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Abstract:
We reviewed 62 total knee arthroplasties by a single surgeon (VR) in
50 Patients. A cemented titanium PFC prosthesis with a tibial keel was used. There
were 25 male and 25 female patients. The mean age was 65 years and 11 months
(range 25 to 80 years). The mean radiological follow up was 14.1 years (range 10 to
20 years). Twelve patients had bilateral surgery undertaken separately. Forty six
patients had osteoarthritis, 3 had rheumatoid arthritis and one JCA.
Four knees underwent revision for aseptic loosening and 1 knee for
deep infection. A total of 5 patients died during this follow up. Four of them died
while being under review of unrelated causes and none showed any significant
loosening at their last follow up. The fifth patient who had the deep infection died
after an above knee amputation following a revision procedure. Two patients suffered
a supra-condylar fracture of the femur after a fall treated successfully with supra
condylar nails.
At 20 years follow-up the survival rate, using revision for all causes as an end-
point, was 92.1%. The survival rate at 20 years with revision for aseptic loosening as
the end point was 93.6%. The survival rate for radiological loosening ( KSRES > 10 )
at 20 years was 92.1%.
The cemented titanium keeled PFC knee prosthesis shows a good 20 year
survivorship with our surgical technique and results are comparable to those
reported of other contemporary knee prostheses.
J.Orthopaedics 2012;8(3)e1
Keywords:
PFC knee replacements, Titanium tibial keel, KSRES Scores, survival analysis.
Introduction:
Total knee replacement is becoming increasingly popular worldwide due to
improvements in the technology and implants ( 1-9).
Clinical decisions for selecting one implant over another must be supported by good
long term results. There have been a number of papers published showing good
medium term survival of cemented PFC knee replacements with modular tibial stem
(1, 13, 16, 20, 23, 24, 25) but there is no publication in the English language literature
on the long-term results of specifically the titanium keeled Tibial PFC prosthesis.
We retrospectively looked at our long term results of the PFC knee replacement using
a titanium tibial keel prosthesis. We used radiological and survival curve analysis,
with strict definitions regarding end points to assess the outcome.
PATIENTS AND METHODS
Between 1990 and 1997, 128 patients had total knee replacements performed by the
senior author (VR). Of these, 50 patients underwent 62 total knee
arthroplasties with a titanium tibial baseplate with keel, a PFC femoral component
and a cruciate preserving posterior lipped polyethylene liner. The implants were
cemented using CMW I Gentamicin loaded cement (DePuy, Leeds, UK).
Excluded from the initial 128, were patients who had a modular tibial tray. There
were 25 male and 25 female patients. The mean age was
65 years and 11 months (range 25 to 80 years). Twelve patients had bilateral surgery
undertaken separately. Forty six patients had osteoarthritis, 3 had rheumatoid arthritis
and one juvenile chronic arthritis. All procedures were undertaken in laminar flow
theatres using body suits, routine prophylactic antibiotics, tourniquet and through a
medial parapatellar arthrotomy.
The two components were always cemented separately using two
separate mixes of cement. The cement was pressurized into the dried cut surface of
the tibia and femur with direct finger pressure and some cement was applied on the
under surface of the components and then the components were implanted.
Continuous constant pressure was applied on the component till the cement had set.
The jig to widen the keel slot in the tibia was never used. To help decrease any
chances of “third body wear” from cement particles in the long term a special effort to
remove extruded cement (cement debridement) was made easier by cementing the
two components separately.
Assessment
Patients were examined at 3 months, 1, 2, 5, 7, 10 years and every 2 years thereafter
with a standard weight bearing antero -posterior and lateral radiograph at each clinic
attendance. Loosening of the arthroplasty was assessed using the Knee Society
Roentgenographic Evaluation System (KSRES).
This system scores radiological
loosening in a knee arthroplasty separately for the femoral, tibial and patella
components which are summed to give a total score. All the assessments and scrutiny
of the records was done entirely by an independent assessor (AK). A total score of
four or less and non progressive is rated as “not significant”, a total score of five to
nine should be “followed for progression”, and a total score of ten or above signifies
“possible or impending failure” regardless of symptoms (10). The mean radiological
follow up was 14.1 years (range: 10 – 20 years). None of the patients were lost to
follow-up but we had 8 patients who had more than 10 years follow up who were
discharged from the clinic to come back if there were any further problems and these
8 patients have not been reviewed in the past 5 years.
Survival analysis
Survival curves were analysed to assess revision for any cause, aseptic loosening and
radiological loosening.
Results :
Complete survival data were reviewed for all 62 knees at a minimum of 10 years post
operatively. The mean radiological follow-up was 14.1 years. The average KSRES
score for all three components, as well as the total score was less than four which is
defined as non significant . Fifty six knees scored less than four ( Fig 1 ) and 6
scored over ten . Five of these 6 required revision while one did not
undergo a revision due to medical reasons.
20 knees required a 8 mm poly insert, 26 knees required a 10 mm polyinsert, 11 knees
required 12.5 mm poly insert and 5 knees required 15 mm poly insert.
Revision surgery
Four knees were revised for aseptic loosening and one for deep infection.
Revision for aseptic loosening was done at 11, 12, 13 and 14 years after the primary
procedure and both the components were revised. One patient with deep infection
had a revision followed by an above-knee amputation and he eventually
died. Four patients died while being under review of unrelated causes and none
showed any significant loosening at their last follow-up. Two patients had traumatic
supracondylar femoral fractures needing a supracondylar nail in the femur and they
healed well without any problems.
