Table of Contents

2019 Month : October Volume : 8 Issue : 43 Page : 3185-3189

Total Knee Arthroplasty- A Prospective Randomised Comparison between Functional Outcomes of Cruciate Retaining and Posterior Stabilising Implants.

Pankaj Mahindra1, Prabhjeet Singh2, Rajnish Garg3, Harpal Singh Selhi4, Maheshinder Singh Chauhan5, Ashwani Soni6

1Department of Orthopaedics, DMCH, Ludhiana, Punjab, India. 2Department of Orthopaedics, SSMMH, Kochi, Kerala, India. 3Department of Orthopaedics, DMCH, Ludhiana, Punjab, India. 4Department of Orthopaedics, DMCH, Ludhiana, Punjab, India. 5Department of Orthopaedics, SPS Hospital, Ludhiana, Punjab, India. 6Department of Orthopaedics, GMCH Chandigarh, Punjab, India.

Corresponding Author:
Prabhjeet Singh,
#199, Vivekananda Park,
Maksudan, Jalandhar,
Punjab, India.
E-mail: drgahra@gmail.com

ABSTRACT

BACKGROUND

Osteoarthritis knee is a leading cause of disability worldwide. Total knee arthroplasty (TKA) is considered as a reliable option to relieve pain and improve lifestyle of patients with osteoarthritis knee. However, there is no single best implant for total knee arthroplasty. Despite being debated since years, the controversy of cruciate retaining (CR) TKA vs Posterior stabilising (PS) TKA is still ongoing. Purpose of our prospective randomised trial is to compare the functional outcomes of CR and PS implants at short term follow-up in patients aged 45 years or more having TKA surgery for OA knee. We hypothesise that there is no difference in outcome of both implants.

METHODS

All the patients having age 45 years or more admitted to our institute for TKA surgery for OA knee were considered to be included in the study. Patients having knee disease other than OA, history of any knee surgery or high tibial osteotomy were excluded. All knees were randomised and divided into groups– CR and PS. Patients were evaluated preoperatively and at latest follow-up using Knee Society (KS) Knee Score, KS Function Score and the Western Ontario and MacMaster Universities Osteoarthritis Index (WOMAC).

RESULTS

104 knees in total, were evaluated with average follow-up of 3.9 ± 1.3 years in CR group and 3.7 ± 1.9 years in PS group. Outcome functional scores WOMAC, KS Knee score and KS Functional score showed significant improvement at final follow-up. However, there is no statistically significant difference among the two groups.

CONCLUSIONS

Both CR and PS designs are comparable in terms of clinical and functional outcome and implant survivorship at short term follow-up. The choice of design depends upon PCL status and surgeon’s preference.

KEY WORDS

Cruciate Retaining, Posterior Stabilized, Range of Motion, Total Knee Replacement, Functional Outcome, Knee Score

How to cite this article

Mahindra P, Singh P, Garg R, et al. Total knee arthroplasty- a prospective randomised comparison between functional outcomes of cruciate retaining and posterior stabilising implants. J. Evolution Med. Dent. Sci. 2019;8(43):3185-3189, DOI: 10.14260/jemds/2019/691

BACKGROUND

Worldwide, osteoarthritis (OA) is estimated to be the leading cause of disability. Earlier, osteoarthritis was known as the most common cause of musculoskeletal pain and disability and affecting mainly elderly population. However, now it is increasingly being diagnosed in younger people in the age group of 35 – 55 years. Several reasons can be attributed to this trend globally and in India including growing obesity, sedentary lifestyle, dependence on unhealthy and junk food and vitamin D deficiency. Osteoarthritis is the precipitating diagnosis for more than 90% of the increasing number of total knee joint replacement operations being undertaken worldwide. Now increasing number of arthroplasties in young population along with increasing life expectancy in operated cases, demands implants and surgeries with more longevity. Total knee arthroplasty (TKA) is considered as a reliable surgical procedure for pain relief in patients with knee osteoarthritis. The standard implant for primary TKA consists of a cemented Cobalt-Chrome femoral component, a polyethylene liner and a titanium tibial baseplate. Some surgeons resurface patella and use polyethylene patellar button. Tibial component can also be a mono-block tibial poly (this significantly reduces cost and has been observed to have equal longevity). There is no debate on importance of correct alignment of components and intra-operative stability of the joint. These factors are of prime importance. Many variations in surgeries had been observed in the past with good outcomes. The two school of thoughts regarding the surgical technique are- “measured resection” and “gap balancing”. Both has their own merits. There is also variability in type of implants. From historical prospective, two basic design groups are “anatomic” and “functional”. Functional approach had better reproducibility. In functional group, Cruciate sacrificing was first developed (the ICHL and the Total Condylar) followed by Posterior stabilised (PS-TKA) design and the Cruciate-Retaining design (CR-TKA). Some authors believe that CR-TKA has better post-operative knee proprioception and kinaesthesia1,2 while others believe that PS TKA has a more reliable femoral rollback, easier ligament balance3,4 and better range of motion (ROM).5

