Long-Term Degradation of Poly-Lactic Co-Glycolide/ b-Tricalcium Phosphate Biocomposite Anchors in Arthroscopic Bankart Repair: A Prospective Study Pietro Randelli, M.D., Riccardo Compagnoni, M.D., Alberto Aliprandi, M.D., Paola Maria Cannaò, M.D., Vincenza Ragone, M.Eng., Alberto Tassi, M.D., and Paolo Cabitza, M.D.
Purpose: To evaluate, using magnetic resonance (MR), the biological efficacy of anchors made of 30% b-tricalcium phosphate and 70% poly-lactic co-glycolide (PLGA) used for the repair of Bankart lesions after shoulder instability. Methods: Twenty consecutive patients who were candidates for surgical treatment for unidirectional, post-traumatic shoulder instability were treated arthroscopically with anchors made of 70% PLGA plus 30% b-tricalcium phosphate preloaded with OrthoCord suture (DePuy Mitek, Raynham, MA). Fifteen of them were evaluated by MR at least 16 months after the intervention. A second evaluation was performed at least 12 months after the first evaluation in the patients in whom implanted anchors were still visible at the first evaluation (n ¼ 5) with a low-intensity signal in all sequences. Two radiologists, with different amounts of experience (15 and 3 years), separately evaluated the MR patterns of the trabecular glenoid bone, the walls of the bone tunnel, and the signal from the anchors. The following parameters were considered in the MR evaluation: integrity of the tunnel edge (grade 0 to 2), intensity of the signal from the anchor site (grade 1 to 3), and presence of cystic lesions. The normal signal from the glenoid trabecular bone has been used as the reference parameter. The anchors were considered independent variables, and thus each one was analyzed individually, even in the same patient. At the final clinical follow-up, a Rowe questionnaire was filled out for each patient. Results: Overall, 44 anchors were evaluated (33 anchors at the first follow-up and 11 anchors at the second follow-up). The mean follow-up period was 28.6 months. With the exception of 2 patients (10%), none of the patients had any episodes of dislocation, having satisfactory postoperative results. No cystic lesions were detected by MR imaging. The interobserver concordance between the 2 radiologists calculated with the Cohen k was substantial (k ¼ 0.780 and k ¼ 0.791 for integrity of tunnel edge and for intensity of signal from anchor site, respectively). Both the integrity of the tunnel border and the intensity of the signal at the site of the anchors that had been implanted more than 24 months before the evaluation were significantly different from those of anchors implanted less than 24 months before the evaluation (tunnel border grade of 0 in 41%, 1 in 50%, and 2 in 9% v 0 in 4.5%, 1 in 50%, and 2 in 45.5% [P ¼ .003]; anchor signal grade of 1 in 41%, 2 in 45.5%, and 3 in 13.5% v 1 in 13.5%, 2 in 41%, and 3 in 45.5% [P ¼ .03]). Analysis of the linear contrasts (analysis of variance) showed a linear increase in the mean values for time to increased tunnel border grade (grade 0, 22 4 months; grade 1, 27 8 months; and grade 2, 29 5 months [P ¼ .02]) and grade of intensity of the signal in the anchor site (grade 1, 24 6 months; grade 2, 26 7 months; and grade 3, 29 7 months [P ¼ .05]). Conclusions: Anchors made of 30% b-tricalcium phosphate and 70% PLGA showed excellent biological efficacy, without causing significant cystic lesions, producing gradual changes in the MR signal that seems to become equivalent to that of the glenoid trabecular bone at a mean of 29 months after implantation. Level of Evidence: Level IV, therapeutic case series.
From Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano (P.R., V.R., P.C.), and Dipartimento di Radiologia (A.A., P.M.C.), IRCCS Policlinico San Donato, Milan; Azienda Ospedaliera “Sant’Anna” (R.C.), Como; and Istituto Ortopedico “Gaetano Pini” (A.T.), Milan, Italy. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received December 14, 2012; accepted September 23, 2013. Address correspondence to Riccardo Compagnoni, M.D., Azienda Ospedaliera “Sant’Anna,” Via Napoleona, 60, Como, Italy. E-mail: riccardo.compagnoni@ gmail.com Ó 2014 by the Arthroscopy Association of North America 0749-8063/12824/$36.00 http://dx.doi.org/10.1016/j.arthro.2013.09.082
A
nterior shoulder instability is the cause of structural lesions that predispose to new episodes of dislocation, thereby impairing the quality of life of the affected patient. Arthroscopic treatment of shoulder instability caused by labral-capsuloligamentous lesions is a very widespread technique that, in many cases, requires the use of anchors, which may be metallic or absorbable.1 Indeed, numerous techniques, involving different instruments and materials, have been described for these repairs and, more in general, for the fixation of soft tissues to bones.
