- Email: [email protected]
Chicken proximal interphalangeal joint as an animal model for human finger joint prosthesis evaluation
Journal of Orthopaedics 20 (2020) 105–110
Contents lists available at ScienceDirect
Journal of Orthopaedics journal homepage: www.elsevier.com/locate/jor
Discussion
Chicken proximal interphalangeal joint as an animal model for human finger joint prosthesis evaluation
T
Yuk Fai Lui∗, Wing Yuk Ip, Momina Shad, Hui Yi Chan Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong
A R T I C LE I N FO
A B S T R A C T
Keywords: Animal model Finger joint prosthesis Osteointegration
A group of chickens was employed as animal model for evaluation of osteointegration, stability and to a lesser extent, functional recovery potential of a newly designed human finger joint prosthesis under long term implantation. Mechanical and Histological test was conducted. Results in our study suggest that while chicken interphalangeal joint could be a potential model for evaluating surgical operation and osteointegration of human finger joint prosthesis, the effectiveness of evaluation in certain areas are far from ideal especially in functional and mechanical evaluation of the prosthesis. Nevertheless, it is suggested that chicken interphalangeal joint can still be a potential model for evaluating new human finger joint prosthesis if enough anchoring and stabilization could be provided because of the similarity in anatomical structure.
1. Introduction In recent decades there are rapid development in total joint replacement for human finger joint. The operation is targeted to replace the diseased joint with an artificial implant in order to restore the natural range of motion and relieving pain among patients suffering from arthritis.1,2 Various kinds of joint prothesis with different designs and materials are undergoing investigation all over the world as part of a continuous effort towards better standard of living for patients. Successfulness of joint prothesis depends on various factors including osteointegration,3 tissue response4,5 and biomechanical reaction,6 etc,1,7–12 which most of these are difficult to interpret by in vitro stimulation due to the complexity of dynamic biological system. Up to date there is no experimental system that can fully replicates or represents a living system to provide an accurate evaluation on implants under in vivo environment. A well-established animal model, therefore, is the most effective and accurate method to provide essential information of the prosthesis in those areas prior to human clinical trial.13–15 Despite the well-known advantage, actual application of animal model for joint prothesis evaluation remains a challenging topic. One major obstacle is that human finger joint is almost unique within animal kingdom and shares similarity only to primates. Anatomically interphalangeal joints are simple hinge joints constructed by two long bones that provide flexion in only one dimension. This feature does not
appear on limb joints in typical laboratory animals such as rats and rabbits which greatly limits possible models for a total joint replacement surgery. Digits of four legged animals also does not share a similar anatomical structure which makes implantation of human finger joint prosthesis impossible. Employing primates as an animal model, however, not only requires high operation cost but also creates ethical issue which is banned in some countries. Therefore there is a need for developing a substitute model which can provide evaluation on finger joint prothesis in terms of tissue response, osteointegration, implant stability, surgical protocol and to a lesser extent, functional analysis under in vitro environment. During our latest development of a distal-phalangeal joint prothesis, chicken was employed as an animal model for in vivo evaluation of osteointegration and tissue response of the prothesis under long term implantation. Chicken interphalangeal joint has been promoted as a model for human finger in some literatures.16,17 One major justification for using chicken as our animal model is that chicken interphalangeal joint of its toes shares a similar anatomy and dimension with human interphalangeal joint. Both joints are simple hinge joints stabilized by surrounding tendons and ligaments while capable of flexion in one axis. The distribution of soft tissue surrounding the joints are also comparable.17 It is therefore possible to conduct a total joint replacement surgery on the chicken interphalangeal joint using a real size prosthesis without any modification in the design and surgical protocol. This feature allows chickens to be the potential candidate as the animal
∗
Corresponding author. E-mail addresses: [email protected] (Y.F. Lui), [email protected] (W.Y. Ip), [email protected] (M. Shad), [email protected] (H.Y. Chan). https://doi.org/10.1016/j.jor.2020.01.018 Received 3 December 2019; Accepted 14 January 2020 Available online 18 January 2020 0972-978X/ © 2020 Professor P K Surendran Memorial Education Foundation. Published by Elsevier B.V. All rights reserved.
Journal of Orthopaedics 20 (2020) 105–110
Y.F. Lui, et al.
