Extract
Minimally invasive surgical techniques have been developed in an effort to
improve functional recovery following total knee
arthroplasty1-13.
A primary concern about minimally invasive surgical techniques is a possible
increase in the rate of complications compared with that associated with
so-called traditional total knee arthroplasty techniques involving a medial
parapatellar arthrotomy. These concerns are well outlined in the physician
advisory statement from the American Association of Hip and Knee Surgeons:
"Minimally Invasive and Small Incision Joint Replacement Surgery:
What Surgeons Should
Consider."14
This pamphlet outlines several features of minimally invasive total knee
arthroplasty that may be associated with an increased rate of
complications:
Minimally invasive surgical techniques have been developed in an effort to
improve functional recovery following total knee
arthroplasty1-13.
A primary concern about minimally invasive surgical techniques is a possible
increase in the rate of complications compared with that associated with
so-called traditional total knee arthroplasty techniques involving a medial
parapatellar arthrotomy. These concerns are well outlined in the physician
advisory statement from the American Association of Hip and Knee Surgeons:
"Minimally Invasive and Small Incision Joint Replacement Surgery:
What Surgeons Should
Consider."14
This pamphlet outlines several features of minimally invasive total knee
arthroplasty that may be associated with an increased rate of
complications:
Increased complexity of minimally invasive surgical techniques may be
associated with increased operative time, which may lead to increased rates of
infection, blood loss, or thromboembolic events.Decreased visualization inherent to minimally invasive surgical techniques
may lead to increased rates of intraoperative fracture, ligament damage, and
neurovascular injury or may lead to malposition of implants and subsequent
early clinical failure.New surgical techniques and instruments developed for minimally invasive
surgical techniques may lead to new complications not commonly seen with
traditional total knee arthroplasty.There is a learning curve while a surgeon develops proficiency with these
new minimally invasive surgical techniques and instrumentation.
Increased complexity of minimally invasive surgical techniques may be
associated with increased operative time, which may lead to increased rates of
infection, blood loss, or thromboembolic events.
Decreased visualization inherent to minimally invasive surgical techniques
may lead to increased rates of intraoperative fracture, ligament damage, and
neurovascular injury or may lead to malposition of implants and subsequent
early clinical failure.
New surgical techniques and instruments developed for minimally invasive
surgical techniques may lead to new complications not commonly seen with
traditional total knee arthroplasty.
There is a learning curve while a surgeon develops proficiency with these
new minimally invasive surgical techniques and instrumentation.
Several studies of minimally invasive total knee arthroplasty have
demonstrated improvements in the early functional recovery following the
surgery1,4-13.
Few authors have reported on complications in detail. Since February 2003, the
mini-subvastus surgical technique has been utilized in >99% of our primary
total knee arthroplasties. In this study, we report the complication rate of
our first 600 minimally invasive total knee arthroplasties performed with the
minisubvastus
technique13,15.
This complication rate is compared with that in a historical control group of
150 traditional total knee arthroplasties. In addition, we evaluated the
learning curve of the mini-subvastus technique with regard to the complication
rate, operative time, and clinical results as surgical experience
increased.
Six hundred primary total knee arthroplasties were performed with the
mini-subvastus surgical technique by one surgeon in 596 patients from March
2003 to September 2005. Data were collected prospectively, and the mean
duration of follow-up was twenty-eight months (range, eighteen to fifty
months). A historical control group of 150 consecutive traditional total knee
arthroplasties performed by the same surgeon utilizing a medial parapatellar
arthrotomy in 148 patients was reviewed for comparison. Demographic
characteristics, including age, body-mass index, diagnosis, and preoperative
knee deformity, were the same for the two groups
(Table I). A cemented
posterior-stabilized implant was used in all knees. All patellae were
resurfaced. A 6% prevalence of patellar clunk syndrome was encountered
following the first 275 total knee arthroplasties. Component design and high
knee flexion were demonstrated as the cause of this complication in a separate
study16; therefore,
patellar clunk syndrome was not addressed in the present study.
Knee-specific complications were determined. Complications were considered
to be major if they required a reoperation. Minor complications included any
problem related to the surgical wound that required oral antibiotics or
increased outpatient surveillance. To evaluate the learning curve, we compared
successive groups of fifty procedures with respect to operative time, clinical
outcome, and knee-specific complications. Clinical outcomes were represented
by knee flexion at one
year17. Statistical
analysis included analysis of variance for comparison of demographic
characteristics and a multivariate stepwise regression model of all variables.
Adjusted odds ratios with 95% confidence intervals are reported.
