Synovitis and artificial ligaments

Periacetabular Tumour Resection under Anterosuperior Iliac Spine Allows Better Alloprosthetic Reconstruction than Above: Bone Contact Matters

Background: Periacetabular resections are more affected by late complications than other pelvic resections. Reconstruction using bone allograft is considered a suitable solution. However, it is still not clear how the bone-allograft contact surface impacts on mechanical and functional outcome. Materials and methods: This paper presents the results of a retrospective analysis of 33 patients with resection of the entire acetabulum and reconstruction with an allograft-prosthetic composite for the period 1999 to 2010. Patients were divided in two groups, based on type of resection. In Group 1. patients had resections under anterosuperior iliac spine allowing the highest bone-allograft surface contact in reconstruction, while in Group 2 patients had resections over it. Results: Mechanical survival of the implant and Musculoskeletal Tumor Society functional score were calculated. Impact of age and artificial ligament were investigated as well. Patients in Group 1 had 38% mechanical failure rate of the implant while patients in Group 2 had 88%. Average functional score was higher in Group 1 compared with patients in Group 2. An artificial ligament was shown to have non-significant impact on survival of the reconstruction in Group 1, while significantly improving survival of reconstruction in Group 2. Conclusion: Bone-allograft contact matters: resection under anterosuperior iliac spine allows better mechanical survival and offers better reconstruction functional scores.

Double-bundle anterior cruciate ligament reconstruction using autologous hamstrings with LARS augmentation demonstrates comparable outcomes to hamstrings alone, without evidence of synovitis or early osteoarthritis

PURPOSE

To compare the clinical and radiological outcomes in patients undergoing anterior cruciate ligament reconstruction (ACLR) with, or without, LARS augmentation.

METHODS

One-hundred and thirty-six patients that underwent double-bundle ACLR with (DB Hams/LARS, n = 67), or without (DB Hams, n = 69), LARS augmentation, were assessed clinically and with Magnetic Resonance Imaging (MRI) at a minimum of 7-years post-surgery. Patients were assessed via patient-reported outcome measures (PROMs), KT-1000 (laxity), isokinetic knee extensor and flexor strength and a 4-hop test battery. Limb symmetry indices (LSIs) were calculated. The Whole-Organ Magnetic Resonance Imaging Score (WORMS) evaluated knee status via MRI. Sport participation, secondary operations, ACL re-tears and contralateral ACL tears were reported.

RESULTS

No differences (n.s.) were observed in demographics, PROMs, KT-1000 scores or strength and hop LSIs. Normal (< 3 mm side-to-side differences) KT-1000 scores were observed in 64 (92.8%) and 59 (88.1%) of DB Hams and DB Hams/LARS patients, respectively. Comparative rates of satisfaction were reported. Knee flexor strength and hop test LSIs were all ˃95% in both groups, which was 94.2% and 96.7% for knee extensor strength in the DB Hams and DB Hams/LARS cohorts, respectively. While 53 (76.8%) and 52 (77.6%) of the DB Hams and DB Hams/LARS patients had returned to pivoting sports, 42 (60.9%) and 41 (61.2%) were participating in pivoting sports at the minimum 7-year review. No difference (n.s.) was observed in the WORMS (12.3 DB Hams, 16.7 DB Hams/LARS). Of the cohort assessed, 8 (11%) DB Hams and 11 (16%) DB Hams/LARS patients had undergone secondary surgery. In addition to one patient in each group that demonstrated ACL rupture on MRI, an additional cohort of patients were excluded from the current analysis due to prior re-tear (DB Hams n = 6, DB Hams/LARS n = 8) or contralateral ACL tear (DB Hams n = 4, DB Hams/LARS n = 4).

CONCLUSIONS

Comparable outcomes were observed after double-bundle ACLR using autologous hamstrings with, or without, LARS augmentation. Therefore, while these outcomes do not justify the additional use of synthetic augmentation given the lack of further benefit and additional cost, higher rates of graft failure, synovitis and early osteoarthritic change previously reported were not observed.

LEVEL OF EVIDENCE

III.

Long-term outcomes of surgery using the Ligament Advanced Reinforcement System as treatment for anterior cruciate ligament tears

AIMS

The aim of this prospective study was to assess the long-term clinical, radiological, functional, and quality of life (QoL)-related outcome of patients treated with the synthetic Ligament Advanced Reinforcement System (LARS) device for anterior cruciate ligament (ACL) rupture.

METHODS

A total of 41 patients who underwent ACL reconstruction with the LARS device (mean age 39.8 years (SD 12.1 ); 32% females (n = 13)) were prospectively included between August 2001 and March 2005. MRI scans and radiographs were performed at a median follow-up of 2.0 years (interquartile range (IQR) 1.3 to 3.0; n = 40) and 12.8 years (IQR 12.1 to 13.8; n = 22). Functional and QoL-related outcome was assessed in 29 patients at a median follow-up of 12.8 years (IQR 12.0 to 14.0) and clinically reconfirmed at latest median follow-up of 16.5 years (IQR 15.5 to 17.9). International Knee Documentation Committee (IKDC) and Tegner scores were obtained pre- and postoperatively, and Lysholm score postoperatively only. At latest follow-up, range of motion, knee stability tests, 36-Item Short Form Health Survey (SF-36), and IKDC scores were ascertained. Complications and reoperations during follow-up were documented.

RESULTS

Cumulative complication rate was 66% (n = 27), with 11 developing within one year from surgery and 16 after one year (including five patients with both early and late complications). Ten graft failures (24%) and eight cases of reactive synovitis were observed (20%). All 11 patients with early complications and ten with late complications underwent reoperation (including five with another surgical procedure for early complications), amounting to a cumulative reoperation rate of 51% (n = 21). Revision ACL reconstruction was performed in one patient (2.4%). Median IKDC at latest follow-up was 89.7 (IQR 78.2 to 93.1), being significantly worse in the event of previous complications. Lachman test was positive in 56% (n = 15) of reconstructed knees. All norm-based SF-36 items were at or above median at latest follow-up, and did not differ depending on development of complications.

CONCLUSION

Despite good functional and QoL-related results in the long term, the cumulative complication rate of 66%, including graft failures and reactive synovitis, has to be viewed with great concern. Cite this article: Bone Joint J 2022;104-B(2):242-248.