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 30, No 2 (February), 2014: pp 165-171
165
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P. RANDELLI ET AL.
In recent years we have seen a succession of anchor models, which differ from each other by composition, size, shape, and fixation method. Historically, metallic anchors have guaranteed satisfactory results, but they may cause shoulder chondral injuries.2 Research has, therefore, been focused on the development of anchors made of absorbable materials. The evolution of bio-materials has led to the development of absorbable anchors whose primary stability is equivalent to that of nonabsorbable implants and that have a similar resistance to mechanical traction.3,4 The absorbable materials used in orthopaedics may be natural or synthetic and must be biocompatible with the tissue into which they are implanted (not creating foreign-body reactions).5-7 The first generation of biodegradable implants in polyglycolic acid was absorbed too quickly and caused foreign-body reactions.8,9 Polylactic acid, which also belongs to the group of poly-a-hydroxy acids, was then used because it degrades much more slowly. The concerns about this material are its long degradation time (a few years) and the lack of studies in the literature showing that it is completely replaced by bone.10,11 Anchors made of ceramic materials based on tricalcium phosphate, often in combination with other polymers, have recently been introduced into the market. Tricalcium phosphate is commonly used in orthopaedics to fill bone defects because its mineral content is similar to that of natural bone, its macro-porosity and micro-porosity have been shown to be osteoconductive, and it has good mechanical resistance and excellent biocompatibility. Studies of interference screws made of tricalcium phosphate and poly-lactic co-glycolide acid (PLGA) used in arthroscopic reconstruction of anterior cruciate ligaments showed fewer peripheral reactions, complete absorption of the anchor in all cases, and signs of osteoconduction in 75% of patients at 50 months.12 The aim of this prospective study was to evaluate, by magnetic resonance (MR) imaging, the biological efficacydin terms of absorption and promotion of bone growthdof anchors made of 30% tricalcium phosphate and 70% PLGA (Lupine Biocryl Rapide; DePuy Synthes, Raynham, MA) used to repair Bankart lesions after recurrent, unidirectional, post-traumatic shoulder instability. The clinical efficacy of arthroscopic stabilization using these anchors was also evaluated. Our hypothesis was that these absorbable anchors had excellent biological efficacy, promoting bone growth without causing significant cystic lesions, and that the intensity of the signal at the site of implantation, as detectable by MR imaging, was equivalent to that of the glenoid trabecular bone at long-term follow-up.
