Stifle radiographs
Findings:
- Along the medial aspect of the patella, extending in a cranioproximomedial to caudodistolateral orientation, an ill-defined, smoothly margined oblique fracture with mild medial displacement of the medial fracture fragment is noted (pink arrows). This fracture is surrounded by mild, smoothly margined, osseous proliferation.

- Centered on the stifle joint, a mild to moderate homogeneous increase in soft tissue opacity results in peripheral displacement of the overlying fat pad/fascial planes.
- Within the proximal body of the fibula, an ill-defined, smoothly margined, mediolaterally oriented discontinuity with mild distal displacement and minimal, smoothly margined, osseous proliferation is noted.
- Observed on the lateral projections, superimposed with the stifle, approximately along the plane of the patellar ligaments, multifocal, ill-defined, punctate mineral opacities are noted.
Conclusions:
- Chronic left medial parasagittal patellar fracture.
- Mild to moderate left stifle joint effusion.
- Multipartite left fibula or chronic fracture.
- Superimposed cutaneous debris vs. dystrophic mineralization of the patellar ligaments.
Due to the location of the fracture and potential ligamentous involvement, an ultrasound was recommended.
Ultrasound of the patellar region
Findings:
- At its origin on the medial aspect of the patella, the medial patellar ligament is moderately thickened and heterogeneously hypoechoic with loss of the normal fiber pattern (yellow arrows).

- (Not imaged) Additionally, the medial femoropatellar ligament has mild to moderate fiber disruption.
- The medial patellar fragment is identified. The margins are markedly irregular and the surrounding soft tissues are mildly to moderately thickened and smoothly marginated.
Conclusions:
- Moderate insertional left medial patellar desmopathy.
- Mild to moderate left femoropatellar desmopathy.
- Chronic left medial parasagittal patellar fracture with mild to moderate regional soft tissue swelling (e.g. fibrosis).
Case outcome:
- Several options including surgery or conservative management were discussed with the owner. Given the chronicity of the fracture, management of with intra-articular corticosteroids was discussed, at the best allowing a return at to lower level dressage. Prognosis for upper level dressage was deemed guarded. In order to evalute the potential success of such therapy, diagnostic analgesia of the femoropatellar joint was pursued:
- Femoropatellar intra-articular block: 70-80% resolution in lameness
- Diagnostic arthroscopy of the stifle was offered, but not elected at this time as it may not be curative and does not guarantee a successful outcome for return to full athletic use.
A little bit more…
- Patellar fractures occur most commonly in jumping horses, due to direct impact of the patella on an obstacle. Alternatively, these fractures may be secondary to a kick injury (Dyson et al., Vautravers et al.).
- Described fracture configuration: (para)sagittal, transverse, comminuted

II: Apical (transverse)
V: Body (transverse)
III: Parasagittal
IV: Sagittal
https://surgeryreference.aofoundation.org/vet/horse/patella/further-reading/etiology-and-fracture-classification
- The most common configuration is a medial parasagittal fracture. These fractures typically occur while the stifle joint is partially flexed, e.g. when jumping. During joint flexion, the patella is fixed in the femoral trochlea (Auer et al.).
- Direct cranial trauma –> patella compressed against the medial trochlear ridge –> result in fracture of the medial aspect of the patella.
- Concurrent fracture of the distal femur has been described with more severe trauma (Dyson et al.).
- A cranioproximal-craniodistal oblique radiograph is essential for the identification of medial patellar fractures, especially for better characterization of its configuration (Dyson et al.).
- Conservative management can result in a successful clinical outcome for certain fracture configurations ().
- Published indications for surgical intervention include (Fowlie et al.):
- Complete disruption of the quadriceps apparatus (most commonly see with transverse fractures)
- A fracture gap wider than 5 mm
- Obvious malalignment of an articular fracture
- Fragments palpable directly under the skin.
- Standard treatment of this condition is arthroscopic removal of the medial fragment. This can be performed for fragments of a size up to one-third of the patella (Auer et al.).
- The outlook for returning to athletic activity after surgically removing medial patellar fragments is reported to be good (Dyson et al., Auer et al.). However, there have been reports of patellar luxation during recovery from general anesthesia, likely due to the loss of medial patellar stability caused by trauma to the medial patellar and femoropatellar ligaments (Auer et al.).

- Internal fixation of patellar fractures is rarely performed, but may be a consideration in horses with transverse fractures or (para)sagittal fractures with a fragment too big for arthroscopic removal (Auer et al., Vautravers et al.).
References:
- Dyson S, Wright I, Kold S, Vatistas N. Clinical and radiographic features, treatment and outcome in 15 horses with fracture of the medial aspect of the patella. Equine Veterinary Journal. 1992 Jul;24(4):264-8.
- Vautravers G, Brandenberger O, Vitte A, Rossignol F. Articular sagittal and medial parasagittal patellar fracture repair using lag screws in two mature horses. Equine Veterinary Education. 2018 Jan;30(1):31-6.
- Auer JA, Kümmerle JM. Fractures of the patella. Equine Veterinary Education. 2018 Jan 1;30(1).
- Fowlie, J.G., Stick, J.A. and Nickels, F.A. (2012) Stifle. In: Equine Surgery, 4th edn., Eds: J.A. Auerand J.A. Stick, Elsevier Saunders, St. Louis. pp 1434-1436.
- Schumacher J, Wilhite R. How to perform arthrocentesis of the compartments of the stifle of the horse.