Extract
Arthritis of the patellofemoral joint is typically an extremely
debilitating condition and is relatively common. Arthritic changes have been
found radiographically in the patellofemoral compartment in isolation in 13.6%
to 24% of women and in 11% to 15.4% of men in two studies of subjects who were
more than fifty-five and sixty years old,
respectively1,2.
When only patients with symptomatic osteoarthritis of the knee were
considered, the prevalence of isolated patellofemoral disease (in patients
over fifty-five years old) ranged from 5% to
8%2,3.
In a cadaver study of 100 individuals who were more than sixty-five years old
at the time of death, 79% had evidence of patellofemoral osteoarthritis,
although it was not in
isolation4.
Arthritis of the patellofemoral joint is typically an extremely
debilitating condition and is relatively common. Arthritic changes have been
found radiographically in the patellofemoral compartment in isolation in 13.6%
to 24% of women and in 11% to 15.4% of men in two studies of subjects who were
more than fifty-five and sixty years old,
respectively1,2.
When only patients with symptomatic osteoarthritis of the knee were
considered, the prevalence of isolated patellofemoral disease (in patients
over fifty-five years old) ranged from 5% to
8%2,3.
In a cadaver study of 100 individuals who were more than sixty-five years old
at the time of death, 79% had evidence of patellofemoral osteoarthritis,
although it was not in
isolation4.
However, despite the frequency of patellofemoral arthritis, and its various
predisposing conditions associated with anterior knee pain, it has
historically proven to be relatively refractory to treatment. This is due, in
part, to the complexity of the problem, and it reflects a possible previous
lack of recognition of the subtleties of the biomechanics at this
articulation.
As our understanding of the disease and the biomechanics of the joint has
improved, the management of patellofemoral arthritis and its antecedent
conditions has also become more clearly defined. Corresponding to the spectrum
of disease associated with the degeneration of the patellofemoral joint, a
range of management options are currently available and they are continuing to
be developed. Although there are areas of controversy, these current treatment
modalities, when appropriately applied, are associated with increasingly
successful patient
outcomes5-9.
There are many current areas of debate with regard to the management of
patellofemoral arthritis, but an appreciation of the biomechanics and function
of the patellofemoral joint underpins all modern interventions. Some of the
current controversies include the precise indications for certain procedures
and the types of soft-tissue and osseous realignment
procedures10.
Developments in chondrocyte culture and implantation have raised the issue of
the use of such treatments in the patellofemoral
joint8,9.
The question of which patients and which conditions are best suited to these
new treatments has also been raised by the recently improved results achieved
with unicompartmental patellofemoral
arthroplasties5,11,12.
Finally, recent literature has been encouraging with regard to the use of
total knee arthroplasty for the treatment of isolated patellofemoral arthritis
in certain, particularly older,
patients3,7,13.
The objectives of this symposium, therefore, were to provide an overview of
the current understanding of patellofemoral arthritis and of the issues
regarding its management and to provide some indication as to how these can be
expected to develop in the near future.
The patellofemoral joint offers challenges because of the unique
orchestration of static (ligamentous and osseous) elements and dynamic
(neuromuscular) factors that contribute to its functional capacity. Specific
elements of the comprehensive examination and investigations critical to
determining the nature of patellofemoral joint disorders are gradually covered
throughout this symposium. To better understand the possible etiology of
patellofemoral arthritis, a brief review of the anatomy of this joint is
detailed.
The patellofemoral joint includes the osseous morphology and its dysplastic
variants. More recently, the radiographic image of the osseous morphology of
the patella has been shown to be mismatched to the topography of its
cartilaginous
surface14. The
primary soft-tissue static stabilizers of the patellofemoral joint are the
medial and lateral patellofemoral and patellotibial
complexes15.
Patellofemoral function is also dependent on limb alignment, which includes
varus or valgus tibiofemoral alignment as well as rotational variances in
femoral version. More recently, the relation of the knee to the pelvic
position and strength has been added as an important stabilizer of the knee
and the patellar elements. This complex orchestration of factors offers
challenges to understanding normal, and thus abnormal, patellofemoral joint
function. Some forms of patellofemoral arthritis are due to abnormal forces;
the challenge is to understand the interplay of the components described
above, before advocating corrective measures.
Despite these challenges, it is useful to try to understand patellar
malalignment as a clinical entity. The dangers of relating patellar
malalignment to a specific single entity, such as an imaged view, is that this
can lead to surgery directed at trying to "correct" the alignment
without understanding how that image relates to the disease process or the
patient presentation. This can create negative consequences for patients,
including unnecessary surgery and/or poor results. This concept is eloquently
discussed by Post et
al.10, who defined
patellofemoral malalignment as "[a] malalignment of forces... a concept
of imbalance that helps explain patellofemoral disorders.... Treatment of
malalignment must include consideration of all contributing forces."
Patellofemoral arthritis is defined as the loss of articular cartilage on
one or both surfaces of the patella and/or in the trochlear groove. Does
malalignment play a role in patellofemoral arthritis? How often is
patellofemoral arthritis associated with radiographic evidence of
patellofemoral malalignment? This is difficult to discern from the literature.
