Abstract:
Background and purpose:
Heterotopic ossification (HO) is one of the major complications
following total hip arthroplasty (THA). The aim of this study is
to evaluate HO and functional status (FS) of the hip joint 5
years after THA and prophylactic postoperative irradiation with
a single dose of 7 Gy.
Methods:
We analyzed a random sample of 100 patients 5 years after THA
and postoperative radiotherapy with a single dose of 7 Gy.
Brooker score (BS) was used to classify the radiographic signs
of HO and Harris-Hip Score (HHS) to assess the FS of the hip
joint. The range of motion was assessed in all directions and
was measured in degrees.
Results:
51% of patients had radiographic evidence of HO; mean HHS 84.8 ±
16.5 points. Height (p = 0.025) and weight (p = 0.008)
correlated positively with the extent of HO. Men developed
significantly higher BS than women (p = 0.009). Duration of
surgery correlated with HHS (p = 0.026). In the category BS 0
vs. BS 1 for the range of motion in degrees, there were
significant correlations for flexion (p = 0.05), adduction (p =
0.03) and sum of motions (p = 0.04) in favour of BS 0. In the
category BS 0 vs. BS 1,2,3,4, there were significant
correlations for flexion (p = 0.07), adduction (p = 0.05), and
sum of motions (p = 0.05) in favour of BS 0. For the range of
motion in points (HHS), no significant correlations with all
categories of HO were found.
Conclusion:
Mild HO of BS 1 can deteriorate the range of motion after THA
significantly. The sum of motion in degrees has been proved a
more sensitive tool for assessing the clinical outcome than the
range of motion in points according to HHS or the total HHS.
J.Orthopaedics 2010;7(4)e12
Keywords:
Heterotopic Ossification; Total Hip Arthroplasty; Postoperative
Prophylactic Irradiation.
Introduction:
Heterotopic ossification (HO) after total hip arthroplasty (THA)
is a relatively common complication and can have an impact on
the functional outcome, occurring in up to 60 to 90% of
patients. The exact mechanism for heterotopic bone formation has
not been thoroughly elucidated; however, it appears to involve
pluripotent mesenchymal cell differentiation into
osteoprogenitor cells after tissue injury or dissection. This
process begins as soon as sixteen hours after injury and is
maximal at thirty-six to forty-eight hours (1).
There are two primary methods of preventing HO: Radiotherapy,
and pharmacotherapy with both selective COX-2 inhibitors and
nonselective COX-1 and COX-2 inhibitors of non steroid
anti-inflammatory drugs (NSAIDs) (2). Perioperative NSAIDs,
apart from low dose aspirin, appear to produce between a one
half and two thirds reduction in the risk of HO. With routine
use, such agents may be able to prevent 15-20 cases of HO among
every 100 THA performed (3).
More recently, a metaanalysis of 9 randomized controlled trials
including 1295 patients reported no statistically significant or
clinically important difference between NSAIDs or radiation in
preventing HO (4).
There has been no randomized study comparing total hip
replacement alone with or without irradiation. Nevertheless, the
available data support the current standards including
single-fraction treatment of 7 Gy given <4 h preoperatively or
<72 h postoperatively for prophylaxis (5).
Both RT concepts achieved a similar low radiologic and
functional failure rate of about 10.9 % and 5%, respectively
(6).
The mostly used radiographic classification for HO is the
Brooker classification (7), based on radiographic findings of HO
at the hip after THA, and includes four classes. According to
Brooker Score (BS) the incidence of HO after THA and no
prophylactic treatment is 43 % for any score and 9% for score
III and IV, depending on risk factors (8). HO is typically
asymptomatic and detected as an incidental finding on
radiographs. BS I and II are considered clinically insignificant
because symptoms rarely manifest with this extent of HO. BS III
and IV are considered to be clinically significant because
symptoms are typically present. In total, only a minority of
patients with HO (10–30%) develop functional impairment (9). The
large number of hip operations, however, leads to a significant
number of patients with clinically significant symptoms (10).
Higher grades of HO can result in significant limitation of
function and can vitiate the benefits of joint replacement (11).
