Aplasia of the patellar tendon rarely has been reported in the
orthopaedic literature. In a MEDLINE search from 1963 through 2004, we found
only four reported
cases1-3:
two had been detected with use of magnetic resonance imaging in patients with
fibular or tibial hemimelia (noted in one patient
each)3, one had been
discovered with use of ultrasound in a nine-day-old girl with tibial
hemimelia1, and one
had been noted in a twenty-five-year-old woman with bilateral congenital
absence of the patellar
tendon2. None of
these three reports described the indications for surgery or the results of
attempted reconstruction.
We present the cases of two patients who had congenital aplasia of the
patellar tendon associated with shortening of the involved limb. One patient
underwent reconstruction of the patellar tendon; the other was treated
nonoperatively. The parents of both patients were notified that data
concerning the cases would be submitted for publication.
Case 1. An eight-year-old boy presented to our
institution with lower-extremity limb-length inequality (with the left lower
limb being shorter than the right).' This condition caused the boy to limp and
interfered with activities of daily living and sports activities.
During pregnancy, the patient's mother had had eclampsia with severe
hypertension. Ten weeks prior to the due date, it became necessary to deliver
the child by cesarean section. The boy weighed 1250 g at birth and was
monitored for ten weeks in the intensive care and intermediate care units. The
family history was negative for musculoskeletal abnormalities, and an older
brother was normal. When the child was two months of age, a skin depression
developed over the lateral aspect of the left femoral condyle and an extension
lag of the knee was observed. When the patient reached six months of age, the
patella was found to be more proximally positioned than normal on both
physical examination and ultrasonography. Plain radiographs showed no
appreciable abnormalities of the knee; however, the patella was not yet
ossified. The diagnosis was a knee flexion contracture due to an
arthrogryposis-like disorder, and physical therapy was recommended. Annual
clinical examinations, performed until the patient was seven years of age,
revealed an active extension lag of 20° to 35°. Repeat radiographs
demonstrated hypoplasia of the femoral condyles as well as a proximally
positioned patella (patella alta).
Physical examination at our institution revealed that the left lower
extremity was 6 cm shorter than the right (with a difference of 3 cm in the
femur and 3 cm in the tibia) and that the knee extensor mechanism was
insufficient. The patient had a unilateral crouched gait because of the
shortening of the left lower extremity. An active extension lag of 40° was
documented. Passive range of motion of the knee was from 10° to 130°,
with a 10° flexion contracture. There was an absence of patellar
engagement with the patellofemoral groove even with the knee in maximum
flexion. No patellar tendon was palpable. Patellar mobility and stability were
essentially normal, and the knee was stable and not painful. The anterior and
posterior cruciate and collateral ligaments were palpated and were found to be
intact and stable. Because of the flexion contracture of the involved knee,
there was a compensatory flexion contracture of the hip as well as ankle
equinus (each of which measured 10° to 15°). No other abnormalities of
the affected or the contralateral extremity were observed during the physical
examination. Repeat radiographs and magnetic resonance images demonstrated a
hypoplastic patella in a more proximal position than normal. The patellar
tendon was absent, and the quadriceps muscle was severely hypoplastic (Figs.
1-A, 1-B,
1-C, 1-D).
After a discussion of nonoperative and operative options, the parents
decided to proceed with patellar tendon reconstruction. A limb-lengthening
procedure was also discussed but was not performed.
Intraoperatively, the patellar tendon was absent and the quadriceps muscle
was fibrotic, with adhesions to the femur. With use of a V-Y quadriceps
mechanism reconstruction and dissection of the adhesions, the hypoplastic
patella was mobilized distally to the patellofemoral groove. The patellar
tendon was reconstructed by doubling the capsule distal to the patella and
using a semitendinosus tendon autograft and a PDS (polydioxanone) cord
(Ethicon, Norderstedt, Germany). Following reconstruction, the passive
intraoperative knee motion was from 0° to 60° of flexion.
Postoperatively, the lower extremity was immobilized in an above-the-knee
cast for ten days. Intermittent passive range-of-motion exercises (with a
flexion arc of 0° to 40°) were then performed for twenty minutes,
three times a day, for one week. To stimulate the quadriceps, a 2-Hz electric
muscle stimulator (Microstim, Hamburg, Germany) with an impulse intensity of
10 to 30 mA and an impulse duration of 7 ms was applied for thirty minutes per
day, starting at two weeks postoperatively and continuing for eight weeks. At
2.5 weeks postoperatively, 60° of passive flexion was allowed during
physical therapy. When physical therapy or passive motion was not being
performed, the lower extremity was immobilized in a custom-made above-the-knee
posterior splint, which was used for six weeks postoperatively without
weight-bearing. Subsequently, the patient received a commercially available
knee sleeve with an incorporated silicone insert that applied no pressure to
the patella (GenuTrain; Bauerfeind, Kempen, Germany). Partial weight-bearing
was then allowed for four weeks, followed by full weight-bearing. The patient
utilized a shoe-lift because of the limb-length inequality. Physical therapy
was continued three times a week, with particular attention focused on
quadriceps strengthening. Wound-healing was unimpaired.
