Partial Flexor Tendon Lacerations Research Articles

Use of a relative motion flexion orthosis after epitendinous zone II flexor tendon repair: A case report

Study designCase report IntroductionRelative motion flexion (RMF) orthoses are emerging as an option for early active motion (EAM) postoperatively. Purpose of the studyTo describe the rationale and implementation of an RMF orthosis to manage a patient after partial zone II epitendinous flexor tendon repairs. MethodsThis case involves a female who sustained partial flexor tendon lacerations to her middle finger in zone II, 60% flexor digitorum superficialis (FDS) and 90% flexor digitorum profundus (FDP). After epitendinous repair she was referred to therapy for EAM with a no orthosis request. The unusual circumstances prompted the therapist, concerned about the risk of tendon rupture to engage in discussion with the surgeon. Following discussion, a decision was made to use an RMF orthosis for controlled EAM to protect the epitendinous zone II FDS and FDP repairs. Outcomes of range of motion (ROM), total active motion (TAM), %TAM, grip, and quickDASH are reported. ResultsNeither the FDP or FDS tendons ruptured, nor were there any joint contractures. “Good” %TAM outcomes were achieved at 12-week postoperatively. Quick DASH scores improved 61 points indicating a clinically meaningful difference of improved function. DiscussionThe lack of a multi-strand core suture repair is unusual in combination with EAM. The positive outcomes reported in this single patient have raised questions about the protective benefit of the RMF orthosis when used with a zone II epitendinous repair of a 90% FDP laceration. Epitendinous repair of a partial (60%) FDS injury, however, is not uncommon and often not repaired at all. ConclusionsIn this single case report the epitendinous repairs of zone II 90% FDP and 60% FDS with digital nerve involvement were successfully managed with an RMF only orthosis. The use of EAM with an epitendinous repair is in conflict to the current surgical and therapy literature.

Flexor Tendon Zone II Repair.

Flexor-tendon injury is a historically challenging problem for orthopaedic surgeons. Much research has been dedicated to finding solutions that offer balance in terms of the strength and ease of the repair versus the rate of complications such as adhesions. The number of core sutures, distance from the tendon edge, and use of an epitendinous stitch have been shown to affect repair strength1-4. A number of configurations have been described for the placement of the suture; however, none has been identified as a clear gold standard5. This article will highlight the preferred tendon repair technique of the senior author (R.J.S.), the Strickland repair with a simple running epitendinous stitch. Relevant anatomy, indications, operative technique, and postoperative management will be discussed. The flexor tendon is typically accessed via extension of the laceration that caused the initial injury. After the neurovascular structures and pulleys are assessed, the tendon is cleaned and prepared for repair. A 3-0 braided nylon suture is utilized for the 4-core strand repair and placed in the Strickland fashion. A 5-0 polypropylene suture is then utilized for the simple running epitendinous stitch. Multiple alternative techniques have been described. These vary in the number of core strands, the repair configuration, the suture caliber, and the use of an epitendinous or other suture. Nonoperative treatment is typically reserved for partial flexor-tendon laceration, as complete tendon discontinuity will not heal and requires surgical intervention. The 4-core strand configuration has been well established to increase the strength of the repair as compared with 2-core strand configurations, while also being easier to accomplish and with less suture burden than other techniques1. The presently described technique has excellent repair strength and can allow for early active range of motion, which is critical to reduce the risk of postoperative adhesions and stiffness. Excellent outcomes have been demonstrated for primary flexor-tendon repair if performed soon after the injury1,2,6,7. Delayed repair may lead to adhesions and poor tendon healing8. Early postoperative rehabilitation is vital for success9. There are advocates for either active or passive protocols10-12. The protocol at our institution is to begin early active place-and-hold therapy at 3 to 5 days postoperatively, which has been shown in the literature to provide improved finger motion as compared with passive-motion therapy13-16.Important Tips:: The proximal end of the tendon may need to be retrieved via a separate incision if it is not accessible through the flexor-tendon sheath.The proximal end of the tendon may be held in place with a 25-gauge needle in order to best place sutures into both ends of the tendon.The epitendinous suture is run around the back wall before the core sutures are tied down, in order to prevent the tendon and repair from bunching up and becoming overly bulky.The entire A4 pulley and the distal A2 pulley can be divided for exposure if necessary.Up to 2 cm of the flexor-tendon sheath can be divided.If there are concomitant digital nerve injuries, repair these after the tendon, in order to avoid damaging the more delicate nerve repair while manipulating the tendon for repair.The most common major complications following tendon repair are formation of adhesions and rerupture. Acronyms and Abbreviations:: FDS = flexor digitorum superficialisFDP = flexor digitorum profundusMCP = metacarpophalangealPIP = proximal interphalangealDIP = distal interphalangeal.

