Determinants of Range-of-Motion (ROM) in Post-Knee Replacement with Low Contact Stress (LCS) Systems:
The Asia Pacific Experience
Suriyapong Saowaprut1, Chumroonkiet Leelasestapom2, Chun-Hsiung Huang3, Seow Kang Hong4, KS
Sivananthan5, Chang-Dong Han6, Woo-Shin Cho7, James Lam8, Peter Ko8, Peter Chiu9 (The Dragon Knee Study Group)
Success of total knee arthroplasty (TKA) has been a function of a number of clinical parameters. Challenges in longevity of the implant coupled with the dynamic functional requirements of daily living have led to technological innovations such as the development of Low-Contact Stress (LCS) Mobile Bearing Total Knee System. While significant amount of data support the clinical value of the LCS Mobile Bearing Total Knee System, evidence pertaining to how this innovation performs according to the Asian lifestyle and culture can be considered wanting.
To this end, the Dragon Knee Study Group was formed with the primary goal of compiling the profile of performance of the LCS Mobile Bearing Total Knee System among the Asia-Pacific population. While performance can be measured in a number of clinical indicators, this paper is focused in identifying significant factors affecting range of motion 2 years post-op among Asian patients 75 years old and less who need total knee arthroplasty using the LCS Mobile Bearing Total Knee System.
Achieving this objective is done through a prospective, multi-center, pre-test-post-test study design in selected Asia Pacific countries, i.e. Malaysia, Singapore, Thailand, Korea, Japan and Hong Kong. Five hundred five (505) knees from 412 patients were included in the study. The mean age of the study population of mostly females is 64.86 + 7.14 years. The anthropometric profile of the group is slightly leaning towards the overweight side with a mean body mass index of 26.77 + 3.79 kg/m2.
Preoperative mean range of motion of the participants is estimated to be 108.13 + 23.65 degrees ranging from 5 to 150 degrees. There is slight increase to 113.94 + 19.94 degrees 2 years post surgery with range from 50 to 155 degrees.
Statistically significant determinants of range of motion post-TKA using LCS Mobile Bearing Total
Knee system include (1) Baseline Range of Motion (p<0.0001); (2) Study Site (p<0.0001); (3) Knee Walking Score (p=0.0009); and Knee Stair Score (p=0.0309). These determinants have been identified through multiple linear regression analysis after thorough correlation analyses to identify possible multi-collinearity and potential confounding. Furthermore, there is no evidence of difference in range of motion between those who received LCS Classic compared to those who received LCS Universal Mobile Bearing Total Knee System — holding for the effects of other factors in the regression model constant. Patellar resurfacing and anthropometry (as represented by weight) are likewise not significant predictors of range of motion 2 years post-TKA using the LCS Mobile Bearing Total Knee System.
The LCS-bearing knee system for total knee arthroplasty (TKA) has been part of the orthopedist’s bag of intervention since its development by Buechel and Pappas. From 1977 onwards, TKA patients have benefited from the highly congruent interface between the femoral components and the polyethylene-bearing surface in which the constraint on movement is offset by mobility at the tibial-bearing interface. With this design, the potential for wear and damage to bearing surfaces is minimized.
In addition, since there is rotational freedom
between the polyethylene-bearing and the tibial tray, torque stresses at the fixation interface are reduced thereby minimizing the risk for potential tibial tray loosening. To date, the LCS mobile-bearing system is available as the Classic or Universal systems where the former carries the rotating platform and meniscal bearing design while the latter carries its rotating platform and AP glide design. These mobile bearing devices have a well documented clinical history.i, ii, iii, iv, v, vi
While more than a 250,000 rotating platforms have been implanted outside the US since 1984, there is a need to assess the performance of the LCS Mobile bearing total knee system that utilizes a rotating platform tibial tray among the Asian Population. To help address this, this paper focuses on understanding the factors affecting the range of motion of patients after undergoing TKA using the LCS Mobile Bearing total knee system 24 months post-surgery.