Fig. 1. (a) Demonstration of the surgical outcome with a 3-D printed prosthesis sample on cadaver; (b) under extension; (c) under induced flexion.
histological and mechanical evaluation. For mechanical evaluation, a special designed clamp was employed to hold the prosthesis. The other end of bone was embedded with epoxy followed by anchoring with metal screws. Pull-out test was conducted by mechanical testing system (MTS 858 mini bionix) at a constant load head velocity of 1mm/s until failure. For histological study, harvested samples was fixed in 10% buffered formalin followed by gradually dehydration in 70%, 95% and 100% ethanol. Dehydrated samples were infiltrated with xylene and embedded in PMMA. PMMA specimen blocks were cut into sections by an embedded diamond cutting band system complete with precision parallel control contact point (EXAKT 300CP) to a thickness about 0.3mm. The sections were attached on transparent slices by methyl methacrylate precision adhesive (EXAKT 7210 VLC) and polished to a final thickness of about 0.07mm by a micro-grinding system before histological staining. An adapted protocol for calcium staining, counter staining with Toluidine blue was employed. Bone sections were placed in 0.5% acidic alcohol for 30 second to remove the surface polymerized MMA followed by washing in tap water to remove residue acidic alcohol. Sections were then immersed in Toluidine blue dye solution and incubate at 60 °C for 30 minutes. 100% ethanol was employed for differentiation after staining. Excess dyes were removed by washing in 100% ethanol and sections were blotted dry on filter paper. Calcium staining was done by immersing Toluidine blue stained sections in Alizarin red dye solution for 5 minutes. Excess dyes were washed away with tap water followed by cleaning and dehydration in 100% ethanol.
model for joint prosthesis evaluation. On the other hand, the different in composition and micro-anatomy of bones between mammal and avian18,19 raise concerns on the effectiveness of the model. Cortex of avian long bones are usually thinner than mammals of the same scales. Avian bones are also filled with air sacs which results in a lower density than mammal counterparts. This structural difference results in the reduction of overall mechanical strength which may leads to failure of implantation. In this short report we will present the situation encountered during surgical operation, post-operation monitoring and final histological results of a total joint replacement operation on a group of chickens using an own developed joint prosthesis. Discussion will focus on whether avian toe joint is a suitable model for in vivo evaluation of human finger prosthesis for future prosthesis development.
2. Material and methods The experiment was conducted on 10 adult chickens purchased from local farm. Proximal-interphalangeal joint of the middle toe was chosen for the surgical operation because of its comparable size with the smallest set of human distal phalangeal joint prosthesis. Other joints were proven to be too small for the operation in our prior surgery on cadaver. The animal was put into general anaesthesia by Isoflurane inhalation. Skin disinfection was then carried out by using an iodophor scrub alternated three times with 70% ethanol followed by soaking with a disinfectant solution. A subcutaneous incision about 1–2 cm was created in the lateral side of the toe joint until the interphalangeal joint is exposed. Joint capsule was intended to be preserved during experimental planning but failed due to lack of space and surgical difficulty. The capsule was removed together with the articular surface together with part of the toes bone by surgical saw. All the tendons and ligaments were kept intent and untouched. The articular surface of the joint was then replaced by the joint prosthesis by press fitting. After insertion of the implant, surrounding soft tissue is reconstructed and stabilized by biodegradable suture. The surgical site was then closed by nylon suture. The toe after operation was demobilized by self-hardening bandage. Surgery was performed on one toe per animal only. Locomotion of the animal was not greatly affected by the immobilization. Pain killer and antibiotics was given when necessary. X-ray inspection was conducted every 5 weeks under general anaesthesia. After 15 weeks from operation, the animals were sacrificed and the joint was harvested for
3. Results All 10 operations were success. The whole surgical operation took an average of 30 minutes to complete under normal circumstances, which was within expectation. One major concern during the operation was the extensive bleeding and slow blood clotting rate of chicken which could lengthen the operation time by a great extent. These extensive bleeding blocked the view into the surgical site and did not stop naturally. Most of the time bleeding could be controlled by wrapping a rubber band which act as a tourniquet around the leg. In three cases the bleeding could only be stopped by electrocautery until the whole incision were sealed which caused certain damage to surrounding tissue. The joint could achieve flexion after the surgical operation. Fig. 1 is a demonstration of the surgical outcome on a chicken cadaver with a 3-D printed prosthesis sample. 106
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Fig. 2. 0-5-10 week X-ray inspection of the 8 surviving chickens.
