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Peripheral Nerve Injury 2. PNI after Total Hip Arthroplasty

Richard_Montgomery 1 February 2021 No Comments

Mr Will Eardley
MSc PgCertMedEd DipSEM(UK&I) MD FRCSEd (Tr&Orth)
Consultant Orthopaedic Trauma and Limb Reconstruction Surgeon
Research Associate, University of York CTU | Honorary Associate, University of Teesside
South Tees Hospitals NHS Trust

Rebecca Edwards, Medical Student, Medical School of the University of Newcastle upon Tyne

Background

Orthopaedic procedures carry the highest risk for nerve injury compared to all other surgeries, and nerve palsy is a recognised complication of total hip arthroplasty (THA)1. The incidence of peripheral nerve injury (PNI) in THA varies in the literature, with reports of 0.09% to 3.7% in primary cases and up to 7.6% of revision cases2. 

Nerve injury can have a huge impact on quality of life, necessitating extensive rehabilitation, pain medication and occasionally, surgery3.  The increasing number of THA surgeries & higher rates of injury in subsequent revision surgeries suggests that PNI will continue to be a clinical problem. For this reason, an awareness of aetiology and management of PNI in THA remains immensely relevant4.  

Risk factors

Although nerve injury in THA is unanticipated, certain populations have been identified as being at higher risk. Firstly, rates of THA nerve injury are higher in those with developmental dysplasia of the hip5. Female sex is described as a risk factor, however the high proportion of female patients with DDH is thought to be a confounding variable2. 

Farrell et al. also concluded that post-traumatic arthritis, the use of a posterior approach, leg lengthening and cementless femoral fixation have significantly increased odds ratios for post-operative injury3. 

An increased incidence of nerve palsy has also been noted in revision surgery2. 

Incidence

Overall, nerve injury associated with THA is rare. In Brown et al.’s review of 17 papers, the incidence was reported as 0.09% to 3.7% in primary cases and up to 7.6% of revision cases2. 

The sciatic nerve and its branches account for over 90% of nerve injuries after THA6. It can present as paraesthesia, neuropathic pain in the back of the legs or foot, and isolated foot drop due to injury of the peroneal division of the nerve2. Reports of its incidence range from 0.05% to 1.92. Farrell et al. described 44 cases of sciatic nerve palsy in 27,004 primary THAs over 30 years, an incidence of 0.16%. Navarro et a. reported 7 sciatic nerve injuries in 1000 cases3. Zappe et al. described 5 palsies in 1820 THA cases, an incidence of 0.3%7. 

Femoral nerve injury during THA is uncommon and occurs less frequently than sciatic nerve palsy3. It typically presents with paraesthesia in the medial aspect of the legs, pain in the femoral area, and difficulties in climbing stairs due to weak quadriceps8. Brown et al. report incidence to be between 0.01 – 2.3%2. Farrell et al. documented 3 cases of femoral nerve palsies in 27,004 primary THAs over 30 years3. Navarro et al. reported 3 femoral nerve palsies in 1000 cases9. Zappe et al. reported 18 palsies in 1820 THA cases, an incidence of 1%7. 

Obturator nerve injury is the rarest, accounting for 1.6% of THA-associated nerve palsies10. Its incidence is reported as 0.01%2. Obturator nerve palsies often present subtly, with medial thigh paraesthesia, groin pain, and adductor weakness. As a result, diagnosis can be difficult and its incidence may be overlooked due to the lack of serious functional impairment6. 

Aetiology

Many studies describe an unknown aetiology in around 50% of cases of nerve injury after THA3,5,10,11. Nerve-specific aetiologies are detailed below. 

Numerous aetiologies for sciatic nerve injury have been reported. These include traction3, direct laceration10, cement damage12, haematoma3, and intra-neural injection of local anaesthetic13. 

Thankfully, laceration of the sciatic nerve is an extremely rare complication with only 1% of THA-associated nerve injuries occurring this way10. 

Traction on the sciatic nerve can arise from manoeuvres such as intra-operative dislocation, reduction, or limb lengthening6. 

