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Comparison of the lateral release rates in the press fit condylar prosthesis and the PFC Sigma prosthesis
The Knee 10 (2003) 193–198
Comparison of the lateral release rates in the press fit condylar prosthesis and the PFC Sigma prosthesis A. Ballantyne, J. McKinley, I. Brenkel* Department Orthopaedic Surgery, Queen Margaret Hospital, Dunfermline, Fife KY 2 0TT, UK Received 8 February 2002; received in revised form 6 September 2002; accepted 9 December 2002
Abstract There are many different total knee replacements on the market. Most have undergone design changes since they were introduced. The manufacturers claim these changes are necessary to improve outcomes of their products. Johnson and Johnson changed their press fit condylar (PFC) knee to PFC Sigma. One of the reasons for the change was to improve patella tracking by combining the deeply radiused trochlear groove of the PFC cruciate sacrificing knee with the natural asymmetrical valgus angle of the PFC cruciate retaining knee. In 1995 we started a prospective audit of our knee replacements. We analysed our early outcomes to test this theory. Group 1 consisted of 468 patients who underwent 543 PFC replacements. Group 2 consisted of 359 patients who underwent 423 Sigma knee replacements. An audit nurse saw all the patients preoperatively and an American Knee Society Score was done. Operative details were recorded. Patients were followed up by an audit nurse at a dedicated knee clinic. The same surgeons using the same instrumentation carried out the operations. The change in design reduced the lateral release rate by 50% from 32 to 16%. The complications were similar in both groups and there was no difference in the outcomes at 6 months. The change in design from the PFC to the Sigma knee has had an effect in reducing the lateral release rate, without affecting the early outcomes. We plan to continue this audit to see if the change leads to less patellar problems in the future. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Lateral release; Total knee replacement
1. Introduction The National Institute for Clinical Excellence (NICE) was set up as a special health authority for England and Wales on 1 April 1999. It is part of the National Health Service (NHS), and its role is to provide patients, health professionals and the public with authoritative, robust and reliable guidance on current ‘best practice’ w1x. NICE issued their guidance primary total hip replacement in March 2000 w1x. The current ‘benchmark’ should be a revision rate of 10% or less at 10 years. Prosthesis should be considered with a minimum of 3 years revision data (Entry Benchmark). Annual review on these prosthesis are required, to ensure they remain consistent with the 10-year benchmark w1x. NICE has not yet issued guidelines on total knee replacements. It is presumed that similar standards will be set. *Corresponding author. Tel.: q44-1383-623623x3041. E-mail address: [email protected] (I. Brenkel).
A recent survey has shown that there are 37 different knee replacements in the UK w2x. Fifty four percent have been introduced since 1990. Only 54% have had any long-term results published in peer review journal w2x. This survey also showed that the most common implants used in the UK are the Insall Burnstein II, press fit condylar (PFC), Kinemax and AGC. Although all have had long-term reviews w3–12x, all have undergone some modifications. The companies would claim that these design changes are necessary because of problems with the initial design. They feel the changes should lead to an improvement in outcome. The PFC modular knee system has undergone some changes, to design, polyethylene and instrumentation, and is now called the PFC Sigma knee. One of the changes (Fig. 1A) combines the deep radiused femoral groove, of the PFC cruciate-substituting design (Fig. 1B), and the asymmetry of the PFC cruciate sacrificing prosthesis, which had a shallow groove (Fig. 1C). It was suggested that by combining the deeply radiused
0968-0160/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 8 - 0 1 6 0 Ž 0 3 . 0 0 0 0 7 - 3
194
A. Ballantyne et al. / The Knee 10 (2003) 193–198
Fig. 1. The PFC Sigma knee (A) combines the deep groove of the PFC posterior cruciate sacrificing knee (B) with the asymmetry of the PFC posterior cruciate retaining knee (C).
