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Research Review By Dr. Brynne Stainsby©


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Date Posted:

July 2019

Study Title:

Association of Hip and Foot Factors with Patellar Tendinopathy (Jumper’s Knee) in Athletes


Mendonça LD, Ocarino JM, Bittencourt NFN et al.

Author's Affiliations:

Department of Physical Therapy, Faculdade de Ciências Biológicas e da Saúde, Universidade Federal dos Vales do Jequitinhonha e do Mucuri, Diamantina, Brazil; Rehabilitation Sciences, Escola de Educação Física, Fisioterapia e Terapia Ocupacional, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil; Sports Physical Therapy, Minas Tênis Clube and Uni-BH University Centre, Belo Horizonte, Brazil; Rehabilitation Science, McMaster University, Hamilton, Canada.

Publication Information:

Journal of Orthopaedic and Sports Physical Therapy 2018; 48(9): 676-684.

Background Information:

Patellar tendinopathy (PT) is an overuse injury associated with jumping and landing, believed to be caused by repetitive forces applied to the patellar tendon (1, 2). It is associated with long-term pain and altered function, which can affect participation in sport and activity (3). Understanding the risk factors associated with this condition is important, as prevention and management strategies are challenging for both athletes and clinicians (3). Given their anatomical relationships, it is possible that impairments of the hip or foot could contribute to PT.

It has been proposed that the hip and/or foot/ankle complex may influence mechanics of the knee through influences on movement patterns or anatomical alignments (4-16). For example, athletes with PT exhibit altered hip and knee movement patterns in the sagittal plane during landing tasks, when compared to pain-free controls (17-19). Deficits in ankle dorsiflexion (DF) and increased foot varus alignment have also been demonstrated to contribute to excessive pronation and increased lower limb internal rotation, which is believed to contribute to increased load through the patellar tendon (4, 9, 20). It is assumed that muscular weakness, range of motion (ROM) impairments and anatomical alignment at the hip and ankle/foot may influence the force distribution patterns at the knee (6, 9, 14, 16, 21-23), and potentially lead to injury.

The aim of this cross-sectional study was to use the classification and regression tree (CART) method to assess impairments of the hip and foot/ankle that are associated with PT in volleyball and basketball athletes.

Pertinent Results:

A total of 311 athletes participated in the preseason screening – 41 were excluded based on the inclusion criteria, and 78 were excluded due to VISA-P score between 80 and 94. A total of 59 athletes (22 female, 37 male) were included in the PT group, and 133 (25 female, 108 male) in the non-PT group. There were no statistically significant differences in descriptive variables between groups (other than VISA-P score, p < 0.001).

The CART model identified passive hip internal rotation (IR) ROM, shank-forefoot alignment (SFA), hip external rotation (ER) torque and hip abductor torque as predictors for PT, as follows:
  • Passive hip IR ROM was the first predictor selected by the CART model, with a cut-off point of 40.76°.
  • In those with lower passive hip IR ROM, the second predictor was SFA with a cut-off point of 16.95°, and hip ER torque was the third predictor with a cut-off point of 0.31 Nm/kg.
  • In those with passive hip IR ROM above 40.76°, the model selected another passive hip IR ROM cut-off point of 44.46° on the second level, and hip abductor torque with a cut-off point of 1.57 Nm/kg on the third level.
With respect to interactions between predictors, the model indicated the interaction of lower values of passive hip IR ROM with lower values of SFA to be best at predicting the absence of PT. The presence of PT was best predicted by the interaction of lower passive hip IR ROM, greater SFA and lower hip ER torque.

The CART model correctly predicted 42/59 athletes with PT (71.2% sensitivity) and 99/133 without PT (74.4% specificity). The area under the ROC curve was 0.77 (95% CI: 0.70, 0.84; standard error 0.03, p < 0.001) and the total prediction of the model was 73.4%.

Clinical Application & Conclusions:

The CART model used in this study demonstrates that variables related to the hip and foot/ankle were associated with the presence or absence of PT. The findings of this model are consistent with other studies that have demonstrated that athletes with appropriate hip IR ROM and proper foot alignment have a decreased probability of demonstrating excessive lower limb IR and less patellar loading during weight-bearing tasks (21, 24). Interestingly, this study showed that athletes with passive hip IR less than or equal to 40.76° but larger varus values of SFA had a 41% less likelihood of having PT when they had greater values of hip ER torque, perhaps suggesting that adequate hip ER strength may help to control lower extremity IR and protect the patellar tendon (25, 26). The authors also hypothesized that adequate hip abductor strength may also be protective for those with high passive hip IR ROM based on the CART model.

