Elongation Patterns of the Collateral Ligaments After Total Knee Arthroplasty Are Dominated by the Knee Flexion Angle

Abstract

The primary aim of this study was to assess the effects of total knee arthroplasty (TKA) implant design on collateral ligament elongation patterns that occur during level walking, downhill walking, and stair descent. Using a moving fluoroscope, tibiofemoral kinematics were captured in three groups of patients with different TKA implant designs, including posterior stabilized, medial stabilized, and ultra-congruent. The 3D in vivo joint kinematics were then fed into multibody models of the replaced knees and elongation patterns of virtual bundles connecting origin and insertion points of the medial and lateral collateral ligaments (MCL and LCL) were determined throughout complete cycles of all activities. Regardless of the implant design and activity type, non-isometric behavior of the collateral ligaments was observed. The LCL shortened with increasing knee flexion, while the MCL elongation demonstrated regional variability, ranging from lengthening of the anterior bundle to slackening of the posterior bundle. The implant component design did not demonstrate statistically significant effects on the collateral elongation patterns and this was consistent between the studied activities. This study revealed that post-TKA collateral ligament elongation is primarily determined by the knee flexion angle. The different anterior translation and internal rotation that were induced by three distinctive implant designs had minimal impact on the length change patterns of the collateral ligaments.

Keywords: collateral ligaments; dynamic fluoroscopy; elongation; gait; total knee arthroplasty.

Figure 1

Three implant designs were investigated in this study: GMK Primary posterior stabilized (left), GMK Sphere (middle), and GMK Primary ultra-congruent design (right).

Figure 2

The ETH moving fluoroscope used to capture the knee joints during dynamic activities (A). Implant component geometries registered to a fluoroscopic image (B). Multi-body knee model including collateral ligament bundles (C).

Figure 3

A medial view of the knee of a representative subject with the GMK Sphere implant at different instances throughout a level walking gait cycle (GC). Linear elements represent each of the anterior (dark brown), intermediate (light brown), and posterior (amber) bundles of the MCL.

Figure 4

Subject-specific elongation patterns of the LCL (top, different color each subject, solid lines represent intra-subject means and shadings represent ± SDs) are shown compared to the average elongation patterns of the three MCL bundles (bottom, solid lines represent inter-subject means and shadings represent ± SDs) during level walking. The vertical dotted line represents the average toe-off time for subjects in the same group.

Figure 5

Average elongation patterns for the LCL (left) and MCL (right) during level walking. The vertical dotted lines represent the average toe-off times for the three groups. Solid lines represent inter-subject means and shadings represent ± SDs.

Figure 6

Average elongation of the LCL (top) and MCL (bottom) during five repetitions of the three studied activities plotted against the knee flexion angle. Average elongations were calculated only over the flexion ranges achieved by all the subjects during all the trials. Solid lines represent inter-subject means and shadings represent ± SDs.

Figure 7

The intra-subject differences in ligament elongations between activities for the three groups of implant designs plotted against the knee flexion angle. Average patterns (solid lines) and standard deviations (shadings) were calculated only over the flexion ranges achieved by all the subjects within an implant design group during all the five included trials.

Figure 8

Variation in the LCL and iMCL elongation due to changes in anterior/posterior translation (left), abduction/adduction rotation (middle), and internal/external rotation (right) of the implant. The base line kinematics captured from a subject with PS design prosthesis during level walking was perturbed in the range of (±5 mm/±5°). The vertical dotted line shows the instant of Toe-off.