**3. Preoperative optimization of hip stability**

Due to the numerous risk factors for instability, a thorough preoperative evaluation and identification of appropriate surgical approach should be performed. Several hip arthroplasty approaches exist with varied evidence on the risk of subsequent instability. Historically, the posterior approach was associated with highest rates of instability [29, 30]. This was reinforced with a subsequent large volume Kaiser series that demonstrated improved stability with the direct anterior approach over traditional posterior approaches [31]. However, recent literature has brought this into question, largely demonstrating that with capsular repair the posterior approach is no superior to alternate approaches [32–34]. Critics highlight the selection bias of these capsular repair/posterior approach papers stating they reflect academic practices and do not adequately reflect the community [35]. Further controversy exists when analyzing large joint registry databases. Both the Australian (122,345 primary THA) and Dutch (166,231 primary THA) Registries demonstrate a reduced risk of instability with the anterior approach [35, 36]. From a revision perspective, it appears that changing approach does not affect overall rate of instability [37]. Ultimately it is recommended that surgical approach be utilized at the discretion and comfort of the surgeon with the recognition that the anterior approach may have improved stability. If the posterior approach is preferred then careful capsular closure should be performed [38, 39].

Preoperative optimization of body mass index (BMI) continues to be an ongoing debate. Multiple studies demonstrate a slight preponderance for instability in cohorts with heavier BMI—with 5% increased risk for each BMI unit exceeding 35 kg/m2 [40, 41]. Although the exact etiology of instability in heavier patients remains unknown, possibly resulting from combinations of deeper surgical field causing implant malposition versus muscular weakness; nonpharmacologic weight loss does seem to work at reducing BMI in some patients [42, 43]. From the perspective of instability, it remains unknown if weight loss causes a clinically significant risk reduction in postoperative instability; however, the generalized physical and mental health benefits certainly warrant an attempt at reducing BMI [44].
