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Both menisci are C-shaped and at-tach to the tibia via bony atat-tach- attach-ments to the tibial plateau; a discoid variant of the lateral meniscus is found in 3.5% to 5% of patients.6

Abstract

Meniscal allograft transplantation is a reasonable treatment option for the young patient with symptomatic meniscal deficiency Although clinical results are promising, in most studies only mixed procedures have been performed, with short- or medium-term follow-up Important potential prognostic factors include patient selection, severity of degenerative changes, limb stability and alignment, graft sizing and processing methods, graft placement, and graft fixation The use of meniscal allograft transplantation should be considered a salvage operation for the difficult clinical dilemma of meniscal deficiency in young patients Nonetheless, in carefully selected patients, this procedure can predictably relieve compartmental symptoms, and, in conjunction with anterior cruciate ligament reconstruction, restore knee stability In addition, the partial restoration of meniscal function provided by this procedure may slow the degenerative arthritic process

Injury to the menisci of the knee can lead to alteration in the stabil-ity and biomechanics of involved joints Meniscal injuries may alter the transmission of loads across the knee joint or may destabilize the knee, especially when injuries are sustained in conjunction with ante-rior cruciate ligament (ACL) injury

Such injuries may lead to clinical and radiographic articular cartilage changes Meniscus repair or partial meniscectomy are common proce-dures that attempt to preserve me-niscal functions, which include load transmission, proprioception, joint lubrication, and stability However, with large tears that require partial

or total meniscal excision, preserva-tion of the meniscus sometimes is impossible Meniscal deficiency may in turn lead to progressive dete-rioration of the articular cartilage, with resultant radiographic joint space narrowing

Meniscal allograft transplanta-tion is a surgical optransplanta-tion for select pa-tients with symptomatic meniscal deficiency Often this deficiency is addressed in conjunction with con-comitant injuries, the most common being tears of the ACL A number of basic science as well as clinical stud-ies have helped clarify the role of the variables that may contribute to suc-cessful meniscal transplantation These factors include patient selec-tion, surgical technique, graft sizing and preservation, graft fixation, and graft placement

Anatomy and Function

The menisci are fibrocartilaginous structures consisting of coarse carti-lage bundles circumferentially ar-ranged to disperse compressive load and radially resist shear.1Water ac-counts for 70% of meniscal compo-sition; collagen (90% of it type I)

Jon K Sekiya, MD

Christopher I Ellingson, MD

Dr Sekiya is Assistant Professor,

University of Pittsburgh Medical Center,

Center for Sports Medicine, Pittsburgh,

PA Dr Ellingson is Lieutenant

Commander, Medical Corps, United

States Navy, Bone and Joint/Sports

Medicine Institute, Department of

Orthopaedic Surgery, Naval Medical

Center Portsmouth, Portsmouth, VA.

The views expressed in this article are

those of the authors and do not reflect

the official policy or position of the

Department of the Navy, Department of

Defense, or the United States

Government.

None of the following authors or the

departments with which they are

affiliated has received anything of value

from or owns stock in a commercial

company or institution related directly or

indirectly to the subject of this article:

Dr Sekiya and Dr Ellingson.

Reprint requests: Dr Sekiya, University

of Pittsburgh Medical Center, Center for

Sports Medicine, 3200 S Water Street,

Pittsburgh, PA 15203.

J Am Acad Orthop Surg

2006;14:164-174

Copyright 2006 by the American

Academy of Orthopaedic Surgeons.

makes up 60% to 70% of the dry

weight.2 Trapped by negatively

charged glycosaminoglycans, water

in the menisci provides resistance to

compressive loads, and two types of

fibrochondrocytes synthesize the

fi-brocartilaginous matrix At birth,

the entire meniscus is vascular, but

by adulthood, only the outer 10% to

30% of vascularity remains, with

blood supplied via the perimeniscal

capillary plexus off the superior and

inferior medial and lateral genicular

arteries.3,4Postulated to have

mech-anoreceptive proprioceptive

func-tion,5type I and II nerve endings are

found at the horn insertions in the

outer portions

Both menisci are C-shaped and

at-tach to the tibia via bony atat-tach-

attach-ments to the tibial plateau; a discoid

variant of the lateral meniscus is

found in 3.5% to 5% of patients.6

The surface area of the anterior

tib-ial bony attachment of the medtib-ial

meniscus is 61 mm2; the posterior

attachment is anterior to the

inser-tion of the posterior cruciate

liga-ment.7Covering a larger portion of

the tibial articular surface, the

later-al meniscus is semicircular, with the

anterior horn attaching adjacent to

the ACL and the posterior horn

at-taching behind the intracondylar

eminence.3With knee flexion,

aver-age excursions of the menisci are

5.2 mm for the medial and 11 mm

for the lateral.8

A primary function of the menisci

is load sharing, which is

accom-plished through improving knee

con-gruency and increasing joint contact

area The medial and lateral menisci

transmit 50% and 70% of their

com-partmental loads, respectively

Me-dial meniscectomy decreases contact

area 50% to 70% and increases

con-tact stress 100%,3 whereas lateral

meniscectomy decreases contact area

40% to 50% but dramatically

in-creases contact stress 200% to 300%

secondary to the relative convex

sur-face of the medial tibial plateau.3

Another function of the menisci

involves their viscoelastic

proper-ties, which aid in shock absorption;