trochlear groove with a natural valgus angle, that the shear forces at the patellofemoral articulation could be reduced w13x. This design was found to reduce medial– lateral shear force on the patella by 39% between 0 and 1008 flexion. It also increased the patellofemoral groove’s contact area by 45% at 908 and 26% at 08, but did not affect tibiofemoral contact area w14x. We prospectively analysed our PFC knee results and compared them to the PFC Sigma knee results to assess the impact of the changes on early clinical results. 2. Patients and methods An audit nurse was employed to prospectively audit patients undergoing consecutive primary total knee arthroplasties from January 1995 to December 2000. Patients were seen 8–10 days prior to surgery in a preassessment clinic. Their age, sex, height, weight and American Knee Society Score w15x were recorded. A preoperative haemoglobin check was done. The body mass index was calculated using the formula weighty height w2x. The patients were admitted 1 day prior to surgery and started on a low molecular weight heparin (Deltaparin 5000U daily) 12 h preoperatively. Three doses of cefuroxime were given. Full length graded elastic stockings were worn until discharge and early mobilisation encouraged. The operation was done through a medial para-patellar approach. A tourniquet was used in all cases and deflated once the dressings were applied. All patients received a Johnson and Johnson cemented knee arthroplasty. Patellar replacement was not done routinely. Patellar tracking was assessed using the no-thumbs technique or a towel clip at the superior border of the patella. Persistent subluxation was treated with a lateral release under direct vision. Group I (January 1995–December 1997) patients received a PFC prosthesis. The prosthesis was modified by the company and called the PFC Sigma knee. Group II (October 1998–December 2000) received this Sigma prosthesis. The instrumentation was the same for both groups. The same six senior consultants at the same institution carried out all arthroplasties. Operative details were recorded including whether a lateral release was done. Continuous passive mobilisation was started 24 h
postoperatively. A 24-h haemoglobin was done and the 24-h haemoglobin drop recorded. The number of patients transfused and the number of units used was also recorded. Postoperative complications and length of stay was noted. LMWH was continued until discharge. Group 1 consisted of 468 patients. Of these 393 patients underwent consecutive unilateral total knee arthroplasties and 75 patients’ bilateral knee replacements. There were 216 males and 252 females. Group 2 consisted of 359 patients. Of these 295 patients underwent consecutive unilateral total knee arthroplasties and 64 patients’ bilateral knee replacements. There were 183 males and 176 females. Patients were followed up prospectively at 6 months knee arthroplasty clinic. The American Knee Society Score was again calculated. Any complications were noted. 2.1. Statistics Analyses were performed using SPSS. Groups were compared using x2 (with Yates correction where appropriate) for categorical data and Student t-test for continuous variables. Statistical significance was established at P-0.05. 3. Results A total of 468 patients who received the PFC prosthesis (group I) and 359 patients received the Sigma prosthesis (group II) were analysed. A total of 543 knee arthroplasties were performed in group I (75 bilateral) of which 51 (9.4%) were PCL sacrificing. In Group II 423 knee arthroplasties (62 bilateral) were performed of which 28 (6.7%) were PCL sacrificing. The patients in these groups were comparable for age, male:female ratio, BMI, preoperative haemoglobin, and preoperative knee score as summarised in Table 1. Operative details were also similar for both groups (Table 1). 3.1. Lateral release Nearly a third (28.9%) of patients with the PFC prosthesis and 15.1% in with the Sigma prosthesis
A. Ballantyne et al. / The Knee 10 (2003) 193–198
195
Table 1 Patient details Prosthesis
PFC
Sigma
P value
Patient details No. of patients Maleyfemale ratio Mean age Mean BMI % Rheumatoid
468 216y252 68.7 29.1 11.4%
359 183y176 68 29.7 8.1%
nya ns ns ns ns
Operative details PCL sacrificing prosthesis Lateral release (%) Tourniquet time
9.4% (51y543) 28.9% (157y543) 69.4 min
6.7% (28y423) 15.1% (64y423) 63.9 min
ns P-0.001 ns
Anaesthesia GA Spinal Other
20% 69% 11%
12% 63% 25%
– – –
Length of hospital stay
11.4 days
9.3 days
P-0.001
Table 2 Lateral release rates and mean 24-h haemoglobin drop PFC
Sigma
Lateral No. of P Lateral No. of P release lateral value release lateral value release release No. of patients 157 Mean Hb drop 24 h 2.7
Fig. 2. Lateral release rates for the PFC and Sigma knee by surgeon.
