CURRENT CONCEPTS
Patellar Tendon Ruptures
JEROME G. ENAD, MD, Portsmouth, Va
ABSTRACT
Background. Isolated rupture of the patellar tendon is a rare injury. Often occurring during
a fall in 20- and 30-year olds, patients may have a preexisting medical condition (eg, history of
steroid use) or a history of repetitive microtrauma to the knee. A high-riding patella on
physical examination and radiographs is pathognomonic.
Methods. Immediate orthopaedic referral for surgical repair is necessary to reestablish knee
extension. Delay in diagnosis can make surgical treatment more difficult. Current methods of
postoperative rehabilitation are evolving.
Results. Evaluative studies based on rating scales show satisfactory clinical and functional
results after surgery. However, time lost from work and recreation may be protracted, and
quadriceps atrophy is often evident.
Conclusions. Ruptures of the patellar tendon should be diagnosed acutely and immediately
referred to an orthopaedic surgeon. The impact of the injury to the patient may be longstanding even after operative treatment. Contemporary surgical and rehabilitative techniques
give the best opportunity for restoration of functional activity.
ISOLATED RUPTURE of the patellar tendon is a
rare but disabling injury. Its peak incidence is
seen in the third and fourth decades.1 Younger
patients tend to sustain the injury as an end
result of microtrauma from repetitive activity,2-4
while tendon degeneration has been postulated as the source of tendon weakening in
older patients.2,4 The pathophysiology of the
injury is believed to be an end-stage failure of
degenerative tendinopathy.5 “Jumpers knee” or
patellar tendonitis may be a lower pre-injury
level of dysfunction across a spectrum.6 Other
predisposing risk factors include medical conditions that result in weakened collagen (eg,
systemic lupus er ythematosus, rheumatoid
arthritis, chronic renal failure, diabetes mellitus, and chronic steroid use)7 and previous
major knee surgery (eg, total knee arthroplasty, anterior cruciate ligament reconstruction with central one third patellar tendon
autograft).8,9
BIOMECHANICS
According to biomechanical studies, knee
extensor forces from the patellar tendon are
From the Department of Orthopaedic Surgery, Naval Medical
Center, Portsmouth, Va.
Reprint requests to Jerome G. Enad, MD, Department of
Orthopaedic Surgery, Naval Medical Center, 620 John Paul Jones
Circle, Portsmouth, VA 23708.
greatest at 60° of flexion. While patellar tendon forces are calculated to generate 3.2 times
body weight while ascending stairs, a force of
17.5 times body weight is estimated to cause
rupture.10 Weakened tendons (eg, microtears,
mucoid degeneration, or calcific tendinopathy) probably require much lower force to fail.
Because the tensile load deformation (ie,
strain) is greater at insertion sites rather than
the middle of the tendon, rupture more commonly occurs at the distal pole of the patella.
DIAGNOSIS
Patellar tendon ruptures tend to occur in
patients younger than 40 years old.1 Patients
older than 40 years tend to rupture the extensor mechanism at the level of the quadriceps
tendon above the superior patellar pole. The
typical history of patellar tendon rupture is of
a forceful eccentric contraction on a flexed
knee, such as that occurring from a jump
landing, weight lifting, or stumbling. The patient is unable to continue activity and cannot
resume weightbearing or does so only with
assistance. Physical examination may show a
hemarthrosis, a proximally displaced patella,
and an incomplete extensor function. Because
the medial or lateral retinaculum may be
intact, active extension against gravity (such as
a straight leg raise) may lead to a missed diagEnad • PATELLAR TENDON RUPTURES
563
A
B
(A) Lateral radiograph of knee with patellar tendon rupture. Notice high-riding location of patella. (B) Lateral radiograph of contralateral knee with normal patella
position.
nosis. However, maintenance of knee extension against a greater force is profoundly
weakened and accentuates pain and deformity. In rare cases of delayed diagnosis, the
patient walks with an altered gait pattern,
flinging the affected leg forward in swing and
showing knee instability in stance. The patient
will also have difficulty rising from a chair or
stair climbing.
CLASSIFICATION
Various classification schemes have been
used to describe patellar tendon ruptures. In
1981, Siweck and Rao1 published the first large
series on primary repairs of patellar tendon
ruptures and arbitrarily divided injuries into
immediate (diagnosis and repair occurring <2
weeks from time of injury) and chronic (diagnosis and repair occurring >2 weeks from time
of injury). In 1984, Kelly et al5 classified injuries as transverse, Z-type, or inverted-U,
based on the configuration of the tear at the
time of surgery. In 1994, Hsu et al11 described
the injuries based on the level of tendon rupture (ie, distal patellar pole, tendon midsubstance, or tibial tubercle). To date, the classification scheme based on chronicity of
diagnosis and treatment has proven to be the
most useful for determining prognosis and
results after surgery.12
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RADIOGRAPHIC STUDIES
Plain radiographs of the knee in the anterior-posterior and lateral planes are helpful in
confirming the diagnosis. A comparison radiograph of the contralateral knee in the lateral
plane is used by the orthopaedist to quantify
the amount of injury and for intraoperative
planning. On the lateral views, a distinctive
high-riding patella, or patella alta, compared
with the contralateral knee is seen (Figure).
The entire patella is located superior to the
level of the intercondylar notch. The InsallSalvati ratio (length from the tibial tubercle to
the inferior patellar pole divided by the length
of patella) is much greater than 1.2 (ratio >1.2
defined as patella alta).13 An avulsed bone fragment attached to the tendon may be seen.
High-resolution ultrasonography and magnetic resonance imaging are other modalities
that orthopaedists have used in questionable
or delayed diagnoses but are unnecessary in
obvious, acute cases.
