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Predictors of Poor Clinical Outcome After
Arthroscopic Labral Preservation, Capsular
Plication, and Cam Osteoplasty in the
Setting of Borderline Hip Dysplasia
Akihisa Hatakeyama,
*
MD, Hajime Utsunomiya,
*
MD, PhD, Shoichi Nishikino,
y
MD,
Shiho Kanezaki,
*
MD, PhD, Dean K. Matsuda,
z
MD, Akinori Sakai,
§
MD, PhD,
and Soshi Uchida,
*
||
MD, PhD
Investigation performed at Wakamatsu Hospital of University of Occupational
and Environmental Health, Kitakyusyu, Japan
Background: Borderline developmental dysplasia of the hip (BDDH) is frequently diagnosed concurrently with cam impingement.
While hip arthroscopy has advanced the treatment of hip joint pathology, including femoroacetabular impingement (FAI), arthro-
scopic treatment for FAI in the setting of BDDH remains a challenge amid a subset of patients. The risk factors of poor clinical
results after hip arthroscopic labral preservation and FAI corrections in the setting of BDDH patients have not been well
established.
Hypothesis: Pre- and intraoperative findings can predict the poor clinical outcomes after hip arthroscopic surgery for FAI in the
setting of BDDH.
Study Design: Case control study; Level of evidence, 3.
Methods: Of patients with BDDH (defined as lateral center edge [LCE] angle between 20°and 25°) who underwent arthroscopic
procedures for FAI between 2009 and 2014, 45 met inclusion criteria (45 hips: 15 males and 30 females). Their mean age was 31.4
years (range, 12-65 years), and the mean LCE angle was 23.2°. Clinical and radiographic follow-up evaluations up to a minimum
of 2 years after surgery were performed for all patients. Failure of the procedure was defined as conversion to subsequent surgery
or having a To
¨nnis osteoarthritis grade of 2, and success was defined as patients who did not need subsequent surgery. Univar-
iate analysis and Cox hazard proportional analysis were performed for both cohorts.
Results: Of 45 patients, 11 (24%) had revision surgery (endoscopic shelf acetabuloplasty for 5 patients, total hip arthroplasty for
2, and revision hip arthroscopy for 2) or advanced to To
¨nnis grade 2 osteoarthritis and thus constituted the failure group. In the
success group, modified Harris Hip Score (median, pre- vs postoperative: 72.1 vs 100, P\.001, Wilcoxon signed-rank test) and
nonarthritic hip score (58.8 vs 98.8, P\.001) were significantly improved at the minimum 2-year follow-up. The median age of the
failure group was significantly higher than that of the success group (47.0 vs 20.0, P\.001, Mann-Whitney Utest). Risk factors of
poor clinical outcomes were identified as follows: age 42 years (hazard ratio [HR], 11.6; 95% CI, 2.5-53.9; P= .002, Cox hazard
model), broken Shenton line (HR, 6.4; 95% CI, 1.9-22.3; P= .003), To
¨nnis angle 15°(HR, 3.9; 95% CI, 1.2-12.9; P= .03), vertical
center anterior (VCA) angle 17°(HR, 5.0; 95% CI, 1.5-17.1; P= .01), To
¨nnis grade 1 at preoperative radiograph (HR, 3.6; 95% CI,
1.1-11.7; P= .04), severe cartilage delamination at acetabulum (HR, 11.8; 95% CI, 3.0-46.1; P\.001), and mild cartilage damage
at femoral head (HR, 8.1; 95% CI, 2.1-30.8; P= .002).
Conclusion: Preoperative predictors of poorer outcomes from hip arthroscopic labral preservation, capsular plication, and cam
osteoplasty in the setting of BDDH are age 42 years old, broken Shenton line, osteoarthritis, To
¨nnis angle 15°, and VCA angle
17°on preoperative radiographs. Intraoperative predictors of poorer outcomes are severe acetabular chondral damage and
even mild femoral chondral damage. Although the patients in the setting of BDDH may have good outcomes from isolated hip
arthroscopy, caution is suggested for those with the aforementioned risk factors.
Keywords: borderline hip dysplasia; arthroscopic surgery; risk factor; predictor of poor clinical outcome; capsular repair
Although hip arthroscopy is recognized as a valuable surgi-
cal approach to treat common hip conditions, such as fem-
oroacetabular impingement (FAI) and labral tears, its use
in the treatment of dysplasia has been controversial and
generally associated with less successful outcomes. Several
The American Journal of Sports Medicine, Vol. XX, No. X
DOI: 10.1177/0363546517730583
Ó2017 The Author(s)
1
studies have reported postoperative subluxations or even dis-
locations of the hip after arthroscopy for hip dysplasia.
6,25
Although capsular repair/plication has been suggested as
being beneficial in this patient subset,
5,16
the clinical out-
comes of arthroscopic surgery for dysplastic hip are not excel-
lent, even with use of capsular closure.
