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Recovery

Bone health and healing

The clearest human result is a small double-blind randomised trial in early avascular necrosis of the hip, where people treated with hyperbaric oxygen had less pain and, at seven-year follow-up, none had needed a hip replacement. For general fracture healing a Cochrane review found no randomised trials either way, and the osteoporosis research so far is in animals, where it improved bone density and structure. We present it as promising but early.

Evidence so far
Early
Reading timeAbout 12 minutes

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Why this is being studied

Bone is living tissue with its own blood supply, constantly being broken down and rebuilt. When that blood supply fails, as in osteonecrosis of the hip, or when a fracture stalls or bone thins with age, the cells that build bone are often working in an oxygen-poor environment. Hyperbaric oxygen raises the amount of oxygen dissolved in the blood, which is why researchers have tested it in each of these settings, with results that range from a small promising trial in early hip osteonecrosis to an evidence gap in fracture healing and rodent-only data in osteoporosis.

Where the evidence stands

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The mechanism

What is going on, and why this might help

What is going on in the body

Bone is living tissue with a rich blood supply, and its ability to heal depends on it. After a fracture, a haematoma forms, inflammatory cells arrive, a soft cartilage callus develops and is gradually replaced by woven and then mature bone. Every stage requires oxygen: osteoblasts that lay down bone are highly metabolically active, and the balance between osteoblasts and bone-resorbing osteoclasts is sensitive to oxygen tension and inflammatory signalling. Non-union, delayed union, osteonecrosis and osteomyelitis all share compromised blood supply and hypoxia at the site. Chronic bone infection is worsened by the fact that antibiotics and white cells penetrate poorly into hypoxic, poorly perfused bone.

Where oxygen comes in

Hyperbaric oxygen raises oxygen tension in bone that is poorly perfused, and in animal models accelerates fracture callus formation and mineralisation. Laboratory studies show that hyperoxia promotes osteoblast differentiation and inhibits osteoclast formation, partly through effects on HIF-1α and RANKL signalling. Angiogenesis via VEGF restores the vascular supply that new bone depends on, and stem-cell mobilisation (Thom 2006) may supply osteoprogenitor cells. In osteomyelitis, hyperbaric oxygen restores the oxygen-dependent killing capacity of neutrophils, is directly toxic to anaerobic organisms and enhances the activity of some antibiotics. Oedema reduction through vasoconstriction is relevant to compartment syndrome and crush injury with bone involvement.

How solid is this

Mixed. For osteoradionecrosis and refractory osteomyelitis the mechanism and clinical evidence are well established. For ordinary fracture healing and non-union, the mechanisms are supported by animal studies and laboratory work, but human trials are few and a Cochrane review found no adequate randomised evidence. For osteoporosis and general bone density there is animal data only. Key references: Marx 1990 (irradiated bone); Al Hadi et al. 2013 (osteoblast and osteoclast effects in vitro).

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The studies

Every study is laid out the same way: what the researchers wanted to find out, who took part, what they actually did, what they found, why it might work and where the limits are. No jargon, and a link to the original if you want to read it yourself.

Each study is laid out the same way: what the researchers asked, who took part, what they did, what they found, why it might work, and where the limits are. The clinician layer at the end of each one carries the numbers.

Paper 1

Hyperbaric oxygen therapy in femoral head necrosis

Camporesi et al. · Journal of Arthroplasty · 2010 · double-blind randomised controlled trial with 7-year follow-up, n=20

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What they asked

Osteonecrosis of the femoral head (also called avascular necrosis) happens when the blood supply to the ball of the hip joint fails and the bone begins to die. In its early stages the bone is still structurally intact, and the question Camporesi and colleagues asked was simple: if you give these people hyperbaric oxygen before the bone collapses, does pain improve, does the joint move better, and can hip replacement be avoided?

