Specific Risks of Total Hip Replacement

Part of The Joint Replacement Guide — Phase 3: Understanding the Risks · Article 15 of 44 · Hip

Key Points

Risks particularly associated with hip replacement include dislocation, a difference in leg length, nerve injury and fracture around the implant.
Dislocation risk has decreased over time, but it has not disappeared. The individual risk depends on the patient, operation and implant.[2]
Surgeons aim to restore leg length while also producing a stable hip with appropriate muscle tension. Exact equality cannot be guaranteed.
A temporary feeling that one leg is longer is not always caused by a true difference in bone length.
Significant nerve injury is uncommon, but recovery is variable and some injuries cause lasting weakness, altered sensation or pain.[1]
These risks should be discussed alongside general risks such as bleeding, infection and blood clots.

Dislocation

A dislocation occurs when the ball of the artificial hip comes out of its socket. It can occur when particular forces or positions overcome the stability of the new joint.

Dislocation is more likely during the early recovery period, while the muscles and other tissues around the hip are healing. However, it can occasionally occur later.

Published rates vary considerably according to the people studied, the implant, surgical technique and length of follow-up. A large systematic review reported an overall rate of approximately 2%, while also finding that dislocation rates had fallen over time.[2] Your own hospital may quote a different figure based on its patients and practice.

Factors that can influence risk include:

previous hip or spinal surgery;
the reason for hip replacement;
muscle weakness or certain neurological conditions;
body weight and general health;
soft-tissue tension;
surgical approach and repair;
positioning of the components; and
the design and size of the implant.

What happens if the hip dislocates?

A dislocated hip is painful and usually makes it impossible to walk normally. The leg may appear shortened or rotated.

It generally requires urgent hospital assessment and an X-ray. The hip can often be returned to position without open surgery. This is called a closed reduction and normally requires sedation or an anaesthetic.

The team may then investigate why the dislocation occurred and recommend temporary movement advice, physiotherapy or a brace. A single dislocation does not always require further surgery. Repeated dislocation, component malposition or another identifiable mechanical problem may require revision surgery.

Hip precautions

Advice about restricted movements after hip replacement varies. Research suggests that extensive precautions are not necessary for every patient, but the evidence does not mean that all precautions should be ignored.[3]

Recommendations should reflect your surgical approach, implant, stability and individual risk factors. Follow the advice given by your own team and ask how long any restriction is intended to continue.

Leg-Length Difference

Surgeons aim to restore comfortable and functional leg length. This has to be balanced with other important objectives, including:

keeping the new joint stable;
achieving appropriate muscle and soft-tissue tension;
positioning and fixing the components safely; and
managing any pre-existing deformity of the hip, pelvis or spine.

For these reasons, exact equality cannot be promised. In some circumstances, accepting a small difference may be safer than compromising the stability or fixation of the hip. A substantial unexpected difference is uncommon but can be disabling.

True and perceived differences

A true or structural leg-length difference is a measurable difference in the length of the limbs after surgery.

A perceived or functional difference means that one leg feels longer even when measurement shows little or no structural difference. This feeling can be affected by:

pelvic tilt;
tight or weak muscles;
a longstanding limp;
spinal curvature;
arthritis in the other hip or a knee;
swelling; and
the body adjusting after correction of a previously shortened hip.

The feeling of unequal length often changes as swelling settles, muscles recover and walking improves. Studies have found that perceived discrepancies commonly reduce over the first few months, but this does not happen for everyone.[4]

What if the difference persists?

If a leg-length difference remains troublesome, the team may assess your gait, pelvis, spine and both legs. Measurement on an X-ray may be appropriate, but it must be interpreted alongside clinical examination.

Management may include:

allowing time for early recovery;
physiotherapy and gait retraining;
treatment of another contributing joint or spinal problem; and
a shoe insert or external shoe raise after appropriate assessment.

Avoid buying a permanent shoe raise very early in recovery without professional advice, because the perceived difference may change. Further surgery solely for leg-length difference is unusual and would normally be considered only when symptoms are substantial and the likely benefit outweighs the risks.

How Hip Stability and Leg Length Are Connected

Hip stability and leg length are closely related. During hip replacement, the surgeon aims to produce a stable, well-functioning joint while restoring leg lengths as evenly as reasonably possible. Stability depends partly on selecting and positioning the implants appropriately and achieving suitable tension in the muscles and other soft tissues surrounding the hip.

These objectives can occasionally conflict. If the soft tissues are too loose, the hip may be less stable and more likely to dislocate. Increasing soft-tissue tension can improve stability but may also lengthen the operated leg. Conversely, attempting to achieve exact leg-length equality at all costs could sometimes leave the hip inadequately tensioned or unstable.

The surgeon therefore has to balance leg length, implant position, movement, soft-tissue tension and stability during the operation. If perfect leg-length equality cannot be achieved safely, securing a stable hip will generally take priority, while keeping any difference as small as reasonably possible. This does not mean that every leg-length difference is intentional or unavoidable, and a clinically significant discrepancy remains an important risk that should be discussed before surgery.