A fair amount of documentation in the literature on patellar arthritis has
shown that the greatest prevalence of chondral wear is on the lateral patellar
facet as seen both clinically and in autopsy
studies16. The
presence of lateral facet arthritis does not equal malalignment, but it does
suggest that the lateral patellar facet becomes overloaded more commonly than
the central or medial aspect of the patella. This suggests that there is some
degree of tilt or malalignment or maldistribution of force in the etiology of
lateral facet arthritis.
With regard to the prevalence of radiographic malalignment in patients
managed with patellofemoral arthroplasty, one series of seventy-two knees
showed that sixty-one (85%) needed some form of realignment procedure at the
time of
arthroplasty17.
Other series of isolated patellofemoral resurfacing arthroplasty have shown
that patellofemoral arthritis associated with malalignment was the most common
clinical presentation in these patient
groups17. This
suggests that patellofemoral malalignment is a factor in the etiology of some
presentations of patellofemoral arthritis. Therefore, a patellar
"realignment" procedure might be appropriate to address this form
of patellar arthritis.
The goals of patellofemoral realignment surgery are to create both a stable
environment for optimal extensor mechanism performance and an appropriate load
transmission for optimal cartilage wear and joint loading.
Soft-tissue realignment surgery to address cartilage disease in the
patellofemoral joint has been described in the literature on patellar
instability. More than 150 variations of patellar realignments have been
reported. These include proximal procedures, such as releasing or lengthening
the lateral retinaculum; imbricating, reattaching, or reconstructing the
medial patellofemoral ligament; and/or advancement of the vastus medialis
obliquus.
Most distal procedures that involve osseous realignment are based on
transferring the tibial tubercle; among the most common such procedures
worldwide is the Elmslie-Trillat procedure (medial transfer of the tibial
tubercle). Anterior tibial tubercle elevation is discussed separately.
The outcome of soft-tissue patellar realignment for the treatment of
patellofemoral pain in the absence of instability is largely unknown. A
literature review showed that most reports typically involve mixed groups that
have both pain and
instability18. Most
studies are retrospective. Few have utilized a valid pain scale or a validated
functional scale.
The clinical importance of the medial patellofemoral ligament
(Fig. 1) in the stability of
the patellofemoral joint against lateral patellofemoral dislocation has been
well established15.
Reestablishment of the checkrein phenomenon of the medial patellofemoral
ligament is an important component of balancing the patellofemoral joint. When
imaging studies show evidence of lateral patellar subluxation, some degree of
laxity of the medial retinacular structures must be involved. Although
subluxation may be evident radiographically, the patient may or may not have
lateral tightness on physical examination. Therefore, to realign a patella
that has radiographic evidence of subluxation, one would need, at a minimum,
to address the soft-tissue patellar restraint provided by the medial
soft-tissue restraints, particularly the medial patellofemoral ligament.
Lateral release is a realignment procedure that historically has been
widely used for the treatment of anterior knee pain. Studies have shown that
the lateral retinacular release relieves anterior knee pain when there is
radiographic documentation of pathologic lateral patellar tilt in the absence
of patellar
instability19,20.
The commonly held belief that a lateral retinacular release causes the patella
to move medially is not borne out by biomechanical studies. The vector of the
lateral retinaculum is a posterior lateral vector. One study revealed that
cutting the lateral retinaculum resulted in a 10% decrease in the lateral
restraining
force21. This
operation, whether open or arthroscopic, should therefore be used only when
there is some tightness or a contracture of the lateral retinaculum that
tethers the lateral border to the patella posterolaterally and when
this is a source of pain and/or pressure-creating forces in the patellofemoral
compartment.
A more specific issue that continues to be debated concerns the concomitant
application of arthroscopic débridement and lateral release.
Satisfactory results are possible for patients with minimal arthritis of the
lateral facet who have patellar tilt and minimal or no
subluxation19,20.
In the face of clinically important arthritis, however, it should be
understood that débridement and release has limited goals with
typically incomplete and unpredictable pain relief and may often be a
precursor of more definitive interventions.
In patients with long-standing patellar tilt and malalignment, a tail, or
large osteophyte, is often apparent on the lateral aspect of the patella
(Fig. 2). There is support in
the literature for excision of this lateral facet, i.e., a partial lateral
patellar facetectomy, so to speak, as it may provide limited relief of the
symptoms of arthritis of the lateral patellofemoral
compartment22.
Therefore, the isolated lateral retinacular release in the treatment of
patellofemoral arthritis may have some applicability when the following
factors are present: (1) lateral patellofemoral arthritis on one or both sides
of the patellofemoral joint, (2) radiographic evidence of tilt without
subluxation, and (3) no clinical history of instability. Combining this
release with a partial lateral facetectomy when there is a large osteophyte
may increase its clinical utility.
Caution is required when soft-tissue patellar repositioning techniques are
considered for patients with a lesion in the central aspect of the trochlear
groove, as there is no evidence to suggest that changing the patellar
position, as an isolated procedure, unloads or relieves the contact forces in
this region.
There has been renewed interest in the role of soft-tissue realignment in
the treatment of patellofemoral chondral wear when it is combined with
surgical procedures that address the damaged cartilage. Proximal soft-tissue
procedures best address the clinical scenario of a patient with lateral
patellar subluxation combined with unipolar lateral patellofemoral compartment
arthritis.