5,13,15,23,25
Uchida et al
23
clearly described what risk factors
worsen clinical outcomes after hip arthroscopy for patients
with hip dysplasia with a lateral center edge (LCE) angle
between 8°and 25°. They concluded that age .38 years,
body mass index (BMI) 23 kg/m
2
, broken Shenton line,
LCE angle 19°, femoral neck shaft angle 140°, and car-
tilage injury were significant risk factors of poor clinical
results after hip arthroscopy for hip dysplasia. In a cohort
study of 166 patients with an LCE angle of 16°to 28°,
Dwyer et al
7
showed that patients with hip dysplasia and
Outerbridge grade I to II cartilage damage on the posterior
femoral head were 43 times more likely to convert to total
hip arthroplasty and that those with grade III to IV carti-
lage damage of the superior acetabulum were 14 times
more likely to convert to total hip arthroplasty. In spite
of these studies, many orthopaedic surgeons are still doing
hip arthroscopic labral procedures for patients in the set-
ting of borderline developmental dysplasia of the hip
(BDDH) without any concerns.
The LCE angle was first introduced by Wiberg
24
as
a measure of acetabular development and the degree of
acetabular coverage for patients with developmental dys-
plastic hip (DDH). BDDH was first described in 1976 by
Fredensborg,
10
who defined an LCE angle of 20°to 25°as
BDDH. The condition of the patients from these studies,
based on arthroscopic surgery for the dysplastic hip, was
a combined category of BDDH and DDH. Utilizing the
LCE angle of Wiberg,
24
Byrd and Jones
3
reported clinical
outcomes after hip arthroscopy for hips categorized as nor-
mal (.25°), DDH (\20°), and BDDH (20°-25°). Although
Domb et al
5
defined BDDH as an LCE angle of 18°to 25°
and reported clinical outcome after hip arthroscopy, we
defined BDDH as an LCE angle of 20°to 25°.
BDDH is still a challenge amid a subset of patients with
the coexistence of an impingement, shallow acetabulum,
and capsular laxity. Several studies showed that the clini-
cal results of hip arthroscopic FAI surgery, including labral
debridement of capsular closure for BDDH, are relatively
favorable.
5,11,17
However, there is a dearth of knowledge
about the predictors of poor clinical outcomes for these
patients. Some patients with BDDH may benefit from hip
arthroscopy for FAI. The first purpose of this study was
to identify the clinical outcomes of hip arthroscopic labral
preservation and cam osteoplasty in our BDDH population.
Our second objective was to identify the predictors of
worsened clinical outcomes after hip arthroscopy for
patients with the coexistence of FAI and BDDH.
METHODS
We retrospectively reviewed the medical records and radio-
graphs of 629 hips from patients undergoing hip arthro-
scopic treatment by a single surgeon (S.U.) between
March 2009 and December 2014. The indications for hip
arthroscopic surgery were persistent groin pain and limited
range of motion, positive provocative maneuvers, refractory
response to nonsurgical treatment, and intra-articular path-
ologic abnormalities, including acetabular labral tearing as
detected by gadolinium-enhanced magnetic resonance
arthrography. Contraindications for hip arthroscopic sur-
gery for DDH included osteoarthritis (OA) (To
¨nnis grades
2 on radiographs), additional severe bone abnormalities
(eg, Perthes disease), slipped capital femoral epiphysis,
and lateral migration of the femoral head. The local institu-
tional review board approved the study, and all study par-
ticipants provided informed consent.
We excluded 548 patients with an LCE angle .25°diag-
nosed as FAI (n = 324), dysplastic hip with LCE angle \20°
(n = 112), capsular laxity (defined as no evidence of radio-
graphic markers of FAI or DDH but symptomatic instabil-
ity on clinical examination as shown by a positive dial test
result; n = 6), pelvic trauma (n = 14), OA (To
¨nnis grades
2; n = 72), and synovial osteochondromatosis (n = 20).
The remaining 81 patients were diagnosed as have border-
line acetabular dysplasia with LCE angles ranging from
20°to 25°. We excluded 36 patients undergoing arthro-
scopic shelf acetabuloplasty. We performed arthroscopic
labral repair, cam osteoplasty, and capsular closure and
included 45 patients in this study (15 male and 30 female;
mean age, 31.4 years; range, 12.0-65.0 years) (Figure 1).
Surgical Technique
First, we assessed any intra-articular pathologic abnor-
malities, including chondrolabral damage, via 2 standard
portals (anterolateral and midanterior) with the patient
in a modified supine position. Traction time was limited
to \2 hours to reduce the risk of neurovascular and skin
injuries. An interportal capsular cut was performed from
the 12- to 3-o’clock position with an arthroscopic knife
and radiofrequency probe to improve visualization and
instrument navigation.
Second, the acetabular rim was freshened with a motor-
ized round bur to facilitate labral healing. We then fixed
the detached labrum with suture anchors (BioRaptor; Smith
||
Address correspondence to Soshi Uchida, MD, PhD, Wakamatsu Hospital of University of Occupational and Environmental Health, 1-17-1, Hamama-
chi, Wakamatsuku, Kitakyushu, 8070024, Japan (email: soushi@med.uoeh-u.ac.jp).
*
Wakamatsu Hospital of University of Occupational and Environmental Health, Kitakyusyu, Japan.
y
Hamamatsu University School of Medicine, Hamamatsu, Japan.
z
The DISC Sports and Spine, Marina Del Rey, California, USA.