meniscectomy has been reported to decrease the shock absorption capa-bilities of the knee by 20%.9 The medial meniscus also acts as a sec-ondary restraint to anterior tibial translation in the ACL-deficient knee; therefore, medial

meniscecto-my in the ACL-deficient knee in-creases tibial translation by 58% at 90°.3The posterior horn of the

medi-al meniscus is especimedi-ally important

in contributing to joint stability.10

Meniscal Allograft Preservation

The four main methods of pre-serving allografts are fresh, cryopre-served, fresh-frozen (deep-frozen), and freeze-dried In accordance with standards established by The Amer-ican Association of Tissue Banks for donor suitability and testing,11 me-nisci are harvested under strict asep-tic conditions within 12 hours of cold ischemic time They may be harvested with or without bone plugs and a small synovial rim for atraumatic handling of the al-lograft.11The allografts are then pro-cessed according to the preservation method

Fresh grafts, maintained at 4°C in lactated Ringer solution, can be stored for up to 7 days only Such limited time for graft sizing and se-rologic testing presents logistical dif-ficulties and limits the use of fresh grafts in clinical practice Further, these grafts have not been shown to improve efficacy in vivo

Cryopreserved allografts main-tain a cell viability of 10% to 40% by use of controlled freezing in a glycerol-containing medium (ie, cryoprotectant) The expense and difficulty of this technique has lim-ited its use, especially given the un-certainty of donor-cell viability Me-niscal allografts are invaded by host cells as early as 4 weeks after trans-plantation.12

Fresh-frozen allograft preserva-tion, in which allografts are stored at approximately −80°C, is a simpler

and less expensive method than cryopreservation Although fresh-frozen allografts lack donor-cell via-bility, the lack of viability has not af-fected allograft survival and meniscal transplant outcomes The use and demand for fresh-frozen me-niscal allografts is increasing Freeze-drying (lyophilization) in-volves the dehydration of allografts during freezing in a vacuum The al-lografts are then thawed and rehy-drated before transplantation Al-though this method allows for indefinite storage, it also produces alterations in the biomechanical properties and the size of the al-lografts Today, freeze-drying has fallen out of use and is not recom-mended

Means for secondary sterilization

of allografts are available but also are not recommended; two examples are ethylene oxide and gamma irradia-tion The use of ethylene oxide has been linked to soft-tissue synovitis caused by its by-products.13 Expo-sure to >2.5 mRad of gamma radia-tion negatively affects the mechani-cal properties of collagen-containing tissues.14Because >3 mRad of

gam-ma irradiation is needed to eliminate human immunodeficiency virus DNA in allograft tissue, the use of gamma irradiation in the steriliza-tion of meniscal allografts is not rec-ommended In addition, according to one series,15 poor clinical results may be associated with gamma irra-diation of the meniscal allograft Meniscal allografts are not type cross-matched with the recipient;16

therefore, occasionally an immune system inflammatory response oc-curs An immunologic study by Ro-deo et al17identified class I and II hu-man leukocyte antigens on frozen meniscal allografts The authors evaluated 28 meniscal allografts (25 patients); all were deep frozen and nonirradiated Nine of ten samples that underwent immunohistochem-ical analysis contained immunoreac-tive cells, but no frank evidence of immunologic rejection was seen In

