Pain around the kneecap, officially termed patellofemoral pain (PFP) accounts for up to 17% of knee pain seen generally, and up to 40% of knee problems seen in the sporting population (Crossley et al 2016), with up to 7% of adolescents between the ages of 15-19 years suffering with the condition (Rathleff 2015).  The condition is more common in young adolescents, especially those active in sport, and is also seen in military recruits.    In addition to active individuals, inactive adolescents who are subjected to a sudden increase in walking and / or stair climbing may also suffer.  In both groups the condition represents an inability of tissue to adapt to increased loading.

Patella location in knee

Patella location in knee

PFP is variously described as anterior knee pain, chondromalacia patellae, patella malalignment syndrome, patellofemoral pain syndrome, and patellofemoral pain.  The condition typically presents as a dull ache over the anterior aspect of the knee, worse following prolonged sitting and when descending stairs.  Although more common in youth, the condition can occur at any age and in seniors it is typically associated with patellofemoral OA (osteoarthrosis).

up to 40% of active individuals get pain around the kneecap at some time

Structure and function of the PF joint

The patella is the largest sesamoid bone (bone lying within a tendon) in the body, attached above to the quadriceps tendon,  and below to the patellar tendon.  Medially and laterally the patellar retinacula (fibrous tissue to the side of the patella) offers support. The breadth of the pelvis and close proximity of the knee creates an outward (valgus) angle of the tibia compared to the femur. Coupled with this, the direction of pull of the quadriceps is along the shaft of the femur and that of the patellar tendon is almost vertical. The difference between the two lines of pull is known as the Q angle and is often considered an important determinant of knee health.  Normal values for the Q angle are in the region of 15–20°.

In full extension the patella does not contact the femur, but lies in a slightly outward (lateral) position. As knee flexion progresses, the patella should move inwards (medially). If it moves laterally it will butt against the prominent lateral femoral condyle and the lateral edge of the patellar groove of the femur. Throughout flexion, different areas of the patella under surface are compressed onto the femur below. At 20° flexion the inferior pole of the patella is compressed, and by 45° the middle section is affected. At 90° flexion, compression has moved to the superior aspect of the knee. In a full squatting position, with the knee reaching 135° flexion, only the medial and lateral areas of the patella are compressed.

Contact areas of the Patella at different degrees of knee flexion (from Norris 2011)

Contact areas of the Patella at different degrees of knee flexion (from Norris 2011)

Patellofemoral loads may be as high as three or four times body weight as the knee flexes in walking, and nine times body weight when descending stairs or walking down a slope . Changes in patellar contact area and contact force make knee angle an important consideration in the selection of exercise during rehabilitation, together with applied load (weight or resistance band) and muscle contraction type.

 

Patient examination

Subjective examination typically presents as a diffuse dull aches over the anterior aspect of the knee.  The pain may be worse with loading in a bent knee position with pain onset on rising from prolonged sitting or with stair climbing.  Typically descending stairs is worse than ascending.  There is rarely a history of specific  injury, rather a history of symptom exacerbation when loading is increased for example through training increase, competition, or an increase in knee loading activity during daily living.

PFP must be differentiated from Patellar tendinopathy, Osgood Schlatters syndrome, and Sinding Larsen-Johannsen disease.  Patellar tendinopathy is more common with jumping actions and commonly presents with pain localised to the inferior pole of the patella (insertion) or patella tendon proper (body).  In Osgood Schlatters syndrome pain is normally restricted to the tibial tubercle.  In SLJ disease there is normally point tenderness to the inferior pole of the patella, as with insertional tendinopathy, but x-ray reveals subtle changes with calcification over longer term.  The condition must be distinguished from traumatic avulsion fracture which shows a definite history of injury.

PFP is reproduced in 80% of patients when performing a squatting action, and tenderness to the patellar edges is seen in 71-75% (Nunes et al 2013), making these two clinical tests important in objective examination.  Traditional grinding tests (patellar compression during quadriceps contraction) have low sensitivity and diagnostic accuracy in PFP (Crossley et al 2016).

 

Patellar taping

Short term (3 months or less) pain relief may often be provided by temporarily changing the position of the patella through taping. Exercising with the taping in place can modify symptoms, and may re-educate muscle sequencing to change patellar alignment (McConnell, 1994). Initially, open web adhesive taping is applied to protect the skin against excessive tape drag. The pull of the final taping is applied using 5 cm zinc oxide tape. Most commonly a medial glide is applied, however taping position and applied stress may be varied to most effectively reduce patient symptoms.  Taping of this type is likely to facilitate patient engagement in rehabilitation (Barton et al 2015).  Where taping cannot be tolerated due to skin irritation, bracing to limit lateral tracking may be used as an alternative for short term relief.

Medial glide patella taping

Medial glide patella taping

Fat pad impingement (Hoffa’s syndrome) may coexist with PFP.  In standing the patella rests on the fat pads, and if the pad is enlarged patella alignment may change.  Relief of fat pad related pain may often be given using a ‘V’ taping attached from the tibial tubercle to run either side of the patella.  The action is to draw the taping upwards so the patella is cradled in the base of the ‘V’.