§
University of Occupational and Environmental Health, Kitakyusyu, Japan.
One or more of the authors has declared the following potential conflict of interest or source of funding: S.U. is a consultant for Smith & Nephew and
Zimmer-Biomet and receives research funding from Smith & Nephew and Stryker.
2Hatakeyama et al The American Journal of Sports Medicine
& Nephew). The suture (Ultrabraid; Smith & Nephew) was
passed circumferentially around the labrum and tied with
the knot at the capsular side of the labrum.
Third, traction was released to evaluate the peripheral
compartment for the presence of a cam lesion. When neces-
sary, we performed cam osteochondroplasty with a motor-
ized round bur.
Fourth, capsular plication through the midanterior por-
tal was performed on the hip at 40°of flexion. We used
a crescent suture passer as a suture shuttle to pass a suture
lasso through the proximal side of the capsulotomy,
retrieving the lasso on the distal side of the capsulotomy
with an Arthro-Pierce 35°Upbiter Penetrator (Smith &
Nephew). We imbricated the capsule by taking large bites
on the distal side with the Arthro-Pierce and then passed
No. 2 Vicryl (Ethicon) or Ultrabraid sutures (Smith &
Nephew) with the lasso for a side-to-side imbrication
stitch. The stitches were tied arthroscopically, with the
knot outside the capsule. Normally, we placed 2 to 3 side-
to-side stiches for capsular closure.
23
Arthroscopic Evaluation
Atthetimeofsurgery,wevisuallyassessedthejoint,record-
ing the presence of chondral lesions on the acetabulum or
femoral head as well as the condition of the labrum. The con-
dition of the femoral head was evaluated according to the
International Cartilage Repair Society (ICRS) classification
system. The condition of the rim lesion of the acetabulum
was evaluated according to the Multicenter Arthroscopy of
the Hip Outcomes Research Network (MAHORN) classifica-
tion of acetabular rim lesions.
Postoperative Recovery
Patients were instructed to use flat-foot weightbearing for
the first 3 weeks. If microfracture was performed during
surgery, weightbearing limitations were extended to 6
weeks. We placed patients in a hip brace (Philippon; Bled-
soe) for 2 to 3 weeks to protect the hip and to limit flexion
(0°-120°), abduction (0°-45°), and rotation (external rota-
tion at 0°). Gentle passive range of motion exercises were
initiated during the first week under the supervision of
a physical therapist. We performed circumduction at 70°
of hip flexion and neutral hip flexion for the first 2 weeks.
Then, continuous passive motion exercises were used to
avoid adhesive capsulitis by applying 0°to 90°of hip flex-
ion for up to 4 hours a day for 2 weeks.
Endurance strengthening was commenced only after
range of motion was maximized and after good stability
in gait and movement was demonstrated. Patients were
allowed progression of physical activity after passive sym-
metric pain-free range of motion and normal gait pattern
were achieved.
Follow-up
Patient follow-up was conducted at 6 months, 1 year, and
2 years. Clinical and radiographic follow-up data were
available for all patients after a minimum of 2 years
(mean, 42.5 months; range, 24.0-72.6 months).
Patients completed a detailed subjective questionnaire
to document outcomes. Included within the questionnaire
was the modified Harris Hip Score (mHHS; of a possible
100 points), which assessed pain and function. In addition,
patients completed the Nonarthritic Hip Score (of a possible
100 points).
Radiographs from several viewpoints were taken for
each patient. Patients had anteroposterior pelvis and
false-profile radiographs taken as part of the protocol by
the senior author (S.U.) to monitor for OA progression, het-
erotopic ossification, and the development of cam or pincer
lesions. Anteroposterior pelvic radiographs with collinear
alignment of the symphysis and coccyx were also obtained.
In addition, preoperative and 1-year postoperative cross-
table lateral views, frog-leg lateral views, and false-profile
views of the hip were obtained.
Figure 1. Flowchart showing the recruitment of patients with
borderline developmental dysplasia of the hip in the study.
DDH, developmental dysplastic hip; OA, osteoarthritis;
LCE, lateral center edge; THA, total hip arthroplasty.
AJSM Vol. XX, No. X, XXXX Hip Arthroscopy for Borderline Hip Dysplasia 3
Radiographic Evaluation
Radiographs of the 45 patients were assessed to determine
the radiographic parameters that were predictors for
a worsened clinical outcome. All radiographic measure-
ments were manually performed by 2 authors (A.H.,
S.K.) with a picture archiving and communication system.
We determined the LCE angle, To
¨nnis angle, femoral neck
shaft angle, presence of a broken Shenton line on pelvic
anteroposterior views, vertical center anterior (VCA) angle
on false-profile view, and alpha angle on cross-table lateral
or modified Dunn views.
4,14,20,24
The LCE angle was utilized to define the lateral cover-
age of the acetabulum.
24
The femoral neck-shaft angle
was calculated by a line through the center of the neck
and the center of the head and a line parallel to the femoral
shaft, as determined by the direction of the shaft below the
lesser trochanter.
1
The To
¨nnis angle was utilized as a mea-
sure of acetabular inclination.
