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The American Journal of Sports
http://ajs.sagepub.com/content/39/10/2187The online version of this article can be found at:
DOI: 10.1177/0363546511416597
2011 39: 2187 originally published online August 9, 2011Am J Sports MedJin Hwan Ahn, Tae Soo Bae, Ki-Ser Kang, Soo Yong Kang and Sang Hak Lee
Knee Significantly Influences Anterior StabilityDeficiengitudinal Tear of the Medial Meniscus Posterior Horn in the Anterior Cruciate Ligament
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Longitudinal Tear of the Medial MeniscusPosterior Horn in the Anterior Cruciate
LigamentDeficient Knee SignificantlyInfluences Anterior Stability
Jin Hwan Ahn,* MD, Tae Soo Bae,y PhD, Ki-Ser Kang,z MD,Soo Yong Kang,z MD, and Sang Hak Lee,|| MDInvestigation performed at Department of Orthopaedic Surgery, Center for JointDiseases and Rheumatism, Kyung Hee University Hospital at Gangdong, Seoul, Korea
Background: Longitudinal tears of the medial meniscus posterior horn (MMPH) are commonly associated with a chronic anterior
cruciate ligament (ACL) deficiency. Many studies have demonstrated the importance of the medial meniscus in terms of limiting
the amount of anterior-posterior tibial translation in response to anterior tibial loads in ACL-deficient knees.
Hypothesis: An MMPH tear in an ACL-deficient knee increases the anterior-posterior tibial translation and rotatory instability. In
addition, MMPH repair will restore the tibial translation to the level before the tear.
Study Design: Controlled laboratory study.
Methods: Ten human cadaveric knees were tested sequentially using a custom testing system under 5 conditions: intact, ACL
deficient, ACL deficient with an MMPH peripheral longitudinal tear, ACL deficient with an MMPH repair, and ACL deficient with
a total medial meniscectomy. The knee kinematics were measured at 0, 15, 30, 60, and 90 of flexion in response to a 134-N
anterior and 200-N axial compressive tibial load. The rotatory kinematics were also measured at 15 and 30 of flexion in a com-
bined rotatory load of 5 Nm of internal tibial torque and 10 Nm of valgus torque.
Results: Medial meniscus posterior horn longitudinal tears in ACL-deficient knees resulted in a significant increase in anterior-
posterior tibial translation at all flexion angles except 90 (P\ .05). An MMPH repair in an ACL-deficient knee showed a significant
decrease in anterior-posterior tibial translation at all flexion angles except 60 compared with the ACL-deficient/MMPH tear state
(P\ .05). The total anterior-posterior translation of the ACL-deficient/MMPH repaired knee was not significantly increased com-pared with the ACL (only)deficient knee but was increased compared with the ACLintact knee (P . .05). A total medial menis-
cectomy in an ACL-deficient knee did not increase the anterior-posterior tibial translation significantly compared with MMPH tears
in ACL-deficient knees at all flexion angles (P. .05). In a combined rotatory load, tibial rotation after MMPH tears or a total medial
meniscectomy in an ACL-deficient knee were not affected significantly at all flexion angles.
Conclusion: This study shows that an MMPH longitudinal tear in an ACL-deficient knee alters the knee kinematics, particularly
the anterior-posterior tibial translation. MMPH repair significantly improved anterior-posterior tibial translation in ACL-deficient
knees.
Clinical Relevance: These findings may help improve the treatment of patients with ACL and MMPH longitudinal tear by suggest-
ing that the medial meniscal repairs should be performed for greater longevity when combined with an ACL reconstruction.
