Surgical hip dislocation in symptomatic cam femoroacetabular impingement: what matters in early good results?

Abstract

In order to assess outcome and possible predictors of early good results, a prospective study on 22 patients who were treated with save surgical hip dislocation for symptomatic isolated cam-type femoroacetabular impingement (FAI) was performed. After a follow-up of 6 and 12 months, standard clinical and radiographic parameters were recorded. A statistically significant improvement of the clinical status according to the Harris hip score could be assessed at six months (p-value = 0.003) and 12 months (p-value = 0.001) post-surgery. By comparing standard clinical and radiographic preoperative parameters with various follow-up outcomes, we revealed no specific parameter with predictive value. These findings are important for centers that have just started to use this surgical technique and are still identifying their learning curve.

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May 12, 2011217
Eu Ro PE an JouR nal oF MED I cal RE SEaRcH
Abstract
In order to assess outcome and possible predictors of
early good results, a prospective study on 22 patients
who were treated with save surgical hip dislocation for
symptomatic isolated cam-type femoroacetabular im-
pingement (FaI) was performed. after a follow-up of
6 and 12 months, standard clinical and radiographic
parameters were recorded. a statistically significant
improvement of the clinical status according to the
Harris hip score could be assessed at six months (p-
value = 0.003) and 12 months (p-value = 0.001) post-
surgery. by comparing standard clinical and radi-
ographic preoperative parameters with various follow-
up outcomes, we revealed no specific parameter with
predictive value. These findings are important for cen-
ters that have just started to use this surgical technique
and are still identifying their learning curve.
Key words: hip, FaI, surgery, outcome, predictors
InTRoDucTIon
Femoroacetabular impingement (FaI) that constitutes
a repetitive impact of the proximal femur against the
acetabular rim is a well known observation in young
adults with persisting groin pain and limited range of
hip motion [1]. Depending on the underlying mecha-
nism, FaI is further classified as cam-, pincer- or
mixed-type. In cam-FaI, the impingement results
from an insufficient femoral head-neck offset that may
cause cartilage and labrum damage especially during
hip flexion. In pincer-FaI, the impingement arises
from focal or general acetabular over-coverage proba-
bly provoking continuous frontal contact between
femoral neck and acetabular labrum during hip flex-
ion. In mixed-FaI, a combination of both mecha-
nisms revealing a damage pattern with combined cam
and pincer pathology may be observed.
FaI by itself is not a disease per definition and a
variety of factors such as biological tissue integrity re-
main important. However, emerging evidence has
been anticipated that the repetitive abnormal abut-
ment between proximal femur and acetabular rim may
eventually lead to early osteoarthritis (oa) of the hip
joint [1-3]. In order to possibly stop or delay the onset
of the same as well as for managing symptoms, surgi-
cal treatment may become necessary [4].
The safe surgical hip dislocation for correction of
the morphological abnormality represents a well estab-
lished technique that proved a low rate of complica-
tion and allows for examination and treatment of the
entire joint during surgery[2, 5-8]. However, recently
only a small number of reports in the English litera-
ture can be referred that depict the clinical outcome of
this approach in various types of FaI [2, 5, 9-12] and
treatment of various grades of FaI is still a point for
discussion - in research meetings as well as in daily
clinical practice.
Therefore, our aim in this study was to evaluate the
clinical outcome of patients who had undergone sur-
gical hip dislocation and debridement due to sympto-
matic cam-FaI within a follow-up of one year. We fur-
ther analyzed preoperative findings in patients with
various outcomes after one year in order to reveal
valuable predictive factors.
METHoDS
STuDy PoPulaTIon
Twenty-two patients with symptomatic cam-FaI that
were identified from the orthopaedic outpatient clinic
were prospectively studied. There were 15 female
(68.2%) and 7 male (31.8%) patients. Mean age was
36.3 years ± 11.4 years (range 19.5 years to 59.5 years).
all patients had impingement that was symptomatic
and warranted surgical intervention. cam-FaI was veri-
fied by clinical examination and imaging studies includ-
ing plain radiographs and MRI. confirmation of diag-
nosis was performed by two senior orthopaedic sur-
geons (RK and MJ) according to previously reported
and well established FaI criteria. There were 14 hip
joints (63.3%) that involved the right side and eight
(36.4%) that involved the left side. The degree of os-
teoarthritis classified by standard Tonnis grades was; in
three cases (13.6%) Tonnis grade 0, in 14 cases (63.6%)
Tonnis grade 1, and in five cases (22.7%) Tonnis grade
2. In this study cohort, no patient revealed Tonnis
grade 3 changes as these would prevent patients from
joint preserving surgery with a promising outcome. The
mean Harris Hip Score (HHS) preoperatively evaluated
was 46.6 ± 18.2 ranging from 21 to 90. Exclusion crite-
ria such as any other hip pathology than cam-FaI, pre-
vious hip surgery, risks or contraindications for MRI
Eur J Med Res (2011) 16: 217-222© I. Holzapfel Publishers 2011
SuRgIcal HIP DISlocaTIon In SyMPToMaTIc caM FEMoRoacETabulaR
IMPIngEMEnT: WHaT MaTTERS In EaRly gooD RESulTS?
