Patellofemoral Pain Syndrome (PFPS)

Patellofemoral pain syndrome (PFPS) — also termed anterior knee pain, chondromalacia patellae (a misnomer — this implies articular cartilage damage which is not always present), or runner`s knee — is the most common cause of anterior knee pain in young active individuals. It is a clinical diagnosis characterised by peripatellar or retropatellar pain, exacerbated by activities that load the patellofemoral joint (squatting, running, stairs, prolonged sitting). Despite its prevalence, the precise pathophysiology remains incompletely understood and management is primarily non-operative.

• Epidemiology: most common knee condition in the general population; incidence approximately 20–25% of all knee complaints in sports medicine; affects females more than males (2:1); peak incidence in adolescents and young adults (15–35 years); bilateral in up to 30–40% of cases; accounting for up to 25% of all knee injuries in runners
• Patellofemoral joint mechanics: the patellofemoral joint reaction force (PFJRF) increases dramatically with knee flexion — approximately 0.5× body weight in walking, 1.3× in climbing stairs, 3–4× in squatting, and up to 7–8× in deep squatting; increased PFJRF in the presence of any malalignment, muscle imbalance, or structural abnormality produces abnormal patellar contact stress, which is the proposed mechanism for pain; the lateral retinaculum, subchondral bone, synovium, and infrapatellar fat pad are the most likely pain generators
• Proposed contributing factors: dynamic valgus (weak hip abductors and external rotators allowing femoral internal rotation and functional valgus during activity — increases the Q-angle dynamically); VMO weakness (inadequate medial stabilisation); lateral retinacular tightness (tilts the patella laterally, increasing lateral facet contact stress); foot pronation (increases internal tibial rotation); structural factors (increased TT-TG, patella alta, trochlear dysplasia)

• History: insidious onset anterior knee pain; aggravated by squatting, stairs (particularly descending), prolonged sitting with the knee flexed (the `cinema sign` or `theatre sign` — pain from prolonged sitting that is relieved by extending the knee); running, jumping; often bilateral; no history of trauma; morning stiffness; giving way (pseudo-giving way — due to pain inhibition of the quadriceps, not true ligamentous instability)
• Cinema sign (theatre sign / movie sign): pain in the anterior knee that develops during prolonged sitting with the knee in flexion (e.g., in a cinema, at a desk, in a car); relief on extending the knee; caused by increased patellofemoral contact pressure in the flexed position loading damaged or sensitised subchondral bone and peripatellar soft tissues; a highly characteristic symptom of PFPS; also positive in patellofemoral OA
• Examination: peripatellar tenderness (medial and/or lateral patellar facet tenderness on patellar compression or tilt); patellar grind test (Clarke`s test — compress the patella and ask the patient to contract the quadriceps; positive if pain or crepitus); J-sign (lateral patellar tracking during terminal knee extension — the patella moves laterally in a J-shaped arc); patellar tilt test; assess hip abductor strength (often weak in PFPS patients); assess for dynamic valgus on single-leg squat (the knee collapses into valgus with femoral internal rotation); assess foot posture (pronation)
• Clarke`s test (patellar grind test): the examiner presses the patella distally and asks the patient to contract the quadriceps; positive if pain is reproduced; often positive in PFPS but low specificity; may also be positive in patellofemoral OA; a painful test in a young active patient without OA is consistent with PFPS

• PFPS is a clinical diagnosis — investigations are not routinely required in typical presentations
• Plain radiographs: AP, lateral (assess patella alta/baja, trochlear morphology, crossing sign), and skyline (Merchant or sunrise view — assess patellar tilt, lateral subluxation, trochlear depth); usually normal in PFPS; assess for early patellofemoral OA changes in older patients
• MRI: for atypical presentations, suspected cartilage damage, or to exclude other diagnoses (medial plica syndrome, fat pad impingement, osteochondral lesion, stress fracture); shows patellar cartilage signal change, patellar tilt, trochlear morphology, and the infrapatellar fat pad; chondromalacia patellae on MRI (cartilage signal change) does not necessarily correlate with symptoms
• Biomechanical assessment: formal 2D or 3D gait analysis; video analysis of running or squat mechanics; assessment of dynamic valgus; used in specialist sports medicine settings to guide rehabilitation targeting

PFPS management is predominantly non-operative; the evidence base strongly supports structured physiotherapy as the cornerstone of treatment. Surgery is rarely required and should only be considered after failure of a prolonged, supervised rehabilitation programme.

