity of the immature repair site. We focus on 2 major areas of advancement: surgical technique modifications and manipulation of the biologic and biochemical environment.

Mechanical strength of the side-to-side versus Pulvertaft weave tendon repair

PURPOSE

The side-to-side (SS) tendon suture technique was designed to function as a repair that permits immediate postoperative activation and mobilization of a transferred muscle. This study was designed to test the strength and stiffness of the SS technique against a variation of the Pulvertaft (PT) repair technique.

METHODS

Flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) tendons were harvested from 4 fresh cadavers and used as a model system. Seven SS and 6 PT repairs were performed, using the FDS as the donor and the FDP as the recipient tendon. For SS repairs, the FDS was woven through one incision in the FDP and was joined with 4 cross-stitch running sutures down both sides and one double-loop suture at each tendon free end. For PT repairs, the FDS was woven through 3 incisions in the FDP and joined with a double-loop suture at both ends of the overlap and 4 evenly spaced mattress sutures between the ends. Tendon repairs were placed in a tensile testing machine, preconditioned, and tested to failure.

RESULTS

There were no statistically significant differences in cross-sectional area (p = .99) or initial length (p = .93) between SS and PT repairs. Therefore, all comparisons between methods were made using measures of loads and deformations, rather than stresses and strains. All failures occurred in the repair region, rather than at the clamps. However, failure mechanisms were different between the 2 techniques-PT repairs failed by the suture knots either slipping or pulling through the tendon material, followed by the FDS tendon pulling through the FDP tendon; SS repairs failed by shearing of fibers within the FDS. Load at first failure, ultimate load, and repair stiffness were all significantly different between SS and PT techniques; in all cases, the mean value for SS was higher than for PT.

CONCLUSIONS

The SS repair using a cross-stitch suture technique was significantly stronger and stiffer than the PT repair using a mattress suture technique. This suggests that using SS repairs could enable patients to load the repair soon after surgery. Ultimately, this should reduce the risk of developing adhesions and result in improved functional outcome and fewer complications in the acute postoperative period. Future work will address the specific mechanisms (eg, suture-throw technique and tendon-weave technique) that underlie the improved strength and stiffness of the SS repair.

The effect of tissue culture on suture holding strength and degradation in canine tendon

The purpose of this study was to assess tendon metabolism and suture pull-out strength after simple tendon suture in a tissue culture model. One hundred and twelve flexor digitorum profundus tendons from 28 dogs were cultured for 7, 14, or 21 days with or without a static tensile load. In both groups increased levels of matrix metalloproteinase (MMP) mRNA was noted. Suture pull-out strength did not decrease during tissue culture. While the presence of a static load had no effect on the pull-out strength, it did affect MMP mRNA expression. This tissue culture model could be useful in studying the effect of factors on the tendon-suture interface.

Enhanced flexor tendon healing through controlled delivery of PDGF-BB

A fibrin/heparin-based delivery system was used to provide controlled delivery of platelet derived growth factor BB (PDGF-BB) in an animal model of intrasynovial flexor tendon repair. We hypothesized that PDGF-BB, administered in this manner, would stimulate cell proliferation and matrix remodeling, leading to improvements in the sutured tendon's functional and structural properties. Fifty-six flexor digitorum profundus tendons were injured and repaired in 28 dogs. Three groups were compared: (1) controlled delivery of PDGF-BB using a fibrin/heparin-based delivery system; (2) delivery system carrier control; and (3) repair- only control. The operated forelimbs were treated with controlled passive motion rehabilitation. The animals were euthanized at 7, 14, and 42 days, at which time the tendons were assessed using histologic (hyaluronic acid content, cellularity, and inflammation), biochemical (total DNA and reducible collagen crosslink levels), and biomechanical (gliding and tensile properties) assays. We found that cell activity (as determined by total DNA, collagen crosslink analyses, and hyaluronic acid content) was accelerated due to PDGF-BB at 14 days. Proximal interphalangeal joint rotation and tendon excursion (i.e., tendon gliding properties) were significantly higher for the PDGF-BB-treated tendons compared to the repair-alone tendons at 42 days. Improvements in tensile properties were not achieved, possibly due to suboptimal release kinetics or other factors. In conclusion, PDGF-BB treatment consistently improved the functional but not the structural properties of sutured intrasynovial tendons through 42 days following repair.

Flexor tenorrhaphy tensile strength: reduction by cyclic loading: in vitro and ex vivo porcine study

The integrity of the repair is critical to maintain coaptation of the severed flexor tendon end until healing has advanced sufficiently. In our hospital, we use a modified Savage repair (four-strand Adelaide technique) using 3-0 Ethibond (Ethicon, Somerville, NJ, USA) for acute flexor tenorrhaphy and an active postrepair mobilization protocol. To explain the apparent differences between the theoretical and actual repair strength of a multistrand repair in a single tension test and the reduced strength of a repair subjected to cyclic loading, we compared single and cyclical tensile loading with different suture in vitro configurations of 3-0 Ethibond (Ethicon, Somerville, NJ, USA; one, two, and four strands) and an ex vivo four-strand repair of freshly divided porcine tendon to calculate the ultimate tensile strength (UTS). Mechanical testing was repeated 15 times with both single tensile and cyclical loading for each suture configuration and porcine repair. In the in vitro model, the presence of a knot in a single strand reduced the UTS by 50%. The stiffness of a knotted strand was substantially less than the unknotted strand but became identical after cyclical loading. There was no statistical significance of the UTS between single and cyclical loading with different numbers of strands in this model. In the ex vivo four-strand porcine repair model, there was a significant reduction in UTS with cyclical loading, which equated to the number of strands times the strength of the knotted strand. This discrepancy can be explained by the change in stiffness of the knotted strand after cyclical loading and has important implications for previous studies of suture tendon repair using single tensile loading where the UTS may have been overestimated. We believe that cyclical loading is more representative of physiological loading after acute flexor tendon repair and should be the testing model of choice in suture tenorrhaphy studies.

Eight-strand core suture technique for repair of intrasynovial flexor tendon lacerations

The concept of intrinsic tendon healing, the idea that tendons can heal primarily without the ingrowth of fibrous adhesions from the surrounding fibrous flexor sheath, has been validated both experimentally and clinically. The goals of the surgical treatment of intrasynovial digital flexor tendon lacerations are twofold: 1) to achieve a primary tendon repair of sufficient strength so as to prevent repair site gap elongation and possible rupture, and 2) to prevent the formation of intrasynovial adhesions that cause loss of tendon excursion within the flexor tendon sheath. It is well accepted that repair site strength, both at time zero and within the first 6 postoperative weeks, is directly related to the number of core suture strands crossing the repair site. The factor that limits more widespread use of multistrand suture techniques remains the surgeon's ability to perform the repair while also minimizing trauma to the tendon stumps and the circumferential epitenon. We describe an 8-strand core suture technique used at our institution that has been tested ex-vivo, in-vivo in canines, and used in human subjects over the last 4 years with excellent results.

