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Anterior Knee Pain: Evaluation, Causes, Investigation & Management

Anterior knee pain (AKP) is one of the most common musculoskeletal presentations in primary care and emergency medicine, affecting athletes, adolescents, and older adults alike. It is not a single diagnosis - it is a symptom complex with a structured differential.

1. Causes and Etiology

A useful framework organizes causes by anatomical structure:

Patellofemoral Causes (most common)

Condition	Key Features
Patellofemoral Pain Syndrome (PFPS)	Most common cause of knee pain overall; gradual onset, no trauma, worse with stairs/prolonged sitting ("movie theater sign"); women > men, typically 20s-30s
Chondromalacia Patellae	Softening and fragmentation of patellar articular cartilage from impact loading and excessive shear stress; crepitation on exam; worse descending stairs
Patellar Maltracking / Subluxation	Abnormal patella tracking due to bony anatomy, soft tissue laxity, muscular imbalance, or rotational deformity; common in adolescent females

As described in Rheumatology (Elsevier, 2022): anterior knee pain can be caused by chondromalacia patellae, patellofemoral maltracking, and medial plica syndrome, and a careful history is essential to establish the exact site and aggravating/relieving factors.

Tendon Pathology

Condition	Key Features
Patellar Tendinopathy ("Jumper's Knee")	Runners, high jumpers, basketball/volleyball players; point tenderness at distal pole of patella or proximal patellar tendon; worse with standing, jumping, or running uphill
Quadriceps Tendinopathy	Less common; tenderness at superior pole of patella

Per Tintinalli's Emergency Medicine: Patellar tendinitis (jumper's knee) presents with pain at the patellar tendon worsened by activity. Steroid injections should be avoided as they predispose to tendon rupture.

Bursitis

Condition	Key Features
Prepatellar Bursitis	Swelling directly over the kneecap; common in carpet layers and people who kneel frequently ("housemaid's knee"); superficial to the lower half of patella
Infrapatellar Bursitis	Common in long-distance runners; can mimic patellar tendinitis

Adolescent-Specific

Condition	Key Features
Osgood-Schlatter Disease	Traction apophysitis at the patellar tendon insertion on the tibial tubercle; pain, tenderness, swelling at tibial tubercle; exacerbated by exercise; resolves with apophyseal fusion
Sinding-Larsen-Johansson Syndrome	Similar mechanism at inferior pole of patella

Per Bailey and Love's Surgery (28th Ed): the extensor mechanism of the knee is a common site of pain in adolescents during growth spurts.

Other Causes

Plica syndrome - thickened medial synovial fold causing snapping and medial anterior pain
Fat pad impingement (Hoffa syndrome) - infrapatellar fat pad caught between femur and tibia
Referred pain - hip pathology (e.g., slipped upper femoral epiphysis) can present as knee pain - always examine the hip
Post-IM nailing - anterior knee pain occurs in 19-73% after tibial intramedullary nailing, likely multifactorial (fat pad scarring, infrapatellar nerve injury, nail prominence)
Patellofemoral osteoarthritis - older patients with anterior joint line tenderness and crepitus

2. Evaluation

History

Onset: gradual (PFPS, tendinopathy) vs. acute (trauma, dislocation)
Location: peripatella, patellar tendon, tibial tubercle
Aggravating factors: stairs (PFPS/chondromalacia), prolonged sitting (PFPS), jumping (tendinopathy), kneeling (bursitis)
Age and activity level: adolescent active male (Osgood-Schlatter), young female athlete (PFPS/maltracking), middle-aged runner (tendinopathy)
Bilateral vs. unilateral: bilateral more unusual - consider systemic causes

Physical Examination

Test	Finding	Suggests
Clarke's test / Patellar grind	Pain on compressing and asking patient to contract quads	PFPS / chondromalacia
Patellar apprehension test	Apprehension/pain on lateral patellar displacement	Patellar subluxation/instability
Single leg squat	Reproduction of anterior pain	PFPS
Patellar glide/tilt	Reduced medial glide, increased lateral tilt	Lateral retinacular tightness
J-sign	Lateral deviation of patella at end of extension	Maltracking
Tibial tubercle tenderness	Point tenderness at tibial tubercle	Osgood-Schlatter
Patellar tendon palpation	Tenderness at inferior patellar pole	Patellar tendinopathy
Prepatellar swelling	Fluctuant swelling anterior to patella	Prepatellar bursitis
VMO assessment	Wasting of vastus medialis oblique	PFPS, maltracking
Hip examination	Abductor strength, rotation	Hip pathology referred pain; gluteal weakness as PFPS risk factor

Rosen's Emergency Medicine notes: gait abnormalities may be present; medial and lateral patellar tenderness is prominent when due to subluxation/dislocation; single-leg squat pain is suggestive of PFPS. Risk factors include gluteal weakness, quadriceps weakness, patellar subluxation, prepatellar bursitis, arthritis, meniscal tears, and quadriceps/patellar tendinopathy.

