A Novel Biomechanical Model for Hip Microinstability

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Christopher Golden
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MS 1 Kotaro Shibata, MD 1,3,4 Timothy Tio, MS 1 Marc R.

Stanford University, Redwood City, United States 2.

1 A Novel Biomechanical Model for Hip Microinstability Leandro Ejnisman, MD 1,2 Adam Johannsen, MD 1 Anthony Behn, MS 1 Kotaro Shibata, MD 1,3,4 Timothy Tio, MS 1 Marc R. Safran, MD 1 1. Stanford University, Redwood City, United States 2. Universidade de São Paulo, São Paulo, Brazil 3. Kyoto University, Kyoto, Japan 4. Nisei-Kobe Medical Center, Kobe, Japan

2 Disclosure No conflict of interest with the current presentation

3 Introduction Hip microinstability is a condition characterized by increased femoral head motion within the acetabulum. It is caused by an insufficient anterior capsule Sources: Ligamentous laxity Post-traumatic Iatrogenic (failed or incomplete capsular closure) Symptoms: Anterior groin pain Worse with extension and external rotation

4 Goals: 1. Develop biomechanical model of hip microinstability 2. Determine importance of capsule and labrum on hip stability Hypothesis: 1. Reproducible cadaveric model for instability possible 2. Both labrum and capsule synergistic in controlling femoral head motion

5 Methods 12 hips from 6 cadaveric pelvis (matched pair) Age <50, no OA or dysplasia Use Instron TM machine & motion capture system for data collection Specimen preparation Stripped of soft tissue down to capsule and bone Set in neutral position using a custom jig Cut potted, and positioned on Instron for testing

100th cycle, and submitted to 1000 cycles Testing conditions Intact state Labral insufficiency (radial +

6 Methods Capsular laxity was created using the Instron to stretch the hip capsule The hip was brought to maximum extension and rotated to 30 Nm per 100 cycles Then, specimen cycled to position of maximum ER at 100th cycle, and submitted to 1000 cycles Testing conditions Intact state Labral insufficiency (radial + chondrolabral tear) Labral insuficiency was created trough a limited capsulotomy under direct vision. The capsule was repaired

7 Results Capsular stretching significantly increased the hip arc of rotation

8 Results Capsular stretching also increased femoral head translation

9 Results The combined model (capsular laxity + labral insufficiency) resulted in more motion than either states in isolation

10 Discussion Unlike prior static testing models, capsular laxity was created via a controlled cyclic stretching protocol after venting of the joint, and this protocol caused a significant increase in femoral rotation and femoral head displacement In a biomechanical model, increased motion and rotation could be seen if a small inadvertent puncture of the capsule happened during dissection or stretching of the capsule. By demonstrating differences between the vented and laxity states, this model shows that the observed results are due to the stretching of the capsule.

11 Discussion Previous biomechanical studies on hip microinstability reached similar findings Jackson et al. reported an increase of ER from 26.3 o to 30.9 o after the creation of the model Han et al. reported an overall increase of 4.1 o in ER and 3.1 o in IR in all positions of flexion examined. They also found an increase in femoral head translation, with the largest occurring during IR, with 0.9 mm of additional medial translation in full extension and 0.95 mm of lateral translation in 90 o of flexion

12 Conclusions The hip microinstability model was validated Increased ROM with cyclic stretching of capsule Capsular laxity caused increased femoral head motion Labral tears cause more motion in the setting of capsular laxity

13 References 1. Abrams GD, Hart MA, Takami K, et al. Biomechanical Evaluation of Capsulotomy, Capsulectomy, and Capsular Repair on Hip Rotation. Arthroscopy. 2015;31(8): Chahla J, Mikula JD, Schon JM, et al. Hip Capsular Closure: A Biomechanical Analysis of Failure Torque. Am J Sports Med. 2017;45(2): Crawford MJ, Dy CJ, Alexander JW, et al. The 2007 Frank Stinchfield Award. The biomechanics of the hip labrum and the stability of the hip. Clin Orthop Relat Res. 2007;465: Han S, Alexander JW, Thomas VS, et al. Does Capsular Laxity Lead to Microinstability of the Native Hip? Am J Sports Med. March 2018: Jackson TJ, Peterson AB, Akeda M, et al. Biomechanical Effects of Capsular Shift in the Treatment of Hip Microinstability: Creation and Testing of a Novel Hip Instability Model. Am J Sports Med. 2016;44(3): Myers CA, Register BC, Lertwanich P, et al. Role of the acetabular labrum and the iliofemoral ligament in hip stability: an in vitro biplane fluoroscopy study. Am J Sports Med. 2011;39 Suppl:85S - 91S. 7. Philippon MJ, Nepple JJ, Campbell KJ, et al. The hip fluid seal--part I: the effect of an acetabular labral tear, repair, resection, and reconstruction on hip fluid pressurization. Knee Surg Sports Traumatol Arthrosc. 2014;22(4): Philippon MJ, Trindade CAC, Goldsmith MT, et al. Biomechanical Assessment of Hip Capsular Repair and Reconstruction Procedures Using a 6 Degrees of Freedom Robotic System. Am J Sports Med. 2017;45(8): Safran MR, Lopomo N, Zaffagnini S, et al. In vitro analysis of peri-articular soft tissues passive constraining effect on hip kinematics and joint stability. Knee Surg Sports Traumatol Arthrosc. 2013;21(7): Shu B, Safran MR. Hip instability: anatomic and clinical considerations of traumatic and atraumatic instability. Clin Sports Med. 2011;30(2):

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