M. Jäger1*, b. bittersohl1*, c. Zilkens1, H. S. Hosalkar2, K. Stefanovska1, S. Kurth1, R. Krauspe1
1orthopedic Department, Heinrich-Heine university Medical School, Düsseldorf, germany,
2orthopedic Department, Rady children's Hospital, San Diego, ucSD, San Diego, ca, uSa
* The first and the second author have equally contributed to
this study.

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and surgical treatment were ruled out. Potential side ef-
fects were clarified to the patients and their written in-
formed consent obtained prior to the study. This study
was approved by the institutional ethic committee.
MEDIcal HISToRy
During the interview, patients were questioned regard-
ing presence and severity of pain, hip joint function
and functional activities. on physical exam, range of
motion was measured. These observations were sum-
marized and scored according to the HHS system.
Symp tomatic FaI was verified clinically by the anterior
impingement sign performed in supine position by
flexing the hip to 90 degrees during adduction and si-
multaneous internal rotation. The test was considered
positive if it would provoke reproducible sharp groin
pain similar to their primary complaint of hip pain.
During follow-up visits, HHS assessment was repeated
six and 12 months post surgery. The HHS after 12
months was used for grading the clinical outcome post
surgery where HHSs between 90 and 100 indicated an
excellent outcome, HHSs between 80 and 89 indicated
a good outcome, HHSs between 70 and 79 represented
fair results, and HHS values below 70 defined a poor
outcome.
PlaIn RaDIogRaPHIc EvaluaTIon
Plain radiographic evaluation was utilized to assess
status and morphology of each hip according to the
Tonnis criteria where Tonnis grade 0 indicates no
signs of osteoarthritis, Tonnis grade 1 proves in-
creased sclerosis and slight joint space narrowing,
Tonnis grade 2 small cysts, moderate joint space nar-
rowing and moderate loss of head sphericity, and
Tonnis grade 3 large cyst formation, severe joint space
narrowing and severe deformity of the femoral head
[13]. Therefore, a standard anterior-posterior radi-
ograph of the pelvis and a lateral (lauenstein) radi-
ograph of the hip were obtained (Fig. 1). on lateral
radiographs, the alpha-angle [14] was measured to
quantify the femoral head-neck offset within the
femoral head-neck junction. The alpha-angle is de-
fined by a parallel drawn within the femoral neck and
a line connecting the center of the femoral head with
the point where the contour of the femoral head ex-
ceeds the femoral head radius (Fig. 2). alpha-angles of
more than 50° are likely for an offset limitation within
the femoral head-neck junction. In order to reveal any
progressing of osteoarthritis following surgery, plain
radiographs were obtained after 12 months and the
Tonnis grading was repeated.
EuRoPEan JouRnal oF MEDIcal RESEaRcH218May 12, 2011
Fig. 1. Standard anterior-posterior radiograph and lauenstein view pre- (a, c) and post-surgery (b, D).
A
C

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MagnETIc RESonancE IMagIng (MRI)
Each patient included in this study underwent MRI
with either intraarticular (MR arthrography, MRa) or
intravenous contrast agent enhancement (indirect MR
arthrography) that was performed in our division or
other established MRI departments with equal techni-
cal equipment and expertise in hip joint MRI. all
MRIs brought to the outpatient visits in our depart-
ment were evaluated regarding quality and date of ac-
quisition. Each patients included in this present study
had appropriate MRI with multidimensional planes
and adequate arthrography effect that was undertaken
not more than three months before surgery. Within
each MR image, femoroacetabular cartilage was as-
sessed in two zones; 1) at the acetabular rim and, 2) at
the center of the joint close to the fovea region. It was
not possible to differentiate between acetabular and
femoral cartilage layers at an image resolution ob-
tained with 1.5T. Therefore, in our study cartilage
analysis included acetabular and femoral cartilage as
one combined entity. The femoroacetabular cartilage
was then evaluated based on the extent of degenera-
tion as used previously [3] for assessment of cartilage
damage in FaI where cartilage grade 0 indicated no
signs of cartilage degeneration (Fig. 3), cartilage grade
1 indicated degeneration only at the acetabular rim,
and cartilage grade 2 represented degeneration extend-
ing medially towards the center of the joint (Fig. 4).
