Evaluation and Treatment of the Medial Patellofemoral Ligament (MPFL)

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Evaluation and Treatment of the Medial Patellofemoral Ligament (MPFL)

Basic Facts:
  • 2-3% of all knee injuries
  • 15-44% recurrence; 49% in those that have previously dislocated twice.
  • ~ 16% re-dislocation in those treated non-op; ~ 33% have residual Sx; remaining 50% will be asymptomatic.
Anatomy:



  • Origin: superior medial aspect of the patella
  • Insertion: space b/n adductor tubercle and medial epicondyle
    • Some fibers blend with VMO
  • Function:
    • As knee flexes, VMO and MPFL pull patella medially to help it remain in trochlea
    • Provides stability against lateral translation
Biomechanics:
  • Provides 50-60% restraint to lateral patellar translation at 0-30 degrees flexion
  • If sectioned, patella displaces laterally even w/ all other medial stabilizers intact
  • Loses tension as the knee is flexed, tightest b/n 25-30 degrees of knee flexion and creates a medial shift; this shift is not appreciated in knees w/ resected MPFL.
  • Patella enters the trochlea around 15-20 degrees of knee flexion
    • With the MPFL resected, there may not be a medial shift at 25-30 degrees, however, there is evidence to suggest that strain on the MPFL increases as flexion ROM increases from 0 degrees to 120 degrees (potential post-op consideration).
  • Provides the most restraint to lateral patellar translation in full extension
    • If the MPFL is lesioned, the forced needed to dislocate the knee in full extension is decreased by 50%
  • Ruptures at mean elongation of 26 +/- 7 mm elongation; average MPFL is 53 mm, so ruptures at about 49% strain in cadaveric specimens
Tear Classification:
  • Type 1:
    • MPFL avulsion from its femoral attachment
  • Type 2:
    • MPFL Midsubstance tear (normally close to femoral attachment).
  • In all knees w/ recurrent dislocation the MPFL was abnormal.
Abnormality Classification: (Essentially the same classification as ligament tear classification).
  • Type 1: No injury by gross inspection, but MPFL femoral attachment is loose
  • Type 2: Scar tissue in the body or the femoral attachment of the MPFL, but both are loose
  • Type 3: Absent type; remnant that lacked continuity or could not be identified
Examination:
  • General
    • Likely TTP near adductor tubercle, medial retinaculum, and the MPFL itself in-between
    • First dislocation will be very traumatic and highly irritable which will significantly limit the acute exam.
    • Assess swelling, ROM, and patellar mobility compared to the contralateral limb.
    • Acutely, attempt to reduce the patella by getting the knee into extension. Do it gently to minimize cartilage damage upon reduction.
Standing Exam:
  • Assess for Miserable Malalignment Syndrome (MMS)
    • Femoral internal rotation
      • Craig’s test: assesses femoral anteversion in prone
        • Prone w/ knee in 90 flexion → palpate greater trochanter → internally and externally rotate and feel when greater trochanter is most prominent → measure amount of IR which is the degree of anteversion (normal is 8-15 degrees)
    • Bayonet deformity of tibia: Likely best seen w/ x-ray
    • External tibial torsion
    • Thigh foot axis test: Assesses tibial rotation in prone
      • Prone w/ knee in 90 flexion → rotate foot and tibia until they feel like they are in the position of least resistance → Measure the angle of the foot with the stationary arm in line with the midline of the thigh (normal is ~ 10 degrees, but varies a good amount)
    • Pronated feet:
      • Can use FPI, but visual assessment should be good enough.
  • MMS Notes:
    • Normal tibial external rotation of about 15 degrees occurs in early childhood
    • Femoral anteversion decreases by about 25 degrees in early childhood
    • A child will normally present with excess anteversion (pigeon-toes) at age 2-4 and will peak around age 5-6. (~10% of children).
    • Normal hip IR is 30-60 degrees, if hip IR > 70 degrees is present, think excessive IR due to likely anteversion. (Normal hip ER is 30-60, so if < 20 degrees, can also suspect anteversion, but make sure excessive IR is also present or restricted ER could be from something else)
    • Patients may present with knee flexed 25-30 degrees due to swelling, and since capsular volume is greatest at 25-30 degrees of flexion this allows them the most comfort. (MPFL is extracapsular however, so if there is significant true capsular swelling there may be some other things torn???)

