MR: Post-operative Knee Assessment William B. Morrison, MD - - PDF document

1

MR: Post-operative Knee Assessment

William.Morrison@jefferson.edu William B. Morrison, MD Professor of Radiology Thomas Jefferson University Hospital Philadelphia, PA

Has There Been Surgery?

• Linear area of low signal

intensity in Hoffa’s fat pad

• Represents footprint of the

arthroscopic cannula

• Susceptibility artifact from

metallic hardware or microscopic metallic fragments

Scope Scar

Each side of patellar tendon: rounded low signal

2 Initially Looks Like Meniscectomy

But no scope scar!

Anterior and superior flip

Question

If you see a small meniscus the differential includes:

1) Post-op partial meniscectomy 2) Tear with flipped fragment 2) Tear with flipped fragment 3) Chronic degenerative tear 4) All of the above

Meniscal Tears

• Diminutive meniscus DDx:

– Post-op partial meniscectomy – Tear with flipped fragment (e.g., bucket-handle) – Chronic degenerative tear

3

Diminutive Meniscus

• Step 1: Look for H/O arthroscopy or “scope

scar”

– If +, meniscal finding may be due to partial meniscectomy meniscectomy

• Step 2: Look for flipped fragments

– Common places:

• Notch
• Anterior, posterior recesses
• Meniscotibial recess
• Caution: scope scar and flipped fragment can

co-exist

Diminutive Meniscus

anteriorly flipped fragment

Fragment Flipped into Meniscotibial Recess

AKA “Boomerang”

4

Criteria for Detecting Meniscal Tears

Grade I II III

• Surfacing (Grade III) signal

diagnostic of tear in the non-

• perated meniscus
• Grade III signal in post-op

meniscus

• Stable intrasubstance signal
• Granulation tissue
• Persistent tear/ retear

Meniscal Surgery: Resection, Repair, Replacement

Meniscal Preservation is the goal

Medial meniscectomy increases contact stress

s/p lateral meniscectomy

increases contact stress 100%; lateral meniscectomy increases contact stress 200-300% Meniscectomy decreases the shock absorbing capacity of the normal knee by 20%

Complete cartilage denudation

NOT ALL MENISCAL TEARS NOT ALL MENISCAL TEARS WARRANT SURGERY!! WARRANT SURGERY!!

Non-operative conservative therapy appropriate: < 1 cm Partial thickness Peripheral aspect of the meniscus Stable type tears (e.g., horizontal)

5 Partial Meniscectomy

Goals:

• Obtain a stable meniscus

with smooth contours Remove displaced

• Remove displaced

meniscal fragments preserving as much meniscal tissue as possible Stress on weight bearing joint surface following meniscectomy directly proportional to amount of meniscal tissue resected

Partial Meniscectomy

Pre-operative 1 year post-op

Altered biomechanical stress on underlying cartilage

y p p

Accelerated cartilage loss following partial meniscal resection- 1 yr follow-up

Meniscal truncation

Question

What is your protocol for evaluation of the post-op knee?

1) Noncontrast MRI 2) Direct MR arthrography (into joint) 2) Direct MR arthrography (into joint) 3) Indirect MR arthrography (intravenous) 4) CT arthrography 5) Depends on type of surgery

6 Conventional MR

May be appropriate if less than 25% of meniscus resected (use criteria for tear in virgin meniscus)

S/p partial meniscectomy with re-tear

Direct MRA

Advantages of gadolinium

Sciulli et al compared arthrography, conventional MR, MR arthrography with iodinated contrast, & MRA -> MRA most accurate 92% White et al compared conventional MR, indirect MR, & MRA -> increased accuracy with MRA but not statistically significant S/p partial meniscectomy with re-tear

Lower viscosity of gad compared to synovial fluid allowing imbibition into small clefts Utilization of T1 pulse sequences with favorable signal to noise Intra-articular distention allowing separation of otherwise apposed torn meniscal edges

Indirect MR arthrography

Enhancement of joint fluid will create greater conspicuity of re-tear T2 Post-operative meniscus with re- tear T1 FS post IV Gd Q: WILL NORMAL GRANULATION TISSUE ENHANCE?

7

HORIZONTAL TEAR OF THE LATERAL MENISCUS NORMAL MEDIAL

CT arthrography

93% sensitivity 89% specificity CTA vs 2nd look arthroscopy*

MEDIAL MENISCUS *Mutschler C, Radiology 2003; 228:635-641.

