TIS
Chapter 13
Patellofemoral Joint: Anatomy, Biomechanics, Rehab
- Anatomy
Femur
- trochlear groove consists of medial and lateral femoral condyles with intervening shallow depression (5-6 mm)
- lateral wall of trochlear groove is more prominent and projects further anteriorly
- structural abnormalities of the trochlear groove predisposing an individual to lateral tracking: flattening or hypoplasia of the trochlear groove (normal groove angle is 130 degrees)
Patella
- articular surface divided by medial ridge into 2 large facets: medial & lateral
- less distinct ridge divides medial facet into 2 facets in most: medial & odd
- indistinct transverse ridges divide the medial & lateral facets into superior, middle and inferior facets
- lateral facet usually larger than medial
- three types of patellas (Wiberg); chondromalacia occurred predominantly in those with small vertical and markedly convex facets
Quadriceps and other soft tissues
- rectus femoris tendon: 8-10 cm in length, triangular in shape with insertion 3-5 cm in width at superior pole patella
- VMO tendon: inserts obliquely at superomedial border of patella, oriented 55-70 degrees in relation to sagittal plane, tendon only a few mm in length; primary stabilizer of patella medially against VL
- vastus lateralis: inserts obliquely at superolateral aspect of patella, oriented 22-45 degrees in relation to sagittal plane, 2.8 cm in length
- lateral expansion of the vastus lateralis with a superficial and deep layer forms the lateral retinaculum; deep layer is the lateral patellofemoral lig: this is a static guide for the patella; this may decrease medial excursion and increase lateral tracking
- Ober: fascial band extending from ITB to lateral and inferior margin of the patella (importance of ITB flexibility)
- medial side also has a PF lig, but it is much weaker than the lateral side
Articulation
- no contact between the femur and patella in full extension; patella lies over an area of thin, smooth synovial tissue on the anterior shaft of the femur, proximal to the trochlear surface (supertrochlear tubercle)
- from extension to flexion, the patella: begins laterally and moves medially as the patella enters the trochlear groove and the tibia derotates; it follows the groove until the knee has flexed to 90 degrees when the patella again moves laterally until it covers the condyle at 135 degrees
- with flexion, patella enters the trochlear groove from the lateral side
- seats in the trochlea at ~20 degrees; at this point, the congruence and compressive forces provide stability
- from 0-20 degrees, stability comes from soft tissues
- Q angle = l0-l2° males and l5-18° for females; several studies have found increased Q angles in those with patellar dislocations
- Biomechanics
Functions of the patella:
- primary function is to increase the force production of the quadriceps; acts like a pulley to increase the mechanical action of the quadriceps
- centralizes the divergent muscles of the quadriceps
- protects the femur
Patellofemoral contact areas (Insall):
0 degrees: patella completely above the femoral articular surface
30 degrees: interior aspect of the patella contacts the uppermost portion of the femoral condyles; contact begins between the LFC and the lateral facet of the patella, but by 30 degrees is evenly distributed on both sides
60 degrees: contact between the superior half of the patellar surface and part of the femoral groove slightly inferior to the contact area at 30 degrees; contact area larger than at 30 deg
90 degrees: contact again between the superior half of the patella and an area of the femoral groove just above the notch; contact area larger than at 60 degrees
120 degrees: contact between the superior aspect of the patella and the areas on the femoral groove immediately surrounding the notch in a kidney shape; quadriceps tendon contact with the troclea also helps to share the compressive load
Dynamic biomechanics: Patellofemoral joint reaction forces:
- directly related to quadriceps force generation
- increases as the angle of flexion increases
- PFJR force reaches 3.3x BW when ascending and descending stairs
- knee bend to 130 degrees increases force to 7.8x BW
- open chain: PFJR force zero at 90 degrees flexion at rest; force increases rapidly to a maximum of 1.4x BW at 36 degrees flexion, and decreases rapidly to .5 BW at full extension
- forces increase faster than contact area increases, so stress/unit area increases rapidly to 90 degrees
- abnormal tracking results in even higher forces/unit area owing to smaller contact area; Hungerford showed that minor lateral shift of the patella can decrease the contact area by 60% and increase stress by 2.5x; surgical procedures attempt to recenter the patella to redistribute the loads; Macquet (Macquet procedure) showed that a 2 cm elevation of the tibial tubercle increased the quadriceps moment and decreased the PF joint reaction force by 50% at 45 degrees flexion
- one study showed a 50% decrease in patellar stress when Q-angle was reduced from 15 to 5 degrees at 30 degrees of flexion
- dynamic stabilizers: ITB, lateral retinaculum, VL, VMO, adductor magnus
- PFJR forces during isokinetic exercise at 60 and 180 degrees was lower (< 1.0 BW) at angles less than 20 degrees and was highest at 70-75 degrees of knee flexion (5.lx BW at 60 degrees/sec and 4.9x BW at 180 deg/sec)
- following ACL reconstruction using central 1/3 patellar tendon, PF contact pressures were no different from control knees
- VMO active throughout entire ROM; maximum at 70 degrees; SAQ trains both the VMO and VL; EMG demonstrates increased activity in the VMO with concurrent hip adduction
