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The patella, fabellae and popliteal sesamoids

image of The patella, fabellae and popliteal sesamoids
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Abstract

A sesamoid bone is a bone embedded within a tendon. Sesamoids are found in locations where a tendon passes over a bone or a joint. This chapter looks at the patella, the fabellae, the popliteal sesamoid. Fracture of the patella; Avulsion of the fabella; Avulsion of the popliteus.

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Figures

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27.1 (a) Patellar fracture in a 2-year-old cat. (b) The cat subsequently went on to sustain an ipsilateral transverse proximal tibial fracture at 8 years of age.
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27.2 A patellar fracture in a Boxer. The dog had run into a wall and sustained a small wound over the stifle. When attempting to bear weight the dog was unable to maintain stifle extension. (a) Mediolateral view of a transverse fracture of the patella. (b) Postoperative mediolateral and (c) craniocaudal views of the fracture repaired with two K-wires and a figure-of-eight tension-band wire.
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27.3 (a–b) A grossly enlarged lateral fabella in a 6-year-old Border Collie. The changes are suspected to be secondary to previous trauma or fracture that has healed with prolific callus formation.
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27.4 An overweight 7-year-old Shetland Sheepdog was presented with chronic right hindlimb lameness of 5 months’ duration. The dog was mainly non-weight-bearing on the right hindlimb, but when it did bear weight, there was a plantigrade stance. On orthopaedic examination the right hock could be hyperflexed even with the stifle extended. Orthogonal mediolateral and craniocaudal radiographs of (a, c) the right and (b, d) the left stifle show that the right fabellae have displaced distally, suggesting a tear or rupture of the origin of the gastrocnemius muscle. (e) Mediolateral and (f) craniocaudal postoperative radiographic views. Surgery was performed by placing sutures from the gastrocnemius muscle, anchored distal to the fabellae, to two bone tunnels in the areas of the gastrocnemius origin. At surgery there was an obvious tear in the lateral gastrocnemius belly, but the tear in the medial belly was less obvious. There was extensive fibrous tissue present, which was not unexpected given the duration of clinical signs. (g) A 2.7 mm calcaneotibial screw was placed, combined with external coaptation, to temporarily hold the hock in extension and therefore relieve tension across the gastrocnemius repair during the early phases of healing; the screw was removed after 6 weeks.
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27.5 Popliteal avulsion in a 4-month-old Labrador Retriever puppy that was presented with sudden onset right hindlimb lameness after playing with another dog. Pain was localized to the right stifle joint. The cranial draw test revealed a normal degree of laxity in the cranial cruciate ligament compatible with the age of the dog. (a) Mediolateral and (b) craniocaudal radiographs and (c) an ultrasonogram of the lateral aspect of the stifle were performed. On the craniocaudal radiographic view there is a defect on the contour of the lateral femoral condyle, and lateral and adjacent to this defect is a mineralized opacity. On the mediolateral radiograph there is some decrease in size of the infrapatellar fat pad, compatible with a mild joint effusion. No bony abnormalities are present on the mediolateral radiograph. The ultrasonogram shows a bony opacity (arrowed) and an underlying concave defect on the femoral condyle just proximal to the tibial plateau. In this puppy it was possible to reattach the bony avulsion fragment with a 2 mm bone screw and washer. The 4-week postoperative (d) mediolateral and (e) craniocaudal radiographic views show the implants in position and evidence of bony callus around the screw head on the craniocaudal radiograph. (c, Courtesy of N Rousset)
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27.6 Application of a pin and tension-band for a transverse patellar fracture. (a) Retrograde placement of a pin in the proximal fragment. A pilot hole can be made first with a drill bit. Drawn by Vicki Martin Design, Cambridge, UK and reproduced with her permission. (b) Fracture held in reduction using small pointed reduction forceps. The pin is advanced into the distal fragment. Drawn by Vicki Martin Design, Cambridge, UK and reproduced with her permission. (c) A wire is passed through the patellar ligament and behind the K-wire at each pole through the lumen of a pre-placed suitably sized hypodermic needle. The needle can be bent slightly to facilitate placement. Drawn by Vicki Martin Design, Cambridge, UK and reproduced with her permission. (d) The tension-band is tightened in a figure-of-eight or loop pattern. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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27.7 Wiring techniques for repair of transverse patellar fractures in the cat. (a) Cranial and (b) lateral views of circumferential wire. (c) Cranial and (d) lateral views of figure-of-eight wire. In both cases the orthopaedic wire is passed through the patellar ligament and distal quadriceps muscle. The wire can be placed in a similar fashion as shown in Figure 27.6c , facilitated by placing a hypodermic needle first. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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27.8 Wire placed around the proximal patella and through the tibial tuberosity to protect a patellar fracture repair or patella tendon repair associated with an unreconstructable patellar fracture. Drawn by Vicki Martin Design, Cambridge, UK and reproduced with her permission.
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27.9 Surgical approach to the lateral fabella. (a) A skin incision is made over the lateral stifle extending from the distal third of the femur to the level of the tibial tuberosity. (b) An incision is made through the fascia along the cranial aspect of the biceps femoris muscle. (c) After retraction of the biceps femoris muscle the lateral fabella is palpable in the gastrocnemius muscle. The peroneal nerve may be encountered caudally. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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27.10 Surgical approach to the medial fabella. (a) A skin incision is made over the medial stifle extending from the distal femur to the level of the tibial tuberosity. (b) The dissection is continued by division between the cranial and caudal bellies of the sartorius muscles. (c) After retraction of the caudal sartorius muscle the medial fabella is palpable in the medial belly of the gastrocnemius muscle, below the branches of the saphenous nerve and femoral artery. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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27.11 A suture is placed around the fabella distally and anchored to a bone tunnel in the region of the supracondylar tuberosities at the origin of the gastrocnemius muscle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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27.12 Surgical approach to the popliteus muscle. Following a lateral approach to the caudolateral aspect of the stifle (see Figure 27.9 ), the deep fascia is dissected to reveal the popliteus muscle immediately caudal to the lateral collateral ligament. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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