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Is Mobile-Bearing Medial Unicompartmental Knee Arthroplasty Appropriate for Asian Patients With the Risk of Bearing Dislocation?
Journal Pre-proof Is mobile-bearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation? Suk-Woong Kang, MD, Kyung-Taek Kim, MD, Youn-Soo Hwang, MD, Won-Ro Park, MD, Jong-Ki Shin, MD, Moo-Ho Song, MD, PhD. PII:
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DOI:
https://doi.org/10.1016/j.arth.2019.12.036
Reference:
YARTH 57699
To appear in:
The Journal of Arthroplasty
Received Date: 16 September 2019 Revised Date:
13 December 2019
Accepted Date: 17 December 2019
Please cite this article as: Kang S-W, Kim K-T, Hwang Y-S, Park W-R, Shin J-K, Song M-H, Is mobilebearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation?, The Journal of Arthroplasty (2020), doi: https://doi.org/10.1016/j.arth.2019.12.036. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Is mobile-bearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation? Suk-Woong Kang, MD, 1 Kyung-Taek Kim, MD, 2 Youn-Soo Hwang, MD, Won-Ro Park, MD, 2 Jong-Ki Shin, MD, 2 Moo-Ho Song MD, PhD. 2 1
2
Department of Orthopedic Surgery, Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Pusan National University School of Medicine, Republic of Korea. 2
Department of Orthopaedic Surgery, Dong-Eui Medical Center
Corresponding author: Moo-Ho Song, MD. PhD. Department of Orthopaedic Surgery, Dong-Eui Medical Center, Yangjeong-ro 62, Busanjin-gu, Busan 47227, South Korea Phone: 82-51-850-8937 Fax: 82-51-850-8943 E-mail: [email protected]
1 2 3
Is mobile-bearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation?
4
-Abstract-
5
Background: Mobile-bearing unicompartmental knee arthroplasty (UKA) is an
6
attractive operation for medial unicompartmental knee arthritis, but unexpected bearing
7
dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose
8
lifestyle involves deeper knee flexion than Westerners. This study investigated whether
9
mobile-bearing medial UKA is appropriate for Asians by analyzing (1) The rate of
10
bearing dislocation, and (2) The results of patients with bearing dislocation.
11 12
Methods: We retrospectively reviewed 531 consecutive mobile-bearing medial UKA in
13
the previous 15 years, including 22 patients with bearing dislocation who had at least 2
14
years of follow-up. The entire patient cohort was divided into two groups: the
15
symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the
16
anatomic bearing group, patients who underwent surgery using the conventional phase
17
III (283 knees) versus the Microplasty® (61 knees) instrumentation systems were
18
compared.
19 20
Results: The overall incidence of bearing dislocation was 4.1% (22/531). Patients
21
with the symmetrical bearing displayed a relatively high dislocation rate of 9.6%
22
(18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic
23
bearing (p < 0.001). In the anatomic bearing group, the dislocation rate with the
24
conventional phase III system was 1.4% (4/283). There were no bearing dislocations in
25
the Microplasty® system group (0%, 0/61) after at least 2 years of follow-up. 1
26 27
Conclusion: Although mobile-bearing medial UKA was reported to have a high
28
incidence of bearing dislocation in Asians, this frequency of dislocation is drastically
29
decreased by bearing design and implantation system improvements. We consider
30
mobile-bearing medial UKA appropriate for Asians.
31 32
Keywords: unicompartmental knee arthroplasty; mobile bearing; Oxford UKA;
33
complications; bearing dislocation.
34 35
Introduction
36 37
Recently, the frequency of unicompartmental knee arthroplasty (UKA) for patients
38
with medial unicompartmental osteoarthritis of the knee has increased due to its
39
advantages of shorter recovery time and lower mortality and morbidity compared to
40
total knee arthroplasty (TKA) [1]. UKA also leads to better postoperative range of
41
motion and better functional abilities than TKA. Thus, UKA is more suitable than TKA
42
for Asians than Westerners as the life-style of Asian requires deeper knee flexion [2].
43
There are two types of UKA: the fixed-bearing and mobile-bearing types. Each type
44
has its advantages and disadvantages [3]. Fully congruent mobile-bearing UKA (also
45
known as Oxford UKA) appears to be an attractive alternative to fixed-bearing UKA in
46
young and active patients as polyethylene wear remains the main failure mechanism of
47
fixed-bearing UKA [4,5,6]. However, unexpected bearing dislocation has been the most
48
common cause of failure after Oxford UKA requiring reoperation. This remains a
49
dilemma for knee surgeons who use mobile-bearing UKA. The risk of bearing 2
50
dislocation is three times higher in Asian patients than in Western patients [7]. Thus, it
51
has been suggested that mobile-bearing UKA may not be an appropriate option for the
52
Asian population, whose cultures involve deep flexion of the knee.
53
However, to the best of our knowledge, there is no report of the incidence of bearing
54
dislocation and long-term results after bearing dislocation in a large series of Asian
55
patients who underwent mobile-bearing UKA. Thus, the purpose of this study was to
56
assess the applicability of mobile-bearing UKA to Asians by retrospectively analyzing
57
(1) The rate of bearing dislocation in different phases of the Oxford knee system, and (2)
58
The long-term results of 22 patients with bearing dislocation among 531 patients who
59
underwent Oxford knee system in the last 15 years.
60
The hypothesis of this study is that mobile-bearing UKA could be appropriate for
61
Asians owing to the improvement of the bearing design and the development of a new
62
implantation system, which lowers the risk of bearing dislocation.
63 64
Materials and Methods
65 66
We obtained institutional review board approval for this retrospective data analysis.
67
Informed consent was not required due to the retrospective nature of the study. Between
68
November 2003 and April 2016, 22 patients with bearing dislocation among 531
69
patients who underwent Oxford medial UKA (Biomet, Warsaw, IN, USA) for treatment
70
of knee osteoarthritis were included in this study. A single surgeon (Song MH)
71
performed all operations using a minimally invasive approach. The demographic
72
characteristics of the patients are shown in Table 1.
73
Clinical results were evaluated using the range of motion (ROM), American Knee 3
74
Society Score (AKSS), and the Western Ontario McMaster University Osteoarthritis
75
Index (WOMAC), both preoperatively and at the last follow-up. Patients were divided
76
into two groups: the old symmetrical bearing group (November 2003 - July 2006, 187
77
knees) and the new anatomic bearing group (August 2006 – April 2016, 344 knees). In
78
the new anatomic bearing group, patients who underwent surgery using the
79
conventional phase III instrumentation system (August 2006 - December 2012, 283
80
knees) and the new Microplasty® instrumentation system (January 2013 – April 2016,
81
61 knees) were compared.
