The authors performed a matched-paired study comparing 22
computer-assisted surgery (CAS)-unicompartmental knee replacement (UKR)
revisions with a similar group of knee replacement revisions performed
conventionally. The aim of the study was to assess differences in implants used
in the revision, surgical time, limb alignment, joint line restoration, and
procedure costs. In the conventional group, there was a higher percentage of
posterior stabilized (PS) and condylar constrained knee (CCK) implants, as well
as a higher percentage of augmentations/stems/offsets. There were no
statistically significant differences in postoperative mechanical axis,
surgical time, or hospital stay. There were fewer outliers and better joint
line restoration in the CAS group. More blood transfusions were performed in
the conventional group, and costs were higher in this group as well.
Revision of failed knee arthroplasty is a challenge because of the
associated problems of bone loss, soft tissue balance, and restoration of the
normal joint line.1 Some researchers believe that unicompartmental
knee replacement (UKR) is highly demanding and associated with technical
difficulties and worse results than primary total knee replacement
(TKR).2-5 Other researchers report conversion of failed UKR to TKR
with no particular intraoperative difficulties and similar results as those for
primary TKR at a short follow-up.6-8 However, almost all authors
report the necessity of using allografts, wedges, stems, and in some cases,
even constrained or semiconstrained implants during UKR
revision.2,3,5,7 For example, despite the availability of more
conservative modern UKR designs, in 2006 Springer et al3 reported
using metal wedge augmentation with 2 long stems in 23% of patients in his
series of 22 UKR revisions.3 More recently Saragaglia et
al9 reported metal wedge augmentation in >60% of patients in his
series of 33 UKR revisions.
Computer-assisted surgery (CAS) has been developed to help surgeons
perform reconstructive procedures, and to improve implants, alignment, and
performances. Various studies have demonstrated the efficacy of CAS in primary
knee replacement surgery, even with different systems.10-16
Furthermore, more accurate implant alignments and more precise bone cuts may
lead to advancements in tissue-sparing surgery.17,18
Nevertheless, few studies have analyzed the use of CAS in revision
procedures.19-21 Perlick et al20 in 2005 reported that
even in revision cases, CAS can achieve similar improved implant alignment as
is achieved with traditional techniques. In 2008, Massin et al19
reported a more reliable joint line restoration using navigation in revision of
failed TKR. However, no study in literature has reported the results of
navigated revision of failed UKR.
We performed a matched-paired study comparing 22 CAS-UKR revisions with
a similar group performed conventionally. The aim of the study was to assess
differences in implants used in the revision, surgical time, limb alignment,
joint line restoration, and procedure costs.
Materials and Methods
Among 878 computer-assisted knee replacements performed since 1999, 22
consecutive navigated UKR revisions were included in the study (group A). In
all cases, the diagnosis was aseptic loose or painful medial implants. No cases
of evident or suspected sepsis were included in the study. Navigation was used
to assist the surgeon in assessing limb alignment, bone cuts, and ligament
balancing. At a minimum follow-up of 12 months, all patients were successfully
matched to patients who had undergone a UKR revision in our hospital using
traditional alignment guides (group B). Every patient was matched for gender,
age, preoperative diagnosis, and intraoperative bone loss according to Anderson
Orthopaedic Research Institute Bone Defect Classification. Patients were
matched with a maximum difference in age of 3 years. In group A, the revision
procedure was performed using a computed tomography (CT)-free computer-assisted
alignment system (OrthoPilot 4.08, 4.2, and 4.3; Aesculap, Tuttlingen,
Germany). In group A all procedures were performed by two of the authors (N.C.,
A.M.); in group B, different surgeons working in our hospital performed the
Twelve months after surgery each patient had long-leg standing
anteroposterior radiographs and lateral radiographs of the knee using the same
standard protocol. We painstakingly collaborated with our radiographers to
obtain consistent films before embarking on this trial. The radiographs were
repeated when malrotation was detected.