required a lateral release (Table 1). This difference was statistically significant (P-0.001). 3.2. Lateral release by surgeon Although the number of lateral release varied for each surgeon, the rate was reduced for each surgeon after the introduction of the Sigma prosthesis (Fig. 2). 3.3. Lateral release and haemoglobin drop The 24-h haemoglobin drop in patients who had the PFC prosthesis was 2.58 gydl. This was not significantly
386 2.5
– ns
64 2.7
359 2.2
– ns
different from the 24-h haemoglobin drop of 2.30 gydl in those patients receiving the Sigma prosthesis. In addition there was no significant difference in the haemoglobin drop in those patients who had a lateral release and those who did not in both groups (Table 2). 3.4. Range of movement preoperatively and 6 months postoperatively There was no significant difference in the pre- or postoperative range of movement (ROM) in patients receiving the PFC and the Sigma prosthesis. This applied to both posterior cruciate retaining and the posterior cruciate sacrificing prosthesis (Table 3). 3.5. American Knee Society Score There was no significant difference in the pre- and
Table 3 ROM (degrees) preoperatively and 6 months postoperatively for the PFC and Sigma prosthesis PFC preoperatively
All patients PCL sacrificing PCL retaining
Sigma preoperatively
PFC 6 months postoperatively
Sigma 6 months postoperatively
Extension
Flexion
ROM
Extension
Flexion
ROM
Extension
Flexion
ROM
Extension
Flexion
ROM
9 9 9
105 100 106
96 91 97
9 7 9
107 108 107
98 99 98
4 4 4
94 95 94
90 91 94
1 1 1
92 92 92
91 91 91
A. Ballantyne et al. / The Knee 10 (2003) 193–198
196 Table 4 AKSS
All patients PCL sacrificing PCL retaining
PFC preoperatively
PFC 6 months postoperatively
Sigma preoperatively
Sigma 6 months postoperatively
27.7 22.4 28.3
80.6 80.9 80.8
25.2 25.6 25.8
83.6 82.8 83.7
postoperative AKSS in patients who received the PFC and those who received the Sigma prosthesis. No significant difference in either group was noted when the posterior cruciate retaining prosthesis was compared with the posterior cruciate sacrificing prosthesis (Table 4). 3.6. Complications The deep infection rate was higher in the group II (1.2%) compared to the group I (0.6%), but this was not statistically significant. The 6 months Mortality rate was similar for both groups (1.5% group I vs. 1.1% group II) (Table 5). The only revision done in the first 6 months was for infection. 4. Discussion The PFC modular knee system reports impressive long-term results w4,10–12x. Buehler et al. w10x report a survivorship of 93.4% at 9 years with revision for any reason the end-point. Survivorship with aseptic loosening as the end-point was 98.7%. These results were comparable to any knee on the market at present w2x. The cruciate sacrificing knee had a deep trochlear groove and the femur was symmetrical. The cruciate retaining knee was asymmetrical with a shallow trochlear groove. Johnson and Johnson introduced changes with the intention of improving long-term wear and improving patel-
lofemoral tracking. The new system is known as the PFC Sigma knee. It has a deep trochlear groove and is asymmetrical (Fig. 1A). We prospectively audited the outcomes following the introduction of the PFC Sigma knee and compared them to a previous cohort of knees who received the PFC total knee system. The groups were comparable demographically including a similar number of cruciate sacrificing knees. Surgical time was on average shorter for the Sigma knee but not statistically so. Most striking was the reduction in the rate of lateral release. This reduced from 28.9 to 15.1% following the introduction of the Sigma knee. The rate of lateral release was reduced for each surgeon. Although the reduction varied between surgeons there was a general decrease in the lateral release rates. Although the surgeons used the same instrumentation and basic technique, slight variations technique may influence the lateral release rates of individual surgeons. These include the degree of external rotation in which the femur is placed w16,17x. Akagi et al. showed that in neutral alignment there was a 36% lateral release rate while with 3–58 of external rotation the lateral release rate dropped to 6% w16x. Reis et al. w18x, however, have shown that such external rotation of the femoral component can lead to numerous secondary problems. Laskin w19x balanced the flexion space without externally rotating the implant by using a neutral femoral component with asymmetrical posterior condyles. This lowered the lateral release rate and anterior knee pain. In our study, although the lateral release rates were
Table 5 Complications Group I
Group II
Deaths (-6 months)
1 1 1 1 2 1
cardiac CVA pneumonia undetermined PE prosatate Ca