82
All statistical analyses were performed using SPSS version 21.0 (IBM Co., Armonk,
83
NY, USA). Differences between the mean pre-operative and post-operative clinical
84
scores were compared using the paired t-tests. Categorical variables were analyzed
85
using the Chi-square test. Using conversion to TKA for any cause as an end-point, a
86
life-table was constructed and survival rates were determined using Kaplan–Meier
87
survival analysis. All analyses were performed using 95% confidence intervals (CI).
88
The level of statistical significance was defined as p < 0.05.
89 90
Results
91 92
Follow-up for the 531 UKA patients lasted for at least 2 years (up to 15 years). A
93
total of 22 bearing dislocations occurred with an overall dislocation rate of 4.1%
94
(22/531). Patients with the old symmetrical bearing displayed a relatively high
95
dislocation rate of 9.6% (18/187). However, this rate was decreased sharply to 1.1%
96
(4/344) after the application of the new anatomic bearing (p < 0.001) (Table 2). In the
97
anatomic bearing group (344 knees), the dislocation rate using the conventional phase 4
98
III instrumentation system (August 2006 - December 2012, 283 knees) was 1.4%
99
(4/283). However, there was no bearing dislocation after using the Microplasty®
100
instrumentation system (January 2013 - April 2016, 61 knees) in at least 2 years of
101
follow-up (p = 0.402) (Table 3).
102
Bearing dislocations occurred in the following order of operation: 6th, 20th, 46th, 54th,
103
56th, 60th, 62nd, 73rd, 96th, 98th, 113th, 129th, 131st, 134th, 138th, 160th, 165th, 169th, 188th,
104
209th, 225th, and 283rd. There were 10 dislocations in the first 100 operations, 9
105
dislocations in the next 100 operations, and 3 dislocations subsequently. After the 283rd
106
operation, in which the last bearing dislocation occurred, an additional 248 operations
107
were performed without dislocations. The 22 bearing dislocation types were 10 anterior,
108
11 posterior, and 1 lateral subluxation (Fig. 1). Of these 22 patients, 19 (86%) patients
109
were treated by the insertion of a thicker bearing, while 3 (14%) patients were treated
110
by a closed manual reduction (Fig. 2, Fig. 3). The details of the patients with bearing
111
dislocation are summarized in Table 4. Among the 22 patients, a second dislocation
112
occurred in 7 patients (32%, 7/22) and a third dislocation occurred in 2 patients (9%,
113
2/22). One patient underwent conversion to TKA in another hospital after the second
114
dislocation, while 2 patients underwent conversion to TKA in our hospital after a third
115
dislocation.
116
The mean follow-up period for the 22 patients after the index operation was 11.3
117
years (6.2 to 14.3). The mean time until the first dislocation after UKA was 3.3 years
118
(0.1 to 9.4). The mean follow-up period from the first dislocation to the last follow-up
119
was 8.1 years (4.3 to 11.9). At the final follow-up, 2 patients had developed lateral
120
osteoarthritis. One patient (Kellgren-Lawrence grade IV, tibiofemoral angle = valgus 4°)
121
required conversion to TKA after 9.5 years. Another asymptomatic patient (Kellgren5
122
Lawrence grade III, tibiofemoral angle = valgus 2°) had been under observation with a
123
follow-up duration of 10.2 years. The mean tibiofemoral angle measured on
124
weight-bearing radiographs in 22 patients with bearing dislocation was 2.75° of varus
125
(varus 8° to valgus 2°) preoperatively and 1.94° of valgus ( varus 1° to valgus 6°) after
126
the index surgery. The mean increase in the thickness of the exchanged bearing was 2.9
127
mm (2 to 4). The mean tibiofemoral angle was 4.88° of valgus (valgus 1° to valgus 9°)
128
after the bearing exchange. The mean preoperative AKSS knee score and function
129
scores were 43.2 (28 to 61) and 47.9 (25 to 60) respectively. These scores were
130
significantly improved to 96.8 (88 to 100) and 91.3 (80 to 100) respectively at the last
131
follow-up (p < 0.001). The mean preoperative WOMAC score was 57.5 (44 to 78). This
132
was also significantly decreased to 8.4 (0 to 27) at the last follow-up (p < 0.001). The
133
mean preoperative ROM was 137.4° (120° to 150°). It was changed to 139.2° (125° to
134
150°) at the last follow-up without any significant difference (p = 0.247).
135
There was no statistically significant difference in the frequency of bearing dislocation
136
according to gender [4% (2/49) in males vs. 4.2% (20/482) in females, p = 0.325] or
137
age [3.5% (5/141) in those younger than 60 years of age vs. 4.4% (17/390) in those
138
older than 60 years, p = 0.678] (Table 5).
139
Three patients died during the study period, due to lung cancer (one patient),
140
myocardial infarction (one patient), and traffic accident (one patient). Except for the 4
141
patients who underwent TKA conversion, 18 patients (82%, 18/22) had a well-
142
functioning prosthesis in situ until their final follow-ups. When conversion to TKA after
143
a bearing dislocation was regarded as the end point, the 5-year survival rate was 85.9%
144
(95% CI: 83 to 100) using the Kaplan-Meier method (Fig. 4).
145
6
146
Discussion
147 148
To the best of our knowledge, this is the first report of the incidence of bearing
149
dislocation in the different phases of the Oxford knee system and long-term follow-up
150
results of patients with bearing dislocations in a large series of Asian patients who
151
underwent mobile-bearing medial UKA.
152
The most important finding of this report is that the incidence of bearing dislocation
153
drastically decreased owing to the improvement in the bearing design and a new
154
implantation system. The shape of the old symmetrical bearing might be an important
155
factor for the high bearing dislocation rate in the early practice of this study. Since the
156
anterior rim (5 mm) of the bearing is higher than its posterior rim (3 mm) from the
157
deepest part of the bearing, posterior dislocation requires more distraction of the joint
158
than anterior dislocation. However, if the bearing is rotated 90°, the entrapment is
159
decreased to 2 mm, and this position makes it easy for backward or forward dislocation
160
of the bearing. The length of the lateral wall in the new anatomic bearing is extended,
161
which significantly restricts bearing rotation and spin out; thus, the bearing dislocation
162
rate was significantly decreased. In addition to changes in the bearing design,
163
mechanical improvements of the implantation system also reduced the risk of bearing
164
dislocation. The new Microplasty® instrumentation system enables closer positioning
165
of femoral and tibial components, which can also decrease the incidence of dislocation
166
by restricting bearing spin [8]. The most common cause of dislocation other than
167
spinning is impingement of bone against the bearing. The Microplasty® system with
168
the anti-impingement guide is much better than the conventional phase III system in
169
preventing impingement [9]. Furthermore, as the Microplasty® system enables more 7
170
flexion of the femoral component, any bone at the back of the knee that could impinge
171
knee flexion is removed to facilitate deep flexion. The last group of patients (61 patients)
172
for whom we used the anatomical bearing and the Microplasty® system had a good
173
postoperative outcome with no case of dislocation (mean follow-up, 4.5 years).