Nerve Injury

Several nerves lie close to the hip and can be affected by traction, pressure, retractors, swelling, bleeding or, rarely, direct injury.

The sciatic nerve—particularly the part controlling ankle and toe movement—is one of the nerves most often involved. The femoral, superior gluteal, obturator and lateral femoral cutaneous nerves can also be affected. The pattern of risk varies with the surgical approach and individual anatomy.

Possible symptoms include:

numbness, tingling or altered sensation;
burning or nerve pain;
weakness of the leg;
difficulty straightening the knee; or
difficulty lifting the foot or toes, known as foot drop.

Minor numbness close to the scar is different from injury to a major nerve and is relatively common after any surgical incision.

How common is significant nerve injury?

Significant nerve injury after primary hip replacement is uncommon. A recent systematic review estimated an overall incidence below 1%, although the included studies differed considerably.[1] Risk can be higher in complex or revision surgery, severe deformity, developmental dysplasia and patients with previous hip surgery.

Does it recover?

The outcome depends on the nerve, cause and severity of the injury. Recovery may take many months because nerves heal slowly. Some people recover fully, some improve but retain symptoms, and others have a permanent deficit.

Recent pooled evidence estimated complete recovery in approximately half of recognised nerve injuries, but the available studies were varied and the estimate is uncertain.[1] It is therefore not appropriate to promise that most injuries will resolve.

Treatment may include observation, physiotherapy, pain treatment, a splint for foot drop and tests such as nerve-conduction studies. Occasionally, urgent imaging or further surgery is needed—for example, if a collection of blood is compressing a nerve.

New or worsening weakness after surgery should be reported promptly rather than left until a routine follow-up appointment.

Fracture Around the Implant

A fracture can occur while the components are being inserted or after surgery. A later fracture around an existing replacement is called a periprosthetic fracture.

Risk may be affected by:

osteoporosis or poor bone quality;
increasing age and frailty;
previous surgery or deformity;
the type of implant and fixation;
technical factors during surgery; and
a fall or other injury after surgery.

A small, stable fracture noticed during the operation may require observation or additional fixation. A more substantial fracture may require cables, plates, screws, a longer implant or revision surgery.

Seek urgent assessment after a fall if you develop marked new hip or thigh pain, deformity or an inability to bear weight.

Surgical Approach and Implant Choice

Surgical approach is one factor affecting dislocation and other complications, but comparisons are difficult because surgeon experience, patient selection, component positioning, implant choice and soft-tissue repair also influence outcomes.

No approach removes every risk. A surgeon may reasonably recommend the approach with which they have appropriate experience and which they believe best suits your anatomy and clinical circumstances. The reasons, material risks and reasonable alternatives should be explained to you.

It is also worth knowing that the National Joint Registry mainly records implants and revision procedures. A dislocation treated without implant revision may not be represented in revision statistics, so an NJR revision rate is not the same as the total dislocation rate.

Questions to Ask Your Surgeon

You may wish to ask:

What is my estimated risk of dislocation?
Will I need any movement precautions, and for how long?
Do I already have a true or apparent leg-length difference?
Are there reasons why exact leg-length equality may not be achievable?
Are any aspects of my anatomy or previous surgery likely to increase nerve or fracture risk?
What symptoms should prompt urgent contact after surgery?
How does the proposed approach or implant help manage my individual risks?

This article provides general information and does not replace your individual consent discussion. Your surgeon should explain the risks that are particularly relevant to your anatomy, health and proposed operation.

References

Nerve injuries after total hip arthroplasty: a systematic review and meta-analysis. Orthopedic Reviews. 2026. Available from: https://pubmed.ncbi.nlm.nih.gov/42040246/
Kunutsor SK, Barrett MC, Beswick AD, et al. Risk factors for dislocation after primary total hip replacement: a systematic review and meta-analysis of 125 studies involving approximately five million hip replacements. Lancet Rheumatol. 2019;1(2)–e121. doi:10.1016/S2665-9913(19)30045-1. Available from: https://pubmed.ncbi.nlm.nih.gov/38229338/
No need for hip precautions after total hip arthroplasty with posterior approach: a systematic review and meta-analysis. Medicine (Baltimore). 2024;103(50). Available from: https://pubmed.ncbi.nlm.nih.gov/39686472/
Iwakiri K, Ohta Y, Fujii T, Minoda Y, Kobayashi A, Nakamura H. Changes in patient-perceived leg length discrepancy following total hip arthroplasty. Eur J Orthop Surg Traumatol. 2021;31:1355–1361. doi:10.1007/s00590-021-02879-4. Available from: https://pubmed.ncbi.nlm.nih.gov/33502598/
National Joint Registry. Hip replacement: information for patients. Available from: https://www.njrcentre.org.uk/patients/hip-replacement/

← Back to the Joint Replacement Guide · Previous: Anaesthetic Risks · Next: Specific Risks of Total Knee Replacement