cartilage degeneration was defined as any evidence of
cartilage changes ranging from signal irregularities to
total thickness loss of femoroacetabular cartilage. The
acetabular labrum was graded “0” indicating a normal
formed labrum (Fig. 3), grade 1 indicating signs of de-
generation such as signal alteration and/or labrum hy-
pertrophy (Fig. 4), grade 2 depicting a labral tear, and
grade 3 indicating the total loss of the labrum.
InTRa-oPERaTIvE analySIS
In all cases surgical intervention included safe surgical
hip dislocation in standard technique that represents
an approach that allows for inspection of the entire
joint surface during surgery (Fig. 5). Hereby, femoro -
acetabular cartilage and acetabular labrum were evalu-
ated for any signs of degeneration. These findings
were clearly documented within a written report and
graded according to the MRI classification used in this
study. all surgeries and intra-operative evaluations
were performed by two senior orthopedic surgeons
(RK and MJ) well trained in these procedures.
STaTISTIcal analySIS
continuous data are provided with mean values and
standard deviations (SD) (±). To determine whether
or not statistically significant difference is present be-
EuRoPEan JouRnal oF MEDIcal RESEaRcH May 12, 2011219
Fig. 2. alpha-angle assessment within the lauenstein view.
The alpha angle is formed by a parallel drawn within the
femoral neck and a line connecting the center of the femoral
head with the point where the contour of the femoral head
exceeds the femoral head radius.
Fig. 3. oblique sagittal PD-weighted MRa image depicting
normal cartilage (a) and normal triangular sharp formation of
the labrum without signal alteration (b). The capsule is ele-
vated from the labrum through the contrast medium filling.
Fig. 4. oblique coronal T1-weighted MRa image depicting
an osseous bump (a), labrum degeneration indicated by
labrum hypertrophy and signal alteration (b), severe cartilage
degeneration extending medially towards the center of the
joint as total cartilage thickness loss at the acetabular rim (c),
and contrast medium filling extra-articular (d). note with
MRa, labral tears and cartilage clefts may be better identified
through the contrast medium filling into the clefts.

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tween preoperative HHSs and follow-up HHSs, the
Student’s-T-Test (parametric variables, independent
samples) was used. In order to reveal existing predic-
tive parameters, we compared preoperative findings in
various grades of HHS after 12 months using the
Mann-Whitney-u-Test (non-parametric variables, two-
sided). For correlation analyses, the Spearman-Rho-
Test (two-sided) was utilized. P-values below 0.05 were
considered to be statistically significant. SPSS® soft-
ware (version 16.0, SPSS Inc., chicago, Il, uSa) was
used for all statistical analyses.
RESulTS
alpha-angle analyses in this study cohort revealed a
considerably increased mean value of 68.9° ± 14.8
(range 48° to 96°). Mean HHSs were as follows: pre-
operatively = 46.6 ± 18.2 ranging from 21 to 90, at six
months follow-up = 66.2 ± 21.9 ranging from 35 to
92 and at 12 months follow up (21 patients included)
= 71.9 ± 20.8 ranging from 35 to 98. The increase of
HHS during six- and 12 months was statistically signif-
icant (p-values = 0.003 and < 0.001). comparing the
HHSs assessed at six- and at 12 months post surgery
this difference did not reach the statistically signifi-
cance level (p-value = 0.522). In two cases (patient 17
and patient 22), no increase in the HHS was noted.
Here, Tonnis grades of 2 and 1 were evaluated. While
in one patient extensive cartilage damage was noted, in
the other MRI revealed signal alterations at the acetab-
ular rim while no macroscopic cartilage damage was
appearing intra-operatively. labrum analysis revealed
degeneration (patient 17) and controversial findings in
patient 22 with a labral tear diagnosed with MRI while
no labral damage was noted during surgery. In one
case (patient 5) a major drop of the HHS was noted
post-surgery that reached from 65 preoperatively to 40
at the 12-month follow-up visit. Interestingly, joint sta-
tus analysis with radiographic-, MRI and inspection
during surgery revealed only slight cartilage changes
while a labral tear was noted within the inspection
through surgical dislocation. In one patient (patient
14) the good outcome after surgical treatment was
only short-termed. While HHS increased from 40 to
89 during a period of 6 months, the same patient
proved a HHS of only 35 with similar complains as
before he underwent surgery at the 12 months follow-
up. Here, no major cartilage or labrum pathologies
have been noted at the beginning of the study. In one
further case (patient 1; age at surgery = 32 years), total
hip arthroplasty (THa) became necessary due to pro-
gressive oa. Hereby, a Tonnis grade of 1 was ob-
served preoperatively while MRI analyses revealed se-
vere cartilage and labrum damage (grade 2 changes).
