Postoperative leg length discrepancy after hip and knee arthroplasty induces measurable TMJ changes without clinical dysfunction

Background: This study investigates the influence of postoperative leg length discrepancy (LLD) on the temporomandibular system (TMS) after total hip or knee replacement (THR/TKR), focusing on long-term effects and functional or positional changes in the temporomandibular joint (TMJ). Methods: A total of 45 patients (31 THR, 14 TKR) from Leipzig University Hospital were prospectively examined preoperatively and after 8–12 weeks. LLD were measured and categorized. A control group of 20 subjects without surgical interventions was used to compare the initial situation, and oral health was assessed using OHIP-G14 questionnaires. Statistical analysis was performed using SPSS version 24. Level of significance was accepted at p  < 0.05. Results: While no patient developed temporomandibular disorders (TMD), functional and positional changes in the TMS were observed postoperatively, particularly in patients with a LLD ≥ 15 mm. Significant changes included increased mouth opening (+ 4.3 mm) and decreased left laterotrusion (-1.98 mm) in the high compensation group. Shifts in condylar position were noted in all spatial axes. No significant changes in function were observed in the control group and in patients with a LLD ≤ 10 mm. The subjective oral health-related quality of life remained unchanged. Conclusions: Postoperative LLD after THR or TKR leads to measurable changes in TMJ position and mandibular function. However, these changes did not lead to clinical TMD within the study period. Trial registration: This study involved examinations only and did not include any intervention. Therefore, trial registration was not required and was not performed. Clinical trial number: not applicable.