Comparison of Magnetic Resonance Imaging and Ultrasound Evaluations of Zone II Partial Flexor Tendon Lacerations: A Cadaveric Study.

Surgical intervention for zone II high-grade partial flexor tendon lacerations is often required when more than half of the tendon width is torn. Reliable noninvasive tests are critical for optimizing clinical decision making. Our team previously investigated the use of ultrasound (US) for identification of high-grade zone II flexor digitorum profundus lacerations. In this study, we compared magnetic resonance imaging (MRI) to US for the evaluation of high-grade partial flexor tendon lacerations in cadaveric specimens. Dissection of 32 digits in 8 fresh-frozen upper extremity cadaveric specimens was performed. The flexor digitorum profundus tendons were randomized into 3 groups: intact, low-grade laceration, and high-grade laceration. A dynamic US examination was performed by a blinded musculoskeletal radiologist. The same specimens underwent hand coil MRI, which was read by the same blinded radiologist. Magnetic resonance imaging test performance metrics were calculated and compared to those computed for the US evaluation. For US evaluation of high-grade lacerations, the sensitivity and specificity were 0.5 and 1.0, with positive likelihood ratio (LR+) and negative likelihood ratio (LR-) values of ∞ and 0.50, respectively. The sensitivity and specificity for MRI evaluation were 0.2 and 1.0, with LR+ and LR- values of ∞ and 0.80. Both US and MRI are adequate at determining the presence of a high-grade laceration. Magnetic resonance imaging was more specific than US in identification of high-grade partial flexor tendon lacerations. Although less specific, US is a reasonable and less-expensive alternative to MRI when evaluating for clinically significant high-grade partial flexor tendon lacerations.

Increasing the level of cytoskeletal protein Flightless I reduces adhesion formation in a murine digital flexor tendon model

BackgroundSurgical repair of tendons is common, but function is often limited due to the formation of flexor tendon adhesions which reduce the mobility and use of the affected digit and hand. The severity of adhesion formation is dependent on numerous cellular processes many of which involve the actin cytoskeleton. Flightless I (Flii) is a highly conserved cytoskeletal protein, which has previously been identified as a potential target for improved healing of tendon injuries. Using human in vitro cell studies in conjunction with a murine model of partial laceration of the digital flexor tendon, we investigated the effect of modulating Flii levels on tenocyte function and formation of adhesions.MethodsHuman tenocyte proliferation and migration was determined using WST-1 and scratch wound assays following Flii knockdown by siRNA in vitro. Additionally, mice with normal and increased levels of Flii were subjected to a partial laceration of the digital flexor tendon in conjunction with a full tenotomy to immobilise the paw. Resulting adhesions were assessed using histology and immunohistochemistry for collagen I, III, TGF-β1and -β3ResultsFlii knockdown significantly reduced human tenocyte proliferation and migration in vitro. Increasing the expression of Flii significantly reduced digital tendon adhesion formation in vivo which was confirmed through significantly smaller adhesion scores based on collagen fibre orientation, thickness, proximity to other fibres and crimping. Reduced adhesion formation was accompanied with significantly decreased deposition of type I collagen and increased expression of TGF-β1 in vivo.ConclusionsThese findings suggest that increasing the level of Flii in an injured tendon may be beneficial for decreasing tendon adhesion formation.

