Establishment of safety parameters for hip posterolateral access to cadavers' ischiatic nerve: an anatomical study

Abstracts

A preferência dos ortopedistas pela via de acesso póstero-lateral do quadril demanda maior atenção e refinamento da técnica cirúrgica, a fim de diminuir complicações intra e pós-operatórias, principalmente iatrogênicas. Embora o déficit neurológico pós artroplastia de quadril seja uma complicação incomum (cerca de 1%), quase 80% desses casos relacionam-se ao nervo isquiático ou a uma de suas divisões. O objetivo desse estudo foi determinar parâmetros de segurança para a via de acesso póstero-lateral do quadril, visando diminuir a incidência de lesão iatrogênica dos nervos isquiático, tibial ou fibular, uma vez que tal assunto ainda não foi abordado pela literatura. Vinte quadris de cadáveres humanos foram estudados e a menor distância entre o limite lateral do n. isquiático e a inserção do m. piriforme foi 27 mm (aferida sob a margem distal desse músculo), bem como a mínima distância entre o limite lateral do n. isquiático e a inserção femoral do m. quadrado da coxa foi 20mm (aferida sobre a margem proximal desse músculo). A determinação desses parâmetros deixa o ortopedista mais seguro para avançar posterior e distalmente pela via de acesso póstero-lateral, mas não minimiza o cuidado com a dissecção e a importância do emprego de técnica cirúrgica apurada.

Anatomia; Quadril; Nervo ciático

ORIGINAL ARTICLE

Establishment of safety parameters for hip posterolateral access to cadavers' ischiatic nerve: an anatomical study

Leandro Luis Auletta^I; Bárbara de Oliveira Manoel^II; Maurício Leal Dias Mongon^III; Mauro Duarte Caron^IV

^IOrthoapedic Doctor, Orthopaedics and Traumatology Department, Hospital das Clínicas, Campinas State University (DOT/HC UNICAMP)

^IIOrthopaedic Doctor, DOT/HC UNICAMP

^IIIOrthopaedic Doctor and Member of the Hip Group, DOT/HC UNICAMP

^IVMaster in Orthopaedics and Head of the Hip Group, DOT/HC UNICAMP

Correspondences to

SUMMARY

Orthopaedic doctors' preference for the posterolateral access of the hip demands further attention and improvement of the surgical technique in order to reduce per- and postoperative complications rates, especially the iatrogenic ones. Although neurological deficit post hip arthroplasty is an uncommon complication (about 1% of the cases), almost 80% of these cases are correlated to the ischiatic nerve or to one of its divisions. The objective of this study was to establish safety parameters for the posterolateral access of the hip, aiming to reduce the incidence rate of iatrogenic injuries of the ischiatic, tibial or fibular nerves, since this subject has not been addressed by literature so far. Twenty human cadavers' hips were studied and the shortest distance between the lateral end of the ischiatic nerve and the insertion of the quadratus muscle of the thigh was 2 mm (measured over this muscle's proximal edge). The establishment of such parameters provides orthopaedic surgeons with more confidence to go posterior and distally through the posterolateral access, but does not minimizes the level of care required to dissection and the importance of using a fine surgical technique.

Keywords: Anatomy, Hip (anatomy), Hip (surgery); Sciatic nerve.

INTRODUCTION

Since hip arthroplasty has become popular, in the late 1960's, palsies and paresthesia of ischiatic and fibular nerves are regarded as rare complications, historically reported on a frequency of 0.5%-2.0%^(1,2,3). Although little prevalent and with a good postoperative prognosis, these neurological changes remain being targeted for studies, since the observation of simple measures by the surgical team, such as limiting the stretching of the operated limb to up to four centimeters or adopting peroperative methods of neural monitoring, may be related to a reduced incidence of these complications⁽⁴⁾. In a series of 3126 hip arthroplasties, only 53 cases were identified of neuropathy on the ipsilateral lower limb to the surgical procedure⁽⁵⁾. The etiology of the neuropathy remained unexplained in 57% of these cases; however, there is a trend towards correlating its cause with the surgical technique employed and to anatomical peculiarities of patients.

According to Schmalzried et al⁽⁶⁾ the prevalence of neurological deficit after a hip arthroplasty is approximately 1% (0.08% - 7.6%), with almost 80% of these cases being correlated to ischiatic nerve or one of its divisions (ischiatic nerve: 27.2%, tibial nerve: 0.4%, fibular nerve: 51.9%). The risk factors identified were the following: female gender, review arthroplasties, and arthroplasties due to hip development dysplasia.

Among the patients presenting postoperative neurological deficit, approximately 15% evolve with strength reduction impairing ambulation, whether associated or not to permanent paresthesia⁽⁶⁾.

The posterolateral access port to the hip is the most commonly used one by orthopaedic surgeons in hip arthroplasties⁽⁷⁾, enabling us to infer that accesses through this port and the occurrence of ischiatic nerve damage are correlated. And, although studies conducted so far have addressed the frequency of nervous injuries in that population, there is no objective description of anatomical safety margins, i.e., distances that, when complied with, would reflect low or no incidence of iatrogenic nerve damage.

