Patellofemoral pain syndrome - causes and treatments
Patellofemoral pain is common in many sportspeople. FitFor Physio Clinical director, Libby Sharp, summarises the factors and treatments available.
Patellofemoral Pain Syndrome (PFPS), which is also known as runners knee, chondromalacia patellae and anterior knee pain, is a generic term used to describe pain at the front of the knee and around the knee cap. PFPS can be associated with a clicking or cracking sound when bending the knee or walking up and down stairs, wasting of the quadriceps muscles if the injury is an old one and tight muscles around the knee joint.
Patellofemoral pain is common in people who do a lot of sport. It is particularly prevalent in adolescent children during the growth spurt in the early teens, when the long bones grow rapidly and the muscles can take some time to catch up. However, despite the frequent occurrence of this condition, the many scientific papers published have not identified a single cause and therefore there may be a number of predisposing factors for PFPS.
Predisposing Factors
There is poor consensus of opinion of the causes of anterior knee pain, but mechanical and biochemical factors must be considered. Biomechanical contributing factors may include: malalignment of the lower extremity and patella, muscular imbalance of the lower limb and overuse factors. Mechanical factors might include trauma or anatomical predisposition.
Biomechanical factors
These may include a Trendelenberg tendency due to weak gluteus medius muscle (VMO) function; tight lateral structures such as the lateral part of the quadriceps muscle (vastus lateralis VL) and iliotibial band (ITB)associated with a chronic lateral patellar tilt; patella alta, which is when the quadriceps muscle is so tight and the kneecap sits high in the femoral groove; finally, increased quadriceps (Q) angle and quadriceps muscle imbalance, leading to mal-tracking of the patella in the femoral groove.
The Q angle
The patella is designed to track smoothly in the vertical groove in the femur and this tracking is brought about by the balance between the inner part of the quadriceps muscle the VMO (vastus medialis oblquus) and the outer part of the quadriceps muscle VL (vastus lateralis). The timing must be right with VMO coming in to action slightly before the outside muscle VL – this is so that the kneecap tracks smoothly in its groove in the thigh bone. If this does not happen, the underside of the kneecap can become irritated and inflamed.
The Q angle is the angle formed by a vertical line drawn from the tip of the patella and a line drawn along the pull of the lateral quadriceps muscle. If this is over 25°, it pulls the patella laterally and out of the grove in the thigh where it should track. This causes the grinding and eventually the wearing of the cartilage at the back of the kneecap.
Patella position and tracking
Lateral tracking (a), lateral rotation (b) and lateral tilting of the patella may all be predisposing factors for anterior knee pain.
The patella is designed for heavy work and seventy-five percent of the under surface is covered by cartilage up to 5mm thick, making it the thickest in the body. It is estimated that 8 times body weight compression force goes through the patellofemoral joint in a knee squat at 90° of knee flexion, which gives some indication of the loading through this joint.
Lower limb chain biomechanics
The position of all the bones of the lower limb chain can influence the tracking of the patella. Poor biomechanics in weight bearing such as increased internal rotation of the thigh might be the result of weakness of the hip abductor muscle gluteus medius; internal rotation of the tibia might arise from rear-foot eversion or over-pronation. Functional valgus position where the knee angulates inwards may lead to lateral patella mal-tracking.
Patellafemoral Pain syndrome (PFPS)
PFPS is a multifactorial disorder. Tightness in quadriceps and calf muscles, weak quadriceps muscles, and faulty landing mechanics can predispose development of PFPS.
The most frequently reported symptom of PFPS is pain, described as a dull, aching discomfort around or behind the kneecap. The pain is felt walking up and down hills and stairs, squatting and weight bearing through a bent knee. Often sitting for a long time such as in the cinema or driving for a long way and getting up from prolonged sitting can also cause pain.
Other causes of anterior knee pain
Jumper’s knee or patella tendinopathy is a condition caused by repetitive jumping in sports such as basketball and netball, where the stretch strain force and high impact overloading can cause an inflammation of the patella tendon. Overuse can result in pain, inflammation and degeneration and the tendon may appear thickened and tender to touch.
