EXTENSOR MECHANISM PROBLEMS IN TOTAL KNEE ARTHROPLASTY

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EXTENSOR MECHANISM PROBLEMS IN TOTAL KNEE
ARTHROPLASTY

• Scott M. Heithoff, DO
• Garden City Hospital

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INTRODUCTION

• Complications related to the extensor mechanism
  are the most frequent reason for reoperation in
  an aseptic TKA.
• The prevalence of complications ranges from 1.5
  to 12 percent.
• Patient selection, operative technique, and
  implant design all influence the frequency of the
  complications.

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POTENTIAL PROBLEMS WITH THE EXTENSOR MECHANISM

1. Patellofemoral Instability
2. Patellar Fractures
3. Patellar Component Loosening
4. Patellar Component Failure
5. Patellar Clunk Syndrome
6. Tendon Rupture

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PATELLOFEMORAL INSTABILITY

• The incidence of patellar subluxation following
  TKA has been reported to be as high as 29.
• Failure to obtain proper tracking can result in
• Patellofemoral pain and crepitus
• Component wear
• Component failure and loosening
• Fracture

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PATELLOFEMORAL INSTABILITY

• Etiologies
• Excessive lateral retinaculum tightness
• Weakness of VMO
• Excessive valgus position of implants
• Rotational malalignment of the femoral and/or
  tibial components
• Patellar component problems
• Disruption of capsular repair

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PATELLOFEMORAL INSTABILITY LATERAL RETINACULUM

• Most common cause of instability is excessive
  tightness of the lateral retinaculum and
  associated weakness of the VMO.
• Intraoperative assessment of patellar tracking is
  critical
• The tourniquet should be released to eliminate
  the tourniquets binding effect on the extensor
  mechanism.
• If the patella subluxes laterally during flexion
  with the no-thumb technique, a lateral release
  should be performed.

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PATELLOFEMORAL INSTABILITY VALGUS POSTION OF
IMPLANTS

• Excessive postoperative limb alignment of greater
  than 10 degreed valgus has consistently
  correlated with patellofemoral problems.
• This can be caused by either excessive valgus
  resection of the distal femur or proximal tibia.
• The high valgus angle increases the Q-angle,
  thereby increasing the lateral force vector on
  the patella.

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PATELLOFEMORAL INSTABILITY ROTATIONAL
MALALIGNMENT

• Internal rotation or medial shift of the femoral
  component places the trochlear groove at a
  greater distance from the patella, leaving the
  patella laterally positioned.
• A small amount of external rotation has been
  shown to improve tracking.

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PATELLOFEMORAL INSTABILITY ROTATIONAL
MALALIGNMENT

• Internal rotation of the tibia results in
  lateralization of the tibial tubercle and
  increase in the Q-angle.

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PATELLOFEMORAL INSTABILITY PATELLAR COMPONENT

• Avoidance of asymmetric patellar resection.
• Re-creating the original thickness with the
  patella-prosthetic composite.
• Slight medialization of the patellar component

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PATELLOFEMORAL INSTABILITY MANAGEMENT

• Conservative treatment (PT with strengthening of
  VMO) may be helpful, but only if components are
  in good position
• Recognize problems intraoperativly and correct
  them before the patient is off the table
• Perform lateral release if needed
• Avoid internal rotation of components
• Avoid excessive valgus cuts

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PATELLOFEMORAL INSTABILITY MANAGEMENT

• Revise components if malaligned
• Proximal vs. distal reconstructive procedures
• Generally, distal procedures should be avoided
  (tibial tubercle osteotomy) because of the the
  high failure and complication rate associated
  with it
• Proximal procedures include
• Lateral release
• VMO advancement

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PATELLOFEMORAL INSTABILITY MANAGEMENT

• VMO advancement

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PATELLAR FRACTURES

• The prevalence of patellar fractures after TKA
  has ranged from 0.1 to 8.5.
• There are multiple factors implicated
• High demand (weight, activity)
• Weak bone
• Surgeon (excessive/inadequate resection, AVN from
  lateral release, component malaignment)
• Trauma

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PATELLAR FRACTURES

• Risk Factors
• Excessive patellar resection (lt15mm patellar
  thickness)
• Minimal patellar resection Increases
  patellofemoral joint reaction forces
• Femoral components with excessive AP diameter
• Asymmetric patellar resection
• Large central peg

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PATELLAR FRACTURES GOLDBERG CLASSIFICATION

• Type I Fractures not involving the implant /
  cement composite or quadriceps mechanism
• Type II Fractures disrupting the quadriceps
  mechanism or the fixation of the implant

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PATELLAR FRACTURES GOLDBERG CLASSIFICATION

• Type IIIA Inferior pole fractures with patellar
  ligament rupture
• Type IIIB Non-displaced inferior pole fractures
  with intact patellar ligament
• Type IV - Lateral fracture-dislocation of the
  patella

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PATELLAR FRACTURES TREATMENT

• Depends on four things
• Integrity of the extensor mechanism
• Stability of the patellar component
• Degree of fracture displacement
• Extent of bony comminution

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PATELLAR FRACTURES TREATMENT

• Nonoperative Tx
• Intact extensor mechanism
• Secure implant
• lt2 cm displacement
• Minimal comminution
• Knee Immobilizer or cylinder cast for 4-6 weeks
  with protected weight bearing, followed by
  progressive weight bearing.