174
Although the sample size was not sufficient to generate a statistically significant result
175
compared to the conventional phase III system (Table 3), we can infer that close
176
placement of femoral and tibial components could result in decreased risk of bearing
177
dislocation by reducing the space available for bearing rotation, which is consistent
178
with the findings of other studies [8,10].
179
The second important finding is that the cause of the high bearing dislocation rate was
180
not only due to surgical inexperience but also due to the implant. We consider this
181
because the incidence of dislocation was the same in our first and second one hundred
182
patients, in which there was no change in the type of implant, except for the last few
183
patients. Among the 22 patients with dislocations, 19 were in the first 200 patients.
184
However, the incidence of dislocation decreased sharply after the application of the
185
anatomic bearing and the new instrumentation system. Therefore, with the current
186
system, the incidence of bearing dislocation is low enough for use in Asian patients who
187
are known to have a high rate of bearing dislocation.
188
The third important finding is that a simple bearing exchange for patients with
189
bearing dislocation could have favorable outcomes for a considerable period of time.
190
Unless there were significant problems such as component malposition or imbalance of
191
the flexion-extension gap, immediate TKA conversion was not required. Despite the
192
reinterventions, the 22 patients with bearing dislocations displayed a relatively good
193
Kaplan-Meyer 5-year survival rate of 85.9%, when we considered TKA conversion as 8
194
the end point.
195
Bearing dislocation rates in Asian patients after Oxford medial UKA have been
196
reported to be 2.9% (Kim et al.), 3% (Lim et al.), or 4% (Song et al.) [11,12,13].
197
These rates are relatively high compared to 0.6% (Pandit et al.), 1% (Price and Svärd),
198
or 1.2% (Lisowski et al.) reported in Westerners [14,15,16]. Conversion to TKA might
199
be the solution to bearing dislocation. However, there have been attempts to simply
200
replace the dislocated bearing with a thicker bearing, while retaining all other
201
components. Gleeson et al. reported satisfactory outcomes after bearing exchange with
202
a thicker bearing for 3 patients with bearing dislocation among 47 patients who
203
underwent Oxford UKA [17]. In a study by Lim et al., bearing dislocation was observed
204
in 12 patients (3%) out of 400 patients who underwent Oxford UKA after a mean
205
follow-up of 5.2 years. Of these 12 patients, 10 patients were treated by the insertion of
206
a thicker bearing while conversion to TKA was performed for 2 patients [12]. Kim et al.
207
reported that the most common complication in 42 patients (2.9%) out of 1441 patients
208
who underwent Oxford UKA was bearing dislocation after a mean follow-up of 7.8
209
years. Twenty-four of these patients were treated by simple bearing exchange, while 18
210
underwent conversion to TKA [11].
211
In this study, the overall frequency of bearing dislocation was 4.1%, which is
212
relatively higher than that in Westerners. Of the 22 patients with bearing dislocation, 19
213
patients had an open bearing exchange with a new thicker bearing, while 3 patients
214
underwent closed manual reduction. A second dislocation occurred in 7 patients. Unless
215
there were major problems, patients were treated by bearing exchange again. Three
216
patients underwent conversion to TKA due to recurrent bearing dislocation and one
217
patient underwent conversion to TKA due to lateral osteoarthritis. Despite a relatively 9
218
high rate of dislocation, only 4 patients (18%, 4/22) required conversion to TKA.
219
Eighteen (82%, 18/22) patients had a well-functioning prosthesis in situ until their last
220
follow-up.
221
When a bearing dislocation occurs for the first time, it is difficult to decide whether
222
to simply replace the bearing or to convert to TKA. Conversion to TKA seems to be
223
necessary in cases of malposition of components or severe imbalance of the flexion-
224
extension gap, which is highly susceptible to re-dislocation. However, if correctable
225
impingement, traumatic incident, or chronic medial collateral ligament (MCL) laxity is
226
the cause of the dislocation, it is advisable to treat with a simple bearing exchange
227
[18,19]. Although exchanging the bearing is unlikely to provide permanent relief and
228
dislocation may recur in the future, it can buy time and significantly postpone the need
229
for conversion to TKA. We recommend that a patient who has undergone bearing
230
exchange should avoid deep flexion or sitting on the floor to reduce the likelihood of re-
231
dislocation.
232
It is difficult to determine the exact cause of bearing dislocation, which could be
233
multifactorial. The possible mechanisms of dislocation are imbalance of the flexion-
234
extension gap, malpositioning of components, including an implantation with a wide
235
mediolateral gap between the femoral and tibial components, chronic laxity of the MCL
236
due to damage or delayed elongation, impingement by the remaining osteophytes in the
237
posterior femoral condyle, traumatic accident, and habitual high knee flexion [9,12,13].
238
Activities requiring deep knee flexion such as squatting, kneeling, and sitting cross-
239
legged are important components of daily living in Asian cultures. In the present study,
240
bearing dislocations were also related to high knee flexion, as described in Table 4.
241
To avoid bearing dislocation, it is necessary to create equal flexion and extension gaps 10
242
intraoperatively, prevent MCL damage, locate femoral and tibial components accurately,
243
remove osteophytes that may collide with the bearing, and recommend a change in
244
lifestyle for patients who have previously experienced a bearing dislocation.
245
There are concerns that mobile-bearing UKA is less appropriate for the Asian
246
population because they have a higher risk of bearing dislocation compared to
247
Westerners. However, as shown in this study, the rate of bearing dislocation decreased
248
significantly with the changes in bearing design and the development of a new
249
implantation system. In our study, the dislocation rate after using the anatomic bearing
250
was 1.1%, which is relatively higher than that of the Oxford designer group (0.6%) [14].
251
However, it is similar to the rates reported in Westerners (Price and Svärd, 1%;
252
Lisowski et al., 1.2%) [15,16]. In addition, the dislocation rate in our study decreased to
253
zero after we switched to the Microplasty® instrumentation system. Thus, in support of
254
our hypothesis, we observed that mobile-bearing medial UKA with the anatomic
255
bearing and the Microplasty® instrumentation system could successfully be used for
256
Asian patients suffering from medial unicompartmental knee arthritis.