The Management of Partial Zone II Intrasynovial Flexor Tendon Lacerations: A Literature Review of Biomechanics, Clinical Outcomes, and Complications

Sir: We read with great interest the recent article entitled “The Management of Partial Zone II Intrasynovial Flexor Tendon Lacerations: A Literature Review of Biomechanics, Clinical Outcomes, and Complications,” by Lineberry et al.,1 published in Plastic and Reconstructive Surgery. We credit the authors for their extensive work in evaluating a large number of studies of variable methodologies, in an attempt to provide clarity on management of partial flexor tendon injuries. We agree with the authors’ conclusions that all suspected partial tendon lacerations should be explored surgically with direct visualization of the flexor tendon. However, we believe the authors are drawing conclusions from outdated research. Only four of 24 studies (16.6 percent) in this review were published after 2008. Over the past decade, there has been a dramatic evolution in flexor tendon management regarding suture material, tenorrhaphy techniques, and greater excursion on the repaired tendon postoperatively. Subsequently, we question the authors’ ability to make recommendations based on these studies, in particular, the grade (percent) of partial tendon laceration necessitating surgical repair and the type of tenorrhaphy when surgical intervention is required. Early active motion following flexor tendon repair encourages intrinsic healing and decreases adhesion formation.2 This postoperative therapy requires a strong, gap-free tenorrhaphy resisting forces up to 30 to 50 N.3,4 Gap formation within the repair is detrimental, as this correlates clinically to adhesion formation and rupture,5 especially for intrasynovial tendon injuries. Our department struggles to comprehend how a simple epitendinous-only repair in a partial flexor tendon laceration greater than 80 percent of the total tendon surface area can resist 2-mm gap formation during forces exerted during early active motion. Consequently, we conducted our own biomechanical assessment of 90 fresh porcine flexor digitorum profundus tendons. Partial lacerations of 70, 80, and 90 percent of the total tendon surface area were created with digital calipers. Thirty tendons in each partial laceration group were divided randomly into (1) no repair, (2) running epitendinous repair with 6-0 Prolene (Ethicon, Inc., Edinburgh, United Kingdom), and (3) four-strand Adelaide technique core repair with 3-0 Ethibond (Ethicon) with an epitendinous suture. Our findings support the authors’ conclusions that nonrepaired partial tendon lacerations of 90 percent have enough residual strength to resist rupture during early active motion. However, the forces creating 2-mm gap formation in partial lacerations of 80 percent (4.9 N) and 90 percent (3.8 N) are well below the requirements for early active motion. Tenorrhaphy with epitendinous sutures only increased resistance to the gapping to 25.1 N in the 80 percent and 15.9 N in the 90 percent partial laceration group. The addition of core suture significantly increased the resistance to 2-mm gap formation in both groups (p < 0.05). Results are displayed in Figure 1.Fig. 1.: A comparison of resistance to 2-mm gap formation between 70, 80, and 90 percent partial flexor digitorum profundus laceration.Up-to-date research on partial flexor tendon lacerations, as evident in this review, is rare. We have demonstrated that an epitendinous-only repair of partial tendon laceration greater than 80 percent does not provide adequate strength to prevent 2-mm gap formation during early active motion. We disagree with the authors’ conclusions and believe that partial tendon laceration greater than 80 percent should be managed similarly to a complete tendon laceration with both a core suture and an epitendinous suture. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Conor M. Sugrue, M.R.C.S., B.C.H., B.A.O.George Rahmani, M.R.C.S., B.C.H., B.A.O.Department of Plastic and Reconstructive SurgeryGalway University HospitalGalway, IrelandGSD CriúGalway, Ireland Jack L. Kelly, F.R.C.S.(Plast.)Department of Plastic and Reconstructive SurgeryGalway University HospitalGalway, Ireland

Ultrasonographic Evaluation of Zone II Partial Flexor Tendon Lacerations of the Fingers: A Cadaveric Study

Accurate assessment of zone II partial flexor tendon lacerations in the finger is clinically important. Surgical repair is recommended for lacerations of greater than 50% to 60%. Our goal was to evaluate ultrasonographic test characteristics and accuracy in identifying partial flexor tendon lacerations in a cadaveric model. From fresh-frozen above-elbow human cadaveric specimens, 32 flexor digitorum profundus tendons were randomly selected to remain intact or receive low- or high-grade lacerations involving 10% to 40% and 60% to 90% of the radioulnar width within Verdan Zone II, respectively. Static and dynamic ultrasonography using a linear array 14-MHz transducer was performed by a blinded musculoskeletal radiologist. Sensitivities, specificities, and other standard test performance metrics were calculated. Actual and measured percentages of tendon laceration were compared by the paired t test. After randomization, 24 tendons were lacerated (12 low- and 12 high-grade), whereas 8 remained intact. The sensitivity and specificity in detecting the presence versus absence of a partial laceration were 0.54 and 0.75, respectively, with positive and negative likelihood ratio values of 2.17 and 0.61. For low-grade lacerations, the sensitivity and specificity were 0.25 and 0.85, compared to 0.83 and 0.85 for high-grade lacerations. Ultrasonography underestimated the percentage of tendon involvement by a mean of 18.1% for the study population as a whole (95% confidence interval, 9.0% to 27.2%; P < .001) but accurately determined the extent for correctly diagnosed high-grade lacerations (-6.7%; 95% confidence interval, -18.7% to 5.2%; P = .22). Ultrasonography was useful in identifying and characterizing clinically relevant high-grade zone II partial flexor digitorum profundus lacerations in a cadaveric model.