Keywords: anterior cruciate ligament; medial meniscus posterior horn tear; meniscal repair
Meniscal injuries associated with acute anterior cruciate
ligament (ACL) tears are reported to range from 15% to
40%, and become much higher with a chronic ACL defi-
ciency.13 Several researchers have demonstrated that lon-
gitudinal tear of the medial meniscus posterior horn
(MMPH) around the meniscocapsular junction is found fre-
quently in knees with chronic deficient ACLs.8,19,25 More
than 75% of medial meniscal (MM) tears in ACL-deficient
knees occur in the peripheral posterior horn according to
a prospective analysis of 575 meniscal tears by Smith
and Barrett.23 However, many surgeons overlook this com-
bined tear because of the poor visualization and benign
appearance of the posterior meniscocapsular junction of
the MM from the anterior portals.1,3 Furthermore,
MMPH peripheral rim tears may heal slowly despite the
rich vascular supply to the red-red zone because the torn
meniscus has some movement proximally against the
meniscocapsular junction.2,3,19A recent clinical study dem-
onstrated that the rate of poor results of repair for MM
The American Journal of Sports Medicine, Vol. 39, No. 10
DOI: 10.1177/0363546511416597 2011 The Author(s)
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tears remains high when nonoperative treatment is used,
even though the nonoperative approach is more effective
for lateral meniscal tears.19,27
Biomechanical studies have demonstrated the impor-
tance of the meniscus, particularly the medial, in stabiliz-
ing the knee joint in chronically ACL-deficient knees.5,15,22
Furthermore, many authors have demonstrated the impor-
tance of the MM in limiting the anterior tibial translation
in response to anterior tibial loads in ACL-deficient
knees.4,17 Papageorgiou et al17 reported that the resulting
forces on the MM were increased by as much as 200% in
response to anterior tibial loads after the ACL had been
transected. Furthermore, they demonstrated a 33% to
50% increase in the in situ forces in the ACL replacement
graft after a medial meniscectomy. More recently, Seon
et al20 confirmed that a subtotal medial meniscectomy in
an ACL-deficient knee increased significantly the anterior
and lateral tibial translations. These results prompted sev-
eral authors to recommend that an ACL-deficient knee be
reconstructed to protect the menisci.7,18,28
The purpose of this study was to quantify the effects ofMMPH longitudinal tears and meniscal repair on ACL-
deficient knees. It was hypothesized that an MMPH tear
in an ACL-deficient knee would increase the anterior-pos-
terior (A-P) tibial translation and combined rotational lax-
ity. It was also hypothesized that MMPH repair could
restore the tibial translation to the level before the menis-
cal tear.
METHODS
Specimen Preparation
Ten fresh-frozen, nonpaired human cadaveric knees, rang-
ing in age from 34 to 74 years (mean, 58 years), were used
in this study. Six were from male donors, and 4 were from
female donors. All knees were macroscopically intact and
showed no evidence of prior surgery, structural abnormal-
ities, or arthritic changes according to a clinical examina-
tion. The specimens were kept frozen at 20C before the
tests and were thawed at room temperature overnight
before the experiment. The knees were dissected carefully,
removing the skin and soft tissue, and leaving the popli-
teus muscle, joint capsule, ligamentous structures, and
surrounding retinaculum intact. The fibular head was
transfixed to the tibia by a 6.5-mm cannulated screw and
spiked washer (Jeil Meditec, Daegu, Korea) to maintainits anatomic position and then the distal part was excised.
The femur and tibia were then sectioned at approximately
25 cm in length from the joint line and secured in thick-
walled aluminum cylinders using denture acryl (Vertex,
Dentimex BV, Zeist, The Netherlands). Care was taken
to center the long axis of the bone within the cylinder,
which is representative of the long axis of the bones. The
knees were protected from dehydration by the intermittent
applications of physiological saline during preparation and
testing periods.
Kinematic Measurements
To measure the kinematics of the knee, each specimen was
mounted firmly in an Instron testing machine (Instron
850I, MTS, Minneapolis, Minnesota). A custom knee jig
was used to hold the denture acrylic potted bone. The potted
bones were then bolted securely within the jigs. The jig
allowed rigid fixation of the femur but provided 5 degrees
of freedom at the tibia (anteroposterior and proximal-distal
translations; and varus-valgus, internal-external rotations,
and flexion-extension). The custom testing jig was specifically
designed with a pulley system to accommodate the manual
application of an anterior and posterior tibial load, as well
as a varus and valgus torque. The application of a load was
achieved by hanging weights from a cable and pulley system.
