Authors : Moatasem Abuelnour, Patrick Carroll, Anant Mahapatra
DOI : 10.18231/j.ijos.2021.016
Volume : 7
Issue : 2
Year : 2021
Page No : 100-105
Background: Although total knee arthroplasty (TKA) is one of the most successful operations in orthopaedic surgery, still approximately 20% of these patients have chronic unexplained pain which affect their life’s quality and post-operative expectations. The New Jersey low contact stress (LCS) knee system (LCS; DePuy Orthopaedics Inc., Warsaw, IN, USA) is one of the most effective knee designs with a well-known long track record. The surgical technique used is a gap balance technique which references the femoral component rotation to a well-designed tibial cut while maintaining soft tissue balance via
appropriate tensioning of collateral ligaments. Aim of this study is to look at any relationship between tibial cut coronal orientation on x-rays and patients satisfaction in relation to pain and function using the validated Oxford Knee Score (OKS).
Hypothesis: A varus tibial cut >3? in LCS TKA can result in femoral component internal rotation, patellar maltracking and chronic knee pain with suboptimal functional results.
Methods: A single surgeon’s TKA cohort using the LCS system was retrospectively evaluated from March 2017 to March 2020. We identified two cohorts of patients, one with a tibial cut angle on x-rays < 3? (59TKAs), and the other cohort with a tibial cut angle> 3? (41 TKAs). They received LCS TKA for right or left knee symptomatic end stage arthritis. We measured the tibial cut angle on antero-posterior (AP) x-rays and we obtained updated OKS by discussion over telephone (due to COVID-19 restrictions) with patients. We analysed our data for the two patient cohorts to look for any statistically significant functional difference.
Results: 100 patients coronal x-rays were finally included in the study. 59 patients were identified to have tibial cut angle < 3?. The average age of the patients 68.75(54-87), average time since surgery 20.4 months (7-43 months), and average OKS of 50.3. 41 patients were identified to have tibial cut angle > 3?. The average age of the patients was 69.45(53-81 years), average time since surgery 19.4 months (7-41months), and average OKS of 45.88. There was statistically significant difference in OKSs with females scoring less than males, with the former average OKS of 46.84 and the latter 50.83 respectively. There were 55 left sided TKAs and 45 right sided TKAs. Only 18 patients had score >55 in this comparison study (4 out of 41 patients with tibial cut angle > 3?, and 14 out of 59 patients with tibial cut angle < 3?). OKS in the group with tibial cut angle < 3? was statistically significantly higher than the group with tibial cut angle > 3? (U=797.5, p=0.004) and statistically more significant for females (U=278, p=0.027) than for males (U=135, p=0.151).
Conclusion: Patients with LCS TKA who had a tibial cut angle < 3? on postoperative and follow-up x-rays achieved better functional scores and less pain than patients with tibial cut angle > 3?. We attribute this to consequential femoral component malrotation and patellar maltracking as a result of a varus tibial cut angle > 3? in this gap balance technique. Surgeons have to be hypervigilant and ensure the tibial cut angle is as close to 90? +/-3? as possible to avoid poorer functional outcomes and unexplained knee pain.
Keywords: Gap balancing, Total knee arthroplasty, Total knee replacement, Tibial cut angle, Varus cut angle, Postoperative knee function, Oxford knee score.