Who took part

Twenty adults (12 men, 8 women) with osteonecrosis on one side only, all graded Ficat stage II. That means the diagnosis was confirmed on imaging but the shape of the femoral head had not yet collapsed. This is a small trial, and it was run at a single Italian hyperbaric unit.

What they did

This was a double-blind, randomised, controlled trial. Half the group breathed 100 per cent oxygen in a pressurised chamber, and the other half breathed compressed air in the same chamber at the same pressure, so neither participants nor assessors knew who was getting the active treatment. Each person had 30 sessions over six weeks. The abstract we worked from does not state the pressure; the full paper and later reviews describe a conventional treatment pressure of around 2.5 ATA for roughly 80 minutes per session. After the six-week blinded phase the code was broken and the air group were offered oxygen too, so from that point the study became an open follow-up rather than a comparison. Pain and hip range of motion were measured through the course, and MRI scans were repeated at 12 months and again at 7 years.

What they found

Pain scores improved significantly in the oxygen group by around the twentieth session, and all measured directions of hip movement improved significantly between sessions 20 and 30. At the seven-year follow-up the authors report that all participants remained substantially pain-free and none had needed a hip replacement. On MRI, 7 of 9 hips that were imaged showed substantial healing of the dead bone. Because everyone eventually received oxygen, the long-term results describe the whole group rather than oxygen versus air.

Why it might work

Early osteonecrosis is fundamentally an oxygen-supply problem: the marrow inside the femoral head is swollen and starved, and pressure inside the bone rises, squeezing what little blood flow remains. Breathing oxygen at raised pressure dissolves far more of it in the plasma, so tissue that a red blood cell cannot easily reach can still receive oxygen. In animal and laboratory work this appears to reduce marrow swelling, lower pressure inside the bone, and support the cells that lay down new bone and new capillaries. The trial did not measure these mechanisms directly.

Limits

Twenty people is a very small trial, and the blinded comparison lasted only six weeks. After that the two groups merged, so the seven-year data have no control arm and cannot tell us how many of these hips would have done well anyway. Only nine hips had the seven-year MRI. Ficat stage II is a specific early stage; the results say nothing about collapsed or arthritic hips. The senior authors are long-standing hyperbaric researchers, and the publication does not report an independent replication. It remains one of the few randomised studies in this condition, which is exactly why later systematic reviews lean on it while cautioning about its size.

Paper 2

Hyperbaric oxygen therapy for promoting fracture healing and treating fracture non-union

Bennett et al. · Cochrane Database of Systematic Reviews · 2005 · systematic review (no eligible RCTs found)

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What they asked

The Cochrane Collaboration produces the most rigorous summaries of medical evidence available. In 2005 Michael Bennett and colleagues asked whether hyperbaric oxygen speeds up the healing of ordinary fractures, or helps fractures that have failed to heal (delayed union and non-union). The idea has a long history in hyperbaric medicine, so the aim was to find out whether the published trials actually supported it.

Who took part

In principle, anyone with a fresh fracture, a slowly healing fracture, or an established non-union enrolled in a randomised trial of hyperbaric oxygen. In practice, the authors found no trials that met their criteria, so no participants were analysed. We worked from the published abstract and Cochrane summary, and the later 2012 update reached the same conclusion.

What they did

The authors searched the Cochrane Bone, Joint and Muscle Trauma Group register, CENTRAL, MEDLINE, EMBASE, CINAHL and the specialist hyperbaric literature, and contacted experts in the field. They were looking specifically for randomised or quasi-randomised controlled trials comparing hyperbaric oxygen with no hyperbaric oxygen, or with a sham treatment, in people with fractures, with outcomes such as time to union, radiographic healing, function or pain. Because no eligible trials were identified, there was no pooled pressure, session length or session count to report.

What they found

Nothing that qualified. The review found no randomised evidence either for or against hyperbaric oxygen in fracture healing or non-union. The authors also pointed out that the treatment can occasionally cause barotrauma to the ears, sinuses and lungs, so the absence of proof of benefit matters when weighing it up. It is important to read this correctly: a Cochrane review that finds no trials is not evidence that a treatment does not work, it is evidence that the question had not been properly tested.