general, although histology scoring

was improved in menisci with no

immune response, there was no

dif-ference in clinical outcome between

the two groups However, the effect

of an immune system inflammatory

response is clinically unknown A

prospective study to evaluate the

lationship between inflammatory

re-sponse and meniscal allograft

rejec-tion or funcrejec-tion is warranted.16

Preclinical Evidence of

Meniscal Allograft Healing

Function

In vitro and animal model studies

have advanced the understanding of

meniscal function, allograft

selec-tion, and the technical

consider-ations of meniscal transplantation

In 14 cryopreserved medial meniscal

allografts performed in a canine

model, Arnoczky et al18showed that

grafts healed to the capsule by

fi-brovascular scar and retained their

normal gross appearance Histologic

examination at 3 months revealed

cellular distribution and metabolic

activity comparable with those of

controls

Medial meniscal transplantation

using autograft, fresh allograft, or

cryopreserved allograft were

com-pared in a goat model.19Evaluation

at 6 months revealed little

histolog-ic difference between implanted

me-nisci and controls In addition, the

allografts had nearly normal

periph-eral vascularity, although

transplant-ed menisci were reporttransplant-ed to have

slightly decreased proteoglycan

con-tent with increased water concon-tent

In another study, the use of a

vascu-larized synovial flap accelerated

re-vascularization of allograft menisci

in rabbits.20No significant difference

was found between cryopreserved

and fresh-frozen allografts in goats,

with nearly complete remodeling of

both types of allografts at 6 and 12

months.21

Using DNA analysis, Debeer et

al22reported the nearly complete

re-population of cryopreserved

menis-cal allograft tissue by host cells in

al-lograft remodeling in a human recipient 1 year after transplanta-tion

A cadaveric biomechanical study

on meniscal allografts demonstrated improved contact areas and de-creased contact pressures after

later-al meniscus later-allograft replacement.23

This study demonstrated the impor-tance of securing both the anterior and posterior horns of meniscal al-lografts With both horns released, contact pressures with allografts were equal to contact pressures in knees after total meniscectomy

Huang et al24 recently reinforced findings that show improved contact pressures in meniscectomized knees after meniscal transplantation

However, the efficacy of meniscal transplantation in slowing degener-ative changes has not consistently been demonstrated In a study of a rabbit model reported by Cummins

et al,25transplants performed imme-diately or at 3 months after medial meniscectomy showed a slowing in the progression of degenerative changes Regardless of the timing of transplantation, groups receiving a transplant had fewer degenerative changes compared with meniscecto-mized controls Yet Aagaard et al26

showed improved prevention of ar-ticular cartilage degeneration in sheep with meniscal allograft trans-plants performed immediately com-pared with 3 months after meniscec-tomy However, Rijk et al27found no significant difference with reference

to subsequent degeneration between meniscectomized rabbit knees and those undergoing immediate or de-layed (6 weeks) meniscal transplan-tation Similarly, using a sheep

mod-el, Edwards et al28 found no difference among total

meniscecto-my, meniscal autograft, or meniscal allograft groups with respect to de-generative changes seen at an aver-age of 21 months postoperatively

In another study, Rijk and Van Noorden29showed significantly (P≤ 0.005) more shrinkage in meniscal allografts implanted 6 weeks after

meniscectomy compared with those implanted immediately after menis-cectomy in a rabbit model Interest-ingly, the cellular content and his-tology of implanted menisci did not differ significantly between the two groups Experimental and clinical studies are needed to evaluate the ef-fect that shrinkage may have on long-term meniscal allograft proper-ties and function

Indications and Preoperative Evaluation

Surgery for the meniscus-deficient knee should be considered only after exhausting all nonsurgical measures Nonsurgical treatment of patients who have undergone menis-cectomy includes using unloading braces, encouraging nonimpact ac-tivities and exercises, and initiating pharmacologic measures When these therapies fail to provide relief

of symptoms or to prevent pro-gression of joint space narrowing, meniscal transplantation may be considered in select patients The exception to nonsurgical therapy may be concomitant ACL and medial meniscus deficiency with significant anteromedial rotatory instability In this situation, earlier intervention of an ACL combined with medial meniscal transplanta-tion may improve stability, ACL graft survival, and eventual clinical outcome.10,30-33

Meniscal transplantation is indi-cated in patients aged <40 years with

an absent or nonfunctioning menis-cus The upper limit is 50 years for patients who are highly active with only limited arthritis and who are not good candidates for arthroplasty These patients have pain localized to the affected compartment with activ-ities of daily living or sports, normal mechanical alignment, and Outer-bridge grade I or II articular changes Contraindications include knee in-stability or marked varus/valgus malalignment, unless these issues can be addressed concurrently Varus/valgus malalignment is

de-fined as asymmetry ≥2° to 4°

com-pared with the contralateral knee or

as the weight-bearing line on long-leg

alignment radiographs falling into

the affected meniscus-deficient

com-partment Additional

contraindica-tions to meniscal transplantation are

age >50 years, osteophytes indicating

bony architectural changes, or

Out-erbridge grade IV articular changes

(unless focal defects are addressed

concomitantly with osteochondral

allograft transplantation or

autolo-gous chondrocyte implantation)

