Abstract
Background: We are not aware of any previous studies in which
independent measurements of function with validated outcome questionnaires
such as the Knee Injury and Osteoarthritis Outcome Score and the International
Knee Documentation Committee score were evaluated five years after
reconstruction of the anterior cruciate ligament. We hypothesized that patient
demographics, mechanism of injury, and intra-articular injuries and their
treatment are factors associated with function five years after reconstruction
of the anterior cruciate ligament.
Methods: A consecutive series of unilateral, arthroscopically
assisted primary reconstructions of the anterior cruciate ligament performed
by one surgeon using a patellar tendon graft was evaluated. Data on patient
demographics, injury variables, and intra-articular lesions noted at the time
of surgery were collected prospectively. Multivariable regression analysis was
used to identify independent predictors of outcomes as measured with five
questionnaires.
Results: Sixty-nine percent (217) of 314 knees with a reconstruction
of the anterior cruciate ligament were followed for an average of 5.4 years.
The average age at the time of the operation was twenty-seven years.
Independent predictors of a worse outcome, which was measured with the overall
Knee Injury and Osteoarthritis Outcome Score, the International Knee
Documentation Committee score, the Lysholm score, and the Western Ontario and
McMaster Universities Osteoarthritis Index score, included the patient's
recollection of hearing or feeling a pop at the time of the injury, a weight
gain of >15 lb (6.8 kg), and no change in educational level since the
surgery. There was a lack of association between the outcome and either the
occurrence or the form of treatment of a meniscal tear or chondromalacia of
the articular cartilage.
Conclusions: To our knowledge, we performed the first prospective
cohort study to evaluate the prognosis following reconstruction of the
anterior cruciate ligament by identifying significant associations between
multiple variables and clinical outcomes as measured with validated
questionnaires. The clinician can counsel patients about the intermediate-term
functional outcomes of reconstructions of the anterior cruciate ligament on
the basis of these findings. Suggestions regarding weight control and future
education may improve intermediate-term outcomes.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.
Intra-articular techniques with a variety of grafts have resulted in
the modern era of reconstruction of the anterior cruciate ligament.
Randomized, controlled trials have previously demonstrated the superiority of
reconstruction compared with primary
repair1-3.
Additional randomized, controlled trials have shown no clinical differences in
outcome between the use of patellar tendon autograft and the use of hamstring
tendon
graft4-11
or between one and two-incision arthroscopic operative
techniques10,12-14.
Thus, reconstructions of the anterior cruciate ligament have been performed to
allow patients to resume activities, especially in sports requiring cutting
and pivoting, and studies have shown overall good short-term
function15,16.
Fewer investigators have evaluated intermediate (five-year) results.
Traditionally, the clinical outcomes of reconstructions of the anterior
cruciate ligament have been judged by measuring anterior-posterior knee
stability combined with the limited use of sport-specific validated outcome
questionnaires. Two recently developed and validated sport-specific knee
outcome questionnaires are the International Knee Documentation Committee
(IKDC) Subjective Knee
Form17 and the Knee
Injury and Osteoarthritis Outcome Score
(KOOS)18. Since
these outcome questionnaires both measure function and evaluate arthritis, the
results provide complementary information not found in smaller studies of
stability after anterior cruciate ligament surgery.
Outcome studies enable sports medicine clinicians to identify potential
predictors of function after reconstructions of the anterior cruciate ligament
and to counsel patients about expected outcomes of the surgery and ways to
potentially improve function by identifying behavior changes that can be
adopted. The deficiencies in the literature on anterior cruciate
reconstruction include a lack of prospective risk-factor analyses at the time
of intermediate (five-year) follow-up, insufficient sample size (underpowered
studies), and a lack of use of sport-specific and knee-specific outcome
questionnaires. In 1991, we established a database to prospectively collect
information on patients undergoing reconstruction of the anterior cruciate
ligament. To our knowledge, we are the first to use a series of validated
outcome questionnaires to evaluate a group of patients at a minimum of five
years following reconstruction of the anterior cruciate ligament. Our
hypothesis19 was
that patient demographics, injury variables, and intra-articular injuries and
their treatment are significantly associated with function (outcomes) at a
minimum of five years following reconstructions of the anterior cruciate
ligament.