Complication after the reconstruction of the old patellar tendon rupture

Introduction. Chronic patellar tendon rupture (PTR) occurs rarely; its frequency and prevalence are unknown. There are very little data on the late patellar tendon reconstruction in rheumatoid arthritis and its complications. Case report. We presented a surgical repair of a PTR with early postoperative rupture of the contralateral patellar tendon for a 21-year-old woman with a past medical history of juvenile rheumatoid arthritis (treated with corticosteroids) who sustained initial injury 11 months prior to the presentation. The contralateral side was used for autograft harvesting. We used bone-tendon-bone (BTB) autograft and allografts followed by double-wire loop reinforcement and immediate postoperative mobilization. The patient was followed for 2 years, and the function of both knees was re-stored completely, with a full active range of motion. In this case, reconstruction of an 11-month-old chronic PTR (with complete resorption of the tendon and completely separated infrapatellar pads, complicated by the contralateral PTR) with BTB autograft and allografts and double wire loop reinforcement gave an excellent functional result. Two years after the surgical treatment, the extensor function of both knees was completely restored with a full range of movements. The patient reported satisfying outcomes and was able to return to all pre-injury activities without the assistance of orthopedic devices. Conclusion. This case report highlights the importance of the early diagnosis and describes operative techniques used in chronic PTR repair and treatments of the early postoperative complications such as rupture of the contralateral tendon.

Hamstring Autograft Anterior Cruciate Ligament Reconstruction Using an All-Inside Technique With and Without Independent Suture Tape Reinforcement

PURPOSE

To compare the (1) rates of complications and reoperations, (2) rate of anterior cruciate ligament (ACL) graft failure, and (3) patient-reported outcomes (PROs) among patients after hamstring autograft ACL reconstruction (ACLR) with and without independent suture tape reinforcement at a minimum 2-year clinical follow-up.

METHODS

We performed a 1:2 matched-cohort comparison of patients who underwent hamstring autograft ACLR with and without independent suture tape reinforcement between July 2011 and July 2017. Patients were matched according to age, sex, body mass index, preinjury Tegner activity score, and concomitant meniscal injury. Medical records were reviewed for demographic characteristics, additional injuries, and concomitant procedures. PRO scores (including Tegner activity, Lysholm, and International Knee Documentation Committee scores) and physical examination findings were collected both preoperatively and at a minimum of 2 years postoperatively.

RESULTS

Overall, 108 patients who underwent ACLR were included: 36 patients (mean age, 25.3 years; range, 13-44 years) with independent suture tape reinforcement and 72 patients (mean age, 24.9 years; range, 13-54 years) without suture tape reinforcement. Overall, 5 of 36 suture tape patients (14%) and 10 of 72 control patients (14%) underwent reoperations. At an average follow-up of 26.1 months in the suture tape cohort and 31.3 months in the control cohort, 1 patient in the suture tape cohort and 4 patients in the control cohort experienced graft failure. There were no statistically significant differences between the suture tape and control groups regarding return-to-sport rate (89% and 88%, respectively), postoperative International Knee Documentation Committee score (94.4 and 93.8, respectively), and postoperative Lysholm score (95.6 and 94, respectively). There was a statistically significant difference between the suture tape and control groups in postoperative Tegner activity score, at 7.1 (95% confidence interval, 6.5-7.6) and 6.4 (95% confidence interval, 6.2-6.6), respectively (P = .026).

CONCLUSIONS

ACLR with hamstring autograft and independent suture tape reinforcement was performed safely with low rates of complications, graft failure, and reoperations with similar PROs, function, and return-to-sport rates when compared with hamstring autograft ACLR without suture tape reinforcement at a minimum 2-year follow-up.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Tendon Descensus Repair (TENDER) - A prospective clinical feasibility study of tendon transplantation for pelvic organ prolapse repair

OBJECTIVE

To show the feasibility of tendon transplantation for minimally invasive pectopexy in pelvic organ prolapse repair.

STUDY DESIGN

Patients with uterine or vaginal vault prolapse (POP-Q point C Stage 2-4) were offered laparoscopic pectopexy by means of autologous semitendinosus tendon transplantation. This paper presents a case series and describes the technique regarding the first 10 patients who underwent surgery. After preparing the vagina or cervix for laparoscopic pectopexy a tendon of the patient's semitendinosus muscle was stripped and brought intraabdominally through the 10 mm trocar. The tendon was fixed between the cervix or vagina and to the pectineal ligaments on both sides of the pelvis.

RESULTS

All operations were performed successfully without complications. Vaginal examination demonstrated the intended elevation of the middle compartment. Mobility and power of the affected leg did not change. Recovery was fast, and discharge was possible between the second and third postoperative day.

CONCLUSION

Our approach demonstrates the feasibility and safety of a laparoscopic pectopexy with a semitendinosus autograft instead of a synthetic mesh. The experience from orthopedic surgery shows that a semitendinosus tendon autograft is long-lasting and stable. In addition, the morbidity on the operated leg is low.

Synovitis following anterior cruciate ligament reconstruction using the LARS device

PURPOSE

The Ligament Augmentation and Reconstruction System (LARS^®) has been at the forefront of a recent revival in the use of synthetic ligaments for ACL reconstruction. However, despite promising short-to-mid-term results its role has been approached with caution due to a high number of major complications in previous synthetic graft designs including mechanical failures, synovitis and osteoarthritis. This study aims to report on the incidence of synovitis in a series of patients undergoing second-look surgery following LARS ACL reconstruction.

METHODS

A retrospective analysis was performed of a single surgeon's series of 12 patients that underwent second-look arthroscopic surgery following primary LARS ACL surgery for indications including mechanical symptoms (meniscal tears/cyclops lesions/chondral flaps) and/or symptomatic instability secondary to LARS failure. In all cases an examination under anaesthesia (EUA) was performed, and a qualitative assessment of the synovium was carried out and graded as normal, reactive or inflammatory. A synovial biopsy was performed in all knees with visible evidence of synovitis and in all cases of LARS failure.

