Total hip replacement (THR) is a highly successful and frequently performed orthopedic procedure designed to alleviate pain and restore mobility in a damaged hip joint. While the long-term prognosis for a new hip is generally excellent, the primary mechanical concern during the initial recovery period is the risk of dislocation. A hip dislocation occurs when the artificial femoral head, or the “ball” of the implant, slips out of the polyethylene-lined acetabular cup, the “socket”. Understanding the specific movements that make the new joint unstable is paramount to a successful and complication-free recovery.
How Surgical Approach Dictates Precautions
The specific movements that patients must avoid following a total hip replacement depend almost entirely on the path the surgeon took to access the hip joint. This path, known as the surgical approach, determines which muscles and stabilizing tissues were cut, detached, or simply moved aside during the operation. Since the muscles and joint capsule provide most of the stability for the new implant, temporary weakness in these structures creates a window of vulnerability.
The two most common methods are the posterior and anterior approaches. The posterior approach accesses the hip from the back, requiring temporary detachment of posterior soft tissues and short external rotator muscles. The anterior approach is often described as “muscle-sparing” because it works through natural intervals between muscle groups, though it can disrupt the anterior capsule. These anatomical differences mean the movements that risk dislocation are opposite for the two procedures.
Movements to Avoid After a Posterior Approach
The posterior approach requires strict precautions because it disrupts the structures that prevent backward movement of the femoral head. The three primary movements to avoid are a combination of flexion, adduction, and internal rotation. These restrictions are generally maintained for the first six to twelve weeks post-surgery while the detached tissues heal and regain their strength.
The primary restriction is avoiding hip flexion past 90 degrees (the angle between the torso and thigh should not be less than a right angle). This movement, which pushes the ball directly against the weakest point of the healing capsule, is often triggered by simple, everyday actions. Examples include bending over to pick something up from the floor, sitting in low chairs or sofas, or leaning forward excessively while seated. Patients are advised to use a raised toilet seat and avoid deep squatting to maintain this safe angle.
Adduction involves crossing the operated leg across the midline of the body, which can lever the ball out of the socket. Patients must avoid crossing their legs while sitting, standing, or lying down. To prevent inadvertent adduction while sleeping, use an abduction pillow or a regular pillow between the knees.
The final movement to avoid is internal rotation, the inward turning of the toes and knee on the operated side. This twisting motion, especially when combined with flexion and adduction, can create the torque necessary to displace the joint. Patients should be mindful of twisting the hip when pivoting to change direction, always taking small steps instead of turning their foot inward while the body rotates.
Movements to Avoid After an Anterior Approach
While the anterior approach is associated with a lower overall rate of dislocation, specific movements can still lead to instability. The movements that threaten the anteriorly-accessed hip are generally the opposite of those restricted after a posterior approach. These precautions are necessary because surgical access temporarily weakens the anterior capsule and the tissues that resist motion in that direction.
The two main movements to avoid are excessive extension and external rotation. Excessive extension involves moving the leg too far backward, which can push the femoral head forward out of the socket. This can occur when trailing the leg behind the body while standing up quickly, or when trying to step backward. Patients should focus on keeping the operated foot forward and avoiding standing on the unoperated leg while reaching far behind with the operated leg.
External rotation, the outward turning of the foot and knee, is the second movement to limit. This motion, particularly when the foot is planted on the ground, can stress the anterior structures that were disturbed during the surgery. Patients should avoid sleeping with the foot flopping outward and be cautious when performing any movement that causes the toes to point excessively away from the body’s center.
Recognizing and Addressing Dislocation
A hip dislocation is a medical emergency requiring immediate attention. Recognizing the signs promptly is vital for effective reduction. The onset of dislocation is typically marked by a sudden, intense pain in the hip or groin area, often accompanied by a distinct popping or clunking sensation.
Following the pain, the patient will experience limited or total inability to move the affected leg or bear weight on it. A visible sign is an unnatural appearance of the leg, which may look shorter than the other limb and be abnormally rotated inward or outward. If any of these symptoms occur, the patient should not attempt to move or be moved by others. The immediate action is to call emergency medical services or contact the surgeon’s office for transport to a facility where the hip can be safely placed back into the socket.