Patellar Tendon Rupture - Knee & Sports

Summary

A traumatic rupture of the patellar tendon caused by a tension overload during activity in a patient at risk.
Diagnosis can be confirmed by physical exam and radiographs for complete tears. Partial tears may need an MRI to confirm the diagnosis.
While partial tears may be treated with immobilization, complete tears are treated with timely surgical repair to optimize the chance of healing.

Etiology

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 diseases
      - associated with bilateral ruptures
        
        systemic lupus erythematous
        
        rheumatoid arthritis
        
        chronic renal disease
        
        diabetes mellitus
    - local
      - patellar degeneration (most common)
      - previous injury
      - patellar tendinopathy
    - other
      - corticosteroid injection
Pathophysiology
- mechanism of injury
  - 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
- pathobiology
  - rupture is usually the result of end stage or long-standing chronic tendon degeneration
Associated conditions
- orthopedic conditions
  - tibial tubercle avulsion
  - patella fractures
  - TKA extensor mechanism rupture
Prognosis
- prognostic variable
  - most important prognostic factor for complete tears is timing of repair
- survival with treatment
  - excellent outcomes seen with early repair

Anatomy

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

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
  - 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
- provocative tests
  - unable to perform active straight leg raise or maintain passively extended knee

Imaging

Radiographs
- recommended views
  - AP and lateral of the knee
    - knee in flexion (ideally 30 degrees)
- optional views
  - merchant or skyline
- findings
  - patella alta seen in complete rupture
  - various measurements indicating patella alta
    - Insall-Salvati ratio is > 1.2
      - normal between 0.8 and 1.2
    - Blackburne-Peel ratio > 1.0
      - normal between 0.5 and 1.0
    - Caton Deschamps ratio > 1.3
      - normal between 0.6 and 1.3
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
    - knee immobilizer
    - hinged knee brace locked in extension
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
  - outcomes
    - biomechanical studies have shown less gap formation with suture anchor repair compared to transosseous repair
    - clinical studies have shown a significant decrease in rerupture rate with use of suture anchor compared to transosseous repair.
- tendon reconstruction
  - indications
    - severely disrupted or degenerative patella tendon
    - chronic tears > 6-8 weeks out from injury
  - techniques
    - ipsilateral semitendinosus or gracilis autograft
    - central quadriceps tendon-patellar bone autograft
    - contralateral bone-patellar tendon-bone autograft or allograft

Techniques

Immobilization in full extension with a progressive weight-bearing exercise program
- protocol similar to post-operative protocol below

Direct primary repair
- approach
  - longitudinal midline incision
  - expose rupture and adjacent retinacula
  - debride the ends of the rupture
  - for subacute tears (> 2 weeks out from injury)
    - quadplasty or scar tissue release to facilitate tendon approximation
- technique
  - 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 #5 non-absorbable transosseous suture
    - drill 2 trans-patellar bony tunnels and pass the sutures through tunnels and tie over the top of patella
    - can be protected with a cerclage wire or nonabsorbable tape between patella and tibial tuberosity
  - suture anchor tendon repair
    - number of anchors debatable
      - most authors advocate for at least 2 anchors
- postoperative rehabilitation
  - may weight bear early with protected knee brace locked in extension
  - 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
  - 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

Tendon reconstruction
- approach
  - retracted patella may require extensive surgical release
    - quadplasty
    - release of scar tissue
- technique
  - graft sources
    - autograft
      - ipsilateral gracilis, semitendinous, and quadriceps autografts have all been used
    - allograft tendon or ligament
  - technique
    - 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

Complications

Knee stiffness
- incidence
  - most common complication
- risk factors
  - delay in surgical treatment
  - delay in initiating post-operative range of motion
- treatment
  - manipulation under anesthesia (MUA)
    - if flexion is <120° at 6-12 weeks post-op
  - lysis of adhesions
    - if flexion is < 120° after >12 weeks post-op
Re-tear
- incidence
  - ~8% with transosseous direct primary repair
    - 1-2% following suture anchor repair
- treatment
  - primary repair
    - if acute and adequate tendon quality remains
  - reconstruction
    - chronic lesions
    - poor tendon quality
Infection
- incidence
  - ~2% following surgery
Quadriceps atrophy
- incidence
  - 2nd most common complication
    - does not compromise return of strength
- treatment
  - physical therapy