• Physiotherapy — the cornerstone: a combination of quadriceps strengthening (VMO in particular), hip abductor and external rotator strengthening (gluteus medius, gluteus maximus — addressing dynamic valgus), and patellofemoral joint loading education; closed kinetic chain exercises (mini squats, step-ups, leg press) are preferred over open chain exercises (straight leg raises) for PFJ loading; evidence from multiple RCTs demonstrates that combined hip and knee strengthening is superior to isolated knee strengthening for PFPS; addressing hip strength is one of the most important recent advances in PFPS management
• Patellar taping (McConnell taping): medial glide taping of the patella to correct lateral tilt; provides short-term pain relief and facilitates exercise engagement; most useful as an adjunct to physiotherapy in the early stages; evidence for long-term benefit is limited but it is a useful tool to facilitate loading exercises
• Foot orthoses: custom or off-the-shelf orthoses for patients with significant foot pronation or lower limb biomechanical abnormality; modest evidence for pain reduction; low risk and worth trying in patients with clear biomechanical contributors
• NSAIDs: short-term pain relief; no evidence for altering the natural history; useful adjunct in the early acute symptomatic phase
• Lateral retinacular release: historically performed arthroscopically for tight lateral retinaculum causing lateral patellar tilt; results are unpredictable; can cause medial patellar instability if the retinaculum is excessively released; not recommended as an isolated procedure unless there is a clearly demonstrable isolated tight lateral retinaculum with no evidence of medial subluxation risk; largely fallen out of favour
• Surgery: reserved for failure of at least 3–6 months of supervised physiotherapy; options depend on the structural abnormality identified — TTO for increased TT-TG (>20 mm) + PFPS; lateral retinacular lengthening (not release) for isolated lateral tilt; trochleoplasty for severe dysplasia; chondroplasty/microfracture for focal chondral damage; outcomes of surgery for PFPS are generally modest

• Hip strengthening in PFPS: multiple RCTs (Fukuda et al. 2010, Ferber et al.) have shown that adding hip abductor and external rotator strengthening to the physiotherapy programme for PFPS produces superior outcomes compared to isolated knee strengthening; hip weakness allows femoral internal rotation and adduction during loading activities, increasing the Q-angle dynamically and the PFJRF on the lateral facet; this is one of the most important shifts in PFPS management over the past 20 years; the gluteus medius is the primary target muscle
• Medial plica syndrome: an inflamed or hypertrophied medial synovial plica (a remnant of the embryological septa dividing the knee joint) can mimic PFPS; features that suggest medial plica rather than PFPS — a palpable tender cord on the medial side of the knee (medial plica is palpable as a tender band medial to the patella at the medial femoral condyle); clicking or snapping; arthroscopic resection is curative if symptoms are refractory to non-operative treatment; the distinction from PFPS is important as surgery (arthroscopic plica resection) has a more predictable outcome for confirmed medial plica syndrome than for isolated PFPS
• Infrapatellar fat pad (Hoffa`s fat pad) impingement: the fat pad lies posterior to the patellar tendon and inferior to the patella; it can become pinched between the patella and the femoral trochlea (particularly in patella baja or after knee injury/surgery); presents with inferior patellar pain, tenderness at the fat pad, and exacerbation with full extension; Hoffa sign (pain on squeezing the fat pad with the knee in extension) is positive; MRI shows fat pad oedema; management: activity modification, corticosteroid injection into the fat pad, physiotherapy; arthroscopic debridement in refractory cases

• PFPS: most common cause of anterior knee pain in young active people; clinical diagnosis; peripatellar pain + cinema sign + aggravation with squatting, stairs, and running
• Cinema sign: pain with prolonged sitting (flexed knee) relieved by extension; highly characteristic of PFPS; also positive in PFJ OA
• PFJRF increases with flexion: ~0.5× BW walking; ~3–4× squatting; ~7–8× deep squat; increased force with malalignment → abnormal contact stress → pain
• Hip strengthening is critical: gluteus medius weakness → femoral internal rotation + dynamic valgus → increased lateral PFJ load; combined hip + knee physio superior to knee alone (multiple RCTs)
• Clarke`s test: compress patella, ask patient to contract quad; pain = positive; consistent with PFPS or PFJ OA; low specificity
• McConnell taping: medial glide taping corrects lateral tilt; short-term pain relief; facilitates exercise; adjunct to physio — not a standalone treatment
• Lateral retinacular release: unpredictable results; risk of medial instability; largely abandoned as isolated procedure
• Medial plica syndrome: mimic of PFPS; palpable medial tender cord; clicking; arthroscopic resection curative; more predictable surgical outcome than isolated PFPS surgery
• Hoffa fat pad impingement: inferior patellar pain; Hoffa sign positive; MRI shows fat pad oedema; injection + debridement if refractory
• Surgery for PFPS: after ≥3–6 months supervised physio failure; address the structural abnormality (TT-TG, lateral tilt, dysplasia, chondral damage); outcomes generally modest