Preoperative physical

examina-tion should include inspecexamina-tion of

stance, gait, and squat and of prior

incisions about the knee

Examina-tion includes joint-line palpaExamina-tion,

McMurray’s test, knee range of

mo-tion, presence of effusion, muscle

strength, and assessment of

ligamen-tous instability Radiographic

stud-ies include weight-bearing 45°

flex-ion posteroanterior, Merchant, and

non–weight-bearing lateral views

us-ing magnification markers Long-leg

alignment radiographs also should

be obtained in order to objectively

evaluate lower extremity

mechani-cal alignment Magnetic resonance

imaging (MRI) provides information

regarding the subchondral bone,

me-nisci, and hyaline cartilage When

previous arthroscopic images are

un-clear or are not available, diagnostic

arthroscopy can accurately define

the extent of meniscectomy and

de-gree of arthrosis

Although sizing and matching of

meniscal allografts to recipient

knees is critical, the tolerance of size

mismatch in knees undergoing

me-niscal transplantation is not known

Sizing of allografts is done using

MRI, computed tomography, or

plain radiographs, or by making

di-rect measurements In patients with

a prior meniscectomy, the

contralat-eral knee may be used for sizing In

a study measuring patient knees,

however, Johnson et al34 reported

variability in meniscal size between

opposite knees The consistent

rela-tionship between meniscal size and

landmarks in plain radiographs re-ported by Pollard et al35often is used

by tissue banks for allograft sizing

Although comparison of MRI scans

to plain radiographs showed that MRI is slightly more accurate at siz-ing allografts, only 35% of menisci measured with MRI came to within

2 mm of the actual size.36

Carpenter et al37compared MRI scans with computed tomography scans and plain radiographs for me-niscal allograft sizing and found that MRI consistently underestimated the anteroposterior and mediolateral sizes of both the medial and lateral menisci; however, MRI was more ac-curate in estimating meniscal height

The authors concluded that com-puted tomography and plain radiog-raphy are more useful in allograft siz-ing but that MRI measurements may improve as experience is gained

McDermott et al38measured the menisci in 22 pairs of cadaveric knees and found that the average medial and lateral meniscal lengths were 45.7 mm and 35.7 mm, respec-tively Additionally, the authors measured the meniscal circumfer-ence, meniscal body width, and overall meniscal width, then corre-lated these measurements with ra-diographic sizing of the tibial pla-teaus By using measurements of the length and width of the medial and lateral tibial plateaus, meniscal size was predicted with a mean error rate

of 5%.38

Huang et al39evaluated the cross-sectional parameters of lateral me-niscal allografts compared with na-tive lateral menisci in cadaveric knees and found increased contact pressures when allografts did not match native menisci The greatest predictor of differences in contact pressures was the difference found in the width of the menisci The au-thors therefore postulated that pro-tocols used to select allografts should focus on cross-sectional pa-rameters to match the native menis-cus, particularly width

Surgical Technique Isolated Meniscal Transplant Surgical Technique

Garrett40 initially used an open technique for medial meniscal trans-plantation, with takedown of the medial collateral ligament with a piece of bone off the medial femur The graft was placed under direct vi-sualization, and subsequent repair of the medial collateral ligament was performed with a screw and washer This technique is no longer used be-cause of the amount of soft-tissue trauma that occures to the medial stabilizing structures of the knee Once the patient is anesthetized, meniscal allograft transplantation begins with an examination to eval-uate range of motion and ligamen-tous instability.31,41-43Meniscal defi-ciency and the condition of the articular cartilage are determined ar-throscopically The involved menis-cus posterior horn and body are débrided to a 1- to 2-mm synovial rim, leaving a vascular source to aid

in graft healing Graft passage and fixation are achieved through a small medial or lateral parapatellar arthrotomy as well as an accessory posteromedial arthrotomy or pos-terolateral incision (for medial or lat-eral meniscal transplantation, re-spectively) (Figure 1) Lateral meniscus grafts are fashioned with a bone bridge, whereas medial grafts are fashioned with bone plugs (Fig-ure 2) Fixation of both horns is crit-ical for proper function23and can be accomplished through a two-bone plug technique,44 through a bone bridge in a trough41,42,45keyhole for the lateral meniscus, with no bone block,23,46,47 or with suture fixa-tion.48

For a medial transplantation, the anterior and posterior bone plugs are pulled into their respective tunnels placed at the native meniscal inser-tion sites For a lateral transplanta-tion, the bone bridge is placed into a bone trough at the anatomic

posi-tions of the anterior and posterior

horns of the lateral meniscus With

either technique, the bone fixation is

secured using a no 2 braided suture

Anatomic placement of meniscal

al-lografts is essential for proper

distri-bution of contact pressures Sekaran

et al49found that nonanatomic place-ment of medial meniscus posterior horn tunnels≥5 mm medially and

≥5 mm posteriorly caused a notable shift in the centroid of contact

pres-sure and increased contact prespres-sures Allograft fixation is then achieved

by suturing to the native meniscus rim with an inside-out technique, starting at the posterolateral or pos-teromedial corner to the midbody to establish position and fit A no 2-0 braided polyester suture on long nee-dles can be used for the inside-out ar-throscopic technique The anterior

to midbody meniscal allograft rim is fixed using a no 0 Ethibond (Ethi-con, Somerville, NJ) suture placed through the parapatellar arthrotomy