Influence of core suture geometry on tendon deformation and gap formation in porcine flexor tendons

The effects of core suture geometry on the mechanics of failure in flexor tendon surgery are investigated. Forty porcine flexor tendons were repaired using a Kessler; a Kessler-Pennington; a double Kessler; a continuous Kessler; and a cruciate repair. At maximum breaking strength, the cruciate repair gapped more then the double Kessler (12.8 mm vs 9.1 mm), but the double Kessler was less strong (37N vs 45 N). Transverse narrowing was 22% and 24% for the Kessler and the Kessler-Pennington, 11% for the double Kessler, and 0% for the continuous Kessler and the cruciate repair. Kessler-type sutures failed by suture breakage and the cruciate repair by pull-out. Under load, the transverse part of the Kessler sutures narrows, allowing longitudinal parts to lengthen, leading to gapping. The double Kessler shortened transverse segment decreases gapping. Eliminating a transverse component (the cruciate repair) decreased gapping, but the cruciate failed at higher loads by suture pull-out.

The effect of muscle loading on flexor tendon-to-bone healing in a canine model

Previous tendon and ligament studies have demonstrated a role for mechanical loading in tissue homeostasis and healing. In uninjured musculoskeletal tissues, increased loading leads to an increase in mechanical properties, whereas decreased loading leads to a decrease in mechanical properties. The role of loading on healing tissues is less clear. We studied tendon-to-bone healing in a canine flexor tendon-to-bone injury and repair model. To examine the effect of muscle loading on tendon-to-bone healing, repaired tendons were either cut proximally (unloaded group) to remove all load from the distal phalanx repair site or left intact proximally (loaded group). All paws were casted postoperatively and subjected to daily passive motion rehabilitation. Specimens were tested to determine functional properties, biomechanical properties, repair-site gapping, and bone mineral density. Loading across the repair site led to improved functional and biomechanical properties (e.g., stiffness for the loaded group was 8.2 +/- 3.9 versus 5.1 +/- 2.5 N/mm for the unloaded group). Loading did not affect bone mineral density or gapping. The formation of a gap between the healing tendon and bone correlated with failure properties. Using a clinically relevant model of flexor tendon injury and repair, we found that muscle loading was beneficial to healing. Complete removal of load by proximal transection resulted in tendon-to-bone repairs with less range of motion and lower biomechanical properties compared to repairs in which the muscle-tendon-bone unit was left intact.

Controlled-release kinetics and biologic activity of platelet-derived growth factor-BB for use in flexor tendon repair

PURPOSE

Surgically repaired intrasynovial tendons are at greatest risk of failure in the first 3 weeks after surgery. Attempts to improve the strength of repair by modifying rehabilitation parameters have not always been successful. Manipulation of the biological environment of the sutured tendon holds great promise for accelerating the repair process. The goals of this study were to examine (1) the range of conditions (eg, dosage, delivery system formulation, presence of cells) over which delivery of platelet-derived growth factor-BB (PDGF-BB) can be sustained from fibrin matrices using a heparin-binding delivery system (HBDS) and (2) the biological activity of the PDGF-BB released from this system on canine tendon fibroblasts in vitro.

METHODS

We examined in vitro release kinetics from cellular and acellular fibrin matrices using enzyme-linked immunosorbent assays. We examined the biologic activity of the PDGF-BB in vitro by measuring cell proliferation (ie, total DNA) and collagen synthesis (ie, proline incorporation).

RESULTS

The acellular release kinetics of PDGF-BB was modulated by varying the ratio of PDGF-BB to heparin (PDGF-binding sites) or the dose of PDGF-BB in the presence of the delivery system. In the presence of canine tendon fibroblasts, the delivery system prolonged the duration of PDGF-BB release from fibrin matrices, thus demonstrating that cells are able to liberate PDGF-BB retained by the HBDS. Sustained delivery of PDGF-BB promoted increased cell proliferation at doses of 0.125 microg/mL and 1.25 microg/mL compared to fibrin without delivery system. Collagen synthesis was enhanced by PDGF-BB at doses of 0.125 microg/mL and 1.25 microg/mL; however, there was an enhancement over fibrin without the delivery system only at the lower dose.

CONCLUSIONS

These results demonstrate that the PDGF-BB released from fibrin matrices containing an HBDS is biologically active and can modulate both cell proliferation and extracellular matrix synthesis, both of which are key factors in the process of tendon repair.

PDGF-BB released in tendon repair using a novel delivery system promotes cell proliferation and collagen remodeling

The purpose of this study was to promote fibroblast proliferation and collagen remodeling in flexor tendon repair through sustained delivery of platelet derived growth factor (PDGF-BB). The release kinetics of PDGF-BB from a novel fibrin matrix delivery system was initially evaluated in vitro. After the in vivo degradation rate of the fibrin matrix was determined using fluorescently tagged fibrin, PDGF-BB was delivered to the site of flexor tendon repair in vivo in a canine model. The effect of PDGF-BB on intrasynovial tendon healing was studied using histology-based assays (cell density, proliferation, and type I collagen expression) and by measuring total DNA levels and reducible collagen crosslink levels. The fibrin matrix delivery system provided sustained release of PDGF-BB in vitro at a rate modulated by the ratio of heparin to growth factor. In vivo, the fibrin matrix remained at the repair site for more than 10 days. Delivery of PDGF-BB led to a qualitative increase in cell density, cell proliferation, and type I collagen mRNA expression. PDGF-BB also led to statistically significant increases in total DNA (20% increase at 7 days, 18% increase at 14 days) and reducible collagen crosslinks (30% increase at 7 days). Sustained delivery of growth factors may be achieved using a novel fibrin-based delivery system. PDGF-BB delivery increased cell proliferation and matrix remodeling and thus may accelerate flexor tendon healing.

Direct tendon attachment and healing to porous tantalum: an experimental animal study

BACKGROUND

The ability to directly attach soft-tissue to metal would have broad clinical application. Previous attempts to obtain normal tendon-to-bone attachment strength have been unsuccessful. In the present study, we hypothesized that when the initial interface mechanical environment is carefully controlled, a highly porous form of tantalum metal would allow the ingrowth of tendon tissue with clinically relevant tendon-to-implant fixation strength approaching that of an intact tendon-to-bone insertion.

