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British Medical Books Health Issues Computerized Tomography

Extensor Mechanism Injuries of the Knee


  • extensor mechanism includes
    • quadriceps muscle & quadriceps tendon
    • medial & lateral retinaculum
    • patellar tendon (ligament)
    • tibial tubercle
    • patellofemoral and patellotibial ligaments
  • superficial location of extensor mechanism make it susceptable to injury
  • extensor mechanism rupture may involve either the quadriceps tendon or patellar ligament and may be either partial or complete
    • complete rupture is rare in young athlete unless assoc. with steroids
    • patellar tendon (ligament) ruptures usually occur in pts < 40 yrs of age
    • quads tendon in pts older than 40 years of age
  • risk factors
    • RA, long-term diabetes mellitus, and long-term steroid use

Diff Dx

  • Osgood-Schlatter disease, Larsen-Johanssen dx.
  • consider anatomic malalignment - chondromalacia
  • MVA (dashboard injury)
  • patellofemoral arthritis in those over 40 yrs
  • RSD
    • disproportionate extensor mechanism pain - following trauma or surgery
    • disproportionate pain, stiffness, skin discoloration, & decreased skin temperature

Rupture of the Quadriceps


  • most common in the 6th & 7th decades
  • probably associated with decreased vasculature
    • more common with cortisone injections, diabetes, chronic renal failure, hyperthyroidism and gout;


  • tear may involve either portion of trilaminar tendon or its entirety
  • usually the tear is initiated centrally and progresses peripherally
  • tendon usually ruptures transversely at the osteotendinous junction
  • its level usually corresponds to amount of flexion at time of injury
  • disruption is associated with intense pain

Clinical Presentation

  • large hemarthrosis
  • freely mobile patella and an impressive loss of extensor function
  • unable to walk
  • look for palpable defect
    • quad tendon usually ruptures transversely just proximal to patella

partial tears

    • an extensor lag usually present
    • MRI may delineate the extent of injury
    • treated non-surgically with immobilization & early range of motion.


  • patella in a lower position than normal - use contralateral patella for comparison


  • show extent of injury

Surgical Treatment

  • rupture repaired within 48 hrs if possible
  • early intervention allows end-to-end repair of the tendon technique
    • make anterior longitudinal incision in midline
    • fibers of rectus femoris tendon sutured to superior pole of patella through drill holes as is done for patellar tendon ruptures
    • roughen the surface of the patella to promote healing
    • take care not to place the drill holes too close to the anterior patellar surface, in order to avoid patellar tilt
    • No 5 Ethibond suture is then passed thru the quadriceps tendon (using the Krachow technique) and then is passed thru the drill holes
    • because rupture nearly always takes place early thru an area of degeneration, consider reinforcement of sutures with fascia strips
    • if the repair is strong, consider not repairing the lateral retinaculum (if it is torn) in order to avoid patellar subluxation

Scuderi technique

  • triangular tongue of tissue distally from the anterior surface of the proximal tendon;
  • the base of the flap is left attached 5 cm above the rupture;
  • the proximal tip of the flap is then turned over the rupture and is sutured in place;
  • turn down triangular distally and suture it in place across rupture;

Codivilla technique:

  • indicated for chronic ruptures where the tendon edges cannot be opposed
  • create a full thickness inverted V flap which ends 1.5 cm above the rupture
  • the tendon edges are repaired with heavy suture;
  • the proximal portion of the inverted V is closed down (coverting it to a verticle line);

Post Operative Care

  • immobilize for 4-6 weeks, then begin ROM, followed by crutch walking for 6-8 weeks

Patellar tendon/ ligament avulsion


  • usually occur in pts. under age of 40
  • most ruptures occur with the knee in a flexed position (around 60°) which are then subject to excessive loading
  • occur at level of inferior patellar pole > level of tibial tubercle
  • tears at inferior patellar pole usually are assoc. with previous patellar tendinitis and local steroid injections


  • pain, swelling
  • palpable defect in patellar ligament
  • high riding patella
  • inability to extend knee (complete tears)

