Biologic anchorage of cruciate ligament prosthesis. Bone ingrowth and fixation of the Gore-Tex ligament in sheep

Advanced Graft Development Approaches for ACL Reconstruction or Regeneration

The Anterior Cruciate Ligament (ACL) is one of the major knee ligaments, one which is greatly exposed to injuries. According to the British National Health Society, ACL tears represent around 40% of all knee injuries. The number of ACL injuries has increased rapidly over the past ten years, especially in people from 26-30 years of age. We present a brief background in currently used ACL treatment strategies with a description of surgical reconstruction techniques. According to the well-established method, the PubMed database was then analyzed to scaffold preparation methods and materials. The number of publications and clinical trials over the last almost 30 years were analyzed to determine trends in ACL graft development. Finally, we described selected ACL scaffold development publications of engineering, medical, and business interest. The systematic PubMed database analysis indicated a high interest in collagen for the purpose of ACL graft development, an increased interest in hybrid grafts, a numerical balance in the development of biodegradable and nonbiodegradable grafts, and a low number of clinical trials. The investigation of selected publications indicated that only a few suggest a real possibility of creating healthy tissue. At the same time, many of them focus on specific details and fundamental science. Grafts exhibit a wide range of mechanical properties, mostly because of polymer types and graft morphology. Moreover, most of the research ends at the in vitro stage, using non-certificated polymers, thus requiring a long time before the medical device can be placed on the market. In addition to scientific concerns, official regulations limit the immediate introduction of artificial grafts onto the market.

Synthetic Patch Rotator Cuff Repair: A 10-year Follow-Up

BACKGROUND

The present study aimed to determine the long-term outcome as a result of the use of synthetic patches as tendon substitutes to bridge massive irreparable rotator cuff defects.

METHODS

All patients who previously had a rotator cuff repair with a synthetic patch (2-mm Gore DUALMESH ePTFE patch; Gore, Flagstaff, AZ, USA; or a 2.87-mm Bard PTFE Felt pledgets; CR Bard, Warwick, RI, USA) were followed-up at a minimum of 8.5 years postoperatively. Assessment of shoulder pain, function, range of motion, strength and imaging was performed.

RESULTS

Six patients had an interpositional repair with a synthetic patch. One patient had died. In the remaining five patients, the mean tear size at repair was 27 cm(2). At 9.7 years postoperatively, all the patches remained in situ and no patient required further surgery. The repair was intact in four out of five patients. Patients had improved external rotation and abduction compared to before surgery (p < 0.02).

CONCLUSIONS

We describe the long-term outcomes of patients who had undergone synthetic patch rotator cuff repair for an irreparable rotator cuff tear. At 9.7 years postoperatively, patients reported less severe and more infrequent pain, as well as greater overall shoulder function, compared to before surgery. Patients also had increased passive external rotation and abduction. All the patches remain in situ and there have been no further operations on these shoulders.

Design Considerations for a Prosthetic Anterior Cruciate Ligament

Anterior cruciate ligament (ACL) tearing is a common knee injury often requiring reconstruction with an autograft or an allograft. A prosthetic ligament replacement with off-the-shelf availability could potentially provide significant advantages over the current options for both patients and surgeons. Limitations of previous prosthetics include lack of biocompatibility and susceptibility to fatigue, creep, and failure of bony incorporation. This paper describes design considerations and possible improvements for the next generation prosthetic ACL. Design controls, as mandated by the FDA, are a systematic set of practices within the design and development process used to ensure that a new medical device meets the needs of the intended users. The specified requirements, called the design inputs, for a prosthetic ACL are discussed pertaining to material and structural properties, resistance to creep and fatigue, ability to support secure initial fixation, biocompatibility, and long-term osseointegration. Design innovations to satisfy the design inputs are discussed with regards to material selection, textile pattern, bone tunnel features, and short term fixation. A risk analysis is presented along with descriptions of proposed testing. Design control methodology and tissue engineering may be used to develop a next generation prosthetic ligament, solving multiple problems, simultaneously, on a holistic level, providing major improvements over earlier devices and current treatment options.

Augmentation of bone tunnel healing in anterior cruciate ligament grafts: application of calcium phosphates and other materials

Bone tunnel healing is an important consideration after anterior cruciate ligament (ACL) replacement surgery. Recently, a variety of materials have been proposed for improving this healing process, including autologous bone tissue, cells, artificial proteins, and calcium salts. Amongst these materials are calcium phosphates (CaPs), which are known for their biocompatibility and are widely commercially available. As with the majority of the materials investigated, CaPs have been shown to advance the healing of bone tunnel tissue in animal studies. Mechanical testing shows fixation strengths to be improved, particularly by the application of CaP-based cement in the bone tunnel. Significantly, CaP-based cements have been shown to produce improvements comparable to those induced by potentially more complex treatments such as biologics (including fibronectin and chitin) and cultured cells. Further investigation of CaP-based treatment in the bone tunnels during ACL replacement is therefore warranted in order to establish what improvements in healing and resulting clinical benefits may be achieved through its application.