The role of lower grades with respect to impairment of the range
of motion is a matter of debate.
Materials
and Methods:
Of all the patients who underwent THA in the Department of
Orthopedics and Traumatology of Evangelical Waldkrankenhaus
Spandau, Berlin, during a period of 12 months, 30% of patients
received postoperative prophylactic hip irradiation. Out of
these patients, and after 5 years from treatment, a random
selection of 100 patients was done for evaluation of
radiographic evidence of HO and FS of the hip joint. THA was
performed in 34 males and 66 females, the mean age at time of
surgery was 65.1± 8.1 years (range 47-82 years), and at time of
evaluation 70.7± 8.2 years (range 55-88 years). Mean height was
167.8±8.8 cm (range 147-194 cm), mean weight 76.0±13.6 Kg (range
49-112 kg) (Table 1).
Surgery:
All patients were operated with THA in the Department of
Orthopedics and Traumatology of the Evangelisches
Waldkrankenhaus Spandau, Berlin, by the same team of surgeons.
All prostheses were implanted for the first time; there was no
replacement of preexisting prosthesis in any patient. The right
joint was treated in 49% of patients and the left joint in 51%
of patients. There was no previous surgery on the ipsilateral
side in any patient. The femoral component of the prosthesis was
cementless in 93% of patients and cemented in 7% of patients.
The mean duration of surgery was 75.9±26.6 minutes (range 29-162
minutes) (Table 1).
Radiotherapy:
All the patients received radiotherapy in Department of
Radiation Oncology, Campus Virchow Klinikum, Charite
Universitätsmedizin Berlin. Radiotherapy was delivered in a
single dose of 7 Gy delivered to the reference point
International Commission on Radiation Units and Measurements
Report 50 (12), with 18-20 MeV maximum photon energy by linear
accelerators MevatronTM or Mevatron KD2TM
(Siemens Medical Solutions, Erlangen, Germany). All patients
underwent simulation, and two parallel-opposed fields (anteroposterior
and posteroanterior) were used. According to patient body size,
a portal of about 12 x 13 cm (± 1cm) using a curved block in the
upper medial part for the inner pelvic region was chosen to
enclose the periarticular soft tissue area, the acetabulum, and
the proximal femur. Timing of radiotherapy after surgery varied
among the patients with an average of 51±19.2 hours (range
3.5-82 hours) (Table 1).
Table 1:
Patients’ characteristics.
Patients |
Number = % |
Mean
±SD |
Range |
Number of patients
Male
Female
Height (cm)
Weight (kg)
Age at surgery (years)
Age at evaluation (years) |
100
34
66 |
167.8 (±
8.8)
76.0 (±
13.6)
65.1 (±
8.1)
70.7 (±
8.2) |
147 – 194
49 – 112
47 - 82
53 - 88 |
Number of hips
Right hip
Left hip |
100
49
51 |
|
|
The prosthesis:
Cementless
Cemented |
93
7 |
|
|
Duration of surgery (minutes) |
|
75.9 (±
26.6) |
29 - 162 |
Interval radiation – surgery (hours) |
|
51.0 (±
19.2) |
3.5 - 82 |
Patient Evaluation:
All the patients were evaluated clinically and radiographically
5 years after treatment. The evaluation was done after patient’s
informed consent. Both the investigators who evaluated the
patients clinically and the investigators who made the
radiographic evaluation were blinded to the results of each
other’s evaluations.
Radiographic Assessment (Brooker Score):
Comparison of radiographs of the pelvis (anterior-posterior) and
hip (anterior-posterior) after 5 years with those radiographs
performed preoperatively and direct postoperatively was done.
Analysis of radiographs was performed by three experts (two
radiotherapists, one radiologist). The presence of HO was
evaluated according to the four-grade classification described
by Brooker et al. (7) (Table 2).
