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Knee Surgery, Sports Traumatology, Arthroscopy
https://doi.org/10.1007/s00167-018-5002-7
KNEE
Implant preloading in extension reduces spring length change
in dynamic intraligamentary stabilization: a biomechanical study
on passive kinematics of the knee
Janosch Häberli
1
· Benjamin Voumard
2
· Clemens Kösters
3
· Daniel Delfosse
4
· Philipp Henle
1
· Stefan Eggli
1
·
Philippe Zysset
2
Received: 6 December 2017 / Accepted: 30 May 2018
© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2018
Abstract
Purpose Dynamic intraligamentary stabilization (DIS) is a primary repair technique for acute anterior cruciate ligament
(ACL) tears. For internal bracing of the sutured ACL, a metal spring with 8 mm maximum length change is preloaded with
60–80 N and fixed to a high-strength polyethylene braid. The bulky tibial hardware results in bone loss and may cause local
discomfort with the necessity of hardware removal. The technique has been previously investigated biomechanically; how-
ever, the amount of spring shortening during movement of the knee joint is unknown. Spring shortening is a crucial measure,
because it defines the necessary dimensions of the spring and, therefore, the overall size of the implant.
Methods Seven Thiel-fixated human cadaveric knee joints were subjected to passive range of motion (flexion/extension,
internal/external rotation in 90° flexion, and varus/valgus stress in 0° and 20° flexion) and stability tests (Lachman/KT-1000
testing in 0°, 15°, 30°, 60°, and 90° flexion) in the ACL-intact, ACL-transected, and DIS-repaired state. Kinematic data of
femur, tibia, and implant spring were recorded with an optical measurement system (Optotrak) and the positions of the bone
tunnels were assessed by computed tomography. Length change of bone tunnel distance as a surrogate for spring shortening
was then computed from kinematic data. Tunnel positioning in a circular zone with r = 5 mm was simulated to account for
surgical precision and its influence on length change was assessed.
Results Over all range of motion and stability tests, spring shortening was highest (5.0 ± 0.2 mm) during varus stress in
0° knee flexion. During flexion/extension, spring shortening was always highest in full extension (3.8 ± 0.3 mm) for all
specimens and all simulations of bone tunnels. Tunnel distance shortening was highest (0.15 mm/°) for posterior femoral
and posterior tibial tunnel positioning and lowest (0.03 mm/°) for anterior femoral and anterior tibial tunnel positioning.
Conclusion During passive flexion/extension, the highest spring shortening was consistently measured in full extension with
a continuous decrease towards flexion. If preloading of the spring is performed in extension, the spring can be downsized
to incorporate a maximum length change of 5 mm resulting in a smaller implant with less bone sacrifice and, therefore,
improved conditions in case of revision surgery.
Keywords ACL repair · Anterior tibial translation · Dynamic intraligamentary stabilization · Knee kinematics
Abbreviations
ACL Anterior cruciate ligament
ATT Anterior tibial translation
CT Computed tomography
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s0016 7-018-5002-7) contains
supplementary material, which is available to authorized users.
* Janosch Häberli
janosch.haeberli@gmail.com
1
Sonnenhof Orthopaedic Centre, Buchserstrasse 30,
3006 Bern, Switzerland
2
Institute for Surgical Technology and Biomechanics,
Stauffacherstrasse 78, 3014 Bern, Switzerland
3
University Hospital Münster, Albert-Schweitzer-Campus 1,
48149 Münster, Germany
4
Mathys Ltd., Robert-Mathys-Strasse 5, 2455 Bettlach,
Switzerland
@Phil_Robichaud
@deepthiw
@JoseServera