Alloplastic TMJ Reconstruction

Abstract

Total Alloplastic Temporomandibular joint reconstruction has been the treatment of choice for extreme cases of Temporomandibular Joint Disease and Pathology. Some of the remarkable advantages that are enjoyed with this device are early functional restoration, long term stability and improved jaw function. The prosthesis can be custom made to the particular individual also. This chapter provides an insight of the basics of Total Alloplastic Temporomandibular joint reconstruction which is evidence based.

1. Introduction

The need for the joint prosthesis comes up with the severity of the joint pathology. Failure of conservative therapies and non-surgical management, and surgical procedures with limited success rates leading to recurrence of the disease form the background for the development of the total alloplastic device for Temporomandibular Joint (TMJ).

The main goal of the reconstruction is to restore the form and function [1] of the jaw. In the yesteryears, Autogenous bones were used in most cases of Temporpmandibular Joint Reconstruction (TMJR). Revision surgeries in cases of TMJR with costochondral grafts need to be considered keeping in mind its excessive growth potential. The autogenous bone in growing individuals pose significant risks that may impair the jaw anatomy and function on a long run frequently leading to readdressing the joint problem. Innumerable evidence now exists in favour of the total joint replacement procedure where the joint anatomy and function being restored focussing more on the Biomechanical aspects [2].

Emerging studies support TMJR in terms of improved quality of life, improved masticatory function, improved jaw movement, speech and anatomy [3, 4, 5].

The device is made up of Cobalt-Chrome-Molybdenum (Co-Cr-Mo) or Titanium (Ti) condylar components with ultrahigh molecular weight polyethylene (UHMWPE) owing to their inert and bio friendly nature. These implants are available as stock fit and custom made that are patient specific.

On reviewing the literature, in the field of alloplastic TMJR, is interesting in that in 1974, Kiehn et al. attempted to construct an alloplastic TMJR prosthesis which was based on the principle used for total hip replacement with vitallium fossa and condyle unit.

In 1982, the vitek- Kent proplast—Teflon (PT) containing process was created (Vitek, Inc., Houston, Texas). What was initially successful was found to be a failure in a long run. In 1989 custom fit total TMJR system based on CAD CAM data was introduced by Techmedia that continues to be successful as of now [6].

In any TMJR, to be successful, some of the biological and mechanical characteristics are to be considered [7, 8, 9].

1. It should simulate the movements of TMJ

2. It should have close adaptability

3. Vivo longevity with regards to simulation of TMJ movements offering perfect imitation of translational movement of condyle without restricting the movements of uninvolved non replaced contralateral joint

4. Choosing a material with appropriate mechanical properties, tensile strength, hardness, elasticity and fatigue coefficience that will prevent stress from being transferred to adjacent bones, which may cause bone resorption and implant loosening.

1.1 Comparative anatomy pertaining to TMJ

The TMJ of mammals is different from other vertebrates, interestingly for functional modifications in that the articulating disc arose as a tendon which became pinched by the joint that is originated by intramembranous bones. Hence the growth depends on cartilaginous structures [10, 11, 12].

The TMJ anatomy size, shape, type of movements, and the load that it can take are species specific such as loss of synovial cavities in whales, loss of primary absence of disc in marsupials (sloths), variation in orientation of joint cavity in rodents, reversal of usual convex concave relationship to turn the mandibular condyle into a female element in sheeps and cattle, size variation and higher loading or lower loading depending on its pre requirement. Eg: crocodiles [13].

Sliding or side to side movement is also a variant. Considering all the animals, the human being’s TMJ anatomy has the most evolved anatomical structures for efficient masticatory function for present day.

1.2 Anatomy of TMJ

The TMJ is a synovial joint of condylar variety [14]. It is also known as ginglimo arthrodial joint. It has two compartments namely the upper joint space and lower joint space lined by cartilaginous cells and divided by a fibrocartilaginous disc.

The upper bony component is formed by the temporal bone and the lower articulating joint is formed by the head of the condylar process of the mandible. The joint cavity is encapsulated by a fibrous capsule that is filled with the synovial fluid. The disc is held in position by the discal ligaments and the lateral pterygoid insertion.

This attachment leads to certain disorders like clicking joint and so on and so surgical anatomy of TMJ should be studied at length before analysing the pathology.

The ligaments supporting the TMJ can be classified into intracapsular and extracapsular.

The intracapsular ligaments are the capsule, the interdiscal ligaments.

The extracapsular ligaments are the ligament of TMJ, stylomandibular ligament and sphenomandibular ligament.

1.3 Freakishness of TMJ

Anatomical considerations of freakishness of TMJ [15] pertaining to healing of alloplastic reconstruction are interesting in that these qualities are not met with in other joints of humankind.

Non weight bearing aspect of TMJ is peculiar. The function of TMJ on one side depends considerably on the health of other side TMJ and occlusal apparatus. This tripartiate relationship is very useful at times and also troublesome while treating TMJ pathologies with alloplastic TMJR.

Abundant vascular supply for the TMJ is any another unique feature. What triggers excellent tendency to heal in comparison with other joint procedures is yet not clearly understood so the whole focus in alloplastic grafting is to limit excessive post-surgical ankyloses to make it success.

