Patella Tendon Rupture - Knee & Sports

Introduction

Disruption of the tendon attaching the patella to the tibial tubercle (the patella is a sesamoid bone making this a tendon, not a ligament)
Epidemiology
- incidence
  - < 0.5% of the US population per year
- demographic
  - most commonly in 3rd and 4th decade
  - male > female
- location
  - quadriceps tendon rupture > patella tendon rupture
- risk factors
  - weakening of collagen structure
    - systemic
      - systemic lupus erythematous
      - rheumatoid arthritis
      - chronic renal disease
      - diabetes mellitus
    - local
      - patellar degeneration (most common)
      - previous injury
      - patellar tendinopathy
    - other
      - corticosteroid injection
Pathophysiology
- mechanism
  - tensile overload of the extensor mechanism
  - most ruptures occur with knee in flexed position
    - greatest forces on tendon when knee flexion > 60 degrees
    - ratio of patellar tendon force to quads tendon force >1 at <45° and <1 at >45°
      - at smaller flexion angle, patellofemoral contact point is at distal pole of patella, giving quads tendon a mechanical advantage
- pathoanatomy
  - 3 patterns of injury
    - avulsion with or without bone from the proximal insertion/inferior pole of patella (most common)
      - strain at tendon-bone interface is 3-4x strain at midsubstance
    - midsubstance
    - distal avulsion from the tibial tubercle
- biology
  - rupture is usually the result of end stage or long-standing chronic tendon degeneration
Outcome
- most important factor is timing of repair

Anatomy

Extensor mechanism of the knee
- quadriceps femoris muscles
- quadriceps tendon
- patella
- patellar tendon
- tibial tubercle
Forces in patellar tendon
- ascending stairs is 3x body weight
- to rupture a normal tendon is 17x body weight
Blood supply
- infrapatellar fat pad
- retinacular structures (medial and lateral inferior geniculate arteries)

Presentation

History
- sudden quadriceps contraction with knee in a flexed position (e.g., jumping sports, missing step on stairs)
Symptoms
- infrapatellar pain
- popping sensation
- difficulty weight-bearing
Physical exam
- inspection
  - elevation of patella height
  - usually associated with a large hemarthrosis and ecchymosis
  - localized tenderness
  - palpable gap below the inferior pole of the patella
- motion
  - unable to perform active straight leg raise or maintain passively extended knee
  - reduced ROM of knee (and difficulty bearing weight) due to pain
    - if only tendon is ruptured and retinaculum is intact, active extension will be possible but will have extensor lag of a few degrees

Imaging

Radiographs
- recommended views
  - AP and lateral of the knee
- optional views
  - merchant or skyline
- findings
  - patella alta seen in complete rupture
  - knee in flexion (ideally 30 degrees), the Insall-Salvati ratio is > 1.2
Ultrasound
- indications
  - suspected acute and chronic injuries
- findings
  - effective at detecting and localizing disruption
  - operator and user-dependent
MRI
- indications
  - differentiate partial from complete tendon rupture
  - most sensitive imaging modality
- findings
  - site of disruption, tendon degeneration, patellar position, and associated soft tissue injuries

Treatment

Nonoperative
- immobilization in full extension with a progressive weight-bearing exercise program
  - indications
    - partial tears with intact extensor mechanism
  - modalities
    - application of a removable knee splint
    - early knee range of motion
Operative
- primary repair
  - indications
    - complete patellar tendon ruptures
    - ability to approximate tendon at site of disruption
  - techniques
    - end-to-end repair
    - transosseous tendon repair
    - suture anchor tendon repair
- tendon reconstruction
  - indications
    - severely disrupted or degenerative patella tendon
  - techniques
    - semitendinosus or gracilis tendon autograft
      - free ends of the tendons are passed through transosseous hole of the patella, and then through a transosseous hole within the tibial tubercle to make a complete circle graft.
    - other options
      - central quadriceps tendon-patellar bone autograft
      - contralateral bone-patellar tendon-bone autograft
      - allograft
- rehabilitation
  - may weight bear early with protected knee extension brace
  - exercises to optimize range of motion and minimizes stress on the repair include
    - passive extension and active closed chain flexion (heel slides)
    - prone open chain knee flexion

Techniques

Direct primary repair
- approach
  - longitudinal midline incision
  - expose rupture and adjacent retinacula
  - debride the ends of the rupture
- end-to-end technique
  - approximate tendon at site of rupture
  - nonabsorbable sutures are woven with locking stitch
- transosseous tendon repair
  - suture the patellar tendon to the patella with a no.5 nonabsorbable transosseous suture
  - can be protected with a cerclage wire or nonabsorbable tape between patella and tibial tuberosity
- postoperative care
  - immediate immobilization
  - weight-bearing status
  - rehabilitation
  - following acute primary repair with suture augmentation - immediate immobilization with full weight-bearing and controlled initiation of knee ROM at 7-10 days, goal of brace free ambulation, full knee extension, and 120 degrees of knee flexion by 6 weeks, and full return to sport at 6 months

Complications

Stiffness (loss of knee flexion)
- prevent this by starting early ROM and quads strengthening
- treat this with MUA if flexion is <120° at 6-8wks
Decreased quadriceps strength
Quadriceps atrophy (does not compromise return of strength)