Key Points
- Total Hip Arthroplasty (THA) patients, especially women, commonly experience significant muscle strength deficits in hip and knee muscles on both the surgical and nonsurgical sides lasting up to 12 months post-surgery.
- Hip abductor muscles are particularly affected, with strength recovering slowly and often remaining below levels seen in healthy individuals even one year after surgery.
- The nonsurgical leg, traditionally used as a comparison for recovery progress, also suffers strength loss, making it an unreliable control.
- Walking ability and daily physical activity remain impaired post-THA, posing challenges for full functional recovery.
- Targeted and prolonged rehabilitation focusing on both legs and relevant muscle groups is essential to maximise recovery and reduce risks of falls or ongoing disability.
- Clinical Implication: It is crucial for Physiotherapists to carry out thorough strength evaluations not only on the surgical leg but also on the nonsurgical side. Rehabilitation programs must include exercises to strengthen hip abductors and knee muscles on both sides. The use of nonsurgical leg strength as a benchmark should be reconsidered, and clinical decisions made with awareness of bilateral deficits up to 12 months post-THA.
- Study Limitation: The study focused exclusively on women, limiting generalisation to men. Additionally, individual variations in rehabilitation adherence, physical activity, and surgical approaches may influence recovery, indicating a need for further multi-centre research that includes diverse populations.
- Patient Implication: Patients should have realistic expectations about the timeline of strength recovery post-THA. Persistent muscle weakness, especially in hip abductors and knee extensors/flexors, is common even after a year. Following a dedicated, professionally guided Physiotherapy plan and striving to increase physical activity levels can optimise recovery and improve quality of life.
Understanding Muscle Strength Loss After Total Hip Arthroplasty
Total Hip Arthroplasty, commonly known as hip replacement surgery, is widely performed to relieve pain and restore mobility in people with severe hip osteoarthritis. While the relief from joint pain after surgery can be dramatic, it’s important to recognise that regaining muscle strength, particularly in the hip and knee, is a gradual process.
Why does muscle strength remain reduced after surgery? Isn’t the surgery supposed to fix the problem? It is true the surgery addresses joint damage, but the muscles around the joint play a vital role in movement and stability. Unfortunately, these muscles weaken before surgery due to pain and disuse. Surgery and the recovery process itself can further affect muscle strength.
This loss is seen not only in the operated leg but surprisingly also in the opposite, nonsurgical leg. For patients and therapists alike, understanding this bilateral muscle weakness is key to creating effective rehabilitation strategies.
What Does Muscle Strength Actually Mean in Recovery?
Muscle strength refers to the force muscles can produce. To walk steadily, climb stairs, and perform daily activities safely, you need strong hip and knee muscles. After THA, the main muscles affected include:
- Hip Flexors: Lift the thigh forward.
- Hip Extensors: Pull the leg backward.
- Hip Abductors: Move the leg sideways away from the body.
- Knee Extensors: Straighten the knee.
- Knee Flexors: Bend the knee.
Each muscle group supports different parts of movement. Weakness in these muscles can lead to difficulty walking, imbalance, and increased risk of falls.
How Was Muscle Strength Assessed in the Study?
The study involved 91 women undergoing unilateral (one leg) THA. For comparison, 46 healthy women without hip or knee pain were measured as controls.
Muscle strength was tested before surgery, then again at 3, 6, and 12 months after surgery. Tests used a handheld device that measures isometric strength—where muscles contract without changing length, such as pushing against an immovable object.
To ensure accuracy:
- Patients’ positions during testing were standardised to isolate the relevant muscle groups.
- Strength was expressed as torque per body weight, considering individual differences in body size.
- Two experienced Physiotherapists conducted the measurements for reliability.
- Walking speed and physical activity levels were also monitored to relate muscle strength to real-world function.
What Did the Results Reveal About Muscle Strength?
The study found persistent muscle weakness on both sides up to 12 months post-THA:
- Hip flexor strength on the operated side recovered to about 85% of healthy controls.
- Hip extensor strength reached 83.5%, while hip abductor strength lagged behind at 76.2%.
- The nonsurgical side also showed deficits: hip abductors were at 79.4%, flexors at 94.8%, and extensors at 83.9% when compared with healthy participants.
- Knee extensors on the surgical leg were about 89.3% as strong as controls; knee flexors slightly weaker at 90.9%.
- Interestingly, knee muscle strength on the nonsurgical side recovered better, almost matching healthy controls by 12 months.
