orthopaedic professionals usually never have the fortune to perform the good office of reduction of patella ( 13 ) . most of patella dislocations are spontaneously reduced and others are reduced easily in emergency department ( 3,4 ) . irreducible patellar dislocations are rare injuries , but those that do occur are mainly directed intra - articular ( 7 ) . we report an exceptionally interesting case of an extra - articular irreducible lateral patella dislocation . a 50-year - old gentleman was brought into emergency with an inability to walk after a fall while walking down hill . ( figure 1 ) lateral dislocation of patella with rotation and obvious tenting of skin his knee was locked in full extension ( unlike some flexion associated with lateral patellar dislocation ) ( 6,8 ) . the patella was rotated about the long axis with the smooth articular surface facing posterolaterally . imaging studies confirmed the clinical findings and also revealed a minor impaction fracture of lateral femoral condyle with arthritic changes in the knee joint ( figure 2 ) . imaging studies showing lateral dislocation of patella with rotation about long axis , patella locked onto lateral femoral condyle ; and insignificant impaction fracture of lateral femoral condyle we attempted closed reduction under sedation and relaxation . we tried to unlock the patella and push it medially while keeping the knee in full extension and the hip in flexion ( to relax the quadriceps ) . we also attempted to flex the knee fully to reduce the patella from the unnatural position , as mentioned in literature ( 8,9 ) . the patient was taken to theatre , keeping in mind the possible need for open reduction . under general anaesthetic and muscle relaxation after appropriate preparation of skin and draping , a bone hook and tinaculum were used to apply traction and attempts were made to slide the patella over the prominent lateral femoral condyle , which was of no avail ( 3 ) . there was a large longitudinal tear in the medial retinaculum ( figure 3 ) with avulsion of attachments from medial border of patella . intra - operative photograph ( before reduction )  tear of medial retinaculum with avulsion of medial attachments of patella the patella was rotated about 70 - 80 degrees with the articular surface facing outwards . the medial border of the patella was hooked on the outer surface of the lateral femoral condyle under the prominent osteophytic ridge . the patella was pulled laterally and a wide periosteum elevator was inserted as a skid between the medial border of the patella and the lateral femoral condyle to unlock the patella from under the osteophytic ridge of the lateral femoral condyle . it was slipped over the lateral femoral condyle with a periosteum elevator . as soon as patella cleared lateral femoral condyle , it flipped back into normal position . we found a small insignificant impaction fracture on the lateral femoral condyle with a prominent osteophytic ridge ( like a shelf ) , which was probably a contributing factor for the patella being locked and irreducible ( in addition to rotation along long axis ) . the knee was placed in a richard 's splint in extension for two weeks while allowing him to touch weight bearing . , gradual rom ( range of motion ) was started in rom brace with quadriceps strengthening exercises . he achieved pain - free full active rom by six weeks without any residual instability of patella . since the first description by cooper in 1844 ( 8) , there have been only a few similar cases reported in orthopaedic literature . from the literature , it is apparent that this type of patella dislocation would result from a blow directly on the medial side while the quadriceps is taut ( 4 ) . this makes the patella ride against the prominent lateral femoral condyle ( which acts as a safeguard to prevent lateral displacement of the patella ) creating torque resulting in rotation of the patella around the longitudinal axis . if this force continues to act , it will push the patella beyond the margin of the lateral femoral condyle over which its medial edge will be locked ( figure 4 ) . sketch showing the path patella must take for lateral dislocation with rotation about long axis . ( f ) : direction of dislocating force , ( a ) : position of patella resulting from it sliding up on lateral femoral condyle , ( b ) : final position of patella , where it gets locked , after medial edge clears lateral condyle it is very natural to assume that any attachments on medial border of patella have to rupture before this kind of dislocation ( 3 ) . it may be possible , though unlikely , to achieve closed reduction of this type of injury , which may increase the risk of iatrogenic osteochondral lesions ( 6 ) . we prefer and recommend performing open reduction to have an opportunity to repair medial torn structures . we believe that this will reduce the tendency of lateral dislocation and restore limb ( quadriceps ) strength to optimum .
acute lateral patellar dislocation is relatively common in younger age group and most likely caused by indirect trauma . 
 about 10% of acute patella dislocations are the result of a direct blow to the medial side . 
 we report a case of irreducible lateral patellar dislocation which is of exceptional interest in that lateral patellar dislocation ( extra - articular ) occurred in comparatively older age group with arthritic knee , there was no direct trauma involved and it was associated with some rotation along long axis , impaction of patella on lateral femoral condyle and was locked underneath osteophytic ridge of lateral femoral condyle , which needed open reduction . 
 this is a very rare injury , first of its kind being reported in australia .