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Arthroscopic Examination
Chapter
23
Arthroscopic Examination Mike W. Ross
References on page 1265
Arthroscopic surgery is arguably the most important advance in management and one of the most important in diagnosis of equine joint disease. Arthroscopic surgery has been a mainstay in managing joint disease since the early 1980s and has mostly replaced arthrotomy. An effective equine surgeon cannot lack extensive arthroscopic surgical experience, and lameness diagnosticians must understand indications and limitations of the technique. Innovators have used the same instruments for bursoscopy and tenoscopy (see Chapter 24). For a complete description of procedures, instrumentation, and principles of arthroscopy, the reader is referred to Diagnostic and Surgical Arthroscopy in the Horse.1
ADVANTAGES AND DISADVANTAGES OF ARTHROSCOPIC SURGERY COMPARED WITH ARTHROTOMY Arthroscopic surgery offers several advantages compared with arthrotomy; however, this type of surgery also has some disadvantages. Both are discussed in the following text.
Advantages Improved Visibility
Improved visibility during arthroscopic examination allows for evaluation of most of the joint compared with the limited view provided by arthrotomy. Even long arthrotomy incisions rarely provide added visibility because overlying capsule, retinaculum, and sheaths make retraction difficult. During arthroscopic examination, cartilage at locations distant to the primary lesion site, synovium, and intraarticular soft tissue structures such as ligaments can be examined. For example, newly described disease conditions involving intercarpal ligaments were not known before arthroscopic examination existed.
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Reduced Trauma and Morbidity
Arthroscopic examination is less traumatic and causes less morbidity. Arthroscopic examination allows surgery to be performed through small incisions and requires less surgical exposure and damage to overlying soft tissues, upholding a time-honored principle of limiting trauma. Little pain is observed in horses after arthroscopic surgery compared with arthrotomy, and many horses appear to ambulate normally. However, in an unblinded study of horses after arthroscopy under general anesthesia, horses showed mild but significant increases in discomfort compared with pain-free controls.2 Complications such as wound dehiscence and seroma formation are minimal. Horses often show pronounced lameness for several days after arthrotomy. After arthroscopic examination and surgery, owners and trainers expect horses to return to full work soon after surgery, an idea that is fueled by widespread reports of human athletes returning to professional sports quickly after arthroscopic surgery. A general misunderstanding is that incision size is the limiting factor. Although arthrotomy does cause short-lived lameness after surgery, the fear that it will delay onset of training is unfounded because the underlying lesion dictates recovery time. Although not recommended, horses with mild conditions such as osteochondritis dissecans, effusion but no lameness, and those that receive prophylactic arthroscopic surgery can resume training a few weeks after arthroscopic examination or arthroscopic surgery. Arthroscopic surgery can be performed within weeks before a sale, and if hair was not clipped, surgical sites are barely noticeable.
Better Cosmetic Results
Improved cosmesis is a definite advantage. Small incisions cause less fibrous tissue formation, and incisions are difficult to identify 2 to 3 months after surgery. Generally the instrument portal (incision), the site through which the arthroscopic instruments are passed and lavage is performed, suffers more trauma than does the arthroscopic portal, and swelling, reactions, and fibrous tissue production are more common.
Earlier Functional Capability
Earlier return to function was once believed to be an advantage of arthroscopic surgery. However, incision size has little to do with lameness except within the first few weeks after surgery. Lameness observed in horses returned to work 4 to 6 weeks after arthroscopic surgery for substantial articular lesions has nothing to do with incision size. When horses undergoing arthroscopic surgery were given only a brief rest, results were unsatisfactory. Incisions heal from side to side, not end to end, and incision size has no effect on articular healing. Lesions must heal as completely as possible before full work can begin—a process that often takes several months. Type and location of lesions are important because horses with osteochondritis dissecans not involving weight-bearing surfaces can start training within 2 to 3 weeks of surgery, if necessary, whereas those with lesions in critical sites, such as the typical carpal osteochondral fragment, must be given 3 to 4 months of rest.
More Versatility
Improved versatility is a definite advantage because joints considered inaccessible, such as the coxofemoral joint, can
be evaluated. Techniques such as repair of third carpal slab fractures, distal third metatarsal (MtIII) or third metacarpal (McIII) fractures, fractures in other joints, and resurfacing techniques can be done using arthroscopic surgery.
Fewer Complications
Arthroscopic surgery results in fewer complications. Arthrotomy of the scapulohumeral, femorotibial, femoropatellar, cubital, and tarsocrural joints has been associated with dehiscence, seroma formation, and infection, but arthroscopic surgery of these joints is safe.
Disadvantages Expensive Instrumentation
Expense of surgical instrumentation is a disadvantage because start-up costs are high, but basic instrumentation is no more costly than routine surgical instruments. Although arthroscopic surgery can be done without video equipment, video arthroscopy is valuable for archiving images. It is much more comfortable than direct-view arthroscopy (looking directly through the eyepiece) because surgery is performed using a comfortably positioned monitor. It allows the procedure to be viewed by others and is valuable in maintaining aseptic technique because breaks in technique often occur during direct-view arthroscopic surgery.
Lack of Surgical Experience
Experience necessary to learn arthroscopic surgery is a disadvantage. Arthroscopic surgery requires skill in stereotactic techniques and orienting and operating without looking at the surgical site, and surgeons must be able to use instruments properly and safely while looking at a monitor. Preoperative planning must be done to ensure that the horse is positioned properly on the operating table and the surgeon has ready access for triangulation. Poor technique may result in iatrogenic damage or extravasation of large amounts of lavage fluid that can severely compromise distention of the joint capsule and thus ability to see adequately within the joint. Experience cannot be gained by simply attending a weekend course but rather by working long hours with cadaver specimens and observing experienced surgeons. Initially arthroscopic surgery can be time consuming until experience is gained, but with experience arthroscopic surgery is faster than arthrotomy.
Equipment Problems
Equipment failures can be a disadvantage, and because arthroscopic examination depends on electricity, a generator should always be available. Instruments are not made to withstand forces applied to cut, grasp, and debride equine bone and, along with the arthroscope, may break.
Improper Case Selection
Case selection is the most important disadvantage. Poor case selection can make arthroscopic surgery difficult and disappointing. Although much information can be gained by arthroscopic examination of any joint, prognosis should be carefully considered when operating on joints in which extensive osteoarthritis exists. Inadequate communication before surgery may leave owners and trainers with too high expectations of results. Often they have little appreciation
Chapter 23 Arthroscopic Examination
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Fig. 23-1 • A, Dorsal 25° proximal medial-plantarodistal lateral oblique digital radiographic image of the right hind (RH) metatarsophalangeal joint (MTPJ) in a 2-year-old Standardbred (STB) trotter showing a typical intraarticularly located plantar process fragment (arrow) easily removed using arthroscopic techniques. This “down angled” oblique radiographic image is useful to evaluate the region between the base of the medial proximal sesamoid bone and the proximal aspect of the proximal phalanx to see these fragments. B, Dorsolateral-plantaromedial oblique digital radiographic image of the RH MTPJ in a 2-year-old STB pacing filly with large nonarticular (large arrow) and small articular (small arrow) plantar process fragments, which were all removed using arthroscopic techniques. To remove fragments outside the joint, a combination of sharp and blunt dissection and use of a synovial resector are necessary.
