It is one of those static, chill days you get in Edinburgh towards the end of winter. Ice sheets the pavements and roads; no wind stirs the blackened branches of the trees; the fallen foliage from the now distant autumn is frost-gilded and crisp underfoot.

I am swathed in multiple layers of merino wool, a scarf covering half my face, and I am holding myself stiffly upright on the very edge of a stool in a small and glaringly lit room. Despite the wool, despite my mittens and sheepskin-lined boots, I am unremittingly, unavoidably cold. Chronic pain, I am discovering, is tiring, draining, domineering: it absorbs all your energy and focus; it drives other thoughts from your head. My body seems unable to keep itself at a liveable temperature, so preoccupied is it with the extreme discomfort of my back.

In the room with me is a doctor from Australia and I am wondering to myself how can he be wearing just a shirt under that white coat? Doesn’t he feel the cold? How can he be unaffected by this temperature?

I have just explained to him that, three days ago, I leaned sideways to move a counter in a game I was playing with my children and I felt a crunch, followed by a rip, and then a horrible shifting sensation as something slid out of place in my lower back. Pain spread like a stain, outwards and upwards, and I have, ever since then, been unable to move, sit, walk or stand without unbelievable agony.

We are, he and I, gazing at an X-ray sheet on a lightbox. I’ve always had a deep fascination for X-rays: what a gift, what an unaccountable power, to be presented with the shaded, layered images of your inner workings, to be granted an oddly prescient glimpse of what you’ll look like in your grave.

Other X-rays have shown me my cranium, with its recognisably ridged nose, my chaos of teeth, pitted with the stark geometry of fillings; I’ve seen the spread bones of my hands, the linear metatarsals of my toes, the neat socket of my ankle. But never this, before now: the astonishing twinned halves of the sacroiliac region.

The Antipodean doctor points out bones, joints, nerves, to help me get my bearings on this strange map of grey and white and black. He says my left sacroiliac joint has slipped out of alignment, causing my current state.

‘And when did you break your sacrum?’ he says, leaning closer to peer at something.

‘What?’ I say, from behind my scarf.

He repeats the question, turning around.

I tilt my head to look up at him and an invisible, answering knife slices through my side. ‘I haven’t broken my sacrum,’ I mutter, wincing, tightening my hold on myself. ‘Or at least . . . I don’t think I have. Have I?’

The doctor raises his eyebrows. ‘You don’t remember?’ he says.

The lower back is a lesson in symmetry, with the curved wings of the pelvis flaring out from the sacrum, which is cupped like an open palm and pierced with a line of paired holes. The coccyx curves up, beneath, a vestigial reminder of our simian origins. On an X-ray, the area resembles a butterfly or silver moth, pinned to a dark velvet board. There are parts of the body which, taken in magnified isolation, look strange or spindly or peculiar or unidentifiable, but the sacral area is unmistakable and unusually beautiful. It is part angel, part lepidopteran, part Rorschach inkblot.

The sacrum, the triangular, pitted central bone, is a complex, multifaceted cog, performing numerous functions. It is crucial for load-bearing, supporting the entire spine above it, and for accommodating the spinal nerves; it articulates with the hip bones, connects with the final lumbar vertebrae, above, and the tail bone, below. Strong ligaments connect it to the ilium bones of the pelvis: these joints are L-shaped and capable of a small amount of movement.

In children, the sacrum is formed of five separate vertebrae, which start to fuse into a single bone at around the age of eighteen. Women’s sacrums tend to be shorter than men’s, with more breadth and curvature, to allow greater capacity in the pelvis.

The term ‘sacrum’, which was coined by eighteenth-century anatomists, comes from the Latin name os sacrum, which means ‘sacred bone’. Before the anatomists came along, the sacrum was also known in English as ‘the holy bone’.

All this anatomical and linguistic information is unknown to me as I perch gingerly in the doctor’s office, as I watch him point to a tiny grey line, like a river seen from a plane, on one side of the sacrum on the lightbox.

I can see what he means. There is evidence of fracture on the bone. I am able to see it. I also know that the X-ray is mine: I can see my name, reversed so that the surname precedes my initial, in the corner. But can I really have broken it and not known? How is that possible?

I look down at my hands, a minuscule movement which causes a shiver of discomfort from my shoulder blades, down to the base of my spine, exactly where the line of fracture must be.

‘I fell,’ I say to the doctor, ‘on a marble floor.’

What I don’t tell him is that we were on holiday, in Italy. That one of my children had been very sick. That it was early spring, Easter time, and my job that week, as the mum, was to get the family back on track, to show them that we were going to have a great time, despite illness and stress and dashes to hospital. I wasn’t exactly wearing a jester’s hat but I might as well have been. I had an assignment from a newspaper to write about a garden of stone monsters, built by a grieving duke for his dead wife. Monsters or no monsters, we were going to enjoy ourselves: I would make sure of it.

One morning, I was with my children beside a pond outside the villa; my son was beside me and my two daughters were chasing emerald-backed lizards in and out of the rosemary bushes. I had drawn up my feet and I was sitting cross-legged in a rickety garden chair. My son said something – I forget what – and I laughed, throwing back my head.

Balance has never been my strong point. I am forever falling sideways, lurching into bookcases or banisters or doorjambs. Turning my head can cause me to topple over. I often trip over things that aren’t actually there.

So I laughed, cross-legged in my chair, and what happened next seemed to occur in slow motion. I saw the median line of the pond edge, the box hedge, the eaves of the villa tilt. The scene of the water, my children, the tiles dropped away from me and I saw instead a flash of treetops, the arrowing path of a bird. I heard the noise before I was aware of the impact: a crashing thud inside the border of my body, travelling upwards in a great sonic wave towards my ear canals.

The next moment, I was supine, in a different place entirely, as if I had dropped through a trapdoor. Here I was on a level with marble flagstones, with feet, with the lip of the pond. It seemed suddenly hard to breathe, to inflate my lungs. I tried to roll sideways, to right myself, but there was a pain so enormous, so severe, at the base of my back that I couldn’t move. It was a large presence, this pain, with tentacles and claws: it gripped me tightly in its clutches, it drove an iron fist into my spine.

My children were crowding round me. I could see their sandalled feet, the hems of their clothes. The youngest was patting me on the arm, saying, Mama, Mama. Tears were streaming from my eyes and I could hear strange, hoarse, gasping sounds.

‘Get your dad,’ I managed to say.

The Hazara
Turn the River