The gliding force and work of flexion in the early days after primary repair of lacerated flexor tendons: an experimental study

The Effect of Flexor Digitorum Profundus Repair Position Relative to Camper Chiasm on Tendon Biomechanics

PURPOSE

The purpose of this study was to investigate the impact of repairing a zone II flexor digitorum profundus (FDP) laceration anatomically versus extra-anatomically on tendon loads and work of flexion (WOF).

METHODS

Twenty digits from 5 cadaveric specimens were tested using an in vitro active finger motion simulator under 2 FDP tendon repair conditions: anatomic and extra-anatomic. Tensile loads in FDP and flexor digitorum superficialis (FDS), WOF, and total active finger range of motion (ROM) were measured using in-line load cells and electromagnetic tracking, respectively.

RESULTS

The anatomic repairs had no effect on tendon loads or WOF for either FDP or FDS. The extra-anatomic repairs increased FDP loads by 32% and decreased FDS loads by 9% compared with those in the intact condition. This pattern was similar for WOF following extra-anatomic repairs, which increased FDP WOF by 31% and decreased FDS WOF by 18%. Comparing the 2 repairs, FDP loads and WOF were 25% and 22% greater, respectively, with extra-anatomic repairs compared with anatomic repairs, with no significant change in FDS. Total active ROM was not affected by either repair.

CONCLUSIONS

In this in vitro cadaveric model, extra-anatomic repairs of FDP increased tendon loads and WOF compared with anatomic repairs.

CLINICAL RELEVANCE

On the basis of this study, reconstitution of the anatomic relationship of FDP and FDS at the Camper chiasm during the repair of zone II flexor tendon lacerations is recommended.

Biomechanical Properties of a Novel Mesh Suture in a Cadaveric Flexor Tendon Repair Model

PURPOSE

Conventional suture repairs, when stressed, fail by suture rupture, knot slippage, or suture pull-through, when the suture cuts through the intervening tissue. The purpose of this study was to compare the biomechanical properties of flexor tendon repairs using a novel mesh suture with traditional suture repairs.

METHODS

Sixty human cadaveric flexor digitorum profundus tendons were harvested and assigned to 1 of 3 suture repair groups: 3-0 and 4-0 braided poly-blend suture or 1-mm diameter mesh suture. All tendons were repaired using a 4-strand core cruciate suture configuration. Each tendon repair underwent linear loading or cyclic loading until failure. Outcome measures included yield strength, ultimate strength, the number of cycles and load required to achieve 1-mm and 2-mm gap formation, and failure.

RESULTS

Mesh suture repairs had significantly higher yield and ultimate force values when compared with 3-0 and 4-0 braided poly-blend suture repairs under linear testing. The average force required to produce repair gaps was significantly higher in mesh suture repairs than in conventional suture. Mesh suture repairs endured a significantly greater number of cycles and force applied before failure compared with both 3-0 and 4-0 conventional suture.

CONCLUSIONS

This ex vivo biomechanical study of flexor tendon repairs using a novel mesh suture reveals significant increases in average yield strength, ultimate strength, and average force required for gap formation and repair failure with mesh suture repairs compared with conventional sutures.

CLINICAL RELEVANCE

Mesh suture-based flexor tendon repairs could lead to improved healing at earlier time points. The findings could allow for earlier mobilization, decreased adhesion formation, and lower rupture rates after flexor tendon repairs.

Results of 4-strand modified Kessler core suture and epitendinous interlocking suture followed by modified Kleinert protocol for flexor tendon repairs in Zone 2

Objective

There has been no consensus in literature for the ideal flexor tendon repair technique. The results of zone 2 flexor tendon lacerations repaired primarily by 4 strand Modified Kessler core suture and epitendinous interlocking suture technique followed by Modified Kleinert protocol were investigated.