for the magnitude of cartilage damage and osteoarthritis (OA), and they only see or hear about the chip fracture(s) visible radiologically. Owners and trainers tend to want to do something, but removal of osteochondral fragments from a carpus or fetlock joint with hopeless OA can be time consuming, cause instrument failures, and, worse, often results in a poor outcome. Poor prognosis associated with some conditions must be well communicated to owners before surgery. For example, we recently reviewed the results of surgical and conservative management of scapulohumeral osteochondrosis and found that overall, prognosis was poor.3 Prognosis varied inversely with the severity of radiological changes, and only 15% of potential racehorses started a race. Four of six nonracehorses were sound for intended use. Surgery did not improve prognosis.3 The fragment size that can be easily removed during arthroscopic surgery is limited, and the instrument portal must be enlarged to accommodate such fragments unless ostectomy is performed. The fragment must be located in the joint or at least close to it, a decision that must be made before surgery because arthroscopic surgery is of little benefit if the fragment is not in the joint or close enough to make the approach reasonable and safe. In the metatarsophalangeal joint, large plantar process fragments from the proximal phalanx are often located extraarticularly, and although they may still be best removed using conventional surgical techniques, I have removed large fragments with arthroscopic instrumentation; surgery is facilitated by use of a motorized synovial resector (Figure 23-1). Differentiation should be made preoperatively between fragments free in a joint, which are accessible to surgical removal, and those embedded in the joint capsule and therefore not readily removed. In the stifle joint,
fragments in the distal aspect of the femoropatellar joint may appear radiologically as if they are in the femorotibial joint. Rare fragments in the caudal pouches of the medial and lateral femorotibial joints can be difficult to retrieve, especially if the precise location cannot be determined radiologically before surgery. The approaches to the difficult caudal pouches of the medial and lateral femorotibial joints were recently refined.4 Highly mobile fragments in a large joint such as the femoropatellar joint can prove challenging to locate. There is still a limited role for arthrotomy in equine surgery. For example, I still prefer to use a small, medial, middle carpal arthrotomy to repair sagittal slab fractures of the third carpal bone (C3) because I believe I can more accurately place the screw in the medial aspect of the C3, between the C3 and the second carpal bone.5 Others prefer a technique using arthroscopic guidance.1
PRINCIPLES, INSTRUMENTATION, AND TECHNIQUE Surgical technique, basic and advanced instrumentation, and approaches are well described elsewhere,1 and in-depth discussion is beyond the scope of this textbook. The basic principle of arthroscopic surgery is to use a rigid 4-mm endoscope to evaluate and perform intraarticular surgery through small incisions. Smaller endoscopes (2.9 mm and smaller) facilitate surgery in smaller joints or to view lesions between joint surfaces. Limited arthroscopic surgery was previously performed through a single incision, and instruments were passed through a second slot in the arthroscopic cannula. Versatility was severely compromised. Triangulation, a versatile technique in use today, uses two distant
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portals so that the arthroscope and instruments create two sides of a triangle. For example, during routine tarsocrural arthroscopy the arthroscopic portal is dorsomedial and the instrument portal is dorsolateral. This allows the tips of the instruments to be in the surgical field from distant points and obviates the need for the arthroscope to be close to the lesion. The end of the arthroscope is angled 25 to 30 degrees, and a different view is obtained by simply rotating it. Endoscopes with angles of 70 and 120 degrees can be used to obtain different views and are useful when triangulation is done with incisions close together. The image must be positioned on the screen to optimize special orientation and facilitate stereotaxis. Arthroscopic surgery can be performed with basic instruments, the most important of which are rongeurs (Ferris-Smith), grasping forceps, bone curettes, lavage cannulae, intraarticular blades, and probes. Arthroscopic surgery depends on the availability of a suitable light source and monitor, digital camera, and recording devices. A fluid delivery system is mandatory, and pumps or other methods to pressurize fluid are preferred to gravity flow systems. Many common lesions removed by arthroscopic surgery are located on the joint margin, and visibility often is compromised when joint capsule and synovium collapse or when bleeding is excessive. Carbon dioxide insufflation is sometimes used and is preferred by some surgeons.6 Carbon dioxide insufflation was effective at maintaining distention of the metacarpophalangeal and metatarsophalangeal joints and gave excellent visibility of lesions, but fluid lavage was necessary when bleeding precluded optimal visibility.7 Lasers are used rarely. Controlled ablation (coblation), using a form of radiofrequency energy to dissolve tissue, is used intraarticularly and in tendon sheaths and bursae (see Chapter 24). Using a new radiofrequency prototype probe, researchers were able to control cartilage cell death significantly better compared with manual debridement and use of a commercially available probe.8 Motorized equipment is useful but expensive. Abrasion arthroplasty units include various motorized burrs to remove and smooth cartilage and bone surfaces and are used in horses with large lesions such as osteochondritis dissecans lesions of the lateral trochlear ridge of the femur. Synovial resectors are alternating, motorized, rotating blades that are helpful in removing synovium and fibrous tissue and are particularly valuable for removal of osteochondral fragments from the dorsal aspect of the distal interphalangeal joint, apical proximal sesamoid fracture fragments, large abaxial fragments originating from the proximal aspect of the proximal phalanx, and fragments from the lateral malleolus of the distal aspect of the tibia, as well as when synovectomy is indicated. The division between diagnostic and surgical arthroscopy is now artificial because the same instruments are used for both. Diagnostic arthroscopy, that is, arthroscopic examination, generally refers to evaluating cartilage, bone, and soft tissues to gain information for diagnosis and prognosis. The client must be warned that although valuable information is always learned, arthroscopic examination may provide little therapeutic benefit. However, I believe a tendency exists to undersell arthroscopic examination because a positive intervention cannot be made unless the joint is evaluated, and much can be learned about lesions with early arthroscopic examination. This is particularly
true in the stifle, carpus and fetlock joints. Arthroscopic examination is indicated in horses with lameness localized to a joint, but in which radiological findings are negative or equivocal. Scintigraphic evidence of subchondral bone injury is common in these horses, and defects, if present, in overlying articular cartilage can be debrided and attempts at resurfacing performed arthroscopically. In young racehorses with early subchondral bone injury, arthroscopic evaluation usually reveals little to no overlying cartilage damage in those portions of the joint visible from conventional arthroscopic approaches (Figure 23-2). In these horses lack of cartilage damage likely explains the lack of obvious clinical signs such as effusion. Management of horses with novel surgical techniques such as subchondral forage or using drugs targeting subchondral bone modeling/remodeling in combination with rest is recommended.
LH
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B Fig. 23-2 • A, Delayed-phase scintigraphic images of a 3-year-old Thoroughbred colt with subchondral bone pain localized to the lateral aspect of the left metatarsophalangeal joint using lateral plantar metatarsal analgesia. Focal increased radiopharmaceutical uptake of the distal, lateral condyle of the third metatarsal bone (MtIII) (arrows) can be seen. Radiographs revealed sclerosis but no radiolucency. B, Intraoperative view of the plantar aspect of the left hind fetlock joint (dorsal is to the left and medial is uppermost) from an arthroscopic portal in the proximal, lateral plantar pouch showing normal-appearing articular cartilage of the lateral condyle of the MtIII overlying subchondral bone injury as depicted scintigraphically. The proximal phalanx (PI) can be seen just distal to synovial membrane between the PI and the base of the lateral proximal sesamoid bone. The entire articular surface cannot be evaluated, but visible articular cartilage appears normal. A subchondral forage technique (three 3.5-mm holes drilled from the lateral condyle into subchondral bone) was used.