1.4 Indications for TMJ alloplastic joints

The decision to take up TMJR [16, 17] has been suggested by various organisations such as national institute of health and care excellence (NICE) in May 2014(8) and the British association of oral and maxillofacial surgeons in 2008(9). A few situations where alloplastic joint reconstruction is preferred are

1. Failed previous alloplastic and/ or autogenous joint reconstruction

2. post traumatic condylar injury

3. Avascular necrosis

4. Reconstruction after tumour ablative surgery

5. Developmental abnormalities

6. Functional deformities

7. Severe inflammatory condition that fail to respond to conservative treatment.

8. It is likely that the use of alloplastic TMJR will be on the increase in paediatric field since such surgery may significantly improve the quality of life and reduce many of the functional limitations.

1.5 Contraindications

Absolute contraindications for alloplastic TMJR are many in which primary consideration is active infection [18, 19, 20, 21]. In acute infection if prosthesis is placed it can lead to micromotion and difficulty to stabilise the process and ultimately leading to failure. Next important contraindication is in those with documented allergy to implant components which may be present before or may manifest after the placement of prosthesis and are generally type IV delayed hypersensitivities.

Placement of fat grafts around the head of condylar components to decrease the tissue exposure to alloy components has been previously proposed by some authors and although this approach is reasonable there is no objective scientific evidence to support this hypothesis. Titanium prosthesis eliminate the possible allergy caused by Chromium cobalt Nickel Molebednum.

Uncontrolled systemic disease is considered yet another contraindication. A proper psychological preparation of preoperative evaluation must be considered essential particularly in elderly patients.

In a growing individual, alloplastic TMJR device necessitates reoperation.

1.6 Case report

A 20 years old male presented with Bilateral recurrent TMJ ankyloses (Figure 1). Initial TMJ injury was manged conservatively (2 years before) and hence no secondary deformities present. After some days he developed progressive Bilateral TMJ ankyloses. On clinical examination the mouth opening was 2 mm. Radiographic features showed development of radiopaque masses of Bilateral TMJ spaces with shortening of ramal height, signifying TMJ ankyloses. Bilateral TMJR with alloplastic device was planned.

Figure 1.

Preoperative limited mouth opening.

1.7 Fabrication of the TMJ implant

Over a period of time, TMJ implants were facing menace due to excessive healing or ankyloses and hence fascia interposed osteoarthroplasty, muscle interposed osseoarthroplasty were carried out but were unsuccessfully (Figure 2).

Figure 2.

Custom made TMJ alloplastic device.

Gap arthroplasty was reasonably successful but the anatomical disfigurement was experienced and hence metal implants were successfully (CO, Ti, Mb) used if allergic reactions were not a problem. At later stages titanium came into rescue to eliminate allergic reactions.

Using such devices had some teething troubles.

1. The implants can be heavy causing discomfort to the patients. The Young’s modulus of titanium is almost 5 times that of cortical bone and results in stress shielding effects [22, 23].

2. It is not cost effective and time consuming

The general difficulty all the surgeons experience were that the readymade implants did not have the ideal requisites of an implant as they do not snuggly fit.

Hence with the development of 3 D reconstruction digitally, the TMJR has come to near perfection.

The process involves making a CT for the patient and subsequent construction of Rapid prototyping (RP).

The resultant model involves the pathology of the TMJ (if any) which requires a trimming of the pathology in the model and 3D reconstruction of the implant digitally.

In this case, the prosthesis was patient specific. It consisted of the fossa and condylar components with the height of the device fabricated so as to compensate for the vertical height lost due to ramal shortening and gap arthroplasty.

The fossa eminence component articular surface was made of ultra-high-molecular-weight polyethylene over the stainless steel frame with 2 mm screw holes.

The stainless steel condylar unit has anteroposterior dimension of 5 mm and mediolateral dimension of 8 mm, with screw holes for fixation (Figure 2).

Intraoperative pictures show the snug fit of the prosthesis (Figure 3a and b).

Figure 3.

(a) TMJ alloplastic device in situ—Right side; and (b) TMJ alloplastic device in situ—Left side.

Thus the main goal of the procedure was achieved viz., mouth opening and jaw function (Figure 4).

Figure 4.

Postoperative mouth opening.

Postoperative check x ray was done to check for the proper positioning of the device (Figure 5).

Figure 5.

Postoperative radiograph confirming the TMJ alloplastic device in situ.

2. Conclusion

Considering the possible disadvantages of autogenous reconstruction of TMJ like unpredictable growth potential and graft fracture the Alloplastic implants constitute a superior option by way of producing predictable healing and functional duplication. The previously mentioned defects of heaviness of the metal and cost effectiveness are the future challenges in the field of TMJR.

Acknowledgments

Dr. Neelakandan RS, Vice chancellor, MAHER University, Chennai, Tamil Nadu.

Conflict of interest

“The authors declare no conflict of interest.”

Notes/thanks/other declarations

I extend my sincere thanks and gratitude to Dr. Gauthami Sundar and Dr. Rajaram for the timely support.