A femoral distractor on the affected knee compartment can assist with graft passage, arthroscopic visualiza-tion (especially of the posterior horn), and graft fixation (Figure 3) Additional techniques for lateral meniscal allograft transplantation include modifications to the bone-bridge-and-trough technique that ac-tually lock in the lateral meniscal al-lograft, thereby providing additional stability to the meniscal horn fixa-tion One popular method includes the keyhole technique,50which uses

a guide and drill to create a round bone trough that then narrows at the surface of the tibial plateau (Figure 4) This allows the bone bridge to

Figure 2

Medial meniscal allograft fashioned with bone plugs attached to the anterior (white arrow) and posterior (black arrow) horns Preplaced sutures are fixed to the posterior horn of the medial meniscal allograft (arrowhead) ACL = anterior cruciate ligament

Figure 3

A femoral distractor can assist with graft passage, posterior horn visualization, and

suture fixation

Figure 1

A,Medial meniscal allograft transplantation with anterior (large arrow) and posterior

(small arrow) bone plugs through transosseous tunnels A combination of

arthroscopically and open placed sutures fix the meniscal allograft to the peripheral

rim B, Lateral meniscal allograft transplantation using a bone bridge The bone

bridge is secured in the tibial trough (large arrow) using transosseous sutures (small

arrow) A combination of arthroscopically and open placed sutures fix the meniscal

allograft to the peripheral rim

lock into the tibial bone trough,

pro-viding additional stability to the

construct Other similar methods

exist, including the “dovetail”

tech-nique Although suture fixation

at-tached to bone plugs or a bone bridge

is usually sufficient for a secure graft

healing, clinically these techniques

offer additional methods for

menis-cal horn fixation stability

Others have recommended suture

attachment without bone for

menis-cal allograft anterior and posterior

horn fixation.48This technique uses

a circumferential osseocancellous

trough combined with transosseous

tibial tunnel fixation of the meniscal

allograft horns (Figure 5)

Recently, the popularity of the

bone-bridge-and-trough technique

has been expanded for use in medial

meniscal allografts Preserving the

circumferential hoop stresses and

se-cure fixation of the anterior and

pos-terior horns of the meniscal allograft

are attractive reasons for using this

technique; however, we caution

against its use because of the

poten-tial for problems resulting from the position of the medial meniscus pos-terior horn, which is directly in line behind the ACL tibial attachment34

(Figure 6) To position this trough without disrupting the ACL attach-ment, the tendency may be to medi-alize the bone trough location,

there-by altering movement of the anatomic location of the posterior and/or anterior horn attachments

This nonanatomic positioning may then significantly alter the biome-chanical properties of the

transplant-ed meniscus.49 However, this may not be a serious issue in the patient undergoing a combined medial me-niscus transplant and ACL recon-struction, which allows the ACL tunnel to be drilled following ana-tomic bone bridge placement

Combined Meniscal Transplantation With Anterior Cruciate Ligament Reconstruction

Meniscal transplantation com-bined with ACL reconstruction is

performed in knees with ACL insuf-ficiency and symptomatic meniscal deficiency Standard femoral and tib-ial tunnels are drilled and prepared before meniscal allograft insertion, and the procedure is performed as previously described.30,31,41,42The use

of patellar tendon allograft decreases associated donor-site morbidity in this complex knee reconstruction Tibial tunnel drilling requires special care because this tunnel often en-croaches on the bone trough for the meniscus.41To circumvent this prob-lem, the ACL graft passage and fem-oral fixation should be done before placing the lateral meniscal allograft

Figure 4

Keyhole technique for lateral meniscal allograft transplantation A, Lateral meniscal

allograft fashioned using the keyhole technique Note that the deeper portion of the

bone bridge (large arrow) for the meniscal allograft is fashioned larger than the

superficial portion (small arrow), which is matched to the corresponding recipient in

the lateral tibia (B) This allows the lateral meniscal allograft to “lock” into the tibial

attachment (Panel A adapted with permission from Cryolife, Marietta, GA.)

