Serial magnetic resonance imaging evaluation of operative site after fixation of patellar tendon graft with bioabsorbable interference screws in anterior cruciate ligament reconstruction

Evaluation of the in vitro cytotoxicity and modulation of the inflammatory response by the bioresorbable polymers poly(D,L-lactide-co-glycolide) and poly(L-lactide-co-glycolide)

Bioresorbable polymers composed of poly(D,L-lactide-co-glycolide) (PDLLGA) and poly(L-lactide-co-glycolide) (PLLGA) have become increasingly popular for the preparation of bone substitute constructs. However, there are reports of a delayed inflammatory reaction occurring months or years after implantation. Due to the long polymer degradation times, in vitro tests carried out at physiological temperature, 37°C, tend to assess only the short-term biocompatibility of these materials. The aim of this work is to develop an in vitro protocol that can be used to assess the long-term cytotoxicity of bioresorbable polymers in a time efficient manner. This study used a previously developed and validated accelerated degradation protocol to obtain samples of PDLLGA and PLLGA at increasing levels of degradation. Samples were then applied to standard ISO 10993-5 direct contact cytotoxicity testing and it was found that PDLLGA samples showed increasing levels of cytotoxicity at the later stages of degradation, with PLLGA samples demonstrating significantly less cytotoxic behaviour. Following concern that accumulation of acidic degradation products in a closed multi-well culture environment could overestimate cytotoxicity, we developed and validated a new dynamic flow culture methodology, for testing the cytotoxicity of these degradable materials, by adapting a commercial "organ on a chip" flow culture system, Quasi Vivo®. In addition to cytotoxicity testing, we have carried out profiling of inflammatory cytokines released by cells in response to degraded PDLLGA and PLLGA, and have suggested mechanism by which lactide-based bioresorbable materials could modulate the inflammatory response through the G-protein coupled receptor (GPCR), hydroxycarboxylic acid receptor 1 (HCA₁). STATEMENT OF SIGNIFICANCE: Bioresorbable materials naturally disintegrate over time when implanted into the body. They are often used to make screws and clips for repair of broken bones. Unfortunately, some patients can react badly to the material, resulting in painful inflammation. Biomaterials scientists are interested in developing materials that are more compatible with the body. However, it is very difficult to predict the long-term compatibility of bioresorbable materials in the lab. In our study, we have developed a method that will allow us to study the effects of the materials as they continue to break down. This will help us understand why the materials may cause inflammation, and will support research into the development of new and improved materials for bone repair.

Rehabilitation of Tibial Plateau Fracture Following Anterior Cruciate Ligament Reconstruction: A Case Report

Objective

The purpose of this case report was to describe the management of a tibial plateau fracture in a patient who had undergone anterior cruciate ligament (ACL) reconstruction 3.5 years earlier.

Clinical Features

A 36-year-old man presented with pain and edema following a fall from a height of approximately 2 m while skateboarding. The patient reported having undergone arthroscopic ACL reconstruction with allograft and bioabsorbable screws 3.5 years earlier. Computed tomography scan revealed a comminuted fracture extending through the graft tunnel, as well as evidence of tunnel widening and incomplete bone resorption and generation within the tibial tunnel.

Intervention and Outcome

A trauma surgeon repaired the plateau fracture with internal fixation. The patient was non-weight bearing for 8 weeks while undergoing rehabilitation in a chiropractic clinic (spinal manipulation, physiotherapy, nutritional support) twice per week and returned to full activity within 3 months.

Conclusions

The patient responded favorably to the treatment protocol, which included rehabilitation by a doctor of chiropractic and co-management with a trauma surgeon.

Paradoxical tunnel enlargement after ACL reconstruction with hamstring autografts when using β-TCP containing interference screws for tibial aperture fixation- prospectively comparative study

BACKGROUND

Tibial aperture fixation with a bioabsorbable interference screw is a popular fixation method in anterior cruciate ligament reconstruction (ACLR). An interference screw containing β-tricalcium phosphate (β-TCP) to improve bony integration and biocompatibility was recently introduced. This study aims to compare the clinical outcomes and radiological results of tunnel enlargement effect between the 2 bioabsorbable fixative devices of pure poly-L-lactic acid (PLLA) interference screws and β-TCP-containing screws, for tibial interference fixation in ACLR using hamstring autografts.

METHODS

Eighty consecutive patients who had undergone double-bundle ACLR between 2011 to 2012 were prospectively reviewed and randomly divided into two groups based on the type of tibial interference screw: 28 were assigned to the pure PLLA screw group (Group A), while the other 29 were assigned to the β-TCP-containing screw fixation group (Group B). Clinical evaluations and radiological analyses were conducted in both groups with a minimum 2- year follow-up.