METHODS

Supraspinatus tendons from forty skeletally mature dogs were reattached to the greater tuberosity between two custom-designed porous tantalum washers. Clinical function as judged on the basis of gait analysis, reattachment fixation strength and stiffness, and tendon function as seen through muscle volume were evaluated preoperatively, immediately postoperatively, and at three, six, and twelve weeks after surgery. Qualitative and quantitative histomorphologic evaluation was performed at three, six, and twelve weeks after surgery.

RESULTS

Gait analysis with use of force-plate measurements demonstrated return to a normal gait pattern by three weeks after surgery. Tendon-implant strength as a percentage of normal, contralateral controls increased significantly, from 39% at the time of surgery to 67% at three weeks, 99% at six weeks, and 140% at twelve weeks (p < 0.0014). The stiffness of the construct also increased and approached that of normal tendon, measuring 47% at the time of surgery, 62% at three weeks, 94% at six weeks, and 130% at twelve weeks (p < 0.0299). Supraspinatus muscle volume initially decreased by 33% but recovered to 92% of normal by twelve weeks (p < 0.01). Histomorphologic evaluation showed Sharpey-like fibers inserting onto the surface of the porous tantalum. Quantitative histomorphometric analysis revealed a time-dependent increase in the density of the collagen tissue filling the metal voids below the implant surface of first the bottom washer and then the top washer.

CONCLUSIONS

Robust biologic ingrowth of tendon into a porous tantalum implant surface can be achieved under conditions of secure initial mechanical fixation. The strength and stiffness of the tendon-implant construct reached normal levels by six to twelve weeks in this animal model.

Enhancing the strength of the tendon-suture interface using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and cyanoacrylate

PURPOSE

Preventing gap or rupture is important to achieving a successful outcome after tendon repair. Weak sutures break; strong sutures fail by pull-out at the tendon-suture interface. In this study, we investigated the use of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and cyanoacrylate to enhance the strength of the tendon-suture interface.

METHODS

Twenty-four canine flexor digitorum profundus tendons were used to test EDC and cyanoacrylate reinforcement methods, with 12 tendons in each group. A single-loop suture technique was used to test the tendon-suture interface strength.

RESULTS

The mean ultimate strengths of the EDC group and the cyanoacrylate group were significantly higher than those of their respective control groups. The stiffness of the group with cyanoacrylate-augmented loops was significantly higher than that of its respective control group. There was no significant difference in stiffness between the 2 reinforcement methods.

CONCLUSIONS

Our results suggest that tendon-suture interface reinforcement may improve the pull-out failure strength of a suture construct and thereby increase the effectiveness of stronger suture materials. Future studies might address the effects of different kinds and methods of reinforcement with various suture materials and constructs and in different tissues.

Biomechanics and histology of intact and repaired digital nerves: an in vitro study

PURPOSE

To investigate the biomechanical properties of intact and repaired cadaver digital nerves.

METHODS

Ultimate tensile failure strength and stiffness were determined in 67 human cadaver digital nerves. Total nerve area, fascicular area, and nonfascicular (connective tissue) area were determined from the metacarpophalangeal to the distal interphalangeal joint in another 35 axial nerve sections to determine regional anatomic variation. Thirty-eight additional digital nerves were transected, and epineural repairs were performed using simple, interrupted sutures. Suture number (2 vs 4), gauge (8-0 vs 9-0), and purchase length (1 mm vs 2 mm) were used in various combinations, and then the repaired nerves were pulled to failure. The mechanism of repair-site failure was determined for each suture. In situ tension of the intact digital nerves was measured during passive metacarpophalangeal and proximal interphalangeal joint motion in another 19 intact digital nerves.

RESULTS

There were no significant differences in failure load or stiffness with respect to the radial or ulnar nerves within a finger or between fingers. The primary tactile side of the finger tended to have a larger diameter digital nerve. Digital nerve failure was more common proximally than distally. Intact digital nerves failed at 6 N with a stiffness of 1 N/mm. Histologic analysis showed that fascicular area and total area decreased from proximal to distal, whereas the nonfascicular-to-fascicular area ratio increased. Four epineural sutures were statistically stronger than 2 sutures. Suture purchase length and gauge did not affect repair strength. The 8-0 nylon sutures failed primarily by cut-out, whereas the 9-0 sutures failed by cut-out or breakage. Repaired nerves failed at 1 to 2 N. Maximal metacarpophalangeal joint hyperextension resulted in 4 N of digital nerve tension. When the metacarpophalangeal joint was not hyperextended, proximal interphalangeal joint motion did not generate tension.

CONCLUSIONS

Similar to flexor tendons, the number of suture strands crossing the repair site was the most important variable affecting digital nerve repair strength in this cadaveric model.

An analysis of factors associated with failure of tendon repair in the canine model

PURPOSE

The canine model is commonly used for flexor tendon repair research. The purpose of this study was to analyze the factors, including laceration mode (partial and complete), suture techniques, therapy methods, and weight-bearing status, associated with tendon repair rupture or gap formation in the canine model in vivo.

METHODS

We reviewed the factors associated with repair failure among 624 flexor tendon repairs in zone II from 242 dogs reported previously from our institution, including both partial and complete lacerations.

RESULTS

We found that weight-bearing due to failure of postoperative immobilization was the most important factor influencing tendon repair rupture or gap formation.

CONCLUSIONS

As has been noted clinically, in our canine model failure and gapping of a flexor tendon repair was primarily the result of uncontrolled loading. Rehabilitation strategies that reduce the risk of catastrophic loading of the repair are critical to reducing the experimental failure rate when using dogs for flexor tendon research. Similar strategies may also reduce such failures in humans.

Gliding Resistance of the Flexor Pollicis Longus Tendon after Repair: Does Partial Excision of the Oblique Pulley Affect Gliding Resistance?

BACKGROUND

After tendon repair, it is critical for the repair site to pass smoothly under the pulley edge to promote gliding and reduce the risk of adhesion or rupture. In this study, the authors assessed the effect of partial excision by "squaring off" the distal edge of the oblique pulley on the gliding resistance of the flexor pollicis longus tendon after repair in vitro.

METHODS

Gliding resistance of 10 human thumbs was measured directly with three different sequential conditions: intact flexor pollicis longus tendon with intact A1 and oblique pulleys (group A), intact pulleys after repair of the tendon (group B), and after repair and excision of the distal triangular part (squaring off) of the oblique pulley (group C).

RESULTS

Gliding resistance increased significantly after repair and squaring off the oblique pulley (group A, 0.22 +/- 0.08 N; group B, 1.29 +/- 0.68 N; and group C, 2.01 +/- 0.84 N).

CONCLUSIONS

Previous studies suggest that the trimming of an annular pulley in the finger would not result in any significant mechanical disadvantage if other parts of the pulley system were intact. However, the authors' results suggest that in the case of the thumb oblique pulley, gliding resistance is increased after trimming and tendon repair, and thus the oblique pulley should be left intact if possible.