walking and weight supporting without major disability. Healing of incision was slower than expected. On two animal there was traces of mild bleeding in the incision after 1 month from the operation. No trace of chronic inflammation was found on any animal. All chickens were terminated in the 15th week after operation. The following table summarized the 0-5-10 week X-ray inspection of the 8 surviving chickens (Fig. 2). Most of the prosthesis suffered from dislocation at the artificial articular surface after 5 weeks of implantation as indicated in the table. These dislocations were not observable externally without X-ray inspection. The most common type of dislocation is the disalignment of the distal and proximal component. Complete separation of the two components was also found in our
All animals were able and willing to stand and walk with both legs immediately after surgery, which was an unexpected behavior. They remained highly active in the first 48 hours after operation. After 48 hours most chicken showed certain degree of depression and recovered within two weeks at most. The natural behaviors of the chickens were not greatly affected throughout the remaining experimental period. One chicken was terminated after 4th week because of severe joint dislocation where the implant punctured the skin. Another chicken was discovered with disease irrelevant to the experiment and was terminated in 3rd week due to ethical and safety consideration. All other chickens remained healthy and could retain their natural behavior throughout the experimental period. All chickens could use their leg in
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calcified tissue could be found surrounding the implant. 4. Discussion All the surgical operation could be proceeded smoothly according to the designed protocol. The similarity in bone anatomy between human and chicken phalanges allows the same operation protocol to be conducted without major modification. The prosthesis can also fit into the phalange of chicken just the same way as its design (Fig. 6). On the other hand, problem encountered in the surgical operation was greater than expected. One major issue is that there is significant different in the rate of blood clotting between avians and mammals. This resulted in extensive bleeding in nearly all 10 operations and in 3 cases the bleeding cannot be controlled by tourniquet which surrounding tissue have to be sealed by electrocautery. This is the major cause for the increase in required operation time. Another concern during the surgical operation is that the cortex of chicken bone is much thinner than mammal (Fig. 7). There was problem in anchoring the prosthesis into the medulla cavity in the desired orientation. The situation is more crucial in the proximal phalange. This rise concern on the stabilization of the implant especially for designs that require press fitting, which was proven later in our experiment. Required strength from pull-out test was as high as 300N in one sample and histological study indicates calcification has took place surrounding the prosthesis. Loosening of implant however is common in our experiment despite the considerable amount of evidence suggests the prosthesis can conduct osteointegration. As mentioned above, loosening of implant occurs more often in the proximal phalange where there is not enough support from surrounding bone. The reduction in bone density and disappearance of bone volume that can be observed under the X-ray photos suggests the prosthesis was subjected to small motion during the healing period. These micro-motions of the implant not only prevent osteointegration and leads to formation of fibrous capsule but also causes degeneration of surrounding bone. Besides bone anatomy, animal behaviour is another factor that caused undesirable movement during the healing period. In our experiment all chickens use their leg in extensive weight bearing, walking and scratching immediately after operation. This introduce unexpected stress and motion to the implant before the completion of osteointegration. Dislocation was the most common failure in our experiment and was found on all employed animals. While loosening of implant partially accounts for dislocation, one major cause of dislocation was the difference between human finger joint and chicken leg joint anatomy. In our prosthesis design we do not expect for hyperextension of the joint. A ridge was therefore incorporated to act as a stopper and a point for stress transmission. In chicken however the first interphalangeal joint was naturally subjected to hyperextension under the animal's own weight during standing and walking (Fig. 8), where the range of motion was far beyond the designed range of our prosthesis. Together with the active behaviour of the chicken immediately after surgical operation, this resulted in early dislocations of the artificial articular surface as soon as days after operation. Complete immobilization of the joint was originally proposed to be a possible solution. External stabilization, however, was proven to be difficult and was of little help. The hyperextension of first interphalangeal joint in chicken is a natural gesture during standing, and casting or bandaging both cannot provide enough shielding and stabilization effect under obstruction of surrounding soft tissue. Throughout our experimental period all chickens did not hastate to use the operated leg in weight bearing and walking and scratching, which further worsen the dislocation. Under histological staining we can observe the great different between avian and mammal bones. Cortex of avian bones are considerably thinner than mammal. Medullar cavity was filled with air sacs which lacks a trabecular structure that can help in supporting the prosthesis. This difference in nature of bone also cause a different outcome after osteointegration. New bone formation around the
Fig. 3. High definition X-ray image of Proximal phalange and prosthesis after 15th weeks of implantation. Osteointegration can be observed on the implant.
experiment (Fig. 2, IV, 5th week). The situation deteriorate over time and no prosthesis can retain in their original orientation after 10 weeks. Besides dislocation, loosening of implant could also be observed in 4 out of 8 cases. Most of the loosening occurred in the proximal phalange, which the cortex surrounding the metal stem disappeared completely after 5–10 weeks of implantation. A circle shallow around the stem of some implants suggests the loosening could be caused by micro motion of the implant during the healing period (Fig. 2, I II, 10th week). Complete loosening of the distal component was relatively fewer and was found in 2 cases (Fig. 2, III IV, 10th week). Distal phalanges were intact and undamaged in most of the samples. On the other hand well anchored implants can also be found on some chickens despite the disalignment of the two components (Fig. 3). Only the proximal component of the prosthesis could be employed in the pull-out test because of the design of the clamp. Out of eight specimens, three was qualified to proceed to the pull-out test. The result is grouped in the following graph. Failure stress ranging from 60N to over 300N which indicates there is osteointegration to the implant (Fig. 4). Under histological staining, calcified tissue could be found proliferating along the implant (Fig. 5). These newly formed bones have a highly porous structure which is morphologically different to those commonly found on small mammals under comparable experiments. Nevertheless the discovery of calcified tissue on the implant surface is good evident for the occurrence of osteointegration. In other cases where there was loosening of implant, a fibrous capsule instead of
Fig. 4. Load-displacement curve of the 3 specimens involved in the pull-out test. Noted that one specimen (indicated by the black line) does not ends with failure of the specimen but the destruction of our clamp because the loading well exceeds the designed limit. 108
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Fig. 5. Section of implant and bone under alizarin red staining counter stain with toluidine blue. Calcified tissue is stained in read while fibrous tissue and nucleus are stained in blue. Cartilage is stained in purple. Left: specimen with loosened implant; Right: Specimen with osteointegration.
