Patellofemoral Pain Syndrome is a common cause of knee pain when running. Expert Lee Herrington, lead clinician at the Knee-Rehab UK knee rehabilitation clinic, explains the causes and treatment approaches for this knee pain.
About Lee Herrington & contact details
What is Patellofemoral Pain Syndrome and what causes it?
"Pain around the knee cap or 'Patellofemoral Pain' is one of the commonest presenting orthopaedic musculoskeletal conditions. The Patellofemoral Joint is formed by the back of the knee cap (Patella) and the lower part of the thigh (Femur). Normally, when the knee bends or straightens, the knee cap glides in a special groove on the thigh bone called the 'Patellofemoral groove', controlled by the quadriceps muscles.
"The most widely accepted theory regarding the cause of Patellofemoral Pain suggests that the symptoms are the result of excessive Patellofemoral Joint stresses owing to abnormal Patella tracking. This Patella mal-tracking is thought to generate excessive strain on the 'Retinacular supports' (tissues around the knee cap), underlying joint capsule and/or the cartilage on the joint surface of the Patellofemoral Joint causing pain (McConnell, 1996 Manual Therapy). The elevated Patellofemoral Joint stress is believed to result from alterations in Patellofemoral Joint reaction forces and / or reduced contact area between the back of the knee cap and the thigh, causing irritation and degradation of the tissues at the back of the knee cap.
"The potential causes of mal-tracking and the associated altered tissue loading are numerous. One of the most common causes reported in the literature is weakness of the Gluteus Maximus and Gluteus Medius muscles. Weakness of these muscles causes the thigh to fall inwards when under load, thus increasing the Q-angle (see note below) and so the lateral pull on the knee cap and localised increases in pressure.
"Weak Quadriceps are consistently associated with Patellofemoral Pain. The inability to fully contact the quadriceps means that the knee cap is not forced as deeply into the 'Trochlear groove' of the thigh bone and so the contact area of the Patellofemoral Joint is decreased, which leads to an increase in stress on another area of the joint surface. There is a somewhat academic, albeit contentious debate among physiotherapists about whether an imbalance exists in one of the thigh muscles called Vastus Medialis Oblique, but apart from being unproven this imbalance is only thought to occur in a small proportion of patients anyway.
"A short Iliotibial Band (ITB) influences both knee cap and shin position. One slip of the ITB called the 'Lateral Retinacular fibres', which attach into the lateral border of the knee cap, will both tilt and pull the knee cap laterally if it is short. The other part of ITB attaches into outerside of the upper shin, if this is short it will rotate the shin outwards and so increase the Q-angle (see note below) and lateral deviation of the knee cap. There are a number of other causes of Patella mal-tracking including short Calf, Rectus Femoris, Adductor Longus and Hamstring muscles - all of which influence Patella tracking, but the major ones have been highlighted first."
Note: The Q-Angle refers to the 'quadriceps angle', which is a measurement of patellofemoral joint mechanics. The Q Angle is measured at the intersection of two lines: one drawn from a bony point at the front of the hip to the mid-point of the knee cap and the other from the mid-point of the knee cap to the insertion point for the Patella tendon, at the upper part of the shin. Research has shown that this Q Angle can be areasonable estimate of the muscle force vectors (direction of muscle pull) over the patellofemoral joint. Further research has suggested that there is an increase risk of PFP if the Q Angle greatly exceeds 15 degrees.
What are the aims of physiotherapy treatment for Patellofemoral Pain Syndrome?
"The aims of treatment are really two-fold. Firstly to relieve the pain, this can be achieved using patella taping or bracing. Acupuncture and electrotherapeutic modalities may also prove useful, along with gentle Patella joint mobilisation by a physio. The second part to treatment is to improve Patella tracking which could involve stretching the short muscles or strengthening the weak ones mentioned above. The specifics of the exercises required should very much depend on the individual patient and what is found on assessment.
"One of the most common reasons for failure when treating Patellofemoral Pain is the patient receiving a generic, rather than a tailored set of exercises. There should not be a one exercise fits all approach to patients with this problem."
How can taping help Patellofemoral Pain Syndrome?
"There are a number of reviews on the effects of patella taping (Crossley 2000 Manual Therapy, Herrington 2000 Critical Reviews in Physical and Rehabilitation Medicine). Essentially it relieves pain, improves contractile ability of the Quadriceps (not necessarily just Vastus Medialis Oblique), improves function because of these two factors and it may also change Patella position."
If physiotherapy treatment and taping is unsuccessful, how effective is surgery for Patellofemoral Pain Syndrome?
"The classical operation done for Patellofemoral Pain is the 'Lateral Release', were the Lateral Retinaculum (soft tissue that supports the knee cap) is divided, with the aim of reducing lateral pull and displacement of the Patella. This operation is successfully but only if increased lateral condyle (outerside of the lower thigh bone) pressure is the cause of the patient's problem. As discussed above this is not the only possible source of pain and care must be taken in differentially diagnosing the appropriate patients for this operation. If joint surface lesions are present in the Patellofemoral Joint many surgeons will use 'Microfracture techniques' (drill small holes in the bone surface to promote healing) or even Osteochondral Autologous Graft Transplantation or Autologous Chondrocyte Implantation (techniques to transplant cartilage to the affected joint surface) . The success of both of these operations is still quite mixed. The majority of surgeons still undertake these procedures only as a last resort.
"Recently, in the USA especially two operations are gaining popularity particularly for those patients who suffer from recurrent Patella dislocation or subluxation. These are repair of the Medial Patellofemoral Ligament and a Trochleoplasty (deepening and reconstruction of the surface of the trochlear groove). Both of these operations appear successful in reducing Patella dislocation/subluxation, but often appear to leave the patient with quite severe Patellofemoral Pain."