The experimental setup provided control over various knee
flexion angles, which were confirmed using a protractor
attached to the jig. The tibial kinematic measurements
were obtained to the nearest tenth of a millimeter using elec-
tronic calipers. Two optical encoders in the joints recorded
the varus-valgus rotational laxity and internal-external rota-
tional laxity of the tibia. Because of the challenges inherent
in defining the physiologic neutral position of the cadaveric
knee, the laxity measurements were defined as the resultant
A-P tibial translation, varus-valgus rotational laxity, and
internal-external rotational laxity of the tibia relative to
the femur when the appropriate force was applied.
Testing Protocol
A custom testing system was sequentially tested under 5
conditions: intact, ACL deficient, ACL deficient with
MMPH peripheral longitudinal tear, ACL deficient with
an MMPH repair, and ACL deficient with a total medial
meniscectomy (Table 1). The knee kinematics were mea-
sured at 0, 15, 30, 60, and 90 of flexion, while the posi-
tions of the knee, which minimized all external forces and
moments applied to the joint throughout the range of flex-
ion from 0 to 90, were recorded. These positions, at which
the knee was effectively unloaded, served as starting
points for the application of an external load as well as
the reference points for the measurements of the kneekinematics throughout each test. The difference between
the starting point and the end point position was calcu-
lated for each test performed for each sectioned state and
flexion angle. The externally applied loading condition in
this study combined 2 forces: 134-N anterior and 200-N
axial compressive tibial load at full extension and 15,
Address correspondence to Sang Hak Lee, MD, Department of Orthopaedic Surgery, Center for Joint Diseases and Rheumatism, Kyung Hee Univer-
sity Hospital at Gangdong, 892 Dongnam-ro, Gangdong-gu, Seoul, 134-727, Korea (e-mail: sangdory@hanmail.net).
*Department of Orthopaedic Surgery, Sungkyunkwan University School of Medicine, Kangbuk Samsung Hospital, Seoul, Korea.yKorea Orthopedics & Rehabilitation Engineering Center, Inchon, Korea.zDepartment of Orthopaedic Surgery, Chung-Ang University, School of Medicine, Seoul, Korea.||Center for Joint Diseases and Rheumatism, Kyung Hee University Hospital at Gangdong, Seoul, Korea.
The authors declared that they have no conflicts of interest in the authorship and publication of this contribution.
2188 Ahn et al The American Journal of Sports Medicine
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30, 60, and 90 of flexion. The combined rotatory kine-
matics were also measured at 15 and 30 of flexion in
a combined rotatory load of 5 Nm of internal tibial torque
and 10 N
m of valgus torque (Figure 1). Under each ofthese loads, the testing system manipulated the knee joint
in 4 degrees of freedom (with a constant selected flexion
angle) until the applied forces were balanced by the knee.
After the kinematics in the intact knee was determined,
the ACL was transected to represent an ACL-deficient con-
dition through a 5-cm longitudinal anteromedial arthrot-
omy. The MMPH peripheral longitudinal tear was made
from the posterior horn to the posteromedial corner at
the meniscocapsular junction through a 5-cm longitudinal
posteromedial arthrotomy (Figure 2). The mean length
of the longitudinal tears measured 2.8 cm (range,
2.4-3.3 cm). The root of the MMPH and midbody of the
MM were preserved in our experimental protocol. The
arthrotomy was repaired in layers by sutures with
2-0 Vicryl suture material. In the next step, the MMPH
tear was repaired using absorbable sutures (No. 0 PDS
[polydioxanone], Ethicon, Somerville, New Jersey). Every
stitch was made with a roughly 4- to 5-mm interval using
a vertically oriented repair technique. Thus, the MMPH
tear in each specimen was repaired by 4 to 5 stitches. Finally,
a total resection of the entire MM, removing the inner portion
of the whole body and the posterior horn, was performed
through the same posteromedial arthrotomy. The arthrotomy
was closed carefully in layers in each step. The external load
was then reapplied with each step and the resulting kinemat-
ics recorded using the testing system. Each knee was tested 2
times at each flexion angle and the results were averaged.