One year postoperatively, the patient's gait had improved. There was still
an active extension lag of 35°. The passive range of motion was from
0° to 90° of flexion. A repeat magnetic resonance imaging scan showed
that the patella was positioned in the patellofemoral groove and that the
reconstructed patellar tendon was intact.
Two years postoperatively, when the patient was ten years old, the gait had
deteriorated and was worse than it had been before the operation. It was
characterized by a persistent short-leg limp with an insufficient quadriceps
mechanism; concentric contraction of the quadriceps did not produce full knee
extension. The patient compensated by swinging the affected limb forward to
passively extend the knee, resulting in a limp. The parents and the patient
were dissatisfied with the outcome of surgery. The child subsequently resumed
physical therapy, and an electronic stimulator was used in an effort to
strengthen the quadriceps muscle. Passive knee motion changed minimally, and
there was a persistent extension lag of 60°
(Fig. 1-E). The patella was
palpable within the patellofemoral groove. The reconstructed patellar tendon
was also palpable. The knee was otherwise stable and not painful. Additional
magnetic resonance images showed that the reconstructed patellar tendon and
the patella were in the physiologic position but that the quadriceps muscle
remained atrophic (Figs. 1-F and
1-G).
Case 2. A 7.5-year-old boy presented to our institution with a
slightly impaired gait due to an insufficient knee extensor mechanism. He was
not limited in activities of daily living or school-related sport activities,
such as gymnastics; however, he could not participate in more vigorous sports,
such as tennis or soccer. There was minimal pain after exertion.
The medical history revealed that, during pregnancy, the boy's mother had
undergone amniocentesis that had resulted in leakage and that had been treated
with bed rest for one week. The child was delivered vaginally on the expected
date and without complications. The birth weight was 2800 g, and there were no
postnatal problems. The family history was negative for pediatric
musculoskeletal abnormalities except for idiopathic scoliosis, in the elder of
two brothers, which had been treated nonoperatively. The patient walked
independently at fourteen months of age. At two years of age, an insufficient
knee quadriceps mechanism was observed on the right side; however, no
radiographs or other studies were performed at that time. When the patient was
four years of age, a developmental delay was diagnosed and, for the first
time, patellar tendon aplasia of the right knee was documented on the basis of
a physical examination and ultrasonographic testing. Radiographs of the right
knee demonstrated that the patella was in a more proximal position than
normal. The treating physicians recommended operative treatment without
specifying their operative strategy.
Physical examination revealed that the patient walked with the involved
extremity externally rotated 30° to 40° and compensated for the
insufficient extensor mechanism by swinging the affected limb forward to
passively extend the knee. The right femur was 2 cm shorter than the left
femur. The tibial lengths were equal. Passive range of motion of the right
knee was from 5° to 150° of flexion, with an active extension lag of
30°. The patella was palpable and mobile, but it was positioned proximal
to the patellofemoral groove (patella alta). No ligamentous instability was
present. A magnetic resonance imaging scan demonstrated that the patella was
of normal size but was lying in a more proximal position than normal and that
the patellar tendon was absent. The quadriceps muscle appeared to be severely
hypotrophic. The ranges of motion of the hip and ankle were normal. Neurologic
examination revealed normal findings. The contralateral extremity was examined
and was deemed normal.
When the patient presented to our institution, we recommended observation
because of the lack of symptoms and the relatively normal function of the
limb. Two years later, when the boy was 9.5 years of age, physical examination
revealed essentially no change in his condition: the gait was still slightly
impaired by the deficient quadriceps muscle, and the knee extension lag was
still 30°.
The patellar tendon is formed during the early stages of fetal
development. It begins to form as early as the sixth week of fetal life as a
detachment from the lower part of the
femur4. It descends
by the third month to lie in the depression between the future femoral
condyles4. The
quadriceps mechanism is then seen coursing over the anterior surface of the
anlage of the patella. According to a study by Gardner and O'Rahilly, a
differentiating patellar tendon was seen in two of nine embryos by six
weeks5. By seven
weeks, the patellar tendon was evident in all nine embryos. At 7.5 weeks, the
medial and lateral patellar retinacula were present, and, by eight weeks, the
knee joint resembled that of an
adult5.
In children, the patella can be difficult to visualize radiographically
because it ossifies late. The ossification of the patella is visible
radiographically by two to four years of age in girls and by three to seven
years of age in
boys6.
Our patients appeared to have a congenital distal femoral deficiency. Both
lacked the patellar tendon and had a short femur, and one had a hypoplastic
patella. To our knowledge, these findings have not occurred in association
with any known syndromes. A common entity that includes a hypoplastic or
absent patella is the nail-patella syndrome (onycho-osteodysplasia syndrome),
which can be associated with hypoplasia of the ischiopubic component of the
pelvis, but to our knowledge there have been no reports of associated patellar
tendon
aplasia4,7-11.