Fig. 6. Surgical outcome on (a) Human cadaver hand (b) Chicken foot. The similarity in anatomical structure near the articular surface can be observed.
prosthesis under in vivo implantation if enough stabilization of the joint can be provided. However, the natural behaviour of chickens including the hyperextension of proximal-interphalangeal joint and the quick recovery in natural behaviour after surgery proven to be the greatest obstruction which cause destabilization and dislocation of the prosthesis within one month after operation. External fixation of the chicken toe is also difficult within ethical consideration. Dislocation of the artificial joint deteriorate over time in most of the cases. Chicken leg is therefore not an ideal model for functional evaluation of finger joint
implants are considerably less dense that those on mammals such as rabbits and rats. The newly formed bones consist of a porous structure which lay around the implant. Pull-out test indicates these porous calcified tissues are able to provide anchoring effect to the implant, but the strength should be considerably lower than the value in mammals including human. In conclusion, chicken can be a suitable model for evaluating surgical procedures and protocol of human finger prosthesis. It can also provide basic information on osteointegration and stability of the 109
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Acknowledgements The project is supported and funded by Hong Kong Productivity Council. References 1. Murray PM. New-generation implant arthroplasties of the finger joints. J Am Acad Orthop Surg. 2003;11(5):295–301. 2. Brannon EW, Klein G. Experiences with a finger-joint prosthesis. J Bone Joint Surg Am. 1959;41-A(1):87–102. 3. Branemark R, et al. Osseointegration in skeletal reconstruction and rehabilitation: a review. J Rehabil Res Dev. 2001;38(2):175–181. 4. Dolwick MF, Aufdemorte TB. Silicone-induced foreign body reaction and lymphadenopathy after temporomandibular joint arthroplasty. Oral Surg Oral Med Oral Pathol. 1985;59(5):449–452. 5. Nalbandian RM, Swanson AB, Maupin BK. Long-term silicone implant arthroplasty. Implications of animal and human autopsy findings. J Am Med Assoc. 1983;250(9):1195–1198. 6. Joyce TJ, Unsworth A. The design of a finger wear simulator and preliminary results. Proc Inst Mech Eng H. 2000;214(5):519–526. 7. Linscheid RL. Implant arthroplasty of the hand: retrospective and prospective considerations. J Hand Surg. 2000;25a(5):796–816. 8. Foliart DE. Swanson silicone finger joint implants - a review of the literature regarding long-term complications. J Hand Surg. 1995;20a(3):445–449. 9. Calnan JS, et al. Development of an artificial finger joint for rheumatoid arthritis. Ann Rheum Dis. 1968;27(5):476. 10. Doi K, Kuwata N, Kawai S. Alumina ceramic finger implants: a preliminary biomaterial and clinical evaluation. J Hand Surg Am. 1984;9(5):740–749. 11. Luther C, Germann G, Sauerbier M. Proximal interphalangeal joint replacement with surface replacement arthroplasty (SR-PIP): functional results and complications. Hand (N Y). 2010;5(3):233–240. 12. Dryer RF, et al. Proximal interphalangeal joint arthroplasty. Clin Orthop Relat Res. 1984(185):187–194. 13. An YH, Friedman RJ. Animal models of orthopedic implant infection. J Investig Surg. 1998;11(2):139–146. 14. Wancket LM. Animal models for evaluation of bone implants and devices: comparative bone structure and common model uses. Vet Pathol. 2015;52(5):842–850. 15. Stadlinger B, et al. Systematic review of animal models for the study of implant integration, assessing the influence of material, surface and design. J Clin Periodontol. 2012;39(Suppl 12):28–36. 16. Athanassopoulos T, Loh CY. The chicken foot digital replant training model. Hand Surg. 2015;20(1):199–200. 17. Vamhidy L, et al. Anatomy of the chicken foot for the experimental investigation in flexor tendon surgery. Acta Chir Hung. 1995;35(1-2):21–33. 18. Aerssens J, et al. Interspecies differences in bone composition, density, and quality: potential implications for in vivo bone research. Endocrinology. 1998;139(2):663–670. 19. Currey JD, Alexander RM. The thickness of the walls of tubular bones. J Zool. 1985;206(Aug):453–468.
Fig. 7. Section of chicken phalange under histological staining. The thin cortex and the lack of dense trabecular structure can be easily observed. Below the articular cartilage the layer of bone is so thin that it can only provide poor initial anchoring to the prosthesis, which is hypothesized to be one of the causes for loosening of implant.
Fig. 8. Chicken employed in our experiment before the surgical operation. It is clear that the joint targeted for the operation (indicated by the read circle) is subjected to hyperextension in the animal's normal standing gesture.
prosthesis. Declaration of competing interest No potential conflict of interest was reported by the authors.
