MRI in ACL reconstructive surgery with PDLLA bioabsorbable interference screws: evaluation of degradation and osteointegration processes of bioabsorbable screws

PURPOSE: Anterior cruciate ligament (ACL) reconstructive surgery has seen significant progress since bioabsorbable interference screws have replaced synthetic metallic screws for ligament graft fixation within the femoral and tibial osseous tunnel. Our study compared the MR images of patients who underwent ACL reconstruction using bioabsorbable interference screws with those of patients who underwent ACL reconstruction using metallic screws to evaluate the MR aspects of degradation and osteointegration processes of bioabsorbable interference screws post-operatively. MATERIALS AND METHODS: Between September 1999 and December 2002 we performed MRI on 40 patients who underwent arthroscopic ACL reconstruction with patellar tendon auto-graft using PDLLA bioabsorbable screws in 35 cases and metallic screws in 5 cases. After surgery, all patients underwent an intensive rehabilitation programme along with clinical evaluation using the standard knee ligament evaluation form of the International Knee Documentation Committee (IKDC) and radiological examinations. MR studies were performed 1, 2 and 3 years post-operatively using a 0.5-Tesla MR scanner with T1- and T2*-weighted and STIR sequences. RESULTS: Thirty-three patients were clinically classified as group A IKDC (full return to sports activity) and 7 patients as group B IKDC. No foreign-body reaction was found in patients treated with bioabsorbable interference screws, both from a clinical point of view and from laboratory exams. Ferromagnetic artefacts were found in all patients treated with metallic interference screws. In patients with bioabsorbable interference screws, degradation of the screws and absence of significant artefacts allowed correct evaluation of the signal of the reconstructed ligament throughout its length, the osseous tunnels and the joint cavity. In 34 of 35 patients with bioabsorbable interference screws, the screw could not be detected due to complete degradation. In 8, 12 and 4 cases, a small cyst-like formation due to screw hydrolysis was present at the screw site within 1, 2 and 3 years from surgery respectively. Only in 4 cases was the process of osteointegration of the screw and bone plug complete 3 years after the operation, with consequent restoration of bone morphology. DISCUSSION AND CONCLUSIONS: The use of bioabsorbable interference screws is a valuable alternative to synthetic metallic fixation implants as the absence of artefacts allows correct post-operative MR follow-up. MRI is the only technique able to visualize all the portions of the transplant and to evaluate the healing process. Bioabsorbable interference screws usually degrade within one year. However, full osteointegration requires a long time and may not be complete 3 years after surgery. The presence of cyst-like formations at the screw site has to be regarded as a normal feature of the screw degradation process. Therefore, the use of bioabsorbable interference screws is recommended as it enables MR follow-up of the knee after ACL reconstruction.     

Intraarticular migration of a broken biodegradable interference screw after anterior cruciate ligament reconstruction

Poly-l-lactic acid biodegradable screws have been used effectively for graft fixation in anterior cruciate ligament (ACL) reconstruction. The overall complication rate associated with the use of this implant is low, although some authors reported complications, such as osteolysis and aseptic effusion of the knee joint. We report a case of a 29-year-old female patient with a failure of a biodegradable interference screw at 22 months after ACL reconstruction using bone–patellar tendon–bone graft. In this illustrated case, the screw broke and migrated into the knee joint. In addition, we performed a detailed review of the medical literature from 1990–2005 to identify possible causes of biodegradable screw failures. We identified six published cases of bioabsorbable interference screw failure with migration into the knee joint. Several authors have reported small diameter of the screw, poor bone quality, bone resorption, and screw divergence as potential causes for intraarticular migration of metallic interference screws. With regard to bioscrews, no specific risk factors for screw breakage and intraarticular migration have been reported. ACL reconstruction with the use of bioabsorbable interference screws for fixation is considered to be reliable. However, we need to be aware of potential problems associated with the use of this implant. Early recognition of bioscrew failure may prevent associated morbidities, such as subsequent cartilage damage.     

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).     

Poly-L-lactic acid — hydroxyapatite (PLLA-HA) bioabsorbable interference screws for tibial graft fixation in anterior cruciate ligament (ACL) reconstruction surgery: MR evaluation of osteointegration and degradation features

Purpose

We evaluated with magnetic resonance imaging (MRI) the degradation and osteointegration features of a new type of bioabsorbable interference (BioRCI) screw composed of poly-L-lactic acid and hydroxyapatite (PLLA-HA) used for tibial graft fixation in anterior cruciate ligament (ACL) reconstruction.

