The study aims to assess the adequacy of a set of clinical and laboratory investigations for identifying the osteosarcopenia status in patients undergoing a hip replacement for a fragility fracture of the femoral neck. The control group will consist of patients undergoing a hip replacement for osteoarthritis, as the decrease in muscle function and bone quality is less severe in this condition than in osteoporosis.

Osteoporotic hip fractures (fragility fractures) are common in older adults, and the risk of adverse outcomes and mortality is higher in patients affected by osteosarcopenia, a geriatric syndrome in which the low bone mineral density and bone microarchitecture deterioration (osteopenia/osteoporosis) are combined with a decline in mass, strength, and functional capacity of skeletal muscle (sarcopenia).

The diagnostic workup currently recommended to establish the severity of osteosarcopenia is hard to implement in individuals who arrive at the orthopedic emergency department with a fragility fracture. On the one hand, the evaluation of motility and physical performance is impracticable in bedridden patients; on the other hand, the surgical treatment priority does not allow performing all the instrumental investigations required for a proper diagnosis. In this context, reliable osteosarcopenia biomarkers could help identify most frail patients and plan for them personalized therapeutic interventions to promote postoperative recovery and reduce the risk of adverse outcomes.

Based on the new knowledge on the pathophysiology of osteosarcopenia, the investigators designed a small-scale study that aims to preliminarily verify the adequacy of a set of clinical and laboratory parameters that could be easily applied in hospitalized patients undergoing hip replacement for a fragility fracture. In particular, the investigators planned to assess the following:

• muscle performance by SARC-F questionnaire (acronym deriving from five domains considered in the questionnaire, i.e., strength, assistance with walking, rising from a chair, climbing stairs, and falls);
• dietary habits through a questionnaire on the intake frequency of food categories;
• histological features of osteoporosis and sarcopenia in tissue samples taken from the surgical site;
• the serum levels of markers associated with muscle-bone cross-talk (Myostatin, Insulin-like growth factor 1);
• the serum levels of the following pro-inflammatory cytokines to get a clearer picture of the presence of the inflammatory state: IL-6, IL-8, TNF-α;
• the serum levels of markers such as FGF-21, GDF15, soluble ST2, interesting markers of bone metabolism, indicators of bone mineral density, and modulators of osteoblast-osteoclast activity;
• the composition of the gut microbiota.

The study includes 100 patients who are candidates for hip replacement surgery (endo- and arthroplasty). As the decrease in muscle function and bone quality is more severe in fragility fractures than in osteoarthritis, the investigators expect to find differences in laboratory and clinical parameters.

Inclusion Criteria:

• Patients who came to observation with femoral neck fracture of possible osteoporotic nature (no or minimal trauma) to be treated with endoprosthesis or hip arthroplasty.
• Competent patients who have signed consent to participate in the study (see Informed Consent section of this protocol).

Exclusion Criteria:

• Previous osteoporotic fractures
• Previous prosthetic surgery for orthopedic diseases
• Pre-existing clinical conditions that led to permanent immobility
• Neoplastic diseases
• Autoimmune diseases
• Severe myopathies
• Chronic viral infections (HBV, HCV, HIV);
• Chronic treatment with anti-osteoporotic drugs, immunosuppressive drugs, and insulin
• Paget's disease

Hospitalized patients admitted at the 1st Orthopaedic and Traumatology Unit of the Istituto Ortopedico Rizzoli (Bologna, Italy).