Chapter 11 The Omega “Ω” Flexor Pulley Plasty

Outline

In this chapter, we present our methods for the Omega plasty used to treat A4 and A2 digital flexor pulleys in primary or delayed primary tendon repair. This procedure expands the inner diameter of the annular pulleys of the flexor sheath, but anatomically it does not disturb the integrity of the pulleys. During surgery one lateral attachment of the annular pulley is entirely released from the corresponding anterior phalangeal bony surface. Our clinical series includes 34 Omega pulley plasties performed in 34 fingers of 27 patients. In 15 patients, 19 pulley plasties were performed with primary repair of flexor tendon rupture, while in the remaining 12 patients, 15 Omega pulley plasties were done concomitantly with delayed primary tendon repair. Among the 34 fingers, 7 fingers subsequently needed tenolysis 3 months after initial surgery. After 7-month mean follow-up, excellent results were seen in 29 fingers (85%), and good in 5 fingers (15%) according to Strickland criteria. The advantage of this subperiosteal surgical release is that it increases pulley diameter and inner volume, which accommodates better tendon gliding.

The surgical management of traumatic flexor tendon injuries, especially in zone 2 (sometimes called “no man’s land”), has always been a controversial subject. These injuries in zone 2 are accompanied by injuries to the digital fibrous sheath. The later the injury is attended to, the more fibrosis and collapse of the digital sheath are likely. The methods for repairing the functional flexor unit (i.e., the finger flexor tendons and their fibro-osseous sheath) are still evolving, testifying to the anatomical as well as the functional complexity of this structure.

The conservative camp proposed the concomitant repair of the digital fibrous tube with the primary suture of the flexor tendon injuries to restore the sheath integrity and avoid the formation of adhesions.^1,² However, the failure of the fibrous sheath to heal and, more dramatically, the risk of creating a constriction to tendon gliding have led several surgeons to abandon this approach.³^–⁸

The repair of injured digital flexor tendons, either primarily or secondarily, is accompanied by an increase in the diameter of the tendon where sutures are placed, increasing resistance to movement.⁹ To avoid this risk, several authors¹⁰^–¹² prefer to deal with the fibrous sheath structure and propose a partial or a complete resection of the A2 or A4 annular pulleys.

Enlarging the digital fibrous sheath by “venting” the pulley is attractive theoretically.¹² However, even if it does improve the local mechanical conditions around the tendon repair site, incision into the pulley structures may decrease digital flexion to a certain degree. Anatomic work has showed that the most remarkable loss of function is caused by resection of the annular pulleys A2 and A4.¹³ We thus began to imagine technical innovations that would resolve this conflict more specifically without affecting the integrity of the annular pulleys.

The Omega (“Ω”) pulley plasty we describe consists of releasing one lateral pulley attachment from its corresponding lateral phalangeal bony surface. The most relevant fact is that this technique preserves the anatomical integrity of the pulley and its continuity with the periosteum and the floor of the digital fibrous sheath. If one attachment is released, the annular pulley moves palmarly and rotates transversally, enhancing its internal space. This procedure may provide better gliding conditions for repaired flexor tendons. We named this technique for pulley plasty Omega, or “Ω,” reflecting the anatomical shape of the annular pulleys cross-sectionally.

Methods and Outcomes

Anatomy of the Fibrous Digital Sheath Tunnel

Though the anatomy of the digital fibrous sheath is familiar, we review some points that are important for explaining the Omega (“Ω”) pulley plasty. The pulleys segmentally distributed along the synovial sheath differ by their sites of insertion and their plasticity.¹⁴ The annular pulleys A1, A3, and A5 (also called articular pulleys), are attached to the palmar joint plates of the metacarpophalangeal (MP), the proximal interphalangeal (PIP), and the distal interphalangeal (DIP) joints, respectively. The lengths of these pulleys change during digital motion, with an approximate 50% retraction after full digital flexion,^13,¹⁵ whereas the A2 and A4 pulleys (bone pulleys) insert on the lateral phalangeal crests in continuity with the lateral periosteum and with the floor of the digital fibrous sheath tunnel. The A2 pulley is situated in the middle and proximal part of the proximal phalanx, and the A4 pulley in the middle third of the middle phalanx. The lengths of the A2 and A4 pulleys change somewhat (less than 25%) during digital flexion.

All the relevant biomechanical studies to date agree, giving functional priority in finger flexion to the A2 and A4 pulleys.^13,¹⁶ It is on these two pulleys that the pulley plasty is performed during tendon repair in zone 2,¹⁷ more precisely in zones 2B and 2C.¹⁸