2 Easy Steps to Identifying Spine Stiffness in a THA Patient
Hip instability remains a leading cause of revision and re-revision total hip arthroplasty (THA). [1,2] Ensuring correct acetabular cup placement in the primary procedure is a critical component in reducing the risk of instability.
Surgeons typically rely on techniques such as preoperative templating, identification of anatomic landmarks, and even use of advanced technologies like computer navigation and robotics to help them position the cup. Those techniques are generally fine for most primary THAs. What about patients with anatomic anomalies that can make cup placement tricky? How do surgeons compensate for this confounding factor?
In the case of one such anomaly – spinal stiffness – the answer is “add anteversion,” Jonathan M. Vigdorchik, MD, from Hospital for Special Surgery in New York, told attendees at ICJR’s inaugural residents and fellows course, Advanced Techniques in Total Hip & Knee Arthroplasty.
Two groups of THA patients are at high risk for dislocation according to research from Dr. Vigdorchik and his former colleagues at NYU Langone Health: those with spinal deformities and those with a stiff spine. [1,2]
Patients with a spinal deformity, they found, had an 8% dislocation rate, compared with 1.5% in the control group.  In patients with a stiff spine, the number of fused spinal levels made a difference: 1.55% for 0 levels of fusion, 2.73% dislocation rate for 1 or 2 levels of fusion, and 4.62% for 3 to 7 levels of fusion. 
They developed a simple technique that can be used during the preoperative workup to determine if a patient has spinal stiffness. It involves only 2 radiographs – a standing lateral and a sitting lateral – and a few lines drawn on those radiographs.
Step 1: Draw a line for the anterior pelvic plane on the standing lateral.
The line will angle backward in a patient with posterior pelvic tilt, which will make the cup more open. Adding anteversion is not necessary in these cases, Dr. Vigdorchik said.
Anterior pelvic tilt (line angling forward) is very rare, seen only in patients with hip flexion contractures or thoracic kyphosis. Bilateral hip replacement will resolve the hip flexion contractures, with no special techniques needed. Thoracic kyphosis, unfortunately, cannot be resolved because the thoracic spine is fixed.
Step 2: Draw a line on top of the sacrum in both the standing and sitting radiographs.
How much does the line move from standing to sitting? If it’s more than 10°, the spine is not stiff and no adjustments are needed to the THA technique. If it’s less than 10°, the spine is stiff (either from surgical fusion or biologic fusion) and the cup is more likely to dislocate after surgery. To compensate, the surgeon should add 25° to 30° of anteversion, Dr. Vigdorchik said.
Click the image above to watch Dr. Vigdorchik’s presentation and learn more about the role of the hip-spine relationship in THA.
Disclosures: Dr. Vigdorchik has disclosed that he is a paid consultant for Corin and Intellijoint.
- DelSole EM, Vigdorchik JM, Schwarzkopf R, Errico TJ, Buckland AJ. Total hip arthroplasty in the spinal deformity population: does degree of sagittal deformity affect rates of safe zone placement, instability, or revision? J Arthroplasty. 2017 Jun;32(6):1910-1917. doi: 10.1016/j.arth.2016.12.039. Epub 2016 Dec 27.
- Buckland AJ, Puvanesarajah V, Vigdorchik J, et al. Dislocation of a primary total hip arthroplasty is more common in patients with a lumbar spinal fusion. Bone Joint J. 2017 May;99-B(5):585-591. doi: 10.1302/0301-620X.99B5.BJJ-2016-0657.R1.