title: Does Patella Tendon Tenodesis Improve Tibial Tubercle Distalization in Treating Patella Alta? A Computational Study.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors: Center for Joint Surgery, Southwest Hospital, The Third Military Medical University, Chongqing, China.|Jacquelin Perry Musculoskeletal Biomechanics Research Lab, Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 E Alcazar Street, CHP-155, Los Angeles, CA, 90089-9006, USA.
authors: Li
authors: L
authors: Yin
authors: Jacquelin Perry Musculoskeletal Biomechanics Research Lab, Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 E Alcazar Street, CHP-155, Los Angeles, CA, 90089-9006, USA.
authors: Tzu-Chieh
authors: TC
authors: Liao
authors: Center for Joint Surgery, Southwest Hospital, The Third Military Medical University, Chongqing, China.
authors: Liu
authors: L
authors: Yang
authors: Jacquelin Perry Musculoskeletal Biomechanics Research Lab, Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 E Alcazar Street, CHP-155, Los Angeles, CA, 90089-9006, USA. powers@usc.edu.
authors: Christopher M
authors: CM
authors: Powers
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D008279:Magnetic Resonance Imaging; D008954:Models, Biological; D019637:Orthopedic Procedures / Q000009:adverse effects / Q000379:methods*; D017847:Patellar Ligament / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D046788:Patellofemoral Pain Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D016059:Range of Motion, Articular; D020127:Recovery of Function; D013314:Stress, Mechanical; D053656:Tenodesis / Q000009:adverse effects; D016896:Treatment Outcome; D055815:Young Adult