Introduction

Arthroscopy has recently become the modality of choice for diagnosis and treatment of many joint diseases in the dog as it happened in the human and equine field years before.¹ The application of arthroscopy to the relatively small joints of the dog has been made possible through the development of small joint arthroscopy equipment, but the appropriate expertise has to be elaborated by the surgeon by extensive training with a steep learning curve. The advantages of minimally invasive arthroscopy compared to standard open arthrotomy are evident and proved clinically by reduced postoperative pain and accelerated recovery.² Arthroscopy improves visualization of articular structures by magnification and illumination, and constant irrigation with fluids. The low morbidity of arthroscopy allows the examination of bilateral or several different joints at the same anaesthetic procedure or consecutive examinations of the same joint for follow up studies (second look arthroscopy). Disadvantages of arthroscopy are the costs of the specialized instrumentation and the necessary extensive training to gain expertise in the procedure. Joints that are routinely inspected and treated by arthroscopy are the stifle, shoulder and elbow. Less frequently accessed joints are the hip, tarsus and carpus. Arthroscopy is performed under general anaesthesia but perioperative pain management is added by intraarticular infusion of local anaesthetics (lidocaine up to 5mg/kg, bupivacaine up to 2mg/kg) preoperatively and local anaesthetics combined with morphine (0.1mg/kg) postoperatively. The risk of infection is minimal with constant joint irrigation during arthroscopy, therefore prophylactic perioperative antibiotics are not indicated.

Elbow Arthroscopy

The elbow joint is probably the easiest joint for the surgeon to get started with arthroscopy as it is covered only with a thin layer of soft tissue under the skin. Introduction of the arthroscope and instruments is performed from medial to the joint and is guided by clear anatomical landmarks.⁴ The main indication for elbow arthroscopy is elbow dysplasia but in addition to this arthroscopy is used for inspection and biopsy sampling of unclear joint pathologies, irrigation of the joint in septic arthritis and video-assisted reduction of intraarticular fractures and incomplete fusion of the humeral condyle.

Elbow Dysplasia (ED)

ED is considered a developmental disease of the elbow and is the most common cause of thoracic limb lameness in juvenile dogs of certain medium to large breed dogs.³ Medial coronoid disease (MCD), osteochondritis dissecans (OCD) of the humeral condyle and ununited anconeal process (UAP) are specific manifestations of ED that may appear single or in concomitance with others in the same joint. The cause of ED is still discussed controversially but elbow incongruence is reportedly a primary contributor to the pathogenesis. MCD includes fissuring and fragmentation of the lateral aspect of the medial coronoid process (FCP) due to cartilage and/or subchondral bone pathology. With arthroscopy the ability to evaluate and grade the degradation of cartilage of the joint surfaces in the elbow joint has dramatically improved. Variations in disease of the medial coronoid process include chondromalacia, avascularity of the subchondral bone, incomplete fragmentation, fragmentation in situ, minimally displaced fragments or fully displaced fragments. Radiographic findings cannot be correlated with the type of MCP. CT is more accurate in differentiation of the type of MCD but is not as conclusive as direct arthroscopic visualisation. Arthroscopy is used in the management of MCD to provide minimally invasive assessment of the disease, to remove the fragments and to debride diseased cartilage and subchondral bone.OCD in the elbow occurs alone or in combination with MCD. An area of abnormally thickened cartilage at the medial and most distal region of the humeral condyle separates partially or completely from the subchondral bone. Arthroscopic treatment includes detachment and removal of the cartilage flap and curettage of the underlying subchondral bone to allow capillary bleeding. Microfracture or abrasion with a burr of the subchondral bone is indicated in chronic cases where bleeding of the subchondral bone is not apparent after curettage. UAP is a disease most frequently seen in German shepherds. The center of ossification of the anconeal process should unite with the ulna until 20 weeks of age. Failure of ossification may be caused by failure of enchondral ossification or incongruence of the joint. Reported surgical therapies include fragment removal, screw/pin fixation and ulnar osteotomy to reduce pressure. Arthroscopy is limited to provide visual assessment of the lesion.