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Med fem
Tib LM
MM
B
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Fig. 23-3 • Intraoperative arthroscopic images of the cranial aspects of the medial femorotibial joint (MFTJ) (A [medial is to the left and proximal is uppermost]) and lateral femorotibial joint (LFTJ) (B [lateral is to the right and proximal is uppermost]) in a 3-year-old Standardbred gelding with an unsual subchondral bone cyst in the proximal lateral aspect of the tibia (arrows) and enlarged, frayed lateral meniscus (LM). A cranial approach to the femoropatellar joint (FPJ) was used to evaluate the stifle and the septae between the FPJ, and the MFTJ and LFTJ were removed to allow examinations through a single approach. In this horse with left hindlimb lameness, clinical signs of stifle pain were not detected, and the horse was referred for scintigraphic examination, which revealed focal, moderately increased radiopharmaceutical uptake in the proximal, lateral aspect of the tibia. Notice the normal medial meniscus (MM) and articular cartilage of the proximal aspect of the tibia (Tib) in the MFTJ and mild undulation of articular cartilage of the distal femur (Med fem). The subchondral bone cyst and torn edge of the lateral meniscus have been debrided (B). Prognosis is guarded at best because of subchondral bone, cartilage, and meniscal injury in the LFTJ.
Scintigraphy and ultrasonography have low sensitivity in the complex stifle joint, and arthroscopic examination should be encouraged. Walmsley et al.,9 in a large case series, found that 47% of horses returned to full use, and prognosis was inversely proportional to severity of meniscal tearing, degree of cartilage damage, and radiological abnormalities (Figure 23-3) (see Chapter 46). Arthroscopic examination may uncover proliferative synovitis, intersesamoidean ligament injury, and intercarpal ligament injury. Intercarpal ligament injury often is associated with OA or osteochondral fragments and can cause hemar throsis and presumably joint instability (Figure 23-4).10,11 Lesions in difficult locations can be successfully evaluated and manipulated arthroscopically. Ten of 11 horses that had subchondral bone cysts of the distal phalanx returned to athletic use after arthroscopic debridement.12 The distal interphalangeal joint can be difficult to evaluate, but a combination of careful manipulation and flexion can improve visibility (Figure 23-5). Changes in articular cartilage are the most important information gained from arthroscopic examination. Prognosis was found to worsen in proportion to the extent of articular cartilage damage in the carpus,13 but all joints are similarly affected. Surface area and depth of damage are important. Widespread damage affecting many cartilaginous surfaces is usually worse than well-defined lesions extending into subchondral bone. Cartilage damage is graded as mild (<20% damage to cartilage and subchondral bone at the primary lesion site), moderate (involvement of apposing bone, but <30% total cartilage and subchondral
bone damage of primary and apposing sites), severe (≤50% of cartilage and subchondral bone damage of primary and apposing sites), and global (extensive cartilage damage visible on most articular surfaces) (Figures 23-6 to 23-8). If cartilage lesions do not extend past the zone of calcified cartilage, healing after surgery will likely be minimal (see Microfracture discussion below). Occult (not radiologically apparent) osteochondral fragments may be identified by arthroscopic examination. Recognition requires inspection and probing, if necessary, after synovial resection. Common sites include the medial aspect of the intermediate carpal and lateral aspect of the radial carpal bones and small fragments involving the proximodorsal aspect of the proximal phalanx. Unexplained tarsocrural effusion (bog spavin) is commonly caused by osteochondritis dissecans fragments of the distal medial malleolus of the tibia, and although fragments may be suspected radiologically, the presence is confirmed and they are removed arthroscopically. Occult or radiologically suspicious subchondral defects of the third carpal bone, the distal aspect of the medial femoral condyle, and the distal aspect of the MtIII and McIII can be confirmed and debrided. Most arthroscopic surgery is performed to remove radiologically apparent osteochondral fragment(s). Grading cartilage damage and subchondral bone damage, along with removing one or more osteochondral fragments, is important in assessing prognosis. Discovery of severe cartilage damage in horses with few radiological changes is common, especially in the carpus and fetlock joints. Whenever possible, all aspects of the joint should be evaluated.
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C-3
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LMCJ
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RMCJ
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Fig. 23-4 • Intraoperative arthroscopic images of the left (A) and right (B) middle carpal joints (MCJs) showing complete tearing of the medial palmar intercarpal ligaments (arrows) in a 2-year-old Thoroughbred filly in race training. The horse was positioned in dorsal recumbency, and distal is uppermost; medial is to the right in A and to the left in B. The arthroscope has been inserted through a dorsolateral portal between the extensor carpi radialis and common digital extensor tendons in both MCJs. Tearing of the medial palmar intercarpal ligament appears as it courses from the third carpal bone (C3) to the radial carpal bone (RC). The intermediate carpal bone (IC) can be seen. Tearing of the medial palmar intercarpal ligament causes hemarthrosis, a condition previously thought to be idiopathic without arthroscopic examination, and can occur in conjunction with osteochondral fragmentation and associated cartilage damage. When the intercarpal ligament is torn, the palmar aspect of the MCJ can be examined, a finding that is impossible if the ligament is intact.
PII
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PII
PIII
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Fig. 23-5 • Intraoperative arthroscopic images before (A) and after debridement (B) of the right hind distal interphalangeal joint (DIPJ) in a yearling Standardbred filly with a history of acute lameness and a small wound at the dorsal aspect of the coronary band. Hair was found in the dorsal aspect of the joint and was removed. With the joint in moderate flexion and the joint surfaces retracted using an arthroscopic elevator, this lesion involving the plantar aspect of the articular surface of the distal phalanx (PIII) can be seen (small arrows). Notice the articulation between the plantar aspect of the PIII and the navicular bone (large arrow). The distal articular surface of the middle phalanx (PII) can be seen.
In racehorses, although cartilage damage and osteochondral fragmentation are often seen dorsally, the palmar/ plantar aspect of the metacarpophalangeal joint or metatarsophalangeal joint often has extensive cartilaginous score lines or large, full-thickness areas of cartilage loss on
the medial aspect of the McIII and the medial articular surface of the proximal sesamoid bone (PSB) and on the lateral aspect of the MtIII and the lateral PSB. In nonracehorse sports horses, changes are most prominent dorsally. Lesions of the patella, sometimes with fragmentation,
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MtIII
P-I
A
B
Fig. 23-6 • Intraoperative arthroscopic images of the dorsomedial aspect of the right metatarsophalangeal joint of a 3-year-old Thoroughbred filly with right hindlimb lameness (dorsal is right, proximal is top). A, A small osteochondral fragment (chip fracture, arrows) of the dorsomedial aspect of the proximal phalanx (P-I) is surrounded by mild cartilage damage. A small partial-thickness “score” line can be seen on the overlying medial condyle of the third metatarsal bone (MtIII). B, The chip fracture has been removed and surrounding mild cartilage damage debrided. This horse returned to successful racing 6 months after arthroscopic surgery.
RC
C-3
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B Fig. 23-7 • Intraoperative arthroscopic images of the right middle carpal joint of a 3-year-old Standardbred colt (dorsal is to the right and proximal is uppermost). A, A small osteochondral fragment (chip fracture, arrows) of the third carpal bone (C3) can be seen; minimal cartilage damage was found on the radiocarpal bone (RC). B, The chip fracture has been removed, and surrounding moderate cartilage damage has been debrided. This horse has a good prognosis for racing soundness.
found during arthroscopic examination explain why some horses with large osteochondritis dissecans lesions of the lateral trochlear ridge of the femur perform poorly. Arthroscopic examination is useful in horses with infectious arthritis to evaluate articular surfaces and synovium, identify and remove foreign material (see Figure 23-5), facilitate removal of fibrin, and perform much more effective and complete lavage than is achieved by throughand-through lavage. Arthroscopic examination usually is reserved for horses with long-standing infections and those
with extensive fibrin accumulation, but the Editors strongly promote its use for acute infection as well. I have not found a good correlation between arthroscopic and ultrasonographic identification of fibrin early in the disease process (the amount of fibrin is overestimated by ultrasonography). Arthroscopic examination can facilitate drain insertion, synovectomy, and debridement or removal of osteochondral defects. Arthroscopic portals can be left open to facilitate drainage after surgery, but this procedure should be used only in horses with refractory infections.