Complications
One patient had lateral patellar subluxation on the radiograph with no functional
disturbance and required no surgical intervention. One patient required revision for
deep infection. Four patients had DVT and 2 patients needed MUA.
Survival analysis
Revision due to any cause
Using revision, for any reason, as the end point, the survival at 14 years was 92.1%
while the 20 year survival rate was still 92.1% (Fig. 2).
Aseptic loosening
Using revision for aseptic loosening as the end point, the survival at 14years was
93.6% while the 20 year survival rate was still 93.6% (Fig. 3).
Radiological loosening
Using radiological loosening as an end point ( KSRES score > 10 ), the survival at
14years was 92.1% while the 20 year survival rate was still 92.1% (Fig. 4).
We had 8 patients who had more than 10 years follow up with no signs of loosening
but were discharged from the clinic to come back if there were any further problems
and were therefore not reviewed in the last 5 years. If we were to assume that these 8
patients failed immediately after their outpatient clinic review, then the survival rate
at 14 years will be 79%, while the 20 year survival rate will still be 79%.
Discussion :
Total knee arthroplasty is an established procedure which greatly improves the quality
of life of the patient (12). Certain criteria are required to ensure accurate
reproducible results in survival analysis. These include strict definitions regarding
end points, evaluations done systematically and having enough patients to allow
statistical validity. The 10 year survival for total knee arthroplasty, using revision
surgery as an end point, is over 91% for a number of well established prostheses
(1, 2, 4, 5, 6, 7, 9, 13, 14, 15, 16, 21, 24, 25).
With the PFC cemented modular system using modular tibial prosthesis, using
revision surgery as an endpoint, Schai reports 90% 10 year survival, Khaw reports
95.5% 10-year survival. (13, 25) which is in line with the published data from other
prostheses (1-9, 11, 14-19, 21, 22, 26-29 )
One criticism of survival analysis is the exclusion from the results of patients who are
failing radiologically or clinically, but who do not undergo surgery.
These may be
elderly or infirm patients who choose or are advised not to undergo revision surgery
even in the presence of symptoms. This results in a falsely high survival rate. Hence,
survival analysis based on radiological assessment is important to quantify impending
failure. One patient in our study had radiological loosening as defined by a KSRES
score greater than ten but did not have revision due to medical reasons. Recalculating
data to account for patients with radiological failures (92.1% at 20 years in this series)
gives more useful information to the surgeon regarding the actual survivorship of the
implant.
Although septic loosening can be iatrogenic in nature, it may slightly mask the
surgical ability to implant a successful prosthesis. Aseptic loosening of an established
prosthesis, however, is a good indicator of surgical technique and quality of the
implant. Poly wear particles over time will contribute to the aseptic loosening of the
prosthesis.
In our study, all the implants that showed KSRES scores of more than 10
showed evidence of significant poly wear. Hence, we feel it is important to record
survival analysis for this separately. The 20 year survival rate of 93.6% in our series is
as good as the published data (11, 14-19) which have shorter follow-up periods.
There are few studies with long term results. Buechel FF et al (3) showed
that survival of the Rotating Platform knee at 16 years was better for cemented
prostheses compared to uncemented prostheses. Using revision as criterion, the
survival rate of uncemented prosthesis was 83% compared to 97.7% for cemented
prosthesis.
The long term results of the anatomic graduated component PCL retaining total knee
replacement published by Ritter et al (22) showed survival of 98.86% at 15 years
using revision due to any cause as an end point.
Van Loon et al (27) published their results using the Kinematic total knee
replacement. The 14 year survival was 82% using revision as an end point.
Our study is the only long term study using only PFC with a titanium tibial keel
prosthesis as all the other long term PFC results were with modular tibial prosthesis.
The survival of PFC with modular tibial prosthesis in a study by Rodricks et al (23)
at 15 years follow up for revision due to any cause was 91.5% and survival for aseptic
loosening was 97.2%.
Malin et al (16) in their study using PFC with a modular tibial prosthesis showed 15
year survival of 87.2% using aseptic loosening leading to revision as an end point.
Santini et al (24) published the medium-term results of the PFC total knee
replacement for the same senior author (VR) with a ten-year survival rate (using
revision for aseptic loosening as an end point) of 97.04%. This series used both types
of tibial prostheses viz. the keeled tibial prosthesis as well as the modular tibial
prosthesis.
There are weaknesses in our paper. First, it is a retrospective study. Secondly, we
have only presented survival analysis with radiological review.
Thirdly, the total
number of patients in the study is small.
Although the same prosthesis was used by other surgeons in the same hospital, we
only reviewed the results of one surgeon (VR) to maintain uniformity
as the surgical technique will have considerable effect on the longevity of the
prosthesis. We feel that our specific meticulous surgical technique as described before
is important to achieve good cement injection and fixation and thereby achieve good
long term survivorship as shown in our series. It is encouraging that the overall
survival rates are in line with other published data even at this longer term follow-up,
although the total numbers are smaller.
conclusion
Our study shows good 20 year survivorship with the titanium keeled cemented PFC
knee prosthesis. Our results are comparable to those of other contemporary knee
prostheses which have been published.
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LEGENDS
Figure 1 – AP / Lat Radiograph of the knee with PFC prosthesis insitu.
Figure 2 – Kaplan Meier curve showing all cases of revision as an endpoint.
Figure 3 – Kaplan Meier curve showing revision for aseptic loosening as an endpoint.
Figure 4 – Kaplan Meier Survival curve showing radiological loosening (KSRES>10) as an endpoint.
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