Figure 5

Osseocancellous trough technique for meniscal allograft fixation The circumferential trough is created medially on the peripheral tibial plateau and on the anterior and posterior horn meniscal attachments using an arthroscopic shaver The anterior and posterior horns of the meniscal allograft are secured to their attachments using transosseous suture fixation and arthroscopically placed inside-out sutures around the peripheral rim (Adapted with permission from Boss A, Klimkiewicz J, Fu FH: Technical innovation: Creation of a peripheral vascularized trough to enhance healing

in cryopreserved meniscal allograft

reconstruction Knee Surg Sports

Traumatol Arthrosc 2000;8:159-162.)

bone bridge The meniscal allograft is

then fixed, as previously described

For medial meniscal allograft

trans-plantation, placement and drilling of

the posterior bone plug tunnel is

fa-cilitated by passing the ACL graft

af-ter the meniscal allograft is secured

In both the medial and lateral

lograft procedures, tibial ACL

al-lograft fixation is performed after

me-niscal allograft placement and

fixation

Postoperative Care

There is no clear consensus

concern-ing rehabilitation protocols for

pa-tients who have undergone meniscal

allograft transplantation; this is a

re-sult, in part, of the lack of scientific

studies on the topic In general,

weight-bearing and range-of-motion

limitations typically are imposed in

a fashion similar to that of a major

meniscal repair, until meniscal

al-lograft healing has occurred (usually

by 8 to 12 weeks) (Figure 7) A

con-comitant ACL reconstruction, when

performed, also affects the

rehabili-tation protocol, with motion empha-sized to prevent arthrofibrosis.51Full hyperextension symmetrical to the contralateral normal extremity typ-ically is the goal in the first few weeks Full weight bearing and flex-ion beyond 90° usually is allowed af-ter 6 to 12 weeks postoperatively

Vigorous, high-impact activities gen-erally are discouraged indefinitely

Fritz et al52 protect meniscal transplants for the first 4 weeks us-ing a hus-inged range-of-motion brace

at 0 to 90° Kohn et al51 use pro-longed epidural anesthesia to facili-tate postoperative continuous pas-sive motion until 0 to 90° is achieved Fritz et al52allow patients

to partially bear weight for the first week, with the brace locked in full extension to avoid shear, whereas Kohn et al51 keep patients non–

weight bearing for 3 weeks Both groups advance weight bearing and discontinue crutches at 4 to 6 weeks for cases in which the patient has 90° to 100° of knee flexion, full knee extension, and minimal or absent swelling, and is able to walk without

a bent-knee gait At 6 weeks, closed chain exercises are started at 0 to 45°, progressing to 75° Patients may return to sedentary work at 1 week, strenuous work at 3 to 4 months, low-impact exercises at 8 weeks, and running after 4 to 5 months Al-though light or moderate sports are allowed at 6 to 9 months, strenuous sports are not recommended

Results

Milachowski et al53 performed the first isolated meniscal allograft transplant in 1984; the authors re-ported the results of 6 fresh-frozen (deep-frozen) and 16 freeze-dried al-lografts in 20 patients with a 14-month follow-up evaluation, includ-ing a second-look arthroscopy (Table 1, available at http:// jaaos.org/cgi/content/full/14/3/164/ DC1) Although fresh-frozen al-lografts were more likely to have an improved clinical appearance, both graft types showed a decrease in size, and neither showed signs of inflam-mation or rejection Reaction at the synovial joint was more pronounced

in the lyophilized group, as was graft shrinkage The authors concluded that, overall, the fresh-frozen lografts showed better results, al-though the failure rates were compa-rable between the two groups Garrett40presented results in 43 patients with a 2- to 7-year fol-low-up Secondary procedures were performed in most of the patients, with 24 concomitant ACL recon-structions, 13 osteotomies, and 11 osteochondral allografts Sixteen fresh and 27 cryopreserved grafts were used Second-look arthroscopy was performed in 28 patients, with

20 grafts found to be intact The main factor in failure was the degree

of arthritis in the knees Two fail-ures occurred in 32 patients with Outerbridge grade III chondromala-cia; 6 failures occurred in 11 patients with grade IV chondromalacia Graft type did not appear to affect outcome

Figure 6

Anterior cruciate ligament insertion site (colored with ink) is in line with the medial

meniscus anterior and posterior horns A, Medial meniscus allograft flipped over

laterally showing the medial extent of the anterior and posterior meniscus

attachments B, Medial meniscus allograft left in situ showing the lateral extent of

