2023 ISAKOS Biennial Congress ePoster
Surgically Modifiable Skeletal and Soft Tissue Variables and the Medial Pivot of the Knee
Peter James McEwen, MBBS FRACS(Orth) FAOrthA DIpModLang , Pimlico, QLD AUSTRALIA
Orthopaedic Research Institute of Queensland, Townsville, Queensland, AUSTRALIA
FDA Status Cleared
Summary
In an arthritic knee and balanced TKA the posterior condylar angle (relative to the sulcus line) correlates with the medial pivot range of the knee.
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Abstract
Introduction.
The pivot range of the knee correlates strongly with the TT-TG offset range of the knee. Understanding what skeletal and soft tissue variables that affect the pivot mechanics of the knee, especially those that are surgically modifiable, is important in optimising pivot mechanics and therefore the TT-TG offset.
Method.
Thirty-three primary, cruciate-retaining total knee arthroplasties were completed using an enhanced optical navigation system. Digital measurements of multiple skeletal and soft tissue balance parameters were taken in both the native and post-implantation states. After testing for normality, continuous variables were analysed for linear correlations with the Pearson Correlation Coefficient. Multiple linear regression was used for multivariate analysis.
Results.
The posterior condylar angle (PCA) from the sulcus line (SL) was the only measured variable with a significant correlation with preoperative pivot range (Pearson, R2=0.266, p=0.002). The PCA and change in medio-lateral position of the most distal point of the trochlear between native and post-implantation states (delta trochlea ML) were the only two measured variables with significant correlations with post-operative pivot range (Pearson, R2=0.443 and p<0.0001 / R2=0.224 and p<0.005 respectively. Multiple linear regression revealed significant effects of both the PCA and delta trochlear ML measures on post-operative pivot range (p=0.0005 and p=0.046 respectively). No soft tissue balance parameter had a significant interaction with post-operative pivot range.
Discussion.
Much attention has been paid to prosthetic design, component alignment, and ligament balance in an attempt to replicate the normal medial pivot TKA which functions to neutralize the TT-TG offset when the patella is under maximum load. The results of this study indicate that in a balanced TKA, the relationship between the posterior condyles and the sulcus line may be an important consideration. It is therefore possible that the PFJ drives the medial pivot of the knee rather than the converse.
Conclusion.
In a balanced CR TKA, patellofemoral skeletal variables, in particular, the PCA, correlate with medial pivot range. It is unknown if prosthetic modification of the PCA subsequently changes the medial pivot range.