One of the major reasons holding me back from my first hip replacement is the fear of dislocation. I’ve had undiagnosed muscle and bone issues since childhood (now in my fifties) and was told I need a hip replacement seven years ago. At this stage I have an offer of surgery but an not even sure if my condition is oesteoarthritis, AVN or both.

But there are complications and unique circumstances in my case which also make me hesitant. One is as I have mentioned, that I have lifelong problems. I haven’t been able to rise from a chair or squat for about 25 years now. I was taken to the hospital once when I was about five after being able to walk but an xray showed nothing and the main symptom wore off in a day and no one believed me about the pain (which was intermittent thereafter). So it worries me that it’s lifelong and I don’t know why.

The other issues is that in the past I had a rough childhood and emotional life as an adult. I did have a slimming disease and have gone down to 60kg (188cm tall male) a few times in life and also drank heavily for about a decade. Both of these conditions can affect muscles. My last bout of both of these was over ten years ago and I’ve been a normal weight since then, but I do deliberately keep myself slim as my hips are in far less pain. During the last bout of slimming I felt the muscles had not returned properly. Around my collar bones, also volume loss in the buttocks. My face is abnormally gaunt also. I was checked a decade ago for myopathy, but a number of doctors put my symptoms down to slimming.

Now I’ve recently had an MRI (without staining). The MRI doctor who read this said the muscle is normal but only looked at it for less than a minute. The report has only two sentences and says arthritis, but he told me verbally it’s AVN. The surgeon I spoke to didn’t bother looking at ithe MRI (when asked) and also didn’t examine me (when asked) and only checked if I can stand on one leg for a few seconds (though I’ve since found out that it’s a 30 second standard test). So basically I live in a developing country where the standards are low (I assume).

Anyway, due to the persistent weakness and reduced appearance of my muscles, I do worry I am at increased risk of dislocation if I proceed and have a replacement. I’ve spoken to ai about it and it thinks, on the balance of things, the weakness and volume loss can be normal arthritis, and disuse due stiffness. I’ve decided to finally use my useless degree and actually do some research into dislocation risk for hip surgery patients and look into any further testing that can guide me towards if I should press for a dual mobility implant. I did ask the surgeon but he said no as I’m a ‘special case’ as my bone doesn’t have a ‘normal cup shape’. So, this research is to let me know what tests to have before I speak to the surgeon again.

Most studies look at an overall incidence of dislocation without seperating any variables and figures are about the same. For example one study by Dargel et al (2014) showed around 2% of dislocations occour within one year. The author noted the most common situations of dislocation were bending forward from standing position (not sure what that means, perhaps getting out of a chair?) and internal rotation of a flexed hip; Internal rotation of a flexed hip is when the hip is bent (flexed) at an angle, like when sitting or lifting the knee, and the thigh or knee is turned inward toward the body’s midline. For example, this could happen if you cross your leg over the other while sitting, pointing the knee inward. In hip replacement patients, this movement can stress the new joint, potentially causing dislocation. Another cause is poor implant positioning, meaning the angle of the implant is wrong, or the fixing or overall size.

59% of dislocations are within the first three months. Late dislocationis afer five years and this tends to be caused by material failure.

The rate of dislocation for people with neuromuscular conditions is 5-8%.

The rate of dislocation for posterior approach is 3.2%

A tripolar cup system can be used for patients with increased risk, but then there is the risk of intraprosthetic dislocation, which is harder to fix and might need special parts. It’s used less overall as it tends to not wear as well.

Another study in the Lancet (2019) was a meta-analysis looking at over 35 thousand reported dislocations and found a 2.1% averabe over six years, the main risk variables were being, socially deprived and a having a history of drug use, a BMI of over 30, AVN or neurological condition. Factors reducing the risk were anterolateral, direct anterior, lateral and posterior with short external rotator and capsule repair (short external rotators are muscles that support the joint and they are moved in replacement, and when they are put back, the surgeon can secure them with stitches; capsule repair refers to tissue that surrounds the joint and is opened or removed to allow access in posterior approach (superpath does not cut these tissues and so both types of repair are not required), larger femeral head, alevated ecetabluar liner (In a normal liner, it’s the same size all around, if elevated, there are two surfaces one of them is lightly longer, which restricts movement slightly but keeps the joint more stable.), dual mobility cups (a small head rotating in a larger plastic shell), cemented fixation and standard femoral neck lengths (the stem is hammered into the femor, and the head in placed over it with a ‘neck’ below what can be standard or slightly longer or shorter to keep the leg length correct, the surgeon tests it during surgery and looks at leg length and if it feels unstable or tight, they might change the neck length) and lastly high surgeon prodedure volume (an experienced surgeon in other words).