Seated Exam:
  • Grasshopper eyes: Patella resting high and lateral - Indicates large degree of patella alta
  • Tibial Tubercle Sulcus Angle
    • Location of tibial tubercle in relation to the center of the patella
    • Angle between a vertical line through midline of patella and line drawn from midline of patella to tibial tubercle
      • Normal angles have been reported b/n 0-10 degrees: look for the excessive ones.
  • Passive and active patellar tracking
    • Passive: have patient lean back a bit so the hamstring does not limit their ability to reach full knee extension
      • Palpate patella as you passively move knee into and out of full extension.
      • The patella should start slightly lateral → move medial during extension → move back laterally toward terminal extension.
      • Excessive lateral glide indicates superficial retinacular tightness, while excessive lateral tilt indicates deep retinacular tightness
    • Active: Patellar movement should be the same, but if the patella fails to move medially during extension, or abrupt lateral displacement between 20-30 degrees occurs, it can be assumed that the VMO is not doing its job. If the amount of lateral displacement is significantly less actively, then it can be assumed that the VMO is doing its job and that much of the lateral displacement is due to passive structures on the lateral side.
      • *** My thoughts: Seems very difficult to assess accurately with your hands, I would make it binary, it is either significantly different or it is not. If you are splitting hairs, I wouldn't hang your hat on this assessment. ***
Supine Exam:
  • Passive Patellar Mobility
    • Assess in 20-30 degrees to engage the trochlea
    • Patellar mobility is measured by quadrants. ¼ width of patella = 1 quadrant
      • 1-3 quadrants of medial or lateral mobility is considered normal
      • < 1 quadrant either direction = hypomobile
      • > 3 quadrants = hypermobile
        • *** My Thoughts: I cannot see how this would be a consistent and accurate way to measure, Might be easier / more consistent to feel for excessive mobility or excessive stiffness??***
  • Swelling/Effusion
    • Measure joint circumference at joint line and 10 cm proximal
    • Joint line should demonstrate swelling
    • 10 cm proximal may be less than contralateral limb indicating atrophy of VMO
Risk Factors for Recurrent Instability:
  • Younger age (< 25) - My thought is that is just because of the higher activity level and that fact that they are more likely to be doing high risk activities/sports.
  • Immature Physes - open and closing physes both considered immature, closed considered mature
    • Proximal tibial physis: closes age 13-15 in females; 15-19 in males
    • Distal femoral physis: closes age 14-16 in females; 16-18 in males
  • Sports related injuries (again, more likely to return to that high risk activity)
  • Patella alta: If the patella rests too high, there is less contact area with the trochlea and thus less stability.
    • Caton deschamps index: Ratio of Patellar tendon length : Patellar articular surface
    • > 1.3 = patella alta
    • Insall Salvati ratio: Patellar tendon length : Length of patella
    • Measured w/ knee in 30 deg flexion w/ lateral radiograph
    • > 1.2 = patella alta
  • Trochlear dysplasia - Assessed with the dejour classification system