Complications after treatment of flexor tendon injuries

The goals of flexor tendon repair are to promote intrinsic tendon healing and minimize extrinsic scarring in order to optimize tendon gliding and range of motion. Despite advances in the materials and methods used in surgical repair and postoperative rehabilitation, complications following flexor tendon injuries continue to occur, even in patients treated by experienced surgeons and therapists. The most common complication is adhesion formation, which limits active range of motion. Other complications include joint contracture, tendon rupture, triggering, and pulley failure with tendon bowstringing. Less common problems include quadriga, swan-neck deformity, and lumbrical plus deformity. Meticulous surgical technique and early postoperative tendon mobilization in a well-supervised therapy program can minimize the frequency and severity of these complications. Prompt recognition of problems and treatment with hand therapy, splinting, and/or surgery may help minimize recovery time and improve function. In the future, the use of novel biologic modulators of healing may nearly eliminate complications associated with flexor tendon injuries.

Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p = 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendon-bone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel.

Flexor tendon suture: a description of two core suture techniques and the Silfverskiöld epitendinous suture

Flexor tendon injuries are commonly treated by orthopedic, plastic, and hand surgeons. Bunnell referred to zone 2 injuries as being in "no-man's land," plagued by poor results after surgical repair. Over the last 30 years, a better understanding of the biology of flexor tendon injuries, advanced surgical techniques, and perhaps most important, improved rehabilitation protocols, have afforded consistently good to excellent results after surgical repair at all levels of injury. Complications such as restrictive adhesions, joint contracture, and repair rupture, although less frequent, can compromise functional recovery.

Zone I flexor tendon rehabilitation with limited extension and active flexion

This article describes an immediate active motion protocol for primary repair of zone I flexor tendons treated with tendon to tendon, or tendon to bone repair, and reviews clinical results. A rehabilitation protocol is proposed that will limit excursion of the zone I repair by blocking full distal interphalangeal (DIP) extension and by applying controlled active tension to both the unrepaired flexor digitorum superficialis (FDS) and the repaired flexor digitorum profundus (FDP). The rehabilitation technique utilized a dorsal protective splint with a relaxed position of immobilization with 30 degrees of wrist flexion, 40 degrees of metacarpophalangeal (MP) joint flexion, and a neutral position for the proximal interphalangeal (PIP) joints without dynamic traction. In addition, within the confines of the dorsal splint, the involved DIP joint was splinted at 40-45 degrees to prevent DIP joint extension during the early wound healing phases. Relaxed composite flexion was used to apply active tension to both the uninjured FDS, and the repaired FDP. This technique applies excursion of approximately 3 mm to the zone I tendon in a limited arc (45-75 degrees). The modified position of active flexion applies low loads of force (< 500 g), even with drag considered. This technique is supported by previous mathematical studies of excursion and internal tendon force, and clinical experience. Forty nine cases treated over a 10-year period were reviewed, and eight were excluded for incomplete follow-up. The use of this protocol for 41 zone I flexor digitorum profundus repairs by 12 different surgeons using varied surgical techniques was evaluated. None of the tendon to tendon repairs used more than two suture strands for the core repairs. Mean total active range of motion was 142 degrees (PIP 95 degrees plus DIP 47 degrees), or 81% of normal. Three tendons ruptured in non-protocol-related incidents and were excluded from the study. Results from this clinical study support the use of limited DIP extension combined with active tension with conventional repair in zone I.

The evolution of early mobilization of the repaired flexor tendon

The most important difference between the various approaches to postoperative digital flexor tendon rehabilitation is how the repaired tendon is treated during the first three to six weeks, in the earliest stages of healing. Early mobilization is the most commonly reported method of managing the healing flexor tendon. There are many different protocols and abundant research to support published approaches to tendon management. With so many choices, today's hand therapist must understand not only what those choices are, but also why and when to use them. There is no one correct way to manage a repaired flexor tendon; the specialist who does not understand how current techniques evolved is ill-equipped to design the appropriate treatment for a given patient. This article presents an overview of management options and how they have been developed over time, with special attention to changes in splint and exercise design in the crucial first few weeks after repair.

Clinical outcomes associated with flexor tendon repair

Review of the outcomes of clinical flexor tendon repairs reported over the past 15 years showed advances in the outcomes with excellent or good functional return in more than three fourths of primary tendon repairs following a variety of postoperative passive/active mobilization treatments. Strickland and Glogovac criteria are the most commonly adopted methods to assess function. Repair ruptures (4%-10% for zone II finger flexors and 3%-17% for the FPL tendon), adhesion formations, and stiffness of finger joints remain frustrating problems in flexor tendon repairs and rehabilitation. Four approaches are suggested to improve outcomes of the repairs and to solve these difficult problems,which include stronger surgical repairs, appropriate pulleys or sheath management, optimization of rehabilitation regimens, and modern biologic approaches.

Flexor tendon biology

Significant advances in the understanding of intrasynovial flexor tendon repair and rehabilitation have been made since the early 1970s. The concept of adhesion-free, or primary tendon healing--that tendons could heal intrinsically without the ingrowth of fibrous adhesions from the surrounding sheath has been validated both experimentally and clinically in studies over the past 25 years. Recent attempts to understand and improve the results of intrasynovial flexor tendon repair have focused upon restoration of the gliding surface, augmentation of early post-operative repair site biomechanical strength and on the elucidation of the molecular biology of early post-operative tendon healing. The goals of the surgical treatment of patients with intrasynovial flexor tendon lacerations remain unchanged: to achieve a primary tendon repair of sufficient tensile strength to allow application of a post-operative mobilization rehabilitation protocol. This program should inhibit the formation of intrasynovial adhesions and restore the gliding surface, while facilitating the healing of the repair site.

Effect of elbow position on canine flexor digitorum profundus tendon tension

Tendon injury in the finger remains a clinical challenge to hand surgeons. A canine model is commonly used to study biological effects of tendon injuries and their treatment. There is an important anatomical difference between human and canine anatomy that may be overlooked, however, namely that most of the flexor digitorum profundus (FDP) muscle in dogs takes its origin from the medial epicondyle of the humerus, whereas in humans this muscle arises purely from the forearm. Therefore, elbow position can affect the tension of this muscle in dogs, while having no effect in humans. The purpose of this study was to measure the effect of elbow position on tendon tension in the canine digit in vitro. Elbow position had a significant effect on tendon tension. Digit motion with the elbow fully flexed resulted in significantly higher tendon tension compared to digit motion with the elbow flexed 90 degrees or fully extended, regardless of digit or wrist position (p<0.05). The tension with the elbow flexed 90 degrees was also significantly higher than with the elbow fully extended (p<0.05). The maximum tendon tension with the elbow fully flexed was more than eight times larger than that of the fully extended elbow (p<0.05). We conclude that, in the canine model, elbow position is an important parameter that affects the passive tension applied to the flexor digitorum profundus, and, by implication, to any repair of that tendon. Dog flexor tendon rehabilitation protocols should therefore specify elbow position, in addition to wrist and digit position.