- Douchette: found a significant improvement in Merchant's congruence angle following 8 weeks of PT; 84% were also painfree after 11 physical therapy visits; there were no differences in the patellofemoral index, Q angle, hamstring flexibility or sulcus angle; those who improved had significant increases in ITB flexibility
- Patellofemoral evaluation
Factors related to patellar dysfunction:
Static factors:
- femoral anteversion
- external tibial torsion
- patella alta (patellar tendon length >120% patella)
- patella baja (PT <80% patellar length)
* i.e.: differences between the two should not be greater than 20%
Dynamic factors:
- VMO:VL EMG activity is 1:1 in normals
- VMO:VL EMG activity is <1:1 in PF dysfunction
- VMO fires before VL in normals
- VL fires before VMO with PF dysfunction
- VMO is inhibited with 20-30 mls of effusion
- increased Q angle
- tight lateral structures
- tight hamstrings and gastroc
- excessive pronation
- VMO insufficiency (pain &/or effusion)
Subjective:
- diffuse anterior knee pain
- pain, often exacerbated by stairs, sitting
- crepitus
- giving way
- swelling
Objective:
Q angle: standing vs. supine; static vs. dynamic; open vs closed chain
Standing: looking for comparable sign
- LE alignment
- walking
- stairs (look for eccentric control)
- squat
- one-leg squat
- one leg standing: glut strength, pelvic control
Sitting:
- mobility - AROM and pain
- patellar tracking - look for "J" sign
- patellar position
Supine:
- atrophy
- effusion
- flexibility
- plica evaluation
- patellar mobility/apprehension
- orientation of patella
- glide: static & dynamic
- tilt: static & dynamic
- rotation
- AP tilt
Sidelying:
- medial glide
- medial tilt
- Ober's test
Radiographs:
- standing AP
- lateral - 30 degrees flexion
Blumensaat's line: the lower pole of the patella should lie on a line projected anteriorly from the intercondylar notch
Insall and Salvati: expression for normal patellar height; patellar tendon length should equal patellar length
- tangential view
- Huphstori view: patient prone with knee flexed 55 degrees, cassette under flexed knees with x-ray beam directed cephalid and inferiorly at 45 degrees from vertical
sulcus angle: angle formed by the lines drawn from the deepest point of the sulcus to the top of the medial and lateral femoral condyles; normal = 118 degrees; as angle increases, the lateral buttress effect of the LFC is lost and lateral tilt, sublux and disloc can result
- Merchant view: patient supine with knee flexed 45 degrees, beam directed caudally and inferiorly 30 degrees from vertical
sulcus angle: as above, with normal = 138 degrees in this position
congruence angle: a measurement of subluxation, determined by bisecting the sulcus angle to establish a reference line, project a second line from the apex of the sulcus to the lowest point of the patella, apex lateral to the reference line is defined as a positive value and medial to the reference line is negative; Merchant calls normal <16° and Aglietti calls normal <4°
- Laurin view: knee flexed 20 degrees in sitting with beam directed cephalid and superior
lateral PF angle: used to evaluate tilt, determined by drawing a line across the femoral condyles and drawing a second line along the lateral facet; divergent lines considered normal, convergent or parallel lines suggest tendency toward instability
PF index: method of detecting "mini-tilt" ratio between thickness of medial and lateral PF interspace; normal 1.6 or less
- Treatment
General Principles:
- decrease effusion
- utilize adductors and gluteals
- use biofeedback
- emphasize quality and timing
- avoid fatigue - program structure
- distinguish types of pain
Acute Phase:
- Goal is pain control and prevention of quadriceps atrophy
- Rest: controlled activity to assistive device depending upon evaluation
- Ice: 2-3x daily for 5-10 min
- Bracing/taping: open patella sleeve, Palumbo or ace depending upon comfort; McConnell
- NSAIDS: non-steroidal antiinflammatory
- control as many factors as possible: work, play issues, shoes, surfaces, etc.
Sub-acute phase:
- Goal is to normalize LE mechanics
- cannot train improper alignment; must improve alignment and then teach muscular control
- control motion at foot: pronation
- control patellar motion: patellar taping; include glide, tilt and rotation components
- stretch lateral structures
- mobilization
- patient self-stretch
- ITB
- hamstrings
- strengthen/train VMO
- use EMG/biofeedback
- can isolate VMO specifically
- work VMO via hip adduction
- closed chain activities: MUST BE DONE PROPERLY!!
- wall slides - feet at least 18" from wall
- heel slides
- Tigny's
- BAPS
- leg press
- lunges
- sport cord
- slide board
- open chain
- KinCom isotonic mode 90-45 or pain-free ROM
- eccentric work - remember shock absorption role of quadriceps
Return to activity:
- Operative treatment
- failure to respond to APPROPRIATE conservative management; sequence versus simultaneuous treatment
- recurrent dislocation/subluxation
- level of patient compliance is a measure of response to surgical management as well
- will depend upon the type of malalignment and changes seen on x-ray or at surgery
Type I: subluxation: may require only a lateral release to adequately reduce; may need VMO advancement and/or medial transfer of the tibial tubercle, especially with increased Q angle; anteromedial transfer may be needed with Type IC to realign and unload PF joint
Type II: subluxation with tilt: IIA & IIB may respond to lateral release alone; may also need proximal and/or distal realignment; IIC will need as above
Type III: tilt alone: IIIA & IIIB respond well to lateral release alone; IIIC as above