RESEARCH DESIGN AND METHODS
The Study Population and Sample Size
While this study focused mainly on the range of motion as an outcome measure, it was part of a broader prospective, multi-center investigation which involved various facets of performance of the LCS Mobile Bearing Total Knee System. It involved patients satisfying the inclusion criteria which included: (a) being able to give consent to participate in the study and comply with post-operative follow-up requirements;(b) patients who were suitable to be treated with a mobile bearing knee system according to the clinical evaluation of the clinical investigators; (c)patients who were suffering from idiopathic osteoarthritis, rheumatoid arthritis, post-traumatic arthritis or any pathology that the clinical investigators think would benefit from primary total knee arthroplasty; (d) patients 75 years old or less at the time of study recruitment; (e) patients of Asian ethnic origin; (f) patients with simultaneous bilateral TKA or staged bilateral TKA if the second procedure was performed within the one-year recruitment period; and (g) unicondylar/high tibial osteotomy conversion patients where conversion was due to disease progression and not due to infection, aseptic loosening or loss of bone stock. From this cohort, patients who do not satisfy the manufacturer’s product insert requirements were excluded from the study. In addition, the following patients were likewise excluded from the study population: (a) those with history of poor compliance to medical therapy; (b) those that require revision surgery; (c) those with gross ligamentous insufficiency; (d) those with severe valgus deformity of 15 degrees or greater; (e) those with severe varus deformity of 20 degrees or greater; (f) those with fixed flexion contracture; and (g) those with age greater than 75 years old.
Each center was encouraged to recruit at least 50 patients during the course of eligibility evaluation. While there was no cap set in the number of patients to be evaluated per site, the study aimed to enroll at least 500 patients/procedures (TKAs) from various study sites in Asia Pacific. This number was sufficient to detect a difference of 0.15 standard deviations away from the true within patient difference — assuming a level of significance (α) of 0.05 and power (1-β) of 0.9.
Recruitment for study participants commenced after securing clearance from the sites’ ethics review board upholding patients’ informed consent and confidentiality of patient records. The methodologies employed in the study were consistent with the ideals of GCP. Compliance to regulatory requirements of the local investigation sites was likewise observed during the conduct of the study.
The Clinical Evaluation Procedures and Surgical Approach Once the consenting patient was deemed eligible to participate, the following clinical
assessments were done with data recorded using appropriate pretested data collection forms: (a) demography; (b) radiographic analysisi; (c) Knee Society Scoreii; (d) Oxford Knee Scoreiii; and (e) SF36 formiv for some selected sites (Korea and Japan only where results are presented in another paper).
Eligible participants were then allocated to either the LCS Classic or the LCS Universal study groups depending on the usual clinical practice of the site investigator. Local clinical practice guidelines determined whether (1) cement or non-cement components were to be used; and (2) the patella were to be resurfaced or not. Pre-operative evaluation was done according to the prevailing protocol implemented by the respective investigation site.
The surgical technique used was based on the published surgical approach for the LCS Mobile bearing total knee system using an approved instrumentation set in accordance to the manufacturer’s instructions. The surgeries were carried out by the designated clinical investigator(s) of the study sites with special focus on the surgical approach, soft tissue resection; bone cuts and soft tissue balancing. Documentation of the details of each surgery was recorded onto the patient details section of the Operative Notes Form of the study.
The Study Follow-up Schedule and Patient Safety
The participants were followed-up post surgery at six weeks, 6 months, 12 months and 24 months. During each of these, the following clinical evaluations were carried out: (a) Knee Society Score; (b) Radiographic analysis; (c) Oxford Knee Score; (d) SF36 Form assessment in selected sites; (e) Anterior Knee Pain; (f) Patellar Tilt; and (g) complications or adverse events assessment.
At any time during the course of the study, all adverse events and all events reported by patients spontaneously were recorded and evaluated accordingly. If the adverse event was deemed device related, the patient participation was withdrawn following a specific withdrawal procedure inclusive of the supporting medical management necessary for the adverse event.
Participant Withdrawal from the Study
Participants with the following circumstances were withdrawn from the clinical investigation: (a) patient request at any time during the duration of the study even without giving a reason and without prejudice to further treatment; (b) at the discretion of the clinical investigator due to poor treatment response, inter-current illness, unsatisfactory compliance and adverse event incidence.