RESULTS

The second-look arthroscopy was performed at a mean of 23 months (7-66) after the index surgery. In 6 (50%) knees the LARS device had failed necessitating removal and revision ACL reconstruction, while in the remaining 6 knees the LARS was still intact. Arthroscopic evaluation of the synovium revealed a normal appearance in 8 knees (67%) and reactive synovitis in 4 knees (23%); of these 4 knees, one had an intact LARS device and 3 had failed LARS. Histological examination from these 4 knees and the 3 knees with graft failures without visible synovitis revealed chronic hypertrophic synovitis (moderate 2, mild 5) in all cases with rare giant cells, consistent with a reaction to foreign body material.

CONCLUSIONS

Foreign body synovitis is a common finding in our series of patients undergoing a repeat arthroscopy following a LARS ACL reconstruction. The histological diagnosis of synovitis was more frequently encountered than an arthroscopic appearance of synovitis. Whilst the results of this case series cannot support a direct causative link between LARS failure and the development of synovitis, this study highlights the need to remain vigilant about the risk of reactive synovitis following LARS ACL reconstruction due to exposure of the knee to foreign body material.

LEVEL OF EVIDENCE

Level IV, case series.

Activity-related outcome in anterior cruciate ligament reconstruction with synthetic ligament advanced reinforcement system

BACKGROUND

Arthroscopic anterior cruciate ligament (ACL) reconstruction with ligament advanced reinforcement system (LARS) had revealed good results with low complication and failure rate in series of studies. The specific candidates for ACL reconstruction with LARS are still unknown anyway. The purpose of this study is to evaluate the activity-related outcome in ACL reconstruction using LARS ligament.

METHODS

A total of 43 unilateral arthroscopic ACL reconstructions with LARS were collected and divided into two groups: group A (preinjury Tegner score ≥ 6, n = 20) and group B (preinjury Tegner score < 6, n = 23). We had analyzed the stability of knee and functional outcome with a minimum of 2-years follow up.

RESULTS

All patients were aware of improvement over the knee stability immediately after ACL reconstruction with LARS. The functional outcome of knee was improved in both groups by analysis with the Lysholm score and modified International Knee Documentation Committee (IKDC) score. The postoperative grading of the knee examination form of modified IKDC grade showed no statistical difference in both groups.

CONCLUSION

Arthroscopic ACL reconstruction with LARS was encouraged as an alternative option even in high sports demand patients.

Anterior Cruciate Ligament Reconstruction Using a Bone-Patellar Tendon-Bone Graft With and Without a Ligament Augmentation Device: A 25-Year Follow-up of a Prospective Randomized Controlled Trial

Background

Various grafts and ligament augmentation devices (LADs) have been used in the search for optimal reconstruction of the anterior cruciate ligament (ACL).

Purpose

To compare 25-year follow-up results after ACL reconstruction using a bone-patellar tendon-bone (BPTB) graft with or without the Kennedy LAD.

Study Design

Randomized controlled trial; Level of evidence, 1.

Methods

One hundred patients undergoing ACL reconstruction between 1991 and 1993 were randomized into 2 groups: reconstruction using a BPTB graft alone (BPTB group, 51 patients) or a BPTB graft with the Kennedy LAD (LAD group, 49 patients). The 25-year follow-up evaluation included a clinical knee examination, patient-reported outcome measures, and an assessment of radiological osteoarthritis (OA) according to the Ahlbäck classification. Additional outcomes were reruptures and knee arthroplasty.

Results

Ninety-three patients (93%) were available for the follow-up evaluation: 48 patients in the BPTB group and 45 in the LAD group. Through telephone calls, 26 patients were excluded from further investigation because of reruptures and arthroplasty in the knee of interest; 67 patients were further investigated. A total of 43 of 44 (98%) and 42 of 44 (95%) patients had negative or 1+ Lachman and pivot-shift test results, respectively. The mean Lysholm score was 85 for the BPTB group and 83 for the LAD group. All mean Knee injury and Osteoarthritis Outcome Score (KOOS) subscale values were ≥73. There were no statistically significant differences between groups in any of these outcomes or regarding the Tegner score, radiological classification of OA, or number of ACL reruptures. Signs of radiological OA were detected in all patients, and severe radiological OA (Ahlbäck grade III, IV, or V) was detected in 32% of patients in the BPTB group and 21% of patients in the LAD group (P = .37). There were 12 patients in the BPTB group and 7 in the LAD group who had documented reruptures (P = .40). One patient in the BPTB group and 6 in the LAD group underwent knee arthroplasty (P = .054).

Conclusion

In the present study, there were no statistically significant differences between groups in any of the outcomes. After 25 years, 19% of patients had reruptures, 27% had severe radiological OA, and 7% underwent knee arthroplasty.

Impact of chemical and physical treatments on the mechanical properties of poly(ε-caprolactone) fibers bundles for the anterior cruciate ligament reconstruction

The anterior cruciate ligament rupture is one of the most common sport injuries. Due to ligaments’ poor healing capacity, surgical intervention is often required. Nowadays, these injuries are managed using replacement autografts or to a lesser extent using artificial ligaments. With the expansion of tissue engineering, more recent researches focus on the development of biodegradable structures that could allow graft functioning while enhancing host integration. The main challenge is to develop a structure that gradually loses its mechanical properties when at the same time the neo-ligament gains in solidity. Mechanical behavior and reconstruction of natural tissue are the two key points for such a successful device. This article evaluates the mechanical consistency of poly(ε-caprolactone) fibers bundles grafted with sodium polystyrene sulfonate, as a candidate for ligament prosthesis. In order to be medically used, PCL fibers need to cope with multiple steps before implantation including extensive washings, knitting, grafting and sterilization processes. The evolution of mechanical properties at each step of the elaboration process has been investigated. The results show that PCL bundles have the same visco-elastic behavior than the native ACL. Nevertheless, when undergoing physical treatments such as ionizing radiations, like UV or β-rays, the material endures a hardening, increasing its stiffness but also its fragility. At this opposite, the thermal radical grafting acts like an annealing step, increasing significantly the elasticity of the PCL fibers. With this chemical treatment, the stiffness is decreasing, leading to higher energy dissipation. Added to the observation of the structure of the material, this demonstrates the possibility of the PCL to modulate it microstructure. In case of orthopedic prosthesis, the need of such a construct is strongly required to avoid distension of the future prosthesis and to restore good knee stabilization, showing the promising future of PCL ligament prosthesis.

