The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 84, Issue 6

Scientific Article | June 01, 2002

Treatment of Partial Lacerations in Flexor Tendons by Trimming : A Biomechanical in Vitro Study

Lionel Erhard, MD; Mark E. Zobitz, MS; Chunfeng Zhao, MD; Peter C. Amadio, MD; Kai-Nan An, PhD

Investigation performed at the Mayo Clinic and Mayo Foundation, Rochester, Minnesota

Lionel Erhard, MD
Mark E. Zobitz, MS
Chunfeng Zhao, MD
Peter C. Amadio, MD
Kai-Nan An, PhD
Orthopedic Biomechanics Laboratory, Mayo Clinic and Mayo Foundation, 200 First Street S.W., Rochester, MN 55905. E-mail address for P.C. Amadio: pamadio@mayo.edu

In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from National Institutes of Health (National Institute of Arthritis and Musculoskeletal and Skin Diseases) Grant AR 44391 and the Mayo Foundation. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

J Bone Joint Surg Am, 2002 Jun 01;84(6):1006-1012

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Abstract

Background: Treatment of a partial laceration in zone 2 of a flexor tendon is controversial. The intact part of the tendon can usually sustain forces of normal unresisted motion, and repaired partially lacerated tendons can actually be weaker than unrepaired ones. However, complications such as triggering or entrapment have been reported in association with unrepaired tendons. The purpose of this study was to measure the biomechanical behavior following trimming of the tendon as an alternative to repair.

Methods: Thirty-six flexor digitorum profundus tendons were harvested from sixteen unpaired fresh-frozen cadaveric human hands and were randomly assigned to be subjected to either 50% or 75% partial laceration, which was either lateral or volar, and were then assigned to no repair, repair with a running suture, or trimming. Mean and maximum gliding resistances were measured as the flexor digitorum profundus glided through the bone-A2 pulley complex and the flexor digitorum superficialis. Values were normalized to those measured in the intact tendon. The tendons were then distracted to failure, and maximum load and stiffness were recorded.

Results: There was triggering or entrapment of eight unrepaired tendons; two cases were severe, and six were minor. When no severe trigger was obvious, the unrepaired tendons had the lowest tendency for gliding resistance, followed by the tendons treated with trimming and then by those treated with the running suture. Overall, the tendons with a volar laceration had higher mean and maximum gliding resistance than those with a lateral laceration (p < 0.05), those with a 75% partial laceration had higher mean gliding resistance than those with a 50% laceration (p < 0.05), and the tendons that were repaired with running suture had higher mean gliding resistance than those treated with trimming (p < 0.05). Tendon strength was not significantly different among the three types of treatment.

Conclusions: From the perspective of gliding resistance after partial tendon laceration, no repair appears necessary unless triggering is a problem. If triggering occurs, then trimming of a partially lacerated tendon may be a reliable alternative to repair, at least in terms of gliding resistance and strength.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Partial lacerations of flexor tendons are not uncommon. The location of the partial laceration may be either lateral or volar, and the management of these injuries, especially those in zone 2, still raises questions. Clinical decisions often have been extrapolated from the results of studies on completely lacerated tendons. Previous biomechanical studies have shown that when a laceration involves =60% of the cross-sectional area, the residual intact tendon remains the strongest link in the muscle-tendon-bone complex ^1,2 . Tendons with such a laceration are capable of sustaining the forces of normal active unresisted motion ^3,4 . Moreover, repairing even a 75% partial laceration can adversely affect tendon strength compared with that of an unrepaired tendon, both in vitro and in vivo ^5-11 . Yet, if one decides not to repair a partial laceration, complications such as triggering, entrapment, and secondary rupture can occur ^12-18 . Triggering creates discomfort during finger motion as the laceration site gets caught on the pulley edge, whereas with entrapment the laceration site is unable to enter the pulley, resulting in a limited range of motion. On the basis of the results of an in vivo canine study, Cooney et al. ⁸ recommended resection of the edges of any partial tendon laceration involving <30% of the cross-sectional area and of any oblique-flap-type of laceration involving =60% of the cross-sectional area. Schlenker et al. ¹⁵ advised resection of a beveled laceration flap if <25% of the cross-sectional area were involved. In a prospective study, al-Qattan ¹⁹ reported excellent results for unrepaired tendons, including some treated with trimming, in fifteen patients with a partial laceration involving >50% of the tendon cross section. However, there is a lack of biomechanical data in the literature on tendon trimming as a method of treatment of partial tendon lacerations.