Indications for surgery:
  • If they fail conservative management
  • See section one for risk factors for recurrent dislocation which should also be considered in decision to perform surgery.
    • For someone who is at a greater risk of re-dislocation, it may be wise to create a more anatomically stable patella than someone at lower risk and the decision to perform surgery may occur earlier.
Surgical Technique:
  • Under anaesthesia the amount of translation, specifically lateral translation is assessed in extension and flexion
  • Arthroscopy is performed to assess for any patello-femoral chondral damage
    • Small tears/loose cartilage may be debrided
    • Large tears may require a chondral repair type procedure
      • ACI, OAT, OCA (osteochondral allograft transplantation)
  • Graft Choices
    • Hamstring (semitendinosis or gracilis), adductor magnus, quad tendon, medial strip of quad tendon
    • Quad tendons can be used while leaving their patellar attachment intact
    • Allografts have also been used with no increased risk of failure due to re-rupture or donor site morbidity.
  • Anchoring:
    • 1) Tunnels placed through the patella and anchoring on the far side with an interface screw.
    • 2) Graft is looped through the patella with no actual fixation to the patella itself.
  • Hamstring Autograft
    • Hamstring tendon is isolated and procured and the graft is passed between soft tissue layers from the patella to its place of attachment on the medial femoral condyle making sure that the graft stays outside the knee capsule.
    • Graft length is measured as the distance from the femoral and patellar sockets with the knee in 30 degrees of flexion with the patella held in a reduced position in the trochlea
    • 15mm is added to accommodate for the distance b/n sockets (this paper was in children, and used anchoring to the patella (may be larger in adults and some techniques will pass graft through a patellar tunnel)
    • Final length is normally somewhere b/n 85-100mm
    • Graft is fixed to the femur w/ a tenodesis screw and free ends are secured w/ a suture loop
    • The free ends of the graft are then docked into the 2 sockets that were created in the patella w/ tenodesis screws with the knee in 30 degrees of flexion.
  • Considerations for youth
    • If the graft is docked proximal to the distal femoral physis, as the child grows, the graft on the femur will migrate superior relative to the patellar graft anchor and will place excess tension on the graft
    • Graft should be placed distal to femoral physis in youth to best preserve graft isometry as the patient grows.
    • Need to be careful during graft placement to not disrupt physis.
  • Video: MPFL reconstruction using hamstring autograft in children and adolescents.
Post-op Rehab:
  • Phase I: Day 1 - Week 6: Protective
  • Phase II: Week 7 - Week 12: Moderate Protection
  • Phase III: Week 13 - Week 16: Minimal Protection
  • Phase IV: Week 17 - Week 20+: Return to full activity
Phase I:
  • Immediately:
    • WBAT and ROM as tolerated
      • This does not mean full weight bearing and full motion, everyone will present a little differently. Work with what they have and let them know that it is ok to move their knee and put weight through it right away, just be smart about it.
      • The soft tissue on the medial side of the knee moves a lot with movement of the knee so it is important to keep all of that moving so it does not stiffen up after the trauma of surgery.
      • Immobilization causes decreased structural properties of ligaments in animal studies after just a couple weeks of immobilization and there is actual subperiosteal bone resorption at the insertion of the ligament as well as microstructural changes w/in the ligament itself.
        • The changes are able to be reversed but reversing the changes takes much longer.
      • 9 weeks of immobilization required 1 year for restoration of normal tissue properties in animal studies.
      • Based on a systematic review of papers with significant methodological flaws, there does not appear to be any difference in radiological or clinical outcomes between immediate ROM and WBAT compared to protected ROM and WB status. 
      • According to this article, Strain on the MPFL increases as knee flexion increases from 0 - 120 degrees. Because of this it is important to not be too aggressive with flexion ROM early.
        • Remember, once the patella engages in the trochlea, the MPFL provides little stability to the patella from a dislocation standpoint, but that does not mean that the MPFL is not under tension.
  • Ice and NMES immediately
    • Ice and NMES help to decrease nerve conduction velocity and help to release endogenous opiates
    • Compression wrapping and elevation will help to decrease swelling, especially over the first few days.
    • NMES also helps increase motor unit synchronization (not really true strength which is movement and load dependent).
  • Patellar Mobilizations immediately if stiff
    • You want about 2 quadrants of patellar mobility medially and laterally after surgery, so if they are way short of that it is appropriate to mobilize a bit.
  • The strength of the graft itself is going to be much stronger than the native ligament, but the risk of failure is not of the graft itself, but rather the anchor point on the medial epicondyle, or medial epicondyle/patella depending on the surgical technique.
  • If they are having a very difficult time getting back flexion ROM, trial some inferior / inferior-medial patellar glides a little short of their flexion limit to augment your basic ROM exercises such as heel slides.
  • Full Weight Bearing by 1-2 weeks
    • Progress them at their own rate, but most people should be full weight bearing by somewhere between 1-2 weeks.
  • Quadriceps exercises
    • Strain on the MPFL increases as degree of flexion increases. Reconstructed MPFL shows greater stiffness than native MPFL, but the strain on the anchors of the surgery indicates caution with increased ranges of flexion, especially early in the rehab process.
    • May be wise to only perform quadriceps exercises near the end range extension early on with a gradual progression of ROM as the graft heals, maybe with NMES at first to make sure that the VMO is firing to help with medial stabilization.
  • CKC Exercises
    • Once patient is full weight bearing, a progressive CKC strengthening program can begin
    • MPFL is stressed in dynamic valgus, so make sure movement patterns are appropriate
    • Work near full extension early and gradually increase ROM as the graft heals.
    • Likely work double leg during this phase and work on weight bearing symmetry.
    • Progress balance to SLS
  • Milestones to Progress:
    • Full WB
    • Ambulation w/o limp or antalgia
    • Full ROM
    • Ability to stand single leg
    • Appropriate patellar mobility of at least 2 quadrants (difficult to accurately assess, but make sure the patella does not feel excessively stiff or loose).
Phase II: Weeks 7-12: Moderate Protection Phase

Goals:
  • Maintain full ROM
  • Maintain Repair
  • Gradual initiation of functional activities
  • Most restrictions have been lifted at this point.
ROM:
  • Should be pretty well established at this point, if they are still missing some, get after it with some higher grade mobilizations and emphasize getting back their full ROM prior to other things.
Exercises:
  • Progress DL strengthening → SL Strengthening / NM Control
  • Squats, lunges, step ups/step downs
  • Hip strengthening
  • Balance board / other balancing activities activities
  • Begin working toward limb symmetry
  • Milestones to progress:
  • Maintain all phase I milestones
  • Full symmetrical or near symmetrical strength of hip, quadriceps and HS
Phase III: Weeks 13-16: Minimum Protection Phase

Goals:
  • Return to full functional activity (not sport) but progress toward full sport activity
  • Running and jumping with appropriate mechanics
  • Full limb strength symmetry
  • Symmetrical Double Leg Jumping (Single leg initiated in phase IV)
  • Progress their confidence, introduce low level return to sport progression, continue to strengthen and improve NM control
Phase IV: Weeks 17-21+: Return to Activity/Sport

Goals:
  • Progression of functional / sport specific activity
  • Full return to all prior sports and recreational activities
Exercises:
  • Progress from DL to SL hopping activities
  • Sagittal → Frontal → Rotational
  • Box → shock absorption → descending box shock absorption → Rebound → descending rebound
  • Agility ladder
  • Box Drills
  • Hurdle drills
  • Direction changes
  • Will likely be scary for them to land on their affected leg so maybe practice jumping off of it and landing on the uninvolved side first then progress to very low level eccentric landing on the involved side (probably with some step and hold activities in phase III which will hopefully improve their confidence when they start hopping).
Resources:

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