Effect of gap size on gliding resistance after flexor tendon repair

BACKGROUND

Gap formation is a common complication after flexor tendon repair and is associated with adhesion formation, tendon rupture, and decreased strength. The purpose of this study was to investigate the effect of gap formation on tendon gliding resistance after flexor tendon repair in a human cadaver model.

METHODS

Twelve index, middle, and ring fingers from four adult human cadaveric hands were used. Gliding resistance versus excursion between the flexor digitorum profundus tendon and the A2 pulley was first measured in intact tendons. After full laceration, each tendon was repaired with the Pennington suture technique and the gliding resistance was measured again. Then, the repaired tendon (a 0-mm gap) was stretched to form a 1-mm gap, and gliding resistance was remeasured. A magnified video image was used to monitor gap size. This process was repeated to evaluate gap sizes of 2, 3, and 4 mm at the repair site. Peak gliding resistance was determined, and the peak gliding resistance was compared among the groups.

RESULTS

No significant difference in peak gliding resistance was detected between repaired tendons without a gap and tendons with a 1-mm gap. Repaired tendons with a 2-mm gap could pass through the A2 pulley; however, peak gliding resistance was significantly higher than that for tendons with a 0 or a 1-mm gap (p < 0.05). When the gap reached > or =3 mm, all tendons caught at the A2 pulley edge, causing a dramatically increased peak gliding resistance.

CONCLUSIONS

The presence of a 2-mm gap after flexor tendon repair significantly increased tendon peak gliding resistance (p < 0.05), while a gap of > or =3 mm further increased peak gliding resistance because of catching at the pulley edge.

Functional efficacy of tendon repair processes

Despite various attempts to repair and replace injured tendon, an understanding of the repair processes and a systematic approach to achieving functional efficacy remain elusive. In this review the epidemiology of tendon injury and repair is first examined. Using a traditional paradigm for repair assessment, the biology and biomechanics of normal tendon, natural healing, and repair are then explored. New treatment strategies such as functional tissue engineering are discussed, including a functional approach to treatment that involves the development of in vivo functional design parameters to judge the acceptability of a repair outcome. The paper concludes with future directions.

Postoperative stiffness and adhesion formation around repaired and immobilized Achilles tenotomies are prevented using a model of heat shock protein induction

BACKGROUND

Tendon repair and subsequent immobilization is frequently complicated by postoperative stiffness secondary to inflammation and peritendinous adhesions. Thermal preconditioning is known to reduce inflammation by inducing formation of cytoprotective heat shock proteins. This study evaluates the role of thermal preconditioning following complete division and repair of the Achilles tendon, with subsequent immobilization, mimicking the typical clinical scenario.

MATERIALS AND METHODS

Twenty-four New Zealand White rabbits were used in the study. The treatment group underwent thermal preconditioning, by elevating their core temperature to 41.5 degrees C for 20 minutes. The Achilles tendon of the hindlimb was divided and repaired 18 hours following thermal preconditioning. The animals were sacrificed following 3 weeks of immobilization. Range of movement of the ankle, tendon gliding, quantity of adhesions, and weight of repaired tendons were assessed.

RESULTS

Loss of range of movement at the ankle was significantly less in the treatment group versus controls (P = 0.02). The quantity of adhesions and weight of the repaired tendons were significantly reduced in the treatment group (P = <0.001 and P = 0.005, respectively). Tendon gliding relative to the surrounding soft tissue was also significantly improved in the treatment group (P = 0.002).

CONCLUSION

Preconditioned animals demonstrated a significantly better range of ankle movement, decreases in adhesion formation and in the gliding, and dimensions of tendons. Thermal preconditioning therefore has the potential to improve clinical results in tendon surgery following repair and immobilization.

Biomechanical and Clinical Evaluation of a Modified 3-Loop Pulley Suture Pattern for Reattachment of Canine Tendons to Bone

OBJECTIVE

To describe a modified 3-loop pulley suture pattern for the reattachment of canine tendons to bone along with a biomechanical comparison with the locking-loop suture.

STUDY DESIGN

In vitro biomechanical study and clinical case report.

ANIMALS OR SAMPLE POPULATION

Biomechanical study: 10 paired gastrocnemius tendons and calcaneii harvested from 5 canine cadavers.

CASE REPORT

a Doberman with avulsion of the gastrocnemius tendon of insertion.

METHODS

Biomechanical study: paired tendons were reattached to the calcaneus with either a modified 3-loop pulley pattern or a locking-loop pattern. Tensile loading to failure was performed. A direct, non-contact, method of gap measurement, using digital video, was used to measure gap formation. Load required to initiate gap formation (defined as load at a 1 mm gap) and to produce a 3 mm gap was evaluated in addition to maximum load and gap at failure.

RESULTS

Mean (+/-SEM) 1 mm gap loads were 31.0+/-4.2 and 17.2+/-2.5 N, mean 3 mm gap loads were 49.1+/-2.4 and 28.9+/-3.2 N, and mean maximum loads were 72.9+/-4.3 and 55.8+/-2.2 N for the modified 3-loop pulley suture and the locking-loop suture, respectively. These differences were statistically significant (P<.05). The gap at failure was similar for both repairs. The clinical case remained sound 7 months postoperatively.

CONCLUSIONS

A modified 3-loop pulley pattern is biomechanically superior to a locking-loop pattern for reattachment of the canine gastrocnemius tendon to bone and may be suitable for clinical use.

CLINICAL RELEVANCE

Tendon repairs with a gap >3 mm are reported to be at increased risk of rupture during the first 6 weeks postoperatively. A modified 3-loop pulley pattern resists gap formation better than a locking-loop pattern.

Pyramid of progressive force exercises to the injured flexor tendon

Postoperative rehabilitation for patients who have sustained a laceration to their flexor tendon apparatus is an important factor in maximizing functional outcome. Quality rehabilitation is characterized by the development of a tailored exercise regimen. There is currently no model available to tailor an exercise regimen for a person with an atypical physiologic response pattern. If rehabilitation protocols were classified according to the criteria of forces applied across a tendon juncture and/or excursion, and a clinical method were available to assist in the identification of optimal tendon loading and/or excursion application, then those individuals with atypical response patterns could be treated more efficiently and effectively. The author conducted a literature review and case study. A model for systematic application of progressive loading exercises to the intrasynovial flexor tendon injury and repair is conceptually developed. The model consists of a pyramidal series of eight specific rehabilitation exercises in the following sequence: passive protected extension, place and hold, active composite fist, hook and straight fist, isolated joint motion, resistive composite fist, resistive hook and straight fist, and resistive isolated joint motion. Concepts are developed to implement a three-point clinical adhesion-grading system. Clinical application of the system is highlighted. An excellent outcome was considered 112% total active motion. A model for systematic application of progressive loading exercises has been conceptually developed in concert with a method for determination of optimal tendon loading. Further substantiation is necessary to validate the proposed theory.