Accuracy of Visual Estimates of Partial Flexor Tendon Lacerations

To determine whether hand surgeons could accurately and consistently estimate the size of partial flexor tendon lacerations. Thirty-two partial flexor tendon lacerations were made in the flexor digitorum profundus tendons of a fresh-frozen cadaveric hand. Four hand surgeons and 5residents estimated the size of the lacerations. Estimates were repeated 3 days later. Magnified images of the laceration cross-section were used to calculate the true size of each laceration. Inter- and intrarater reliability were calculated using the intraclass correlation coefficient. Accuracy was measured with the mean bias error and the mean absolute error. Interrater and intrarater reliabilities were both high. There was a high level of consistency for both surgeons and residents. In terms of accuracy, there was a 3% bias toward underestimation. The mean absolute error was 11%. There was no statistically significant difference between the accuracy of attending hand surgeons and that of residents. Participants were less accurate when estimating lacerations close to a 60% laceration threshold for surgical repair (lacerations in the 50%-70% range). For lacerations within this range, an incorrect management decision would have been made 17% of the time, compared with 7% of the time for lacerations outside that range. The accuracy and reliability of surgeon estimates of partial flexor tendon laceration size were high for surgeons and residents. Accuracy was lower for lacerations close to the threshold for repair. Visual estimation is acceptable for evaluating partial flexor tendon lacerations, but it may be less reliable for lacerations near the threshold for repair. Therefore, surgeons should be cautious when deciding whether or not to repair partial lacerations in the borderline range.

Effect of triggering and entrapment on tendon gliding properties following digital flexor tendon laceration: in vitro study on turkey tendon

The optimal management of partial flexor tendon laceration is controversial and remains a clinical challenge. Abnormal tendon gliding (triggering and entrapment) was assessed at the A2 pulley in 40 turkey tendons in three groups: intact, partially divided (palmar or lateral), and trimmed. Testing was of gliding resistance and friction coefficient at 30° and 70° of flexion, loaded with 2 and 4 N. We observed for triggering and entrapment. The changes in gliding properties were compared and analysed using Wilcoxon matched pair testing. A significant difference was found in the change in gliding properties of intact to lacerated and lacerated to trimmed tendons and between tendons that glided normally compared with those exhibiting triggering or entrapment. This suggests that palmar and lateral lacerations which, through clinical examination and visualization, are found to glide normally should be treated with early mobilization. However, partial lacerations that exhibit triggering or entrapment should be trimmed.

COMPARISON OF THREE DIFFERENT PERIPHERAL SUTURING TECHNIQUES FOR PARTIAL FLEXOR TENDON LACERATIONS: A CONTROLLED IN-VITRO BIOMECHANICAL STUDY

Surgical repair is advocated for partial flexor tendon lacerations deeper than 70%. We compared gliding resistance with three different peripheral repairs in partial flexor tendon lacerations. Thirty flexor tendons and A2 pulleys were harvested from turkey toes. Gliding resistance was measured for all intact tendons. The tendons were then lacerated to 50% and repaired with a modified Kessler core suture and either a Silfverskiold or Halsted repair or a simple running suture and gliding resistance was measured. Compared to the intact tendon, the increase in gliding resistance after surgical repair was 100% with the Halsted repair, 80% with the Silfverskiold repair and 60% with a running suture (p = 0.05). In conclusion, a simple running suture caused less resistance to gliding compared to the other techniques when repairing partial flexor tendon lacerations and we recommend its use when surgical repair is needed.

