Knee extensor mechanism Flashcards
Patellofemoral joint patellar instability lateral patellar compression syndrome Idiopathic chondromalacia patellae quads tendon rupture patella tendon rupture
1
Q
Describe the dynamic stability of the patella?
A
- Vastus medialis- medial restraint to lateral translation
- vastus lateralis- lateral restraint to medial translation
2
Q
Describe the static stability to patella?
A
-
Medial patellofemoral ligament (MPFL)
- femoral insertion between medial epicondyle and adductor tubercle
- primary restraint in first 20o of knee flexion
- patellotibial ligament
- retinaculum
-
Lateral retinaculum
- 10% of total restraint
-
medial patellomeniscal ligament
- 13% of total restraint
3
Q
What is the blood supply to the patella?
A
- Superior, medial and lateral geniculate arteries
- inferior, medial and lateral geniculate arteries
- anterior geniculate artery
- descending geniculate artery
4
Q
What is the function of the patella?
A
- Transmits tensile forces generated by quads to patellar tendon
- increases lever arm of extensor mechanism
- **patellectomy decreases extension force by 30%
5
Q
What is the Qangle?
A
Quads vs patella tendon
- the angular difference between the quads tendon and patella tendon insertion => Q angle
creates a lateral force across the patellofemoral joint - A line drawn from the anterior superior iliac spine to middle of patella to tibial tuberosity
- Normal is males 13 degrees, females 18 degrees
6
Q
What measurements can be made on an xray for patella?
A
- patellar height- install-salvati ratio
- lateral patellofemoral angle- normal angle that opens up laterally
- congruence angle normal -6 degrees
7
Q
What is CT and MRI useful for in patella disease?
A
- CT
- better visualisation of patellofemoral alignment/fx
- trochlear geometry
- MRI
- best modality to assess articular cartilage ( T2)
8
Q
Describe patellar instability?
A
- classified into
-
Acute traumatic
- M=F
- May occur from direct blow
-
Chronic patholaxity
- >F
- Recurrent subluxation episodes
- assoc w maligament
- Most commonly occurs in 2-3 rd decade
9
Q
What are the risk factors for patellar instability?
A
- Ligament laxity= ehler’s danlos syndrome
- Dysplastic vastus medialis oblique
- lateral displacement of patella
-
patella alta
- patella doesn’t articulate with sulcus, losing its constraint effects
- Trochlear dysplasia
- excess lateral patellar tilt ( measured in extension)
- Increased Q angle
- Previous patellar instability event
-
‘miserable malalignment syndrome’
- 3 things that -> increase q angle
- femoral anteversion
- genu valgum
- external tibial torsion/pronated feet
10
Q
What is the pathophysiology of patellar instability?
A
- Usually non contact twisting injury with knee extended & foot externally rotated
- pts usually reflexively contract quads therby reducing patella
- osteochondral fx often occur as patella relocates
- Direc blow- less common
11
Q
What is the usual site of avulsion of the MPFL?
A
- At origin
- Between femoral medial epicondyle and adductor tubercle
12
Q
What is the presentation of patellar instability?
A
- complaints of instablity
- anterior knee pain
- 0/E
- acute dislocation= haemarthrosis
- medial sided tenderness - over MPFL
-
increase in patellar translation - in quadrant of 3- midline 0
- normal is <2 quadrants of translation
- increased Q angle
-
patellar apprehension
- passive lateral translation-> guarding & sense of apprehension
-
J sign
- excessive lateral translation in extension which pops into groove as patella engages the trochlea early in flexion
- assoc with patella alta
13
Q
What is seen on xrays of patellar instability?
A
- Medial patellar facet fx - most common
- Lateral femoral condyle fx
- lateral xray
- patellar height
- blumenstat’s line extended to inferior pole of patella in 30 degrees if flexion
- Install-salvatti index normal (0.8-1.2)
- Sunrise/merchant’s view
- best for patella tilt
- lateral patellofemoral angle
- congruency angle
14
Q
What can be measure on CT for patellar instability?
A
- The tibial tubercle- trochlear groove distance
- if >20 mm need tibial tubercle medialisation osteotomy
- (A) first drawing a line from the trough of the trochlea perpendicular to the line connecting the posterior condyles. These lines are superimposed onto an image through the tibial tubercle (B), and the TT-TG distance is measured as that between the above-described line and the tibial tubercle (distance AB).
*
15
Q
What is the tx of adult patellar instability?
A
- Adult instability
- NSAIDS, activity modification, physio
- mainstay
- short term immobilisation then 6 wks of controlled motion
- emphasis on
- closed chain short arc quads exercises
- quads strengthening
- core & hip strengthening to imporve limb position & balance
- consider aspiration for tense effusion
Operative
- Arthrosopic debridement vs repair of osteochondral fragment
-
MPFL repair
- acute 1st time w bony fragment
- direct repair done in first few days
-
MPFL reconstruction w autograft/allograft
- for recurrent instability
- gracilis or semitendinous used
- femoral origin can be found on xray- schottle point
-
Fulkerson- type osteotomy ( ant & medial tibial tubercle transfer)
- anteromedial displacement of osteotomy and fixation. if tibail tubercle trochlear groove distance is >20mm on CT.correct TT-TG to 10-15mm
-
Tibial tubercle distalization
- for patella alta
-
Lateral release
- if excessive lateral tilt ot tightness after medialisation
- Trochleoplasty
16
Q
What is the tx of paeds patellar instability?
A
- same principles as adult but
- must preserve the physis
- DON’T do a tibial tubercle osteotomy ( will harm the growth plate of prox tibia)
17
Q
What are the complications of patellar instability?
A
-
Recurrent dislocation
- redislocation rates w non op tx maybe high at 2-5yrs
-
medial patellar dislocation and medial patellofemoral arthritis
- almost exclusively iatrogenic as result of prior patellar stabilisation surgery
27
Q
Describe the classification of idiopthic chondromalacia patellae?
A
- Outerbridge
- Type 1 = Softening
- Type 2 =Fissures
- Type 3= Crabmeat changes
- Type 4= exposed subchondral bone
29
Q
What imaging is best for idiopthic chondromalacia patellae?
A
- Xray
- chondrosis
- shallow sulcus, patella alta/baja, lateral patella tilt
- CT
- trochlear geometry
- TT-TG distance
- torsion of limb
- MRI
- best modality to assess articular cartilage
37
Q
Describe the tehnique for chronic rupture repair?
A
- Midline approach
- often the tendon retracts 5cm if >2 wks
- repair with similar technique to acute but a tendon lengthening proceedure may be necessary
- Codivilla V to Y lengthning
- auto or allograft tissue may be needed to secure quads tendon to patella
39
Q
Describe the epidemiology of patellar tendon rupture?
A
- Incidence
- common 3-4th decade
- M>F
- location
- quads>patella
- Risk factors
-
weakening collagen
- SLE
- Rheumatoid arthritis
- chronic renal disease
- diabetes mellitius
- Local
- patellar degeneration- most common
- previous injury
- patellar tendinopathy
-
weakening collagen
42
Q
What is seen on imaging of patellar tendon rupture?
A
Xray
- patella alta
- install- salvati ratio >1.2
USS
- effective at detecting /localising rupture
MRI
- most senstive to detect
