Small Animal Arthroscopy: 30 Years Of Learning

Courtesy of Dr. Timothy McCarty

Stifle menicscal injury.

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July 18 of this year will mark 30 years since I performed my first arthroscopic procedure. I performed this first arthroscopy on the stifle of a dog with an undiagnosed hind leg lameness and was able to diagnose a partially ruptured cranial cruciate ligament.

Since that day I have performed more than 2,000 arthroscopic procedures on more than 1,500 cases. This saga has truly been a learning experience for me and, with the knowledge gained by all of those performing arthroscopy in small animals, it has been a learning experience for the profession. 

Arthroscopy has redefined our understanding of joint disease in dogs and has changed how we treat many of these disorders. 
My first attempts at arthroscopy were primitive at best as I did not have a video camera system. I could only look; I could not do.   

My primary motivation was that we could not diagnose the cause of lameness in anything but the most obvious cases. In the early 1980s, we were just beginning to recognize medial coronoid process disease in the elbow, but to make a diagnosis required performing an open arthrotomy.  

Clients were not excited about performing an open invasive major surgery just to make a diagnosis. This problem was solved with arthroscopy, allowing diagnosis utilizing a minimally invasive procedure that was readily accepted by clients and well tolerated by patients.

With improvement in instrumentation and as my technical skills improved I was able to incorporate corrective surgery into my armamentarium. My first operative successes were with removal of shoulder osteochondritis dissecans cartilage fragments and debriding the bed of the cartilage defect. A long list of operative procedures have been added to this procedure to now include almost all intra-articular surgeries.

The three joints most commonly examined arthroscopically are the shoulder, elbow and stifle. The radiocarpal, hip and tibiotarsal joints are also amenable to arthroscopy but have far fewer indications.

The Shoulder
Indications for shoulder joint arthroscopy include front leg lameness when pain can be localized to the shoulder joint or there is detectable instability, swelling or crepitus on physical examination.

Indications also include radiographic changes, abnormal ultrasound findings and joint pathology identified with an MRI or CT.
The most common indication for shoulder arthroscopy is OCD, and the diagnosis is typically made prior to arthroscopy based on physical and radiographic findings. I did not expect to find anything new or different when I started performing arthroscopy for shoulder OCD and was primarily interested because this condition can be effectively treated surgically with this minimally invasive technique, which is less painful for the patient with less tissue trauma and faster recovery.

I also determined that I could see better and do a better job of removing fragments and cleaning the bed of the lesion with arthroscopy than with an open approach. I did, however, find changes in joints that had not been previously described and developed a better understanding of the effect of OCD on the whole shoulder joint. A diffuse widespread villus synovitis is commonly present and generalized chondromalacia is also typically present with varying degrees of severity.

The bed of the OCD lesion has been found to have three different appearances that affect how this part of the procedure is addressed. The exposed bone in the bed of the lesion can be rough, freshly exposedsubchondral bone with visible blood supply; chronically exposed bone with scattered areas of cartilage that has attempted to repair the defect; and as a smooth brown layer of a vascular necrotic bone. Each defect is treated differently.

A new finding has been a cartilage defect with exposed bone found in the central area of the glenoid cartilage that is not anatomically associated with the OCD lesion and is smooth with feathered cartilage margins.

Ununited caudal glenoid ossification center has also been established as a clinically significant diagnosis with removal of the fragment using arthroscopy associated with resolution of shoulder pain and lameness.    

This lesion is seen on lateral radiographs as a mineralized density caudal to the caudal margin of the glenoid articular surface and is typically separated from the scapula with a radiographically visible lucent line.

In young dogs this is thought to be a developmental abnormality. Removal with arthroscopy is relatively easy using the same portals as for OCD. 

Soft tissue injuries to the tendons and ligaments that support the shoulder joint are being more commonly diagnosed as we gain experience with arthroscopy.

Any or all of the shoulder support structures can be injured. This can occur as injury to an isolated structure or as a widely varied combination of injuries.

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The most common single injury is to the bicipital tendon. This has in the past been called "bicipital tenosynovitis” but this is a misnomer and comes from seeing the synovial reaction that can occur  around the origin of the tendon. This synovial reaction is not related to the condition of the bicipital tendon but is a reaction to any inflammatory process in the shoulder joint and is not the cause of the joint pain, but is a secondary reaction to other pathology.
Lameness or shoulder pain associated with the bicipital tendon is due to an injury to the bicipital tendon with partial rupture of the tendon. 
Other intra-articular soft tissue structures that can be injured include the medial glenohumoral ligament, the subscapularis tendon, the lateral labrum and the caudal joint capsule. The supraspinatus tendon is a periarticular structure but its tendon of insertion, when damaged, can be seen through the joint capsule cranial and lateral to the bicipital tendon.

The Elbow
When I first started performing elbow arthroscopy it was to use a minimally invasive technique to make a diagnosis before open surgery. Now arthroscopy is the standard of care for managing medial coronoid process disease (MCPD).

