Almost every patient who has had a hip replacement is given a leaflet at discharge listing the "three precautions": do not bend the hip past 90 degrees, do not cross the legs over the midline, and do not rotate the hip inwards. Many people wrongly believe these rules "must be kept for life". As a result, some patients sit down in fear every time, do not dare to bend over to tie their shoelaces, and even stay inactive for a long time out of panic. This one-size-fits-all fear is in fact out of step with the latest medical evidence.
The core conclusion first. Traditional medical advice asks patients to avoid hip flexion past 90 degrees, adduction past the midline and internal rotation for several weeks after a hip replacement, to prevent dislocation. However, several randomised controlled trials show that relaxing these everyday restrictions does not increase the dislocation rate (1.03% in the restricted group against 0.68% in the relaxed group, OR 0.658, p=.647, Tetreault 2020; 1.5% in the strict group against 1.0% in the relaxed group, van der Weegen 2016). That said, "not increasing the dislocation rate" does not mean zero risk for everyone. In practice the restrictions should be adjusted individually to the surgical approach and personal risk, and finding the right degree of that adjustment is the focus of what follows.
How the three precautions (excessive flexion, adduction across the midline, internal rotation) relate to dislocation
To understand when the restrictions can be relaxed, one first needs to know why these three movements were listed as precautions. Dislocation of an artificial hip is not as simple as "it comes out with a hard push". There is a mechanical principle behind it. When the artificial femoral neck hits the edge of the cup (impingement), the point of impact becomes a pivot. If the limb keeps moving in that direction, the femoral head is levered out of the cup (Brown 2014). The traditional three precautions are exactly the combinations of angles most likely to trigger this levering.
- Excessive flexion: sitting too low or leaning forward to tie shoes, so that the femoral neck hits the front edge of the cup and levers the head backwards
- Adduction across the midline: crossing the legs, sitting cross-legged or pressing the knees together moves the femoral head towards the side where the joint capsule is weaker
- Internal rotation: turning the toes inwards in a flexed position is the final push that moves the femoral head out of the cup
- The capsule and muscles cut during surgery take time to heal, and early stability depends mainly on the geometry of the implant and not on soft tissue
- Whether the posterior capsule is repaired, and whether the repair heals, is a key factor in the stability of the posterior approach
- After a few weeks, as soft tissue repairs and proprioception returns, the dislocation risk of the same movement falls markedly
In other words, the logic behind setting precautions is that "in the early period after surgery the soft tissues have not healed, and stability relies on the geometry of the implant alone". Once the repaired tissue at the back has healed and muscle tone has returned to normal, the mechanical need for protection changes accordingly. What is really dangerous clinically is often a combined movement in which flexion, adduction and internal rotation occur together, and not the range of movement in a single direction. When the restrictions can be eased step by step, and how the recovery timeline after total hip replacement should be planned, are explained stage by stage on another page.
How the precautions differ between the posterolateral and anterior approaches
A point patients most often overlook is that which direction an artificial joint dislocates in, and which movements to guard against in daily life, depends largely on the surgical approach. Applying the same "three precautions" leaflet to patients with different approaches makes it much less accurate. The posterolateral approach enters from behind the buttock and cuts the posterior capsule and the external rotator muscles, so the structural weak point is at the back. The anterior approach is the opposite, and its weak point is at the front (Brown 2014).
- The posterior capsule and external rotators are cut, so the weak point is at the back
- The most dangerous combination: flexion plus adduction plus internal rotation (the femoral head dislocates backwards)
- The traditional "three precautions" were essentially written for this approach
- The posterior muscles are not cut, and the weak point is at the front
- The movement to watch more is extension plus external rotation (the femoral head dislocates forwards)
- Copying the internal rotation precaution of the posterolateral approach may not match the real weak point
The link between surgical approach and direction of dislocation is not just theory. A pooled analysis of 30 trials with 11,562 patients compared the direct anterior approach with the posterior approach and found a trend towards a higher dislocation rate with the posterior approach, although the difference was not statistically significant (stratified randomised trials OR 0.63, p=0.65; Awad 2023). Note that the aim of that study was to compare the approaches in general, and it is cited here only to support the point that "dislocation risk varies with the approach", not as a direct trial of precautions. The practical lesson for patients is clear: first confirm with the doctor which surgical approach was used, so that the list of precautions in hand really points at the weak direction of the joint, and do not copy another patient's leaflet blindly.
