Flexor tendon-pulley interaction after annular pulley reconstruction: a biomechanical study in a dog model in vivo

Feasibility of Homodigital Flexor Digitorum Superficialis transposition, a new technique for A2-C1 pulleys reconstruction: A kinematic cadaver study

INTRODUCTION

Homodigital flexor digitorum superficialis transposition (HFT) is proposed as a new technique for A2-C1 pulley reconstruction. Flexor digitorum superficialis is transposed on the proximal phalanx and inserted on the pulley rims, crossing over flexor digitorum profundus and acting as a pulley.

MATERIALS AND METHODS

The kinematic feasibility was investigated in a cadaveric bowstring model (after A2 and C1 pulley removal) on 22 fingers (thumb excluded).

RESULTS

HFT was effective in restoring the correct flexion of proximal and distal interphalangeal joints, compared to bowstring model. No adverse events were registered.

CONCLUSION

HFT is a feasible technique. Clinical application is encouraged.

Flexor tendon grafts for pulley reconstruction - Morphological aspects

BACKGROUND

Pulleys are crucial to convert flexor tendon excursion into angular motion at the metacarpophalangeal and interphalangeal joints. Loss of pulley function can lead to significant impairment of hand function and may require surgical reconstruction. This reconstruction can be achieved using different flexor tendons grafts, such as the intrasynovial flexor digitorum superficialis (FDS) or the extrasynovial palmaris longus (PL). However, there is limited knowledge on the micromorphology of human pulleys and the suitability of flexor tendon grafts for their reconstruction remains elusive.

METHODS

In the present cadaver study A2 and A4 pulleys were compared with FDS and PL tendons by means of scanning electron microscopy (SEM), histology and immunohistochemistry. Surface morphology, core structure and vascularization of the specimens were analyzed.

RESULTS

SEM imaging of the gliding surfaces revealed morphological differences between tendons and pulleys. Moreover, the core structure of FDS samples was characterized by bundles of individual collagen fibrils whereas PL tendons exhibited a less hierarchical microstructure. In contrast, pulleys consisted of lamellar sheets of densely packed collagen fibrils. Finally, immunohistochemical analyses revealed that the flexor tendons and pulleys contain similar numbers of CD31⁺ microvessels, indicating a comparable tissue vascularization.

CONCLUSION

This study provides novel SEM and immunohistochemical insights into the micromorphology of human pulleys and flexor tendon grafts. Intrasynovial flexor tendons may be particularly suitable for pulley reconstruction and preserving the paratenon may be crucial for graft revascularization.

The Effect of Pulley Reconstruction on Maximum Flexion, Bowstringing, and Gliding Coefficient in the Setting of Zone II Repair of FDS and FDP: a Cadaveric Investigation

PURPOSE

The purpose of this experiment was to determine the effect of A2 pulley reconstruction on gliding coefficient (GC), bowstringing, and proximal interphalangeal (PIP) joint maximum flexion angle after zone II repair of flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) lacerations.

METHODS

Fresh frozen cadaver forearms were mounted, and the wrist and MCP joints fixed. FDS and FDP tendons were dissected free, and sequential loads were applied while digital images were captured. The dissected digit with intact native A2 pulley, FDS, and FDP tendons was used as the control (group 1). Zone II lacerations followed by four-stranded repair of FDP plus epitendinous suture and repair of FDS were then performed, and the data recorded (group 2). A2 pulley excision and reconstruction with a loop of palmaris longus autograft was then completed and the specimens sequentially loaded and photographed (group 3). Using the digital images, GC, bowstringing, and maximum flexion angle were calculated.

RESULTS

No difference in maximum flexion angle was observed across the three testing conditions. Zone II laceration and subsequent FDS and FDP tendon repair significantly increased the GC for group 2 specimens; however, pulley reconstruction alleviated some of this increase for group 3. Bowstringing was significantly greater after pulley reconstruction, with a mean increase of 1.9 mm at maximum flexion for group 3 specimens relative to group 1 controls.