257
This study had some limitations. First, the effect of a learning curve cannot be
258
ignored when comparing the incidence of bearing dislocation between the two bearing
259
groups and the two instrumentation systems. Second, it is difficult to directly compare
260
the results of the Microplasty® instrumentation system with those of the conventional
261
phase III instrumentation system, because the patients who received the Microplasty®
262
system had a short follow-up duration, with those who received the conventional phase
263
III system had a long follow-up period. However, we believe that the results of the
264
Microplasty® instrumentation system are better than those of the conventional phase III
265
instrumentation system, based on other recent reports [8,10]. 11
266 267
Conclusion
268
Although the use of mobile-bearing medial UKA in Asian patients was previously
269
shown to have a high incidence of bearing dislocation, recent improvements in the
270
bearing design and the new Microplasty® instrumentation system have remarkably
271
reduced the rate of this complication. Therefore, mobile-bearing medial UKA with the
272
current system is an appropriate option for Asian patients with knee osteoarthritis, if the
273
patients are carefully selected and proper surgical techniques are applied.
274 275
References
276 277
1. Koh IJ, Kim MW, Kim JH, Han SY, In Y. Trends in High Tibial Osteotomy and
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Knee Arthroplasty Utilizations and Demographics in Korea From 2009 to 2013. J
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Arthroplasty 2015;30:939.
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2. Kim MS,
Koh IJ, Choi YJ, Lee JY, In Y. Differences in Patient-Reported
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Outcomes Between Unicompartmental and Total Knee Arthroplasties: A Propensity
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Score-Matched Analysis . J Arthroplasty 2017;32: 1453.
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3. Peersman G, Stuyts B, Vandenlangenbergh T, Cartier P, Fennema P. Fixed- versus
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mobile-bearing UKA: a systematic review and meta-analysis. Knee Surg Sports
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Traumatol Arthrosc 2015;23(11):3296.
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4. Kendrick BJ, Simpson DJ, Kaptein BL, et al. Polyethylene wear of mobile-bearing
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unicompartmental knee replacement at 20 years. J Bone Joint Surg [Br] 2011; 93(4):470.
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5. Parratte S, Pauly V, Aubaniac JM, Argenson JN. No long-term difference between
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fixed and mobile medial unicompartmental arthroplasty. Clin Orthop Relat Res 12
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2012;470:61.
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6. Streit MR, Streit J, Walker T, et al. Minimally invasive Oxford medial
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unicompartmental knee arthroplasty in young patients. Knee Surg Sports Traumatol
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Arthrosc 2017;23:1.
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7. Kim SJ, Postigo R, Koo S, Kim JH. Causes of revision following Oxford phase 3
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8. Koh IJ, Kim JH, Jang SW, Kim MS, Kim C, In Y. Are the Oxford(®) medial
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Surg Res 2016;102(2):183.
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9. Goodfellow J, O'Connor J, Pandit H, Dodd C, Murray D. Unicompartmental
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Arthroplasty with the Oxford Knee. Surgical technique : Cemented or cementless
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implantation with Microplasty instrumentation. 2nd ed. Oxford University Press,
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2015: 137.
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10. Tu Y, Xue H, Ma T, et al. Superior femoral component alignment can be achieved
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with Oxford microplasty instrumentation after minimally invasive unicompartmental
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knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2017;25(3):729.
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11. Kim KT, Lee S, Lee JI, Kim JW. Analysis and Treatment of Complications after
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Unicompartmental Knee Arthroplasty. Knee Surg Relat Res 2016;28(1):46.
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12. Lim HC, Bae JH, Song SH, Kim SJ. Oxford phase 3 unicompartmental knee
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replacement in Korean patients. J Bone Joint Surg [Br] 2012;94:1071.
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13. Song MH, Kim BH, Ahn SJ, Yoo SH, Lee MS. Early complications after
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minimally invasive mobile-bearing medial unicompartmental knee arthroplasty. J 13
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14. Pandit H, Jenkins C, Gill HS, et al. Minimally invasive Oxford phase 3
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15. Price AJ, Svärd U. A second decade lifetable survival analysis of the Oxford unicompartmental knee arthroplasty. Clin Orthop Relat Res 2011;469:174.
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16. Lisowski LA, van den Bekerom MP, Pilot P, van Dijk CN, Lisowski AE. Oxford
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14
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Table 1
Demographics of patients.
Characteristics
Value
Case number
22
Gender (female : male)
20 : 2
Mean follow-up (years)
9.6 (range, 6.6-12.5)
Mean age (years)
67.6 (range, 56-78)
Mean height (cm)
157.9 (range, 150-175)
Mean weight (kg)
62.9 (range, 53-78)
Mean body mass index (kg/m2)
Table 2
25.2 (19.9-29.4)
Comparison of dislocation rate between the old symmetrical bearing and the new
anatomic bearing Characteristics
old
new
Number of case
187
344
18 (9.6%)
4 (1.1%)
0.000
dislocation
7
0
0.005
Conversion to TKA
3
0
0.015
st
1 dislocation 2
nd
Table 3
p-value
Comparison of anatomic bearing dislocation rate between the conventional phase III
system and the Microplasty system Characteristics
Conventional
Microplasty
Number of case
283
61
1st dislocation
4 (1.4%)
0
Conversion to TKA
0
0
Table 5 Gender
Age
p-value
0.402
Comparison of dislocation rate according to gender and age Male
Female
p-value
2/49 (4%)
20/482 (4.2%)
0.325
Less than age of 60
More than age of 60
5/141 (3.5%)
17/390 (4.4%)
0.678
Table 4 Case
Details of 22 bearing dislocations Time after
Type and Cause
Treatment
Outcome
Anterior DL, Washing clothes while
Open bearing
Good result at 8y, Expired
squatting
exchanges
due to lung cancer
Anterior DL, Wiping floor with
Closed manual
Good result at 9y, Expired
kneeled knees
reduction
due to myocardial
primary operation 1
2
1m, 1y8m
2y5m
infarction 3
4
5
6
3m, 6y10m
5m, 5y2m
6m
1y4m, 3y6m
Posterior DL, Flexing the knee to