One study (Brooks, 2013) found that leg length issues attributed to dislocations, and late dislocations can be caused by abductor weakness and infection. Larger heads and dual mobility implants make the hip mechanically harder to dislocate, helping prevent late dislocation even if muscles are weak or soft tissues are damaged.

A large study (Jameson, 2011) using the British NHS found an increase in femoral head size (above 36mm) reduced risks with no change in five year revision rates.

Another study (Khan M.A et al, 1981) also found a 2.1% rate overall. One reason can be the acetabular cup to vertically or too anteverted. Worryingly, after dislocation, only 62% of people were OK, the rest required further surgery.

Superpath

The potential saving grace in my situation is that, by chance, I have found a local surgeon that performs superpath, which is a relatively new approach that avoids cutting muscle or dislocating the bone to position the implant. One study (Yang et al, 2025) compared a superpath group to a convential control group in geriatric patients with a high risk of dislocation. I think they had femoral head fractures. In the control group, there were 8 dislocations, and NONE in the superpath group. There was lower reoperation rate in superpath and mortality rates were the same. The approach (lateral-posterior) means cutting the back or the side of the hip, then cutting or detatchnig the muscles,which gives good visiblity. The superpath approach is a smaller incision at the top of the ?thigh and the work is carried out between the muscles with no cutting.

Another study (Kay, A et al, 2021) found NO dislocations. They noted that normal hip replacements have a 2-3% dislocation rate with 77% within one year. They followed 214 patients with phone calls and also checked medical records. They found NO dislocations with superpath, a 2.3 day average to discharge and an average leg length discrepency of 3.5mm (which I think is low).

Assessing Risk

The main muscles to check when assessing dislocation risk. Gluteus medius and minimus (outer pelvis). They abduct (move the hip away from the body) and stablise the pelvis duringwalking and standing. They prevent the remoral head from shifting laterally or superiorliy.

Gluteus maximus. The largest buttock muscles, pelvis and sacrum to femur and ilotibial ???. They extend and rotate the hip. Prevents posterior dislocation, esp sitting, squatting or rising in lateral-posterior aproaches.

Illiopsos. Spine and pelvis to the femu?? Lifts the thigh. Adds anteroir stability, prevents dislocatio anteriorliy,expecially extesion or external rotttiron.

Short external rotators, are dep inthe pelvis. Prevents posterior dislocation. They are spared in superpath, Prone to atrophy in extreme weight loss.

Abductors. Inner thigh, pubis to femur. Abducts leg (pulls in towards the middle) for overall stability.

So in thinking about this, remenber that a history of drinking can cause muscle fiber damage. Also, it’s a good idea to look at bone quality, especially when looking at the superpath approach because of the femoral head breaks, the superpath approach might have to be abaondoned and converted, possibly to posterior, which would be an absolute worse case scenario.

Actual tests

Manual muscle test against force.

Gluteus medius. LIe on side, life leg up to test abduction strength.

Gluteus maximus – lie face down, extend hip back against resistence.

Illopsoas – sit and life leg for resistence

Short external rotators. sit rotate foot out against resistence.

So the tests are graded. Less than four shows instablility and a dislocation risk.

Trendelenburg test. Stand of one leg. If the pelvis drops, there are weak gluteus medius minimus.

Palpitation and inspection, feel and visually check eg. buttock or thigh muscles.

Ultrasound, especially for ?superficial muscles like gluteus maximus or abdutors.

EMG shows whether the nerves are properly activating a muscle, helping identify if weakness is due to nerve or muscle problems, but it does not directly measure strength. It does clarify neuropathy though.

Function test

single leg, thirty seconds to check gluteal strength.

Gait analysis. Limp or pelvic drop (trendelenburg gait) indicates gluteal weakness.

Sit to stand test – weak gluteus maximus or iliopsoas.

A Dexa scan or bioelectrical impedance – qualifies lean muscle massa. Low index <7kl/M2 confirms sarcopenia from slimming and weak stabalizers. A dexa scan can also assess bone quality.