DISCUSSION

Strong flexor tendon repairs are needed to prevent gap formation and subsequent triggering; however, the increased bulk from these large repairs can itself produce deleterious triggering, as well as tendon abrasion. Pulley reconstruction, in the setting FDP and FDS repair (group 3), significantly reduced the GC relative to tendon repair alone (group 2). While bowstringing was significantly greater after pulley reconstruction (group 3), it averaged only 1.9 mm over group 1 specimens and did not compromise maximum flexion angle compared to the uninjured controls (group 1) or the isolated tendon repair digits (group 2).

Flexor tendon pulley reconstruction

Pulley reconstruction remains a challenging intellectual and technical exercise. When performed correctly, however, it can be a gratifying procedure that provides much improved function of the digit. As described in this article, there are many different techniques by which the pulley can be reconstructed. Each of these techniques has distinct advantages and disadvantages. The hand surgeon should be familiar with each of these techniques and the general principles of pulley reconstruction as laid out in this article. With this knowledge base, the treating surgeon is able to tailor the procedure performed to the exact anatomy and clinical situation of each patient. Although great strides have been made over the past half century, more clinical research is needed to determine the best technique, not just in the cadaver model, but also in the complex model of the living human hand.

Hyaluronic acid diminishes the resistance to excursion after flexor tendon repair: An in vitro biomechanical study

Adhesion between the tendon and tendon sheath after primary flexor tendon repair is seen frequently, and postoperative finger function is occasionally unsatisfactory. A reduction of the friction may facilitate tendon mobilization, which in turn may reduce the risk of the adhesion and restriction of range of motion. We considered the possibility of utilizing the hyaluronic acid (HA) as a lubricant. To evaluate the effect of HA, the gliding resistance between the canine flexor digitorum profundus tendon repaired by a modified Kessler suture technique with running epitendinous suture and the annular pulley located on the proximal phalanx (corresponding to the A2 pulley in humans) was evaluated and compared before and after administration of HA. The HA solution measurement groups were identified as follows; intact tendon as a control; repaired tendon; tendon soaked in 0.1, 1, and 10 mg/ml HA. The resistance increased after repairing, then it decreased after soaking in 10 mg/ml HA solution. The results of this study revealed that HA diminishes the excursion resistance after flexor tendon repair. We believe that some style of administration of the HA might reduce the excursion resistance and prevent adhesion until the synovial surface is fully developed.

The effect of partial A2 pulley excision on gliding resistance and pulley strength in vitro

PURPOSE

The purpose of this study was to investigate the effect of partial excision of the A2 pulley on the gliding resistance and the strength of the residual pulleys in a human in vitro model with or without tendon repair.

METHODS

We used 32 cadaveric human fingers from 11 cadavers. The A2 pulley was excised successively 25%, 50%, and 75%, cutting either from the distal toward the proximal edge or from the proximal toward the distal edge. The peak gliding resistance between intact or repaired tendon and partially excised pulley was measured. After the gliding resistance test the pulley breaking strength and stiffness were measured.

RESULTS

The peak gliding resistance exhibited the same statistical trends for the intact tendon and the repaired tendon groups. In the intact tendon groups the sequential excision of the A2 pulley from the distal toward the proximal edge had no significant effect on peak gliding resistance. With the A2 pulley cut from the proximal toward the distal edge, however, there was a significant increase in peak gliding resistance with 25% remaining pulley distally (0.82 N) compared with intact (0.42 N), 75% (0.57 N), and 50% (0.63 N) pulley remaining proximally. The 25% distal portion of the A2 pulley had a significantly higher breaking strength than the 25% proximal portion (160 N vs 96.7 N, respectively). Similarly the stiffness was greater in the distal portion compared with the proximal portion (120 N/mm vs 70.5 N/mm).