The purpose of this study was to determine whether trimming alters the gliding or strength characteristics of flexor digitorum profundus tendons with a partial laceration in zone 2. The gliding resistance and strength after three types of treatment (no repair, repair with a running suture, and trimming) were compared. These parameters were also compared according to the degree of laceration (50% or 75%) and the location of the laceration (volar or lateral).

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Fig. 1:: Device for creating volar tendon lacerations, consisting of (1) an electronic caliper, (2) a thumb roller, (3) a control switch zero button, (4) a razor blade, (5) a moving block, and (6) a tendon groove.

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Fig. 2:: Trimming procedure.

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Fig. 3:: Test device for measuring gliding resistance. FDP = flexor digitorum profundus, and FDS = flexor digitorum superficialis.

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Fig. 4:: Load cell readings (F1 and F2) during excursion of an unrepaired tendon with severe triggering. A: the laceration site reaches the distal edge of the A2 pulley. A to B: the distal portion of the tendon becomes trapped against the pulley edge. B: the laceration site succeeds in passing the distal edge of the A2 pulley, creating a trigger.

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Fig. 5:: Mean gliding resistance expressed as the percentage increase compared with the value for the intact tendon. The error bars indicate standard deviations.

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Fig. 6:: Maximum gliding resistance expressed as the percentage increase compared with the value for the intact tendon. The error bars indicate standard deviations.

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TABLE I: Experimental Design

Degree of Laceration	Laceration Site	No. of Tendons	Gliding Testing Sequence	Strength Testing
75%	Lateral	6	Unrepaired	Unrepaired
75%	Lateral	6	Partial running suture	Partial running suture
75%	Lateral	6	Trimming	Trimming
75%	Volar	6	Unrepaired, partial running suture, trimming	Trimming
50%	Lateral	6	Unrepaired, partial running suture, trimming	Trimming
50%	Volar	6	Unrepaired, partial running suture, trimming	Trimming

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TABLE I: Experimental Design

Degree of Laceration	Laceration Site	No. of Tendons	Gliding Testing Sequence	Strength Testing
75%	Lateral	6	Unrepaired	Unrepaired
75%	Lateral	6	Partial running suture	Partial running suture
75%	Lateral	6	Trimming	Trimming
75%	Volar	6	Unrepaired, partial running suture, trimming	Trimming
50%	Lateral	6	Unrepaired, partial running suture, trimming	Trimming
50%	Volar	6	Unrepaired, partial running suture, trimming	Trimming

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TABLE II: Results of Tensile Testing

*The values are given as the mean and the standard deviation.

Degree of Laceration	Laceration Site	Treatment	Maximum Load* (N)	Stiffness* (N/mm)
75%	Lateral	Unrepaired	209.4 ± 52.5	47.0 ± 11.1
75%	Lateral	Partial running suture	222.7 ± 29.3	53.6 ± 11.1
75%	Lateral	Trimming	226.0 ± 42.6	45.9 ± 9.9
75%	Volar	Trimming	198.7 ± 79.8	45.9 ± 15.6
50%	Lateral	Trimming	268.2 ± 51.1	71.6 ± 14.1
50%	Volar	Trimming	264.9 ± 85.1	57.4 ± 19.8

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TABLE II: Results of Tensile Testing

*The values are given as the mean and the standard deviation.

Degree of Laceration	Laceration Site	Treatment	Maximum Load* (N)	Stiffness* (N/mm)
75%	Lateral	Unrepaired	209.4 ± 52.5	47.0 ± 11.1
75%	Lateral	Partial running suture	222.7 ± 29.3	53.6 ± 11.1
75%	Lateral	Trimming	226.0 ± 42.6	45.9 ± 9.9
75%	Volar	Trimming	198.7 ± 79.8	45.9 ± 15.6
50%	Lateral	Trimming	268.2 ± 51.1	71.6 ± 14.1
50%	Volar	Trimming	264.9 ± 85.1	57.4 ± 19.8

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Specimen Preparation

Thirty-six flexor digitorum profundus tendons were excised from the second, third, and fourth digits of sixteen unpaired cadaveric fresh-frozen human hands. The hands had been stored at -20Â°C and thawed overnight at room temperature. The age of the donors at the time of death ranged from thirty-nine to ninety-eight years (mean, 76.8 years).