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MtIII
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Lat PSB
C Fig. 23-8 • Intraoperative arthroscopic images of the plantar aspect of the left metatarsophalangeal joint in a 7-year-old Standardbred stallion showing severe cartilage and subchondral bone damage from end-stage osteoarthritis that developed from maladaptive bone remodeling. A, A large erosive lesion of the lateral condyle of the third metatarsal bone (MtIII) has been debrided (dorsal is to the left and proximal is uppermost). This area is difficult to see, and the arthroscope is positioned between MtIII and the lateral proximal sesamoid bone with the joint in as much extension as possible. The proximal, plantar aspect of the proximal phalanx (P-I) can be seen. B, Severe loss of articular cartilage with exposed subchondral bone (arrows) can be seen on the lateral proximal sesamoid bone. C, The technique known as microfracture has been performed in the area of complete cartilage loss on the lateral proximal sesamoid bone, but prognosis is hopeless for racing soundness.
SURGICAL PROCEDURES The specific indications and surgical procedures are discussed in other chapters. Dorsal and palmar/plantar, medial and lateral, and cranial and caudal approaches have been described; the approach, choice of portals, fluid delivery, and instrumentation vary among joints and surgeons. Positioning the horse on the operating table is important to allow access to the involved joint(s), and repositioning may be necessary. Both lateral and dorsal recumbency are used successfully, and choices are based on the surgeon’s experience and the number of joints affected. Although standing arthroscopy of the fetlock and
other joints has been described,14 I prefer to use general anesthesia. Minimally invasive surgery such as arthroscopic surgery continues to be developed in horses. Standard procedures include fragment removal, debridement and curettage, partial synovectomy, and incision of adhesions. Reduction, fragment removal, and screw placement in horses with condylar fractures of the McIII or the MtIII can be done using arthroscopic surgery, obviating the need for arthrotomy. A technique to insert one or more cortical bone screws to repair frontal slab fractures of the third carpal bone was an early advance that has led to use of a similar technique to repair radial carpal bone and ulnar carpal
Chapter 23 Arthroscopic Examination
bone slab fractures, PSB fractures, and other unusually located articular fractures.15 An alternative to arthroscopic debridement of subchondral bone cysts of the medial femoral condyle—injection of the cyst lining with cor ticosteroids under arthroscopic guidance—appears to give similar clinical results.16 Thirty-five of 52 horses (67%) were considered successful. Horses with unilateral subchondral bone cysts did better than those with bilateral cysts, and the existence of osteophytes on preoperative radiographs had a negative impact on success.16
Cartilage Resurfacing
Recently cartilage resurfacing techniques have been used in experimental horses and in a limited number of clinically affected horses. Repair strategy involves creating access to stem cells, growth factors, and blood in subchondral bone to assist in cartilage repair or transplantation (grafting) of tissues, osteochondral grafts, or cells (chondrocytes). Partial- or full-thickness cartilage defects that do not penetrate the subchondral plate heal incompletely or not at all. An important principle in cartilage repair is to curette through the layer of calcified cartilage and perforate the subchondral plate to allow influx of healing elements. Extensive curettage seems to be self-defeating because exposure of large areas of denuded subchondral bone is associated with poor prognosis and often is found in horses with naturally occurring OA. Unfortunately, many defects already involve complete erosion into subchondral bone, at least around and apposing the primary lesion site. A technique known as microfracture of the subchondral plate has been introduced and involves using a 45- or 90-degree orthopedic awl (micropick) to create small perforation sites into subchondral bone in the area of cartilage damage.17,18 Studies have shown that removal of the calcified cartilage layer alone, or perforation of the layer with the microfracture technique, improves the amount and quality of repair tissue, but this tissue lacks the bio mechanical and histological character of hyaline cartilage.19 The procedure is currently being used, but objective results compared with routine procedures have not been published. Nixon20 has considerable experience in transplantation resurfacing techniques and is focusing current efforts on using autogenous fibrin laden with insulin-like growth factor–1 and chondrocytes harvested from neonatal foals. An arthroscopic technique using a two-component system was used to implant the graft in experimental and clinically affected horses with defects in the carpus and subchondral cystic lesions of the medial femoral condyle and in the fetlock joint. Early results appeared promising. More recently mesenchymal stem cell grafts improved early healing of full-thickness cartilage lesions; however, there was no significant long-term difference between stem cell–treated and control defects.21 In an osteochondral fragment model evaluating articular cartilage and subchondral bone healing and synovitis, injection of either adipose-derived or bone marrow–derived stem cells had similar results to controls.22 It was suggested that the use of stem cells might be beneficial in joints with soft tissue injuries. A technique called mosaic arthroplasty involves using arthroscopic procedures to harvest osteochondral pegs (grafts) from the trochlear groove or the medial border of
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the medial trochlear ridge of the femur and implant them in distant recipient sites.23-26 Grafts harvested and implanted using special instruments have better congruence than previously reported osteochondral grafting techniques, most using donor sites in the sternum. Mosaic arthroplasty has been used to manage osteochondral defects and subchondral bone cysts in the medial condyle of the femur, the fetlock joint, and the C3 and was proposed to be useful when conservative management failed.23-26 Seven of 10 horses returned to the previous level of performance after surgery.26 However, in an experimental study the technique was questioned because although there was good incorporation of bony portions of the grafts into recipient subchondral bone, there was substantial cartilage degeneration.24 Large osteochondral flaps (osteochondritis dissecans) in the stifle, tarsocrural, and fetlock joints have been successfully reattached, rather than removed, using polydioxanone pins.27
Postoperative Care
Aftercare instructions differ depending on the joint(s) involved, severity of cartilage damage, surgeon’s experience, economic factors, and competition schedules. Ban dage and wound care, administration of antiinflammatory, analgesic, and antimicrobial therapy, and suture removal are routine. Decisions about rehabilitation time should be based on the extent of the damage and its location, but often are made based on the perceived need for a quick return to training and performance. Intraarticular therapy with hyaluronan and polysulfated glycosaminoglycans (PSGAG) is often recommended, and although such therapy may be beneficial to reduce inflammatory changes in joints early after surgery, little evidence exists that repair is augmented. I generally recommend intraarticular hyaluronan 14 and 28 days after surgery in horses with mild or moderate cartilage damage and PSGAG, administered intraarticularly 3, 5, and 7 weeks after surgery, for horses with severe or global cartilage damage. Treatment with PSGAG given intramuscularly beginning 2 weeks after surgery (once weekly for 8 weeks) is recommended.
COMPLICATIONS The infection rate after arthroscopic surgery is low, but not zero, and is generally less than other soft tissue and orthopedic procedures performed in the same hospital. Poor case selection and failure to remove the intended fragments are the most common important complications. Intraoperative radiographs should be obtained if any doubt exists about fragments (number and size) removed. Extravasation of fluid, most commonly at the instrument portal but occasionally at the arthroscopic portal, occurs frequently and is of little concern. Fibrous tissue formation at the instrument portal is common if a large amount of cartilage and bony debris is flushed from the joint or removal of several osteochondral fragments required extensive manipulation. Prolonged drainage from any portal should be managed as potential infectious arthritis. Synovial fistulae occur rarely, but they may require repair. Damage to overlying tendons may cause aesthetically unpleasing tenosynovitis that usually responds to injections, but occasionally repair of synoviosynovial fistulae is necessary.
