History
A 13-year-old Selle Francais gelding, used for show jumping, was evaluated for acute left hind limb lameness acquired during solitary turnout. The horse had a grade 5/5 lameness and carried the limb in maximal flexion. Initial evaluation (performed 10 minutes following acute injury) revealed an inability to bear weight or extend the affected hind limb. Attempts to manually extend the left hind limb were unsuccessful. Initially, no heat or swelling was identified. Approximately 1.5 hours after injury, substantial amounts of pitting edema with sensitivity to palpation developed along the dorsal aspect of the stifle joint, proximal aspect of the patella, and distal portion of the quadriceps muscles. Joint effusion was difficult to detect because of the position of the hind limb. Radiographs of the left stifle joint were obtained with the joint in the flexed position (Figure 1).
Flexed lateromedial (A) and cranioproximal-craniodistal (skyline; B) radiographic views of the left stifle joint of a 13-year-old Selle Francais gelding evaluated for acute left hind limb lameness characterized by the horse's limb in maximal and continuous flexion.
Citation: Journal of the American Veterinary Medical Association 237, 5; 10.2460/javma.237.5.499
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
Distal displacement of the patella with cranial rotation (tipping) of the proximal aspect of the patella is evident along with remodeling along the distal aspect of the patellar apex (Figure 2). The flexed cranioproximal-craniodistal oblique (skyline) radiographic image revealed a complete articular fracture of the caudomedial aspect of the patella with fragmentation and minimal displacement. The clinical and radiographic evaluation of the horse's condition was consistent with a disruption in the quadriceps apparatus. Ultrasonographic examination of the stifle joint confirmed the presence of a patellar fracture with fragmentation, tearing of the quadriceps femoris muscle (primarily the rectus femoris muscle) at its patellar insertion, and considerable hemorrhage and edema of the surrounding tissues (Figure 3).
Same radiographic views (A and C) as in Figure 1 as well as a flexed lateromedial radiographic view (B) of a stifle joint of a clinically normal horse. On the lateromedial view of the horse of this report, notice the distal displacement and cranial tipping of the patella (arrow; A), compared with the position of the patella (arrow) in the clinically normal horse (B). On the cranioproximal-craniodistal oblique radiographic view (C) of the stifle joint, notice the fracture (arrow) on the medial aspect of the patella.
Citation: Journal of the American Veterinary Medical Association 237, 5; 10.2460/javma.237.5.499
Sagittal ultrasonographic image of the craniomedial aspect of the left patella of the horse of this report. Notice the outline of the patella (thin arrows) and the fracture gap with fragmentation (wide arrow). For orientation purposes, proximal is to the left on the image.
Citation: Journal of the American Veterinary Medical Association 237, 5; 10.2460/javma.237.5.499
Comments
The horse was treated medically with firocoxib PO, 1% diclofenac sodium cream topically, butorphanol IM, pentoxifylline PO, standing wraps applied to the opposite hind limb for support, and confinement via stall rest. Five days after the injury, the horse was able to ambulate in the stall and lie down. Seven days after the initial injury, the horse was observed placing the sole of the left hind foot to the ground but remained non–weight bearing on the limb. Sequential ultrasonographic examinations revealed substantial improvement in edema and hemorrhage previously observed within the quadriceps muscles. Ten days after injury, the horse had a grade 4/5 left hind limb lameness at the walk. Over the next several months, the horse progressively improved, returned to light riding work (at 5 months), and successfully competed in its first jumping competition 8 months after the injury.
The initial examination of this horse revealed a disruption of the passive stay apparatus, hence the inability to extend the left hind limb. This disruption, along with the presence of the equine reciprocal apparatus (specifically the superficial digital flexor muscle) created the unusual clinical signs of a severe lameness with the hind limb in full flexion.1 The quadriceps femoris muscle consists of 4 heads: the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis muscles. Their combined insertion on the patella and parapatellar fibrocartilage along with a double layered aponeurosis of the tensor fasciae latae and cranial division of the biceps femoris muscles are responsible for extension of the stifle joint.1
This condition has been reported previously by McIlwraith and Warren2 as a distal luxation of the patella. In that report, a Thoroughbred had a history of upward fixation of the patella and a medial patellar ligament desmotomy 15 months earlier. The horse of the present report had no history of previous injury, surgery, or disease of the stifle joint. The radiographic remodeling of the distal aspect of the patella may suggest a chronic inflammatory process; however, this was not clinically evident nor identified previously. The initial prognosis for recovery of this horse was considered questionable for healing of the quadriceps apparatus, reduction of the patella along the proximal femoral trochlea, and the unavoidable mechanical overload of the opposing limb. However, a successful outcome was achieved with conservative and supportive therapy.
1. Kainer RA. Functional anatomy of equine locomotor organs. In: Stashak TS, ed. Adams’ lameness in horses. 4th ed. Philadelphia: Lea & Febiger, 1987;56–70.
2. McIlwraith CW, Warren RC. Distal luxation of the patella in a horse. J Am Vet Med Assoc 1982; 181:67-69.
