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
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
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.
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
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
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.
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.
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.
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
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
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
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
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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