23
Arthroscopic Examination Mike W. Ross
References on page 1265
Arthroscopic surgery is arguably the most important advance in management and one of the most important in diagnosis of equine joint disease. Arthroscopic surgery has been a mainstay in managing joint disease since the early 1980s and has mostly replaced arthrotomy. An effective equine surgeon cannot lack extensive arthroscopic surgical experience, and lameness diagnosticians must understand indications and limitations of the technique. Innovators have used the same instruments for bursoscopy and tenoscopy (see Chapter 24). For a complete description of procedures, instrumentation, and principles of arthroscopy, the reader is referred to Diagnostic and Surgical Arthroscopy in the Horse.1
ADVANTAGES AND DISADVANTAGES OF ARTHROSCOPIC SURGERY COMPARED WITH ARTHROTOMY Arthroscopic surgery offers several advantages compared with arthrotomy; however, this type of surgery also has some disadvantages. Both are discussed in the following text.
Advantages Improved Visibility
Improved visibility during arthroscopic examination allows for evaluation of most of the joint compared with the limited view provided by arthrotomy. Even long arthrotomy incisions rarely provide added visibility because overlying capsule, retinaculum, and sheaths make retraction difficult. During arthroscopic examination, cartilage at locations distant to the primary lesion site, synovium, and intraarticular soft tissue structures such as ligaments can be examined. For example, newly described disease conditions involving intercarpal ligaments were not known before arthroscopic examination existed.
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Reduced Trauma and Morbidity
Arthroscopic examination is less traumatic and causes less morbidity. Arthroscopic examination allows surgery to be performed through small incisions and requires less surgical exposure and damage to overlying soft tissues, upholding a time-honored principle of limiting trauma. Little pain is observed in horses after arthroscopic surgery compared with arthrotomy, and many horses appear to ambulate normally. However, in an unblinded study of horses after arthroscopy under general anesthesia, horses showed mild but significant increases in discomfort compared with pain-free controls.2 Complications such as wound dehiscence and seroma formation are minimal. Horses often show pronounced lameness for several days after arthrotomy. After arthroscopic examination and surgery, owners and trainers expect horses to return to full work soon after surgery, an idea that is fueled by widespread reports of human athletes returning to professional sports quickly after arthroscopic surgery. A general misunderstanding is that incision size is the limiting factor. Although arthrotomy does cause short-lived lameness after surgery, the fear that it will delay onset of training is unfounded because the underlying lesion dictates recovery time. Although not recommended, horses with mild conditions such as osteochondritis dissecans, effusion but no lameness, and those that receive prophylactic arthroscopic surgery can resume training a few weeks after arthroscopic examination or arthroscopic surgery. Arthroscopic surgery can be performed within weeks before a sale, and if hair was not clipped, surgical sites are barely noticeable.
Better Cosmetic Results
Improved cosmesis is a definite advantage. Small incisions cause less fibrous tissue formation, and incisions are difficult to identify 2 to 3 months after surgery. Generally the instrument portal (incision), the site through which the arthroscopic instruments are passed and lavage is performed, suffers more trauma than does the arthroscopic portal, and swelling, reactions, and fibrous tissue production are more common.
Earlier Functional Capability
Earlier return to function was once believed to be an advantage of arthroscopic surgery. However, incision size has little to do with lameness except within the first few weeks after surgery. Lameness observed in horses returned to work 4 to 6 weeks after arthroscopic surgery for substantial articular lesions has nothing to do with incision size. When horses undergoing arthroscopic surgery were given only a brief rest, results were unsatisfactory. Incisions heal from side to side, not end to end, and incision size has no effect on articular healing. Lesions must heal as completely as possible before full work can begin—a process that often takes several months. Type and location of lesions are important because horses with osteochondritis dissecans not involving weight-bearing surfaces can start training within 2 to 3 weeks of surgery, if necessary, whereas those with lesions in critical sites, such as the typical carpal osteochondral fragment, must be given 3 to 4 months of rest.
More Versatility
Improved versatility is a definite advantage because joints considered inaccessible, such as the coxofemoral joint, can
be evaluated. Techniques such as repair of third carpal slab fractures, distal third metatarsal (MtIII) or third metacarpal (McIII) fractures, fractures in other joints, and resurfacing techniques can be done using arthroscopic surgery.
Fewer Complications
Arthroscopic surgery results in fewer complications. Arthrotomy of the scapulohumeral, femorotibial, femoropatellar, cubital, and tarsocrural joints has been associated with dehiscence, seroma formation, and infection, but arthroscopic surgery of these joints is safe.
Disadvantages Expensive Instrumentation
Expense of surgical instrumentation is a disadvantage because start-up costs are high, but basic instrumentation is no more costly than routine surgical instruments. Although arthroscopic surgery can be done without video equipment, video arthroscopy is valuable for archiving images. It is much more comfortable than direct-view arthroscopy (looking directly through the eyepiece) because surgery is performed using a comfortably positioned monitor. It allows the procedure to be viewed by others and is valuable in maintaining aseptic technique because breaks in technique often occur during direct-view arthroscopic surgery.
Lack of Surgical Experience
Experience necessary to learn arthroscopic surgery is a disadvantage. Arthroscopic surgery requires skill in stereotactic techniques and orienting and operating without looking at the surgical site, and surgeons must be able to use instruments properly and safely while looking at a monitor. Preoperative planning must be done to ensure that the horse is positioned properly on the operating table and the surgeon has ready access for triangulation. Poor technique may result in iatrogenic damage or extravasation of large amounts of lavage fluid that can severely compromise distention of the joint capsule and thus ability to see adequately within the joint. Experience cannot be gained by simply attending a weekend course but rather by working long hours with cadaver specimens and observing experienced surgeons. Initially arthroscopic surgery can be time consuming until experience is gained, but with experience arthroscopic surgery is faster than arthrotomy.
Equipment Problems
Equipment failures can be a disadvantage, and because arthroscopic examination depends on electricity, a generator should always be available. Instruments are not made to withstand forces applied to cut, grasp, and debride equine bone and, along with the arthroscope, may break.
Improper Case Selection
Case selection is the most important disadvantage. Poor case selection can make arthroscopic surgery difficult and disappointing. Although much information can be gained by arthroscopic examination of any joint, prognosis should be carefully considered when operating on joints in which extensive osteoarthritis exists. Inadequate communication before surgery may leave owners and trainers with too high expectations of results. Often they have little appreciation
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Fig. 23-1 • A, Dorsal 25° proximal medial-plantarodistal lateral oblique digital radiographic image of the right hind (RH) metatarsophalangeal joint (MTPJ) in a 2-year-old Standardbred (STB) trotter showing a typical intraarticularly located plantar process fragment (arrow) easily removed using arthroscopic techniques. This “down angled” oblique radiographic image is useful to evaluate the region between the base of the medial proximal sesamoid bone and the proximal aspect of the proximal phalanx to see these fragments. B, Dorsolateral-plantaromedial oblique digital radiographic image of the RH MTPJ in a 2-year-old STB pacing filly with large nonarticular (large arrow) and small articular (small arrow) plantar process fragments, which were all removed using arthroscopic techniques. To remove fragments outside the joint, a combination of sharp and blunt dissection and use of a synovial resector are necessary.
