Does Total Hip Arthroplasty Influence the Development and Localization of Sacral Insufficiency Fractures?

Defining the canal for ischial and pubic screws in cup revision surgery

Purpose

When revising acetabular cups, it is often necessary to provide additional stabilisation with screws. In extensive defect situations, the placement of screws caudally in the ischium and/or pubis is biomechanically advantageous. Especially after multiple revision operations, the surgeon is confronted with a reduced bone stock and unclear or altered anatomy. In addition, screw placement caudally is associated with greater risk. Therefore, the present study aims to identify and define safe zones for the placement of caudal acetabular screws.

Methods

Forty-three complete CT datasets were used for the evaluation. Sixty-three distinctive 3D points representing bone landmark of interests were defined. The coordinates of these points were then used to calculate all the parameters. For simplified visualisation and intra-operative reproducibility, an analogue clock was used, with 12 o’clock indicating cranial and 6 o’clock caudal.

Results

A consistent accumulation was found at around 4.5 ± 0.3 hours for the ischium and 7.9 ± 0.3 hours for the pubic bone.

Conclusions

The anatomy of the ischium and pubis is sufficiently constant to allow the positioning of screws in a standardised way. The interindividual variation is low — regardless of gender — so that the values determined can be used to position screws safely in the ischium and pubis. The values determined can provide the surgeon with additional orientation intra-operatively when placing caudal acetabular screws.

Sacral Insufficiency Fractures

»

Primary osteoporosis is the most common cause of sacral insufficiency fractures (SIFs). Therefore, a multidisciplinary team approach is necessary for treatment of the fracture and the underlying biologic pathology, as well as prevention of future fragility fractures.

»

The presentation of SIFs typically includes lower back or buttock pain after a ground-level fall or without an identified trauma. Symptoms often have an insidious onset and are nonspecific; consequently, a delay in diagnosis and treatment is common. Clinicians need to have a high index of suspicion, particularly in high-risk patients.

»

Postmenopausal women who are >55 years of age are the most common demographic affected by SIFs. Other risk factors include osteoporosis, history of a prior fragility fracture, local irradiation, long-term corticosteroid use, rheumatoid arthritis, metabolic bone disorders, vitamin D deficiency, pregnancy, history of prior multilevel spinal fusion, and malignancy.

»

Typical imaging on computed tomography (CT) shows sclerosis of cancellous bone in the sacral ala, with or without a discrete fracture line or displacement. Magnetic resonance imaging is more sensitive than CT and shows hypointense signal on T1-weighted sequences and hyperintensity on T2-weighted or short tau inversion recovery sequences.

»

The treatment of SIFs is dependent on the severity of symptoms, fracture displacement, and instability of the pelvis. Accepted treatments include nonoperative rehabilitation, sacroplasty, iliosacral screw fixation, transsacral bar or screw fixation, transiliac internal fixation, and lumbopelvic fixation.