Methods Twenty consecutive patients who were candidates for surgical treatment for unidirectional, post-traumatic
shoulder instability and who were treated arthroscopically with tricalcium phosphateePLGA anchors (Lupine Biocryl Rapide) were recruited for this study. Patients included in this study underwent surgery between August 2008 and April 2010. The study protocol was approved by the province’s institutional ethics committee (authorization No. 2265; approved June 6, 2008), and the patients included in the study gave informed consent for their participation, after having received detailed information on the study. Inclusion and Exclusion Criteria The inclusion criteria were (1) a clinical history of at least 1 episode of anterior shoulder dislocation (documented by reduction in a hospital), (2) a positive apprehension test, and (3) a Bankart or anterior labroligamentous periosteal sleeve avulsion lesion confirmed by intraoperative examination. The exclusion criteria were (1) capsular lesions (humeral or reverse humeral avulsion of the glenohumeral ligaments), (2) presence of a bony Bankart and engaging Hill-Sachs lesion confirmed by intraoperative examination, (3) neurologic deficits or disturbances, (4) concomitant SLAP-type lesion, (5) concomitant lesions of the rotator cuff or cartilage damage, (6) previous surgery on the shoulder to be treated, and (7) comorbid conditions. Surgical Technique Operations were performed with patients under regional anesthesia or associated general anesthesia and an interscalene block. Patients were placed in the lateral decubitus position with the arm maintained at 40 of abduction and 15 of anterior flexion, in neutral rotation. A complete arthroscopic examination was performed by use of a standard posterior portal, and a Bankart lesion was found in all the patients included in our study. The lesion was completely mobilized and detached from the glenoid. An arthroscopic grasper was then used to pull the lesion superiorly. The glenoid subchondral bone was exposed with an arthroscopic shaver and a dedicated curette. Usually, 2 or 3 drill holes of 2.9 mm were created in the anterior glenoid rim with a dedicated driller. The drill holes were directed medially, away from the articular surface of the glenoid. An anchor made of 70% PLGA plus 30% b-tricalcium phosphate preloaded with OrthoCord suture (DePuy Mitek, Raynham, MA) was inserted into each glenoid drill hole to the desired depth. The anterior structures were re-tensioned by means of an arthroscopic sliding knotting technique. This step was repeated for all the anchors inserted to repair the capsulolabral complex. Rehabilitation Protocol After the operation, the joints were immobilized in a sling (Ultrasling 1; DJO, Vista, CA) for 25 days. Assisted
167
ANCHOR DEGRADATION AFTER BANKART REPAIR
physiotherapy was started on the 25th day after the intervention, and external rotation was limited to 0 until 2 months after the intervention. Muscle strengthening and return to sporting activities were allowed gradually, starting at 2 months after the operation. Clinical and Radiologic Evaluation The patients were evaluated clinically before the intervention and at least 16 months after it, by a single examiner not involved in the surgical operation. At the final clinical follow-up, a Rowe questionnaire for shoulder instability was filled out for each patient and the number of new subluxations reported by the patients was also recorded.13 The MR imaging evaluation of the patients was performed with a 1.5-T instrument (Sonata; Siemens, Malvern, PA). Scans were performed in the axial, sagittal, and coronal oblique planes, by use of turbo spin-echo T1weighted (TSE T1w), proton densityeweighted, and short tau inversion recovery (STIR) sequences (Table 1). Two radiologists, with different amounts of experience (15 and 3 years), separately evaluated the MR patterns of the trabecular glenoid bone, the walls of the bone tunnel, and the signal from the anchors. During the evaluation of the bone tunnel, particular attention was given to the low-intensity signal that expresses the border effect5 and the signal from within the tunnel, with the normal signal from the trabecular glenoid bone used as the reference parameter. Three grades were considered during the evaluation of the integrity of the tunnel border: grade 0, the wall of the tunnel is easily identifiable and characterized by a thin, uninterrupted low-intensity signal in all sequences; grade 1, partial discontinuity of the walls of the tunnel; or grade 2, lack of a detectable border. The intensity of the signal from the site of the implanted anchor was also analyzed with respect to the signal from the trabecular glenoid bone and divided into 3 grades: grade 1, a hyperintense signal in STIR sequences and hypointense signal in TSE T1w sequences, interpretable as an early stage; grade 2, incomplete isointensity of the signals in the STIR and TSE T1w sequences, which can be considered as an intermediate stage of bone apposition; and grade 3, isointense signals from bone ingrowth and the trabecular glenoid in the STIR and TSE T1w sequences, considered to indicate late-stage or completed bone apposition.