1 1 1 1
E. coli pneumonia and sepsis pneumonia PE undetermined
Deep infection
2 Pseudomonas 1 Staph albus
2 1 1 1
Staph aureus Pseudomonas MRSA no organism on culture
A. Ballantyne et al. / The Knee 10 (2003) 193–198
reduced there was no difference in the postoperative range of motion at 6 months between the groups. In addition the AKSS at 6 months postoperatively was no different between the groups. When we compared the PCL retaining and the PCL sacrificing prosthesis again we were unable to demonstrate any difference in the postoperative ROM or in the AKSS at 6 months. This study suggests that the design of the PFC Sigma knee has improved the patellar tracking and reduced the requirement for a lateral soft tissue release without compromising early outcome. A reduction in the lateral release rate may be beneficial for a number of reasons. The lateral superior geniculate vessel is commonly sacrificed during a lateral release w20x. The resulting avascularity has been implicated in patella complications w21,22x. Ritter, w23x, however, found that lateral release increases the risk of patella fractures with or without saving the lateral geniculate artery. This was backed up by a further study w22x, from the same unit. They found the only benefit of saving the lateral geniculate artery was to improve postoperative flexion w24x. Grace and Sim w25x quoted patellar fracture rates of 0.05% for the unsurfaced patella and 0.33% for re-surfaced patella. It has been argued that lateral release may increase postoperative blood loss and therefore the potential for allogenic blood transfusion and its associated risks. However, this study showed no significant difference in the haemoglobin drop when comparing patients with a lateral release to those without. A lateral release has also been associated with and increased incidence of wound discolouration and wound infection w26x. Although the long-term benefits of these changes to the prosthetic design can only be speculated on, it is apparent that the changes in the trochlear groove on the femoral component do appear to have improved patellar tracking. This has resulted in a reduction in the lateral release. Short-term outcomes show that the knee scores are unchanged following the introduction of the PFC Sigma knee. We hope to continue our prospective follow-up of these patients at 3 years to assess anterior knee pain and the number of patients that require secondary patellar surgery. Acknowledgments We would like to thank the following people for the help in setting up and running this prospective audit. Lorraine McComiskie, Audit Nurse Fife Acute Hospital; Wilma Addison, Audit Nurse Fife Acute Hospital; Jeanette MacDonald, Physiotherapist Victoria Hospital, Kirkcaldy.
197
References w1x Available from http:yywww.nice.org.uk. w2x Liow RY, Murray DW. Which primary total knee replacement. Ann R Coll Surg Engl 1997;79:335 –340. w3x Aglietti P, Buzzi R, De Felice R, Giron F. The Insall-Burnstein total knee replacement in Osteoarthritis. A 10 year minimum follow up. J Arthroplasty 1999;14:560 –565. w4x Shai PA, Thornkill TS, Scott RD. Total knee arthroplasty with the PFC. Results at a minimum of ten years and a survivorship analysis. J Bone Jt Surg Part B 1998;80:850 –858. w5x Ritter MA, Worland R, Saliski J, et al. Flat on flat, nonconstrained compression moulded polyethylene total knee replacement. Clin Orthop 1995;321:78 –85. w6x Li PL, Zamora J, Bently G. The results at 10 years of the Insall-Burnstein 11 TKR. J Bone Jt Surg Part B 1999;81:647. w7x Emerson RH, Higgins LL, Head WC. The AGC total knee prosthesis at average 11 years. J Arthroplasty 2000;15:418 – 423. w8x Emmerson KP, Moran CG, Pinder IM. Survivorship analysis of the kinematic Stabilizer total knee replacement. J Bone Jt Surg Part B 1996;78:441 –445. w9x Weir DJ, Moran CG, Pinder IM. Kinematic condylar total knee arthroplasty. J Bone Jt Surg Part B 1996;78:907 –911. w10x Buehler KO, Venn-Watson E, D’Lima DD, Colwell CW. The press-fit condylar total knee system: 8–10-year results with a posterior cruciate retaining design. J Arthroplasty 2000;15(6):698 –701. w11x Petersilge WJ, Oishi CS, Kaufman KR, Irby SE, Colwell CW. The effect of trochlear design on patellofemoral shear and compressive forces in total knee arthroplasty. Clin Orthop 1994;309:124 –130. w12x Khaw FM, Kirk LM, Gregg PJ. Survival analysis of cemented press fit condylar total knee arthroplasty. J Arthroplasty 2001;16:161 –167. w13x Available from http:yywww.pinstruments.comyproductsyjandjy sigmaydetails. w14x PFC Sigma Total Knee System International Symposium. International edition. Orthopaedics Today 1997;5. w15x Insall JN, Dorr LD, Scorr RD, Scott WN. Rationale of the knee society clinical