Randomised controlled trials and pooled analyses of relaxing protective restrictions and dislocation rates
The traditional idea of keeping the rules for life has been shaken over the past decade by a number of well-designed medical studies. Several randomised controlled trials and pooled analyses of the posterolateral approach have compared early dislocation rates directly between patients who "follow routine precautions strictly" and those with "relaxed or minimal restrictions", and the conclusions are quite consistent: relaxing the restrictions did not make dislocation worse.
Taking the data from these four studies together, the clinical signal is very clear: for patients having an elective total hip replacement through the posterolateral approach by an experienced surgeon, removing or relaxing routine precautions does not raise the early dislocation rate. On the contrary, it eases the patient's anxiety and lets the patient return to normal daily life sooner. This also explains why more and more orthopaedic teams internationally have given up the earlier fixed rule of strict compliance for several weeks and moved to a plan based on individual risk. For how to move safely in daily life once the restrictions are relaxed, the specific guidance is on the page about everyday aids and safe movements after hip replacement.
Large real-world data: dislocation rates after routine precautions were stopped
Because randomised controlled trials always have limited numbers, some may ask whether withdrawing precautions in real clinical settings, involving hundreds of thousands of patients, carries hidden risks. Data from large national health administrative databases and national registries in several countries also reach the same conclusion: no clear rise in the dislocation rate.
UK national health administrative data (Machin 2022)
- Covered 114 hospitals and 229,057 elective primary total hip replacements in all
- Before and after the traditional postoperative precautions were stopped, the proportion of patients with dislocation stayed the same at 0.8%
- The rate of readmission within 30 days of surgery also did not rise. This is large-scale real-world clinical evidence
Danish national hip arthroplasty register (Iljazi 2024)
- Followed 14,799 patients. After the routine recommendation of precautions was stopped, the 3-month dislocation rate was 2.9%, against 3.5% before
- After adjustment, ARR 1.4 (95% CI 0.9–2.2), not statistically significant
- The difference was not significant, partly thanks to the large rise in use of 36 mm large femoral head components after the guideline revision
In addition, another randomised non-inferiority trial of the posterolateral approach (408 patients) found a dislocation rate of 1.48% in the restricted group (who had to sleep on their backs) and 1.46% in the group with relaxed sleeping positions, establishing "non-inferiority" (Peters 2019). This means that relaxing sleeping position restrictions is no worse than strict compliance. One reminder is needed, though. The low dislocation rate in the Danish registry data is partly supported by the mechanical advantage of modern large femoral heads, and safety does not come automatically from simply "dropping the rules". This leads to the question of the limits of risk, covered in the next section. Weight-bearing progression and gait retraining after surgery are another rehabilitation priority, and they are covered on the page about weight bearing and gait training after total hip replacement.
Understanding the limits of this evidence
If only the surface conclusion is read, patients can easily misread "relaxing the restrictions" as "being free to move through large ranges and ignore protection altogether". It must be stressed that the conclusion of the medical research is that "relaxing routine restrictions at group level does not raise the overall dislocation rate", and it is by no means a guarantee that "anyone doing any movement carries zero risk". In fact, joint dislocation remains one of the main reasons for revision surgery after a hip replacement, and the three limits of the existing evidence need to be faced objectively.
Three points to bear in mind when interpreting these studies:First, the level of evidence in most of the related studies is low (low to very low). The general direction is credible, but how large the real risk is remains not very certain in numbers (Korfitsen 2023). Second, the very low dislocation rates in some studies owe much to the widespread use of 36 mm large femoral head components today, which make the joint itself more stable, and this cannot be credited entirely to "removing the protective rules" (Iljazi 2024). Third, even where research confirms that minimal protection is safe, the premise is usually that "the surgery was done by an experienced surgeon and combined with a large enough femoral head" (Kornuijt 2016, with 0 dislocations in the minimal precautions group against 1 in the standard group, p=0.32). The safest approach is therefore to keep sensible protection in the early period after surgery, avoid combined movements of large range, and then relax step by step according to the doctor's assessment, and not to behave from the start as if nothing had happened.
In other words, what the latest medical evidence overturns is the rigid doctrine of "keep the rules for life", and not the basic principle that "appropriate protection is needed in the early period after surgery". What patients should really ask the healthcare team is not simply "do I still need to follow the rules?" but "given my surgical approach, the size of my femoral head component and my physical condition, which movements must be guarded against, for how long, and at which stage can they be relaxed?" This is the core value of an individual rehabilitation assessment, and it is the key question the series of articles on rehabilitation after total hip replacement aims to answer for patients.