RESULTS

There was no significant difference in subjective or objective clinical outcome between the 2 groups. In radiological analyses, the use of a β-TCP-containing screw reduced tunnel widening in the portion of the tunnel with screw engagement compared to the pure PLLA screw, while the use of a β-TCP-containing screw resulted in greater tunnel enlargement in the proximal portion of the tunnel without screw engagement than use of a pure PLLA screw.

CONCLUSION

Use of a β-TCP-containing interference screw in tibial aperture fixation reduced tunnel enlargement in the vicinity of the screw, whereas greater enlargement occurred proximal to the screw end relative to use of a pure PLLA interference screw. These paradoxical enlargements in use of β-TCP containing screws suggest that for reducing tunnel enlargement, the length of the interference screw should be as fit as possible with tunnel length in terms of using soft grafts.

LEVEL OF EVIDENCE

II, Prospectively comparative study.

TRIAL REGISTRATION

Retrospectively registered with ClinicalTrials.gov. (NCT02754674) , Date of trial registration: February 10, 2016.

Comparison of Poly-L-Lactic Acid and Poly-L-Lactic Acid/Hydroxyapatite Bioabsorbable Screws for Tibial Fixation in ACL Reconstruction: Clinical and Magnetic Resonance Imaging Results

Background

The purpose of this study was to compare the clinical and radiological results of 2 different tibial fixations performed using bioabsorbable screws with added hydroxyapatite (HA) and pure poly-L-lactic acid (PLLA) screws in anterior cruciate ligament (ACL) reconstruction.

Methods

A total of 394 patients who underwent arthroscopic ACL reconstruction between March 2009 and June 2012 were retrospectively reviewed. Of those, 172 patients who took the radiological and clinical evaluations at more than 2 years after surgery were enrolled and divided into 2 groups: PLLA group (n = 86) and PLLA-HA group (n = 86). Both groups were assessed by means of the Lysholm score, International Knee Documentation Committee (IKDC) subjective knee score, and Tegner activity score. Stability was evaluated using the KT-2000 arthrometer. Magnetic resonance imaging was performed to evaluate tibial tunnel widening, screw resorption, osteoingeration, and foreign body reactions.

Results

The PLLA-HA group showed significant reduction in the extent of tibial tunnel widening and foreign body reactions and significant increase in screw resorption compared to the pure PLLA group (p < 0.001 for both). In contrast, postoperative Lysholm score, Tegner activity score, IKDC score, and side-to-side difference on the KT-2000 arthrometer showed no significant differences between groups (p = 0.478, p = 0.906, p = 0.362, and p = 0.078, respectively). The PLLA group showed more significant widening in the proximal tibial tunnel than the PLLA-HA group (p = 0.001). In the correlation analysis, proximal tibial tunnel widening revealed a positive correlation with knee laxity (r = 0.866) and a negative correlation with Lysholm score (r = −0.753) (p < 0.01 for both).

Conclusions

The HA added PLLA screws would be advantageous for tibial graft fixation by reducing tibial tunnel widening, improving osteointegration, and lowering foreign body reactions. Even though no clinically significant differences were noted between the pure PLLA group and PLLA-HA group, widening of the proximal area of the tibial tunnel showed a tendency to increase knee laxity measured using the KT-2000 arthrometer.

Biodegradable Materials: Anchors and Interference Screws

Biodegradable implants allow clarity in postoperative imaging, easier revision, and fewer concerns about associated tissue damage. It is important to appreciate that different biodegradable materials have different properties and different degradation rates. Faster degradation can be associated with a greater inflammatory response. However, inflammation is a normal part of the degradation process. The concern arises when the inflammation is clinically significant.

The Natural History of Biointerference Screw Cyst and New Bone Formation in Anterior Cruciate Ligament Reconstruction: 16-Year Follow-up

BACKGROUND

A variety of fixation devices are available for anterior cruciate ligament reconstruction (ACLR). Bioabsorbable screws allow imaging postoperatively without image artefact, as with magnetic resonance imaging (MRI). There is also the perceived benefit of screw resorption and subsequent host tunnel bone ingrowth.

PURPOSE/HYPOTHESIS

The purpose of this study was to document the natural history of poly L-lactic acid (PLLA) bioabsorbable interference screws. Manufacturers claimed that screws would be resorbed and replaced by new bone within 2 years. The hypothesis was that these screws take considerably longer to achieve this claim.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Ten consecutive patients undergoing routine ACLR with a PLLA bioabsorbable RCI screw (Arthrex) and a standard 4-strand hamstring graft technique were assessed via MRI and telephone questionnaire at 1, 2, 4, 7, 10, and 16 years postoperatively.