Open bearing
Good result at 10y2m
kneel
exchanges
Anterior DL, Doing chores while
Open bearing
Conversion to TKA at
squatting
exchange
other hospital
Anterior DL, Working in a farm while
Open bearing
Good result at 6y6m, Lost
squatting
exchange
to follow up
Posterior DL, Gardening while
Open bearing
Good result at 5y2m,
squatting
exchange
Expired due to traffic accident
7 (Fig 1)
8
9
10
11
12 (Fig 2)
4y3m
1y4m
6m
2y3m, 4y8m
1y4m
4y, 11y3m
Lateral subluxation, Using a squat
Closed manual
toilet
reduction
Posterior DL, Standing up from a low
Open bearing
chair
exchange
Posterior DL, Getting up from a floor
Open bearing
TKA conversion due to
exchange
lateral OA at 9y6m
Open bearing
Conversion to TKA after
exchange
3rd dislocation at 6y
Posterior DL, Deep flexion while
Open bearing
Good result at 9y6m
dancing
exchange
Anterior DL, Sitting cross-legged
Closed manual
Open bearing exchange
reduction
after 2nd dislocation at
Anterior DL, Using a toilet
Good result at 11y5m
Good result at 11y2m
11y 3m. 13
4y6m
Anterior DL, Slipped on the floor
Open bearing
Good result at 11y
exchange 14
15
3y
5y2m, 7y
Posterior DL, Working while
Open bearing
Good result at 9y1m
squatting
exchange
Anterior DL, Putting on socks
Open bearing
Conversion to TKA after
exchange
3rd dislocation
16 (Fig 3)
17
18
19
20
3y3m
5y2m
4y9m
2y10m
9y3m
Anterior DL, Crossing a leg while
Open bearing
Good result at 10y6m
sitting on a sofa
exchange
Posterior DL, Stumbling down on a
Open bearing
Asymptomatic lateral OA,
bus
exchange
Good result at 10y4m
Posterior DL, Sitting cross-legged on
Open bearing
Good result at 10y2m
the floor
exchange
Posterior DL, Sudden change of
Open bearing
direction while walking
exchange
Anterior DL, Falling down from stairs
Open bearing
Good result at 8y10m
Good result at 12y6m
exchange 21
9y5m
Posterior DL, Lifting a heavy object
Open bearing
Good result at 12y2m
exchange 22
3y4m
Posterior DL, Using a toilet
Open bearing
Good result at 10y11m
exchange
DL, dislocation ; Fig, figure ; OA, osteoarthritis ; TKA, total knee arthroplasty ; y, years ; m, months
S0883-5403(19)31185-4
DOI:
https://doi.org/10.1016/j.arth.2019.12.036
Reference:
YARTH 57699
To appear in:
The Journal of Arthroplasty
Received Date: 16 September 2019 Revised Date:
13 December 2019
Accepted Date: 17 December 2019
Please cite this article as: Kang S-W, Kim K-T, Hwang Y-S, Park W-R, Shin J-K, Song M-H, Is mobilebearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation?, The Journal of Arthroplasty (2020), doi: https://doi.org/10.1016/j.arth.2019.12.036. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Inc.
Is mobile-bearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation? Suk-Woong Kang, MD, 1 Kyung-Taek Kim, MD, 2 Youn-Soo Hwang, MD, Won-Ro Park, MD, 2 Jong-Ki Shin, MD, 2 Moo-Ho Song MD, PhD. 2 1
2
Department of Orthopedic Surgery, Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Pusan National University School of Medicine, Republic of Korea. 2
Department of Orthopaedic Surgery, Dong-Eui Medical Center
Corresponding author: Moo-Ho Song, MD. PhD. Department of Orthopaedic Surgery, Dong-Eui Medical Center, Yangjeong-ro 62, Busanjin-gu, Busan 47227, South Korea Phone: 82-51-850-8937 Fax: 82-51-850-8943 E-mail: [email protected]
1 2 3
Is mobile-bearing medial unicompartmental knee arthroplasty appropriate for Asian patients with the risk of bearing dislocation?
4
-Abstract-
5
Background: Mobile-bearing unicompartmental knee arthroplasty (UKA) is an
6
attractive operation for medial unicompartmental knee arthritis, but unexpected bearing
7
dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose
8
lifestyle involves deeper knee flexion than Westerners. This study investigated whether
9
mobile-bearing medial UKA is appropriate for Asians by analyzing (1) The rate of
10
bearing dislocation, and (2) The results of patients with bearing dislocation.
11 12
Methods: We retrospectively reviewed 531 consecutive mobile-bearing medial UKA in
13
the previous 15 years, including 22 patients with bearing dislocation who had at least 2
14
years of follow-up. The entire patient cohort was divided into two groups: the
15
symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the
16
anatomic bearing group, patients who underwent surgery using the conventional phase
17
III (283 knees) versus the Microplasty® (61 knees) instrumentation systems were
18
compared.
19 20
Results: The overall incidence of bearing dislocation was 4.1% (22/531). Patients
21
with the symmetrical bearing displayed a relatively high dislocation rate of 9.6%
22
(18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic
23
bearing (p < 0.001). In the anatomic bearing group, the dislocation rate with the
24
conventional phase III system was 1.4% (4/283). There were no bearing dislocations in
25
the Microplasty® system group (0%, 0/61) after at least 2 years of follow-up. 1
26 27
Conclusion: Although mobile-bearing medial UKA was reported to have a high
28
incidence of bearing dislocation in Asians, this frequency of dislocation is drastically
29
decreased by bearing design and implantation system improvements. We consider
30
mobile-bearing medial UKA appropriate for Asians.
31 32
Keywords: unicompartmental knee arthroplasty; mobile bearing; Oxford UKA;
33
complications; bearing dislocation.
34 35
Introduction
36 37
Recently, the frequency of unicompartmental knee arthroplasty (UKA) for patients
38
with medial unicompartmental osteoarthritis of the knee has increased due to its
39
advantages of shorter recovery time and lower mortality and morbidity compared to
40
total knee arthroplasty (TKA) [1]. UKA also leads to better postoperative range of
41
motion and better functional abilities than TKA. Thus, UKA is more suitable than TKA
42
for Asians than Westerners as the life-style of Asian requires deeper knee flexion [2].
43
There are two types of UKA: the fixed-bearing and mobile-bearing types. Each type
44
has its advantages and disadvantages [3]. Fully congruent mobile-bearing UKA (also
45
known as Oxford UKA) appears to be an attractive alternative to fixed-bearing UKA in
46
young and active patients as polyethylene wear remains the main failure mechanism of
47
fixed-bearing UKA [4,5,6]. However, unexpected bearing dislocation has been the most
48
common cause of failure after Oxford UKA requiring reoperation. This remains a
49
dilemma for knee surgeons who use mobile-bearing UKA. The risk of bearing 2
50
dislocation is three times higher in Asian patients than in Western patients [7]. Thus, it
51
has been suggested that mobile-bearing UKA may not be an appropriate option for the
52
Asian population, whose cultures involve deep flexion of the knee.
53
However, to the best of our knowledge, there is no report of the incidence of bearing
54
dislocation and long-term results after bearing dislocation in a large series of Asian
55
patients who underwent mobile-bearing UKA. Thus, the purpose of this study was to
56
assess the applicability of mobile-bearing UKA to Asians by retrospectively analyzing
57
(1) The rate of bearing dislocation in different phases of the Oxford knee system, and (2)
58
The long-term results of 22 patients with bearing dislocation among 531 patients who
59
underwent Oxford knee system in the last 15 years.