the anterior and posterior meniscus attachments

van Arkel and de Boer,54in 1995,

reported the results of 23

cryopre-served allografts at 2- to 5-year

follow-up There were 20 clinical

successes and 3 failures requiring

graft removal The authors

consid-ered the failures to be secondary to

uncorrected alignment No immune

response was noted in the failures

Cameron and Saha55 performed

allograft transplantation of 67

fresh-frozen irradiated grafts in 63

pa-tients Osteotomies were performed

in 34 patients; the average medial

compartment varus was 7.1°, and

average lateral compartment valgus,

5.9° Mean follow-up was 31

months, and the success rate using

the Lysholm knee rating scale was

87% The authors emphasized that

limb alignment is important in the

outcome of meniscal

transplanta-tions and recommended the need for

further research to determine

whether the meniscal allograft or

re-alignment procedure was more

im-portant in achieving pain relief In

eight patients who had had prior

un-successful realignment procedures,

insertion of the meniscal allograft

resulted in one excellent, four very

good, and three good results A

pro-spective study comparing

realign-ment with and without meniscal

al-lograft would help determine

whether it was the realignment

with or without the meniscal

trans-plant, or both, that was responsible

for improved outcomes

Carter56 had favorable outcomes

in 45 of 46 patients evaluated at an

average of 2.9 years Three grafts

par-tially failed, and one graft

complete-ly failed, requiring three partial

meniscectomies and one total

me-niscectomy These failures were

at-tributed to patient selection in two

cases, technical error in one, and

noncompliance in one

Internation-al Knee Documentation Committee

(IKDC) scores revealed that all but

the patient with complete graft

fail-ure had improvement in pain

Second-look arthroscopy in 38

pa-tients showed healing at the

menis-cal capsular repair site MRI was not useful in evaluating graft integrity because no correlation was found be-tween abnormal signal intensity and second-look arthroscopies that re-vealed no abnormalities

Noyes and Barber-Westin15 re-ported results of 96 meniscal al-lografts performed in 82 patients

Fresh-frozen grafts exposed to 2.5 mRad of gamma irradiation were used Most grafts were fixed only at the posterior horn; no grafts were se-cured by both the anterior and poste-rior horns Twenty-nine of the 96 grafts failed within 24 months, requir-ing removal; these were not included

in the follow-up Of the 67 meniscal transplants evaluated at 2 to 5 years,

27 failed Overall results for all 96 al-lograft transplantations were 9%

healed, 31% partially healed, 58%

failed, and 2% lost to follow-up A correlation between arthritic changes and meniscal healing was observed Stollsteimer et al57reported results

of 23 allografts in 22 patients followed for an average of 40 months All al-lografts were nonirradiated and cryopreserved; surgery was arthro-scopically assisted with implantation using a bone plug technique Postop-erative joint space narrowing mea-sured radiographically averaged 0.88 mm Bilateral knee MRI was per-formed in 12 patients All patients improved clinically, as measured at final follow-up with Tegner, Lysholm, and IKDC scores In addition, allograft size was noted to have shrunk to an average of 63% of the normal con-tralateral side; the significance of the observed allograft shrinkage is not known

Figure 7

Arthroscopic images of healing of a medial meniscal allograft 4 months after

transplantation A, Suture fixation of medial meniscal allograft using arthroscopically placed, vertical mattress, inside-out sutures (arrow) B, Healed posterior horn that

is stable with arthroscopic probing (arrow) C, Restoration of normal contour of the junction of the midbody and posterior horn (arrow) D, Healed midbody peripheral

rim verified by direct arthroscopic visualization and probing (arrow) FC = femoral condyle, M = meniscus, TP = tibial plateau

All 18 patients evaluated by Rath

et al58 an average of 5.4 years after

meniscal allograft transplantation

had a marked decrease in pain and

improvement in function No joint

space narrowing was observed on

45° posteroanterior weight-bearing

radiographs; however, 8 of 22

al-lografts tore during the study period

(5 as a result of trauma) After initial

positive outcomes, these allograft

failures required six partial and two

total meniscectomies secondary to

mechanical symptoms Excised

al-lografts were examined

histological-ly and found to have reduced

cellu-larity and cytokine expression

compared with controls Two

pa-tients, both requiring total

menis-cectomy after failure, requested

re-implantation secondary to return of

symptoms after the removal of

al-lograft menisci; these two patients

were included in the study from

time of reimplantation It is

postu-lated that allograft menisci have a

reduced functionality secondary to

repopulation with fewer cells, as

measured by this decrease in growth

factor production

Verdonk59found a notable

differ-ence in preoperative and

postopera-tive pain scores, with 87% of

postop-erative patients stating that they

would undergo transplantation

again There were no significant

dif-ferences between isolated medial or

lateral meniscus transplants

Wirth et al60 reported the

long-term results of 23 meniscal

trans-plantations with simultaneous ACL

reconstructions, measured an average

of 3 and 14 years postoperatively

Seventeen lyophilized and six

deep-frozen grafts were used Although

MRI and arthroscopy demonstrated

a reduction in the size of lyophilized

grafts, all patients improved in

Lysholm scores Deep-frozen

menis-cal allograft patients did better in

both objective and subjective results

compared with lyophilized allograft

patients

van Arkel and de Boer61recently

evaluated 63 meniscal allografts in 57

patients at an average follow-up of

60 months Thirty-four patients had isolated lateral meniscal transplanta-tion, 17 had isolated medial meniscal transplantation, and 6 had combined transplantation Preoperative insta-bility secondary to ACL deficiency or meniscectomy was present in 21 pa-tients; postoperative stability was achieved in 11 of these patients Al-lograft failure, measured by persis-tent pain or mechanical failure, oc-curred in 13 transplantations (5 lateral, 7 medial, and 1 medial and lateral) The cumulative survival rate

of lateral, medial, and combined al-lografts was 76%, 50%, and 67%, re-spectively Rupture of the ACL had a

significant (P = 0.003) negative

corre-lation with successful medial menis-cal transplantation Additionally, lat-eral meniscal transplantations did

significantly (P = 0.004) better than

medial transplantations clinically

Biomechanical function and ana-tomic differences likely explain this difference Medial meniscal allograft survival should improve with con-current ACL reconstruction in the ACL-deficient knee