It stands to reason that removing pressure from an arthritic portion of a
joint should allow symptomatic relief. This is the essence of tibial tubercle
transfer in the treatment of patellofemoral arthritis. It also forms the basis
for other osteotomy-based corrections of patellofemoral malalignment secondary
to valgus or rotational deformities, but these are not commonly encountered
causes of isolated patellofemoral arthritis. Realignment of the extensor
mechanism has been thought to provide relief because of the restoration of
normal alignment and mechanical function. An important corollary is often
overlooked, however. Realignment by transfer of the tibial tubercle can also
unload a fragmented painful surface of the patellofemoral joint. Historically,
transfer of the tibial tubercle with operations such as the Maquet and Hauser
procedures have met with poor results and are no longer indicated. The Hauser
procedure, for example, resulted in late severe osteoarthritis and was an
example of procedures based on measurements of abnormality of the
tibial tubercle according to the "Q angle." These procedures,
however, did not account for the variability in the normal values of the Q
angle or the potential increase in loading of the medial patellar facet (and
thus the subsequent possibility of medial tibiofemoral compartment arthritis)
caused by overzealous medial transfer of the tibial
tubercle10,23-25.
The key principles in successful tibial tubercle transfer for the treatment
of patellofemoral arthritis are as follows:
Restore or maintain proper balance of the extensor mechanism.Transfer load off a painful, degenerated area onto better cartilage.
Transfer the tibial tuberosity medially to unload the lateral aspect of the
patella and anteriorly to unload the distal aspect of the
patella26.Be sure to treat retinacular sources of pain.Perform tibial tubercle transfer in a way that allows early motion and
prompt healing.
Restore or maintain proper balance of the extensor mechanism.
Transfer load off a painful, degenerated area onto better cartilage.
Transfer the tibial tuberosity medially to unload the lateral aspect of the
patella and anteriorly to unload the distal aspect of the
patella26.
Be sure to treat retinacular sources of pain.
Perform tibial tubercle transfer in a way that allows early motion and
prompt healing.
Selection of Patients for Tibial Tubercle Transfer Osteotomy
Tibial tubercle transfer in the treatment of patellofemoral arthritis is
particularly attractive for younger patients. Buuck and Fulkerson demonstrated
long-term success and an increase in activity levels at four to twelve years
after anterior transfer of the tibial
tubercle6. When it
is properly done for the right indications, tibial tubercle transfer therefore
holds the potential for a permanent solution to patellofemoral arthritis pain
and dysfunction related to malalignment.
The surgeon must first determine the part of the patellofemoral joint that
needs to be unloaded by reviewing the findings of a detailed history, physical
examination, radiographs with the knee in 45° of flexion combined with
precise lateral views; magnetic resonance imaging scans, and arthroscopy. All
of the findings of these studies should correlate. For example, if the patient
sustained a dashboard injury or a crush injury of the patellofemoral joint
with the knee in flexion, the patellar articular lesion is likely to be
proximal since this area articulates with the femur when the knee is
flexed.
To select the correct osteotomy, one must understand that moving the tibial
tubercle anteriorly shifts contact on the patella such that more proximal
patellar articular cartilage comes into contact earlier in the flexion arc.
This is highly desirable when there is a distal patellar articular lesion that
can be taken out of contact by anteriorization of the tibial tubercle. Most
patients with malalignment-related patellofemoral breakdown have lateral and
distal articular
lesions26. Anterior
and medial transfer of the tibial tubercle, then, is well suited for the
typical patient with malalignment-related patellofemoral breakdown. Pidoriano
et al. established that the grade of articular lesion was far less
important than the location of a lesion in determining the likelihood
of success following anteromedial tibial tubercle
transfer27. In
patients with malalignment, however, the surgeon may need to compensate
additionally for dysplasia of the quadriceps or
trochlea23,28.
In most such patients, we use proximal retinacular balancing or reconstruction
as
needed29,30.
Once the location of a pain-producing lesion has been documented, the
osteotomy design should be straight-forward. If there is a lateral articular
lesion and lateral tracking, the patella should be moved medially with use of
a Trillat (straight medial) tibial tubercle
transfer31. If
there is a purely distal articular lesion with healthy proximal cartilage with
normal alignment (relatively uncommon), a straight anteriorization of the
tibial tubercle is most appropriate. If the patella has been overloaded
medially from previous surgery and there is medial articular cartilage
breakdown, sometimes associated with medial patellar
subluxation32,
anterolateral tibial tubercle transfer may be most
appropriate33.
The most common presentation that we see is lateral and distal patellar
breakdown related to lateral patellar tracking. It is best treated with
anteromedial tibial tubercle transfer with use of an oblique
osteotomy34,35.
One also must consider the fact that restoration of the normal alignment of
the extensor mechanism reduces chronic retinacular strain around the anterior
aspect of the
knee36 and improves
function and, therefore, may make future knee joint arthroplasty less
complicated.
