A foot turning inward, commonly referred to as a “toe-in gait,” after total hip replacement (THR) surgery can be confusing for patients. This change represents a loss of the natural, slightly outward rotation of the leg. The hip joint is the body’s largest ball-and-socket joint, and altering its mechanics directly affects the entire limb below it. While the procedure relieves pain, the resulting change in leg alignment can cause this noticeable rotation. Understanding the interplay of new prosthetic components, muscle function, and nerve pathways helps explain why this symptom occurs.
Understanding Post-Surgical Hip Alignment
The hip joint controls the rotation of the entire leg, dictating whether the foot points straight ahead or rotates inward or outward. A primary objective of total hip replacement is to restore the leg’s rotational alignment to a stable and functional position. This is achieved by ensuring the prosthetic components are implanted with the correct degree of rotational orientation, known as version.
The natural femoral bone has an angle called femoral anteversion, where the neck of the femur angles forward relative to the knee joint. Surgeons aim to replicate this angle when placing the new femoral stem. When combined with the rotational position of the acetabular cup, this creates a “combined anteversion” that keeps the hip stable and allows for a natural gait. If the overall rotational alignment is altered, the resulting change translates directly down the leg, manifesting as a foot that turns in or out.
Mechanical Causes of Internal Rotation
The most direct reason for a post-operative toe-in gait involves the precise positioning of the implanted prosthetic components. The new hip joint consists of a cup placed in the pelvis (acetabulum) and a stem inserted into the thigh bone (femur). A slight misplacement of either part can mechanically force the leg into an internally rotated position.
Internal foot rotation is often linked to excessive anteversion in the femoral stem. Anteversion describes a forward rotation of the stem within the femur. If this angle is greater than the ideal range (typically 30 to 45 degrees combined anteversion), it forces the leg to rotate inward. This excessive forward angle means the hip is more stable in an internally rotated position, causing the foot to point toward the midline.
Even deviations of just a few degrees in component placement can translate into a significant, noticeable rotation at the foot. The precise alignment of the socket also plays a role, as its rotational position contributes to the total combined version of the hip. If the combined version is too high, the hip has a higher functional stability in internal rotation.
The surgeon uses specialized tools and imaging to achieve the correct alignment, but individual patient anatomy and surgical challenges can make precise positioning difficult. The resulting mechanical malalignment effectively locks the leg into a new rotational position determined by the prosthetic hardware.
Biological Factors Contributing to Toe-In Gait
Beyond the mechanical position of the implant, the surrounding soft tissues play a significant role in the final walking pattern. Post-operative muscle weakness and imbalance are common biological factors that affect how the foot lands and pushes off. The muscles responsible for externally rotating the hip, such as the gluteus maximus and the deep small rotators, are often temporarily weakened during the surgical approach.
If the external rotator muscles are weak, the stronger internal rotator muscles can overpower them, leading to an inward rotation of the leg during walking. This muscle imbalance is exacerbated by long-term disuse and compensation patterns that existed before the hip replacement. The body’s new alignment may also be a compensatory strategy to stabilize the joint or reduce strain on the healing muscles.
A less common factor is a transient neurological issue caused by irritation or stretching of the sciatic nerve during the operation. The sciatic nerve runs close to the hip joint and controls many of the lower leg muscles. While nerve palsy causing foot drop is rare, a less severe irritation can temporarily impair muscle function, leading to an internally rotated gait pattern until the nerve recovers.
Managing and Correcting Foot Rotation
The first step in addressing a foot that turns inward is a thorough physical examination and gait analysis, often combined with post-operative X-rays. Imaging allows the medical team to assess the exact position of the acetabular cup and the femoral stem, quantifying the mechanical alignment. This information helps determine whether the rotation is primarily a mechanical issue or one stemming from muscle weakness.
For the majority of patients, the problem relates to muscle and gait mechanics, and non-surgical management through physical therapy is the standard approach. The treatment focuses on gait training to consciously correct foot placement while walking. Specific exercises target the strengthening of the hip’s external rotators and abductors, which are the muscles that pull the leg outward and stabilize the pelvis.
Physical Therapy Techniques
Exercises like the clamshell, side-lying leg lifts, and standing hip external rotation help restore the strength and endurance needed to hold the leg in a neutral position. Consistent practice is required to retrain muscle memory and integrate the corrected movement pattern into daily walking. Surgical revision to correct component alignment is considered only in severe cases where malalignment causes recurrent instability, dislocation, or significant functional impairment that physical therapy cannot resolve.