Advances in operative technique and instrumentation have enabled surgeons
to perform total hip arthroplasty through smaller
incisions1.
Minimally invasive total hip arthroplasty has been defined by an incision
length of 10 to 12 cm or
less2-8.
Proponents of this technique believe the potential benefits to be a reduction
in soft-tissue trauma, shorter intraoperative time, less perioperative blood
loss, less postoperative pain, more rapid rehabilitation, earlier hospital
discharge, and improved cosmetic
appearance1-6,8-18.
Critics believe that the disadvantages include reduced operative
visualization, a steep learning curve, an increased risk of neurovascular
complications, a higher prevalence of dislocation, excessive skin trauma, and
compromised implant fixation and
positioning1,7,19-24.
Most reports on the results of small-incision total hip arthroplasty have
been based on retrospective cohort studies or prospective case series with or
without comparison with a historical or matched
cohort2,3,5-8,10-18.
We are aware of only two prospective, randomized clinical studies comparing
total hip arthroplasty involving use of a posterior small incision with that
involving a traditional long
incision4,9.
In the present prospective, randomized, blinded study, the hypothesis was
that patients treated with a total hip arthroplasty with a small posterior
incision would have better results than those treated with a long posterior
incision with regard to the achievement of the goals of early pain relief and
functional recovery and that more patients in the mini-incision group would be
candidates for hospital discharge by the second postoperative day. The
difference in our study, compared with others, was that patients in both
groups were actively encouraged to achieve these goals rather than allowing a
passive recovery. These goals were selected because the foremost theoretic
advantages of minimally invasive surgery are to reduce postoperative pain and
to provide more rapid recovery.
Patient Selection
Institutional review board approval was obtained, and all patients gave
their informed consent before participating in this study. All patients
scheduled to undergo unilateral primary total hip arthroplasty between January
2004 and October 2005 were considered to be candidates. The exclusion criteria
included previous surgery on the affected hip, a pathological condition of the
hip that required an extensile exposure, same-day bilateral total hip
replacement, and inflammatory polyarthritis. The patients were informed that
they would be blinded for six months with regard to the technique that had
been used.
Two hundred and sixty-three patients (293 hips) underwent primary total hip
arthroplasty during this time-period. Thirty patients (sixty hips) had a
same-day bilateral operation, and two patients (two hips) had rheumatoid
polyarthritis. One hundred and seventy-one of the 231 patients who were
eligible chose not to enroll in the study, all because they would have no
choice with regard to the incision. Sixty patients (sixty hips) consented to
participate in the study and were randomized into two groups. Enrollment was
stopped after the sixty hips had been included because of the difficulty of
recruiting patients and because 80% statistical power to detect a difference,
at the 0.05 level, in the comparison of the pain and function criteria had
been achieved.
Treatment Protocol
The patients were actively encouraged to follow the protocols rather than
allow a passive recovery. Each patient attended a preoperative class that
explained the operation, the preoperative and postoperative care, and the
postoperative recovery and
rehabilitation25.
They were taught to use an analog scale of 0 to 10 points (with 0 indicating
no pain and 10 indicating the worst pain) and instructed regarding the
postoperative rehabilitation program. Fifty-seven of the sixty patients
donated one unit of autologous blood at least two weeks preoperatively, and
the blood was reinfused into each patient intraoperatively or early in the
postoperative period. A patient was discharged home when he or she, the
physical therapist, and the physician agreed that the patient was able to
function independently.
The same anesthesia and operating teams were involved in every procedure.
The operations were performed by two surgeons (L.D.D. and W.T.L.), one of whom
had experience with 400 posterior minimally invasive total hip arthroplasties
and the other of whom had performed 100 such procedures prior to the onset of
the
study5,10,25.
Twenty-nine patients treated with a small incision and twenty-seven patients
treated with a long incision received epidural anesthesia with 60 to 80 mg of
1% ropivacaine (Naropin) and 80 mg of 1.5% to 2% lidocaine with epinephrine.
No narcotics were used in the epidural. The patients were sedated with
propofol (Diprivan). One patient treated with a mini-incision and three
treated with a long incision had general anesthesia. No intravenous narcotics
were used during the operation with either anesthesia regimen. Patients with
epidural anesthesia were not intubated, and the airway was controlled with
laryngeal mask anesthesia. The epidural catheter was removed in the operating
room at the completion of the procedure; the patients were awake and able to
move the lower limbs in the recovery room.