Allograft Anterior Cruciate Ligament Reconstruction Utilizing Internal Brace Augmentation

Anterior cruciate ligament (ACL) tears are among the most common sports-related injuries. Although studies have reported reliable outcomes with allograft tissue, several studies have shown a higher failure rate in younger patients. Although ACL graft augmentation has been met with varying levels of success, internal bracing of an allograft represents a promising area in ACL reconstruction. The purpose of this article is to detail allograft preparation involving a collagen-coated, ultrahigh-molecular-weight polyethylene/polyester suture tape as an internal brace augmentation for ACL reconstruction using the all-inside ACL GraftLink Technique (Arthrex, Naples, FL).

Synthetic devices for reconstructive surgery of the cruciate ligaments: a systematic review

PURPOSE

The role of synthetic devices in the management of the cruciate ligament-injured knee remains controversial. The aim of this systematic review was to assess the safety and efficacy of synthetic devices in cruciate ligament surgery.

METHODS

A systematic review of the electronic databases Medline, Embase, and The Cochrane Library (issue 1, 2014) on January 13, 2014, was performed to identify controlled and uncontrolled trials. Trials that assessed the safety and efficacy of synthetic devices for cruciate ligament surgery were included. The main variables assessed included rates of failure, revision, and noninfective effusion and synovitis. Patient-reported outcome assessments and complications were also assessed where reported.

RESULTS

From 511 records screened, we included 85 articles published between 1985 and 2013 reporting on 6 synthetic devices (ligament augmentation and reconstruction system [Ligament Augmentation and Reconstruction System (LARS; Surgical Implants and Devices, Arc-sur-Tille, France)]; Leeds-Keio [Xiros (formerly Neoligaments), Leeds, England]; Kennedy ligament augmentation device [3M, St Paul, MN]; Dacron [Stryker, Kalamazoo, MI]; Gore-Tex [W.L. Gore and Associates, Flagstaff, AZ]; and Trevira [Telos (limited liability company), Marburg, Germany]). The heterogeneity of the included studies precluded meta-analysis. The results were analyzed by device and then type of reconstruction (anterior cruciate ligament [ACL]/posterior cruciate ligament [PCL]/combined ACL and PCL). The lowest cumulative rates of failure were seen with the LARS device (2.6% for ACL and 1% for PCL surgery). The highest failure rate was seen in the Dacron ACL group (cumulative rate, 33.6%). Rates of noninfective synovitis and effusion ranged from 0.2% in the LARS ACL group to 27.6% in the Gore-Tex ACL group. Revision rates ranged from 2.6% (LARS) to 11.8% (Trevira-Hochfest; Telos). Recent designs, specifically the LARS, showed good improvement in the outcome scores. The mean preoperative and postoperative Lysholm knee scores were 54 and 88, respectively; the mean preoperative and postoperative Tegner activity scale scores were 3.3 and 6, respectively.

CONCLUSIONS

Preliminary results for newer-generation devices, specifically the LARS, show lower reported rates of failure, revision, and sterile effusion/synovitis when compared with older devices.

LEVEL OF EVIDENCE

Level IV, systematic review of Level II through IV studies.

Mega-granuloma After Using the Universal Clamp for Adolescent Idiopathic Scoliosis: What Is It and Can It Be Prevented?

STUDY DESIGN

Clinical case series.

OBJECTIVE

To characterize the postoperative course and histopathology of peri-implant tissue of adolescent idiopathic scoliosis patients who experienced postoperative development of an aseptic soft tissue reaction, with granulomas adjacent to the sublaminar polyethylene terephthalate strap-titanium clamp used in Zimmer's Universal Clamp (UC) spinal fixation system after spinal surgery.

BACKGROUND SUMMARY

The UC was designed for use with spinal deformity procedures in place of pedicle screws, hooks, or sublaminar wiring in fusion constructs. Recent studies of the UC lack emphasis on implant-related postoperative complications.

METHODS

A total of 26 consecutive patients who underwent spinal deformity correction for scoliosis were reviewed for implant-related postoperative complications. Histology, scanning electron microscopy with energy-dispersive X-ray spectroscopy, fractional culture/biopsy, and Gram stain examination of the peri-implant tissue of patients with complications was performed.

RESULTS

The authors reviewed 26 cases for correction of scoliosis. Two patients with adolescent idiopathic scoliosis who used the UC experienced implant-related complications with development of an aseptic soft tissue reaction with granulomas adjacent to the sublaminar polyethylene terephthalate straps-titanium clamp mechanism of the UC 8 months after AIS correction surgery. There were no signs or symptoms of wound infection. Gram stain revealed no organisms. There were many neutrophils and the surface of the wound revealed rare Staphylococcus aureus but the deep portions of the wounds were negative for organisms. Histopathology revealed extensive granulation tissue and histiocytes with engulfed birefringent particles or debris, and scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis revealed macrophages containing many particles identified as titanium.

CONCLUSIONS

adolescent idiopathic scoliosis patients who use the novel UC construct may develop postoperative foreign-body reaction.

Biodegradation of a magnesium alloy implant in the intercondylar femoral notch showed an appropriate response to the synovial membrane in a rabbit model in vivo

Degradable magnesium alloys are promising biomaterials for orthopedic applications. The aim of this study was to evaluate the potential effects on both the synovial membrane (synovialis) and the synovial fluid (synovia) of the degradation products of a MgYREZr-pin implanted in the intercondylar femoral notch in a rabbit model. Thirty-six animals were randomized into two groups (MgYREZr or Ti6Al4V alloy) of 18 animals each. Each group was then divided into three subgroups with implantation periods of 1, 4, and 12 weeks, with six animals in each subgroup. The initial inflammatory reaction caused by the surgical trauma declined after 12 weeks of implantation, and elucidated a progressive recovery of the synovial membrane. Compared with control Ti6Al4V pins, there were no significant differences between the groups. However, after 12 weeks, recovery of the synovial membrane was more advanced in the titanium group, in which 92% showed no signs of synovitis, than in the magnesium group. A cytotoxicity test with L929 cells and human osteoblasts (HOB) was also conducted, according to EN ISO 10993-5/12, and no toxic leachable products were observed after 24 h of incubation. In conclusion, the MgYREZr alloy seems to be a suitable material for intra-articular degradable implants.