RESULTS

At 4-year follow-up, no resorption of the screw or bone formation had occurred. At 7-year follow-up, absorption of 7 screws was complete, cyst formation had occurred in 3 patients, and 5 patients had new bone formation. At 10-year follow-up, all screws were reabsorbed, cyst formation was evident in only 2 cases, and 7 patients had evidence of new bone formation. At 16-year follow-up, cyst formation was only present in 1 patient, and all patients had evidence of new bone formation. All patients had an intact anterior cruciate ligament and had returned to preinjury sporting activity.

CONCLUSION

PLLA bioabsorbable screws take longer to resorb than previously thought by the manufacturers (ie, 2 years). New bone formation is evident in 100% of patients by 16 years. Cyst formation does not occur in all patients with a bioabsorbable screw implant. In the 3 patients demonstrating the presence of a cyst, no associated adverse effects were found with regard to anterior cruciate ligament graft survival or instability.

Induction of bone ingrowth with a micropore bioabsorbable suture anchor in rotator cuff tear: an experimental study in a rabbit model

BACKGROUND

The bioabsorbable suture anchor is probably one of the most commonly used tools in arthroscopic shoulder operations. However, there is controversy about whether the bioabsorbable anchor is replaced by bone. The object of this study is to evaluate bone ingrowth into the micropore bioabsorbable suture anchor and the differences in the biomechanical properties of a micropore anchor and a nonpore anchor.

MATERIALS AND METHODS

A total of 16 microsized holes (diameter, 250 ± 50 μm; depth, 0.2 mm) were made on the bioabsorbable anchors with a microdrill. Twelve adult New Zealand White rabbits were randomly divided into two groups: group A (n = 6), the nonpore bioabsorbable suture anchor group, and group pA (n = 6), the micropore bioabsorbable suture anchor group. Microcomputed tomography was used at 4 and 8 weeks postoperatively to evaluate ingrowth by bone volume fraction (BVF), which was measured by calculating the ratio of the total volume of bone ingrowth to that of the region of interest. For pullout strength testing, 3 additional rabbits (6 limbs) were used for mechanical testing.

RESULTS

The mean BVF was higher in group pA (0.288 ± 0.054) than in group A (0.097 ± 0.006). The micropore anchor had a higher pullout strength (0.520 ± 0.294 N) than the nonpore anchor (0.275 ± 0.064 N).

CONCLUSION

Micropore bioabsorbable suture anchors induced bone ingrowth and showed higher pullout strength, despite processing.

In vivo degradation characteristics of bioabsorbable cross-pins in anterior cruciate ligament reconstruction

BACKGROUND

We evaluated degradation of bioabsorbable femoral cross-pins following anterior cruciate ligament (ACL) reconstruction.

METHODS

Four patients underwent ACL reconstruction using hamstring autograft with femoral fixation provided by a polylactic acid/polyglycolic acid copolymer (LactoSorb L15) cross-pin. Serial computed tomography (CT) scans were performed of the reconstructed knees at approximately 6 weeks, 4 months, 1 year and 2 years, postoperatively. A radiologist evaluated the scans for density of pins and surrounding bone and pin morphology.

RESULTS

The cross-pins demonstrated a relative reduction in density of 7.7%, 49.1%, and 75.0% at 4 months, 1 year and 2 years, respectively. Bone density values adjacent to the pin decreased by an mean of 8.6% between 6 weeks and 4 months. At one year an additional 14.2% reduction in bone density was seen but at 2 years the relative reduction in bone density had decreased to 7.4%. Evaluation of pin morphology revealed that minimal change had occurred after 6 weeks. At 4 months all of the pins were showing some morphologic changes on the surface, but none had fractured. After 1 year, two of the pins had fractured. By 2 years all of the pins had fractured. None of the pins had completely reabsorbed at 2 years postoperatively.

CONCLUSIONS

LactoSorb L15 cross-pins for femoral fixation in ACL reconstruction remain largely unchanged 4 months postoperatively, suggesting that this device maintains the necessary structural integrity to allow early integration of soft tissue grafts within bone tunnels.

LEVEL OF EVIDENCE

IV, case series.

Migration of "bioabsorbable" screws in ACL repair. How much do we know? A systematic review

PURPOSE

Although bioabsorbable screws promise to degrade within months up to several years after implantation, often this does not happen. In fact, other problems such as screw breakage, tunnel enlargement, allergic or foreign body reactions, cyst or abscess formation, and delayed migration of "biodegradable" screws have been reported. This study aims to provide relevant basic science knowledge and recent insights concerning "biomaterials" currently used in fixation devices for anterior cruciate ligament (ACL) repair. A systematic review on the topic of screw "migration" is provided.