The PS implant is designed with the goal of mechanical alignment where tibial and femoral cuts are made perpendicular to the mechanical axis. PS knees are often easier to balance as compared to CR knees because of lesser number of ligaments to be balanced. On the other hand, CR design uses native PCL to prevent anterior dislocation of the femur during knee flexion. So, there is no cam-post mechanism and therefore no need for box cut and hence it preserves bone. The main rationale behind CR knee design is that PCL is critical to normal knee kinematics.

However, the recent reviews and meta-analysis did not find any significant difference in knee scores, radiological outcomes and complications between PS and CR knee replacement.6-8 Despite being debated since years, the controversy of CR total knee arthroplasty (TKA) vs PS TKA is still ongoing. In our prospective randomised trial, we compared the functional outcomes of CR and PS implants at short term follow-up in patients age 45 years or more having TKA surgery for OA knee. We hypothesise that there is no difference in outcome of both implants.

METHODS

This is a prospective randomized trial study. All the patients having age 45 years and more admitted to our institute for TKA surgery for OA knee were considered to be included in the study. It is assumed that patient admission for total knee replacement surgery in our hospital has prevalence rate of 7.5% based on previous data. Assumptions: Confidence Level = 95% Precision (d) = ± 5%. For estimation of sample size, the following formula has been used n= (Z2α X P X (1-P))/d2 where; Zα = Value of standard normal variate corresponding to α level of significance [P = Likely value of parameter, Q = 1 – P,D. = margin of errors which is a measure of precision]. With these assumptions the sample size works out as 106 i.e. 53 each group. One patient in the PS group where bilateral knee replacement was done, was lost to follow up. So final data is based upon 53 knees in CR group whereas 51 knees in PS group. Written informed consent was taken from patients before enrolling them in study. Patients having knee disease other than OA were excluded. Patients with history of any knee surgery or high tibial osteotomy were excluded. All knees were randomised at the time of admission using computer generated charts and were divided into two groups. Group CR for CR implants and group PS for PS implants. After getting all the clearances for surgery, TKA was done by standard parapatellar approach in all cases. Surgery with intramedullary rod for femoral cuts, extramedullary guide for tibial cuts, and spacer block for appropriate ligament balancing was performed in all patients. Patella was resurfaced in all patients and all implants were fixed with cement.

A well-informed written consent was taken from all the patients before including them in study and all the patients were explained about the type of implants used. Post-operatively patients underwent a standard rehabilitation program consisting of early ROM and weight-bearing exercises as tolerated. All patients received prophylactic anticoagulants and antibiotics as necessary. Patients were evaluated preoperatively and at latest follow-up using Knee Society (KS) Knee Score, KS Function Score and the Western Ontario and MacMaster Universities Osteoarthritis Index (WOMAC).9,10,11 The study was approved by ethical board of our institute.

Statistical Analysis

Statistical analysis was done using software Statistical Package for the Social Sciences (SPSS). Kolmogorov-Smirnov test was used to determine normal distribution of data. Continuous variables were compared using Student T test. Paired T-test was used to compare preoperative data with latest follow-up. p-Value was determined and value less than 0.05 was considered significant.