Why it might work

Fractures heal through a sequence of inflammation, soft callus, hard callus and remodelling, and each stage needs oxygen. The fracture site is often poorly supplied because the injury has torn small vessels, and bone-forming cells and the collagen they secrete are oxygen-hungry. Laboratory and animal studies suggest higher oxygen availability supports new capillary growth and the cells that build bone. That is the rationale the reviewers set out, but rationale is not the same as clinical proof.

Limits

The principal limit is the empty result: with no trials to analyse, the review cannot estimate any effect size in either direction. Searching stopped in 2003 for this version. Non-union is a heterogeneous problem (infection, poor fixation, smoking and diabetes all play a part), so any future trial would need careful patient selection. The 2012 update again found no eligible trials, and the review has since been withdrawn from active updating by Cochrane, meaning the question remains formally open.

Paper 3

Hyperbaric oxygen therapy for osteoporosis: a systematic review of preclinical evidence and mechanisms

Wang et al. · Bone · 2026 · systematic review of 6 animal studies

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What they asked

Osteoporosis is the gradual thinning of bone that raises fracture risk with age, after the menopause, and after long periods of immobility. Wang and colleagues asked whether animal experiments show that hyperbaric oxygen can slow or reverse this bone loss, and if so, by what biological routes. This is a review of preclinical work, not a clinical trial; there were no human participants.

Who took part

Six animal studies published between 2016 and 2025, all in rats (Wistar or Sprague-Dawley), with between 18 and 75 animals each. The models of osteoporosis varied: removal of the ovaries to mimic the menopause, chemically induced ageing, hind-limb unloading to mimic bed rest or weightlessness, and spinal cord injury. No human data were included.

What they did

The authors systematically searched the major databases up to November 2025, selected studies that met predefined criteria, and assessed each for risk of bias. Across the six studies the hyperbaric protocols mostly used 2.0 to 2.2 ATA with 85 to 100 per cent oxygen for 40 to 60 minutes, daily or five days a week, for a total of 10 to 60 sessions. One study used a much milder protocol of 1.3 ATA with 40 per cent oxygen. Because the models, doses and outcome measures differed so much, the authors described the findings narratively rather than combining them into a single statistical estimate.

What they found

Every included study reported a benefit. Treated rats showed higher bone mineral density, better trabecular architecture (the internal scaffolding of bone), and greater mechanical strength than untreated osteoporotic rats. Blood markers of bone building (such as osteocalcin and bone-specific alkaline phosphatase) rose while markers of bone breakdown (such as CTX and TRAP-5b) fell. The consistency is encouraging, but the authors note that uniformly positive results in a small literature can itself be a warning sign of publication bias.

Why it might work

Bone is constantly remodelled by two cell types in balance: osteoclasts that dissolve old bone and osteoblasts that build new. The studies point to several ways oxygen under pressure may tip that balance. It appeared to shift the OPG/RANKL signalling system away from osteoclast activation, to reduce sclerostin (a brake on the bone-building Wnt pathway), to lower inflammatory messengers such as TNF-alpha and IL-1-beta, to raise antioxidant enzyme activity, and to promote growth factors that build the tiny blood vessels bone depends on. In the spinal injury model, nerve-derived peptides that stimulate bone formation also rose.

Limits

Six small rodent studies with different models and different doses cannot be combined into one number, and none of this has been tested in people with osteoporosis. Risk of bias was mixed: outcome assessors were often not blinded, some studies lost animals, and only English-language papers were searched. Rats do not experience menopause or fragility fractures in the way humans do. The review authors themselves call for standardised dosing and properly powered human trials before any clinical conclusion is drawn, and we would echo that. There is no evidence here that hyperbaric sessions change fracture risk in people.