Radiographs were assessed by an independent radiologist blinded to the
original procedure to determine the mechanical axis of the limb (hip-knee-ankle
[HKA] angle) as primary radiologic outcome measure. The desired prosthesis
alignment was considered to be an HKA angle of 180°. The number and
percentage of outliers (prostheses with any alignment parameter beyond 3°
of the desired value for HKA angle) was determined. Joint line restoration was
performed according to Figgie’s indications, assessing the differences
with the opposite untreated side on the lateral radiographs and considering 0
mm as the ideal value.22
The surgical time, implants adopted for the revisions, length of
hospital stay, and percentage of blood transfusions for each patient were
considered in the final assessment. We estimated mean costs for the procedure
by implant used and hospital charges. Mean implant costs were estimated using a
fixed price for every implant component (wedges, offsets, and stems) and using
a mean price derived from costs quoted by the 2 main companies supplying our
hospital. Mean hospital charges were estimated using mean hospital stay and
mean blood transfusion costs for both groups. Furthermore, we considered a mean
fixed extra cost of about €336 more for procedure in the navigated group
typical of innovative surgical procedures like computer-assisted surgery as
suggested in 2006 by Dong and Buxton.10
Statistical analysis was carried out using SPSS for Windows Release 11.0
(SPSS Inc, Chicago, Illinois). Differences between the 2 groups were measured
with an independent Student’s t test or Mann-Whitney nonparametric
test depending on the data distribution of the continuous variables.
Differences in the percentage of outliers for each parameter were tested using
a Fisher exact test. A P value of <.05 was considered statistically
significant for all analyses.
Preoperative values are presented in Table 1 and postoperative values
are presented in Table 2. In group A, mean patient age at the time of revision
was 71.8 years (range, 62-83 years) with a mean of 7.5 years (range, 2-15
years) elapsing from the original UKR surgery. In group B, mean patient age at
the time of revision was 73.6 years (range, 66-81 years) with a mean of 8.2
years (range, 3-16 years) elapsing from the original UKR surgery. There were 14
female and 8 male patients for each group. The mean preoperative HKA angle was
174.1° (range, 172°-179°) and 175.1° (range, 173°-178°)
for the navigated group and the manual group, respectively. Preoperatively, the
mean Knee Society Score was 42.9 (range, 39-48) in the UKR group and 41.4
(range, 37-50) in the TKR group. The preoperative functional score was 46.9
(range, 42-53) for group A and 45.3 (range, 41-50) for group B.
No intraoperative or postoperative complication related to surgical
technique was registered except the intraoperative breakage of a K-wire used to
secure tracker fixation to the bone in the navigated group, without any
influence on the final result (Figures 1, 2). The mean surgical time was longer
in group A (104.3 minutes [range, 85-132 minutes] than in group B (98.8 minutes
[range, 80-122 minutes]); there was no statistically significant difference
between the 2 groups.
Figure 1: All poly
tibial plateau aseptic loosening in a medial UKR.
Computer-assisted UKR revision of a CR TKR with intraoperative breakage of a
K-wire used to secure tracker fixation to the bone. There was no influence on
the final result.
Intraoperatively, according to the Anderson Orthopaedic Research
Institute Bone Defect Classification, there were 10 cases of grade I and 12
cases of grade II for each group.
In group A, the revision procedure was performed using again a UKR in 2
cases, a Bi-UKR in 1 case (Figure 3), a cruciate retaining (CR) TKR in 7 cases,
and a PS TKR in 12 knees (Figure 4). In group B, the revision procedure was
performed using a CR TKR in 5 cases, a PS TKR in 14 cases, and a CCK TKR in 3
cases. A 4-mm metal wedge augmentation was used in 3 cases in group A. Five
4-mm metal wedge augmentations and one 8-mm metal wedge augmentation were used
in group B. Bone allografts were used in 2 cases only in group B. Two 80-mm
uncemented tibial stems were used in group A, and two 80-mm and three 120-mm
uncemented tibial stems were used in group B.