Shoulder Arthroscopy

Indications for shoulder arthroscopy are diagnostic joint inspection, biopsy samples of articular structures, osteochondritis dissecans, avulsion or rupture of the bicipital tendon, tenosynovitis, avulsion or incomplete fusion of the caudal centre of ossification of the glenoid tubercle of the scapula, soft tissue injuries leading to shoulder instability, insertion tendinopathy of the supraspinatus muscle and video-assisted reduction of intraarticular fractures.

Osteochondritis Dissecans (OCD)

OCD results from a disturbance in endochondral ossification. A loose fragment of cartilage elevates into the joint or completely detaches from the underlying bone. Free cartilage fragments become lodged in the caudal joint pouch or adjacent and eventually into the biceps tendon sheath. Clinically lameness is present as soon as cartilage is cracked full thickness down to the subchondral bone and synovial fluid gets in contact with subchondral bone and inflammation is present. Large and giant breed dogs are commonly affected, males are more prone to the disease and joints are frequently affected bilateral. Clinical signs often develop between 4 and 8 month of age. In the shoulder the affected area of cartilage is located at the caudomedial surface of the humeral head. Treatment of OCD includes removal of the cartilage flap and curettage of the subchondral bone. Treatment by arthroscopy is minimally invasive and bilateral procedures are possible during the same anaesthetic session. The arthroscope is introduced from lateral into the joint and the instrument portal is positioned caudal to the arthroscope by triangulation.⁴ The flap often is too large to be removed in one piece. Curettage of the subchondral bone is achieved by use of a hand shaver or curette. Necrotic bone is removed until active bleeding can be appreciated. Mesenchymal cells of the blood stream will be transported to the surface and eventually metaplasia to fibrocartilage may cover the surface. Prognosis for OCD of the shoulder joint is good but degenerative osteoarthritis may be expected down the road.

Avulsion of the Biceps Tendon, Tenosynovitis

Biceps tenosynovitis is an inflammation of the biceps brachii tendon and the surrounding tendon sheath. The cause is either a direct or indirect trauma to the biceps tendon or tendon sheath. Repetitive microtrauma may be an inciting factor and cause partial or complete tearing of the tendon. Mineralisation of the supraspinatus tendon also may cause secondary mechanical irritation of the biceps tendon. Affected dogs are usually medium to large breed dogs and middle-aged or older. Active and working dogs are more prone to be affected. Clinically intermittent or progressive forelimb lameness that worsens after exercise is seen. Pain may be elicited with direct palpation over the biceps tendon, especially with flexion of the shoulder joint keeping the elbow joint in full extension. The diagnosis may be confirmed by radiography and ultrasound. Arthroscopic inspection of the insertion of the biceps tendon at the supraglenoid tubercle of the scapula confirms the diagnosis. Treatment consists in release of all biceps tendon remnants arthroscopically with scissors, meniscal knife, punch biopsy forceps, motorised shaver or radiofrequency unit.⁵ The instrument portal is established cranial to the arthroscope. After the complete release of the biceps tendon the tendon vanishes distal into the tendon sheath with flexion of the shoulder joint. Tenodesis with screw and washer fixation of the biceps tendon to the proximal humerus is not necessary and does not influence outcome positively.

Avulsion or Incomplete Fusion of the Caudal Glenoid Ossification Centre of the Scapula

The presence of a secondary caudal glenoid ossification centre is described in dogs. Radiographically incomplete fusion appears as a small radiodense projection located just caudal to the glenoid in the lateral shoulder view. In most cases this may be an incidental finding on radiographs of the shoulder. Lameness occurs when an osteochondral fragment is loose in the joint capsule and causes inflammation and pain. Pain can be elicited with hyperflexion of the shoulder joint. The diagnosis is assumed by exclusion of other shoulder problems and confirmed arthroscopically. The fragment is loosened from the joint capsule and removed. The caudal rim of the glenoid is cleaned by curettage with a hand shaver or curette. Prognosis with correct diagnosis is good.