22
The Sharp angle was also
utilized as a measure of the acetabular index.
21
The VCA
angle was utilized as a measure of the anterior coverage
of the acetabulum.
14
The alpha angle was measured for
identifying cam-type impingement. The presence of
a cam deformity was defined as an alpha angle .55°on
plain radiographs. We used the highest alpha angle of
the 2 views (anteroposterior pelvic and lateral) for each
hip.
18
A broken Shenton line is indicative of superior fem-
oral head subluxation or dislocation, strongly suggesting
DDH. We determined the presence of a broken Shenton
line if the inferior femoral neck projection was cephalad
to the superior arch of the obturator foramen on standing
anteroposterior pelvic radiograph.
20
We also evaluated all
preoperative and yearly radiographic conditions for osteo-
arthritic changes with the To
¨nnis classification system.
22
The inter- and intraobserver reproducibility of these
radiographic parameters was investigated. For intraob-
server reliability, a hip surgeon (S.U.) measured each radio-
graph 3 times, with an interval of at least 1 week between
measurements. For interobserver reliability, 2 hip surgeons
(A.H., S.K.) measured each radiograph; each performed the
radiograph review independently and was blinded to the
clinical data and details of radiology reports. Intraclass cor-
relation coefficients (ICCs) and corresponding 95% CIs were
calculated to quantify inter- and intraobserver reliability for
continuous variables. The weighted kvalue was used to
determine a broken Shenton line and To
¨nnis classification;
kvalues and ICCs of 1.0 are indicative of perfect agreement.
The strength of agreement was interpreted as the following
ICC values: 0.80, almost perfect agreement; 0.61 to 0.80,
substantial agreement; 0.41 to 0.60, moderate agreement;
and 0.21 to 0.40, fair agreement. Based on the standards
for the kstatistic proposed by Landis and Koch,
12
our meas-
urements were in substantial agreement.
Statistical Analysis
The preoperative predictors leading to subsequent surgery
in patients with dysplasia were identified with univariate
Cox hazard proportional and log-rank test analyses.
Patients were divided into 2 groups: a success group (34
hips) and a failure group (11 hips). Failure was defined
as conversion to total hip arthroplasty, rotational acetabu-
lar osteotomy, or arthroscopic shelf acetabuloplasty. In
addition, patients were considered part of the failure group
if the To
¨nnis OA classification progressed to grade 2.
We compared cross-sectional data, including demo-
graphic and radiographic factors, between the success and
failure groups with univariate analyses. Patient age in the
2 groups was compared with the Mann-Whitney Utest
and Fisher exact test. Radiographic measurements—
including the LCE angle, Sharp angle, To
¨nnis angle, alpha
angle, femoral neck-shaft angle, and VCA angle—were com-
pared with the Mann-Whitney Utest. Values are presented
as medians and ranges. We compared categorical and
binary variables, such as presence of a broken Shenton
line or cartilage damage, between the 2 groups with the
Fisher exact test. We identified the best cutoff value that
maximizes the sum of the sensitivity and specificity for
each preoperative factor with the use of receiver operating
characteristic (ROC) curve analysis. The area under the
curve (AUC) was calculated for different factors, including
age, sex, BMI, surgery site, and radiographic parameters
(eg, LCE angle, Sharp angle, and To
¨nnis angle). The level
of cartilage damage was based on the MAHORN classifica-
tion and divided into low grade (0-2) and high grade
(3-5) and based on the ICRS classification of femoral head
as either normal (grade 0) or mild-high (grade 1-4). These
subgroups were compared with the log-rank test.
The relationship between the radiographic parameters
and cartilage damage of the femoral head and acetabular
rim lesion was analyzed with the Mann-Whitney Utest
for median values and the Fisher exact test for percentages
between groups.
Patients were divided into 2 groups: those above and
below the cutoff value determined by ROC curve analysis.
Patientsex,age,BMI,LCEangle,Sharpangle,To
¨nnis angle,
alpha angle, femoral neck-shaft angle, VCA angle, MAHORN
lesion grade, and ICRS lesion grade were analyzed. Indepen-
dent predictors of reoperation after the initial hip arthro-
scopic treatment were identified by calculating the hazard
ratio (HR) with the Cox proportional hazard model.
Using ROC curve analysis, we found the optimum cutoff
value of various indices to evaluate survivorship. We ana-
lyzed survivorship using the Kaplan-Meier method as an
endpoint of conversion to subsequent surgery or time of
progression toward To
¨nnis OA grade 2. Survival rates,
with 95% CIs, were presented and compared with the
log-rank test. Statistical analyses were performed with
the SPSS software package (v 21; SPSS Inc). A Pvalue
\.05 was considered statistically significant.
RESULTS
Patient Demographics
At preoperative examination, the mean LCE angle of the
45 study patients was 23.2°61.7°(range, 20°-25°); the
mean Sharp angle was 43.7°63.3°(range, 38°-50°); and
the mean alpha angle was 72.0°612.6°(range, 42°-90°).
4Hatakeyama et al The American Journal of Sports Medicine
There were 42 patients with a cam lesion. These patients
underwent labral repair, cam osteochondroplasty, and cap-
sular closure. The 3 remaining patients without a cam
lesion underwent labral repair and capsular closure only.