rating score. Clin Orthop 1989;248:134. w16x Akagi M, Matsusue Y, Mata T, et al. Effect of rotational alignment on patellar tracking in total knee arthroplasty. Clin Orthop Relat Res 1999;366:155 –163. w17x Kaper BP, Woolfrey M, Bourne RB. The effect of built in external femoral rotation on patellofemoral tracking in the genesis II total knee arthroplasty. J Arthroplasty 2000;15:964 – 969. w18x Reis MD, Salehi A, Laskin RS, Bourne RB, Rand JA, Gustilo RB. Can rotational congruity be achieved in both flexion and extension when the femoral component is externally rotated in total knee arthroplasty. Knee 1998;5:37 –42. w19x Laskin RS. Patellar tracking and flexion space balancing using a femoral component with asymmetrical femoral condyles. Knee 1999;6:87 –93. w20x Ritter MA, Campbell ED. Postoperative patellar complications with or without lateral release during total knee arthroplasty. Clin Orthop 1987;219:163 –168. w21x Lewonowski K, Dorr LD, McPherson EJ, Huber G, Wan Z. Medialization of the patella in total knee arthroplasty. J Arthroplasty 1997;12:161 –167. w22x Scuderi G, Scharf SC, Meltzer LP, Scott WN. The relationship of lateral releases to patellar viability in total knee arthroplasty. J Arthroplasty 1987;2:209 –214. w23x Ritter MA, Herbst SA, Keating SA, et al. Patellofemoral complications following TKA. The effect of lateral release and
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sacrifice of the superior geniculate artery. J Arthroplasty 1996;11:368 –376. w24x Ritter MA, Pierce MJ, Zhou H, et al. Patellar complications (total knee arthroplasty). Effect of lateral release and thickness. Clin Orthop 1999;367:149 –157.
w25x Grace JN, Sim FH. Fracture of the patella after total knee arthroplasty. Clin Orthop 1988;23:168 –175. w26x Johnson DP, Eastwood. Lateral patellar release in knee arthroplasty. Effect on wound healing. J Arthroplasty 1992;7(Suppl):427–431.
Comparison of the lateral release rates in the press fit condylar prosthesis and the PFC Sigma prosthesis A. Ballantyne, J. McKinley, I. Brenkel* Department Orthopaedic Surgery, Queen Margaret Hospital, Dunfermline, Fife KY 2 0TT, UK Received 8 February 2002; received in revised form 6 September 2002; accepted 9 December 2002
Abstract There are many different total knee replacements on the market. Most have undergone design changes since they were introduced. The manufacturers claim these changes are necessary to improve outcomes of their products. Johnson and Johnson changed their press fit condylar (PFC) knee to PFC Sigma. One of the reasons for the change was to improve patella tracking by combining the deeply radiused trochlear groove of the PFC cruciate sacrificing knee with the natural asymmetrical valgus angle of the PFC cruciate retaining knee. In 1995 we started a prospective audit of our knee replacements. We analysed our early outcomes to test this theory. Group 1 consisted of 468 patients who underwent 543 PFC replacements. Group 2 consisted of 359 patients who underwent 423 Sigma knee replacements. An audit nurse saw all the patients preoperatively and an American Knee Society Score was done. Operative details were recorded. Patients were followed up by an audit nurse at a dedicated knee clinic. The same surgeons using the same instrumentation carried out the operations. The change in design reduced the lateral release rate by 50% from 32 to 16%. The complications were similar in both groups and there was no difference in the outcomes at 6 months. The change in design from the PFC to the Sigma knee has had an effect in reducing the lateral release rate, without affecting the early outcomes. We plan to continue this audit to see if the change leads to less patellar problems in the future. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Lateral release; Total knee replacement
1. Introduction The National Institute for Clinical Excellence (NICE) was set up as a special health authority for England and Wales on 1 April 1999. It is part of the National Health Service (NHS), and its role is to provide patients, health professionals and the public with authoritative, robust and reliable guidance on current ‘best practice’ w1x. NICE issued their guidance primary total hip replacement in March 2000 w1x. The current ‘benchmark’ should be a revision rate of 10% or less at 10 years. Prosthesis should be considered with a minimum of 3 years revision data (Entry Benchmark). Annual review on these prosthesis are required, to ensure they remain consistent with the 10-year benchmark w1x. NICE has not yet issued guidelines on total knee replacements. It is presumed that similar standards will be set. *Corresponding author. Tel.: q44-1383-623623x3041. E-mail address: [email protected] (I. Brenkel).