Porcine small intestine submucosa as a flexor tendon graft

An attractive strategy for tendon tissue engineering is the use of natural extracellular matrices as scaffold materials. One matrix that has been shown to promote healing and regeneration of neotissue in various applications is porcine-derived small intestinal submucosa. It was the objective of this study to investigate small intestinal submucosa for intrasynovial flexor tendon grafting in a canine model. We hypothesized that at 6 weeks small intestinal submucosa grafts would undergo host cell infiltration, neovascularization, and replacement by host neotendon. We also hypothesized that small intestinal submucosa grafts would be incorporated by the host without extensive adhesions to surrounding tissues and therefore maintain normal digit function. An intrasynovial tendon autograft was used as a gold standard. At 6 weeks the intrasynovial tendon autografts remained viable, contained normal numbers of cells along their length, and had minimal peritendinous adhesions. Four of six autografts had normal function as determined by rotation of the distal interphalangeal joint. Also at 6 weeks, the small intestinal submucosa grafts had host cell infiltration, neovascularization, and wavy, oriented tissue. However, ubiquitous adhesions together with impaired function in all cases suggest that small intestinal submucosa grafts in the configuration used are not suitable as full-length intrasynovial grafts in this tendon and animal model.

The three-loop pulley suture versus two locking-loop sutures for the repair of canine achilles tendons

OBJECTIVE

To compare a 3-loop pulley suture pattern with 2 locking-loop sutures for the repair of components of the canine Achilles mechanism.

STUDY DESIGN

In vitro biomechanical study.

ANIMALS

Forty-eight paired tendons collected from 9 canine cadavers.

METHODS

Paired tendons were repaired with either a 3-loop pulley suture or 2 locking-loop sutures and tensile tested to failure. To ensure accurate anastomosis gap measurement a direct, non-contact, method of gap measurement, using digital video, was devised. Load initiating gap formation (defined as load at a 1 mm gap) and load producing a 3 mm gap were evaluated in addition to maximum load, gap at failure, mode of failure, and time spent placing the sutures.

RESULTS

Maximum load values were similar for both repairs. The mean 1 mm gap loads were 44.0 and 18.4 N, and the mean 3 mm gap loads were 56.3 and 34.7 N, for the 3-loop pulley pattern and the 2 locking-loops, respectively; these differences were statistically significant. The 3-loop pulley pattern was faster to place and resulted in a smaller gap at failure. All but 2 repairs failed by suture pull out.

CONCLUSIONS

The 3-loop pulley pattern is more resistant to gap formation during tensile loading, and is quicker to place, than 2 locking-loop sutures.

CLINICAL RELEVANCE

Gap formation can significantly delay tendon healing. Tendon repairs with a gap >3 mm are reported to be at increased risk of rupture during the first 6 weeks postoperatively.

Early weightbearing and ankle mobilization after open repair of acute midsubstance tears of the achilles tendon

PURPOSE

To study the effects of early weightbearing and ankle mobilization after acute repair of ruptured Achilles tendon.

STUDY DESIGN

Comparative longitudinal study.

METHODS

Patients in group 1 were postoperatively immobilized with their ankle in gravity equinus, they were encouraged to bear weight on the operated limb as soon as possible to full weightbearing, and they received a single cast change at 2 weeks, with the ankle accommodated in an anterior splint in a plantigrade position, allowing the ankle to be plantar flexed fully but not dorsiflexed above neutral. Patients in group 2 were immobilized with their ankle in full equinus with a cast change at 2 weeks, when the ankle was immobilized in mid equinus, and at 4 weeks, when the ankle was immobilized in a plantigrade position, and they were advised to bear weight.

RESULTS

Patients in group 1 attended fewer outpatient visits, completely discarded their crutches at an average of 2.5 weeks, and more were satisfied with the results of surgery. At ultrasonography, the average thickness of the repaired tendon was 12.1 mm, with no difference in the thickness of the ruptured tendon regardless of postoperative management. There was no significant difference in isometric strength between the two groups.

CONCLUSIONS

Early weightbearing with the ankle plantigrade is not detrimental to the outcome of repair after acute rupture of the Achilles tendon and shortens the time needed for rehabilitation. However, strength deficit and muscle atrophy are not prevented.

Two-portal repair of canine flexor tendon insertion site injuries: histologic and immunohistochemical characterization of healing during the early postoperative period

PURPOSE

In vivo animal studies have indicated that the complex structure of the tendon-bone interface may not be restored after repair even under optimal conditions. Controversy exists about the histologic findings in the early postoperative period after tendon reattachment to bone; this may have impact on biomechanical properties. The objective was to study the histologic structure and immunohistochemical staining of the tendon-bone interface in a large model of digital flexor tendon-bone repair. The hypothesis was that the tendon-bone interface matures and assumes a progressively more anatomic histologic and immunohistochemical appearance during the first 6 weeks after repair.

METHODS

Twenty-four canine flexor digitorum profundus tendons were released from their insertion by sharp dissection and repaired to bone. The forelimb was immobilized after surgery and 10 minutes of daily passive motion rehabilitation was performed. Dogs were killed at 10, 21, and 42 days after surgery. Hematoxylin-eosin and immunohistochemical staining for types I, II, and II collagen were performed.

RESULTS

Although at both 10 and 21 days after surgery substantial inflammation was seen at the tendon-bone repair site, this had decreased markedly by 42 days. Although direct apposition of tendon to bone was seen at 42 days, the mature tendon-bone insertion site was not recreated by this time. Staining for types I and III collagen was diffuse throughout the tendon-bone insertion throughout the interval examined.

CONCLUSION

These findings suggest that at 6 weeks after surgery the intact tendon-bone repair site shows minimal histologic and molecular similarity when compared with unoperated specimens.

Neovascularization of the flexor digitorum profundus tendon after avulsion injury: an in vivo canine study

PURPOSE

The changes in matrix material properties and intrinsic vascularization that have been noted in intrasynovial tendon stumps after avulsion injury may be of considerable clinical relevance with regard to the results of surgical repair. Our objective was to determine both the time course and the source of neovascularization of the tendon stump in an in vivo canine model of flexor digitorum profundus (FDP) avulsion after a clinically relevant delay in diagnosis.