Everyday protective principles in the early period after surgery (not a replacement for the surgeon's instructions)
Relaxing restrictions does not mean letting go of protection. In the first few weeks after surgery, while the soft tissue is still healing, keeping a few simple and sensible protective habits fits the mechanical principle of "avoid extreme combined movements" without leaving the patient unable to move at all, as the old rules did. The practical main principles below can be used together with the specific instructions of the surgeon.
Protective habits suggested for the early period after surgery
- Never make a combined movement that adds together flexion, adduction and internal rotation
- If the surgery was through the posterolateral approach, it is best to keep a pillow between the legs when sleeping, to stop the operated leg moving inwards across the midline of the body
- When getting up, going to the toilet and getting in and out of bed, slow down and do it step by step in separate parts, and avoid sudden twisting turns
Where there is no need to be over-anxious or over-restrictive
- Evidence from large group studies shows that moderately relaxing sleeping and sitting restrictions does not raise the risk of dislocation (Peters 2019)
- A systematic review pooling 7 studies and 6,900 patients found dislocation rates of 2.2% with precautions and 2.0% without, almost no difference (Crompton 2020)
- Overly strict activity restrictions can in fact slow the recovery of function, make the patient more anxious and raise the risk of losing independence
The exact degree of strictness for each person, for example the approach used, the femoral head size, and any history of revision, still has to be decided by the surgeon and physiotherapist. If a patient has just gone home in Hong Kong and does not know how to turn the instructions on the hospital leaflet into movements that are practical at home, when Nova Health's registered physiotherapists provide ahome physiotherapyservice, they first check the patient's surgical approach and femoral head size, and then, by stage of recovery, turn that one-size-fits-all fear into individual guidance that is relaxed step by step by movement combination and timetable. During recovery, strengthening the hip abductors and gluteal muscles is equally important for rebuilding steady gait, and the details of this training are on a separate page about hip abductor and gluteal training to prevent falls.
High-risk combined movements common in Hong Kong homes
Applying overseas medical research to actual living conditions in Hong Kong reveals something: what most easily leads patients into a high-risk combination of movements is often not deliberately crossing the legs but the basic everyday movement of getting up from a seat. The reason has much to do with the fact that seats and toilets in local homes are generally low and spaces narrow.
Low toilets and cramped spaces
- Bathrooms in Hong Kong homes are generally narrow, and when the patient sits on a toilet of standard height the hip is often already flexed past 90 degrees
- In home assessments in the early period after surgery, what the physiotherapist most often has to deal with is the risk of excessive hip flexion because the toilet is too low
- This page mainly explains the mechanical principles, and practical steps such as fitting a raised toilet seat are explained in detail on the page about daily living
Sofas that are too low and low beds
- Homes in tenement buildings and older estates in Hong Kong often have sofas with very low seats, or beds set low
- When an older person tries to push up from such a low seat, the legs naturally flex the hip and press inwards (adduction) at the same time, which is exactly the high-risk combination the posterolateral approach most needs to avoid
- In such cases the seat height must be raised and the way of getting up changed, so that the combined movements that overlap are done separately
This is where a physiotherapist home assessment is most valuable. The therapist works on the combined movements that the patient's real home setting tends to trigger (flexion, adduction and internal rotation occurring at the same time) by changing the environment and adjusting the movements. This lowers the risk of posterior dislocation more reliably than asking the patient to memorise angle figures. In fact the patient education page on total hip replacement from the Hong Kong College of Orthopaedic Surgeons (HKCOS) also sets out the points for preventing dislocation after surgery, including not crossing the legs, not flexing the hip past 90 degrees, avoiding excessive internal or external rotation, and keeping a pillow between the legs when sleeping (see orthoinfo-hkcos.org). In the public system, hospitals under the Hospital Authority all offer total joint replacement and follow-up physiotherapy after surgery, and members of the public with general enquiries can call 2300 6555. In addition, orthopaedic teams in Hong Kong and university research groups (for example the joint replacement team of the Department of Orthopaedics and Traumatology at the University of Hong Kong / Queen Mary Hospital) have in recent years begun research comparing the results of traditional and minimal hip precautions, and the overall academic direction is likewise towards individual assessment and moderate relaxation of routine restrictions.