Anteromedial Tibial Tubercle Transfer
An oblique osteotomy behind the tibial tubercle
(Fig. 3), tapered to the
anterior tibial cortex distally, allows dramatic unloading of the lateral and
distal aspect of the patella while restoring proper tracking of the extensor
mechanism. This procedure is performed through a longitudinal incision; the
osteotomy is cut from anteromedial to posterolateral, starting adjacent to the
medial aspect of the tibial tubercle, preferably with use of a cutting slot
guide (Fig. 4). It is
imperative that the osteotomy be monitored as it exits the lateral tibial
cortex. This is accomplished by retracting the anterior tibial muscle. This
lateral cut is then connected to a transverse cut proximal to the tibial
tubercle, and the osteotomized fragment is shifted anteriorly and medially
along the osteotomy plane. The transferred tibial tubercle is then fixed
securely with two cortical lag screws so that the patient can start early
motion. It is the procedure of choice for distal and lateral patellofemoral
arthritis related to chronic patellofemoral malalignment
(Fig. 5). Blood loss is minimal
with this type of surgery, incisional pain is less severe than that following
knee arthroplasty (since the incision is pretibial instead of peripatellar),
and immediate motion is possible (and encouraged). Skin problems and
compartment syndrome have not been noted following transfer of the tibial
tubercle through a flat, oblique osteotomy. Osteotomies are less desirable in
patients who smoke, are grossly obese, or are diabetic, but they are
attractive for younger patients for whom longevity is expected.
Anteromedial tibial tubercle transfer is an important adjunct to
patellofemoral resurfacing procedures. The surgeon must decide when unloading
with an anteromedial transfer of the tibial tubercle is sufficient in the
treatment of an articular lesion. Selectively, autologous or allograft
osteochondral core transfer may be a helpful adjunct, particularly on the
trochlear side.
To maximize the likelihood of a successful tibial tubercle transfer, the
surgeon must create a precise osteotomy, tapered to the anterior cortex
distally, to avoid creating a stress-riser in the tibia. Fixation must be
secured with cortical lag screws. Early range of motion is very important in
these patients, but weight-bearing must be protected for at least six weeks as
Stetson et al. showed a higher rate of tibial fracture with immediate
weight-bearing37. A
more recent study has shown that tibial fracture is more likely if the tibial
osteotomy creates a distal
stress-riser38. In
other words, technical precision is of paramount importance in achieving an
optimal result. Of course, transferring load onto healthy articular cartilage
and off diseased, painful cartilage is the goal of this type of surgery.
When patellofemoral changes are diffuse, as in a crush injury or following
patellar fracture, patellofemoral replacement may become necessary. In
general, however, anteromedial transfer of the tibial tubercle is the best
option in a young patient with distal and/or lateral patellar articular
lesions, even when there is bone on bone laterally.
When autologous chondrocyte implantation is being considered for the repair
of a cartilage defect, it is critical that the etiology and the underlying
cause or abnormal pathomechanics of the defect are accurately identified. The
diagnosis and correction of these underlying abnormalities are crucial to a
successful outcome with autologous chondrocyte implantation. It is now clear
that a failure to fully appreciate this point explains the disappointing early
results of resurfacing of the patella. In a study from Sweden published in
1994, autologous chondrocyte transplantation was successful (a good or
excellent result) in only two of seven
patients39.
However, in later
reports8,9,
in which patellar tracking was also addressed with realignment of the extensor
mechanism at the time of transplantation, eleven of seventeen patients had a
good or excellent result at two
years9 and this
improved to thirteen of the seventeen patients at ten
years8. The
importance of correcting the underlying cause of the chondral injury cannot be
underestimated.
As previously mentioned, Pidoriano et al. demonstrated that with the
anteromedial tibial tubercle osteotomy, a successful clinical outcome
correlates with the location of the patellar articular
lesion27. Patients
with type-I (inferior pole) or type-II (lateral facet) lesions were
substantially more likely to have a good or excellent result than were those
with type-III (medial facet) or type-IV (proximal pole or diffuse)
lesions27. Central
trochlear lesions were associated with medial patellar lesions, and these
patients had a poorer result.
Localization of the articular cartilage injury at the time of
reconstruction is therefore important to determine whether osteotomy alone may
predict a successful outcome. Despite the mediocre results to date, as
discussed above, cartilage repair of patellar type-III and IV lesions, as well
as trochlear lesions, may still be useful in improving the clinical outcome
for these difficult lesions when they are associated with patellar maltracking
or when there is normal tracking but no other options exist.
Clinical Evaluation and Technical Considerations in Autologous
Chondrocyte Implantation
Autologous chondrocyte implantation is indicated in the management of focal
chondral defects in the knee. The cartilage space must be documented as intact
on standard radiographs, to indicate that the overall joint space is patent,
the margins are well shouldered, and the cartilage loss is not diffuse, but
contained.
The standard workup for these patients includes a thorough review of the
history and a careful physical examination of the axial alignment as well as
the patellofemoral joint. A routine series of radiographs is made for all
patients; these include standing anteroposterior, 45° posteroanterior
flexion weight-bearing (Rosenberg), lateral, and skyline (Merchant)
radiographs and a 54-in (1.37-m) axial alignment radiograph. When maltracking
is suspected on clinical examination, a computed tomography scan is performed,
with the leg in extension and with and without quadriceps contraction, to
assess lateral patellar subluxation, the presence of dysplasia of the
trochlea, and patellar height. Correction of any underlying pathomechanic
disorder that is identified can thus be planned in combination with the
cartilage repair.