Materials and methods

Thirty-one patients underwent arthroscopic surgery for ACL reconstruction using doubled gracilis and semitendinosus tendons fixed to the tibial tunnel with PLLA-HA (BioRCI-HA) screws. Two groups of patients were evaluated, one group 10–13 months after surgery and the other after 30–40 months. The standard knee ligament evaluation form of the International Knee Documentation Committee (IKDC) was used for clinical assessment and MRI for the radiological assessment.

Results

MRI after 10–13 months revealed findings referable to healing and integration of the bone-graft-screw system, findings that disappeared at later follow-up examinations. The BioRCI-HA screw remained constantly visible in all patients, although with changes in signal intensity over time.

Conclusions

BioRCI-HA screws allow adequate primary stability and superior osteoconduction and biocompatibility in comparison with plain PLLA screws. The absence of ferromagnetic artefacts allows accurate MRI follow-up and adequate evaluation of ligament synovialisation, screw degradation and graft osteointegration.     

The unpredictable material properties of bioabsorbable PLC interference screws and their adverse effects in ACL reconstruction surgery

The aim of this study was to look at the clinical outcome of polylactide carbonate (PLC) interference screws in knee ligament reconstruction surgery. We prospectively followed up 59 patients who underwent primary hamstring anterior cruciate ligament (ACL) reconstructions using PLC (Calaxo screw; Smith and Nephew, Andover, MA) screws to secure the graft in the tibial tunnel. The average age was 34 years (range 17–55 years, SD 8.93). Twenty-three (39%) patients presented with complications [synovitis in 15% (nine) patients, prominent tibial swelling in 34% (20) patients and both in seven patients]. In comparison, similar complications were not seen in two groups of 59 age and sex matched patients in whom PLLA (Bio RCI; Smith and Nephew, Andover, MA) screws or Titanium (RCI; Smith and Nephew, Andover, MA) screws were used by the same surgeon. The problems encountered in the PLC screw group did not adversely affect knee stability. Six patients underwent exploration of the tibial tunnel site. A sterile white cheesy substance was removed, leaving an empty tibial tunnel. The ACL graft was found to be well attached to tibial tunnel in all cases. The PLC screw diameter, surface area or tibial tunnel diameter did not have any correlation to the occurrence of complications. Two patients required multiple washouts, one of whom developed a deep infection. The degradation of PLC screws does not follow the gradual and controlled pattern demonstrated in the ovine model. The unpredictable screw degradation, and the reaction to it can lead to serious clinical consequences.     

Tibial tunnel widening after bioresorbable poly-lactide calcium carbonate interference screw usage in ACL reconstruction

Developing bio-absorbable interference screws for anterior cruciate ligament (ACL) reconstruction has proven to be a challenging task. The aim of this study was to investigate the osteogenetic response of poly-lactide carbonate (PLC) interference screws in ACL reconstruction in humans. Ten patients (median age, 28 years) underwent arthroscopic ACL reconstruction with semitendinosus/gracilis tendon graft and a PLC interference screw. The patients were scanned with a multi-slice CT scanner 2 weeks and 1 year postoperatively. Fourteen days postoperatively a mean tunnel widening of 78% [52%; 110%] was observed. At 1-year follow-up, the mean tunnel widening was 128% [84%; 180%]. No sign of bone replacement or bone ingrowth was observed. Factors such as accelerated rehabilitation, micro-motions, and early screw degradation might be responsible for this large tunnel widening. Our results demonstrate the difficulty in translation of preclinical data. This study illustrates the need for extensive preclinical investigation of new materials for clinical purposes.     

Bioabsorbable interference screw versus bioabsorbable cross pins: influence of femoral graft fixation on the clinical outcome after ACL reconstruction

Purpose

The aim of this study was to evaluate the clinical outcome and differences in anterior–posterior laxity of ACL reconstruction using a bioabsorbable interference screw for femoral graft fixation when compared to femoral bioabsorbable cross pin fixation.