The mean difference between the origin and the end point
position was calculated for each test performed for each sec-
tioned state flexion angle.
Statistical Analysis
The knee laxity measurements were repeated for 2 trials
and the mean value was used for data analysis. The
TABLE 1
Experimental Protocol and Data Acquireda
Protocol Data Acquired
I. Intact joint
External loading conditions Intact joint kinematics at all flexed angles:
A. 134-N anterior tibial load (1) anterior tibial translation
B. 200-N axial compressive tibial load (2) valgus-varus angle
(3) internal-external rotations
Combined rotatory load (apply loads A and B) Intact joint kinematics at 15 and 30 of flexion:
C. 10 Nm of valgus load (4) internal-external rotations
D. 5 Nm of internal tibial torque
II. ACL-deficient joint
Transect ACL
Apply loads A and B ACL-deficient joint kinematics at all flexed angles(1), (2), (3)
Apply loads A, B, C, and D ACL-deficient joint kinematics at 15 and 30 of flexion(4)
III. MMPH tear with ACL-deficient joint
Make MMPH peripheral longitudinal tear
Apply loads A and B ACL-deficient joint kinematics at all flexed angles(1), (2), (3)
Apply loads A, B, C, and D ACL-deficient joint kinematics at 15 and 30 of flexion(4)
IV. MMPH repair with ACL-deficient joint
Repair MMPH tear Apply loads A and B ACL-deficient joint kinematics at all flexed angles(1), (2), (3)
Apply loads A, B, C, and D ACL-deficient joint kinematics at 15 and 30 of flexion(4)
V. Total medial meniscectomy with ACL-deficient joint
Perform total medial meniscectomy
Apply loads A and B ACL-deficient joint kinematics at all flexed angles(1), (2), (3)
Apply loads A, B, C, and D ACL-deficient joint kinematics at 15 and 30 of flexion(4)
a ACL, anterior cruciate ligament; MMPH, medial meniscus posterior horn.
Figure 1. Schematic illustration of testing systems with
a right cadaveric knee specimen.
Vol. 39, No. 10, 2011 Medial Meniscus Posterior Horn Tear and Knee Stability 2189
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reliability of measurements was assessed by the intraclass
correlation coefficient (ICC), which quantifies the propor-
tion of the variance attributable to variability between
measurements. Because all variables were measured within
each specimen, statistical analysis of the knee kinematics
was performed using a Friedman test with Bonferroni cor-
rection or 2-way analysis of variance. All statistical analyses
were carried out using SAS version 9.13 software (SAS
Institute Inc, Cary, North Carolina). P values \ .05 were
considered significant.
RESULTS
The ICC for test-retest reliability of the measurement was
greater than 0.9, ranging from 0.99 to 0.92, for all meas-
urements. This value indicated that all measurements
had excellent reproducibility.
