Chapter 24 Tenoscopy and Bursoscopy
The advantages of arthroscopy as a diagnostic and therapeutic approach to joints1 have prompted the development of applications for other synovial cavities (see Chapter 23). Tenoscopy is the term used to describe endoscopy of synovial tendon sheaths, usually using a rigid arthroscope.2 Bursoscopy is used for endoscopy of bursae.
Tenoscopy has many advantages. Traditional approaches to tendon sheaths, requiring long incisions over highly mobile areas, are associated with substantial postoperative risks, including wound dehiscence and ascending sheath infection.3 These techniques are invasive, time consuming, and offer limited visibility of tendovaginal structures.2,3 Endoscopic approaches to the carpal tunnel in people have been described4,5 and have provided substantial improvements in terms of decreased morbidity, scarring, and loss of function compared with open techniques.4,6 Tenoscopy in the horse was first described for the examination of the digital flexor tendon sheath (DFTS).1,2 Since the early 1990s, other applications have been described.7-11
Standard arthroscopic equipment is used, including arthroscope, sleeve, and obturators; arthroscopic cannulae; probes; grasping forceps; and Ferris-Smith rongeurs. Sharp tenotomes, curettes, and meniscectomy scissors should also be available. A standard 4.0-mm, 25- to 35-degree forward angle arthroscopic endoscope is adequate for most sheaths and bursae, although thinner endoscopes may be useful for extensor sheaths. Light source and video camera apparatuses are as for arthroscopy. Motorized synovial resectors are particularly useful because debridement or synovectomy using hand-operated instruments can be tedious in large tendon sheaths.
Coblation technology (ArthroCare Corporation, Austin, Texas, United States) is a new technology that uses radiofrequency to vaporize soft tissues. I now use radiofrequency probes (Arthrowands, ArthroCare Corporation) to remove proliferative synovial tissue and masses, and a hook radiofrequency blade (Saber 30, ArthroCare Corporation) to carry out annular or retinaculum desmotomy. An added advantage is improved hemostasis.
The basic principles of arthroscopy are also valid in tendon sheaths and bursae (see Chapter 23). The sheath usually is distended with fluids to facilitate insertion of the cannula. However, this is not necessary for the carpal and tarsal sheaths, which are not approached through distended pouches.9,10 It is generally recommended that the portal be created with a scalpel and the cannula inserted using a blunt, conical obturator to avoid damaging the tendons. A thorough knowledge of the normal endoscopic anatomy of the sheath is paramount for several reasons. First, all the surfaces are covered by synovium and look alike, making identification of the structures difficult. Second, normal anatomical structures such as vinculae and plicae (adhesion-like formations carrying blood vessels to the tendon from the parietal sheath), endotendon (reflection of the synovial membrane, which forms a continuous band attaching the tendon to the sheath along its length), and synovial folds are apparent. These should not be damaged because they participate in the blood supply of tendons within the sheathed portion.12-14
Triangulation techniques are applied for instruments using separate portals. These should be created as close as possible to the lesion, although the shape of the sheath often dictates the position of the portals. The longitudinal arrangement of the sheaths and tunnel-like enclosures within retinacula often make triangulation difficult; therefore it may be useful to perform retinaculum desmotomy to improve access to some lesions, or to create instrument portals so that instruments are inserted opposite and toward the endoscope lens.
The DFTS is the most common site of tenosynovitis. Endoscopy is indicated as a diagnostic procedure to examine lesions of the surfaces of the deep digital flexor tendon (DDFT), superficial digital flexor tendon (SDFT), and parietal surface of the sheath. High-definition ultrasonography allows noninvasive examination of the sheath, its contents, and peripheral tissues, and provides more accurate information about the internal architecture of tendons.15 However, differentiating some adhesions, tears, and superficial fraying of the tendons may be difficult ultrasonographically.16-19 Tenoscopy is useful for debridement of masses, such as proliferative (villonodular) synovitis-like lesions and other lesions within the sheath, adhesiolysis, removal of debris, and synovectomy in infectious tenosynovitis.2,19,20 A technique for desmotomy of the palmar annular ligament under endoscopic control has been described to avoid inadvertent damage to the tendons, manica flexoria, and other peritendovaginal structures.21
The advantages of tenoscopy over traditional open surgery are similar to those recognized for arthroscopy over arthrotomy. They include decreased morbidity and more rapid return to normal function of the sheath and reduced risks of complications, such as wound breakdown, infection, fibrosis, and ankylosis.