V tape to unload patella fat pads

V tape to unload patella fat pads

 

Foot biomechanics & orthoses

During normal running gait, the subtaloid joint (STJ) is slightly supinated (high arch) at heel strike. As the foot moves into ground contact, the joint pronates (low arch), pulling the lower limb into internal rotation and unlocking the knee. As the gait cycle progresses, the STJ moves into supination again, externally rotating the leg as the knee extends (locks) to push the body forward. This biomechanical action is combining mobility and shock absorption (STJ pronation and knee flexion) with rigidity and power transmission (STJ supination and knee extension), and shows the intricate link between foot and knee function.

Excessive pronation (left) corrected with an orthotic (right)

Excessive pronation (left) corrected with an orthotic (right)

If STJ pronation is excessive or prolonged, external rotation of the lower limb will be delayed. At the beginning of the stance phase, STJ pronation should have finished but if it continues the tibia will remain externally rotated, stopping the knee from locking. The leg must compensate to prevent excessive strain on its structures, and so the femur rotates instead of the tibia and the knee is able to lock once more. As the femur rotates internally in this manner, the patella is forced to track laterally.

In many circumstances the patella can cope with this extra stress, but if additional malalignment factors exist, such as ante version of the femur (internal rotation), VMO weakness or tightness of the lateral retinaculum the lateral patellar tracking may cause symptoms . Biomechanical assessment of the lower limb is useful as part of an objective examination in the management of this condition. If hyper pronation is present, it may be corrected using changes in footwear, patient education and / or orthotic prescription to reduce knee symptoms to give short term benefits of symptom modification.

Not all patients with PFP benefit from foot orthosis.  Benefit can be predicted by greater midfoot mobility, reduced dorsiflexion motion range, and immediate PF pain improvement when performing a single leg squat while wearing an orthotic (Crossley et al 2016).

 

Rehabilitation

Exercise therapy which combines hip and knee actions (rather than knee movement in isolation) is a mainstay of treatment with this condition both to reduce pain and increase function in the short, medium, and long term (Crossley et al 2016).

Where individuals get pain to assessment of a single leg squat,  lower limb alignment may be addressed as part of motor control training in the short term to modify symptoms.  If patients show a trendelenberg sign (hip adduction, tibial medial rotation and foot pronation) this movement should be modified using a temporary orthotic and patient re-education to determine if symptoms reduce.

Enhancing hip strength can be achieved by both open and closed chain actions.  Closed kinetic chain (CKC) is more functional, mimicking the weight bearing action which loads the leg.  However leg loading in the early stages of the condition may exacerbate symptoms and so open chain may be used until pain settles.  Additionally, CKC actions will work the hip and knee together, which may not be required in the present of irritable knee structures.  Open chain gluteal actions such as the traditional clam shell in crook side lying,  and the fire hydrant, and donkey kick in kneeling together with hip scissor actions are useful starting points.

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Clam shell exercise

Fire hydrant exercise

Fire hydrant exercise

Donkey kick action

Donkey kick action

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Supported single knee bend

Supported single knee bend

 

Motion range and resistance is progressed with the aim of reducing pain intensity and frequency during daily living actions, and enhancing tissue load tolerance.  CKC actions can be begun partial weight bearing progressing to full weight bearing.  Single leg squat, step-down (eccentric) and full step (concentric-eccentric) exercises may all be performed initially holding a wall bar in the gym or chair back / pole at home.  Focussing on lower limb alignment to avoid excessive hip adduction may reduce symptoms, and the symptom free movement range and type should  initially be chosen.  As tissue tolerance is enhanced, both range and alignment should be varied to increase movement variability.  Varying training in this way may avoid building fear of certain movement types and encouraging behaviours which avoid actions out of fear of symptom reproduction (hypervigilance).

Resistance should be increased to build lower limb strength, and specific motor control actions may give way to more traditional gym based lower limb exercises such as leg press, squat variations, deadlift (bent leg and straight leg), and lunge actions with increasing weight and varying motion ranges and speed.  Sport or task specific movement should also be incorporated to regain confidence in the limb.

See our videos of exercise and taping on YouTube

References

Norris, CM (2011)  Patellofemoral pain syndrome.  In:  Managing Sports Injuries (4th ed)  pages 166-171.  Elsevier.  Oxford.

Crossley, KM., Callaghan, M.J.,  and Linschoten R (2016)  Patellofemoral pain.  Br J Sports Med 50: 247-250

Crossley, KM Stefanik, J et al (2016) 2016 Patellofemoral pain consensus statement from

the 4th International Patellofemoral Pain Research Retreat, Manchester. Part 1:   Br J Sports Med 2016 50: 839-843

Rathleff, MS (2016)  Patellofemoral pain during adolescence:  Much more prevalent than appreciated.  Br J Sports Med 50(14):831-832 

Nunes GS, Stapait EL, Kirsten MH, et al. (2013) Clinical test for diagnosis of patellofemoral pain syndrome: Systematic review with meta-analysis. Phys Ther Sport 14:54–9.