ARTHROSCOPIC ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION WITH LARS ARTIFICIAL LIGAMENT: AN 8–15-YEAR FOLLOW-UP

The aim of this study was to evaluate the clinical results of anterior cruciate ligament (ACL) reconstruction with an artificial ligament of the Ligament Augmentation and Reconstruction System (LARS) via an 8–15-year follow-up. Between January 1996 and January 2003, 38 patients received arthroscopic anterior cruciate reconstruction with the LARS artificial ligament at the Show Chwan Memorial Hospital, Changhua, Taiwan. Among them, 28 cases were included in this study. Excluding two failure cases, 26 cases were involved in the statistical analysis of various clinical assessments. The mean follow-up period after reconstruction was 11.4 ± 1.9 years. Assessment of clinical results included physical examination, magnetic resonance imaging, radiography, KT-1000 arthrometer test for knee stability, range of motion measurement, Lysholm score, and Tegner scale activity evaluations. The outcomes showed that among these 28 follow-up patients, there were two failure cases. The survival rate of LARS ligament reconstruction in this long-term follow-up was 92.9%. Among the 26 clinical assessed cases, the stability of the knee joint was improved as the anterior translation displacement measured by arthrometer reduced from 7.0 ± 3.1 mm (range: 4–17 mm) pre-operatively to 1.7 ± 1.7 mm (range: 0–6 mm) post-operatively. The Lysholm score improved from 39.7 ± 11.5 pre-operatively to 85.9 ± 19.6 post-operatively. Tegner activity scale improved from 3.2 ± 1.5 pre-operatively to 5.4 ± 2.4 post-operatively. All three improvements have statistic significance as the p-values were less than 0.05. In conclusion, ruptured ACL reconstruction with LARS artificial ligament has a survival rate of 92.9% and complication rate of 28.6% in this 8–15-year follow-up.

Bone-patellar tendon-bone autograft versus LARS artificial ligament for anterior cruciate ligament reconstruction

The optimized graft for use in anterior cruciate ligament (ACL) reconstruction is still in controversy. The bone-patellar tendon-bone (BPTB) autograft has been accepted as the gold standard for ACL reconstruction. However, donor site morbidities cannot be avoided after this treatment. The artificial ligament of ligament advanced reinforcement system (LARS) has been recommended for ACL reconstruction. The purpose of this study is to compare the midterm outcome of ACL reconstruction using BPTB autografts or LARS ligaments. Between July 2004 and March 2006, the ACL reconstruction using BPTB autografts in 30 patients and LARS ligaments in 32 patients was performed. All patients were followed up for at least 4 years and evaluated using the Lysholm knee score, Tegner score, International Knee Documentation Committee (IKDC) score, and KT-1000 arthrometer test. There were no significant differences between the two groups with respect to the data of Lysholm scores, Tegner scores, IKDC scores, and KT-1000 arthrometer test at the latest follow-up. Our study demonstrates that the similarly good clinical results are obtained after ACL reconstruction using BPTB autografts or LARS ligaments at midterm follow-up. In addition to BPTB autografts, the LARS ligament may be a satisfactory treatment option for ACL rupture.

Second-look arthroscopic findings and clinical results after polyethylene terephthalate augmented anterior cruciate ligament reconstruction

PURPOSE

Based on the revival of artificial ligaments containing polyethylene terephthalate, this study aimed to evaluate objective intra-articular findings within scheduled second-look arthroscopy, patient-reported clinical outcome and stability after isolated augmented ACL reconstruction with polyethylene terephthalate (Trevira®) augmented patella-bone-tendon-bone graft.

METHODS

In a retrospective analysis of our institutional database, we found 126 patients with polyethylene terephthalate (Trevira®) augmented ACL reconstruction. All these patients underwent standardised second-look arthroscopic evaluation when removal of the augmentation became necessary. These second-look arthroscopic analyses focused on graft integration and remodelling in line with the polyethylene terephthalate augmentation. Arthroscopic re-examination comprised a graft evaluation including a structural and functional classification according to the Marburger Arthroscopy Score (MAS). Additional clinical evaluation was performed via the IKDC score and the scores of Tegner and Lysholm. Instrumental anterior laxity testing was carried out with a KT-1000™ arthrometer. Furthermore, a correlation analysis between the clinical parameters, the instrumental stability assessment and the corresponding arthroscopic graft condition was performed.

RESULTS

The arthroscopic evaluation showed rupture of 87 (69 %) of 126 augmentation devices. In 27 (31 %) of these 87 cases, synovial reactions were found particularly in the anterior compartment. An intact synthetic augmentation with signs of graft integration with intact synovial coating was only found in 30 %. Evaluation according to the MAS showed good to excellent structural and functional characteristics in 88 % of patients. Presence of a type III graft (MAS) was found in an additional 11 %. A rudimentary (type IV) graft was only detected once. Eighty-five percent of patients were graded A or B according to IKDC score. The Lysholm score was 92.4 ± 4.8. Correlation analysis demonstrated a significant relationship between clinical outcome according to the IKDC score (p<0.05), instrumental stability performance according to the KT-1000™ assessment (p<0.05) and the corresponding arthroscopic graft evaluation according to the MAS.

CONCLUSION

Graft integration and remodelling has complex and multi-factorial origins, particularly with artificial augmentation. Correlation analysis showed a significant relation between clinical condition, instrumental stability performance and arthroscopic graft constitution. The release of polyethylene terephthalate fibres caused inflammation of synovial tissue of the knee. Characteristic sub-clinical graft changes of structural, morphological and functional qualities of the inserted graft appear on second-look arthroscopy despite good clinical results.

Anterior cruciate ligament reconstruction: a systematic review of polyethylene terephthalate grafts

BACKGROUND

The ligament advanced reinforcement system (LARS) ligament is an artificial polyester ligament made from polyethylene terephthalate (PET) that is used for primary anterior cruciate ligament (ACL) reconstructive surgery. Recent media attention has resulted in a high awareness of this reconstructive option among patients; however, the outcomes compared with autograft are controversial.

OBJECTIVES

A systematic review of the literature was undertaken to examine the outcomes following LARS and long-term PET artificial grafts in ACL reconstructive surgery. The ultimate objective was to determine whether the LARS ligament should be incorporated into routine practice.

METHODS

A systematic search strategy from 1970 to June 2010 was used to retrieve relevant studies. Inclusion of articles was established through application of a predetermined protocol, independent assessment by two reviewers and a final consensus decision.