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PATELLAR FRACTURES TREATMENT

• Surgical options
• Secure Implant
• A partial patellectomy with repair of extensor
  mechanism provides a better result than attempts
  at ORIF
• Loose Implant
• Removal of loose component, cement, and avascular
  pieces
• Deficient bone stock precludes prosthetic
  reimplantation
• Patelloplasty

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PATELLAR COMPONENT LOOSENING

• Uncommon Incidence lt2 in most studies
• Causes
• Cementing into deficient bone
• Component malposition
• Patellar subluxation
• AVN patella
• Osteoporosis

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PATELLAR COMPONENT LOOSENING TREATMENT

1. Component revision if bone stock allows
2. Component removal and patellar arthroplasty
   (smoothing of the remaining patella without
   resurfacing)
3. Patellectomy

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PATELLAR COMPONENT FAILURE

• Most complications have been associated with
  metal-backed designs.
• Proposed advantages to metal-backed patella's
• Decreasing patellar surface strains
• Lessening delamination by supporting the poly
• Allows for cementless patellar component fixation
• Failure of metal-backed designs
• Poly-metal plate dissociation
• Peg-plate dissociation
• Metal plate fracture

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PATELLAR COMPONENTFAILURE

• Poly-metal plate dissociation

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PATELLAR CLUNK SYNDROME

• Condition resulting from the development of a
  fibrous nodule at the junction of the posterior
  aspect of the quadriceps tendon and proximal pole
  of the patella.
• With knee flexion, the nodule enters the
  intercondylar notch of the femoral prosthesis
• As the knee is extended, the nodule becomes
  entrapped within the notch
• At 30 to 45 deg, enough tension is placed on the
  fibrous nodule to cause it to clunk out of the
  notch

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PATELLAR CLUNK SYNDROME
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PATELLAR CLUNK SYNDROME

• Etiologies
• Femoral components with a sharp anterior edge at
  the superior aspect of the intercondylar notch
• Malpositioning of the patellar component beyond
  the proximal border of the patella
• Postoperative scarring
• Alterations of joint line, patellar height, or
  patellar thickness

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PATELLAR CLUNK SYNDROME

• Treatment
• Revision of components if positioned incorrectly
• Debridement of fibrous nodule
• Open
• Arthroscopically

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TENDON RUPTURE QUADRICEPS TENDON

• Rupture of the quadriceps or patellar tendon is
  an infrequent complication of TKA 0.17 to
  0.55
• Quadriceps tendon rupture is associated with
  lateral release due to devascularization of the
  tendon or extension of the release to proximally
• Treat with resection of the rupture zone back to
  healthy tissue, mobilization of the quadriceps,
  and preparation of the proximal patellar pole for
  tendon reattachment
• A No. 5 nonabsorbable suture weaved through the
  quads and anchored to the patella via drill holes
  provides secure fixation

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TENDON RUPTURE PATELLAR TENDON

• Etiologies
• Inadvertent intraoperative detachment from the
  tibial tubercle during exposure
• Stiff knee with limited motion use rectus snip
• Patients with previous HTO
• Residents
• Late rupture due to impingement of the prosthesis
  on the tendon
• Traumatic rupture

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TENDON RUPTURE PATELLAR TENDON

• Intraoperative rupture
• The tendon can be repaired or reattached using
  No. 5 nonabsorbable suture, synthetic tape, screw
  or staple fixation.
• Usually as long as the problem is recognized
  early and delt with accordingly, this may be all
  that is necessary.
• If the repair in tenuous, autograft
  semitendinosis may be used.

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TENDON RUPTURE PATELLAR TENDON
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TENDON RUPTURE PATELLAR TENDON

• Late ruptures
• Long standing ruptures can be complicated by
  contractures of the extensor mechanism
• Allograft tendon is usually used in these
  circumstances
• If all else fails, a knee arthrodesis can be used
  as a salvage procedure.

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CONCLUSIONS

1. Patellofemoral complications are a frequent cause
   of revision surgery
2. To avoid most problems, put the components is
   correctly
3. Internal rotation is death
4. Dont be afraid to use a lateral release
5. Dont cut tendons!