Hip Flexor Strain. Causes, Symptoms and Treatment

The hip flexors are a group of muscles that work together to shorten the angle between your upper leg and your trunk, causing hip flexion. They act counter to the hip extensors, playing a major part in most physical activities, like walking, running, biking and swimming. Hip flexor injuries are common in sports, but they can also affect non-athletes and sedentary populations. With proper training and certain lifestyle changes, most hip flexor injuries can be avoided. 

Learn about the anatomy and function of the hip flexors, common causes and types of injuries, and the most effective treatment approaches to eliminate and prevent hip flexor pain. 

Hip Flexor Anatomy and Function

Hip flexion involves several key structures, including muscles, joints, and connective tissues that support and stabilize the hip.

Primary hip flexor muscles include:

• The iliopsoas is the main hip flexor, made up of the psoas major and the iliacus. It originates at the lumbar spine, and inserts at the femur, linking the trunk and the upper leg. 
• The rectus femoris is a muscle of the quadriceps group. It acts at both the hip and the knee, causing hip flexion and knee extension.
• The sartorius is the body’s longest muscle, beginning at the pelvis and traveling to the tibia. It acts as a hip flexor, but also rotates the hip outward (external rotation) and aids in abduction, moving the leg away from the body’s midline. 
• The tensor fasciae latae (TFL) originates at the anterior iliac spine and outer iliac crest, and inserts into the iliotibial band (IT band). The TFL assists in hip flexion, abduction, and internal rotation.
• The pectineus is a small muscle located in the medial thigh that flexes and adducts the hip.
• The adductor longus and brevis, and the gracilis are secondary muscles that assist in hip flexion.

The hip joint has a ball-and-socket architecture, where the femoral head rotates within the acetabulum, allowing for hip flexion up to 140°. During flexion, the hip is supported by strong ligaments, tendons and fascia to enable force transmission and provide stability. The femoral nerve innervates the iliopsoas, rectus femoris, and sartorius, while the obturator nerve innervates the pectineus and adductor muscles. Blood to the hip flexors is supplied by the femoral and iliac arteries. 

Common Causes of Hip Flexor Injuries

Hip flexor strains occur when the muscles or tendons in the hip flexor group – mainly the iliopsoas, rectus femoris, and sartorius – are overstretched or torn. 

Common causes of hip flexor strains include:

• Repetitive overuse from sports or exercise.
• Tight and weak hip flexors from too much sitting or driving. 
• Rapid directional changes or sudden explosive movements.
• Traumatic fall or collision.
• Inadequate warmup before physical activity.
• Poor flexibility due to lack of stretching.
• Too much stretching during activities like gymnastics, ballet, yoga or martial arts.
• Weakness of the core, gluteal and/or hamstring muscles, placing extra stress on the hip flexors.
• Muscle imbalances from overtraining the hip extensors while neglecting the hip flexors.
• Previous injuries that were never properly rehabilitated.

In athletic populations, hip flexor injuries generally arise from overuse during kicking, sprinting, or rapid directional changes. Injuries to the hip flexor tendons can involve ruptures and avulsions that lead to degeneration if not properly rehabilitated.

In sedentary populations, constant sitting makes the hip flexors weak and tight, while the hip extensors become weak and lax, causing hip instability. At the same time, the core muscles also weaken, affecting the entire hip and pelvic complex, and increasing the risk of injury. 

Hip Flexor Strain Assessment

Hip flexor strains can range from mild discomfort due to overstretched muscles, to severe pain from a muscle tear or tendon avulsion. Proper assessment is key to determining appropriate treatment. 

1. Assessment begins with a physical exam to look for swelling, limping, or changes in posture. 
2. The practitioner may palpate the hip and groin region to identify points of tenderness. 
3. An active range-of-motion assessment where lifting the knee to the chest causes pain or limited hip action can indicate a strain. 
4. A passive range-of-motion assessment involves the practitioner moving the patient’s leg to look for signs of stiffness or pain.
5. Strength is assessed by pushing the bent knee downward while the patient resists. Assessing both legs can reveal whether the affected leg is weaker.
6. Functional testing may involve walking, stair climbing, or performing a single-leg squat to look for pain or weakness. 
7. The Thomas Test is performed by the patient lying on their back with both legs extended, then drawing one knee to the chest. If the opposite thigh lifts off the table, it may indicate tight or strained hip flexors.  
8. The straight leg raise is performed by lifting the leg at the hip with a straight knee. Pain in the hip flexor area suggests a strain.

While such assessments may indicate a hip flexor strain, they cannot accurately determine the severity of the injury. Imaging with dynamic high-resolution ultrasonography allows for observation of the structures of the hip in motion, in real time. With ultrasound, we can determine if pain is generated from muscles, tendons, nerves, or a combination of causes.

Rectus Femoris Tendon Pain

The rectus femoris muscle originates from two tendon heads – the direct head originating at the anterior inferior iliac spine (AIIS), and the indirect head originating from the superior acetabular rim. Due to its double origin and the fact that it acts at both the knee and the hip, the rectus femoris can be prone to tendon injuries that cause severe hip flexor pain.

Common rectus femoris tendon injuries include: 

• Tendinopathy, where the tendon undergoes degenerative changes due to repetitive overuse, causing stiffness and pain.
• Enthesiopathy, due to pain and inflammation at the tendon’s bony attachment, a common condition in repetitive kicking sports like soccer.
• Avulsion injury, caused by a sudden forceful contraction that rips the tendon away from its bony attachment, sometimes pulling a small piece of bone with it.

