This is a relatively new field in knee surgery - that of replacing the absent or very damaged meniscus - or part of it - by using a donor meniscus or an engineered scaffold.
Modern knee surgeons should be competent in the procedures of meniscal repair. There are some tears, however, that defy repair whatever the skill and understanding of the surgeon. In these patients, meniscal tissue removal will be necessary to avoid leaving a loose flap that can extend the tear and aggravate the symptoms. This may lead to secondary problems, and patients may feel it worth while to try and restore the original anatomy with a graft or a scaffold.
A meniscus transplant is a surgical procedure to replace the entire meniscus and its rim with a donor meniscus harvested from a human donor and purchased from a tissue bank. Such a procedure is still in the domain of the super-specialist and will not be offered at most orthopaedic units although the procedure is becoming more mainstream.
objectives of meniscus transplant
Realistic objectives of modern meniscal transplant are to relieve pain, improve function and protect the vulnerable joint cartilage of the femur and tibia bone. It is not realistic that patients are told that they will get back to full competitive sporting activities. Patients need to understand they are protecting the joint until a later date in the future when they may be able to benefit from improved techniques. Any patient who does indeed find that they are non-symptomatic and are able to return to full function are the lucky ones.
ideal candidate for meniscus transplant
The ideal patient for meniscal transplant -
- should be older than 30 years but less than 50 years
- would likely have had a previous total or subtotal meniscectomy, resulting in chronic pain
- in standing X-rays at 45 degrees flexion, there should not be less than 2mm space between femur and tibia
- there should be no, or only minimal, bone showing through the worn joint cartilage on the top surface of the tibia
- the patient should not be obese
contraindications to meniscus transplant
The surgeon is likely to refuse to perform a meniscal transplant if -
- the rounded end (condyle) of the femur has already become flattened
- the top of the tibia is concave, which means it won't seat the transplant well
- the alignment of the long bones in more than 2-3 degrees from normal, unless the patient agrees to have this alignment corrected by osteotomy prior to the meniscal transplant
- the knee is unstable - especially if there is ACL (anterior cruciate ligament) instability, again in this instance unless surgical reconstruction of the ligament is undertaken prior to the meniscal implant
- there has been prior knee arthrofibrosis
- there has been prior joint infection
- there is significant arthritis in the joint between patella and femur
harvest and preservation controversies
Donor menisci are supplied by tissue banks who are reponsible to the processing and sterilisation. The procedures of tissue processing and secondary sterilisation are still evolving, and 'products' include fresh frozen, irradiated, or cryopreserved grafts, as well as those prepared via proprietary chemical techniques. The so-called sterilisation processes may not prevent contamination and do not guarantee a sterile graft. The patient is likely to be given prophylactic antibiotics intravenously during the surgery, and the patient will also be carefully monitored after surgery for any signs of infection.
As yet there is also no standard protocol to determine the size of the donor meniscius The size is generally estimated from X-rays or MRI scans sent to the tissue bank, who also receive details of the recipient's height, weight and gender. Of course it is important to make sure that the donor graft is correctly medial or lateral - the lateral donor meniscus should preferably be more than 10% larger than the native one Photographs can also be sent from the tissue bank to the surgeon with the potential graft placed against a metric ruler so that the surgeon makes final choice. Some surgeons will show the graft to the patient before putting them to sleep for the operation.
The tissue bank usually supplies the donor meniscus as a block comprised of the top of the tibia bone with the medial and lateral menisci still in place. The donor tissue will have been tested for such conditions as HIV and hepatitis, and will have been frozen and the cells will no longer be alive. Although this is a transplant, it is not necessary for the patient to take medications to prevent rejection - the transplant becomes replaced in time by the patient's own cells.
There is no standardisation of surgical technique. Some surgeons transplant the meniscus without any bone attached to it, while others advocate that a bony bridge or bone plugs on the meniscal horns are used to ensure a good strong fixation of the graft.
If bony fixation is used, there is usually a difference between the medial and the lateral meniscus. In the medial meniscus the surgeon will prepare a central bone bridge or two bone plugs matched to two tunnels to into which the bone plugs will be pulled and fixed. In the case of the lateral meniscus a central bone bridge will be prepared with a corresponding slot in the tibial plateau, and the two will be dovetailed together.
short term and long term outcomes
Orthopaedic surgeons should keep in mind that transplanted menisci cannot restore perfectly the normal meniscal function but just improve function with a possible cartilage protection effect in the meniscectomised knee. Correction of leg alignment and ligament instability prior to the transplant are critical to the long term functioning of a meniscal transplant.The patient and the family should be educated beforehand about modifying expectations and changing their sporting activities.
In the short term, the majority of meniscal transplant patients can expect decreased pain and a certain amount of protection of the joint cartilage. Unfortunately in the long term quite a high percentage of transplants deteriorate, tear or shrink, leading to decrease in function, and very few really completely restore the functionality of the original meniscus. MRI scans are commonly used as a relatively reliable and noninvasive evaluation method for long term evaluation of the graft.
The young patient who has had a meniscectomy presents a special problem. Surgeons are likely to be reluctant to perform a meniscal graft when the young patient has high expectations but there are so many known issues, especially if the patient has no symptoms yet. Young patients will probably be advised to cut back on their expectations and activities, and understand that they need to buy time until better procedures are available to them.
Meniscus tear surgery and meniscus replacement. Vaquero J and Forriol F. Muscles Ligaments Tendons J. 2016 Jan-Mar; 6(1): 71–89.
In this technique a synthetic meniscus (eg. collagen meniscus) is used as a scaffold for the body to replace the meniscus. The scaffold, in the shape of a meniscus, is purchased commercially, and can be trimmed into shape to allow the scaffold to fill any size and shape of defect in the patient's meniscus. The scaffold is soaked in blood from the patient before it is inserted, and then during healing the patient's own cells migrate into the scaffold and new tissue is formed. The original scaffold eventually disappears as it is biodegradable and resorbable. Tissue engineering is a rapidly progressing science. With the progress being made in stem cell, progenitor cell, and matrix technologies the available options are widening.
These procedures are still only being done in a few centres around the world and not every orthopaedic surgeon is familiar with the finer details. Even in the best hands it is unreasonable to expect a perfect result in a knee which has already been subject to sufficient stress to have lost the meniscus (i.e. probably an injury, years of meniscal problems, maybe early arthritis of femur and tibia, and finally meniscectomy). But in some cases a perfect result is obtained - so one has to be guided by the surgeon involved.