Bone Plug versus Suture-Only Fixation of Medial Meniscus Allograft Transplants. Biomechanical study

Luiz Felipe Ambra1,2, Amy Phan2, Jack Farr3, Andreas H. Gomoll2.1Universidade Federal de São Paulo, 2Brigham and Women’s Hospital, 3OrthoIndy Hospital

1511283-Ap.jpg1511283-Lateral.jpg

The objective of this study was to evaluate the contact load

characteristics of medial meniscus allograft transplantation

performed by bone-plug versus soft-tissue suture-only fixation

in cadaveric knees.

Our null hypothesis was that there would not be significant

differences between the two fixation groups with regard to load

contact pressures and distribution.

Objetivo

Material and Methods

Meniscal allograft transplantation is a suitable option to treat

meniscal insufficiency. Restoring anatomical reconstruction is

critical to recover the proper function of the meniscus in its

chondroprotective and stability role. In this regard, anatomic

positioning and fixation of the attachment sites are

appreciated to be of critical importance. For medial meniscus

transplant two different techniques has been describe: one two

bone plugs are routinely utilized, one for each meniscal root

is placed within bone tunnels in the anatomical footprint of

the medial meniscus. An alternative technique is to remove

the attachment of the meniscal root from bone graft and use

suture only fixation through drill holes in the tibia. There is

debate on whether the suture only fixation technique

reproduces the same rigidity in fixation as compared to the

bone plug technique.

Background

Table 1. Cadaveric informationKnees (N) 9

Side (left/right) 5 4

Gender (Male/Female) 5 4

Age (mean/±SD) [year] 46.9 2.2

Weight (mean/±SD) [Kg] 76.3 26.3

Height (mean/±SD) [m] 1.57 0.17

Study design: controlled laboratory study.

SpecimenWere used fresh-frozen human cadaveric knee. All the

specimens was evaluated using MRI and XR. Only cadaveric

specimens without evidence of significant degenerative

changes were included in the study.

Meniscal Sizing

Size- and side-matched medial meniscus allografts were

obtained based on XR measurements (Pollard method).

The mismatch between the meniscal allograft size and

radiographic measurement did no exceed 1mm.

Figure 1. Meniscal measurement by pollard method

The mismatch between the meniscal allograft size and

radiographic measurement did no exceed 1mm. Figure 2

demonstrated the a good match size between native meniscus

and the respective graft.

Figure 2. The meniscus native after meniscectomy (right), and respective meniscal allograft (left).

Testing Equipment

Compression force: • INSTRON 8871 servo-hydraulic testing system.

Contact pressure: • A Model 4011 I-Scan sensor (Tekscan Inc, Boston, Mass)

Bone-plug Fixation

Soft tissue only

Meniscal Transplantation preparation technique

Allograft medial meniscus were prepared by fashioning bone

plugs (10x10mm, wide x height) of the anterior and posterior

root attachments. Drill holes in the center of the bone plugs

were made with a 1.2mm drill bit. Heavy suture was run

through the bone plug and secured to the meniscal root in a

locking stitch configuration. The bone plugs were pulled in the

bone tunnels created in the anatomic location of the footprint of

the anterior and posterior horn attachment to the tibia. The

suture were tied over a bone bridge in the anterior tibia. The

meniscal horns and body will be sutured using vertical

mattresses and tied over the capsule

The meniscal horns were detached from the bone plugs,

preserving the suture which were pulled from the bone plug

prior to detachment. The bone plugs were secured in the bone

tunnels with bone cement. The suture attached to the

posterior and anterior horns were pulled through the drill

holes and the suture tied over the anterior tibia. The meniscal

horns and body were sutured using vertical mattresses and

tied over the capsule

The tibia and femur were individually potted in methyl

methacrylate cement. Then the knee was fixed into an

Instron with the tibiofemoral joint surface oriented parallel to

the floor. The knee was constrained but allowing for varus/

valgus angulations.

Contact sensor was inserted underneath the meniscus from

anterior to posterior with minimal disruption of the

meniscocapsular attachments.

Figure 3: Cadaveric knee fixed to the testing apparatus

All the specimens was tested in the following sequence:

Native Meniscec-tomized

Bone-plug

Suture-only

Testing protocol:

• Axial Load: 700N

• Knee Flexion: 0, 30 and 60 degrees.

Results

Data Acquisition

• Mean contact stress on the medial compartment (Mpa)

• Peak contact stress on the medial compartment (Mpa)

• Contact area on the medial compartment (mm2)

The results of mean and peak contact stress and contact area

were compared between intact, meniscectomized, MAT-bone

and MAT-suture using analysis of variance (Dunn test). The

level of significance was set at p ≤ 0.05.

0

100

200

300

400

500

600

0degrees 30degrees 60degrees

[mm

2 ]

ContactArea

Normal Menicectomized Bone-plug Suture-only

**

** *

Meniscectomy significantly increased mean contact pressure

and the contact area was significant reduced in comparison

with the native condition at 0, 30 and 60 degrees (p<0.0001).

Although the peak contact pressure was higher in the

meniscectomy group, it was not statistically significant. Suture

only resulted in higher contact pressure and smaller contact

area than bone plug fixation and native condition. The

difference was statistically significant in 0 and 30 degrees of

flexion. Regardless of technique, no significant differences

were found between transplanted meniscus and native

condition in 60 degrees of flexion.

The following graphs shows the mean contact area, mean

contact pressure and mean peak pressure in each group in 0, 30

and 60 degrees of flexion.

0

0.5

1

1.5

2

2.5

3

3.5

4

0degrees 30degrees 60degrees

[Mpa]

MeanContactPressure

Normal Menicectomized Bone-plug Suture-only

0

1

2

3

4

5

6

7

8

0degrees 30degrees 60degrees

[Mpa]

MeanPeakContactPressure

Normal Menicectomized Bone-plug Suture-only

*

**

* *

*Difference statistically significant (p<0.05) in comparison with native condition.

Native Menisectomized Bone-plug Suture-only

Figure 4: Contact pressure maps on the medial tibia plateau for a typical knee under different meniscal conditions at 0 degrees of flexion.

Conclusion

This study demonstrated that meniscal allograft transplantation

can restore load parameters close to the native condition. Bone-

plug technique has demonstrated improved femorotibial

contact pressure than isolate soft-tissue fixation. This study is

unique in utilizing size-matched meniscal transplants and using

the same transplant for bone plug and suture-only fixation, thus

reducing confounding factors.