Patellar Tendon Rupture
Summary
Patellar Tendon Rupture is a complete disruption of the knee extensor mechanism, typically occurring in younger patients (<40 years) (Contrast with Quadriceps Tendon rupture in >40s). It usually results from eccentric loading (e.g., landing from a jump) on a flexed knee. The hallmark physical sign is a palpable infrapatellar gap and the inability to perform a straight leg raise (SLR). X-rays show Patella Alta (High riding patella). Treatment is surgical repair (End-to-End) followed by protected rehabilitation. Neglected ruptures lead to retraction and severe disability. [1,2,3]
Key Facts
- The "Rule of 40":
- <40 years: Patellar Tendon Rupture (Athletes).
- >40 years: Quadriceps Tendon Rupture (Degenerative).
- The "Toothpaste" Effect: The tendon ends look like shredded mop ends. Primary repair is challenging and requires strong sutures (Krackow technique) woven through the tendon to hold.
- Systemic Risk Factors: Steroid use, Fluoroquinolone antibiotics (Ciprofloxacin), Rheumatoid Arthritis, Diabetes. All weaken the collagen matrix.
Clinical Pearls
"The SLR Test": If a patient with a swollen knee CANNOT lift their heel off the bed (Straight Leg Raise), they have disrupted their extensor mechanism. It is either a patella fracture, quad rupture, or patellar tendon rupture. Beware: Pain inhibition can mimic failure. If in doubt, aspirate the hematoma and inject local anaesthetic.
"Hidden by Swelling": The palpable gap can be masked by a large hematoma within hours. Always trust the SLR test and X-ray.
"Missed Diagnosis": Often misdiagnosed as a "knee sprain" in ER because the patient can walk (by locking their knee in extension using gluteals) but cannot extend actively.
Demographics
- Age: <40 years (Mean 30-35).
- Sex: Male >> Female.
- Mechanism:
- Eccentric Load: Landing from a jump (Basketball, Volleyball). The quadriceps contracts to decelerate the body, but the knee is flexing.
- Direct Blow: Kicking edge of a step (rare).
Risk Factors
- Patellar Tendonitis (Jumper's Knee): Chronic microtears weaken the tendon.
- Systemic Disease: SLE, RA, Diabetes, Renal Failure (Secondary hyperparathyroidism).
- Drugs:
- Corticosteroids (Injections or Systemic).
- Anabolic Steroids.
- Fluoroquinolones (Ciprofloxacin).
Anatomy
- The Patellar Tendon (Ligament) connects the inferior pole of the patella to the tibial tubercle.
- Dimensions: Approximately 30mm wide and 50mm long.
- Strength: Tensile strength is enormous (10-15x body weight). Rupture requires significant force or pre-existing degeneration.
- Retinaculum: The medial and lateral expansions. If these tear (complete rupture), SLR is lost. If they remain intact (partial), SLR is weak but possible.
Mechanism of Rupture
- Eccentric Contraction: The quadriceps fires maximally to decelerate the body (landing) while the knee is flexing. The force exceeds the tendon's threshold.
- Location: Usually at the inferior pole of the patella (Proximal insertion). Mid-substance tears are rare. Tibial tubercle avulsions occur in adolescents (Osgood-Schlatter background).
Symptoms
Signs
X-Ray (Lateral)
- Patella Alta: The patella is displaced proximally.
- Insall-Salvati Ratio: Tendon Length (TL) / Patella Length (PL).
- Normal: 1.0 (range 0.8-1.2).
- Patella Alta (Rupture): >1.2.
- Patella Baja (Quad tear/Scarring): <0.8.
- Avulsion: May see a flake of bone from the inferior pole.
Ultrasound
- Fast, cheap. Shows disruption of fibers. Can sustain gap dynamically.
- Operator dependent.
MRI (Gold Standard)
- Confirms diagnosis.
- Distinguishes partial vs complete.
- Assesses retinacular damage (medial/lateral extent) - important for surgical planning.
- Evaluates intra-articular pathology.
SUSPECTED TENDON RUPTURE
(Gap + Unable to SLR + Patella Alta)
↓
IS IT COMPLETE?
(Can they hold leg straight?)
┌────────────┴─────────────┐
NO (Intact) YES (Complete)
↓ ↓
PARTIAL TEAR COMPLETE RUPTURE
(Rare) ↓
↓ SURGICAL REPAIR
EXTENSION BRACE (Within 2 weeks)
(6 weeks) ↓
Mid-substance? Avulsion?