Clinicians may use the results of this study in order to create personalized prevention programs for athletes at risk of developing PT. For athletes in jumping sports, attempting to achieve adequate passive hip IR ROM, adequate SFA and high hip ER torque may decrease their likelihood of developing PT. These factors could also be addressed in those diagnosed with PT in order to help with recovery, however, specific interventions could not be elucidated due to the design of this study.

Study Methods:

  • Professional male and female volleyball and male basketball athletes in Brazil who participated in sport at least 12 hours per week (in the previous season), who did not have Osgood-Schlatter disease or anterior knee pain not related to the patellar tendon, and no history of lower limb surgery or patellar tendon steroid injection, were eligible to participate. Athletes with PT were defined as those with tenderness or pain at the inferior pole of the patella.
  • The severity of PT symptoms was assessed by the Victorian Institute of Sport Assessment-patella (VISA-P) questionnaire, which is scored from 0-100 points with a score of less than 80 indicating severe PT. A score greater than 95 points indicated an athlete who did not have PT. Those with scores between 80-94 were excluded from the study (22, 27).
  • Preseason assessment of all athletes included: shank-forefoot alignment (SFA), ankle dorsiflexion (DF) ROM, iliotibial band (ITB) flexibility, passive hip internal rotation (IR) ROM, and hip external rotator (ER) and abductor isometric strength. Six pilot studies were conducted to determine each measurement’s reliability (intraclass correlation coefficient [ICC]) and two examiners with at least five years experience were trained in all tests to obtain acceptable ICC values. Participants were assessed bilaterally.
  • The examiners who performed the preseason screening were blinded to the participant’s group assignment (severe PT or no PT).
  • Data from the more symptomatic leg was used for athletes with PT, and data from the dominant leg (identified by asking athlete which leg they would use to kick a ball) was used for those without PT.
  • Descriptive statistics of the VISA-P questionnaire score, age, height, weight, sex, ITB flexibility, hip abductor torque, hip ER torque, passive hip IR ROM, ankle DF ROM and SFA were used to characterize the sample.
  • CART (classification and regression tree) analysis was used to determine the factors and interactions that were associated with the presence or absence of PT (28). Through statistical analysis of the data, CART analysis selects the predictors and the cut-off points that best classify individuals in the outcome category (PT) based on the strength of their association with the outcome. By dividing the data based on the cut-off values, the data is eventually classified into a tree.
  • Following the development of the CART model, a receiver operating characteristic (ROC) curve was created to verify the accuracy of the CART model (5), with a probability of type I error of 0.05.
  • Prevalence ratios were calculated for each terminal node of the CART model to investigate the strength of the associations.

Study Strengths / Weaknesses:

  • Pilot studies were conducted to ensure appropriate reliability of the tests (measured via ICC), and experienced examiners were used.
  • The VISA-P is a valid and reliable questionnaire for the assessment of patellar tendinopathy.
  • Examiners were blinded to the athlete’s group.
  • Accuracy of the model was assessed statistically.
  • The authors recognized and commented on the limitations of mathematical modeling and cautioned on appropriate interpretation of results.
  • It is important to interpret the results with caution as a cross-sectional study cannot determine causal relationships between variables. Future, prospective studies should be conducted to determine whether the factors identified in this study could be considered as a risk profile for the occurrence of PT.
  • It is also important to consider that the CART model and the cut-off points are specific to the population (professional volleyball and basketball players), which limits the generalizability of the findings.
  • Some of the participants in this study were undergoing physical therapy at the time of testing, and it is not known how this may have affected the results (if at all).
  • Additional factors (such as quadriceps and hamstring strength and flexibility, duration of sport participation, hours of sport played, position, etc.) that could contribute to lower limb biomechanics were not accounted for in the model, and thus may be considered in future studies.

Additional References:

  1. Bahr MA, Bahr R. Jump frequency may contribute to risk of jumper’s knee: a study of interindividual and sex differences in a total of 11,943 jumps video recorded during training and matches in young elite volleyball players. Br J Sports Med 2014; 48: 1322-1326.
  2. Hale SA. Etiology of patellar tendinopathy in athletes. J Sport Rehabil 2005; 14: 259-272.
  3. Cook JL, Purdam CR. The challenge of managing tendinopathy in competing athletes. Br J Sports Med 2014; 48: 506-509.
  4. Backman LJ, Danielson P. Low range of ankle dorsiflexion predisposes for patellar tendinopathy in junior elite basketball players: a 1-year prospective study. Am J Sports Med 2011; 39: 2626-2633.
  5. Cichanowski HR, Schmitt JS, Johnson RJ et al. Hip strength in collegiate female athletes with patellofemoral pain. Med Sci Sports Exerc 2007; 39: 1227-1232.
  6. Dierks TA, Manal KT, Hamill J et al. Proximal and distal influences on hip and knee kinematics in runners with patellofemoral pain during a prolonged run. J Orthop Sports Phys Ther 2008; 38: 448-456.
  7. Feng Y, Tsai TY, Li JS, et al. Motion of the femoral condyles in flexion and extension during a continuous lunge. J Orthop Res 2015; 33: 591-597.
  8. Khayambashi K, Fallah A, Movahedi A et al. Posterolateral hip muscle strengthening versus quadriceps strengthening for patellofemoral pain: a comparative control trial. Arch Phys Med Rehabil 2014; 95: 900-907.
  9. Mendonça LD, Verhagen E, Bittencourt NF et al. Factors associated with the presence of patellar tendon abnormalities in male athletes. J Sci Med Sport 2016; 19: 389-394.
  10. Merican AM, Amis AA. Iliotibial band tension affects patellofemoral and tibiofemoral kinematics. J Biomech 2009; 42: 1539-1546.
  11. Myer GD, Ford KR, Khoury J et al. Biomechanics laboratory-based prediction algorithm to identify female athletes with high knee loads that increase risk of ACL injury. Br J Sports Med 2011; 45: 245-252.
  12. Powers CM. The influence of abnormal hip mechanics on knee injury: a biomechanical perspective. J Orthop Sports Phys Ther 2010; 40: 42-51.
  13. Scattone Silva R, Ferreira AL, Nakagawa TH et al. Rehabilitation of patellar tendinopathy using hip extensor strengthening and landing-strategy modification: case report with 6-month follow-up. J Orthop Sports Phys Ther 2015; 45: 899-909.
  14. Scattone Silva R, Nakagawa TH, Ferreira AL et al. Lower limb strength and flexibility in athletes with and without patellar tendinopathy. Phys Ther Sport 2016; 20: 19-25.
  15. Souza RB, Draper CE, Fredericson M et al. Femur rotation and patellofemoral joint kinematics: a weight-bearing magnetic resonance imaging analysis. J Orthop Sports Phys Ther 2010; 40: 277-285.
  16. van der Worp H, van Ark M, Roerink S et al. Risk factors for patellar tendinopathy: a systematic review of the literature. Br J Sports Med 2011; 45: 446-452.
  17. Mann KJ, Edwards S, Drinkwater EJ et al. A lower limb assessment tool for athletes at risk of developing patellar tendinopathy. Med Sci Sports Exerc 2013; 45: 527-533.
  18. Rosen AB, Ko J, Simpson KJ et al. Lower extremity kinematics during a drop jump in individuals with patellar tendinopathy. Orthop J Sports Med 2015; 3: 2325967115576100.
  19. Souza RB, Arya S, Pollard CD et al. Patellar tendinopathy alters the distribution of lower extremity net joint moments during hopping. J Appl Biomech 2010; 26: 249-255.
  20. Richards DP, Ajemian SV, Wiley JP et al. Relation between ankle joint dynamics and patellar tendinopathy in elite volleyball players. Clin J Sport Med 2002; 12: 266-272.
  21. Bittencourt NF, Ocarino JM, Mendonça LD et al. Foot and hip contributions to high frontal plane knee projection angle in athletes: a classification and regression tree approach. J Orthop Sports Phys Ther 2012; 42: 996-100.
  22. de Vries AJ, van der Worp H, Diercks RL et al. Risk factors for patellar tendinopathy in volleyball and basketball players: a survey-based prospective cohort study. Scand J Med Sci Sports 2015; 25: 678-684.
  23. Lee TQ, Morris G, Csintalan RP. The influence of tibial and femoral rotation on patellofemoral contact area and pressure. J Orthop Sports Phys Ther 2003; 33: 686-693.
  24. Souza TR, Pinto RZ, Trede RG et al. Late rearfoot eversion and lower-limb internal rotation caused by changes in the interaction between forefoot and support surface. J Am Podiatr Med Assoc 2009; 99: 503-511.
  25. Lephart SM, Abt JP, Ferris CM et al. Neuromuscular and biomechanical characteristic changes in high school athletes: a plyometric versus basic resistance program. Br J Sports Med 2005; 39: 932-938.
  26. Willy RW, Davis IS. The effect of a hip strengthening program on mechanics during running and during a single-leg squat. J Orthop Sports Phys Ther 2011; 41: 625-632.
  27. van Wilgen P, van der Noord R, Zwerver J. Feasibility and reliability of pain pressure threshold measurements in patellar tendinopathy. J Sci Med Sport 2011; 14: 477-481.
  28. Lemon SC, Roy J, Clark MA, Friedmann PD et al. Classification and regression tree analysis in public health: methodological review and comparison with logistic regression. Ann Behav Med 2003; 26: 172-181.

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