Abstract
The aim of this critical review is to determine what constitutes an ideal disc replacement material and whether any of the existing materials reported in the literature satisfy the requirements of an effective disc substitute following temporomandibular joint (TMJ) discectomy. Over the last half century a myriad of interpositional materials have been used in the TMJ but nearly all have been less than successful. The disasters that followed the early use of alloplastic interpositional implants in the 1980s prompted the increased use of autogenous grafts in the 1990s. Whilst studies by the author on the use of dermis-fat grafts have been largely positive, there are still concerns that make the dermis-fat graft a less than ideal interpositional material for use in discectomized joint cavities. In reviewing the literature, it is clear that there is still no ideal interpositional material that satisfies all the criteria for replacement of a missing articular disc following TMJ discectomy.
A diseased or deformed disc that interferes with the smooth, pain free function of the temporomandibular joint (TMJ), and is beyond salvage, is a candidate for discectomy . Discectomy of the TMJ has the longest follow-up studies of any surgical procedure for the management of TMJ internal derangement with long-term (>5 year) positive outcomes . At least four studies studied patients for a minimum of 20 years following TMJ discectomy and found complete resolution in pain and restriction free diet in almost all patients. A recent 5 year follow-up study of 15 consecutive patients selected using strict inclusion criteria, who had unilateral TMJ discectomies without replacement, found that 87% of patients (13 of 15) fulfilled the criteria for successful TMJ surgery as proposed by the 2nd International Consensus Meeting . There are other TMJ discectomy studies showing similar positive long term outcomes , but most were hampered by inconsistent inclusion and success criteria.
In all discectomy patients reviewed there were significant changes in the condylar morphology of the operated joint . A gerberg & L undberg suggested that the altered radiographic morphology in the operated joints was the result of altered joint loading following discectomy . Some animal studies have found the condylar alteration following discectomy to resemble degenerative joint disease at the histological level , whilst other animal studies showed the condylar changes were primarily a remodelling response to the changed joint dynamics resulting from a missing disc rather than degenerative changes. Clinical studies involving magnetic resonance imaging (MRI) , support the opinion that the radiographic changes of the condyle are adaptive rather than degenerative because the reduced symptoms do not correlate with the significant condylar changes seen following discectomy which reflects the results of non-surgical studies that show a natural tendency for symptoms of intra-articular pathology to improve with time .
Whilst the literature clearly points to the long-term success of TMJ discectomy without replacement , there is still concern about the crepitus and regressive remodelling that takes place in the condyle. The aim of this critical review is to determine what constitutes an ideal disc replacement material and whether any of the existing materials reported in the literature satisfy the requirements of an effective disc substitute following TMJ discectomy.
Despite the success of long-term studies of TMJ discectomy, there is a perception amongst surgeons that disc replacement is required to help reduce the significant joint remodelling and crepitus that is seen following discectomy alone . Over the last half century a myriad of interpositional materials have been used in the TMJ ( Table 1 ), but nearly all have been less than successful, and some have spawned a generation of total joint replacements .
| Graft | Examples | Comments |
|---|---|---|
| No replacement | – | Symptomatic relief up to 30 years follow-up Crepitus & regressive remodelling of condyle |
| Alloplastic | Sialastic | |
| Teflon–proplast | ||
| Methylmethacrylate | ||
| Fossa prosthesis | Metal, plastic | |
| Allogeneic | Cartilage | Lyophilized, freeze-dried |
| Dura | Cryopreserved | |
| Xenograft | Collagen | Bovine source |
| Cartilage | ||
| Autogenous | Muscle | Temporalis |
| Fascia | Temporalis, pericranial, fascia lata | |
| Cartilage | Ear, rib, sternum | |
| Skin | Full thickness, dermis | |
| Fat | Abdomen, buttocks | |
| Combined | Muscle-fascia, dermis-fat | |
Alloplastic materials
The use of alloplastic materials to reconstruct or replace diseased tissues of the TMJ began with disastrous results when sialastic, and then teflon–proplast implants, were used to replace the articular disc following TMJ discectomy procedures in the late 1970s and early 1980s . Reports of inflammatory reactions associated with these alloplastic implants abound in the literature . D olwick & A ufdemorte described a foreign body reaction with giant cell infiltrate surrounding the sialastic implant and in an adjacent lymph node. C huong & P iper reported severe bone erosion with cerebrospinal fluid leakage surrounding the TMJ proplast–teflon implant. Joints containing alloplastic implants were found at operation to be severely inflamed with signs of gross destruction of the surrounding structures. Before these implants were withdrawn from the market in 1988, up to 20,000 were implanted in the USA alone . The disasters that followed the early use of alloplastic interpositional implants in the 1980s , such as sialastic and proplast–teflon as disc replacement materials , steered the increased use of autogenous grafts in the 1990s .
