Through the use of pressure-sensitive color film under static loading
conditions, intra-joint loads, contact area, and contact pressure
have been determined. Intra-joint loads have also been elucidated
through the use of computationally intensive computer simulations.
We present an experimental technique and loading mechanism that
can provide dynamic intra-joint loads during range of motion. The
goal of the study was to establish a dynamic range-of-motion testing
protocol encompassing measurement of intra-joint loads while retaining
the characteristics of joint compressive loads under minimal constraints
to motion.
Materials and Methods
Cadaveric knee specimens were mounted in a testing frame as shown
in Figure 1.
The quadriceps muscle was fastened to the hydraulic actuator of
a materials testing machine (MTS Systems, Eden Prairie, Minnesota)
through the proximal insertion site of the patellar tendon. The
vastus lateralis and medialis and hamstrings muscles were each loaded
with 45 N of tensile load at angles of 17°, 50°, and 0°, respectively,
in relation to the femoral axis as described by Lieb and Perry1. A knee flexion moment was generated
by a 90-N force equally distributed on both sides of the tibial
fixture. All pulleys were terminated and mounted with free rotating
swivel joints to reduce external bending moments (Fig. 1).
To account for the varied stiffness of the knee during range
of motion, an external goniometer mounted at the approximate center
of knee rotation was used by the servohydraulic controller as control
feedback for the actuator motion. This feedback provided reduced
actuator displacement rates at increased flexion angles, at which
increased resistance to knee motion was encountered as a result
of muscle forces. For all of the specimens tested, knee range of
motion was from 15° to 75° as measured with the goniometer. Each
knee was subjected to six loading cycles. To record dynamic intra-joint loads,
a total of ten 0.076-mm-thick film pressure sensors (Force Sensing
Technologies, Chicago, Illinois) were preconditioned and calibrated
for load2. The sensors were placed
on the anterior, mid-body, and posterior regions of both menisci
as well as on the proximal and distal aspects of the medial and
lateral regions of the patella (Fig. 2).
The sensors were secured in position with cyanoacrylate glue on
the non-sensing surface of the sensor exterior to the joint. The
dynamic voltage output from each thin film sensor was converted
to a load with use of the calibration curve specific to each sensor.
In order to compare regions within and between knee specimens, the
regional dynamic load data were normalized to the peak quadriceps
load.
Results and Discussion
The data illustrated reproducible loading patterns for the various
locations over the six cycles of applied loading. The dynamic data
reflected the load-bearing distribution under the knee menisci.
In the intact state, the lateral meniscus sustains a greater load
than the medial meniscus does. This finding is in keeping with those
in the current literature.
We described a method for determination of intra-joint loads during
dynamic range of motion. This method can be applied to the analysis
of intact, abnormal, and reconstructed joints of the musculoskeletal
system. The data obtained in this study reflect joint loads only
at the location of the thin film sensors. The diameter of each sensor
is 6 mm. However, the placement of multiple sensors within "central" areas
of distinct regions allowed assessment of patterns of change of
joint loads measured dynamically over a continuum of motion.
Numerous operative procedures have been proposed for the treatment
of recurrent dislocation of the patella and patellofemoral malalignment.
Medial transfer of the tibial tuberosity has been commonly used
(Figs. 3-A and 3-B).
Although surgical realignment is usually successful in correcting
patellar instability, its rates of success for alleviating anterior
knee pain are variable and less reliable3,4.
Normalization of the patterns of patellofemoral contact may therefore
be important design considerations in the treatment of recurrent
dislocations of the patella and patellofemoral malalignment. Previous
studies have demonstrated the effect of patellar realignment upon
the patellofemoral contact pressure5-10.
However, these studies did not include measurements of tibiofemoral
joint loading7. Moreover, it has
been reported that medial transplantation of the tibial tuberosity
diminishes control of lateral rotation of the tibia by the quadriceps
and increases varus loading within the knee11.
In this investigation, clinical medialization was defined as
the incremental medial transfer of the tibial tuberosity from the lateral
position to the original insertion site. Over-medialization was
defined as transfer of the tibial tuberosity up to 15 mm medial
to the original insertion site.
Goal of the Study
The goal of this study was to investigate the effect of tibial tuberosity
transfer on intra-joint articular cartilage loading through a range
of motion with use of dynamic thin film sensors in a model employing
quadriceps and hamstrings loading.
