What causes foot internal rotation during ambulation after a total hip replacement, and how should it be evaluated and managed?

Internal Foot Rotation After Total Hip Replacement

The patient's foot turning inward during walking after total hip replacement is most likely due to increased internal rotation of the femur at rest—a well-documented biomechanical change that occurs after THA, averaging 9-13° of internal rotation compared to preoperative positioning.

Understanding the Mechanism

This internal rotation phenomenon is a normal biomechanical consequence of total hip arthroplasty that affects the entire lower extremity alignment:

• The femur shifts into internal rotation at rest after THA, with studies showing mean increases of 11° 1 to 13.1° 2 in the early postoperative period
• This internal rotation persists long-term, remaining at approximately 9.7° internally rotated at 2+ years post-surgery 2
• The rotational change affects the entire kinetic chain, increasing lateral patellar tilt by an average of 4° 1

Patient-Specific Risk Factors

Certain patients are more prone to developing increased internal rotation 3:

• Female patients (versus male)
• Younger patients (versus older)
• Those with greater preoperative femoral anteversion
• Those with lesser preoperative femoral rotation angles
• Patients undergoing leg lateralization during surgery 2

Evaluation Algorithm

Step 1: Rule Out Serious Complications First

Before attributing this to benign biomechanical changes, exclude:

Footdrop (peroneal nerve injury) 4:

• Check for weakness in ankle dorsiflexion and toe extension
• Assess for sensory deficits on dorsum of foot
• Higher risk if revision THA, intraoperative nerve injury, or hemorrhage occurred

Abductor muscle dysfunction 5:

• Observe for Trendelenburg gait (pelvic drop on contralateral side during stance)
• Assess hip abductor and extensor strength
• Look for reduced eccentric contraction of hip abductors

Step 2: Initial Imaging

Obtain AP and lateral hip radiographs 6 as the initial imaging study for any symptomatic hip prosthesis. This is the appropriate first-line evaluation.

Critical caveat: Be aware that limb rotation affects the apparent radiographic positioning of femoral components—internal rotation causes pseudovarus positioning 7. Ensure standardized positioning for accurate assessment.

Step 3: Advanced Imaging if Indicated

If radiographs are concerning or symptoms suggest specific pathology 6:

• For suspected soft tissue injury (abductor tendon, trochanteric bursitis): Ultrasound or MRI hip without contrast
• For suspected infection: Image-guided hip aspiration with synovial fluid analysis (most useful test), or MRI, or WBC/sulfur colloid scan
• For acute trauma: CT hip without IV contrast
• For component evaluation when infection excluded: CT or MRI hip without contrast

Management Approach

If Evaluation is Reassuring (No Nerve Injury, No Abductor Dysfunction)

This is likely physiologic internal rotation—reassure the patient and focus on functional rehabilitation:

1. Physical therapy emphasizing:

   • Hip external rotator strengthening (especially if posterior approach was used without adequate repair 8)
   • Gait training with focus on foot progression angle
   • Hip abductor and extensor strengthening to prevent compensatory gait patterns

2. Patient education:

   • Explain this is a common biomechanical change after THA
   • The internal rotation typically stabilizes after the early postoperative period
   • Functional outcomes generally remain excellent despite the rotational change

3. Monitor for secondary issues:

   • Ipsilateral knee pain (from altered mechanics and increased patellar tilt)
   • Gait abnormalities that may affect daily activities

If Pathology is Identified

• Footdrop: Ankle-foot orthosis, physical therapy, possible nerve exploration if acute and severe
• Abductor dysfunction: Intensive strengthening program focusing on eccentric hip abductor control and concentric hip extensor strengthening 5
• Posterior structure failure: May require surgical repair if causing instability 8

Key Clinical Pitfalls

• Don't assume all intoeing is benign: Always rule out footdrop and abductor dysfunction first
• Don't over-interpret radiographic component positioning: Remember that internal rotation creates pseudovarus appearance 7
• Don't ignore the surgical approach: Posterior approaches without adequate capsular and external rotator repair have significantly decreased rotational support 8
• Don't forget the kinetic chain: Internal hip rotation affects the entire leg, including knee and ankle mechanics 1

The majority of patients with internal foot rotation after THA have physiologic femoral internal rotation that requires only reassurance and targeted rehabilitation, but systematic evaluation is essential to identify the minority with treatable complications.