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
18
Q
What is lateral patellar compression syndrome?
A
- Improper traking of the patella in trochlear groove
- caused by tight lateral retinaculum
- leads to excessive lateral tilt without excessive patellar mobility
19
Q
What is the miserable triad?
A
- A term coined for anatomical characteristics that leads to an increase in Q angle adn exacerbation of patellofemoral dysplasia
- include
- femoral anteversion
- genu valgum
- external tibial torsion/promated feet
20
Q
What is the presentation of lateral patellar compression syndrome?
A
- Pain on climbing the stairs
- theatre sign - pain w sitting for long periods of time
O/E
- Pain w compression of patella & moderate lateral facet tenderness
- inability to evert the lateral edge of patella
21
Q
what is seen on xray of lateral patellar compression syndrome?
A
- Patellar tilt in lateral direction
22
Q
What is the tx of lateral patellar compression syndrome?
A
Non operative
-
NSAIDS, activity modification, physio
- mainstay of tx
- vastus medialis strengthening
- closed chain short arc quads exercises
Operative
-
Arthroscopic lateral release
- objective evidence of lateral tiliting
-
Patellar realignment surgery
-
Maquet ( tubercle anteriorization)
- only for distal pole lesions
- only elevate 1cm or risk skin necrosis
-
Elmslie-Trillat ( medialisation)
- instability in lateral direction
-
Fulkerson alignement surgery
- tubercle anterioisation and medialisation
- CI superior medial arthrosis
-
Maquet ( tubercle anteriorization)
23
Q
Describe the technique of arthroscopic lateral release?
A
- Use superior portal to show medial facet doen’t articuate w trochlea at 40o of knee flexion
- ensure adeqyate Haemostasis
- post op the patella should be passively tilted to 80o
- complications
- perisistent / worse night pain
- patellar instability w medial translation
24
Q
What is idiopathic chondromalacia patellae?
A
- Condition characterised by idiopathic articular changes of the patella
- aka anterior knee pain/patellofemoral syndrome
- occur in adolescents/ young adults
- F>M
- pathophysiology
- poorly understood
- maybe roughening or damage to the undersurface cartilage of patella
- limb malalignment
- muscle weakness
- chondral lesions
- patella maltracking
25
Name any associated conditions of idiopthic chondromalacia patellae?
* **Miserable malalignment syndrome**
* femoral anteversion
* External tibial torsion/pronated feet
* genu valgum
26
Describe the pain receptors of the knee?
* Subchondral bone has weak potential to generate pain signals
* **Anterior fat pad & joint capsule have highest potential for pain signals**
27
Describe the classification of idiopthic chondromalacia patellae?
* **Outerbridge**
* Type 1 = Softening
* Type 2 =Fissures
* Type 3= Crabmeat changes
* Type 4= exposed subchondral bone
28
What is the presentation of idiopthic chondromalacia patellae?
* Diffuse pain in peripatellar/retropatellar area
* worse on climbing/descending the stairs
* worse w prolonged sitting w knees bent
* squatting/kneeling
O/E
* Quads muscle atrophy
* signs of patella maltracking
* increased femoral anteversion or tibial ext rotation
* lateral subluxation of patella or loss medial patellar mobility
* positive patella apprehension tx
* pain w compression of patella
29
What imaging is best for idiopthic chondromalacia patellae?
* 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
30
What is the tx for idiopthic chondromalacia patellae?
Non operatively
* **Rest , rehab and nsaids**
* done for minimum of 1 year
* rehab on VMO strengthening
* core strengthening
* closed chain short arc quads exercises
Operative
* **Arthroscopic Debridement**
* Outbrigde 2-3 chondromalacia
* mechanical debridement/radiofrequency debridement
* **Lateral retinacular release**
* Tight lateral retinacular capsule
* open vs arthroscopic
* **Patellar realignment surgery**
* **MPFL reconstruction**
* **Maquet (** anterior tubercle elevation)
* **Fulkerson** ( anterior -medialisation)
* **Elmsie- Trillat osteotomy**
31
Describe the epidemiology of quadriceps tendon rupture?
* **Rupture of quads tendon -\> disruption in the extensor mechanism**
* more common than patellar tendon rupture
* pts \>40 yrs
**M\>F** 8:1
* Occurs in nondominnat limb \>2 as often
* location
* **usually at insertion of patella**
* Risk factors
* **diabetes**
* **renal failure**
* **rheumatoid arthritis**
* Hyperparathyroidism
* connective tissue disorders
* steriod use
32
What is the classification of quads tendon ruptures?
* Partial
* Complete
33
What is the presentation of quadriceps tendon rupture?
* **Tenderness at site**
* **papable defect** within 2cm of superior pole
* unable to **SLR**= complete
* unable to SLR against resistance
34
What is seen on xrays with quadriceps tendon rupture?
* Patella baja
35
Describe the tx of quadriceps tendon rupture?
Nonoperatve
* **Knee brace**
* partial tear w intact quads mechanism
Operative
* **Primary repair w reattachment to patella**
* complete rupture w loss of extensor mechanism
36
Describe teh surgical repair of quads tendon?
* Midline incision
* longitudinal 3 drill holes in patella
* non absorable 5.0 ethibond sutures in running locking fashion then thru drill hole in patella
* retinaculum repair with heavy absorbable sutures
* ideally knee should be able to flex to 90o post repair
* post op
* inital immobilistion in brace
* eventual flexibility and strengthening exercises
37
Describe the tehnique for chronic rupture repair?
* 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
38
What are the complications of quads tendon rupture?
* **Strength deficit**
* 33-50%
* **Stiffness**
* **Functional impairment**
* 50% pts are unable to return to prior level of activity/sports
39
Describe the epidemiology of patellar tendon rupture?
* 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
40
What is the pathophysiology of patellar tendon rupture?
* Mechanism
* tensile overload of extensor mechanism
* most ruptures occue w knee in flexed position
* greatest forces on tendon when knee \>60o
* 3 patterns of injury
* **avulsion w or without bone from inferior pole- most common**
* midsubstance
* distal avulsion from tibial tubercle
* \*\*\*rupture is usually the result of end stage or long standing chronic tendon degeneration\*\*\*
41
What is the presentation of patellar tendon rupture?
* Sudden quads contraction w knee in lfexed position
symptoms
* infrapatella pain
* popping sensation
* difficulty WB
O/E
* Elevation of patella height
* large haemarthrosis/ecchymosis
* **unable to active SLR or maintain extended knee**
42
What is seen on imaging of patellar tendon rupture?
Xray
* **patella alta**
* install- salvati ratio \>1.2
USS
* effective at detecting /localising rupture
MRI
* most senstive to detect
43
What is the tx of patellar tendon rupture?
Nonoperative
* **immobilisation in full extension w progressive wb exercise programme**
* partial tears w intact extensor mechanism
Operative
* **Primary repair**
* complete patella tendon ruptures
* end to end repair
* tranosseous tendon repair- can be protected by cerclage wre between patella & tibial tuberosity
* suture anchor repair
* **Tendon reconstruction**
* severely disrupted or degenerative patella tendon
* semitendinous or gracilis tendon harvesting
* free tendon ends are passed thru transosseous hole of patella, thru thru transosseous hole of tibial tubercle to make a circular graft
* post op
* **passive extension & active close chain flexion ( heel slides)**
* **prone open chain knee flexion**