The DFTS is organized primarily around the DDFT, which it completely surrounds from the junction between the third and distal quarters of the metacarpal or metatarsal region to the level of the proximal interphalangeal joint, before tapering dorsally to the DDFT to the proximal border of the distal sesamoid bone.12,13,15,22 At the level of the metacarpophalangeal joint, the DFTS also surrounds the SDFT, except for a wide mesotendon over the palmar/plantar aspect of the tendon. At this level the DFTS is bound dorsally by the proximal scutum, a fibrocartilage covering the palmar (plantar) surfaces of the proximal sesamoid bones (PSBs) and intersesamoidean ligament, and palmarly by a tough transverse ligament, the palmar (plantar) annular ligament (PAL), thus forming a nonelastic canal through which both digital flexor tendons run independently. In the pastern region the SDFT separates into two branches and is no longer within the DFTS. The DFTS is bound dorsally by the distal sesamoidean ligaments and palmarly (plantarly) by two broad digital annular ligaments.
The proximal pouch bulges when distended proximal to the PAL and PSBs and contains a number of long villi in normal horses. Several small, subcutaneous pouches appear between the insertions of the PAL and digital annular ligaments abaxially and over the palmar (plantar) aspect of the DDFT in the midpastern region. A number of vascular structures are found, including two large vinculae forming a V-shaped adhesion-like structure between the dorsal surface of the DDFT and the dorsal sheath wall in the proximal pastern. Densely packed villi often are found in that area. The wide palmar mesotendon prevents examination of the palmar aspect of the SDFT in the fetlock region. Immediately proximal to this level, the manica flexoria forms a smooth, thin membrane originating from the axial surfaces of the SDFT and surrounding the DDFT dorsally.
The technique for tenoscopic exploration of the DFTS has been described in detail.2 The term palmar is used in the following description for either palmar or plantar. The horse may be placed in lateral recumbency with the affected limb uppermost for a lateral approach or lowermost for a medial approach. The choice of a lateral or medial portal is dictated by the site of the suspected lesion. However, if no definite lesion has been observed ultrasonographically and if a potential tear is suspected, the horse is best placed in dorsal recumbency with the limb attached to a frame or hoist so that the digit is in slight flexion. This decreases hemorrhage during the procedure. An Esmarch bandage and tourniquet may also be used.
The DFTS is distended with 10 to 20 mL of physiological solution through a needle inserted in the palmar aspect of the midpastern region. Overdistention of the DFTS is avoided because it causes flexion of the digit. A 5-mm longitudinal incision is made through the skin, immediately distal to the PAL, lateral or medial to the DDFT, and 0.5 to 1 cm palmar to the neurovascular bundle, which must be carefully avoided. A stab incision is made into the DFTS, taking care to avoid damaging the DDFT, and the cannula, with a conical obturator inserted in a proximal direction, between the DDFT and dorsal sheath wall (Figure 24-1). The DFTS is lavaged through an 18-gauge needle inserted in the proximal pouch. The obturator is replaced with the endoscope, and examination is carried out from proximal to the level of the portal by rotation and gradual withdrawal. The proximal pouch is examined, followed by the abaxial aspects of the two tendons. Flexion of the fetlock joint allows insertion of the endoscope between the SDFT and DDFT without damage to the manica flexoria. The endoscope is finally rotated around the SDFT on the side of the portal to inspect the mesotendon. Examination of the opposite side is made possible by flexion of the fetlock and rotation of the arthroscope window palmarly.
The endoscope is then pushed across the DFTS, between the DDFT and dorsal sheath wall, to avoid exiting the DFTS. The endoscope is then redirected distally. The distal part of the DFTS is examined by gradual withdrawal of the endoscope. The vinculae are visible in the proximal pastern region, between the dorsal surface of the DDFT and dorsal wall (Figure 24-2). Palmarly and farther distally, bifurcation of the SDFT branches forms a manica-like ring around the DDFT (Figure 24-3).
Fig. 24-2 Tenoscopic view of the dorsal aspect of the deep digital flexor tendon (DDFT) in the proximal pastern region, showing one of the vinculae (V) between the DDFT and dorsal wall (Sh) of the digital flexor tendon sheath.
Fig. 24-3 Tenoscopic view of the palmar aspect of the deep digital flexor tendon (DDFT) in the proximal pastern region, showing the manica-like ring (arrow) surrounding the DDFT, between the two superficial digital flexor tendon (SDFT) branches (within the abaxial sheath walls). The dorsal wall (Sh) of the digital flexor tendon sheath is rich in long villi.