60
The hypothesis of this study is that mobile-bearing UKA could be appropriate for
61
Asians owing to the improvement of the bearing design and the development of a new
62
implantation system, which lowers the risk of bearing dislocation.
63 64
Materials and Methods
65 66
We obtained institutional review board approval for this retrospective data analysis.
67
Informed consent was not required due to the retrospective nature of the study. Between
68
November 2003 and April 2016, 22 patients with bearing dislocation among 531
69
patients who underwent Oxford medial UKA (Biomet, Warsaw, IN, USA) for treatment
70
of knee osteoarthritis were included in this study. A single surgeon (Song MH)
71
performed all operations using a minimally invasive approach. The demographic
72
characteristics of the patients are shown in Table 1.
73
Clinical results were evaluated using the range of motion (ROM), American Knee 3
74
Society Score (AKSS), and the Western Ontario McMaster University Osteoarthritis
75
Index (WOMAC), both preoperatively and at the last follow-up. Patients were divided
76
into two groups: the old symmetrical bearing group (November 2003 - July 2006, 187
77
knees) and the new anatomic bearing group (August 2006 – April 2016, 344 knees). In
78
the new anatomic bearing group, patients who underwent surgery using the
79
conventional phase III instrumentation system (August 2006 - December 2012, 283
80
knees) and the new Microplasty® instrumentation system (January 2013 – April 2016,
81
61 knees) were compared.
82
All statistical analyses were performed using SPSS version 21.0 (IBM Co., Armonk,
83
NY, USA). Differences between the mean pre-operative and post-operative clinical
84
scores were compared using the paired t-tests. Categorical variables were analyzed
85
using the Chi-square test. Using conversion to TKA for any cause as an end-point, a
86
life-table was constructed and survival rates were determined using Kaplan–Meier
87
survival analysis. All analyses were performed using 95% confidence intervals (CI).
88
The level of statistical significance was defined as p < 0.05.
89 90
Results
91 92
Follow-up for the 531 UKA patients lasted for at least 2 years (up to 15 years). A
93
total of 22 bearing dislocations occurred with an overall dislocation rate of 4.1%
94
(22/531). Patients with the old symmetrical bearing displayed a relatively high
95
dislocation rate of 9.6% (18/187). However, this rate was decreased sharply to 1.1%
96
(4/344) after the application of the new anatomic bearing (p < 0.001) (Table 2). In the
97
anatomic bearing group (344 knees), the dislocation rate using the conventional phase 4
98
III instrumentation system (August 2006 - December 2012, 283 knees) was 1.4%
99
(4/283). However, there was no bearing dislocation after using the Microplasty®
100
instrumentation system (January 2013 - April 2016, 61 knees) in at least 2 years of
101
follow-up (p = 0.402) (Table 3).
102
Bearing dislocations occurred in the following order of operation: 6th, 20th, 46th, 54th,
103
56th, 60th, 62nd, 73rd, 96th, 98th, 113th, 129th, 131st, 134th, 138th, 160th, 165th, 169th, 188th,
104
209th, 225th, and 283rd. There were 10 dislocations in the first 100 operations, 9
105
dislocations in the next 100 operations, and 3 dislocations subsequently. After the 283rd
106
operation, in which the last bearing dislocation occurred, an additional 248 operations
107
were performed without dislocations. The 22 bearing dislocation types were 10 anterior,
108
11 posterior, and 1 lateral subluxation (Fig. 1). Of these 22 patients, 19 (86%) patients
109
were treated by the insertion of a thicker bearing, while 3 (14%) patients were treated
110
by a closed manual reduction (Fig. 2, Fig. 3). The details of the patients with bearing
111
dislocation are summarized in Table 4. Among the 22 patients, a second dislocation
112
occurred in 7 patients (32%, 7/22) and a third dislocation occurred in 2 patients (9%,
113
2/22). One patient underwent conversion to TKA in another hospital after the second
114
dislocation, while 2 patients underwent conversion to TKA in our hospital after a third
115
dislocation.
116
The mean follow-up period for the 22 patients after the index operation was 11.3
117
years (6.2 to 14.3). The mean time until the first dislocation after UKA was 3.3 years
118
(0.1 to 9.4). The mean follow-up period from the first dislocation to the last follow-up
119
was 8.1 years (4.3 to 11.9). At the final follow-up, 2 patients had developed lateral
120
osteoarthritis. One patient (Kellgren-Lawrence grade IV, tibiofemoral angle = valgus 4°)
121
required conversion to TKA after 9.5 years. Another asymptomatic patient (Kellgren5
122
Lawrence grade III, tibiofemoral angle = valgus 2°) had been under observation with a
123
follow-up duration of 10.2 years. The mean tibiofemoral angle measured on
124
weight-bearing radiographs in 22 patients with bearing dislocation was 2.75° of varus
125
(varus 8° to valgus 2°) preoperatively and 1.94° of valgus ( varus 1° to valgus 6°) after
126
the index surgery. The mean increase in the thickness of the exchanged bearing was 2.9
127
mm (2 to 4). The mean tibiofemoral angle was 4.88° of valgus (valgus 1° to valgus 9°)
128
after the bearing exchange. The mean preoperative AKSS knee score and function
129
scores were 43.2 (28 to 61) and 47.9 (25 to 60) respectively. These scores were
130
significantly improved to 96.8 (88 to 100) and 91.3 (80 to 100) respectively at the last
131
follow-up (p < 0.001). The mean preoperative WOMAC score was 57.5 (44 to 78). This
132
was also significantly decreased to 8.4 (0 to 27) at the last follow-up (p < 0.001). The
133
mean preoperative ROM was 137.4° (120° to 150°). It was changed to 139.2° (125° to
134
150°) at the last follow-up without any significant difference (p = 0.247).
135
There was no statistically significant difference in the frequency of bearing dislocation
136
according to gender [4% (2/49) in males vs. 4.2% (20/482) in females, p = 0.325] or
137
age [3.5% (5/141) in those younger than 60 years of age vs. 4.4% (17/390) in those
138
older than 60 years, p = 0.678] (Table 5).
139
Three patients died during the study period, due to lung cancer (one patient),
140
myocardial infarction (one patient), and traffic accident (one patient). Except for the 4
141
patients who underwent TKA conversion, 18 patients (82%, 18/22) had a well-
142
functioning prosthesis in situ until their final follow-ups. When conversion to TKA after
143
a bearing dislocation was regarded as the end point, the 5-year survival rate was 85.9%
144
(95% CI: 83 to 100) using the Kaplan-Meier method (Fig. 4).