USE FULL STRENGTH CONTRAST

Conventional MRI Partial Meniscectomy Normal MR Appearance

• Small truncated meniscus
• No grade III signal

Conventional MRI Partial Meniscectomy Criteria for a Retear

• 1. Grade III signal

– Fluid within the line

• n T2
• 2. Displaced meniscal

fragment

• 3. Tear in a new

location

8

Conventional MRI Partial Meniscectomy Criteria for a Retear

• 1. Grade III signal

– Fluid within the line

• n T2
• 2. Displaced meniscal

fragment

• 3. Tear in a new

location

Conventional MRI Partial Meniscectomy Criteria for a Retear

• 1. Grade III signal

– Fluid within the line

• n T2
• 2. Displaced meniscal

fragment

• 3. Tear in a new

location

• Conventional MR
• Accuracy: 65-82%
• Sensitivity: 60-86%
• Accuracy improved if
• <25% meniscus resected

Conventional MR Pitfall

• Grade III signal: T1-weighted or PD sequence only
• Indeterminate

9

• Grade 3 signal on T1

image- conventional MR

Routine MRI indeterminate for tear

• Follow-up direct

MR arthrogram

• No contrast enters

meniscus

• No evidence of tear

MR Arthrography Partial Meniscectomy

• Direct Arthrogram
• Indirect Arthrogram
• Surfacing gadolinium signal = tear
• Direct and Indirect MRA similar accuracy

Meniscal Repair

• Traumatic lesions within the vascular zone (within 3

mm of the meniscosynovial junction) generally greater than 8 mm with minimal damage to the meniscal body

Minority of tears are amenable to repair

10

Meniscal Repair

Success rates variable

• Tear length

A t h i

• Acute or chronic
• Lateral or medial
• ACL injury

Meniscal Repair

All inside Inside-out Outside-in

Meniscal Suturing

11

Meniscal Repair

T1 T1 Granulation tissue

The Big Pitfall

Suture

• Prior to repair
• Following repair

T1 T1

Repair of Peripheral Tear

Meniscal Suturing

Pitfall: Granulation tissue may resemble tear

Recurrent medial joint line pain following earlier meniscal repair

• Direct MR arthrogram
• Contrast enters meniscus: demonstrating a retear

12

Meniscal Repair: Recurrent Tear

• Fluid enters area of repair on

T2

• Irregular margins
• Displacement, widening
• Increasing parameniscal

cyst size

Conventional MR

+Contrast enters area of repair

• During the first year

granulation tissue may enhance with indirect MR arthrography

Direct MRA

Meniscal Arrow

• Recurrent meniscal tear
• Displaced meniscal arrow

resulting in linear chondral defect

Meniscal Transplantation

Free graft with separate bone plugs “Keyhole” technique Native meniscal rim- repair techniques to suture to meniscal transplant

13

Meniscal Transplantation

• Pre-operative imaging

mandatory

– Wt bearing 45 degree flexion PA view

• Jt space narrowing

Mensical graft sizing via radiographs, MR, or CT

Meniscal transplant sizing via CT A

• Jt space narrowing,

significant OA – Long-leg alignment radiographs

• Mechanical axis

– MRI

• Cartilage integrity

Assessed at the level of the articular tibial plateau, with “A” bisecting the tibial spines

Meniscal Transplantation

• <40yo
• Pain, swelling
• Unresponsive to

conventional treatment Mi i l OA

• Minimal OA

Meniscal Transplantation

Anterior horn Body

Normal dark signal within the transplant meniscus

Posterior horn

14

MR Evaluation of the Meniscal Transplant

FOLLOW UP: LOOK FOR

Rath, et al; 36% of transplanted menisci torn at 5 years

FOLLOW-UP: LOOK FOR

• Tear (Grade 3 signal, morphology, fragment)
• Change in position
• Shrinkage
• Arthrofibrosis
• Articular cartilage damage

Meniscal Transplantation

Arthroscopically proven meniscal transplant re-tear

Meniscal Transplantation

• Malpositioned (extruded)

meniscal transplant

15

MRI of the Painful Knee Following Meniscal Surgery

• Post-meniscectomy (recurrent pain)

– Residual tear/ retear of meniscus Articular cartilage damage – Articular cartilage damage – Osteoarthritis – Intraarticular bodies – Spontaneous osteonecrosis

Question

Which cause is most common?

