Abnormal patellar loading may lead to femoral trochlear dysplasia: an experimental study of patellar hypermobility and patellar dislocation in growing rats

Abstract

Background This animal study aimed to explore the effects of patellar hypermobility and patellar dislocation on the developing femoral trochlea. Methods Seventy-two 3-week-old Wistar rats were randomly divided into three groups. The sham group (SG) underwent simple incision and suture of the skin and subcutaneous tissue; the patellar hypermobility group (PHG) underwent medial and lateral retinacular release and pie-crusting technique for the patellar ligament; the patellar dislocation group (PDG) underwent plication of the medial patellofemoral retinaculum. Twelve rats in each group were euthanized at 3 and 6 weeks postoperatively, respectively, and specimens were collected. The bony sulcus angle (BSA), cartilaginous sulcus angle (CSA), trochlear sulcus depth (TSD), and thickness of the cartilage on the lateral facet (CTL), medial facet (CTM), and center (CTC) of the trochlea were measured on hematoxylin and eosin-stained sections. Results In the PHG and PDG, the femoral condyles became blunt, the trochlear groove became shallower, and cartilage became thicker compared with the SG. Compared with the SG, the PHG and PDG had significantly larger BSA and CSA values at 3 (p < 0.05) and 6 weeks (p < 0.005), and a significantly shallower TSD (p < 0.05). At 3 weeks, all cartilage thicknesses in the PHG and the CTC and CTM in the PDG were significantly thinner than in the SG (PHG vs. SG: p = 0.009 for CTL, p < 0.001 for CTM, p = 0.003 for CTC; PDG vs. SG: p = 0.028 for CTC, p = 0.048 for CTM). At 6 weeks, the CTC was thicker in the PHG and PDG than the SG (PHG vs. SG: p = 0.044; PDG vs. SG: p = 0.027), and the CTL was thinner in the PDG than the SG (p = 0.044). Conclusion Patellar hypermobility and patellar dislocation may result in trochlear dysplasia that worsens with age. Excessive or insufficient loading leads to trochlear dysplasia.

Patients with trochlear dysplasia have dysplastic medial femoral epiphyseal plates

“…The explanation for this in previous studies [19, 20, 33, 37] is that the lack of stress stimulation to the medial condyle in the laterally dislocated patella leads to delayed development of the medial condyle, resulting in dysplasia of the medial trochlea. Thus, osteogenesis of the epiphyseal plate is affected by mechanical stress [7, 33, 35] and influences the formation of trochlear morphology, which may be an important intermediate link in the development of trochlear dysplasia.…”

“…The explanation for this in previous studies [19,20,33,37] is that the lack of stress stimulation to the medial condyle in the laterally dislocated patella leads to delayed development of the medial condyle, resulting in dysplasia of the medial trochlea. Thus, osteogenesis of the epiphyseal plate is afected by mechanical stress [7,33,35] and inluences the formation of trochlear morphology, which may be an important intermediate link in the development of trochlear dysplasia. It was found that there are signiicant positive correlations among the area of the medial growth plate, medial TPD, height of the medial condyle and capacity of the proximal trochlear groove, which consistent with previous indings.…”

“…According to Wolf's Law [5], bone structure changes in response to abnormal mechanical stress caused by poor patellar trochlear engagement are also indicative of trochlear dysplasia. The patellofemoral joint of animals in different developmental phases treated by severing the medial patellofemoral ligament from the patella in previous animal experiments [13, 18, 33, 37] revealed the transformation of the anatomical structure of the femoral trochlea from normal to dysplastic. The anatomical change is most likely caused by abnormal alignment and consequent unusual stress.…”

Midterm Outcomes of Isolated Medial Patellofemoral Ligament Reconstruction for Patellar Instability in Ehlers-Danlos Syndrome

“…Trochlear dysplasia may result from insufficient loading patterns in the patellofemoral joint secondary to hyperlaxity. 39 There was a statistically significant increase in patellar height and tilt in patients who had failed isolated MPFLR in our cohort. A cautious approach is warranted when correction of the patellar tilt is considered in patients with hyperlaxity, as lateral retinacular release can lead to iatrogenic medial instability.…”

Distal femoral torsion is correlated with higher‐grade trochlear dysplasia and shorter anterior condyles in patients with patellar dislocation and increased femoral torsion

“…The correlations between distal torsion and dysplastic anterior condyles and trochlea may be due to the abnormal mechanical stimuli that are applied to the anterior condyles and trochlea, which may be caused by increased distal torsion [13, 27]. Liao et al [14] reported that the internal rotation of the femur resulted in a significantly higher octahedral shear stress and hydrostatic pressure.…”