The initial arthroscopic procedure failed in 11 (24.4%) of
the 45 patients. Nine patients who underwent subsequent
surgery were included in the failure group. Two patients
progressed to total hip arthroplasty because of progressive
OA with lateral migration of the femoral head; 2 under-
went revision arthroscopy (trimming for osteophyte at
cotyloid fossa, labral repair, cam osteochondroplasty,
microfracture at acetabulum) because of progression of
OA and labral retear; and 5 underwent arthroscopic shelf
acetabuloplasty. Eight patients did not show any improve-
ment in the mHHS, with a median preoperative score of
68.1 (range, 23.1-79.2) and a median score of 75.9 (range,
42.9-84.7) at the time of revision surgery. There were 34
patients who did not undergo subsequent surgery; in the
success group, the median mHHS was 72.1 (range, 12.0-
95.7) preoperatively and 100 (range, 84.7-100.0) at final
follow-up, and the median Nonarthritic Hip Score was
58.8 (range, 28.8-97.5) preoperatively and 98.8 (range,
65.0-100.0) at final follow-up (P\.001, Wilcoxon signed-
rank test). Both scores significantly improved at the latest
follow-up (Figure 2).
Inter- and Intraobserver Reliability
We assessed the inter- and intraobserver reliability of the
radiographic measurements. The inter- and intraobserver
ICCs of the LCE angle were 0.631 and 0.714, respectively.
The inter- and intraobserver ICCs of the Sharp angle,
To
¨nnis angle, femoral neck-shaft angle, and VCA angle
were 0.933 and 0.839, 0.790 and 0.935, 0.946 and 0.963,
and 0.931 and 0.950. However, the inter- and intraobserver
reliabilities of the alpha angle were 0.622 and 0.772, sug-
gesting substantial agreement. In addition, the inter- and
intraobserver Cohen kcoefficients for a broken Shenton
line (0.751 and 0.842) and the To
¨nnis grade (0.935 and
1.000) indicated almost perfect agreement (Table 1).
Finally, the measurements of a single observer (S.U.)
were adopted for further analysis.
Univariate Analysis Comparing
the Success and Failure Groups
Univariate analysis showed significant differences
between the 2 groups in the presence of age, broken Shen-
ton line, To
¨nnis grade 1, MAHORN grade 3 to 5, and ICRS
grade 1 (Table 2). The median age in the failure group
was significantly higher than that in the success group
(47 vs 20 years; P= .001). The preoperative VCA angle in
the failure group was significantly smaller than that in
the success group (16°vs 23°;P= .016). The incidence of
broken Shenton line in the failure group was significantly
higher than that in the success group (45% vs 6%;
P= .004). The preoperative To
¨nnis grade in the failure
Figure 2. Box plot showing results of the success group preoperatively and 6, 12, and 24 months after surgery. (A) modified Harris Hip
Score and (B) Nonarthritic Hip Score. Line, median; box, interquartile range; asterisks and circles, outliers. Error bars indicate 95% CI.
TABLE 1
Inter- and Intraobserver Reliability of the
Preoperative Radiographic Measurements
Determined With Correlation or Kappa Coefficients
a
r/ Kappa
Interobserver Intraobserver
Lateral center edge angle 0.631 0.714
Sharp angle 0.933 0.839
To
¨nnis angle 0.790 0.935
Vertical center edge angle 0.931 0.950
Alpha angle 0.622 0.772
Femoral neck-shaft angle 0.946 0.963
Broken Shenton line 0.751 0.842
To
¨nnis grade 0.935 1.000
a
For each r/kappa value, P\.001.
AJSM Vol. XX, No. X, XXXX Hip Arthroscopy for Borderline Hip Dysplasia 5
group was significantly higher than that in the success
group (55% vs 15%; P= .014). The prevalence of high-grade
cartilage damage (MAHORN grade 3-5) in the failure
group was significantly higher than that in the success
group (73% vs 12%; P\.001). The prevalence of cartilage
injury at femoral head (ICRS grade 1) in the failure
group was significantly higher than that in the success
group (45% vs 9%; P= .018).
There were no significant differences of BMI (P= .555),
side of surgery (P= .503), preoperative mHHS (P= .261),
preoperative Nonarthritic Hip Score (P= .728), LCE angle
(P= .523), Sharp angle (P= .948), alpha angle (P= .367),
and femoral neck-shaft angle (P= .730) in the univariate
analysis (Table 2).
ROC Curve Analysis
ROC curve analysis was performed to decide the cutoff
value of several parameters between the success and fail-
ure groups. The cutoff of age was decided at 41.5 years
(AUC, 0.88; 95% CI, 0.770-0.981; sensitivity, 81.8%; speci-
ficity, 88.2%; P\.001). The cutoff of To
¨nnis angle was
decided at 14.7°(AUC, 0.64; 95% CI, 0.441-0.837; sensitiv-
ity, 45.5%; specificity, 85.3%; P= .170). The cutoff of VCA
angle was decided at 17.5°(AUC, 0.745; 95% CI, 0.547-
0.943; sensitivity, 63.6%; specificity, 87.1%; P= .017).