┌──────┴──────┐
Suture Anchors/
Repair Transosseous
Repair
Timing
- Acute (<2 weeks): Direct primary repair. Best outcome.
- Chronic (>6 weeks): Tendon retracts and scars. Primary repair usually impossible. Requires reconstruction.
Technique: Primary Repair
- Approach: Midline incision.
- Preparation: Debride mop-ends. Expose inferior pole of patella. Drill 3 parallel tunnels (Transosseous) OR insert Suture Anchors.
- Suture Configuration:
- Krackow Stitch: A locking loop stitch running up and down the tendon sides using #5 FiberWire (High strength).
- Pass sutures through tunnels/anchors and tie with knee in extension.
- Augmentation: Usually not needed for acute repair. Historically, a wire circlage loop was used to protect the repair, but this requires removal.
Chronic Reconstruction
- If retracted, the patella is stuck in Alta.
- Requires Z-plasty lengthening of quadriceps OR Achilles Tendon Allograft (Bone block into tibia, tendon woven through patella).
The Balance
- Must protect the repair (Don't pull it apart) vs Prevent stiffness (Arthrofibrosis).
Protocol
- Weeks 0-2: Hinge brace locked in Extension. NWB or TTWB.
- Weeks 2-6: Passive flexion 0-45°, then 0-90°. Active flexion prohibited.
- Weeks 6-12: Full Weight Bearing. Wean brace. Active extension permitted.
- Months 3-4: Light jogging.
- Months 6: Return to sport (Explosive activity).
1. Re-rupture
- Risk: ~5%.
- Cause: Non-compliance with brace or fall.
2. Stiffness (Arthrofibrosis)
- Very Common. Loss of flexion.
- Prevention: Early passive range of motion.
- Treatment: MUA or Arthroscopic lysis of adhesions.
3. Patella Baja (Low Patella)
- If repaired too tight (shortened tendon).
- Result: Anterior knee pain, impingement, restricted flexion.
- Pearl: Ideally verify patella height with Fluoroscopy intra-operatively compared to normal side.
4. Quadriceps Weakness
- Persistent atrophy (10-20% deficit) is common even with good repair.
Repair Techniques
- Multiple biomechanical studies show Transosseous Tunnels and Suture Anchors have equivalent pull-out strength. Anchors are faster but more expensive. Transosseous is the classic "Gold Standard".
Early Motion
- Modern protocols favor "Early Active Mobilization" (protected range) over casting. Studies show less stiffness and no increase in rupture rate.
What happened?
The strong rope (tendon) that connects your kneecap to your shin bone has snapped. This means your thigh muscles are disconnected from your lower leg—like a clutch cable snapping in a car.
Can it heal on its own?
No. The ends are pulled apart by the strong thigh muscles. They will never meet. Surgery is mandatory to sew them back together.
How do you fix it?
We use very strong sutures to weave the tendon ends back together and tie them to the bone.
How long to recover?
It is a slow process. You will be in a longer leg brace for 6 weeks. It takes 6 months to return to sports like football or basketball.
- Siwek CW, et al. Ruptures of the extensor mechanism of the knee joint. J Bone Joint Surg Am. 1981.
- Matava MJ. Patellar tendon ruptures. J Am Acad Orthop Surg. 1996.
- Rosso F, et al. Patellar tendon rupture: outcomes after surgical repair. Knee Surg Sports Traumatol Arthrosc. 2015.
Q1: How do you differentiate Patellar vs Quadriceps Tendon Rupture? A:
- Patellar: Age <40. Gap below patella. Patella Alta (High).
- Quadriceps: Age >40. Gap above patella. Patella Baja (Low).
Q2: What is the Insall-Salvati Ratio? A: Length of Patellar Tendon (LT) / Length of Patella (LP).
- Normal = 1.0 (range 0.8-1.2).
- >1.2 = Patella Alta (Patellar Tendon Rupture).
- <0.8 = Patella Baja (Quad Rupture or scarring).
Q3: Describe the Krackow Suture technique. A: A locking loop suture technique used for tendons. It involves intermittent locking loops along the side of the tendon to grasp the fibers securely, preventing "cheese-wiring" or pull-out. It creates a very strong grasp of the tendon end.
Q4: What drug class is associated with spontaneous tendon rupture? A: Fluoroquinolones (e.g., Ciprofloxacin). They increase expression of Matrix Metalloproteinases (MMPs) which degrade collagen. Also Corticosteroids.
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