Preoperative planning for total hip arthroplasty is the process of deciding how the arthritic or fractured hip will be reconstructed before surgery. Templating is one part of that process. It estimates component size and position, but the wider plan also includes exposure, fixation, leg length, offset, centre of rotation, stability risk, blood loss, implant inventory and bailout options.

The need for planning is universal. A routine osteoarthritis hip still needs an AP pelvis, a lateral view and a clear plan for cup and stem sizing. A complex hip requires more: dysplasia, protrusio, post-traumatic deformity, previous osteotomy, retained metalwork, childhood hip disease, fracture neck of femur, obesity, osteoporosis and spinal stiffness can all make a standard template misleading.

Poor planning causes predictable problems: wrong component availability, poor exposure strategy, inadequate restoration of leg length or offset, malpositioned hip centre, unstable trial reduction, intraoperative fracture, unplanned cement conversion, inability to remove metalwork or a rushed decision to use an implant that is not ideal.

Good planning improves theatre efficiency and reduces avoidable surprises. It also improves consent, because the surgeon can explain why the hip is routine or complex, what reconstruction is intended and what alternatives may be needed if the anatomy is different from the radiograph.

The mechanism of planning is biomechanical reconstruction. The native hip transmits load through a centre of rotation, a femoral offset, an abductor lever arm and a leg-length relationship. THA changes these variables. If the reconstruction shortens offset, the abductors work at a disadvantage and the hip may feel weak or unstable. If length is overcorrected, the patient may have nerve stretch, pain or dissatisfaction. If the cup is placed too high or too lateral, hip mechanics and wear may suffer. If the femoral stem is undersized or malaligned, fixation may fail.

The most important planning variables are:

• Hip centre: restore or deliberately reconstruct the centre of rotation.
• Cup position: size, medialisation, inclination, version, coverage and screw plan if needed.
• Femoral fixation: cemented, cementless, hybrid, modular, long stem or special implant.
• Neck cut: level and orientation that allow the planned stem and length restoration.
• Offset: femoral and global offset, abductor tension and impingement-free motion.
• Leg length: planned correction balanced against nerve and soft-tissue safety.
• Version and stability: combined anteversion, impingement, spinopelvic mechanics and head/liner choice.

For templating, classification should make the case easier to plan. The most useful classification is not a single named system; it is a practical complexity assessment.

Clinical assessment for THA templating is not just the diagnosis of arthritis. It is an operative planning assessment.

History

Ask about pain, walking distance, walking aids, instability symptoms, previous hip surgery, childhood hip disease, fracture history, spine disease, neurological disease, infection risk, anticoagulation, metal allergy history and patient priorities. Clarify perceived leg-length inequality, shoe raises and whether the patient would prefer equal length, stability or nerve safety if a tradeoff is unavoidable.

Examination

Examine gait, Trendelenburg sign, fixed flexion deformity, abduction contracture, true and apparent leg length, pelvic obliquity, lumbar stiffness, rotational profile, hip range of motion, abductor power, knee deformity, foot deformity and neurovascular baseline. The examination helps explain why the radiographic plan may not match the functional limb length.

Radiograph quality determines template quality. If the image is not fit for planning, the safest decision is to repeat or extend imaging.

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Standard imaging set

• AP pelvis: both hips, pelvis centred, visible teardrops, obturator foramina, lesser trochanters and proximal femora.
• Cross-table lateral or lateral hip: femoral morphology, version clues, osteophytes and anterior/posterior deformity.
• Calibration marker: placed at the level of the greater trochanter or hip where possible; poor marker position reduces accuracy.
• Full-length femur: previous fracture, osteotomy, deformity, retained implants, long stem planning or suspected canal abnormality.
• Standing and sitting lateral pelvis/spine: spinal stiffness, lumbar fusion, sagittal imbalance or high dislocation-risk planning.

CT, EOS and three-dimensional planning

CT or EOS is useful when two-dimensional templating cannot answer the question: severe dysplasia, protrusio, post-traumatic deformity, previous osteotomy, rotational deformity, retained metalwork, custom implant planning or unclear acetabular bone stock. Three-dimensional planning can improve anatomical understanding and size prediction in complex cases, but it does not remove the need for intraoperative judgement.

Management in this topic means the planning process that leads to a safe operation.

Templating technique should be systematic and repeatable.

Step-by-step 2D digital templating

1. Confirm patient, side and image quality.
2. Calibrate magnification using a marker at hip level when available.
3. Draw or recognise pelvic reference lines and check rotation.
4. Template the acetabulum: hip centre, cup size, medialisation, inclination, coverage and screw plan.
5. Template the femur: neck cut, stem size, fixation, offset option, version and canal fit.
6. Compare planned reconstruction with the contralateral side only if the opposite hip is reliable.
7. Estimate leg-length correction and offset restoration.
8. Record the expected sizes and adjacent sizes.
9. List implants, instruments and backup equipment.
10. Reassess the plan intraoperatively after exposure, trialling and stability testing.

Intraoperative checks

The operation should test the preoperative plan. Check the neck cut before broaching. Assess acetabular landmarks before reaming. During trial reduction, assess stability in extension and external rotation, flexion and internal rotation, soft-tissue tension, impingement, leg length and offset. If the trial hip is unstable, do not close because the template looked acceptable.

Complex primary THA should be recognised before the day of surgery. The radiograph below shows a dysplastic hip reconstruction example. It is included because complex anatomy requires a different planning mindset: hip centre, acetabular deficiency, femoral canal shape, version, shortening, offset and backup implants all need to be considered before theatre.

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Templating errors are not theoretical; they appear as operative and postoperative complications.

The literature supports templating as a useful planning tool, but not as a perfect size predictor. Digital templating commonly predicts implant size within one size in many series, with accuracy affected by radiograph quality, calibration, body habitus, implant system, surgeon experience and abnormal anatomy. Three-dimensional planning may improve anatomical understanding and size prediction in complex cases, but routine primary THA still depends on good radiographs and intraoperative judgement.

THA templating is a structured reconstruction plan. Start with adequate calibrated imaging, define the clinical goal, then plan the acetabulum, femur, leg length, offset, stability and backup implants. The plan should be specific enough to prepare theatre and consent the patient, but flexible enough to change when the bone, trials or stability assessment prove that the template is wrong.