RESULTS

Demographics (Table 1)

Total 104 knees in 68 patients were included in the study who underwent TKA from December 2013 to May 2015. 36 patients underwent bilateral and 32 patients underwent unilateral TKA. Mean age in CR group was 60 years and 62 years in PS group. In group CR 17 patients underwent bilateral CR TKA and 12 patients underwent unilateral CR TKA. In group PS 12 patients underwent bilateral PS TKA and 20 patients underwent unilateral PS TKA. In 7 patients CR TKA was done on one side and PS TKA was done on other side. These 7 patients were included in both groups while doing demographic evaluation.

 

Preoperative Parameters (Table 2)

Both groups had preoperative varus malalignment. Mean ROM was slightly better in PS group; however, it was not statistically significant. Both groups had poor knee functional outcome scores preoperatively and the difference among two groups was not statistically significant.

 

Outcome Measures (Table 3)

Average follow-up was 3.9 years in CR group and 3.7 years in PS group. Mean ROM is better in PS group at 5 months and at final follow-up, but the difference was not significant statistically. Also, there was no statistically significant difference among two groups at 5 months or final follow-up in view of tibia-femoral angle, KS Knee score and KS Functional score. There was no revision surgery in any group till last follow-up.

 

Group CR (n=36)

Group PS (n=39)

Mean Age (Years)

60

62

Bilateral TKA

17

12

Unilateral TKA

12

20

Mix TKA

7

7

Male: female

6:30

13:26

Table 1. Demographic Profile of Patients

 

 

Group CR

(n=53)

Group PS

(n=51)

p

Tibio-femoral angle(varus)

6.85±2.48

6.39±2.96

0.395

ROM

89.23±18.57

94.61±10.67

0.074

WOMAC score

67.45±8.23

70.25±4.89

0.058

KS knee score

45.8±4.1

46.5±5.1

0.446

KS function score

35.8±7.9

34.6±8.4

0.565

Table 2. Pre-Operative Clinical Evaluation of 104 Knees

 

 

Group CR (n=53)

Group PS (n=51)

p

Final Follow-up (Mean years)

3.9± 1.3

3.7±1.9

0.245

Tibio-Femoral Angle

(5 mth follow-up)

2.04±0.78

2.53±0.78

0.214

(final follow-up)

2.1±0.71

2.6±0.67

0.208

ROM

(5 mth follow-up)

118±16.79

122±9.29

0.206

(final follow-up)

117±15.62

120±10.34

0.432

WOMAC score

 

 

 

(5 mth follow-up)

5.92±1.86

7.45±2.56

0.214

(final follow-up)

6.24±1.92

7.52±1.96

0.312

KS knee score

 

 

 

(5 mth follow-up)

90.5±6.4

89.5±7.8

0.768

(final follow-up)

91.4±7.8

92.6±7.5

0.684

KS Function Score

(5 mth follow-up)

85.7±6.5

87.6±6.8

0.257

(final follow-up)

84.6±7.2

88.6±8.4

0.723

Table 3. Follow-Up Clinical Evaluation of 104 Knees

 

 

DISCUSSION

Pain relief, restoration of knee kinematics, function and long-term implant survivorship are the desirable outcomes of successful knee arthroplasty.12 Multiple designs have been devised till date for achieving above said outcomes. However, CR and PS remain commonly used designs in present time.13 The superiority of one design over another is still matter of ongoing discussion. Numerous studies have been done till date in order to compare functional or biomechanical superiority of these designs (Table 4).14 Most of the studies have small sample size and laid emphasis on radiological, kinematics and short-term functional analysis. Both type of prosthesis has been proven safe and reliable in the treatment of severe arthritis. Both designs are comparable in terms of functional outcome and complications and there were no statistically significant differences.15,16

Merits of CR design includes better restoration of knee kinematics similar to native knee, enhanced femoral rollback during flexion, greater articular stability, proprioception, thin bone cuts and less blood loss17-19. Demerits include high polyethylene wear as femoral rollback in absence of intact anterior cruciate ligament is mere combination of rolling and sliding leading to generation of high contact stresses.20

PS design is recommended in inflammatory conditions leading to PCL degeneration and in cases with chronic PCL pathology. Advantages include easy technique, more comfortable soft tissue balancing, enhanced stability, better (ROM) and patella-femoral kinematics.21,22 Demerits include patellar clunk and increased wear due to post.23,24

Alignment and ROM- In our study, there was marked improvement in tibio-femoral angle from preoperative values. However, there was no difference among the groups and both groups had slight valgus alignment at final follow-up. There was slight increase in ROM in PS group at final follow-up, but that difference was not statistically significant. Berick et al reported statistically significant greater knee flexion and (ROM) with PS design, however clinically irrelevant7.