TREATMENT
Surgical repair is necessary to reestablish
optimal extensor function in athletes and
nonathletes. Nonoperative treatment is ineffective and has few indications. Immediate
repair within 2 to 6 weeks of the injury has
been shown to produce superior results.1,5,11 In
delayed diagnoses more than 6 weeks, quadriceps contracture and fibrous adhesions make
the surgical repair and restoration of patellar
tendon length more complicated.1,14 The typical repair is approached anteriorly through
the knee joint. The rupture tendon ends are
isolated and the edges debrided. Thick, nonabsorbable sutures are woven through the tendon and an end-to-end repair or reattachment
to the patella is done. Patellar height is reapproximated to that of contralateral knee. Delayed cases can be more difficult and may
require preoperative traction on the patella to
restore length.1,14
Restoration of patellofemoral alignment influences knee biomechanics and patellofemoral tracking. While functional results can vary,
better results are often seen when the Insall
ratio reapproximates that of the contralateral
knee.4,15,16 Restoration of patellar tendon length
optimizes knee extensor function and may
diminish later patellofemoral symptoms.4,15
Subtle differences in surgical techniques
have been reported in the literature, though
direct comparisons between methods have not
yet been examined due to the rarity of the
injury. Some surgeons have used wire cerclages to reinforce repairs.1,3,5,11,14 Others have
used hamstring tendons to replace or augment the patellar tendon.14,15 Synthetic materials have also been used to reinforce the
repair.2,5,16-18 No reports to date have directly
compared results between any of these surgical techniques.
POSTOPERATIVE REHABILITATION
It was generally accepted that the knee
should be immobilized in extension postoperatively for the tendon to heal without tension
on the repair. Therefore, 6 weeks of immobilization in a cylinder cast was done routinely
by many surgeons with generally good
results. 1,2,11,16 However, some authors have
reported acceptable results using early rangeof-motion exercises without strict immobilization in a cast.4,15,17 Levy et al17 and Lindy et al4
noted that adequate reinforcement of the
repair with a strong cerclage obviated the
need for postoperative immobilization. Currently, no study has directly compared immobilization with early motion after the same surgical technique. However, with current
knowledge in tendon healing and nutrition
supporting the initiation of gentle, controlled
movement early after the repair, more sur-
geons are starting passive knee motion immediately after surgery.
RESULTS
Siweck and Rao1 published the first large
series on primary repairs of quadriceps and
patellar tendon ruptures in 1981, grading results based on range of motion and quadriceps strength. Using this scale, various authors
have achieved 70% to 96% good and excellent
results for primary repairs.1,11,16 Later, Kelly et
al5 developed a more comprehensive evaluative scale, assessing clinical results based on
physical examination, functional results based
on pain and activity level, and strength using
Cybex testing. Eight of 10 patients in their
study achieved good or excellent functional
and clinical results, but 5 of 9 patients exhibited fair or poor strength. Kuechle and Stuart2
reported on six elite athletes who had repair,
and all patients achieved good or excellent
functional, clinical, and strength results.
Other authors on patellar tendon repairs
have reported results based on criteria of
Siweck and Rao,1,11,16 criteria of Kelly et al,2,5
knee scores established for other knee conditions,15,18 or clinical findings alone.4,14,17
Few studies have reported on return to
activities after repair. Kelly et al5 reported on
nine patients returning to their previous level
of activity in 5 to 8 months, noting that the
more active competitors (ie, professional athletes) returned sooner. Kuechle and Stuart2
reported that five athletic patients returned to
their previous levels of function at an average
of 18 months, though return to some level of
athletic activities was sooner. Again, pre-injury
level of athleticism appeared to play a role.
More frequent unsatisfactory results have
also been noted in older patients due to decreased strength and problems in regaining
motion and stability.16 Further, in repairs done
≥2 weeks after injury, quadriceps atrophy and
more unsatisfactory results are reported.1,14
Author’s Experience
In a recent review over a 3-year period at a
tertiary care military medical facility, I found
that 21 active duty patients (aged 22 to 40
years; mean, 32 years) had patellar tendon
repair. No patient had any medical risk factor
for a patellar tendon rupture. All but one sustained the injury while playing basketball. Ten
patients reported a history of pre-injury inferior knee pain. All had primary repair with a
nonabsorbable synthetic cerclage. Eight paEnad • PATELLAR TENDON RUPTURES
565
tients were immobilized in knee extension,
with a cast or brace for 6 weeks with weightbearing as tolerated before initiating strength
and motion exercises. Thirteen patients were
started on passive range-of-motion therapy
immediately after surgery, with weightbearing
as tolerated. Quadriceps strengthening was
started at 6 weeks postoperatively.
At an average follow-up of 17 months, clinical results based on Kelly et al5 classified 8
cases as excellent, 6 good, 5 fair, and 2 poor.
Functional results based on Kelly et al5 classified 4 cases as excellent, 7 good, 5 fair, and 5
poor. Although not statistically significant,
quadriceps atrophy and lack of full extension
tended to associate with poorer clinical and
functional results. With the numbers available,
no significant difference was detected in clinical and functional results between the early
and delayed-motion treatment groups.
CONCLUSIONS
Patellar tendon ruptures can have a significant effect on the athletic and nonathletic
patient. The diagnosis can be made acutely
with a careful history and physical examination. Predisposing medical conditions and
activity level may present as risk factors. Upon
diagnosis, immediate orthopaedic referral is
necessary to avoid costly delays in definitive
surgical repair. The impact of the injury to the
patient may be long-standing, even after operative treatment. Contemporary surgical and
rehabilitative techniques give the best opportunity for restoration of functional activity.
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