Figure 3: A, Painful
medial UKR with an overcorrection of the mechanical axes and B, revision with a
Figure 4: A, B,
Aseptic loosening of the tibial metal backed component with clear radiologic
bone loss. C, D, Computer-assisted UKR revision to a PS TKR with a medial wedge
and long tibial stem.
At the latest follow-up, the mean Knee Society Score was 80.04 (range,
74-88) and 77.9 (range, 73-87) for group A and B, respectively.23 No
statistically significant difference was seen for the Knee Society Score
between the 2 groups. The mean functional score was 82.3 (range, 70-100) for
group A and 77.9 (range, 69-90) for group B. No statistically significant
difference was seen for the functional score between the 2 groups.
In the navigated group, the patients remained in the hospital for a mean
of 7.1 days (range, 4-10 days); in the traditional group, patients remained a
mean of 8 days (range, 4-13 days). Postoperatively, patients in group B
required a mean of 1.4 blood transfusions (range, 0-2) compared with 0.7
(range, 0-3) in group A.
At latest follow-up, the mean HKA angle was 179.4° (range,
177°-181°) in the navigated group and 178.1° (range,
175°-182°) in the traditional group with no statistical differences.
All the navigated revision implants were positioned within 3° of an ideal
HKA angle of 180° compared with 5 cases of outliers in group B. Joint line
restoration was calculated in 20 patients in group A and in 19 patients in
group B; 2 cases in group A and 3 cases in group B were excluded because a TKR
had already been done on the opposite knee. At the latest follow-up,
restoration of the joint line was statistically better in group A than in group
B, with a mean value being statistically closer to 0 mm (Table 2).
Analyzing the mean cost of the procedure, considering mean implant cost,
hospital costs, and a fixed extra cost for the navigated group, we estimated a
mean of €131.4 less for each procedure in the navigated group.
Unicompartmental knee replacement revision has been considered either a
challenging procedure or a routine primary replacement, according to different
authors’ experiences. Springer et al23 in 2006 considered
conversion of failed UKR to TKR as a technically demanding procedure and
advocated careful preoperative planning. Reviewing the New Zeland Joint
Arthroplasty National Register in 2010, Pearse et al24 reported a
poorer outcome of a UKR converted to a primary TKR compared with a primary TKR.
Likewise, Levine et al8 in 1996 and Châtain et
al5 in 2004 indicated that results of revision of failed UKRs are
superior to those of failed TKRs and failed high tibial osteotomy, and were
similar to their results of primary TKRs. Furthermore, Johnson et
al7 reported similar clinical results between revised UKR and
primary TKR at a 10-year follow-up.
One of the main difficulties during this surgical procedure is to
address bone loss, which is a greater complication in revision procedures
following the first generations of UKRs compared with procedures that used more
conservative modern designs. Padgett et al4 have reported technical
difficulties in revision procedures and failures following the use of cement to
treat large bony defects, suggesting the need for bone augmentations, metal
wedges, stems, and even constrained implants.
Theoretically, CAS can offer different advantages in these complicated
cases. In 2007, Thielemann et al21 pointed out how navigation can
help surgeons achieve a neutral mechanical alignment of the limb and a restored
joint line even in TKR revision. Furthermore navigation provides the surgeon
further information to avoid extensive use of augmentations and bone grafts
with precise data on bone cuts, limb alignment and soft tissue balancing. In
our experience of >800 implants, CAS has created a new concept of
tissue-sparing surgery based not on shorter surgical approaches but rather on
less invasive implants.
This is the first study in the literature to report the results of a
series of CAS-UKRs and to compare the results with a matched traditional group.
At first follow-up, we detected no difference in clinical outcomes, but
this was not the main objective of the study. Nevertheless, we demonstrated no
difference in surgical time or rate of complications, even using navigation. As
in previous reports in literature for primary TKRs, we demonstrated an improved
mechanical axis with a significantly lower number of outliers compared with the
traditional group. Furthermore, joint line was restored more anatomically in
the navigated group.