When a patient is considered a candidate for autologous chondrocyte
implantation, arthroscopy is performed to assess the diameter and depth of the
lesion and any maltracking. A cartilage biopsy specimen is also obtained from
the non-weight-bearing portion of the superior intercondylar notch at this
point for the cell culture process. Approximately 200 to 300 mg of articular
cartilage is sent in a sterile transport medium to be commercially cultured
and cryopreserved. The transplantation procedure is then performed as
previously
described40.
Technical issues that are specific to autologous chondrocyte implantation in
the patellofemoral joint include a suture technique that restores the
articular surface shape of the patella and the trochlea
(Fig. 6) as well as a
soft-tissue tensioning at the end of the procedure that allows the normal
medial-to-lateral and proximal-to-distal patellar glide without overstuffing
the patellofemoral joint.
We believe that the factors that determine the success of cartilage repair
include alignment and tracking, joint stability, chondral defect size, the
integrity of the menisci, and finally the patient's predisposition to
osteoarthritis as evidenced by poor-quality articular cartilage. Hence, if
there is =2° of mechanical malalignment from a neutral mechanical axis
in the tibiofemoral joint in combination with a large chondral defect, then a
varus or valgus-producing osteotomy should accompany the cartilage repair on
the weight-bearing condyles. If there is evidence of patellar subluxation and
tilt on clinical examination and/or computed tomography, then an anteromedial
tibial tubercle transfer is performed in combination with resurfacing of the
patella or trochlea, or both.
The principles of postoperative therapy include functional rehabilitation
that avoids resisted open-chain activities. Rehabilitation in the first six
weeks includes restoration of the tibiofemoral range of motion as well as
patellar mobility to prevent infrapatellar tendon contracture. This is
accomplished with aggressive deep friction, mobilization, and stretches as
well as continuous passive motion for six weeks postoperatively and stationary
bicycle use beginning at four weeks. Muscle tone is reestablished with
isometric leg lifts, muscle contractions, and stationary bicycling. As the
patella and trochlea experience maximal contact forces between 40° and
70° of flexion, open-chain quadriceps extensions through this range of
motion are avoided.
Results of Autologous Chondrocyte Implantation
Minas and
Bryant41 performed
a seven-year, prospective cohort study of forty-five patients who underwent
autologous chondrocyte implantation for the treatment of full-thickness
chondral defects of the patella or trochlea, or both. The average age of the
patients at the time of surgery was 36.9 years (range, fifteen to fifty-four
years). The average duration of follow-up was 47.5 months (range, twenty-four
to eighty-six months). A patient survey showed that 71% were satisfied with
the outcome, 16% were neutral, and 13% were dissatisfied. Eighty-seven percent
of the patients said they would choose the surgery again. Overall, 71% of the
patients rated the results as good to excellent; 22%, as fair; and only 7%, as
poor. The largest improvement in sports activity rating, surprisingly, was for
the patients with the most severely injured knees. Large clinical improvements
at a significant level were documented with use of the Short Form-36 (SF-36),
the Knee Society score, the Western Ontario and McMaster University
Osteoarthritis Index (WOMAC), and the modified Cincinnati knee score
(Table I).
Twenty-nine (64%) of the forty-five subjects required an osteotomy for the
treatment of tibiofemoral or patellofemoral malalignment, or both. The
osteotomy effect alone would not account for the high success rate, according
to the results described by Pidoriano et
al.27, because of
the size and location of these chondral defects.
Typically, patients start to have pain relief by four to six months after
surgery. Non-impact sports activities are commenced at nine months
postoperatively, and full-impact activities are begun by eighteen months
postoperatively. Maximal improvement may take as long as three years for
patients who have large areas of chondrocyte implantation, as additional time
is needed for graft maturation.
The graft failed in eight patients (18%). Of the eleven patients with a
Workers' Compensation claim, five had a graft failure. Failure of the graft
was considered a partial or full failure (which was evidenced by delamination
or detachment of the graft from the adjacent cartilage and subchondral bone as
seen at arthroscopy or on magnetic resonance imaging, or as evidenced by
fibrous or fibrocartilage repair) regardless of a good clinical outcome. These
results are similar to those found by Peterson et al., who addressed patellar
maltracking at the time of surgery or corrected it prior to the time of
autologous chondrocyte
implantation9. The
results in their patients remained durable for up to ten years after
implantation8. These
are excellent outcomes for patients with difficult problems.
The data in the study by Minas and Bryant showed that when type-III and IV
chondral injuries to the patella as well as the central part of the trochlea
were resurfaced, patients had good clinical pain relief and improved function
regardless of whether there had been preexisting patellofemoral maltracking
requiring a Fulkerson osteotomy. Autologous chondrocyte implantation remains
the treatment of choice for disabling anterior knee pain resulting from large
erosive chondral defects (4 to 6 cm2 on the average) when the
radiographic joint space remains intact.
However, when collapse of the joint space can be seen on the Merchant or
skyline radiograph, cartilage repair with autologous chondrocyte implantation
is no longer possible. The procedure relies on intact, full-thickness
cartilage margins to maintain the joint space so that the growing cartilage
repair tissue may fill the defect. With joint space collapse, a
unicompartmental patellofemoral or total knee arthroplasty may be
considered.