Fifteen of 20 patients who underwent arthroscopic treatment with anchors made of 30% b-tricalcium phosphate and 70% PLGA were evaluated by MR at least 16 months after the intervention, with scans targeted to assess the glenoid and the area of implantation of the anchors. A second radiologic evaluation was carried out at least 12 months after the first evaluation only in patients who had had the first MR evaluation at no less than 24 months (n ¼ 5) and in whom the first MR evaluation showed a hyperintense signal in the STIR sequences and a hypointense signal in the TSE T1w sequences with clearly recognizable tunnel walls characterized by a thin, continuous, low-intensity signal in all the sequences. The anchors were considered independent variables, and thus each one was analyzed individually, even in the same patient. The following parameters were considered in the MR evaluation: cystic reactions, integrity of the tunnel edge, and intensity of the signal from the anchor site. To enable easier coding of the signal and to evaluate its evolution over time, MR and computed tomography (CT) examinations of the anchor were performed immediately after its implantation into the trabecular bone of a human femoral head. This step enabled us to identify the characteristics of the anchor signal when biological degradation of the absorbable implant was still not under way (estimated time
Purpose: To evaluate, using magnetic resonance (MR), the biological efficacy of anchors made of 30% b-tricalcium phosphate and 70% poly-lactic co-glycolide (PLGA) used for the repair of Bankart lesions after shoulder instability. Methods: Twenty consecutive patients who were candidates for surgical treatment for unidirectional, post-traumatic shoulder instability were treated arthroscopically with anchors made of 70% PLGA plus 30% b-tricalcium phosphate preloaded with OrthoCord suture (DePuy Mitek, Raynham, MA). Fifteen of them were evaluated by MR at least 16 months after the intervention. A second evaluation was performed at least 12 months after the first evaluation in the patients in whom implanted anchors were still visible at the first evaluation (n ¼ 5) with a low-intensity signal in all sequences. Two radiologists, with different amounts of experience (15 and 3 years), separately evaluated the MR patterns of the trabecular glenoid bone, the walls of the bone tunnel, and the signal from the anchors. The following parameters were considered in the MR evaluation: integrity of the tunnel edge (grade 0 to 2), intensity of the signal from the anchor site (grade 1 to 3), and presence of cystic lesions. The normal signal from the glenoid trabecular bone has been used as the reference parameter. The anchors were considered independent variables, and thus each one was analyzed individually, even in the same patient. At the final clinical follow-up, a Rowe questionnaire was filled out for each patient. Results: Overall, 44 anchors were evaluated (33 anchors at the first follow-up and 11 anchors at the second follow-up). The mean follow-up period was 28.6 months. With the exception of 2 patients (10%), none of the patients had any episodes of dislocation, having satisfactory postoperative results. No cystic lesions were detected by MR imaging. The interobserver concordance between the 2 radiologists calculated with the Cohen k was substantial (k ¼ 0.780 and k ¼ 0.791 for integrity of tunnel edge and for intensity of signal from anchor site, respectively). Both the integrity of the tunnel border and the intensity of the signal at the site of the anchors that had been implanted more than 24 months before the evaluation were significantly different from those of anchors implanted less than 24 months before the evaluation (tunnel border grade of 0 in 41%, 1 in 50%, and 2 in 9% v 0 in 4.5%, 1 in 50%, and 2 in 45.5% [P ¼ .003]; anchor signal grade of 1 in 41%, 2 in 45.5%, and 3 in 13.5% v 1 in 13.5%, 2 in 41%, and 3 in 45.5% [P ¼ .03]). Analysis of the linear contrasts (analysis of variance) showed a linear increase in the mean values for time to increased tunnel border grade (grade 0, 22 4 months; grade 1, 27 8 months; and grade 2, 29 5 months [P ¼ .02]) and grade of intensity of the signal in the anchor site (grade 1, 24 6 months; grade 2, 26 7 months; and grade 3, 29 7 months [P ¼ .05]). Conclusions: Anchors made of 30% b-tricalcium phosphate and 70% PLGA showed excellent biological efficacy, without causing significant cystic lesions, producing gradual changes in the MR signal that seems to become equivalent to that of the glenoid trabecular bone at a mean of 29 months after implantation. Level of Evidence: Level IV, therapeutic case series.
From Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano (P.R., V.R., P.C.), and Dipartimento di Radiologia (A.A., P.M.C.), IRCCS Policlinico San Donato, Milan; Azienda Ospedaliera “Sant’Anna” (R.C.), Como; and Istituto Ortopedico “Gaetano Pini” (A.T.), Milan, Italy. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received December 14, 2012; accepted September 23, 2013. Address correspondence to Riccardo Compagnoni, M.D., Azienda Ospedaliera “Sant’Anna,” Via Napoleona, 60, Como, Italy. E-mail: riccardo.compagnoni@ gmail.com Ó 2014 by the Arthroscopy Association of North America 0749-8063/12824/$36.00 http://dx.doi.org/10.1016/j.arthro.2013.09.082
A
nterior shoulder instability is the cause of structural lesions that predispose to new episodes of dislocation, thereby impairing the quality of life of the affected patient. Arthroscopic treatment of shoulder instability caused by labral-capsuloligamentous lesions is a very widespread technique that, in many cases, requires the use of anchors, which may be metallic or absorbable.1 Indeed, numerous techniques, involving different instruments and materials, have been described for these repairs and, more in general, for the fixation of soft tissues to bones.
