# Subject-Specific Mechanisms of Knee Laxity

> **NIH NIH R21** · HOSPITAL FOR SPECIAL SURGERY · 2020 · $232,320

## Abstract

Project Summary /Abstract
Restoring rotatory laxity is critical to reestablishing joint function after knee ligament injuries such as rupture of
the anterior cruciate ligament (ACL). In fact, excessive rotatory laxity is associated with a nearly two-fold increase
in risk of early ACL graft failure. Unfortunately, patient-to-patient variability in rotatory laxity is immense and
the mechanisms driving rotatory laxity are difficult to unravel. This complexity stems from the numerous soft
tissues of the knee, the interplay of ligament slack length (the length at which the ligament begins to carry force)
and stiffness, and the tremendous variability in ligament structural properties. Consequently, no clear clinical
guidelines exist for how to best reestablish an individual patient’s rotatory laxity when treating knee ligament
injuries, especially to the ACL. Our long-term goal is to develop clinical guidelines to treat knee ligament injury
based on the patient-specific stabilizing mechanisms controlling rotatory laxity. This mechanistic understanding
would set the foundation for more personalized, predictable treatments by enabling a surgeon to tailor ligament
reconstruction to restore rotatory laxity on an individual basis. The specific goal of the proposed research is to
develop a novel computer algorithm to identify critical combinations of ligaments and ligament properties (slack
length and stiffness) that control rotatory laxity on a patient-specific basis. Inputs to this computer algorithm
are: 1) geometric data including articular and meniscal shapes as well as ligament attachment sites obtained from
3D imaging; and 2) the rotatory laxity of the knee obtained through clinical examination. A statistically-
augmented computational model of the knee will then output the specific ligaments and ligament properties that
drive rotatory laxity. The first aim focuses on: 1) obtaining measurements of rotatory laxity in cadaver knees and
2) building baseline computer models of these knees. The second aim derives subject-specific ligament properties
via statistical calibration and validates the properties using independent cadaveric biomechanical data from Aim
1. The hypothesis guiding this work is that ligaments and ligament properties driving rotatory laxity interact
nonlinearly and vary from knee-to-knee. The expected outcome will be an algorithm to identify the ligaments
and the ligament properties that are most important to restore rotatory laxity on a patient-specific basis. The
contribution is significant because it will enable personalized, precise treatments of ligament injury tailored to
the ligaments and ligament properties of individual patients. This contribution has high potential for clinical
translation because it will guide surgeons on how to tune their surgeries to reduce high failure rates following
ACL reconstruction. This statistically-enhanced, patient-specific modeling framework will provide the clinical
and research communities with...

## Key facts

- **NIH application ID:** 9828066
- **Project number:** 5R21AR073388-02
- **Recipient organization:** HOSPITAL FOR SPECIAL SURGERY
- **Principal Investigator:** Carl Imhauser
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $232,320
- **Award type:** 5
- **Project period:** 2018-12-01 → 2021-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9828066

## Citation

> US National Institutes of Health, RePORTER application 9828066, Subject-Specific Mechanisms of Knee Laxity (5R21AR073388-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9828066. Licensed CC0.

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