Autogenous grafts
Temporalis flaps , auricular cartilage and dermis grafts have been reported with seemingly good results. Most autogenous grafts have been used to replace failed alloplastic implants, which means there are few reports of autogenous grafts placed at the time of the discectomy. According to M cKenna there are too few data and too many variables to show that autogenous graft placement at the time of discectomy produces superior results to discectomy alone. This is inspite of numerous animal studies that appear to demonstrate the benefits and advantages of the various interpositional grafts following discectomy, which have not been adequately demonstrated in appropriate clinical studies . The temporalis muscle/fascia is the most popular interpositional material for reasons of close proximity and ease of use. Some less popular materials are considered below.
Ear cartilage
Several authors have described the implantation of cartilage in the TMJ. Perko was the first to report the use of fresh autogenous auricular cartilage for disc repair . This was followed by numerous papers that extolled the benefits of auricular cartilage grafts for the replacement of the disc. I oannides & M altha studied disc replacement in the TMJ of guinea pigs using autogenous auricular and sternal cartilage. T ucker et al. reported autogenous cartilage implantation following discectomy in primate TMJs. These authors concluded that autogenous auricular cartilage retained its viability without reactive or resorptive changes and appeared to be suitable as an autogenous tissue graft in both experiments. Later studies revealed a tendency for the auricular grafts to fragment, proliferate and result in fibrous ankylosis of the TMJ with progressive limitation of mouth opening, so they have since fallen out of favour.
Dermis grafts
Dermis has been used for the repair of the TMJ disc as well as for the treatment of ankylosis by many authors since Loewe first introduced dermal grafting in 1913 . The dermis graft was first introduced by Georgiade et al. in 1957 as an interpositional graft in the management of TMJ ankylosis . In 1962, Georgiade described the use of autogenous dermis graft as a disc replacement following TMJ discectomy . Since then, there have only been a few clinical studies published on the use of dermis grafts for disc repair and disc replacement material in the TMJ . Data on the use of autogenous grafts at the time of primary discectomy are limited as most reports are of patients who have undergone repeat TMJ surgery following previous failed arthrotomies . One study of 64 dermal grafts reported only three cases in which the graft was placed at the time of the primary discectomy . As far as can be ascertained, there has been only one clinical paper published on the use of the dermis graft at the same time as the discectomy . The clinical study by Dimitroulis of 35 joints in 29 patients demonstrated that dermis grafts were effective in reducing joint sounds, but the author conceded that dermis grafts were difficult to anchor and failed to prevent regressive remodelling of the condyle.
Fat grafts
As early as 1914, Murphy described the transplantation of autogenous free fat grafts into joints. In 1925, Lexer reported that multiple small fat grafts do not survive as well as a single large fat graft when he found that the volume of the original graft can shrink to two-thirds of its original volume after 1 year. The shrinkage of free fat grafts was confirmed by Peer who also found that after 1 year, free fat grafts lose, on average, 45% of their original volume following transplantation.
Two studies by Kanamori et al. that looked at the fate of autogenous free fat grafts used in posterior lumbar spine decompression surgery confirmed that fat tissue does survive long term. In the first study , MRI was used to determine that the grafted fat reduced in size to 57% after 42 days and 33% after 1 year compared with the graft imaged 3 days following transplantation. The signal intensity of the fat graft was lower than that of the subcutaneous fat tissues in the first 6 weeks following transplantation but the intensity had fully recovered to normal by 1 year . This is in contrast to a study by Van Akkerveeken et al. , who used computed tomography scanning to investigate the size of autogenous fat graft measured at operation and 2 years later and found no change in the size of the fat graft in 15 of 21 patients. In the second part of the same study by Kanamori et al. , histological specimens were procured of the fat graft tissue on repeated lumbar surgery. At the light microscopy level, using haematoxylin-eosin stains, the histological specimens showed that the grafted fat used in the posterior lumbar surgery demonstrated reduced size and quality of the fat globules, compared with normal fat tissue.
Other studies have postulated that autogenous free fat grafts prevent scar formation by acting as an effective haemostatic agent and a space filler that prevents the accumulation of blood and serum, which would otherwise turn into scar or bone. This finding has led clinicians to use autogenous free fat grafts as a means of minimizing the occurrence of excessive joint fibrosis and heterotopic calcification when undertaking total joint replacements, particularly in the TMJ .