1) Articular cartilage damage 2) Osteoarthritis 2) Osteoarthritis 3) Intraarticular bodies 4) Spontaneous osteonecrosis

Articular cartilage damage overlying meniscal repair site

• Most common source of recurrent pain
• Occurs in up to 40% of patients
• Altered weight-bearing following meniscal resection/ repair

16

Articular Cartilage Evaluation: Direct Versus Indirect MR Arthrography

Direct Arthrography Indirect Arthrography

Osteoarthritis

• Related to the amount
• f meniscus resected
• 40% incidence following

total meniscectomy

• Joint space narrowing
• Cartilage thinning
• Osteophyte formation
• Subchondral marrow

change

Intraarticular Bodies

• Fragmentation of articular

cartilage

• Begin as cartilagenous

bodies

• Subtle on MR imaging

17

Question

Spontaneous osteonecrosis represents

1) True osteonecrosis – all of the time 2) Subchondral insufficiency fracture that may progress to osteonecrosis 3) A complication related to prolonged tourniquet time during surgery

“Spontaneous Osteonecrosis”

• Medial femoral condyle; subchondral insufficiency fracture
• Osteopenic patients
• Acute onset of pain/ 2-18 months; 50% heal; 50% collapse

67 y.o. male- golfing injury

• Medial meniscal

tear

• 6 months post-
• p
• Acute onset

medial joint line pain

18 HYALINE CARTILAGE CARTILAGE

Regatte RR, Akella SV, Reddy R. Depth-dependent proton magnetization transfer in articular cartilage.J Magn Reson Imaging. 2005 Aug;22(2):318- 23. Masi JN, Sell CA, Phan C, Han E, Newitt D, Steinbach L, Majumdar S, Link TM. Cartilage MR imaging at 3.0 versus that at 1.5 T: preliminary results in a porcine model. Radiology. 2005 Jul;236(1):140-50. Koo S, Gold GE, Andriacchi TP. Considerations in measuring cartilage thickness using MRI: factors influencingreproducibility and accuracy. Osteoarthritis Cartilage. 2005 Jun 13; [Epub ahead of print] Glaser C. New techniques for cartilage imaging: T2 relaxation time and diffusion-weightedMR imaging. Radiol Clin North Am. 2005 Jul;43(4):641-53, vii Lang P, Noorbakhsh F, Yoshioka H. MR imaging of articular cartilage: current state and recent developments.Radiol Clin North Am. 2005 Jul;43(4):629-39, vii. Filidoro L, Dietrich O, Weber J, Rauch E, Oerther T, Wick M, Reiser MF, Glaser C. High-resolution diffusion tensor imaging of human patellar cartilage: feasibility and preliminary findings. Magn Reson Med. 2005 May;53(5):993-8. Fischbach F, Bruhn H, Unterhauser F, Ricke J, Wieners G, Felix R, Weiler A, Schroder RJ. Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2-weighted fast spin echo, T1-weighted two-dimensional and three-dimensional gradient echo pulse sequences.Acta Radiol. 2005 Feb;46(1):67-73.

Hyaline Cartilage Surgery

Current Therapies

Cartilage Repair

– OATS – Microfracture – Cartilage transplantation – Proteoglycans???

Kornaat PR, Reeder SB, Koo S, Brittain JH, Yu H, Andriacchi TP, Gold GE. MR imaging of articular cartilage at 1.5T and 3.0T: comparison of SPGR and SSFP sequences. Osteoarthritis Cartilage. 2005 Apr;13(4):338-44. McWalter EJ, Wirth W, Siebert M, von Eisenhart-Rothe RM, Hudelmaier M, Wilson DR, Eckstein F. Use of novel interactive input devices for segmentation of articular cartilage from magnetic resonance images.Osteoarthritis Cartilage. 2005 Jan;13(1):48-53. Roemer FW, Guermazi A, Lynch JA, Peterfy CG, Nevitt MC, Webb N, Li J, Mohr A, Genant HK, Felson DT. Short tau inversion recovery and proton density-weighted fat suppressed sequences for the evaluation of osteoarthritis of the knee with a 1.0 T dedicated extremity MRI: development of a time-efficient sequence protocol.Eur Radiol. 2005 May;15(5):978-87. Epub 2005 Jan 5. Gougoutas AJ, Wheaton AJ, Borthakur A, Shapiro EM, Kneeland JB, Udupa JK, Reddy R. Cartilage volume quantification via Live Wire

• segmentation. Acad Radiol. 2004 Dec;11(12):1389-95.

Watrin-Pinzano A, Ruaud JP, Olivier P, Grossin L, Gonord P, Blum A, Netter P, Guillot G, Gillet P, Loeuille D. Effect of proteoglycan depletion on T2 mapping in rat patellar cartilage. Radiology. 2005 Jan;234(1):162-70. Mosher TJ, Smith HE, Collins C, Liu Y, Hancy J, Dardzinski BJ, Smith MB. Change in knee cartilage T2 at MR imaging after running: a feasibility

• study. Radiology. 2005 Jan;234(1):245-9.