The patellofemoral joint is susceptible to both primary osteoarthritis and
secondary osteoarthritis because of the large forces transmitted across small
contact areas and the high prevalence of anatomical abnormalities or
dysplasia.
Patellofemoral dysplasia is increasingly recognized as the underlying cause
of multiple symptoms within the patellofemoral articulation, such as
dislocation and painful instability, and it often results in secondary
osteoarthritis if not reconstructed.
The first report of a patellofemoral replacement, to our knowledge, was the
McKeever screw-on Vitallium patellar shell, which was introduced in
195542. The designs
evolved through various materials until 1979, when the Lubinus patellar glide,
or total patellofemoral replacement, was
reported43.
Patellofemoral arthroplasty has the potential advantages of retaining the
menisci and cruciate ligaments and thereby the natural kinematics of the knee
joint; however, the shortcoming of this procedure to date has been the
durability of the arthroplasty. Previous cohort studies of several different
patellofemoral designs have described indifferent
results12,17,44,45.
For example, in a study of seventy-six knees, the Lubinus prosthesis had a
failure rate of 50% at eight
years46. The main
reasons for failure have been persistent malalignment, wear, impingement, and
disease progression.
However, better results are emerging with the Avon patellofemoral
replacement11,12
(Stryker Orthopaedics, Limerick, Ireland), which is specifically designed to
address the reasons for failure described above
(Figs. 7-A, 7-B, and 7-C). The
design of the Avon replacement is based on the patellofemoral compartment of
the Kinemax Plus total knee replacement (Stryker Orthopaedics). The femoral
flange is shallow and broad, allowing unconstrained capture of the patella
into a deeper trochlea with flexion. The patellar button is offset and
uniquely chamfered on its medial side to create an odd facet and avoid
impingement on the medial femoral condyle in deep flexion. The femoral
component is lateralized slightly and externally rotated to aid patellar
tracking. Four component sizes are available. An added advantage of the use of
components based on a total knee design is that even if the patellofemoral
replacement is successful, this design facilitates later conversion to a total
knee replacement if it should become necessary as a result of disease
progression. We believe that some technical points are important to follow in
the procedure. These include the circumferential incision of the synovial
membrane adjacent to the patella with definition of the edges of the patella
to facilitate accurate resection. Sufficient soft-tissue release to allow a
positive patellar tilt test is important and typically includes release of the
patellofemoral ligament and the retinaculum from any lateral osteophyte, which
in turn should be
resected47.
Accurate measurement of the patellar thickness is obviously critical for
symmetric resection.
In vitro biomechanical studies (unpublished data) have demonstrated the
stability of the patella and contact pressures that are similar to those of
the normal joint, and in vivo kinematic studies (unpublished data) have shown
that the Avon patellofemoral replacement mimics the normal knee.
The first replacements were implanted in September 1996 and were entered
into a prospective
study5. The outcome
was assessed with use of pain scores, the Bartlett patellar score, and the
Oxford knee score. To date, 307 knees have been treated and 159 knees were
reviewed at two to five years. The improvement in pain and function scores was
maintained in the medium term (Table
II)5.
Movement increased from 114° to 120° at five years. Four patients had
malalignment develop, and one of them required distal soft-tissue realignment.
No knee had a deep infection, fracture, wear, or loosening. Eighteen (6%) of
the 307 knees had evidence of disease progression in the tibiofemoral joint,
and fifteen of them required revision to a total knee replacement. The
functional results in these patients are similar to those after a total knee
replacement5,11,12,48.
The results of the cohort of patients who were less than fifty-five years
old and were followed for a minimum of five years are even more encouraging
(Table
II)5.
The underlying diagnosis in this group was secondary osteoarthritis in a much
higher proportion than in the overall group. As the osteoarthritis was
predominantly secondary to trauma, e.g., patellar fracture, the other
compartments of the knee were typically relatively uninvolved, providing a
probability of a lower long-term rate of disease progression at the
tibiofemoral articulation.
The results to date suggest that this improved design has potentially
eliminated the previous problems of malalignment and early wear. The patients
had a low rate of complications and an excellent range of
movement5. Disease
progression in the tibiofemoral joint remains a potential problem. This type
of prosthesis offers a reasonable alternative to total knee replacement in
patients with isolated patellofemoral disease, particularly in those who are
considered too young for a total joint replacement. The use of patellectomy in
these younger patients has been associated with poor results and failure in up
to 47%, with variable amounts of pain relief, substantial loss of power,
instability, and extensor lag
reported49,50.
One important variant to remember, however, is the potential role of
anteromedial transfer of the tibial tubercle in knees with isolated lateral
facet lesions, as the procedure has been associated with good results, even in
knees with advanced (bone-on-bone)
disease27. Current
indications for patellofemoral arthroplasty, therefore, include isolated
patellofemoral disease with minimal or no malalignment in a younger patient
who would otherwise consider undergoing a patellectomy because of the severity
of the symptoms.
Although in some respects counterintuitive, the use of total knee
arthroplasty for the treatment of isolated patellofemoral arthritis has
recently been confirmed as an effective method of managing this condition in
the older
age-group3,7.