Although limb lengthening is accepted as a cause of nerve injury and has been reported as a significant risk factor, there is no evidence for the maximum degree a limb can be safely lengthened3. For example, Barrack reports nerve palsy in 14 of 46 cases where leg length was increased >4cm, compared to 0 of 54 cases in which lengthening was <4 cm10. 

However, Farrell et al. report a case of nerve palsy at an increased limb length of only 1.9cm3. This represents an unpredictable ‘grey area’ for safe limb lengthening which makes preventing nerve injury more challenging. 

Haematoma after THA can compress the sciatic nerve and thus lead to a palsy. Depending on the degree of the bleed, the palsy can present acutely or in a delayed manner. Factors which make a diagnosis of haematoma more likely include a progressively worsening palsy associated with a disproportionately severe degree of pain5,14. 

Cement extrusion has been reported to cause thermal damage to the sciatic nerve directly or result in scar tissue which leads to compression3,12. Some authors recommend intra-operative x-rays to assess for cement leak15. 

The common peroneal branch of the sciatic nerve is particularly vulnerable to damage from excessive tension, owing to its tethering to the fibular head and relative lack of supportive connective tissues16. This could occur secondary to peri-operative compression from haematoma, metalware or positioning, and traction due to retractors, limb lengthening or dislocation11. Moreover, the common peroneal nerve is located laterally and superficially, meaning it is at a higher risk of laceration from the posterior surgical approach16. 

The primary mechanism of femoral nerve injury is damage from improperly placed anterior Hohmann retractors. In a cadaveric study, McConaghie et al. demonstrate how careful positioning of the anterior retractor in contact with the rim of the acetabulum offers protection to the femoral nerve from the bulk of iliopsoas17. If contact with the acetabulum is lost, or variations in patient’s anatomy mean the correct position cannot be maintained, the retractor can pass either superficial to the iliopsoas or through the bulk of the iliopsoas. This results in the tip of the retractor lying over the femoral nerve, which can be compressed if pressure is put on the retractor. 

The obturator nerve is rarely injured during hip arthroplasty. However, due to its anatomical position close to the anterior quadrants of the acetabulum, it is vulnerable to damage from reamers, cement, or screws5. 

Prevention

As described above, risk factors for THA-associated nerve injury such as DDH, female sex and revision surgery have been reported. Therefore, management of these injuries can begin pre-operatively, with identification of at-risk individuals. In high-risk cases, surgeons should carefully review imaging & templating, and plan the surgical approach so as to minimise damage to nerves from retractors and unacceptable leg lengthening18. 

Intra-operatively, surgeons must remain conscious of the risk of nerve injury by the various mechanisms; this awareness should minimize the minimise the incidence. Navarro et al. found that increased intra-operative awareness of the sciatic nerve reduced rate of palsy by over 50%9. Their methods to increase awareness included palpation of the sciatic nerve at the beginning of the operation to determine the location and tension, placement of posterior retractors as guided by the localisation of the nerve, and final assessment of the impact of intra-operative changes on the tension and compression of the nerve. Other technical factors that may help decrease the incidence of nerve damage include ensuring adequate exposure and thorough haemostasis to properly visualise the anatomy, deliberate control of scalpels and reamers, and precise placement of fixation screws5. 

Diagnosis 

Nerve injuries are commonly a clinical diagnosis, therefore meticulous pre- and post-operative neurological examination must be performed and documented. Unfortunately, diagnostic delays are common. 

Pritchett reports that 50% of patients with nerve injury waited over 10 days for diagnosis, with a mean time of 6 months1. It is recommended that a thorough neurological examination should be done the same day of the operation and every day at the ward round18. Despite this, Farrell et al. found that 64.7% of patients whose nerve palsy was diagnosed over 24 hours after surgery had normal post-operative examination findings recorded3. This could represent either inadequate examination technique or the gradual onset of nerve injury caused by compression from slow-growing haematoma. Either way, it is clear that repeat examinations are needed to improve identification of nerve injuries. 

