Dislocation Patella

Fig. 21.22 (a) Dislocation of the patella to expose the trochlear groove, (b) deepening of the groove trochlear with the aid of gouge forceps, (c) fixing the biosynthesized cellulose membrane with 6-0 synthetic absorbable sutures, (d) suturing the joint capsule and retinaculum in type of points of suture, with 3-0 monofilament nylon thread, and (e) suture the skin with simple stitches apart... 

Most commonly these are associated with an acute traumatic lateral dislocation of the patella. The fragment is therefore usually from the lateral femoral condyle or the patella itself (Rorabeck and Bobechko 1976). 

The patient may undergo a knee arthroscopy. The surgeon can take this opportunity to fully examine the knee under the anaesthetic, in particular to look for signs of a patella dislocation. The haemarthrosis is washed out. This gives better visualisation which is required to identify the area of cartilage loss and to find the dislodged fragment. 

Patellar fractures can occur from direct and indirect mechanisms, with a direct force being the commonest cause. Potential mechanisms include a powerful quadriceps contraction, a direct anterior blow which may result in an open fracture and patellar dislocation or relocation. It is important to differentiate a fracture from a bipartite patella which has a characteristic location and smooth margins. 

Fractures of the patella also occur in association with femoral shaft, condylar, proximal tibia and posterior dislocation of the hip ( dashboard injury ). 

Traumatic acute patellofemoral joint dislocation is uncommon in children. The patella almost always dislocates laterally. Certain anatomical variants predispose to dislocation. These include patella alta, trochlea dysplasia and genu valgum. 

A lateral dislocation causes damage to the medial patello-femoral ligament and vastus medialis obliq-uis. It can also cause an osteochondral fracture from either the lateral femoral condyle which may be sheared of by the patella or alternatively there may be an avulsion of the medial facet of the patella. 

Rorabeck CH, Bobechko WP (1976) Acute dislocation of the patella with osteochondral fracture a review of 18 cases. J Bone joint Surg 58B 237-240... 

Carter C, Sweetman R (1960) Recurrent dislocation ofthe patella and of the shoulder their association with familial joint laxity. J Bone Joint Surg (Br) 42 721-727 Comhalia A, Arandes JM, Alemany X, Ramon R (1995) Acromioclavicular dislocation with epiphyseal separation of the coracoid process report of a case and review of the literature. J Trauma 38 812-815 Curtis RJ (1990) Operative management of children s fractures of the shoulder region. Orthop Clin North Am 21 315-324... 

Patellar cartilage abnormalities can occasionally be detected with US on the medial facet of the patella and maybe related to lateral patellar dislocation. US can image an osteochondral fracture as a focal defect of cartilage and irregularity of the hyperechoic line representing the subchondral bone plate (Fig. 14.54). Although US can detect these changes, it should be... 

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