The flexor tendon system in zone 2 was exposed through a Bruner palmar approach, and the sheath was incised at the distal edge of A2 pulley. At that level, the volar surface of the flexor digitorum profundus was marked with the finger in full extension and in full flexion, with tension on the tendon maintained by pulling on it at the wrist level. The distance between the two marks was considered the tendon excursion. A partial transverse laceration was created at a level 10 mm distal to the proximal excursion mark. The laceration was made on either the lateral or the volar surface, through either 75% or 50% of the native diameter. At the specified tendon location, the human flexor digitorum profundus consists of two equivalent bundles separated by a groove ^20,21 . Lateral tendon lacerations were performed under 3.5Â¥ magnification by completely lacerating one bundle, for the 50% lacerations, and then lacerating half of the remaining bundle, for the 75% lacerations ¹ . Because the flexor digitorum profundus is flat anteroposteriorly, with no anatomically reliable landmarks, we designed a device for creating partial volar lacerations. A razor blade was fixed to the moving jaw of an electronic caliper (Mitutoyo Digimatic, Kawasaki, Japan) ( Fig. 1 ). A cylindrical block with an adjustable groove for the tendon and a frontal fence for the blade was attached to the opposite jaw of the caliper. The cutting-caliper was held vertically in a frame and was set at zero when the blade contacted the bottom of the groove. The groove width matched the tendon width. A 0.5-N weight was attached to the tendon ends as it was inserted into the groove. The blade then cut the tendon to a specified depth. An elliptical cross section was used to calculate the depth of cut that corresponded to an involvement of 50% or 75% of the cross-sectional area.

The trimming procedure consisted of resecting two wedges, from the deepest point of the laceration to the previously marked limits of tendon excursion under the pulley ( Fig. 2 ). The repair technique was a partial simple running suture of 6/0 nylon that left the unlacerated fibers undisturbed.

The study design randomized two degrees of laceration (50% and 75%), two locations of laceration (lateral and volar), and three types of treatment (no repair, partial running suture, and trimming). In order to maximally utilize the available specimens, the tendons with a volar laceration and those with a 50% lateral laceration were sequentially tested for gliding resistance under conditions of no repair, then repair with a partial running suture, and then trimming. After testing of the gliding resistance, the trimmed tendons were evaluated for breaking strength. The tendons with a 75% lateral laceration were assigned to individual groups for treatment with no repair, running-suture repair, or trimming. After the gliding test was performed, these tendons were tested to failure. Thus, the strengths after the different treatments were compared among the tendons with a 75% lateral laceration, and the effects of the site and degree of laceration were evaluated among trimmed tendons. Table I provides a summary of the testing sequence.

Gliding Properties

The proximal and middle phalanges were harvested with the flexor system intact, and the proximal interphalangeal joint was fixed in full extension with a longitudinal 1.5-mm Kirschner wire. As the proximal edge of the A2 pulley is sometimes difficult to isolate ²² , we considered the A1-A2 pulley complex a single entity. The frictional interaction between the flexor digitorum profundus and the flexor digitorum superficialis and pulley complex was measured during the excursion of the flexor digitorum profundus, simulating flexion. An et al. ²³ and Uchiyama et al. ²⁴ previously described the concept of arc of contact for measurement of friction and its application to the tendon-pulley unit. The specimen preparation was immersed in a saline solution bath, volar side upward, and mounted on a custom testing device ( Fig. 3 ). The proximal part of the flexor digitorum profundus was connected to a tensile load transducer (F2) through a ring load cell and was connected to a mechanical actuator with a linear potentiometer. The distal part of the flexor digitorum profundus was linked to another tensile load transducer (F1) and to a 4.9-N weight through a mechanical pulley. To maintain a more physiological gliding environment in zone 2, the flexor digitorum superficialis was kept intact and was fixed to the frame at a 40Â° angle to the horizontal plane under a tension of 2 N. The arc of contact between the pulley and the flexor digitorum profundus tendon was set at 50Â°, as described by Uchiyama et al. ²⁵ , by positioning the proximal and distal flexor digitorum profundus cables to angles of 3Â° and 20Â°, respectively, with the horizontal plane.