Knee Kinematics in Response to 134-N Anterior
and 200-N Compressive Tibial Load
When a combined 134-N anterior and 200-N axial compres-
sive tibial load was applied, the A-P tibial translation of the
ACL-intact knee ranged from 7.16 0.9 mm at full extension
to 9.0 6 2.9 mm at 30 of flexion (Figure 3, Table 2). The
largest A-P tibial translation of the ACL-intact knee was
observed at 15 and 30 of flexion as 8.6 6 2.1 mm and
9.0 6 2.9 mm, respectively. After the ACL was resected,
the A-P tibial translation under combined loads in the
ACL-deficient knees was significantly larger than in the
intact knee at all flexion angles selected (P\ .05). Medial
meniscus posterior horn tears in the ACL-deficient knees
resulted in an additional increase in A-P tibial translation
at all flexion angles except 90 (P\ .05). These increases
in A-P tibial translation differed according to the flexion
angle, from a minimum of 1.7 6 0.8 mm at 90 of flexion
to a maximum of 5.2 6 1.2 mm at 15 of flexion. Medial
meniscus posterior horn repair in the ACL-deficient knee
reduced A-P tibial translation significantly at all flexion
angle except 60 (P \ .05). After MMPH repair in the
ACL-deficient knee, the A-P tibial translation was not sig-
nificantly increased compared with the ACL-onlydeficient
knee at all flexion angles (P . .05). Furthermore, a total
medial meniscectomy in the ACL-deficient knees did not
increase the A-P tibial translation significantly compared
with the MMPH peripheral tears in the ACL-deficient knee
at all flexion angles, which ranged from 11.3 6 6.3 mm at
90 of flexion to 19.5 6 5.9 mm (P . .05).
The coupled varus-valgus and internal-external rota-tions in response to the combined 134-N anterior and
200-N axial compressive tibial load were also measured
and are shown Tables 3 and 4. Both varus-valgus and
internal-external rotations in ACL-deficient knees were
not affected significantly by the MMPH tears or total
medial meniscectomy at all flexion angles (P . .05).
Knee Kinematics in Response to a
Combined Rotatory Load
The resulting internal-external tibial rotation in response
to a 5-Nm internal tibial torque with a 10-Nm valgus tor-
que was increased by each step: the ACL resection, MMPHtear, and total medial meniscectomy at 15 and 30 of knee
flexion although there were no significantly differences
(P . .05). The resulting tibial rotation was decreased by
MMPH repair in the ACL-deficient knee at 15 and 30
of knee flexion. However, no statistically significant differ-
ences also could be found at any flexion angle among each
step at 15 and 30 of knee flexion (P . .05) (Table 5).
DISCUSSION
The effect of an MMPH longitudinal tear in ACL-deficient
knees on the kinematics of the knee has not been reported.
This biomechanical study showed that an MMPH
Figure 2. Schematic drawings show that a peripheral longi-
tudinal tear of the medial meniscus posterior horn (MMPH)
was made from the posterior horn to the posteromedial cor-
ner at the meniscocapsular junction (A) and the MMPH tear
was repaired using absorbable sutures (B).
Figure 3.Anterior translation of the tibia under anterior andcompressive tibial load in 5 different knee conditions. Statis-
tical significances were noted between intact and anterior
cruciate ligament (ACL) resect groups, ACL resect and ACL
resect 1 meniscus tear groups, and ACL resect 1 meniscus
tear and ACL resect 1 meniscus repair groups at most flex-
ion angles. An asterisk represents statistical significance
(P\ .05); error bars represent the standard deviation.
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longitudinal tear in ACL-deficient knees increased the ante-
rior translation of the tibia. Medial meniscus posterior hornrepair using an absorbable suture material in an ACL-defi-
cient knee reduced A-P tibial translation significantly at
most flexion angles. In addition, no significant difference
was observed between the total medial meniscectomy and
MMPH longitudinal tear in the A-P tibial translation of
the tibia. In this study, an MMPH longitudinal tear in the
ACL-deficient knee resulted in similar kinematic changes
to that with a total medial meniscectomy under a combined
anterior and axial compressive tibial load.
