Chapter 5 Osteochondral Mosaicplasty

László Hangod, Gábor Vásárhelyi, László Rudolf Hangody

Introduction

Full-thickness defects of weight-bearing articular surfaces have poor healing capacity and cause pain, effusion, and impaired joint function. Fibrocartilage-type repair promoted by different marrow stimulation techniques has limited value because of moderate biomechanical features of the regenerative tissue. Cell therapies—such as autologous chondrocyte implantation—and osteochondral transfer techniques aim to create more durable hyaline cartilage surface in the defected area. Transplantation of autologous osteochondral blocks has been used for several decades and results in long-lasting survival of the transplanted hyaline cartilage. However, this technique had only limited practical value because of missing proper donor areas and congruency problems. Mosaicplasty is a recent modification of osteochondral transplantation using several small osteochondral cylinders instead of one big block of bone and cartilage tissue. By linear graft harvest from the less weight-bearing periphery of the trochlea donor site, availability can be managed and a mosaic-like implantation technique can provide proper contouring in the defected area. After preclinical experimental work, mosaicplasty was introduced into the clinical practice on February 6, 1992.

Surgical Principles and Objective

Step 1. Arthroscopic examination is performed to determine size, type, and exact site of the defected area as well as other intraarticular conditions. Depending on size and location, an arthroscopic or miniarthrotomy procedure can be determined.

Step 2. Preparation of defect site is done by sharp curettage and abrasion arthroplasty.

Step 3. Graft harvest is performed by tubular harvesting chisel from the less weight-bearing periphery of the femoral condyles above the level of sulcus terminalis.

Step 4. Mosaic-like implantation of the grafts is applied into drilled tunnels to cover the defect.

Goal. Repair of defected surface by composite cartilage layer consisting of transplanted hyaline cartilage and smaller amount of fibrocartilage created by previous abrasion arthroplasty. Average content of hyaline cartilage in the composite tissue is about 80%.

Advantages

• Durable gliding surface in the defected area

• One-step procedure

• Minimal surgical costs

• Relatively short rehabilitation

Disadvantages

• Application is limited by donor site access (1.0 to 4.0 cm²)

• Possible donor site morbidity

• Healing of graft ⇔ host tissue interfaces is not always optimal

• Technical difficulties

Indications

• Symptomatic, focal chondral or shallow osteochondral defects of the weight-bearing articular surfaces. Optimal outcome can be achieved at 1.0 to 2.5 cm² defect size, but indication can be extended until 4.0 cm². Smaller femoral condylar defects can be treated arthroscopically, whereas bigger defects and patellofemoral, tibial damages require a miniarthrotomy approach.

• The best outcome can be achieved at femoral condylar defects. Tibial results are slightly decreased, whereas patellofemoral implantations have moderate long-term success.

• Underlying biomechanical problems should be clarified and addressed by concomitant procedures such as anterior cruciate ligament (ACL) reconstruction, high tibial osteotomy, and meniscus surgery.

• Age should be under 50 to 55 years.

Contraindications

• Osteoarthritis or advanced degenerative changes

• Tumor, metabolic, or synovial diseases

• Osteoporosis

• Instabilities or malalignments (these biomechanical issues should be corrected during the same surgery or before the mosaicplasty)

• Limited range of motion (ROM)—less than 120-degree knee flexion

Patient Information

• Depending on biomechanical status, concomitant procedures may be necessary parallel with the mosaicplasty (ACL reconstruction, high tibial osteotomy, meniscus surgery, etc.).

• There may be altered weight-bearing status and limited walking ability in early postoperative period. Possible donor site discomfort may occur.

• Common surgical risks include intraarticular hemorrhage, wound-healing problems, septic complications, and thromboembolism.

Preoperative Workup

• Standard weight-bearing radiographs in two planes (AP should be a long radiograph to determine the exact axis). Magnetic resonance imaging (MRI) is needed. Gadolinium enhanced magnetic resonance imaging can be useful.

• Single shot antibiotics before the inflation of tourniquet is recommended.

• Proper thrombosis prophylaxis is advised for 6 weeks after the surgery (Clexane 60 mg/day sc.).

Surgical Instruments

A standard arthroscopy set is required, including a leg holder. A low-speed powered drill is also necessary. Several companies provide high-level instrumentation for cylindrical osteochondral transfer. The senior author developed an instrumentation that offers special advantages for multiple graft transplantation (MosaicPlasty Complete System, Smith & Nephew, Inc., Andover, Mass).