The cutoff of alpha angle was decided at 74.5°(AUC,
0.594; 95% CI, 0.404-783; sensitivity, 72.7%; specificity,
55.9%; P= .355). The cutoff of femoral neck-shaft angle
was decided at 132.5°(AUC, 0.538; 95% CI, 0.340-0.736;
sensitivity, 50.0%; specificity, 70.6%; P= .716) (Table 3).
Kaplan-Meier Survival Analysis
We investigated the survivorship of subgroups, divided
according to the cutoff values by ROC curve analysis (Fig-
ure 3). Kaplan-Meier survivorship after a minimum of 2
years, with reoperation (Shelf acetabuloplasty, total hip
arthroplasty, and revision arthroscopy) as the endpoint,
revealed the following survivorship values: 14 hips with
age .42 years, 50.0% (P\.001, log-rank test); 31 hips
with age 42 years, 93.5% (P\.001, log-rank test); 7
hips with broken Shenton line, 42.9% (P= .002, log-rank
test); 11 hips with preoperative To
¨nnis grade 1, 63.6%
(P= .025, log-rank test); 8 hips with the cartilage injury
at the femoral head with ICRS grade .1, 50.0% (P=
.001, log-rank test); and 12 hips with severe cartilage dam-
age at the rim with MAHORN grade 3 to 5, 41.7% (P\
.001, log-rank test).
Cox Proportional Hazard Model Analysis
As revealed with Cox proportional hazard model analysis
with reoperation, patients were likely to undergo reopera-
tion if their age was .42 years (P= .002; HR, 11.6; 95% CI,
2.5-53.9), Shenton line was broken (P= .002; HR, 6.4; 95%
TABLE 2
Univariate Analysis Comparing Success and Failure Groups
a
Success Group Failure Group PValue
b
No. of patients 34 11
Age, y 20 (12-65) 47 (23-61) .001
Female sex 20 (59) 10 (91) .070
Body mass index, kg/m
2
21.7 (15.3-30.3) 20.1 (17.7-25.0) .555
Left-side surgery 17 (50) 4 (36) .503
Preoperative modified Harris Hip Score 72.1 (12.0-95.7) 68.1 (23.1-79.2) .261
Preoperative Nonarthritic Hip Score 58.8 (28.8-97.5) 60.0 (45.0-73.8) .728
Positive broken Shenton line 2 (6) 5 (45) .004
Lateral center edge angle, deg 24 (20-25) 23 (20-25) .523
Sharp angle, deg 44 (38-50) 44 (38-49) .948
To
¨nnis angle, deg 11 (3-31) 12 (6-23) .176
Vertical center anterior angle, deg 23 (10-38) 16 (5-32) .016
Alpha angle, deg 73 (42-90) 80 (51 -90) .367
Femoral neck shaft angle, deg 135 (123-148) 133 (127-141) .730
Preoperative To
¨nnis grade 1 5 (15) 6 (55) .014
Acetabular cartilage delamination \.001
MAHORN 0-2 30 (88) 3 (27)
MAHORN 3-5 4 (12) 8 (73)
Cartilage damage of femoral head .018
ICRS 0 31 (91) 6 (55)
ICRS 1 1 (3) 3 (27)
ICRS 2 0 (0) 1 (9)
ICRS 3 2 (6) 1 (9)
ICRS 4 0 (0) 0 (0)
a
Data are presented as median (range) or No. (%). ICRS, International Cartilage Repair Society; MAHORN, Multicenter Arthroscopy of
the Hip Outcomes Research Network.
b
Mann-Whitney Utest and x
2
test. Bold indicates P\.05.
6Hatakeyama et al The American Journal of Sports Medicine
CI, 1.9-22.3), To
¨nnis angle was .15°(P= .028; HR, 3.9;
95% CI, 1.2-12.9), VCA angle was \17°(P= .010; HR,
5.0; 95% CI, 1.5-17.1), preoperative To
¨nnis OA classifica-
tion was grade .1(P= .037; HR, 3.6; 95% CI, 1.1-11.7),
cartilage damage at the rim was MAHORN grade 3 to 5
(P\.001; HR, 11.8; 95% CI, 3.0-46.1), and femoral head
chondral damage was grade .1(P\.002; HR, 8.1; 95%
CI, 2.1-30.8) (Table 4).
Complications
No complications were observed in this study group.
DISCUSSION
The current study demonstrates the nearly 25% failure
rate after hip arthroscopy for BDDH patients with an
LCE angle of 20°to 25°. The major risk factors for poor sur-
gical outcomes are as follows: advanced age (42 years,
11.6 times), broken Shenton line (6.4 times), preoperative
OA (To
¨nnis grade 1, 3.6 times), smaller VCA angle (17°,
5 times) severe acetabular rim chondral damage
(MAHORN grade 3-5, 11.8 times), and mild femoral head
chondral damage (ICRS 1, 8.1 times). Minor risk factors
include a larger To
¨nnis angle (15°, 3.9 times).
There are recent studies that examined clinical out-
comes after hip arthroscopy for BDDH. Domb et al
5
reported significantly improved clinical outcome scores
after hip arthroscopy for 22 patients \40 years old with
BDDH (LCE angle 18°-25°), and the failure rate was 9%.