There were eleven major complications (1.8%) requiring a reoperation after
the 600 minimally invasive total knee arthroplasties
(Fig. 1). Five knees (0.8%)
required revision; two of them (0.3%) required a two-stage revision because of
a deep infection, and the other three (0.5%) had isolated tibial loosening.
Six knees (1.0%) had an additional knee procedure but did not require
revision. Two of them had a distal femoral fracture, sustained in a fall three
and eight weeks postoperatively; neither femur was notched at the time of the
primary total knee arthroplasty. One knee had an open patellar realignment;
one, treatment of a late patellar tendon rupture; and one, treatment of an
isolated rupture of the medial collateral ligament sustained in a fall. An
additional knee dislocated in a fall and was treated with a closed reduction.
Forty knees (6.7%) required increased outpatient surveillance because of
wound-related concerns. A deep infection did not develop in any of these knees
(Table II).
Six reoperations (4.0%) were performed after the 150 traditional total knee
arthroplasties; there were three deep infections 2.0% requiring two-stage
revision, two cases of isolated tibial loosening (1.3%) requiring revision,
and one patellar tendon rupture (0.7%) that occurred six months after the
surgery (Fig. 1). Twenty-two
knees (14.7%) required increased surveillance because of wound-related
concerns. A deep infection requiring revision ultimately developed in two of
these knees (Table II).
Using multivariate analysis, we determined that the rate of major and minor
complications was independent of the surgical technique; however, complication
rates were dependent on surgical experience with the new mini-subvastus
surgical technique. For each additional fifty procedures performed, the rate
of major complications was reduced by 16% (adjusted odds ratio = 0.84, 95%
confidence interval = 0.72 to 0.98, p = 0.02). The rate of minor complications
did not decrease significantly as surgical experience increased.
The average operative time increased from seventy-four minutes for the
traditional total knee arthroplasties to eighty-two minutes for the first 100
minimally invasive total knee arthroplasties (p = 0.034)
(Fig. 2). The average operative
time for the next 100 minimally invasive procedures was equivalent to that in
the control group, and it decreased to sixty-five minutes for the last 400
minimally invasive procedures (p = 0.024).
The mean knee flexion at one year was significantly greater following the
first fifty minimally invasive total knee arthroplasties (125°) than it
was in the traditional-arthroplasty group (114°) (p < 0.001). There was
no further increase in knee flexion as experience with the minimally invasive
surgical procedure increased (Fig.
3).
A primary concern about minimally invasive surgical techniques is that
limited exposure will lead to increased complications that jeopardize the
long-term outcome of the
arthroplasty14.
Early clinical results have supported these concerns, with an increase in
complications following minimally invasive total hip arthroplasty compared
with the rates following conventional total hip
arthroplasty18. In
addition, increased complication rates have been reported during an initially
steep learning curve for minimally invasive total hip
arthroplasty19.
Several studies have demonstrated improvements in the early functional
recovery following minimally invasive total knee arthroplasty compared with
that following traditional total knee arthroplasty done with a medial
parapatellar
arthrotomy1-13.
However, most of these studies provided only early clinical follow-up data.
Few authors have reported on complications in detail. In the current report,
we presented complete details on knee complications that occurred following
our first 600 mini-subvastus total knee arthroplasties, performed between
March 2003 and September 2005. This minimally invasive technique was used for
>99% of the primary total knee arthroplasties done at our institution,
rather than in selected
patients13.
Demographic analysis demonstrated that the study group was similar to other
large cohorts of patients treated with total knee
arthroplasty20-22.
The mean age was seventy-one years, with a range from forty-two to ninety-two
years. Ninety-one percent of the patients in the study group were overweight,
and 11% were morbidly obese with a body-mass index of >40. Knee deformity
ranged from 35° of valgus to 24° of varus.
The mini-subvastus technique did not lead to an increased rate of
complications compared with that in historical controls treated with a
traditional total knee arthroplasty. In addition, there was no increase in
complications compared with those in published
reports20-22
of large series of traditional total knee arthroplasties. Our rate of eleven
(1.8%) of 600 knees having complications requiring an additional knee
procedure is consistent with the results reported by Vessely et al., who found
equal rates of reoperations for septic failure, aseptic failure, and
non-implant-related
complications21.
All nonimplant-related procedures in our series were performed to address
complications that have been previously described in the literature on
traditional total knee arthroplasty.
Five minimally invasive arthroplasties failed and required component
revision in our series. This 0.36% annualized failure rate through two years
compares favorably with rates in other large series. In a study of 2036
posterior stabilized total knee arthroplasties with a fourteen-year follow-up,
Font-Rodriguez et al. determined an annualized failure rate of up to
0.51%22. Most
reports on complications following total knee arthroplasty have demonstrated
that the majority occur during the first two years after
surgery20,21.