Addressing the correlation between nervous injury and access port, the objective of the present study was to assess anatomical parameters in cadavers and to determine a safety zone for posterolateral access to the hip so as to reduce the incidence and prevalence of ischiatic nerve injuries during a surgical procedure.

MATERIALS AND METHODS

At the Anatomy Laboratory, 20 human male and female cadavers' hips were dissected through an 'open book'

The distance between the lateral limit of ischiatic nerve emergence under pyriform muscle and the femoral insertion of the same muscle was measured, which will be referred to as ischiatic-quadrate of the tight distance - (DIQ) (Figure 3).

The distances were measured by all the authors at different times, and the results presented refer to the simple arithmetic average among the four values. A Mitutoya Pachymeter was employed for taking measurements.

RESULTS

The ischiatic-pyriform distance was, in average, 39 mm (standard deviation = 6.74, median = 37, mode = 37), ranging from 27 to 54 mm, while the ischiatic-quadrate of the thigh distance was, in average, 29.35 mm (standard deviation = 4.66, median = 30, mode = 30), ranging from 20 to 38 mm. The measurements are reported on Table 1.

DISCUSSION

The selection of a safer access port, meaning one presenting lower risks of postoperative complications has been widely discussed⁽⁸⁾, however, a study comparing the posterolateral port to the lateral access port didn't show significant difference for ischiatic nerve injury incidence⁽⁸⁾. Other parameters, such as postoperative Trendelenburg gait, were not significantly different as well.

In clinical practice, the posterolateral access port is preferred by hip surgeons, which is justified by the lack of need to disconnect the medium gluteal muscle and by a better access to the acetabulum, enabling an easy insertion of the acetabular component of prostheses or osteosynthesis material.

Femoral insertions of the pyriform and quadrate of the thigh muscles were chosen for being parameters of easy peroperative visualization, so that, when distances of 27 mm (from the pyriform muscle - on a straight line on its lower margin) and 20 mm (from the quadrate of the thigh muscle - on a straight line on its proximal margin) are respected, the risk of injuring the sciatic nerve would be minimized.

CONCLUSION

The awareness about the safety margins for posterolateral access to the hip in what concerns the ischiatic nerve makes an orthopaedic doctor willing to perform hip arthroplasties or surgeries such as acetabular fractures osteosynthesis (through this very access port) more confident to advance posterior and distally. Based on this study, conducted with formol-preserved cadavers, we can conclude that the minimum distance obtained as a safety parameter to avoid iatrogenic injuries of the ischiatc nerve would be 27 mm (average: 39 mm) from the insertion of the pyriform muscle, and 20 mm (average: 29.35 mm) from the insertion of the quadrate of the thigh muscle, emphasizing that these determinant factors (insertions of the pyriform and quadrate of the thigh muscles) have been chosen because of the peroperative ease to locate and identify them at the posterolateral hip access.

Nevertheless, an accurate surgical technique and a careful dissection remain critical to avoid iatrogenic nervous injuries, once individual variations exist.

REFERENCES

• 1. Johnson NA, Pellicci PM, Tsairis P, Salvati EA. Nerve injury in total hip arthroplasty. Clin Orthop Relat Res. 1983;(170):214-22.
• 2. Solheim LF, Hagen R. Femoral and sciatic neuropathies after total hip arthroplasty. Acta Orthop Scand. 1978;51:531-4.
• 3. Weber ER, Daube JR, Coventry MB. Peripheral neuropathies associated with total hip arthroplasty. J. Bone Joint Surg Am. 1976;58:66-9.
• 4. Edwards BN, Tullos HS, Noble PC. Contributory factors and etiology sciatic nerve palsy in total hip arthroplasty. Clin Orthop Relat Res. 1987;(218):136-41.
• 5. Schmalzried TP, Amstutz HC, Dorey FJ. Nerve palsy associated with total hip replacement. J Bone Joint Surg Am 1991;73:1074-80.
• 6. Schmalzried TP, Noordin S, Amstutz HC. Update on nerve palsy associated with total hip replacement. Clin Orthop Relat Res. 1997;(344):188-206.
• 7. Franco JS, Lourenço, PRB, Delocco FO. Vias de acesso cirúrgico ao quadril. In: Pardini Junior AG, Souza JMG, organizadores. Clínica Ortopédica. Rio de Janeiro: Médici; 2001. p.949-71.
• 8. Jolles BM, Bogoch ER. Surgical approach for total hip arthroplasty: direct lateral or posterior? J Rheumatol 2004;31:1790-6.

*

posterior access port (

Figure 1), identifying and proximally isolating the ischiatic nerve and its divisions, as well as the femoral insertion of pyriform, superior gemellus, external obturator, inferior gemellus and quadrate of the thigh muscles.

Publication Dates

• Publication in this collection
  14 Nov 2008
• Date of issue
  2008