Yoldas et al42evaluated 31 patients with meniscal transplants, twenty of which were combined with ACL re-constructions, with a minimum 2-year follow-up Thirty of the 31 pa-tients had a normal or nearly normal rating according to IKDC knee func-tion and activity level Nineteen of the knees that underwent combined meniscal transplant and ACL recon-struction were normal or nearly nor-mal according to IKDC stability test-ing The average single-leg hop and vertical jump was 85% that of the contralateral limb No progressive joint space narrowing was seen on ra-diographic examination

Sekiya et al62 evaluated 25 pa-tients who underwent isolated

later-al menisclater-al transplantation at an av-erage follow-up of 3.3 years Bony fixation of the allograft was per-formed in 17 patients; 8 patients had suture fixation of the anterior and posterior horns of the meniscal

al-lograft In these patients, 79% had normal or nearly normal scores cording to IKDC knee function, ac-tivity level, and overall subjective ratings Medical Outcomes Study 36-Item Short Form (SF-36) physical and mental component summary scores revealed that transplant recip-ients performed at higher levels than age- and sex-matched population controls The average scores for the single-leg hop and vertical jump test were 91% and 85%, respectively, of the contralateral limb There was no joint space narrowing seen over time

on radiographic examination In ad-dition, radiographic preoperative and postoperative joint space measure-ments of the involved lateral

com-partment were significantly (P ≤ 0.05) associated with mean lower subjective assessment, symptoms, sports activity score, Lysholm score, and final IKDC rating at latest follow-up Finally, patients treated with the bony technique had

signif-icantly (P≤ 0.05) better range of mo-tion, according to IKDC criteria, at latest follow-up compared with the suture fixation group

Sekiya et al31 also evaluated 28 patients who underwent combined meniscal transplantation with ACL reconstruction (average follow-up, 2.8 years) Of these patients, 86% to 90% had normal or nearly normal scores, according to IKDC overall subjective and symptoms assess-ment Combined ACL and meniscal transplantation patients scored at higher levels on SF-36 physical and mental component summary scores than did age- and sex-matched popu-lations Ninety percent of the pa-tients also had normal or nearly nor-mal scores by Lachman’s scoring system and pivot-shift testing

KT-1000 testing at both 20 lb and at maximum manual demonstrated an average of 1.5 mm of increased ante-rior translation compared with the normal contralateral knee No joint space narrowing was seen over time

on radiographic examination.31

Recently, Graf et al30

retrospec-tively reviewed nine patients who

had undergone combined medial

me-niscal transplantation and ACL

re-construction (minimum follow-up,

8.5 years; average follow-up, 9.7

years) One allograft was removed

be-cause of the presence of a presumed

low-grade infection Seven of eight

patients had normal or nearly normal

IKDC scores while remaining at their

preoperative radiographic score

lev-els without progression Six of eight

patients were extremely pleased with

their knee function and were highly

active in recreational sports Six of

eight patients also had normal or

nearly normal scores, according to

IKDC functional testing Finally, all

eight patients stated that they would

recommend the procedure to a friend

and would undergo the procedure

again, given similar circumstances.30

Summary

Meniscal transplantation continues

to evolve as a treatment for difficult

meniscal injuries that necessitate

partial or total meniscectomy Initial

clinical results are promising, but

long-term clinical outcomes remain

to be established Important surgical

factors include patient selection,

limb stability and alignment, graft

sizing, graft placement, and graft

fix-ation Currently, meniscal allograft

transplantation should be considered

a salvage operation for symptomatic

meniscal deficiency in the young

tient Nonetheless, with careful

pa-tient selection, this procedure can

predictably relieve compartmental

pain and restore knee stability (for

medial meniscal transplantation)

when associated with combined ACL

reconstruction In addition, meniscal

allograft transplantation may

par-tially restore native meniscal

func-tion, as is seen with slowing of the

degenerative arthritic process in

transplanted meniscus-deficient knee

compartments

References

Evidence-based Medicine: Studies referenced are primarily case-control reports of meniscal allografts (level III) There are no prospective, ran-domized studies on this topic to date (level I, II studies)

Citation numbers printed in bold

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