Data Management and Statistical Analyses
Data were encoded, verified and validated using a customized data management system. Descriptive statistics were computed while multiple variable linear regression analysis was deployed to identify the determinants of range of motion among those with LCS Mobile Bearing Total Knee System. Correlation analyses were also done among the various independent variables to assess possible multicollinearity and to evaluate possible confounding. From here, the multiple-variable regression models were developed and reviewed accordingly.
General Characteristics of the Study Population
Five hundred five (505) knees from 412 patients were included in the study. Most of the participants are females (88.35%). The participants’ ages ranged from 25 to 75 years old with a mean of 64.86 + 7.14 years. The distribution of the knees according to laterality can be seen in Figure 1.
Figure 1. Distribution of the Study
Population According to Knee Laterality, Asia Pacific LCS Study, 2012.
The anthropometric profile of study population was slightly skewed to the overweight side. Measures of central tendency of the anthropometric profile of the study population can be seen in Table 1 below.
Table 1. Anthropometric Profile of the Study Population, Asia Pacific LCS Study, 2012.
Majority of the knees enrolled in the study came from Hong Kong, Thailand and Korea. Two-hundred seventy-five (275) knees received LCS Universal (54.46%) while 230 knees received LCS Classic (45.54%). About 60% of the knees enrolled did not involve patellar resurfacing.
The participation of the various study sites according to number of knees enrolled is presented in Figure 2.
Figure 2. Distribution of Study Knees
According to Country, Asia Pacific LCS Study, 2012.
Range of Motion Profile
The baseline range of motion of the study population was estimated to be 108.13 + 23.65 degrees with range from 5 to 150 degrees. This was apparently increased to 113.94 + 19.94 degrees 2 years post surgery with range from 50 to 155 degrees.
Further analysis suggested that the change in range of motion between baseline and 2-years post procedure was heterogeneous across the various study sites. This can be seen in Figure 3 — where significant increase in mean range of motion 2-years post-op is evident among patients from Thailand 2 site, i.e. the reference site.
Multiple variable linear regression analysis was employed to determine the factors affecting range of motion of patients undergoing LCS Mobile Bearing Total Knee Arthroplasty. Following the conceptual framework presented in Figure 4, the following factors have been identified to be significant predictors of range of motion 2-year post TKA using LCS Mobile Bearing Total Knee Arthroplasty:
• Baseline Range of Motion (p<0.0001); • Study Site (p<0.0001);
• Knee Walking Score (p=0.0009);; and
• Knee Stair Score (p=0.0309).
Figure 3. Comparison of Mean Range of Motion Between Baseline and 2-Years Post-TKA, Asia Pacific LCS Study, 2012.
The linear regression model has a coefficient of determination (r2) equal to 67.5% (p<0.0001).
Other factors included in the model but did not reach statistical significance include:
• Patellar resurfacing (p = 0.2907);
• LCS Device Type (p=0.5327); and
• Weight (p=0.4579)
This suggests that given the sample size power of the study, patellar resurfacing, LCS device type, i.e. whether LCS Universal or LCS Classic, and weight are not significant predictors of range of motion among those who undergo TKA using LCS Mobile Bearing Total Knee System.
Details of the final multiple linear regression model can be found in Table 2.
Figure 4. Conceptual Framework Relating Factors Affecting Knee Range of Motion, Asia Pacific LCS Study, 2012.
Table 2. β-coefficients of Hypothesized
Determinants of Range of Motion 2-years Post-TKA using LCS Mobile Bearing Total Knee System, Asia Pacific LCS Study, 2012.
Table 2 suggests an inverse relation between preoperative range of motion and post-op range of motion 2 years post TKA holding for the effects of other variables in the model constant.
Moreover, the reference site (Institute of Orthopedics, Lerdsin General Hospital, Department of Medical Services Surgery, The Medical Ministry of Public Health Council) was identified as having the apparent highest range of motion post-TKA using LCS Mobile Bearing Total Knee System (p<0.05).