RESULTS

Twelve articles met the inclusion criteria for the LARS ligament. The methodology of the identified articles was poor. Only short-term outcomes were available. These results were good with low complication rates. Eleven articles reported on other PET grafts and recorded long-term follow-up of more than 4 years. These grafts had poor outcomes and a high rate of complications. No meta-analysis was possible.

CONCLUSIONS

There are surprisingly few studies reporting on LARS ligament outcomes. The literature has poor methodological quality. Short-term results for the LARS ligament appear good, with faster recovery times compared with autografts. Final short-term results are not significantly different from autograft. There is real concern that late failure and iatrogenic osteoarthritis may occur based on the results of other PET grafts.

Aseptic arthritis after ACL reconstruction by Tape Locking Screw (TLS®): report of two cases

In Tape Locking Screw (TLS(®)) ligamentoplasty, transplant bone fixation uses polyethylene terephthalate (PET). We report two cases of aseptic arthritis following anterior cruciate ligament (ACL) reconstruction using this material. Diagnosis was founded on negative sampling and complete cure following arthroscopic lavage and synovectomy without curative antibiotherapy. This complication was also described with other synthetic materials used in this indication (Dacron, PFTE, carbon), and with PET as transplant material but never as bone fixation material. The physiopathological hypothesis is in terms of PET particle release in the suprapatellar bursa; sinking the strips into the bone as fully as possible on implantation could avoid impingement. Longer TLS(®) ligamentoplasty series with adequate follow-up will be needed in order to estimate the true incidence of this complication.

Single-stage anterior cruciate ligament revision with bone-patellar tendon-bone: a case-control series of revision of failed synthetic anterior cruciate ligament reconstructions

PURPOSE

The purpose of this study was to investigate the clinical results of single-stage revision anterior cruciate ligament reconstruction (ACLR) after synthetic ligament failure.

METHODS

The subjects comprised 20 patients who underwent revision ACLR after synthetic ligament failure. All revisions were performed with bone-patellar tendon-bone graft, and bone tunnel expansion after removal of synthetic materials was treated with bone plugs sized and trimmed as necessary to fill the bone tunnels. Clinical results were assessed at a mean of 2.8 years postoperatively, followed by comparison with the results of 20 primary ACLRs selected as case-matched controls. Assessment included the Lysholm score, International Knee Documentation Committee (IKDC) evaluation, instrumented laxity testing, and radiologic examination.

RESULTS

Bone tunnel enlargement to 11 mm in diameter or greater was found in 10 of 20 revision ACLRs. However, favorable anteroposterior stability was obtained at final follow-up (1.4 +/- 2.0 mm in revision ACLR group and 1.5 +/- 1.5 mm in primary ACLR group). The overall Lysholm score improved significantly from preoperatively to final follow-up, but the revision ACLR group showed significantly worse results for the pain parameter than the primary ACLR group. The final IKDC results also showed significant postoperative improvement, but the number of cases with grade C was significantly higher in the revision ACLR group than in the primary ACLR group, which was attributed to radiologically confirmed osteoarthritis in the revision ACLR group.

CONCLUSIONS

Single-stage revision ACLR with bone-patellar tendon-bone graft after synthetic ligament failure yielded favorable results in terms of IKDC grade, Lysholm score, and anteroposterior stability, despite enlarged bone tunnels after removal of synthetic material. Inferior results for the radiologic and pain parameters of the IKDC and Lysholm scores were attributed to osteoarthritic changes inherent to the revision ACLR group.

LEVEL OF EVIDENCE

Level III, therapeutic case-control study.

Anterior cruciate ligament reconstruction with LARS artificial ligament: a multicenter study with 3- to 5-year follow-up

PURPOSE

The aim of this multicenter study was to evaluate the clinical outcome of anterior cruciate ligament (ACL) reconstruction by use of the Ligament Advanced Reinforcement System (LARS) artificial ligament (Surgical Implants and Devices, Arc-sur-Tille, France) with 3- to 5-year follow-up.

METHODS

From August 2004 to July 2006, 159 patients with ACL rupture underwent arthroscopic ACL reconstruction with LARS artificial ligament at 4 orthopaedic sports medicine centers in China. They were retrospectively followed up for 50 +/- 6 months (range, 36 to 62 months). Outcome assessment included physical examination, KT-1000 arthrometer testing (MEDmetric, San Diego, CA), magnetic resonance imaging, radiography, Lysholm score, Tegner score, International Knee Documentation Committee score, and subjective satisfaction rate. Quadriceps and hamstring isokinetic strength was evaluated in 68 patients.

RESULTS

The side-to-side difference in anterior translation (injured side - uninjured side) measured by KT-1000 arthrometer was 1.5 +/- 1.6 mm (range, -1 to 7 mm) postoperatively, and knee stability was significantly improved compared with preoperative data (P < .0001). Quadriceps and hamstring isokinetic peak torque of the injured limb expressed as a percentage of the contralateral limb was 93.6 +/- 10.7 and 95.8 +/- 12.0, respectively. The Lysholm score improved from 65.1 +/- 12.3 points (range, 30 to 95 points) preoperatively to 94.5 +/- 7.0 points (range, 65 to 100 points) postoperatively (P < .0001). The Tegner score improved from 3.1 +/- 1.6 (range, 0 to 6) preoperatively to 6.1 +/- 1.5 (range, 1 to 9) postoperatively (P < .0001). According to the International Knee Documentation Committee score, 94% of patients were graded A or B at last follow-up. Ninety-three percent of patients were very satisfied or satisfied with their outcome. LARS artificial ligament rupture occurred in 3 patients; knee synovitis developed in 1 of these patients.

