Understanding the normal and abnormal post-operative MRI appearances after meniscal allograft transplant

Learning Objectives:

To know the current indications for meniscal allograft transplantation (MAT)
To become familiar with the different techniques used in MAT.
Expected post-operative MRI appearances and common complications after MAT
To know the MRI techniques best used for followup of meniscal allografts.

Transcript

1. Understanding the normal and
   abnormal post-operative
   appearances after meniscal
   allograft transplant TIMOTHY WOO
   NATHAN JENKO
   NICOLE BAUSCH
   NICHOLAS SMITH
   UNIVERSITY HOSPITAL COVENTRY AND WARWICKSHIRE
   CLIFFORD BRIDGE ROAD, COVENTRY, UK
   TIMOTHY.WOO@UHCW.NHS.UK
   

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2. Introduction
   • The menisci are a crucial load bearing structure of the knee helping
   to decrease peak contact pressure and removal and debridement of
   irreparable (“white-zone”) meniscal tears greatly accelerate
   development of knee cartilage damage and osteoarthritis1,2
   • The first human meniscal allograft transplant was performed in
   19843 and since then thousands of procedures have been
   performed worldwide
   • Timing of transplant and the patient groups likely to benefit are still
   debated as well as whether it is truly chondroprotective
   • It is well-tolerated and has proven short to medium term
   symptomatic benefit
   Image credit Wikimedia commons: https://commons.wikimedia.org/wiki/File:Meniscus_tear_2010_-_closeup.JPG
   

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3. Learning Objectives
   • To know the current indications for meniscal allograft transplantation (MAT)
   • To become familiar with the different techniques used in MAT and the
   different graft types.
   • Expected post-operative MRI appearances and common complications after
   MAT
   • To know the MRI techniques best used for follow-up of meniscal allografts.
   

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4. Indications
   1. Unicompartmental pain in the
   presence of a total or subtotal
   meniscectomy
   2. As a concomitant procedure to ACL
   reconstruction if meniscus deficiency is
   believed to be a contributing factor to
   failure
   3. As a concomitant procedure to
   cartilage repair in a meniscus deficient
   compartment.
   1. Articular cartilage loss Outerbridge grade 3
   or above
   2. Any ligamentous deficiency or
   malalignment not surgically treatable.
   3. Inflammatory arthritis or previous septic
   arthritis
   4. Severe obesity (although no specific BMI
   threshold has been agreed on)
   5. Paediatric patient/immature skeleton
   Contraindications
   No age limit above which MAT not thought to be beneficial
   Consensus statement from the International Meniscus Reconstruction Experts Forum in 20154
   

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5. Evidence
   Several large case studies explore the outcomes following MAT, but the majority of these are
   only Level IV evidence (One long term level III study5)
   Heterogenous in outcome measures, exclusion criteria and patient cohort selection.
   1. Well-tolerated
   procedure with low
   failure rate (~10%)
   and low rate of
   complication
   (~14%6)
   2. All studies
   demonstrate increase
   in Patient Reported
   Outcome Measures
   (e.g. 55.7(poor) →
   81.3(good) mean
   improvement on
   Lysholm scale)7 and
   benefits maintained
   at 14 years
   3. No difference in
   PROMs or
   complication rates
   between operative
   techniques
   4. Uncertainty as to whether there is a chondroprotective
   effect:
   2 studies using contralateral
   knee control showed no
   radiographic progression8,9
   Other studies show progression
   of OA but often without
   adequate controls10,11.
   Probably there is a small chondroprotective effect but
   masked by a heterogenous cohort
   

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6. Operative Techniques
   BONE BRIDGE TECHNIQUE
   • Meniscus is harvested together with
   the meniscal roots attached to a
   “bone bridge” from the donor tibia.
   • An identical receptor site is cut into
   the patient’s native tibia and the
   bone bridge attached with the
   meniscal roots using suture anchors
   or interference screws.
   • Can be used for both medial and
   lateral meniscus
   BONE PLUG TECHNIQUE
   • Meniscus is harvested together with small bone plugs
   from the donor tibia, one attached to each root by long
   sutures
   • Suture tunnels are drilled from the root attachments to
   the anterior tibial cortex and the root sutures with the
   bone plugs are pulled through, tensioned and fixed –
   usually with a device such an endobutton
   SOFT TISSUE TECHNIQUE
   • No bone graft is used – Suture
   tunnels are drilled and used as
   for the bone plug technique
   • Some authors believe that the
   suture tunnel technique is not
   suitable for affixing the lateral
   meniscus due to the root
   proximity and risk of tunnel
   coalescence although there is
   no proven increased risk
   After root fixation, the remainder of
   the donor meniscus is attached to the
   recipient’s residual meniscal rim
   (if any) and/or joint capsule.
   