110
Contents lists available at ScienceDirect
Journal of Orthopaedics journal homepage: www.elsevier.com/locate/jor
Discussion
Chicken proximal interphalangeal joint as an animal model for human finger joint prosthesis evaluation
T
Yuk Fai Lui∗, Wing Yuk Ip, Momina Shad, Hui Yi Chan Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong
A R T I C LE I N FO
A B S T R A C T
Keywords: Animal model Finger joint prosthesis Osteointegration
A group of chickens was employed as animal model for evaluation of osteointegration, stability and to a lesser extent, functional recovery potential of a newly designed human finger joint prosthesis under long term implantation. Mechanical and Histological test was conducted. Results in our study suggest that while chicken interphalangeal joint could be a potential model for evaluating surgical operation and osteointegration of human finger joint prosthesis, the effectiveness of evaluation in certain areas are far from ideal especially in functional and mechanical evaluation of the prosthesis. Nevertheless, it is suggested that chicken interphalangeal joint can still be a potential model for evaluating new human finger joint prosthesis if enough anchoring and stabilization could be provided because of the similarity in anatomical structure.
1. Introduction In recent decades there are rapid development in total joint replacement for human finger joint. The operation is targeted to replace the diseased joint with an artificial implant in order to restore the natural range of motion and relieving pain among patients suffering from arthritis.1,2 Various kinds of joint prothesis with different designs and materials are undergoing investigation all over the world as part of a continuous effort towards better standard of living for patients. Successfulness of joint prothesis depends on various factors including osteointegration,3 tissue response4,5 and biomechanical reaction,6 etc,1,7–12 which most of these are difficult to interpret by in vitro stimulation due to the complexity of dynamic biological system. Up to date there is no experimental system that can fully replicates or represents a living system to provide an accurate evaluation on implants under in vivo environment. A well-established animal model, therefore, is the most effective and accurate method to provide essential information of the prosthesis in those areas prior to human clinical trial.13–15 Despite the well-known advantage, actual application of animal model for joint prothesis evaluation remains a challenging topic. One major obstacle is that human finger joint is almost unique within animal kingdom and shares similarity only to primates. Anatomically interphalangeal joints are simple hinge joints constructed by two long bones that provide flexion in only one dimension. This feature does not
appear on limb joints in typical laboratory animals such as rats and rabbits which greatly limits possible models for a total joint replacement surgery. Digits of four legged animals also does not share a similar anatomical structure which makes implantation of human finger joint prosthesis impossible. Employing primates as an animal model, however, not only requires high operation cost but also creates ethical issue which is banned in some countries. Therefore there is a need for developing a substitute model which can provide evaluation on finger joint prothesis in terms of tissue response, osteointegration, implant stability, surgical protocol and to a lesser extent, functional analysis under in vitro environment. During our latest development of a distal-phalangeal joint prothesis, chicken was employed as an animal model for in vivo evaluation of osteointegration and tissue response of the prothesis under long term implantation. Chicken interphalangeal joint has been promoted as a model for human finger in some literatures.16,17 One major justification for using chicken as our animal model is that chicken interphalangeal joint of its toes shares a similar anatomy and dimension with human interphalangeal joint. Both joints are simple hinge joints stabilized by surrounding tendons and ligaments while capable of flexion in one axis. The distribution of soft tissue surrounding the joints are also comparable.17 It is therefore possible to conduct a total joint replacement surgery on the chicken interphalangeal joint using a real size prosthesis without any modification in the design and surgical protocol. This feature allows chickens to be the potential candidate as the animal
∗
Corresponding author. E-mail addresses: [email protected] (Y.F. Lui), [email protected] (W.Y. Ip), [email protected] (M. Shad), [email protected] (H.Y. Chan). https://doi.org/10.1016/j.jor.2020.01.018 Received 3 December 2019; Accepted 14 January 2020 Available online 18 January 2020 0972-978X/ © 2020 Professor P K Surendran Memorial Education Foundation. Published by Elsevier B.V. All rights reserved.
Journal of Orthopaedics 20 (2020) 105–110
Y.F. Lui, et al.
Fig. 1. (a) Demonstration of the surgical outcome with a 3-D printed prosthesis sample on cadaver; (b) under extension; (c) under induced flexion.