From its extension position, the tendon was pulled proximally into flexion by the actuator at a rate of 2 mm/sec. A reversed actuator movement allowed the tendon to return to its extension position, pulled by the weight. The latter maintained the system under tension during the experiment and simulated passive finger extension.

Data were registered during total excursion at a rate of 20 Hz. The distal load cell, F1, linked to the weight, remained constant during excursion. The frictional force during flexion (F2flexion - F1) and the frictional force during extension (F1 - F2extension) were calculated. The gliding resistance during the whole movement is the average of flexion and extension frictional forces as (1/2)*(F2flexion - F2extension). The mean gliding resistance for each tendon and the peak during flexion were calculated. Before laceration, a gliding test of each tendon in the intact state was performed, and all of the data were normalized as a ratio of this reference.

Strength Properties

Tendons were fixed in clamps with interdigitating grooves in a servohydraulic testing machine (MTS, Minneapolis, Minnesota) and underwent tensile loading to failure. The grip-to-grip distance was 30 mm. Tendons were distracted at a rate of 20 mm/min until rupture, and tensile forces and grip-to-grip displacement data were collected at a rate of 20 Hz. From the load versus grip-to-grip displacement curve, we obtained maximum failure load and tendon stiffness (slope of the linear region).

Statistical Analysis

Sample size requirements were determined by a power calculation. Prior studies of gliding resistance ²⁶ have shown that normal tendon friction averages 0.29 14 N and a tendon with a standard modified Kessler repair has an average friction of 0.81 0.25 N. This difference, 0.5 N (51 g-f), is, we believe, the smallest difference that is likely to be clinically relevant. To detect such a difference with an alpha of 0.05 and a power of 0.85, for a two-sided comparison, six specimens were required per experimental group. We have no comparable data with which to assess power for the breaking-strength determinations, but a literature review suggested that differences between repair types are likely to be small and therefore very large sample sizes would be needed to show a significant difference. Thus, we elected to use the sample size of our outcome measure of primary interest, gliding resistance, as the relevant parameter.

The data from the gliding tests were analyzed with use of three-way analysis of variance comparing the data according to the site of laceration, amount of laceration, and treatment. Since all results were normalized to the result for the intact tendon, independence among treatments was assumed. If significant differences were shown, a Tukey-Kramer post-hoc test for multiple comparisons was performed. Data obtained from the strength tests were analyzed with two-way analysis of variance in the trimmed-tendon group to assess whether there were measured differences according to the degree of laceration or the site of laceration. The different treatments were compared in the group with a 75% lateral laceration with a one-way analysis of variance followed by a Tukey-Kramer post-hoc test if significant differences were observed. A significance level of p < 0.05 was used in all cases.

Results

Introduction | Materials and Methods | Results | Discussion | References

Gliding Properties

There was some degree of triggering or entrapment of eight unrepaired tendons during the testing. There was severe triggering of one tendon (with a 75% volar laceration) when the laceration site reached the distal edge of the A2 pulley, but the tendon was able to pass through the pulley. One other tendon (with a 75% volar laceration) was completely entrapped at the pulley edge and was unable to glide further. The entrapped tendon was subjected to the test again, severe triggering occurred ( Fig. 4 ), and that result was used for analysis. The remaining triggering events were less severe, demonstrated by a small sudden peak on the force curve. Such triggering was seen during the testing of three tendons with a volar laceration (one with a 75% laceration and two with a 50% laceration) and of three with a lateral laceration (one with a 75% laceration and two with a 50% laceration).

Mean gliding resistance was significantly affected by the degree of laceration (p < 0.01), location of the laceration (p < 0.01), and type of treatment (p < 0.01). There were no significant interactions among the three factors. Volar lacerations produced significantly greater mean gliding resistance than did lateral lacerations (p < 0.05), 75% lacerations produced significantly greater mean gliding resistance than did 50% lacerations (p < 0.05), and trimming of the tendon or no repair both produced lower mean gliding resistance than did a running suture (p < 0.05) ( Fig. 5 ). There were no significant differences in maximum gliding resistance due to the degree of laceration (p = 0.11) or the type of treatment (p = 0.63). However, the site of the laceration had a significant effect, with lateral lacerations producing lower maximum gliding resistance than volar lacerations (p < 0.05) ( Fig. 6 ).

