Bundle pattern of the flexor digitorum profundus tendon in zone II of the hand: a quantitative assessment of the size of a laceration

Secondary Procedures following Flexor Tendon Reconstruction

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand the indications and management options for secondary flexor tendon reconstruction, including tenolysis, tendon grafting, and tendon transfers. 2. Understand the reconstructive options for pulley reconstruction. 3. Understand the options for management of isolated flexor digitorum profundus injuries.

SUMMARY

Despite current advances in flexor tendon repair, complications can still occur following surgery. This article presents the spectrum of treatment options for secondary flexor tendon reconstruction ranging from tenolysis to one- and two-stage tendon grafting, and tendon transfers. In addition, an overview of pulley reconstruction and the treatment of isolated flexor digitorum profundus injuries are discussed. A management algorithm for secondary flexor tendon reconstruction is provided.

The suture loop holding capacity of flexor digitorum profundus tendon within and outside the digital tendon sheath

In a previous study we found that the strength of a Kessler core suture in the flexor tendon was greater in flexor zone 2 than in zone 3. To further investigate the material properties of the flexor tendon without the influence of a locking suture configuration, we measured the ultimate strength of a simple loop suture in the flexor digitorum profundus tendon in zones 1, 2, and 3. Eight cadaver flexor digitorum profundus tendons were tested in 10 mm increments with a 3-0 polyester suture loop pull-out test in the mid-substance of the tendon. The mean strength in zones 1 and 2 (26.7 N, SD 5.6) was significantly higher than the mean strength in zone 3 (17.7 N, SD 5.4). We conclude that the difference is owing to variations of the structure of the flexor tendon in different sections of the tendon, as the suture configuration was a simple loop without a locking or grasping component.

Tendon reconstruction with adjacent finger hand tendon

Whether it is a primary or a delayed flexor digitorum profundus (FDP) repair, no general consent has been found, and no perfect treatment has been imposed. The authors utilize 2 new techniques for FDP reconstruction that allow immediate postoperative mobilization and excellent functional outcome. Harvesting of the donor hemi tendon, both FDP and flexor digitorum superficialis, is the closest match in terms of muscle agonism and excursion, and does not result in an imbalance of forces across the donor joint with the potential complications that this may create.

Biomechanical analysis of partial flexor tendon lacerations in zone II of human cadavers

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

Cadaveric transverse zone II partial flexor tendon lacerations have residual tensile strength greater than the force required for protected active mobilization.

Biomechanics of the flexor tendons

This article examines basic tendon biomechanics, the anatomy and mechanics of digital flexor tendons, and the digital flexor pulley system. It also explores the various models that have tried to simulate the motion of the flexor tendons and several testing modalities that have been used. Finally, clinical applications are considered, including the biomechanics of flexor tendon repairs and tendon transfers. As we reach limits in the care of flexor tendon injuries, research into molecular, biochemical, and micromechanical methods of tendon repair will become the forefront of future investigation.

Reproducible volar partial lacerations in flexor tendons: a new device for biomechanical studies

A device was designed to create clinically relevant, precise partial flexor digitorum profundus tendon lacerations for in vitro studies but can be adapted for in vivo studies. This caliper-based system utilizes a direct measurement of the tendon height and assumes an elliptical cross section to select the depth of the cut. The accuracy was tested on 60 cuts on 12 human tendons lacerated to an expected 50% or 75% of their cross-sectional area, based on the assumption that the cross-section was elliptical in shape. The cuts were made in portions of the tendon that varied in cross-sectional shape and size. The cut surface of the laceration was colored with Methylene blue and then the laceration was completed. The tendon cross-section was digitally imaged and the respective areas of the stained and unstained regions were evaluated using image-processing software. The mean lacerated areas were 52% (SD 5%) and 73% (SD 6%) for targeted lacerations of 50% and 75%, respectively. The device thus appears to be accurate within an acceptable 5% margin of error from the expected area, and adaptable to intra- and inter-tendinous size variations.

Treatment of partial lacerations in flexor tendons by trimming. A biomechanical in vitro study

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.

Treatment of flexor tendon injuries: surgeons' perspective

Medical researchers continue to explore the flexor tendon's response to injury and repair. In recent years, hand surgery and therapy publications have focused on the biomechanics of suture techniques and the benefits of early postoperative motion on surgically repaired flexor tendons. Laboratory and clinical studies have shown that stronger suture techniques can withstand the strain of immediate active motion without a significant risk of tendon rupture or gap formation. Newly proposed therapy techniques and anatomic studies defining the effects of wrist and digital position on tendon excursion share the goals of achieving early motion and reducing restrictive adhesions. Clinical studies have evaluated the various imaging modalities used to diagnose postoperative adhesions. Other clinical surveys have detailed the use of pedicled autograft and allograft tendons in staged reconstruction. Histologic and immunologic researchers have concentrated on cellular activation patterns following tendon injury and the effects of pharmacologic agents, such as hyaluronan and aprotinin, on tendon healing and adhesion formation.