Purpose The application of robotics in the operating theatre for total knee arthroplasty (TKA) remains controversial. As with all new technology, the introduction of new systems is associated with a learning curve and potentially associated with extra complications. Therefore, the aim of this study is to identify and predict the learning curve of robot-assisted (RA) TKA. Methods A RA TKA system (MAKO) was introduced in April 2018 in our service. A retrospective analysis was performed of all patients receiving a TKA with this system by six surgeons. Operative times, implant and limb alignment, intraoperative joint balance and robot-related complications were evaluated. Cumulative summation (CUSUM) analyses were used to assess learning curves for operative time, implant alignment and joint balance in RA TKA. Linear regression was performed to predict the learning curve of each surgeon. Results RA TKA was associated with a learning curve of 11-43 cases for operative time (p < 0.001). This learning curve was significantly affected by the surgical profile (high vs. medium vs. low volume). A complete normalisation of operative times was seen in four out of five surgeons. The precision of implant positioning and gap balancing showed no learning curve. An average deviation of 0.2° (SD 1.4), 0.7° (SD 1.1), 1.2 (SD 2.1), 0.2° (SD 2.9) and 0.3 (SD 2.4) for the mLDFA, MPTA, HKA, PDFA and PPTA from the preoperative plan was observed. Limb alignment showed a mean deviation of 1.2° (SD 2.1) towards valgus postoperatively compared to the intraoperative plan. One tibial stress fracture was seen as a complication due to suboptimal positioning of the registration pins. Conclusion RA TKA is associated with a learning curve for surgical time, which might be longer than reported in current literature and dependent on the profile of the surgeon. There is no learning curve for component alignment, limb alignment and gap balancing. Level of evidence IV.

Introduction: In situ fixation (ISF) is currently still the ‘gold standard’ treatment for slipped capital femoral epiphysis (SCFE) and has shown acceptable results at mid-term follow-up. This study aims to evaluate functional, clinical and radiographic long-term outcomes after this procedure. Methods: We reviewed 64 SCFE patients (76 SCFE hips) treated with ISF between 1983 and 1998. 82.9% were stable hips and 17.1% unstable according to Loder’s definition. Initial radiographs demonstrated a mild slip in 50%, moderate in 41.3% and severe in 8.7% based on the Southwick angle. Long-term outcomes were assessed using the modified Harris Hip Score (mHHS), University of California at Los Angeles (UCLA) and Tegner activity scores, visual analogue scale (VAS) pain, VAS function, flexion-adduction-internal rotation (FADIR) test, extent of internal-rotation at 90° of hip flexion and Tönnis classification for hip osteoarthritis (OA). Results: 10 (15.6%) SCFE hips were converted to a total hip replacement (THR) after a mean of 16 years. 38 (59.4%) patients underwent a clinical and radiographic examination after a mean follow-up of 23 (range 18–33) years. 12 (18.8%) patients were lost to follow-up. 74% of SCFE hips demonstrated degenerative change on radiography or were converted to THR (Tönnis 1: 33.3%, 2: 18.5%, 3 or THR: 22.2%). There were 3 cases of avascular necrosis (AVN) all in unstable hips. Mean mHHS was 86.8/100, UCLA activity score 7.5/10, Tegner activity score 3.8/10, VAS pain 1.7/10 and VAS function 1.5/10. 20% of SCFE hips were found to have a positive FADIR-test and a limited internal-rotation of 19.7° versus 36.1° ( p < 0.001) in contralateral normal hips. Discussion: This long-term follow-up study of ISF for SCFE shows that although complication rates in terms of AVN are low, a high number of patients become symptomatic and have a limited function. Degenerative changes are common with 22.2% of hips developing end-stage hip OA (Tönnis 3 or THR). It is important that patients and parents are informed about these risks.