Patellofemoral malalignment associated with patella alta may cause pain and arthritis; because of this, the condition sometimes is treated surgically. Two common procedures are tibial tubercle distalization with or without patellar tendon tenodesis. However, the biomechanical consequences of these interventions for patella alta are not clearly understood.Questions/purposes
We evaluated changes in patellofemoral joint contact mechanics after tibial tubercle distalization and tibial tubercle distalization combined with patella tendon tenodesis. Specifically, we asked: (1) Are there biomechanical differences between these two types of procedures? (2) Is there an ideal range to distalize the patella?Methods
Subject-specific finite-element models were created for 10 individuals with patella alta (mean Insall-Salvati ratio of 1.34 ± 0.05). Input parameters for the finite-element models included subject-specific joint geometry, quadriceps muscle forces, and weightbearing patellofemoral joint kinematics. Virtual operations were conducted to simulate the two procedures. For distalization, the tibial tubercle and patella were displaced distally 4 mm to 20 mm in 4-mm increments based on the original model. At each level of distalization, the patella tendon was attached back to its original insertion to simulate the additional tenodesis procedure. Cartilage stress, contact area, and contact forces were quantified and compared between procedures and distalization levels.Results
Distalization and distalization + tenodesis reduced patellofemoral joint stress compared with the baseline of 1.02 ± 0.11 MPa. Distalization led to lower cartilage stress than distalization + tenodesis, and the effect size was relatively large (0.88 ± 0.10 MPa vs 0.92 ± 0.10 MPa; mean difference, 0.04 MPa [95% CI, 0.02 MPa-0.05 MPa], p < 0.01; effect size of 1.64 [Cohen's d], with Insall-Salvati ratio decreased to 0.95). For both procedures, the trend of stress reduction plateaued when the Install-Salvati ratio approached 0.95.Conclusions
Cartilage stress appears lower using distalization as opposed to distalization + tenodesis in this finite-element analysis simulation. An Insall-Salvati ratio of 0.95 may be an ideal level for distalization; further distalization does not show additional benefits.Clinical Relevance
This study suggests that distalization may result in less stress than distalization + tenodesis, therefore future clinical research might be preferentially directed toward evaluating isolated distalization procedures.