For a maximal efficiency of joint rotation in the hand, there are some pulleys; the transversal carpal ligament, the palmar aponeurosis and some pulleys along the digits. Those pulleys consist of 5 annular and 3 cruciform pulleys.
Clinically Relevant Anatomy
The most important ones are the A2 and the A4 pulleys, situated at the palmar side of the digits. The A2 pulley is continuous with the periosteum of the proximal phalanx and the A4 pulley is in the middle of the middle phalanx.
The annular pulleys are optimised for the purpose of flexor tendon positioning and gliding. In the A2 pulley, there were identified 3 layers:
- In the outmost layer is a loosely arranged areolar tissue containing a fine capillary network. It’s also continuous with the synovial membrane that provides nutrient vascular supplies to the pulley.
- The middle layer of the pulley is densely arranged with collagen bundles, those are oriented perpendicular to the long axis of the flexor tendon. This optimised the resistance of the pulley.
- The innermost layer, corresponds to the gliding surface of the pulley. It is composed of collagen bundles, oriented parallel with the flexor tendon. That optimised the gliding between the flexor tendon en the pulley. Within this layer, elongated elastin fibrils were regularly positioned within the collagen fiber array.
A fresh pulley injury results in local swelling, tenderness, and pain over the affected area. The main indicator to identify if a total rupture of a pulley has occurred is the appearance of the clinical bowstringing (In this case; when the finger is in flexion, the flexor tendon is taking the shortest line between the top and the base of the finger. Instead of following the phalange).
This method is very conclusive, but you can only use it with a total rupture of the pulley.
A recent study about the diagnostic procedure of the pulley, was a comparison between the effectiveness of ultrasonography and MRI (Magnetic Resonance Imaging) scanning.
This study showed us that the ultrasonography is a better diagnostic tool than the MRI. Not only because it’s an inexpensive method but also because you can have more precision and a better view with the ultrasonography.
Pulley injuries can be classified according to 3 grades:
- Grade III: Complete rupture of the pulley causing bowstring of the tendon. Symptoms are: locally pain at the pulley, heard a PO or CRACK, swelling, pain when squeezing or climbing, pain during finger extension
- Grade II: Partial rupture of the pulley. Symptoms: locally pain at the pulley, pain while extending the finger and while climbing
- Grade I: Sprain in the finger ligament. Symptoms: Locally pain, pain when squeezing or climbing
The tension of the grafts was evaluated to have an idea of the tension that is recommended in a new graft. The tension of a healthy pulley is between 0,49N and 1,69N.
On the bases of those findings, it is recommended that reconstructed pulley be tensioned to approximately 1N.
Free extrasynovial tendon grafts are the most common method currently in use for pulley reconstruction. The A2 and A4 are recommended to be reconstructed using multiple loops of free extrasynovial tendon grafts in the same place where the original digital pulley was. The strength of the repaired pulley is correlated with the number of loops in the tendon. However, recent studies suggest that intersynovial donor tendons may be more efficient as free extrasynovial tendon graft. The intersynovial grafts had less frictions, what gives a better mobility in the digits.
Another method reports on the use of the dorsal wrist retinaculum for the reconstruction of the annular digital pulleys. About 8 cm. of the retinaculum is necessary for the reconstruction of each digital pulley. It is recommended that the undersurface of the extensor retinaculum is orientated toward the tendon for better gliding. An independent biomechanical assessment of this pulley reconstruction concluded that this method gives a limitation in mechanical effectiveness. The ever-present Rim, is a tendon weave technique that is based on the remnant of the ruptured pulley. The advantage of this technique is that the long pulley structure retains the flexor tendon in close proximity to the bone. It is a very efficient technique but has also been shown to be one of the weakest pulley reconstruction methods.
Physical Therapy Management
Rohrbough indicates that there remains some disagreement between researchers as to the treatment of pulley tears.. Stretching is recognized as an important promoter of the formation of strong compacted scar tissue. Stretching involves pulling the finger in the varus direction, effectively hyperextending the metacarpophalangeal joint and PIP joint. An alternative therapy such a squeezing a ball may be useful. Such therapy is useful in promoting healing in the injury, it does not prevent atrophy of other healthy tissues.
Minor A2 pulley injuries or partial tears with no evidence of bowstringing can be treated with either firm circumferential taping for 2 to 3 months to permit healing. The effectiveness of pulley taping was tested and the effect was maximized (10% of bowstringing force) when the tape is positioned near the distal end of the proximal phalanx. The tape absorbed progressively less bowstringing force as the force produced at the fingertip increased; non-stretch, zinc oxide tape of 1.3 cm width was used. This result has two implications. Firstly, taping is likely to be most effective during the earlier stages of rehabilitation when the forces produced by the fingers are lower. Secondly, taping is unlikely to prevent pulley injuries, as these are likely to occur when forces on the pulley are maximal.
- Digital Flexor Sheath: Repair and Reconstruction of the Annular Pulleys and Membranous Sheath
- Analysis of the gliding pattern of the canine flexor digitorum profundus tendon through the A2 pulley, Shigeharu Uchiyama1, Peter C. Amadio, Lawrence J. Berglund, Kai-Nan An Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905, USA Accepted 15 January 2008
- Zone II Combined Flexor Digitorum Superficialis and Flexor Digitorum Profundus Repair Distal to the A2 Pulley Jeffrey M. Pike, MD, Richard H. Gelberman, MD
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