A Biomechanical Assessment of Repair Versus Nonrepair of Sheep Flexor Tendons Lacerated to 75 Percent

The benefit of repairing a 75% partial flexor tendon laceration remains controversial. The purpose of this study was to assess the degree of gap formation with and without repair when the 75% lacerated tendon is subjected to cyclic loading. Repair with only a peripheral suture was compared to that using a core and peripheral repair technique. Sixteen deep flexor tendons from sheep hind limbs were lacerated to 75% of the tendon diameter. The cut tendons were loaded for 100 cycles from 3 N up to 30 N and then back to 3 N, at a rate of 0.2 Hz. Gap formation was measured at 0 and 100 cycles. Tendons were then randomized into 2 repair groups of 8 each: group 1 was repaired with only a simple, running peripheral suture (6-0 polypropylene monofilament), whereas group 2 was repaired with a modified Kessler core suture (4-0 silicone-coated braided polyester) plus a peripheral suture (6-0 polypropylene monofilament). Repaired tendons were tested for 500 cycles, and the gap was measured at 0, 100, and 500 cycles. After cycling, gap was measured at 100 N load, and the peak loads were determined on static failure testing. The 75% partially lacerated tendons had >2 mm gap at 100 cycles. This gap was significantly reduced by peripheral or peripheral plus core repairs (p < .001). There was no difference in gap formation between tendons with peripheral repair only and those with both peripheral and core repairs. Gap formation in repaired tendons remained <or=1 mm at 500 cycles. After cycling, neither gap formation at 100 N load or the peak loads on failure testing differed between the 2 repair groups. There is a large gap when an unrepaired 75% partial laceration is cyclically loaded. This gap is significantly reduced with a peripheral repair whether or not a core suture is used.

Biomechanical Analysis of Partial Flexor Tendon Lacerations in Zone II of Human Cadavers

Biomechanical Analysis of Partial Flexor Tendon Lacerations in Zone II of Human Cadavers

Biomechanical Analysis of Partial Flexor Tendon Lacerations in Zone II of Human Cadavers

The aims of this study were to examine nonrepaired 90% partial lacerations of human cadaver flexor digitorum profundus (FDP) tendon after simulated active motion, and to assess the residual ultimate tensile strength. Partial, transverse zone II flexor tendon lacerations were made in the volar 90% of the tendon substance in 10 FDP tendons from 5 fresh-frozen human cadaver hands. The tendons were cycled in the curvilinear fashion described by Greenwald 500 times to a tension 25% greater than the maximum in vivo active FDP flexion force measured by Schuind and colleagues. The tendons were then loaded to failure using the same curvilinear model. No tendons ruptured during cycling. Triggering occurred in 3 tendons. All 3 began triggering early in the cycling process, and continued to trigger throughout the remainder of the 500 cycles. The observed triggering mechanics in each case involved the interaction of the proximal face of the lacerated tendon with Camper's chiasm and the pulley edges during extension. The load to failure value of the 90% partially lacerated tendons averaged 141.7 +/- 13 N (mean +/- standard deviation). Tendon failure occurred by delamination of the intact collagen fibers from the distal, discontinuous 90% of the tendon. Cadaveric transverse zone II partial flexor tendon lacerations have residual tensile strength greater than the force required for protected active mobilization.

Trigger finger after partial flexor tendon laceration: two case reports and review of the literature

Trigger finger after partial flexor tendon laceration: two case reports and review of the literature

Conservative management of zone II partial flexor tendon lacerations greater than half the width of the tendon.

Over a 5-year-period 15 patients with zone II partial flexor tendon lacerations that were larger than half the width of the tendon were treated conservatively without tendon suturing. Surgical exploration was done with a digital block and the flexor tendons were observed as the patient fully extended and flexed the finger. If present, the cause of triggering was determined and eliminated by trimming any beveled tendon edge, resection of the involved pulleys, and repair of the flexor sheath. Early protected mobilization was started the first day after injury using a dorsal splint. At 4 weeks after injury the splint was removed and exercises against resistance were started. None of the patients had triggering or rupture of the flexor tendons. Using the Strickland-Glogovac evaluation method, results were excellent in 93% of cases and good in the remaining 7%. It was concluded that conservative management of zone II partial flexor tendon lacerations larger than half the width of the tendon is safe as long as certain guidelines regarding the prevention of triggering and protected mobilization are applied.