Finally, we demonstrated in the navigated group a less frequent use of
more invasive implants. Likewise, despite similar bone loss classification in
the navigated group, we had the choice of using a Uni or a Bi-uni to revise a
failed one with no CCK implant.
In 2007, Saldanha et al,6 using traditional alignment
systems, advocated use of augmentations and wedges only in selected cases, and
83% of his cases did not require any form of reconstruction for bone loss.
Furthermore, he reported a mean thickness of the tibial component, including
the polyethylene insert, to be only slightly thicker than after primary TKR.
Similarly, in our study we tried to reduce the need for wedges and
augmentations in both the groups; according to our results, this was possible
more frequently in the navigated group.
No intramedullary alignment system, less invasive surgeries, cheaper
implants, and less need for bone transfusions could reduce the cost of the
procedure, even with the addition of a fixed higher cost for the adoption of
navigation. In our study, we demonstrated a mean reduction in cost of
€121.4 when using navigation rather than traditional methods of revision
of failed UKR.
Using modern software and following computer suggestions for a minimal
bone cut and for an ideal joint line, we could recreate a more anatomic
revision in terms of implant alignment and joint line restoration using less
invasive implants. We believe that the advantages of CAS are demonstrated in
such complicated cases as UKR revision. Using CAS, surgeons can appreciate the
possibility of restoring limb alignment and joint line using tissue-sparing
procedures while also realizing a cost savings in these demanding procedures.
- Engh GA, Ammeen DJ. Bone loss with revision total knee arthroplasty:
defect classification and alternatives for reconstruction. AAOS Instr Course
Lect. 1999; 48:167-175.
- Barrett WP, Scott RD. Revision of failed unicondylar unicompartmental
knee arthroplasty. J Bone Joint Surg Am. 1987; 69(9):1328-1335.
- Springer BD, Scott RD, Thornhill TS. Conversion of failed
unicompartmental knee arthroplasty to TKA. Clin Orthop Relat Res. 2006;
- Padgett DE, Stern SH, Insall JN. Revision total knee arthroplasty for
failed unicompartmental replacement. J Bone Joint Surg Am. 1991;
- Châtain F, Richard A, Deschamps G, Chambat P, Neyret P.
Revision total knee arthroplasty after unicompartmental femorotibial
prosthesis: 54 cases. Rev Chir Orthop Reparatrice Appar Mot. 2004;
- Saldanha KA, Keys GW, Svard UC, White SH, Rao C. Revision of Oxford
medial unicompartmental knee arthroplasty to total knee arthroplasty: results
of a multicentre study [published online ahead of print May 23, 2007].
Knee. 2007; 14(4):275-279.
- Johnson S, Jones P, Newman JH. The survivorship and results of total
knee replacements converted from unicompartmental knee replacements [published
online ahead of print Feb 1, 2007.]. Knee. 2007; 14(2):154-157.
- Levine WN, Ozuna RM, Scott RD, Thornhill TS. Conversion of failed
modern unicompartmental arthroplasty to total knee arthroplasty. J
Arthroplasty. 1996; 11(7):797-801.
- Saragaglia D, Estour G, Nemer C, Colle PE. Revision of 33
unicompartmental knee prostheses using total knee arthroplasty: strategy and
results [published online ahead of print June 18, 2008]. Int Orthop.
- Dong H, Buxton M. Early assessment of the likely cost-effectiveness
of a new technology: a Markov model with probabilistic sensitivity analysis of
computer-assisted total knee replacement. Int J Technol Assess Health
Care. 2006; 22(2):191-202.
