Keywords
two-incision technique - dysplasia - total hip arthroplasty - osteonecrosis
Muscle sparing approaches for total hip arthroplasties (THAs) have been advocated
in the past two decades. The two-incision approach technique is one of the muscle
sparing approaches. The technique has the potential benefits of avoiding muscle and
tendon damage, less intraoperative blood loss, rapid patient recovery, and shortened
hospitalization but might increase complications such as fractures, nerve injury,
and implants malposition, so it required a steep learning curve.[1]
[2]
[3]
[4]
[5]
[6] The ideal cup position, stem alignment, and proper leg length and offset are the
keys to a successful THA. Our previous study has demonstrated that using of intraoperative
fluoroscopy or imageless navigation system can increase the accuracy of cup and stem
alignment for the two-incision THA.[7]
Osteonecrosis of the femoral head (ONFH) and hip dysplasia often lead to end stage
hip osteoarthritis and need THAs. Different to ONFH, hip dysplasia have altered acetabular
version and femoral torsion. The altered anatomy may increase the difficulties of
implant positioning especially with the muscle sparing two-incision technique that
the surgical field exposure is restricted. In the medical literature, a study comparing
the clinical outcomes of the two-incision THA between ONFH and hip dysplasia patients
has not been reported. The purpose of this study was to investigate whether the clinical
outcomes, the implant positions, and the complications would be different by using
the two-incision THA on patients with ONFH or hip dysplasia.
Material and Methods
From September 2003 to March 2010, a single surgeon had performed 175 two-incision
THAs on 157 patients.[8] By excluding cases with primary osteoarthritis, ankylosing spondylitis, rheumatoid
arthritis, Legg-Calve-Perthes disease, and posttraumatic arthritis, 159 hips in 151
patients (68 female and 83 male) were included as the study cohort and were divided
into 2 groups. Group 1 had 99 hips (93 patients) with ONFH. Group 2 had 60 hips (58
patients) with hip dysplasia. Hip dysplasia was defined based on the criteria of Sharp's
angle more than 43° and the coverage of the femoral head less than 75%.[9] Only mild dysplasic hips in the Crowe I or II classes were included.[10] Demographic data including age, gender, body mass index, preoperative Harris hip
score (HHS) and the Western Ontario and McMaster University Osteoarthritis Index (WOMAC)[11] were recorded ([Table 1]). All THAs were performed with the two-incision technique as described previously.[7] The operative time, amount of blood loss, wound length, length of hospital stay,
size of implants, and complications were recorded. Postoperatively, patients were
encouraged to ambulate as soon as possible by protected weight bearing with double
crutches for 6 weeks and a single crutch for another 6 weeks. Clinical follow-up included
radiological examinations, HHS, and WOMAC scale at 3 weeks, 6 weeks, 12 weeks, 6 months,
and yearly after the surgery.
Table 1
Patient demographics
|
Group 1 (ONFH)
|
Group 2 (Dysplasia)
|
p-value
|
|
Male: Female
|
75:24
|
14:46
|
|
|
Age (years)
|
48.5 ± 12.8
|
61.5 ± 12
|
<0.001[*]
|
|
BMI
|
24.2 ± 3.5
|
25.2 ± 4.3
|
0.112
|
|
Preoperative function
|
|
Harris hip score
|
56.8 ± 12.0
|
59.8 ± 10.7
|
0.090
|
|
WOMAC
|
56.6 ± 12.1
|
59.0 ± 9.4
|
0.183
|
Abbreviation: BMI, body mass index = body weight/(body height)2
* Statistically significant difference at p ≤ 0.05.
Radiological analysis included standard pelvis anteroposterior radiograph taken postoperatively
and at 3 months, 6 months, and yearly in the follow-up. The angle of cup inclination
and anteversion, the stem alignment, and the ratio of canal filling were recorded
according to the standard protocols.[12]
[13]
[14] Any implant migration, loosening, or early failure of the components were recorded.
Results
All 159 hips were followed with functional and radiographic studies. The age and gender
distribution were significantly different with younger age (48.5 ± 12.8 years) and
predominantly male gender (74%) in the ONFH group as compared with older age (62 ± 12
years) and predominantly female gender (76%) in the dysplasia group ([Table 1]). The preoperative HHS and WOMAC scale were similar in both groups.
