Let’s talk about runner’s knee (patellofemoral pain syndrome). Despite it being one of the most – if not the most – common injury that we see when treating runners in musculoskeletal practice, it remains one of the most varied, and therefore poorly treated conditions (Barton et al, 2012).
Anatomy of Runner’s Knee
To begin with, let’s take a look at the anatomy; the foundation of biomechanics and rehabilitation. The Patellofemoral Joint is the secondary joint within the knee complex, formed by the Trochlea Groove of the Femur and the Patella. It also involves (but is not limited to) the Patella Tendon, many bursae, the infrapatella fat pad (Hoffa’s Pad) and the knee capsule and associated ligaments.
Because of the location, pain within this region is often given the umbrella term of ‘anterior knee pain’ but for the sake of clemency within this piece, I’ll refer to this kind of ‘runner’s knee’ as Patellofemoral Joint Pain using the abbreviation PFJP.
Both the Trochlea Groove and Patella are lined with the thickest articular cartilage in the body, excellent at withstanding joint reaction forces. Maintaining optimal alignment of this joint is essential to pathology free function, which we will discuss later on in this article.
Clinically, the two most common sub-groups of Patellofemoral Pain Syndrome that we see are ‘Hoffa’s Fat Pad Impingement’ and ‘Excess Lateral Pressure Syndrome’. There are other subgroups such as Quadriceps/Patella Tendinopathy, Supra/Pre Patella Bursitis, Bipartite Patella and Plica Syndrome (if you believe!), but these will not be discussed here.
Hoffa’s Pad Impingement
Impingement of the infrapatella fat pad was first described in the literature by Hoffa in 1903, hence the name.
The structure is highly innervated and vascular, making it a strong source of both inflammatory and nocioceptive pain.
Symptoms will usually be consistent with a hyperextension injury or provoked by stairs or prolonged standing. Initial clinical management should focus on reducing the inflammatory component of the condition by way of unloading/rest and will also respond well to cryotherapy and/or compression (sometimes by way of Kinesiology Taping, again if you believe!).
If symptoms persist, some oral anti-inflammatory medication or an ultrasound-guided corticosteroid injection tend to usually be very effective.
Excessive Lateral Pressure Syndrome
Excessive Lateral Pressure Syndrome (ELPS) is often not quite so clear cut. Excessive contact between the lateral aspect of the trochlea groove and the lateral facet of the patella will adversely load the Patellofemoral joint.
However, because articular cartilage is poorly innervated and minimally vascular, it has a low capacity for both producing pain and tissue repair.
It is only when the adverse load is so great that stress is transferred to the subchondral bone that pain usually arises. This happens in the presence of extreme load (high training volume as an example), or over time as the articular cartilage degenerates.
Athletes can often be damaging their Patellofemoral Joint without even realising it and only present for treatment when they experience pain.
Knee Hyperextension and Over-striding Running Style
As mentioned previously, if there is a movement pattern that the Hoffa’s Fat Pad dislikes it is hyperextension of the knee (moving beyond 0o of Extension). This is the most common skeletal hypermobility pattern that we seen in athletes, which will only be accentuated by the most common running technique flaw that we see, the over-stride. Having your foot strike so far ahead of your centre of mass greatly increases the chance of you landing on a very rigid lower limb, risking hyperextension.
An over-stride also reduces the efficiency of your running gait, forcing your lower limb to tolerate braking forces as opposed to your Glute/Hamstring complex producing forward momentum. To improve this movement flaw, athletes should focus on reducing their stride length and increasing cadence, gaining greater hip extension through Glut/Hamstring training to improve terminal stance position and gaining greater eccentric (inner-range) Quad control to limit hyper-extension forces.
This highlights the necessity of ensuring that newly acquired movement patterns from rehabilitation carry over into functional movement, with the running gait being a beautiful example of this.
Dynamic Knee Valgus
Of all the things that we do not yet know the answer to in the world of sports medicine, we do know this: diminished hip muscle function and thus a valgus position of the knee is consistently shown to be predictive of runner’s knee (PFPS) in athletes (Barton et al, 2012). This is a consistent conclusion of all prospective studies (the most recent of which is Noehren et al, 2012) and subsequent systematic reviews completed on the subject. Dr Christopher Powers (2010) does an excellent job of explaining how this movement pattern adversely loads the Patellofemoral joint. I’ll leave the academics in the audience to take what they need from his excellent clinical commentary.
IMAGE © Journal of Orthopaedic & Sports Physical Therapy
For the patients amongst us, essentially we now understand that in closed chain activity (foot fixed on the ground), it is inappropriate movement of the femur relative to the patella that alters the alignment of the joint , as opposed to the patella moving relative to the femur (what we used to believe). An internal rotation and adduction moment of the femur will cause excess contact between the lateral aspect of the trochlea groove and the lateral facet of the patella, leading to pain.
Whatever the cause, eradicating this faulty movement pattern will often go a long way towards rehabilitating Patellofemoral Pain Syndrome and so many other lower limb conditions.
Remember that it is not always weakness or inhibition responsible, as our external colleague The Sports Physio (@AdamMeakins) recently pointed out on Twitter, a stiff ankle joint or overactive adductor muscles can also be at fault (Padua et al, 2012).
Seek the advice of an excellent physiotherapist who can identify the root cause of your imbalance and set you on the path of correction. Please remember that whilst an athlete may have great movement patterns in clinical analysis, they may not necessarily retain them at mile X of their marathon. Never underestimate the impact of fatigue and thus the role of both physiological and muscle endurance.
Barton et al (2012). Conservative management of Patellofemoral pain syndrome: integrating the evidence base with physiotherapist’s clinical reasoning. J Sci Med Sports (15) S188-S264.
Barton et al (2012). Gluteal muscle activity and patellofemoral pain syndrome: a systematic review. Br J Sports Med (Published Ahead of Print).
Padua et al (2012). Neuromuscular characteristics of individuals displaying excessive medial knee displacement. J Athl Train (47) 525-536.
Powers (2010). The influence of abnormal hip mechanics on knee injury: a bio mechanical perspective. JOSPT (40) 42-51.
Noehren et al (2012). Prospective evidence for a hip etiology in Patellofemoral pain. Med Sci Sport Ex (Published Ahead of Print).Last updated on August 26th, 2019.