- Lüring C, Oczipka F, Perlick L, Tingart M, Grifka J, Bäthis
H. Two year follow-up comparing computer assisted versus freehand TKR on joint
stability, muscular function and patients satisfaction [published online ahead
of print Oct 22, 2008]. Knee Surg Sports Traumatol Arthrosc. 2009;
- Seon JK, Park SJ, Lee KB, Li G, Kozanek M, Song EK. Functional
comparison of total knee arthroplasty performed with and without a navigation
system [published online ahead of print June 28, 2008]. Int Orthop.
- Kim SJ, MacDonald M, Hernandez, Wixson RL. Computer assisted
navigation in total knee arthroplasty: improved coronal alignment. J
Arthroplasty. 2005; 20(7 suppl 3):123-131.
- Lin Chin P, Ying Yang K, Jin Yeo S, Lo NN. Randomized control trial
comparing radiographic total knee arthroplasty implant placement using computer
navigation versus conventional technique. J Arthroplasty. 2005:
- Bathis H, Perlick L, Tingart M, Luring C, Zurakowski D, Grifka J.
Alignment in total knee arthroplasty. A comparison of computer-assisted surgery
with the conventional technique. J Bone Joint Surg Br. 2004;
- Jenny JY, Boeri C. Computer-assisted implantation of a total knee
arthroplasty: a case-controlled study in comparison with classical
instrumentation. Rev Chir Orthop Reparatrice Appar Mot. 2001;
- Confalonieri N, Manzotti A, Montironi F, Pullen C. Tissue sparing
surgery (TSS) in knee reconstruction: unicompartmental (UKA), patellofemoral
(PFA), UKA + PFA, Bi-unicompartmental (Bi-UKA) arthroplasties [published online
ahead of print July 8, 2008]. J Orthop Traumatol. 2008: 9(3):171-177.
- Confalonieri N, Manzotti A, Pullen C, Ragone V. Mini-incision versus
mini-incision and computer-assisted surgery in total knee replacement: a
radiological prospective randomised study [published online ahead of print Sept
19, 2007]. Knee. 2007; 14(6):443-447.
- Massin P, Boyer P, Pernin J, Jeanrot C. Navigated revision knee
arthroplasty using a system designed for primary surgery. Comput Aided
Surg. 2008; 13(4):179-187.
- Perlick L, Lüring C, Tingart M, Grifka J, Bäthis H.
Revision prosthetic of the knee joint. The influence of a navigation system on
the alignment and reconstruction of the joint line. Orthopade. 2006;
- Thielemann FW, Clemens U, Hadjicostas PT. Computer-assisted surgery
in revision total knee arthroplasty: early experience with 46 patients.
Orthopedics. 2007; 30(suppl 10):132-135.
- Figgie HE III, Goldberg VM, Heiple KG, Moller HS III, Gordon NH. The
influence of tibial-patellofemoral location on function of the knee in patients
with the posterior stabilized condylar knee prosthesis. J Bone Joint Surg
Am. 1986; 68(7):1035-1040.
- Insall JN, Dorr LD, Scott RD, Scott WN. 1998 Rationale of the Knee
Society clinical rating system. Clin Orthop Relat Res. 1989;
- Pearse AJ, Hooper GJ, Rothwell A, Frampton C. Survival and
functional outcome after revision of a unicompartmental to a total knee
replacement: the New Zealand National Joint Registry. J Bone Joint Surg
Br. 2010; 92(4):508-512.
Drs Confalonieri and Manzotti are from the 1st Orthopedic Departement,
C.T.O. Hospital, Instituti Clinici di Istituti Clinici di Perfezionamento,
Milan, Italy. Dr Chemello is from Clinica Ortopedica, Università degli
Studi di Padova, Italy. Dr Cerveri is from the Bioengineering Department,
Politecnico di Milano, Milan, Italy.
Drs Confalonieri and Manzotti receive Congress sponsorship from B. Braun
Aesculap. Drs Chemello and Cerveri have no relevant financial relationships to
Correspondence should be addressed to: Manzotti Alfonso, MD, Via S.
Pertini 21, 20040 Cambiago (Milan), Italy.