Table 2: Brooker grading system of heterotopic
ossification
Score |
Ossification visible on radiogram |
0 |
No soft-tissue ossification |
1 |
Separate small foci of ossification about the hip |
2 |
Ossification projecting from the proximal femur or pelvis
with ≥ 1 cm between opposing bone surfaces |
3 |
Ossification projecting from the proximal femur or pelvis
with < 1 cm between opposing bone surfaces |
4 |
Ossification completely bridging the proximal femur and
pelvis |
Functional Outcome Assessment (Harris Hip Score):
Functional outcome was assessed with the modified Harris Hip
Score (13) (Table 4). Assessment of this score based on 2 parts,
a patient-based part (the subjective categories, pain and
function), and an investigator-based part (physical examination
categories, deformity and range of motions). Based on a total of
100 points possible, each of these four categories was awarded a
certain number of points. Pain with a maximum of 44 points,
function with 47 points, deformity with 4 points, and range of
motions with 5 points were awarded. The score of 90-100 was
reported as excellent functional results, 80-89 good, 70-79
fair, 60-69 poor, and below 60 failed.
Functional treatment results were defined as passive ROM of hip
joint measured with a standard goniometer as described by Pohl
(14).
Calculation of the Range of Motion:
We measured the range of motion in degrees in the four
directions (hip flexion, extension, adduction, and abduction)
and for the 2 rotations (internal rotation, external rotation),
and then calculated the sum of the ranges of motions in degrees.
Correlation between radiographic finding (BS) and Functional
outcome (HHS):
In order to find if the radiographic evidence of HO has an
impact on functional outcome of the hip joint, we correlated the
radiographic evidence of HO scored according to Brooker system
with each category of functional outcome measured in points
according to Harris Hip Score, and also with the range of motion
measured in degrees.
Statistical Analysis:
The categorical variables were described with their absolute and
relative values, and the continuous variables were defined with
their mean ± standard deviation (SD), and range (minimum and
maximum). Comparisons of frequencies of categorical variables
were tested using Fisher’s exact test and chi-square analysis.
Because of small sample size, the non-parametric Wilcoxon-Mann
Whitney test was used for comparisons of the means of continuous
variables. The confidence interval was set to 95% and the
p-value to 0.05. The calculations were performed by using
Statistical Package for Social Sciences (SPSS, Chicago, IL).
Results :
Radiographic outcome (Brooker Classification):
Fifty one patients (51%) had radiographic evidence of HO at 5
years. Thirty three patients (33%) had HO of Brooker’s grade 1,
9 patients (9%) grade 2, nine patients (9%) grade 3, while no
patient developed grade 4 (Table 3).
Table 3:
Distribution of Patients according to Brooker grading system.
Brooker Score |
Number = %
(100) |
Brooker score 0 |
49 |
Brooker score 1 |
33 |
Brooker score 2 |
9 |
Brooker score 3 |
9 |
Brooker score 4 |
0 |
Evaluating prognostic factors for HO development, patients with
a body height >168 cm developed significantly more HO than
patients ≤168cm (p = 0.025). Weight in the categories >75
kg and ≤75 kg also showed a positive correlation with HO of
higher degree (p = 0.008). Men developed significantly
more HO than women (p = 0.009). Duration of surgery in
the categories >71 minutes and ≤71 minutes also showed a
positive correlation with HO of higher degree (p = 0.02).
The following factors were found not to correlate significantly
with HO: Age, and interval between radiotherapy and surgery.
Functional outcome (HHS):
The clinical score according to modified HHS at 5 years was
almost excellent for the vast majority of patients with an
overall mean score of 84.8 ± 16.5 points (range 24.7-100
points). The subjective category of HHS pain was appraised as
36.2 ± 8.8 points (range 10-44 points), the subjective category
function 39.7 ± 9.2 (range 6-47 points). The physical
examination results of the range of motion component of HHS were
rated as 4.9 ± 0.25 (range 2.6-5) (Table 4).
