Investigation into the use of teriparatide in the treatment of stress fractures.

Primary outcome is healing on MRI, secondary outcomes are pain, time spent in rehabilitation and future stress fractures. This study will help the investigators understand how to treat stress fractures in the future.

Teriparatide is a drug that is designed to have a similar effect on the body as parathyroid hormone. Parathyroid hormone is made naturally in the body and is released in response to low calcium levels. It helps to maintain bone health and repair bone damage. Parathyroid hormone and medicines like teriparatide can strengthen bones and are often given to people with osteoporosis (a condition that weakens bones, making them more likely to break) to reduce the risk of fractures. Recent studies have also shown benefits in people with stress fracture injuries, a form of bone damage sometimes caused by repetitive exercise. The investigators want to know if teriparatide is also beneficial to healthy, younger people who have a stress fracture injury.

Inclusion Criteria:

1. Signed informed consent form;
2. Participant must be aged 18 - 40 years inclusive;
3. Participant must have a lower limb stress fracture, either unilateral or bilateral, as confirmed via MRI scan;
4. Undergoing phase 1 or 2 training within an Army training establishment;
5. Blood Tests within reference range. Minor abnormalities will be assessed by the PI. Patients will still be entered if these are felt to be of no clinical importance.
6. Participants able to adhere to the visit schedule and protocol requirements.

Exclusion Criteria:

1. Hypersensitivity to the active Parathyroid Hormone substance or any of the excipients listed in the SmPC.
2. Pre-existing hypercalcaemia.
3. Patients with skeletal malignancies or bone metastases.
4. Any contraindications that would prevent the participant from undergoing an MRI scan.
5. Concurrent therapy that, in the investigators opinion, would interfere with the evaluation of the safety or efficacy of the study medication.
6. Pregnancy, suspected pregnancy or breastfeeding. Female participants must have a negative serum pregnancy test at screening and be willing and able to use a "highly effective" method of contraception, as per the Clinical Trial Facilitation Group (CTFG) guidance.
7. Severe renal impairment. Participants with moderate renal impairment will be treated with caution at the Principal Investigator's discretion and in accordance with the SmPC.
8. Metabolic bone diseases including hyperparathyroidism and Paget's disease of the bone.
9. Unexplained elevations of alkaline phosphatase.
10. Prior external beam or implant radiation therapy to the skeleton.
11. Patients participating in a concurrent drug trial.
12. Presentation with open epiphyses during the diagnostic MRI scan.
13. Participants with depression, as identified by completion of the Columbia-Suicide Severity Rating Scale (C-SSRS) at Baseline.

Blinded assessment of MR scans