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 30, No 2 (February), 2014: pp 165-171
165
166
P. RANDELLI ET AL.
In recent years we have seen a succession of anchor models, which differ from each other by composition, size, shape, and fixation method. Historically, metallic anchors have guaranteed satisfactory results, but they may cause shoulder chondral injuries.2 Research has, therefore, been focused on the development of anchors made of absorbable materials. The evolution of bio-materials has led to the development of absorbable anchors whose primary stability is equivalent to that of nonabsorbable implants and that have a similar resistance to mechanical traction.3,4 The absorbable materials used in orthopaedics may be natural or synthetic and must be biocompatible with the tissue into which they are implanted (not creating foreign-body reactions).5-7 The first generation of biodegradable implants in polyglycolic acid was absorbed too quickly and caused foreign-body reactions.8,9 Polylactic acid, which also belongs to the group of poly-a-hydroxy acids, was then used because it degrades much more slowly. The concerns about this material are its long degradation time (a few years) and the lack of studies in the literature showing that it is completely replaced by bone.10,11 Anchors made of ceramic materials based on tricalcium phosphate, often in combination with other polymers, have recently been introduced into the market. Tricalcium phosphate is commonly used in orthopaedics to fill bone defects because its mineral content is similar to that of natural bone, its macro-porosity and micro-porosity have been shown to be osteoconductive, and it has good mechanical resistance and excellent biocompatibility. Studies of interference screws made of tricalcium phosphate and poly-lactic co-glycolide acid (PLGA) used in arthroscopic reconstruction of anterior cruciate ligaments showed fewer peripheral reactions, complete absorption of the anchor in all cases, and signs of osteoconduction in 75% of patients at 50 months.12 The aim of this prospective study was to evaluate, by magnetic resonance (MR) imaging, the biological efficacydin terms of absorption and promotion of bone growthdof anchors made of 30% tricalcium phosphate and 70% PLGA (Lupine Biocryl Rapide; DePuy Synthes, Raynham, MA) used to repair Bankart lesions after recurrent, unidirectional, post-traumatic shoulder instability. The clinical efficacy of arthroscopic stabilization using these anchors was also evaluated. Our hypothesis was that these absorbable anchors had excellent biological efficacy, promoting bone growth without causing significant cystic lesions, and that the intensity of the signal at the site of implantation, as detectable by MR imaging, was equivalent to that of the glenoid trabecular bone at long-term follow-up.
Methods Twenty consecutive patients who were candidates for surgical treatment for unidirectional, post-traumatic
shoulder instability and who were treated arthroscopically with tricalcium phosphateePLGA anchors (Lupine Biocryl Rapide) were recruited for this study. Patients included in this study underwent surgery between August 2008 and April 2010. The study protocol was approved by the province’s institutional ethics committee (authorization No. 2265; approved June 6, 2008), and the patients included in the study gave informed consent for their participation, after having received detailed information on the study. Inclusion and Exclusion Criteria The inclusion criteria were (1) a clinical history of at least 1 episode of anterior shoulder dislocation (documented by reduction in a hospital), (2) a positive apprehension test, and (3) a Bankart or anterior labroligamentous periosteal sleeve avulsion lesion confirmed by intraoperative examination. The exclusion criteria were (1) capsular lesions (humeral or reverse humeral avulsion of the glenohumeral ligaments), (2) presence of a bony Bankart and engaging Hill-Sachs lesion confirmed by intraoperative examination, (3) neurologic deficits or disturbances, (4) concomitant SLAP-type lesion, (5) concomitant lesions of the rotator cuff or cartilage damage, (6) previous surgery on the shoulder to be treated, and (7) comorbid conditions. Surgical Technique Operations were performed with patients under regional anesthesia or associated general anesthesia and an interscalene block. Patients were placed in the lateral decubitus position with the arm maintained at 40 of abduction and 15 of anterior flexion, in neutral rotation. A complete arthroscopic examination was performed by use of a standard posterior portal, and a Bankart lesion was found in all the patients included in our study. The lesion was completely