METHOD

The FDP tendon was released from bone directly by sharp dissection and the vinculum brevis profundus was lacerated, simulating an avulsion injury with interruption of the vascular supply to the tendon stump. After death at 7 and 21 days, tendon vascularity was evaluated with India ink injection and clearing using a modified Spalteholtz technique.

RESULTS

All 7-day specimens showed an absence of vascularity compared with the controls. In all 21-day specimens a direct vascular supply originated from local fibrovascular adhesions contacted the stump on its surface and blood vessels penetrated the tendon stump circumferentially. Progressive vascularization of the avulsed tendon stump occurred between 7 and 21 days after injury, originating from fibrovascular adhesions to the surrounding synovial sheath.

CONCLUSIONS

Whereas previous studies of intrasynovial flexor tendon laceration and repair have shown a progressive proximal to distal neovascularization of the FDP during the early postoperative period, longitudinal proximal to distal growth from the proximal blood supply of the FDP was not observed toward the unrepaired tendon stump.

Tendon healing in vitro: promotion of collagen gene expression by bFGF with NF-kappaB gene activation

PURPOSE

Matrix synthesis of intrasynovial tendon cells and activation of nuclear transcription factors are pivotal to promotion of flexor tendon healing. We investigated the effects of basic fibroblast growth factor (bFGF) on synthesis of type I collagen and activation of nuclear transcription factor kappaB (NF-kappaB) in an in vitro culture model of intrasynovial tenocytes.

METHOD

Tenocytes obtained from explant culture of rabbit intrasynovial tendon segments were treated with bFGF at concentrations of 0, 2, and 10 ng/mL. Expression of type I collagen and NF-kappaB genes was determined by quantitative analysis of products of reverse-transcription polymerase chain reactions. Proliferation of the cells was assessed by incorporation of bromodeoxyuridine into the DNA of the cells.

RESULTS

Expression levels of type I collagen and NF-kappaB genes of tenocytes were increased significantly by bFGF. Cell proliferation as indicated by DNA labeling was promoted significantly by bFGF. Expression of the NF-kappaB gene increased proportionately to the amounts of bFGF stimulating the cells and was correlated with increases in proliferation rate of tenocytes.

CONCLUSIONS

Results of this study show that expression of type I collagen and NF-kappaB genes is promoted manifestly by bFGF. The effects were proportionate to in vitro proliferation rates of tenocytes. The study indicated that matrix synthesis of flexor tendons can be promoted by bFGF and that NF-kappaB may play a pivotal role in initiating proliferation and type I collagen synthesis of tenocytes.

Tendon surface modification by chemically modified HA coating after flexor digitorum profundus tendon repair

Carbodiimide derivatized HA (cd-HA) is less soluble in water than normal HA, and therefore has an increased tissue residence time. The purpose of this study was to study the effect of cd-HA gel on gliding and repair integrity during simulated repetitive motion of a repaired tendon in vitro. A total of 36 flexor digitorum profundus (FDP) tendons from six adult mongrel dogs were used and divided into three groups of control, simple HA, and cd-HA. The gliding resistance between the FDP and the proximal pulley, FDS, and bone was measured before laceration and after modified Kessler technique repair at 1, 5, 10, 50, 100, 200, 300, 400, and 500 cycles. After gliding testing, failure load, tendon stiffness, and resistance to gap formation were measured. The results showed from the first cycle to the 10th cycle, there were no significant differences in gliding resistance between the three testing groups (p > 0.05). From the 50th cycle onwards, the friction was significantly lower in the cd-HA gel group than in the control group (p < 0.05). Neither breaking strength, nor tendon stiffness, nor resistance to gap formation of the repairs were significantly different between the three groups (p > 0.05).

Aggressive active mobilization following zone II flexor tendon repair using a two-strand heavy-gauge locking loop technique

In vitro and in vivo experimental studies have shown that a new two-strand technique increases the tensile strength of flexor tendon repair and eliminates gap formation at the healing repair site. The purpose of the current study was to clinically evaluate the new technique, followed by an aggressive active mobilization program. Seven digits with zone II flexor tendon lacerations were treated using the technique, employing a heavy (2-0) braided polyester suture. The patients were encouraged to perform active mobilization of the injured digits by themselves with almost a full range of flexion and extension after they were instructed by the surgeon for few days from the first postoperative day. All patients were followed up for at least 6 months, except for one, with whom contact was lost in 14 weeks postoperatively. Six of the seven digits were evaluated as excellent in 6 months by the original Strickland criteria, thus showing that the combination of the new repair technique and aggressive active mobilization is effective for zone II flexor tendon repair.

Recent progress in flexor tendon healing

Although advances in the treatment of flexor tendon injuries have led to improved clinical outcomes during the past several decades, a subset of patients continue to experience a loss of function. Using a canine model of sharp transection of the flexor digitorum profundus tendon followed by repair and rehabilitation using clinically relevant techniques, we have examined the influence of multistrand suture and postoperative rehabilitation variables on digital function and tendon strength. Our findings highlight the critical role of repair technique in providing a stiff and strong repair and indicate that continued refinement of suture techniques is warranted in order to minimize repair-site elongation (gap). Gap formation continues to occur at a high frequency, and the formation of gaps greater than 3 mm delays the accrual of repair-site strength that occurs with time. Furthermore, our results indicate that passive-motion rehabilitation that produces a moderate amount of tendon excursion (2 mm) at low levels of tendon force (5 N) is sufficient to inhibit adhesion formation and to promote healing. Increases in excursion or force beyond these levels do not accelerate the healing process. These findings suggest that we are approaching the limit of the extent to which we can modulate healing by manipulating rehabilitation variables such as tendon excursion and force. Future advances will probably require manipulation of the biological factors that promote healing.

Repair of flexor digitorum profundus tendon avulsions from bone: an ex vivo biomechanical analysis

Avulsions or distal transections of the flexor digitorum profundus tendon are typically repaired by direct suture of the tendon stump to the distal phalanx. The optimal repair technique to withstand in vivo rehabilitation forces is unknown. Our objective was to determine the time-zero tensile mechanical properties of 4-strand tendon-bone repair site constructs performed with 3-0 and 4-0 sutures and with modified Kessler and modified Becker grasping techniques. We hypothesized that the 3-0 modified Becker grasping suture technique not described previously for the reattachment of tendon to bone would show improved biomechanical properties compared with the 4-0 or modified Kessler techniques. All modified Kessler repairs failed by suture pullout from the tendon, whereas all modified Becker repairs failed by rupture of the suture at the tendon-bone junction. Although the 3-0 modified Becker repair group showed greater ultimate force then the other groups (p <.01), tendon-bone gap observed did not differ markedly between Becker or Kessler groups. Neither suture caliber nor repair technique had a notable effect on strain at 20-N force, suggesting that early gap formation at the tendon-bone repair site may occur regardless of technique.

