Abstract
When clinically significant impingements of the temporomandibular joint (TMJ) exist, simple introduction of an arthroscope into the superior compartment can be difficult. Bone mass and volume of lateral fossa, lateral eminence, and tubercle impingements can be too large for micro-arthroscopic shaving rotors to manage efficiently. This paper presents examples of Types I–III impingements with pictorial modifications of open arthroplasty techniques for management.
Employment of dual photon imaging and standardization of coronal imaging in examination of the temporomandibular joint (TMJ) has improved the ability to diagnose joint impingements. A classification system has been established and biomechanical mechanisms of development suggested. Initiation of orthopaedic joint failure is viewed to be initial detachment of the lateral disc/capsule attachments to the lateral condyle and failure of the lateral collateral ligament integrity. Multiple finite element studies have confirmed stress fields which project laterally in the joint during function and are maximized during condylar translation and eccentric jaw functions. With tension forces predominating during TMJ function, impingements are viewed as naturally developing reactions to these tension functional force fields and joint loading; especially when orthopaedic instability has been longstanding. An impingement and its impact on the dynamic orthopaedics of joint translation and eccentric loading during mastication function should be appreciated prior to choice of initial surgical management.
In all clinically significant impingements, the volume of impingement removal from the lateral fossa rim to the articular tubercle can be too voluminous to remove with micro-arthroscopic osseous shaving techniques. Simple atraumatic introduction of an arthroscope can prove to be a significant challenge if the lateral lipping of an impingement is significant. Forcing the issue further could weaken the lateral disc/capsule attachments to the lateral condyle. Such weakening could create future potential progression of derangement loads in this area during translation function.
The progression of Wilkes II derangement to Wilkes III derangement is seen to be associated with advanced inferior compartment disc/capsule abnormities which could impact translational and eccentric functional instabilities. Both arthroscopic and arthroplasty surgical techniques must account for these biomechanical principles when surgical rehabilitation of patients with longstanding orthopaedic dysfunction is considered. Type III impingements and lateral condyle osteophytes must be accounted for as a potential aetiology of lower compartment and disc surface shear damage. Some mechanism of repair and re-securing of the lateral disc/capsule ruptures must be part of surgical objectives.
The purpose of this paper is to provide images of three categories of impingement and surgical management. Modifications of surgical technique are presented when arthroplasty is performed as the primary procedure in management of significant TMJ impingements and reinforcement of ruptured or torn collateral attachments.
Surgical technique
The open arthroplasty technique has been described and illustrated previously. When elimination of Type I lateral fossa, tubercle, and Type II eminence impingements and condyle osteophytes is the surgical goal, modification of the technique is required.
After the lower layer of the temporalis fascia is exposed, it is used as the guide to the zygomatic arch. Further blunt dissection defines the lateral arch, lateral fossa, rim of the fossa and forward to the lateral eminence. The superior joint space is injected with 0.5% bupivacaine local anaesthesia. An ophthalmic beaver blade is used to enter the superior joint space and a nerve hook retracts the lateral ligament and disc/capsule inferiorly. Care is taken if imaging reveals a significant osseous overhang or fossa rim lipping as the beaver blade must be directed superiorly in order to not damage the superior or lateral aspects of the disc/capsule. Often a large plica may be encountered and the disc/capsule may be adherent to the entire lateral fossa rim and its interior, superior sloping curvature. A small freer elevator is used for blunt dissection and release of the disc/capsule. Disc/capsule adhesions must be released from just anterior to the petrotympanic fissure to anterior to the tubercle in order to expose the extent of the anterior–posterior magnitude of the impingement. Often release of a large destabilizing plica is necessary in the region. At this point, the lower layer of temporalis fascia and periosteum is elevated off the lateral aspect of the fossa rim and arch from just anterior to the petrotympanic suture to anterior to the tubercle, up to the superior level of the arch. This essentially creates a pocket of fascia and ligament tissue for future closure with a ligament flap which will now be generated ( Fig. 1 A and B ).