Our first patient had been diagnosed with arthrogryposis multiplex
congenita at six months of age. At the time that the patient presented to our
institution, we believed that this diagnosis was unlikely because the
contracture of the hip, knee, and ankle seemed secondary to the absent
patellar tendon and the short extremity. No dimpling of other joints was
present, and the patient lacked the classic appearance of a "wooden
doll." However, in retrospect, it is possible that the patient had a
monomelic form of this disorder. The quadriceps muscle was of a firm and
fibrotic consistency, which would be consistent with the findings associated
with the myopathic form of
arthrogryposis12,13.
In the case of our second patient, the child's mother had undergone
amniocentesis, which had resulted in leakage of amniotic fluid. Theoretically,
the child's lower extremity could have been injured during this procedure;
however, we could not find any reports of a similar case.
Patients with tibial or fibular hemimelia may have an absent patellar
tendon1,3.
The presence or absence of a functioning quadriceps mechanism has a
considerable impact on the treatment of tibial hemimelia in that the decision
to perform fibular centralization or knee disarticulation is made on the basis
of whether there is a functioning quadriceps
mechanism1,14,15.
If the quadriceps mechanism is absent or insufficient, reconstructive
procedures in which fibular centralization is performed are not
recommended14,15.
The rationale for this recommendation is that the success of centralization of
the fibula depends on the function of the knee, which depends on an intact
quadriceps mechanism. Quadriceps muscle insufficiency may result in a flexion
deformity of the
knee1.
To our knowledge, only four cases of patellar tendon aplasia have been
reported1-3.
Two cases were found on magnetic resonance imaging in patients with fibular or
tibial hemimelia3.
The third case was discovered with use of ultrasound in a nine-day-old girl
with tibial
hemimelia1.
Clinically, the knee was flexed and no active extension was observed.
Radiographs revealed shortening of the femur and absence of the tibia, and
ultrasonography of the knee demonstrated no tibial anlage or patellar tendon.
In that patient, disarticulation of the knee was performed because of a fixed
flexion deformity of the knee and absence of the quadriceps
tendon1. The fourth
case, reported by Messina et al., was noted in a twenty-five-year-old woman
who had bilateral congenital absence of the patellar
tendon2. That
patient had presented for the treatment of right knee pain that had begun two
weeks earlier, after a twisting injury. She reported an acute onset of
swelling, one episode of locking, and increasing fullness and pain along the
lateral aspect of the knee. She had no history of knee trauma or knee problems
and was an active dancer who practiced for as long as four hours each day. She
was also active in sports, participating in both basketball and volleyball.
The initial physical examination revealed a mild crouched gait. The quadriceps
muscle had normal mass and tone. Marked bilateral patella alta was noted.
Observation of patellar tracking revealed an absence of patellar engagement
with the patellofemoral groove until the knee was in 120° of flexion. The
passive range of motion of the knee was from 0° to 135° or 140° of
flexion bilaterally. A bilateral active extensor lag of 8° to 12° was
present. The absence of the patellar tendons was confirmed on magnetic
resonance imaging2.
No specific therapy was documented in that
report2.
Treatment of an absent patellar tendon is of uncertain value. The patient
with bilateral congenital patellar tendon aplasia who was described by Messina
et al.2, for
example, was well adapted to the defect. That patient was very active in
sports, and the absence of the patellar tendons was unknown prior to the
injury. In contrast, one of our patients (Case 1) was limited in activities of
daily living and sports activities. He had 6 cm of lower-extremity shortening,
hypoplasia of the patella, aplasia of the patellar tendon, and hypoplasia of
the quadriceps muscle. The absence of the patellar tendon caused a knee
extension lag and a flexion contracture. Because functional deficits were
present, the patient was offered surgical treatment to improve the
biomechanics of the knee joint. Intraoperatively, the quadriceps muscle
appeared severely fibrotic and had fatty infiltration. Despite the fact that
the patellar tendon was successfully reconstructed, as seen both clinically
and on magnetic resonance imaging, the functional outcome two years after the
operation was disappointing because the quadriceps muscle had not regained
function. Postoperatively, the gait was worse than it had been before surgery,
despite intensive physical therapy.
Observation was recommended for our second patient (Case 2), who was of a
similar age but who had minimal symptoms. The clinical course of this patient
was unchanged during two years of follow-up; however, the long-term outcome is
unknown.
The two cases described in the present report should alert the clinician
that a knee extension lag in a child may, in rare cases, be caused by an
absent patellar tendon. If operative reconstruction is considered, functional
recovery may fail as a result of long-standing atrophy of the quadriceps
muscle and tendon. On the basis of these two cases, we cannot give a clear
recommendation for surgical reconstruction as the treatment for this rare
condition. We recommend that, before the decision is made to perform a
surgical reconstruction, the clinician should thoroughly document the
existence of a functioning quadriceps muscle, the presence of which will
optimize the possibility of a satisfactory functional recovery. ?