Methods

128 fingers of 89 patients who had flexor tendon laceration in zone 2 built the working group. Functional outcomes were evaluated using the Strickland formula. A statistical analysis was made between Strickland scores and some parameters such as age, gender, follow-up time, co-existing injury existence, repair time, single or multiple finger injury, tendon rupture and the effect of FDS injury and repair.

Results

Excellent, good, fair, poor results were obtained from 71 (55.5%), 46 (35.9%), 8 (6.3%), 3 (2.3%) fingers, respectively. Time of the repair has a significant effect on the strickland scores. Surgery performed within the first 24 hours following the injury gave better results. 3 fingers (2.3%) had tendon ruptures. Existence of ruptures affected the results significantly. Co-existing injuries were found that they did not have any effect on the results. In the fingers in which both FDP and FDS tendons were lacerated, no significant relationship was found between only FDP repair, both FDP and FDS repair and single FDS slip repair. Additionally no significant relationships between follow-up time, gender, single or multiple finger injury and Strickland scores were observed. 13 fingers (10.1%) had PIP joint contracture above 20°.

Conclusion

The low rupture rate (2.3%) and 91.4% ‘good’ and ‘excellent’ scoring rates in our series support the idea that modified Kessler 4-strand core suture and epitendinous interlocking suture repair combined with modified Kleinert protocol gives satisfactory results. Repair time is one of the most important factors affecting the functional results and surgery should not be delayed if there is an experienced surgeon available.

Level of evidence

Level IV, therapeutic study.

A Novel Adhesion Index for Verifying the Extent of Adhesion for the Extensor Digitorum Communis in Patients with Metacarpal Fractures

This study aims to determine if the relative displacement between the extensor digitorum communis (EDC) tendon and its surrounding tissues can be used as an adhesion index (AI) for assessing adhesion in metacarpal fractures by comparing two clinical measures, namely single-digit-force and extensor lag (i.e., the difference between passive extension and full active extension). The Fisher–Tippett block-matching method and a Kalman-filter algorithm were used to determine the relative displacements in 39 healthy subjects and 8 patients with metacarpal fractures. A goniometer was used to measure the extensor lag, and a force sensor was used to measure the single-digit-force. Measurements were obtained twice for each patient to evaluate the performance of the AI in assessing the progress of rehabilitation. The Pearson correlation coefficient was calculated to quantify the various correlations between the AI, extensor lag, and single-digit-force. The results showed strong correlations between the AI and the extensor lag, the AI and the single-digit-force, and the extensor lag and the single-digit-force (r = 0.718, −0.849, and −0.741; P = 0.002, P < 0.001, and P = 0.001, respectively). The AI in the patients gradually decreased after continuous rehabilitation, but remained higher than that of healthy participants.

The effect of barbed suture tendon repair on work of flexion

PURPOSE

To compare the work of flexion, ultimate strength, and gap resistance of a conventional 4-strand tendon repair to a knotless barbed-suture 4-strand tendon repair.

METHODS

Tendon repairs were performed on 16 cadaver flexor digitorum profundus tendons using either a 4-strand double Kessler repair or a similar but knotless 4-strand repair with a unidirectional barbed suture. Work of flexion, gap resistance during cyclical loading, and ultimate strength of both techniques were determined and their means compared.

RESULTS

There was no difference in mean maximum load and gap formation between the 2 techniques. Work of flexion was higher for the barbed-suture repair group compared with the traditional repair group (39 N·mm vs 31 N·mm).

CONCLUSIONS

The higher work of flexion in the barbed-suture group suggests that barbed suture may negatively affect tendon gliding within the flexor tendon sheath.

CLINICAL RELEVANCE

Knotless barbed-suture tendon repair leads to increased work of flexion compared with traditional flexor tendon repairs, which may result in an increased rupture incidence.