Surgical Technique
The length of the small incisions was 10 ± 2 cm, and the length of
the long incisions was 20 ± 2 cm. If a patient was randomized to the
mini-incision group, the operation was performed entirely through the small
incision; then, during the completion of the closure of the wound, the skin
incision alone was extended to 20 cm. Thus, all of the skin incisions in the
two groups were ultimately of the same length and, except for the operating
team, everyone involved in the study (i.e., the patient, nurses, physical
therapists, occupational therapists, and those who performed the data
collection) was blinded to the actual extent of the deep-tissue surgery.
The Navitrack Imageless Computer Hip System (ORTHO-soft, Montreal, Quebec,
Canada) was used for twenty-seven of the thirty mini-incision operations and
for twenty-four of the thirty long-incision procedures. The posterior
mini-incision arthroplasties were done with instrumentation specific for that
procedure25. In our
technique, there were five differences between the mini and long-incision
operations: (1) no incision was made into the tensor fasciae latae in the
mini-incision group; (2) the gluteus maximus muscle was split for only 6 cm in
the mini-incision group compared with 10 to 12 cm in the long-incision group;
(3) in the mini-incision group the only capsular incisions were a 3 to 4-cm
posterior capsular flap that was repaired at the completion of the operation
and an incision through the medial aspect of the capsule, whereas in the
long-incision group the anterior-superior aspect of the capsule was excised
and the medial aspect of the capsule and the reflected head of the rectus
femoris muscle were incised; (4) the gluteus maximus tendon was not released
from its insertion onto the femur in the mini-incision group, but it was
released in the long-incision group and then repaired at the completion of the
arthroplasty; and (5) the quadratus femoris muscle was not released from its
insertion onto the femur in the mini-incision group, but it was released in
the long-incision group.
A standardized multimodal analgesic protocol, which does not include
parenteral narcotics, was used for the management of postoperative pain in
each patient as previously
described5,25.
Prophylaxis against deep vein thrombosis included administration of Ecotrin
(oral enteric-coated acetylsalicylic acid), use of bilateral intermittent
pneumatic compression calf devices (FP 5000; Huntley Health Care, Eatontown,
New Jersey), and rapid mobilization of the patient. Discharge medications for
the patients included Celebrex (celecoxib), 200 mg twice daily, for three
weeks and whatever pain medications the patient used in the hospital.
Functional rehabilitation was begun on the day of the surgery for all but
four patients (two in each group). Patients were treated by physical
therapists twice a day, and they began walking independently within their
hospital room when that was approved by the physical therapists. After
discharge, the patients were instructed to walk every day, gradually
increasing their distance with a goal of 1 mile (1.6 km). No physical therapy
following discharge was prescribed.
Data Collection
All data were collected prospectively each day during the hospitalization
by individuals who were blinded to the operative technique used for that
patient. The data were analyzed by a research team that was not directly
involved with the patient care.
The preoperative clinical data that were recorded included age, gender,
left or right hip, diagnosis, weight, height, body mass index, Harris hip
score, and American Society of Anesthesiologists
(ASA)26 grade. The
hemoglobin and hematocrit levels were determined just prior to the operation
and again on the first postoperative day. All fifty-seven patients who had
predonated autologous blood received that blood as a transfusion; no
allogeneic blood was given.
Intraoperative data included the duration of the surgery, the length of the
incision, intraoperative complications, and technical difficulties.
Intraoperative blood loss was estimated and combined with the blood loss
accumulated in a Hemovac drain that was left in place only for the first eight
to twelve hours after surgery.
A cementless Converge cup (Zimmer, Warsaw, Indiana) was used in all sixty
patients. The cup had a Durasul liner (Zimmer) in twenty-seven mini-incision
procedures and twenty-four long-incision procedures, and it had a Metasul
liner (Zimmer) in three mini-incision procedures and six long-incision
procedures (p = 0.82). The femoral component was a noncemented Anatomic Porous
Replacement stem (Zimmer) in twenty-nine hips with a mini-incision and
twenty-eight hips with a long incision. A cemented Apollo stem (Zimmer) was
used in the remaining three hips.
The pain score was verbalized by the patient to the nursing staff prior to
administration of medication and again thirty minutes after the medication had
been taken. Any administration of parenteral narcotics was recorded. The pain
medications were converted to equianalgesic milligrams of morphine, with use
of conversion tables, for statistical comparison of the amount of medications
used for each
patient27. These
tables gave the conversions to milligrams of morphine by percentage (e.g., 50%
to 67% of the estimated oral equianalgesic dose), so there was some
approximation of the conversion doses for these medications.
