Early Aseptic Tibial Loosening in Total Knee Replacement – A Gender and Obesity Related Complication
- 1. FRCS Locum Consultant Orthopaedic surgeon, GWH Swindon
- 2. FRCS Orthopaedic registrar, GWH Swindon
- 3. FRCS, Consultant orthopaedic surgeon, Specialist Knee Surgeon, GWH Swindon
Abstract
Obesity is growing year on year in the western world, as is the need for knee arthroplasty. High BMI is associated with early tibial failure through aseptic loosening.
A case series of 12 consecutive revisions for tibial base plate mechanical failure was identified from a knee replacement cohort of 5,736 patients. We collected data on patient demographics, operative details and outcomes.
All failures occurred in high BMI females. There was a high proportion who had risk factors for osteoporosis. All cases were revised to at least a stemmed tibia, the majority to a constrained condylar construct. The revision surgery carried a high complication risk.
Early proximal tibial failure is a rare complication of total knee replacement surgery and there is an identifiable set of risk factors. This complication is therefore potentially preventable.
Keywords
Aseptic tibial failure, total knee replacement, revision knee replacement, obesity, complication
Citation
Deo SD, Jonas SC, Jhaj J (2022) Early Aseptic Tibial Loosening in Total Knee Replacement – A Gender and Obesity Related Complication. Ann Orthop Rheumatol 9(1): 1099.
Introduction
Total knee replacement (TKR) is an extremely successful intervention with long term survival of >90% at 15 years and beyond[1]. Obesity is predicted to rise in the western world at alarming rates over the next 2 decades. The role of obesity as a cause of implant failure and increasing risk of revision is controversial with some authors suggesting little impact on revision rates [2-6], while others report significant effect on the factors leading to revision [6-9]. The most frequent mode of failure of TKR is aseptic tibial loosening [9] which is influenced by stresses across the implant-bone interface [10,11]. These stresses are increased by obesity leading to the greater potential for aseptic loosening [10,11]. Gunst et al 2015 demonstrate double the aseptic tibial loosening leading to double the revision rate in those patients with a BMI of >35kg/m2 . Other studies show osteolysis rates 5 times higher if the BMI>40kg/m2 4, though the clinical impact of the identified osteolysis patterns were less clearly defined.
Implant design may be influential in protection against tibial failure. Reis et al 2013 report their series of short tibial keels, albeit not in an obese population, had greater osteolysis presumably due to reduced protection from shear forces. These factors will clearly be greater in the obese patient[10,11].
There were observed isolated cases of early proximal tibial failures in our Institution and we aimed to compile a case series to assess potential risk factors for this issue with potential measures to mitigate this issue.
Patients and Methods
A retrospective review via departmental database search yielded a case series of 12 consecutive patients over a 12 year timespan (2010 to 2021) who had undergone revision knee replacement surgery for tibial component. Data were collected on patient demographics, operative details of primary and revision operations, components used, alignment pre and post operatively and indication. Complications and further surgery performed were recorded. During this time period, 5.736 primary knee replacement procedures were undertaken at our Institution. A comparator dataset of all primary total knee replacements was available via the hospital’s database.
Data were analysed using Microsoft Excel.
Results
All patients identified were female with a mean age of 60 years (range 46-76). Mean BMI was 41 (range 33-54). Eleven of the 12 (92%) patients had significant medical comorbidities, of whom 6 of the 11(55%) had significant risk factors for bone ‘failure’ such as inflammatory arthritis, diabetes and/or hypothyroidism. The initial indication for arthroplasty was primary osteoarthritis in 10 patients (83%) post-traumatic osteoarthritis in 1 (8%) and revision of a medial UKR in 1 other (8%). The majority of components revised were the Triathlon TKR using a primary tibial implant in 7 of the 12 (58%) (Stryker, Newbury, UK), others included Nexgen in 3 (25%), 1 AGC (Zimmer-Biomet, Swindon UK) and 1 PFC Sigma (Depuy Synthes, Leeds UK). Revision took place a mean of 58 months (range 10-162) following the index primary TKR All were indicated for revision due to mechanical collapse of the tibia.
Radio-graphic review of the initial x-rays of the primary TKRs showed the tibial component was implanted within 3 degrees of the mechanical axis in 10 of 12 (83%) of patients and was 5 degrees varus in the other 2 cases. The posterior slope was of normal parameters in all cases.
At time of data collection 1 patient was still awaiting revision surgery. The others had been revised of which 8 of 12 had undergone full revision to varus-valgus constrained condylar total knee replacements and 3 underwent a tibia only revision. Stems were used in all cases and a metaphyseal cone was used in one tibia.
Complications occurred in 5 (45%) of patients during the revision surgery and included; bilateral pulmonary emboli (1 case), intra-operative tibial fracture (1 case), periprosthetic femoral fracture (1 case) and infection resulting in debridement with implant retention (2 cases). Both peri-prosthetic fractures were managed operatively giving a re-operation rate of 36%. The tibial fracture occurred intra-operatively, but the other complications required re-admission, giving a readmission rate of this cohort of 36%. There were no deaths in the early postsurgical period, within 90 days of revision surgery.
| Case series cohort N=12 |
Institution TKR population cohort n= 5,736 | |
|---|---|---|
| Age Mean (range) |
60 (46-76) | 69 (39-92) |
| Gender No of females (%) |
12 (100%) | 3212 (56%) |
| BMI Mean (range) |
41 (33-54) | 31 (17-69) |
| Re-admission rate Within 42d of admission |
36% | 9% |
| Re-admission rate Within 42d of admission |
36% | 0.3% |
There were stark demographic differences between the case series group and the Institution’s overall knee replacement population as shown in Table 1.
Figure 1: 70 year old lady, BMI 40 at index surgery. Revision 10 months post index primary.
Case examples are shown in Figures 1 and 2
Figure 2: 48 year old lady, BMI 48, at index sugery. Revision 49 months post index primary.
Discussion
Obesity is a growing disease with rates increasing year on year. Arthroplasty in these patients is associated with higher complications at every stage.
Tibial aseptic loosening is likely to be a function of excess stresses on the tibial cancellous bone [12-14] and focal osteolysis. We demonstrate an association between high BMI females, over all with smaller implant sizes, who may also have risk factors for osteoporosis. Increased pressure per unit area has been shown to increase tibial failure in the obese patient [15].
Martin et al 2018 suggest that a blanket policy of stemming tibias in all patients over the BMI of 35kg/m2 is not cost effective [16]. Our series indicates that there is a smaller subset of patients who are at greater risk and need implant driven protection. These are female patients with high BMI, predominantly smaller plateaus and risk factors for osteoporosis.
Our series is predominantly Triathlon TKR (Stryker, Newbury, UK) which may be vulnerable to tibial failure in the obese due to a shorter keel in its primary tibial implant than other implant designs13 although its performance in the UK national joint registry would suggest it is amongst the best performing knee replacements in terms of revision risk and survival [14].
Findings
In our consecutive series of 12 patients who presented with tibial mechanical failure, all were female, with a high BMI, the majority BMI over 40, with a tendency to smaller tibial sizes.
Conclusion, Limitations and Recommendations
This study is limited by the small patient numbers and the retrospective nature of data collection. Further work could be performed on a registry level, further identifying if these risk factors and risk quantification which may lead to more definitive advice for this patient sub-set and may promote a change in practice.
We recommend that a stemmed tibial construct should be used in female patients with an elevated BMI, particularly if it is over 40.
References
14. UK national joint registry annual report 2022.