Partial tears

  • ability to extend knee, but full extension may be lacking
  • with partial patellar tendon ruptures may not be able to extend the knee due to pain and knee effusion
  • consider knee aspiration and injection of lidocaine


  • lateral
    • may reveal small avulsion from inferior patellar pole
    • patella alta evident using Insall ratio, or using the Blackburne method
    • inferior patellar border will lie above Blumensaat’s line

Non Operative Treatment

  • only for partial patellar ligament disruption
  • complete tears of the patellar ligament require surgical repair
  • end-to-end suturing may not be attainable for delayed or late repair

Operative Technique

  • end-to-end sutures
    • longitudinal incision from inferior pole of patella to the tibial tubercle;
    • frayed tendon edges sharply debrided
    • using a double armed No 5 Ethibond, a whipped locking stitch performed along each tendon margin
    • two vertically oriented drill holes are made in the patella, which allow both suture arms to be carried thru the patella and tied over the top (from Lindy et al 1995)
    • residual gaps in the tendon repair are repaired with a running 2-0 Vicryl Suture
    • if the repair is strong, consider not repairing the lateral retinaculum (if it is torn) in order to avoid patellar subluxation

Re-enforcement Technique

    • serves as an adjunct to tendon repair and protects the tendon repair - patient is started on early motion
    • 5mm Mersilene tape is passed thru a transverse drill hole made thru the tibial tubercle, is then woven thru the para-patellar retinaculum on both sides
    • tape is tied on both sides with the knee in 90° of flexion (after tourniquet is released)

Use of wire for augmentation

Post Op ROM

  • passive ROM allowed in the immediate postoperative phase;
  • full wt bearing allowed (using knee immobilizer)

Avulsion of the Tibial Tubercle

  • avulsion frx of tibial tuberosity along with a Salter Harris type-III frx of proximal tibial physis
  • need to distinguish tibial tubercle avulsion from Osgood Schlatter disease (which has no physeal involvement);
    • where as Osgood Schlatter disease involves the anteiror surface of the tubercle, the true tubercle frx is an avulsion of the apophysis
  • avulsion fractures tend to occur between ages 12-16 years;


  • develops its own center of ossification by age 17, it blends in with ossification center of tibial epiphysis

Clinical Presentation

  • swelling, pain, & tenderness directly over tuberosity;
  • knee is held in 20-40 deg of flexion because of spasm of hamstrings;
  • pts may or may not be able to extend knee against resistance;
  • may sense a freely movable triangular fragment of bone;
  • compartment sy. may occur in some cases;


  • patella alta (degree depends on displacement of tuberosity)

Assessment of Reduction

  • lateral X-ray of knee in full extension allows evaluation of reduction
  • with residual displacement > 0.5 cm, ORIF is performed;

Classification (Watson Jones) & Treatment

Type I: (most common)

  • type 1A: incomplete separation of fragment from metaphysis;
  • type 1B: complete separation;


  • pts usually can actively extend knee - but not against resistance;


  • adequacy of reduction can be determined by position of patella compared with that in the unaffected limb;
  • when residual displacement is < 5 mm, treat in cyclinder cast with knee extended for 6 weeks
  • ORIF is indicated if > 5 mm of displacement persists;

Type II:

  • tubercle epiphysis lifted anteriorly & proximally, separating tubercle ossification center as well as partially separating the non articular portion of the proximal epiphysis
    • Type 2A: complete tubercle frx without comminution
    • Type 2B: complete tubercle frx with comminution;


  • pts usually cannot extend knee against resistance;


  • displaced grade II and III frx usually require ORIF;
  • need to identify any intra-articular involvement since this always requires anatomic reconstruction;
  • post op:
    • 4-6 weeks of immobilization in cyclinder cast;
    • no unprotected activities for 6 months;

Type III:

  • frx propagates from tuberosity in a proximal and posterior direction so that it involves the articular portion of the proximal tibial epiphysis
    • Type 3A: single displaced fragment;
    • Type 3B: comminuted displaced fragments;


  • displaced grade II and III frx usually require ORIF;
  • articular incongruenty must be restored