CONCLUSIONS

ACL reconstruction with LARS artificial ligament used in patients with the ACL stump preserved in the acute and chronic phases has a very good outcome at mean of 50 months' follow-up. The overall complication rate for ACL reconstruction with LARS artificial ligament is 5.7%, and knee synovitis developed in only 1 case.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Synthetic grafts for anterior cruciate ligament rupture: 19-year outcome study

Artificial ligaments for ACL replacement have been widely used in the 1980s and early 1990s in orthopaedic surgery. Synthetic devices have been utilized either as a prosthetic material or as an augmentation for a biological ACL graft substitute. The initial enthusiasm surrounding the introduction of synthetic graft materials stemmed from their lack of donor morbidity, their abundant supply and significant strength of these devices. The disadvantages in long-term follow-up were found to be cross-infections, immunological responses, tunnels osteolysis, femural and tibial fractures, foreign-body synovitis and knee osteoarthritis. A total of 126 patients were treated with artificial ACL substitution with polyethylene terephthalate (PET) synthetic ligaments in our Institute between 1986 and 1990. Of the original group, 51 sportsmen aged 15 to 40 were followed-up at a mean of 19years (range 17.5 to 20.6years) after surgery. Assessment was made with KOOS and IKDC score, Tegner activity scale, clinical examination, KT-1000 arthrometer, and X-ray evaluation. Of the 51 patients followed-up, 27.5% were found to have ruptured their PET ligaments and 100% presented degenerative osteoarthritis at the X-ray evaluation according to Ahlbäck radiological classification of arthritis. The objective evaluation showed functional impairment in 29.4% with an average reduction of 3 points in the Tegner activity scale. The osteoarthritis observed in all patients prompted us to avoid the diffusion of this surgical technique. Although in theory well-conceived, studies have yet to substantiate the function of these augmentation devices or to show clinical better results than those achieved with isolated autograft or allograft ACL substitutes.

Anterior cruciate ligament reconstruction with synthetic grafts. A review of literature

Anterior cruciate ligament (ACL) rupture, one of the most common knee injuries in sports, results in anteroposterior laxity, which often leads to an unstable knee. Traditional ACL reconstruction is performed with autograft; disadvantages of this technique are donor site morbidity and a long rehabilitation period. In the 1980s, artificial ligaments became an attractive alternative to biological grafts. The initial enthusiasm surrounding their introduction stemmed from their lack of donor morbidity, their abundant supply and significant strength, immediate loading and reduced postoperative rehabilitation. Synthetic grafts made of different materials such as carbon fibers, polypropylene, Dacron and polyester have been utilised either as a prosthesis or as an augmentation for a biological ACL graft substitute. Nevertheless, every material presented serious drawbacks: cross-infections, immunological responses, breakage, debris dispersion leading to synovitis, chronic effusions, recurrent instability and knee osteoarthritis. Recently, a resurgence of interest in the use of synthetic prostheses has occurred and studies regarding new artificial grafts have been reported. Although many experimental studies have been made and much effort has been put forth, currently no ideal prosthesis mimicking natural human tissue has been found.

Anterior cruciate ligament revision reconstruction: results in 107 patients

BACKGROUND

Although techniques and options for suitable graft substitutes for anterior cruciate ligament surgery continue to improve, failures occur because of many reasons. Errors in surgical techniques seem to be important reasons.

HYPOTHESIS

Inappropriate positioning of the tunnels may be the most important reason for these failures. Anatomical anterior cruciate ligament revision reconstruction, using autografts, may yield acceptable outcomes.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

This retrospective study involved 148 anterior cruciate ligament revision reconstructions performed in our hospital using autografts. One hundred and seven patients were followed up at a mean of 72.9 +/- 20.6 months. Clinical evaluation was performed using the Lysholm score, the Tegner rating system, the International Knee Documentation Committee evaluation form, and the KT-1000 arthrometer. Radiographs were evaluated for signs of osteoarthritis according to the Jaeger and Wirth classification.

RESULTS

Inappropriate positioning of the tunnels was the most important reason (63.5%) for anterior cruciate ligament reconstruction failure. The average Lysholm score improved significantly at the follow-up (88.5 +/- 12.4 vs 51.5 +/- 24.9; P < .001). Moreover, the average Tegner activity score improved significantly compared with the activity score before revision surgery (6.3 +/- 1.8 vs 2.8 +/- 1.8; P < .001). The International Knee Documentation Committee score was A in 17 cases, B in 45, C in 37, and D in 8. Radiographic evaluation revealed that 33 patients had degenerative findings of grade I, 35 of grade II, 16 of grade III, and 2 of grade IV.

CONCLUSION

Anatomical anterior cruciate ligament revision reconstruction provides satisfactory midterm results as far as stability and function of the knee are concerned. In spite of these favorable subjective and objective results, the radiological evaluation revealed a significant progression of osteoarthritis.

Gross osteolytic tibia tunnel widening with the use of Gore-Tex anterior cruciate ligament prosthesis: a radiological, arthrometric and clinical evaluation of 17 patients 13-15 years after surgery

BACKGROUND

Postoperative widening of the bone tunnels have been found after anterior cruciate ligament reconstruction using autologus bone-patellar tendon-bone or hamstring tendon grafts. These changes seem to be of no clinical significance in a short to midterm follow-up. We investigated if a synthetic graft evokes the same bone tunnel widening and if it is of clinical significance in a longterm follow-up.

METHODS

We examined 17 patients, 13-15 years after their anterior cruciate ligament reconstruction using a Gore-Tex ligament prosthesis. The follow-up consisted of clinical examination, K-1000 arthrometric measurement, Tegner, Lysholm and IKDC scores, and CT examination of their tibia bone tunnels. 6 patients had been reoperated before follow-up, 3 because of graft rupture and 3 because of effusion and/or pain.

RESULTS

5 patients were graded as normal (n = 2) or nearly normal according to the IKDC score, and 4 of these patients still had their Gore-Tex prosthesis intact. 15 of the patients had a tibia bone tunnel wider than the drilled 7.9 mm diameter, ranging from 9.6 to 26 mm. These changes in the bone tunnels were in some cases without symptoms and could not be detected with arthroscopy, clinical examination, arthrometry or evaluation scores. We do not know whether they are progressive.

INTERPRETATION

Based on our findings, we recommend that patients who have had a Gore-Tex anterior cruciate ligament reconstruction should be examined not only clinically or by questionnaire, but also with CT.

10-16 year results of Leeds-Keio anterior cruciate ligament reconstruction

Following initial enthusiasm in the late 1980s, the use of artificial ligament substitutes for anterior cruciate ligament (ACL) reconstruction has declined. However, the disadvantages of donor site morbidity for autologous graft and concerns about cross-infection from allogenic material have resulted in a maintained interest in prosthetic ligament substitutes. This study presents the outcome of ACL substitution using the Leeds-Keio (LK) polyester ligament at a mean of 13.3 years (range 10-16 years). Outcome was assessed using the International Knee Documentation Committee score, the Lysholm knee score, Tegner activity scale and American Knee Society Score and laxity by clinical examination and the Stryker Knee Laxity Tester. Standardized radiographs were taken to assess for evidence of degenerative change. The objective scoring tests showed that all patients experienced some degree of symptoms from their knee but functional impairment varied widely. Of the group, 28% were known to have ruptured their LK ligament and 56% had increased laxity compared with their opposite knee but no correlation could be shown between rupture, increased laxity and poor function. Of particular concern, all post-operative knees had radiographic signs of degenerative change compared with a rate of 39% in the contralateral knees.