The meniscal tear patterns that occur in ACL-deficient
knees have been studied widely. Cerabona et al6 reported
that in 50 patients, most of the medial meniscal tears were
peripheral and posterior. Indelicato and Bittar
10
also
demonstrated that most medial meniscal tears in ACL-defi-
cient knees were peripheral posterior horn tears. Morerecently, Smith and Barrett23 prospectively studied 575
meniscal tears to evaluate the locations of meniscal tears
associated with ACL injuries. They found that peripheral pos-
terior horn tears of the medial meniscus were the most com-
mon type of tear (230 of 575 [40%]) by a statistically
significant amount. These findings are in agreement with
most theories suggesting that peripheral posterior horn tears
are caused by the recurrent trauma sustained by the MM
while acting as a bumper in the ACL-deficient knee. There-
fore, this study focused on MMPH tears in ACL-deficient
knees. The data conclusively show that MMPH tears in
ACL-deficient knees alter the knee kinematics, particularly
the anterior translation.
TABLE 2
Mean Values (6Standard Deviation) of Anterior Translation (mm) of the Tibia
Under 134-N Anterior and 200-N Compressive Tibial Load in 5 Different Knee Conditionsa
Knee Condition 0 15 30 60 90
Intact 6.9 6 0.9 8.6 6 2.1 9.0 6 2.9 7.1 6 1.9 6.6 6 2.0
ACL resect 10.16
1.9
b
14.26
3.6
b
14.86
4.7
b
11.86
2.2
b
8.96
3.2
b
ACL resect/MMPHT 13.96 2.4c 18.7 6 4.8c 16.8 6 4.8c 13.9 6 3.7c 9.8 6 4.1
ACL resect/MMPHR 12.06 2.2d 15.6 6 3.7d 14.8 6 4.4d 12.4 6 4.3 8.1 6 3.9d
ACL resect/TMM 13.66 4.1e 18.8 6 6.1e 16.9 6 5.5e 14.6 6 5.7e 9.8 6 6.2e
aACL, anterior cruciate ligament; MMPHT, medial meniscus posterior horn tear; MMPHR, medial meniscus posterior horn repair; TMM,
total medial meniscectomy.bP\ .05 when compared with the intact knee.cP\ .05 when compared with the ACL-resected knee.dP\ .05 when compared with the ACL-resected/MMPHT knee.eP\ .05 when compared with the ACL-resected/MMPHR knee.
TABLE 3
Mean Values (6Standard Deviation) of Valgus-Varus Angle (deg) of the Tibia
Under 134-N Anterior and 200-N Compressive Tibial Load in 5 Different Knee Conditionsa
Knee Condition 0 15 30 60 90
Intact 0.2 6 1.1 0.5 6 1.0 0.8 6 1.6 0.6 6 0.9 1.2 6 2.0
ACL resect 1.26 0.7 1.6 6 2.6 2.7 6 3.7 3.0 6 3.4 2.2 6 2.9
ACL resect/MMPHT 1.56 2.8 0.5 6 6.3 2.6 6 3.4 3.2 6 4.3 1.7 6 4.2
ACL resect/MMPHR 0.36 1.8 2.6 6 4.0 3.4 6 4.0 3.4 6 4.6 1.6 6 3.4
ACL resect/TMM 0.66 1.4 0.5 6 2.6 2.5 6 6.8 0.3 6 6.2 1.0 6 6.8
aThere were no significant differences between the groups at all selected flexion angles. ACL, anterior cruciate ligament; MMPHT, medial
meniscus posterior horn tear; MMPHR, medial meniscus posterior horn repair; TMM, total medial meniscectomy.
TABLE 4
Mean Values (6Standard Deviation) of Internal Rotation Angle (deg) of the Tibia
Under 134-N Anterior and 200-N Compressive Tibial Load in 5 Different Knee Conditionsa
Knee Condition 0 15 30 60 90
Intact 2.3 6 2.5 4.9 6 3.9 5.3 6 5.3 3.7 6 3.0 3.3 6 2.9
ACL resect 1.36 1.4 3.2 6 3.7 1.7 6 3.9 0.7 6 3.2 0.2 6 3.3
ACL resect/MMPHT 1.06 1.1 1.3 6 3.6 1.0 6 4.0 0.5 6 3.4 0.6 6 4.7
ACL resect/MMPHR 1.66 2.0 2.9 6 3.8 0.6 6 3.6 0.3 6 5.9 1.9 6 4.5
ACL resect/TMM 2.36 1.3 1.5 6 3.4 0.2 6 6.7 1.2 6 4.7 3.1 6 5.9
aThere were no significant differences between the groups at all selected flexion angles. ACL, anterior cruciate ligament; MMPHT, medial
meniscus posterior horn tear; MMPHR, medial meniscus posterior horn repair; TMM, total medial meniscectomy.