Beginning in 1991, data on all reconstructions of the anterior
cruciate ligament were entered prospectively into a database designed to
record patient demographics, injury variables, time to surgery, classification
and treatment of intra-articular injuries (articular cartilage and meniscal),
reconstruction technique, and the major components of rehabilitation. The
recorded demographic and injury variables are shown in
Table I. The intraoperative
factors included non-instrumented laxity measurements made with the patient
under anesthesia and intra-articular injuries and their treatment as recorded
on a scaled diagram and converted to a numeric classification as previously
described19. Each
of the six articular cartilage surfaces (medial tibial plateau, medial femoral
condyle, lateral tibial plateau, lateral femoral condyle, patella, and
trochlear groove) were analyzed separately to record the size of the area of
chondromalacia on each surface and to grade the chondromalacia on each surface
with use of a modified Outerbridge
scale20 (Grade I =
softening, Grade II = superficial changes, Grade III = deep changes, and Grade
IV = exposed bone). Injuries and treatment of the meniscus were considered
separately. Variables regarding the ligament reconstruction included whether
the procedure was primary or a revision, the type of graft, the operative
technique, and the major rehabilitation milestones.
After approval had been obtained from our institutional review board, the
records of the first 340 patients treated, between September 13, 1991, and
June 30, 1997, with two-incision arthroscopically assisted reconstruction of
the anterior cruciate ligament with a patellar tendon autograft by the senior
one of us (K.P.S.) were reviewed. All patients had been followed for a minimum
of five years following the surgery. We believe that this group represented
>80% of the patients who presented for clinical evaluation of a deficient
anterior cruciate ligament by that surgeon during that time period. Meniscal
repairs were performed with use of inside-out suture techniques until June
1996. Then, all were done as inside repairs with bio-absorbable arrows
(Bionix, Toledo, Ohio) for the next year. Chondral injuries were treated with
simple débridement.
Only primary unilateral reconstructions of the anterior cruciate ligament
were included in the study; revision reconstructions were excluded. Patients
with deficiency or a reconstruction of the anterior cruciate ligament in the
contralateral knee were also excluded, so that the measured outcomes would be
related only to the reconstructed knees included in the study. Patients with
associated injuries of the posterior cruciate ligament and the posterolateral
corner were excluded as well. Also, at the time of follow-up, three patients
who were known to have died, one patient with a total knee replacement, and
nine patients in whom the primary reconstruction had been revised less than
five years following the initial surgery were excluded. We recognize that the
ten patients who underwent knee replacement or reconstruction of the revision
had a failure of the original reconstruction, but it would not have been
appropriate to compare the data derived with the validated outcome instruments
for these patients with those derived for the rest of our cohort. A review of
the intra-articular pathological findings and demographics of the ten patients
with a failure did not reveal apparent differences from the rest of our
cohort.
Following the above exclusions, 314 patients remained in the study.
After the patients gave informed consent, they were asked to complete an
eleven-page questionnaire, which they returned by mail. The questionnaire
included four validated outcome instruments, a review of systems, questions
regarding additional surgery, and questions regarding any changes in social or
demographic information. The four validated outcome assessment tools included
two sport-specific forms (the
KOOS18 and
IKDC17), a
well-documented scale for assessing lower-extremity osteoarthritis (the
Western Ontario and McMaster Universities Osteoarthritis Index
[WOMAC])21, and a
general health assessment measure (Short Form-36
[SF-36])22,23.
Finally, the questionnaire-based Lysholm
scale24 was
included so that we could compare this study with previous studies and
measures of anterior cruciate instability.
Descriptive statistics are presented as means and standard deviations or as
medians and interquartile ranges for the continuous variables, as appropriate.
Frequencies and percentages are used to summarize the categorical variables.
The overall KOOS18
and its five subscales (quality of life, functional-sports-recreation,
activities of daily living, pain, and symptoms), the overall
WOMAC21 and its
three subscales (stiffness, pain, and physical function), the subjective IKDC
questionnaire17,
the Lysholm24
scale, and both the mental and physical components of the
SF-3622,23
were scored as described in the original references.
Table I lists the potential
predictors of outcome that were assessed.
Univariable regression modeling was completed separately for each outcome
with use of linear or logistic regression analysis, as appropriate. When
markedly non-normally distributed data were identified, transformations were
used prior to analysis and then back-transformations were used for
interpretations. Multivariable modeling was used to adjust for the covariates
and to identify a set of independent predictors for each outcome. Furthermore,
the statistical modeling involved assessment of both multicolinearity and
possible interactions among the predictor variables. Independent predictors
for each outcome were identified and interpretations of the results were
summarized with the details of the models as well as with an interpretation of
the relationships between each predictor and outcome. During the
model-building process, variables were allowed to enter the model if the p
value was <0.15 (trend toward significance), and they were allowed to stay
in the model if the p value was =0.05. Results were considered significant
when the p value was =0.05. SAS software (version 8.2; SAS Institute, Cary,
North Carolina) was used for the statistical analysis.
