A single type of varus knee does not exist: morphotyping and gap analysis in varus OA

Abstract

PurposeTo achieve a higher level of satisfaction in patients having undergone Total Knee Arthroplasty (TKA), a more personalized approach has been discussed recently. It can be assumed that a more profound knowledge of bony morphology and ligamentous situation would be beneicial. While CT/MRI can give 3D information on bone morphology, the understanding of the ligamentous situation in diferent lexion angles is still incomplete. In this study, the dynamic gap widths of a large number of varus knees were assessed in various lexion angles, to ind out whether all varus knees behave similar or have more individual soft tissue patterns. Additionally, it was investigated whether the amount of varus deformity or other patient factors have an efect on joint gap widths. Methods A series of 1000 consecutive TKA patients, including their CAS data and patient records were analyzed. Joint gap widths in multiple lexion angles (0°, 30°, 60°, 90°) were measured in mm and diferences between the joint gaps were compared. A "standard" varus knee was deined as follows: (1) Lateral extension gap greater than medial, (2) lateral lexion gap greater than medial, and (3) lexion gap greater than extension gap. The percentage of fulillment was tested for each and all criteria. To measure the inluence of varus deformity on gap width diference, three subgroups were formed based on the deformity. Data were analyzed at 0°, 30°, 60° and 90° lexion. The efect of patient factors (gender, BMI, age) on gap sizes was tested by performing subgroup analyses. Results Only 444 of 680 (65%) patients met all three varus knee criteria. The lateral extension gap (4.1 mm) was signiicantly larger than the medial extension gap (0.6 mm) in 657 (97%) patients and the gap diference highly correlated with the amount of varus deformity (r 2 = 0.62). In all lexion positions, however, no correlation between gap diferences and varus deformity existed. Women had signiicantly larger extension and lexion gaps. Age and BMI showed no signiicant efect on gap widths. Conclusion Varus knees show a large inter-individual variability regarding gap widths and gap diferences. The amount of varus deformity correlates highly with the medio-lateral gap diference in extension, but not in any lexion angle. As varus knees are not all alike, a uniform surgical technique will not treat all varus knees adequately and the individual gap sizes need to be analyzed and addressed accordingly with an individualized balancing technique. Which inal balancing goal should be achieved needs to be analyzed in future studies. Level of evidence Level III.

How does the use of quantified gap-balancing affect component positioning and limb alignment in robotic total knee arthroplasty using functional alignment philosophy? A comparison of two robotic platforms

“…However wide variations in laxity have been demonstrated in non-arthritic knees [16]. Furthermore, it has been observed for varus-aligned knees, there is greater laxity in the lateral than the medial compartment, and more laxity in flexion than extension [16], although some more recent studies suggest that laxity in flexion may be equal to that in extension [9]. Whilst these subtle variations exist in the literature to defining what is a well-balanced knee, many authors accept some asymmetry between the medial and lateral compartments [9-16, 34, 35].…”

“…A commonly utilized approach is one that aims for equal laxity in the medial and lateral compartments in full extension, with a slight lateral laxity being acceptable in flexion. This definition is based on the observation that the medial compartment is constrained by the rigid medial soft tissue structures of the knee (superficial and deep medial collateral ligament complex) and is relatively immobile, compared to the lateral compartment that shows a larger amount of femoral rollback and is more lax, particularly in flexion [9][10][11][12][13][14][15][16], similar to that seen in the native knee, and is supported by published literature [17].…”

Functional Alignment Philosophy in Total Knee Arthroplasty—Rationale and Technique for the Valgus Morphotype Using an Image Based Robotic Platform and Individualized Planning

“…Resection of the PCL increases flexion laxity and can create a medial-lateral compartment mismatch if not adjusted appropriately [ 54 ]. Several definitions of balancing have been described, with many accepting some asymmetry between the medial and lateral compartments [ 55 , 56 , 57 , 58 , 59 , 60 ]. It is unclear if native balancing targets should be replicated in prosthetic designs that are cruciate deficient, and the optimal balancing targets for varus and valgus morphotypes in the tibiofemoral compartments remains elusive.…”

Digital TKA Alignment Training with a New Digital Simulation Tool (Knee-CAT) Improves Process Quality, Efficiency, and Confidence

“…Multiple authors have shown that a horizontal joint line, which is the alignment target in mechanical alignment, is present only in 20% of patients, and the mean medial proximal tibia angle (MPTA) is 87 degrees instead of 90 degrees [ 14 , 15 , 16 ]. Hazratwala et al showed on more than 4000 pre-operative knees a wide variation in bony knee morphology, which is quantitatively normally distributed [ 17 ].…”