In the early operative period the primary goal was to remove free fragments, but that has progressed to include subtotal medial coronoidectomy, and removal of osteophytes that interfere with joint movement.

The most important thing learned from elbow arthroscopy for MCPD is the wide variability of the pathology that is present.

There can be a free coronoid process fragment with normal cartilage on all articular surfaces, multiple fragments, fixed fragments where all that is seen is a fissure line in the cartilage surface of the medial coronoid process,  or no fragment normal cartilage with fissure lines in the deep bone of the coronoid process or areas of variable bone density in the coronoid process.

Cartilage damage can vary from none to almost complete loss of cartilage from the medial half of the semiulnar notch and from the entire medial ridge of the humoral condyle. It has also been interesting to see that the severity of the lameness, the amount of elbow pain and the extent of the radiographic changes do not necessarily correlate with the intra-articular damage to the joint seen with arthroscopy.
One of the very important factors in managing elbows with MCPD is early diagnosis and intervention. If we can address this condition early when there is minimal or no cartilage damage, especially to the cartilage on the medial ridge of the humoral condyle, we have a much better chance of achieving an acceptable result than if we wait until there is extensive grade five cartilage damage over a large area of the humoral condyle and ulna.

End stage joints can be helped but not fixed with arthroscopy. I have also added stem cell therapy for managing elbow joints with success. When we have an effective elbow prosthesis, it will improve the management of the elbow joints that are truly beyond the scope of less aggressive procedures.

OCD of the elbow joint is an uncommon but significant occurrence and can occur with or without MCPD. OCD lesions can be seen on radiographs of the elbow joint in most but not all cases.

Determining for sure if the changes in an elbow are from OCD or MCPD prior to arthroscopy is not necessary because arthroscopy portals for approaching both conditions are the same. What is important is to remember to evaluate the medial ridge of the humoral condyle while performing the arthroscopic procedure even if there is significant medial coronoid process pathology. It is very easy to forget to look for OCD when focused on the medial coronoid process.

Removal of ununited anconeal process fragments can be facilitated with arthroscopic guidance. The approach uses the same portals that are used for MCPD and OCD of the elbow and a caudomedial operative portal for removal of the UAP fragment.

This operative portal is more like a small arthrotomy because it needs to be large enough the remove the large UAP.

The most important advantage of arthroscopy for this procedure is that the majority of UAP cases also have MCPD that needs to be addressed to maximize results.

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Arthroscopy also allows a smaller surgical approach to the caudal joint compartment and allows for evaluation and removal of any residual bone fragments or debris after removal of the UAP.

There are limited indications for arthroscopy of the carpal joint or, more accurately, the radiocarpal joint. The most common indication is removal of "carpal chips.” These small fracture fragments can come from the dorsal margin of the distal radius or from the radial carpal bone.

Other indications include synovial biopsy for diagnosis of immune mediated arthritis, assessing soft tissue injuries to the joint and for evaluating radial carpal bone fractures. 

The Hip
Arthroscopy of the hip joint is primarily indicated to assess cartilage surfaces of the femoral head and acetabulum before performing pelvic osteotomies in young dysplastic dogs.

If the cartilage on the dorsal aspect of the femoral head is damaged or gone, or if the weight bearing surface of the acetabulum is damaged or is too narrow due to loss of its lateral margin, then the prognosis for long-term good results with pelvic osteotomy is significantly reduced.

It is interesting that the worse the subluxation the better the chance for healthy cartilage on the femoral head because wear in these cases is on the medial aspect of the femoral head. With less severe subluxation, cartilage damage occurs on the dorsal surface of the femoral head that will be the new weight-bearing surface after acetabular rotation with the pelvic osteotomy.

The hip joint of a young dysplastic dog is the easiest joint to access with arthroscopy.

The Stifle
The stifle joint is one of the most difficult joints to effectively examine with arthroscopy.
Portal placement is easy but examination once in the joint and performing operative procedures is hampered by the fat pad, the complex anatomy of the joint, and especially due to the extensive villus synovial reaction that occurs with cruciate ligament injuries.

This reaction fills the joint with synovial fronds, and because cruciate ligament injuries are the most common diagnosis made with arthroscopy of the stifle joint, this is a major issue.

Effective arthroscopy of the stfle joint requires use of an arthroscopic shaver and an arthroscopic radio frequency ablation device to remove sufficient fat pad and synovium to create an adequate visual field.

Once this has been achieved, diagnostic and operative procedures become feasible.
The classic cruciate ligament rupture does not need arthroscopy to make a diagnosis but arthroscopy is needed to accurately evaluate the joint for meniscal injuries and to assess the condition of the cartilage surfaces.

One of the most important things I have learned performing arthroscopy of the stifle in dogs with cruciate ligament injuries is that the cartilage damage is diffuse, including all the cartilage surfaces.