Liaison with neurology can be helpful if nerve palsy is suspected, as they can provide advice on the role of further investigation such as electromyography (EMG) testing16.  

Management 

If no specific cause of nerve injury is identified, often no immediate intervention is indicated5. Although potentially frustrating for patients, there is chance for spontaneous improvement and (at least partial) nerve recovery may be seen with follow-up5. Therefore, we should be aware of the role of expectant management. 

PNI patients should be managed with appropriate physiotherapy to maintain joint & muscle range, walking aids and orthoses5,6. 

For those with common peroneal palsy and the resultant foot drop, an ankle-foot-orthosis maintains the ankle in a neutral or dorsiflexed position, preventing contractures and aiding with walking16. 

For femoral nerve injury, long leg braces can be helpful1. 

Medically, we can support patients with neuropathic pain or abnormal sensations with gabapentin or pregabalin1. Patients may also benefit from referral to a specialist pain clinic12. 

We must not neglect managing the psychological complications of nerve injury. Functional impairment can lead to loss of employment and income, inability to care for one’s self, and huge emotional distress. Therefore, active listening, supportive follow-up, formal counselling and consideration of antidepressant medications all have a role in managing THA nerve palsy1. 

Options for surgical management depend on the cause of nerve palsy. In cases of direct nerve compromise such as haematoma or cement extrusion, patients benefit from urgent decompression surgery6,10,19. Butt et al. found that patients with suspected haematoma who were surgically explored within 48 hours recovered completely (one patient recovered within two hours), whereas those with delayed diagnoses and expectant management experienced lasting neurological deficits, including a persistent complete foot drop 49 weeks after the initial surgery14. Farrell et al. propose that urgent exploration is also warranted in cases of documented limb-lengthening and acute sciatic nerve palsy3. In this instance, therapeutic shortening of the limb can be achieved by substituting a smaller femoral stem8. 

The role of surgical management becomes less clear when there is indeterminate aetiology of the nerve injury. Patients who are managed expectantly may experience no improvement or unacceptable functional impairment due to their injury, and thus the question of interventional treatment is raised6. 

Procedures such as neurolysis, tendon transfer and nerve grafts can be worthwhile, but patients must be suitably counselled on the risk of further complications. Studies have shown significant improvement in both neuropathic pain and motor function following neurolysis of the sciatic nerve1,20, with intervention before 12 months post-PNI producing the most favourable outcomes21. 

Outcomes 

Outcomes of THA-associated nerve injury can be devastating for patients, who experience pain and disability. Disability following THA can be particularly distressing for patients who elect for the procedure for pain relief and functional improvement in osteoarthritis. Oldenburg and Muller report that at a mean follow up of 107 months, 56.1% of patients complained of weakness, and 51.2% complained of pain. Gait was also restricted or dependent on orthoses in 61%18. Farrell et al. report 45.6% of patients relying on canes/crutches, and 10.9% of patients requiring analgesia for Complex Regional Pain Syndrome related to the nerve palsy3.  Such disability and pain due can lead to serious consequential injury. Fleischman et al. found that 16.7% of patients with femoral nerve paly suffered falls, which all resulted in significant adverse outcomes including periprosthetic fractures and dislocation22. 

Recovery of nerve injuries can be slow and unpredictable. Oldenburg and Muller report that at a mean follow up time of 107 months 17% of patients reported complete recovery, 39% described partial recovery and 44% claimed no improvement at all18. Farrell et al. also reported that the majority of patients with nerve injury never recovered pre-operative strength3. For the minority who did recover completely, it took an average of 21.1 months3. Markers of poor prognosis, as described by Barrack, include painful dysesthesia and complete motor and sensory palsy10. This being said, Zappe et al. described positive findings in recovery of ‘light’ nerve injuries (defined as MRC grade 3-4). In their study, 90.9% of light injuries recovered completely in a median time of 13 months7. They also report that femoral nerve injuries have the most favourable prognosis, with complete recovery in 59% of femoral lesions compared to only 25% of sciatic7.