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7. Graft types
   Allografts currently available are either fresh frozen
   or cryopreserved with fresh frozen generally being
   preferred but there is no difference in outcome
   measures between groups. Rarely, fresh grafts are
   also used although these have logistical challenges.
   Fresh frozen soft
   tissue meniscal
   allograft:
   Figure from
   Spalding T. et al.
   (2015)12
   Previously, lyophilised grafts
   were also used, but these
   demonstrated graft
   shrinkage at second look
   arthroscopy and outcomes
   similar to meniscectomy
   groups in early case series13
   Grafts are stored in antibiotic
   solution while frozen to
   prevent pathogen transfer.
   Previously, some grafts were
   irradiated, but this also was
   found to compromise graft
   quality and this is no longer
   common practice.
   Artificially engineered graft material is much less commonly
   used with available products such as Collagen Meniscal
   Implant (Ivy Sports Medicine, Germany) which is composed
   of Achilles tendon Type I collagen and acellular polyurethane
   polymer scaffold (Actifit, Orteq Bioengineering, UK), but
   these are only usable for partial meniscal defects and require
   a viable meniscal rim and at least one root attachment.
   

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8. MRI technique
   ROUTINE IMAGING
   • Most of the fixation used in meniscal
   allograft transplant is non-metal except
   for the endobutton which is distant from
   the graft fixation
   • 3 Tesla imaging with fluid sensitive fat
   saturated structural sequences such as
   fat-saturated proton-density images using
   a dedicated knee coil in three orthogonal
   planes
   Proton-density weighted coronal MRI of the knee
   with a lateral meniscal transplant showing peripheral
   suture artefact
   ARTHROGRAPHY
   • Some authors advocate the use of
   arthrography to investigate graft/capsule
   healing as this is obscured by suture
   artefact. However, the clinical benefit of
   this is debated.
   • Arthrography can be used to tell
   between non-displaced graft tears and
   healing tissue and to investigate
   arthrofibrosis.
   

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9. Normal post-operative appearances
   SIGNAL
   • Similar to ACL graft
   • Initial T1/T2 high signal
   peaking at 6m then declining
   to T1/T2 low signal over the
   next 18 months
   SHRINKAGE/EXTRUSION
   • Commonly seen and not
   associated with worse PROMs15
   • However, thought undesirable
   as represents incompetence of
   graft
   GRAFT/CAPSULE HEALING
   • Assessed by fluid/contrast tracking
   between graft and capsule
   • Thought desirable – especially in soft
   tissue only fixations.
   • However, even arthrography
   underestimates healing14
   LINEAR DEFECTS
   • Not of clinical consequence
   unless16:
   • Increasing on serial imaging
   • True fluid signal
   • Painful
   Normal MRI of soft tissue only fixation lateral meniscus allograft
   Top: Normal appearances of the two suture tunnels on sagittal PDFS
   and T1-weighted images (arrowheads)
   Bottom: linear high signal in posterior horn found at arthroscopy to be
   unresorbed suture material
   

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10. Complications
    INFECTION
    • As with other joint procedures,
    superficial and deep joint
    infections are non-specific on
    imaging presenting early with
    synovitis and effusion
    SUTURE FAILURE
    • Root suture fixation sites are a potential site of failure in
    soft tissue fixation
    • Sutures should run continuously between the suture tunnel
    and the donor root
    • Anterior horn suture can often be poorly defined and
    detecting tears/suture failure here has low specificity
    Sagittal and coronal PD-weighted MRI of lateral meniscal allograft
    showing apparent absent anterior horn with no meniscal material visible
    continuous with the suture tunnel suggestive of a suture failure/tear
    The allograft was normal on arthroscopy.
    Early post-operative MRI of a patient with
    lateral meniscal allograft after re-presenting
    with tibial wound infection. PD-weighted
    sagittal images showing infrapatellar fat pad
    oedema, synovial thickening and effusion
    suspicious for joint infection
    

