Summer is here, and with that warm weather comes more walkers and joggers on the streets of Toronto. Dusting off your running shoes and hitting the pavement for the first can cause aches and pains in our knees.
When considering common causes of knee pain during running, we need to consider muscle weakness and imbalances above and below the knee. This blog will explore how weakness in the hip contributes to patellofemoral pain (PFPS).
Patellofemoral pain syndrome results from excessive forces applied across the joint between the patella (kneecap) and femur (thigh bone). If our knee mechanics are suboptimal and we participate in a repetitive type task (running, cycling) we put a great deal of stress on the patellofemoral joint. Over time this repeated insult can result in cartilage wear, joint irritation, pain and inflammation.
A lot of the attention with respect to PFPS prevention is placed on the quadriceps, specifically the strength of a muscle called VMO. Today we are going to look higher up, into the hip and pelvis at one often deconditioned muscle group of critical importance, the glutes.
A recent systematic review by Barton et al analyzed 10 case-control studies to investigate the contribution of gluteal muscle strength to the cause, presentation, and management of patellofemoral pain syndrome.
Authors found moderate to strong evidence indicating that gluteus medius activity is delayed and of shorter duration during stair climbing tasks in PFPS sufferers. The delayed and shorter activation of the gluteus medius muscle results in an impaired ability to control hip and knee motion.
When the gluteal muscles are not functioning properly it can cause our pelvis to move excessively. Another consequence is excessive knee movement or what is called dynamic knee valgus. If we have gluteal weakness during activities where we are standing on one leg this may cause our knee to cave-in towards the midline of our body (valgus position) When the knee assumes a more valgus (midline or caved-in) position, we get a rotation of the femur (thigh) and tibia (lower leg) and an increased pronation of the foot and ankle. Compare picture A below (which shows proper mechanics) and picture B (which shows the faulty movement caused by a weak gluteal muscles).
These abnormal movement through the hip, knee, and ankle cause increased stress through the patellofemoral joint, which can develop into patellofemoral pain syndrome.
Looking in more detail at these faulty movements, recent studies have demonstrated a link between patellofemoral pain and the increase of femoral (thigh) internal rotation and adduction (mideline movement) that occurs when the glutes are weak (Powers 2003).
Powers et al in 2003 concluded that excessive femoral adduction (caving in) during athletic movements can be the result of weakness of the hip rotators, in particular, the gluteus medius. Also, the parts of the gluteus maximus and the tensor fascia latae muscles. These muscles assist in abduction at the hip and may, if weak, contribute to excessive thigh adduction (Powers et al. 2003).
Another study by Prins in 2009 demonstrated that females with PFPS demonstrate hip weakness compared to healthy control subjects (Prins 2009).
One final study by Dierks and colleagues measured the strength of hip muscles before and after a fatiguing run in PFPS sufferers and concluded gluteus medius endurance may be more important than raw strength in prevention of PFPS (Dierks 2008). Runners with PFPS showed weaker hip abductor (away from midline) strength and greater hip adduction (toward midline) movement during running, which became more pronounced with distance running (fatigue). This finding suggests that our rehabilitation of the gluteus medius should be directed at endurance rather than pure strength and power.
Performing a clamshell exercise is a great way to get started on activating and strengthening the gluteal muscles. Here is a great video by Mike Reinold showing proper form during the clamshell exercise:
Another great exercise that targets the gluteus medius in manner similar running/walking is the hip hike. This video demonstrates proper mechanics during this exercise:
Rehab and treatment of patients with patellofemoral pain should not overlook the gluteal musculature as a contributing factor. The clinical picture is often more complicated than it seems. Recent literature supports the idea that a dynamic knee valgus caused by internal rotation and adduction of the femur is the mechanism of injury in PFPS. One must not neglect the biomechanics of the foot and ankle and their contribution to lower extremity kinematics, but this is a topic for a future discussion.
Dr. Brennan Dynes BA (Hons), DC
Barton CJ, Lack S, Malliaras P, Morrissey D. Gluteal muscle activity and patellofemoral pain syndrome: a systematic review. Br J Sports Med. 2013 Mar;47(4):207-14
Dierks TA, Manal KT, Hamill J, Davis IS. Proximal and distal influences
on hip and knee kinematics in runners with patellofemoral pain during a prolonged run. J Orthop Sports Phys Ther. 2008;38:448-456.
Powers CM. The influence of altered lower-extremity kinematics on patello- femoral joint dysfunction: a theoretical perspective. J Orthop Sports Phys Ther. 2003;33:639-646.
Prins MR, van der Wurff P. Females with patellofemoral pain syndrome have weak hip muscles: a systematic review. Aust J Physiother. 2009;55:9-15.