METHODS

A PubMed search combining all the key terms was done looking for complications related to late migration of "bioabsorbable" screws used in ACL reconstruction without inferior time limitation up to January 2012. Only clinical reports were included. Reference lists of reports were checked to detect others not identified by the original search. A pre-publication search was performed to identify the most recent relevant articles.

RESULTS

A total of ten articles referred to migration of "bioabsorbable" interference screws. Most cases reported on poly-L-lactic acid-based screws. Migration was noticed between 3 and 22 months postoperatively. It was noticed both in the tibia and the femur and with the application of several types of graft.

CONCLUSION

Migration is a possible complication of "bioabsorbable" interference screws. The information related to all clinical implications of the so-called "biodegradable screws" remains scarce and probably suffers from the phenomenon of publication bias. The complexity of possible reactions occurring in the human body is difficult to reproduce under controlled laboratory conditions.

Bio-interference screw cyst formation in anterior cruciate ligament reconstruction--10-year follow up

PURPOSE

This study used serial MRI to assess the absorption of a poly l-lactide Bioabsorbable interference screw used in the anterior cruciate ligament reconstruction with a 4-strand hamstring technique.

METHODS

A consecutive series of ten patients undergoing anterior cruciate ligament reconstruction a 4-strand hamstring technique were assessed with magnetic resonance imaging (MRI) scans at 1, 2, 4, 7 and 10 years postoperatively.

RESULTS

No resorption had occurred after 4 years in any of the patients. By 7 years screw absorption was complete in seven patients and had progressed in three. New cyst formation occurred in 3 patients between 5 and 7 years. Half the patients displayed small fluid collections within the tibial tunnels. At 10 years all screws were fully absorbed; however cyst formation was common, including the development of a new cyst in the period between 7 and 10 years in one patient. None of the patients had instability, persistent effusions, or clinically detectable adverse reactions to the screws.

CONCLUSIONS

This study has shown that poly l-lactide bioabsorbable screws take longer to resorb than initial in vitro data suggested. It is unclear whether ganglion formation within the tibial tunnel is related to screw resorption or the hamstring graft. The theoretical advantages of bioabsorbable screws must be weighed against these findings.

Graft fixation alternatives in anterior cruciate ligament reconstruction

Reconstruction of the anterior cruciate ligament is a frequently performed procedure that has had outstanding results. Outcomes are dependent upon an early postoperative physical therapy program that stresses early motion. Early rehabilitation demands rigid intraoperative mechanical fixation of the graft since therapy begins before biologic incorporation of the graft in the bone tunnels. Regardless of the graft substitute chosen, many methods of fixation are available. The best fixation technique depends on several factors, including graft choice and surgeon comfort. The figures are not documented in this paper. We review current methods available for graft fixation in anterior cruciate ligament surgery.

Osteoconductive properties of poly(96L/4D-lactide)/beta-tricalcium phosphate in long term animal model

The objective of this study was to determine the effect of calcium phosphate mineral content on the bone in-growth at the expense of composite of co-polylactide polymer charged with 2 different ratios of β-TCP granules (10 and 24 w-% of β-TCP). The evaluation was realized in a long term rabbit bone model. After 24, 48 and 76 weeks, the implants were examined by micro CT, scanning electron microscopy (SEM) using backscattered electron (BSE) and light microscopy (polarized and blue light microscopy). No foreign body reaction was detected during the 76 weeks follow-up in any of the test samples. Polymer hydrolysis began at approximately 24 weeks, by 76 weeks, the pure polymer implant had begun to release P(96L/4D)LA particles and show signs of peripheral localized bone resorption. A decrease in the amount of CaP was noticed between 24 and 76 weeks in both 10 wt-% and 24 wt-% β-TCP/P(96L/4D)LA composites. The study showed that the highest bone in-growth was with 24 wt-% β-TCP/P(96L/4D)LA composite. Bone in-growth and mineralization were evident for the composites associated with specific peripheral bone architecture. Fluorescent labelling demonstrated high bone in-growth and remodeling at the interface, while for pure co-polymer no bone remodeling or bone activity was maintained after 48 weeks. The study demonstrated the positive effect of calcium phosphate content into P(96L/4D)LA. This kind of composite is a suitable resorbable osteoconductive matrix, which provides long term stability required for ligament fixation device.

A clinical review of bioabsorbable interference screws and their adverse effects in anterior cruciate ligament reconstruction surgery

Bioabsorbable material screws are widely used in various surgical specialties. One popular application is their use as interference screws in anterior cruciate ligament (ACL) reconstruction surgery. Despite their routine use, a major concern with bioabsorbable materials in surgery has been the incidence of adverse events. Various case reports, series reports and studies in the past years have reported complications specific to the use of bioabsorbable interference screws intra operatively and at different time periods post operatively. The aim of this literature review is to summarize the clinical studies where bioabsorbable screws have been used in ACL reconstruction surgery and in particular to highlight any specific complications and adverse effects related to the use of these materials.