mobilized and detached from the glenoid. An arthroscopic grasper was then used to pull the lesion superiorly. The glenoid subchondral bone was exposed with an arthroscopic shaver and a dedicated curette. Usually, 2 or 3 drill holes of 2.9 mm were created in the anterior glenoid rim with a dedicated driller. The drill holes were directed medially, away from the articular surface of the glenoid. An anchor made of 70% PLGA plus 30% b-tricalcium phosphate preloaded with OrthoCord suture (DePuy Mitek, Raynham, MA) was inserted into each glenoid drill hole to the desired depth. The anterior structures were re-tensioned by means of an arthroscopic sliding knotting technique. This step was repeated for all the anchors inserted to repair the capsulolabral complex. Rehabilitation Protocol After the operation, the joints were immobilized in a sling (Ultrasling 1; DJO, Vista, CA) for 25 days. Assisted
167
ANCHOR DEGRADATION AFTER BANKART REPAIR
physiotherapy was started on the 25th day after the intervention, and external rotation was limited to 0 until 2 months after the intervention. Muscle strengthening and return to sporting activities were allowed gradually, starting at 2 months after the operation. Clinical and Radiologic Evaluation The patients were evaluated clinically before the intervention and at least 16 months after it, by a single examiner not involved in the surgical operation. At the final clinical follow-up, a Rowe questionnaire for shoulder instability was filled out for each patient and the number of new subluxations reported by the patients was also recorded.13 The MR imaging evaluation of the patients was performed with a 1.5-T instrument (Sonata; Siemens, Malvern, PA). Scans were performed in the axial, sagittal, and coronal oblique planes, by use of turbo spin-echo T1weighted (TSE T1w), proton densityeweighted, and short tau inversion recovery (STIR) sequences (Table 1). Two radiologists, with different amounts of experience (15 and 3 years), separately evaluated the MR patterns of the trabecular glenoid bone, the walls of the bone tunnel, and the signal from the anchors. During the evaluation of the bone tunnel, particular attention was given to the low-intensity signal that expresses the border effect5 and the signal from within the tunnel, with the normal signal from the trabecular glenoid bone used as the reference parameter. Three grades were considered during the evaluation of the integrity of the tunnel border: grade 0, the wall of the tunnel is easily identifiable and characterized by a thin, uninterrupted low-intensity signal in all sequences; grade 1, partial discontinuity of the walls of the tunnel; or grade 2, lack of a detectable border. The intensity of the signal from the site of the implanted anchor was also analyzed with respect to the signal from the trabecular glenoid bone and divided into 3 grades: grade 1, a hyperintense signal in STIR sequences and hypointense signal in TSE T1w sequences, interpretable as an early stage; grade 2, incomplete isointensity of the signals in the STIR and TSE T1w sequences, which can be considered as an intermediate stage of bone apposition; and grade 3, isointense signals from bone ingrowth and the trabecular glenoid in the STIR and TSE T1w sequences, considered to indicate late-stage or completed bone apposition.
Fifteen of 20 patients who underwent arthroscopic treatment with anchors made of 30% b-tricalcium phosphate and 70% PLGA were evaluated by MR at least 16 months after the intervention, with scans targeted to assess the glenoid and the area of implantation of the anchors. A second radiologic evaluation was carried out at least 12 months after the first evaluation only in patients who had had the first MR evaluation at no less than 24 months (n ¼ 5) and in whom the first MR evaluation showed a hyperintense signal in the STIR sequences and a hypointense signal in the TSE T1w sequences with clearly recognizable tunnel walls characterized by a thin, continuous, low-intensity signal in all the sequences. The anchors were considered independent variables, and thus each one was analyzed individually, even in the same patient. The following parameters were considered in the MR evaluation: cystic reactions, integrity of the tunnel edge, and intensity of the signal from the anchor site. To enable easier coding of the signal and to evaluate its evolution over time, MR and computed tomography (CT) examinations of the anchor were performed immediately after its implantation into the trabecular bone of a human femoral head. This step enabled us to identify the characteristics of the anchor signal when biological degradation of the absorbable implant was still not under way (estimated time
