M. Glyde, BVSc, MACVSc, MVS, HDipUTL, DECVS
At the end of this session you will be able to:
- Identify the instruments that simplify stifle joint exploration and how to use them
- Recognise differences between the medial and lateral menisci
- Identify the location of a meniscal injury
The keys to simplifying stifle joint surgery are an understanding of:
- The surgical anatomy of the stifle joint – familiarity with surgical anatomy aids confidence, intraoperative decision-making and simplifies surgery overall
- The preparation, positioning and intraoperative manipulation of the stifle joint that will simplify stifle joint exposure and maximize visualization
- The equipment that will simplify exposure
- How to perform a stifle joint arthrotomy and effectively examine the joint structures
- Common surgical procedures involving the stifle joint
Preparation and Positioning
Surgical preparation and draping are most easily performed with the limb suspended with adhesive tape from a drip stand or roof bolt. The limb should be clipped circumferentially from the proximal thigh to just proximal to the hock joint for most stifle joint surgeries. After routine surgical preparation the animal can be moved into the operating room with the limb still suspended.
Positioning the animal in dorsal recumbency simplifies stifle joint exploration. “Free draping” rather than field draping will allow the surgeon to have maximum vision and intraoperative manipulation of the stifle joint.
It is important that the final drape layer is of waterproof material as lavage is necessary in most stifle joint surgeries. Non-waterproof drapes will increase the risk of bacterial contamination through strike-through.
Equipment for Effective Stifle Joint Exploration Includes
- 1 Gelpi self-retaining retractor
- 1 stifle joint distractor (or alternatively a narrow-bladed 10–12 mm Hohmann retractor)
- 1 sharp-pointed Senn retractor
- 1 meniscal probe
- 1 mosquito haemostat or meniscal forceps
- Frazier suction tip (#6 or 8) and suction
- Effective surgical lighting
- Sterile lavage solution
Surgical Approach for Stifle Joint Exploration
The specifics of the various surgical approaches to the stifle joint are beyond the scope of this session. Arthroscopy has been shown to provide superior meniscal detail, greater sensitivity in detecting meniscal damage, reduced patient morbidity and a significantly lower occurrence of late or subsequent meniscal injury than for arthrotomy.
This session will focus on arthrotomy. Both the lateral and medial approaches have relative advantages and disadvantages. Both provide equally good vision and access to the menisci. Which side the surgeon chooses is personal preference and is usually determined by the type of cruciate stabilization surgery that is to be performed.
In both cases a “mini arthrotomy” rather than a full arthrotomy is completely adequate to provide adequate visualization to confirm the presence of cruciate disease and explore the menisci and adequate access for any necessary meniscal surgery.
The mini arthrotomy incision is from the level of the distal pole of the patella to the tibial plateau. Recognise that the infrapatellar fat pad is cranial to or outside the synovial part of the joint, so it is not necessary to incise through the fat pad. The incision through the synovial membrane runs immediately proximal to the fat pad and extends proximally to the level of the distal pole of the patella.
In a typical cruciate disease case, there is chronic thickening of the synovial membrane and so the use of electrosurgery to control small arterial vessels in the thickened capsule in combination with suction is very useful.
A Gelpi retractor is inserted to transversely retract the capsular incision.
To properly inspect the menisci when cranial cruciate ligament rupture exists and the joint is unstable, it is essential that distraction or cranial drawer of the tibia is achieved and maintained throughout the procedure.
Effective inspection of the menisci when no cruciate instability is present is not possible without arthroscopy. It should be noted that when no instability exists, such as in early cases of cruciate disease, it is very uncommon to have isolated meniscal injuries that are significant.
In these cases where there is no instability in either flexion or extension when examined under general anesthesia, it is reasonable to assume that there is no significant meniscal injury. An arthrotomy (or arthroscopy) to confirm that early cruciate disease with partial tearing of the cranial cruciate ligament is present, however, would be necessary. Careful probing of the cranial cruciate ligament with the meniscal probe will usually identify torn cruciate fibres in these cases.
In cases where cruciate instability is present, 2 methods exist to create and maintain distraction or cranial drawer of the tibia at arthrotomy.
The first method is the use of a self-retaining stifle joint distractor. The proximal tip of the distractor is placed in the proximal part of the intercondylar fossa. The intercondylar fossa is the origin of the caudal cruciate ligament, so care should be taken when placing the proximal tip to avoid damage to the ligament.
The distal tip of the distractor is positioned caudal to and under the intermeniscal ligament. The intermeniscal ligament is not able to be visualized because it is covered by the fat pad. Gentle retraction of the Gelpi retractor distally helps retract the fat pad distally and provide better access to place the distal tip of the stifle distractor immediately caudal to the intermeniscal ligament. Alternatively, the Senn retractor can be used for this purpose.