Shoulder Instability

Chronic persistent shoulder lameness in middle-aged to older dogs may be caused by shoulder instability. Lameness is often accentuated with exercise and is most of the time not improved with non-steroidal medication. The fibrous capsule, glenohumeral ligaments and surrounding cuff muscles of the shoulder joint are injured. Overstretched or torn joint capsule or collateral ligaments cause shoulder instability. Strained cuff muscles cause fibrosis and mineralization of the muscle tendon unit. Pain on manipulation of the shoulder, and muscle atrophy are evident in most cases. Clinical examination for instability may be difficult to interpret.⁶ Examination under anaesthesia shows a bilateral difference in abduction/adduction and cranio-caudal stability. To perform an abduction test the animal is positioned in lateral recumbency. The elbow and shoulder joints are fixed in extension and the scapula is stabilized with one hand. An abduction force to the distal limb is applied with the other hand and the maximal abduction angle is measured with a goniometer. Abduction angles >45° or asymmetry compared to the contralateral side is considered pathologic. The diagnosis may be confirmed by exclusion of other shoulder problems and arthroscopic evaluation. Conservative treatment includes temporary immobilisation followed by controlled mobilisation and eventually intraarticular corticosteroid instillation. Surgical treatment consists of open medial or lateral reconstruction of capsular and ligament tears. Arthroscopic imbrication or video-assisted reconstruction may be the future. Capsular thermal contracture by a radiofrequency unit (OPES®, Arthrex; Oratec Vulcan®, Smith & Nephew) is attempted for mild to moderate joint laxity as a result of capsular or ligament stretching. The effect is explained by denaturation of collagen link proteins with subsequent contracture and scar tissue formation. Postoperative controlled mobilisation is essential for success. Prognosis is guarded depending on the degree of instability.

Stifle Arthroscopy

Arthroscopy of the stifle joint is technically more demanding as elbow and shoulder joints.¹ Adequate visualisation requires the use of a motorized shaver and electrocautery by radiofrequency, as well as flow management with more fluid and higher pressure. Standard arthroscopic instruments as used for elbows and shoulders are adequate. Instead of a 2.4/2.7mm arthroscope a 3.5 or 4.0mm may be used in the stifle joint with an increased quality and resolution of the monitor image. Standard instruments for handling the intraarticular tissues are used. Special instruments to treat meniscal lesions are available (reverse cutting meniscal knife, left or right curved punch forceps). Hyperemia of the inflamed synovial membrane or fat body is frequently encountered in the stifle and effective hemostasis is performed by increased irrigation flow by a fluid ingress pump and a large-diameter (3.5mm) fenestrated egress canula. The chronically inflamed fat bad prevents the view of the cruciate ligaments and the menisci and therefore has to be removed. A motorized shaver with 3.5mm full radius resector blades is excellent to cut an appropriate sized window into the fat pad to visualize the intercondylar notch and its structures. A radiofrequency unit bipolar (ArthroCare) or monopolar (Oratec Vulcan, OPES) is helpful for control of hemorrhage and tissue ablation. Indications for stifle arthroscopy are OCD lesions of the medial or lateral femoral condyle, partial or complete rupture of the cranial or caudal cruciate ligaments, meniscal injuries, avulsion or rupture of the tendon of the long digital extensor muscle, exploration and biopsy sampling of unclear joint pathologies and irrigation of the joint in septic arthritis. In combination with a Tibia Plateau Leveling Osteotomy (TPLO) or Tibial Tuberosity Advancement (TTA) a sometimes indicated "meniscal release" may be performed arthroscopically.⁷ Treatment of OCD consists of removal of the osteochondral flap and curettage of the subchondral bone. Cranial cruciate ligament rupture is treated by a combination of arthroscopic inspection, debridement of cruciate remnants, meniscal evaluation and treatment of bucket handle tears followed by an open TPLO or TTA or minimally invasive extracapsular stabilisation procedure.

References

1.  Beale, Hulse, Schulz, Whitney. Small Animal Arthroscopy 2003.

2.  Hoelzler, et al. Vet Surg 2004; 33:146.

3.  Fitzpatrick, et al. Vet Surg 2009; 38:213.

4.  Rochat. Veterinary Clinics of North America: Small Animal Practice 2001; 31:761.

5.  Bergenhuyzen, et al. Vet Comp Orthop Traumatol 2010; 23:51.

6.  Pucheu, et al. Vet Comp Orthop Traumatol. 2008; 21:368.

7.  Luther, et al. Vet Surg 2009; 38:250.