Fiber-based tissue-engineered scaffold for ligament replacement: design considerations and in vitro evaluation

The anterior cruciate ligament (ACL) is the major intraarticular ligamentous structure of the knee, which functions as a joint stabilizer. It is the most commonly injured ligament of the knee, with over 150,000 ACL surgeries performed annually in the United States. Due to limitations associated with current grafts for ACL reconstruction, there is a significant demand for alternative graft systems. We report here the development of a biodegradable, tissue-engineered ACL graft. Several design parameters including construct architecture, porosity, degradability, and cell source were examined. This graft system is based on polymeric fibers of polylactide-co-glycolide 10:90, and it was fabricated using a novel, three-dimensional braiding technology. The resultant micro-porous scaffold exhibited optimal pore diameters (175-233 microm) for ligament tissue ingrowth, and initial mechanical properties of the construct approximate those of the native ligament.

Surface roughness of ceramic femoral heads after in vivo transfer of metal: correlation to polyethylene wear

BACKGROUND

A dark metallic-appearing smear, resembling a lead pencil mark, may be seen on a ceramic femoral head component at revision total hip arthroplasty. The purpose of this study was to investigate the hypothesis that such a mark on a retrieved ceramic femoral head is associated with increased surface roughness of the head and increased polyethylene liner wear in total hip replacement.

METHODS

Fifteen ceramic prosthetic femoral heads retrieved from fifteen patients at revision arthroplasty were examined in this study. Thirteen heads had been in vivo for an average of 10.8 years (range, 7.8 to 14.2 years). The remaining two heads had been in vivo for less than one month. The surface roughness characteristics of the explanted ceramic heads, the linear wear of the polyethylene liner, and the patient activity levels after the primary replacement and before the revision were determined.

RESULTS

Four of the thirteen ceramic heads that had been in vivo for >/=7.8 years had severe smears (>6% of the surface area), and the remaining nine heads had slight smears (<6% of the surface area). The two heads that had been in vivo less than one month had severe smears. The mean Ra and Rpm, the values for surface roughness, were 44.95 nm and 571.15 nm, respectively, in the hips with slightly smeared regions and 180.77 nm and 1245.88 nm, respectively, in the hips with severely smeared regions (p = 0.002). The mean linear liner wear rate was 0.10 mm/yr in the hips with slightly smeared heads and 0.19 mm/yr in the hips with severely smeared heads (p = 0.002). The activity score for all patients was 5 or 6 points on a 6-point scale.

CONCLUSIONS

The results of this study confirm the hypothesis that a visual dark metallic-appearing smear on a ceramic femoral head correlates with increased surface roughness of the head and increased polyethylene wear. These findings imply that contact of a ceramic femoral head with a metallic material, such as may occur with femoral head reduction or dislocation of a total hip replacement, is best avoided to prevent this metallic smear phenomenon.

Anterior cruciate ligament regeneration using braided biodegradable scaffolds: in vitro optimization studies

The anterior cruciate ligament (ACL) is the most commonly injured intra-articular ligament of the knee, and limitations in existing reconstruction grafts have prompted an interest in tissue engineered solutions. Previously, we reported on a tissue-engineered ACL scaffold fabricated using a novel, three-dimensional braiding technology. A critical factor in determining cellular response to such a graft is material selection. The objective of this in vitro study was to optimize the braided scaffold, focusing on material composition and the identification of an appropriate polymer. The selection criteria are based on cellular response, construct degradation, and the associated mechanical properties. Three compositions of poly-alpha-hydroxyester fibers, namely polyglycolic acid (PGA), poly-L-lactic acid (PLLA), and polylactic-co-glycolic acid 82:18 (PLAGA) were examined. The effects of polymer composition on scaffold mechanical properties and degradation were evaluated in physiologically relevant solutions. Prior to culturing with primary rabbit ACL cells, scaffolds were pre-coated with fibronectin (Fn, PGA-Fn, PLAGA-Fn, PLLA-Fn), an important protein which is upregulated during ligament healing. Cell attachment and growth were examined as a function of time and polymer composition. While PGA scaffolds measured the highest tensile strength followed by PLLA and PLAGA, its rapid degradation in vitro resulted in matrix disruption and cell death over time. PLLA-based scaffolds maintained their structural integrity and exhibited superior mechanical properties over time. The response of ACL cells was found to be dependent on polymer composition, with the highest cell number measured on PLLA-Fn scaffolds. Surface modification of polymer scaffolds with Fn improved cell attachment efficiency and effected the long-term matrix production by ACL cells on PLLA and PLAGA scaffolds. Therefore based on the overall cellular response and its temporal mechanical and degradation properties in vitro, the PLLA braided scaffold pre-coated with Fn was found to be the most suitable substrate for ACL tissue engineering.