Comparison of the bioabsorbable and metal screw fixation after ACL reconstruction with a hamstring autograft in MRI and clinical outcome: a prospective randomized study

There has never been an MRI study of tunnel widening comparing bioabsorbable to metal screw fixation in autologous hamstring anterior cruciate ligament (ACL) reconstruction. We randomized 62 patients to hamstring ACL reconstruction with either a bioabsorbable (n=31) or metal screw (n=31) fixation. The evaluation methods were clinical examination, KT-1000 arthrometric measurement, the International Knee Documentation Committee and Lysholm scores, and MRI. There were no differences between the groups preoperatively. Fifty-five patients (89%) were available at a minimum of 2-year follow-up (range 24-36 months). There was tunnel widening in both groups, but the increase was significantly greater in the AP dimension of the femoral tunnel in the bioabsorbable screw group compared to metal group (P=0.01). The tibial tunnels showed no intergroup difference. Ninety-four percent of the knees were normal or nearly normal according to the IKDC scores and the average Lysholm score was 91 with no intergroup difference. The follow-up AP tibial tunnel diameter was smaller with normal knee laxity compared to abnormal knee laxity. The graft failure rate in the bioabsorbable screw group was 23% (7/31 patients) and 6% (2/31 patients) in the metal screw group. The use of bioabsorbable screws resulted in more femoral tunnel widening, and more graft failures compared to metal screws. The tunnel widening in the tibia was associated with the knee laxity (P=0.02).

MRI evaluation of the tibial tunnel/screw/tendon interface after ACL reconstruction using a bioabsorbable interference screw

This article describes the complex relationship between graft, bone, and biologic interference screw. Orthopedic surgeons have just begun to understand this complex biologic relationship. Clinical outcome measurements tell very little about the biology in bone tunnels.

Sterile pretibial abscess after anterior cruciate reconstruction from bioabsorbable interference screws: a report of 2 cases

We report 2 cases of extra-articular pretibial sterile abscesses with minimal osteolysis after anterior cruciate ligament reconstruction with poly-L-lactic acid bioabsorbable interference screw fixation. No joint involvement was evident in either case. Both patients underwent surgical exploration for incision, drainage, and excision with debridement of the biodegradable screw debris from the tibial bone tunnel. The cystic area in case 1 contained 8 mL of chalky white fluid with fragments of particulate matter. Microscopic evaluation revealed birefringent foreign material in a benign histiocyte-lined cyst. We encountered 20 mL of chalky white material during surgical debridement in case 2. Intraoperative cultures and Gram's stain were negative. Both patients had an uneventful recovery after surgical debridement and were able to return to their athletic activities. To our knowledge, this is the first case report of a local reaction to poly-L-lactic acid bioabsorbable interference screws after anterior cruciate ligament reconstruction.

Pretibial ganglion-like cyst formation after anterior cruciate ligament reconstruction: a consequence of the incomplete bony integration of the graft?

We report a case of subcutaneous pretibial ganglion, with direct communication to the tibial tunnel after an autologous reconstruction of the anterior cruciate ligament with hamstring tendons. The tibial graft fixation was with a 9 mm poly-L-lactide interference screw 5 years earlier. The screw had undergone complete resorption at the time the cyst occurred. No joint inflammatory reaction or graft insufficiency was detected. The patient underwent cyst excision and curettage of the tibial tunnel with full recovery. This complication seems to be the consequence of a direct communication between the joint and the pretibial subcutaneous tissue through a fibrous tibial tunnel and would have occurred, as there is no full osteointegration of the graft due to the resorption of the bioabsorbable interference screw.

Biodegradable Composite Implants

Biodegradable implants are established in the field of operative sports medicine. So-called composite implants are increasingly used. The idea to improve biocompatibility and osteoconductivity of biodegradable polymers by modifying them with a ceramic component, has led to the development of these composite implants. Today, an increasing variety of composite implants are available. They have substantially different material characteristics, which depend on matrix polymer choice and the additional ceramic. The material characteristics influence the mechanical properties, in vivo degradation, the osseous replacement and the host-tissue response. It is important to understand their biologic base for a better knowledge of the advantages and risks associated with using composite implants in the field of operative sports medicine. The purpose of this review is to focus on current developments in biodegradable composite implants and their biologic base.