Table 4:
Harris-Hip-Score of hip function. For comparison the results of
our study are added. The postoperative values including mean (±SD)
and range of values are given.
|
|
Points |
Postoperative values |
|
|
|
Mean
±SD
(Range) |
A. Pain |
|
44† |
36.2
±
8.8 (10-44) |
|
None |
44 |
|
|
Slight pain |
40 |
|
|
Mild pain |
30 |
|
|
Moderate pain |
20 |
|
|
Marked pain |
10 |
|
|
Totally disabled |
0 |
|
B. Function |
|
47† |
39.7
±
9.2 (6-47) |
Limp |
|
11 |
9.5
±
2.8 (0-11) |
|
None |
11 |
|
|
Slight |
8 |
|
|
Moderate |
5 |
|
|
Severe |
0 |
|
Support |
|
11† |
9.6
±
2.8 (0-11) |
|
None |
11 |
|
|
Cane for long walks |
7 |
|
|
Cane most of time |
5 |
|
|
One crutch |
3 |
|
|
Two canes |
2 |
|
|
Two crutches |
1 |
|
Walking |
|
11† |
8.8
±
2.3 (2-11) |
|
Unlimited |
11 |
|
|
Six blocks |
8 |
|
|
2-3 blocks |
5 |
|
|
Indoors only |
2 |
|
|
Bed and chair only |
0 |
|
Sitting |
|
5† |
4.7
±
1.1 (0-5) |
|
Ordinary chair |
5 |
|
|
High chair |
3 |
|
|
Unable |
0 |
|
Transportation |
|
1† |
0.9
±
0.3 (0-1) |
|
Yes |
1 |
|
|
No |
0 |
|
Walking stairs |
|
4† |
2.8
±
1.2 (0-4) |
|
Normally without using a railing |
4 |
|
|
Normally using a railing |
2 |
|
|
In any manner |
1 |
|
|
Unable to do stairs |
0 |
|
Put on Shoes and Socks |
|
4† |
3.2
±
1.1 (0-4) |
|
With ease |
4 |
|
|
With difficulty |
2 |
|
|
Unable |
0 |
|
C. Absence of Deformity |
|
4† |
n.e.†† |
|
Less than 30° fixed flexion contracture |
1 |
|
|
Less than 10° fixed abduction |
1 |
|
|
Less than 10° fixed internal rotation in extension |
1 |
|
|
Limb length discrepancy less than 3.2 cm |
1 |
|
D. Range of Motion |
|
5† |
4.9
±
0.3 (2.6-5) |
|
Flexion (140°*) |
1 |
|
|
Abduction (40°*) |
1 |
|
|
Adduction (40°*) |
1 |
|
|
External Rotation (40°*) |
1 |
|
|
Internal Rotation (40°*) |
1 |
|
Total hip score |
|
|
84.8
±
16.5 (24.7-100) |
†total
points possible for category
††not
evaluated
*normal
SD= standard deviation
Regarding prognostic factors for the postoperative functional
outcome, patients with a duration of surgery of >71 minutes
performed significantly worse in comparison to patients with a
duration of ≤71 minutes (HHS 80.8 vs. 88.6, p = 0.026).
The following factors were found not to correlate significantly
with HHS: Age, gender, weight, height and interval between
radiotherapy and surgery.
A prognostic factor for the range of motion component of HHS was
weight: Those in the categories ≤75 kg and >75 kg showed a
strong negative correlation with higher score (Score 4.95 for
lower weight vs. 4.93 for higher weight, p = 0.001).
Patients with a duration of surgery >71 minutes performed
significantly worse in comparison to patients with a duration of
≤71 minutes (Score 4.89 vs. 4.99, p = 0.007). Male
patients performed worse than female patients (p =
0.013). The following factors were found not to correlate
significantly: Age, height and interval between radiotherapy and
surgery.
Correlation between radiographic signs of HO (BS) and
postoperative functional
outcome (HHS):
The radiographic signs of HO graded with Brooker score was found
not to be correlated with the functional outcome evaluated with
HHS (p = 0.946).
Also for the range of motion in points (according HHS), there
were no significant differences between all categories of HO
graded with BS evaluated. For the subjective component of
function as evaluated by HHS and subjective component pain
according to HHS, there were no differences between all
categories examined, nor could be found significant correlations
for the total HHS score (Table 5).
Table 5:
Correlation of mean range of motion and grade of heterotopic
ossification (BS) in the categories 0 vs. 1 and 0 vs.1,2,3,4.
