Total Reconstruction of the Temporomandibular Joint with a Stock Prosthesis

Indications for temporomandibular joint (TMJ) reconstruction include bony ankylosis, failed previous alloplastic and autogenous joint replacement, posttraumatic condylar injury, avascular necrosis, posttumor reconstruction, developmental abnormalities, functional deformity, and severe inflammatory conditions that have failed to resolve with conservative treatments. Successful TMJ replacement requires careful preoperative planning, reasonable patient expectations, proper intraoperative technique, regimented postoperative physical therapy, close follow-up, and adequate pain management. Achieving successful TMJ replacement often requires multidisciplinary care from oral and maxillofacial surgeons, pain specialists, internists, physical therapists, and general dentists to optimize patient outcome.

Alloplastic joint reconstruction currently offers several advantages compared with autogenous replacements. These advantages include lack of donor morbidity, reduced intraoperative surgical time, immediate functioning, the ability to correct malocclusion (with bilateral replacement), and, most importantly, improved predictability. The most widely used autogenous graft for TMJ reconstruction is the costochondral graft. Compared with alloplastic joint reconstruction, costochondral grafting has a higher complication rate. Complications include graft resorption, overgrowth, and ankylosis. Alloplastic joint reconstruction allows for a stable platform in which retrognathia and facial asymmetry may be corrected in a single surgical procedure.

Unacceptable failure rates have been reported in previous alloplastic TMJ implant systems, which have provided valuable input for the development of newer implants approved by the US Food and Drug Administration (FDA). Appreciation of biomechanical and orthopedic principals, along with appropriate clinical trials, has helped in the development of safe and effective devices. These devices still have limitations, such as finite life expectancy, limited translation, the development of wear debris, and the size of the devices. Because fewer patients are requiring revision arthroplasty from previous failed devices, it can be expected that more primary joint reconstruction will be performed for conditions such as severe inflammatory arthritides, trauma, and ankylosis. A stock prosthetic device has the advantages of immediate availability, single-stage surgery, no need for recapitulation from a stereolithic model, and lower cost. Contraindications to alloplastic joint placement include the presence of active infection, skeletal immaturity, and severe or compromised bone deformity. Patients with severe bone anatomic discrepancies may be candidates for patient-matched custom implants.

Preoperative planning

Preoperative planning begins with a careful history and physical examination. Documentation should include the number of open and closed TMJ surgeries. Pain scores should be quantified, and analgesic use should be noted. Patients with a history of multioperated joints and chronic pain may benefit from an evaluation from a pain specialist before surgery. Many patients with severe rheumatic conditions are on immunosuppressive medications. Coordination for the temporary cessation of these medications (eg, glucocorticoids, disease-modifying antirheumatic drugs, and anticytokine medications) in the perioperative period is important to prevent infection and promote healing. Good communication with the patient’s rheumatologist is paramount. Many imaging modalities are available to assess the patient. At this institution, all patients receive a panorex and computed tomography scan to visualize the existing bone and bone quality as well as the proximity of adjacent vital structures. The patient is then counseled, and appropriate expectations of function and pain relief are discussed.

Procedure

Prep and Positioning

Strict adherence to aseptic technique is crucial to minimize postoperative infection. Hair should first be removed from the proposed incision site, typically to the superior portion of the helix. Tape is then used to pull remaining hair back and prevent its entry during the operation. A head wrap is then applied, and the skin is prepped. A urological drape is adapted and used as a sterile barrier to manipulate the mandible during the operation ( Fig. 1 ). Minimizing contamination from the oral cavity is critical to reduce postoperative infections. Once this is complete, the ear canal is irrigated with antibiotic solution. A preoperative antibiotic should be given during this time to ensure adequate tissue levels before incision. At this institution, patients are given cefazolin and metronidazole unless a penicillin allergy is present, in which case clindamycin is the prophylactic antibiotic of choice. Attention to sterile technique, especially when alternating between the surgical site and the oral cavity, is the most important step in preventing prosthetic infection.

Fig. 1
( A ) Patient draped. ( B ) Modified urological dressing. ( C ) Urological dressings allowing sterile manipulation of the mandible; also note Tegaderm covering the nares to limit contamination.

Exposure

Attention is first directed to the preauricular region, where an endaural incision is used ( Fig. 2 ). This approach is chosen both for its improved cosmetic outcome and because the incision is farther from the prosthesis. The endaural incision requires a stepped dissection to the joint, which increases the tissue coverage over the implant. Once the TMJ is fully dissected, the ramus is then exposed via a modified retromandibular incision. The neck is exposed before any osteotomy, to ensure rapid access to the underlying vasculature if difficult-to-control bleeding is encountered. The incision is marked by placing a gloved finger from the lobule of the ear to the angle of the mandible. A marking pen is then used to identify the incision 1 finger breadth below the angle of the mandible to avoid the marginal mandibular nerve. The incision starts approximately 1 cm below the lobule of the ear and continues to the premasseteric notch. Dissection is carried down through the superficial layer of the deep cervical fasci, with the aid of a nerve stimulator until the sternocleidomastoid muscle is identified. From this point, a Kelly is used to bluntly dissect anterior to the sternocleidomastoid muscle. Then, the direction of the dissection is changed to parallel the inferior border of the mandible until the posterior belly of the digastric is identified. A 15 blade is used to incise the pterygomasseteric sling along the avascular aponeurosis. With the aid of an Obwegeser periosteal elevator, the masseter is cleanly dissected off the mandible to expose the entire ramus, allowing communication between the 2 incisions in a safe subperiosteal plane. Care is taken to minimize trauma between the small bridge of tissue between the 2 incisions because the facial nerve travels in this tissue.

