Chapter 90 - Subchondral cysts Flashcards
What are subchondral cystic lesions (SCLs)?
SCLs are areas of reduced bone density or cyst-like lesions in equine joints.
Where are SCLs typically found?
They usually occur in the subchondral bone beneath articular cartilage in weight-bearing areas of joints.
What can SCLs cause in horses?
They can potentially cause lameness and can be challenging to treat.
What types of cystic lesions are included in SCLs?
SCLs can be uni- or multiloculated, and some may appear large in the metaphysis of long bones.
What are some mechanisms that lead to the development of SCLs?
Mechanisms include osteochondrosis, trauma, articular sepsis, and inflammation.
What is osteochondrosis?
A condition involving retained, thickened cartilage that can contribute to SCL development.
What is a common location for SCLs related to osteochondrosis?
The medial condyle of the femur.
How can trauma lead to SCL formation?
Trauma can create communication between the subchondral bone and the joint, allowing synovial fluid to induce necrosis.
Figure 90-1. (A) Radiographic view of a SCL in the MFC of the stifle joint of a 3-year-old mare. The lesion is in the center of the weight-bearing area of the condyle and is characterized by a radiolucency, well demarcated from the surrounding normal bone by a thin sclerotic rim. (B) Dorsolateral-plantaromedial oblique radiographic view of a distal tibia showing a mild radiolucent area (arrows) visible in the distal metaphysis.
Figure 90-2. (A) Dorsoproximal-palmarodistal oblique image of a distal sesamoid bone of a 4-year-old mare presented with lameness. A parasagittal fracture of the distal sesamoid bone with a wide line is visible. (B) Three months later: a large circular radiolucent zone (SCL) is visible over the fracture line.
Figure 90-3. Radiographic image of the right stifle of a 12-year-old mare presented with recurrent lameness 15 months after débridement of a large femoral SCL (white arrows). A large SCL of the medial tibial condyle (black arrows) as well as osteophytes on the proximomedial aspect of the tibia and the distal aspect of the femur are visible.
Figure 90-4. Postmortem specimen of a distal sesamoid bone showing a SCL in cross section. (a) Communication into the joint; (b) sclerotic border of the SCL; (c) the contents of the SCL consist of a mixture of fibrous tissue, fibrocartilage, and necrotic bone, and can be filled with synovial-like fluid.
Figure 90-5. View of a stifle joint of a 4-year-old Quarter Horse mare presenting with effusion of the left femoropatellar joint and a SCL in the medial femorotibial joint.
Figure 90-6. Flexed lateromedial image of the left stifle of an 11-year-old Quarter Horse, showing a large SCL in the MFC.
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Figure 90-7. (A) Dorsoplantar view of the left hock of a Warmblood yearling presenting with severe lameness and effusion of the talocrural joint. Periosteal reactions are visible lateral to the fourth tarsal bone (arrow). (B) On the dorsal plane CT image, a small SCL in the fourth tarsal bone is visible (arrow).
Figure 90-8. (A) Dorsopalmar radiographic view of a SCL in the proximal aspect of P1. The SCL is located sagittally and surrounded by mild sclerosis (arrows). There is no obvious radiographic fissure formation. (B) In the dorsal CT view of the same lesion within the proximal sagittal aspect of P1, a SCL (arrow) is visible within the sagittal groove. (C) Transverse CT view of the same SCL showing a clear short incomplete fissure (black arrow) extending from the SCL (white arrow) dorsally, not penetrating the cortex.
What did a study find about SCLs and cartilage defects in ponies?
Experimental cartilage defects led to the development of subchondral cystic cavities.
How can inflammation contribute to SCLs?
Inflammatory mediators may lead to bone resorption and impaired healing.
What was revealed in a study of 703 SCL lesions?
The majority were found in the medial femoral condyle, followed by the phalanges.
What percentage of SCLs occur in males?
62%.
Which horse breeds are most affected by SCLs?
Thoroughbreds, American Quarter Horses, and Standardbreds are among the most affected.
Are SCLs more common in a specific age group?
They primarily affect younger horses.
What is the size range of SCLs?
They can range from a few millimeters to over 3 cm.
What is typically seen in the histology of SCLs?
They usually have a fibrous lining and may contain fibrous tissue and necrotic bone.
What changes might occur in the cartilage overlying an SCL?
Signs of matrix degradation can be observed near the canal.
Do SCLs always cause lameness?
No, they may or may not be associated with lameness.
What factors can cause lameness associated with SCLs?
Pain from synovitis, intraosseous pressure, or intracystic pressure.
How can flexion tests affect lameness in horses with SCLs?
They usually exacerbate the lameness.
What is a typical radiographic finding of SCLs?
A dome-shaped or round-to-oval subchondral lucency with a surrounding sclerotic rim.
What imaging technique is superior for diagnosing SCLs?
Computed Tomography (CT).
What does CT reveal about SCLs that radiographs might miss?
It can detect the exact localization and communication between the SCL and adjacent cartilage.
Can scintigraphy be used for diagnosing SCLs?
Yes, it can identify occult lesions not visible on radiographs.
What is the initial nonsurgical treatment for SCLs?
Rest and the use of nonsteroidal anti-inflammatory drugs (NSAIDs).
What is the success rate of nonsurgical treatment for SCLs?
Success rates range from 45% to 64%.
What role do bisphosphonates play in treating SCLs?
They inhibit bone resorption and can be used to improve lameness.
What is the first approach in the surgical treatment of SCLs?
Intraarticular injection of steroids is often the first approach.
What was the success rate of corticosteroid injections in one study?