The abdominal dermis-fat graft
In 2004, Dimitroulis first reported the use of abdominal dermis-fat grafts in TMJ surgery in 11 patients with TMJ ankylosis. Dimitroulis et al. have undertaken a number of studies using abdominal dermis-fat grafts as interpositional material following TMJ discectomy.
Dermis-fat grafts are most commonly used as orbital implants in anophthalmic sockets in paediatric patients . Dermis-fat grafts have also been used for augmentation rhinoplasties, closure of palatal fistulae and to restore the concave deformity following parotidectomy as well as to prevent Frey’s syndrome . According to Mackay et al. , the dermal layer is the vasoinductive layer for the underlying adipose graft and is usually placed facing against the subadjacent subcutaneous layer for optimal blood supply when used to augment and reconstruct major volumetric soft tissue defects. No evidence to substantiate the above statement was provided. As far as can be ascertained, there have been only two reports in the literature describing the use of dermis-fat grafts as interpositional material in the surgical management of TMJ ankylosis .
According to Dimitroulis fat grafts alone are easily fragmented, but when attached to dermis the fat tends to be more stable and less likely to fragment when handled and manipulated into a cavity such as a gap arthroplasty. Dermis-fat grafts are easily sculptured with fine scissors to fit neatly into any size cavity which, as reported by Dimitroulis , is the greatest advantage of this material over other interpositional materials already reported. Studies of the fate of dermis-fat grafts in non load-bearing areas such as human orbits and pig ears have demonstrated little change in the volume of the graft . In some cases, the dermis-fat graft in paediatric patients has grown in volume with the growth of the patient .
Various studies by Dimitroulis et al. demonstrate that abdominal dermis-fat is a promising graft material that satisfies most, but not all, of the criteria for an ideal interpositional graft following TMJ discectomy ( Table 2 ). There is evidence to support the long-term safety of dermis-fat in the disc-less TMJ cavity . The presence of dermis-fat is an effective barrier to joint ankylosis as it prevents new bone formation . This was especially evident in an animal study in which new condyles failed to regenerate in the presence of fat in the young adult rabbit. Further studies showed that abdominal dermis-fat does survive when transplanted to the TMJ although the rabbit model suggests that initial necrosis of the fat component of the graft is eventually replaced by neoadipogensis .
| Criteria for the ideal TMJ disc replacement material |
|---|
| Long term safety |
| -Data >2 years available |
| Adequate bulk |
| -Fills up the whole joint cavity |
| Good handling properties |
| -Remains intact during transfer |
| -Easy to sculpture during operation |
| -Can be easily moulded to fit the entire joint space |
| Easy to procure |
| -Simple & quick operation |
| -Minimal donor morbidity |
| -Hidden scar |
| Abundantly available |
| -Excess tissue available than what is required |
| -Can be harvested from multiple sites |
| Survives the intra-joint environment |
| -Able to adapt to the functional joint demands |
| -Does not fragment or degenerate over time |
| Facilitates normal joint function |
| -Reduces joint noises |
| -Permits full range of joint motion |
| -Allows pain free joint function |
| Prevents bone formation and joint ankylosis |
| -Acts as an effective barrier to calcification |
| -Eliminates heterotopic bone formation |
| Protects condyle from severe remodelling |
| -Provides a buffer between the articular surfaces |
| -Counteracts the process responsible for condylar degeneration |
Whilst the average size of the dermis-fat graft initially placed in the joint cavity following discectomy was 2.4 cm 3 , the grafts that were subsequently retrieved in a recent study by Dimitroulis measured an average 1.57 cm 3 . This suggests in vivo shrinkage of the graft by about one-third of the original volume that was placed. The MRI study by Dimitroulis et al. demonstrated that the fat present surrounding the mandibular condyle was measured at 3.1 cm 3 which was almost one-third (29%) larger than the original size of the dermis-fat graft that was initially placed into the joint. This indicates that the graft had grown in vivo , which could only be explained by the process of neoadipogenesis that was suggested by the rabbit study . The large discrepancy between the average sizes of the grafts found on MRI (i.e. 3.1 cm 3 ) compared with the average size of the grafts that were surgically retrieved (1.57 cm 3 ) may be explained by the possibility that only the graft material interposed within the joint space was excised, and that a large component of the dermis-fat graft outside the functional joint cavity (about 50%) was left in situ . If that is the case, the results of Dimitroulis would help to explain the composition of the ‘grey matter’ found in the joint space on MRI . Effectively, the grafts retrieved in the Dimitroulis study were the ‘grey matter’ seen on MRI in the Dimitroulis et al. study, which demonstrated extensive collagen fibres that were interspersed with islands of mature adipose tissue and remnants of dermal elements such as sweat glands and hair follicles as seen under light microscopy. The ratio of fat to non-fat tissue in the retrieved specimens in the Dimitroulis study were no more than 40% of the total specimen, which would explain the absence of a strong fat signal in the ‘grey matter’ that was readily found interposed within the actual joint space on MRI in the Dimitroulis et al. The results of the Dimitroulis retrieval study indicate that the dermis-fat graft undergoes increased fibrotic changes over time in response to the functional demands of the joint environment which it occupies. All the retrieved specimens demonstrated evidence of the basic fat and dermal elements, albeit in lesser quantities compared with the graft that was originally implanted.