3. Investigation

Imaging

X-rays (first-line):

AP, lateral, and skyline (axial/sunrise) view of the patella
Skyline view assesses patellofemoral joint space, patellar tilt, and lateral subluxation (see image below)
Lateral view allows measurement of Insall-Salvati ratio (patellar tendon length : patellar length; >1.2 = patella alta, a risk factor for maltracking)
Standard knee X-rays assess for osteoarthritis, loose bodies, and tibial tubercle changes

Skyline X-ray showing bilateral patellae - note the patellofemoral joint congruence. Lateral subluxation of the patella is visible when present.

Skyline X-ray showing bilateral patellofemoral joints. Lateral subluxation of the patella is assessed on this view. - Rheumatology (Elsevier, 2022)

Lateral knee X-ray demonstrating Insall-Salvati ratio measurement: patellar length 48mm, patellar tendon length 72mm - this is patella alta (ratio >1.2).

Lateral knee X-ray with Insall-Salvati ratio measurement (patellar length 48mm / patellar tendon length 72mm = 0.67 - within normal range; ratio >1.2 indicates patella alta). - Rheumatology (Elsevier, 2022)

MRI:

Indicated when: X-rays are negative but significant symptoms persist, suspected cartilage pathology, soft tissue abnormalities (plica, fat pad), or diagnosis is unclear
Best modality for chondromalacia grading, MPFL injury after dislocation, tendon tears

Ultrasound:

Useful for real-time assessment of patellar/quadriceps tendons
Can detect bursitis, guide aspiration, and assess tendon integrity
Preferred for evaluating tendinopathy and bursitis

Note: PFPS is a clinical diagnosis. Imaging is used to exclude other causes and assess structural abnormalities, not to confirm PFPS itself.

4. Management

Conservative (First-Line for Most Causes)

Physiotherapy - cornerstone of treatment:

VMO strengthening (vastus medialis oblique) to correct lateral tracking
Hip abductor and external rotator strengthening - 2025 meta-analysis (PMID 39934098) confirms that combined hip + knee strengthening is superior to knee strengthening alone for PFPS
Knee extensor training - systematic review (PMID 40861009) supports its role in PFPS
Hamstring and quadriceps stretching
Activity modification and load management

Analgesics:

NSAIDs for short-term pain relief to facilitate physiotherapy initiation
Avoid NSAIDs long-term; avoid corticosteroid injections around patellar tendon (rupture risk)

Orthotic support:

Patellar taping (McConnell technique) to correct lateral tracking
Foot orthotics for overpronation
Patellar tracking braces - some benefit, though efficacy not clearly established per Rosen's
Activity modification: avoid prolonged knee flexion, modify sitting position

Osgood-Schlatter: relative rest and analgesia; resolves with apophyseal fusion.

Bursitis: NSAIDs, activity modification, aspiration if large/septic.

Surgical (for refractory cases)

Lateral retinacular release - for severe lateral tightness / maltracking
Tibial tubercle osteotomy (Fulkerson procedure) - anteromedialization of tibial tubercle for chondromalacia and maltracking
Trochleoplasty / MPFL reconstruction - for recurrent patellar dislocation
Arthroscopic debridement - for unstable chondral fragments in chondromalacia patellae
Plica excision - for symptomatic medial plica

Per Bailey and Love's: "Many operations improve patellar tracking and these include options for realignment of the extensor mechanism both proximally and distally."

Emerging / Adjunct Treatments

A 2025 systematic review (PMID 41009572) on PRP for patellofemoral arthritis and anterior knee pain found some evidence of benefit, though its role remains investigational and not yet standard of care.

Summary Algorithm

Anterior Knee Pain
       |
   History & Exam
       |
   Adolescent? ──Yes──> Check tibial tubercle → Osgood-Schlatter
       |                Check inferior patellar pole → Sinding-Larsen
       |
   Young adult, active?
       |
   Gradual, peripatella, worse stairs/sitting ──> PFPS (clinical dx)
       |
   Tendon point tenderness ──> Patellar tendinopathy
       |
   Anterior swelling ──> Bursitis
       |
   Trauma, dislocation ──> Maltracking/subluxation, X-ray/MRI
       |
   X-ray: AP + Lateral + Skyline
   ± MRI if needed
       |
   Management:
   Physiotherapy (VMO + hip abductors) → NSAIDs → Taping/Orthotics
   → Surgery if conservative fails (>6 months)

Sources:

Rosen's Emergency Medicine, Concepts and Clinical Practice - PFPS: foundations, clinical features, diagnostic testing, and management
Bailey and Love's Short Practice of Surgery, 28th Ed - anterior knee pain in adolescents, extensor mechanism
Rheumatology, 2-Volume Set (Elsevier, 2022) - chondromalacia, patellofemoral maltracking, imaging
Tintinalli's Emergency Medicine, Comprehensive Study - patellar tendinitis
Goldman-Cecil Medicine - bursitis classification
Recent PubMed: Hip + knee strengthening meta-analysis 2025 | Knee extensor training SR 2025 | PRP for PFPS SR 2025

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