CONCLUSIONS

After A2 pulley excision the size and location of the remaining pulley affects the resulting gliding resistance, stiffness, and failure strength. At the most extreme excision level tested the residual 25% distal segment of the pulley exhibited significantly greater peak gliding resistance compared with the 25% proximal segment, as well as greater strength and stiffness. If excision of the A2 pulley is limited to 50% (either proximally or distally), however, there is little increase in gliding resistance and the retained strength of the pulley is substantial. These data support the clinical practice of partial pulley excision, up to a limit of 50%, to facilitate exposure and tendon repair.

Gliding characteristics and gap formation for locking and grasping tendon repairs: a biomechanical study in a human cadaver model

PURPOSE

The purpose of this study was to compare the frictional characteristics and mechanical properties of various locking and grasping suture techniques in a human in vitro model of flexor tendon repair.

METHODS

Forty-five cadaveric human flexor digitorum profundus tendons were transected in zone II and repaired using 1 of 5 core suture methods (n = 9 per group): either grasping (modified grasping Kessler, modified Lee) or locking (Pennington, modified Pennington, locking Lee) loop suture techniques. All repairs used 4-0 Supramid looped core suture and an epitenon running suture of 6-0 nylon. Gliding resistance at the tendon-pulley interface was measured along with failure strength and gap formation. The force to produce 0.5-, 1.0-, 1.5-, and 2.0-mm gaps were measured.

RESULTS

One of the locking repairs, the locking Lee, had a gliding resistance significantly higher than that of one of the grasping repairs (modified grasping Kessler) and the other 2 locking repairs (Pennington, modified Pennington) (p <.05). There was no significant difference between the other grasping (modified Kessler, modified Lee) and locking (Pennington, modified Pennington) suture configurations (p =.21). The maximum force of one of the locking repairs, the modified Pennington repair (48.0 N; standard deviation, 3.9) was significantly higher than the other locking and grasping repairs (p <.05). The force required to produce more than 1.5 mm of gap for the modified Pennington repair was also significantly higher than that for some of the other grasping (modified Kessler, modified Lee) and locking (Pennington) repairs (p <.05).

CONCLUSIONS

The lack of significant difference in gliding resistance among the similarly designed modified grasping Kessler, Pennington, and modified Pennington repairs (overall mean, 0.87 N; standard deviation, 0.16) suggests that the locking loop configuration itself does not adversely affect tendon gliding resistance. The modified Pennington repair increased not only ultimate strength but also resistance to gap formation more than 1.5 mm.

Remodeling of the gliding surface after flexor tendon repair in a canine model in vivo

Maintaining a smooth lubricated surface between the flexor tendon and sheath after tendon repair is very important for restoration of digit function. We studied the tendon surface after tendon repair mechanically in a canine model in vivo by measuring frictional force. One hundred and twenty flexor digitorum profundus (FDP) tendons were lacerated to 80% of their cross-section and repaired with either a modified Kessler (MK) or Becker (MGH) repair. The postoperative therapeutic regimen was either synergistic wrist and digit motion (SWM) or passive digit flexion and extension with the wrist fixed in 45 degrees of flexion (FIX). The dogs were sacrificed at one, three, or six weeks postoperatively. Thirty six FDP tendons from normal paws served as the control group, with each control tendon tested in two different conditions: intact and immediately after partial laceration and repair (0 time), making a total of five different timing points (intact, 0 time, one week, three weeks, and six weeks) for each repair type and each postoperative therapy. Frictional force between tendon and proximal pulley was evaluated after breaking any adhesions. Compared to intact tendons, friction was significantly increased immediately after tendon repair. The friction of the MK repair was significantly less than that of the MGH repair at all time and therapy groups, except at six weeks in the SWM group. For the MGH repair, at six weeks friction in the SWM group was significantly less than friction in the FIX group. This study showed that postoperative tendon gliding depends on the method of tendon repair and the postoperative therapy regimen. Furthermore, we have demonstrated that the gliding surface after tendon repair remodels with time.