False magnetic resonance imaging persistence of a biodegradable anterior cruciate ligament interference screw with chronic inflammation after 4 years in vivo

Surgeons should be aware that the degradation kinetics of biodegradable implants likely influence the rate of osseous integration, and depend on numerous factors such as polymer weight, crystallinity, and stereocopolymer ratio. We present a case of inflammatory reaction at a polylactide tibial interference screw site more than 4 years after primary anterior cruciate ligament (ACL) reconstruction. This inflammation was presumptively treated as an infection with surgical irrigation and debridement. Preoperatively, the screw was clearly delineated by magnetic resonance imaging (MRI), yet was grossly absent at surgery. Postoperative MRI confirmed thorough debridement and complete absence of the screw. This report shows that not only can a late inflammatory reaction occur, after up to 4 years in vivo, but that the MRI may show a persistent screw despite significant biodegradation. False MRI-persistent screws should be considered when critically reviewing studies that use MRI in the methods for evaluating biodegradable implants. More importantly, false MRI-persistent screws may have significant ramifications when planning revision surgery after primary ACL reconstruction having used interference screws that can degrade over several years.

Long-term absorption of poly-L-lactic Acid interference screws

PURPOSE

To evaluate the long term in vivo degradation of poly-L-lactic acid (PLLA) interference screws with computed tomography (CT) and radiography as used in patellar tendon autograft anterior cruciate ligament (ACL) reconstruction.

METHODS

A total of 20 patients who had undergone patellar tendon autograft ACL reconstruction fixed with PLLA screws at least 7 years earlier were evaluated by physical examination, radiography, and CT to determine whether PLLA screw reabsorption and bone ingrowth had occurred. This study was granted Institutional Review Board approval. Lysholm, Tegner, Cincinnati, and International Knee Documentation Committee (IKDC) scores were obtained. CT data were measured in Hounsfield units.

RESULTS

In all, 15 men and 5 women were evaluated 104 months after surgery (range, 89 to 124 months). CT and radiography demonstrated that the bone plug had fused to the tunnel wall, and that no intact interference screw was left. A parallel, threaded, and corticated screw tract was visible adjacent to the bone plug. No bone ingrowth had occurred at the screw site, although, occasionally, minimal calcification was seen. This was never as dense as cancellous bone, and no trabeculae were ever present. No positive pivot-shift test results were obtained. Lysholm, Tegner, and Cincinnati scores were 83, 5.6, and 75, respectively, at follow-up. Average KT difference was 0.7 mm.

DISCUSSION

PLLA interference screws completely degraded, and the resulting area demonstrated a low Hounsfield count, consistent with soft tissue 7 years after insertion. No significant bone ingrowth occurred at the screw site. Femoral and tibial ACL tunnels were absent of anything but fibrous tissue and usually had a sclerotic cortical lining.

CONCLUSION

PLLA biodegradable ACL screws eventually disappear completely. PLLA material is not replaced by bone. ACL graft tunnels are filled with nonossified material. This study provides a baseline for comparison with other biodegradable interference screws that may encourage bone ingrowth as they degrade.

LEVEL OF EVIDENCE

Level IV (no or historical control).

Tibial plateau fracture after anterior cruciate ligament reconstruction: Role of the interference screw resorption in the stress riser effect

We report a case of tibial plateau fracture after previous anterior cruciate ligament (ACL) reconstruction using patellar tendon autograft and bioabsorbable screws 4 years previously. The fracture occurred through the tibial tunnel. The interference screw had undergone complete resorption and the tunnel widening had increased. The resorption of the interference screw did not simultaneously promote and foster the growth of surrounding bone tissue. Therefore, the area of reactive tissue left by the screw resorption in an enlarged bone tunnel may lead to vulnerability of the tibial plateau. Stress risers would occur following ACL reconstruction if either resorption is not complete or bony integration is not complete.

Biological performance of a new β-TCP/PLLA composite material for applications in spine surgery:In vitro andin vivo studies

The objective of this research was to carry out an in vitro and in vivo study of the biological performance of PLLA/beta-TCP composite materials, to estimate the scope of their potential applications in bone surgery. Samples with increasing beta-TCP (0-60% w/w) contents were processed by injection molding. The in vitro study consisted of an evaluation of inflammatory potential by assaying the IL-1alpha secreted by monocytes, and then cell proliferation (counting) and phenotype expression (PAL and I collagen) in human osteogenous cells. The in vivo study was carried out using cylindrical implants of composite materials composed of composite materials containing 0 or 60% beta-TCP and pure beta-TCP, respectively. The implants were inserted in femoral sites in rabbits, using the Kathagen protocol. Each animal received a 60% implant, with either a 0 or a 100% implant in the contralateral femur, so that the materials could be compared with one another. Five animals were examined for each material and implantation period, giving a total of 30 animals. This study showed that adding increasing percentages of beta-TCP to a lactic acid polymer matrix stimulated the proliferation of human osteogenous cells and synthesis of the extracellular bone matrix in a dose-dependent manner. In vivo results indicate that, in comparison with pure PLA, tricalcium phosphate-containing composite materials had faster degradation kinetics, caused less inflammatory reaction, and promoted contact osteogenesis. The composite material containing 60% beta-TCP demonstrated a similar performance to pure tricalcium phosphate bone grafts in terms of osteogenesis, and is apparently compatible with the production of intra-osseous implants for situations representing high levels of mechanical strain.