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An anterior tibial load of 134 N was chosen because the
ACL is a major restraint to the anterior tibial translation
and it simulates clinical tests, such as the Lachman or ante-
rior drawer tests, which are commonly used for diagnosingan ACL injury.15 Another important physical examination
of an ACL injury and reconstruction is the pivot-shift test,
during which a combined internal and valgus torque is
applied to the knee. Kanamori et al11 recommended the
application of low internal torque in combination with val-
gus torque to simulate a pivot-shift test when evaluating
ACL-deficient knee joints. Therefore, a 5-Nm internal tibial
torque and a 10-Nm valgus torque were used to simulate
the pivot-shift test. However, tibial rotation and valgus-
varus angle were not significantly changed after MMPH
tears or total medial meniscectomy. Furthermore, no signif-
icant differences were observed in the internal tibial rota-
tions under compressive tibial loads and combined rotatorloads among 5 knee conditions, although our data showed
a similar trend in tibial internal rotation after MMPH tear
in ACL-deficient knees. These results may suggest that
the combined internal and valgus torques are an inefficient
loading condition for investigating the rotational laxity in
cadaveric specimens.12 Comprehensive loading conditions
are required to truly assess the ability of the ACL and
MMPH to restrain tibial rotations. To more accurately
mimic in vivo loading conditions, larger forces such as those
from the quadriceps and hamstring muscles will be needed.
Some authors have reported that many acute stable
peripheral longitudinal meniscal tears with an acute
ACL injury either heal spontaneously or the symptoms
resolve without an extension of the tear in 58% to 69% of
cases.9,26 Shelbourne and Rask21 reported that of stable
peripheral vertical MM tears treated with abrasion and
trephination, most (94%) remain asymptomatic without
stabilization. However, 2 recent reports described different
healing results of medial or lateral meniscal tears left in
situ during an ACL reconstruction. Yagishita et al27
reported that the overall healing rate of 41 medial menis-
cal tears left without repair, including completely and
incompletely healed tears, was significantly lower than
that of 42 lateral meniscal tears (61% vs 79%). Pujol and
Beaufils19 also reported that the high prevalence of fail-
ures of medial meniscal tears left in situ during an ACL
reconstruction raises concern, even though a conservative
approach is more effective for the lateral meniscus. Previ-
ous reports1,3 showed that a torn posterior meniscocapsu-
lar structure moved inferiorly against the remaining
meniscus, displacing the tear during knee flexion. This
motion of the torn MM can partially explain the slow heal-
ing observed in MMPH peripheral rim tears despite the
rich vascular supply to the red-red zone. Therefore, we rec-
ommend that MMPH tears in ACL-deficient knees be trea-
ted more aggressively using a vertically oriented suturing
technique that was previously reported,1,3 an arthroscopic
modified all-inside suture technique of Morgan et al16
using 2 posteromedial portals. Absorbable meniscal fixa-
tors are not believed to be sufficient for this type of tear
because these tears require secure fixation to the capsule,
which cannot be provided by the new bioabsorbable devi-
ces. Previous clinical reports reported a clinical success
rate of 96.4% (135 of 140) for modified all-inside meniscal
repairs with a concomitant ACL reconstruction.2 The pres-
ent study also demonstrated that vertically oriented
MMPH repairs in ACL-deficient knees reduced A-P tibialtranslation significantly at all flexion angles except 60 to
a level not increased significantly, compared to the ACL-
onlydeficient knee at all flexion angles.