Methods

Clinical outcome was evaluated among 59 patients 1?year after arthroscopic ACL reconstruction with hamstrings graft in a prospective, non-randomised study. In 31 cases, femoral fixation of the graft was performed using a bioabsorbable interference screw. In 28 cases, two bioabsorbable cross pins were used for femoral fixation. Patients were evaluated using Tegner, Lysholm and Marshall scores, the visual analogue scale for pain and KT-1000 arthrometer measurement.

Results

No significant difference (P?≥?0.05) was observed at follow-up for the knee scores. The average Tegner score was 5.83 points (±2.00) for the interference screw fixation and 5.83 points (±1.24) for the cross pin fixation; the average Lysholm score was 93.58 (±5.79) to 92.72 (±6.34) points; and the average Marshall score 46.72 (±2.4) to 47.30 (±2.35) points. No significant difference was found for the visual analogue scale for pain. KT-1000 arthrometer measurement revealed a significant (P?<?0.05) difference in the mean side-to-side anterior translation at all applied forces. At 67?N, the mean difference was 1.53?mm (±1.24) in the interference screw group and 0.47?mm (±1.18) in the cross pin group (P?<?0.05). At 89?N, the mean differences were 1.85?mm (±1.29) versus 0.59?mm (±1.59), respectively, (P?<?0.05), and maximum manual displacements were 2.02?mm (±1.26) versus 1.22?mm (1.18; P?<?0.05).

Conclusions

In ACL reconstruction with hamstrings graft, similar clinical results are obtained for the use of bioabsorbable cross pins when compared to bioabsorbable interference screws for femoral fixation. Cross pin fixation was superior with regard to the anteroposterior laxity as measured with KT-1000.     

Biomechanical analysis of femoral tunnel pull-out angles for anterior cruciate ligament reconstruction with bioabsorbable and metal interference screws

BACKGROUND: Fixation strength of metal and bioabsorbable interference screws has not been evaluated while varying the anterior cruciate ligament graft tension angle. HYPOTHESIS: There is no difference in fixation strength between 2 types of interference screws for anterior cruciate ligament graft fixation while the graft tension angle is varied relative to the femoral tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-eight anterior cruciate ligament reconstructions were performed using immature porcine femurs stripped of soft tissue and doubled-over porcine flexor digitorum profundus tendon grafts. Specimens were randomized to bioabsorbable or titanium interference screw fixation. Specimens were randomized to one of three pull angles (0 degrees , 30 degrees , 60 degrees ) representing loading at different knee flexion angles (n = 8/group). Reconstructed ligaments were tensioned to 10 N followed by 200 loading cycles between 10 and 150 N and a final failure test. Construct elongation (mm) at 100 and 200 cycles and failure load (N) were analyzed using a 2-way analysis of variance (P < .05). RESULTS: Screw material interacted significantly with graft tension angle, as the bioabsorbable screw specimens demonstrated significantly greater fixation strength when tensioned at greater angles. Specimens fixed with bioabsorbable screws showed significantly less elongation at both 100 and 200 cycles and significantly greater failure load compared with titanium screws. CONCLUSION: Bioabsorbable interference screws acutely have increased fixation strength compared with titanium interference screws for anterior cruciate ligament grafts loaded at greater tension angles. CLINICAL RELEVANCE: The strength of anterior cruciate ligament reconstruction fixation increases with increasing divergence between the tension angle and femoral tunnel, a condition seen when the knee approaches full extension.     

Endoscopic reconstruction of the anterior cruciate ligament using bone-patellar tendon-bone grafts fixed with bioabsorbable or metal interference screws: a prospective randomized study of the clinical outcome

BACKGROUND: During the past decade, bioabsorbable interference screws have become increasingly popular in endoscopic reconstructions of the anterior cruciate ligament. With these screws, there is no need for a second operation for removal and no complicating factor if later revision surgery is necessary. Several pullout studies have found similar results between metal and bioabsorbable interference screws; however, few studies have investigated the clinical outcome. HYPOTHESIS: There is no difference in the clinical outcome of bioabsorbable interference screws compared with metal screws. STUDY DESIGN: Randomized controlled clinical trial; Level of evidence, 1. METHODS: Forty-one patients were randomized for the use of either metal interference screws (20 patients) or bioabsorbable poly-l-lactic acid screws (21 patients). The patients were followed with clinical examinations at 6, 12, and 24 weeks and at 1 and 2 years postoperatively. RESULTS: Subjective knee function was better in the patients in the metal screw group; they had less pain at rest, a higher Tegner score, a higher Lysholm score, and better subjective knee function at 2 years compared to the bioabsorbable screw group. However, there was no difference in stability between the groups.Conclusion and CLINICAL RELEVANCE: Because of the inferior results in the bioabsorbable screw group in our study, and until larger studies show otherwise, we do not find the advantages of using bioabsorbable screws sufficient to warrant the routine use of poly-L-lactic acid screws in anterior cruciate ligament reconstructions.     