Revision anterior cruciate ligament reconstruction

Revision ACL surgery is indicated in patients who present with pathologic anterior laxity on clinical examination that reproduces their symptoms of instability during activities of daily living or athletic activities. The goals of the revision ACL surgery are to stabilize the knee, prevent further injury to the articular cartilage and menisci, and maximize the patient's function. Successful revision ACL surgery requires a thorough preoperative evaluation, including a detailed history, physical examination, and radiographic evaluation. Preoperative planning begins with a determination of the mechanisms of failure for the initial ACL reconstruction. Often a primary, as well as secondary cause, for failure can be identified. The determination of the cause of failure is the first step in a carefully-constructed treatment plan, which includes consideration of skin incisions to be used, method of graft removal, hardware removal, the need for a staged procedure or concomitant surgery, graft material selection, tunnel placement, graft fixation, and postoperative rehabilitation protocol. Despite the most meticulous planning, unanticipated findings may be encountered in the operating room, and the preoperative plan should have enough flexibility to accommodate these developments. Finally, it is crucial to counsel the patient preoperatively to limit his or her expectations regarding their surgical outcome. Given the complexity of revision ACL reconstruction, patient expectations must be adjusted to realistically match the potential for success. With proper planning, attention to detail, and appropriate patient expectations, revision ACL surgery can result in a beneficial and satisfying patient outcome.

Computational and Experimental Study of Performance of an Artificial Ligament: DacronTM yarn

The success rate of reconstructing the Anterior Cruciate Ligament (ACL) with prosthetic ligaments is currently low both in humans and animals. The stress distribution in prosthetic ligaments that causes failure is very complex and not yet understood. Therefore, we have begun to develop a Finite Element Model of a prosthetic ACL. Here we describe the normal and contact stresses in Dacron(TM) yarn (a multi-fibrillar structure) using input data based on experimental measurements of the load and strain of six designed yarns. The results show that the normal and contact stresses in the fibres of the ACL yarn are directly proportional to the yarn strains. Increasing the twisting length (transverse deformation) of the yarn increases the normal stress in the fibres and the yarn modulus, but decreases the contact stresses between the fibres. The structural properties of a yarn are dependent on the specific arrangement of various filament types. Increasing the distance between the longitudinal (symmetry) axes of the filaments and the axis of symmetry of the yarn decreases the stresses.

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.

Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction

With today's increasing emphasis on sporting activities, the incidence of anterior cruciate ligament injuries has also increased. Epidemiologic studies estimate that the prevalence of anterior cruciate ligament injuries is about 1 per 3000 Americans. Management of these injuries has evolved from nonoperative treatment to extracapsular augmentation and primary ligament repair to anterior cruciate ligament reconstruction. Treatment of these injuries has significantly improved over the last few decades with the application of knowledge gained from both basic science and clinical research. This article is composed of two parts. The first part reviews the biology and biomechanics of the injured anterior cruciate ligament and the basic science of reconstruction. In the second part, to be published later, current operative concepts of reconstruction, as well as clinical correlations, are reviewed. Summarizing the latest information on basic scientific as well as clinical studies regarding the anterior cruciate ligament, this article intends to demonstrate the correlation between the application of basic science knowledge and improvement of clinical outcomes.

Long-term results of anterior cruciate ligament reconstruction with a Dacron prosthesis. The frequency of osteoarthritis after seven to eleven years

In this prospective study we investigated 70 patients with chronic anterior instability who underwent anterior cruciate ligament reconstruction with a Dacron prosthesis. Fifty-five (79%) patients could be followed up at a mean of 9 years. Within the follow-up time, 44% (29 of 66) of the prostheses were diagnosed as ruptured; the annual rupture frequency was 5%. Second reconstructions were performed for 20 patients (29%), 5 patients had third reconstructions, and 9 patients wanted no further surgical treatment. Fifty-two patients (74% of the original group) underwent radiographic examination. Eighty-three percent (43) of these patients had radiographic changes in the operated knee, and 40% (21 of 52) had joint space reduction up to 50%. The rate of radiographically detected osteoarthritis was increased 10 times compared with the normal knee. Patients with medical instability and patients older than 30 years at the initial operation had more severe osteoarthritic changes. Based on the functional results of the patients with a ligament in place after 9 years, only 14% (10) of the original group had acceptable stability and knee function.

Particle-induced synthesis of collagenase by synovial fibroblasts: an immunocytochemical study

The response of synoviocytes to wear particles has been implicated in several orthopaedic pathologies, including the synovitis associated with the failure of synthetic anterior cruciate ligament (ACL) replacements. To study the interactions of particles with synovial fibroblasts at the level of the individual cell, we employed immunocytochemistry, with use of antiserum, to lapine interstitial collagenase. Cultures of the HIG-82 lapine synovial cell line showed only weak immunofluorescence under resting conditions. Incubation with phorbol myristate acetate or autocrine factors known as cell-activating factors (CAFs) induced marked changes in morphology and intense immunofluorescence. This technique then was used to study the effects of standard particles of latex and of particles generated from two prosthetic ACL materials, Dacron and carbon. Internalized particles of latex, Dacron, and carbon all induced collagenase. Particles of latex that were too large for endocytosis failed to induce collagenase, whereas particles of carbon and, in particular, Dacron that remained extracellular, still provoked considerable synthesis of collagenase. Thus, both the size and the physical properties of these materials influence their ability to activate synoviocytes. Certain cells that appeared by visual inspection to contain no particles nevertheless produced collagenase when in co-culture with cells that did contain particles. This is consistent with earlier biochemical data showing that phagocytosis, in addition to inducing collagenase, also provokes the release of CAFs, which then activate additional cells in the culture. More rarely, cells were identified which, although containing particles, did not stain positively for collagenase.(ABSTRACT TRUNCATED AT 250 WORDS)