Kornaat PR, Doornbos J, van der Molen AJ, Kloppenburg M, Nelissen RG, Hogendoorn PC, Bloem JL. Magnetic resonance imaging of knee cartilage using a water selective balanced steady-state free precession sequence.J Magn Reson Imaging. 2004 Nov;20(5):850-6.

Or ‘masking’ symptoms

– NSAIDS – Synvisc

MSK radiology research around the world has centered on cartilage imaging

Result: increased emphasis on identification, categorization of cartilage lesions

Autologous Osteochondral Transplantation (AOT)

Autologous bone with overlying cartilage cored from non- weightbearing areas of the joint and transferred into the

Generally indicated for chondral lesions 1.5 – 3 cm

cartilage defect

MosaicPlasty OATS (Osteochondral Autograft Transplant Surgery) SDS (Soft Delivery System) COR Disadvantages- donor site morbidity, limited supply of grafts, long rehab

19 Osteochondral Autograft Transplant Surgery (OATS)

DONOR SITE

EVENTUALLY FILLS IN WITH BONE

MR Appearance of Harvest Site

• Defect in supratrochlear region

(initially fluid filled)

• Fills in with fibrocartilage during the

first year

• Dark on T1- and T2-weighted images

OATS

IMPLANT SITE

CONGRUITY OF THE ARTICULAR SURFACE IS NECESSARY SURFACE IS NECESSARY “COBBLESTONE” NORMAL

20

OATS

Typical Appearance

OATS

Pre-op Post-op Pre-op Post-op

OATS

“COBBLESTONE” PATTERN: NORMAL AS LONG AS OVERALL SURFACE IS CONGRUENT

21

Revascularization of Osteochondral Graft

• First two weeks
• Avascular graft
• No enhancement of “plug”
• Four to six weeks
• Plug revascularizes
• Enhancement of “plug”

OATS

Persistent subchondral bone marrow edema

Poor graft incorporation

Subchondral cysts

Osseous incorporation between 6- 14 wks subchondral marrow edema can be present initially and should resolve as graft incorporates; when solid maturation occurs, normal fatty marrow is seen within and around the plugs

OATS

22

Osteochondral Allograft (OCA)

Osteochondral segment harvested from cadaver and transplanted to cartilage defect Potential risks of immunologic rejection of the allograft and disease transmission from donor to recipient

Microfracture

• Perforations (microfractures) in

subchondral bone plate

• Stem cell migration
• Fibrin clot
• Disorganized hyaline/fibrocartilage

Advantages- cost effective, technically g y feasible, supportive clinical data Disadvantages- does not reproduce hyaline cartilage

Microfracture – NBA Player

Medial compartment symptoms prevent play

23 4 MONTHS LATER

REMAINS SYMPTOMATIC

S/P MICROFRACTURE

7 MONTH FOLLOW-UP

Playing without symptoms

13 MONTHS LATER

Recurrent symptoms

24

PD T2 SPGR

Microfracture (Abrasion Chondroplasty)

SPGR May fill in with bone

Cartilage Healing

without surgery

Low signal fibrocartilage

Autologous Chondrocyte Implantation

Cells harvested from healthy non-weightbearing area of the joint are cultured and then re- injected at site of cartilage injury

Advantage- potential restoration of hyaline cartilage Disadvantage- 2 invasive procedures, highly technique dependent requiring lab support, unpredictable results NOT indicated in OA

25

ACI- MR Appearance

Complete fill of cartilage defect with repair tissue that restores contour of articular surface, as early as 3 weeks post-op; signal intensity of the graft variable and often differs from native cartilage- subchondral edema acceptable early, should resolve over time Interface between ACI and native cartilage may be indiscernable or appear as a sharp bright line Complicatons: hypertrophy of the periosteum,post-operative adhesions (may be attached to ACI graft- infrapatellar fat pad, suprapatellar, & infrapatellar recesses)

OCD Repair

Fixation with self- tapping screw Unstable OCD lesion

Displaced fragment post-op

Ligament Reconstruction and Repair p

26

Anterior Cruciate Ligament Graft

Types of ACL Graft

• 1. Bone-Patellar Tendon-Bone (BTB)
• 2. Hamstring (Semitendinosus and Gracilis Autograft)

MR Appearance of BTB ACL Graft 0 to 3 months

• Graft is avascular
• MR signal

characteristics are identical to native patellar tendon

• Dark on T1- and T2-

weighted images

MR Appearance of BTB ACL Graft 4 to 8 months

• Graft revascularization
• Increased T1- and T2-

signal

• Normal graft should not

have fluid signal within graft on T2-weighted images

27

MR Appearance of BTB ACL Graft >12 months

• Ligamentization occurs
• MR appearance similar to

native ACL appearance native ACL appearance

• Dark on T1- and T2-

weighted images; may have intermediate stranding in distal fibers

MR Appearance of Hamstring ACL Graft

• Fluid present between

separate strands of graft

• Hamstring graft

progresses through the same stages as a BTB graft.