Clinical outcome of anterior cruciate ligament reconstruction with quadrupled hamstring tendon graft and bioabsorbable interference screw fixation

BACKGROUND: To date, there has been no publication of clinical follow-up data on patients who have undergone quadrupled hamstring tendon autograft anterior cruciate ligament reconstruction with bioabsorbable screw fixation. PURPOSE: To report the results of quadrupled hamstring tendon autograft anterior cruciate ligament reconstruction with bioabsorbable interference screw fixation. STUDY DESIGN: Retrospective review. METHODS: Sixty-five patients (66 knees) were retrospectively identified by chart review as having undergone quadrupled hamstring tendon autograft anterior cruciate ligament reconstruction with bioabsorbable interference screw fixation with a minimum 2-year follow-up. RESULTS: Data were collected on 48 knees in 47 patients (73%) at an average 30.2 months (range, 24 to 43) after surgery. Thirty-six patients (37 knees) returned for clinical evaluation (56% return) and subjective follow-up only was obtained in 11 patients (17%). The mean Lysolm knee score was 91 (range, 45 to 98), with a mean of 97 for the uninvolved knee. The mean Tegner activity score was 5.7 (range, 3 to 7). The KT-1000 arthrometer mean side-to-side difference for manual maximum displacement was 2.03 mm (range, -1 to 8). The mean International Knee Documentation Committee knee score was 83 (range, 47 to 100). Patients who underwent associated partial meniscectomy or meniscal repair had significantly lower International Knee Documentation Committee scores than patients without associated procedures (P < 0.01). CONCLUSIONS: Quadrupled hamstring tendon autograft anterior cruciate ligament reconstruction with bioabsorbable interference screw fixation is comparable with other methods of anterior cruciate ligament reconstruction in terms of patient satisfaction, knee stability, and function.     

Recurrent locking of knee joint caused by intraarticular migration of bioabsorbable tibial interference screw after arthroscopic ACL reconstruction

Two cases are reported in which, after ACL reconstruction with autologous hamstring grafts, tibial polylactide interference screws migrated into the knee joint. Clinically, both patients presented with recurrent locking of the joint. In one case, a broken 15 mm-long tip of the screw was found intra-articularly. In the other case, the whole screw had migrated into the joint cavity. The degradation process of polylactic acid, operative technique and bone quality are discussed as possible reasons for these complications.     

Double-bundle versus single-bundle anterior cruciate ligament reconstruction: a prospective,randomize clinical study

Anatomical observation and biomechanical studies have shown that the anterior cruciate ligament (ACL) mainly consists of two distinct bundles, the anteromedial (AM) bundle and posterolateral (PL) bundle. Conventional single-bundle ACL reconstruction techniques have focused on the restoration of the AM bundle while giving limited attention to the PL bundle. The purpose of this prospective, randomized clinical study is to compare the outcomes of ACL reconstruction when using either double-bundle or single-bundle technique and bioabsorbable interference screw fixation, and similar rehabilitation with both techniques. Sixty-five patients were randomized into either double-bundle (n = 35) or single-bundle (n = 30) ACL reconstruction with hamstring tendons and bioabsorbable screw (Hexalon, Inion Company, Tampere, Finland) fixation in both groups. The evaluation methods were clinical examination, KT-1000 arthrometer measurements, radiographic evaluation, as well as International Knee Documentation Committee and Lysholm knee scores. There were no differences between the study groups preoperatively. For an average of 14 months of follow-up (range 12–20 months), 30 patients of the double-bundle group and 29 patients of the single-bundle group were available (91%). At the follow-up, the rotational stability, as evaluated by pivot shift test, was significantly better in the double-bundle group than in the single-bundle group. However, in anterior stability of the knee, there was no significant difference between the groups. None of the patients in the double-bundle group had graft failure, while four patients in the single-bundle group had. In addition, knee scores were equal at the follow-up, and all the results were significantly better at the follow-up than preoperatively, in both groups.     