There were no differences in regard to the operation time, blood loss, wound size,
length of hospital stay, and the postoperative HHS or WOMAC scale between the two
groups ([Table 2]). The ONFH group had more male patients and the cup size was significantly bigger
(p = 0.028) with a trend of larger stem size (p = 0.072) as compared with the dysplasia group. The cup inclination angle was 43.7° ± 4.8°
in the ONFH group and 42.8° ± 5° in the dysplasia group (p = 0.25) and the cup anteversion angle was 17.6° ± 7.6° in the ONFH group and 14.2° ± 8.2°
in the dysplasia group (p = 0.009). There was no difference in femoral canal fill ratio between the two groups
(ONFH:94 ± 4%, Dysplasia: 95 ± 5% ; p = 0.088). With a mean follow-up of 9.6 ± 1.5 years, there were three revision cases
in the cohort with one septic loosening in the dysplasia group and two stem revision
in the ONFH group due to periprosthetic fractures. No dislocation in either group
was noted in the study. The overall implant survival rate was 98% in the ONFH group
and 98.3% in the dysplasia group, respectively. There were four patients with intraoperative
fracture (two in greater trochanter and two in proximal femur) in the ONFH group.
For the dysplasia group, there were six patients with intraoperative fracture (two
in greater trochanter and four in proximal femur). The lateral femoral cutaneous nerve
(LFCN) injury was noted in 26 cases in the ONFH group and eight cases in the dysplasia
group. The incidence of LFCN injury was approximately 21% by using the two-incision
THA technique.
Table 2
Surgical results and implant positions
|
Group 1 (ONFH)
|
Group 2 (Dysplasia)
|
p-value
|
|
Operation time (min)
|
157.6 ± 45.2
|
150.5 ± 37.5
|
0.303
|
|
Blood loss (mL)
|
692.9 ± 396.7
|
617.7 ± 219.0
|
0.127
|
|
Wound length (cm)
|
9.8 ± 1.6
|
9.8 ± 1.6
|
0.851
|
|
Hospital stay (days)
|
5.6 ± 2.2
|
5.4 ± 1.5
|
0.499
|
|
Cup
|
|
Size(mm)
|
53.6 ± 2.4
|
52.7 ± 2.8
|
0.028*
|
|
Inclination (°)
|
43.7° ± 4.8°
|
42.8° ± 5°
|
0.254
|
|
Anteversion (°)
|
17.6° ± 7.6°
|
14.2° ± 8.2°
|
0.009*
|
|
Outlier
|
5/99 (5.1%)
|
6/60 (10%)
|
|
|
Stem
|
|
Size(mm)
|
12.6 ± 1.5
|
12.1 ± 1.5
|
0.072
|
|
Canal fill ratio (%)
|
94 ± 4
|
95 ± 5
|
0.088
|
Discussion
Muscle sparing approaches have become popular recently in the fields of joint arthroplasty
and other orthopedic surgeries. Compared with conventional methods for THA, they theoretically
use smaller wound, less soft tissue damage, shorter operative time, shorter hospital
stays, less blood loss, and quicker recovery.[15] Among the muscle sparing approaches, the two-incision approach had been enthusiastically
advocated but gradually lost its popularity due to the increase risks of complications
such as femoral fracture or implant malposition related to the limited visualization
in the surgical fields and a steep learning curve.[16]
[17] Fehring et al reported catastrophic complications by using this two-incision technique
as a warning for inexperienced surgeons.[16] Bal et al stated that the rates of complications such as femoral fracture, dislocation,
lateral femoral cutaneous nerve injury, and repeat surgery associated with the two-incision
technique for THA were very high even by a surgeon who was experienced with a single
small incision for THA.[18] Pagnano et al reported that the two-incision approach had higher complications (14%
versus 5%) including calcar fractures, dislocation, and femoral nerve palsy as compared
with posterior cases.[19] As a contrast, Lee et al reported 2 to 3.1% intraoperative periprosthestic fracture
rate for the two-incision THA and the complication rates could be diminished with
increasing experience and use of intraoperative fluoroscopic guidance.[7]
[20]
[21] There were 10 cases (6.3%) with intraoperative femoral fractures, 34 cases (21.4%)
with temporary LFCN palsy, and 3 revision cases (one for septic loosening in the dysplasia
group and two for the stem revision in the ONFH group for periprosthetic fracture).