145
6
146
Discussion
147 148
To the best of our knowledge, this is the first report of the incidence of bearing
149
dislocation in the different phases of the Oxford knee system and long-term follow-up
150
results of patients with bearing dislocations in a large series of Asian patients who
151
underwent mobile-bearing medial UKA.
152
The most important finding of this report is that the incidence of bearing dislocation
153
drastically decreased owing to the improvement in the bearing design and a new
154
implantation system. The shape of the old symmetrical bearing might be an important
155
factor for the high bearing dislocation rate in the early practice of this study. Since the
156
anterior rim (5 mm) of the bearing is higher than its posterior rim (3 mm) from the
157
deepest part of the bearing, posterior dislocation requires more distraction of the joint
158
than anterior dislocation. However, if the bearing is rotated 90°, the entrapment is
159
decreased to 2 mm, and this position makes it easy for backward or forward dislocation
160
of the bearing. The length of the lateral wall in the new anatomic bearing is extended,
161
which significantly restricts bearing rotation and spin out; thus, the bearing dislocation
162
rate was significantly decreased. In addition to changes in the bearing design,
163
mechanical improvements of the implantation system also reduced the risk of bearing
164
dislocation. The new Microplasty® instrumentation system enables closer positioning
165
of femoral and tibial components, which can also decrease the incidence of dislocation
166
by restricting bearing spin [8]. The most common cause of dislocation other than
167
spinning is impingement of bone against the bearing. The Microplasty® system with
168
the anti-impingement guide is much better than the conventional phase III system in
169
preventing impingement [9]. Furthermore, as the Microplasty® system enables more 7
170
flexion of the femoral component, any bone at the back of the knee that could impinge
171
knee flexion is removed to facilitate deep flexion. The last group of patients (61 patients)
172
for whom we used the anatomical bearing and the Microplasty® system had a good
173
postoperative outcome with no case of dislocation (mean follow-up, 4.5 years).
174
Although the sample size was not sufficient to generate a statistically significant result
175
compared to the conventional phase III system (Table 3), we can infer that close
176
placement of femoral and tibial components could result in decreased risk of bearing
177
dislocation by reducing the space available for bearing rotation, which is consistent
178
with the findings of other studies [8,10].
179
The second important finding is that the cause of the high bearing dislocation rate was
180
not only due to surgical inexperience but also due to the implant. We consider this
181
because the incidence of dislocation was the same in our first and second one hundred
182
patients, in which there was no change in the type of implant, except for the last few
183
patients. Among the 22 patients with dislocations, 19 were in the first 200 patients.
184
However, the incidence of dislocation decreased sharply after the application of the
185
anatomic bearing and the new instrumentation system. Therefore, with the current
186
system, the incidence of bearing dislocation is low enough for use in Asian patients who
187
are known to have a high rate of bearing dislocation.
188
The third important finding is that a simple bearing exchange for patients with
189
bearing dislocation could have favorable outcomes for a considerable period of time.
190
Unless there were significant problems such as component malposition or imbalance of
191
the flexion-extension gap, immediate TKA conversion was not required. Despite the
192
reinterventions, the 22 patients with bearing dislocations displayed a relatively good
193
Kaplan-Meyer 5-year survival rate of 85.9%, when we considered TKA conversion as 8
194
the end point.
195
Bearing dislocation rates in Asian patients after Oxford medial UKA have been
196
reported to be 2.9% (Kim et al.), 3% (Lim et al.), or 4% (Song et al.) [11,12,13].
197
These rates are relatively high compared to 0.6% (Pandit et al.), 1% (Price and Svärd),
198
or 1.2% (Lisowski et al.) reported in Westerners [14,15,16]. Conversion to TKA might
199
be the solution to bearing dislocation. However, there have been attempts to simply
200
replace the dislocated bearing with a thicker bearing, while retaining all other
201
components. Gleeson et al. reported satisfactory outcomes after bearing exchange with
202
a thicker bearing for 3 patients with bearing dislocation among 47 patients who
203
underwent Oxford UKA [17]. In a study by Lim et al., bearing dislocation was observed
204
in 12 patients (3%) out of 400 patients who underwent Oxford UKA after a mean
205
follow-up of 5.2 years. Of these 12 patients, 10 patients were treated by the insertion of
206
a thicker bearing while conversion to TKA was performed for 2 patients [12]. Kim et al.
207
reported that the most common complication in 42 patients (2.9%) out of 1441 patients
208
who underwent Oxford UKA was bearing dislocation after a mean follow-up of 7.8
209
years. Twenty-four of these patients were treated by simple bearing exchange, while 18
210
underwent conversion to TKA [11].
211
In this study, the overall frequency of bearing dislocation was 4.1%, which is
212
relatively higher than that in Westerners. Of the 22 patients with bearing dislocation, 19
213
patients had an open bearing exchange with a new thicker bearing, while 3 patients
214
underwent closed manual reduction. A second dislocation occurred in 7 patients. Unless
215
there were major problems, patients were treated by bearing exchange again. Three
216
patients underwent conversion to TKA due to recurrent bearing dislocation and one
217
patient underwent conversion to TKA due to lateral osteoarthritis. Despite a relatively 9
218
high rate of dislocation, only 4 patients (18%, 4/22) required conversion to TKA.
219
Eighteen (82%, 18/22) patients had a well-functioning prosthesis in situ until their last
220
follow-up.
221
When a bearing dislocation occurs for the first time, it is difficult to decide whether
222
to simply replace the bearing or to convert to TKA. Conversion to TKA seems to be
223
necessary in cases of malposition of components or severe imbalance of the flexion-
224
extension gap, which is highly susceptible to re-dislocation. However, if correctable
225
impingement, traumatic incident, or chronic medial collateral ligament (MCL) laxity is
226
the cause of the dislocation, it is advisable to treat with a simple bearing exchange
227
[18,19]. Although exchanging the bearing is unlikely to provide permanent relief and
228
dislocation may recur in the future, it can buy time and significantly postpone the need
229
for conversion to TKA. We recommend that a patient who has undergone bearing
230
exchange should avoid deep flexion or sitting on the floor to reduce the likelihood of re-
231
dislocation.
232
It is difficult to determine the exact cause of bearing dislocation, which could be
233
multifactorial. The possible mechanisms of dislocation are imbalance of the flexion-
234
extension gap, malpositioning of components, including an implantation with a wide
235
mediolateral gap between the femoral and tibial components, chronic laxity of the MCL
236
due to damage or delayed elongation, impingement by the remaining osteophytes in the
237
posterior femoral condyle, traumatic accident, and habitual high knee flexion [9,12,13].
238
Activities requiring deep knee flexion such as squatting, kneeling, and sitting cross-
239
legged are important components of daily living in Asian cultures. In the present study,
240
bearing dislocations were also related to high knee flexion, as described in Table 4.
