I'd like to thank my co-authors as well as Anna for allowing us to present our disclosures as listed in the app. So the surgical correction of patellofemoral instability is complex. And since its description in 1978 by Larson et al, several biomechanical studies have focused on increased medial patellar instability following lateral release, while only few have investigated the contribution of the lateral retinaculum encapsule to lateral patellar stability. Therefore, the objective of the current study was to quantitatively evaluate the effects of limited and targeted lateral retinacular encapsular release on the lateral stability of the patella at varying flexion angles as a function of constant force. We used six pairs of fresh frozen bilateral cadaveric knees with an average age of 52.2 and excluded specimens of age over 65, prior surgery, knee pathology, trauma, history of cancer, or being bedridden. Specimens were potted in the perfect lateral position and diagnostic arthroscopy was used to confirm ligamentous integrity, normal trochlear morphology, and absence of significant patellofemoral arthritis. A caliper was then used to measure the patellar length in order to place an eye screw in the midpoint of the patella in the sagittal plane. All specimens were tested in the intact state with a one kilogram load applied to the quadriceps tendon. The knee was positioned directly below the load cell of the MTS machine, and the eye screw fixed in the patella was secured to the load cell with a steel cable. A tensile force was then applied at one millimeters per second until a 20 newton direct lateral force was being applied to the patella. Load and lateral translation of the patella was then recorded at 40 hertz, and the final displacement at 20 newtons was recorded. Testing was conducted at zero, 10, 20, 30, 45, 60, and 90 degrees of flexion. Following testing in the intact state, the senior author performed a limited open lateral retinaculum and capsular release as seen in the diagram to the right in blue. This is in contrast to prior descriptions of lateral release that are more indiscriminate as seen in the purple. Lateral displacement between the intact and lateral release states were then compared using a paired T-test. So diagnostic arthroscopy revealed intact specimens with normal patellofemoral anatomy. We found that the largest lateral mean displacement occurred at 10 degrees of knee flexion and the least amount of lateral displacement at 90 degrees of flexion in all specimens. Lateral displacement was significantly greater at all degrees of flexion in lateral release states compared to the intact specimens and the largest difference in lateral displacement in the lateral release state compared to the intact specimens occurred in full extension was greater than 30%. This chart displays the lateral displacement relative to the intact specimens. The blue bars represent the lateral release specimens compared to the green. You can see the greatest increase at zero degrees of extension. So the current study adds to a growing body of literature by demonstrating increased lateral patellar translation at all flexion angles compared to intact specimens. Prior biomechanical studies performed larger lateral releases as compared to the current one which is more reflective of our modern understanding of the lateral patellofemoral restraint. All prior studies also studied the force required to laterally translate the patella minimum distance versus in the current study we applied a constant force and measured a distance. We believe this is a more sensitive way of measuring lateral patellar displacement in cadaveric specimens. Regardless of the methodology, our results suggest that lateral releases should not be a routine component of instability correction if the true goal is to achieve patellar stability. Limitations include specimen age that is not representative of typical patellar instability population and we also assume normal patellofemoral alignment. In conclusion, limited lateral retinacular encapsular release results in increased lateral translation and patellar instability at all degrees of knee flexion. This procedure should be used with extreme caution when combined with other procedures for patellar instability and also, as we know, may result in medial instability if used alone. Thank you.

surgical correction

patellofemoral instability

lateral retinacular release

displacement

patellar instability