Fukui et al
11
also reported good clinical outcome scores
after hip arthroscopy for 85 patients with BDDH, for which
the failure rate was 15%. In these 2 studies, authors
defined only revision surgery or conversion of total hip
arthroplasty as clinical failure. Nawabi et al
17
reported
a failure rate of 4.3% in an age- and sex-matched control
study based on clinical outcome scores after hip arthros-
copy for BDDH and FAI. Authors defined revision surgery,
conversion to total hip arthroplasty, as well as mHHS \70
as clinical failures. In our study, the failure rate was 24%,
which appears higher than the aforementioned studies. In
this study, failure was defined as conversion to total hip
arthroplasty, rotational acetabular osteotomy, or arthro-
scopic shelf acetabuloplasty. Patients were also considered
part of the failure group if the To
¨nnis OA classification pro-
gressed to grade 2. In addition, compared with the cur-
rent study, patients were younger in the studies by
Domb et al
5
and Nawabi et al.
17
In this study, the failure
rate for patients \42 years old was 6.5%, similar to the
rate of the aforementioned studies. In addition, these pre-
vious studies
5,17
did not analyze the risk factor of worsened
clinical outcomes. The current study, though similar to the
previously mentioned studies, provides risk factors associ-
ated with failure after hip arthroscopy for patients with
BDDH. The results show that the arthroscopic surgery
for BDDH can provide excellent results based on careful
patient selection and awareness of factors associated with
failure
In this current study, the HR of age was the highest
(11.6) among all factors, and the cutoff value was 42 years
old. Philippon et al
19
reported the clinical results of arthro-
scopic FAI correction for patients .50 years old, and the
conversion rate to total hip replacement was 20%.
TABLE 3
Receiver Operating Characteristic Curve Analysis
a
Cutoff
Value
Area Under
the Curve 95% CI Sensitivity, % Specificity, % PValue
Youden
Index
Age, y 41.5 0.876 0.770-0.981 81.8 88.2 \.001 0.700
Body mass index, kg/m
2
— 0.438 0.248-0.627 — — .54 —
Lateral center edge angle, deg — 0.567 0.359-0.774 — — .509 —
Sharp angle, deg — 0.493 0.287-0.700 — — .947 —
To
¨nnis angle, deg 14.7 0.639 0.441-0.837 45.5 85.3 .170 0.308
Vertical center anterior angle, deg 17.5 0.745 0.547-0.943 63.6 87.1 .017 0.507
Alpha angle, deg 74.5 0.594 0.404-0.783 72.7 55.9 .355 0.286
Femoral neck shaft angle, deg 132.5 0.538 0.340-0.736 50.0 70.6 .716 0.206
a
Data on the receiver operating characteristic curve analysis about preoperative parameters. Dashes (—) indicate not applicable. Bold
indicates P\.05.
TABLE 4
Cox Proportional Hazard Model Analysis
a
Hazard Ratio 95% CI PValue
Age 42 y 11.6 2.50-53.9 .002
Broken Shenton line 6.43 1.85-22.3 .003
To
¨nnis angle 15°3.87 1.16-12.9 .028
Vertical center anterior
angle 17°
4.99 1.46-17.1 .010
Femoral neck shaft
angle 132°
2.85 0.80-10.1 .105
To
¨nnis grade 1 3.56 1.08-11.7 .037
Severe delamination,
MAHORN 3-5
11.8 3.04-46.1 \.001
Femoral head cartilage
damage, ICRS 1-4
8.09 2.12-30.8 .002
a
All factors except femoral neck shaft angle were statistically
significant (P\.05; denoted in bold). ICRS, International Carti-
lage Repair Society; MAHORN, Multicenter Arthroscopy of the
Hip Outcomes Research Network.
AJSM Vol. XX, No. X, XXXX Hip Arthroscopy for Borderline Hip Dysplasia 7
Moreover, in a case series of patients with dysplasia,
Uchida et al
23
indicated that age 38 years was a risk factor
of revision surgery or poor mHHS, with an HR of 5.7. These
results strongly suggest that the indication of isolated hip
arthroscopy for borderline dysplastic hip should be deliber-
ately considered when the patient is .40 years old.
A broken Shenton line has been regarded as an impor-
tant risk factor for dysplastic patients. Uchida et al
23
reported that 11 of 28 patients (39.2%) had a broken
Shenton line (HR = 18.3), concluding it as one of the
most important risk factors for patients with hip dysplasia.
Similarly, our findings indicate that it is a significant risk
factor even though the prevalence of a broken Shenton line
in this study (7 of 45 patients, 16%) is less than that in the
case series of DDH.
In this study, the presence of osteoarthritic changes on
preoperative radiograph is described as a risk factor of poor
clinical result. Philippon et al
19
reported that osteoar-
thritic change with the joint space 2 mm in radiographs
worsened clinical results among patients with FAI. In
the current study, osteoarthritic change of even To
¨nnis
grade 1 was not negligible among patients with borderline
dysplasia. Regarding cartilage damage, our study findings
are consistent with other recent studies. Dywer et al
7
stated
that mild cartilage damage (Outerbridge I or II) at the fem-
oral head was a serious risk factor (odds ratio, 43.0). In the
current study, even ICRS 1 cartilage damage was a severe
risk factor (HR, 8.1). Regarding acetabular chondrosis,
mild cartilage damage could be discounted; however, severe
cartilage damage or delamination was an obvious risk factor
in the current and previous studies.