Symptoms of rectus femoris tendon strain include:

• Pain or tenderness in the front of the thigh, hip, or groin region.
• Stiffness or discomfort during movement, especially when lifting the leg, running, or climbing stairs.
• Swelling or warmth in the groin area.
• Weakness or difficulty flexing the hip.

A tendon rupture or avulsion can cause severe pain and instability, and failure to treat tendon injuries can lead to reduced performance and ongoing tendon degeneration. When operated by a trained and experienced clinician, high-resolution ultrasonography can help to determine the exact location and severity of injury. 

Hip Flexor Strain Treatment

Treatment of hip flexor strains is aimed at reducing pain, promoting healing, and restoring function. Treatment strategies are progressive, based on the specific characteristics of the injury. 

Hip flexor rehab progresses in phases:

• In the acute phase (48-72 hours), rest, icing, and compression of the strained region are recommended to reduce pain and inflammation. Gentle mobility exercises may be okay, but avoid high-intensity activities like running, kicking, and jumping.
• During the subacute phase (1-2 weeks) gentle stretching of the hip flexors, quadriceps, and hamstrings can help to prevent stiffness. Isometric leg raises can help to maintain strength. Treatments like shockwave therapy, dry needling, orthobiologics, and myofascial release can help to promote tissue healing. 
• Depending on the severity of injury, dynamic stretches and strengthening exercises for the hip flexors, glutes, core, and hamstrings can begin in 2 to 6 weeks. Eccentric exercises with emphasis on the muscle lengthening phase can aid in tendon and muscle recovery, with the goal of restoring full range of motion and functional mobility. 
• The rehabilitation phase includes targeted strengthening of hip flexors, glutes, and core, sport-specific drills, and progressive loading, with a gradual return to normal activities

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Recovery timelines can vary, and should not be regarded as absolute – your injury rehab should never be rushed: 

• Mild strains can take 1-3 weeks to heal, with proper rest and rehab.
• Moderate strains can take 4-8 weeks, depending on the extent of damage.
• Severe strains and avulsions can take upwards of 3 months, depending on the amount and type of damage. 

Orthobiologics and Shockwave Therapy for Hip Flexor Strains

Regenerative therapies and orthobiologic injections are advanced sports medicine treatments that help to accelerate tissue healing. Orthobiologic solutions are derived from the body’s own tissues or from donors, and include treatments such as platelet-rich plasma (PRP), bone marrow aspirate concentrate (BMAC), adipose-derived stem cells, and mesenchymal stem cells (MSCs). 

Such therapies trigger a regenerative response at the cellular level by activating growth factors, stem cells, and signaling molecules to accelerate tissue repair, reduce inflammation, and promote soft tissue regeneration. 

Benefits of orthobiologics for hip flexor strains include:

• Faster healing and recovery by stimulating collagen production, new blood vessel formation (angiogenesis), and muscle fiber regeneration.
• Reduced pain and inflammation thanks to growth factors that modulate the inflammatory response.
• Improved vascularization and nutrient delivery to damaged tissues.
• More organized collagen deposition in tendon injuries.
• Accurate targeting under ultrasound guidance, in an outpatient setting.
• Creates an injury-resistant biologic environment in high-level athletes.

Extracorporeal shockwave therapy (ESWT) works synergistically with orthobiologics, adding a mechanical stimulus that activates stem cells, enhances circulation, and accelerates tissue remodeling. When combined, this dual approach can significantly accelerate healing and improve patient outcomes. 

Hip Flexor Rehab Requires a Multifacted Approach

Orthobiologics are not stand-alone solutions, but they can be highly effective when used in conjunction with other therapeutic approaches. Intelligent rehabilitation takes into account the unique biomechanics of the patient and the specifics of the injury. By addressing both biological and mechanical factors, we can strive to restore pre-injury performance levels and reduce the risk of future injuries. 

A successful rehab program includes:

• Biomechanical and gait analysis.
• Static and dynamic posture assessment.
• Progressive loading protocols, with structured eccentric and concentric exercises.
• Restoration of harmonious balance between hip flexors, hip extensors and deep core stabilizers. 
• Neuromuscular retraining that incorporates dynamic neuromuscular stabilization (DNS), proprioceptive drills, and controlled plyometrics to re-establish reflex stability and restore coordinated muscle firing patterns.
• Gradual reintroduction of sport-specific skills under guided supervision.

Preventing Hip Flexor Injuries

You can dramatically reduce your risk of hip flexor injuries by adopting and adhering to a few preventative strategies: 

• Take time to warm up your muscles before training or competition.
• Maintain balance in muscle tension by strengthening and stretching the quadriceps, hamstrings, and glutes.
• Avoid sudden increases in training intensity or volume.
• Take frequent breaks from sitting throughout the day to stretch and move around.
• Daily walking is an inexpensive and easy way to optimize hip flexor function.
• Strengthen your core muscles to promote hip and pelvic stability. 
• Wear supportive footwear throughout the day, especially during exercise. 
• Pay attention to posture when standing, sitting and exercising. 

Get Advanced Hip Flexor Rehab in NYC

Advancements in technology have brought with them multiple new approaches for musculoskeletal injury rehabilitation, and NYDNRehab has kept pace, offering a broad range of regenerative and orthobiologic therapies for injury healing. Our high-tech lab equips us to accurately assess your gait and biomechanics, and track your progress. Our 20+ years of experience and Dr. Kalika’s expertise in diagnostic ultrasonography  make NYDNRehab the clinic of choice for hip flexor injuries in NYC.

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