Strength Properties

All but two tendons with a 50% laceration, one volar and one lateral, failed at the clamp site. The mode of failure was identical for all tendons with a 75% lateral laceration. A vertical shear started between the intact and lacerated regions, resulting in fiber rupture in the central portion of the tendon linked to the clamps. The failure of the tendons with a volar laceration appeared to finally occur at the site of laceration, but it also followed a shearing mode starting close to the clamps. Our results under these conditions represent a minimal load capacity for the tendons.

The tests of the tensile properties of the tendons with a trimmed laceration site revealed no significant difference in maximum load as a result of either the degree (p = 0.06) or the location of the laceration (p = 0.58). The measure of tendon stiffness showed a significant difference as a result of the degree of laceration (p < 0.01) but none due to the location of the laceration (p = 0.27) ( Table II ). Testing of the tendons with a 75% lateral laceration showed no significant differences in maximum load (p = 0.78) or stiffness (p = 0.43) among the three types of treatment.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

In the gliding tests, the tendons with a volar laceration had significantly greater friction than did those with a lateral laceration. In the testing model, the volar surface of the tendon makes direct contact with the A2 pulley. Therefore, it is logical that the tendon would be more sensitive to changes in friction following a disturbance of its volar surface and that the propensity for triggering would be higher.

Unrepaired tendons, when triggering did not occur, and trimmed tendons, with either degree or location of laceration, had lower friction than did the tendons repaired with the running suture. Although we only tested the results of a running suture, published results of a modified Kessler repair of 75% lateral lacerations showed increases of 209% and 233% in mean and maximum gliding resistance, respectively, compared with the values for an intact tendon ²⁶ . A core suture has the added disadvantage of more suture material, and this may be a factor in the higher friction with this method. Our decision to limit our repair to a running suture was based on this concern as well as on the fact that other studies ^7,8 have shown that repairs with a core suture are detrimental to healing of partially lacerated tendons. Our own data on breaking strength support this, as even the tendons with a 75% laceration did not fail in their midsubstance but rather at the clamp. The stress riser at the clamping site, not the partial laceration, was the weakest link, and even then the breaking strength of the unrepaired tendons was far greater than that following any known method of tendon repair.

In clinical studies consisting of thirty-four and fourteen patients, respectively, Wray and Weeks ²⁷ and McGeorge and Stilwell ²⁸ found no complications and good results without repairing partial lacerations, even those larger than 75% of the cross section of the tendon. However, a transient trigger finger did develop in one patient. There are also other published cases documenting triggering ^13-17 , entrapment ^12,15 , or rupture ¹⁵ associated with a previously undiagnosed partial laceration of the flexor tendon. All injuries occurred in zone 2, with the exception of a case ¹⁶ in which the tendon triggered at the wrist level under the proximal edge of the flexor retinaculum. The operative findings were, in most cases, appendage-like formations at the level of the tendon wound ^12-15,17 , a synovial mass ¹⁶ , or a bulbous scar ¹⁵ . The mechanism of these complications was clarified by al-Qattan et al. ¹⁸ , in a study of twenty-eight sheep tendons that had been partially lacerated transversely and left unrepaired. Seven cases of initial triggering were associated with bunching of the tendon edges, one case of late triggering was associated with formation of a synovial mass, and two cases of entrapment were caused by flap formation. Flap formation is not necessarily caused by an oblique laceration, as it can also be a secondary effect of bunching, with the tendon splitting along longitudinal fibers. Moreover, in zone 2, triggering can even occur within an intact sheath ¹² , as the inner aspect of the sheath is not a continuous smooth surface ²⁹ . Before attaching, the thin part of the sheath overlaps the pulleys, especially the distal edge of the A2 pulley, creating a pocket where triggering can be observed.