Category |
BS 0 vs. BS 1 |
BS 0 vs. BS 1,2,3,4 |
|
BS 0 |
BS 1 |
p |
BS 0 |
BS 1,2,3,4 |
p |
Flexion† |
119.4 |
112.8 |
0.05 |
119.4 |
114.0 |
0.07 |
Extension† |
0.41 |
0.0 |
n.s. |
0.41 |
0.0 |
n.s. |
Internal rotation† |
24.0 |
22.0 |
n.s. |
24.0 |
22.5 |
n.s. |
Erternal rotation† |
29.2 |
29.7 |
n.s. |
29.2 |
29.5 |
n.s. |
Abduction† |
36.2 |
35.0 |
n.s. |
36.2 |
35.2 |
n.s. |
Adduction† |
24.0 |
21.5 |
0.03 |
24.0 |
22.1 |
0.05 |
Sum of motions† and rotations† |
233.2 |
221.0 |
0.04 |
233.2 |
223.1 |
0.05 |
Range of Motiont†† |
4.94 |
4.94 |
n.s. |
4.94 |
4.95 |
n.s. |
Function†† |
39.2 |
39.5 |
n.s. |
39.2 |
40.1 |
n.s. |
Pain†† |
35.8 |
35.7 |
n.s. |
35.8 |
36.6 |
n.s. |
Total†† |
83.9 |
83.9 |
n.s. |
83.9 |
85.5 |
n.s. |
†
degrees
††
points according HHS
n.s = no significance
Correlation between radiographic signs of HO (BS) and range of
motion (in degrees):
By evaluating the postoperative results for the range of motion
(in degrees) in the four directions and two rotations (flexion,
extension, abduction, adduction, external rotation, internal
rotation), there were significant correlations between
radiographic signs of HO in categories BS 0 vs. BS 1, and
flexion (119.4 vs. 112.8, respectively, p = 0.05), and
also adduction (24 vs. 21.5, respectively, p = 0.03).
Furthermore we found significant correlations between
radiographic signs of HO in categories BS 0 vs. BS 1,2,3,4 and
flexion (119.4 vs. 114, respectively, p = 0.07), and also
adduction (24 vs. 22.1, respectively, p = 0.05).
For the total sum of motions (in degrees) in the four directions
and for rotations there were significant correlations with BS 0
vs. BS 1 (233.2 vs. 221.0, respectively, p = 0.04), and
with BS 0 vs. 1,2,3,4 (233.2 vs. 223.1, respectively, p =
0.05) (Table 5).
Discussion :
Coventry and Scanlon (15) demonstrated that fractionated RT
given postoperatively could successfully be used in the
prevention of HO. As illuminated in a review by Balboni et al.
(5), there was a substantial evolvement of irradiation for
prevention of HO after THA since then. Pellegrini et al. (16)
proved in a prospective randomized trial the efficacy of
single-fraction irradiation (8 Gy vs. 5x2 Gy). Healy et al. (17)
established the currently accepted dose of 7 Gy demonstrating
significant worse results with 5.5 Gy. Seegenschmiedt et al.
(18), in a randomized trial (with doses of different biological
effectivness) and Gregoritch et al. (19), in a (small sample
sized) randomized trial of 7-8 Gy launched the use of
preoperative irradiation.
At present, doses of approximately 7 Gy are given, for
prophylaxis of HO, mostly in one fraction and often
preoperatively. Yet, there is some evidence that the application
of preoperative application of RT for prevention of HO does not
result in the same low overall incidence of HO according to BS
of all grades. Koelbl et al. (20) found for preoperative
irradiation, in comparison to a historical control group, a
higher rate of mild (BS 1) HO. Gregoritch et al. (19) observed
for preoperative (vs. postoperative) irradiation an increase
percentage of mild and moderate HO. Seegenschmiedt et al. (18)
observed in the preoperative (vs. postoperative) irradiated
group more cases of mild HO and a higher rate of change of BS by
(merely) one category towards a higher score.