histological and mechanical evaluation. For mechanical evaluation, a special designed clamp was employed to hold the prosthesis. The other end of bone was embedded with epoxy followed by anchoring with metal screws. Pull-out test was conducted by mechanical testing system (MTS 858 mini bionix) at a constant load head velocity of 1mm/s until failure. For histological study, harvested samples was fixed in 10% buffered formalin followed by gradually dehydration in 70%, 95% and 100% ethanol. Dehydrated samples were infiltrated with xylene and embedded in PMMA. PMMA specimen blocks were cut into sections by an embedded diamond cutting band system complete with precision parallel control contact point (EXAKT 300CP) to a thickness about 0.3mm. The sections were attached on transparent slices by methyl methacrylate precision adhesive (EXAKT 7210 VLC) and polished to a final thickness of about 0.07mm by a micro-grinding system before histological staining. An adapted protocol for calcium staining, counter staining with Toluidine blue was employed. Bone sections were placed in 0.5% acidic alcohol for 30 second to remove the surface polymerized MMA followed by washing in tap water to remove residue acidic alcohol. Sections were then immersed in Toluidine blue dye solution and incubate at 60 °C for 30 minutes. 100% ethanol was employed for differentiation after staining. Excess dyes were removed by washing in 100% ethanol and sections were blotted dry on filter paper. Calcium staining was done by immersing Toluidine blue stained sections in Alizarin red dye solution for 5 minutes. Excess dyes were washed away with tap water followed by cleaning and dehydration in 100% ethanol.
model for joint prosthesis evaluation. On the other hand, the different in composition and micro-anatomy of bones between mammal and avian18,19 raise concerns on the effectiveness of the model. Cortex of avian long bones are usually thinner than mammals of the same scales. Avian bones are also filled with air sacs which results in a lower density than mammal counterparts. This structural difference results in the reduction of overall mechanical strength which may leads to failure of implantation. In this short report we will present the situation encountered during surgical operation, post-operation monitoring and final histological results of a total joint replacement operation on a group of chickens using an own developed joint prosthesis. Discussion will focus on whether avian toe joint is a suitable model for in vivo evaluation of human finger prosthesis for future prosthesis development.
2. Material and methods The experiment was conducted on 10 adult chickens purchased from local farm. Proximal-interphalangeal joint of the middle toe was chosen for the surgical operation because of its comparable size with the smallest set of human distal phalangeal joint prosthesis. Other joints were proven to be too small for the operation in our prior surgery on cadaver. The animal was put into general anaesthesia by Isoflurane inhalation. Skin disinfection was then carried out by using an iodophor scrub alternated three times with 70% ethanol followed by soaking with a disinfectant solution. A subcutaneous incision about 1–2 cm was created in the lateral side of the toe joint until the interphalangeal joint is exposed. Joint capsule was intended to be preserved during experimental planning but failed due to lack of space and surgical difficulty. The capsule was removed together with the articular surface together with part of the toes bone by surgical saw. All the tendons and ligaments were kept intent and untouched. The articular surface of the joint was then replaced by the joint prosthesis by press fitting. After insertion of the implant, surrounding soft tissue is reconstructed and stabilized by biodegradable suture. The surgical site was then closed by nylon suture. The toe after operation was demobilized by self-hardening bandage. Surgery was performed on one toe per animal only. Locomotion of the animal was not greatly affected by the immobilization. Pain killer and antibiotics was given when necessary. X-ray inspection was conducted every 5 weeks under general anaesthesia. After 15 weeks from operation, the animals were sacrificed and the joint was harvested for
3. Results All 10 operations were success. The whole surgical operation took an average of 30 minutes to complete under normal circumstances, which was within expectation. One major concern during the operation was the extensive bleeding and slow blood clotting rate of chicken which could lengthen the operation time by a great extent. These extensive bleeding blocked the view into the surgical site and did not stop naturally. Most of the time bleeding could be controlled by wrapping a rubber band which act as a tourniquet around the leg. In three cases the bleeding could only be stopped by electrocautery until the whole incision were sealed which caused certain damage to surrounding tissue. The joint could achieve flexion after the surgical operation. Fig. 1 is a demonstration of the surgical outcome on a chicken cadaver with a 3-D printed prosthesis sample. 106
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Fig. 2. 0-5-10 week X-ray inspection of the 8 surviving chickens.