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11. NON-INCORPORATION OF BONEPLUGS/BONE-BRIDGE
    • The bonegraft should be visible on immediate and
    sometimes at 3 month post-operative imaging but
    should be completely incorporated by 6 months.
    • Signs of failure are as elsewhere with progressive
    sclerosis and cortication and persistent fluid cleft at
    MRI.
    GRAFT TEAR
    • Graft tear is the most common indication for non-
    routine followup MRI.
    • Linear high signal is normal in the graft meniscus
    usually representing suture material or
    granulation/epithelisation but tear is favoured if:
    • Displaced fragment
    • Increasing fluid signal over serial MRI scans esp if new
    cartilage defect
    • Imbibition of contrast on MRI arthrogram
    Sagittal PD-weighted MRI of a
    lateral meniscal allograft showing
    flipped tear of the posterior horn
    of the graft with empty posterior
    compartment (arrowhead)
    Immediate and 3 month postoperative radiographs showing normal
    incorporation of tibial bone-bridge of a lateral meniscal allograft
    

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12. ARTHROFIBROSIS
    • As with ACL graft reconstruction,
    meniscus transplant can rarely result in
    intra-articular scar mass formation or
    arthrofibrosis which usually presents as
    progressive restriction of range of
    movement.
    • Low signal soft tissue foci – often more
    evident on non-fat-saturated images are
    sometimes seen and MRI arthrography
    can sometimes also be helpful but most
    patients in which this is suspected
    progress to arthroscopy.
    PROGRESSION OF OSTEOARTHRITIS
    • In the medium to long term, progression
    of cartilage loss is important to note as
    this can indicate a functionally
    incompetent graft and can relate to
    recurrent patient pain (imaging after two
    years is often only undertaken in the
    context of new symptoms).
    • This can sometimes necessitate graft
    revision or in some cases joint
    replacement.
    Left: 1 year postoperative and
    Right: 3 year postoperative
    coronal PD-weighted MRI studies
    of a patient with lateral meniscal
    allograft and new symptoms
    showing definite interval cartilage
    degeneration despite meniscal
    allograft
    T1-weighted MRI through the intercondylar notch
    of a patient with lateral meniscal allograft with
    bone-bridge technique showing low signal scar in
    the infrapatellar fatpad and notch in keeping
    with arthrofibrosis
    

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13. Conclusion
    Meniscal allograft transplant is an increasingly
    popular choice for young to middle aged patients
    with significant meniscal injuries and is proven to
    have at least short to medium term symptomatic
    benefits.
    There is an increasing chance of coming across a
    patient who has undergone one of these
    procedures in the past and it is important that
    radiologists know the details of current and past
    surgical techniques and expected post-operative
    MRI appearances of these grafts to accurately
    assess re-injury. Lateral meniscal allograft in situ postfixation arthroscopic image
    From Spalding et al.12
    

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14. References
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    2. Papalia R, Del Buono A, Osti L, Denaro V, Maffulli N. Meniscectomy as a risk factor for knee osteoarthritis: a systematic review. Br Med Bull. 2011;99:89-106.
    3. Milachowski KA, Weismeier K, Wirth CJ. Homologous meniscus transplantation. Experimental and clinical results. Int Orthop. 1989;13(1):1-11.
    4. Getgood A, LaPrade RF, Verdonk P, Gersoff W, Cole B, Spalding T; IMREF Group. International Meniscus Reconstruction Experts Forum (IMREF) 2015 Consensus Statement on the Practice of
    Meniscal Allograft Transplantation. Am J Sports Med. 2017 May;45(5):1195-1205.
    5. van der Wal RJP, Nieuwenhuijse MJ, Spek RWA, Thomassen BJW, van Arkel ERA, Nelissen RGHH. Meniscal allograft transplantation in The Netherlands: long-term survival, patient-reported
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