MRI of the ACL Graft

• Lax Knee

– Graft disruption – Stretched graft

• Lack of Full Extension

– Graft impingement – Loose bodies – Arthrofibrosis

• Recurrent Trauma

– Internal derangement

28

Lax Knee: Disrupted ACL Graft

• Discontinuity of fibers
• Consider age of graft

Lax Knee: Stretched Graft

• Knee lax on physical exam
• Graft intact with posterior bowing of fibers noted on MR

imaging

ACL Graft Impingement

• Tibial Tunnel placed anterior
• Graft impacts roof of

intercondylar notch during extension of knee

• MRI Findings
• Anteriorly placed tibial

tunnel

• Increased signal in graft
• Kinking of graft

29

Decreased ROM: Graft Impingement

• Anterior placement of tibial tunnel
• Kinking of ACL graft
• Increased signal within graft fibers

Graft Impingement

• Graft fibers intact
• Increased signal in fibers
• Fibers kinking and rubbing against roof of intercondylar

notch

Decreased ROM: Arthrofibrosis

• Diffuse scarring in the

anterior fat pad

• Can be painful and limit

motion of the knee

30

Decreased ROM: Arthrofibrosis

• Cyclops lesion (limits full extension of knee, anterior knee

pain)

• Focal nodule of scar tissue just anterior to ACL graft
• Dark on P.D. and T2-weighted images

Decreased ROM: Loose Bodies

• Loss of full extension, decreased range of motion, locking
• Loose bodies can be subtle on MR imaging
• Can be cartilaginous or osseous

Decreased ROM: Foreign Body

• Locking and pain 6

weeks following ACL repair

31

Decreased Range of Motion

• Basketball injury following

ACL reconstruction

MRI of the ACL Graft

• ACL Reconstruction

– Lax Knee

• Stretched graft
• Disrupted graft
• Disrupted graft

– Lack of Full Extension

• Graft impingement
• Loose bodies
• Arthrofibrosis

– Following Trauma

• Internal derangement

Ganglion Cyst

• Associated with degeneration or partial tear of graft
• Usually involves the tibial tunnel (presents as mass or with

pain)

• More common in hamstring graft

32

Fluid in Tunnel of Hamstring Graft

• Normal finding during first year
• Does not lead to ganglion

formation

Patellar Tendon Harvest Site

• BTB graft harvested from the middle 1/3 of the patellar

tendon

• Defect seen in tendon and bone on MR imaging
• Defect fills in with tendon-like material during the first year

Harvest Site Complications

• Anterior Knee pain- common
• Patellar tendonitis

>10mm thick after one year

33

Harvest Site Complications

• Anterior Knee pain
• Patellar fracture

Hamstring Tendon Harvest Site

• Immediate post-op- Fluid seen within harvest track

Hamstring Tendon Harvest Site

• Tendon regenerates from proximal to distal
• Tendon appears normal within 8 months; 80% original

strength

34

Posterior Cruciate Ligament

• PCL twice as strong as ACL
• PCL less commonly injured (usually
• nly partially torn)
• Conservative therapy usually

adequate

• PCL reconstruction
• Indicated in high performance

athletes

• Indicated if significant instability/

multiple ligamentous injuries

PCL Reconstruction

• MR appearance of PCL graft
• Initially thickened with increased signal on T1- and T2-
• Fibers become better defined by the end of the first year
• Extensive arthrofibrosis is commonly seen

PCL Reconstruction

• By one year; fibers are well defined and dark on all pulse

sequences

35

Collateral Ligament Injuries

• Grade I/II sprains treated conservatively
• Grade III sprains / disruptions- when combined with other

injuries

• treated with stapling or suturing

Medial Collateral Ligament Repair

• MR appearance
• Metallic artifact at repair site
• Persistent thickening of repaired ligament

Posterolateral Corner Reconstruction

• MR appearance
• Metallic artifact at repair site
• Persistent thickening of repaired ligament

36

THANK YOU!