for the magnitude of cartilage damage and osteoarthritis (OA), and they only see or hear about the chip fracture(s) visible radiologically. Owners and trainers tend to want to do something, but removal of osteochondral fragments from a carpus or fetlock joint with hopeless OA can be time consuming, cause instrument failures, and, worse, often results in a poor outcome. Poor prognosis associated with some conditions must be well communicated to owners before surgery. For example, we recently reviewed the results of surgical and conservative management of scapulohumeral osteochondrosis and found that overall, prognosis was poor.3 Prognosis varied inversely with the severity of radiological changes, and only 15% of potential racehorses started a race. Four of six nonracehorses were sound for intended use. Surgery did not improve prognosis.3 The fragment size that can be easily removed during arthroscopic surgery is limited, and the instrument portal must be enlarged to accommodate such fragments unless ostectomy is performed. The fragment must be located in the joint or at least close to it, a decision that must be made before surgery because arthroscopic surgery is of little benefit if the fragment is not in the joint or close enough to make the approach reasonable and safe. In the metatarsophalangeal joint, large plantar process fragments from the proximal phalanx are often located extraarticularly, and although they may still be best removed using conventional surgical techniques, I have removed large fragments with arthroscopic instrumentation; surgery is facilitated by use of a motorized synovial resector (Figure 23-1). Differentiation should be made preoperatively between fragments free in a joint, which are accessible to surgical removal, and those embedded in the joint capsule and therefore not readily removed. In the stifle joint,
fragments in the distal aspect of the femoropatellar joint may appear radiologically as if they are in the femorotibial joint. Rare fragments in the caudal pouches of the medial and lateral femorotibial joints can be difficult to retrieve, especially if the precise location cannot be determined radiologically before surgery. The approaches to the difficult caudal pouches of the medial and lateral femorotibial joints were recently refined.4 Highly mobile fragments in a large joint such as the femoropatellar joint can prove challenging to locate. There is still a limited role for arthrotomy in equine surgery. For example, I still prefer to use a small, medial, middle carpal arthrotomy to repair sagittal slab fractures of the third carpal bone (C3) because I believe I can more accurately place the screw in the medial aspect of the C3, between the C3 and the second carpal bone.5 Others prefer a technique using arthroscopic guidance.1
PRINCIPLES, INSTRUMENTATION, AND TECHNIQUE Surgical technique, basic and advanced instrumentation, and approaches are well described elsewhere,1 and in-depth discussion is beyond the scope of this textbook. The basic principle of arthroscopic surgery is to use a rigid 4-mm endoscope to evaluate and perform intraarticular surgery through small incisions. Smaller endoscopes (2.9 mm and smaller) facilitate surgery in smaller joints or to view lesions between joint surfaces. Limited arthroscopic surgery was previously performed through a single incision, and instruments were passed through a second slot in the arthroscopic cannula. Versatility was severely compromised. Triangulation, a versatile technique in use today, uses two distant
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portals so that the arthroscope and instruments create two sides of a triangle. For example, during routine tarsocrural arthroscopy the arthroscopic portal is dorsomedial and the instrument portal is dorsolateral. This allows the tips of the instruments to be in the surgical field from distant points and obviates the need for the arthroscope to be close to the lesion. The end of the arthroscope is angled 25 to 30 degrees, and a different view is obtained by simply rotating it. Endoscopes with angles of 70 and 120 degrees can be used to obtain different views and are useful when triangulation is done with incisions close together. The image must be positioned on the screen to optimize special orientation and facilitate stereotaxis. Arthroscopic surgery can be performed with basic instruments, the most important of which are rongeurs (Ferris-Smith), grasping forceps, bone curettes, lavage cannulae, intraarticular blades, and probes. Arthroscopic surgery depends on the availability of a suitable light source and monitor, digital camera, and recording devices. A fluid delivery system is mandatory, and pumps or other methods to pressurize fluid are preferred to gravity flow systems. Many common lesions removed by arthroscopic surgery are located on the joint margin, and visibility often is compromised when joint capsule and synovium collapse or when bleeding is excessive. Carbon dioxide insufflation is sometimes used and is preferred by some surgeons.6 Carbon dioxide insufflation was effective at maintaining distention of the metacarpophalangeal and metatarsophalangeal joints and gave excellent visibility of lesions, but fluid lavage was necessary when bleeding precluded optimal visibility.7 Lasers are used rarely. Controlled ablation (coblation), using a form of radiofrequency energy to dissolve tissue, is used intraarticularly and in tendon sheaths and bursae (see Chapter 24). Using a new radiofrequency prototype probe, researchers were able to control cartilage cell death significantly better compared with manual debridement and use of a commercially available probe.8 Motorized equipment is useful but expensive. Abrasion arthroplasty units include various motorized burrs to remove and smooth cartilage and bone surfaces and are used in horses with large lesions such as osteochondritis dissecans lesions of the lateral trochlear ridge of the femur. Synovial resectors are alternating, motorized, rotating blades that are helpful in removing synovium and fibrous tissue and are particularly valuable for removal of osteochondral fragments from the dorsal aspect of the distal interphalangeal joint, apical proximal sesamoid fracture fragments, large abaxial fragments originating from the proximal aspect of the proximal phalanx, and fragments from the lateral malleolus of the distal aspect of the tibia, as well as when synovectomy is indicated. The division between diagnostic and surgical arthroscopy is now artificial because the same instruments are used for both. Diagnostic arthroscopy, that is, arthroscopic examination, generally refers to evaluating cartilage, bone, and soft tissues to gain information for diagnosis and prognosis. The client must be warned that although valuable information is always learned, arthroscopic examination may provide little therapeutic benefit. However, I believe a tendency exists to undersell arthroscopic examination because a positive intervention cannot be made unless the joint is evaluated, and much can be learned about lesions with early arthroscopic examination. This is particularly
true in the stifle, carpus and fetlock joints. Arthroscopic examination is indicated in horses with lameness localized to a joint, but in which radiological findings are negative or equivocal. Scintigraphic evidence of subchondral bone injury is common in these horses, and defects, if present, in overlying articular cartilage can be debrided and attempts at resurfacing performed arthroscopically. In young racehorses with early subchondral bone injury, arthroscopic evaluation usually reveals little to no overlying cartilage damage in those portions of the joint visible from conventional arthroscopic approaches (Figure 23-2). In these horses lack of cartilage damage likely explains the lack of obvious clinical signs such as effusion. Management of horses with novel surgical techniques such as subchondral forage or using drugs targeting subchondral bone modeling/remodeling in combination with rest is recommended.
LH
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B Fig. 23-2 • A, Delayed-phase scintigraphic images of a 3-year-old Thoroughbred colt with subchondral bone pain localized to the lateral aspect of the left metatarsophalangeal joint using lateral plantar metatarsal analgesia. Focal increased radiopharmaceutical uptake of the distal, lateral condyle of the third metatarsal bone (MtIII) (arrows) can be seen. Radiographs revealed sclerosis but no radiolucency. B, Intraoperative view of the plantar aspect of the left hind fetlock joint (dorsal is to the left and medial is uppermost) from an arthroscopic portal in the proximal, lateral plantar pouch showing normal-appearing articular cartilage of the lateral condyle of the MtIII overlying subchondral bone injury as depicted scintigraphically. The proximal phalanx (PI) can be seen just distal to synovial membrane between the PI and the base of the lateral proximal sesamoid bone. The entire articular surface cannot be evaluated, but visible articular cartilage appears normal. A subchondral forage technique (three 3.5-mm holes drilled from the lateral condyle into subchondral bone) was used.
