Patellofemoral complications
After total knee artroplasty
Dr. B. Haghpanah - M.D.
Azad University
Patello femoral complications:
1. Patello femoral instability
2. Patellar fracture
3. Patellar component failure
4. Patellar component loosening
5. Patellar clunk syndrome
6. Extensor mechanism rupture
Patello femoral Instability:
A. Extensor mechanism imbalance:
• In which the lat. Retinaculum is too tight or medial soft
tissues are too loose.
• If lat. Retinaculum is too tight. Lat release is indicated,
if possible sparing the sup. Lat. geniculate A.
• Medial retinacular laxity may occur with postoperative
rupture of the medial capsular repair.
• Some authors have advised closing the retinacular
capsular layer with the knee in 90° of the flexion.
• The knee should be placed through a full range of
motion after medial capsular closure.
B. Malpositioned patellar, femoral or tibial components:
• Also may lead to patellofemoral instability.
I. Excessive lateral patellar facet resection. May lead to
tilting of the patellar component. (the level of lat. Facet
resection must be much shallower than the medical facet)
• Lateral placement of the patellar component on the cut
surface of the patella. Can lead to lat. Subluxation of the
patella in extension.
II. Malposition of the tibial component in an internally rotated
position increase the Q angle by moving the tibial tubercle
laterally and the increased Q angle leads to lateral
subluxation.
• The tibial component should be centered on the medial
border of the tibial tubercle. With any deviation into
external rotation.
III.Internal rotation and medial translation of the femoral
component make the trochlea more medial relative to
the extensor mechanism leading to lat subluxation.
• The posterior femoral condyles, epicondylar axis and
anterposterior axis all are useful for intra operative
evaluation of femoral component rotational alignment in
the primary TKA.
• In revision arthroplasty, the position of the previous
component and the epicondylar axis are the only
landmarks available for this assessment.
• Surgical treatment of patellar subluxation is based on the
cause.
• The components should be inspected for malposition
and if necessary they should revised.
• If the components are positioned appropriately surgical
efforts to improve patellar tracking should proceed in
stepwise fashion.
1. Lateral retinacular release should be performed
first.
2. If patellar subluxation persists a proximal patellar
realignment procedure should be done
(advancement of vastus medialis)
3. Distal realignment procedures such as the tibial
tubercle osteotomy should be undertaken with
extreme caution because serious functional loss
would result if nonunion occurred.
Patellar fracture: (0.5%)
• It is correlated with multiple factors, excessive patellar
resection, vascular compromise secondary to lateral
release, patellar maltracking, excessive joint line
elevation, knee flexion of more than 115°, trauma,
thermal necrosis of PMMA and revision.
• There is a statistically significant association between
lateral release and patellar fracture.
• Nonunion and hardware failure after I.F. of patellar
fracture in TKA are frequent.
• The recommended treatment of displaced and non
displaced fractures with no extensor lag and no
loosening of patellar component is non operative.
• If operative treatment of patellar fracture is necessary
component malalignment should be corrected.
 Periprosthetic patellar fractures have been
classified according to the integrity of extensor
mechanism and stability of the implant.
Type I:
– Fractures with an intact extensor mechanism
and stable implant.
– Should be treated non operatively with a knee
immobilizer or cylinder cast for 6 weeks.
Type II:
– Displaced fractures with extensor mechanism
discontinuity.
– Should be treated operatively with tension Band
wiring and retinacular repair.
Type III:
– Fractures with loose patellar component.
• Should be treated by excision of implant, it
should not be replaced because may impair
fracture healing.
• Stable patellar component that impair fracture
fixation also should be removed.
• Proximal or distal pole fractures should be treated
with partial patellectomy and suture repair.
• When extreme communication or poor bone stock is
seen patellectomy and extensor mechanism repair
is indicated.
Patellar component failure
• Metal – backed patellar components failed by various
mechanism:
1) Fatigue fracture of metal base plate
2) Delamination of the polyethylene
3) Failure of the ingrowth interface
4) Wear in areas of thin polyethylene
• Clinically, the onset of a knee effusion, patello femoral
crepitus or audible squeaking and scraping suggest
component failure.
• Early revision of the failed components is recommended to
prevent extensive metallosis of the knee.
• Revision consists of exchange of tibial polyethylen insert,
synovectomy and revision or removal of patellar component.
Patellar component loosening:
• Predisposing factors are:
1. Deficient bone stock
2. Component malposition and subluxation
3. Patellar fracture
4. Osteonecrosis of the patella
5. Loosening of other knee components.
• More symptomatic patients require revision,
component removal or patellectomy depending on
the status of the remaining patellar bone.
Patellar clunk syndrome:
• First was described by Hozack in association
with P.S. knee artroplasties.
• A fibrous nodule forms on the posterior surface
of the quadriceps tendon, just above the
superior pole of the patella.
• This nodule can become entrapped in the
intercondylar notch of the femoral prosthsis and
cause the knee to POP or clunk at
approximately 30 to 45 degree of knee flexion
when the knee is actively extended.
• Two causes for this condition have been proposed:
1) Proximal placement of patellar button.
The prominent button could impinge on the
quadriceps tendon with resultant fibrous tissue
proliferation.
2) Femoral component design is another possible
cause.
Posterior stabilized femoral components with
high, sharp femoral sulcus could impinge on the
quadriceps tendon.
• The recommended treatment is arthroscopic
debridement of the nodule.
• Arthrotomy and nodule excision is indicated when.
1. Recurrence after arthroscopic treatment occur.
2. Loose or malpositioned patellar components
that may require revision.
• Insall recommended a limited synovectomy of the
posterior surface of the quadriceps tendon when
performing a P.S. knee Arthroplasty.
Rupture of the quadriceps or the
patellar tendon. (0.1% to 0.55%)
1. Quadriceps rupture is related to lateral release
because of vascular compromise and extension of
release anteriorly that weaken the tendon.
• For partial tear non operative treatment is
recommended.
• Surgical repair is advocated for complete tears,
although the results, are suboptimal.
2. Patellar tendon rupture:
• Is associated with previous knee surgery.
• Knee manipulation and distal realignment
procedures of extensor mechanism.
• Treatments of patellar tendon rupture after TKA
including: Direct repair, augmentation with hamstring
tendons or synthetic ligament substitutes.
Gastrocnemius flap, and use of the extensor mechanism
allograft. It is better to tension the allograft with knee in
full extension.
• Non of these procedures has been routinely successful.
• If patellar bone stock allows distal primary repair seems
warranted with the addition of a tension band wire from
the proximal patella to the tibial tubercle or hamstring
augmentation or both.
• When patella is absent or insufficient for distal repair
extensor mechanism allograft reconstruction or
gastrocnemius muscle flap should be considered.