A recent survey has shown that there are 37 different knee replacements in the UK w2x. Fifty four percent have been introduced since 1990. Only 54% have had any long-term results published in peer review journal w2x. This survey also showed that the most common implants used in the UK are the Insall Burnstein II, press fit condylar (PFC), Kinemax and AGC. Although all have had long-term reviews w3–12x, all have undergone some modifications. The companies would claim that these design changes are necessary because of problems with the initial design. They feel the changes should lead to an improvement in outcome. The PFC modular knee system has undergone some changes, to design, polyethylene and instrumentation, and is now called the PFC Sigma knee. One of the changes (Fig. 1A) combines the deep radiused femoral groove, of the PFC cruciate-substituting design (Fig. 1B), and the asymmetry of the PFC cruciate sacrificing prosthesis, which had a shallow groove (Fig. 1C). It was suggested that by combining the deeply radiused
0968-0160/03/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. PII: S 0 9 6 8 - 0 1 6 0 Ž 0 3 . 0 0 0 0 7 - 3
194
A. Ballantyne et al. / The Knee 10 (2003) 193–198
Fig. 1. The PFC Sigma knee (A) combines the deep groove of the PFC posterior cruciate sacrificing knee (B) with the asymmetry of the PFC posterior cruciate retaining knee (C).
trochlear groove with a natural valgus angle, that the shear forces at the patellofemoral articulation could be reduced w13x. This design was found to reduce medial– lateral shear force on the patella by 39% between 0 and 1008 flexion. It also increased the patellofemoral groove’s contact area by 45% at 908 and 26% at 08, but did not affect tibiofemoral contact area w14x. We prospectively analysed our PFC knee results and compared them to the PFC Sigma knee results to assess the impact of the changes on early clinical results. 2. Patients and methods An audit nurse was employed to prospectively audit patients undergoing consecutive primary total knee arthroplasties from January 1995 to December 2000. Patients were seen 8–10 days prior to surgery in a preassessment clinic. Their age, sex, height, weight and American Knee Society Score w15x were recorded. A preoperative haemoglobin check was done. The body mass index was calculated using the formula weighty height w2x. The patients were admitted 1 day prior to surgery and started on a low molecular weight heparin (Deltaparin 5000U daily) 12 h preoperatively. Three doses of cefuroxime were given. Full length graded elastic stockings were worn until discharge and early mobilisation encouraged. The operation was done through a medial para-patellar approach. A tourniquet was used in all cases and deflated once the dressings were applied. All patients received a Johnson and Johnson cemented knee arthroplasty. Patellar replacement was not done routinely. Patellar tracking was assessed using the no-thumbs technique or a towel clip at the superior border of the patella. Persistent subluxation was treated with a lateral release under direct vision. Group I (January 1995–December 1997) patients received a PFC prosthesis. The prosthesis was modified by the company and called the PFC Sigma knee. Group II (October 1998–December 2000) received this Sigma prosthesis. The instrumentation was the same for both groups. The same six senior consultants at the same institution carried out all arthroplasties. Operative details were recorded including whether a lateral release was done. Continuous passive mobilisation was started 24 h
postoperatively. A 24-h haemoglobin was done and the 24-h haemoglobin drop recorded. The number of patients transfused and the number of units used was also recorded. Postoperative complications and length of stay was noted. LMWH was continued until discharge. Group 1 consisted of 468 patients. Of these 393 patients underwent consecutive unilateral total knee arthroplasties and 75 patients’ bilateral knee replacements. There were 216 males and 252 females. Group 2 consisted of 359 patients. Of these 295 patients underwent consecutive unilateral total knee arthroplasties and 64 patients’ bilateral knee replacements. There were 183 males and 176 females. Patients were followed up prospectively at 6 months knee arthroplasty clinic. The American Knee Society Score was again calculated. Any complications were noted. 2.1. Statistics Analyses were performed using SPSS. Groups were compared using x2 (with Yates correction where appropriate) for categorical data and Student t-test for continuous variables. Statistical significance was established at P-0.05. 