Fig. 2
Endaural and modified retromandibular incision providing access for total joint replacement.
( Inset courtesy of Biomet Microfixation, Jacksonville, FL; with permission.)

Osteotomy

A 2-step osteotomy has been developed to minimize risk to the internal maxillary artery and ensure adequate bone removal for the fossa component ( Fig. 3 ). With the TMJ fully exposed, 2 Dunn-Dautrey retractors and a condylar neck retractor are placed deep in the condylar neck to aid in visualization and protect deeper structures. A 1-mm fissure bur is used to perform the condylectomy. An osteotomy is performed by first starting at the midpoint of the condylar neck, while sparing the medial cortex. The cut is then extended both anteriorly and posteriorly. A T-bar osteotome is then used to complete the condylectomy. The condyle is then grasped with a bone-holding forceps and the lateral pterygoid is carefully dissected free. At this point, significant bleeding may occur, and the surgeon should be ready to control any hemorrhage with the aid of hemostatic agents. Once the condyle is removed, this creates space and allows the surgeon to superiorly reposition the ramus. This maneuver allows easier access to the second step of the osteotomy and places this bone cut away from the internal maxillary artery. To ensure sufficient space for the fossa, bone should be removed to just below the most inferior point of the coronoid notch by making a curvilinear shaped osteotomy. Again, great care should be taken to protect deep soft tissue structures with the aid of the Dunn-Dautrey retractors, considering that the internal maxillary artery normally runs approximately 3 mm medial from the midsigmoid notch. This osteotomy is performed in a similar fashion to that described earlier, with approximately 90% of the bone removed with the fissure bur and completion accomplished with a T-bar osteotome.

Fig. 3
Two step osteotomy. ( A ) Initial condylectomy with use of Dunn-Dautrey retractors to protect deeper structures. ( B ) Superior repositioning of the ramus to allow for improved access to the second-stage osteotomy and increased distance from the internal maxillary artery. ( C ) Location of 2-step osteotomies; note curvilinear shape of black line if coronoidectomy is not required.
([ A , B ] Courtesy of Biomet Microfixation, Jacksonville, FL; with permission.)

Fossa Placement

Secure fossa placement requires tripod stability, which is achieved by reducing the articular eminence with a reciprocating rasp ( Fig. 4 ). The cutting surface of the available rasp matches the width of the 3 available fossa sizes. Because most anatomic variation is found in the articular eminence, once this area is flattened, a stock fossa is easily secured in place ( Fig. 5 ). Correct angulation is critical to minimize dislocation and allow maximal opening. The fossa component should parallel the Frankfurt horizontal plane. A sizer is available to aid in fossa selection. Placement is then initiated by securing the fossa with 2 screws ( Fig. 6 ). Correct alignment is checked before additional screws are placed. The tip of a nerve stimulator can be used to determine that adequate bone is available along the zygomatic arch before the final screws are placed.

Fig. 4
( A , B ) Rasp overlying fossa, note length of rasp matches width of fossa.

Fig. 5
( A ) Flattening of articular eminence and lateral surface of ramus in preparation of prosthesis. ( B ) Prepped articular eminence. ( C ) Proper position of fossa. ( D ) Intraoperative placement of fossa.
( Courtesy of Biomet Microfixation, Jacksonville, FL; with permission.)

Fig. 6
Instrumentation. ( A ) Condylar implant sizer. ( B ) Fossa sizers. ( C ) Standard implant placed with 2.7-mm screws; 3.1-mm emergency screws are available. ( D ) Three sizes of fossa implant. The implant is made of ultrahigh-molecular-weight polyethylene. The fossa is set with 2.0-mm screws.

Placement of Mandibular Component

Before the condylar replacement, the patient is placed in intermaxillary fixation (IMF). Great care should be taken to avoid contamination of the surgical wounds from the oral cavity. Contamination is avoided by using a separate instrument set, reprepping and draping the patient, and glove changes before returning to the surgical wounds. Once the patient has been placed in IMF, a sizer is used to choose the appropriate implant length. The available implants include 45, 50, and 55 mm (see Fig. 6 ). The prosthesis is also available in narrow and standard; the standard has more available screw holes for patients with compromised bone. Care should be taken to ensure that the screw holes used do not encroach on the inferior alveolar nerve, which is easily accomplished with the aid of standard radiographs. Once the implant is selected, it should be seated in the posterior aspect of the fossa to allow for maximal incisal opening ( Fig. 7 ). Two screws are placed to fixate the prosthesis, the wounds are covered with antibiotic-soaked sponges, and the occlusion is checked. Again, care is required to avoid cross-contamination from the oral cavity. At this time, the surgeon should also check for anterior dislocation. Once satisfactory occlusion is achieved, the prosthesis is then fixated with 4 to 6 screws ( Figs. 8 and 9 ).

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Total Reconstruction of the Temporomandibular Joint with a Stock Prosthesis
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