Methods. A retrospective review of 80 patients with unilateral slipped capital femoral epiphysis from 1998–2012 was undertaken to determine the outcome of the unaffected hip. All patients were treated with either prophylactic single Richards screw fixation or observation of the uninvolved hip and were followed up for at least 12 months. The unaffected hip of 44 patients (mean age 12.6 years, range 9–17) had simultaneous prophylactic fixation and 36 patients (mean age 13.4 years, range 9–17.4) were managed with observation. Results. Sequential slip of the unaffected hip was noted in 10 patients (28 per cent) in the observation group and only in 1 patient (2 per cent) in the group managed with prophylactic fixation. A Fisher's exact test showed significantly high incidence of sequential slip in unaffected hips when managed with regular observation (p-value 0.002). Only 3 cases had symptomatic hardware on the unaffected side after prophylactic fixation with one requiring revision of the metal work; one had superficial wound infection treated with antibiotics. No cases had AVN or chondrolysis. Conclusion. Simultaneous prophylactic fixation of the unaffected hip significantly reduces the incidence of sequential slip in unilateral SCFE with minimal complications. Level of evidence. III

A painful “dreaded black line” (DBL) has been associated with progression to complete fractures in atypical femur fractures (AFF). Adjacent sclerosis, an unrecognized radiological finding, has been observed in relation to the DBL. We document its incidence, associated features, demographics and clinical progression. We reviewed plain radiographs of 109 incomplete AFFs between November 2006 and June 2021 for the presence of sclerosis adjacent to a DBL. Radiographs were reviewed for location of lesions, and presence of focal endosteal or periosteal thickening. We collected demographical data, type and duration of bisphosphonate therapy, and progression to fracture or need for prophylactic stabilization, with a 100% follow up of 72 months (8 – 184 months). 109 femurs in 86 patients were reviewed. Seventeen sclerotic DBLs were observed in 14 patients (3 bilateral), involving 15.6% of all femora and 29.8% of femora with DBLs. Location was mainly subtrochanteric (41.2%), proximal diaphyseal (35.3%) and mid-diaphyseal (23.5%), and were associated with endosteal or periosteal thickening. All patients were female, mostly Chinese (92.9%), with a mean age of 69 years. 12 patients (85.7%) had a history of alendronate therapy, and the remaining 2 patients had zoledronate and denosumab therapy respectively. Mean duration of bisphosphonate therapy was 62 months. 4 femora (23.5%) progressed to complete fractures that were surgically managed, whilst 6 femora (35.3%) required prophylactic fixation. Peri-lesional sclerosis in DBL is a new radiological finding in AFFs, predominantly found in the proximal half of the femur, at times bilateral, and are always associated with endosteal or periosteal thickening. As a high proportion of patients required surgical intervention, these lesions could suggest non-union of AFFs, similar to the sclerotic margins commonly seen in fractures with non-union. The recognition of and further research into this new feature could shed more light on the pathophysiological progression of AFFs