Biomechanical analysis of knotless flexor tendon repair using large-diameter unidirection barbed suture

PURPOSE

In traditional flexor tendon repairs, suture knots can be sites of weakness, impair tendon healing, stimulate an inflammatory response, and increase the bulk of the tendon repair. Because of this, there has been an increased interest in knotless flexor tendon repair using barbed suture. Since knots are not required, it may be possible to increase the strength of the tendon repair by using a large-diameter barbed suture. The purpose of this study was to biomechanically compare a traditional four-strand tendon repair using 3-0 braided polyester with a similar knotless four-strand tendon repair using 0 unidirectional barbed suture.

METHODS

Twenty-two matched cadaveric flexor digitorum profundus tendons were lacerated and assigned to repair by a four-strand modified Kirchmayr-Kessler technique using 3-0 braided polyester (n = 11) or knotless four-strand modified Kirchmayr-Kessler repair using 0 unidirectional barbed suture (n = 11). Repaired tendons were linearly distracted to failure at 20 mm/min after 1 N preload. Maximum load and load at 2-mm gap formation were recorded. Maximum load and load at 2-mm gap formation were compared with the Student's t test, and p values ≤ 0.05 were considered significant.

RESULTS

The mean maximum load of the barbed, knotless suture repair was higher than that of the traditional repair (52 vs. 42 N). There was no difference between the two groups in the mean load required to produce a 2-mm gap.

CONCLUSIONS

The four-strand knotless tendon repairs using a large-diameter unidirectional barbed suture were stronger than the traditional four-strand repairs using 3-0 braided polyester, and had similar 2-mm gap resistance.

Clinical use of a combined grasping and locking core suture technique for flexor tendon repair in zone II

Previous authors have used either a grasping or a locking technique for flexor tendon repair in zone II. A combined (grasping and locking) 10-strand repair was used by the author in 22 adults (n = 28 fingers) with lacerations of both flexor tendons in zone II. The combined repair is known to be strong (mean tensile strength of 164 N), and the technique was used in selected cases who were thought to be at higher risk of rupture either because of excessive digital oedema (in early tendon repairs) or because of tendon retraction (in late primary tendon repairs). The 10-strand repair was bulky and, hence, only the profundus tendon was repaired; and "venting" of the pulley system was done proximal to the repair site as recommended by other authors. Supervised early active mobilisation was done immediately after the operation. At final follow-up, the outcome was calculated using the original Strickland-Glogovac grading system. There were no ruptures and the final outcome was considered excellent in 19 patients (n = 25 fingers), good in two patients (n = 2 fingers), and fair in the remaining patient (n = 1 finger). It was concluded that the bulky 10-strand repair may be used for zone II finger flexor tendon lacerations as long as a profundus-(?) only repair and "venting" of the pulley system are performed.

Tendon healing, edema, and resistance to flexor tendon gliding: clinical implications

Early flexor tendon healing is characterized by peak cellular apoptosis of both inflammatory and tendon cells in the first week, followed by progressively greater tenocyte proliferation in the second and third weeks. Tenocyte apoptosis is a predominant event, but proliferation of tenocytes is minimal in the middle and late healing periods. Edematous subcutaneous tissues, edema of the tendon, the intact annular pulleys, and extensor tendons all greatly contribute to the resistance. Careful consideration of the contributing factors and dynamics offers insight into strategies to reduce repair rupture and maximize tendon gliding through surgery and postoperative motion protocols.

Managing the injured tendon: current concepts

Despite advances in understanding of the mechanical aspects of tendon management with improved suture technique and early stress application with postoperative therapy, clinical results remain inconsistent after repair, especially within the synovial regions. Complementary research to enhance the intrinsic pathway of healing, suppress the extrinsic pathway of healing, and manipulate frictional resistance to tendon gliding is now the focus of current basic science research on tendons. In the future, application of these new biologic therapies may increase the "safety zone" (or tolerance for load and excursion without dysfunctional gapping) as therapists apply stress to healing tendons and may alter future rehabilitation protocols by allowing greater angles of motion (and thus tendon excursion), increased external load, and decreased time in protective orthoses (splints). However, at this time, the stronger repair techniques and the application of controlled stress remain the best and most well-supported intervention after tendon injury and repair in the recovery of functional tendon excursion and joint range of motion. The hand therapist's role in this process remains a critical component contributing to satisfactory outcomes.

