In this study, we used alloplastic TJR for reconstruction of congenital mandibular deformities in growing patients with CMH. We achieved mandibular movement of 16.4–20.1 mm in the sagittal direction. Over the follow-up period of 24–42 months, no long-term complications occurred. The maximal interincisal opening achieved at the last follow-up was 31.67 ± 7.93 mm, and all implants were functional.

The application of alloplastic TJR in the construction of congenital mandibular deformities is rare, and only a few case reports have been published to date, mostly focused on non-growing patients [27,28,29,30,31]. The treatment of patients with alloplastic TJR in general, in adults, and in juvenile patients differs markedly across countries and healthcare systems. Nevertheless, this approach is increasingly used worldwide, since VSP and CAD/CAM techniques have been introduced and allowing for patient-specific prosthesis design [25, 31]. Patient-matched prostheses are not only used because of their perfect anatomical fit to challenging anatomical sites, but mainly because it is possible to implement virtually planned mandibular movements in their design and combine them with conventional (and bimaxillary) orthognathic surgery [29, 30, 32,33,34]. In conventional orthognathic surgery, a reliable TMJ is needed to ensure long-term skeletal and occlusional success. This is absent in cases with congenital TMJ deformities. Thus, TJR can be considered a line extension of orthognathic surgery, in cases with severe TMJ deformities.

Our findings demonstrated the feasibility of patient-matched TJR combined with orthognathic surgery in the treatment of CMH, even in multiply pretreated growing patients. Follow-up in the medium term showed adequate TMJ function with a corrected and symmetrized stable skeletal and occlusional situation that could not be achieved by previous autologous reconstruction or distraction osteogenesis. In addition, it facilitates extensive sagittal mandibular movements without a skeletal relapse. Furthermore, TJR can be used to increase the vertical ramus height and camouflage lost facial prominences, such as the mandibular angle.

There is a common misconception that in distraction osteogenesis and costochondral grafting in CMH cases, deficient bone needs to be replaced by distraction or bone alone, in order to correct the deformity. However, neither distraction nor bone grafting, including costochondral grafts, can create a stable soft tissue envelope that undergoes hyperplasia and provides significant improvement, as they focus on re-establishing the bony deficiency alone. After grafting or distraction, the soft tissue envelope is temporarily stretched, but the deficiency and scarring again lead to retraction of the soft tissue envelope in the long term. This results in relapse of the distraction and graft resorption. Consequently, there are currently only two options: firstly, to use rigid, non-resorbable materials that are strong enough to resist soft tissue retraction and maintain the surgical outcome in the long term and, secondly, to improve the soft tissue envelope prior to or simultaneously with the grafting procedure or distraction.

The list of potential complications associated with costochondral grafts is extensive. In addition to inducing pneumothorax, the graft must be placed in a nonexistent or rudimentary glenoid fossae. The graft also has to be attached to a rudimentary or severely malformed ramus, usually in areas with scarring, poor vascularization, and a deficient soft tissue envelope, particularly in severe forms of hemifacial macrosomia. Some authors have reported that the orientation of the rib at the graft site during surgery might be challenging, and that the graft dislodged laterally or superiorly. Most importantly, costochondral grafts have shown unpredictable growth and may fracture in the costochondral joint. Finally, there is the risk of graft infection, resorption, pain, relapse, and facial nerve damage [35]. Moreover, the risk of temporary or permanent facial nerve palsy is not negligible in cases with complex congenital deformities, massive ankylosis, and multiple operated joints, independent of implanted materials.

Although alloplastic TJR does not increase the quantity and quality of deficient soft tissues, the prosthesis is sufficiently rigid to preserve the steady state of a stretched soft tissue envelope. A few case reports of TJR in congenital deformities have been published and showed promising results [29,30,31]. The surgical risk of TJR is comparable to that of any autologous procedure or distraction, since the same surgical approaches are used. Even if the risk for rib grafts is thought to be low, TJR carries no risk of donor-side morbidity, and there are no bone grafts to be lost or resorbed. However, alloplastic materials can also become infected, and periprosthetic joint infections (PJIs) are difficult to treat. Allergic reactions to implant materials can also occur (cobalt, chromium, molybdenum, nickel, and polyethylene). Moreover, 8–12 weeks are required for the manufacturing of the prosthesis.

Alloplastic materials do not have any growth potential, but they can deliver predictable short- and long-term clinical situations. Costochondral grafts have an inherent growth potential but are unpredictable [15]. Long-term reports of mandibular growth in children who underwent reconstruction with costochondral grafts showed that excessive growth occurred on the treated side in 54% [27, 28, 36,37,38,39,40]. An investigation of mandibular growth after costochondral grafting supported previous experiments regarding the inability of the graft to adapt to the growth velocity of the new environment. Furthermore, no mandibular growth can be expected on the affected side of patients with CMH, particularly those with Pruzansky III, where no TMJ is present. In the present study, we also showed that maxillary growth in a 9-year-old female with ankylosis due to failed costochondral grafts and a relapse following distraction and conventional interpositional gap arthroplasty (case No. 2), was not affected by bilateral TJR (Fig. 5). LG Mercuri stated, that “These patients could be better off undergoing alloplastic TMJ TJR, knowing that revision and/or replacement surgery may likely be required in the future depending on growth, rather than incurring continued failures with autogenous tissues that will also very likely require further surgical intervention in the future” [27].

Case 3—Fusion of initial/pre-distraction (surgery prior to TJR) CBCT-scan and postoperative/post-TJR CBCT-scan. Patient suffered from severe bilateral mandibular hypoplasia with permanent tracheotomy and being unable to eat. Red arrow indicates large distance mandibular movement between initial situation and situation after TJR (45 mm). Movement between post-distraction and post-TJR situation was 20.1 mm (Table 2). Green arrow indicates maxillary growth between both CBCT-scans

The long-term outcomes of TJR of the TMJ in patients with CMH are promising. The literature shows a > 90% success rate after 20 years of TJR in general [41,42,43]. Furthermore, prosthesis exchange to material wear can be ignored, because even the replaced TMJ is considered to be a non-load-bearing joint. Friction wear is unlikely to occur during functional use. However, this needs to be proven by long-term follow-up studies of these patients and materials. CMH is a rare disease, that’s why our study is limited by its small sample size. The number of CMH patients treated with our presented technique and the follow-up period have to be increased in future studies.