This instrumentation provides five different diameters, from 2.7 mm to 8.5 mm, and supports an arthroscopic technique as well. Beside these reusable instruments disposable chisels, drill bits, and tamps are also available to provide ideal conditions for precise graft harvest and tunnel preparation (Dispoposplasty System, Smith & Nephew, Inc., Andover, Mass). A fluid management system may support the procedure.

Anesthesia and Positioning

For arthroscopic or open mosaicplasty, regional, spinal, or general anesthesia is need. The use of tourniquet is highly recommended. The procedure should be performed in supine position allowing 120-degree flexion during the surgery.

Surgical Technique)

The following explanations relate to the figures identified.

Step 1

An arthroscopy is performed to examine the intraarticular conditions. The type, site, and size of the defect is determined, and the quality of other chondral surfaces as well as donor site availability are checked (Fig. 5-1).

FIGURE 5-1 Determination of perpendicular approach to the defect.

Choosing a procedure (arthroscopic or miniarthrotomy) depends on the type, size, and exact location of the defect determined during arthroscopy.

As placing the grafts perpendicular to the surface is paramount to the success of the operation, the first task is to determine whether an arthroscopic or open procedure is required.

Patellotrochlear and tibial lesions always require an open procedure.

Most of the femoral condylar defects can be managed arthroscopically. Take care in making the viewing and working portals.

Use a 1.2-mm K-wire or 18-gauge spinal needle initially to locate the portal sites.

Step 2

Use a full-radius resector or curette and a knife blade to bring the edges of the defect back to good hyaline cartilage at a right angle (Fig. 5-2).

FIGURE 5-2 Abrasion arthroplasty of the subchondral bone.

Clean the base of the lesion with an arthroscopic burr or half-round rasp to viable subchondral bone. Abrasion arthroplasty of the defect site promotes fibrocartilage grouting from the bony base.

Step 3

Because tapping the cutting edge of the guide into the bony base and removing it can mark the defect site, use the drill guide to determine the number and size (2.7, 3.5, 4.5, 6.5, and 8.5 mm in diameter) of grafts needed (Fig. 5-3).

FIGURE 5-3 Planning the optimal filling.

Step 4

Filling of the defect by same-sized contacting rings allows a filling rate of about 70% to 80%, but use of additional sizes to cover the dead spaces and cutting the grafts into each other can improve the coverage up to 90% to 100% (Fig. 5-4).

FIGURE 5-4 Maximal filling by overlapping grafts.

This way of filling is technically more demanding and requires more graft harvest. Finally, measure the depth of the defect with the laser marks of the dilator.

Step 5

The medial femoral condyle periphery of the patellofemoral joint above the line of the notch is the most preferred harvest site (Fig. 5-5).

FIGURE 5-5 Graft harvest by tubular chisel from the medial periphery of the patellofemoral joint.

The lateral femoral condyle above the sulcus terminalis and, in exceptional cases, the notch area can serve as additional donor areas.

Grafts harvested from the notch area have less favorable features because they have concave cartilage caps and less elastic underlying bone.

In case of arthroscopic mosaicplasty, the medial patellofemoral periphery has easier access than the lateral one as fluid distension can promote lateral positioning of the patella and may provide easier perpendicular positioning for the harvesting chisel.

The best view for harvesting grafts is obtained by introducing the scope through the standard contralateral portal. Extend the knee and use the standard ipsilateral portal to check the perpendicular access to the donor site. Extended position should provide perpendicular access to the most superior donor hole. Gradual flexion allows the harvest of additional grafts from the lower portions of the patellofemoral periphery. If the standard portals do not allow a perpendicular approach, use a spinal needle or a K-wire to determine the location of additional harvesting portals.

Once the necessary portal has been determined, introduce the proper-sized tube chisel filled with the appropriate harvesting tamp.

Once the site has been clearly identified, the chisel is located perpendicular to the articular surface and driven by a hammer to the appropriate depth.

The minimal length of the graft should be at least two times its diameter, but, as a rule, take 15-mm-long grafts to resurface chondral lesions and 25-mm-long plugs for osteochondral defects.

It is important to hold the chisel firmly to avoid its shifting at the cartilage–bone interface, producing a crooked graft. By flexing the knee, lower sites can be obtained. The lower limit is the level of the top of the intercondylar notch (sulcus terminalis). Insert the appropriate harvesting tamp into the cross-hole in the tubular chisel and use it as a lever. The chisel should be toggled, not rotated, causing the graft to break free at the chisel tip. Eject the grafts from the chisel by sliding the appropriately sized chisel guard over the cutting end. Use the tamp to push out the graft onto gauze in a saline-wetted basin.

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