Resorbable Implants in Knee Surgery

New Technologies - New Trends

Rodica Marinescu1, D.Laptoiu1, D.Popescu2, A.Antoniac2

1Colentina Clinical Hospital Bucharest, 2 University Politehnica of Bucharest,

Romania

Introduction

“ …..In ACL reconstruction, those elements that the surgeon is able to influence include the followings : Patient selection Graft selection Tunnel/graft positioning Graft tensioning and fixation Treatment of concomitant injuries Postoperative rehabilitation...“

T. Swenson and F. Fu 1995 Arthroscopy

Graft Choice

Chadwick C. Prodromos Arthroscopy 2005

Patellar tendon remains a largely used graft

PhysiologyGraft serves as scaffold - relatively

rapidly incorporated by the host

Graft Evolution similar to avascular necrosis: Cell Death: first phase - fibroblasts die

but graft acts as scaffold for new ingrowths = inflammatory stage.

Revascularization: New cells grew into graft = starts @ 20 days and is completed @ 6 months. Graft strength << drops as low as 11% !!!!

Remodeling: Strength slowly returns but it never returns to its level at the very beginning. = The fibers become more organized - longitudinal pattern.

Importance of Strong Early Fixation

Graft fixation is crucial in ACL reconstruction; is the weakest link in the initial 6- to 12-week period, when healing of the graft to the host bone occurs.

The graft must be able to withstand early rehabilitation, which can consist of forces as high as 450 to 500 N. The fixation can cause failure due to overstrain or creep during the postoperative period of healing. Early Fixation failure - usually occurs on tibial side. Late Fixation failure - Femoral side – position (conflict etc)

Falconiero Arthroscopy 1998

Found that vascularity and fiber pattern were the same for graft as in normal ACL after only 6 months which he felt was the strongest evidence to early return to play.

Fixation DevicesIn recent years, a large number of fixation

devices have been proposed, making the fixation of a doubled free tendon graft more reliable than in the past...

G. Milano et al. 2006 Arthroscopy

Interference – tunnel

enlargement

Osteolysis

1. First option: Ameliorate interference fixation

Better Design

Use of Composites

IntroductionThe main advantage of biodegradable implants

is that they gradually degrade after they fulfilled their functions

A Weiler

IntroductionLiterature also quotes that the healing process

may be stimulated by the successive loss of the mechanical properties of the implant during degradation, corresponding with the increasing loading on the healing tissue.

Production and research quickly react to surgeon-requested design changes for the biofunctionalization of resorbable implants within the sports medicine field.

Material/MethodWe evaluated several clinical applications

comprising resorbable pins and interference screws for the surgery of the anterior cruciate ligament, resorbable augmentation devices for ligaments and tendons.

MethodSome important information about the

bioresorbable screw degradation in vivo could be obtained after the retrieval analysis of explanted implant from various clinical reasons using advanced microscopical technique like scanning electron microscopy and atomic force microscopy.

ESEM of retrieved screw – fissuring and cavitation at 6 months

MethodUnfortunately for research purpose but good for

patients, just a few clinical failures of this type of implants are reported.

CT Image of resorbed screw (phantom) at 30 months follow-up

MethodThe degradation behavior cannot be predicted

exactly in vivo, as it is influenced not only by the chemistry and the implant design but also by the localization of the implant in the tissue.

Weiler et al: birefringent fragments found at 24 months

ResultsOsteolytic reactions, which we documented with

some umplants, had clinical consequences in most instances.

Aurabiomat StudyFEA test were

conducted with ANSYS v11 software

The results of the push-in and pull-out tests indicate that both the screw thread form and cutting head have a significant effect on the holding strength of the screw.

Material/MethodThe mechanical properties of these polymers

were improved in a series of experimental studies by special techniques in order to obtain composite biomaterials.anorganic particles such as hydroxyapatite are

mixed within the degradable polymer matrix.

several disadvantages = related to their stiffness behavior. The degradation behavior of the materials can be controlled by the production of copolymers and by the molecular weight of the polymers.

Aurabiomat Study

INSTRON UNIVERSAL LOYD

Biocompatibility/hemotoxcity

ResultsIn general, the biocompatibility of the composite

resorbable implants used today is good and the observed complication rate is very low.

Fused Deposition Modeling

ResultsFixation should

facilitate graft-tunnel healing, producing a normal histological transition zone between the host bone and the graft.

Pending ResultsResorbable implants should offer good

mechanical properties until incorporation of the graft has occurred.

2. Second option: Cortico-cancellous Fixation

Cortical-cancellous suspension fixation achievied with transcondylar devices seemed to offer the best results in terms of graft elongation, fixation strength and stiffness…..

G. Milano - C Fabbriciani 2006 Arthroscopy

Load resistance (N)

9799591003

0

400

800

1200

Clark 1998 (Crosspin) Brown 1998 (Transfix) Brown 1998 (Bone Mulch)

Cortico-cancellous Fixation

ACL surgery should aim for a good primary fixation and a simpler technique.Goal=to obtain a graft behavior comparable with the native ligament

Cortico-spongious distribution of load = better

Transfemoral FixationAdvantage: complete tunnel/graft contact-no

device interference.

