Meniscal tears are extremely common. The menisci directly influence the transmission of forces, distribution of load, amount of contact force, and pressure distribution patterns. Thus the menisci serve many vital functions to the knee joint, and thus the preservation of meniscal tissue through repair is desirable. Not all meniscal tears are indications for surgical repair, and each patient must be evaluated carefully for suitability of these procedures. It has been well documented that meniscal healing is enhanced in the setting of a stable anterior cruciate ligament (ACL) reconstruction. Techniques have gradually evolved and improved from initial open repairs to inside-out and outside-in suture repairs to the newer all-inside repair methodology. The gold standard is still the inside-out vertical mattress suture repairs.
There are two different causes for meniscal injuries:
Traumatic tears result from a sudden load being applied to the meniscal tissue which is severe enough to cause the meniscal cartilage to fail and damage the hoop stresses. These usually occur from a twisting injury or a blow to the side of the knee that cause the menisci to be levered against and compressed.
Degenerative meniscal tears This is a natural process of dehydration of the inner centre of the meniscus that can begin in the late 20’s and progresses with age. The meniscus becomes less viso-elastic and thus less compliant and as a result fails with only minimal trauma. Usually there is no clear contributory history or a violent event which can be blamed as the cause of the tear. Degenerative tears are extremely uncommon in younger patients.
Types of Meniscal Tears
Meniscus tears are described by the tear pattern. Tears occur in either the horizontal or vertical direction. They can be purely cleavage tears or may exit the superior or the inferior surface or both. Tears confined to the anterior horn of the cartilage however are unusual. Typically tears begin in the posterior horn and then can extend forward into the middle body and even the anterior horn. Although the goal of meniscus surgery is altruistic, many types of tears are not repairable. A meniscus tear requires a blood supply to heal which is present only in the peripheral third of the meniscus or the Red-Red zone. Repairs in the Red-White zones have been attempted with only just acceptable long term good outcomes. Thus current recommendations dictate that repairs generally be limited to the peripheral region.
Indications for Repair
All of the following factors are carefully considered before embarking on repair:
The ideal type of meniscal tear to consider repairing is the peripheral tear. This is also referred to as the red-red area tears, indicating the degree of vascularity. This tear is amenable only to suture repair. Clinically commonly though, tears are located in the red-white region, which has an acceptable successful repair rate when bio absorbable devices are used.
2. Morphology of the tear
Short tears of 1-2 cm have a better outcome. The mobile, single, vertical longitudinal tear located in the outer one-third is ideal for repair. Degenerative horizontal cleavage tears, complex tears or flap tears usually give poor results.
3. Patient factors
Non compliant patient who are unable to follow rehabilitation protocols are generally poor candidates for repairs. The younger patients have a higher success rate. If the ACL is damaged or deficient, ACL reconstruction at the same sitting yields superior results.
In summary, the best candidate for meniscal repair is the young compliant patient with a 2 cm long peripheral longitudinal meniscal tear.
- Tears greater than 3 cm. These yield poor results.
- Transverse tears in the periphery, do not heal. A minimum of 3 mm tissue at the periphery is necessary for adequate repair.
- Flap tears, radial cleavage tears, or vertical tears with secondary lesions that extend into the avascular inner 2/3 of meniscus should not be repaired.
- Chronic displaced bucket handle tears.
- Multi-ligamentous instability is a relative contraindication to repair
Meniscal Reconstruction Techniques
A. Meniscal Repair
B. Meniscal Replacement
Repairs are performed on tears near the outer 1/3 of the meniscus where a good blood supply exists, or on large tears that would require a near-total resection. The torn portion of the meniscus is repaired by using either sutures or bio absorbable.
These devices include arrows, barbs, staples, or tacks that approximate the torn edges of the meniscus to encourage healing.
There are many different arthroscopic procedures that can be divided into three main groups. These descriptions refer to the placement of the stabilising suture or device.