These observations were confirmed during intra-oper-
ative inspection of the hip joint.
Twelve months post-surgery, in six cases (28.6%)
outcome was classified excellent, three (14.3%) were
classified good, five (23.8%) as fair and seven (33.3%)
proved poor results. comparison of preoperative ob-
servations based on the 12 month outcome grading re-
vealed no statistically significant difference except for
the HHS assessed at six months between patients with
excellent outcome and those who proved poor results
as well as for labrum observations between the group
with excellent outcome and the one with a good out-
come although this analysis is limited due to a small
number of cases. Statistically significant correlation
could be revealed only between the 6-month- and 12-
month-HHS (r = 0.657, P-value = 0.001).
DIScuSSIon
The safe surgical hip dislocation for deformity correc-
tion in FaI is a potential approach that allows for in-
spection and necessary corrections as trimming of the
acetabulum and femoral head-neck region of the en-
tire joint. In this matter, previously reported studies
revealed mostly positive results at a short and midterm
follow-up [2,5,9-12]. However, with regard to the high
number of FaI cases who underwent safe surgical hip
dislocation, these study cohorts were relatively small
and in some cases inhomogeneous. There is still de-
bate on when to perform surgery and how the out-
come may be most likely in various stages of pre-exist-
ing damage. understandably this information is critical
in decision making that need to be provided to the pa-
tient when discussing diagnosis and subsequent treat-
ment scheme. The aim of this study was therefore to
prospectively assess the clinical short-term outcome
post-surgery during a follow-up of one year in FaI.
We prospectively performed this study in 22 cam-
FaI patients who proved no other hip deformity than
cam-FaI. Subjects with pincer or mixed FaI types
were not included. We intended to study the clinical
outcome in this particular study cohort and to exam-
ine pre- and postoperative observations in order to
make out potential factors that may be of value to pre-
dict the outcome of this surgical approach. our re-
sults revealed a statistically significant improvement of
the clinical status according to the HHSs assessed 6
months (p-value = 0.003) and 12 months (p-value =
0.001) post-surgery. The difference between the 6-
month and 12-month HHS was low and did not reach
the statistically significance level (p-value = 0.522) in-
EuRoPEan JouRnal oF MEDIcal RESEaRcH 220May 12, 2011
Fig. 5. Intra-operative photograph of the exposed femoral
head of patient 1 following safe surgical dislocation demon-
strating severe and extensive full thickness cartilage abrasion.
Total hip replacement became necessary within 6 months fol-
low-up.

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dicating a notable prognostication degree in the short-
term follow-up. However, a long-term evaluation of
this study cohort will have to confirm this observa-
tion.
by comparing standard clinical and radiographic
preoperative parameters with various follow-up out-
comes, we revealed no parameter with predictive value.
correlation between outcome and all parameters as-
sessed preoperatively was weak and not statistically
significant. In this study cohort, we noted no increase
in the HHS in two cases (9.1%). Here, a mixture of
findings was observed preoperatively. In one case
(4.6%) a major drop of the HHS was noted post-
surgery. Interestingly, diagnostic assessment with plain
radiographs, MRI and inspection during surgery re-
vealed only mild cartilage changes. In one patient (pa-
tient 4.6%) the good outcome was merely short-
termed. While the HHS increased from 40 to 89 dur-
ing a period of 6 months, the same patient proved a
HHS of only 35 with similar complains as before he
underwent surgery at the 12 months follow-up. at the
last patient visit 18 months post-surgery, the same pa-
tient reached a HHS of 90 (data not provided in this
study). In one patient (4.6%), hip replacement became
necessary due to progressive symptoms. Hereby, se-
vere cartilage and labrum damage (Figure 5) was not-
ed. understandably these observations were based on
individual nature and extent of involvement in each
subject.
our results are in keeping with previously reported
studies. beck et al. [5] evaluated the mid-term outcome
of FaI patients at a mean follow-up of 4.7 years uti-
lizing the Merle d’ aubigné system that involves a rat-
ing of pain, ambulatory status and RoM where a max-
imum of six points for each subgroup can be reached.
