Patellar Dislocation and Fracture After Medial Patellofemoral Ligament Reconstruction in a Patient With Osteogenesis Imperfecta

Abstract

Background: Patellar instability is a common orthopedic condition in the pediatric population. Many factors contribute to patellar instability, including trochlear dysplasia. However, patellar instability and its treatments are not well documented in the literature for patients with osteogenesis imperfecta. Case Report: After medial patellofemoral ligament (MPFL) reconstruction, a 17-year-old male with osteogenesis imperfecta had a patellar dislocation that resulted in a patellar fracture. The patient subsequently had a revision of his MPFL reconstruction, and at 2½ years postoperation has had no episodes of recurrent patellar instability. Conclusion: The combination of bone fragility, trochlear dysplasia, and strength of the allograft used for MPFL reconstruction compared to the patient's bone strength led to dislocation and patellar fracture. Research into alternative methods for patellar fixation and postoperative physical therapy protocols for patients with osteogenesis imperfecta is needed. Special considerations must be made for this patient population.

Keywords: Osteogenesis imperfecta; patella; patellar dislocation; patellar ligament.

Figure 1.

Axial fat-suppressed proton density-weighted magnetic resonance imaging from the initial evaluation in the emergency department shows disruption to the medial patellofemoral ligament-vastus medialis oblique complex in the left knee (arrow).

Figure 2.

Sagittal fat-suppressed proton density-weighted magnetic resonance imaging shows a left transverse patellar fracture (arrow) after the dislocation occurred at physical therapy.

Figure 3.

(A) Preoperative merchant view x-ray of the patient's left knee demonstrates maltracking. (B) Postoperative merchant view x-ray of the patient's left knee demonstrates improvement in articular constraint and tracking.

Figure 4.

Axial fat-suppressed proton density-weighted magnetic resonance imaging (MRI) shows trochlear dysplasia and the measurements taken for determining the trochlear depth ([59 + 58.1] ÷ 2) – 56.5 = 2.05 mm. An axial MRI 3 cm above the joint line is needed to calculate the trochlear depth. The average distance of the medial and lateral facets from a line tangential to the femoral condyles is subtracted from the distance of the trochlear groove to that same tangential line. A value <3 mm is considered shallow and consistent with trochlear dysplasia.

Figure 5.

Anterior posterior hip-to-ankle x-ray demonstrates mild genu valgum.