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Med fem
Tib LM
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Fig. 23-3 • Intraoperative arthroscopic images of the cranial aspects of the medial femorotibial joint (MFTJ) (A [medial is to the left and proximal is uppermost]) and lateral femorotibial joint (LFTJ) (B [lateral is to the right and proximal is uppermost]) in a 3-year-old Standardbred gelding with an unsual subchondral bone cyst in the proximal lateral aspect of the tibia (arrows) and enlarged, frayed lateral meniscus (LM). A cranial approach to the femoropatellar joint (FPJ) was used to evaluate the stifle and the septae between the FPJ, and the MFTJ and LFTJ were removed to allow examinations through a single approach. In this horse with left hindlimb lameness, clinical signs of stifle pain were not detected, and the horse was referred for scintigraphic examination, which revealed focal, moderately increased radiopharmaceutical uptake in the proximal, lateral aspect of the tibia. Notice the normal medial meniscus (MM) and articular cartilage of the proximal aspect of the tibia (Tib) in the MFTJ and mild undulation of articular cartilage of the distal femur (Med fem). The subchondral bone cyst and torn edge of the lateral meniscus have been debrided (B). Prognosis is guarded at best because of subchondral bone, cartilage, and meniscal injury in the LFTJ.
Scintigraphy and ultrasonography have low sensitivity in the complex stifle joint, and arthroscopic examination should be encouraged. Walmsley et al.,9 in a large case series, found that 47% of horses returned to full use, and prognosis was inversely proportional to severity of meniscal tearing, degree of cartilage damage, and radiological abnormalities (Figure 23-3) (see Chapter 46). Arthroscopic examination may uncover proliferative synovitis, intersesamoidean ligament injury, and intercarpal ligament injury. Intercarpal ligament injury often is associated with OA or osteochondral fragments and can cause hemar throsis and presumably joint instability (Figure 23-4).10,11 Lesions in difficult locations can be successfully evaluated and manipulated arthroscopically. Ten of 11 horses that had subchondral bone cysts of the distal phalanx returned to athletic use after arthroscopic debridement.12 The distal interphalangeal joint can be difficult to evaluate, but a combination of careful manipulation and flexion can improve visibility (Figure 23-5). Changes in articular cartilage are the most important information gained from arthroscopic examination. Prognosis was found to worsen in proportion to the extent of articular cartilage damage in the carpus,13 but all joints are similarly affected. Surface area and depth of damage are important. Widespread damage affecting many cartilaginous surfaces is usually worse than well-defined lesions extending into subchondral bone. Cartilage damage is graded as mild (<20% damage to cartilage and subchondral bone at the primary lesion site), moderate (involvement of apposing bone, but <30% total cartilage and subchondral
bone damage of primary and apposing sites), severe (≤50% of cartilage and subchondral bone damage of primary and apposing sites), and global (extensive cartilage damage visible on most articular surfaces) (Figures 23-6 to 23-8). If cartilage lesions do not extend past the zone of calcified cartilage, healing after surgery will likely be minimal (see Microfracture discussion below). Occult (not radiologically apparent) osteochondral fragments may be identified by arthroscopic examination. Recognition requires inspection and probing, if necessary, after synovial resection. Common sites include the medial aspect of the intermediate carpal and lateral aspect of the radial carpal bones and small fragments involving the proximodorsal aspect of the proximal phalanx. Unexplained tarsocrural effusion (bog spavin) is commonly caused by osteochondritis dissecans fragments of the distal medial malleolus of the tibia, and although fragments may be suspected radiologically, the presence is confirmed and they are removed arthroscopically. Occult or radiologically suspicious subchondral defects of the third carpal bone, the distal aspect of the medial femoral condyle, and the distal aspect of the MtIII and McIII can be confirmed and debrided. Most arthroscopic surgery is performed to remove radiologically apparent osteochondral fragment(s). Grading cartilage damage and subchondral bone damage, along with removing one or more osteochondral fragments, is important in assessing prognosis. Discovery of severe cartilage damage in horses with few radiological changes is common, especially in the carpus and fetlock joints. Whenever possible, all aspects of the joint should be evaluated.
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C-3
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Fig. 23-4 • Intraoperative arthroscopic images of the left (A) and right (B) middle carpal joints (MCJs) showing complete tearing of the medial palmar intercarpal ligaments (arrows) in a 2-year-old Thoroughbred filly in race training. The horse was positioned in dorsal recumbency, and distal is uppermost; medial is to the right in A and to the left in B. The arthroscope has been inserted through a dorsolateral portal between the extensor carpi radialis and common digital extensor tendons in both MCJs. Tearing of the medial palmar intercarpal ligament appears as it courses from the third carpal bone (C3) to the radial carpal bone (RC). The intermediate carpal bone (IC) can be seen. Tearing of the medial palmar intercarpal ligament causes hemarthrosis, a condition previously thought to be idiopathic without arthroscopic examination, and can occur in conjunction with osteochondral fragmentation and associated cartilage damage. When the intercarpal ligament is torn, the palmar aspect of the MCJ can be examined, a finding that is impossible if the ligament is intact.
PII
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Fig. 23-5 • Intraoperative arthroscopic images before (A) and after debridement (B) of the right hind distal interphalangeal joint (DIPJ) in a yearling Standardbred filly with a history of acute lameness and a small wound at the dorsal aspect of the coronary band. Hair was found in the dorsal aspect of the joint and was removed. With the joint in moderate flexion and the joint surfaces retracted using an arthroscopic elevator, this lesion involving the plantar aspect of the articular surface of the distal phalanx (PIII) can be seen (small arrows). Notice the articulation between the plantar aspect of the PIII and the navicular bone (large arrow). The distal articular surface of the middle phalanx (PII) can be seen.
In racehorses, although cartilage damage and osteochondral fragmentation are often seen dorsally, the palmar/ plantar aspect of the metacarpophalangeal joint or metatarsophalangeal joint often has extensive cartilaginous score lines or large, full-thickness areas of cartilage loss on
the medial aspect of the McIII and the medial articular surface of the proximal sesamoid bone (PSB) and on the lateral aspect of the MtIII and the lateral PSB. In nonracehorse sports horses, changes are most prominent dorsally. Lesions of the patella, sometimes with fragmentation,
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MtIII
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Fig. 23-6 • Intraoperative arthroscopic images of the dorsomedial aspect of the right metatarsophalangeal joint of a 3-year-old Thoroughbred filly with right hindlimb lameness (dorsal is right, proximal is top). A, A small osteochondral fragment (chip fracture, arrows) of the dorsomedial aspect of the proximal phalanx (P-I) is surrounded by mild cartilage damage. A small partial-thickness “score” line can be seen on the overlying medial condyle of the third metatarsal bone (MtIII). B, The chip fracture has been removed and surrounding mild cartilage damage debrided. This horse returned to successful racing 6 months after arthroscopic surgery.
RC
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B Fig. 23-7 • Intraoperative arthroscopic images of the right middle carpal joint of a 3-year-old Standardbred colt (dorsal is to the right and proximal is uppermost). A, A small osteochondral fragment (chip fracture, arrows) of the third carpal bone (C3) can be seen; minimal cartilage damage was found on the radiocarpal bone (RC). B, The chip fracture has been removed, and surrounding moderate cartilage damage has been debrided. This horse has a good prognosis for racing soundness.
found during arthroscopic examination explain why some horses with large osteochondritis dissecans lesions of the lateral trochlear ridge of the femur perform poorly. Arthroscopic examination is useful in horses with infectious arthritis to evaluate articular surfaces and synovium, identify and remove foreign material (see Figure 23-5), facilitate removal of fibrin, and perform much more effective and complete lavage than is achieved by throughand-through lavage. Arthroscopic examination usually is reserved for horses with long-standing infections and those
with extensive fibrin accumulation, but the Editors strongly promote its use for acute infection as well. I have not found a good correlation between arthroscopic and ultrasonographic identification of fibrin early in the disease process (the amount of fibrin is overestimated by ultrasonography). Arthroscopic examination can facilitate drain insertion, synovectomy, and debridement or removal of osteochondral defects. Arthroscopic portals can be left open to facilitate drainage after surgery, but this procedure should be used only in horses with refractory infections.