Soft-tissue interference fixation: bioabsorbable screw versus metal screw

PURPOSE

To compare the biomechanical properties of eccentrically positioned bioabsorbable and titanium interference screws for quadrupled hamstring tendon graft (QHTG) fixation.

TYPE OF STUDY

In vitro, biomechanical study.

METHODS

In 10 paired cadaveric tibiae and femurs (mean age, 66.5 years; range, 53 to 81 years), QHTG fixation was performed in tunnels sized to within 0.5 mm of QHTG diameter using either a titanium (RCI; Smith & Nephew Donjoy, Carlsbad, CA) or a bioabsorbable (BioScrew; Linvatec, Largo, FL) screw of equal size. Constructs then underwent biomechanical load-to-failure testing on a servo-hydraulic device at 20 mm/min.

RESULTS

Load at failure was greater for femoral-side QHTG fixation using the bioabsorbable screw than the titanium screw (486 +/- 223.7 N v 246 +/- 99.1 N, P = .006); however, displacement did not differ (P = .81). There were no statistically significant differences between groups for tibial side load at failure (P = .54), stiffness (P = .44), or displacement (P = .50). Screw thread-induced graft laceration was more frequently observed in the titanium screw group (9 of 10 grafts during femoral-side testing, 0 of 10 grafts during tibial-side testing) than in the bioabsorbable screw group (0 of 10 grafts during femoral-side testing, 1 of 10 grafts during tibial-side testing).

CONCLUSIONS

BioScrew interference screw fixation was comparable or superior to RCI titanium interference screw fixation. BioScrew interference screw fixation also produced less screw thread-induced laceration of the QHTG during load-to-failure testing.

CLINICAL RELEVANCE

Use of a biodegradable interference screw positioned directly against a soft-tissue graft provides fixation properties similar to those of a metal interference screw.

MR imaging evaluation of the postoperative knee: ligaments, menisci, and articular cartilage

The surgical management of knee injuries has increased in recent years. Postoperative magnetic resonance (MR) imaging of the knee following surgical intervention serves an important role in the diagnostic evaluation of patients with recurrent or residual symptoms following surgical intervention. MR imaging additionally assists in the noninvasive documentation of temporal changes at the surgical site potentially reflective of procedural success, or failure. Background understanding of the common surgical procedures performed, their normal postoperative MR imaging appearance, and imaging features of potential procedural complications are essential in the accurate evaluation of patients following prior knee surgery. The focus of the following article is to review the clinical and MR imaging features of the postoperative knee following prior surgical treatment of ligamentous, meniscal, and articular cartilage injuries of the joint.

The natural history of a bioabsorbable interference screw used for anterior cruciate ligament reconstruction with a 4-strand hamstring technique

PURPOSE

The purpose of this study was to assess radiologically the rate of absorption of the Arthrex poly L-lactide bioabsorbable interference screw (Arthrex, Naples, FL) used in anterior cruciate ligament reconstruction with a 4-strand hamstring technique.

TYPE OF STUDY

Case series.

METHODS

Eight sequential patients undergoing anterior cruciate ligament reconstruction with a 4-strand hamstring technique were assessed with magnetic resonance imaging (MRI) scans at 1, 2, and 4 years postoperatively.

RESULTS

There was no radiologic evidence of absorption of the screw on any of the scans. The MRI appearance remained essentially unchanged from 1 to 4 years with the exception of the presence of a small cyst in the tibial tunnel of one of the patients. No edema was seen associated with the tibial tunnel in any of our patients.

CONCLUSIONS

There are several quoted theoretical advantages to using bioabsorbable screws. The rate of absorption is dependent on material, weight, and degree of crystallization. In our series using an amorphous low crystallization poly L-lactide screw, there was no evidence of any progression to absorption 4 years after implantation. This may be because all series quoted to date look at absorption using a bone-patellar tendon-bone graft.

LEVEL OF EVIDENCE

Level IV.

The effect of outlet fixation on tunnel widening

PURPOSE

To compare the development of tibial tunnel widening after a standard bone-patellar tendon-bone autograft (BPTB) to a flipped BPTB that allows interference screw outlet fixation with a bone plug at both femoral and tibial tunnels, and to identify any observable clinical effect. The hypothesis of this study was that the outlet fixation achieved by the flipped BPTB technique results in diminished tunnel widening at the site of the bone plug. Type

TYPE OF STUDY

Nonrandomized control trial.

