Augmented Grafts: Synthetic/Allograft/Autograft

Abstract

Still a lot of controversies and unsolved problems are in the focus for reaching an optimal treatment of the ruptured Anterior Cruciate Ligament. Historically there has been a long search for solutions in the acute repair as well as for an anatomic reconstruction. In this chapter an overview of the development in the acute repair initially recommended by Palmer and O’Donoghue. Long term results reported by Feagan,Lysholm and others showed unacceptable results in 30-50%. Augmentation of the repair by adding autologous tissues like fascia lata strips, hamstrings tendons,ilieotibal band or medial longitudinal retinaculum improved the results but increased the extent of open surgery. Shelbourne recommended instead of acute repair a late arthroscopic reconstruction and showed less arthrofibrosis and better ROM.

In the struggle to improve the ACL reconstruction different autografts, allografts and synthetic prosthesis have been tried with varying results. More anatomic reconstruction with double bundle autografts with more anatomic placement have not so far proven superiority to single bundle grafts.The weakness of the avascular auto- and allografts is the necrosis and the reduced strength during the long processes of revascularization,tissue resrption,cell migration,new matrix production and maturation ending up in ligamentization over 12 months or more. The use of non degradable synthetics has not been of any benefit as augmentation or prosthesis and most of them are taken off the market.(LAD,Gore-Tex,Leeds Keio,Dacron.LARS,carbon fiber.) Degradable grafts (polydioxanone(PDS),polycaprolacton(PCL) with anatomic design and biomechanical characteristics of ACL may in the future be an option?

In the search for optimal treatment the acute repair of the ACL may be reconsidered in the adolescent and young athletes where periosteal and bony avulsions are frequent. An optimal anatomy would be preserved by reinsertion and with a degradable augmentation. Maybe an artificial ACL with fibroblasts grown and exerted and adapted to physical stimuli in a biologic chamber will be a future solution. To achieve this the surgeons must participate in a multidisciplinary network of researchers in basic sciences; biomaterials, cell biology and biomechanics.

Keywords

ACL, acute repair, allograft, anatomic, autograft, degradabe, double double, grafts, late reconstruction, non-degradable, single bundle, synthetic, triple bundle

Keywords

ACL, acute repair, allograft, anatomic, autograft, degradabe, double double, grafts, late reconstruction, non-degradable, single bundle, synthetic, triple bundle

Introduction

The anterior cruciate ligament (ACL) is the primary and most important stabilizer of the knee joint. Rupture of the ACL is the most common serious ligament injury, and untreated or in spite of conservative treatment, it may progress into posttraumatic osteoarthritis accelerated by strenuous sports like football, long-distance running, and so on. After surgical treatment with acute repair alone of ACL ruptures, and after chronic instability with late ACL reconstruction (iliotibial band), most actual techniques using autografts like the central third of the patellar tendon or multiple loops of the hamstring tendons, iliotibial band, quadriceps tendon, and so on still result in many patients having unsatisfactory short- or long-term outcomes. Remaining rotatory instability and progressive anterior laxity and clinical instability, along with pain and donor site morbidity, an increasing number of re-ruptures, and meniscus and articular cartilage lesions, have caused reoperations in 30% of cases and late posttraumatic osteoarthritis in football players in 50% of cases. These insufficient treatments have resulted in a continued search for better surgical treatments to reproduce the anatomic functional structure of ACL and improve the mechanical properties and strength of the graft materials. Looking for new ways has lead to the use of autografts, allografts, and synthetic materials historically as an augmentation in acute repair of ACL, and as an augmentation or as a prosthesis in early or late reconstructions of ACL.

Autograft Augmentation of Acute Repair of Anterior Cruciate Ligament

Palmer in his 1938 thesis and O’Donoghue recommended acute repair in the treatment of ACL, and for a period this was done all over the world but with about 30%–50% unacceptable results according to Feagin, Lysholm and Gillquist, and Odensten et al. Augmentation of the acute repair was mostly done with a fascia lata strip, iliotibial tract, semitendinosus, gracilis tendons, or medial longitudinal retinaculum to provide increased strength and protection during healing. They reported improved long-term results in up to 90% of cases. Shelbourne et al. found less arthrofibrosis and stiffness, and better range of motion and muscle function with training in the acute phase instead of performing acute repair. He thus advocated the use of delayed primary ACL reconstruction at 6–8 weeks as a planned elective procedure, making it also easier to plan the surgical program and gain OR time as well as improved results.

Autografts, Allografts, and Synthetics for Anterior Cruciate Ligament Reconstruction

The most common autografts used in early and late ACL reconstructions by arthroscopic techniques are the central third of the patellar tendon with adjacent bone included, multiple loops of the hamstrings tendons, iliotibial tract, and the quadriceps tendon. These avascular grafts are all undergoing necrosis followed by revascularization, cellular invasion, resorption with phagocytosis of necrotic tissue, and migrating fibroblasts for matrix production with type I collagen to restore the ligament structures and the mechanical properties like strength and elasticity. This ligamentization process takes about 12 months to reach maturation and restored functional capacity. However, the reconstruction of the functional anatomic structures of ACL by using single-bundle grafts has not been achieved, as no actual autografts or allografts are restoring the structure of a normal ACL, and neither has going from single bundle to double bundles (anteromedial and posterolateral). Precise positioning of the graft fixation in anatomical footprints in the bone is still not achieved, but perhaps a triple-bundle design including the intermediate bundle could come closer to anatomic function. The augmentation of autografts and allografts using nondegradable synthetic devices as well as nondegradable synthetic prosthesis has been researched and tried over 100 years with disappointing results (silver wire, silk sutures, ligament augmentation device (LAD), Gore-Tex, Leeds Keio, Dacron, ligament advanced reinforcement system (LARS) carbon fiber) and high complication rates. However, so far neither techniques nor synthetic designs have come close to the normal anatomy to adequately restore the lifetime function of the ACL. Consequently most of the nondegradable synthetic devices have been taken off the market (see Chapter 18 ).

Nondegradable Biologic Graft (Xenograft)

Xenograft from a bovine foot extensor tendon with stabilization of the collagens by paraldehyde was used as a permanent prosthesis, not undergoing any remodeling with short-term promising results, but only 50% had an acceptable end result. However, over time re-ruptures due to fatigue and fragmentation caused serious inflammation; synovial thickening and instability were frequent and required reoperations. Thus xenograft should not be used.

Degradable Synthetic Devices for Anterior Cruciate Ligament Augmentation or Prosthesis

The high failure rate of nondegradable augmentation devices and prostheses has increased the interest in degradable materials. For tissue repair and tissue regeneration in the musculoskeletal system, the use of degradable-resorbable devices for temporary support of the tissue repair area over time is necessary until functional tissue healing has been achieved. Besides being a mechanical support, the device should be porous to allow revascularization and cellular ingrowth. Devices being slowly degradable will allow tensional forces to act on the cellular production of the matrix, adapting to the increasing loading of the graft over the healing period to mature tissue. This may be achieved if the device is able to recapture its original length after loading, being more elastic and not too stiff in mimicking the biomechanical characteristics of the human ACL.

Polydioxanone

Among the first synthetic materials used for degradable devices was polydioxanone (PDS). It was used as an augmentation to support the acute repair of ACL or the autograft ACL. The high stiffness of the PDS led to stress-shielding phenomena by unloading the autograft from tensional stimulation of the fibroblasts. The degradation/resorption of the PDS band is achieved by hydrolysis, and the time to reduce its strength by 50% is 2 months. This time period is too short to protect the healing phase of the repair or the graft over the rehabilitation phase and during return to sport.

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