- Free nerve endings and specialized end-receptors are
present within the menisci. The most densely inner-
vated regions are the anterior and posterior horns of
both menisci (Lo et al, 2003).
•Nerve fibers originate in the perimeniscal tissues and
radiate into the peripheral 30% of the meniscus. - Three receptor types have been identified—Ruffini
endings, Golgi tendon organs, and pacinian corpus-
cles. - It is hypothesized that the nerves play a proprioceptive
role in normal joint function. Meniscal derived signals
generated during deformation and loading may be
important to joint-position sense, and for protective
neuromuscular reflex control of joint motion and
loading (Lo et al, 2003).
NUTRITION OF THE MENISCI
- The bulk of meniscus nutrition is supplied by the syn-
ovial fluid, most notably to the avascular regions. - Nutrients reach the tissue via passive diffusion and
mechanical pumping with intermittent compression
during loading (Lo et al, 2003).
BIOMECHANICS AND MENISCAL
FUNCTION
- The menisci serve in load transmission, shock absorp-
tion, lubrication, prevention of synovial impingement,
synovial fluid distribution, stability, and improved
gliding motion (Rath and Richmond, 2000). - Long term follow-up demonstrates that virtually all
knees after total meniscectomy develop degenerative
changes, and this is less frequent following partial
meniscectomy (Fairbank, 1948; Andersson-Molina,
Karlsson, and Rockborn, 2002).
MENISCUS MOTION
•With knee flexion from 0°to 120°, the menisci move
posteriorly. In the midcondylar, parasagittal plane, the
medial meniscus moves approximately 5.1 mm, and
the lateral 11.2 mm (Arnoczky and McDevitt, 2000).
- The medial meniscus lacks the controlled mobility of
the lateral meniscus. - Posterior motion of the medial meniscus is guided by
the deep MCL, and semimembranosus, while anterior
translation is caused by the push of the anterior
femoral condyle (Simon et al, 2000). - The posterior oblique fibers of the deep MCL limit
motion in rotation, and therefore the medial meniscus
is at increased risk of tear (Arnoczky and McDevitt,
2000; Klimkiewicz and Shaffer, 2002).- The lateral meniscus is stabilized, and motion guided,
by the popliteus tendon, popliteomeniscal ligaments,
popliteofibular ligament, meniscofemoral ligaments,
and lateral capsule. - Meniscal motion allows continued load distribution
during changes of position of the joint, during which
the radius of curvature of the femoral condyles
changes (Simon et al, 2000).
KNEE STABILITY- The medial meniscus provides greater restraint to ante-
rior translation than the lateral, by acting as a buttress
(Levy, Torzilli, and Warren, 1982; Levy et al, 1989).
•ACL deficient knees demonstrate increased anterior
translation when subjected to an anteriorly directed
force, and this translation increases significantly with
combined meniscectomy at all angles of flexion. This
confirms the role of the ACL as a primary restraint to
anterior translation, and demonstrates that the medial
meniscus acts as a secondary stabilizer to resist ante-
rior translation (Levy, Torzilli, and Warren, 1982).
•With sufficient anterior translation (in the ACL defi-
cient knee), the posterior horn of the medial meniscus
is wedged between the tibial plateau and the femoral
condyle, and is the mechanism suggested for the
resistance provided by the meniscus. - In contrast, the soft tissue attachments of the lateral
meniscus do not affix the lateral meniscus as firmly to
the tibia. Combined lateral meniscectomy and ACL
sectioning does not increase anterior translation sig-
nificantly over ACL sectioning alone. This implies
that the greater mobility of the lateral meniscus pre-
vents it from contributing as efficiently as a posterior
wedge to resist anterior translation of the tibia on the
femur (Levy et al, 1989).
ADDITIONAL FUNCTIONAL ROLES
OF THE MENISCI- The menisci serve additional functional roles, includ-
ing load bearing, and shock absorption (Rath and
Richmond, 2000). The menisci transmit large loads
across the joint, and their contact areas change with
different degrees of knee flexion and rotation. - Up to 50–70% of compressive load is transmitted
through the menisci in extension, and 85% at 90°of
flexion (Greis et al, 2002; Arnoczky and McDevitt,
2000; Rath and Richmond, 2000; Klimkiewicz and
Shaffer, 2002).
344 SECTION 4 • MUSCULOSKELETAL PROBLEMS IN THE ATHLETE