Abstract
Introduction
After TKR, excessive tension within the lateral retinaculum can lead to joint instability, component wear, stiffness and pain. The spatial distribution of strain in the lateral retinculum is unknown, both in the native knee and after TKR. In this study we measure the magnitude and distribution of mechanical strain in the lateral retinaculum with knee flexion, both in the native knee and after TKR. We hypothesize that:
- 1.
Strain in the lateral retinaculum will increase as a function of flexion.
- 2.
Some regions of the lateral retinaculum experience greater strain than others.
- 3.
TKR will affect the magnitude and location of strain during knee flexion.
Materials and Methods
A fiduciary grid of approximately 40–70 markers was attached to the exposed lateral retinacula of five fresh frozen cadaveric knees in order to allow tracking of soft-tissue deformation. Each knee was flexed from 0–120° in a 6 degree-of-freedom custom activity simulator that physiologically loaded the knee during a squatting maneuver. During simulation, the displacement of each fiduciary point was measured using visible-light stereo-photogrammetry. The fiduciary grid divided into four distinct regions for strain analysis. Using the grid of the native knee in full extension as the initial state, the average principal strain in each region was calculated as a function of flexion. Measurements were repeated after TKR was performed using a contemporary implant system.
Results
In the native knee, average retinacular strain increased dramatically with knee flexion (30°: 12% vs 120°: 25%; p = 0.007). The greatest strain was observed in the supero-lateral region in high flexion (34% at 120°). No significant change in strain with flexion was seen in the infero-medial region bordering the patellar ligament (10% at 30° to 15% at 120°; p > 0.05). After TKR, retinacular strains increased by an average of 13% in extension when compared to the native knee. In flexion, strains decreased following arthroplasty by an average of 4% at 30° and 6% at all other angles. The largest strains were observed in the supero-lateral region and were comparable to strain observed in the native knee (34% at 120°). The greatest decrease in strain after TKR was observed in the supero-medial region (26% vs 16% at 90°).
Conclusions
In the native knee, average lateral retinacular strains are greatest mid- to high-flexion as the retinaculum tightens to constrain patellar motion. The superior regions of the retinaculum, where the iliotibial band-patellar fibers are located, experience the most strain, especially in higher flexion. After TKR, strain in the supero-medial region decreases while strain in the supero-lateral region remains comparable to the native knee, suggesting the geometry of the native knee along