Materials and Methods
Six frozen human cadaver knees were obtained from three women
and three men with a mean age of fifty-four years (range, thirty-eight
to seventy-one years) at the time of death. To reproducibly control
the position of the tibial tuberosity following detachment from
the tibia, a medialization device was fabricated (Fig. 4). To standardize
insertion of the device among the specimens, the following orientation
method was employed. The coronal plane of the tibia was determined
to be collinear with a plane parallel to the floor with the knee
in full extension. A tibial trough was fabricated with a channel
orientation parallel with the coronal plane. The direction of the
channel axis across the anterior surface of the tibia was parallel
to the knee joint. The device was fixed with screws placed through
the tibia. The device permits controlled medial-lateral translation
of the tibial tuberosity with use of a screw guide and a sliding
mechanism. A screw penetrating the detached bone block of the tuberosity
was used to locate and lock the position of the tuberosity during
testing.
The zero-displacement condition was defined as the position of
the tibial tuberosity within the medialization device that corresponded
to the original position of the intact insertion. The device facilitated
transfer of the tibial tuberosity up to 15 mm in either the medial
or the lateral direction with respect to the original insertion
site. Lateral displacements represent pathological conditions found
clinically.
Results and Discussion
Changes in the position of the tibial tuberosity from the intact, normal
position create changes in the distribution of intra-joint loading,
within both the tibiofemoral joint and the patellofemoral joint.
Interestingly, the patterns of change in joint loading effected
by tibial tuberosity transfer are similar despite the direction
of the change of the tuberosity position (Fig. 5). In general,
tuberosity transfer in a medial or lateral direction away from normal
results in elevations of joint loads in the anterior and middle
regions of the medial tibiofemoral compartment and in the anterior
region of the lateral compartment while decreasing loads in the
middle and posterior regions of the lateral compartment. Likewise,
pathological positions of the tibial tuberosity (medial or lateral)
result in elevations of loads on the medial patellar facet.
More than 100 surgical procedures have been proposed for the treatment
of recurrent dislocation of the patella and patellofemoral malalignment12-21. Despite these numerous procedures,
few can correct a deficiency of the lateral femoral condyle when
one is present22,23. Anterior
osteotomy of the lateral femoral condyle, introduced by Albee in
1915, was designed to elevate the lateral femoral condyle and deepen
the trochlea22. It has been recommended
for refractory patellar dislocations associated either with patella
alta or with hypoplasia of the femoral trochlea (Figs. 6-A and 6-B).
However, to our knowledge, since 1915 only one clinical report on
the long-term results of this procedure has been published and there
have been no reports on the biomechanical effects24.
Goal of the Study
The goal of this study was to investigate the effects of anterior femoral
trochlear osteotomy on intra-joint patellofemoral loading through
a range of motion with use of dynamic thin film sensors in a model
employing both quadriceps and hamstrings loading.
Materials and Methods
Six frozen human cadaver knees were obtained from three women
and three men with a mean age of fifty-four years (range, thirty-eight
to seventy-one years) at the time of death. After anterolateral
capsulotomy, the external condyle was osteotomized from a point
just anterior to the weight-bearing surface of the tibiofemoral
articulation in full extension to a point 10 mm proximal to the
trochlea (Fig. 7).
The osteotomy was carried to a depth approximating the midpoint
of the trochlea. The lateral condyle was elevated, producing an
incomplete fracture near the trochlear groove (Figs. 8-A, 8-B, and 8-C).
Prefabricated aluminum wedges, 3, 6, and 10 mm in height, were used
to simulate bone grafts of various sizes (Fig. 9).
Results
The patterns of patellofemoral joint loading seen in this dynamic
study are consistent with those reported in the literature in studies
in which static joint loads were used. The distal regions of the
patella are loaded more in the early phase of knee flexion, with
progressive proximal migration of patellar contact as the knee travels
into further flexion (Fig. 10).
Discussion
Use of a 10-mm-wedge anterior femoral (Albee) osteotomy resulted
in the greatest increase in patellofemoral joint loads within the
distal region of the medial and lateral patellar facets in the early
phases of knee flexion (15° to 40°). In the normal, intact condition,
these loads remain elevated throughout the entire range of measured
knee flexion. At no point does a 3-mm-wedge elevation of the lateral
femoral trochlea result in any major elevation of patellofemoral
joint pressure. Interestingly, 6 and 10-mm-wedge elevations result
in (significantly) less load within the proximal region of the medial
patellar facet with knee flexion beyond 60°. Wedge elevations of
3 and 6 mm result in reduced loads within the distal region of the
lateral patellar facet, compared with that in the normal, intact
condition, throughout all degrees of motion.
