CURRENT CONCEPTS IN BIOMECHANICAL INTERVENTIONS FOR PATELLOFEMORAL PAIN

Abstract

Patellofemoral pain (PFP) has historically been a complex and enigmatic issue. Many of the factors thought to relate to PFP remain after patients' symptoms have resolved making their clinical importance difficult to determine. The tissue homeostasis model proposed by Dye in 2005 can assist with understanding and implementing biomechanical interventions for PFP. Under this model, the goal of interventions for PFP should be to re-establish patellofemoral joint (PFJ) homeostasis through a temporary alteration of load to the offended tissue, followed by incrementally restoring the envelope of function to the baseline level or higher. High levels of PFJ loads, particularly in the presence of an altered PFJ environment, are thought to be a factor in the development of PFP. Clinical interventions often aim to alter the biomechanical patterns that are thought to result in elevated PFJ loads while concurrently increasing the load tolerance capabilities of the tissue through therapeutic exercise. Biomechanics may play a role in PFJ load modification not only when addressing proximal and distal components, but also when considering the involvement of more local factors such as the quadriceps musculature. Biomechanical considerations should consider the entire kinetic chain including the hip and the foot/ankle complex, however the beneficial effects of these interventions may not be the result of long-term biomechanical changes. Biomechanical alterations may be achieved through movement retraining, but the interventions likely need to be task-specific to alter movement patterns. The purpose of this commentary is to describe biomechanical interventions for the athlete with PFP to encourage a safe and complete return to sport.

Level of evidence: 5.

Keywords: Foot; hip; knee; rehabilitation; running.

Figure 1.

The patellofemoral joint and related structures experience three aspects of loading a) the peak load per step, b) how quickly this load is applied (rate of loading and 3) the total accumulation of load during an activity. These metrics are important to consider in the development of rehabilitation programs for individuals with patellofemoral pain.

Figure 2.

Patellofemoral joint stress during three different types of quadriceps strengthening exercises: EXT-VR represents a free weight attached to the distal lower leg. EXT-CR represents a knee extension machine that applies constant resistance. Squat relates to a squatting maneuver. Patellofemoral joint strees is dependent on the external moment arm, amount of resistance and the direction of force application. Figure reprinted with permission from Powers CM, Ho KY, Chen YJ Souza RB, Farrokhi S. Patellofemoral joint stress during weight-bearing and non-weight-bearing quadriceps exercises. J Orthop Sports Phys Ther. May 2014; 44(5): 320-327.

Figure 3.

The interaction between external loads and the external moment arm during common quadriceps strengthening exercises. Figure 3A: During the single leg squat, the external moment arm (MA) increases as the depth of the squat also increases resulting in increasing quadriceps forces and patellofemoral joint stress through 90 degrees of knee flexion. Corresponds with “Squat” in Fig. 2. Figure 3B: Patient performing open chain knee extension with a weight mounted at the levle of the lower leg (non tap figure). The external moment arm (MA) increases as the knee extends, resulting in increasing quadriceps forces and patellofemoral joint stress as the knee nears full extension. Corresponds with “EXT-VR” in Fig. 2. Figure 3C: During open chain knee extension on knee extension machine with a cable and weight stack system, the external moment arm (MA) remains constant throughout the range, resulting in relatively stable quadriceps forces and patellofemoral joint stress. Corresponds with “EXT-CR” in Fig. 2.

Figure 4.

Runner with patellofemoral pain demonstrating reduced space between the medial femoral condyles i.e., reduced knee window, suggestive of high levels of hip adduction and hip internal rotation of the right lower extremity.

Figure 5.

Open source software and a webcam can be used to provide real-time feedback on frontal plane running mechanics. This video technique is useful if the treadmill has a large controller console that prevents the runner from seeing their reflection in a full-length mirror.

Figure 6.

Commercially available running computer enables the real-time calculation of running cadence (step rate).