METHODS

The postoperative radiographs of 67 BPTB anterior cruciate ligament (ACL) reconstructions were retrospectively reviewed; 31 had conventional BPTBs and 36 had the bone plugs flipped at the tibial end to achieve interference screw fixation of the bone plug at the tibial outlet as well as the femoral outlet. Biodegradable interference screws (PLLA) were used in all cases, which facilitated tunnel measurements. One week after surgery, the maximal tibial bone tunnel widths were measured on anteroposterior and lateral radiographs 1 cm below the tibial plateau. These initial postoperative measurements were compared with measurement from radiographs taken annually thereafter. Clinical information including Lysholm, Tegner, IKDC activity, Lachman, pivot-shift, and range of motion data was also obtained and compared for the 2 groups.

RESULTS

In the conventional BPTB group, at an average follow-up of 28 months, 28 of 31 (90%) showed at least a 2-mm increase (20%) in the tibial tunnel width. The mean maximum tunnel width increase was 2.2 mm. In the flipped BPTB group, at an average follow-up of 31 months, none of these 36 showed any increase in tunnel size. In fact, 15 patients had no distinct tibial tunnel remaining and, of the other 21, the average remaining tunnel width was 3 mm. The clinical results evaluating the Tegner, Lysholm, IKDC activity levels, KT, and physical examination parameters showed no significant differences between these 2 groups. The tunnel width decreased during the first year, but remained unchanged after 12 months. No tunnel dilation was observed with bone plug outlet fixation while 90% of the conventional group had at least a 20% increase (P <.001).

CONCLUSIONS

Outlet fixation with the flipped BPTB technique decreased the tibial tunnel width 1 cm below the plateau while 90% of the conventional BPTB patients demonstrated an average widening of 20%.

Bone tunnel remodeling at the site of biodegradable interference screws used for anterior cruciate ligament reconstruction: 5-year follow-up

PURPOSE

The purpose of this prospective study was to review, using expanded clinical-assessment tools, the long-term results of the local effects of a bioabsorbable interference screw (copolymer 85/15 D,L lactide/glycolide) in anterior cruciate ligament (ACL) reconstruction.

TYPE OF STUDY

This prospective study was initiated in May 1993. The inclusion criteria for patient selection included rupture of the ACL in athletic patients without involvement of the collateral ligaments, arthroscopic ACL reconstruction using middle third of the ligamentum patella, and magnetic resonance imaging (MRI) and plain radiographic examinations of the knee joint during follow-up.

MATERIALS

Between May 1993 and October 1994, 32 patients were enlisted in the study; 48 patients did not fit the inclusion criteria. There were 25 men 7 women. The average age was 29.1 years (range, 19 to 50 years). There were 21 right knees and 11 left knees. The follow-up examinations were performed by an independent examiner. There were 28 patients available for follow-up at a medium of 5.2 years (range, 4.1 to 6.4 years). The evaluation included various testing systems (i.e., OAK, IKDC, Lysholm) as well as MRI and plain radiographic studies to investigate the longevity of the implant and potential adverse effects of this new bioabsorbable material.

RESULTS

The clinical results were good. The OAK score (Orthopädische Arbeitsgruppe Knie) showed 93% excellent and good results, and 7% fair results. The IKDC and Lysholm scores were 92% and 96% good and excellent results, respectively. MRI showed bone remodeling and new bone formations at the site of the implant in the femoral as well as in the tibial bone tunnel at follow-up. No cystic or osteolytic changes where seen on MRI or plain radiographs.

CONCLUSIONS

This study showed the correlation between histology and MRI: there was minimal surgical-site edema, minimal reaction to this material, and complete replacement by new bone formation of the previous site of this implant. At 5 years, this bioabsorbable interference screw appeared clinically safe and effective for fixation of bone blocks during ACL reconstruction and MRI showed complete absorption and replacement with new bone.

Biodegradable implants in sports medicine: the biological base

Biodegradable implants are increasingly used in the field of operative sports medicine. Today, a tremendous variety of implants such as interference screws, staples, sutures, tacks, suture anchors, and devices for meniscal repair are available. These implants consist of different biodegradable polymers that have substantially different raw material characteristics such as in vivo degradation, host-tissue response, and osseous replacement. Because these devices have become the standard implant for several operative procedures, it is essential to understand their biological base. The purpose of this report is to provide a comprehensive insight into biodegradable implant biology for a better understanding of the advantages and risks associated with using these implants in the field of operative sports medicine. In particular, in vivo degradation, biocompatibility, and the osseous replacement of the implants are discussed. A standardized classification system to document and treat possible adverse tissue reactions is given, with special regard to extra-articular and intra-articular soft-tissue response and to osteolytic lesions.