Tendon adhesion measured by a video-assisted gliding test in a chicken model

We developed a video-assisted gliding test to evaluate the gliding force and the flexion angle with unrestricted joint motion. Tendon adhesion was induced in a chicken model of flexor digitorum profundus (FDP) injury at the annular pulley region of the long toe. The chicken feet were harvested immediately after injury, and 2 weeks and 6 weeks after injury. During the gliding test, the injured FDP was pulled for 15 mm then returned to its initial position. The test was recorded using a video camera and registered to the gliding test mechanical data. The maximum flexion angle and gliding resistance were calculated. The maximum flexion angle was significantly decreased from 78 (SD 10) in controls to 42 (SD 22) in tendons with injury, while gliding resistance was significantly increased in week 2 (0.06, SD 0.05) and week 6 (0.07, SD 0.01) after injury.

Strength of tendon repair decreases in the presence of an intact A2 pulley: biomechanical study in a chicken model

PURPOSE

Pulleys have an important role in digital flexion, but little is known about how the strength of a tendon repair is affected by a major pulley. We evaluated the difference in strengths of flexor tendon repairs in the pulley area when the pulley was intact or divided in a chicken tendon injury model.

METHODS

In each of 100 long toes of 50 Leghorn chickens, a complete, transverse laceration of the flexor digitorum profundus tendon was made in the region of the A2 pulley and was repaired surgically. The A2 pulley was preserved or was completely divided longitudinally. The toes were harvested by disarticulating through the knee joint, and placed at full extension, at 20 degrees , 40 degrees , or 60 degrees of distal interphalangeal (DIP) joint flexion, and at 40 degrees , 80 degrees , or 120 degrees of combined DIP and proximal interphangeal (PIP) joint flexion, and tendon repairs were loaded to failure in a materials testing machine. The force required for ultimate failure was statistically compared for each group.

RESULTS

Ultimate tendon repair strength was significantly lower in toes with the A2 pulley intact than in those with the pulley vented when the toes were placed at full extension and at all tested degrees of DIP and PIP joint flexion, except at the most marked flexion. After A2 pulley division, tendon repair strength was 30% to 60% higher than flexed toes with the pulley intact. With an intact pulley, the tendon repair strength in the flexed toes was significantly lower than that in the fully extended toes, but after A2 pulley division, the strength was similar at all toe positions except at the most marked flexion.

CONCLUSIONS

Chicken tendon repairs are substantially weaker when the A2 pulley is intact than when the pulley is completely divided. Loading of the tendon repair against an intact major pulley adversely affects repair strength. These findings suggest that tendon repair is less likely to fail when the A2 pulley is divided than when the pulley is intact; pulley venting may decrease the likelihood of repair ruptures.

Flexor tendon repair in zone 2 using a six-strand 'figure of eight' suture

The tensile strength of three different flexor tendon repair techniques were tested in vitro: the modified Kessler technique (a two-strand repair), two 'figure of eight' sutures (a four-strand repair) and three 'figure of eight' sutures (a six-strand repair). The mean breaking forces for the three techniques were 48.0 N, 73.1 N and 93.3 N, respectively, and the differences were highly significant (p < 0.0001). In a prospective clinical study, a total of 45 patients (50 fingers) with clean-cut complete lacerations of both flexor tendons in zone 2 were included. The protocol used the three 'figure of eight' suture techniques for (profundus only) tendon repair, 'venting' of the pulleys, and post-operative immediate active range of motion that ensured full active extension of the proximal interphalangeal joint. One repair (2%) ruptured. In the remaining 49 repairs, the result was considered excellent in 39 (78%) and good in 10 (20%) using the Strickland and Glogovac grading system.