Lameness resolved in 67% of treated horses.
What does surgical treatment of SCLs typically involve?
Surgical débridement under arthroscopic or transcortical approaches.
What did research indicate about the spontaneous resolution of SCLs?
Some lesions may spontaneously resolve without treatment.
What additional diagnostic information can ultrasonography provide?
It can clarify the relationship between SCLs and the joint.
What are the potential side effects of bisphosphonates in horses?
Colic, mild CNS symptoms, nephrotoxicity, and bone fragility.
What is a potential issue with the injection of corticosteroids?
The risk of recurrence of clinical signs is high.
What condition can lead to the development of SCLs in horses?
Articular sepsis can also be a contributing factor.
How can traumatic events influence lameness onset in older horses?
They may correlate with ongoing intraarticular inflammation.
What can be seen on CT scans of SCLs that indicates bone communication?
Discontinuous subchondral bone and prominent channels leading away from the cyst.
Why might some horses with SCLs not experience lameness?
The lesions may not always induce sufficient pain or dysfunction to cause noticeable lameness.
Figure 90-9. Dorsal CT view of a left fetlock of a 15-year-old Warmblood horse with acute severe lameness. There is an irregular SCL in the medial proximal aspect of P1; moreover, a channel (arrow) between the cyst and the medial cortex of P1 is visible.
Figure 90-10. Dorsal T2-weighted image of a right hind foot showing a high signal SCL (arrow) in the distal phalanx at the insertion of the lateral collateral ligament of the DIP joint.
Figure 90-11. (A) Intraoperative arthroscopic view under CO2 insufflation of a MFC showing a “Mercedes star” irregularity. (B) With the help of hypodermic needles, the optimal location for the instrument portal is identified. (C) Débridement of the cystic cavity is performed with an arthroscopic curette or a shaver. (D) Finally, all the content of the cyst has been removed, and the subchondral bone is visible
Figure 90-12. (A) Dorsopalmar radiographic view of a right MCP joint of a 12-year-old Warmblood presenting with acute, severe lameness. In the medial proximal aspect of the proximal phalanx an ill-defined radiolucent area is visible (arrows). (B) In the dorsal CT view of the same lesion, a SCL is visible. With the help of a commercially aiming device, the direction of the drill is planned on CT. (C) Intraoperative dorsal CT image showing the 4.5-mm drill bit entering the cystic lesion.
Figure 90-14. Mosaic arthroplasty. (A) SCL located in the MFC of a 5-year-old Hungarian half-bred mare, viewed through an arthrotomy. (B) Postoperative view after insertion of two differently sized osteochondral grafts taken from the medial femoral trochlea of the unaffected limb of the same horse. (C) Typical appearance of a 9-month follow-up arthroscopic view of a 6.5-mm defect created on the MFC and treated with an osteochondral graft in a 2-year-old research horse. (D) Typical appearance of an 8-month follow-up arthroscopic view of a donor site at the medial femoral trochlea. The defect is covered with uniform fibroid tissue. (
Figure 90-15. (A) Preoperative dorsopalmar radiographic view of a SCL in the distal articular aspect of the proximal phalanx. The cyst was curetted and filled with tricalcium phosphate granules through a transosseous approach. (B) Dorsopalmar radiographic view 2 years later. Tissue of bone density is filling the former SCL completely.
Figure 90-16. (A) Immediate postoperative caudocranial radiographic view of a SCL in the distal right MFC in a 2-year-old Arabian filly presenting with lameness. The cyst was débrided by arthroscopy and the cavity was filled with fibrin-based hydrogel and PTH1-34. (B) Follow-up radiographs 12 months later of the horse seen in (A). Note that bone density has increased considerably, and the SCL is hardly visible on radiographs.
Figure 90-17. (A) Postoperative dorsopalmar radiographic view of a SCL in the sagittal groove of the proximal phalanx of a 7-year-old mare, presenting with severe lameness. A 4.5-mm cortical screw has been inserted through the cyst in lag fashion. (B) Dorsopalmar radiographic view of a SCL in the second phalanx of a 13-year-old mare, presenting with lameness in the right hind limb, 2 months after surgery. The SCL had been treated with a cortex screw inserted in lag fashion. Two months later, the mare was sound at the trot.
Figure 90-18. (A) Craniocaudal radiographic view of the left cubital joint of a 19-year-old Warmblood gelding presenting with lameness, showing a large SCL in the medial epiphysis of the radius (arrows). (B) Postoperative view of the left cubital joint seen in (A). The cyst has been débrided through a transcortical approach (arrows), the cystic cavity has been filled with recombinant human bone morphogenetic protein-2, and a 4.5-mm cortical screw has been inserted through the cyst in neutral fashion. (C) Six months later the cystic lesion is almost not visible and the horse was sound at the trot.
Figure 90-19. (A) Dorsopalmar radiographic view of the distal MCIII depicting a cystic lesion that involved the entire medial condyle. (B) The defect was approached transcortically using an 8-mm drill bit and filled with injectable biodegradable bone cement (chronOS Inject). (C) The 12-month follow-up radiograph shows satisfactory healing of the defect. The animal was pain free at the walk and trot, despite the loss of medial joint space.
Figure 90-20. (A) Immediate postoperative caudocranial radiographic view of a SCL in the distal right MFC in a 3-year-old Warmblood mare presented with lameness. The cyst was débrided by arthroscopy and the cavity was filled with four titanium balls (arrows). (B) The follow-up radiograph 5 months later shows an increase of density of the cystic lesion (arrows), the mare was sound at the trot.