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C Fig. 23-8 • Intraoperative arthroscopic images of the plantar aspect of the left metatarsophalangeal joint in a 7-year-old Standardbred stallion showing severe cartilage and subchondral bone damage from end-stage osteoarthritis that developed from maladaptive bone remodeling. A, A large erosive lesion of the lateral condyle of the third metatarsal bone (MtIII) has been debrided (dorsal is to the left and proximal is uppermost). This area is difficult to see, and the arthroscope is positioned between MtIII and the lateral proximal sesamoid bone with the joint in as much extension as possible. The proximal, plantar aspect of the proximal phalanx (P-I) can be seen. B, Severe loss of articular cartilage with exposed subchondral bone (arrows) can be seen on the lateral proximal sesamoid bone. C, The technique known as microfracture has been performed in the area of complete cartilage loss on the lateral proximal sesamoid bone, but prognosis is hopeless for racing soundness.
SURGICAL PROCEDURES The specific indications and surgical procedures are discussed in other chapters. Dorsal and palmar/plantar, medial and lateral, and cranial and caudal approaches have been described; the approach, choice of portals, fluid delivery, and instrumentation vary among joints and surgeons. Positioning the horse on the operating table is important to allow access to the involved joint(s), and repositioning may be necessary. Both lateral and dorsal recumbency are used successfully, and choices are based on the surgeon’s experience and the number of joints affected. Although standing arthroscopy of the fetlock and
other joints has been described,14 I prefer to use general anesthesia. Minimally invasive surgery such as arthroscopic surgery continues to be developed in horses. Standard procedures include fragment removal, debridement and curettage, partial synovectomy, and incision of adhesions. Reduction, fragment removal, and screw placement in horses with condylar fractures of the McIII or the MtIII can be done using arthroscopic surgery, obviating the need for arthrotomy. A technique to insert one or more cortical bone screws to repair frontal slab fractures of the third carpal bone was an early advance that has led to use of a similar technique to repair radial carpal bone and ulnar carpal
Chapter 23 Arthroscopic Examination
bone slab fractures, PSB fractures, and other unusually located articular fractures.15 An alternative to arthroscopic debridement of subchondral bone cysts of the medial femoral condyle—injection of the cyst lining with cor ticosteroids under arthroscopic guidance—appears to give similar clinical results.16 Thirty-five of 52 horses (67%) were considered successful. Horses with unilateral subchondral bone cysts did better than those with bilateral cysts, and the existence of osteophytes on preoperative radiographs had a negative impact on success.16
Cartilage Resurfacing
Recently cartilage resurfacing techniques have been used in experimental horses and in a limited number of clinically affected horses. Repair strategy involves creating access to stem cells, growth factors, and blood in subchondral bone to assist in cartilage repair or transplantation (grafting) of tissues, osteochondral grafts, or cells (chondrocytes). Partial- or full-thickness cartilage defects that do not penetrate the subchondral plate heal incompletely or not at all. An important principle in cartilage repair is to curette through the layer of calcified cartilage and perforate the subchondral plate to allow influx of healing elements. Extensive curettage seems to be self-defeating because exposure of large areas of denuded subchondral bone is associated with poor prognosis and often is found in horses with naturally occurring OA. Unfortunately, many defects already involve complete erosion into subchondral bone, at least around and apposing the primary lesion site. A technique known as microfracture of the subchondral plate has been introduced and involves using a 45- or 90-degree orthopedic awl (micropick) to create small perforation sites into subchondral bone in the area of cartilage damage.17,18 Studies have shown that removal of the calcified cartilage layer alone, or perforation of the layer with the microfracture technique, improves the amount and quality of repair tissue, but this tissue lacks the bio mechanical and histological character of hyaline cartilage.19 The procedure is currently being used, but objective results compared with routine procedures have not been published. Nixon20 has considerable experience in transplantation resurfacing techniques and is focusing current efforts on using autogenous fibrin laden with insulin-like growth factor–1 and chondrocytes harvested from neonatal foals. An arthroscopic technique using a two-component system was used to implant the graft in experimental and clinically affected horses with defects in the carpus and subchondral cystic lesions of the medial femoral condyle and in the fetlock joint. Early results appeared promising. More recently mesenchymal stem cell grafts improved early healing of full-thickness cartilage lesions; however, there was no significant long-term difference between stem cell–treated and control defects.21 In an osteochondral fragment model evaluating articular cartilage and subchondral bone healing and synovitis, injection of either adipose-derived or bone marrow–derived stem cells had similar results to controls.22 It was suggested that the use of stem cells might be beneficial in joints with soft tissue injuries. A technique called mosaic arthroplasty involves using arthroscopic procedures to harvest osteochondral pegs (grafts) from the trochlear groove or the medial border of
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the medial trochlear ridge of the femur and implant them in distant recipient sites.23-26 Grafts harvested and implanted using special instruments have better congruence than previously reported osteochondral grafting techniques, most using donor sites in the sternum. Mosaic arthroplasty has been used to manage osteochondral defects and subchondral bone cysts in the medial condyle of the femur, the fetlock joint, and the C3 and was proposed to be useful when conservative management failed.23-26 Seven of 10 horses returned to the previous level of performance after surgery.26 However, in an experimental study the technique was questioned because although there was good incorporation of bony portions of the grafts into recipient subchondral bone, there was substantial cartilage degeneration.24 Large osteochondral flaps (osteochondritis dissecans) in the stifle, tarsocrural, and fetlock joints have been successfully reattached, rather than removed, using polydioxanone pins.27
Postoperative Care
Aftercare instructions differ depending on the joint(s) involved, severity of cartilage damage, surgeon’s experience, economic factors, and competition schedules. Ban dage and wound care, administration of antiinflammatory, analgesic, and antimicrobial therapy, and suture removal are routine. Decisions about rehabilitation time should be based on the extent of the damage and its location, but often are made based on the perceived need for a quick return to training and performance. Intraarticular therapy with hyaluronan and polysulfated glycosaminoglycans (PSGAG) is often recommended, and although such therapy may be beneficial to reduce inflammatory changes in joints early after surgery, little evidence exists that repair is augmented. I generally recommend intraarticular hyaluronan 14 and 28 days after surgery in horses with mild or moderate cartilage damage and PSGAG, administered intraarticularly 3, 5, and 7 weeks after surgery, for horses with severe or global cartilage damage. Treatment with PSGAG given intramuscularly beginning 2 weeks after surgery (once weekly for 8 weeks) is recommended.
COMPLICATIONS The infection rate after arthroscopic surgery is low, but not zero, and is generally less than other soft tissue and orthopedic procedures performed in the same hospital. Poor case selection and failure to remove the intended fragments are the most common important complications. Intraoperative radiographs should be obtained if any doubt exists about fragments (number and size) removed. Extravasation of fluid, most commonly at the instrument portal but occasionally at the arthroscopic portal, occurs frequently and is of little concern. Fibrous tissue formation at the instrument portal is common if a large amount of cartilage and bony debris is flushed from the joint or removal of several osteochondral fragments required extensive manipulation. Prolonged drainage from any portal should be managed as potential infectious arthritis. Synovial fistulae occur rarely, but they may require repair. Damage to overlying tendons may cause aesthetically unpleasing tenosynovitis that usually responds to injections, but occasionally repair of synoviosynovial fistulae is necessary.