Nerve injury following THA can also have implications on the surgeon. In one study1, 62% of patients claimed to lose confidence in their surgeon post-injury. These patients stated reasons such as delayed or missed diagnosis (44%), poor communication (69%) and lack of discussion of future options (80%). 

46% of patients sought legal counsel after their injury1. Interestingly, most medico-legal cases in THA nerve palsy involve failure to make a timely diagnosis or poor post-operative management rather than the origin of the injury19, as evidenced by the patient perspectives detailed above. Perhaps this is also due to the fact that that 50% of palsies have no clear cause3,5,10,11, and thus proof of error is more difficult. 

However, it is clear that we must listen to patients’ concerns to appropriately support them through recovery. Patients value discussions about possible management options and we must think holistically to cater to their individual needs. 

Conclusion

Peripheral nerve injury is a rare yet potentially debilitating complication of total hip arthroplasty. Although risk of injury cannot be completely eliminated, it can be mitigated somewhat by increased intra-operative awareness of anatomy and procedure. Regular examination can facilitate prompt diagnosis and allow appropriate management plans to be initiated. 

Prognosis is generally recognised to be poor and most patients never recover completely. This has implications for patient quality of life but also medico-legally for the surgeon. 

The surgeon who is embarrassed/in denial & avoids frank discussions with the patient is making a mistake and compounding the problem. Even if you think it wasn’t your fault, it certainly isn’t the patient’s fault either. Expressing regret at the occurrence, and careful clinical evaluation/documentation are important. You should explain the next steps in management and the timescale to the patient.

It is very important to maintain open communication channels with patients to support their individual needs. 

References

  1. Pritchett J. Outcome of surgery for nerve injury following total hip arthroplasty. International Orthopaedics. 2017;42(2):289-295.
  2. Brown G, Swanson E, Nercessian O. Neurologic injuries after total hip arthroplasty. Am J Orthop. 2008;37(4):191-7
  3. Farrell C, Springer B, Haidukewych G, Morrey B. Motor Nerve Palsy Following Primary Total Hip Arthroplasty. The Journal of Bone & Joint Surgery. 2005;87(12):2619-2625.
  4. De Fine M, Romagnoli M, Zaffagnini S, Pignatti G. Sciatic Nerve Palsy following Total Hip Replacement: Are Patients Personal Characteristics More Important than Limb Lengthening? A Systematic Review. BioMed Research International. 2017;2017:1-7. Available from: doi:10.1155/2017/8361071
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  8. Yang, I. Neurovascular Injury in Hip Arthroplasty. Hip & Pelvis. 2014;26(2):74-78. Available from: doi: 10.5371/hp.2014.26.2.74 
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  11. Park J, Hozack B, Kim P, Norton R, Mandel S, Restrepo C, Parvizi J. Common Peroneal Nerve Palsy Following Total Hip Arthroplasty. The Journal of Bone & Joint Surgery. 2013;95(9):55. Available from: doi:10.2106/JBJS.L.00160.
  12. Birch R, Wilkinson M, Vijayan K, Gschmeissner S. Cement Burn of the Sciatic Nerve. The Journal Of Bone And Joint Surgery. 1992;74(5):731-733
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  14. Butt A, McCarthy T, Kelly I, Glynn T, McCoy G. Sciatic nerve palsy secondary to post- operative haematoma in primary total hip replacement. The Journal Of Bone And Joint Surgery. 2005;87(11):1465-1467
  15. Zwolak P, Eysel P, Michael J. Femoral and obturator nerves palsy caused by pelvic cement extrusion after hip arthroplasty. Orthop Rev. 2011;3(1) Available from: doi: 10.4081/or.2011.e6
  16. Su E. Retraction: Post-operative neuropathy after total hip arthroplasty. The Bone & Joint Journal. 2017;99:46-49
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  18. Oldenburg M, Miller R. The frequency, prognosis and significance of nerve injuries in total hip arthroplasty. International Orthopaedics. 1997;21:1-3
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