walking and weight supporting without major disability. Healing of incision was slower than expected. On two animal there was traces of mild bleeding in the incision after 1 month from the operation. No trace of chronic inflammation was found on any animal. All chickens were terminated in the 15th week after operation. The following table summarized the 0-5-10 week X-ray inspection of the 8 surviving chickens (Fig. 2). Most of the prosthesis suffered from dislocation at the artificial articular surface after 5 weeks of implantation as indicated in the table. These dislocations were not observable externally without X-ray inspection. The most common type of dislocation is the disalignment of the distal and proximal component. Complete separation of the two components was also found in our
All animals were able and willing to stand and walk with both legs immediately after surgery, which was an unexpected behavior. They remained highly active in the first 48 hours after operation. After 48 hours most chicken showed certain degree of depression and recovered within two weeks at most. The natural behaviors of the chickens were not greatly affected throughout the remaining experimental period. One chicken was terminated after 4th week because of severe joint dislocation where the implant punctured the skin. Another chicken was discovered with disease irrelevant to the experiment and was terminated in 3rd week due to ethical and safety consideration. All other chickens remained healthy and could retain their natural behavior throughout the experimental period. All chickens could use their leg in
107
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calcified tissue could be found surrounding the implant. 4. Discussion All the surgical operation could be proceeded smoothly according to the designed protocol. The similarity in bone anatomy between human and chicken phalanges allows the same operation protocol to be conducted without major modification. The prosthesis can also fit into the phalange of chicken just the same way as its design (Fig. 6). On the other hand, problem encountered in the surgical operation was greater than expected. One major issue is that there is significant different in the rate of blood clotting between avians and mammals. This resulted in extensive bleeding in nearly all 10 operations and in 3 cases the bleeding cannot be controlled by tourniquet which surrounding tissue have to be sealed by electrocautery. This is the major cause for the increase in required operation time. Another concern during the surgical operation is that the cortex of chicken bone is much thinner than mammal (Fig. 7). There was problem in anchoring the prosthesis into the medulla cavity in the desired orientation. The situation is more crucial in the proximal phalange. This rise concern on the stabilization of the implant especially for designs that require press fitting, which was proven later in our experiment. Required strength from pull-out test was as high as 300N in one sample and histological study indicates calcification has took place surrounding the prosthesis. Loosening of implant however is common in our experiment despite the considerable amount of evidence suggests the prosthesis can conduct osteointegration. As mentioned above, loosening of implant occurs more often in the proximal phalange where there is not enough support from surrounding bone. The reduction in bone density and disappearance of bone volume that can be observed under the X-ray photos suggests the prosthesis was subjected to small motion during the healing period. These micro-motions of the implant not only prevent osteointegration and leads to formation of fibrous capsule but also causes degeneration of surrounding bone. Besides bone anatomy, animal behaviour is another factor that caused undesirable movement during the healing period. In our experiment all chickens use their leg in extensive weight bearing, walking and scratching immediately after operation. This introduce unexpected stress and motion to the implant before the completion of osteointegration. Dislocation was the most common failure in our experiment and was found on all employed animals. While loosening of implant partially accounts for dislocation, one major cause of dislocation was the difference between human finger joint and chicken leg joint anatomy. In our prosthesis design we do not expect for hyperextension of the joint. A ridge was therefore incorporated to act as a stopper and a point for stress transmission. In chicken however the first interphalangeal joint was naturally subjected to hyperextension under the animal's own weight during standing and walking (Fig. 8), where the range of motion was far beyond the designed range of our prosthesis. Together with the active behaviour of the chicken immediately after surgical operation, this resulted in early dislocations of the artificial articular surface as soon as days after operation. Complete immobilization of the joint was originally proposed to be a possible solution. External stabilization, however, was proven to be difficult and was of little help. The hyperextension of first interphalangeal joint in chicken is a natural gesture during standing, and casting or bandaging both cannot provide enough shielding and stabilization effect under obstruction of surrounding soft tissue. Throughout our experimental period all chickens did not hastate to use the operated leg in weight bearing and walking and scratching, which further worsen the dislocation. Under histological staining we can observe the great different between avian and mammal bones. Cortex of avian bones are considerably thinner than mammal. Medullar cavity was filled with air sacs which lacks a trabecular structure that can help in supporting the prosthesis. This difference in nature of bone also cause a different outcome after osteointegration. New bone formation around the
Fig. 3. High definition X-ray image of Proximal phalange and prosthesis after 15th weeks of implantation. Osteointegration can be observed on the implant.
experiment (Fig. 2, IV, 5th week). The situation deteriorate over time and no prosthesis can retain in their original orientation after 10 weeks. Besides dislocation, loosening of implant could also be observed in 4 out of 8 cases. Most of the loosening occurred in the proximal phalange, which the cortex surrounding the metal stem disappeared completely after 5–10 weeks of implantation. A circle shallow around the stem of some implants suggests the loosening could be caused by micro motion of the implant during the healing period (Fig. 2, I II, 10th week). Complete loosening of the distal component was relatively fewer and was found in 2 cases (Fig. 2, III IV, 10th week). Distal phalanges were intact and undamaged in most of the samples. On the other hand well anchored implants can also be found on some chickens despite the disalignment of the two components (Fig. 3). Only the proximal component of the prosthesis could be employed in the pull-out test because of the design of the clamp. Out of eight specimens, three was qualified to proceed to the pull-out test. The result is grouped in the following graph. Failure stress ranging from 60N to over 300N which indicates there is osteointegration to the implant (Fig. 4). Under histological staining, calcified tissue could be found proliferating along the implant (Fig. 5). These newly formed bones have a highly porous structure which is morphologically different to those commonly found on small mammals under comparable experiments. Nevertheless the discovery of calcified tissue on the implant surface is good evident for the occurrence of osteointegration. In other cases where there was loosening of implant, a fibrous capsule instead of
Fig. 4. Load-displacement curve of the 3 specimens involved in the pull-out test. Noted that one specimen (indicated by the black line) does not ends with failure of the specimen but the destruction of our clamp because the loading well exceeds the designed limit. 108
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Fig. 5. Section of implant and bone under alizarin red staining counter stain with toluidine blue. Calcified tissue is stained in read while fibrous tissue and nucleus are stained in blue. Cartilage is stained in purple. Left: specimen with loosened implant; Right: Specimen with osteointegration.
