Meniscus Transplantation: Diagnosis, Operative Techniques, and Clinical Outcomes

Chondroprotective Effects

The overall goal of meniscus transplantation is to protect the articular cartilage from subsequent deterioration. To date, few experimental investigations have been conducted on large animal models to determine the ability of a transplant to provide chondroprotective effects. Szomor and associates conducted a study in which medial meniscectomy, medial meniscus autografts, and medial meniscus allografts were performed in 24 sheep. The grafts were placed into the anatomic anterior and posterior horn attachment sites and secured to the tibial plateau with three suture anchors. At 16 postoperative weeks, both the allograft and autograft knees demonstrated a 34% to 40% reduction in the score for macroscopic damage to the articular cartilage and an approximate 50% reduction in the area of damage to the articular cartilage compared with the meniscectomized knees. However, neither of the grafts provided complete protection, which the investigators hypothesized could have been caused by nonisometric positioning and tensioning and graft fixation. Histologic analysis revealed that the allografts had fibrinoid degeneration, areas of hypocellularity, and cloning of meniscus cells.

Kelly and colleagues developed a meniscus allograft surgical technique that attempted to restore the anatomic anterior tibial and posterior femoral meniscal attachments in a sheep model. Fixation of the allografts was accomplished through bone tunnels. Lateral meniscus allografts were implanted into 17 animals, and lateral meniscectomies were performed in 24 animals. Gross inspection, histologic analysis, biomechanic testing, MRI, and T2 mapping of the central weight-bearing portion of the lateral tibial plateau performed 2 and 4 months postoperatively demonstrated protective effects of the allografts. Significantly decreased cartilage wear and increased cartilage stiffness were found in the allografted joints compared with the meniscectomized knees. However, at 4 months after surgery, the allografted knees had significantly worse values for these outcome measures than the intact knees. The authors noted the successful use of MRI with T2 mapping to detect early articular cartilage degeneration.

Knee Joint Contact Mechanics After Meniscus Transplantation

Alhalki and coworkers measured the maximum pressure, mean pressure, and contact area of the medial tibial articular surface after medial meniscectomy and implantation of ipsilateral medial meniscus autografts and cryopreserved allografts in 10 cadaveric knees (mean age, 70 years). The autografts and allografts were implanted using bone plug fixation through anterior and posterior horn transtibial tunnels. The allografts significantly reduced normalized maximum and mean contact pressures by 75% compared with meniscectomized knees. In addition, the maximum pressure was restricted to a small region of the contact area. The authors hypothesized that a reduction of this magnitude could mitigate the rate of cartilage wear compared with that in a meniscectomized knee. However, the allografts did not restore normal contact mechanics and demonstrated greater variability in normalized maximum and mean contact pressures than the autografts. The authors concluded that the variability in contact mechanics could have been caused by poor matching of the 3-dimensional geometry of the allograft to the recipient knee. Dimensions for the allograft were matched from standard anteroposterior (AP) and lateral radiographs in the transverse plane. Studies by Paletta and associates and Haut and colleagues revealed that measurements made in the transverse plane only weakly predict the cross-sectional shape of the meniscus.

The effect of the size of lateral meniscus allografts (in comparison with native menisci) on tibial plateau contact mechanics was investigated by Dienst and coworkers. Allografts that were 17.5% larger than native menisci had significantly greater contact forces across the articular cartilage. Allografts sized 10% smaller than native menisci resulted in increased forces across the meniscal tissue, which the authors hypothesized could cause early transplant failure. The authors concluded that the surgeon should select lateral meniscus transplants (LMT) that are slightly larger than native menisci (rather than smaller) to reduce the risk of early failure.

Paletta and associates investigated the effects of lateral meniscectomy, cryopreserved lateral meniscus transplantation with bone plug fixation, and lateral meniscus transplantation without fixation of the anterior and posterior horn attachments. The study involved 10 cadaver knees less than 48 years of age. The lateral meniscal transplants increased total contact area from 42% to 65% compared with meniscectomized knees at all flexion angles (0, 30, and 60 degrees), However, there remained a residual 17% to 23% decrease in contact area compared with intact knees. Release of the horn attachments resulted in a contact area that was identical to meniscectomized specimens. McDermott and associates assessed the effects of lateral meniscal transplantation with and without bone block fixation in eight cadaver knees. These investigators reported no difference between the two methods in peak contact pressures compared with intact knees. The cadaver specimens used in the study were ages 81 to 98 years, and all had moderate to severe degenerative changes. In addition, no formal size matching was performed with the allografts and recipient knees.

Effect of Fixation and Location of Meniscus Transplants

The method of fixation of meniscus transplants to the surrounding tissues is believed to be paramount in subsequent load-bearing function and chondroprotective effects. The goal is to reproduce the normal attachment sites, allowing lateral and medial transplants to remain in their anatomic locations and move normally throughout knee motion. The use of a transplant with bone for fixation incorporated with either a central bone bridge or a two-tunnel technique (as described later in this chapter) is, in our opinion, required to obtain these goals. Soft tissue meniscus transplants, without bone fixation, are not recommended. Although soft tissue transplants are far easier to prepare and implant surgically, scientific data are inadequate to support that the soft tissue ends of the meniscus implant will heal and provide the circumferential tension in the meniscus that is required for function ( Fig. 24-1 ).

The importance of securing the anterior and posterior horns of an LMT was documented by Chen and colleagues, who investigated a variety of surgical methods for meniscus implantation. Using an autograft cadaver model, the study revealed that a transplant that had either a bony bridge or bone plug fixation of both horns produced contact area, peak contact pressure, and average central pressure results similar to those of an intact meniscus. Procedures in which either only one horn was secured or neither horn was secured demonstrated a loss of mechanical function and subsequent expected benefit from the transplant.

Alhalki and coworkers compared three fixation methods of medial meniscus autografts in cadaver knees to determine which method restored tibial contact mechanics closest to normal. The experimental design tested bone plug fixation alone, bone plug fixation combined with peripheral suturing of the transplant to the native rim, and suturing of the horns through bone tunnels combined with peripheral suturing of the transplant to the native rim. The study revealed that bone plug fixation produced contact mechanics closest to normal; however, the maximum pressure was significantly greater than that in the intact knee. There was no benefit in adding peripheral sutures to the bone plug fixation model. Importantly, fixation with sutures only did not restore normal contact mechanics and was not recommended by the investigators.

Verma and associates measured medial compartment peak pressure, mean pressure, and contact area in eight cadaver knees to determine whether a difference existed between medial meniscus transplants (MMTs) implanted with a bone plug technique and those with a bone trough technique. The data indicated no difference between the two techniques for all three variables, which were restored to values similar to those measured in the intact knees. The authors cited clinical advantages with the trough technique for both medial and lateral meniscus transplantation.

The effect of variations in placement of the posterior horn attachment of an MMT were investigated by Sekaran and colleagues. Using a cadaver autograft model, the posterior horn tunnel was placed either in its anatomic position or 5 mm posterior to the anatomic location. The study showed that placing the posterior horn tunnel 5 mm medial to its anatomic position caused an increase in normalized maximum pressure, a posterior shift in the location of the center of the contact area, and an increase in the normalized mean pressure. Placing the posterior horn tunnel 5 mm posterior was not as detrimental; however, this location resulted in a significant shift in the centroid of contact area. The authors concluded that surgeons should place the posterior horn tunnel as close to its anatomic position as possible, with a tolerance limit of less than 5 mm medial and 5 mm posterior to this location.