In this study cohort, radiographic assessment revealed
pistol grip deformity in four and an aspheric shape of
the femoral head in seven hips indicating a cam-FaI
mechanism. The acetabulum proved abnormal mor-
phological features such as retroversion in five-, coxa
profunda in five-, protrusion in three-, and marginal
dysplasia in one hip pointing towards a pincer compo-
nent. a clear differentiation between the various FaI-
types was not undertaken. There was a significant im-
provement (p-value = 0.015) in the Merle d’ aubigné
score from a preoperative value of 14.1 to 16.5 points
at the latest follow-up and the pain score improved
statistically significant (p-value = 0.005) from 2.9
points preoperatively to 5.1. Interestingly, five out of
19 subjects (26.3%) needed THa within the follow-up
duration. In the study of 23 FaI patients by Murphy
et al.[2] similar results with a statistically significant in-
crease in the Merle d’ aubigné score (13.2 versus 16.9)
with seven cases (30.4%) where THa became neces-
sary were noted. Hereby, ten patients had isolated
cam-FaI, one proved pincer-FaI, and 12 revealed a
mixed FaI type. Superior results could be revealed by
Espinosa et al.[10] by retrospectively comparing safe
surgical hip dislocation for FaI treatment with (n =
35) and without (n = 25) labrum re-fixation. Hereby, a
post-operative Merle d’ aubigné score of 17 within
the group where the labrum was re-fixated and 15
where no re-fixation was undertaken was noted. The
mean preoperative Merle d’ aubigné score in both
groups was 12. a clear differentiation between various
FaI types in this follow-up study of two years was not
performed. Peters and Erickson [12] reported in their
study cohort of 29 FaI patients (30 hips) a statistically
significant (p-value < 0.0001) increase of the mean
HHS from 70 to 87 within a follow-up of two years.
cam-FaI was diagnosed in 14 hips while pincer-FaI
was noted in one case and 15 hips proved radiographic
signs indicating a mixed FaI mechanism. The mean
follow-up in this study was 32 months. Interestingly,
eight hips (26.7%) revealed radiographic progression
of oa and four of these eight patients (13.3%) need-
ed THa in order to manage symptoms. Similar results
were reported by beaulé at al. [9] in a study of 37 hips
in 34 patients with symptomatic cam-FaI where clini-
cal grading scales such as the Western ontario and
McMaster universities osteoarthritis Index (WoM-
ac) at a mean follow-up of 3.1 years. Hereby, nine pa-
tients (20.5%) underwent screw removal from the
greater trochanter because of persistent bursitis and
six of the thirty-four patients (13.6%) were unsatisfied
with the clinical outcome, however, none of the sub-
jects underwent additional hip reconstructive surgery.
The authors concluded femoral head-neck offset cre-
ation following safe surgical dislocation of the hip
joint is an effective approach in cam-FaI treatment
and may in most cases improve the overall quality of
life. graves and Mast [11] revealed in their retrospec-
tive study a significant increase of the Merle
D'aubigne score from a preoperatively assessed value
of 13 to a post-operative score of 16.8 and postulated
that surgical dislocation improves symptoms in pa-
tients with limited radiographic signs of arthritis who
are experiencing impingement-related hip pain. The
study included 36 cam- and 12 pincer-FaI hips. Fur-
ther studies on the outcome of FaI treatment using
arthroscopic [15-21] or arthroscopically assisted tech-
niques [22] are published with similar promising re-
sults that may be a potential alternative in cases with
minor morphological abnormality and less damage in
particular in cam-FaI but may be limited in cases
where major pathological morphology and degenera-
tion is present.
This study has limitations. First, our study popula-
tion with 22 cam-FaI patients is relatively small. Fur-
ther studies should involve a larger study population
and various types of FaI. Second, in few cases preop-
erative cartilage grading was based on indirect MR
arthrography which may be less effective compared to
direct arthrography (MRa). Furthermore, in all cases
MRI was performed utilizing a 1.5 T system. There-
fore, clear differentiation between acetabular and
femoral cartilage was not possible and thus cartilage
analysis included acetabular and femoral cartilage as
one combined entity. consequently, we may have
missed lesions, which could be better identified with
MRa and/or 3T MR systems. Third, we performed
this study using current standards in FaI diagnosis
whereas advanced tools for hip joint diagnosis could
be reported recently that may be valuable in the deci-
sion making progress in choosing the right therapy ap-
proach at the right time [3,23-25].
In summary, the benefit from safe surgical disloca-
tion in this present study of symptomatic cam-FaI pa-
EuRoPEan JouRnal oF MEDIcal RESEaRcHMay 12, 2011 221