A 51-year-old healthy bricklayer male, born in eastern Europe, presented with right-knee pain caused by a fall on the knee during his work, a few weeks prior. During his childhood, a clinically evident bilateral dislocation of patella was observed and described without the assistance of imaging. Nevertheless, the pathology was asymptomatic, and he never reported difficulty in walking. Therefore, the malformation had never been treated and the patient conducted a normal life including time served in the army.\nPhysical examination revealed that the patient could walk normally, with a very mild stumble on the right knee, which was referred as absent before the trauma. There was conspicuous muscle wasting of each thigh (particularly on the medial side, with a clear depression on the vastus medialis) and 15° of genu valgum. The patellae were lying laterally to the lateral femoral condyle with the knee in the position of full extension () and they displaced more laterally during the flexion (). The proximal tibiae were rotated outward. The knees could be extended actively against maximum resistance, with full range of motion. Both the femoral quadriceps worked as knee extensors, and their strength was 5/5. The knees showed no signs of instability or ligamentous deficiency. The right knee was painful on the lateral side, and the clinical signs were positive for pathology of the lateral meniscus.\nRoentgenograms of bilateral knees revealed small, laterally displaced patellae with slight degenerative changes in the tibiofemoral joints with subluxated tibia (). The medial joint spaces were widened. Lateral roentgenograms showed marked lateral rotation deformities of the tibiae (). A skyline view showed an increased deep of the trochlear groove, with laterally dislocated patellae forming a sort of new joint with the lateral aspect of the condyle ().\nMagnetic resonance imaging (MRI) showed a lesion with dislocation of the lateral meniscus on the right knee. On both sides, the MRI confirmed the dislocation of the patellae, a severe hypoplasia of the medial side of the femoral quadriceps, and an external rotation of the proximal tibia particularly evident on the tibial tuberosity ().\nIn order to identify a possible aetiology of the malformation, the patient underwent electromyography/electroneurography, which showed normal function of all the separate portions of the quadriceps muscles thus not explaining the origin of this malformation.\nThe clinical and the imaging findings suggested a lesion of the lateral meniscus as the probable cause of the pain. Therefore, we performed a knee arthroscopy, whose intraoperative findings confirmed the MRI. During the surgery, we performed just a selective arthroscopic meniscectomy.\nAfter the operation, the patient followed a simple protocol of rehabilitation: 15 days of relative rest with partial bearing and low-molecular-weight heparin therapy, then progressive full recover of activities. Quickly, the knee showed satisfactory improvement, with no pain in walking and a complete range of motion, as before the operation, and comparable to the other knee.\nDuring the last clinical evaluation, 12 months after surgery, written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
The patient was an 11-year-old Caucasian boy without any relevant familiar history or comorbidity. He referred to our clinic complaining disability in walking and running with frequent falls (due to the lack of power in knee extensor mechanism). His parents said that despite the absence of pain, the functional limitation of both his knees was at the base of a serious psychological discomfort, conditioning his relationship with peers.\nOn objective examination, his lower limbs revealed mild genu valgum and tibial proximal lateral torsion. Both patellae were on the lateral aspect of the femoral condyle displacing even further during knee flexion. Femoral quadriceps function was present but this muscle was working as a flexor instead of extensor of the knee. It was observed that he was unable to actively extend both knees from the flexed position; passive range of motion (ROM) was complete and was not painful. At the upper limbs, there was a mild deficit in ROM of both elbows. There were no pathological deviation of the spine; normal clinical finding of both feet. The anterior-posterior lateral and axial knee X-rays showed bilateral, superolaterally displaced and hypoplastic patellae and reduction of the trochlear groove (, , ).\nThe extensor mechanism was studied by magnetic resonance imaging (MRI): Both quadriceps were hypotrophic with the vastus medialis enveloped over the trochlear groove which appeared flattened and dysmorphic. The patellar tendons were bilaterally lateralized and stretched. The anterior cruciate ligament could not be identified. On both sides, MRI confirmed the lateral dislocation of the patellae ().\nElbows X-ray showed a slight posterior dislocation of the radial head and absence of radioulnar synostosis. The diagnosis of CDP was confirmed. Surgical correction of the deformity was then proposed to regain walking and running function, with the aim of reduce the grade of the deformity improving the patient quality of life and his psychological well-being.