Patellar Tendinitis

Patellar tendinopathy, commonly known as Jumper's Knee, is an overuse injury describing pain at the inferior pole of the patella. It is characterized by focal degeneration of the proximal patellar tendon.

Epidemiology:

• Prevalence: High in jumping sports (volleyball 40%, basketball 30%)
• Age: Typically 15-30 years old
• Gender: Male greater than Female (2:1)
• Risk Factors:
  • Extrinsic: Hard playing surfaces, increased training volume
  • Intrinsic: Poor quadriceps flexibility, vertical jump height (higher jumpers at higher risk), ankle dorsiflexion stiffness

Anatomy:

• Patellar Tendon: Connects patella to tibial tubercle
• Inferior Pole: Most common site of pathology (proximal posterior aspect of tendon)
• Vascularity: Posterior proximal insertion is a relatively hypovascular zone ("watershed area")

Pathophysiology (Tendinosis vs Tendinitis):

• Historically termed "tendinitis" implying inflammation
• Current understanding: Degenerative process (Tendinosis)
• Histology:
  1. Angiofibroblastic hyperplasia: Neovascularization with nerve ingrowth (pain source)
  2. Mucoid degeneration: Increased ground substance
  3. Collagen disorganization: Loss of parallel type I collagen bundles
  4. Absence of inflammatory cells: No neutrophils or macrophages

The Continuum Model (Cook & Purdam):

Rather than a binary "inflamed versus degenerate" view, tendon pathology is best understood as a continuum, which guides load-based rehabilitation:

History:

• Anterior knee pain localized to inferior patellar pole
• Aggravated by jumping, landing, deceleration (eccentric load)
• "Movie sign" (pain with prolonged sitting) - can overlap with PFPS
• History of recent increase in training volume

Physical Examination:

Bassett's Sign Explained:

• Extension: Patterns tendon is lax; inferior pole palpation is possible.
• Flexion (90 deg): Tendon tightens ("trampoline"); deep palpation of the posterior aspect of the proximal tendon is impalpable.
• Positive sign = Tenderness present in extension, absent in flexion.

1. Radiographs (X-ray):

• Usually normal
• May show:
  • Elongated inferior patellar pole (impingement theory)
  • Intratendinous calcification (chronic)
  • Osgood-Schlatter or Sinding-Larsen-Johansson sequelae

2. Ultrasound (US):

• First-line imaging modality
• Findings:
  • Tendon thickening
  • Hypoechoic area (focal degeneration)
  • Doppler flow (neovascularization) - correlates with pain
• Advantages: Dynamic, cheap, bilateral comparison

3. MRI:

• High sensitivity (95%)
• Findings: Increased signal intensity on T2/STIR in proximal posterior tendon
• Useful to rule out other pathology (meniscus, cartilage, bone edema)
• Note: MRI signal abnormalities can be present in asymptomatic athletes ("imaging-clinical mismatch"). Treat the patient, not the scan.

Tendon Rupture:

• The most devastating complication
• Rare in virgin cases, risk increases with multiple steroid injections
• Requires complex surgical reconstruction (often needs augmentation due to poor tissue quality)

Saphenous Nerve Injury:

• Infrapatellar branch runs transversely across proximal tibia/tendon
• Transverse incisions risk injury causing lateral numbness
• Longitudinal incisions safer

• Conservative: 60-80% success rate with proper eccentric program
• Surgical: 70-90% good/excellent results
• Return to Play:
  • 50-60% return to previous level of sport
  • Many return to sport but at a lower level or with residual symptoms
• Refractory cases: Consider other diagnoses (Hoffa's fat pad, plica) or look for biomechanical contributors (hip/ankle).

Global Epidemiology:

• Patellar tendinopathy is fundamentally a load-related overuse disorder, so prevalence tracks explosive leg-extensor sport worldwide rather than any single region. In a cross-sectional study of 613 elite Norwegian athletes, overall current prevalence was 14.2%, peaking at 44.6% in volleyball and 31.9% in basketball, with zero cases in cycling and orienteering.
• Symptoms are typically chronic and performance-limiting: mean symptom duration was 32 months and mean VISA score 64 in affected athletes.
• Men are affected roughly twice as often as women (13.5% versus 5.6% in the same elite cohort), consistent with greater jump height and explosive loading.

Outcome Measurement (international standard):

• The VISA-P (Victorian Institute of Sport Assessment - Patella) is the validated, internationally adopted patient-reported outcome (8 items, 0-100). It was developed and validated with excellent reliability (r greater than 0.95) and is the comparator used in essentially all modern trials. Cross-culturally adapted versions exist in many languages, making it the common currency for comparing studies across countries.

Practice Variation:

• There is no joint-registry equivalent for tendinopathy (registries cover arthroplasty/implants), so the evidence base is trial- and consensus-driven rather than registry-driven.
• Practice differs mainly in the interventional middle ground: PRP, sclerosing/high-volume injection and extracorporeal shockwave are used more readily in some sports-medicine systems (often physician-led, before any surgical referral), whereas other systems move from supervised loading straight toward surgical opinion. The high-level evidence for these adjuncts remains limited, so their use reflects local resources and clinician preference rather than strong guideline mandate.
• The one near-universal agreement across all guidance is that structured progressive loading is first line and intratendinous corticosteroid is avoided because of rupture risk and inferior long-term outcomes.