241
To avoid bearing dislocation, it is necessary to create equal flexion and extension gaps 10
242
intraoperatively, prevent MCL damage, locate femoral and tibial components accurately,
243
remove osteophytes that may collide with the bearing, and recommend a change in
244
lifestyle for patients who have previously experienced a bearing dislocation.
245
There are concerns that mobile-bearing UKA is less appropriate for the Asian
246
population because they have a higher risk of bearing dislocation compared to
247
Westerners. However, as shown in this study, the rate of bearing dislocation decreased
248
significantly with the changes in bearing design and the development of a new
249
implantation system. In our study, the dislocation rate after using the anatomic bearing
250
was 1.1%, which is relatively higher than that of the Oxford designer group (0.6%) [14].
251
However, it is similar to the rates reported in Westerners (Price and Svärd, 1%;
252
Lisowski et al., 1.2%) [15,16]. In addition, the dislocation rate in our study decreased to
253
zero after we switched to the Microplasty® instrumentation system. Thus, in support of
254
our hypothesis, we observed that mobile-bearing medial UKA with the anatomic
255
bearing and the Microplasty® instrumentation system could successfully be used for
256
Asian patients suffering from medial unicompartmental knee arthritis.
257
This study had some limitations. First, the effect of a learning curve cannot be
258
ignored when comparing the incidence of bearing dislocation between the two bearing
259
groups and the two instrumentation systems. Second, it is difficult to directly compare
260
the results of the Microplasty® instrumentation system with those of the conventional
261
phase III instrumentation system, because the patients who received the Microplasty®
262
system had a short follow-up duration, with those who received the conventional phase
263
III system had a long follow-up period. However, we believe that the results of the
264
Microplasty® instrumentation system are better than those of the conventional phase III
265
instrumentation system, based on other recent reports [8,10]. 11
266 267
Conclusion
268
Although the use of mobile-bearing medial UKA in Asian patients was previously
269
shown to have a high incidence of bearing dislocation, recent improvements in the
270
bearing design and the new Microplasty® instrumentation system have remarkably
271
reduced the rate of this complication. Therefore, mobile-bearing medial UKA with the
272
current system is an appropriate option for Asian patients with knee osteoarthritis, if the
273
patients are carefully selected and proper surgical techniques are applied.
274 275
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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Table 1
Demographics of patients.
Characteristics
Value
Case number
22
Gender (female : male)
20 : 2
Mean follow-up (years)
9.6 (range, 6.6-12.5)
Mean age (years)
67.6 (range, 56-78)
Mean height (cm)
157.9 (range, 150-175)
Mean weight (kg)
62.9 (range, 53-78)
Mean body mass index (kg/m2)
Table 2
25.2 (19.9-29.4)
Comparison of dislocation rate between the old symmetrical bearing and the new
anatomic bearing Characteristics
old
new
Number of case
187
344
18 (9.6%)
4 (1.1%)
0.000
dislocation
7
0
0.005
Conversion to TKA
3
0
0.015
st
1 dislocation 2
nd
Table 3
p-value
Comparison of anatomic bearing dislocation rate between the conventional phase III
system and the Microplasty system Characteristics
Conventional
Microplasty
Number of case
283
61
1st dislocation
4 (1.4%)
0
Conversion to TKA
0
0
Table 5 Gender
Age
p-value
0.402
Comparison of dislocation rate according to gender and age Male
Female
p-value
2/49 (4%)
20/482 (4.2%)
0.325
Less than age of 60
More than age of 60
5/141 (3.5%)
17/390 (4.4%)
0.678
Table 4 Case
Details of 22 bearing dislocations Time after
Type and Cause
Treatment
Outcome
Anterior DL, Washing clothes while
Open bearing
Good result at 8y, Expired
squatting
exchanges
due to lung cancer
Anterior DL, Wiping floor with
Closed manual
Good result at 9y, Expired
kneeled knees
reduction
due to myocardial
primary operation 1
2
1m, 1y8m
2y5m
infarction 3
4
5
6
3m, 6y10m
5m, 5y2m
6m
1y4m, 3y6m
Posterior DL, Flexing the knee to
Open bearing
Good result at 10y2m
kneel
exchanges
Anterior DL, Doing chores while
Open bearing
Conversion to TKA at
squatting
exchange
other hospital
Anterior DL, Working in a farm while
Open bearing
Good result at 6y6m, Lost
squatting
exchange
to follow up
Posterior DL, Gardening while
Open bearing
Good result at 5y2m,
squatting
exchange
Expired due to traffic accident
7 (Fig 1)
8
9
10
11
12 (Fig 2)
4y3m
1y4m
6m
2y3m, 4y8m
1y4m
4y, 11y3m
Lateral subluxation, Using a squat
Closed manual
toilet
reduction
Posterior DL, Standing up from a low
Open bearing
chair
exchange
Posterior DL, Getting up from a floor
Open bearing
TKA conversion due to
exchange
lateral OA at 9y6m
Open bearing
Conversion to TKA after
exchange
3rd dislocation at 6y
Posterior DL, Deep flexion while
Open bearing
Good result at 9y6m
dancing
exchange
Anterior DL, Sitting cross-legged
Closed manual
Open bearing exchange
reduction
after 2nd dislocation at
Anterior DL, Using a toilet
Good result at 11y5m
Good result at 11y2m
11y 3m. 13
4y6m
Anterior DL, Slipped on the floor
Open bearing
Good result at 11y
exchange 14
15
3y
5y2m, 7y
Posterior DL, Working while
Open bearing
Good result at 9y1m
squatting
exchange
Anterior DL, Putting on socks
Open bearing
Conversion to TKA after
exchange
3rd dislocation
16 (Fig 3)
17
18
19
20
3y3m
5y2m
4y9m
2y10m
9y3m
Anterior DL, Crossing a leg while
Open bearing
Good result at 10y6m
sitting on a sofa
exchange
Posterior DL, Stumbling down on a
Open bearing
Asymptomatic lateral OA,
bus
exchange
Good result at 10y4m
Posterior DL, Sitting cross-legged on
Open bearing
Good result at 10y2m
the floor
exchange
Posterior DL, Sudden change of
Open bearing
direction while walking
exchange
Anterior DL, Falling down from stairs
Open bearing
Good result at 8y10m
Good result at 12y6m
exchange 21
9y5m
Posterior DL, Lifting a heavy object
Open bearing
Good result at 12y2m
exchange 22
3y4m
Posterior DL, Using a toilet
Open bearing
Good result at 10y11m
exchange
DL, dislocation ; Fig, figure ; OA, osteoarthritis ; TKA, total knee arthroplasty ; y, years ; m, months