Whilst the discectomy procedure is largely responsible for the resolution of joint pain and dysfunction, the quality of life study by Dimitroulis et al. showed abdominal dermis-fat was a safe procedure and helps promote smooth, pain-free joint function. The two most recent studies by Dimitroulis revealed that the dermis-fat graft is not always successful, as it fails to protect the condyle from further degeneration in one-third of cases and the ultimate fate of a joint replacement in 7% of cases. Despite the short-comings, the evidence presented by Dimitroulis et al. supports the safety and effectiveness of the dermis-fat graft as an interpositional material in the TMJ.
Whilst the studies undertaken by Dimitroulis et al. have been largely positive, there are still concerns that make the dermis-fat graft a less than ideal interpositional material for use in discectomized joint cavities. A major concern is the degeneration of the one in three condyles that was found in the radiological study by Dimitroulis . Other related studies have provided supporting evidence for the long-term safety of the dermis-fat graft. It is likely that the degeneration of the mandibular condyles found in the two studies by Dimitroulis was triggered by unknown intrinsic reactions within the condyles and not related to the presence of the dermis-fat graft. The process of idiopathic condylar resorption, which occurs in the joints of young females where the disc is present and intact , lends further weight to the idea that condylar degeneration may be linked to intrinsic factors unrelated to the presence of the dermis-fat graft.
A final concern with respect to the dermis-fat is the need to harvest the graft from a distant site which creates the problem of additional donor site scarring that is easily visible, and particularly problematic for the younger patients. Even though the harvest technique is relatively simple and the donor site morbidity and potential risks are relatively small, there is still the need to focus on a material that eliminates the requirement for a second surgical procedure.
Autogenous grafts
Temporalis flaps , auricular cartilage and dermis grafts have been reported with seemingly good results. Most autogenous grafts have been used to replace failed alloplastic implants, which means there are few reports of autogenous grafts placed at the time of the discectomy. According to M cKenna there are too few data and too many variables to show that autogenous graft placement at the time of discectomy produces superior results to discectomy alone. This is inspite of numerous animal studies that appear to demonstrate the benefits and advantages of the various interpositional grafts following discectomy, which have not been adequately demonstrated in appropriate clinical studies . The temporalis muscle/fascia is the most popular interpositional material for reasons of close proximity and ease of use. Some less popular materials are considered below.
Ear cartilage
Several authors have described the implantation of cartilage in the TMJ. Perko was the first to report the use of fresh autogenous auricular cartilage for disc repair . This was followed by numerous papers that extolled the benefits of auricular cartilage grafts for the replacement of the disc. I oannides & M altha studied disc replacement in the TMJ of guinea pigs using autogenous auricular and sternal cartilage. T ucker et al. reported autogenous cartilage implantation following discectomy in primate TMJs. These authors concluded that autogenous auricular cartilage retained its viability without reactive or resorptive changes and appeared to be suitable as an autogenous tissue graft in both experiments. Later studies revealed a tendency for the auricular grafts to fragment, proliferate and result in fibrous ankylosis of the TMJ with progressive limitation of mouth opening, so they have since fallen out of favour.
Dermis grafts
Dermis has been used for the repair of the TMJ disc as well as for the treatment of ankylosis by many authors since Loewe first introduced dermal grafting in 1913 . The dermis graft was first introduced by Georgiade et al. in 1957 as an interpositional graft in the management of TMJ ankylosis . In 1962, Georgiade described the use of autogenous dermis graft as a disc replacement following TMJ discectomy . Since then, there have only been a few clinical studies published on the use of dermis grafts for disc repair and disc replacement material in the TMJ . Data on the use of autogenous grafts at the time of primary discectomy are limited as most reports are of patients who have undergone repeat TMJ surgery following previous failed arthrotomies . One study of 64 dermal grafts reported only three cases in which the graft was placed at the time of the primary discectomy . As far as can be ascertained, there has been only one clinical paper published on the use of the dermis graft at the same time as the discectomy . The clinical study by Dimitroulis of 35 joints in 29 patients demonstrated that dermis grafts were effective in reducing joint sounds, but the author conceded that dermis grafts were difficult to anchor and failed to prevent regressive remodelling of the condyle.