The clinical significance of HO of mild (BS 1) or moderate (BS
2) grade is not established yet nor does a consensus exist in
the literature. The knowledge of the correlation between HO of
lower or medium grade with clinical outcome would facilitate the
decision for or against the (risk-adapted) indication for
prophylactic treatment and clinical parameters could support
morphologic criteria to define the significance of HO in the
context of controversial matters like pre- vs. post-operative
application of irradiation, higher or lower doses or irradiation
vs. NSAIDs. A number of studies have reported possible
associations of even mild or moderate HO with decreased range of
motion at the hip, an important observation considering the
large number of patients treated annually.
In our study, the clinical examination measuring the range of
motion (in degrees, for four directions and two rotations) and
the sum of motions (in degrees) has proved helpful, clarifying
the significance of differences, more than the range of motion
in points (according HHS), the subjective component of motion or
pain, or the range of motion in points (according to HHS). Neal
outlined in a comprehensive review, that the clearest
associations were the effects of HO on range of motion in
degrees reflecting the greater sensitivity and precision than
when compared to the cruder measures for overall function (21).
For the postoperative range of motion in degrees, we found
significant correlations in the categories BS 0 vs. BS 1 for
flexion (p = 0.05) and for adduction (p = 0.03),
in the categories BS 0 vs. BS 1,2,3,4 for flexion (p =
0.07) and for adduction (p = 0.05). There were no
correlations in all other categories evaluated against another.
For the sum of motions (in the four directions and two
rotations) there were significant correlations for HO of BS 0
vs. 1 (p = 0.04) and BS 0 vs. 1,2,3,4 (p = 0.05)
(Table 5).
For the postoperative range of motion (in points according to
HHS), there we found no significant differences in all
categories evaluated against another. The sum of the motions (in
degrees) proved as valuable in different studies too, even if
comparatively sparse data are available about BS grade 1 or 1,2
compared to no HO. Burd et al. (22) correlated in 166 patients
with fracture of the acetabulum, the grade of HO with hip
motion. HO of BS 1-3 did not decrease the range of motion of the
hip except in flexion, where they found a significant
relationship (p = 0.011) with the grade of HO, and even
HO grade 1 was associated with a decreased amount of flexion. In
the study by Effenberger et al. (23) the range of flexion was
reduced in patients with HO of BS 2.
In our study, as well for the postoperative range of motion
(according HHS in points, as evaluated by clinical examination)
and the subjective components of function and pain according to
HHS there were no differences between all categories of BS
examined. Several studies approved that the HHS for BS 0, 1, 2
did not differ significantly from that for grades 3 and 4.
Kienapfel et al. (24) showed in a study of 154 patients
evaluated for correlation of radiologic and clinical failure,
that there was no correlation between the BS and the clinically
evaluated range of motions (according to HHS). The category of
pain in HHS correlated significantly only with the range of
motion parameters (p = 0.025), not with BS. Ashton et al.
compared HHS with BS to give a functional assessment of overall
hip function. The distribution of the several BS grades in the
groups with HHS of >80 and <80 were not significantly different
(25). Effenberger et al. (23) found in a review of 143 revision
arthroplasties no correlation between pain score and BS (p
= 0.755) (22). Grohs et al. (26) also found no correlation
between the HHS and the BS. Fransen et al. (27) showed that
patients with BS 3 and 4 had higher pain and disability scores
than those with less severe grades of ectopic bone formation,
though this trend was not significant. Yet, there are other
studies claiming a correlation between BS and HHS.
Seegenschmiedt et al. (6) published within the results of German
patterns of care study that patients who developed a radiologic
failure (especially with a high BS of 3–4), a higher functional
failure rate was experienced.
In summary, the applied treatment scheme of irradiation with 7
Gy within 72 hours (3 days) after total hip joint replacement
surgery proved successful with respect to the endpoints HO,
functional status and range of motion. The overall incidence of
any grade HO was low, both radiologically and clinically. We
could confirm the significance of even mild HO (BS 1) with
respect to deterioration of the range of motion of the hip. The
sum of motion (in degrees) has been proved a more sensitive tool
for assessing the clinical outcome than the range of motion (in
points according HHS) or the total HHS.
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