- Throughout, walking speed measured by the Timed “Up & Go” test was reduced, and step counts were significantly lower than those of healthy women.
Why Is The Opposite Leg Weak Too?
But why is my other leg weaker, even though it wasn’t operated on?
Several reasons explain this:
- Reduced Overall Activity: After surgery, many patients limit movement to avoid pain or imbalance, reducing muscle use in both legs.
- Compensatory Gait Patterns: To protect the operated leg, people shift weight differently, causing underuse and weakness in the other leg.
- Chronic Changes: Long-term disease caused muscle loss before surgery, affecting both legs.
This bilateral weakness means the nonsurgical leg should not be the sole point of comparison when assessing recovery.
What Are The Consequences of Muscle Weakness Post-THA?
Weaker hip and knee muscles can lead to:
- Slower, less stable walking.
- Increased risk of falls due to poor balance.
- Difficulty performing daily activities independently.
- Reduced ability to return to sports or physical hobbies.
Therefore, strength deficits are not just numbers but have real-life impacts on safety and quality of life.
How Does Recovery Progress Over Time?
Strength improves steadily from before surgery to 12 months afterward, but recovery is incomplete at one year. Here’s a deeper look:
- By 3 months, many muscle groups remain significantly weaker.
- At 6 months, strength improves but hip abductors are still only about 70% as strong as healthy controls.
- At 12 months, strength of hip flexors and extensors approaches 80–85%, but hip abductors stay lower around 76%.
- Knee extensors improve to near 90%, though some weakness persists.
- The nonsurgical leg shows a slower but clear recovery, except hip abductors remain weak.
Why Are Hip Abductors More Affected?
Hip abductors have a key role in balancing the pelvis during walking. They can be particularly injured during surgery or weakened by pre-existing muscle loss.
Moreover, hip abductors tend to recover more slowly due to:
- Possible surgical trauma despite muscle-sparing techniques.
- Long periods of inactivity before surgery.
- Fat infiltration in muscles reducing effective strength.
Therapists must prioritise hip abductor strengthening to support gait and prevent falls.
What Role Does Physical Activity Play?
Daily step counts were significantly lower in patients after THA at all measured times. Low activity might slow down strength recovery by limiting muscle use.
However, increasing physical activity alone doesn’t guarantee strength gains. This suggests a need for specific strength exercises alongside encouraging movement.
How Should Physiotherapy Be Tailored?
Based on these findings, Physiotherapists should:
- Assess the strength of both legs carefully, focusing on hip abductors and knee extensors/flexors.
- Develop programmes that target weak muscle groups with progressive resistance exercises.
- Encourage safe increases in daily physical activity.
- Monitor walking ability and balance with tests like the TUG.
- Avoid using the nonsurgical leg alone as a recovery benchmark.
- Educate patients on the typical timeline and variability of recovery.
- Promote long-term rehabilitation adherence, as some deficits last beyond 12 months.
Do Men Recover Differently?
This study included only women to reduce variability due to known sex differences in muscle strength. Women often have lower baseline muscle strength and may experience different recovery patterns.
More research is needed to confirm if men follow the same trend, but the principle of bilateral weakness and the focus on specific muscle groups likely applies to all.
Can Patients Fully Return To Sports or Active Hobbies?
Returning to sports is often an important goal after THA. However, sufficient muscle strength and balance are crucial to prevent injury.
Patients should expect to take time—often many months—to build up the strength needed for safe sports participation.
Physiotherapy focused on hip and knee strength, combined with gradual skill training, supports this return.
What Are The Limits Of This Study?
It is important to know that:
- The study’s findings may not apply to men or younger patients.
- Rehabilitation protocols varied somewhat, which can affect progress.
- Measurement of muscle strength, even though reliable, has intrinsic limitations.
- Physical activity levels and motivation influence outcomes and vary greatly.
- A 3-week hospital stay could influence early strength changes.
Despite these limitations, the study provides valuable insights into persistent muscle weakness patterns after THA.
If you or someone you know is recovering from hip replacement and wants support, please contact us to speak our knowledgeable Physiotherapist.
References
Sekita, J., Takahira, N., Watanabe, H., Kusaba, A., & Kondo, S. (2024). Identifying deficits in hip and knee muscle strength on the surgical and nonsurgical sides in women up to 12 months after total hip arthroplasty. Physical Therapy, 104. https://doi.org/10.1093/ptj/pzae099
