PurposeSulcus‐deepening trochleoplasty (TP) effectively treats patellofemoral (PF) instability (PFI) caused by high‐grade trochlear dysplasia (TD), but current evidence is based on small case series. We hypothesised, that TP would result in significant functional improvements and a low re‐dislocation rate but would not accelerate the progression of PF cartilage deterioration.MethodsWe retrospectively reviewed all TP cases performed by a single surgeon between 2015 and 2021. Inclusion criteria were postoperative Magnetic resonance imaging (MRI) >6 and >12 months and a clinical follow‐up >12 months. Patients with simultaneous cartilage repair, open physes or incomplete records were excluded. Clinical outcomes were assessed using pre‐ and postoperative scores, postoperative Banff Patellofemoral Instability Instrument (BPII) 2.0 and Knee Injury and Osteoarthritis Outcome Score (KOOS), re‐dislocation rate and patient satisfaction. PF cartilage was evaluated via Area Measurement and Depth & Underlying Structures (AMADEUS) scores preoperatively, at 6 months and at the final follow‐up.ResultsWe included 113 patients (25.8 ± 8.3 years) with high‐grade TD (Dejour B–D; mean lateral inclination angle: −2.9 ± 9.1°), 85% of whom had advanced cartilage lesions. All underwent TP, lateral retinacular lengthening (LRL) and medial patellofemoral ligament reconstruction (MPFL‐R). After 34.8 ± 20.9 months, function, pain levels and Tegner scores improved significantly (p < 0.001). KOOS dimensions were: symptoms 79.9 ± 13.5, pain 86.4 ± 12.1, activity 91.9 ± 8.3, sports 71.7 ± 22.2 and quality‐of‐life 58.1 ± 23.8. BPII 2.0 was 64.3 ± 31.4. Preoperative AMADEUS scores (55.2 ± 17.4) remained stable at 6 months (p = 0.343) but improved to 58.4 ± 16.0 at 28.6 (12–89) months (p = 0.004). Complication and re‐dislocation rates were 5.3% and 1.8%, with 93% patient satisfaction.ConclusionSulcus‐deepening TP with MPFL‐R and LRL yields good to excellent short‐term results without progressive chondral deterioration, enabling patients to return to their prior or higher activity levels despite advanced preoperative chondral lesions. TP can be considered a safe, joint‐preserving technique for PF stabilisation.Level of EvidenceLevel III, retrospective cohort study.