Fig. 6. Surgical outcome on (a) Human cadaver hand (b) Chicken foot. The similarity in anatomical structure near the articular surface can be observed.
prosthesis under in vivo implantation if enough stabilization of the joint can be provided. However, the natural behaviour of chickens including the hyperextension of proximal-interphalangeal joint and the quick recovery in natural behaviour after surgery proven to be the greatest obstruction which cause destabilization and dislocation of the prosthesis within one month after operation. External fixation of the chicken toe is also difficult within ethical consideration. Dislocation of the artificial joint deteriorate over time in most of the cases. Chicken leg is therefore not an ideal model for functional evaluation of finger joint
implants are considerably less dense that those on mammals such as rabbits and rats. The newly formed bones consist of a porous structure which lay around the implant. Pull-out test indicates these porous calcified tissues are able to provide anchoring effect to the implant, but the strength should be considerably lower than the value in mammals including human. In conclusion, chicken can be a suitable model for evaluating surgical procedures and protocol of human finger prosthesis. It can also provide basic information on osteointegration and stability of the 109
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Acknowledgements The project is supported and funded by Hong Kong Productivity Council. References 1. Murray PM. New-generation implant arthroplasties of the finger joints. J Am Acad Orthop Surg. 2003;11(5):295–301. 2. Brannon EW, Klein G. Experiences with a finger-joint prosthesis. J Bone Joint Surg Am. 1959;41-A(1):87–102. 3. Branemark R, et al. Osseointegration in skeletal reconstruction and rehabilitation: a review. J Rehabil Res Dev. 2001;38(2):175–181. 4. Dolwick MF, Aufdemorte TB. Silicone-induced foreign body reaction and lymphadenopathy after temporomandibular joint arthroplasty. Oral Surg Oral Med Oral Pathol. 1985;59(5):449–452. 5. Nalbandian RM, Swanson AB, Maupin BK. Long-term silicone implant arthroplasty. Implications of animal and human autopsy findings. J Am Med Assoc. 1983;250(9):1195–1198. 6. Joyce TJ, Unsworth A. The design of a finger wear simulator and preliminary results. Proc Inst Mech Eng H. 2000;214(5):519–526. 7. Linscheid RL. Implant arthroplasty of the hand: retrospective and prospective considerations. J Hand Surg. 2000;25a(5):796–816. 8. Foliart DE. Swanson silicone finger joint implants - a review of the literature regarding long-term complications. J Hand Surg. 1995;20a(3):445–449. 9. Calnan JS, et al. Development of an artificial finger joint for rheumatoid arthritis. Ann Rheum Dis. 1968;27(5):476. 10. Doi K, Kuwata N, Kawai S. Alumina ceramic finger implants: a preliminary biomaterial and clinical evaluation. J Hand Surg Am. 1984;9(5):740–749. 11. Luther C, Germann G, Sauerbier M. Proximal interphalangeal joint replacement with surface replacement arthroplasty (SR-PIP): functional results and complications. Hand (N Y). 2010;5(3):233–240. 12. Dryer RF, et al. Proximal interphalangeal joint arthroplasty. Clin Orthop Relat Res. 1984(185):187–194. 13. An YH, Friedman RJ. Animal models of orthopedic implant infection. J Investig Surg. 1998;11(2):139–146. 14. Wancket LM. Animal models for evaluation of bone implants and devices: comparative bone structure and common model uses. Vet Pathol. 2015;52(5):842–850. 15. Stadlinger B, et al. Systematic review of animal models for the study of implant integration, assessing the influence of material, surface and design. J Clin Periodontol. 2012;39(Suppl 12):28–36. 16. Athanassopoulos T, Loh CY. The chicken foot digital replant training model. Hand Surg. 2015;20(1):199–200. 17. Vamhidy L, et al. Anatomy of the chicken foot for the experimental investigation in flexor tendon surgery. Acta Chir Hung. 1995;35(1-2):21–33. 18. Aerssens J, et al. Interspecies differences in bone composition, density, and quality: potential implications for in vivo bone research. Endocrinology. 1998;139(2):663–670. 19. Currey JD, Alexander RM. The thickness of the walls of tubular bones. J Zool. 1985;206(Aug):453–468.
Fig. 7. Section of chicken phalange under histological staining. The thin cortex and the lack of dense trabecular structure can be easily observed. Below the articular cartilage the layer of bone is so thin that it can only provide poor initial anchoring to the prosthesis, which is hypothesized to be one of the causes for loosening of implant.
Fig. 8. Chicken employed in our experiment before the surgical operation. It is clear that the joint targeted for the operation (indicated by the read circle) is subjected to hyperextension in the animal's normal standing gesture.
prosthesis. Declaration of competing interest No potential conflict of interest was reported by the authors.
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