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• Modular neck (MN) implants can restore the anatomy, especially in deformed hips such as sequelae of development dysplasia.

• Early designs for MN implants had problems with neck fractures and adverse local tissue, so their use was restricted to limited indications.

• Results of the latest generation of MN prostheses seem to demonstrate that these problems have been at least mitigated.

• Given the results of the studies presented in this review, surgeons might consider MN total hip arthroplasty (THA) for a narrower patient selection when a complex reconstruction is required.

• Long MN THA should be avoided in case of body mass index > 30, and should be used with extreme caution in association with high offset femoral necks with long or extra-long heads. Cr-Co necks should be abandoned, in favour of a titanium alloy connection.

• Restoring the correct anatomic femoral offset remains a challenge in THA surgeries.

• MN implants have been introduced to try to solve this problem. The MN design allows surgeons to choose the appropriate degree and length of the neck for desired stability and range of motion.

Cite this article: EFORT Open Rev 2021;6:751-758. DOI: 10.1302/2058-5241.6.200064

• Hip, spine, and pelvis move in coordination with one another during activity, forming the lumbopelvic complex (LPC).

• These movements are characterized by the spinopelvic parameters sacral slope, pelvic tilt, and pelvic incidence, which define a patient’s morphotype.

• LPC kinematics may be classified by various systems, the most comprehensive of which is the Bordeaux Classification.

• Hip–spine relationships in total hip arthroplasty (THA) may influence impingement, dislocation, and edge loading.

• Historical ‘safe zones’ may not apply to patients with impaired spinopelvic mobility; adjustment of cup inclination and version and stem version may be necessary to achieve functional orientation and avert complications.

• Stem design, bearing surface (including dual mobility), and head size are part of the armamentarium to treat abnormal hip–spine relationships.

• Special attention should be directed to patients with adult spine deformity or fused spine because they are at increased risk of complications after THA.