21 - 23 The concept of spino-pelvic balance is equally as important as recognizing that nerve compression and an imbalance of the hip musculature can cause weakness in the posterior hip muscles, resulting in hip dislocation.

The consensus is to always treat the hip first, unless there is concern of imminent paralysis from severe spinal stenosis. 20, 21 Patients can present with pain in the lower back, buttocks, and groin and can also have leg pain with radiating symptoms. It is not uncommon for the aging population to develop both hip and spine involvement in the arthritic process. In a patient with a hip replacement, this can result in posterior dislocation of the prosthesis. 15, 16, 17, 18, 19 Resultant spino-pelvic stiffness after lumbar fusion interferes with the ability of the pelvis to flex in a seated position, causing the hip to remain in a less anteverted position. 2, 4, 7, 9, 13, 14 Recently, publications are alluding to a correlation between the spine and hip stability, particularly the angle of the pelvis relative to the spine in patients with a history of lumbar spinal fusion surgery. The question of hip stability continues to be studied, and we are still learning more and more regarding this phenomenon. 10, 11 Further studies exposed the risks and complications associated with MoM hip replacements, and this had led to a dramatic decline in the number of MoM hips implanted in the United States over the past few years. In 2006, there was a renewed interest in metal-on-metal (MoM) bearing surfaces in hip arthroplasty due to the decreased risk of dislocation with larger head sizes and the idea that MoM would have less wear than metal-on-polyethylene bearing surfaces. Because a hip resurfacing procedure most closely maintains the biomechanical features of the native hip, it is generally felt that it is a more anatomic form of hip reconstruction and inherently as stable as the original hip. 8, 9 For example, if during a hip resurfacing, the native femoral head minimum diameter is 46 mm, then the final femoral head implant size would be 44 mm in diameter. 6, 7 With hip resurfacing, hip surgeons are able to resurface a femoral head to on average −2 mm of the native femoral head minimum diameter measurement. 3 - 5 One of the effects of using a larger femoral head diameter is that it increases the jump distance or degree of translation of the femoral head center before dislocation occurs. Studies on these larger femoral head sizes have demonstrated a decreased incidence of dislocation.

2 After the advent of highly cross-linked polyethylene, prosthetic femoral head diameters increased to 36, 38, 40, and 44 mm. 1 Hip replacements originally used femoral head diameters that were in the range of 22 mm in the 1960s, increasing to 28 mm in the 1990s and up to 32 mm in the mid-2000s. An anatomic skeletal femoral head varies in diameter, and on average, a female femoral head is 42.2 mm and a male femoral head is 48.4 mm. Traditional hip replacement can be inherently unstable.

Living with a spinal cord stimulator