The knee menisci are fibrocartilaginous structures that play
a critical role in the biomechanics of the knee joint. They transmit
the bulk of the compressive forces between the femur and the tibia
in addition to distributing stresses over the articular cartilage,
absorbing shock, and contributing to joint lubrication. The ability
to perform these mechanical functions is based on the intrinsic
material properties of menisci as well as their gross anatomic structure
and attachments25. A considerable
number of studies have elucidated the various roles of the meniscus
and have shown the importance of this structure in normal knee joint
function26,27. The protective
effect of the meniscus is primarily due to its ability to transmit
and properly distribute load over the tibial plateau. Several experimental
techniques that involve intra-articular casting, load/deflection
curves arthrography, photoelastic coating, and direct measurement
have been used to examine the load transmission characteristics
of the meniscus and the efficacy of meniscectomy28,29.
Both clinical and biomechanical studies have demonstrated detrimental
effects of meniscectomy, with changes in contact area and peak contact
stresses as well as radiographic alteration of the joint space30. It is assumed that the mechanical
effects of meniscectomy, meniscal repair, or meniscal transplantation
alter the native load transmission through the knee during range
of motion. However, to our knowledge, no one has yet investigated
the effect of these surgical procedures on the overall dynamic function
of the knee. Allograft meniscal transplantation has been suggested
as a means to alleviate future degeneration31-35.
While several reports have demonstrated the efficacy of transplants,
there have been few investigations of the biomechanical effects
of meniscal transplantation in the human knee36-38.
Goal of the Study
The goal of this study was to investigate the effects of lateral meniscal
repair, removal, and transplantation on intra-joint knee loading
through a range of motion with use of dynamic thin film sensors
in a model employing both quadriceps and hamstrings loading.
Materials and Methods
Eight fresh-frozen human cadaver knees were obtained from individuals
with a mean age of seventy years (range, twenty-two to eighty-six
years) at the time of death. Anteroposterior and lateral radiographs
were made to permit size-matching for cryopreserved lateral meniscal
allograft transplants (CryoLife, Kennesaw, Georgia). Small arthrotomies
were performed to allow placement of the dynamic thin film sensors
in the patellofemoral joint as well as in the lateral and medial tibiofemoral
joints.
Small anterior and posterior lateral arthrotomies were performed
and the lateral meniscus was incised longitudinally, mimicking a
bucket-handle tear, which was subsequently repaired with several
longitudinal sutures. This lateral-meniscal-repair knee model was
tested, and the respective joint pressures were recorded. The meniscal
repair sutures were removed from the repaired lateral meniscus,
and the bucket-handle tear was removed. This resulted in a subtotal-lateral-meniscectomy
knee model, which was subjected to mechanical testing. The meniscectomized
knee model was then used for the cryopreserved lateral meniscal
allograft transplant. A trough technique (Fig. 11) for anchoring
the anterior and posterior horns of the lateral meniscus as a bone
block was employed.
The lateral meniscal allograft transplant was introduced into the
knee through the small lateral arthrotomy sites (Fig. 12). The lateral
meniscal allograft was then sutured to the remaining host rim with
several longitudinally placed sutures from anterior to posterior.
This lateral-meniscal-allograft-transplant knee model was tested
in the same manner as previously described, and the respective joint
pressures were recorded.
Results and Discussion
In general, repair of the meniscus leads to load transmission through
the knee that is closer to normal than is that after a total meniscectomy.
While there is some discrepancy with respect to the normal loading
patterns, a repaired meniscus provides better physiological load
transmission through the knee over a range of motion than does direct
articular cartilage contact (Fig. 13).
While a meniscal transplant does reproduce an intact pattern of
loading at various sites within the knee, the lack of biological
anchoring around the meniscal rim reduces the direct load transmission
through the meniscus and may transfer the excess load to other elements
comprising the knee. The reduced loading of the patella and the
lateral tibiofemoral compartment may be due to the mismatch in height
between the native and allograft menisci. The planar dimensions
of the graft were generally excellent. However, the insertion of healthy
menisci from young individuals into more elderly patients, who often
have degraded joints, can itself be an issue. Unless specimens from
young individuals are available for in vitro testing,
similar studies involving meniscal transplantation will have comparable
limitations with respect to allograft size-matching.
Each of the above tested surgical conditions had an effect not only
on the lateral but also on the medial compartment of the knee. Furthermore,
it can be seen that alteration in the load transmission through
the knee with use of meniscal surgical techniques can also influence
patellofemoral joint mechanics.
Note: The investigators express their appreciation for support of
these studies to CryoLife Incorporated and the Research Program
Committee of the Cleveland Clinic Foundation.
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