3. Results A total of 468 patients who received the PFC prosthesis (group I) and 359 patients received the Sigma prosthesis (group II) were analysed. A total of 543 knee arthroplasties were performed in group I (75 bilateral) of which 51 (9.4%) were PCL sacrificing. In Group II 423 knee arthroplasties (62 bilateral) were performed of which 28 (6.7%) were PCL sacrificing. The patients in these groups were comparable for age, male:female ratio, BMI, preoperative haemoglobin, and preoperative knee score as summarised in Table 1. Operative details were also similar for both groups (Table 1). 3.1. Lateral release Nearly a third (28.9%) of patients with the PFC prosthesis and 15.1% in with the Sigma prosthesis
A. Ballantyne et al. / The Knee 10 (2003) 193–198
195
Table 1 Patient details Prosthesis
PFC
Sigma
P value
Patient details No. of patients Maleyfemale ratio Mean age Mean BMI % Rheumatoid
468 216y252 68.7 29.1 11.4%
359 183y176 68 29.7 8.1%
nya ns ns ns ns
Operative details PCL sacrificing prosthesis Lateral release (%) Tourniquet time
9.4% (51y543) 28.9% (157y543) 69.4 min
6.7% (28y423) 15.1% (64y423) 63.9 min
ns P-0.001 ns
Anaesthesia GA Spinal Other
20% 69% 11%
12% 63% 25%
– – –
Length of hospital stay
11.4 days
9.3 days
P-0.001
Table 2 Lateral release rates and mean 24-h haemoglobin drop PFC
Sigma
Lateral No. of P Lateral No. of P release lateral value release lateral value release release No. of patients 157 Mean Hb drop 24 h 2.7
Fig. 2. Lateral release rates for the PFC and Sigma knee by surgeon.
required a lateral release (Table 1). This difference was statistically significant (P-0.001). 3.2. Lateral release by surgeon Although the number of lateral release varied for each surgeon, the rate was reduced for each surgeon after the introduction of the Sigma prosthesis (Fig. 2). 3.3. Lateral release and haemoglobin drop The 24-h haemoglobin drop in patients who had the PFC prosthesis was 2.58 gydl. This was not significantly
386 2.5
– ns
64 2.7
359 2.2
– ns
different from the 24-h haemoglobin drop of 2.30 gydl in those patients receiving the Sigma prosthesis. In addition there was no significant difference in the haemoglobin drop in those patients who had a lateral release and those who did not in both groups (Table 2). 3.4. Range of movement preoperatively and 6 months postoperatively There was no significant difference in the pre- or postoperative range of movement (ROM) in patients receiving the PFC and the Sigma prosthesis. This applied to both posterior cruciate retaining and the posterior cruciate sacrificing prosthesis (Table 3). 3.5. American Knee Society Score There was no significant difference in the pre- and
Table 3 ROM (degrees) preoperatively and 6 months postoperatively for the PFC and Sigma prosthesis PFC preoperatively
All patients PCL sacrificing PCL retaining
Sigma preoperatively
PFC 6 months postoperatively
Sigma 6 months postoperatively
Extension
Flexion
ROM
Extension
Flexion
ROM
Extension
Flexion
ROM
Extension
Flexion
ROM
9 9 9
105 100 106
96 91 97
9 7 9
107 108 107
98 99 98
4 4 4
94 95 94
90 91 94
1 1 1
92 92 92
91 91 91
A. Ballantyne et al. / The Knee 10 (2003) 193–198
196 Table 4 AKSS
All patients PCL sacrificing PCL retaining
PFC preoperatively
PFC 6 months postoperatively
Sigma preoperatively
Sigma 6 months postoperatively
27.7 22.4 28.3
80.6 80.9 80.8
25.2 25.6 25.8
83.6 82.8 83.7
postoperative AKSS in patients who received the PFC and those who received the Sigma prosthesis. No significant difference in either group was noted when the posterior cruciate retaining prosthesis was compared with the posterior cruciate sacrificing prosthesis (Table 4). 3.6. Complications The deep infection rate was higher in the group II (1.2%) compared to the group I (0.6%), but this was not statistically significant. The 6 months Mortality rate was similar for both groups (1.5% group I vs. 1.1% group II) (Table 5). The only revision done in the first 6 months was for infection. 4. Discussion The PFC modular knee system reports impressive long-term results w4,10–12x. Buehler et al. w10x report a survivorship of 93.4% at 9 years with revision for any reason the end-point. Survivorship with aseptic loosening as the end-point was 98.7%. These results were comparable to any knee on the market at present w2x. The cruciate sacrificing knee had a deep trochlear groove and the femur was symmetrical. The cruciate retaining knee was asymmetrical with a shallow trochlear groove. Johnson and Johnson introduced changes with the intention of improving long-term wear and improving patel-