可吸收界面螺钉及腘绳肌腱重建前交叉韧带疗效分析

目的探讨关节镜下应用可吸收界面螺钉及腘绳肌腱对陈旧性膝关节前交叉韧带损伤的患者进行重建的临床疗效。方法对15例陈旧性前交叉韧带损伤患者行关节镜下重建手术,术后均随访1年,比较术前、术后膝关节稳定性、自觉症状、关节功能等,用Lysholm中的八项评分标准进行对比。结果 14例患者重建后膝关节的活动度及稳定性良好,1例差,优良率93.3%。结论关节镜下可吸收界面螺钉结合腘绳肌腱重建前交叉韧带是治疗陈旧性前交叉韧带的可靠术式,能够近期恢复膝关节的功能。     

MR imaging and metallic implants for anterior cruciate ligament reconstruction: assessment of ferromagnetism and artifact.

Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.     

Magnetic resonance imaging analysis of bioabsorbable interference screws used for fixation of bone-patellar tendon-bone autografts in endoscopic reconstruction of the anterior cruciate ligament

BACKGROUND: Metal interference screws can cause problems if revision is needed and can interfere with magnetic resonance imaging. Bioabsorbable screws have been developed to prevent these problems, but the rate of resorption and integration is not well understood. HYPOTHESIS: Poly-L-lactic acid interference screws will be resorbed 2 years after anterior cruciate ligament reconstruction. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: The study group consisted of 19 patients with isolated anterior cruciate ligament ruptures reconstructed with bone-patellar tendon-bone autografts fixed with poly-L-lactic acid interference screws using an endoscopic technique. Magnetic resonance imaging was used to evaluate resorption of the screws, bony integration of the screws, and integration of the bone blocks after 2 years. RESULTS: At 2 years, the mean reduction in the volume of the femoral screws was 64% and of the tibial screw was 63%. Bony integration of the femoral bone block was considered good in 17 patients and fair in 2 patients. Integration of the tibial bone block was considered good in 16 patients and fair in 1 patient who demonstrated widening of the tibial tunnel. Osteolysis around the screws was seen in 3 patients in the femur and none in the tibia. CONCLUSION: The mean reduction in volume of the poly-L-lactic acid screws as measured by magnetic resonance imaging after 2 years was approximately two thirds. The integration of the bone blocks was considered good in 90% of the patients. Osteolysis around the screws was visible in 16% of the patients. CLINICAL RELEVANCE: Two years after ACL reconstruction using poly-L-lactic acid interference screws, the surgeon can expect to find approximately one third of the volume of the screw remaining in the bone tunnels.     

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.

Level of evidence

Systematic review including case-reports, Level V.     

Press-fit fixation in reconstruction of anterior cruciate ligament,using bone–patellar tendon–bone graft

We studied arthroscopic reconstruction of the anterior cruciate ligament (ACL) using patellar ligament-bone graft fixed to the femur by press-fit technique. The main feature of this technique was a stable bony fixation on the femoral site without using interference screws or other fixation devices. We treated 42 patients with ACL rupture by this technique; clinical examination was carried out preoperatively and at 3 months, 6 months, and then every 6 months using the standard criteria for evaluation of the IKDC (mean follow-up 29 months, 22–41). CT and MRI were performed 6 months postoperatively. According to IKDC score 37 knee (88%) were graded as normal or nearly normal, 4 (10%) as abnormal, and one (2%) as severely abnormal, none of the poor results was due to instability. Reconstruction of the ACL by press-fit technique is a more anatomically oriented method of fixation without the complications of interference screws at the femoral attachment of the graft.     