The intermeniscal ligament lies immediately cranial to the insertion of the cranial cruciate ligament. Even in cases of complete cranial cruciate rupture, the insertional end of the cranial cruciate is visible and can be used as a guide to find the intermeniscal ligament.
Once both tips of the distractor are in the correct location, the joint is distracted. Provided the distal tip is correctly positioned caudal to and loading the intermeniscal ligament, it will not pull out. If the distractor is pulling out distally, it is because the tip has been placed into the fat pad instead of caudal to the ligament. Slight extension of the leg with the distractor in place will partly open the caudal aspect of the femorotibial joint and facilitate examination of the caudal horn of the menisci. The caudal horn of the medial meniscus is the area where the vast majority of significant meniscal injuries occur.
Various stifle distractors and sizes are available. A “speedlock”/“spinlock” locking mechanism is preferable to a ratchet locking system.
The stifle joint distractor simplifies exploration of the stifle joint in nearly all cases. Combined with a Gelpi retractor, meniscal probe and good lighting and suction, it allows single-handed examination of the stifle joint.
The second method for creating effective distraction of the stifle joint to examine the menisci involves a combination of a narrow-bladed (12 mm or less) Hohmann retractor and a sharp-pointed Senn retractor and necessitates a surgical assistant.
A Gelpi retractor is placed as previously described. The Senn retractor is placed into the infrapatellar fat pad and the tibia pulled cranially.
The point of the Hohmann retractor is inserted through the intercondylar space of the femur and carefully hooked over the caudal aspect of the tibial plateau, taking care not to damage the caudal cruciate ligament.
The Hohmann retractor is then used to lever the tibia cranially and the femur caudally by pushing the handle of the Hohmann retractor in a caudal direction against the femoral trochlea. Use of a narrow-bladed Hohmann is necessary to avoid damaging the articular cartilage of the trochlea ridges.
Single-handed exploration is not possible with this method.
Relevant Meniscal Anatomy: What Do You Need to Know to Diagnose and Treat Meniscal Injury?
The menisci are biconcave, C-shaped fibrocartilaginous discs with their open part directed towards the axis of the bone. The medial and lateral menisci are remarkably different to each other.
In cross-section, the menisci are wedge-shaped, being thickest on their convex abaxial border and thinnest on the concave axial border. The menisci are held in position by 6 meniscal ligaments. To treat a meniscal tear to the caudal horn of the medial meniscus, you will need to cut part or all of the caudal meniscotibial ligament. So….. you need to be very familiar with the meniscal anatomy if you are going to safely and effectively treat meniscal injuries in cruciate disease cases.
Both menisci are attached to the tibia by a cranial and caudal meniscotibial ligament. Each of these 4 ligaments is a short strong ligament on the axial or central end of each meniscus.
The menisci are attached to each other by an intermeniscal ligament that joins their cranial horns and lies immediately cranial to the tibial insertion of the cranial cruciate ligament.
The caudal horn of the lateral meniscus is also attached to the caudal part of the medial femoral condyle by the meniscofemoral ligament of the lateral meniscus. The medial meniscus lacks any femoral attachment.
The medial meniscus is also firmly secured abaxially or peripherally to the joint capsule and the medial collateral ligament. Conversely, the lateral meniscus has no attachment to the lateral collateral ligament and has limited caudal capsular attachments, especially in the region of the popliteal tendon. It is only the cranial part of the lateral meniscus that has a firm capsular attachment.
It is this difference in attachment of the menisci that renders the medial meniscus less mobile than the lateral meniscus and explains the much higher incidence of damage to the medial meniscus.
Why Are Significant Lateral Meniscal Injuries Rare?
The lateral meniscus, because of its meniscofemoral ligament and minimal capsular attachments, moves with the lateral femoral condyle and is not subject to significant abnormal shear forces after cranial cruciate rupture.
The medial meniscus, however, being firmly attached to the tibial plateau, is subject to shear force when cranial cruciate instability exists. In this situation, the medial femoral condyle moves caudally on flexion and cranially on extension of the stifle joint. This movement of the medial condyle is resisted by the caudal horn of the medial meniscus and subjects it to abnormal shear forces which ultimately result in damage. Because menisci function as stabilizing “shock absorbers,” they are designed to take compressive loads but are unable to withstand shearing forces.
When using the meniscal probe to detect meniscal injuries (nearly all significant injuries occur to the caudal horn of the medial meniscus), the right-angled probe is turned flat to pass between the meniscus and the tibia. In a normal medial meniscus, the probe cannot be passed caudal to the caudal edge of the meniscus because it is attached to the capsule. The probe is turned with the tip facing dorsally and gentle traction on the caudal horn confirms no capsular tearing when there is no luxation of the horn cranially.
The probe tip is then used on the dorsal sloped surface of the caudal horn of the medial meniscus with the tip pointing down towards the meniscus. If a bucket handle (partial circumferential) tear is present, the probe tip will drop into the tear and the torn piece can be dislodged.