Augmentation with a Gore-Tex patch for repair of large rotator cuff tears that cannot be sutured

The objective of this study was to determine the effectiveness of augmentation with a Gore-Tex patch in reconstruction of rotator cuff tears that cannot be repaired by direct suture. Twenty-eight shoulders of 27 patients underwent this procedure. The average age at surgery was 62 years, the average duration of symptoms before surgery was 16 months, and the average follow-up period was 44 months. The shoulders were classified into two groups according to patch size (anteroposterior dimension up to 2 cm or greater than 2 cm). The clinical outcome was evaluated by using the shoulder surgery classification system issued by the Japanese Orthopaedic Association (JOA score), and the postoperative isometric abduction strength at 90 degrees of abduction was assessed by the method of Constant. The average total JOA score improved from 57.7 to 88.7 points, a statistically significant change. There was no difference in the improvement in score between shoulders treated with small patches (12 shoulders) and those treated with large patches (16 shoulders). The average abduction strength was 6.2 kg in the small-patch group and 1.5 kg in the large-patch group, with a statistically significant difference between the two groups. Good clinical results, especially pain relief, could be achieved with this procedure in both the small- and the large-patch groups, but good abduction strength was obtained only in the small-patch group. The mechanism of the improvement by this procedure is still controversial.

No bone ingrowth into the tibia tunnel in anterior cruciate ligament-reconstructed patients: a 1-year prospective quantified CT study of 10 patients reconstructed with an autologous bone-patellar tendon-bone graft

10 patients with major instability symptoms due to an acute anterior cruciate ligament injury were operated on with a bone-patellar tendon-bone reconstruction. Tibial condyle bone mineral density (BMD), bone ingrowth and changes in diameter in the tibia bone tunnel were studied with quantified computed tomography (QCT) postoperatively and after 1, 3, 6 and 12 months. We found no sign of bone ingrowth in the form of increased bone mineral density (BMD) in the bone tunnels in any of the patients. The tunnel diameter increased in all patients during the first postoperative months. After 1 year, 5 patients had a smaller diameter than at the first postoperative examination, 2 had the same diameter as immediately after surgery and 2 patients had a larger diameter. A sclerotic zone developed in all patients along the perimeter of the tunnel during the 3-6 months of follow-up. The BMD in the tibial condyle decreased at 3 months; it then increased, but between 6 and 12 months, it levelled out and was slightly lower than postoperatively. In conclusion, we found no growth of bone into the tunnel and tendinous part of the graft during the first postoperative year.

Mechanical properties of medical grade expanded polytetrafluoroethylene: the effects of internodal distance, density, and displacement rate

Expanded polytetrafluoroethylene (e-PTFE) is used successfully in a multitude of biomedical and clinical applications. The success of this biomaterial is due to its microporous structure that allows biointegration for fixation, as well as overall mechanical integrity. The mechanical properties and degree of tissue ingrowth depend on the microstructure of the expanded polymer foam, yet little is known about the correlation of the internodal distance and other microstructural features with the monotonic tensile properties. Complete structure-property correlation can be used to provide invaluable knowledge for the design of biomedical devices. The purpose of this study was to investigate the monotonic tensile properties of e-PTFE over a range of medically relevant microstructural features and manufacturing parameters. The microstructural and manufacturing parameters considered were internodal distance, linear density, volumetric density, and reduction ratio. Additionally, the effect of displacement rate on mechanical properties was studied. We found that the ultimate stress and strain increased linearly with linear density (R2 = 0.88 and 0.67, respectively). Surprisingly, elastic modulus did not correlate with any parameter measured and only weak correlations were found between all properties and internodal distance. The yield and ultimate stresses increased with increasing displacement rate (R2 = 0.88 and 0.57, respectively). The findings from this study indicate that linear density is a better predictor of mechanical properties than internodal distance and may be the preferred parameter to control when specifying a material for implantation in load bearing situations.

The surgical anatomy of the stifle joint in sheep

OBJECTIVE

To provide a detailed description of the surgical anatomy of the stifle joint in sheep.

STUDY DESIGN

The results from analysis of cadaveric dissections (14 stifle joints) and stifle radiographs (8 sets of mediolateral and craniocaudal radiographs) are presented.

ANIMALS

Skeletally mature ewes of mixed breeds.

CONCLUSIONS

Although the anatomy of the ovine stifle joint is similar to that of the human knee joint, a number of unique features were identified. These included the presence of the tendon of the m. extensor digitorum longus on the craniolateral aspect of the stifle joint, the absence of a cranial meniscofemoral ligament (ligament of Humphrey) in the caudal joint space, and attachment of the patellar tendon to the cranial pole of the patella (rather than to the distal pole, as in humans). The implications of these differences are discussed with reference to the suitability of the ovine stifle as a surgical model for the human knee joint.