Sr. No.

Author

Study

Sample size

(Patient/ knee)

TKA Type

Mean Age

Outcome Measures

Follow-Up

Revision Surgery

Superiority

 

 

 

 

CR

PS

CR

PS

 

 

 

 

1

Singleton N (2019)

Prospective cohort

NA/

1287

794

493

73

70

WOMAC, Oxford

10 Years

NA

NO

2

Migliorini F

(2019)

Meta-

Analysis

4052/

4884

2403

2481

69

69

WOMAC, KSS clinical and ufnctional, ROM, Complications

3.39 Years

NO difference

NO

3

Serna-Berna R

(2018)

Retrospective

Case-control

NA/

479

268

211

68

70

WOMAC, KSS, SF-12, ROM, Patient satisfaction

10 Years

NO difference

NO

4

Longo

(2017)

Systematic review

4445/

5407

2591

2816

69

69

WOMAC, KSS, HSS, Oxford, ROM

0.5 Years

minimum

NO

difference

NO

5

Beaupre L

(2016)

RCT

100

51

49

68

68

WOMAC,

RAND-36

10 Years

NO difference

NO

6

Verra W

(2014)

Meta-

Analysis

1877/

2347

1156

1191

71

70

WOMAC, KSS, HSS, ROM

1 Year minimum

NO

difference

NO

7

Bercik M

(2013)

Meta-

Analysis

1114/

1265

660

605

NA

NA

ROM, WOMAC, SF-36

NA

NO

difference

NO

8

Li N

(2012)

Meta-

Analysis

888/

963

492

441

68

68

ROM, KSS

2 YEARS

minimum

 

NO

difference

NO

9

Lozano-Calderón

(2012)

Multicenter

prospective

740/

844

441

403

65

65

ROM, pain level, KSS-FD, KAS, SF-36

2 Years

NO

difference

NO

10

Soni A

(2019)

RCT

68/

104

53

51

60

62

ROM, KS score, KS Function score, WOMAC, tibiofemoral alignment

3.7 Years

NIL

NO

Table 4. Compiled Data from Similar Studies in the Past Literature

 

Knee Function

Knee function was evaluated using validated score like WOMAC and KSS Clinical and Functional. There was no statistically significant difference among CR and PS groups at 5 months and at final follow-up. The findings of our study are in total agreement with the recent literature. The functional outcomes reported in recent studies have been mentioned in Table 4. For determining functional outcome, choice of scoring is very essential. Both WOMAC and Oxford knee score mentioned in various studies are validated scores.25,26 However prime consideration should be given to minimally clinical important difference (MCID).27 It refers to quantification of minimal clinical difference, a patient and surgeon can appreciate with respect to scoring method. Younger patients having high functional demands undergoing TKA should be evaluated with a new score high activity arthroplasty score (HAAS).28

Implant Survivorship

Most of the studies have shorter follow-up period than our study. We found only two recent studies having longer follow-up period.10,16 There was no difference in longevity of these two designs at 10 years follow-up. There was no revision surgery in our study till last follow-up. On the positive side, our study is a prospective randomized trial and having adequate sample size. We used different manufacture designs so our results can be generalized to the commonly used CR and PS designs. The limitation of our study is a short follow-up period. Although there was no revision surgery, a longer follow-up is necessary for predicting implant longevity. However, more research is required to be done in younger age group patients (Between 45 -60 years) as knee arthroplasty is increasingly being done in this age group owing to increase incidence of obesity, leading to early arthritis. Further high quality RCTs may be needed for evaluating stair climbing ability.

CONCLUSIONS

Both CR and PS designs are comparable in terms of clinical and functional outcome and implant survivorship at short term follow-up. The choice of design depends upon PCL status and surgeon’s preference.

 

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