Functional activities were recorded daily by the physical therapists. They
recorded the distance walked, the ability of the patient to transfer and walk
safely, and the assistive device used for safety during the second of two
daily physical therapy sessions on each postoperative day and at the time of
discharge. The time of discharge was determined as the number of hours between
the patient's return to a hospital room from the recovery room and the time
that he or she was discharged from the hospital.
Postoperative follow-up data were collected at six weeks and six months
with use of a patient-generated Harris hip score and the patient's grade of
the result as excellent, very good, good, fair, or
poor28. Manual
muscle testing was performed to evaluate the strength of straight-leg raising
and hip abduction, which was graded on a scale of 0 to
529. The
questionnaires used to obtain the patient-generated data were either completed
by the patient during the office visit or were mailed to the patient for
completion.
Gait analysis was performed preoperatively and at six weeks and three
months postoperatively with the Intelligent Device for Energy Expenditure and
Activity (IDEEA) (Mini-Sun, Fresno,
California)30. This
gait analysis can be performed in an office hallway and provides accurate
recordings of the onset, duration, and frequency of stride characteristics as
well as detailed analysis of each phase of the gait
cycle30. The gait
performance exercise consisted of patients walking freely at a comfortable
stride speed, with or without an assistive device as needed, for 200 ft (61 m)
(slow walking); walking at the quickest rate possible for 200 ft (fast
walking); and walking through a marker course to evaluate a defined cadence
pattern for 200 ft (zigzag walking). Fifteen parameters of gait analysis were
measured, including velocity, cadence, stride length, step length, single
support, double support, single/double support ratio, swing duration, step
duration, cycle duration, pulling acceleration, swing power, ground impact,
foot fall, and push-off.
Radiographic Analysis
An independent investigator (Z.W.), blinded to the surgical technique,
measured the immediate postoperative and six-month follow-up anteroposterior
pelvic and Lauenstein lateral radiographs to determine the inclination,
anteversion, and fixation of the cup; the fit and alignment of the cementless
stem; and the quality of the cement mantle in the three patients with a
cemented stem. Cup inclination was measured from the inter-teardrop
line31; cup
anteversion, with use of the method of Dorr and
Wan32; and cup
fixation, with the method of Udomkiat et
al.33. Stem
alignment was measured on the anteroposterior pelvic
radiograph31, and
the quality of the cement of the cemented stems was assessed with the method
described by Barrack et
al.34. Comparison
of the limb lengths was based on the distance from the midpoint of the lesser
trochanter to the interischial line, and the offset was determined by
comparison of the distance from the center of the femoral head to the femoral
shaft axis. Heterotopic ossification was graded with the method of Brooker et
al.35.
Statistical Analysis
Statistical analysis was done with use of the SPSS software package (SPSS,
Chicago, Illinois). A Kolmogorov-Smirnov test for normal distribution was used
before further statistical analysis was conducted. A chi-square test was used
for dichotomous values, and t tests were done for continuous values. The
Mann-Whitney U test was done for nonparametric variables. General linear model
repeated-measures analysis was used to compare gait characteristics, and this
test provides analysis of variance when the same measurement is made several
times on each subject. A p value of <0.05 was considered to be significant
for each alpha analysis. Power analysis was done for each statistical
comparison performed.
Because the difference in body mass index between the two study groups
(27.6 compared with 30.2) had a p value of 0.07, a univariate analysis of
variance (analysis of covariance) was done to identify any influence of
demographics on the comparison between the two groups. Use of pain medicine
and the pain score before and after administration of the medicine on the day
of the surgery and on the first and second postoperative days were selected as
the dependent variables; the type of incision (mini or long) and gender were
selected as the fixed factors; and age, weight, and body mass index were
selected as the covariates.
There were no significant differences between the two groups with regard to
the demographic factors or the preoperative body mass index, pain score, limp
score, patient-generated Harris hip score, or ASA grade
(Table I). Twenty-seven
patients in the mini-incision group and twenty-five patients in the
long-incision group had a diagnosis of osteoarthritis; the remaining patients
had posttraumatic arthritis, developmental dysplasia of the hip, or
osteonecrosis.
The surgical times and hematologic parameters for the two groups are
presented in Table II. There
was a significant postoperative reduction in the hemoglobin and hematocrit
levels in each group (p = 0.001), but there were no significant differences
between the groups. Fifty-seven of the sixty patients received an
intraoperative transfusion of one unit of autologous blood, which was part of
the anesthetic protocol.