This approach is not advocated for younger patients with isolated
patellofemoral arthritis. Of course, a full course of nonsurgical management
should be attempted first, as is the case before most surgical interventions
described in this symposium. Nonoperative management of these patients
includes physical therapy (with quadriceps and hamstring stretching along with
vastus medialis obliquus strengthening and isometric and short-arc
closed-chain concentric and eccentric muscle strengthening), bracing, oral
medications and injections, and activity modification.
The exact age at which total knee arthroplasty becomes a viable option for
the treatment of patellofemoral arthritis is debatable and case-dependent.
However, it is currently believed that, in general, these patients should be
more than fifty-five years
old7. In the past,
younger patients have generally been considered candidates for realignment
procedures or patellectomy. The latter procedure has had poor results, as
already noted, but it is hoped that the newer developments in treatment, which
were also described earlier in this symposium, will continue to improve the
options for these younger
patients49,50.
Careful adherence to correct techniques and component alignment are well
recognized as being crucial to the success of any total knee arthroplasty.
These issues are of even more critical importance in the treatment of isolated
patellofemoral disease and its typical association with abnormal mechanics and
alignment. Particular attention must be directed toward the correction of
extensor mechanism alignment, and, indeed, it has been found that the rate of
lateral retinacular release in these patients is as high as 68%, which is as
much as three times that in standard total knee
arthroplasty3,13.
The same investigators also reported that the rate of proximal extensor
mechanism realignment was 10% in this patient group.
Although the technique of total knee arthroplasty for patellofemoral
disease is, in essence, the same as that for tricompartmental
disease—leaving aside the debate as to whether the patella should be
routinely resurfaced—the procedure is typically a more challenging
technical undertaking for patellofemoral disease, and some points merit
emphasis. It is critical to avoid internal rotation and medialization of both
the tibial and femoral components. Well-described landmarks such as the
epicondylar axis, axis of Whiteside, posterior condyles, and the tibial
tuberosity should all be carefully checked to ensure that there is adequate
external rotation and lateralization of these components to facilitate
accurate patellar tracking. Excessive femoral valgus and oversizing of the
femoral component are also to be avoided for the same reasons. The patellar
component itself should be medialized for greatest stability. It is also
important to achieve an evenly resected patellar surface, parallel to the
nonarticular surface, to accommodate the patellar component. This avoids a
lack of congruity, tilting, and thus maltracking of the prosthetic
patellofemoral articulation. It is, however, important to be aware of the
potential for exaggerated thinning of the lateral facet in these knees; a
degree of controlled underresection of this facet may be required to maintain
adequate bone stock. Restoration or maintenance of the native joint line is
also important, and the creation of an overly thick or thin patellar construct
is to be avoided.
Once the components have been selected, a trial reduction and assessment of
tracking (we prefer the use of the so-called no-thumbs technique of Insall) is
vital. As stated above, a higher rate of lateral release in these knees can be
anticipated3,13,51.
Although the release in these knees may be relatively extensive, it is
worthwhile attempting to preserve the superior lateral geniculate artery. This
minimizes further vascular insult to the patella, which may have been
compromised somewhat by the typical medial parapatellar approach and fat pad
resection. Maintaining sufficient patellar vascularity will obviously diminish
the rate of later complications, such as osteonecrosis and
fracture51. In
cases in which a retinacular release is necessary, we preserve the distal
(tibial) attachment of the fat pad and release the proximal (patellar)
attachment. The proximal pole of the fat graft is then transposed laterally to
close the gap created by the retinacular release. We believe that this serves
two purposes: (1) it minimizes the severity of vascular injury to the patella,
and (2) it minimizes the formation of subcutaneous hematoma and postoperative
drainage. It is noteworthy in this regard that lateral release has been
reported to increase the prevalence of patellar fracture from 15% to >50%
overall52.
Although implant design considerations and their impact on patellofemoral
kinematics are somewhat outside the scope of this report, issues to be
cognizant of include the dimensions and symmetry of the trochlear groove, the
congruence of the femoral and patellar components, and the symmetry of the
patellar component itself.
Results with total knee arthroplasty for the treatment of patellofemoral
arthritis have been very good and are associated with reliable pain relief.
Admittedly, three main reports on this management approach have noted a high
rate of residual postoperative patellar tilt, asymmetrically resurfaced
patellae, and residual
subluxation3,7,13,
reflecting the technical complexity inherent in these cases. Nonetheless, the
patients in those studies achieved uniformly good-to-excellent results in
terms of pain relief, results that were superior to those achieved by
comparison groups that had total knee arthroplasties performed for other
conditions. Although preoperative anterior knee pain was more prevalent in the
patients with patellofemoral arthritis than in those with tricompartmental
arthritis, equal numbers of patients reported residual anterior knee pain
following total knee
arthroplasty3,13.
Also, despite the fact that the ability of patients with patellofemoral
arthritis to climb stairs preoperatively was less than that of patients with
tricompartmental disease, postoperatively the patients with patellofemoral
arthritis had a greater ability to climb stairs in a bipedal manner and had
higher Knee Society
scores3.
