Femur Dislocation: Common Nerve Injuries, Symptoms, and Management

What nerve is injured in femur dislocation?

While multiple nerves can be affected in a femur dislocation, the sciatic nerve is by far the most commonly injured due to its anatomical proximity and course relative to the hip joint, particularly in posterior dislocations.

Understanding Femur Dislocation

A femur (thigh bone) dislocation occurs when the head of the femur is forced out of the acetabulum (hip socket). This is a severe orthopedic injury, typically resulting from high-energy trauma, such as motor vehicle accidents or significant falls. Given the robust ligamentous and muscular structures surrounding the hip, considerable force is required to dislodge the femoral head.

Femur dislocations are primarily classified by the direction of displacement:

• Posterior Dislocation (Most Common): The femoral head is displaced backward out of the acetabulum. This accounts for approximately 85-90% of all hip dislocations.
• Anterior Dislocation (Less Common): The femoral head is displaced forward.
• Central Dislocation (Rare): The femoral head is driven directly through the acetabulum into the pelvis, often associated with acetabular fractures.

The specific nerves at risk depend heavily on the direction of dislocation and the associated forces and potential fractures.

The Primary Nerve at Risk: The Sciatic Nerve

The sciatic nerve is the largest single nerve in the human body, originating from the sacral plexus (L4-S3 nerve roots). It passes deep to the gluteus maximus muscle and descends down the posterior aspect of the thigh. Its close anatomical relationship to the posterior aspect of the hip joint makes it highly vulnerable in posterior hip dislocations.

Mechanism of Injury: In a posterior hip dislocation, the femoral head is driven posteriorly, directly impacting, stretching, or compressing the sciatic nerve as it exits the pelvis and courses over the posterior aspect of the hip joint. This can lead to:

• Neurapraxia: A temporary disruption of nerve conduction, typically resolving within weeks to months.
• Axonotmesis: Damage to the axon with preservation of the myelin sheath, leading to more prolonged recovery.
• Neurotmesis: Complete transection of the nerve, requiring surgical repair and having the poorest prognosis.

Symptoms of Sciatic Nerve Injury: Injury to the sciatic nerve can manifest with a range of symptoms, impacting both motor and sensory functions:

• Foot Drop: Weakness or inability to dorsiflex the ankle (lift the foot), leading to a characteristic high-stepping gait. This is due to damage to the common fibular (peroneal) division of the sciatic nerve.
• Inability to Evert Foot: Weakness or paralysis of the muscles that turn the sole of the foot outwards.
• Sensory Loss: Numbness, tingling, or altered sensation along the lateral lower leg, dorsum of the foot, and sole of the foot.
• Weakness in Hamstring Muscles: Though less common with isolated dislocation, severe injury can affect knee flexion.

Other Nerves Potentially Affected

While the sciatic nerve is the most frequent casualty, other nerves can be injured depending on the dislocation type and associated trauma:

• Femoral Nerve:

  • Anatomy: Originates from the lumbar plexus (L2-L4), passes under the inguinal ligament, and supplies the anterior thigh muscles (quadriceps femoris) and sensation to the anterior thigh and medial leg.
  • Risk: Primarily at risk in anterior hip dislocations, where the femoral head is driven anteriorly, potentially compressing or stretching the femoral nerve. It can also be injured by direct trauma or iatrogenically during surgical reduction.
  • Symptoms: Weakness in knee extension, difficulty with hip flexion, and sensory loss over the anterior thigh and medial leg.

• Obturator Nerve:

  • Anatomy: Originates from the lumbar plexus (L2-L4), passes through the obturator foramen, and innervates the adductor muscles of the thigh and a small area of sensation on the medial thigh.
  • Risk: Less commonly injured but can be affected in anterior or central dislocations, or in conjunction with pelvic fractures.
  • Symptoms: Weakness in hip adduction (bringing the legs together) and sensory changes on the medial aspect of the thigh.

• Superior and Inferior Gluteal Nerves:

  • Anatomy: Branches of the sacral plexus (L4-S2) that innervate the gluteal muscles (e.g., gluteus medius, minimus, and maximus).
  • Risk: Can be stretched or compressed in severe posterior dislocations, especially if there's significant soft tissue avulsion or associated pelvic fractures.
  • Symptoms: Weakness in hip abduction (superior gluteal nerve) leading to a Trendelenburg gait, or weakness in hip extension (inferior gluteal nerve).

Clinical Presentation and Diagnosis

Upon presentation, a patient with a femur dislocation will experience severe pain and inability to move the affected leg. The leg will typically be held in a characteristic position:

• Posterior Dislocation: Shortened, adducted, and internally rotated.
• Anterior Dislocation: Abducted, externally rotated, and slightly flexed.

Diagnosis involves:

• Physical Examination: A thorough neurological assessment is crucial to evaluate motor strength, sensation, and reflexes in the affected limb, specifically checking for signs of nerve injury before and after reduction.
• Imaging: X-rays confirm the dislocation and identify any associated fractures (e.g., femoral head, acetabulum, pelvis). CT scans may be used to further assess bone fragments, joint congruity, and nerve impingement.

Management and Prognosis

The immediate priority for a femur dislocation is prompt, gentle reduction of the femoral head back into the acetabulum. This should ideally occur within 6 hours to minimize the risk of complications such as avascular necrosis (death of bone tissue due to loss of blood supply) and post-traumatic arthritis.

Management of Nerve Injury:

• Observation: Many nerve injuries, especially neurapraxia, resolve spontaneously over weeks to months following successful reduction.
• Rehabilitation: Physical therapy is essential to regain strength, range of motion, and function. Specific exercises target muscles weakened by nerve damage.
• Surgical Intervention: In cases of complete nerve transection (neurotmesis), persistent compression, or nerve entrapment by bone fragments, surgical exploration and repair may be considered.
• Prognosis: The recovery of nerve function varies widely depending on the severity and type of injury. Neurapraxia has an excellent prognosis, while axonotmesis and neurotmesis have longer recovery periods and less predictable outcomes. Some residual weakness or sensory deficits may persist.

Importance for Fitness Professionals and Enthusiasts

Understanding the potential for nerve injury in femur dislocations is critical for fitness professionals and individuals engaged in high-impact activities:

• Injury Prevention: While direct prevention of high-energy trauma is challenging, awareness reinforces the importance of safety measures in sports and daily life.
• Client Assessment: For trainers, knowing the common complications of such injuries allows for a more informed assessment of clients with a history of hip dislocation. Look for persistent gait abnormalities, muscle weakness, or sensory deficits.
• Rehabilitation Guidance: While not directly involved in acute care, fitness professionals can support the long-term rehabilitation process, understanding the specific limitations imposed by nerve damage and adapting exercise programs accordingly. This includes focusing on strengthening residual muscle function and maintaining joint mobility.
• Referral: Recognizing signs of nerve injury (e.g., new or worsening foot drop, persistent numbness) in a client with a history of hip trauma necessitates immediate referral back to a medical professional.

Conclusion

Femur dislocations are severe orthopedic injuries with a significant risk of associated nerve damage. The sciatic nerve is the most frequently affected, particularly in posterior dislocations, leading to potential foot drop and sensory deficits. While other nerves like the femoral and obturator can also be involved, prompt diagnosis, immediate reduction, and diligent neurological assessment are paramount for optimizing patient outcomes and minimizing long-term disability. For those in the fitness and health fields, this knowledge underscores the complexity of severe musculoskeletal trauma and the importance of a comprehensive, interdisciplinary approach to recovery and rehabilitation.