First-time patellar dislocation with resultant habitual dislocation two years later, which was not demonstrated on plain X-rays halfway: a case report
© Ohki et al; licensee BioMed Central Ltd. 2010
Received: 3 April 2010
Accepted: 14 September 2010
Published: 14 September 2010
We present an instructive case of habitual left patellar dislocation in which the patella had appeared odd due to lateral tilt relative to contralateral side, but had been radiologically confirmed to be on the trochlea at 1 year prior to the referral. An 11-year-old girl presented to our hospital 2 years after the left patella had dislocated with a 'giving way' when cutting to the left. Our physical and radiological examinations confirmed that the left patella was laterally tilted in the patellar groove with the knee in extension but was dislocated in flexion beyond 45°. In spite of these findings, she had been untreated at the previous hospital since all plain X-rays, including a skyline patellar view, had failed to demonstrate the dislocation. Consequently, in addition to reconstruction of medial patellofemoral ligament, she had to undergo a lateral retinacular release, which might have been unnecessary if treated earlier. This case illustrates that first-time patellar dislocation can gradually lead to habitual dislocation subsequently, and that cautious physical examinations in regard to patella tracking are essential since radiological examinations do not always reveal the pathophysiology of patellar instability.
Acute patellar dislocation can result in anterior knee pain, recurrent dislocation and patellofemoral arthritis, but rarely in habitual dislocation, defined as a dislocation that occurs every time the knee is flexed . In contrast to recurrent dislocation, which occurs as an isolated and intermittent sequela of injury, the transition to a habitual dislocation after an initial dislocation has not yet been clarified. We report a case of habitual patellar dislocation that appeared odd to the patient's family due to lateral tilt compared with contralateral patella, but was left untreated because plain X-rays (including skyline view) did not demonstrate significant patellofemoral malalignment 1 year prior to the referral.
Two years prior to presentation to our hospital, an 11-year-old girl recognized that her left patella was dislocated with a 'giving way' when cutting to the left. She was capable of repositioning it by herself and saw an orthopedic surgeon who did not point out any skeletal abnormalities on plain X-ray. After 1 year had passed, her father noticed that her knee looked odd; however, it was again diagnosed as intact by another surgeon. Since the deformity gradually became apparent, she was referred to our hospital. Although her body height and weight belonged to the lower 10th percentile, she did not have any associated anomalies that present with patellar instability, such as Down syndrome  or Kabuki make-up syndrome [3, 4]. She also denied any history of injections into the quadriceps muscle.
Since the epiphyseal plates were opened, a proximal realignment by reconstruction of the medial patella femoral ligament (MPFL) combined with a lateral retinaculum release was scheduled. Under anesthesia medial parapatellar instability as well as lateral tightness were significant manually. Intraoperatively, contracture of the lateral patellar retinaculum and scar formation of MPFL were noted. The fibrosis of the vastus lateralis was substantially released to obtain adequate balancing. The MPFL was then reconstructed with Leeds-Keio artificial ligament that was overlapped with the MPFL remnant and medial retinaculum according to previously published articles [6, 7]. Using a double-stapling technique, the ligament was fixed to the femoral side just distal to the adductor tubercle while avoiding damage to the growth plate, the color of which could be differentiated from the adjacent bone by macroscopic observation.
The clinical significance of this case underscores the difficulties inherent in early diagnosis of habitual patellar dislocation even using the skyline view. Although the patella had looked odd to her father due to tilting compared with contralateral side, it had been radiologically confirmed to be on the trochlea at 1 year prior to the referral. This case also demonstrates the time course from the initial patellar dislocation to habitual dislocation, which has not been reported previously. It implies that first-time patellar dislocation can gradually lead to habitual dislocation as well as recurrent dislocation.
Previous articles have reported that 40 to 60% of patients with first-time patellar dislocation have advanced to recurrent dislocation [8, 9] due to several predisposing factors, including patella alta, abnormal patellar morphology, trochlear dysplasia, increased Q angle with lateralized tibial tuberosity, genu valgum, ligament hyperlaxity, external tibial torsion, and increased femoral anteversion , [10–13]. In contrast with recurrent dislocation, the factors contributing to the onset of habitual dislocation and its time course from initial dislocation have not been elucidated despite previous reports of an association with quadriceps fibrosis due to muscle injections [14–16], quadriceps contracture , and abnormal attachment of the iliotibial tract to the patella , none of which were applicable to our case. Among the various parameters evaluated in our case, modified Q angle, sulcus angle, and lateral deviation angle showed aberrations. Further studies, using either meta-analysis or cases series, are needed to determine the factors that predispose an initial dislocation to become a habitual dislocation. Such research will allow more effective treatment of patellar dislocation by predicting the course after first-time dislocation.
In addition to the lateral reticular release, MPFL reconstruction was applied to our case. Since the epiphyseal plate was still open, the femoral attachment site was shifted from the original point to a point just posterior to medial femoral epicondyle and distal to the adductor tubercule and growth plate. Considering the length patterns reported previously , it is suggested that the reconstructed ligament be slightly loose in flexion. We have confirmed that the patella in our patient is stable in the femoral groove with the knee in greater than 60° of flexion. At 2 years after surgery, our patient is capable of bending her knee fully without fear of dislocation. Since the patient is in her growth spurt, we will continue close follow-up to ensure a good clinical outcome for our patient.
We emphasize that, had it been suspected 1 year earlier that this case would eventually lead to habitual dislocation, the lateral retinacular release would not have been required [1, 20]. Thus, the possibility of habitual dislocation should be considered if patella appears odd and different from the opposite side in extension, even if the radiological examinations do not show apparent dislocation.
Initial patellar dislocation can gradually lead to resultant habitual dislocation, and cautious physical examinations regarding patella tracking are essential since radiological examinations, including skyline view, do not always reveal the pathophysiology of patellar instability.
Written informed consent was obtained from the parent of 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.
We are grateful to Dr. Iwao Egawa for kindly providing us with the plain X-ray films. We also thank Prof. Toshiro Otani and Dr. Motoyasu Inoue, whose discussion helped us to determine the surgical procedures.
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