The debate regarding the use of this procedure currently centers on the
fact that it can appear that a tricompartmental arthroplasty is an excessive
response to a unicompartmental condition. Although more conservative
approaches, in particular patellofemoral arthroplasty (which has had
increasingly encouraging results), would be theoretically more satisfactory,
total knee arthroplasty currently remains the most proven and predictable
single procedure in this specific population of older patients with
patellofemoral
disease5,7,13,42,48.
Total knee arthroplasty, therefore, remains a reasonable option for these
patients until its reliably excellent results can be equaled by other
interventions.
It is clear that there is a complex spectrum of patellofemoral disease
often culminating in arthritis. There is a correspondingly wide array of
management options, depending on the exact nature of the disease in an
individual. This complexity dictates that, when a patient who has anterior
knee pain is seen, a determination of the precise etiology is essential. It is
only through an accurate identification of the problem that the correct
treatment modality can be established. The importance of determining the
etiology has been emphasized throughout this symposium, and we have presented
current viewpoints regarding the appropriate treatment modalities depending on
the nature of the patellofemoral disease encountered.
Although its role is still not fully defined, patellar malalignment has
been shown to be an important factor in the etiology of patellofemoral
arthritis. Utmost care is required, however, in determining how malalignment
relates to the disease process or the painful situation in an individual
patient in order to ensure appropriate surgical interventions. Procedures
strictly involving soft tissue, such as isolated lateral retinacular release,
can have a useful if somewhat limited role in the treatment of patellofemoral
arthritis. Such procedures are particularly suited to patients with lateral
patellar subluxation combined with unipolar lateral patellofemoral compartment
arthritis, but they should be avoided when there is a lesion in the central
part of the trochlear groove.
Tibial tubercle transfer has proven to be very successful for patients with
patellofemoral arthritis who still possess healthy cartilage onto which the
patellar tracking can be transferred. As with all procedures for the treatment
of patellofemoral disorders, the results depend on proper patient selection
and the proficiency of the surgeon. It is important to be aware of the correct
indications for this procedure and to be proficient in the technical aspects
of its performance in order to obtain satisfactory outcomes free of
complications. The great advantage of the tibial tubercle transfer is that it
can provide a permanent solution for the pain and dysfunction associated with
malalignment-related patellofemoral arthritis. This is particularly important
when considering younger patients who may have more limited treatment options
than their older counterparts.
Cartilage resurfacing also represents a very promising treatment option
with the potential for long-term resolution of disease and symptoms, which may
be particularly advantageous in younger patients. The ultimate goal of this
approach, in combination with tibial tubercle transfer, is to supplant the
need for patellectomy or arthroplasty in younger patients with relatively
early disease. Again, careful adherence to patient selection criteria and
accurate technical performance are crucial to the success of autologous
chondrocyte implantation. Substantial improvements in the understanding and
technique of this procedure in the patellofemoral articulation have led to
improved results and more reliable outcomes. Once established, this technique
may become the treatment of choice for large, erosive chondral defects
associated with disabling anterior knee pain.
As with other procedures described in the present report, patient selection
is critical to the success of patellofemoral arthroplasty. A candidate for the
procedure should have isolated patellofemoral disease, which is not
inflammatory, and should have no substantial maltracking. Although ideally
there should be no tibiofemoral disease, the presence of grade-III
chondromalacia in the tibiofemoral articulation is a definite
contraindication. With the improvements in the results currently being
reported, patellofemoral arthroplasty may be a solution for younger active
patients with debilitating disease who would otherwise be candidates for
patellectomy. Prosthetic design is critical to success, and there is currently
a need for high-quality, long-term prospective data to define the role of
patellofemoral arthroplasty.
It seems increasingly likely that, with the improving results of modern
patellofemoral arthroplasty and alternative procedures, the use of total knee
arthroplasty for the treatment of patellofemoral arthritis will eventually be
outmoded. For the moment, however, these alternatives do not provide rates of
consistently excellent pain relief and functional improvement that are equal
to those achieved with total knee arthroplasty in the older patient
population. There are important technical challenges in applying total knee
arthroplasty to these patients, and the procedure is not recommended for
younger patients.
Despite the progress in the treatment of patellofemoral arthritis, it
remains difficult to achieve absolute unanimity on the best course of
treatment for a given patient. As more evidence is obtained from good-quality,
prospective, long-term clinical studies with regard to both the etiology and
management of this disease, we can anticipate increasing agreement on these
issues. Such studies, though, have traditionally proven difficult to perform
and by their nature take some time to come to fruition. This is a microcosm of
many of the issues faced in current orthopaedic practice, in which definitive
evidence often lags behind clinical developments. What is needed is
information regarding which patients with maltracking or anterior knee pain
will progress to arthritis and thus would benefit from early, less aggressive
interventions. When arthritis does occur, we need to know which patients are
best suited to the current management options through long-term outcomes
analysis. Specific controversial and topical areas that can be expected to
profit from better evidence include the relative roles for chondral
reconstruction, redirection osteotomies, and patellofemoral arthroplasty.
Therefore, although the treatment of patellofemoral arthritis is not fully
resolved, there are currently many exciting areas of progress. These advances
offer considerable promise that this previously poorly managed spectrum of
disease will ultimately prove amenable to a defined set of graduated
interventions, thus ensuring satisfactory symptomatic and functional outcomes
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