Range of motion in the knee post TKA is an important outcome indicator of the success of the procedure. It will affect the patients’ ability to satisfactorily perform activities of daily living such as sitting and navigating through stairways. In many instances, it is a key factor in deciding and encouraging patients whether or not a total knee arthroplasty is warranted. This can also be the basis of rehabilitative modalities after the surgical intervention.
In this study, 4 factors have been identified to be statistically significant predictors of range of motion 2-years post TKA using LCS Mobile Bearing Total Knee System. The identification of baseline range of motion as a determinant of post-TKA range of motion is consistent with observation of other investigators.i,ii, iii
The regression model likewise suggests that the study site is a significant predictor of post-op range of motion. This can be presumably due to the inherent subtle uniqueness of surgical techniques between and among the study sites in spite of the general recommendations provided by the device manufacturer on the surgical approach. These differences across study sites can be seen in Figure 5 below.
Figure 5. Comparison of Range of Motion
Between Baseline and 2-Years Post-TKA by Study Sites, Asia Pacific LCS Study, 2012.
Knee scores have likewise been shown as a factors affecting range of motion. What is interesting however is that knee scores pertaining to stairs score at 2-years is positively associated with range of motion while knee scores pertaining to walking score at 2 years is negatively associated with range of motion. Some may think that this may be related to the patient’s motivation for rehabilitation intervention. Unfortunately, more details of the actual rehabilitative intervention for each patient in the study were not collected to support this hypothesis.
Moreover, contrary to the observations by several investigatorsi, ii suggesting the role of implant design in the final range of motion post-TKA, this study suggests that there is no difference in range of motion 2-year post-TKA between those patients who received LCS Universal when compared to those who received LCS Classic after controlling for the effects of preoperative range of motion, study site, patellar resurfacing, weight and knee scores (sample size power = 90%). This observation is consistent with the hypothesis of
Walley et al (2007).iii
A closer look on the relationship between the implant used and the study sites suggest that some association exists between these 2 hypothesized predictors. In fact, when the study site, patellar resurfacing, knee scores and anthropometry were removed from the model, LCS Classic was found to have a mean of 19.3 degrees less than LCS Universal as regards to range of motion (p<0.0001). The coefficient of determination in this case was reduced to 57.13%.
Review of other possible sources of bias in the study brings the team to the study of Lavernia et al (2008)iv where they demonstrated the inherent challenges of measuring range of motion in patients who have undergone TKA. This phenomenon may introduce some non-differential information bias to the study. However, the study methodology employed radiographic angulations between the long axis of the femur and the long axis of the tibia to measure the range of motion. As many consider this methodology as the gold standard in range of motion assessment, the risk for information bias can be mitigated.
In the final analysis, total knee arthroplasty remains to be a good option to improve clinical outcomes of patients who need surgical intervention for degenerative joint disease of the knee. The use of LCS Mobile Bearing Total Knee System can contribute to that end. While this study may have adequate sample size, further studies may be necessary to effectively partition the effect of surgical technique, of the study site and of the surgical implant on the final outcome on range of motion post-TKA.
1Institute of Orthopedics, Lerdsin General Hospital, Department of Medical Services Surgery, The Medical Ministry ofPublic Health Council(Reference Site)
2 Department of OrthopedicsBhumibo1 Adulyadej Hospital, The Royal Thai Air Force, Phaholyothin RoadBangken, Bangkok 10220 Thailand
3Mackay Memorial Hospital, 92, Sec 2, ChungSan North Road, Taipei, Taiwan
4Singapore General Hospital, Outram Road, Singapore 169608
5OrthopedicsSpecialist Clinic, Fatimah Hospital, Jalan Dato Lau Pak Khuan, 31400 Ipoh, Perak, Malaysia 6Department of OrthopedicSurgery, Yonsei University College of Medicine, CPO Box. 8044, Seoul, Korea
7 Department of OrthopedicSurgery, Asan Medical Center, 3881 PoongnapDong, SongpaGu, Seoul, Korea
8Department of Orthopedics& Traumatology, Pamela Youde Nethersole Eastern Hospital, Chai Wan
9Department of OrthopedicSurgery, The University of HongKong, Room 516, Professional Block, Queen Mary Hospital, Pokfulam, Hong Kong
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