Consequence: no tunnel enlargement

Fixation DevicesFixation

Ultimate Failure Load (N)

Stiffness (N/m)

Patellar Tendon    

Metal interference screw 558 —

Bioabsorbable interference screw (compression systems) 552 —

RigidFix (Mitek) (cortico-cancellous suspension systems) 2005

RetroButton Arthrex (cortical suspension systems) 1083

Soft Tissue (Femoral)    

EndoButton (Smith & Nephew Endoscopy, Andover, MA) 1,086 79

RigidFix (Mitek) 868 77

BioScrew (Linvatec) 589 66

RCI Screw (Smith & Nephew Endoscopy) 546 68

Soft Tissue (Tibial)    

Intrafix (Ethicon)25 1,332 223

WasherLoc (Arthrotek) 975 87

Tandem spiked washer 769 69

BioScrew 612 91

SoftSilk (Acufex Microsurgical, Mansfield, MS) 471 61

Aim of the Study Radiological and functional measurements

after anterior cruciate ligament (ACL) reconstruction with a bone-tendon-bone (BTB) graft and transfemoral fixation

Femoral Implants Investigations included assessment of bony

integration conditions regarding the use of two bioabsorbable transfemoral sistems for femoral graft fixation [TransFix (Arthrex Inc., Naples, FL) versus RigidFix (DePuy Mitek Inc, Raynham, MT).

42 mm42 mm

2.7

mm

2.7

mm

3 X 40 and 3 X 50 mm

Surgical TechniqueTranstibial guide

InstrumentationNot so simple

Demographic Data A total of 22 patients with isolated

complete anterior cruciate ligament rupture underwent arthroscopic reconstruction via two different fixation methods using patellar bone autografts. Averg. 31 years old (19-43) ,

Male:female ratio 1:1 Graft size 10mm / 30 mm-40 to 50 mm-

25 to 35 mm Cartilage injuries 10 cases (2 cases with

mozaicplasty for Outerbridge IV)

Pre-injury sport level – high risk competitive sports grade 8, 9 Tegner scale

Overall Clinical ResultsTechnique BTB Preop Lysholm Postop Lysholm IKDC

Rigidfix 57,4 94,4 A 8B 2C 2D 0

Transfix 57,3 95,4 A 7B 2C 1D 0

ResultsMRI + RX

ResultsThe femoral tunnel was almost

invisible in all patients on Xrays;

Fibrous fixation with incomplete resorbtion was noted in two Transfix cases on MRI.

Biological advantage6 m 10 y

Results

There was no significance between the two groups in terms of laxity testing at one year follow-up.

Tibial tunnel placement was physiological in 90% and femoral in 96% of the cases

ComplicationsAt surgery time, two cases of

RigidFix versus five of Transfix had intraoperative complications (incorrect placement of pins, guide wire rupture etc).

Iliotibial frictionInsufficient soft

tissues release Cossey

Arthroscopy 2006

+Intraoperative direct visualization with the scope

Pin protrusionTechnical error?

Cossey Arthroscopy 2006

Insufficient insertion

Too oblique insertion – possible slippage

Twisting nitinol wireSingle use

Yeong Seuk Lee KSSTA 2008

Pin fracture (ST)Canulated , longer device

Hard bone

– Cossey Arthroscopy 2006

Pin deformationMore in ST

than BTB

MalpositionRam Misra, Arthroscopy 2006

Even so…

IKDC score demonstrated favorable functional results (A and B class, normal – nearly normal) with no statistical connection with the intraoperative complications.

Discussion BTBClinical Evidence for Early Return to Play

Effect of early versus late return to vigorous activities on the outcome of anterior cruciate ligament reconstruction. Glasgow et al. American journal of Sports Medicine. 1993.

Effect (mean 5 months) versus late (mean 9 months) return to vigorous cutting activity on long-term outcome of anterior cruciate reconstruction was studied in 64 patients.

By clinical examination, subjective evaluation, KT 1000 there was no difference in either group.

Discussion BTB - STBiological Healing at attachment site

In the early stages the most likely place of failure will be at the fixation site in the bone tunnels. Tendon-healing in a bone tunnel: A biomechanical and

histological study in the dog. Rodeo et al. JBJS 1993.

20 adult mongrel dogs and looked for pullout strength of ST tendon fixed into a tibial tunnel drill hole similar to BTB. Found that up to 8 weeks tendon pulled from bone but after 12 weeks the graft torn midsubstance. ST Compared to BTB healing which takes on fracture healing

type characteristics = healing - typically occurs at 6 weeks. Transfemoral Fixation = circular contact graft -tunnel

Discussion BTB TF FixationConclusion = Return to Play Criteria

Return to play based on full range of motion with “good” muscle strength and muscle balance.

Can compare side to side hamstring and quad strength at least 85% compared to contralateral of quad and 100% of

hamstring

Functional testing can provide a global assessment of the ability of the knee to perform sports-related activities Can use single leg hop, timed single leg hop for 3-5 m, and the

vertical jump for functional testing (85% compared to opposite side).

ConclusionsFemoral fixation with

bioabsorbable cross-pins shows a biological bony incorporation of a patellar tendon graft.

It allows rapid rehabilitation protocols corelated to high profile sports

Thank You!