The quest to find the cause(s) of patellofemoral pain has traditionally looked like the search for the Fountain of Youth: the more we searched for it, the more elusive it became. In 2003, Katchburian et al. reviewed the measurement of patellar tracking and concluded that the definition of normal patellar tracking remains "an elusive goal."1 Patel et al. in 2003 used magnetic resonance imaging with joint-loading to assess patellofemoral contact area and patellofemoral kinematics2. They found lateral patellar subluxation and tilt in normal knees and postulated that the patellar tilt and subluxation that are observed during arthroscopy of the extended knee joint may not represent a pathologic condition.
Perhaps the end of the quest is near. Now, in their ambitious study entitled, "Patellofemoral Joint Kinematics in Individuals with and without Patellofemoral Pain Syndrome" MacIntyre et al. have used contemporary technology (magnetic resonance imaging) to track patellofemoral motion in order to determine whether or not there is any relationship between patellofemoral pain and patellofemoral joint kinematics and malalignment.
Using a validated magnetic resonance imaging-based method of image-guided assessment of patellofemoral joint kinematics, these investigators studied three groups of individuals: those with patellofemoral pain and no obvious clinical malalignment, those with patellofemoral pain and obvious clinical malalignment, and normal volunteers without any knee problems. Five different knee flexion angles were used while the subjects applied a load of at least 152 N (34.2 lb) through the heel against a spring.
Their assessment of patellar rotations and patellar translations revealed basically no differences among groups in the overall pattern of patellar motion. There was a great deal of variability in each group as well as a large overlap across groups. In the symptomatic group with malalignment, the patella was positioned more laterally throughout the full range of motion tested. At 19° of flexion, the patellae in symptomatic patients were positioned 2.25 mm more laterally than the patellae in the control group, and this difference was barely significant (p = 0.049).
The authors concluded that most patients with patellofemoral pain syndrome did not demonstrate abnormalities in patellar tracking during loaded knee flexion. They further noted that "other causative mechanisms must be explored to develop effective diagnostic and treatment strategies . . . ."
A strength of this study is that the authors used a validated magnetic resonance imaging-based method of assessing patellofemoral joint techniques under conditions that attempted to "physiologically" load the knee joint.
We do have some concerns, however, that the three groups may not have been perfectly matched. The symptomatic group without malalignment was older, (mean age, 36.0 years) compared with the symptomatic group with malalignment (mean age, 30.9 years) and the control group (mean age, 30.4 years); p values were also not provided to verify whether or not this difference was statistically significant. While no model is perfect, one could argue that loading through the heel to enable alignment with the axis of the scanner bore did not adequately represent physiological loading. Additionally, use of a compression spring could only verify that an applied load of at least a minimum of 152 N (34.2 lb) was being maintained, but the system could not verify how well subjects maintained the desired loads without "overshooting" the target goal. In theory, to enable effective low-resolution imaging, the load would have to be maintained for thirty-eight seconds at each knee flexion angle. With use of a foam pad behind the knee for proprioceptive feedback rather than for knee support, questions arise regarding the consistency of transverse and frontal plane femoral alignment. Lastly, the model represents a static rather than a dynamic method of measuring patellar motion.
The question the authors raise in the Introduction, i.e., whether, to date, the absence of a known association between specific kinematic parameters and patellofemoral pain means that no consistent relationship truly exists, or whether such an association is simply beyond our current technology of measurement, is closer to being answered as a result of their study. Their work adds further support to the statement by Sanchis-Alfonso: "To think of anterior knee pain or patellar instability as somehow being necessarily tied to PFM [patellofemoral malalignment] is an oversimplification that has positively stultified progress toward better diagnosis and treatment."3
We worry that these authors and others may be moving to "throw the baby out with the bath water." Malalignment of the extensor mechanism probably has a role in the multifactorial pathogenesis of patellofemoral pain and altered patellofemoral biomechanics. The contribution of extensor mechanism malalignment to patellofemoral pain and altered biomechanics may change on the basis of the frequency and magnitude of physiological weight-bearing and non-weight-bearing loading conditions4. Future studies that make use of a more physiological loading model to compare patellofemoral joint alignment and pain responses of the patient both in weight-bearing and non-weight-bearing conditions may help in the elucidation of this difficult question.
*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
1. Katchburian MV, Bull AM, Shih YF, Heatley FW, Amis AA. Measurement of patellar tracking: assessment and analysis of the literature. Clin Orthop Relat Res. 2003;412:241-59.
2. Patel VV, Hall K, Ries M, Lindsey C, Ozhinsky E, Lu Y, Majumdar S. Magnetic resonance imaging of patellofemoral kinematics with weight-bearing. J Bone Joint Surg Am. 2003;85:2419-24.
3. Sanchis-Alfonso V. Background: patellofemoral malalignment versus tissue homeostasis. Myths and truths about patellofemoral disease. In: Sanchis-Alfonso V, editor. Anterior knee pain and patellar instability. London: Springer; 2006. p 11.
4. Powers CM, Ward SR, Fredericson M, Guillet M, Shellock FG. Patellofemoral kinematics during weight-bearing and non-weight-bearing knee extension in persons with lateral subluxation of the patella: a preliminary study. J Orthop Sports Phys Ther. 2003;33:677-85.