- Inside-out: Originally described by Henning, the success rate approaches 80 %. The needle goes from inside the knee to outside the knee. To ensure safe passage of needles from inside to out or outside to in, a postero-medial or postero-lateral incision is usually used. Multiple vertical loops of non-absorbable material placed 5 mm apart on the superior and inferior surface provides the best repair.
- Outside-in techniques: Vertical or horizontal mattress sutures are used to repair the meniscal tear. The suture may either be absorbable or nonabsorbable. This remains controversial.
- All inside techniques now usually use biodegradable devices to appose the meniscal tear. These implants can be inserted without any additional incisions and the risk of iatrogenic neurovascular damage is very low.
Polymers used for repairs
- Bio absorbable implants are made from polyglycolic acid (PGA), polylevolactic acid (PLLA), or polydioxanone (PDS), which can all degrade into carbon dioxide and water.
- PLLA is more crystalline and takes longer to degrade. This degradation occurs most rapidly near the centre of the implant and progresses outward, producing a mantle of polymer on the outside.
- PGA has been associated with more lytic reaction around the device. The device may be reinforced with fibre to increase the strength. Not all of these devices are created equal. The original arrow was made with self-reinforced PLLA. The arrow was shown to have the same pullout strength as the horizontal loop suture.
- The BioStinger is also made from PLLA. The Mitek anchor is made from both the PDS and the nonabsorbable Prolene. Arthrotek has used Lactosorb (a copolymer) in a staple configuration that is resorbed in 9 to 15 months.
Results of Repair
- Some, but not all, meniscal repairs heal and some heal incompletely. There have been follow-up studies for inside-out, outside-in and some all inside techniques (T fix, Biofix, Fibrin glue).
- Many of the implants available are relatively new and have no studies to support their use. Studies that report clinical assessments have higher ‘healing rates’ than those using second look arthroscopy. Only around 50% of unhealed tears can be predicted prior to arthroscopy.
- Taking all series, 81-95% have a clinically acceptable outcome but only 23-73% are completely healed on arthroscopy. The lowest figures are for isolated tears in stable knees and the highest figures are with synchronous ACL reconstruction.
- Many other tears heal incompletely (17-37%) or do not heal (7-50%). Most of the studies have short follow-up (less than two years) and because of different indications for repair and different patient populations (e.g. with or without ACL reconstruction), comparison between the various series is difficult.
Experimental attempts have been made to replace damaged meniscus. This new technology has been performed on a few patients.
Collagen meniscus implant: A scaffold of collagen is inserted into the patient’s knee. Over time, a new meniscus may grow within the joint. This procedure is currently in FDA trials in the United States and has just been approved as an accepted surgical procedure in Europe.
Meniscal transplant: This procedure involves transplanting a meniscus from a donor into the injured knee. Only a limited number of surgeons perform this procedure on a routine basis. The long-term outcomes are being evaluated.
In general, for an isolated meniscal repair:
- Full weight bearing is not permitted for 1 – 6 weeks after surgery, depending on the type of injury and repair.
- Many surgeons brace the knee and restrict motion for 6 weeks, to prevent excessive flexion and extension.
- Range of motion exercises begin anywhere from 0 – 6 weeks after surgery, depending on the type of repair.
- Strengthening exercises begin once full range of motion has returned.
- Return to vigorous activities, such as sports, may begin 3 – 4 months after repair. Persistent pain, mechanical symptoms, or stiffness after meniscal repair may indicate the need for further treatment. If the meniscus does not heal, its revision or removal may be necessary
- Injury of the meniscus accounts for one of the most frequent traumatic afflictions of the knee joint.
- Meniscus tears occur in either the horizontal or vertical direction, or a combination of both.
- A meniscus tear requires a blood supply to heal which is present only in the peripheral third of the meniscus.
- Indications for repair mainly depend on location of the lesion and stability of the knee.
- Meniscal repair in the ACL deficient knee results in poorer results.
- Different arthroscopic techniques can be divided into three main groups: Inside-out; Outside in and all inside.
- Rehabilitation after meniscal repair depends on the size of the tear, stability of the repair, and other injuries.
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