Of the 340 patients who underwent unilateral reconstruction of the
anterior cruciate ligament, thirteen were excluded at the follow-up
evaluation: three had died, one had had a total knee arthroplasty, and nine
had had failure of the graft and subsequent revision. Of the 327 patients who
remained, 230 (70%) completed the questionnaire at a minimum of five years
postoperatively. However, for thirteen patients, the procedure had been
entered into the database as a revision reconstruction of the anterior
cruciate ligament, so they were excluded. Thus, 217 patients (69.1%) with a
unilateral primary reconstruction of the anterior cruciate ligament were
evaluated at the time of final follow-up. Of the 30% who were lost to
follow-up, 10% could not be located and 20% were contacted but did not
complete the questionnaire. In addition, intra-articular data on three (1.4%)
of the 217 patients were lost.
The average age of the 217 patients at the time of follow-up was 27
± 9.5 years. One hundred and nineteen patients (55%) were male. The
average duration of follow-up was 5.4 ± 1.7 years. The majority of the
patients (167 [77%] of the 217) were injured in sports activities, and 154
(71%) recalled hearing or feeling a pop at the time of injury. One hundred and
sixty-nine injuries (78%) were noncontact injuries, and 161 injuries (74%) did
not involve jumping. In the half-decade since the surgery, 130 (60%) of the
patients had increased their educational level.
Eighty-six percent (184) of the patients had a normal medial collateral
ligament, 2% (five) had a Grade-I injury of the medial collateral ligament
(with =5mm of laxity), 9% (nineteen) had a Grade-II injury (with 6 to 10 mm
of laxity), and 3% (six) had a Grade-III injury (with >10 mm of laxity).
Ninety-nine percent of the patients had a normal lateral collateral ligament,
and only three had a Grade-II injury.
The meniscal injuries and their treatment are shown in
Table II, and the locations of
the articular cartilage lesions are presented in
Table III. There were more
lateral meniscal tears than medial meniscal tears, and partial tears were seen
primarily in the lateral meniscus. Medial meniscal repair was performed in 22%
(forty-eight) of the patients. The percentage of knees that were normal or had
Grade-I chondromalacia ranged from 78% to 97% across the six articular
surfaces. Only ten surfaces had Grade-IV chondromalacia. In summary, the
cohort in this study comprised primarily young patients with a variety of
meniscal tears and treatment who only rarely had Grade-II or greater
chondromalacia observed at surgery.
The independent predictors of outcome, as measured with the overall KOOS,
the IKDC questionnaire, and the Lysholm questionnaire, are shown in
Table IV. A lack of further
education (p = 0.009) and a pop heard or felt at the time of injury (p = 0.03)
were associated with a significantly worse KOOS. A lack of further education
(p = 0.01) and weight gain of >15 lb (6.8 kg) were associated with a
significantly worse WOMAC score (p = 0.04). Weight gain of >15 lb had the
largest impact on outcome, with a maximum of a 7-point difference in the IKDC
score compared with the score associated with weight loss. Both the sound or
feeling of a pop at the time of injury and the change in the educational level
were associated with smaller average differences in the outcome measures. A
lack of further education was identified as a significant predictor of the
SF-36 score (p = 0.02).
A summary of analysis of the KOOS and WOMAC subscales demonstrated several
variables that were not significant predictors of overall scores.
Chondromalacia of the medial tibial plateau was a significant predictor of the
KOOS pain subscale score (p = 0.01), and more than eight years between the
injury and the surgery was significantly associated with both a lower KOOS
pain score (p = 0.04) and a lower WOMAC pain score (p = 0.02).
More importantly, several variables commonly believed to be important
predictors of function and outcome were not found to be significant. These
included the presence of a meniscal tear and its treatment as well as
chondromalacia of the patellofemoral, femoral, and/or tibial articular
cartilage. In addition, gender, age, sports activity, contact injury, a
jumping mechanism, and the onset of swelling within hours after the injury
were not predictors of function or outcome five years after reconstruction of
the anterior cruciate ligament.