The damage is not confined just those surfaces affected by the instability.  
I have also learned that meniscal injuries involve both the medial and lateral menisci. Not only is arthroscopy less invasive than an open arthrotomy, but the magnification of the arthroscope, camera and monitor allows us to see things that we cannot see even with an open arthrotomy. The extent of chondromalacia, meniscal damage and villus synovial reaction cannot be appreciated during an open arthrotomy.    

There is an endless discussion about the progression of radiographic changes following tibial plateau leveling osteotomies and the use of these findings to denigrate the efficacy of the procedure. No one has correlated the progression of radiographic changes with the condition of the joint at the time of surgery.   

When the severity of the changes is appreciated, it is understandable that there will be a progression of radiographic changes no matter what we do.

One of the other important learning experiences has allowed me to diagnose cruciate ligament injuries at a much earlier stage before there is significant cartilage or meniscal damage.

In these cases the diagnosis can be made before there is any joint instability, before joint thickening or swelling, before there is a medial buttress, before there are any radiographically detectable bony changes, and sometimes before there is joint pain that can be elicited on physical examination.

If there is a hind leg lameness that is not attributed to other pathology, the finding of increased intra-articular fluid density on a lateral radiograph (fat pad displacement) has a greater than 90 percent correlation with cranial cruciate ligament injury. The extent of the injury may not be appreciated with an open arthrotomy and arthroscopy is required to make this diagnosis.

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When cruciate ligament injuries are diagnosed at this stage, there is far less joint damage. The injured ligament can be left in place and in many cases the injured ligament will heal following a TPLO, leaving a stable joint.

Because of this, there is no need for meniscal release because the joint will be stable.
Theoretically there will be better results with less progression of radiographically evident degenerative joint disease. Second-look arthroscopy in some of these early surgical interventions have revealed pristine joints with no indication of pathology and a completely healed normal cranial cruciate ligament, normal cartilage surfaces, and no synovitis.

Evaluation of meniscal injuries is also facilitated with arthroscopy.

Small meniscal tears that cannot be seen without magnification are not uncommon and addressing them at the time of initial surgery can reduce the risk of progression to become clinically significant requiring a second surgery.
Stifle arthroscopy has also found that the incidence of lateral meniscal injuries is greater than the incidence of medial meniscal injuries. The most common lateral meniscal injury is fraying of the cranial one-quarter to one-third of the axial margin of the meniscus and is present in almost all stifles with cranial cruciate ligament injuries.

Most of these are too fine to see without magnification with the arthroscopy system. Partial and total meniscectomies can be performed arthroscopically but are technically difficult and are greatly facilitated with a stifle retractor to help open the joint space.
Medial meniscal release, although controversial, can be performed with arthroscopy by transecting the caudomeniscal ligament. 

I understand the detrimental effects of meniscal release from an engineering or biomechanical perspective, but we do not know the true clinical effects because we have not correlated the preoperative condition of joints with long term follow-up of released and non-released menisci.

The incidence of cranial cruciate ligament injuries as an indication for stifle arthroscopy is so great that it dwarfs all other pathologies in this joint. OCD of the stifle joint can be diagnosed and operated with arthroscopy with better but still insufficient results.  Meniscal injuries without cruciate ligament damage, although common in people, are very rare or nonexistent in the dog. I thought that I saw one, but now I realize that I probably just missed the cruciate ligament injury.

Long digital extension tendon injuries and avulsions are diagnosed and managed with arthroscopy, as are the same pathologies to the popliteal tendon.

Unfortunately, one of the causes of radiographically detectable increased fluid density that makes up the small percentage of cases that are not due to cruciate ligament injuries is intra-articular neoplasia.
These joints appear completely different arthroscopically from those with cruciate ligament disease. Biopsy of these tumors can be performed effectively with arthroscopy.
Tibiotarsal Joint
Tibiotarsal arthroscopy is uncommonly performed and is probably the most difficult of the six listed joints to access, diagnose and effectively operate on. 
The most common indication for and diagnosis with arthroscopy of the tibiotarsal joint is OCD. Like the stifle, even with arthroscopic removal of the OCD lesion, results are still inadequate.  

Other diagnoses with arthroscopy in the tibiotarsal joint include intra-articular fractures, immune mediated arthritis and sepsis.

The most significant disadvantage or downside of arthroscopy is its difficulty to perform and the long, steep learning curve.

Becoming proficient at arthroscopy can be done; if I can learn arthroscopy, anyone can, and it is truly worth learning.

With arthroscopy we can see more with less trauma, in less time, while causing less pain, allowing faster recovery and achieving better results than with any other intervention.

There is much that we do not know about application of arthroscopy in small animal practice, and since I started performing arthroscopy 30 years ago, I think I have come up with more new questions than new answers.

I firmly believe that arthroscopy is the most significant advance in small animal orthopedics that I have seen during my professional career.

Dr. McCarthy is a diplomate emeritus of the American College of Veterinary Surgeons and practices at Cascade Veterinary Referral Center in Tigard, Ore. He is editor of "Veterinary Endoscopy for the Small Animal Practitioner” (Elsevier, 2005).



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