Patients with a long incision had more pain before the administration of
medications on each postoperative day. The differences were significant on day
1 and at the time of discharge (Table
III). The doses of pain medication (measured in equianalgesic
milligrams of morphine) in the mini-incision and long-incision groups,
respectively, were 32.7 ± 17.3 mg and 33.7 ± 24.1 mg on the day
of surgery; 45.6 ± 20.3 mg and 50.9 ± 19.5 mg on day 1; and 31.2
± 22.9 and 41.5 ± 20.0 mg on day 2. Intravenous narcotics were
needed by seven (23%) of the thirty patients who had a long incision and by
one patient (3%) who had a mini-incision (p = 0.03, power = 0.7).
The two groups differed significantly with regard to the need for an
assistive device. Patients with a mini-incision used less support for walking
on postoperative days 1 and 2. On day 1, eight used a cane, seven used one
crutch, twelve used two crutches, and none used a walker, whereas the
respective numbers for the patients with a long incision were two, thirteen,
nine, and three (p = 0.044). On day 2, five patients in the mini-incision
group used a cane, four used one crutch, six used two crutches, and four used
a walker; the respective numbers for the patients treated with a long incision
were zero, six, nine, and ten (p = 0.048). (The numbers do not equal thirty
because some patients were discharged home on the mornings of day 1 and day
2.) Twenty-six (87%) of the thirty patients treated with a mini-incision used
a single assistive device (a cane or single crutch) at the time of discharge
compared with sixteen (53%) of the patients treated with a long incision (p =
0.005, power = 0.83). There was no significant difference in walking distance
at the time of discharge between the two groups.
The length of the hospital stay was shorter in the mini-incision group
(63.2 ± 13.3 hours compared with 73.6 ± 23.5 hours in the
long-incision group; p = 0.04, power = 0.52). Twenty-nine (97%) of the thirty
patients with a mini-incision and twenty (67%) of the thirty with a long
incision achieved the goal of discharge by the second postoperative day (p =
0.003, power = 0.91). Fifty-nine of the sixty patients were discharged to
home. One patient with a mini-incision was discharged to a rehabilitation
unit.
By six weeks postoperatively, there was no difference in the clinical
outcome between the two groups as measured with the patient-generated Harris
hip score and with manual muscle testing of straight-leg-raising and
side-lying-abduction (gluteus medius) power. The mean patient-generated Harris
hip score at six months was 96.8 points for the patients with a small incision
and 96.0 points for those with a long incision. At six months, the outcome, as
assessed by the patient, was excellent in twenty-one patients in the
mini-incision group and twenty-seven in the long-incision group, very good in
eight patients in the mini-incision group and one patient in the long-incision
group, good in two patients in the long-incision group, and fair in one
patient in the mini-incision group.
Complete gait-analysis data were obtained for twenty-five patients
(thirteen with a mini-incision and twelve with a long incision). The
demographic characteristics were comparable between these two groups. All
patients showed improvement, between the preoperative and postoperative
evaluations, in all gait-analysis characteristics (p = 0.001), and no
differences were observed between the patients with a mini-incision and those
with a long incision.
Radiographic measurements showed no significant differences between the two
groups. The measurements of clinical importance are listed in
Table IV. Only one hip in each
group had any heterotopic ossification, which was Grade 1 in one and Grade 2
in one. The change in the center of rotation of the hip was within 5 mm in
both groups.
There were no intraoperative complications or technical difficulties. None
of the incisions required intraoperative conversion to a longer incision.
There were two reoperations in each group. In the mini-incision group, one
reoperation was done to treat an infection and the other was done because of a
periprosthetic fracture. In the long-incision group, both reoperations were
done to treat a periprosthetic fracture. The three periprosthetic fractures
were sustained in falls at home. There were no dislocations during the first
postoperative year. One patient with a long incision had a symptomatic deep
venous thrombosis in the calf diagnosed at three months.
Compared with the traditional posterior incision, the posterior minimally
invasive operation provided better perioperative pain control, resulted in
better early function, and allowed an earlier discharge to home. Cosmetic
appearance was not a factor because all patients had a skin incision of the
same length. The primary benefits of the mini-incision procedure were derived
in the early perioperative period as no significant clinical differences were
observed during subsequent follow-up assessments. These early differences may
have been measured in our patients but not in other randomized
studies4,9
because we encouraged patients to achieve these goals rather than permitting
passive recovery.