We used new validated outcome questionnaires to evaluate a
prospectively collected series of two-incision patellar tendon reconstructions
of the anterior cruciate ligament performed by one surgeon. After a minimum of
five years of follow-up, several independent predictors of outcome were
identified. Surprisingly, meniscal injury and its treatment and the status of
the articular cartilage did not significantly influence the intermediate
outcome. The present study had two unique attributes: (1) we were, to our
knowledge, the first to use the KOOS and IKDC outcome questionnaires for
functional evaluation to identify independent predictors, and (2) we performed
one of the largest prospective five-year studies of arthroscopically assisted
reconstructions of the anterior cruciate ligament with a patellar tendon
autograft.
With the apparent clinical and scientific acceptance of reconstructions of
the anterior cruciate ligament as a means of enabling athletes to regain
function, as assessed at two years postoperatively, the next critical question
is: which variables determine intermediate (five-year) and long-term function?
Identifying significant variables, some of which are potentially modifiable,
can direct resources to additional research, and the education of patients,
about these variables. Clearly, longitudinal data on this cohort after ten
years of follow-up are required to further evaluate the role of
intra-articular injuries with regard to treatment outcomes and function.
Outcome measures have gained importance in sports medicine, and they have
increasingly become dependent on patient satisfaction. In a review of outcome
measurement for anterior cruciate-deficient knees, Johnson and
Smith25 recommended
the use of validated instruments, including the Lysholm, IKDC, and KOOS
scores. They thought that the KOOS was attractive but cumbersome and that the
IKDC score will remain popular because of the international influence of the
committee that formulated it. They believed that the original IKDC 1991 scale
and the Cincinnati rating scale have not been adequately validated and may
lack reliability. In a subsequent study, Marx et al. demonstrated high
validity, reliability, and responsiveness for the Cincinnati rating scale when
used to assess
athletes26.
There has been a paucity of studies evaluating arthroscopically assisted
reconstructions of the anterior cruciate ligament with patellar tendon
autograft at five years. Four such
studies27-30
had several deficiencies. First, they were retrospective reviews. Second, they
did not employ validated outcome measures. Third, they lacked sufficient power
or sample size to evaluate a minimum of eight major intra-articular injury
variables (six articular cartilage surfaces and two menisci) as potential
predictors of function or outcome. Also, although they documented meniscal
tears at surgery, neither chondromalacia nor treatment of intra-articular
injuries was factored into the analysis, in which the primary outcome variable
was instrumented measurement of laxity.
In two additional studies, reconstructions of the anterior cruciate
ligament were evaluated at eight to ten years postoperatively. The most
relevant review, by Wu et
al.31, was a
prospective ten-year follow-up study of sixty-three (of 103) reconstructions
with patellar tendon autograft. The IKDC, Tegner, and Lysholm scales as well
as instrumented laxity measurements and single-leg hop tests were used for
evaluation. The IKDC and Lysholm scores were lower for patients who had
undergone any type of meniscal resection than they were for those with intact
menisci. The authors did not control for multiple confounding variables as
they did not utilize multivariable regression modeling. When they controlled
for the degree of arthritis or chondromalacia associated with a meniscal
injury, the meniscal effect was no longer significant. They concluded that
meniscal tears should be repaired, if possible, to improve outcome.
In a follow-up study of subjective outcomes, Shelbourne and
Gray32 utilized a
modified Noyes questionnaire and the 1994 IKDC evaluation form at an average
of 8.6 years after reconstructions of the anterior cruciate ligament. They did
not use the current IKDC outcome form or the KOOS, WOMAC, or SF-36 instrument.
In their review, 928 (75%) of their original group of 1231 patients were
available for subjective evaluation and 482 (39%) were available for objective
evaluation at the time of follow-up. This study demonstrates the near
impossibility of achieving a 70% rate of long-term in-person follow-up in this
population of young, mobile individuals. The objective evaluation included
measurement with a KT-1000 arthrometer, assessment of quadriceps strength with
a Cybex dynamometer, the single-leg hop test, range-of-motion measurements,
and radiographs, including 45° flexion posteroanterior weight-bearing
views. The authors concluded that partial or total medial or lateral
meniscectomy and damaged articular cartilage lowered the quality of the
subjective results, as assessed with the Noyes questionnaire.