Flexor tendon repair, healing and rehabilitation: a brief commentary

Twenty years ago, we concluded that it was useless to use suture material strong enough to allow early mobilisation, since material of this sort creates problems in the form of connective tissue reaction and even tendon necrosis. It is better to use what is called "the blocked suture", which abolishes muscle tension on the repair, and, therefore, makes it possible to bring the tendon ends accurately together by fine sutures too weak to resist any muscle fore.19

This statement, from Claude Verdan's Founders Lecture to the American Society for Society of the Hand only 30 years ago, highlights the dramatic rate of change in our understanding and clinical approach to flexor tendon repair. At the time these words were spoken, Verdan and some of his more adventurous contemporaries were challenging the currently accepted dictum that repair of flexor tendons divided in the digit should not be attempted. This early work on the primary repair of flexor tendons by Verdan,20 Kleinert and associates,12 and Kessler and Nissim,11 among others, forever changed the landscape of Bunnell's "no man's land",and paved the way for the clinical advances and explosion of research into flexor tendon healing and repair that have occured in the last several decades.

The rigidity of repaired flexor tendons increases following ex vivo cyclic loading

Transected flexor tendons are typically treated by suture repair followed by rehabilitation that generates repetitive tendon loading. Recent results in an in vivo canine model indicate that during the first 10 days after injury and repair, there is an increase in the rigidity of the tendon repair site. Our objective was to determine whether or not ex vivo cyclic loading of repaired flexor tendons causes a similar increase in repair-site rigidity. We simulated 10 days of rehabilitation by applying 6000 loading cycles to repaired canine flexor tendons ex vivo at force levels generated during passive motion rehabilitation; we then evaluated their tensile mechanical properties. High-force (peak force, 17 N) cyclic loading increased repair-site rigidity by 100% and decreased repair-site strain by 50%, whereas low-force (5 N) loading did not change the properties of the repair site. This mechanical conditioning effect may explain, in part, the changes in tensile properties observed after only 10 days of healing in vivo. Mechanical conditioning of repaired flexor tendons by repetitive forces applied during rehabilitation may lead to increases in repair-site rigidity and decreases in strain, thereby altering the mechanical loading environment of tissues and cells at the repair site.

In vitro cyclic tensile testing of combined peripheral and core flexor tenorrhaphy suture techniques

Early tenorrhaphy mobilization increases repair site strength and decreases adhesions. Preliminary unpublished data suggest that early active mobilization improves clinical outcome compared with traditional passive motion protocols. We loaded cadaver flexor profundus tendon repairs to 8.0 kg (78.4 N) for up to 5,000 cycles to simulate the loads and cycle number of our active flexor tendon rehabilitation protocol. 3-0 Ethibond (Ethicon, Somerville, NJ) and 6-0 Prolene (Surgi-pro; US Surgical, Norwalk, CT) were used for core and peripheral sutures, respectively. Four different groups were tested: 2-strand Tajima core suture with either a running interlocking (2R) or a Silfverskiöld cross-stitch (2S) peripheral suture and 4-strand Tajima plus horizontal mattress core suture with either a running interlocking (4R) or a Silfverskiöld peripheral suture (4S). Repairs failed in the suture midsubstance or at the knot. There was considerable variability within groups and no significant difference in the number of cycles to failure between the 2R, 4R, and 2S repairs, which failed after 2 +/- 2, 304 +/- 249, and 560 +/- 987 cycles, respectively. All 4S repairs were intact after 5,000 cycles. Our data suggest that flexor tenorrhaphy with the 4S repair can withstand the cyclic loads we estimate would be present during an active rehabilitation protocol.

The insertion site of the canine flexor digitorum profundus tendon heals slowly following injury and suture repair

Treatment of injuries of the flexor digitorum profundus (FDP) tendon insertion site has changed little during the past 50 years, in part because there are no reports describing flexor tendon insertion site healing. Our objective was to assess the effects of repair technique and post-operative time on tendon-bone healing using a canine model of injury and repair. We transected 48 FDP tendons from 24 dogs at their insertions and repaired them using either a four- or eight-strand suture technique. We assessed the mechanical properties of the repaired tendon-bone construct, tendon collagen biochemistry, and distal phalanx bone mineral density (BMD) at 0, 10, 21 and 42 days. Suture method had no significant effect on any outcome (p > 0.05). In particular, use of an eight-strand double modified Kessler technique did not result in increased stiffness or strength compared to a four-strand technique. With time, the repair site became stiffer, as demonstrated by a 230% increase in rigidity and a 50% decrease in strain from 0 to 42 days. However, from 0 to 42 days the ultimate force of the insertion site did not increase. This lack of increase in ultimate force was consistent with decreases in collagen content, non-reducible crosslinks and distal phalanx BMD. Taken together, our results indicate that the canine FDP tendon heals slowly after it is injured at its insertion site and sutured onto the distal phalanx. While these findings may be limited to the particular repair method we used, they demonstrate a need for devising new treatment strategies to improve healing of flexor tendon insertion site injuries.

The effect of variations in applied rehabilitation force on collagen concentration and maturation at the intrasynovial flexor tendon repair site

The biochemical means by which accelerated rehabilitation alters intrasynovial flexor tendon repair site collagen synthesis and extracellular matrix maturation are not fully understood. We hypothesized that an increased level of applied rehabilitative force in a clinically relevant animal model would hasten the maturation of the repair site extracellular matrix as demonstrated by total collagen and collagen cross-link assessment. Twenty-eight flexor digitorum profundus tendons from 14 adult dogs were transected and repaired. The animals received either low- or high-force rehabilitation and were killed 10, 21, and 42 days after surgery. A 10-mm segment of tendon surrounding the repair site was obtained. Biochemical analysis showed that total collagen concentration was significantly reduced at each time point, that the reducible cross-link ratio of dihydroxylysinonorleucine to hydroxylysinonorleucine was significantly increased at each time point, and that the nonreducible pyridinoline cross-link content was significantly decreased at 10 days in both rehabilitative groups. Total collagen content did not vary to a statistically significant degree with either time or as a function of rehabilitation type. Based on these findings several clinically relevant observations can be made. Increasing collagen concentration and repair site maturation do not explain the previously demonstrated increased tensile properties of tendon that occur between 3 and 6 weeks after repair. Higher force rehabilitation does not alter the biochemical composition of the healing tendon through 6 weeks. Coupled with other recent data these findings suggest that high-force rehabilitation does not stimulate accelerated healing after intrasynovial flexor tendon repair.