Arthroscopy: The Journal of Arthroscopic & Related Surgery
Current ConceptsSurgical Biomechanics of the Patellofemoral Joint
Section snippets
Patellar Stability
There are 3 principal factors at the knee that affect patellar stability: articular geometry, muscle actions, and passive soft-tissue restraints. Patellar stability results from a balance of the associated forces.
Patellar Tracking
The tracking of the patella has been evaluated by use of such a wide variety of techniques that it is difficult to construct a picture that is consistent with the findings of all the various studies that have attempted to address this issue.11 As Katchburian et al.11 have stated, “the definition of normal patellar tracking remains an elusive goal.”
Patellar motion can be described in 6 degrees of freedom: medial/lateral translation, superior/inferior translation, anterior/posterior translation,
Contact Areas
The contact areas of the patellofemoral joint have generally been measured in vitro via methods such as pressure-sensitive film, silicone rubber casting, and dye staining. More recently, magnetic resonance imaging (MRI) techniques have been used to calculate in vivo contact areas.14 Contact areas can be described both on the patella and on the trochlear groove. On the patella, the contact area moves from inferior to superior from 0° to 90°, whereas on the trochlea, the contact area moves from
Loads Across Patellofemoral Joint
Although the perception of the patellofemoral joint is often that it is not in the vertical load-bearing column, there is evidence that it is exposed to high loads in various activities. Given its limited contact areas, there can be very high stresses at the articular surfaces.
There have been various models used for calculating the loads across the patellofemoral joint. Early models were both generic and static, as well as being only 2-dimensional. Initially, the patellofemoral joint was
Lower Limb Alignment and Patellofemoral Joint
The effect of lower limb alignment can be viewed in terms of the principle that the skeleton dictates where the load will cross the patellofemoral joint. Any variation from optimal skeletal alignment may result in abnormal forces acting on the patellofemoral joint causing either ligament failure with subsequent subluxation or cartilage failure (or both).
Skeletal alignment must be viewed in all 3 planes, not only the coronal and sagittal planes. Thus varus and valgus are 2-dimensional coronal
Influence of Lower Limb Dynamics on Patellofemoral Dysfunction
The patellofemoral joint needs to be assessed in the context of the whole of the lower limb and indeed the whole body.
On landing from a jump, some patients show “medial collapse” of the knee. This can be measured, or at least conceptualized, by the so-called dynamic (functional) Q angle. An important question is whether the dynamic Q angle is determined from the hip down or from the foot up. The former suggests that increased femoral adduction and internal rotation at the hip are fundamental to
Concept of “Malalignment”
The term malalignment is frequently used in the setting of patellofemoral joint problems. However, some persons can function normally even if their knees do have “malaligned” patellae.
Rather than attempt to define normal and abnormal alignment, it may be more useful to determine statistical thresholds for specific measurements, above which there are associations with clinical problems such as patellar dislocation. This allows for the contribution of other variables to the creation of a clinical
Overview
Most of the literature that examines the effects of various realignment procedures addresses the effects on patellofemoral alignment rather than joint loading. Those studies that have addressed patellofemoral loading have tended to focus on altering the Q angle. It is also important to remember that changes in one site of the knee, such as the patellofemoral joint, may induce changes in other parts of the knee, such as the tibiofemoral compartments.50
Bracing
In patients with patellofemoral pain, the
Conclusions
This review has attempted to present objective data as far as possible, but it is clear that there are still many gaps in our knowledge, as well as conflicting data about issues as fundamental as the orientation of the trochlear groove in the normal knee. Comparison of studies is often difficult because of the varying methodologies used by researchers. As new imaging and measurement tools become available, the sophistication of the analyses of the biomechanics of the patellofemoral joint
Acknowledgment
The authors gratefully acknowledge the contributions of Masataka Deie (Japan), David Dejour (France), Edwin Dillon (South Africa), Don Eckhoff (United States), Abbas Madani (Iran), Philippe Neyret (France), Bob Teitge (United States), Darius Witonski (Poland), and Jacques Vallotton (Switzerland) who all participated together with the authors in the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine Knee Committee Current Concepts meeting held in October 2006 in
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