A deep infection requiring two-stage revision developed after two (0.3%) of
the minimally invasive surgical procedures. This deep infection rate is
consistent with that in previous large series of traditional total knee
arthroplasties. Keating et al. reported a 1.7% infection rate following 3100
primary total knee arthroplasties performed with a medial parapatellar
arthrotomy20.
Similarly, in a study of 1008 traditional primary total knee arthroplasties,
sixteen knees (1.6%) were revised because of infection, usually during the
first two years after the
operation21.
Statewide discharge data from California demonstrated an infection rate of
1.00% (2229 of 222,684) at one year following total knee
arthroplasty23.
Three patients (0.5%) required revision because of isolated tibial
loosening following the minimally invasive surgery. Two of these knees had a
decreased postoperative tibiofemoral angle (<3°), whereas the third
knee had excellent postoperative alignment. Component malalignment has been
shown to be the leading cause of aseptic failure of total knee
arthroplasty24. The
prevalence of tibiofemoral malalignment has been demonstrated to be as high as
15% with the use of traditional total knee arthroplasty
techniques25.
Decreased visualization, new surgical techniques, and new instrumentation have
been suggested as causes of malalignment seen after minimally invasive total
knee
arthroplasty14. We
previously reported a computed tomography analysis of implant alignment in
minimally invasive total knee arthroplasty that showed a decrease in the
accuracy of the alignment of the femoral component secondary to the
instrumentation and surgical
technique26. These
concerns were addressed with new instruments and an altered technique after
our initial 150 minimally invasive total knee procedures. Both of the
malaligned knees that failed in the present series were in this initial group
of 150 arthroplasties.
A weakness of this study is that the follow-up was short-term, with the
duration ranging from eighteen to fifty months and averaging twenty-eight
months. Ongoing follow-up is certainly required. Previous studies have,
however, demonstrated that major failures tend to occur early after total knee
arthroplasty. More than half of all failures leading to revision total knee
arthroplasty have been shown to occur in the first two years
postoperatively27.
In a study of 3145 arthroplasties, Keating et al. found failures in the first
five years postoperatively and no new failures between five and fifteen years
postoperatively20.
Minor complications (wound-related concerns) occurred in 6.7% of the 600
knees treated with minimally invasive total knee arthroplasty in our study. No
full-thickness wound breakdown occurred. No knee with a wound-related concern
required additional surgery, intravenous antibiotics, or admission to the
hospital. The prevalence of wound-related concerns did not increase with use
of the new surgical technique.
There is a learning curve as a surgeon develops expertise with a new
surgical technique or instrumentation. The concern is that this stage of
surgical skill development may be too severe, leading to increased
complications, or too long such that an average-volume surgeon may not be able
to develop proficiency in a reasonable time-frame. The learning curve
associated with the mini-subvastus surgical technique was evaluated by
assessing the operative time, clinical outcomes, and complications as surgical
experience increased. The duration of the first 100 mini-subvastus total knee
arthroplasties was significantly increased, to eighty-two minutes compared
with seventy-four minutes for the traditional total knee arthroplasty
technique. There was no increase in either major or minor complications
associated with these first 100 procedures. New surgical instruments, a
modified surgical sequence, and alterations in retractor placement and knee
positioning were developed during this learning-curve phase. As surgical
experience with the mini-subvastus technique increased, there was a
significant decrease in both the operative time and the complication rate. For
each additional fifty procedures performed, the rate of major complications
decreased by 16%. In contrast to other minimally invasive total knee
arthroplasty techniques, the mini-subvastus technique involves use of an
anterior approach and smaller versions of standard instruments. This customary
exposure and surgical sequence minimize the learning curve associated with
this procedure.
Knee flexion is only one of several clinical results examined to evaluate
total knee arthroplasty. Knee flexion at one year following the first fifty
minimally invasive procedures was increased compared with that in the
traditional control group (p < 0.001). While there was no further increase
in knee flexion as experience with the minimally invasive procedure increased,
patients in this study did benefit from the minimally invasive technique
independent of the learning curve.
In conclusion, the mini-subvastus surgical technique did not lead to an
increased complication rate in comparison with the rate in our historical
control group or with rates reported in the literature on traditional total
knee arthroplasty. Additionally, we did not encounter new modes of failure of
total knee arthroplasties performed with the mini-subvastus technique. During
an initial learning curve of approximately 100 mini-subvastus arthroplasties,
clinical results improved significantly without an increase in complications.
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