Järvelä et
al.33
retrospectively reviewed the results of primary reconstruction of the anterior
cruciate ligament in seventy-two patients (from an original group of 102) who
returned for follow-up five to nine years (average, seven years)
postoperatively. The patients were divided into two groups: Group A
(thirty-four patients) had an isolated injury of the anterior cruciate
ligament, and Group B (thirty-eight patients) had associated injuries,
including ten medial and twelve lateral meniscal tears treated with a partial
or subtotal meniscectomy as well as nineteen ruptures of the medial collateral
ligament, two ruptures of the lateral collateral ligament, and one rupture of
the posterior cruciate ligament. All ligament ruptures, except for one of the
medial collateral ligament, were treated with primary repair. The two groups
were evaluated with use of the Lysholm, Marshall, and IKDC scores. There were
no differences in outcome between the two groups, except that Group B required
more repeat surgery, including manipulation (two knees), lysis of adhesions
(eight), and partial meniscectomy (six). There was no mention of chondral
injury in this study.
In the current study, we did not detect a difference in outcomes, at a
minimum of five years postoperatively, on the basis of the status of the
meniscus or the articular cartilage, or their treatment, at the time of
surgical reconstruction. This difference between our findings and those of Wu
et al.31 and of
Shelbourne and
Gray32 may reflect
the shorter average duration of follow-up in our study, the use of different
validated outcome measures, or the control of multiple confounding variables.
However, the planned longer-term follow-up of this cohort may reveal different
results with regard to intra-articular injuries.
The observation that weight gain of >15 pounds and a failure to advance
to a higher educational level resulted in worse intermediate outcomes suggests
two behaviors that potentially could be modified to improve outcome. It is
unknown whether weight gain leads to increased stress on the knee or is a
secondary consequence of a lack of regular physical activity. However,
postoperative counseling stressing that regular exercise can control weight
gain and perhaps lead to an improved five-year outcome could potentially
motivate patients. How a change in educational level alters outcome is less
certain. Higher education may lead to jobs requiring less intensive physical
labor or it may help individuals to develop better coping strategies. To our
knowledge, these observations have not been reported, and the issues have not
even been addressed, in previous studies of reconstructions of the anterior
cruciate ligament. Functional demand on the knee is a critical issue that is
potentially related to the findings regarding weight gain and educational
level in this study. Unfortunately, no validated measure of activity level was
available at the time that these patients were enrolled. We included this
measure in our current studies.
This study had several limitations, including the evaluation of the results
of only one fellowship-trained surgeon at one institution and the lack of
objective physical examination data (measurement of anteroposterior laxity,
imaging, and objective functional testing). The majority of the studies in the
literature involve the results of a single surgeon at a single institution,
which limits the generalizability of the findings to other orthopaedists, but
we intend to address this concern in the future with the addition of patients
treated by other surgeons and at other institutions into the database.
Previous studies have demonstrated a lack of correlation between objective
knee laxity and subjective outcome. Snyder-Mackler et
al.34 performed a
study of twenty patients with an anterior cruciate-deficient knee, ten of whom
were classified as compensators (individuals who returned to all sports
activities without operative treatment) and ten of whom were classified as
noncompensators (patients who ultimately underwent reconstruction of the
anterior cruciate ligament). Objective knee laxity, as evaluated with a
KT-2000 arthrometer, was actually greater in the compensators. No significant
differences in subjective outcomes, as measured with the Lysholm and Knee
Outcome Scores, were noted between the two groups. In a study evaluating
muscle timing and recruitment with anterior tibial translation, Wojtys and
Huston35 also
obtained subjective data. They noted no relationship between the subjective
outcome and the amount of anterior translation. Finally, in a recent review of
the results of hamstring reconstructions of the anterior cruciate ligament,
Williams et al.36
concluded that the functional outcome did not correlate with measurements of
laxity with a KT-1000 arthrometer.
The strengths of our study include the use of validated sport-specific
questionnaires as well as historical "gold standard" outcome
measures for lower-extremity osteoarthritis (the WOMAC and SF-36). These
outcome measures were designed and validated to be the primary measure of
function. In this setting, objective knee laxity becomes less relevant than
patient-based outcome. The use of questionnaires enabled us to evaluate a
large cohort of patients with a high rate of follow-up (nearly 70%).
Currently, we are involved in what we believe will be the ideal, but
practical, prospective study. The study includes the use of validated outcome
and activity instruments prior to surgery and at two, five, and ten years
postoperatively, with a goal of a >80% rate of follow-up.
In conclusion, we used sport-specific questionnaires to identify several
independent predictors of outcome at a minimum of five years after
reconstructions of the anterior cruciate ligament. The predictors include the
patient's recollection of hearing or feeling a pop at the time of injury, no
change in educational level, and a weight gain of >15 lb. Meniscal tears
and their treatment as well as the presence or absence and degree of chondral
injury were not found to be significant predictors of future function. A
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