With a mean follow-up of 9 to 10 years, the overall implants survival rate is 98%
in the ONFH group and 98.3% in the dysplasia group. We believed these results might
be related to the modified technique we had used for the two-incision technique. First,
we positioned our patients in the standard lateral decubitus position. The setting
and orientation are more comfortable and familiar for surgeons who use direct lateral
or posterior approach. Second, we changed the direction of the anterior incision wound
90° to the original technique. Our incision therefore can span from the lesser trochanter
to the greater trochanter that greatly improves the visualization of the surgical
field for both the acetabulum and proximal femur. Yoon et al also reported excellent
results by adopting a similar strategy in the patients positioning but used the Watson-Jones
interval for the two-incision THAs.[22]
The original two-incision technique has the inherent difficulty of surgical field
visualization, therefore an intraoperative fluoroscopy is routinely needed. It should
be more cautious for the implant malposition especially in patients with hip dysplasia
that underdeveloped acetabulum and excessive anteverted proximal femur are the common
anatomic variations. Bal et al retrospectively compared two patient groups treated
with two-incision THA or single-incision THA and found a substantially higher numbers
of fractures, reoperation, cup malposition, and nerve injuries in the two-incision
group.[18] However, Amman et al found the position of acetabular component was more accurate
in the MIS THA group because of the use of intraoperative imaging.[23] Other researchers, including Williams et al,[24] Teet et al,[25] and Siguier et al,[26] also claimed that mini-incision THA does not compromise the component position or
dislocation. To our knowledge, no study reported the implant position, functional
results, and complications in patients with relative normal anatomy (ONFH) or abnormal
anatomy (hip dysplasia) by using the two-incision technique. This study analyzed 159
hips with ONFH or hip dysplasia and found the cup inclination, stem alignment; femoral
canal fill ratio, hospital course, functional results, complications, and prosthesis
survival were not different between them. The only differences were a relatively bigger
cup in the ONFH patients (maybe gender related) and a less anteverted cup in the dysplasic
hip patients. In the series, no major complications and no dislocation were found
during the follow-up.
ONFH has been known to affect young male patients.[27] On the other hand, developmental dysplasia of the hip is the common cause of secondary
hip osteoarthritis and the prevalence ranges from 5.4 to 12.8% among different ethnic
groups.[28]
[29] The female gender is one of the known risk factors for dysplasic hips, and these
patients usually end up with THA at younger age eventually.[30] Due to undeveloped acetabulum, the acetabulum anatomy in dysplasic hip patients
usually characterized with deficiencies in anterolateral and superior wall and lacks
of bone stock medially. Because the ideal acetabular cup size and position are difficulty
in dysplasic hip patients with THA, muscle sparing approaches such as the two-incision
technique should not be recommended. In this study, only mild dysplasic hips in the
Crowe I or II classes were included. As the final result, the average cup anteversion
was 17.6° in the ONFH group and 14.2° in the dysplasic hip group. The majority of
the cups were in the recommended safe zone with only 5.1% and 10% outliers, respectively.
Nevertheless, no dislocation or cup loosening were found in this series. This may
be due to the two-incision technique could preserve the tissue integrity and improve
the tissue tension postoperatively. It was also interesting to note that the dysplasic
hips had less anteverted cups as compared with the ONFH hips. The two-incision technique
described herein used a modified incision that can effectively improve the surgical
field exposure. By improving the exposure, we can visualize the trial components to
determine the ideal compliant position by matching the cup and stem routinely.[31]
[32] The final position of the less anteverted cups in the dysplasic hips reflected the
anatomic characteristics of anterolateral deficiency of acetabulum and more anteverted
proximal femur. With these less anteverted and adequately inclined cups, the stability
of the THAs in dysplasic hips could be well maintained.
The overall implant survival rate was satisfactory with 98.1% at 9.6 ± 1.5 years.
We found by using the modified two-incision technique, patients with dysplasic hips
could have similar results in the functional outcome, surgical results, and prosthesis
survival as ONFH hips. However, there are many limitations of this study. The retrospective
nature of this study could not conclude the merits of the two-incision technique to
other approaches because case selection bias existed. Difficult patients with severe
hip dysplasia, ONFH hips after salvage procedures, morbid obesity, or other comorbidities
were not included in this study. The sample size was small with only 159 hips analyzed.
The series was a single surgeon's experience that used a modified two-incision technique
and could not represent a common scenario for the original two-incision technique.
However, all cases could be followed up in the study period, and the results were
analyzed independently. All cases used the same implants by the same technique. Most
importantly, the modified two-incision technique with the improved surgical field
exposure has not been critically analyzed on hips with different anatomic characteristics.
In summary, we found the modified two-incision technique could achieve good to excellent
clinical results and implant survival on selected patients with either ONFH or hip
dysplasia