Next, a blunt dissection between the lower fascia layer and the disc/capsule is generated. In essence, the entry level to develop this pocket is started in the region of the inferior lateral sulcus. A small freer working anterior and posterior defines this pocket plane from the posterior lateral condyle region to just below the tubercle. Bleeding may be present in this layer and generated pocket if significant rupture of the disc/capsule to the condyle exists. Forceps cautery is used for management. Attempts must be made to define and separate the disc/capsule attachments from the lateral ligament layer above this level. Once defined, a vertical incision in the ligament posteriorly is made of no more than 2–3 mm depth towards the inferior but superior to the neural and vascular structure emerging from the region posterior to the condyle. An anterior based lateral ligament flap is bluntly divided and separated from the underlying lateral disc/capsule attachments ( Fig. 2 B ). It is temporarily kept out of the reperative field with a suture. At this point, tears or areas of detachment of the disc/capsule to the condyle can be identified which should correspond to the area of detachment confirmed on preoperative coronal magnetic resonance imaging (MRI). In advanced derangements (Wilkes III), often this attachment is grossly flaccid, hyperemic, and ecchymotic. An appraisal of degree of flaccidity is made and an assessment of what will be necessary to mobilize the disc/capsule and reinforce congruency with the head of the condyle by repair and reinforcement of the ruptured capsule attachments. This is assessed but at this point the lower joint space is not entered.
A Wilkes retractor is placed and the joint distracted. It is important that the lower stabilizing pin is placed above sufficient and strong periosteum or capsule attachment for re-attachment of the lateral ruptured capsule. If sufficient exposure of the superior–lateral joint space has been created, the lateral most extent of the impingement should be appreciated at this point ( Fig. 2 B ). Depending on the mass of osseous lipping, a number 2 or 3 round burr is used first at the level of the fossa apex, defining the depth and lateral curvature of the fossa. The rim is further relieved laterally, anteriorly and medially depending on the size and nature of the impingement ( Fig. 2 C). Relief is carried anterior to the tubercle. Diamond rasps are used to create a lateral convexity and feathered curvature to the lateral eminence and anterior to the tubercle ( Fig. 2 D).
In Type I or II impingements with no coronal imaging of significant lateral osteophyte formation of the condyle, the inferior joint space may not have to be opened completely. In Wilkes III derangement, it is recommended the visualization of the lower lateral one-third of the inferior disc surface be visualized and examined for tearing of the posterior inferior lamina. In Wilkes II derangements with Type I or II impingement, only a small horizontal incision inferior to the lateral condyle pole is made in order to allow inferior, posterior, and lateral re-approximation of the lateral disc capsule to re-establish disc/capsule congruency to the condyle. This corrects the gross flaccidity of the disc/capsule interfering with translation and eccentric function. These functions are duplicated to check the integrity of the re-enforcement.
If a significant lateral osteophyte of the condyle exists, the inferior compartment must be opened more completely for exposure, and removal of the osteophyte and thorough inspection of the inferior disc surface ( Fig. 3 A–E ). If translational shear has irreversibly damaged the majority of the disc in the lower compartment, discectomy may be elected if late stage Wilkes III or IV derangement is present and necessary viscoelastic properties of the disc/capsule have been lost. Minimal entrance into the posterior attachment is made if capsular repair is performed. If discectomy is performed, synovial layers are re-approximated together from the superior and inferior joint spaces with the goal of closing any central vascular portion of the excised attachment. Not only is the irreversibly damaged disc/capsule removed, but all fossa impingements and condylar osteophtyes. Essentially, this operation could be considered a procedure to convert a complicated four-surfaced system to a two-surfaced system capable of functioning to meet curvilinear general plane motion functional orthopaedic demands when the disc/capsule has been irreversibly damaged and functional demands of the joint can no longer be met ( Fig. 4 ).