Partial lacerations of human digital flexor tendons: A biomechanical analysis

The biomechanical properties of human flexor tendons with partial lacerations have not been previously studied. To determine the loss of tensile strength with varying degrees of partial laceration, tensile tests were performed on 2 matched groups of human cadaver flexor tendons: One group had 50% while the other had 75% transverse volar lacerations of the anteroposterior diameter. The mean failure load of the 50%-lacerated tendons was 93% higher than that of the 75%-lacerated tendons. The forces tolerated by the lacerated tendons before failure were also compared to those measured in vivo during physiologic loading. The breaking loads of both 50%- and 75%-lacerated tendons far exceeded the in vivo forces measured in human flexor tendons during unresisted active finger movement (up to 34 N). Further, the breaking loads of 50% lacerations was higher than the in vivo forces during resisted active finger movement (up to 117 N). This study demonstrates that the threshold load levels to rupture of 50% and 75% lacerations are higher than physiologic load levels measured during active motion, suggesting that partial flexor tendon lacerations of up to 75% can withstand in vivo forces associated with active unresisted mobilization of the digital flexor tendon.

New technique for producing uniform partial lacerations of tendons.

Previous experimental studies of partial flexor tendon lacerations have used tendons cut by hand with magnification and a scalpel. When we biomechanically tested chicken flexor tendons lacerated by hand through 75% of their cross-sectional area, the tensile strength of the residual tendons varied substantially among specimens from different chickens as well as between digit matched pairs of tendons from the same animal. A device was designed that uses standard scalpel blades to create a uniform tendon laceration by leaving a constant area of tendon intact regardless of original tendon size or shape. With the instrument we have called the "tenotome," a second group of chicken flexor tendons were lacerated through 75% of their cross-sectional area. Biomechanical testing of the tendons cut with the tenotome showed significantly less variation when compared with the tendons cut by hand. Use of the tenotome permits the establishment of a more uniform model for partial flexor tendon injuries, and potentially decreases the number of specimens needed to demonstrate statistical significance.

Treatment of partial flexor tendon lacerations: The effect of tenorrhaphy and early protected mobilization: Bishop AT, Cooney WP, Wood MB J Trauma 26:301–312 Apr 1986

Treatment of partial flexor tendon lacerations: The effect of tenorrhaphy and early protected mobilization: Bishop AT, Cooney WP, Wood MB J Trauma 26:301–312 Apr 1986

Treatment of partial flexor tendon lacerations: the effect of tenorrhaphy and early protected mobilization.

Controversy exists in the literature regarding the proper treatment of partial flexor tendon lacerations. In this study, a novel nonweightbearing canine model was developed in order to closely approximate human flexor tendon conditions. The relative effects of immobilization, early protected mobilization, tenorrhaphy, and no repair of flexor tendon healing were evaluated by paired comparisons of four experimental groups (24 animals). Parameters evaluated after a 35-day healing period included tendon excursion, breaking strength, energy absorption, and stiffness. The contralateral digit-matched profundus tendon served as a normal control. Eight additional animals were studied histologically and by scanning electron microscopy. Data analysis revealed statistically significant adverse effects on breaking strength, stiffness, and energy absorption when repaired by modified Kessler technique. Early motion improved excursion and stiffness significantly, and resulted in more nearly normal tendon morphology than immobilized tendons. Thus, we conclude that partial flexor tendon lacerations of 60% cross-sectional area are optimally treated without tenorrhaphy and with early mobilization.

Three complications of untreated partial laceration of flexor tendon—Entrapment, rupture, and triggering.

Three patients developed complications as a result of unrepaired and untreated partial laceration of flexor tendons. In one, narrowly based flaps of the tendons became entrapped in a rent in the flexor tendon sheath. In a second, delayed rupture of the flexor pollicis longus occurred when force was applied to the tendon 2 weeks after the injury. In the third, triggering of the thumb occurred 2 months after a laceration which passed through the annular pulley into the tendon.

Three complications of untreated partial laceration of flexor tendon—Entrapment, rupture, and triggering

Three patients developed complications as a result of unrepaired and untreated partial laceration of flexor tendons. In one, narrowly based flaps of the tendons became entrapped in a rent in the flexor tendon sheath. In a second, delayed rupture of the flexor pollicis longus occurred when force was applied to the tendon 2 weeks after the injury. In the third, triggering of the thumb occurred 2 months after a laceration which passed through the annular pulley into the tendon.