Most of the benefits of posterior small-incision total hip replacement have
been inferred from retrospective cohort studies or prospective case series
with or without comparison with historical or matched
cohorts2,3,
5-8,
10-18.
In a randomized study of twenty-eight patients treated with a small (8-cm)
incision and thirty-two patients treated with a 15-cm incision, Chimento et
al.4 found less
blood loss and less limping in the small-incision group at six weeks but no
functional difference between the groups at one and two years postoperatively.
In another randomized study, Ogonda et
al.9 compared 109
patients with an incision of =10 cm with 110 patients with an incision of
16 cm and found the only difference to be less blood loss in the mini-incision
group; all other radiographic and functional parameters were comparable at six
weeks. Although Chimento et al. found less limping at six weeks in their
mini-incision group, neither we nor Ogonda et
al.9,36,37
found any differences in the results of the clinical examination or gait
analysis at six weeks or thereafter. The surgical technique used by Chimento
et al., for both the long and small incisions, was similar to ours, with
release of the gluteus maximus tendon and the quadratus muscle in the
long-incision group. Ogonda et al. described their surgical techniques simply
as differing in terms of the length of the skin
incision9.
Our in-hospital results favoring use of the small incision may be
attributable to our technique of surgical dissection of deep tissues, our pain
management technique (which did not differ between groups), or the temporal
challenges placed on the goals to be met; it is not possible to quantify the
influence of those factors. The similarity of the results between the
small-incision and long-incision groups by six weeks in our study and in the
other two randomized
studies4,9
suggests that, regardless of the details of the surgical technique, the
ultimate results of the two procedures, performed by experienced surgeons, are
equivalent.
There are several limitations of this study. The first limitation was the
size of the comparative groups, which did not allow the power to reach 80% in
the analyses of several measurements. On the other hand, we did have adequate
power to measure differences in pain and function. The second limitation of
this study is its generalizability. We have a dedicated joint-replacement team
and do not know how reproducible these results would be without such a team.
Thirdly, we used computer navigation for predictable component placement,
which is not universally employed in small-incision surgery. We recognize,
however, that satisfactory component placement in posterior mini-incision
operations without the use of computer navigation has been
documented2-6,8,9,11,12,16,17.
A fourth limitation is that our randomized groups were enrolled from a pool
from which 171 patients had been eliminated. This created a selection bias,
not between the randomized groups but in a comparison of our results with
those in other studies. This is an inherent possibility in all randomized
studies in which the investigators do not enroll 100% of the patients who are
candidates for the study. A fifth limitation of this study was that we did not
assess the long-term results for these patients. However, we consider the
primary benefits of small-incision surgery to be derived in the early
perioperative period, and we compared the results in that period. We also
assume that if there is no increase in complications or changes in the
positions of the component, there is no reason to believe that the long-term
results would differ from those seen in the short
term38. The sixth
limitation was that our technique for conventional total hip arthroplasty may
differ from that of other surgeons. We routinely released the gluteus maximus
tendon and quadratus femoris muscle and incised the anterior-superior aspect
of the capsule.
The most prevalent complication in these patients was postoperative
fracture from a fall, which occurred in both the short and the long-incision
groups. The gait analysis showed significant postoperative improvement in all
of the patients who were evaluated, but the measurements were not normal in
either group. Therefore, in the first six postoperative weeks, some patients
do not have adequate lower-limb strength or balance to be completely safe.
Rapid-recovery protocols may give patients the confidence to perform
activities, or walk without assistive devices, before they should. We now
emphasize to patients that they have reduced lower-limb strength and balance
and that they need to be safe and not exceed their capabilities. For instance,
older patients, who have the most difficulty with balance, are encouraged to
use a walker when they get up at night until they have regained a safe level
of balance.
This study demonstrated in-hospital benefits of the posterior mini-incision
total hip replacement for early reduction of pain and increases in function.
All other measured clinical outcomes were equivalent by six weeks. We believe
that the surgeon and the patient should make the ultimate decision about the
operation and, if a long incision is preferable, it should be performed. If
the patient's surgical preference cannot be chosen, additional time should be
spent in educating that patient about the reasons necessitating the surgeon's
recommendation. A patient who feels that he or she is a part of the medical
decision-making process is more likely to take responsibility for the outcome.
We continue to do mini-incision surgery as we have shown that it is safe and
that it provides early pain relief and good functional results. ?