So here’s my summary (plus some interpretation) of the editorial on the homeostasis model:
There are several factors previously suggested to have been the cause of, or related to, PFP – strength, flexibility, patellar tracking, quadriceps angle, joint shape, depression, fear-avoidance – but there is insufficient evidence that any one of these is causative. *We shouldn’t be blaming these*.
Biomechanical factors will often remain after symptoms have resolved.
The goal of interventions is to re-establish homeostasis (the normal, healthy pain-free environment within the joint) through a temporary alteration of load, then incrementally restoring the envelope of function to the baseline level or higher.
Kinematic patterns (the way people move) thought to be causative i.e. pelvis dropping, knee moving inwards etc. are just as likely to be the effect of knee pain, not the cause of.
Rehab needs to consider (1) peak loads, (2) rate of load and (3) cumulative load. For example, running 1km requires 800-1000 steps with multiple of bodyweight so rehab and progression needs to consider and reflect these. *this is very complex!*
Adding resistance to body weight exercises is required if a clinician wishes to attain peak quadriceps forces that are of same magnitude as those seen during jumping e.g. a vertical jump is equivalent to 7x bodyweight
High loads are not dangerous, rather loads that exceed a tissue’s conditioned capacity. When an acute load exceeds the chronic load and the conditioned capacity, that is when the joint becomes symptomatic.
In those with PFP, the quads are on average 10% weaker (which is not visible) than in normal controls and quadriceps weakness is an established risk factor suggestive of inadequate chronic training load and low envelope of function. The mechanisms of pain reduction from 8 weeks of quad strengthening are unknown.
Using a mirror is an effective means to changing hip and pelvis mechanics, but that control and change in movement does not transfer to altered running mechanics
Increasing cadence (step rate) by 5-10% reduces knee joint contact forces by 10-20% (this is a good thing).
Forefoot running increased achilles load by >10% which equates to almost a 50x bodyweight increase in load over a mile (potentially not a good thing) – this may help the knee pain but overload the Achilles and cause it to become symptomatic instead.
Running with orthoses (6 weeks) can reduce symptoms but changes are not due to altered kinematics
Pain should be no higher than 2/10 with minimal or no pain after activity
It is possible to alter the way someone moves during a therapeutic exercise e.g. performing a single leg squat, but unless that’s done while running i.e. while running watching the legs via a monitor in real-time, those changes are task specific and almost certainly *not* going to translate into an altered running gait.
It has been suggested that people with PFP have “weak glutes” (specifically glute medius or the lateral rotators) where in fact those muscles may be *stronger* in those who have PFP. (don’t blame the glutes!)
Exercises intended to strengthen the glute medius and lateral rotators (the posterolateral hip) do not change hip mechanics in those with PFP, but may improve pain.
Loads can be modified in several ways at the hip, knee and ankle however the beneficial effects are not likely due to any long-term biomechanical changes.
Clinicians are encouraged to introduce therapeutic exercise which are aimed at altering biomechanics i.e. if someone’s knee moves inwards (valgus collapse) under load, use cues to do the opposite. These may reduce symptoms and alter load, but will unlikely change the mechanics long-term or during running.
Determining the likely forces and load through the knee joint with different exercises, loads and angles is bloody complicated!! It’s likely going to be a little hit-and-miss and guided by symptoms.
Appropriately grading a return to usual running volumes is equally challenging. ‘Runners’ would likely benefit from an electronic means of recording the three variables for someone to accurately grade their rehab program.