lofemoral tracking. The new system is known as the PFC Sigma knee. It has a deep trochlear groove and is asymmetrical (Fig. 1A). We prospectively audited the outcomes following the introduction of the PFC Sigma knee and compared them to a previous cohort of knees who received the PFC total knee system. The groups were comparable demographically including a similar number of cruciate sacrificing knees. Surgical time was on average shorter for the Sigma knee but not statistically so. Most striking was the reduction in the rate of lateral release. This reduced from 28.9 to 15.1% following the introduction of the Sigma knee. The rate of lateral release was reduced for each surgeon. Although the reduction varied between surgeons there was a general decrease in the lateral release rates. Although the surgeons used the same instrumentation and basic technique, slight variations technique may influence the lateral release rates of individual surgeons. These include the degree of external rotation in which the femur is placed w16,17x. Akagi et al. showed that in neutral alignment there was a 36% lateral release rate while with 3–58 of external rotation the lateral release rate dropped to 6% w16x. Reis et al. w18x, however, have shown that such external rotation of the femoral component can lead to numerous secondary problems. Laskin w19x balanced the flexion space without externally rotating the implant by using a neutral femoral component with asymmetrical posterior condyles. This lowered the lateral release rate and anterior knee pain. In our study, although the lateral release rates were
Table 5 Complications Group I
Group II
Deaths (-6 months)
1 1 1 1 2 1
cardiac CVA pneumonia undetermined PE prosatate Ca
1 1 1 1
E. coli pneumonia and sepsis pneumonia PE undetermined
Deep infection
2 Pseudomonas 1 Staph albus
2 1 1 1
Staph aureus Pseudomonas MRSA no organism on culture
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reduced there was no difference in the postoperative range of motion at 6 months between the groups. In addition the AKSS at 6 months postoperatively was no different between the groups. When we compared the PCL retaining and the PCL sacrificing prosthesis again we were unable to demonstrate any difference in the postoperative ROM or in the AKSS at 6 months. This study suggests that the design of the PFC Sigma knee has improved the patellar tracking and reduced the requirement for a lateral soft tissue release without compromising early outcome. A reduction in the lateral release rate may be beneficial for a number of reasons. The lateral superior geniculate vessel is commonly sacrificed during a lateral release w20x. The resulting avascularity has been implicated in patella complications w21,22x. Ritter, w23x, however, found that lateral release increases the risk of patella fractures with or without saving the lateral geniculate artery. This was backed up by a further study w22x, from the same unit. They found the only benefit of saving the lateral geniculate artery was to improve postoperative flexion w24x. Grace and Sim w25x quoted patellar fracture rates of 0.05% for the unsurfaced patella and 0.33% for re-surfaced patella. It has been argued that lateral release may increase postoperative blood loss and therefore the potential for allogenic blood transfusion and its associated risks. However, this study showed no significant difference in the haemoglobin drop when comparing patients with a lateral release to those without. A lateral release has also been associated with and increased incidence of wound discolouration and wound infection w26x. Although the long-term benefits of these changes to the prosthetic design can only be speculated on, it is apparent that the changes in the trochlear groove on the femoral component do appear to have improved patellar tracking. This has resulted in a reduction in the lateral release. Short-term outcomes show that the knee scores are unchanged following the introduction of the PFC Sigma knee. We hope to continue our prospective follow-up of these patients at 3 years to assess anterior knee pain and the number of patients that require secondary patellar surgery. Acknowledgments We would like to thank the following people for the help in setting up and running this prospective audit. Lorraine McComiskie, Audit Nurse Fife Acute Hospital; Wilma Addison, Audit Nurse Fife Acute Hospital; Jeanette MacDonald, Physiotherapist Victoria Hospital, Kirkcaldy.
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