Condylar Resorption Following Single-Jaw and Bimaxillary Orthognathic Surgery: A Retrospective Comparative Radiographic Study

Technical Summary: Condylar Resorption Following Single-Jaw and Bimaxillary Orthognathic Surgery

Problem Statement
Progressive condylar resorption is a recognized complication following orthognathic surgery that can compromise skeletal stability, occlusal outcomes, and long-term treatment success. While the association between orthognathic procedures (such as Le Fort I osteotomy and bilateral sagittal split osteotomy) and postoperative condylar changes is established, the comparative influence of single-jaw versus bimaxillary surgical approaches on the incidence and extent of condylar resorption remains inadequately clarified. Existing literature often suffers from heterogeneity in diagnostic criteria, imaging modalities, and follow-up durations, leading to inconsistent conclusions. Furthermore, most available data focus on isolated mandibular procedures, leaving a gap in direct comparative analyses between surgical modalities.

Methodology
This study employed a retrospective comparative observational design, adhering to STROBE guidelines, conducted at Meenakshi Ammal Dental College and Hospital, Chennai, India.

• Study Population: The cohort consisted of 22 patients who underwent orthognathic surgery between January 2019 and December 2024. Patients were equally divided into two groups: Group I (Single-jaw surgery, n=11) and Group II (Bimaxillary surgery, n=11).
• Inclusion/Exclusion: Inclusion criteria required a diagnosis of skeletal Class II or III deformity, completion of BSSO (alone or with Le Fort I/genioplasty), and availability of complete preoperative and postoperative radiographs at 3, 6, and 12 months. Patients with pre-existing TMJ disorders, previous orthognathic surgery, craniofacial syndromes, or incomplete records were excluded.
• Radiographic Assessment: Condylar height was measured using standardized orthopantomograms (OPGs) obtained preoperatively and at 3, 6, and 12 months postoperatively. Measurements followed the Borstlap et al. method, calculating total ramus height parallel to a tangent through the highest point of the condyle. A reduction exceeding 6% of the preoperative value was defined as indicative of condylar resorption.
• Statistical Analysis: Data were analyzed using IBM SPSS Statistics version 26.0. Intragroup comparisons (preoperative vs. postoperative) utilized the paired t-test, while intergroup comparisons used the independent-samples t-test. A p-value < 0.05 was considered statistically significant.

Key Contributions
The primary contribution of this work is a direct radiographic comparison of condylar height changes between single-jaw and bimaxillary orthognathic surgery groups within a controlled retrospective framework. The study utilizes a standardized measurement protocol (Borstlap method) to assess the temporal pattern of resorption over a 12-month period. It specifically addresses the lack of comparative data regarding whether bimaxillary surgery confers a higher risk of condylar height reduction compared to single-jaw procedures.

Results

• Intragroup Findings: Both the single-jaw and bimaxillary groups demonstrated statistically significant reductions in condylar height postoperatively (p < 0.001). This indicates that measurable condylar remodeling occurs regardless of the surgical approach.
• Intergroup Findings: The bimaxillary group exhibited a slightly greater mean reduction in condylar height (1.1 ± 0.3 mm right; 1.1 ± 0.4 mm left) compared to the single-jaw group. However, intergroup comparison revealed no statistically significant difference between the two groups (Right side: p = 0.499; Left side: p = 0.389).
• Temporal Pattern: Radiographic evidence of condylar height reduction became apparent predominantly within the first postoperative year. Measurable changes were identified in six patients at 6 months and in 16 patients by 12 months, suggesting that the majority of postoperative condylar changes occur within this timeframe.

Significance and Claims
The authors claim that postoperative condylar adaptation is a common biological response following orthognathic surgery, rather than a phenomenon exclusive to a specific surgical modality. While the bimaxillary group showed a trend toward greater condylar height reduction, the lack of statistical significance suggests that the extent of remodeling is unlikely to depend solely on whether one or both jaws are operated upon. Instead, the authors posit that factors such as the magnitude and direction of skeletal movement, condylar seating, fixation methods, and individual adaptive capacity play more critical roles.

The study emphasizes that the absence of a statistically significant difference between surgical approaches should not be interpreted as a lack of clinical relevance. Given the trend toward greater reduction in bimaxillary cases and the multifactorial nature of resorption, the authors conclude that careful surgical planning and routine postoperative radiographic follow-up are essential for all patients, particularly those requiring large skeletal movements or those with pre-existing TMJ abnormalities. The paper acknowledges limitations, including the retrospective design, small sample size, and the use of two-dimensional imaging, and calls for future prospective multicenter studies with larger samples and three-dimensional imaging to further validate these findings.