7,23
This result clearly
indicates the importance of improved preoperative imaging
assessment of cartilage status to help determine the best
candidates for hip arthroscopy in general and hip arthros-
copy in BDDH in particular.
We observed interesting findings regarding acetabular
coverage. Compared with the success group, the median
VCA angle of the failure group was significantly lower,
and the To
¨nnis angle was significantly higher. However,
there was no significant difference between the success
and failure groups regarding LCE angle or Sharp angle.
The LCE angle of Wiberg
24
and the Sharp angle
21
are
widely used because of the relative ease of measurement
on anteroposterior radiograph. However, anterior coverage
of the acetabulum cannot be quantified with these methods,
since they measure lateral acetabular coverage. VCA angle
(vertical center anterior) was first described by Lequesne
and Laredo
14
as a possible measurement of acetabular ante-
rior coverage. Although a relatively lower reliability of VCA
angle in patients with hip dysplasia was reported,
23
we
demonstrated high inter- and intraobserver reliability.
Hence, we found it important to evaluate the acetabular
coverage 3-dimensionally, including anterior coverage and
acetabular inclination (To
¨nnis angle).
Uchida et al
23
also previously described the risk factors
of poor clinical outcome for DDH. The similar risk factors
compared with the current study were older age, broken
Shenton line, severe acetabular cartilage delamination
(MAHORN grade 3-5), and chondral damage of femoral
head. However, as compared with the current study, the
different risk factors were higher BMI (23 kg/m
2
) and fem-
oral neck-shaft angle (.140°). The higher BMI provides
force on the cartilage of the acetabulum and femoral
head in hips with lower coverage of acetabulum, as in dys-
plastic hips. The higher femoral neck-shaft angle provides
shear force on the acetabular cartilage. In this study, there
was lower load for cartilage of the acetabulum and femoral
head because of the wider coverage of the acetabulum as
compared with the dysplastic hip.
Figure 3. Kaplan-Meyer survivorship. (A) patients aged 42
and \42 years, (B) patients with and without a broken Shen-
ton line, (C) patients with a To
¨nnis grade 1-4 and 0, (D) a
follow-up cohort divided into low- and high-grade groups
based on the MAHORN grade of the acetabular rim, (E) a
follow-up cohort divided into low- and high-grade groups
based on the ICRS grade of the femoral head, (F) patients
with To
¨nnis angles 15°and \15°, (G) patients with VCA
angles 17°and .17°. ICRS, International Cartilage Repair
Society; MAHORN, Multicenter Arthroscopy of the Hip Out-
comes Research Network; VCA, vertical center anterior.
8Hatakeyama et al The American Journal of Sports Medicine
Limitations
Our study had a number of limitations. First, our study
population was small, and it lacked a control group. A
study with a larger population may be necessary to per-
form additional statistical analyses, such as logistic regres-
sion analysis. Second, the data were limited because of the
follow-up time, which was a minimum of 2 years. Further
studies to investigate longer follow-up clinical outcomes
would more clearly elucidate the factors involved in
a poor long-term outcome after this arthroscopic technique.
Third, because the size and location of cartilage damage
were not precisely recorded, our results could be affected.
Nonetheless, we believe that the ICRS and MAHORN clas-
sification systems that we used provided adequate clinical
guidance to evaluate cartilage damage. Fourth, this was
a retrospective study, and a randomized controlled trial
with a longer term follow-up would certainly provide infor-
mation that is more useful; however, such a study may be
difficult to perform. Fifth, we did not evaluate femoral or
acetabular version on computed tomography. The effect
of femoral and acetabular version in patients with hip
pathology
2,8,9
has not been firmly established. Further
investigation is necessary to clarify whether femoral ante-
version could alter the clinical outcome after hip arthro-
scopic surgery for treating DDH. Sixth, a broken Shenton
line signifies the lateralization of femoral head and hip
instability; however, it is a qualitative method. Further
analysis, including dynamic imaging study, may be
required to quantify the instability of the hip.
CONCLUSION
Patient age .40 years, broken Shenton line, and preoper-
ative osteoarthritic change are predictors of poorer out-
comes from hip arthroscopy in the treatment of BDDH.
Preoperative predictors of poorer outcomes from iso-
lated hip arthroscopy, including capsular repair, are age
.40 years, broken Shenton line, OA, To
¨nnis angle 15°,
and VCA 17°. Intraoperative predictors of poorer out-
comes are severe acetabular chondral damage and even
mild femoral chondral damage. Although patients with
BDDH may have good outcomes from isolated hip arthros-
copy, caution is suggested for those with the aforemen-
tioned risk factors.
ACKNOWLEDGMENT
The authors thank Dr Shinsuke Sakoda and Tsuyoshi Fur-
uko for their help collecting data.
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