Patients will be eligible for inclusion into the trial if:

• They have early symptomatic atraumatic AVN of the hip (Ficat Score 1 or 2 using MRI)

• They are aged greater than or equal to 18 years

Patients will be excluded from this trial if they have/are:

• Not confirmed their diagnosis (Ficat 1 or 2), using MRI, within the last 12 months

• Renal function (creatinine clearance) of <30ml/min (tested within the last 3 months)

• Adjusted serum calcium levels outside local reference range (tested within the last 3 months)

• Established osteoarthritis (Kellgren-Lawrence ≥2)

• Previous AVN, femoral head deformity, prior hip surgery or hip fracture in the index hip

• Current pathology (e.g. osteoporosis) that requires treatment with bisphosphonates

• Received previous anti-osteoporosis therapy (excluding calcium or vitamin D supplements) that lasted more than 4 weeks for oral treatment or any length of parenteral treatment

• Contraindications to MRI

• Contraindications to alendronate therapy (including hypocalcaemia) as listed in the SmPC

• Planning a pregnancy in the next 24 months or are currently pregnant or breastfeeding

• Not using appropriate contraception and of child bearing age

• A planned joint preserving surgical procedure of the hip

• Unable or unwilling to provide informed consent

• Unable to commit to follow-up regime

• Already enrolled in an interventional clinical trial