Comparison of Acetabular Shell Position Using Patient Specific Instruments vs. Standard Surgical Instruments: A Randomized Clinical Trial Travis Small, DO, Viktor Krebs, MD, Robert Molloy, MD, Jason Bryan, MS, Alison K. Klika, MS , Wael K. Barsoum, MD Department of Orthopaedic Surgery, Cleveland Clinic-A41, Cleveland, Ohio abstract article info Article history: Received 16 July 2013 Accepted 7 October 2013 Keywords: total hip arthroplasty patient specific instruments acetabular cup preoperative planning Total hip arthroplasty (THA) survivorship relies largely upon appropriate acetabular cup placement. The purpose of this prospective randomized controlled trial was to determine whether the use of a preoperative 3D planning software in combination with patient specific instrumentation (PSI) results in improved cup placement compared with traditional techniques. Thirty-six THA patients were randomized into standard (STD) or PSI technique. Standard approach was completed using traditional techniques, while PSI cases were planned and customized surgical instruments were manufactured. Postoperative CT scans were used to compare planned to actual results. Differences found between planned and actual anteversion were −0.2° ± 6.9° (PSI) and −6.9° ± 8.9° (STD) (P = 0.018). Use of 3D preoperative planning along with PSIs resulted in significantly greater anteversion accuracy than traditional planning and instrumentation. © 2014 Elsevier Inc. All rights reserved. Total hip arthroplasty (THA) is an extremely successful procedure, improving range of motion and decreasing pain to improve patients' quality of life [1–3]. However, malpositioning of the acetabular cup can result in premature implant failure requiring revision [4–10]. The number of primary THAs performed in the United States increased from 7.99 per 100,000 people in 2001 to 10.3 in 2007 [11] according to Ravi et al. In a study by Wera et al, the most common cause of revision THA was due to cup malpositioning (33%) [10]. Currently, implant placement in THA relies on navigation, crude instrumentation, or exclusively on a surgeon's intraoperative assessment of limited anatomic landmarks with the use of generic, mechanical instruments designed for all patients with differing severities of pathology and unique anatomy. Accurate acetabular cup positioning in THA decreases the risk of dislocation [12–15], impingement [16,17], and all component wear rate [18–20]. Component wear rate on both hard-on-hard and hard- on-soft bearing surfaces from edge loading at high abduction angles has been reported [20]. The traditional methods of using preoperative radiographs (e.g., anteroposterior pelvis and hip) for planning and standard surgical instrumentation have shown potential for inaccu- racy which varies with surgeon experience [21,22]. Factors that contribute to inaccurate cup placement include approach, patient positioning [23] and BMI [24]. Minimizing the risk of cup malalign- ment and subsequent revision THA through correct placement is a modifiable risk factor that could reduce the rate of revision THA and its burden to the health system. As shown by Bozic et al from the nation-wide inpatient sample (NIS), revision THA had an average length of stay of 6.2 days and hospital charges of $54,553 in 2006 and is the leading cause of early revision in THA [25]. Historically the recommended range of values for anteversion is 15° ± 10° and abduction is 40 ± 10° as originally described by Lewinneck [15]. However, Yoon et al [26] determined that the correct safe zone changes according to the amount of version and abduction as shown by a circle with a radius of 14° from 39° abduction and 21° anteversion, as opposed to the classic rectangle represented safe zones [13,15]. Their study illustrated the importance of understanding safe zones which should be individualized for each patient due to the dynamic nature of cup positioning and patient anatomy. Once this is achieved, reproducing the values in the OR remains its own separate challenge. It has been shown that free-hand cup placement is accurate only 70.5% of the time [22]. The most widely used method of placing a cup involves planning the surgery with preoperative radiographs and attempting to reproduce the plan with standard surgical instruments which fail to account for a patient's unique pelvic anatomy and position on the operating table. Transferring the plan from the radiographs to the OR can be difficult due to a patient's unique anatomy and the differences defined by Murray [27] between radiographic, operative, and anatomic planes of version and abduction. Surgeon experience using an alignment guide attached to a reamer handle is used to obtain 45° abduction referencing the floor and 20° anteversion referencing the longitudinal axis of the patient. Assessing the position of the pelvis relative to the patient and the OR using standard instruments can lead to malpositioned acetabular components [23]. The Journal of Arthroplasty 29 (2014) 1030–1037 The Conflict of Interest statement associated with this article can be found at http://dx. doi.org/10.1016/j.arth.2013.10.006. Reprint requests: Alison Klika, MS, Department of Orthopaedic Surgery-A41, Cleveland Clinic 9500 Euclid Ave. Cleveland, OH 44195. 0883-5403/2905-0034$36.00/0 – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.10.006 Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org