The results of our gliding tests support the finding that triggering of unrepaired tendons can occur, but our experiment did not take into consideration the effect of repetitive motion on an unrepaired tendon in vivo. Nevertheless, we believe that trimming is an alternative to repair for preventing gliding complications after partial tendon lacerations. However, since our testing model did not produce triggering of all unrepaired tendons, we cannot unequivocally state that trimming would be indicated in every case. Previous clinical reports have shown that when an appendage-like formation was found to be responsible for triggering or entrapment ^13-17 , a late resection produced a satisfactory outcome for all patients.

Our results with regard to tendon strength suggest that trimming of the tendons affected neither the maximum load at failure nor the stiffness of tendons with a 50% or 75% laceration. This finding agrees with that of McCarthy et al. ² , who showed that resection of a 3 to 4-mm segment of tendon from the laceration site did not affect the tensile properties of the tendon-bone complex. Although we had a large number of failures that seemed to initiate at the clamp-tendon interface, the maximum loading, even in the tendons with a 75% laceration, was approximately 200 N. This is comparable with the failure load of 204 N in a report of human tendons in which a 75% lateral laceration had been repaired with a modified Kessler suture ³⁰ . Since in vivo measurements have revealed a maximum of 118 N of force along the flexor digitorum profundus during tip pinch ⁴ , the residual strength of a tendon with even a 75% partial laceration would seem sufficient to permit early active motion.

Repair of the 75% lateral lacerations with a partial running suture did not produce any advantage with regard to strength compared with no repair or trimming. Several studies of animal tendons have compared the tensile properties of repaired and unrepaired partially lacerated flexor tendons ^5-11,31 . A nearly universal advantage was found in the unrepaired groups, especially in in vivo studies in which the effects of the repair on tendon-healing were considered. Moreover, when tendon ruptures occurred before the animals were killed in in vivo studies, they were more common in the sutured tendons ^5-7,9 . We theorize that the suture itself may be responsible for tendon weakening by introducing a defect into the strong intact part of the tendon and by disturbing the healing process with the presence of a foreign body ^7,8,32 .

The results of the present study must be interpreted in the context that cadaver specimens were used and that healing effects were thus not considered. Seyfer and Bolger ³³ studied tendon-healing after resecting 10 mm of one bundle of fifty-four flexor digitorum profundus tendons in monkeys. After two weeks, the incisional gap was filled by a smooth fibrinous mass, and fibroblasts were invading the region. At twenty-one days, disorganized collagen was partially effacing the injured area. Scanning electron microscopy showed a surface resembling that of the normal adjacent tendon. By three months, the injured surface was grossly identical to the surface of the normal tendon, although the resected area never completely filled in and scanning electron microscopy showed the tendon surface to be rougher than normal. In studies of chickens, at four weeks after a partial (50%) laceration, the site of injury was filled by collagen fibers with longitudinal orientation ³⁴ and a "synovial-like" layer rapidly covered the laceration site ⁹ . In a study of dogs, this layer appeared to be very smooth on scanning electron microscopy ⁷ .

We believe that the most logical way to treat partial lacerations, and one consistent with our findings, was described in a prospective study of fifteen patients with a laceration of the flexor tendon consisting of >50% (mean, 71%; range, 55% to 90%) of its cross-sectional area ¹⁹ . At the time of the exploration, the tendon was left unrepaired if no triggering was observed, but if triggering was present the edges of the laceration were trimmed or =75% of the pulley was resected. If the triggering was still present, a primary repair was performed. The results at a minimum of six months postoperatively were excellent in 93% of the cases and good in 7%.

In summary, our in vitro biomechanical data support the use of trimming for the treatment of partial lacerations of =75% of the cross section of the flexor tendon, especially when triggering is present. The trimming procedure had no effect on immediate tendon strength and avoided both the introduction of a foreign body (suture) and interference with the pulley system.

References

Introduction | Materials and Methods | Results | Discussion | References

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Topics

lacerations ; tendon ; flexor tendon ; running sutures ; in vitro study

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Lionel Erhard, Mark E. Zobitz, Chunfeng Zhao, Peter C. Amadio, Kai-Nan An; Treatment of Partial Lacerations in Flexor Tendons by Trimming A Biomechanical in Vitro Study. The Journal of Bone & Joint Surgery. 2002 Jun;84(6):1006-1012.

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