Osgood-Schlatter’s ‘disease’ can cause a painful lump below the kneecap, on the tibial tuberosity where the patella tendon inserts, in children and adolescents during the growth spurt during puberty. It occurs most often in children who participate in a lot of sports that involve running, jumping and swift changes of direction. Although more common in boys, the gender gap is narrowing as more girls become involved with sports. The condition usually resolves on its own, once the child’s bones stop growing.
Dislocation of the patella can occur following a blow to the kneecap or may be a complication of hypermobility. The patella generally dislocates laterally (toward the outside of the knee). This occurs more commonly in women because of anatomic differences in the angle aligning the femur and tibia.
Iliotibial band (ITB) friction syndrome
The Iliotibial band (ITB) is a sheath of thick, fibrous reinforcement of the tensor fascia latae (TFL) muscle. It runs down the outside of the thigh and attaches to the outside of the tibia (shin bone) and the lateral condyle of the thigh bone. It helps to straighten the knee joint and extend, abduct and turn out the hip. It is a strong component of the lateral support of the knee and if it is tight can cause the kneecap to track laterally. In some people, the band as it passes over the outside of the knee joint can rub and flick in front of the epicondyle when straightening the knee and flick behind when bending. Pain is typically felt on the outside of the knee and when running.
Treatment and self help
Good physiotherapy and podiatry advice can help to diagnose biomechanical problems and offer advice. Orthotics can help to realign the foot and prevent torsion of the thigh and lower leg. Stretches for ITB, quads, hamstring and calf muscles are vital to assist realignment of the patella. Strengthening for the quadriceps in particular – but also the hamstring muscle – is essential to support, balance and control functional movement of the knee and the patella. It is also important to strengthen the lateral rotators and abductors of the hip joint to prevent the knee collapsing inwards on single knee bends and lunges. Balance and the use of a wobble board is important to improve coordination and proprioception. Sometimes taping around the knee is helpful to facilitate muscles to realign the patella and reduce pain. Wearing good supportive shoes with built-in shock absorbing materials and suitable for the surfaces used in sport are essential. When running or playing on hard surfaces, such as at the beginning of the winter season, shock absorbing heel pads or soles are advisable.
In acute episodes, and in the case of patella dislocation ice, rest and avoiding repetitive movements is also advised. With Osgoods-Schlatter’s in adolescents, it is important to reduce activities but to continue to stretch and strengthen the quads and hamstring muscles. In the case of dislocation an Xray or MRI scan and a consultation with a knee specialist may be needed, particularly with recurrent dislocation. Ice and anti-inflammatory medication can help in acute flare ups. Finally, a regulated and progressive exercise programme is needed to return to full function.
References
Erkocak OF, Altan E, Altintas M, Turkmen F, Aydin BK, Bayar A. Lower extremity rotational deformities and patellofemoral alignment parameters in patients with anterior knee pain. Knee Surg Sports Traumatol Arthrosc. 2015 May 1.
Petersen W1, Ellermann A, Gösele-Koppenburg A, Best R, Rembitzki IV, Brüggemann GP, Liebau C. Patellofemoral pain syndrome. Knee Surg Sports Traumatol Arthrosc. 2014 Oct;22(10):2264-74.
Pal S, Draper CE, Fredericson M, Gold GE, Delp SL, Beaupre GS, Besier TF (2011) Patellar maltracking correlates with vastus medialis activation delay in patellofemoral pain patients. Am J Sports Med 39(3):590–598
Wolf Petersen, Andree Ellermann, Andreas Gösele-Koppenburg, Raymond Best, Ingo Volker Rembitzki, Gerd-Peter Brüggemann, and Christian Liebau. Patellofemoral pain syndrome Knee Surg Sports Traumatol Arthrosc. 2014; 22(10): 2264–2274
Park K, Seo K. Effects of a functional foot orthosis on the knee angle in the sagittal plane of college students in their 20s with flatfoot. J Phys Ther Sci. 2015 Apr;27(4)