Many studies have reported the important stabilizing
role of the MM. In 1982, Levy et al14 demonstrated that
the posterior horn of the MM as a mechanical block contrib-
uted significantly to restraining the primary anterior trans-
lation of the knee after sectioning of the ACL. The work by
Sullivan et al24 in 1984 supports this concept. As a result,
the present belief of many researchers is that the MM is
a secondary restraint to an A-P tibial translation that
becomes much more important with the loss of ACL func-
tion. More recently, Seon et al20
showed the effect of an ACL reconstruction on the kinematics of the knee with
a combined ACL deficiency and subtotal meniscectomy
under anterior tibial and simulated quadriceps loads. Their
study demonstrated that a subtotal medial meniscectomy in
ACL-deficient knees increased the A-P tibial translation
and lateral shift of the tibia. The present study showed
that MMPH longitudinal tears in an ACL-deficient knee
resulted in similar kinematic changes with a total medial
meniscectomy under a combined anterior and axial com-
pressive tibial load. Therefore, MMPH longitudinal tears
should be repaired in the setting of an ACL reconstruction
to restore the optimal knee kinematics and function.
This study had some limitations. First, the biomechani-
cal test setup was obtained only for time-point zero, without
the possibility of taking the influence of muscle function into
consideration. And the testing setup is not 6 degrees of free-
dom load cell with a robotic testing system. However, the
ICC for test-retest reliability of the measurement was
greater than 0.9, ranging from 0.99 to 0.92, for all measure-
ments. Further research will be directed to evaluate this
testing protocol under simulated muscle load and in the
in vivo situation. Second, an open technique was used to
resect the ACL and perform MMPH tear, MMPH repair,
and medial meniscectomy procedures. Although the incision
and repair of the arthrotomy were performed carefully to
avoid potential bias from changes in capsular tension, the
TABLE 5
Mean Values (6Standard Deviation) of Internal Rotation
Angle (deg) of the Tibia Under Combined Rotatory Load
in 5 Different Knee Conditionsa
Knee Condition 15 30
Intact 7.96
4.4 8.86
4.6 ACL resect 10.26 5.1 10.8 6 5.9
ACL resect/MMPHT 13.06 5.7 12.9 6 7.0
ACL resect/MMPHR 9.96 4.9 8.8 6 4.0
ACL resect/TMM 12.86 6.8 11.0 6 5.3
aThere were no significant differences between the groups at all
selected flexion angles. ACL, anterior cruciate ligament; MMPHT,
medial meniscus posterior horn tear; MMPHR, medial meniscus
posterior horn repair; TMM, total medial meniscectomy.
2192 Ahn et al The American Journal of Sports Medicine
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8/8
open technique, particularly a posteromedial arthrotomy,
may affect the knee kinematics in rotation and posterior
translation. Third, these tests were performed in older
cadaveric knee specimens. A different pattern of ligamen-
tous versus bony injury may be seen in younger knees, rep-
resenting the typical patient population that may sustain
these types of injuries. Fourth, this is a cadaveric in vitro,
time-zero study; therefore, we are unable to determine the
effects of biologic processes on the suture material fixation
and meniscal healing in vivo. Furthermore, our design facil-
itated a repeated-measures analysis of kinematics using the
same specimen under different loading conditions. This may
be influenced subsequently by the effects of chronic relaxa-
tion and stretching of specimen. Finally, the rate of stress
testing does not reproduce the rate of loading at the time
of the actual injury to the knee.
This study shows that an MMPH longitudinal tear in
an ACL-deficient knee alters the knee kinematics, partic-
ularly the anterior tibial translation. MMPH repair
reduces significantly the increased anterior tibial transla-
tion in ACL-deficient knees. These findings may helpimprove the treatment of patients with ACL and MMPH
longitudinal tears by suggesting that the MM repairs
should be undertaken for greater longevity of results
when combined with an ACL reconstruction.
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