Anterior cruciate ligament reconstruction using autografts and double biodegradable femoral cross-pin fixation: functional,radiographic and MRI outcome after 2-year minimum follow-up

Double biodegradable cross-pins are increasingly used for femoral fixation in arthroscopically assisted reconstruction of the anterior cruciate ligament (ACL). There are no studies combining functional outcome analysis, radiographs and magnetic resonance images (MRI) to evaluate this technique. The authors examined 45 patients after ACL reconstruction using double biodegradable femoral cross-pin fixation and biodegradable tibial interference screw fixation with a minimum follow-up of 24 months. Clinical evaluation included International Knee Documentation Committee (IKDC) and modified Lysholm score. Radiographic analysis included standard X-rays in anterior–posterior and lateral views and Telos stress device measurements. MRI was analyzed to obtain information about hardware, intra-articular graft, osseous graft-integration and cartilage. IKDC score revealed 28 (62.2%) patients with normal knee function (group A), 15 (33.3%) patients with nearly normal (group B) knee function and 2 (4.4%) patients with abnormal knee function (group C). The Lysholm score was 94.6 (±7.2) in the operated knee and 98.8 (±7.4) in the non-operated knee. Mean Telos stress device values were +4.6 (±2.6) in the operated and +3.9 (±2.4) in the non-operated knee. MRI showed an intact intra-articular graft in all but one patient. Complete femoral graft integration was seen in 88.9% and complete tibial graft integration in 86.7%. Biodegradable cross-pins were partially or fully visible in all patients. The biodegradable tibial interference screw was fully visible in 16 (35.6%) and partially visible in 20 (44.4%) patients. Thirty-one (68.9%) patients showed signs of cartilage degeneration on MRI at follow-up. The graft fixation with double biodegradable pin fixation appears to be a reliable technique for ACL reconstruction providing a stable close-to-joint graft fixation.     

Polymer-hydroxyapatite composite versus polymer interference screws in anterior cruciate ligament reconstruction in a large animal model

The aim of the study was to assess the hard tissue response of a composite hydroxyapatite/poly L-lactic acid (HA/PLLA) interference screw for anterior cruciate ligament (ACL) reconstruction compared to a standard PLLA screw. Twelve skeletally mature rams underwent unilateral ACL reconstruction using an autologous bone-patellar tendon graft. Each animal received either two test HA/PLLA interference screws or two control PLLA interference screws. Animals were sacrificed at 6 and 12 months post-implantation and the operated knees excised. Undecalcified sections of the screw and surrounding tissues were cut from resin embedded samples and stained; sections were approximately parallel to the longitudinal axis of the screws. A quantitative assessment of bone formation between each screw type (PLLA vs. HA/PLLA) and adjacent tissue in both the tibia and femur was undertaken using automated image analysis (KS400, Zeiss, UK). The inflammatory response of each screw type was assessed by histological evaluation. New bone formation along the perimeter of the screw threads was statistically significantly higher with the HA/PLLA than the PLLA alone. The inflammatory response as assessed semi-quantitatively by histologically determining the number of inflammatory cells present in the tissue adjacent to the implant, was higher for PLLA than HA/PLLA. Significantly increased new bone formation and decreased inflammatory cells were observed in vivo with the composite screw in comparison with the standard polymer. A novel HA/PLLA composite biomaterial in the form of an interference screw demonstrated an improved hard-tissue response compared to PLLA in a large animal ACL reconstruction. This study determined the differences in the tissue response between PLLA and a composite material of HA/PLLA. The improved tissue related outcomes observed in vivo, may be of benefit clinically in ACL reconstruction.     

Initial fixation strength of bioabsorbable and titanium interference screws in anterior cruciate ligament reconstruction. Biomechanical evaluation by single cycle and cyclic loading

We evaluated the initial bone-patellar tendon-bone graft fixation strength of bioabsorbable as compared with titanium interference screws in anterior cruciate ligament reconstruction using matched pairs of porcine knees. Ten pairs underwent single-cycle failure loading at a rate of 50 mm/min, and 10 pairs underwent cyclic loading at half-hertz frequency. The cyclic loading started with 100 load cycles between 50 and 150 N. We then progressively increased loads in 50-N increments after each set of 100 cycles. After 100 cycles at 850 N, the specimens were loaded to failure at a rate of 50 mm/min. In the single-cycle failure loading test, the mean ultimate failure loads (+/-SD) for the bioabsorbable (837 +/- 260 N) and titanium interference screws (863 +/- 192 N) were not significantly different, nor were the mean yield loads or the stiffness of the fixation. In the cyclic loading test, the yield loads were 605 +/- 142 N and 585 +/- 103 N for the bioabsorbable and titanium interference screws, respectively (no significant difference). Although there was no significant difference in the ultimate failure load, more bone block fractures were found in the grafts fixed with a titanium interference screw. Bioabsorbable interference screw fixation thus seems to provide a reasonable alternative to titanium screws.