Fat grafts
As early as 1914, Murphy described the transplantation of autogenous free fat grafts into joints. In 1925, Lexer reported that multiple small fat grafts do not survive as well as a single large fat graft when he found that the volume of the original graft can shrink to two-thirds of its original volume after 1 year. The shrinkage of free fat grafts was confirmed by Peer who also found that after 1 year, free fat grafts lose, on average, 45% of their original volume following transplantation.
Two studies by Kanamori et al. that looked at the fate of autogenous free fat grafts used in posterior lumbar spine decompression surgery confirmed that fat tissue does survive long term. In the first study , MRI was used to determine that the grafted fat reduced in size to 57% after 42 days and 33% after 1 year compared with the graft imaged 3 days following transplantation. The signal intensity of the fat graft was lower than that of the subcutaneous fat tissues in the first 6 weeks following transplantation but the intensity had fully recovered to normal by 1 year . This is in contrast to a study by Van Akkerveeken et al. , who used computed tomography scanning to investigate the size of autogenous fat graft measured at operation and 2 years later and found no change in the size of the fat graft in 15 of 21 patients. In the second part of the same study by Kanamori et al. , histological specimens were procured of the fat graft tissue on repeated lumbar surgery. At the light microscopy level, using haematoxylin-eosin stains, the histological specimens showed that the grafted fat used in the posterior lumbar surgery demonstrated reduced size and quality of the fat globules, compared with normal fat tissue.
Other studies have postulated that autogenous free fat grafts prevent scar formation by acting as an effective haemostatic agent and a space filler that prevents the accumulation of blood and serum, which would otherwise turn into scar or bone. This finding has led clinicians to use autogenous free fat grafts as a means of minimizing the occurrence of excessive joint fibrosis and heterotopic calcification when undertaking total joint replacements, particularly in the TMJ .
The abdominal dermis-fat graft
In 2004, Dimitroulis first reported the use of abdominal dermis-fat grafts in TMJ surgery in 11 patients with TMJ ankylosis. Dimitroulis et al. have undertaken a number of studies using abdominal dermis-fat grafts as interpositional material following TMJ discectomy.
Dermis-fat grafts are most commonly used as orbital implants in anophthalmic sockets in paediatric patients . Dermis-fat grafts have also been used for augmentation rhinoplasties, closure of palatal fistulae and to restore the concave deformity following parotidectomy as well as to prevent Frey’s syndrome . According to Mackay et al. , the dermal layer is the vasoinductive layer for the underlying adipose graft and is usually placed facing against the subadjacent subcutaneous layer for optimal blood supply when used to augment and reconstruct major volumetric soft tissue defects. No evidence to substantiate the above statement was provided. As far as can be ascertained, there have been only two reports in the literature describing the use of dermis-fat grafts as interpositional material in the surgical management of TMJ ankylosis .
According to Dimitroulis fat grafts alone are easily fragmented, but when attached to dermis the fat tends to be more stable and less likely to fragment when handled and manipulated into a cavity such as a gap arthroplasty. Dermis-fat grafts are easily sculptured with fine scissors to fit neatly into any size cavity which, as reported by Dimitroulis , is the greatest advantage of this material over other interpositional materials already reported. Studies of the fate of dermis-fat grafts in non load-bearing areas such as human orbits and pig ears have demonstrated little change in the volume of the graft . In some cases, the dermis-fat graft in paediatric patients has grown in volume with the growth of the patient .
Various studies by Dimitroulis et al. demonstrate that abdominal dermis-fat is a promising graft material that satisfies most, but not all, of the criteria for an ideal interpositional graft following TMJ discectomy ( Table 2 ). There is evidence to support the long-term safety of dermis-fat in the disc-less TMJ cavity . The presence of dermis-fat is an effective barrier to joint ankylosis as it prevents new bone formation . This was especially evident in an animal study in which new condyles failed to regenerate in the presence of fat in the young adult rabbit. Further studies showed that abdominal dermis-fat does survive when transplanted to the TMJ although the rabbit model suggests that initial necrosis of the fat component of the graft is eventually replaced by neoadipogensis .