Significant lateral meniscal injuries are rare. The same procedure with the meniscal probe can be used on the caudal horn of the lateral meniscus; however, this must be done in full recognition of the completely different attachment of the lateral to the medial meniscus.
It is normal to be able to pass the probe caudally between the ventral surface of the caudal horn of the lateral meniscus and the tibia because there is no tight capsular attachment as there is on the medial side.
Bucket handle tears can be identified in the same way as for a medial meniscus however.
Small radial tears of the cranial horn of the lateral meniscus are common; however, these are of little clinical significance.
There Are 5 Key Points to Remember About Meniscal Anatomy When You Are Doing Meniscal Surgery:
- The medial and lateral menisci are different.
- The caudal meniscotibial ligament of the medial meniscus. Very commonly either a part of this ligament or all of this ligament needs to be transected to remove either a partial tear or a complete caudal pole tear, respectively. There is no capsular attachment at the area of the caudal meniscotibial ligament; the meniscal probe can pass freely dorsal and ventral to the ligament.
- The menisco-femoral ligament of the lateral meniscus. This is the largest of the meniscal ligaments and while normal is very different to the medial meniscus.
- The medial meniscus is firmly attached to the tibial plateau. The medial meniscus is firmly attached to the tibial plateau through peripheral attachments to the joint capsule and the medial collateral ligament. The lateral meniscus has no attachment to the lateral collateral ligament and has no caudal capsular attachments. Only the cranial third of the lateral meniscus has capsular attachments. It is this difference in attachment of the menisci that renders the medial meniscus less mobile than the lateral meniscus and explains the much higher incidence of damage to the medial meniscus in the cranial cruciate deficient stifle joint. When using a meniscal probe to inspect the menisci, it is important to recognise that the capsule should be firmly attached to the entire periphery of the medial meniscus.
- Normal menisci are gloss white. Damaged menisci typically have a matt or roughened appearance and are discoloured.
Treatment of Meniscal Injury
Surgery is the treatment of choice for meniscal injury. Conservative treatment is not recommended due to the avascular nature of the majority of the meniscus and consequent lack of healing. Only the peripheral 10–15% of the meniscus has a significant blood supply. The remainder of the meniscus receives nutrition from the synovial fluid. Dogs with untreated meniscal injuries remain with significant lameness despite treatment of their cruciate disease.
It is important to assume a meniscal injury is present in all cruciate ruptures where instability is present until proven otherwise on exploratory arthrotomy / arthroscopy. Meniscal injury has been shown to be present in dogs with cruciate instability in 30–60% of cases.
Meniscal injury is rare in dogs with early cruciate disease before instability develops. Early diagnosis of cruciate disease before instability develops is key to preventing meniscal damage and the problems associated with that.
Meniscal injury – treatment goals: Remove all of, BUT ONLY THE DAMAGED PART of the meniscus. Most commonly it is the caudal horn of the medial meniscus that is damaged.
There are three common types of meniscal injury:
- Bucket handle (partial circumferential) tears
- Peripheral capsular detachment
- Radial tears
All occur predominantly only in the caudal 1/3 of the medial meniscus between the medial collateral ligament and the caudal meniscotibial ligament.
Bucket handle tears are the most common meniscal injury. These are longitudinal tears (parallel to the circular orientation of the collagen fibres) named as the inner part of the meniscus is axially displaced resembling the handle of a bucket. Probing with a meniscal probe may be necessary to “unmask” a bucket handle tear. When probing, it is important to remember that in the normal medial meniscus passage of the probe dorsally and ventrally over the meniscus will not cause damage or separation and that (other than at the area of the caudal meniscotibial ligament) the probe can not be passed caudally beyond the meniscus due to the close attachment of the joint capsule to the medial meniscus. (This is not the case with the lateral meniscus where the probe passes freely dorsally and ventrally). Multiple bucket handle tears can be present in the caudal horn and careful probing is necessary.
Peripheral capsular detachment is similar to a large bucket handle tear with complete detachment of the caudal pole of the meniscus from the joint capsule.
Radial or transverse tears are full-thickness tears radiating from the inner concave (axial) border.
Partial meniscectomy (removal of only the damaged part of the meniscus) is strongly preferable to total meniscectomy.
Axial partial meniscectomy is the removal of the “bucket handle” part of a bucket handle tear. This leaves the periphery of the meniscus intact and, unless the bucket handle is very large, preserves some of the load-bearing capacity of the meniscus.
Caudal pole hemimeniscectomy is the removal of the entire caudal pole of a detached medial meniscus. While this is necessary in cases where the entire caudal horn is detached, it inactivates the shock-absorbing capacity of the meniscus and increases the severity of subsequent osteoarthritis similar to total meniscectomy.